Skip main navigation

Apolipoprotein A-I and Its Role in Lymphocyte Cholesterol Homeostasis and Autoimmunity

Originally publishedhttps://doi.org/10.1161/ATVBAHA.108.183442Arteriosclerosis, Thrombosis, and Vascular Biology. 2009;29:843–849

Abstract

Objective— The purpose of this study was to determine the effects of an atherogenic diet on immune function in LDLr−/−, ApoA-I−/− mice.

Methods and Results— When LDLr−/−, ApoA-I−/− (DKO), and LDLr−/− (SKO) mice were fed an atherogenic diet, DKO had larger peripheral lymph nodes (LNs) and spleens compared to SKO mice. LNs were enriched in cholesterol and contain expanded populations of T, B, dendritic cells, and macrophages. Expansion of all classes of LN cells was accompanied by a ≈1.5-fold increase in T cell proliferation and activation. Plasma antibodies to dsDNA, β2-glycoprotein I, and oxidized LDL were increased in DKO, similar to levels in diet-fed Faslpr/lpr mice, suggesting the development of an autoimmune phenotype. Both LN enlargement and cellular cholesterol expansion were “prevented” when diet-fed DKO mice were treated with helper dependent adenovirus expressing apoA-I. Independent of the amount of dietary cholesterol, DKO mice consistently showed lower plasma cholesterol than SKO mice, yet greater aortic cholesterol deposition and inflammation.

Conclusions— ApoA-I prevented cholesterol-associated lymphocyte activation and proliferation in peripheral LN of diet-fed DKO mice. A ≈1.5-fold increase in T cell activation and proliferation was associated with a ≈3-fold increase in concentrations of circulating autoantibodies and ≈2-fold increase in the severity of atherosclerosis suggesting a common link between plasma apoA-I, inflammation, and atherosclerosis.

Diet-fed DKO mice exhibit accumulation of cholesterol in skin draining LNs. This accumulation was associated with an expansion and activation of T and B lymphocytes and increased concentrations of circulating autoantibodies. Diet-fed DKO mice also showed increased aortic atherosclerosis compared to SKO mice despite having lower levels of plasma cholesterol. These results suggest that apoA-I is important in regulating specific inflammatory pathways as they relate to the development of atherosclerosis.

High concentrations of plasma high-density lipoproteins (HDL) are a well-established negative risk factor for coronary heart disease (CHD).1 Apolipoprotein A-I (apoA-I), which makes up approximately 70% of HDL protein, is secreted by the liver and intestine and is essential for HDL formation and function.2 The formation of HDL depends on the ATP binding cassette transporter A1 (ABCA1) which effluxes cholesterol onto apoA-I,3 whereas ABCG1, another member of the ABC transporter family, primarily effluxes cholesterol to HDL particles.4 Recent studies demonstrate that HDL apoA-I is an antiinflammatory mediator modulating the progression of atherosclerosis through immune cell function.

A direct link between immune cell function and lipoprotein metabolism was recently demonstrated when lymphotoxin and LIGHT produced by T cells were found to regulate plasma triglyceride levels.5 Moreover, monocyte populations may take on dendritic cell (DC)-like characteristics, migrate into an atherosclerotic lesion, become cholesterol enriched, and migrate out, contributing to the stability of the plaque.6,7 Interestingly, hyperlipidemic apoE−/− and LDLr−/− mice show reduced migration of DCs between skin and LNs, but when HDL or apoA-I was administered normal migration was restored.8

Based on these associations, it has been speculated that HDL apoA-I and autoimmunity are linked. Humans with autoimmune disorders such as systemic lupus erythematosus (SLE) and rheumatoid arthritis (RA)9 and mouse models of these disorders are associated with increased atherosclerosis,10,11 with SLE and RA patients showing decreased HDL levels when compared to control subjects.12 The correlation among autoimmune disease, atherosclerosis, and plasma HDL apoA-I raises the possibility of a common link involving all 3 factors. We therefore undertook the current studies to investigate this link and found that apoA-I can modulate immune cell function by regulating cellular cholesterol balance, which in turn prevents LN cell expansion, activation, and the progression of atherosclerosis.

Materials and Methods

LDLr−/−, ApoA-I−/− (DKO), LDLr−/− (SKO), and B6.MRL-Faslpr/J (Faslpr/lpr) mice were fully backcrossed into the C57BL/6 background.13,14 All mice were housed at the Wake Forest University Medical Center. The Wake Forest University Medical Center Committee for Animal Care and Use approved all procedures. For a more detailed description of Materials and Methods see the supplemental materials (available online at http://atvb.ahajournals.org).

Results

Cholesterol Accumulation and Expansion in Peripheral Lymph Nodes

After 10 weeks on an atherogenic diet,13,14 DKO mice acquired enlarged peripheral LNs, compared to SKO mice, shown in Figure 1A and 1A′, respectively. The enlargement of the DKO LNs was associated with increased Oil Red O staining (Figure 1C and 1C′), not seen in SKO mice. When fed an atherogenic diet for longer than 10 weeks, DKO mice develop skin lesions attributable to excessive scratching.13,14 To reduce the contribution of “open lesions” to the current studies, mice were fed diet for 10 weeks, at which time external skin abnormalities were not present as shown in supplemental Figure I. Although Figure 1 shows only brachial LNs, inguinal, axillary, and superficial cervical LNs were also enlarged in diet-Fed DKO mice. LNs from DKO weighed an average of 9.6±0.8 mg, while SKO LNs weighed 2.2±0.5 mg (n=5 to 10 mice per genotype, P<0.05).

Figure 1. Cholesterol accumulation in the lymph nodes of LDLr−/−, ApoA-I−/− mice. Gross, histological, and chemical analysis of 10-week diet-fed DKO and SKO LNs (A, A′ and C, C′), and spleens (B, B′ and D-D′), respectively. Oil red O-stained sections of LNs are shown in C and C′ and of spleens in D and D′. The mean±SD of total lymphocytes and spenocytes from chow and diet-fed mice are plotted in E and F and represent 3 independent experiments with 4 to 5 mice per genotype. G and H show the mean±SD for LN and splenic cholesterol mass, respectively, measured by GC for 4 and 10-week diet-fed mice and for 10-week chow-fed mice with 8 to 10 mice per genotype. Unlike letters indicate statistical significance at P<0.05.

Autoimmune disorders typically show enlargement of peripheral LN accompanied by immune cell expansion and the production of autoantibodies. In a mouse model of autoimmunity, Faslpr/lpr, enlargement of both LNs and spleen15,16 with age has been docummented.17,18 In the current studies we chose to compare DKO and SKO LN immune cell expansion with that in the Faslpr/lpr mouse.17,18 After 10 weeks of chow, Faslpr/lpr mice had enlarged LN and spleens (data not shown) that contained a large number of immune cells compared to chow-fed DKO and SKO mice (Figure 1E). However, DKO mice consuming the atherogenic diet for 10 weeks had as many LN cells as 10-week chow-fed Faslpr/lpr and contained ≈10-fold more LN cells than SKO mice. The atherogenic diet initiated a 2.5-fold increase in the total number of LN cells in Faslpr/lpr mice compared to their chow-fed counterparts, suggesting a cholesterol driven LN cell expansion even in the Faslpr/lpr genetic environment.

Figure 1G shows that LN enlargement and intense Oil Red O staining was associated with the increase in the mass of LN cholesterol as measured by GC. The increase in DKO LN cholesterol content occurred as early as 4 weeks after initiating the diet, whereas both SKO and Faslpr/lpr mice did not show significant LN cholesterol increase in response to diet.

DKO mice also had enlarged spleens compared to SKO mice, as shown in Figure 1B and 1B′. DKO spleens weighed an average of 159.6±69.8 mg, whereas SKO spleens weighed 91.8±13.7 mg. Despite the enlargement, Oil Red O staining showed minimal lipid accumulation as shown in Figure 1D and 1D′. Neither splenocyte number (Figure 1F), nor GC-derived cholesterol content (Figure 1H), was different between DKO, SKO, and Faslpr/lpr mice.

Diet-Induced Expansion of Lymph Nodes Immune Cells

Studies of the effect of the atherogenic diet on specific LN cell populations, Figure 2, dot plots (A through D) and total cell number (A′ through D′), are shown for double negative T (DNT) cells (CD3+CD4CD8B220+; A and A′); naïve B cells (IgM+B220+; B and B′); DCs (CD3CD11c+; C and C′); and macrophages (CD11cCD11b+F4/80+; D and D′). For each cell type, diet-fed DKO LN cell expansion was ≈8-fold higher than chow-fed DKO mice. SKO mice showed a less dramatic ≈2.5-fold increase in response to diet. Although a large number of specific T cell subsets were investigated, including regulatory T cells (data not shown), only DNT cells are shown, because all subsets increased in diet-fed DKO mice. Increased numbers of DNT cells, CD3+CD4CD8B220+, are characteristic of the loss of self-tolerance in Faslpr/lpr mice.19,20 Dietary cholesterol consumption increased specific LN cell numbers in both DKO and Faslpr/lpr mice, although Faslpr/lpr mice apparently did not need cholesterol feeding to stimulate expansion.

Figure 2. Expansion of lymph node cell populations. A to D show dot plots for 4 lymphocyte populations, whereas A′ to D′ show the corresponding total cell numbers, mean±SD, for 10-week chow and diet-fed mice. A and A′ show DNT cells (CD3+CD4CD8B220+); B and B′ show naïve B cells (IgM+B220+); C and C′ show DCs (CD3CD11c+); and D and D′ show macrophages (CD11cCD11b+F4/80+). Faslpr/lpr mice, a model of SLE, were studied for comparison. All dot plots were gated on viable cells with additional gating for the CD3+B220+ cell population (A) and for the CD11c population (D). Results represent 3 independent experiments with 4 to 5 mice per genotype. Unlike letters indicate statistical significance at P<0.05.

In contrast to the LN cells, splenocyte populations were not different between DKO and SKO mice, as shown in supplemental Figure II for DNT cells (A and A′); naïve B cells (B and B′); and DCs (C and C′). Only the macrophage population (D and D′) showed significant increases for chow versus diet-fed DKO mice. A simplification of the data contained in Figure 2 and supplemental Figure II are shown in supplemental Figure IIIA through IIIC for spleen and in supplemental Figure IIID through IIIF for the LN, showing changes in DKO relative to SKO mice for 10 weeks chow, and 4 and 10 weeks atherogenic diet.

LN T and B cells Accumulate Cholesterol Ester in Response to Diet

All cell types except macrophages showed a ≈2-fold increase in their esterified cholesterol (EC) content after 10 weeks on the atherogenic diet. Remarkably, DC contained the largest mass of TC compared to all other LN cell types. Figure 3A shows a statistically significant increase in the EC/TC ratio for B, T, and dendritic cells in DKO versus SKO mice. Although not statically significant (P<0.08), DKO macrophages also appeared to follow this trend. The increase in the EC/TC ratio was attributable to an increase in the total mass of EC (Figure 3B), and not to a decrease in the mass of free cholesterol (Figure 3C).

Figure 3. Lymphocyte specific cholesterol and cholesterol ester mass. A shows the ratio of esterified cholesterol to total cholesterol (EC/TC). The mean±SD for LN cell populations are plotted in B and C. The masses were determined by GC/MS of sorted LN cells from 10-week diet-fed DKO and SKO mice. The results are based on 4 independent experiments with 5 mice per genotype. Asterisks indicate statistical significance differences at P<0.05.

T Cell Activation

The activation state and functionality of T cells, CD4+CD69high, and CD8+CD69high populations are shown in supplemental Figure IVA and IVB for LNs and IVC and IVD for spleen. These data show that the percent of CD69high cells was significantly higher in 10-week chow-fed Faslpr/lpr mice LNs compared to chow-fed DKO or SKO mice. However, in response to 10 weeks of the atherogenic diet both Faslpr/lpr and DKO mice showed ≈1.5-fold increase in the percent of CD69high cells, suggesting a heightened activation state in response to dietary cholesterol.

Proliferation of CD4+CD44high Cells

Proliferation of effector CD4+CD44high and CD8+CD44high T cells was studied by measuring BrdU incorporation into LNs and spleens of 10-week diet-fed DKO and SKO mice. Supplemental Figure V (top and bottom panels A through C) shows the results for LN and spleen for DKO mice which had ≈1.5-fold more CD4+CD44high cells in their LNs, averaging 52.5%, versus 35.0% in SKO mice, whereas mice not receiving BrdU showed a background of ≈0.1%. BrdU incorporation. For CD8+CD44high cells, shown in supplemental Figure V (top and bottom panels D through F, for LN and spleen, respectively), incorporation was similar between genotypes. These data suggest that CD4+CD44high effector T cells in diet-fed DKO mice undergo selective proliferation.

Circulating Autoantibodies in Response to Diet

In light of the increased numbers of activated and DNT cells in 10-week diet-fed DKO LNs the development of an autoimmune disorder was considered. Plasma autoantibodies for dsDNA shown in Figure 4 indicates that DKO, like Faslpr/lpr mice, had a 2-fold increase in autoantibodies levels. The relative levels for β2-glycoprotein (β2-GPI) and oxidized LDL (oxLDL) were measured in 10-week diet-fed DKO, SKO, and Faslpr/lpr mice and are shown in supplemental Figure VIA and VIB, respectively. These autoantibodies also showed increases similar to that seen in Faslpr/lpr mice.

Figure 4. Dietary cholesterol induction of plasma autoantibodies. Relative levels of antidsDNA in response to an atherogenic diet. Autoantibodies were measured in the plasma from 10-week chow and diet-fed DKO, SKO, and Faslpr/lpr mice. The values represent the mean±SD of 4 to 12 mice per genotype. Unlike letters indicate statistical significance at P<0.05.

LN Cholesterol Accumulation Is Prevented by Plasma ApoA-I

We next tested whether the presence of plasma apoA-I would prevent LN cholesterol accumulation. Four weeks before starting the atherogenic diet, DKO mice were injected with helper-dependent adenovirus expressing human apoA-I (HD Ad ApoA-I)21,22 whereas “Control” mice were injected with an equal amount of HD-Ad that did not carry the apoA-I gene. Figure 5A shows that the plasma apoA-I levels plateaued by 4 weeks and remained constant at ≈40 mg/dL to the end of the study. LN cholesterol content after 8 weeks on diet is shown in Figure 5B. Compared to control vector-treated mice, diet-fed DKO mice expressing apoA-I had normal levels of LN cholesterol, similar to TgWT ApoA-I mice that have plasma apoA-I concentrations of ≈110 mg/dL. DKO mice expressing the mutant apoA-I, Tg L159R, have plasma levels of a mutant form of human apoA-I at ≈10 mg/dL.23 In these mice LN cholesterol levels were intermediate between control and HD Ad ApoA-I mice, but this low level was sufficient to reduce LN cell expansion. Plasma autoantibodies to dsDNA (data not shown) in diet-fed HD Ad and TgWT ApoA-I mice were similar to those measured in diet-fed SKO mice, whereas diet-fed control (no ApoA-I) DKO dsDNA autoantibody levels were similar to diet-fed DKO (Figure 4).

Figure 5. Plasma apoA-I prevents cholesterol accumulation in lymph nodes. A shows the increase in plasma apoA-I concentrations after injection of HD Ad ApoA-I or Control (empty HD vector)21,22 into DKO (LDLr−/−, ApoA-I−/−) mice. Mice began the atherogenic diet 4 weeks after injection to allow for maximum expression of plasma apoA-I and continued on diet for a total of 8 weeks. B shows the LN cholesterol content for the DKO mice, for 8-week diet-fed DKO mice expressing wild-type human apoA-I (TgWT ApoA-I) and for 8-week diet-fed DKO mice expressing Tg L159R ApoA-I, a mutant apoA-I that impairs reverse cholesterol transport. LN cholesterol from GC analysis is expressed as the mean±SD of μg total cholesterol per mg LN protein with 3 to 6 mice per genotype. Unlike letters indicate statistical significance at P<0.05. TgWT ApoA-I in DKO mice have apoA-I plasma concentrations ≈110 mg/dL, whereas DKO mice expressing L159R ApoA-I have plasma apoA-I concentrations ≈10 mg/dL.23

Atherosclerosis Development Is Independent of Plasma Cholesterol

Previous studies have shown that DKO and SKO mice fed diets containing the same amount of dietary cholesterol (0.1% cholesterol) have different total plasma cholesterol (TPC) levels.13,14 SKO mice have a 2.5-fold higher TPC than DKO mice, and yet the 2 genotypes had similar levels of aortic cholesterol accumulation.13,14 To quantify atherosclerosis when TPC was similar, the amount of dietary cholesterol fed to each genotype was adjusted based on their differential responses. DKO mice were fed 0.5% cholesterol, 5-fold more than the standard 0.1% diet, whereas SKO mice were fed the same base diet containing 0.05% cholesterol. Even with these manipulations, after 10 weeks DKO mice still had a lower TPC, 736±58 mg/dL, than did SKO mice, 1048±55 mg/dL. Both the VLDL and HDL particle diameters were significantly larger in diet-fed DKO compared to SKO mice, with no significant difference in LDL diameter between genotypes (see supplemental Table I). The plasma triglyceride level was not statistically different between DKO and SKO mice, 206±85 mg/dL versus 215±55 mg/dL (n=7 mice per genotype). Although HDL particles were larger in size in DKO mice they made up less than 5% to 10% of the d >1.21 g/mL mass compared to SKO mice. The increased HDL particle diameter likely indicates the presence of LDL/HDL transition particles enriched in apoE13,14 and devoid of apoA-I.

The extent of atherosclerosis was quantified by both morphometric evaluation of oil red O-stained aortic root and by measuring the total aortic cholesterol mass. Supplemental Figure VIIA shows representative oil Red O sections from the aortic root for each genotype. The percent of lesion for DKO and SKO mice was 42.7±3.8% versus 33.4±3.4%, respectively (mean±SD of n=5, with P<0.05). These measurements were supported by total aortic cholesterol mass (shown in supplemental Figure VIIB). Both male and female DKO mice had a statistically significant increase in total aortic cholesterol mass compared to male and female SKO mice. The aortas from DKO mice had a 3-fold increase in IL-1β mRNA after 8 and 16 weeks on an atherogenic diet when compared to matched SKO mice and shown in supplemental Figure VIIC), suggesting a heightened inflammatory state in the DKO aortic environment.

Discussion

Our studies demonstrate that in response to an atherogenic diet DKO mice develop enlarged skin draining LNs that contain expanded populations of CE enriched lymphocytes. The cellular expansion and cholesterol loading affected the major classes of LN cells, including T cells, B cells, DCs, and to a lesser extent macrophages. Associated with these morphological changes was a 1.5-fold increase in the proliferation of CD4+CD44high T cells, but not CD8+CD44high T cells. Changes in T cell proliferation and activation occurred in conjunction with the production of plasma autoantibodies and inflammatory cell infiltrates in the dermis. In contrast, diet-fed SKO mice did not show an increase in LN size or cellularity even after consuming the atherogenic diet for 24 weeks (M. Zabalawi, unpublished observations, 2008). However, after long-term diet feeding ≈50% of SKO mice presented skin lesions that were not associated with LN enlargement, cholesterol accumulation, or cellular expansion as seen in diet-fed DKO mice. These studies demonstrate that plasma apoA-I prevented the phenotype by preventing LN enlargement, cholesterol loading, as well as accumulation of skin cholesterol in DKO mice.13,14 Taken together these results suggest a direct link between apoA-I, cholesterol metabolism, inflammation and autoimmunity.

Based on these results we speculate that cholesterol accumulates in skin draining LNs under hypercholesterolemic conditions because of inefficient or nonexistent cellular cholesterol efflux. As cholesterol accumulates in lymphocytes, the lack of apoA-I slows or prevents cholesterol efflux from these cells and eventually leads to disruption in cellular function. Lymphocyte proliferation and activation, as well as cytokine production, exacerbates atherosclerosis and eventually leads to loss of self-tolerance and skin pathogenesis. LN immune cells play a vital role in atherosclerosis progression and regression from the formation of foam cells24 to the migration of DCs from atherosclerotic plaques to LNs,6,7 although the precise role apoA-I plays in these processes remain undefined. T and B cells, as well as DCs, are believed to migrate between atherosclerotic lesions and regional LNs25 and contribute to disease progression or regression. In one study, the migration of DCs in diet-fed apoE−/− and LDLr−/− mice showed impaired migration from the skin to the LNs, which was reversed by administering apoA-I.8

In autoimmune disorders CD4+T cells are primarily responsible for the pathogenic anti-DNA autoantibody production in Faslpr/lpr mice.18 In these studies proliferation of CD4+CD44high T cells, but not CD8+CD44high cells, was similar to that seen in a mouse model of SLE.18 In addition, CD69, an early T cell activation marker involved in signal transduction, cell proliferation, and cytokine secretion, was higher in SLE patients than in controls,26 and it is also higher in our model. Another significant similarity characteristic of autoimmune disorders in mouse models of SLE was the increase in DNT cells.20 The defect in lpr mice is caused by insertion of a retroviral transposon into the second intron of fas that interferes with its ability to bind to the FAS ligand and mediate cell death through apoptosis. LNs in lpr mice enlarge in part from a massive expansion of DNT cells. As more T cells are produced the autoimmune process attacks tissues and organs including the skin, kidney, and joints. As in human SLE patients, one mechanism of tissue damage involves autoantibody and immune complex deposition, as well as increased infiltration of select tissues by lymphocytes.19

Both human and animal studies have shown a convincing link between autoimmune disorders and atherosclerosis with a number of autoimmune “mouse models” exhibiting advanced atherosclerosis.10,11,27 Stanic et al showed that in a mouse model of autoimmunity, atherosclerotic progression was worsened by the lack of self-tolerance,11 whereas Gu et al, using quantitative trait analysis of the MRL/lpr autoimmune mouse, provided further evidence for a link between autoimmunity and HDL metabolism.28 In human patients suffering from autoimmune disorders HDL levels are significantly decreased.12,29,30

In light of these connections we compared the extent of atherosclerosis between SKO and DKO mice. In a previous study, DKO and SKO mice were fed 0.1% cholesterol and 10% palm oil for 16 weeks.14 This diet produced a 2.5-fold higher TPC in SKO mice compared to DKO mice; however, despite the large difference in TPC, both genotypes developed similar atherosclerosis.13,14 In an attempt to adjust TPC levels DKO mice were fed 10-fold more dietary cholesterol than SKO mice. Under these conditions SKO mice still had ≈1.5-fold higher plasma cholesterol, but the DKO mice developed ≈2-fold greater atherosclerosis, clearly demonstrating the protective effects of HDL apoA-I.

Although DKO mice share several common characteristics with autoimmune mouse models including skin lesions31 and advanced atherosclerosis, one aspect which remains unusual was the enormous accumulation of cholesterol in the skin. After 12 to 16 weeks on diet,13,14 diet-fed DKO mice die of inflammation induced by the massive skin cholesterol accumulation and its resulting pathogenesis as opposed to the renal failure and glomerulonephritis seen in 28- to 30-week chow-fed Faslpr/lpr mice. The presence of activated T cells in DKO LN and skin (A. Wilhelm, unpublished observations, 2009) suggests that skin is the primary site of pathogenesis in DKO mice.

DKO mice accumulate 2.5-fold more whole body cholesterol compared to SKO mice13 fed the same diet, with skin being the primary site of cholesterol accumulation.13 However, the accumulation of cholesterol in the skin of diet-fed DKO mice is not unique, but similar in magnitude to that reported for diet-fed LXRα−/−, apoE−/− mice that had a 2.5-fold increase in whole body cholesterol compared to apoE−/− only mice with lipid accumulation occurring predominately in the skin.32 This unusual phenotype has been previously described in other mouse models that carry disruptions in cholesterol homeostatic genes including, eg, ACAT1−/−, LDLr−/−33 and ABCA1−/−, LDLr−/−3,34 suggesting that disruption in immune cell cellular cholesterol mobilization may be a common mechanism leading to the skin cholesterol accumulation phenotype. This is in contrast to apoC-I transgenic mice, where apoC-I modulates plasma triglyceride metabolism and was associated with severe skin lesions, infiltration of inflammatory cells, but no skin cholesterol accumulation.35 Other cholesterol homeostatic models, such as in ABCG1−/− mice, show severe cholesterol accumulation, but predominately in the lungs.4,36,37 In ABCG1−/− mice this was accompanied by an increase in inflammatory cells and cytokines in the lung that were largely absent from the plasma compartment.36 Despite this, the skin is a common tissue affected in autoimmune disorders such as SLE,31,38,39 but these lesions are not usually associated with cholesterol accumulation. Thus, it remains to be determined whether cholesterol-loaded inflammatory cells enter the skin in response to a specific stimulus or if a constant infiltration of cholesterol in the skin via LDL causes lymphocyte migration and activation, thereby triggering the resulting phenotype.

In conclusion, we have demonstrated that apoA-I prevents lymphocyte cholesterol accumulation, activation, and proliferation in skin draining LNs of diet-fed DKO mice. An increase in T cell activation and proliferation was linked to increased levels of circulating autoantibodies and a ≈2-fold increase in aortic cholesterol accumulation. These results strongly suggest a common link between plasma apoA-I, inflammation, and atherosclerosis.

Apolipoprotein A-I and Its Role in Lymphocyte Cholesterol Homeostasis and Autoimmunity: Correction

In the article that appeared on page 843 of the 29.6 issue, the NIH grant number was listed incorrectly. It should have been HL-64163. A correction for this article has been printed in the August 2009 issue of Arteriosclerosis, Thrombosis, and Vascular Biology.

Reference:

Wilhelm AJ, Zabalawi M, Grayson JM, Weant AE, Major AS, Owen J, Bharadwaj M, Walzen R, Chan L, Oka K, Thomas MJ, and Sorci-Thomas MG. Apolipoprotein A-I and its role in the lymphocyte cholesterol homeostasis and autoimmunity. Arterioscler Thromb Vasc Biol. 2009;29:843–849.

Received May 12, 2008; revision accepted February 27, 2009.

Sources of Funding

M.S.T. was supported by NIH HL-49373 and HL-64143; A.S.M. was supported by NIH HL-089310 and The Lupus Research Institute, New York; J.M.G. was supported by an American Cancer Society Research Scholar Grant #RSG-04 to 066-01 MBC and NIH A1-068952. A.J.W. received an NIH T32 Kirschtein NRSA HL091797-01. We gratefully acknowledge the Texas AgriLife Research project #8738 to R.L.W. The generation of HD Ad ApoAI was supported by grants HL-51586 to L.C. and HL-73144 to K.O. The Trace MS was purchased with funds from the NC Biotechnology Shared Instrumentation Program and the Winston-Salem Foundation.

Disclosures

None.

Footnotes

Correspondence to Mary G. Sorci-Thomas, Department of Pathology, Section on Lipid Sciences, Wake Forest University School of Medicine, Medical Center Blvd, Winston-Salem, NC 27157. E-mail

References

  • 1 Gordon T, Castelli W, Hjortland M, Kannel W, Dawber T. High density lipoprotein as a protective factor against coronary heart disease. The Framingham Study. Am J Med. 1977; 62: 707–714.CrossrefMedlineGoogle Scholar
  • 2 Zannis V, Chroni A, Krieger M. Role of apoA-I, ABCA-I, LCAT, and SR-BI in the biogenesis of HDL. J Mol Med. 2006; 84: 276–294.CrossrefMedlineGoogle Scholar
  • 3 Aiello RJ, Brees D, Bourassa P-A, Royer L, Lindsey S, Coskran T, Haghpassand M, Francone OL. Increased atherosclerosis in hyperlipidemic mice with inactivation of ABCA1 in macrophages. Arterioscler Thromb Vasc Biol. 2002; 22: 630–637.LinkGoogle Scholar
  • 4 Baldan A, Tarr P, Vales CS, Frank J, Shimotake TK, Hawgood S, Edwards PA. Deletion of the transmembrane transporter ABCG1 results in progressive pulmonary lipidosis. J Biol Chem. 2006; 281: 29401–29410.CrossrefMedlineGoogle Scholar
  • 5 Lo JC, Wang Y, Tumanov AV, Bamji M, Yao Z, Reardon CA, Getz GS, Fu YX. Lymphotoxin {beta} receptor-dependent control of lipid homeostasis. Science. 2007; 316: 285–288.CrossrefMedlineGoogle Scholar
  • 6 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 USA. 2006; 103: 3781–3786.CrossrefMedlineGoogle Scholar
  • 7 Randolph GJ, Ochando J, Partida-Sanchez S. Migration of dendritic cell subsets and their precursors. Annu Rev Immunol. 2008; 26: 293–316.CrossrefMedlineGoogle Scholar
  • 8 Angeli V, Llodra J, Rong JX, Satoh K, Ishii S, Shimizu T, Fisher EA, Randolph GJ. Dyslipidemia associated with atherosclerotic disease systemically alters dendritic cell mobilization. Immunity. 2004; 21: 561–574.CrossrefMedlineGoogle Scholar
  • 9 Salmon JE, Roman MJ. Subclinical atherosclerosis in rheumatoid arthritis and systemic lupus erythematosus. Am J Med. 2008; 121: S3–8.CrossrefMedlineGoogle Scholar
  • 10 Feng X, Li H, Rumbin AA, Wang X, La Cava A, Brechtelsbauer K, Castellani LW, Witztum JL, Lusis AJ, Tsao BP. ApoE−/−Fas−/− C57BL/6 mice: a novel murine model simultaneously exhibits lupus nephritis, atherosclerosis, and osteopenia. J Lipid Res. 2007; 48: 794–805.CrossrefMedlineGoogle Scholar
  • 11 Stanic AK, Stein CM, Morgan AC, Fazio S, Linton MF, Wakeland EK, Olsen NJ, Major AS. Immune dysregulation accelerates atherosclerosis and modulates plaque composition in systemic lupus erythematosus. Proc Natl Acad Sci USA. 2006; 103: 7018–7023.CrossrefMedlineGoogle Scholar
  • 12 Bresnihan B, Gogarty M, FitzGerald O, Dayer J-M, Burger D. Apolipoprotein A-I infiltration in rheumatoid arthritis synovial tissue: a control mechanism of cytokine production? Arthritis Res Ther. 2004; 6: R563–R566.CrossrefMedlineGoogle Scholar
  • 13 Zabalawi M, Bharadwaj M, Horton H, Cline M, Willingham M, Thomas MJ, Sorci-Thomas MG. Inflammation and skin cholesterol in LDLr−/−, apoA-I−/− mice: link between cholesterol homeostasis and self-tolerance? J Lipid Res. 2007; 48: 52–65.CrossrefMedlineGoogle Scholar
  • 14 Zabalawi M, Bhat S, Loughlin T, Thomas MJ, Alexander E, Cline M, Bullock B, Willingham M, Sorci-Thomas MG. Induction of fatal inflammation in LDL receptor and ApoA-I double-knockout mice fed dietary fat and cholesterol. Am J Pathol. 2003; 163: 1201–1213.CrossrefMedlineGoogle Scholar
  • 15 Weant AE, Michalek RD, Khan IU, Holbrook BC, Willingham MC, Grayson JM. Apoptosis regulators Bim and Fas function concurrently to control autoimmunity and CD8+ T cell contraction. Immunity. 2008; 28: 141–143.CrossrefMedlineGoogle Scholar
  • 16 Katagiri T, Cohen P, Eisenberg R. The lpr gene causes an intrinsic T cell abnormality that is required for hyperproliferation. J Exp Med. 1988; 167: 741–751.CrossrefMedlineGoogle Scholar
  • 17 Jabs DA, Kuppers RC, Saboori AM, Burek CL, Enger C, Lee B, Prendergast RA. Effects of early and late treatment with anti-CD4 monoclonal antibody on autoimmune disease in MRL/MP-lpr/lpr mice. Cell Immunol. 1994; 154: 66–76.CrossrefMedlineGoogle Scholar
  • 18 Giese T, Davidson WF. Evidence for early onset, polyclonal activation of T cell subsets in mice homozygous for lpr. J Immunol. 1992; 149: 3097–3106.CrossrefMedlineGoogle Scholar
  • 19 Crispin JC, Oukka M, Bayliss G, Cohen RA, Van Beek CA, Stillman IE, Kyttaris VC, Juang YT, Tsokos GC. Expanded double negative T cells in patients with systemic lupus erythematosus produce IL-17 and infiltrate the kidneys. J Immunol. 2008; 181: 8761–8766.CrossrefMedlineGoogle Scholar
  • 20 Ford MS, Young KJ, Zhang Z, Ohashi PS, Zhang L. The immune regulatory function of lymphoproliferative double negative T cells in vitro and in vivo. J Exp Med. 2002; 196: 261–267.CrossrefMedlineGoogle Scholar
  • 21 Pastore L, Belalcazar LM, Oka K, Cela R, Lee B, Chan L, Beaudet AL. Helper-dependent adenoviral vector-mediated long-term expression of human apolipoprotein A-I reduces atherosclerosis in apo E-deficient mice. Gene. 2004; 327: 153–160.CrossrefMedlineGoogle Scholar
  • 22 Belalcazar LM, Merched A, Carr B, Oka K, Chen K-H, Pastore L, Beaudet A, Chan L. Long-term stable expression of human apolipoprotein A-I mediated by helper-dependent adenovirus gene transfer inhibits atherosclerosis progression and remodels atherosclerotic plaques in a mouse model of familial hypercholesterolemia. Circulation. 2003; 107: 2726–2732.LinkGoogle Scholar
  • 23 Owen JS, Bharadwaj MS, Thomas MJ, Bhat S, Samuel MP, Sorci-Thomas MG. Ratio determination of plasma wild-type and L159R apoA-I using mass spectrometry: tools for studying apoA-IFin. J Lipid Res. 2007; 48: 226–234.CrossrefMedlineGoogle Scholar
  • 24 Ludewig B, Laman JD. The in and out of monocytes in atherosclerotic plaques: Balancing inflammation through migration. Proc Natl Acad Sci USA. 2004; 101: 11529–11530.CrossrefMedlineGoogle Scholar
  • 25 Hansson GK, Libby P. The immune response in atherosclerosis: a double-edged sword. Nat Rev Immunol. 2006; 6: 508–519.CrossrefMedlineGoogle Scholar
  • 26 Bonelli M, Savitskaya A, Steiner CW, Rath E, Smolen JS, Scheinecker C. Phenotypic and functional analysis of CD4+ CD25- Foxp3+ T cells in patients with systemic lupus erythematosus. J Immunol. 2009; 182: 1689–1695.CrossrefMedlineGoogle Scholar
  • 27 Aprahamian T, Rifkin I, Bonegio R, Hugel B, Freyssinet JM, Sato K, Castellot JJ Jr, Walsh K. Impaired clearance of apoptotic cells promotes synergy between atherogenesis and autoimmune disease. J Exp Med. 2004; 199: 1121–1131.CrossrefMedlineGoogle Scholar
  • 28 Gu L, Johnson MW, Lusis AJ. Quantitative trait locus analysis of plasma lipoprotein levels in an autoimmune mouse model: interactions between lipoprotein metabolism, autoimmune disease, and atherogenesis. Arterioscler Thromb Vasc Biol. 1999; 19: 442–453.CrossrefMedlineGoogle Scholar
  • 29 Frostegard J. Autoimmunity, oxidized LDL and cardiovascular disease. Autoimmunity Reviews. 2002; 1: 233–237.CrossrefMedlineGoogle Scholar
  • 30 Hyka N, Dayer J-M, Modoux C, Kohno T, Edwards CK, III, Roux-Lombard P, Burger D. Apolipoprotein A-I inhibits the production of interleukin-1{beta} and tumor necrosis factor-{alpha} by blocking contact-mediated activation of monocytes by T lymphocytes. Blood. 2001; 97: 2381–2389.CrossrefMedlineGoogle Scholar
  • 31 Umeuchi H, Kawashima Y, Aoki CA, Kurokawa T, Nakao K, Itoh M, Kikuchi K, Kato T, Okano K, Gershwin ME, Miyakawa H. Spontaneous scratching behavior in MRL/lpr mice, a possible model for pruritus in autoimmune diseases, and antipruritic activity of a novel κ-opioid receptor agonist nalfurafine hydrochloride. Eur J Pharmacol. 2005; 518: 133–139.CrossrefMedlineGoogle Scholar
  • 32 Bradley MN, Hong C, Chen M, Joseph SB, Wilpitz DC, Wang X, Lusis AJ, Collins A, Hseuh WA, Collins JL, Tangirala RK, Tontonoz P. Ligand activation of LXR-beta reverses atherosclerosis and cellular cholesterol overload in mice lacking LXR-alpha and apoE. J Clin Invest. 2007; 118: 2337–2346.Google Scholar
  • 33 Accad M, Smith SJ, Newland DL, Sanan DA, King LE, Jr., Linton MF, Fazio S, Farese RVJ. Massive xanthomatosis and altered composition of atherosclerotic lesions in hyperlipidemic mice lacking acyl CoA:cholesterol acyltransferase 1. J Clin Invest. 2000; 105: 711–719.CrossrefMedlineGoogle Scholar
  • 34 Aiello RJ, Brees D, Francone OL. ABCA1-deficient mice: insights into the role of monocyte lipid efflux in HDL formation and inflammation. Arterioscler Thromb Vasc Biol. 2003; 23: 972–980.LinkGoogle Scholar
  • 35 Jong MC, Gijbels MJJ, Dahlmans VEH, van Gorp PJJ, Koopman S-J, Ponec M, Hofker MH, Havekes LM. Hyperlipidemia and cutaneous abnormalities in transgenic mice overexpressing human apolipoprotein C1. J Clin Invest. 1998; 101: 145–152.CrossrefMedlineGoogle Scholar
  • 36 Wojcik AJ, Skaflen MD, Srinivasan S, Hedrick CC. A critical role for ABCG1 in macrophage inflammation and lung homeostasis. J Immunol. 2008; 180: 4273–4282.CrossrefMedlineGoogle Scholar
  • 37 Baldan A, Gomes AV, Ping P, Edwards PA. Loss of ABCG1 results in chronic pulmonary inflammation. J Immunol. 2008; 180: 3560–3568.CrossrefMedlineGoogle Scholar
  • 38 Hasegawa M, Fujimoto M, Takehara K, Sato S. Pathogenesis of systemic sclerosis: Altered B cell function is the key linking systemic autoimmunity and tissue fibrosis. J Dermatol Sci. 2005; 39: 1–7.CrossrefMedlineGoogle Scholar
  • 39 Zoller M, Gupta P, Marhaba R, Vitacolonna M, Freyschmidt-Paul P. Anti-CD44-mediated blockade of leukocyte migration in skin-associated immune diseases. J Leukoc Biol. 2007; 82: 57–71.CrossrefMedlineGoogle Scholar