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HDL and Reverse Cholesterol Transport

Basic Mechanisms and Their Roles in Vascular Health and Disease
Originally published Research. 2019;124:1505–1518


    Cardiovascular disease, with atherosclerosis as the major underlying factor, remains the leading cause of death worldwide. It is well established that cholesterol ester-enriched foam cells are the hallmark of atherosclerotic plaques. Multiple lines of evidence support that enhancing foam cell cholesterol efflux by HDL (high-density lipoprotein) particles, the first step of reverse cholesterol transport (RCT), is a promising antiatherogenic strategy. Yet, excitement towards the therapeutic potential of manipulating RCT for the treatment of cardiovascular disease has faded because of the lack of the association between cardiovascular disease risk and what was typically measured in intervention trials, namely HDL cholesterol, which has an inconsistent relationship to HDL function and RCT. In this review, we will summarize some of the potential reasons for this inconsistency, update the mechanisms of RCT, and highlight conditions in which impaired HDL function or RCT contributes to vascular disease. On balance, the evidence still argues for further research to better understand how HDL functionality contributes to RCT to develop prevention and treatment strategies to reduce the risk of cardiovascular disease.

    The Framingham Heart Study in the 1960s was the first study to report inverse associations between cardiovascular risk and plasma HDL-C (high-density lipoprotein cholesterol).1 This landmark discovery inspired investigations into the mechanisms by which HDL confers atheroprotection, leading to the identification of the reverse cholesterol transport (RCT) pathway.2 RCT is defined as the process by which cholesterol moves out of cells in peripheral tissues (including foam cells in atherosclerotic plaques), enters the circulation, and is excreted in the feces. HDL’s cardiovascular protective effect has conventionally been attributed to its ability to act as both the acceptor of cholesterol from cells and as the cholesterol carrier in the RCT pathway, including delivery to the liver. It has been estimated from observational studies that cardiovascular risk decreases by ≈2% to 3% per 1-mg/dL increase in HDL–C.3 Implicit in this view is that the level of HDL-C in the plasma is a faithful biomarker of the ability of the HDL particles to mediate RCT. In 2019, this is now recognized to be an oversimplification as HDL-C measurements do not necessarily reflect either the overall abundance of HDL particles, the distribution of HDL subspecies,4 or RCT capacity.5 Additionally, data from human genetic studies6 and a host of negative HDL-raising clinical trials have led to much controversy over the HDL hypothesis. This controversy, however, should not negate the strong experimental evidence that a major function of HDL particles is to mediate RCT and that an increased understanding of the mechanisms by which this is accomplished represents a chance to revise and refine the HDL hypothesis. The framework of this review is illustrated in the Figure, with the points made in the legend discussed in detail below.


    Figure. Key steps of reverse cholesterol transport (RCT). RCT begins with the removal of cholesterol from arterial foam cells that are of vascular smooth muscle cell (V-mac) or macrophage origin (left). This is the rate-limiting step of the RCT pathway and requires the efflux of free cholesterol to cholesterol acceptors such as nascent or mature HDL (high-density lipoprotein) along with macrophage egress from the plaques. While RCT from macrophage foam cells requires the cholesterol pumps ABCA1 and ABCG1 (ATP-binding cassette proteins A1 and G1), mechanisms regulating RCT from intimal vascular smooth muscle cells that have transdifferentiated to macrophage-like foam cells (V-mac) are not well understood, though cholesterol efflux from V-macs appears defective relative to macrophage foam cells. Intimal-derived HDL cholesterol can reach the liver 1 directly through binding the hepatic HDL receptor SR-B1 (scavenger receptor class B type 1) that selectively removes cholesteryl ester (CE) from HDL2 and HDL3 or 2 indirectly via apoB-containing lipoproteins (VLDL [very-low-density lipoprotein] or LDL [V/LDL])—to which cholesterol is transferred by the action of CETP (cholesterol ester transfer protein)—that are cleared by hepatic LDLR (middle). PLTP (phospholipid transfer protein) also plays an important role in regulating HDL metabolism through HDL remodeling. Finally, the last step of the RCT pathway is cholesterol excretion into the feces (right). This can occur through biliary cholesterol excretion or transintestinal cholesterol efflux (TICE) that mediate ≈25% and 33% of total fecal neutral sterol loss, respectively. LCAT indicates lecithin:cholesterol acyltransferase; LXR, liver X receptors; and OSBP, oxysterol-binding protein.

    Cholesterol Efflux and Peripheral Cells

    All mammalian cells require cholesterol, with the highest concentration in the plasma membrane and the lowest in the endoplasmic reticulum (ER) membrane. The amount of free cholesterol is maintained in a relatively narrow range, making cellular cholesterol homeostasis essential for normal cell function. Based on pioneering data from many laboratories,2,7 RCT came to be described as the process by which HDL acts as the specific cholesterol acceptor that transports excess cholesterol stores within peripheral tissues to the plasma, and then delivers it to the liver, where it can be directly excreted into the bile or be metabolized into bile acids/salts before excretion. These studies naturally stimulated much research in a variety of in vitro systems, to investigate at the cellular level the initial step of RCT. Herein, we will focus on the roles of macrophages and vascular smooth muscle cells (VSMCs) in the early steps of the RCT process, given their crucial role in the development of cardiovascular diseases (CVDs), especially atherosclerosis. We will also discuss other aspects of the RCT pathway, including its quantitative assessment in vitro and in vivo.


    Macrophage extracellular cholesterol is primarily derived from the internalization of plasma lipoproteins or from the efferocytosis of apoptotic cells, which enter the cellular pool together with newly synthesized cholesterol. To prevent toxicity, surplus cholesterol is effluxed from the cells to extracellular acceptors or converted to cholesteryl ester (CE) and stored in cytosolic lipid droplets (LDs). There are many mechanisms by which cells are defended against cholesterol toxicity. For example, the LXRs (liver X receptors), key sterol-sensitive transcription factors in macrophages that regulate intracellular cholesterol (reviewed in Hong and Tontonoz8), are induced by excess cholesterol. LXRs, in turn, drive the expression of numerous genes within the efflux pathway, including ABCA1/G1 (ATP-binding cassette proteins A1 and G1), which are key cellular cholesterol transporters. Adding to the effort to reduce cellular sterol content, LXR also controls the expression of the inducible degrader of the LDLR (low-density lipoprotein receptor; IDOL), an E3 ubiquitin ligase that promotes the degradation of the LDLR. This limits further uptake of exogenous cholesterol via LDLR.9 Another defensive response to elevated cell cholesterol is the inhibition of the processing of the SREBP (sterol regulatory element-binding protein), leading to decreased expression of genes that regulate cholesterol synthesis (HMGCR) and uptake (LDLR). Yet, another consequence of cellular cholesterol excess is the reduced expression of a small microRNA encoded in SREBP’s intronic region, miR-33, which among its targets of translational repression are the mRNAs encoding numerous factors in the RCT pathway (ABCA1, NPC [Niemann-Pick Type C]-1, ABC11, and ATP8B1).10–12 miR-33a is encoded in the intron of the SREBP-2 gene in mice and humans, while its isoform miR-33b is encoded within the SREBP-1 gene in higher mammals.12 Notably, inhibition of miR-33 in mice and nonhuman primates holds therapeutic promise as it has been shown to enhance RCT,12–14 protect against atherosclerosis15–17 and promote atherosclerosis regression,14,18 though some controversy surrounds its role in regulating hepatic triglyceride and fatty acid metabolism.19–22 A recent report by the Fernandez-Hernando group demonstrates that repression of ABCA1 is the primary mechanism by which miR-33 regulates macrophage cholesterol efflux and atherogenesis.23 Although miR-33 is the most characterized of the miRNAs that regulate RCT, there are at least 10 others that also have targets in this pathway (reviewed in Feinberg and Moore24).

    ABCA1 and ABCG1 are critical receptors for the initial step of RCT in atherosclerotic plaques, that is, cholesterol efflux out of foam cells.25–28 Foam cells are traditionally thought to be cholesterol-laden macrophages originating from monocytes, but as reviewed below, they can also be macrophage-like cells originating from cholesterol-laden VSMCs.29–33 Before efflux, cholesterol must be in its free (unesterified) form to be pumped out of cells. This is the case in vitro and in vivo, including in atherosclerosis, where the rate-limiting step in RCT is hydrolysis of LDs in vascular foam cells to generate free cholesterol for efflux.34–36 Consistent with this are several studies reporting that stimulation or inhibition of macrophage foam cell CE hydrolysis regulates RCT and atherosclerosis.37–41 LD cholesterol undergoes constitutive cycles of hydrolysis and re-esterification. Free cholesterol released from LDs via CE hydrolysis can either traffic to the plasma membrane and be effluxed to a cholesterol acceptor, or, in a futile cycle be re-esterified by the ER-resident protein ACAT (acyl-CoA:cholesterol acyltransferase).42,43 Original studies by Brown and Goldstein characterizing this futile cycle indicated that cytoplasmic CE hydrolysis in macrophage foam cells was mediated by extra-lysosomal, cytoplasmic neutral CE hydrolases.42,44 Nevertheless, knocking down or out potential CE hydrolases in macrophages never entirely abolishes cellular CE hydrolysis.36 The importance of addressing the missing regulators of CE hydrolysis is underscored by the many studies to date showing that increasing the hydrolysis of LD CE increases cholesterol efflux and is antiatherogenic.36

    A key insight into CE hydrolysis came from the observation that the loading of macrophages with proatherogenic lipoproteins can activate autophagy, promote sequestration and delivery of LDs to lysosomes for degradation, and enhance RCT from macrophage foam cells.45 Autophagy is a ubiquitous cellular process by which cytoplasmic components are degraded within lysosomes. There are 3 types of autophagy in mammalian cells: (1) macroautophagy, where cargo is sequestered in de novo formed autophagosomes that subsequently fuse with lysosomes, (2) microautophagy, where cargo is taken into lysosomes by invagination and pinching of the lysosomal membrane into the lysosome lumen, and (3) chaperone-mediated autophagy, where single proteins are recognized by chaperones and delivered to lysosomes via a membrane translocation complex.46 Macroautophagy—referred to as autophagy hereafter—is the subtype most relevant to this review and can sequester cytosol in bulk or selectively. This pathway depends on numerous autophagy proteins that organize into functional complexes that orchestrate the autophagic process, first generating the limiting membranes or phagophores that elongate in cup-shaped structures that engulf cytoplasmic cargo, fusing to become autophagosomes.47 Subsequent autophagosome fusion with lysosomes releases the autophagic body, or in the case of RCT—LDs, into the lysosome lumen where they are degraded. LAL (Lysosomal acid lipase), encoded by the LIPA gene in humans, is responsible for the hydrolysis of LD-associated CE to generate free cholesterol for efflux.45 Genome-wide association studies have identified several loss of function mutations in LIPA as causative of Wolman disease, cholesterol ester storage disease, and coronary artery disease (CAD).48

    Targeted LD degradation by autophagy, or lipophagy, represents a novel pathway to regulate RCT, and it is thought that enhancing autophagy holds promise to promote lipid clearance from the atherosclerotic vascular wall. In particular, atherosclerosis development is associated with a progressive defect in autophagy in cells positive for macrophage markers MOMA-2 (monocyte/macrophage antibody) and CD11b in the plaque,49 and defective clearance of cargo tagged by the autophagy marker p62/SQSTM1 is readily observed by detection of its accumulation in whole aortic protein lysates.49,50 Further, inhibition of autophagy pathways in mice promotes atherosclerosis development by reduced lipophagy and lysosome-mediated cholesterol cellular efflux, which contributes to inflammasome hyperactivation, elevated cell death, and defective efferocytosis within plaques.36,49,51 A critical role for autophagy and lysosomal biogenesis to suppress atherosclerosis development is supported by studies showing that systemic miR-33 inhibition or macrophage overexpression of the master transcriptional regulator of autophagy and lysosomal genes, TFEB (transcription factor EB), restores plaque macrophage autophagy, improves efferocytosis and inflammation, and ultimately reduces atherosclerosis burden.50,52

    The routes by which free cholesterol generated at the site of lipid lipolysis (within lysosomes or at the LD surface) reaches the ABCA1 and ABCG1 cholesterol transporters on the plasma membrane depends on both vesicular and nonvesicular trafficking pathways, although the precise mechanisms are poorly characterized.53,54 The general working hypothesis is that cholesterol transporters sit at the plasma membrane and await delivery of cholesterol to be effluxed; but, this is an oversimplification as these can be motile, as exemplified by ABCA1 that continuously shuttles between the plasma membrane and endolysosomal compartments.55 This shuttling is a regulated process that is impeded by hypoxia.56,57 ABCG1 relocalizes from the Golgi and ER to the plasma membrane following LXR activation to stimulate efflux to HDL.58 This involves ABCG1 concentrating on intracellular endocytic vesicles (eg, recycling endosomes) to apparently redistribute sterols to the plasma membrane outer leaflet on fusion, so that cholesterol desorbs to exogenous lipid acceptors such as HDL.59 Transporters that possess distinct subcellular localizations likely preferentially efflux cholesterol from specific intracellular pools; for instance, apoA-I/ABCA1 retroendocytosis is required for efficient cholesterol efflux under lipid-loaded conditions60 and conversely, ABCA1-mediated cholesterol efflux is primarily dependent on autophagy for its cholesterol source.45

    Another cholesterol trafficking pathway is mediated by OSBP (oxysterol-binding)-ORPs (related proteins). They constitute a family of lipid binding/transfer proteins that can facilitate nonvesicular transfer of cholesterol between lipid bilayers, increasing the efficiency of cholesterol transport between subcellular membranous organelles. Roles for many of the ORPs within this family (12 members in total) as sterol sensors or transporters at distinct subcellular sites have been recently reviewed.61 Recently, ORP6 was found to regulate cholesterol efflux and HDL homeostasis, suggesting that it may represent a novel regulator of the RCT pathway,62 yet mechanisms by which ORP6 and other ORP members may regulate this pathway are poorly understood. Other key mediators of interorganelle lipid trafficking that may represent potential therapeutic enhancers of RCT include the soluble lipid transfer proteins StAR (steroidogenic acute regulatory protein) D4, MLN64, and NPC proteins.63 More recently, Aster proteins have emerged as novel mediators of nonvesicular cholesterol transport at contact sites between the plasma membrane and ER, providing a new mechanism by which HDL-derived cholesterol can be mobilized through the selective HDL cholesterol uptake pathway.64

    Vascular Smooth Muscle Cells

    While much of the focus on the early steps of RCT has been on defining mechanisms of efflux from macrophages, there have also been investigations on VSMCs. VSMC plasticity in atherosclerosis is well recognized; for example, in the media of atherosclerotic arteries, they are considered to be contractile and can become proliferative, migrate to the intima, where they are synthetic, and exhibit the loss of many markers of the VSMC in the contractile state, such as smooth muscle cell actin and myosin heavy chain.30 Though it has been long appreciated that VSMC in the intima can also take up cholesterol through a variety of pathways,29,65,66 phenotypic changes in these VSMC-foam cells at the molecular level had not been systematically studied. In 2003, it was shown that loading mouse primary VSMC with cholesterol in vitro resulted in the concurrent loss of VSMC marker expression and the gain of macrophage-associated gene expression.67

    One implication of these findings is that conventional histological markers used to identify macrophages in plaques would include cells of VSMC lineage. Three studies using lineage-marking approaches in mice31,32,68 and a variety of assays for human plaques69 were published in quick succession to confirm that, indeed, there are macrophage-appearing cells of VSMC origin in human and mouse plaques. These results have also been replicated in studies examining the clonality of VSMC in atherosclerotic plaques in mice.70,71 The percent of the macrophage-marker positive cells of VSMC origin varied among the studies, but it was substantial in all, ranging from 30% to 70% (increasing with the stage of disease). The molecular regulation of this transition process has been studied mainly in vitro, where it was shown that cholesterol loading suppresses miR-143/145, resulting in reduced expression of the canonical VSMC regulatory transcription factors, SRF (serum response factor) and myocardin. Suppression of miR-143/145 also increased levels of KLF4 (Kruppel-like factor 4), a regulator of macrophage gene expression.72 Consistent with the in vitro implication of KLF4 in the acquisition of macrophage features is the work from the Owens lab, which showed that in VSMC-specific KLF4-deficient mice, the percentage of macrophage-like cells derived from VSMC in atherosclerotic plaques was ≈50% versus those in control mice.32 A recent study has also implicated integrin β3 in the transition of VSMC to macrophage-like cells in mouse atherosclerotic plaques.71

    The relevance of cholesterol efflux to the macrophage-like transition of VSMC is suggested by the results in vitro that by providing cholesterol acceptors (HDL or apoA-I) to cholesterol-loaded cells, this completely reversed their macrophage-like phenotypes to the preloaded VSMC state.31 Evidence that impaired efflux may be operating in vivo, and thereby sustaining the effects of cholesterol loading, comes from 2 strands of evidence. First, as Choi et al73 have shown, ABCA1 expression is reduced in intimal-like VSMC (derived from arteries of Wistar-Kyoto rats) and in vitro, these cells exhibit less binding of apoA-I compared with those isolated from the medial layer. Similarly, ABCA1 expression was found to be low in human intimal VSMC, more so in advanced relative to early atherosclerosis.69 Recently, CD45 cells (presumably VSMC-derived) from ApoE−/− mice were also found to exhibit reduced ABCA1 expression relative to CD45+ (presumably monocyte-derived) foam cells.33

    Such changes would be likely to make cholesterol taken up by intimal VSMC linger and not readily enter the RCT pathway. It should be noted, however, that in other studies, cholesterol loading of murine VSMC increased their ABCA1 mRNA expression.31,32,67 Reconciling the apparent discrepancies between the results, which may have been caused by species differences, experimental conditions, etc, will require more investigation, but whatever the level of ABCA1 expression there is, it does not seem to be sufficient to prevent accumulation in vitro or in vivo when VSMC are exposed to elevated levels of cholesterol.

    Second, though VSMC-derived foam cells exhibit impaired phagocytosis relative to macrophages, compared with contractile VSMC, they are considerably more active (>5-fold).31 The cholesterol content of the more phagocytic cells would, therefore, be expected to contribute to VSMC-foam cell formation beyond the effects of hypercholesterolemia. In contrast to the data for phagocytosis, efferocytosis was not different in vitro between VSMC and cholesterol-loaded VSMC, suggesting that autophagic capacity may be submaximal in VSMC compared with macrophages.31 As autophagy is an important factor providing intracellular cholesterol to the efflux pathway,45 its potential limitation might be a contributor to impaired VSMC-foam cell cholesterol efflux. Further aggravating the cellular cholesterol imbalance in VSMC-foam cells is that apparently another homeostatic mechanism to promote efflux when cells are cholesterol-loaded, namely, the induction of LXR-regulated pathways, fails to become activated in vitro.73

    If the current speculation that transitioned VSMC have negative contributions to atherosclerosis are true, then the value of restoring cholesterol efflux to intimal VSMC becomes clear. An interesting question arises: how do the efflux capacities of distinct foam cell populations differ from one another? The answer would have implications in designing therapeutic strategies to target all or a subset of foam cells in the plaque to maximally promote RCT.

    Reverse Cholesterol Transport

    Though HDL is thought to have many functions,74–76 overwhelmingly its ability to promote RCT is considered key to its atheroprotection. This has stimulated much research in enhancing RCT. Although this pathway has been actively studied for several years, mechanistic understanding of ABC family mediated lipid export and nascent HDL biogenesis remains incomplete, with basic pieces of the puzzle such as structural information of the ABC subfamily only just emerging.77 Although ABCA1 preferentially lipidates small HDL particles, specifically apoA-I to form nascent HDL,78,79 ABCG1 stimulates net cholesterol efflux to larger HDL but not to lipid-poor apoA-I.80 Moreover, as alluded to above, ABCA1 trafficking between the cell surface and late endocytic vesicles is functionally important to stimulate cholesterol efflux out of endosomal/lysosomal compartments to lipid-free apoA-I,55,81,82 while ABCG1 is an intracellular sterol transporter that promotes cholesterol trafficking from the ER to the plasma membrane.59 In turn, efflux to HDL involves passive diffusion of cholesterol as well as active cholesterol transfer, and ABCA1, ABCG1, as well as unrelated SR-B1 (scavenger receptor class B type 1), mediate lipid transfer to HDL.83–86 After cholesterol transfer to HDL particles, the next step in HDL biology is esterification of the acquired cholesterol by LCAT (lecithin:cholesterol acyltransferase) to form CE, giving rise to mature HDL. Remodeling of HDL particles can occur through the hydrolysis of HDL triglycerides and phospholipids, mediated by hepatic lipase and endothelial lipase, respectively.87 In humans (but not mice), CE in the HDL core can be transferred to triglyceride-rich lipoproteins by CETP (cholesteryl ester transfer protein) for elimination via hepatic clearance in the liver through the LDLR, or selectively taken up via SR-B1 acting as a hepatic receptor for CE on HDL. Therefore, RCT to the liver of cholesterol derived from peripheral cells in humans involves 2 routes; (1) direct (HDL-SR-B1) and (2) indirect (HDL-LDL/VLDL-liver LDLR). In the liver, the CE is hydrolyzed and the free cholesterol is either converted to bile acids or transported by ABCG5 and ABCG8 into the bile for excretion into the feces.

    Three conceptual approaches to enhancing RCT have been proposed: (1) improve macrophage cholesterol efflux, (2) improve HDL functionality (ie, its capacity to accept or transport cholesterol), and (3) improve hepatic cholesterol uptake and biliary/intestinal excretion.88 As research has continued, this third possibility has been informed by mounting evidence that several HDL-independent routes can promote RCT and that cholesterol removal from the body may not require hepatobiliary cholesterol excretion.89 Thus, the term RCT currently encompasses all potential routes of net cholesterol flux from peripheral tissues into the feces,90 including artificial ones that have therapeutic potential. For example, non-HDL particles of 2-hydroxypropyl-β-CD (cyclodextrin) are artificial cholesterol acceptors and have been shown in vivo to mediate RCT and atheroprotection.91,92

    Other modalities to increase RCT include liposomes,93–95 the red blood cell compartment, which can act as a cholesterol sink to increase RCT,96 microparticle-mediated cholesterol efflux,97 and synthetic nanoparticles and HDL mimetics that not only serve to package and deliver therapeutic drugs such as LXR agonists or statins to the arterial wall to stimulate cholesterol efflux but can also extract plaque cholesterol.98–100 There are also efforts to increase LCAT activity so that more free cholesterol can be esterified, increasing the amount loaded into HDL.101 There is renewed interest in hepatic SR-B1 as a target, based on the work from Rader and colleagues showing loss of function SR-B1 mutations in people are associated with increased cardiovascular risk, despite elevated HDL-C.102 This is consistent with mouse models in which deficiency of SR-B1 increased HDL-C but paradoxically increased atherosclerosis.103 In these studies, SR-B1 deletion or loss of function impaired RCT, consistent with the growing body of evidence highlighting that HDL function and cholesterol flux are ultimately better determinants of atheroprotection than absolute HDL-C concentrations. However, it should be noted that another study found that rare mutations that disrupt SR-B1 function associates with HDL-C but not CAD risk.104

    In addition to the hepatobiliary route of cholesterol elimination, there is also transintestinal cholesterol efflux (TICE).90 While hepatobiliary cholesterol secretion involves the transfer of cholesterol from hepatocytes into the bile canaliculus,105 in TICE cholesterol is transported directly from blood, through the enterocytes, into the lumen of the intestine.106 These fecal cholesterol routes—hepatobiliary and TICE—are estimated to account for 65% and 35% of cholesterol elimination in humans,106 respectively. The nuclear hormone receptors LXR and FXR (farnesoid X receptor) are important regulators of cholesterol excretion, by controlling the transcription and activity of numerous cholesterol transporters and bile synthesis enzymes.105–107

    Although cholesterol itself can be secreted into the bile for excretion from the body, synthesis, and excretion of bile acids comprise the major cholesterol catabolism pathway in mammals.108 Thus, LXR and FXR both represent potential therapeutic targets to stimulate TICE and biliary cholesterol secretion and promote RCT.107,109 Because hepatic LXR activation also stimulates lipogenesis, leading to steatohepatitis,110 devising a strategy to selectively activate nuclear receptors in the intestinal lumen to promote TICE without inducing hepatic lipogenesis may represent a targeted approach to circumvent this issue. In addition, miRNAs add an extra level of regulation to cholesterol metabolism by exerting post-transcriptional negative control of certain genes, including ABCB11 and ATP8B1,111 suggesting anti-miRNA therapies.

    Quantification of RCT

    The controversy surrounding HDL-C as a reliable biomarker of HDL function, including the promotion of RCT, does not contradict the view held by many that increasing RCT will contribute to reducing atherosclerosis and the risk of cardiovascular events.75,112,113 Indeed, an independent inverse association between HDL cholesterol efflux capacity (CEC) and incident cardiovascular events has been shown both in the Dallas Heart Study and in the European Prospective Investigation of Cancer-Norfolk study.114,115 In addition, quantification of cholesterol mass efflux capacity in CAD and stroke cohorts derived from the Multi-Ethnic Study of Atherosclerosis indicate a protective role for HDL-mediated efflux in patients with CAD albeit not those with stroke.116 Thus, considerable efforts have been made to develop measurements of RCT in vitro and in vivo, especially with an eye to test approaches to increase it, such as those suggested above.

    In vitro, commonly used are assays of the first step in RCT, the efflux of cellular cholesterol. In this type of assay, cells are first incubated with radioactive [3H or 14C]-cholesterol or, alternatively, fluorescent BODIPY (boron-dipyrromethene)-cholesterol to label intracellular cholesterol pools, after which transfer of the labeled cholesterol from the cells to an extracellular cholesterol acceptor, such as apoA-I or HDL, is measured over time.117–119 One must consider several factors when designing a cholesterol efflux experiment,120 for example, the exogenous cholesterol acceptor and label to be used, keeping in mind how this might affect net cholesterol flux given that efflux to α-HDL may be bidirectional, so that the correlation of BODIPY-cholesterol efflux and that of 3H-cholesterol to pre-β-HDL and α-HDL may differ.118 A variation of these assays, originally developed by Rothblat, Rader, and colleagues,5 has been used to assess the CEC of HDL isolated from human subjects to determine its correlation between HDL CEC and cardiovascular risk.114,115,121,122 A number of such studies (but not all123) have found an independent inverse association between HDL CEC and incident cardiovascular events, supporting HDL CEC as a metric of cardiovascular risk superior to HDL-C. Nevertheless, side-by-side comparisons of the radiolabeled and the fluorescently labeled cholesterol method is necessary to determine if this accounts for differences among studies and the correlation of HDL CEC with HDL-C.

    Turning to assays in vivo, a simple assay developed by Rader et al has been used to quantify RCT in experimental mouse models. This consists of injecting macrophages loaded with radiolabeled cholesterol into the peritoneal cavity of mice, and measuring the appearance of the radiolabel into the plasma, liver, and feces over time.124 The major limitation of this assay is that it does not consider the bidirectional movement of cholesterol in and out of macrophages, and thus one cannot draw conclusions about the net outward flux of cholesterol mass. To circumvent this, macrophage-specific RCT might be better quantified using techniques in which macrophages are trapped into the site of injection using semipermeable hollow fibers or Matrigel plugs, and these implants are removed so that cholesterol mass content may be determined at the end of the assay.125,126 More recently, Cuchel et al127 adapted the conventional RCT method to allow for quantification of RCT in humans. This method involves intravenous delivery of 3H-cholesterol nanoparticles, followed by blood and sample collection to quantify tracer counts in plasma, non-HDL, and HDL fractions, as well as fecal fractions. This is an exciting advance in the field, providing a feasible approach to quantify RCT in vivo in humans. A combination of this methodology along with HDL CEC quantification and advanced modalities in imaging, such as intravascular ultrasonography, optical coherence tomography, and near-infrared spectroscopy to facilitate in situ plaque imaging may together provide a better assessment of whole-body RCT capacities in humans and allow for clinical testing of new drugs for the treatment of CAD.128

    Selected Topics in Cholesterol Efflux, HDL Biology, and RCT

    Atherosclerosis Prevention and Regression

    A chronic inflammatory disease, atherosclerosis begins with the accumulation of apoB-containing lipoproteins and their cholesterol in the artery wall. In response to arterial lipoprotein/lipid buildup and retention, macrophages are recruited to the intima and take up the modified lipoproteins and their lipids by multiple processes,129 leading to the formation of foam cells that secrete inflammatory mediators and promote the development of early atherosclerotic lesions. These lesions develop into disease-causing advanced plaques in the process commonly referred to as atherosclerosis progression. Once advanced atherosclerotic plaques are established, the process by which they undergo a reduction in one or more standard parameters (size, lipid content, foam cell content, and macrophage inflammation) is termed atherosclerosis regression. Macrophage RCT is the mechanism by which atherosclerotic plaques may rid themselves of cholesterol, and, as noted earlier, is still considered as an essential target to inhibit atherosclerosis progression and promote atherosclerosis regression.

    Besides cholesterol efflux, macrophage RCT may also involve cholesterol removal from plaques by another mechanism, namely by the emigration of the macrophages themselves. Plaque foam cell population numbers are determined by cell recruitment, proliferation in situ, emigration, and cell death.130 Historically, atherosclerosis progression studies have placed a major emphasis on understanding mechanisms of monocyte recruitment into the vascular wall and devising strategies to block their influx into plaques.130 Recent studies, however, show that there are also factors that determine macrophage retention within and egress from plaques,130 and if these are manipulated appropriately, can lead to reductions in macrophage numbers and the cholesterol they contain, resulting in regression in murine models. One of the emigration factors is the CCR7 (C-C chemokine receptor type 7),131 whose transcription is regulated in part by a sterol response element in its promoter.132 When HDL levels were raised in ApoE−/− mice, the SREBP pathway in plaque macrophages was activated, and macrophage emigration was stimulated.132

    Another study reported that raising HDL in ApoE−/− mice as a consequence of using an apoE-encoding adenovirus to reduce non-HDL hyperlipidemia decreased plaque macrophage content by 74% after 4 weeks of apoE complementation. This was attributed to a marked reduction in monocyte recruitment to plaques but not to CCR7-dependent egress of macrophages from plaques.133 The role of CCR7 in some models of murine atherosclerosis regression was confirmed in a recent study, in which it was shown that deficiency of LRP1 increased RCT and CCR7 expression in plaque macrophages, and promoted atherosclerosis regression, which was associated by the appearance of plaque macrophages in lymph nodes.134 Thus, egress of macrophages and perhaps other leukocytes from plaques is likely a significant contributor to net RCT in certain, but not all, contexts (see below on Lymphatics and RCT). Whether foam cells of VSMC origin can also emigrate from plaques and the extent to which they may do so relative to classical macrophage foam cells remains to be determined.

    Lymphatics and RCT

    There is a growing interest in the role of lymphatics in RCT. Lymphatic capillaries have been localized in the adventitia of atherosclerotic plaques, where they play an important role in the drainage of local inflammatory cells and cytokines and protect against atherosclerosis development.135 The lymphatic vasculature is also critical for the removal of cholesterol from macrophages in RCT, accounting for 50% of cholesterol delivery from cholesterol-loaded macrophages into the plasma compartment.136 Moreover, lymphatic insufficiency in mice disrupts proper lipoprotein metabolism (eg, elevated cholesterol and triglyceride levels in VLDL and LDL fractions) and vascular homeostasis, leading to accelerated atherosclerosis.137 These findings are in agreement with previous studies showing that interstitial fluid supports RCT; whereas plasma mainly contains α-HDL particles that are the predominant carriers of CE to hepatocytes, interstitial fluid provides a metabolic environment that drives the conversion of α-HDL to pre-β-HDL, the main acceptor of free cholesterol from peripheral tissues.138

    HDL particles can be partitioned into several subclasses according to the specific isolation or separation technique applied.139 By ultracentrifugation, 2 HDL subclasses can be obtained: HDL2 (1.063–1.125 g/mL) and HDL3 (1.125–1.21 g/mL). In turn, agarose gel electrophoresis separates HDL based on surface charge and shape into α- or pre-β-migrating particles (α-HDL or pre-β-HDL). Pre-β-HDL primarily consists of poorly lipidated apoA-I and is the substrate for ABCA1 that transfers phospholipids and cholesterol to apoA-I to generate nascent discoidal HDL.140 In turn, α-HDL represents mature HDL that arises from the esterification of free cholesterol into CE by LCAT, and α-HDL can subsequently be further lipidated through the action of ABCG1 and SR-B1 (Figure).

    Whether apoB-containing lipoproteins, which can also serve as cholesterol acceptors to facilitate RCT depending on the gradient, also enter peripheral tissues and drain into the lymph to regulate RCT remains to be investigated. In addition, more research is needed to understand how artery tertiary lymphoid organs form in the adventitia during atherosclerosis and to determine their role in regulating the immune response during atherosclerosis and how they may modulate RCT flux. For example, these lymphoid aggregates secrete chemokines that may promote foam cell retention, which may in turn increase plaque lipid burden.141

    Diabetes Mellitus

    As an example in which impairment in one or more components of RCT may underlie increased CVD risk, we will discuss diabetes mellitus. Diabetes mellitus, both type 1 and type 2, represent significant global health issues, with CVD accounting for 65% of mortality in this population.142 Additionally, the metabolic syndrome, a disorder associated with increased risk of developing type 2 diabetes mellitus, is unequivocally linked to increased risk for premature CVD and death.143 Type 2 diabetes mellitus and the metabolic syndrome have a number of associated pathologies, including insulin resistance, obesity and high plasma triglycerides, and, relevant to RCT, low levels of HDL-C and apoA-I, reduced HDL particle (HDL-P) number and dysfunctional HDL-Ps.144–150 Thus, there are a number of facets of RCT which likely contribute to heightened CVD risk in diabetic and metabolic syndrome patient populations.

    One mechanism for the impaired HDL-P function may be related to the formation of advanced glycation endproducts (AGEs), which are nonenzymatic modifications of proteins that occur in vivo in patients with diabetes mellitus. Glycation of HDL and apoA-I is proposed to impair their functionality by reducing both their CEC and antioxidant capacity.18,151–156 Additionally, in vitro, high glucose and AGE-modified proteins impair macrophage CEC by downregulation of the transporters ABCA1 and ABCG1, attributable to increased local production of reactive oxygen species.79,157–160 Consistent with this, numerous murine and human studies report decreased expression of ABCA1 and ABCG1 in monocytes and macrophages isolated from diabetic mice and people, translating to decreased myeloid CEC.99,161–164

    Mechanistically, reduced CEC transporter levels under diabetic conditions in vivo are mediated, in part, by the receptor for AGE (RAGE),161,163 which would be expected to be stimulated by the AGE-production noted above. This was recently highlighted by Daffu et al163 who reported that incubation of murine macrophages or human THP-1 (human leukemic cell line) cells with the model glycated protein CML (carboxy methyl lysine)-AGE reduced Abca1 and Abcg1 mRNA and protein expression via its interaction with RAGE. Reductions in the expression levels of these receptors resulted in decreased cholesterol efflux to apoA-I and HDL.163 Further, consistent with other studies,165–169 it was found that diabetes mellitus enhanced both atherosclerosis progression and impaired regression and that global deletion of RAGE overcame these defects by restoration of ABCA1 and ABCG1, promoting macrophage CEC despite ongoing hyperglycemia.163,170

    Restoration of global and myeloid ABCA1/ABCG1 expression and improvements to CVD outcomes under diabetic conditions is likely to be multifaceted. In addition to being essential for the removal of cholesterol from plaque macrophages,28 ABCA1 and ABCG1 regulate the proliferation of hematopoietic stem and progenitor cells to control the abundance of blood monocytes.27 Given the link between myelopoiesis and CVD risk,130,171 suppression of this process is likely to directly inhibit the progression of atherosclerotic lesions and promote lesion regression.166 Diabetes mellitus can suppress hematopoietic precursor cell ABCA1 and ABCG1 levels, promoting myelopoiesis and atherosclerosis.165 Furthermore, inhibition of miR-33, a negative regulator of cellular ABCA1 and ABCG1, suppresses leukocytosis and reduces plaque macrophage inflammation in diabetic mice.165 Despite persisant hyperglycemia, suppression of miR-33 not only restored essential cholesterol transporters and reduced myelopoiesis, but it also promoted inflammation resolution in established plaques. Additionally, unpublished work from the Fisher lab has found that raising apoA-I/HDL levels in diabetic mice, in the absence of glucose control, can restore atherosclerosis regression, in part, by overcoming defective CEC in hematopoietic stem cells (Barrett et al, In Revision). These complementary studies highlight the importance of effective CEC at both the level of the bone marrow and plaque under diabetic settings to reduce CVD morbidity and mortality risk.

    As with nondiabetic populations, the relationship of HDL-C to effective RCT in diabetic patients with CVD risk remains to be conclusively determined. However, given that macrophage CEC to plasma from diabetic subjects is overwhelmingly reported to be reduced compared with healthy controls,139,172–175 and the inverse relationship between glucose tolerance and plasma CEC,115,176 it is tempting to speculate that either restoring or enhancing in vivo RCT capacity within this population would reduce the incidence of CVD-linked disorders.

    Functional Properties of HDL in Cholesterol Efflux, RCT, and Beyond

    Factors to consider about the functionality of HDL include its pleiotropic actions besides cholesterol efflux. The bases for these actions likely involve the heterogeneity of HDL particles. For example, independent of its ability to mediate RCT by serving as a cholesterol acceptor, HDL is also known to exert potent antioxidant and anti-inflammatory effects that can improve RCT, retard plaque progression, and promote plaque regression.75,177 Indeed, overexpression of an HDL-associated protein that confers antioxidant properties to HDL, paraoxonase 1, improves the efflux capacity of HDL, and drives RCT in mice.178 HDL exists as subpopulations, classified based on their physicochemical properties: density (HDL2 and HDL3), shape (discoidal and spherical), protein (apoA-I, A-II, or both), surface charge, and size.139 The bulk of RCT is linked to apoA-I, which cycles between lipid-poor (pre-β-HDL) and -rich (α-HDL) forms of HDL, a remodeling event that, as noted earlier, can occur in the interstitial fluid of tissues to generate pre-β-HDL. This process is essential to RCT given that just 5% of plasma apoA-I exists as pre-β-HDL, the principal acceptors of cholesterol from peripheral cells.138,179,180 Proteomic analyses reveal that the composition of HDL is more complex than anticipated, containing ≈200 diverse proteins distributed among various HDL subclasses. In addition to protein and lipid cargo, HDL can transport functional noncoding RNAs, such as miRNAs, and this pool of lipoprotein-associated RNA can be altered in disease.181,182 It is now appreciated that how specific HDL functions (in CEC/RCT, thrombosis, inflammation, etc) are related to HDL compositional heterogeneity in humans and how HDL subspecies may be altered during CAD could lead to the identification of new diagnostic tools and therapies.139,183–185

    Concluding Remarks

    The quest for HDL-raising therapies has been long-standing in the fields of lipoprotein metabolism and CVD, as reflected in the past by physicians routinely prescribing drugs to boost HDL-C in patients. These therapies are now thought to be ineffective in reducing CVD risk.186 In addition, several clinical studies failed to show that raising HDL-C levels (eg, by niacin187,188 or CETP inhibition189) improves CVD outcomes, and Mendelian randomization studies also find that HDL-C levels are not predictive of CVD events.183 These and other studies highlight that while we have observed numerous successes in the development of multiple LDL-cholesterol lowering therapies that have translated into beneficial clinical outcomes, comparable advances in RCT-enhancing strategies through raising HDL-C are lacking. An example of the need for such enhancement independent of HDL-C may be found in the data from the CETP inhibitor trials. In particular, it may be more than a coincidence that the failure of torcetrapib to lower CVD events despite raising HDL-C by ≈72%190 was also associated with its failure to promote whole-body RCT in a fecal sterol excretion assay.191

    It should be noted that in none of the studies mentioned above and in many similar ones has HDL function been ascertained, leaving open the possibility that HDL function is the key attribute for CVD risk reduction.113 HDL function as a clinically important factor has found traction not only in the aforementioned CEC studies, but also finds some support from some but not all (eg, Nicholls et al192) infusion studies of recombinant HDL and HDL-like particles. Notably, however, all of the infusion studies to date are of limited significance, as they have been either too short to assess effects on CVD outcomes, very small in subject number, or both. For example, in one small study, the intravenous infusion of a single dose of reconstituted HDL led to acute changes in plaques in the superficial femoral artery, with a reduction in lipid content, macrophage size, and measures of inflammation, but there were only 20 subjects.193 In a larger study of subjects post-acute coronary syndromes (47 subjects completed the protocol), 5 weekly injections of a recombinant HDL-like particle (designated ETC-216) containing ApoA-Imilano-phospholipid complexes194 resulted in a 4.2% decrease from baseline in coronary atheroma volume as measured by intravascular ultrasound.

    A similar study was conducted with a formulation of wild-type ApoA-I (designated CSL111).195 The results were similar to the ETC-216 trial, in that plaque volume was decreased, but to a lesser extent (3.4%), perhaps because of a shorter course of treatment (4 weeks) or other differences between the studies. Again, there are no CVD outcome data in either trial. There is great interest, therefore, in the AEGIS II trial (ApoA-I Event Reducing in Ischemic Syndromes II), in which apoA-I in a proprietary formulation of lipids to simulate HDL particles (CSL112), is being administered to subjects with the acute coronary syndrome. With an estimated enrollment of 17 400, participants will be randomized to receive either CSL112 or a placebo, administered through intravenous infusion once a week for 4 consecutive weeks. The primary end point is the first occurrence of a major adverse cardiovascular event, cardiovascular death, myocardial infarction, or stroke within 90 days, and the expected completion date is 2022.187

    In spite of the controversies, on-balance we think that raising levels of functional HDL in those at risk for CVD events may yet represent a viable therapy to suppress atherosclerosis progression and promote atherosclerosis regression. This belief is based on the established biological effects of functional HDL that we have summarized, as well as the encouragement from the clinical studies, (114,193–195) although at present they fall short as definitive trials, especially with regard to the relationship between raising levels of functional HDL and MACE. This raises the parallel need for more trials of the type that AEGIS II represents, as well as mechanistic studies to further understand the factors that regulate HDL’s impact on CVD independent of the plasma concentration of HDL-C.

    Nonstandard Abbreviations and Acronyms


    ATP-binding cassette proteins A1 and G1


    acyl-CoA:cholesterol acyltransferase


    advanced glycation endproducts


    coronary artery disease


    C-C chemokine receptor type 7




    cholesteryl ester


    cholesterol efflux capacity


    cholesteryl ester transfer protein


    cardiovascular disease


    endoplasmic reticulum


    farnesoid X receptor


    high-density lipoprotein cholesterol


    Kruppel-like factor 4


    lysosomal acid lipase


    lecithin:cholesterol acyltransferase


    low-density lipoprotein cholesterol


    low-density lipoprotein receptor


    lipid droplets


    liver X receptors


    Niemann-Pick Type C


    oxysterol-binding related proteins


    oxysterol-binding proteins


    receptor for advanced glycation endproducts


    reverse cholesterol transport


    scavenger receptor class B type 1


    sterol regulatory element-binding protein


    serum response factor


    steroidogenic acute regulatory protein


    transintestinal cholesterol efflux


    very-low-density lipoprotein


    vascular smooth muscle cells


    Correspondence to Edward A. Fisher, New York University School of Medicine, 435 E 30th St, Science Bldg, New York, NY 10016, Email
    Mireille Ouimet, University of Ottawa Heart Institute, 40 Ruskin St, Room H4229, Ottawa, ON K1Y 4L7, Canada, Email


    • 1. Wilson PW, Garrison RJ, Castelli WP, Feinleib M, McNamara PM, Kannel WB. Prevalence of coronary heart disease in the Framingham offspring study: role of lipoprotein cholesterols.Am J Cardiol. 1980; 46:649–654.CrossrefMedlineGoogle Scholar
    • 2. Glomset JA, Janssen ET, Kennedy R, Dobbins J. Role of plasma lecithin:cholesterol acyltransferase in the metabolism of high density lipoproteins.J Lipid Res. 1966; 7:638–648.CrossrefMedlineGoogle Scholar
    • 3. Gordon DJ, Probstfield JL, Garrison RJ, Neaton JD, Castelli WP, Knoke JD, Jacobs DR, Bangdiwala S, Tyroler HA. High-density lipoprotein cholesterol and cardiovascular disease. Four prospective American studies.Circulation. 1989; 79:8–15.LinkGoogle Scholar
    • 4. Hutchins PM, Ronsein GE, Monette JS, Pamir N, Wimberger J, He Y, Anantharamaiah GM, Kim DS, Ranchalis JE, Jarvik GP, Vaisar T, Heinecke JW. Quantification of HDL particle concentration by calibrated ion mobility analysis.Clin Chem. 2014; 60:1393–1401. doi: 10.1373/clinchem.2014.228114CrossrefMedlineGoogle Scholar
    • 5. de la Llera-Moya M, et al. The ability to promote efflux via ABCA1 determines the capacity of serum specimens with similar high-density lipoprotein cholesterol to remove cholesterol from macrophages.Arterioscler Thromb Vasc Biol. 2010; 30:796–801. doi: 10.1161/ATVBAHA.109.199158LinkGoogle Scholar
    • 6. Voight BF, Peloso GM, Orho-Melander M, et al. Plasma HDL cholesterol and risk of myocardial infarction: a mendelian randomisation study.Lancet. 2012; 380:572–580. doi: 10.1016/S0140-6736(12)60312-2CrossrefMedlineGoogle Scholar
    • 7. Pittman RC, Steinberg D. Sites and mechanisms of uptake and degradation of high density and low density lipoproteins.J Lipid Res. 1984; 25:1577–1585.CrossrefMedlineGoogle Scholar
    • 8. Hong C, Tontonoz P. Liver X receptors in lipid metabolism: opportunities for drug discovery.Nat Rev Drug Discov. 2014; 13:433–444. doi: 10.1038/nrd4280CrossrefMedlineGoogle Scholar
    • 9. Zhang L, Reue K, Fong LG, Young SG, Tontonoz P. Feedback regulation of cholesterol uptake by the LXR-IDOL-LDLR axis.Arterioscler Thromb Vasc Biol. 2012; 32:2541–2546. doi: 10.1161/ATVBAHA.112.250571LinkGoogle Scholar
    • 10. Marquart TJ, Allen RM, Ory DS, Baldán A. miR-33 links SREBP-2 induction to repression of sterol transporters.Proc Natl Acad Sci U S A. 2010; 107:12228–12232. doi: 10.1073/pnas.1005191107CrossrefMedlineGoogle Scholar
    • 11. Najafi-Shoushtari SH, Kristo F, Li Y, Shioda T, Cohen DE, Gerszten RE, Näär AM. MicroRNA-33 and the SREBP host genes cooperate to control cholesterol homeostasis.Science. 2010; 328:1566–1569. doi: 10.1126/science.1189123CrossrefMedlineGoogle Scholar
    • 12. Rayner KJ, Suárez Y, Dávalos A, Parathath S, Fitzgerald ML, Tamehiro N, Fisher EA, Moore KJ, Fernández-Hernando C. MiR-33 contributes to the regulation of cholesterol homeostasis.Science. 2010; 328:1570–1573. doi: 10.1126/science.1189862CrossrefMedlineGoogle Scholar
    • 13. Rayner KJ, Esau CC, Hussain FN, et al. Inhibition of miR-33a/b in non-human primates raises plasma HDL and lowers VLDL triglycerides.Nature. 2011; 478:404–407. doi: 10.1038/nature10486CrossrefMedlineGoogle Scholar
    • 14. Rayner KJ, Sheedy FJ, Esau CC, Hussain FN, Temel RE, Parathath S, van Gils JM, Rayner AJ, Chang AN, Suarez Y, Fernandez-Hernando C, Fisher EA, Moore KJ. Antagonism of miR-33 in mice promotes reverse cholesterol transport and regression of atherosclerosis.J Clin Invest. 2011; 121:2921–2931. doi: 10.1172/JCI57275CrossrefMedlineGoogle Scholar
    • 15. Horie T, Baba O, Kuwabara Y, et al. MicroRNA-33 deficiency reduces the progression of atherosclerotic plaque in ApoE-/- mice.J Am Heart Assoc. 2012; 1:e003376. doi: 10.1161/JAHA.112.003376LinkGoogle Scholar
    • 16. Ouimet M, Ediriweera HN, Gundra UM, et al. MicroRNA-33-dependent regulation of macrophage metabolism directs immune cell polarization in atherosclerosis.J Clin Invest. 2015; 125:4334–4348. doi: 10.1172/JCI81676CrossrefMedlineGoogle Scholar
    • 17. Rotllan N, Ramírez CM, Aryal B, Esau CC, Fernández-Hernando C. Therapeutic silencing of microRNA-33 inhibits the progression of atherosclerosis in Ldlr-/- mice–brief report.Arterioscler Thromb Vasc Biol. 2013; 33:1973–1977. doi: 10.1161/ATVBAHA.113.301732LinkGoogle Scholar
    • 18. Duell PB, Oram JF, Bierman EL. Nonenzymatic glycosylation of HDL and impaired HDL-receptor-mediated cholesterol efflux.Diabetes. 1991; 40:377–384.CrossrefMedlineGoogle Scholar
    • 19. Goedeke L, Salerno A, Ramírez CM, Guo L, Allen RM, Yin X, Langley SR, Esau C, Wanschel A, Fisher EA, Suárez Y, Baldán A, Mayr M, Fernández-Hernando C. Long-term therapeutic silencing of miR-33 increases circulating triglyceride levels and hepatic lipid accumulation in mice.EMBO Mol Med. 2014; 6:1133–1141. doi: 10.15252/emmm.201404046CrossrefMedlineGoogle Scholar
    • 20. Horie T, Nishino T, Baba O, et al. MicroRNA-33 regulates sterol regulatory element-binding protein 1 expression in mice.Nat Commun. 2013; 4:2883. doi: 10.1038/ncomms3883CrossrefMedlineGoogle Scholar
    • 21. Karunakaran D, Richards L, Geoffrion M, Barrette D, Gotfrit RJ, Harper ME, Rayner KJ. Therapeutic inhibition of miR-33 rromotes fatty acid oxidation but does not ameliorate metabolic dysfunction in diet-induced obesity.Arterioscler Thromb Vasc Biol. 2015; 35:2536–2543. doi: 10.1161/ATVBAHA.115.306404LinkGoogle Scholar
    • 22. Price NL, Rotllan N, Canfrán-Duque A, Zhang X, Pati P, Arias N, Moen J, Mayr M, Ford DA, Baldán Á, Suárez Y, Fernández-Hernando C. Genetic dissection of the impact of miR-33a and miR-33b during the progression of atherosclerosis.Cell Rep. 2017; 21:1317–1330. doi: 10.1016/j.celrep.2017.10.023CrossrefMedlineGoogle Scholar
    • 23. Price NL, Rotllan N, Zhang X, Canfrán-Duque A, Nottoli T, Suarez Y, Fernández-Hernando C. Specific disruption of abca1 targeting largely mimics the effects of miR-33 knockout on macrophage cholesterol efflux and atherosclerotic plaque development.Circ Res. 2019; 124:874–880. doi: 10.1161/CIRCRESAHA.118.314415LinkGoogle Scholar
    • 24. Feinberg MW, Moore KJ. MicroRNA regulation of atherosclerosis.Circ Res. 2016; 118:703–720. doi: 10.1161/CIRCRESAHA.115.306300LinkGoogle Scholar
    • 25. Cuchel M, Rader DJ. Macrophage reverse cholesterol transport: key to the regression of atherosclerosis?Circulation. 2006; 113:2548–2555. doi: 10.1161/CIRCULATIONAHA.104.475715LinkGoogle Scholar
    • 26. Westerterp M, Murphy AJ, Wang M, et al. Deficiency of ATP-binding cassette transporters A1 and G1 in macrophages increases inflammation and accelerates atherosclerosis in mice.Circ Res. 2013; 112:1456–1465. doi: 10.1161/CIRCRESAHA.113.301086LinkGoogle Scholar
    • 27. Yvan-Charvet L, Pagler T, Gautier EL, Avagyan S, Siry RL, Han S, Welch CL, Wang N, Randolph GJ, Snoeck HW, Tall AR. ATP-binding cassette transporters and HDL suppress hematopoietic stem cell proliferation.Science. 2010; 328:1689–1693. doi: 10.1126/science.1189731CrossrefMedlineGoogle Scholar
    • 28. Yvan-Charvet L, Ranalletta M, Wang N, Han S, Terasaka N, Li R, Welch C, Tall AR. Combined deficiency of ABCA1 and ABCG1 promotes foam cell accumulation and accelerates atherosclerosis in mice.J Clin Invest. 2007; 117:3900–3908. doi: 10.1172/JCI33372MedlineGoogle Scholar
    • 29. Allahverdian S, Chaabane C, Boukais K, Francis GA, Bochaton-Piallat ML. Smooth muscle cell fate and plasticity in atherosclerosis.Cardiovasc Res. 2018; 114:540–550. doi: 10.1093/cvr/cvy022CrossrefMedlineGoogle Scholar
    • 30. Gomez D, Owens GK. Smooth muscle cell phenotypic switching in atherosclerosis.Cardiovasc Res. 2012; 95:156–164. doi: 10.1093/cvr/cvs115CrossrefMedlineGoogle Scholar
    • 31. Vengrenyuk Y, Nishi H, Long X, Ouimet M, Savji N, Martinez FO, Cassella CP, Moore KJ, Ramsey SA, Miano JM, Fisher EA. Cholesterol loading reprograms the microRNA-143/145-myocardin axis to convert aortic smooth muscle cells to a dysfunctional macrophage-like phenotype.Arterioscler Thromb Vasc Biol. 2015; 35:535–546. doi: 10.1161/ATVBAHA.114.304029LinkGoogle Scholar
    • 32. Shankman LS, Gomez D, Cherepanova OA, Salmon M, Alencar GF, Haskins RM, Swiatlowska P, Newman AA, Greene ES, Straub AC, Isakson B, Randolph GJ, Owens GK. KLF4-dependent phenotypic modulation of smooth muscle cells has a key role in atherosclerotic plaque pathogenesis.Nat Med. 2015; 21:628–637. doi: 10.1038/nm.3866CrossrefMedlineGoogle Scholar
    • 33. Wang Y, et al. Smooth muscle cells contribute the majority of foam cells in ApoE (Apolipoprotein E)-deficient mouse atherosclerosis [published online February 21, 2019].Arterioscler Thromb Vasc Biol. doi: 10.1161/ATVBAHA.119.312434.Google Scholar
    • 34. Goldberg IJ, Reue K, Abumrad NA, et al. Deciphering the role of lipid droplets in cardiovascular disease: a report from the 2017 National Heart, Lung, and Blood Institute Workshop.Circulation. 2018; 138:305–315. doi: 10.1161/CIRCULATIONAHA.118.033704LinkGoogle Scholar
    • 35. Ghosh S, Zhao B, Bie J, Song J. Macrophage cholesteryl ester mobilization and atherosclerosis.Vascul Pharmacol. 2010; 52:1–10. doi: 10.1016/j.vph.2009.10.002CrossrefMedlineGoogle Scholar
    • 36. Ouimet M, Marcel YL. Regulation of lipid droplet cholesterol efflux from macrophage foam cells.Arterioscler Thromb Vasc Biol. 2012; 32:575–581. doi: 10.1161/ATVBAHA.111.240705LinkGoogle Scholar
    • 37. Igarashi M, Osuga J, Uozaki H, et al. The critical role of neutral cholesterol ester hydrolase 1 in cholesterol removal from human macrophages.Circ Res. 2010; 107:1387–1395. doi: 10.1161/CIRCRESAHA.110.226613LinkGoogle Scholar
    • 38. Son SH, Goo YH, Choi M, Saha PK, Oka K, Chan LC, Paul A. Enhanced atheroprotection and lesion remodelling by targeting the foam cell and increasing plasma cholesterol acceptors.Cardiovasc Res. 2016; 109:294–304. doi: 10.1093/cvr/cvv241CrossrefMedlineGoogle Scholar
    • 39. Zhao B, Song J, Chow WN, St Clair RW, Rudel LL, Ghosh S. Macrophage-specific transgenic expression of cholesteryl ester hydrolase significantly reduces atherosclerosis and lesion necrosis in Ldlr mice.J Clin Invest. 2007; 117:2983–2992. doi: 10.1172/JCI30485CrossrefMedlineGoogle Scholar
    • 40. Ghosh S. Early steps in reverse cholesterol transport: cholesteryl ester hydrolase and other hydrolases.Curr Opin Endocrinol Diabetes Obes. 2012; 19:136–141. doi: 10.1097/MED.0b013e3283507836CrossrefMedlineGoogle Scholar
    • 41. Sekiya M, Osuga J, Nagashima S, et al. Ablation of neutral cholesterol ester hydrolase 1 accelerates atherosclerosis.Cell Metab. 2009; 10:219–228. doi: 10.1016/j.cmet.2009.08.004CrossrefMedlineGoogle Scholar
    • 42. Brown MS, Goldstein JL, Krieger M, Ho YK, Anderson RG. Reversible accumulation of cholesteryl esters in macrophages incubated with acetylated lipoproteins.J Cell Biol. 1979; 82:597–613.CrossrefMedlineGoogle Scholar
    • 43. McGookey DJ, Anderson RG. Morphological characterization of the cholesteryl ester cycle in cultured mouse macrophage foam cells.J Cell Biol. 1983; 97:1156–1168.CrossrefMedlineGoogle Scholar
    • 44. Brown MS, Ho YK, Goldstein JL. The cholesteryl ester cycle in macrophage foam cells. Continual hydrolysis and re-esterification of cytoplasmic cholesteryl esters.J Biol Chem. 1980; 255:9344–9352.CrossrefMedlineGoogle Scholar
    • 45. Ouimet M, Franklin V, Mak E, Liao X, Tabas I, Marcel YL. Autophagy regulates cholesterol efflux from macrophage foam cells via lysosomal acid lipase.Cell Metab. 2011; 13:655–667. doi: 10.1016/j.cmet.2011.03.023CrossrefMedlineGoogle Scholar
    • 46. Singh R, Cuervo AM. Autophagy in the cellular energetic balance.Cell Metab. 2011; 13:495–504. doi: 10.1016/j.cmet.2011.04.004CrossrefMedlineGoogle Scholar
    • 47. Hamasaki M, Yoshimori T. Where do they come from? Insights into autophagosome formation.FEBS Lett. 2010; 584:1296–1301. doi: 10.1016/j.febslet.2010.02.061CrossrefMedlineGoogle Scholar
    • 48. Zhang H, Reilly MP. LIPA variants in genome-wide association studies of coronary artery diseases: loss-of-function or gain-of-function?Arterioscler Thromb Vasc Biol. 2017; 37:1015–1017. doi: 10.1161/ATVBAHA.117.309344LinkGoogle Scholar
    • 49. Razani B, Feng C, Coleman T, Emanuel R, Wen H, Hwang S, Ting JP, Virgin HW, Kastan MB, Semenkovich CF. Autophagy links inflammasomes to atherosclerotic progression.Cell Metab. 2012; 15:534–544. doi: 10.1016/j.cmet.2012.02.011CrossrefMedlineGoogle Scholar
    • 50. Ouimet M, Ediriweera H, Afonso MS, Ramkhelawon B, Singaravelu R, Liao X, Bandler RC, Rahman K, Fisher EA, Rayner KJ, Pezacki JP, Tabas I, Moore KJ. microRNA-33 regulates macrophage autophagy in atherosclerosis.Arterioscler Thromb Vasc Biol. 2017; 37:1058–1067. doi: 10.1161/ATVBAHA.116.308916LinkGoogle Scholar
    • 51. Liao X, Sluimer JC, Wang Y, Subramanian M, Brown K, Pattison JS, Robbins J, Martinez J, Tabas I. Macrophage autophagy plays a protective role in advanced atherosclerosis.Cell Metab. 2012; 15:545–553. doi: 10.1016/j.cmet.2012.01.022CrossrefMedlineGoogle Scholar
    • 52. Sergin I, Evans TD, Zhang X, et al. Exploiting macrophage autophagy-lysosomal biogenesis as a therapy for atherosclerosis.Nat Commun. 2017; 8:15750. doi: 10.1038/ncomms15750CrossrefMedlineGoogle Scholar
    • 53. Iaea DB, Maxfield FR. Cholesterol trafficking and distribution.Essays Biochem. 2015; 57:43–55. doi: 10.1042/bse0570043CrossrefMedlineGoogle Scholar
    • 54. Hölttä-Vuori M, Ikonen E. Endosomal cholesterol traffic: vesicular and non-vesicular mechanisms meet.Biochem Soc Trans. 2006; 34:392–394. doi: 10.1042/BST0340392CrossrefMedlineGoogle Scholar
    • 55. Chen W, Wang N, Tall AR. A PEST deletion mutant of ABCA1 shows impaired internalization and defective cholesterol efflux from late endosomes.J Biol Chem. 2005; 280:29277–29281. doi: 10.1074/jbc.M505566200CrossrefMedlineGoogle Scholar
    • 56. Parathath S, Mick SL, Feig JE, Joaquin V, Grauer L, Habiel DM, Gassmann M, Gardner LB, Fisher EA. Hypoxia is present in murine atherosclerotic plaques and has multiple adverse effects on macrophage lipid metabolism.Circ Res. 2011; 109:1141–1152. doi: 10.1161/CIRCRESAHA.111.246363LinkGoogle Scholar
    • 57. Parathath S, Yang Y, Mick S, Fisher EA. Hypoxia in murine atherosclerotic plaques and its adverse effects on macrophages.Trends Cardiovasc Med. 2013; 23:80–84. doi: 10.1016/j.tcm.2012.09.004CrossrefMedlineGoogle Scholar
    • 58. Wang N, Ranalletta M, Matsuura F, Peng F, Tall AR. LXR-induced redistribution of ABCG1 to plasma membrane in macrophages enhances cholesterol mass efflux to HDL.Arterioscler Thromb Vasc Biol. 2006; 26:1310–1316. doi: 10.1161/01.ATV.0000218998.75963.02LinkGoogle Scholar
    • 59. Tarling EJ, Edwards PA. ATP binding cassette transporter G1 (ABCG1) is an intracellular sterol transporter.Proc Natl Acad Sci U S A. 2011; 108:19719–19724. doi: 10.1073/pnas.1113021108CrossrefMedlineGoogle Scholar
    • 60. Azuma Y, Takada M, Shin HW, Kioka N, Nakayama K, Ueda K. Retroendocytosis pathway of ABCA1/apoA-I contributes to HDL formation.Genes Cells. 2009; 14:191–204. doi: 10.1111/j.1365-2443.2008.01261.xCrossrefMedlineGoogle Scholar
    • 61. Kentala H, Weber-Boyvat M, Olkkonen VM. OSBP-related protein family: mediators of lipid transport and signaling at membrane contact sites.Int Rev Cell Mol Biol. 2016; 321:299–340. doi: 10.1016/bs.ircmb.2015.09.006CrossrefMedlineGoogle Scholar
    • 62. Ouimet M, Hennessy EJ, van Solingen C, Koelwyn GJ, Hussein MA, Ramkhelawon B, Rayner KJ, Temel RE, Perisic L, Hedin U, Maegdefessel L, Garabedian MJ, Holdt LM, Teupser D, Moore KJ. miRNA targeting of oxysterol-binding protein-like 6 regulates cholesterol trafficking and efflux.Arterioscler Thromb Vasc Biol. 2016; 36:942–951. doi: 10.1161/ATVBAHA.116.307282LinkGoogle Scholar
    • 63. Mesmin B, Maxfield FR. Intracellular sterol dynamics.Biochim Biophys Acta. 2009; 1791:636–645. doi: 10.1016/j.bbalip.2009.03.002CrossrefMedlineGoogle Scholar
    • 64. Sandhu J, Li S, Fairall L, et al. Aster proteins facilitate nonvesicular plasma membrane to ER cholesterol transport in mammalian cells.Cell. 2018; 175:514–529.e20. doi: 10.1016/j.cell.2018.08.033CrossrefMedlineGoogle Scholar
    • 65. Wolfbauer G, Glick JM, Minor LK, Rothblat GH. Development of the smooth muscle foam cell: uptake of macrophage lipid inclusions.Proc Natl Acad Sci U S A. 1986; 83:7760–7764.CrossrefMedlineGoogle Scholar
    • 66. Frontini MJ, O’Neil C, Sawyez C, Chan BM, Huff MW, Pickering JG. Lipid incorporation inhibits Src-dependent assembly of fibronectin and type I collagen by vascular smooth muscle cells.Circ Res. 2009; 104:832–841. doi: 10.1161/CIRCRESAHA.108.187302LinkGoogle Scholar
    • 67. Rong JX, Shapiro M, Trogan E, Fisher EA. Transdifferentiation of mouse aortic smooth muscle cells to a macrophage-like state after cholesterol loading.Proc Natl Acad Sci U S A. 2003; 100:13531–13536. doi: 10.1073/pnas.1735526100CrossrefMedlineGoogle Scholar
    • 68. Feil S, Fehrenbacher B, Lukowski R, Essmann F, Schulze-Osthoff K, Schaller M, Feil R. Transdifferentiation of vascular smooth muscle cells to macrophage-like cells during atherogenesis.Circ Res. 2014; 115:662–667. doi: 10.1161/CIRCRESAHA.115.304634LinkGoogle Scholar
    • 69. Allahverdian S, Chehroudi AC, McManus BM, Abraham T, Francis GA. Contribution of intimal smooth muscle cells to cholesterol accumulation and macrophage-like cells in human atherosclerosis.Circulation. 2014; 129:1551–1559. doi: 10.1161/CIRCULATIONAHA.113.005015LinkGoogle Scholar
    • 70. Chappell J, Harman JL, Narasimhan VM, Yu H, Foote K, Simons BD, Bennett MR, Jørgensen HF. Extensive proliferation of a subset of differentiated, yet plastic, medial vascular smooth muscle cells contributes to neointimal formation in mouse injury and atherosclerosis models.Circ Res. 2016; 119:1313–1323. doi: 10.1161/CIRCRESAHA.116.309799LinkGoogle Scholar
    • 71. Misra A, Feng Z, Chandran RR, Kabir I, Rotllan N, Aryal B, Sheikh AQ, Ding L, Qin L, Fernández-Hernando C, Tellides G, Greif DM. Integrin beta3 regulates clonality and fate of smooth muscle-derived atherosclerotic plaque cells.Nat Commun. 2018; 9:2073. doi: 10.1038/s41467-018-04447-7CrossrefMedlineGoogle Scholar
    • 72. Liao X, Sharma N, Kapadia F, et al. Krüppel-like factor 4 regulates macrophage polarization.J Clin Invest. 2011; 121:2736–2749. doi: 10.1172/JCI45444CrossrefMedlineGoogle Scholar
    • 73. Choi HY, Rahmani M, Wong BW, Allahverdian S, McManus BM, Pickering JG, Chan T, Francis GA. ATP-binding cassette transporter A1 expression and apolipoprotein A-I binding are impaired in intima-type arterial smooth muscle cells.Circulation. 2009; 119:3223–3231. doi: 10.1161/CIRCULATIONAHA.108.841130LinkGoogle Scholar
    • 74. Choi HY, Hafiane A, Schwertani A, Genest J. High-density lipoproteins: biology, epidemiology, and clinical management.Can J Cardiol. 2017; 33:325–333. doi: 10.1016/j.cjca.2016.09.012CrossrefMedlineGoogle Scholar
    • 75. Fisher EA, Feig JE, Hewing B, Hazen SL, Smith JD. High-density lipoprotein function, dysfunction, and reverse cholesterol transport.Arterioscler Thromb Vasc Biol. 2012; 32:2813–2820. doi: 10.1161/ATVBAHA.112.300133LinkGoogle Scholar
    • 76. Rye KA, Barter PJ. Cardioprotective functions of HDLs.J Lipid Res. 2014; 55:168–179. doi: 10.1194/jlr.R039297CrossrefMedlineGoogle Scholar
    • 77. Qian H, Zhao X, Cao P, Lei J, Yan N, Gong X. Structure of the human lipid exporter ABCA1.Cell. 2017; 169:1228–1239.e10. doi: 10.1016/j.cell.2017.05.020CrossrefMedlineGoogle Scholar
    • 78. Assmann G, Gotto AM. HDL cholesterol and protective factors in atherosclerosis.Circulation. 2004; 109:III8–II14. doi: 10.1161/01.CIR.0000131512.50667.46LinkGoogle Scholar
    • 79. Tang C, Oram JF. The cell cholesterol exporter ABCA1 as a protector from cardiovascular disease and diabetes.Biochim Biophys Acta. 2009; 1791:563–572. doi: 10.1016/j.bbalip.2009.03.011CrossrefMedlineGoogle Scholar
    • 80. Wang N, Lan D, Chen W, Matsuura F, Tall AR. ATP-binding cassette transporters G1 and G4 mediate cellular cholesterol efflux to high-density lipoproteins.Proc Natl Acad Sci U S A. 2004; 101:9774–9779. doi: 10.1073/pnas.0403506101CrossrefMedlineGoogle Scholar
    • 81. Neufeld EB, Remaley AT, Demosky SJ, Stonik JA, Cooney AM, Comly M, Dwyer NK, Zhang M, Blanchette-Mackie J, Santamarina-Fojo S, Brewer HB. Cellular localization and trafficking of the human ABCA1 transporter.J Biol Chem. 2001; 276:27584–27590. doi: 10.1074/jbc.M103264200CrossrefMedlineGoogle Scholar
    • 82. Chen W, Sun Y, Welch C, Gorelik A, Leventhal AR, Tabas I, Tall AR. Preferential ATP-binding cassette transporter A1-mediated cholesterol efflux from late endosomes/lysosomes.J Biol Chem. 2001; 276:43564–43569. doi: 10.1074/jbc.M107938200CrossrefMedlineGoogle Scholar
    • 83. Phillips MC, Johnson WJ, Rothblat GH. Mechanisms and consequences of cellular cholesterol exchange and transfer.Biochim Biophys Acta. 1987; 906:223–276.CrossrefMedlineGoogle Scholar
    • 84. Rothblat GH, Phillips MC. High-density lipoprotein heterogeneity and function in reverse cholesterol transport.Curr Opin Lipidol. 2010; 21:229–238.CrossrefMedlineGoogle Scholar
    • 85. Kennedy MA, Barrera GC, Nakamura K, Baldán A, Tarr P, Fishbein MC, Frank J, Francone OL, Edwards PA. ABCG1 has a critical role in mediating cholesterol efflux to HDL and preventing cellular lipid accumulation.Cell Metab. 2005; 1:121–131. doi: 10.1016/j.cmet.2005.01.002CrossrefMedlineGoogle Scholar
    • 86. Vaughan AM, Oram JF. ABCG1 redistributes cell cholesterol to domains removable by high density lipoprotein but not by lipid-depleted apolipoproteins.J Biol Chem. 2005; 280:30150–30157. doi: 10.1074/jbc.M505368200CrossrefMedlineGoogle Scholar
    • 87. Annema W, Tietge UJ. Role of hepatic lipase and endothelial lipase in high-density lipoprotein-mediated reverse cholesterol transport.Curr Atheroscler Rep. 2011; 13:257–265. doi: 10.1007/s11883-011-0175-2CrossrefMedlineGoogle Scholar
    • 88. Khera AV, Rader DJ. Future therapeutic directions in reverse cholesterol transport.Curr Atheroscler Rep. 2010; 12:73–81. doi: 10.1007/s11883-009-0080-0CrossrefMedlineGoogle Scholar
    • 89. Temel RE, Brown JM. A new framework for reverse cholesterol transport: non-biliary contributions to reverse cholesterol transport.World J Gastroenterol. 2010; 16:5946–5952.MedlineGoogle Scholar
    • 90. Brufau G, Groen AK, Kuipers F. Reverse cholesterol transport revisited: contribution of biliary versus intestinal cholesterol excretion.Arterioscler Thromb Vasc Biol. 2011; 31:1726–1733. doi: 10.1161/ATVBAHA.108.181206LinkGoogle Scholar
    • 91. Mendelsohn AR, Larrick JW. Preclinical reversal of atherosclerosis by FDA-Approved compound that transforms cholesterol into an anti-inflammatory “Prodrug”.Rejuvenation Res. 2016; 19:252–255. doi: 10.1089/rej.2016.1849CrossrefMedlineGoogle Scholar
    • 92. Zimmer S, Grebe A, Bakke SS, et al. Cyclodextrin promotes atherosclerosis regression via macrophage reprogramming.Sci Transl Med. 2016; 8:333ra50. doi: 10.1126/scitranslmed.aad6100CrossrefMedlineGoogle Scholar
    • 93. Pownall HJ, Ehnholm C. Enhancing reverse cholesterol transport: the case for phosphatidylcholine therapy.Curr Opin Lipidol. 2005; 16:265–268.CrossrefMedlineGoogle Scholar
    • 94. Rodrigueza WV, Mazany KD, Essenburg AD, Pape ME, Rea TJ, Bisgaier CL, Williams KJ. Large versus small unilamellar vesicles mediate reverse cholesterol transport in vivo into two distinct hepatic metabolic pools. Implications for the treatment of atherosclerosis.Arterioscler Thromb Vasc Biol. 1997; 17:2132–2139.LinkGoogle Scholar
    • 95. Stein O, Oette K, Haratz D, Halperin G, Stein Y. Sphingomyelin liposomes with defined fatty acids: metabolism and effects on reverse cholesterol transport.Biochim Biophys Acta. 1988; 960:322–333.CrossrefMedlineGoogle Scholar
    • 96. Hung KT, Berisha SZ, Ritchey BM, Santore J, Smith JD. Red blood cells play a role in reverse cholesterol transport.Arterioscler Thromb Vasc Biol. 2012; 32:1460–1465. doi: 10.1161/ATVBAHA.112.248971LinkGoogle Scholar
    • 97. Hafiane A, Genest J. ATP binding cassette A1 (ABCA1) mediates microparticle formation during high-density lipoprotein (HDL) biogenesis.Atherosclerosis. 2017; 257:90–99. doi: 10.1016/j.atherosclerosis.2017.01.013CrossrefMedlineGoogle Scholar
    • 98. Sanchez-Gaytan BL, Fay F, Lobatto ME, Tang J, Ouimet M, Kim Y, van der Staay SE, van Rijs SM, Priem B, Zhang L, Fisher EA, Moore KJ, Langer R, Fayad ZA, Mulder WJ. HDL-mimetic PLGA nanoparticle to target atherosclerosis plaque macrophages.Bioconjug Chem. 2015; 26:443–451. doi: 10.1021/bc500517kCrossrefMedlineGoogle Scholar
    • 99. Tang J, Baxter S, Menon A, et al. Immune cell screening of a nanoparticle library improves atherosclerosis therapy.Proc Natl Acad Sci U S A. 2016; 113:E6731–E6740. doi: 10.1073/pnas.1609629113CrossrefMedlineGoogle Scholar
    • 100. Duivenvoorden R, Tang J, Cormode DP, et al. A statin-loaded reconstituted high-density lipoprotein nanoparticle inhibits atherosclerotic plaque inflammation.Nat Commun. 2014; 5:3065. doi: 10.1038/ncomms4065CrossrefMedlineGoogle Scholar
    • 101. Hafiane A, Genest J. HDL, Atherosclerosis, and Emerging Therapies.Cholesterol. 2013; 2013:891403. doi: 10.1155/2013/891403CrossrefMedlineGoogle Scholar
    • 102. Zanoni P, Khetarpal SA, Larach DB, et al.; CHD Exome+ Consortium; CARDIoGRAM Exome Consortium; Global Lipids Genetics Consortium. Rare variant in scavenger receptor BI raises HDL cholesterol and increases risk of coronary heart disease.Science. 2016; 351:1166–1171. doi: 10.1126/science.aad3517CrossrefMedlineGoogle Scholar
    • 103. Hoekstra M. SR-BI as target in atherosclerosis and cardiovascular disease - a comprehensive appraisal of the cellular functions of SR-BI in physiology and disease.Atherosclerosis. 2017; 258:153–161. doi: 10.1016/j.atherosclerosis.2017.01.034CrossrefMedlineGoogle Scholar
    • 104. Helgadottir A, Sulem P, Thorgeirsson G, Gretarsdottir S, Thorleifsson G, Jensson BÖ, Arnadottir GA, Olafsson I, Eyjolfsson GI, Sigurdardottir O, Thorsteinsdottir U, Gudbjartsson DF, Holm H, Stefansson K. Rare SCARB1 mutations associate with high-density lipoprotein cholesterol but not with coronary artery disease.Eur Heart J. 2018; 39:2172–2178. doi: 10.1093/eurheartj/ehy169CrossrefMedlineGoogle Scholar
    • 105. Dikkers A, Tietge UJ. Biliary cholesterol secretion: more than a simple ABC.World J Gastroenterol. 2010; 16:5936–5945.MedlineGoogle Scholar
    • 106. Paalvast Y, de Boer JF, Groen AK. Developments in intestinal cholesterol transport and triglyceride absorption.Curr Opin Lipidol. 2017; 28:248–254. doi: 10.1097/MOL.0000000000000415CrossrefMedlineGoogle Scholar
    • 107. Xu Y, Li F, Zalzala M, Xu J, Gonzalez FJ, Adorini L, Lee YK, Yin L, Zhang Y. Farnesoid X receptor activation increases reverse cholesterol transport by modulating bile acid composition and cholesterol absorption in mice.Hepatology. 2016; 64:1072–1085. doi: 10.1002/hep.28712CrossrefMedlineGoogle Scholar
    • 108. Russell DW. The enzymes, regulation, and genetics of bile acid synthesis.Annu Rev Biochem. 2003; 72:137–174. doi: 10.1146/annurev.biochem.72.121801.161712CrossrefMedlineGoogle Scholar
    • 109. Pelton PD, Patel M, Demarest KT. Nuclear receptors as potential targets for modulating reverse cholesterol transport.Curr Top Med Chem. 2005; 5:265–282.CrossrefMedlineGoogle Scholar
    • 110. Jakobsson T, Treuter E, Gustafsson JÅ, Steffensen KR. Liver X receptor biology and pharmacology: new pathways, challenges and opportunities.Trends Pharmacol Sci. 2012; 33:394–404. doi: 10.1016/ Scholar
    • 111. Ouimet M, Moore KJ. A big role for small RNAs in HDL homeostasis.J Lipid Res. 2013; 54:1161–1167. doi: 10.1194/jlr.R036327CrossrefMedlineGoogle Scholar
    • 112. Rader DJ, Tall AR. The not-so-simple HDL story: is it time to revise the HDL cholesterol hypothesis?Nat Med. 2012; 18:1344–1346. doi: 10.1038/nm.2937CrossrefMedlineGoogle Scholar
    • 113. Hewing B, Moore KJ, Fisher EA. HDL and cardiovascular risk: time to call the plumber?Circ Res. 2012; 111:1117–1120. doi: 10.1161/CIRCRESAHA.112.280958LinkGoogle Scholar
    • 114. Rohatgi A, Khera A, Berry JD, Givens EG, Ayers CR, Wedin KE, Neeland IJ, Yuhanna IS, Rader DR, de Lemos JA, Shaul PW. HDL cholesterol efflux capacity and incident cardiovascular events.N Engl J Med. 2014; 371:2383–2393. doi: 10.1056/NEJMoa1409065CrossrefMedlineGoogle Scholar
    • 115. Saleheen D, Scott R, Javad S, Zhao W, Rodrigues A, Picataggi A, Lukmanova D, Mucksavage ML, Luben R, Billheimer J, Kastelein JJ, Boekholdt SM, Khaw KT, Wareham N, Rader DJ. Association of HDL cholesterol efflux capacity with incident coronary heart disease events: a prospective case-control study.Lancet Diabetes Endocrinol. 2015; 3:507–513. doi: 10.1016/S2213-8587(15)00126-6CrossrefMedlineGoogle Scholar
    • 116. Shea S, Stein JH, Jorgensen NW, McClelland RL, Tascau L, Shrager S, Heinecke JW, Yvan-Charvet L, Tall AR. Cholesterol mass efflux capacity, incident cardiovascular disease, and progression of carotid plaque.Arterioscler Thromb Vasc Biol. 2019; 39:89–96. doi: 10.1161/ATVBAHA.118.311366LinkGoogle Scholar
    • 117. Rothblat GH, de la Llera-Moya M, Favari E, Yancey PG, Kellner-Weibel G. Cellular cholesterol flux studies: methodological considerations.Atherosclerosis. 2002; 163:1–8.CrossrefMedlineGoogle Scholar
    • 118. Sankaranarayanan S, Kellner-Weibel G, de la Llera-Moya M, Phillips MC, Asztalos BF, Bittman R, Rothblat GH. A sensitive assay for ABCA1-mediated cholesterol efflux using BODIPY-cholesterol.J Lipid Res. 2011; 52:2332–2340. doi: 10.1194/jlr.D018051CrossrefMedlineGoogle Scholar
    • 119. Waddington EI, Boadu E, Francis GA. Cholesterol and phospholipid efflux from cultured cells.Methods. 2005; 36:196–206. doi: 10.1016/j.ymeth.2004.12.002CrossrefMedlineGoogle Scholar
    • 120. Robichaud S, Ouimet M. Quantifying cellular cholesterol efflux.Methods Mol Biol. 2019; 1951:111–133. doi: 10.1007/978-1-4939-9130-3_9CrossrefMedlineGoogle Scholar
    • 121. Khera AV, Cuchel M, de la Llera-Moya M, Rodrigues A, Burke MF, Jafri K, French BC, Phillips JA, Mucksavage ML, Wilensky RL, Mohler ER, Rothblat GH, Rader DJ. Cholesterol efflux capacity, high-density lipoprotein function, and atherosclerosis.N Engl J Med. 2011; 364:127–135. doi: 10.1056/NEJMoa1001689CrossrefMedlineGoogle Scholar
    • 122. Khera AV, Demler OV, Adelman SJ, Collins HL, Glynn RJ, Ridker PM, Rader DJ, Mora S. Cholesterol efflux capacity, high-density lipoprotein particle number, and incident cardiovascular events: an analysis from the JUPITER trial (justification for the use of statins in prevention: an intervention trial evaluating rosuvastatin).Circulation. 2017; 135:2494–2504. doi: 10.1161/CIRCULATIONAHA.116.025678LinkGoogle Scholar
    • 123. Li XM, Tang WH, Mosior MK, Huang Y, Wu Y, Matter W, Gao V, Schmitt D, Didonato JA, Fisher EA, Smith JD, Hazen SL. Paradoxical association of enhanced cholesterol efflux with increased incident cardiovascular risks.Arterioscler Thromb Vasc Biol. 2013; 33:1696–1705. doi: 10.1161/ATVBAHA.113.301373LinkGoogle Scholar
    • 124. Zhang Y, Zanotti I, Reilly MP, Glick JM, Rothblat GH, Rader DJ. Overexpression of apolipoprotein A-I promotes reverse transport of cholesterol from macrophages to feces in vivo.Circulation. 2003; 108:661–663. doi: 10.1161/01.CIR.0000086981.09834.E0LinkGoogle Scholar
    • 125. Annema W, Tietge UJ. Regulation of reverse cholesterol transport - a comprehensive appraisal of available animal studies.Nutr Metab (Lond). 2012; 9:25. doi: 10.1186/1743-7075-9-25CrossrefMedlineGoogle Scholar
    • 126. Weibel GL, Hayes S, Wilson A, Phillips MC, Billheimer J, Rader DJ, Rothblat GH. Novel in vivo method for measuring cholesterol mass flux in peripheral macrophages.Arterioscler Thromb Vasc Biol. 2011; 31:2865–2871. doi: 10.1161/ATVBAHA.111.236406LinkGoogle Scholar
    • 127. Cuchel M, Raper AC, Conlon DM, et al. A novel approach to measuring macrophage-specific reverse cholesterol transport in vivo in humans.J Lipid Res. 2017; 58:752–762. doi: 10.1194/jlr.M075226CrossrefMedlineGoogle Scholar
    • 128. Chhatriwalla AK, Rader DJ. Intracoronary imaging, reverse cholesterol transport, and transcriptomics: precision medicine in CAD?J Am Coll Cardiol. 2017; 69:641–643. doi: 10.1016/j.jacc.2016.12.003CrossrefMedlineGoogle Scholar
    • 129. Tabas I, Williams KJ, Borén J. Subendothelial lipoprotein retention as the initiating process in atherosclerosis: update and therapeutic implications.Circulation. 2007; 116:1832–1844. doi: 10.1161/CIRCULATIONAHA.106.676890LinkGoogle Scholar
    • 130. Moore KJ, Sheedy FJ, Fisher EA. Macrophages in atherosclerosis: a dynamic balance.Nat Rev Immunol. 2013; 13:709–721. doi: 10.1038/nri3520CrossrefMedlineGoogle Scholar
    • 131. Trogan E, Feig JE, Dogan S, Rothblat GH, Angeli V, Tacke F, Randolph GJ, Fisher EA. Gene expression changes in foam cells and the role of chemokine receptor CCR7 during atherosclerosis regression in ApoE-deficient mice.Proc Natl Acad Sci U S A. 2006; 103:3781–3786. doi: 10.1073/pnas.0511043103CrossrefMedlineGoogle Scholar
    • 132. Feig JE, Shang Y, Rotllan N, Vengrenyuk Y, Wu C, Shamir R, Torra IP, Fernandez-Hernando C, Fisher EA, Garabedian MJ. Statins promote the regression of atherosclerosis via activation of the CCR7-dependent emigration pathway in macrophages.PLoS One. 2011; 6:e28534. doi: 10.1371/journal.pone.0028534CrossrefMedlineGoogle Scholar
    • 133. Potteaux S, Gautier EL, Hutchison SB, van Rooijen N, Rader DJ, Thomas MJ, Sorci-Thomas MG, Randolph GJ. Suppressed monocyte recruitment drives macrophage removal from atherosclerotic plaques of Apoe-/- mice during disease regression.J Clin Invest. 2011; 121:2025–2036. doi: 10.1172/JCI43802CrossrefMedlineGoogle Scholar
    • 134. Mueller PA, Zhu L, Tavori H, Huynh K, Giunzioni I, Stafford JM, Linton MF, Fazio S. Deletion of macrophage low-density Lipoprotein Receptor-Related Protein 1 (LRP1) accelerates atherosclerosis regression and increases C-C chemokine receptor type 7 (CCR7) expression in plaque macrophages.Circulation. 2018; 138:1850–1863. doi: 10.1161/CIRCULATIONAHA.117.031702LinkGoogle Scholar
    • 135. Milasan A, Ledoux J, Martel C. Lymphatic network in atherosclerosis: the underestimated path.Future Sci OA. 2015; 1:FSO61. doi: 10.4155/fso.15.61CrossrefMedlineGoogle Scholar
    • 136. Martel C, Li W, Fulp B, Platt AM, Gautier EL, Westerterp M, Bittman R, Tall AR, Chen SH, Thomas MJ, Kreisel D, Swartz MA, Sorci-Thomas MG, Randolph GJ. Lymphatic vasculature mediates macrophage reverse cholesterol transport in mice.J Clin Invest. 2013; 123:1571–1579. doi: 10.1172/JCI63685CrossrefMedlineGoogle Scholar
    • 137. Vuorio T, Nurmi H, Moulton K, Kurkipuro J, Robciuc MR, Ohman M, Heinonen SE, Samaranayake H, Heikura T, Alitalo K, Ylä-Herttuala S. Lymphatic vessel insufficiency in hypercholesterolemic mice alters lipoprotein levels and promotes atherogenesis.Arterioscler Thromb Vasc Biol. 2014; 34:1162–1170. doi: 10.1161/ATVBAHA.114.302528LinkGoogle Scholar
    • 138. Miller NE, Olszewski WL, Hattori H, Miller IP, Kujiraoka T, Oka T, Iwasaki T, Nanjee MN. Lipoprotein remodeling generates lipid-poor apolipoprotein A-I particles in human interstitial fluid.Am J Physiol Endocrinol Metab. 2013; 304:E321–E328. doi: 10.1152/ajpendo.00324.2012CrossrefMedlineGoogle Scholar
    • 139. Kontush A, Lindahl M, Lhomme M, Calabresi L, Chapman MJ, Davidson WS. Structure of HDL: particle subclasses and molecular components.Handb Exp Pharmacol. 2015; 224:3–51. doi: 10.1007/978-3-319-09665-0_1CrossrefMedlineGoogle Scholar
    • 140. Wang S, Smith JD. ABCA1 and nascent HDL biogenesis.Biofactors. 2014; 40:547–554. doi: 10.1002/biof.1187CrossrefMedlineGoogle Scholar
    • 141. Yin C, Mohanta SK, Srikakulapu P, Weber C, Habenicht AJ. Artery tertiary lymphoid organs: powerhouses of atherosclerosis immunity.Front Immunol. 2016; 7:387. doi: 10.3389/fimmu.2016.00387CrossrefMedlineGoogle Scholar
    • 142. Haffner SM, Lehto S, Rönnemaa T, Pyörälä K, Laakso M. Mortality from coronary heart disease in subjects with type 2 diabetes and in nondiabetic subjects with and without prior myocardial infarction.N Engl J Med. 1998; 339:229–234. doi: 10.1056/NEJM199807233390404CrossrefMedlineGoogle Scholar
    • 143. Okada K, Hibi K, Gohbara M, et al. Association between blood glucose variability and coronary plaque instability in patients with acute coronary syndromes.Cardiovasc Diabetol. 2015; 14:111. doi: 10.1186/s12933-015-0275-3CrossrefMedlineGoogle Scholar
    • 144. Taskinen MR. Diabetic dyslipidaemia: from basic research to clinical practice.Diabetologia. 2003; 46:733–749. doi: 10.1007/s00125-003-1111-yCrossrefMedlineGoogle Scholar
    • 145. Garg A. Dyslipoproteinemia and diabetes.Endocrinol Metab Clin North Am. 1998; 27:613–25, ix.CrossrefMedlineGoogle Scholar
    • 146. Wilson PW, Meigs JB, Sullivan L, Fox CS, Nathan DM, D’Agostino RB. Prediction of incident diabetes mellitus in middle-aged adults: the Framingham offspring study.Arch Intern Med. 2007; 167:1068–1074. doi: 10.1001/archinte.167.10.1068CrossrefMedlineGoogle Scholar
    • 147. Hwang YC, Ahn HY, Park SW, Park CY. Association of HDL-C and apolipoprotein A-I with the risk of type 2 diabetes in subjects with impaired fasting glucose.Eur J Endocrinol. 2014; 171:137–142. doi: 10.1530/EJE-14-0195CrossrefMedlineGoogle Scholar
    • 148. Lachin JM, Orchard TJ, Nathan DM; DCCT/EDIC Research Group. Update on cardiovascular outcomes at 30 years of the diabetes control and complications trial/epidemiology of diabetes interventions and complications study.Diabetes Care. 2014; 37:39–43. doi: 10.2337/dc13-2116CrossrefMedlineGoogle Scholar
    • 149. Asleh R, Levy AP. Divergent effects of alpha-tocopherol and vitamin C on the generation of dysfunctional HDL associated with diabetes and the Hp 2-2 genotype.Antioxid Redox Signal. 2010; 12:209–217. doi: 10.1089/ars.2009.2829CrossrefMedlineGoogle Scholar
    • 150. Patel DC, Albrecht C, Pavitt D, Paul V, Pourreyron C, Newman SP, Godsland IF, Valabhji J, Johnston DG. Type 2 diabetes is associated with reduced ATP-binding cassette transporter A1 gene expression, protein and function.PLoS One. 2011; 6:e22142. doi: 10.1371/journal.pone.0022142CrossrefMedlineGoogle Scholar
    • 151. Curtiss LK, Witztum JL. Plasma apolipoproteins AI, AII, B, CI, and E are glucosylated in hyperglycemic diabetic subjects.Diabetes. 1985; 34:452–461.CrossrefMedlineGoogle Scholar
    • 152. Hedrick CC, Thorpe SR, Fu MX, Harper CM, Yoo J, Kim SM, Wong H, Peters AL. Glycation impairs high-density lipoprotein function.Diabetologia. 2000; 43:312–320. doi: 10.1007/s001250050049CrossrefMedlineGoogle Scholar
    • 153. Ferretti G, Bacchetti T, Marchionni C, Caldarelli L, Curatola G. Effect of glycation of high density lipoproteins on their physicochemical properties and on paraoxonase activity.Acta Diabetol. 2001; 38:163–169.CrossrefMedlineGoogle Scholar
    • 154. Low H, Hoang A, Forbes J, Thomas M, Lyons JG, Nestel P, Bach LA, Sviridov D. Advanced glycation end-products (AGEs) and functionality of reverse cholesterol transport in patients with type 2 diabetes and in mouse models.Diabetologia. 2012; 55:2513–2521. doi: 10.1007/s00125-012-2570-9CrossrefMedlineGoogle Scholar
    • 155. Nobécourt E, Tabet F, Lambert G, Puranik R, Bao S, Yan L, Davies MJ, Brown BE, Jenkins AJ, Dusting GJ, Bonnet DJ, Curtiss LK, Barter PJ, Rye KA. Nonenzymatic glycation impairs the antiinflammatory properties of apolipoprotein A-I.Arterioscler Thromb Vasc Biol. 2010; 30:766–772. doi: 10.1161/ATVBAHA.109.201715LinkGoogle Scholar
    • 156. Hoang A, Murphy AJ, Coughlan MT, Thomas MC, Forbes JM, O’Brien R, Cooper ME, Chin-Dusting JP, Sviridov D. Advanced glycation of apolipoprotein A-I impairs its anti-atherogenic properties.Diabetologia. 2007; 50:1770–1779. doi: 10.1007/s00125-007-0718-9CrossrefMedlineGoogle Scholar
    • 157. Passarelli M, Shimabukuro AF, Catanozi S, Nakandakare ER, Rocha JC, Carrilho AJ, Quintão EC. Diminished rate of mouse peritoneal macrophage cholesterol efflux is not related to the degree of HDL glycation in diabetes mellitus.Clin Chim Acta. 2000; 301:119–134.CrossrefMedlineGoogle Scholar
    • 158. Ohgami N, Nagai R, Miyazaki A, Ikemoto M, Arai H, Horiuchi S, Nakayama H. Scavenger receptor class B type I-mediated reverse cholesterol transport is inhibited by advanced glycation end products.J Biol Chem. 2001; 276:13348–13355. doi: 10.1074/jbc.M011613200CrossrefMedlineGoogle Scholar
    • 159. Isoda K, Folco EJ, Shimizu K, Libby P. AGE-BSA decreases ABCG1 expression and reduces macrophage cholesterol efflux to HDL.Atherosclerosis. 2007; 192:298–304. doi: 10.1016/j.atherosclerosis.2006.07.023CrossrefMedlineGoogle Scholar
    • 160. Hussein MA, Shrestha E, Ouimet M, Barrett TJ, Leone S, Moore KJ, Hérault Y, Fisher EA, Garabedian MJ. LXR-mediated ABCA1 expression and function are modulated by high glucose and PRMT2.PLoS One. 2015; 10:e0135218. doi: 10.1371/journal.pone.0135218CrossrefMedlineGoogle Scholar
    • 161. Mauldin JP, Nagelin MH, Wojcik AJ, Srinivasan S, Skaflen MD, Ayers CR, McNamara CA, Hedrick CC. Reduced expression of ATP-binding cassette transporter G1 increases cholesterol accumulation in macrophages of patients with type 2 diabetes mellitus.Circulation. 2008; 117:2785–2792. doi: 10.1161/CIRCULATIONAHA.107.741314LinkGoogle Scholar
    • 162. Passarelli M, Tang C, McDonald TO, O’Brien KD, Gerrity RG, Heinecke JW, Oram JF. Advanced glycation end product precursors impair ABCA1-dependent cholesterol removal from cells.Diabetes. 2005; 54:2198–2205.CrossrefMedlineGoogle Scholar
    • 163. Daffu G, Shen X, Senatus L, Thiagarajan D, Abedini A, Hurtado Del Pozo C, Rosario R, Song F, Friedman RA, Ramasamy R, Schmidt AM. RAGE suppresses ABCG1-mediated macrophage cholesterol efflux in diabetes.Diabetes. 2015; 64:4046–4060. doi: 10.2337/db15-0575CrossrefMedlineGoogle Scholar
    • 164. Machado-Lima A, Iborra RT, Pinto RS, Sartori CH, Oliveira ER, Nakandakare ER, Stefano JT, Giannella-Neto D, Corrêa-Giannella ML, Passarelli M. Advanced glycated albumin isolated from poorly controlled type 1 diabetes mellitus patients alters macrophage gene expression impairing ABCA-1-mediated reverse cholesterol transport.Diabetes Metab Res Rev. 2013; 29:66–76. doi: 10.1002/dmrr.2362CrossrefMedlineGoogle Scholar
    • 165. Distel E, Barrett TJ, Chung K, Girgis NM, Parathath S, Essau CC, Murphy AJ, Moore KJ, Fisher EA. miR33 inhibition overcomes deleterious effects of diabetes mellitus on atherosclerosis plaque regression in mice.Circ Res. 2014; 115:759–769. doi: 10.1161/CIRCRESAHA.115.304164LinkGoogle Scholar
    • 166. Nagareddy PR, Murphy AJ, Stirzaker RA, Hu Y, Yu S, Miller RG, Ramkhelawon B, Distel E, Westerterp M, Huang LS, Schmidt AM, Orchard TJ, Fisher EA, Tall AR, Goldberg IJ. Hyperglycemia promotes myelopoiesis and impairs the resolution of atherosclerosis.Cell Metab. 2013; 17:695–708. doi: 10.1016/j.cmet.2013.04.001CrossrefMedlineGoogle Scholar
    • 167. Parathath S, Grauer L, Huang LS, Sanson M, Distel E, Goldberg IJ, Fisher EA. Diabetes adversely affects macrophages during atherosclerotic plaque regression in mice.Diabetes. 2011; 60:1759–1769. doi: 10.2337/db10-0778CrossrefMedlineGoogle Scholar
    • 168. Kanter JE, Kramer F, Barnhart S, Duggan JM, Shimizu-Albergine M, Kothari V, Chait A, Bouman SD, Hamerman JA, Hansen BF, Olsen GS, Bornfeldt KE. A novel strategy to prevent advanced atherosclerosis and lower blood glucose in a mouse model of metabolic syndrome.Diabetes. 2018; 67:946–959. doi: 10.2337/db17-0744CrossrefMedlineGoogle Scholar
    • 169. Willecke F, Yuan C, Oka K, Chan L, Hu Y, Barnhart S, Bornfeldt KE, Goldberg IJ, Fisher EA. Effects of high fat feeding and diabetes on regression of atherosclerosis induced by low-density lipoprotein receptor gene therapy in LDL receptor-deficient mice.PLoS One. 2015; 10:e0128996. doi: 10.1371/journal.pone.0128996CrossrefMedlineGoogle Scholar
    • 170. Senatus LM, et al. Role of Receptor for Advanced Glycation End Products (RAGE) in regression of diabetic atherosclerosis.Arterioscler Thromb Vasc Biol. 2017; 37:A48.LinkGoogle Scholar
    • 171. Barrett TJ, Murphy AJ, Goldberg IJ, Fisher EA. Diabetes-mediated myelopoiesis and the relationship to cardiovascular risk.Ann N Y Acad Sci. 2017; 1402:31–42. doi: 10.1111/nyas.13462CrossrefMedlineGoogle Scholar
    • 172. Syvänne M, Castro G, Dengremont C, De Geitere C, Jauhiainen M, Ehnholm C, Michelagnoli S, Franceschini G, Kahri J, Taskinen MR. Cholesterol efflux from Fu5AH hepatoma cells induced by plasma of subjects with or without coronary artery disease and non-insulin-dependent diabetes: importance of LpA-I:A-II particles and phospholipid transfer protein.Atherosclerosis. 1996; 127:245–253.CrossrefMedlineGoogle Scholar
    • 173. Autran D, Attia N, Dedecjus M, Durlach V, Girard-Globa A. Postprandial reverse cholesterol transport in type 2 diabetic patients: effect of a lipid lowering treatment.Atherosclerosis. 2000; 153:453–460.CrossrefMedlineGoogle Scholar
    • 174. Attia N, Nakbi A, Smaoui M, Chaaba R, Moulin P, Hammami S, Hamda KB, Chanussot F, Hammami M. Increased phospholipid transfer protein activity associated with the impaired cellular cholesterol efflux in type 2 diabetic subjects with coronary artery disease.Tohoku J Exp Med. 2007; 213:129–137.CrossrefMedlineGoogle Scholar
    • 175. Zhou H, Shiu SW, Wong Y, Tan KC. Impaired serum capacity to induce cholesterol efflux is associated with endothelial dysfunction in type 2 diabetes mellitus.Diab Vasc Dis Res. 2009; 6:238–243. doi: 10.1177/1479164109344934CrossrefMedlineGoogle Scholar
    • 176. Annema W, Dikkers A, de Boer JF, van Greevenbroek MM, van der Kallen CJ, Schalkwijk CG, Stehouwer CD, Dullaart RP, Tietge UJ. Impaired HDL cholesterol efflux in metabolic syndrome is unrelated to glucose tolerance status: the CODAM study.Sci Rep. 2016; 6:27367. doi: 10.1038/srep27367CrossrefMedlineGoogle Scholar
    • 177. Feig JE, Hewing B, Smith JD, Hazen SL, Fisher EA. High-density lipoprotein and atherosclerosis regression: evidence from preclinical and clinical studies.Circ Res. 2014; 114:205–213. doi: 10.1161/CIRCRESAHA.114.300760LinkGoogle Scholar
    • 178. Ikhlef S, Berrougui H, Kamtchueng Simo O, Zerif E, Khalil A. Human paraoxonase 1 overexpression in mice stimulates HDL cholesterol efflux and reverse cholesterol transport.PLoS One. 2017; 12:e0173385. doi: 10.1371/journal.pone.0173385CrossrefMedlineGoogle Scholar
    • 179. Liang HQ, Rye KA, Barter PJ. Cycling of apolipoprotein A-I between lipid-associated and lipid-free pools.Biochim Biophys Acta. 1995; 1257:31–37.CrossrefMedlineGoogle Scholar
    • 180. Wróblewska M, Kortas-Stempak B, Szutowicz A, Badzio T. Phospholipids mediated conversion of HDLs generates specific apoA-II pre-beta mobility particles.J Lipid Res. 2009; 50:667–675. doi: 10.1194/jlr.M800399-JLR200CrossrefMedlineGoogle Scholar
    • 181. Michell DL, et al. Isolation of high-density lipoproteins for non-coding small RNA quantification.J Vis Exp. 2016. doi: 10.3791/54488.CrossrefMedlineGoogle Scholar
    • 182. Vickers KC, Palmisano BT, Shoucri BM, Shamburek RD, Remaley AT. MicroRNAs are transported in plasma and delivered to recipient cells by high-density lipoproteins.Nat Cell Biol. 2011; 13:423–433. doi: 10.1038/ncb2210CrossrefMedlineGoogle Scholar
    • 183. Heinecke J. HDL and cardiovascular-disease risk–time for a new approach?N Engl J Med. 2011; 364:170–171. doi: 10.1056/NEJMe1012520CrossrefMedlineGoogle Scholar
    • 184. Heinecke JW. The HDL proteome: a marker–and perhaps mediator–of coronary artery disease.J Lipid Res. 2009; 50(Suppl):S167–S171. doi: 10.1194/jlr.R800097-JLR200CrossrefMedlineGoogle Scholar
    • 185. Shah AS, Tan L, Long JL, Davidson WS. Proteomic diversity of high density lipoproteins: our emerging understanding of its importance in lipid transport and beyond.J Lipid Res. 2013; 54:2575–2585. doi: 10.1194/jlr.R035725CrossrefMedlineGoogle Scholar
    • 186. Keene D, Price C, Shun-Shin MJ, Francis DP. Effect on cardiovascular risk of high density lipoprotein targeted drug treatments niacin, fibrates, and CETP inhibitors: meta-analysis of randomised controlled trials including 117,411 patients.BMJ. 2014; 349:g4379. doi: 10.1136/bmj.g4379CrossrefMedlineGoogle Scholar
    • 187. Behring C. Study to Investigate CSL112 in Subjects With Acute Coronary Syndrome (AEGIS-II). Scholar
    • 188. Investigators, A.-H, et al. Niacin in patients with low HDL cholesterol levels receiving intensive statin therapy.N Engl J Med. 2011; 365:2255–2267. doi: 10.1056/NEJMoa1107579CrossrefMedlineGoogle Scholar
    • 189. Armitage J, Holmes MV, Preiss D. Cholesteryl ester transfer protein inhibition for preventing cardiovascular events: JACC review topic of the week.J Am Coll Cardiol. 2019; 73:477–487. doi: 10.1016/j.jacc.2018.10.072CrossrefMedlineGoogle Scholar
    • 190. Barter PJ, Caulfield M, Eriksson M, et al.; ILLUMINATE Investigators. Effects of torcetrapib in patients at high risk for coronary events.N Engl J Med. 2007; 357:2109–2122. doi: 10.1056/NEJMoa0706628CrossrefMedlineGoogle Scholar
    • 191. Brousseau ME, Diffenderfer MR, Millar JS, Nartsupha C, Asztalos BF, Welty FK, Wolfe ML, Rudling M, Björkhem I, Angelin B, Mancuso JP, Digenio AG, Rader DJ, Schaefer EJ. Effects of cholesteryl ester transfer protein inhibition on high-density lipoprotein subspecies, apolipoprotein A-I metabolism, and fecal sterol excretion.Arterioscler Thromb Vasc Biol. 2005; 25:1057–1064. doi: 10.1161/01.ATV.0000161928.16334.ddLinkGoogle Scholar
    • 192. Nicholls SJ, Andrews J, Kastelein JJP, et al. Effect of serial infusions of CER-001, a pre-β high-density lipoprotein mimetic, on coronary atherosclerosis in patients following acute coronary syndromes in the CER-001 atherosclerosis regression acute coronary syndrome trial: a randomized clinical trial.JAMA Cardiol. 2018; 3:815–822. doi: 10.1001/jamacardio.2018.2121CrossrefMedlineGoogle Scholar
    • 193. Shaw JA, Bobik A, Murphy A, Kanellakis P, Blombery P, Mukhamedova N, Woollard K, Lyon S, Sviridov D, Dart AM. Infusion of reconstituted high-density lipoprotein leads to acute changes in human atherosclerotic plaque.Circ Res. 2008; 103:1084–1091. doi: 10.1161/CIRCRESAHA.108.182063LinkGoogle Scholar
    • 194. Nissen SE, Tsunoda T, Tuzcu EM, Schoenhagen P, Cooper CJ, Yasin M, Eaton GM, Lauer MA, Sheldon WS, Grines CL, Halpern S, Crowe T, Blankenship JC, Kerensky R. Effect of recombinant ApoA-I Milano on coronary atherosclerosis in patients with acute coronary syndromes: a randomized controlled trial.JAMA. 2003; 290:2292–2300. doi: 10.1001/jama.290.17.2292CrossrefMedlineGoogle Scholar
    • 195. Tardif JC, Grégoire J, L’Allier PL, Ibrahim R, Lespérance J, Heinonen TM, Kouz S, Berry C, Basser R, Lavoie MA, Guertin MC, Rodés-Cabau J; Effect of rHDL on Atherosclerosis-Safety and Efficacy (ERASE) Investigators. Effects of reconstituted high-density lipoprotein infusions on coronary atherosclerosis: a randomized controlled trial.JAMA. 2007; 297:1675–1682. doi: 10.1001/jama.297.15.jpc70004CrossrefMedlineGoogle Scholar


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