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Hepatic Inhibition of ANGPTL3 Mimics the Molecular Hallmarks of Hypothyroidism

Originally publishedhttps://doi.org/10.1161/ATVBAHA.124.320817Arteriosclerosis, Thrombosis, and Vascular Biology. 2024;44:1098–1100

Metabolic dysfunction–associated steatotic liver disease (MASLD), previously referred to as nonalcoholic fatty liver disease, constitutes a highly prevalent liver condition that encompasses a spectrum of disease severities with a total global prevalence of 30% in the adult population.1 While MASLD is initially benign when only hepatic steatosis is present, the disease can progress to inflammatory metabolic dysfunction–associated steatohepatitis (previously referred to as nonalcoholic steatohepatitis), fibrosis, and, eventually, cirrhosis and hepatocellular carcinoma. Pathogenesis and disease progression are often paralleled by insulin resistance, oxidative stress, and excessive adipokine signaling, suggesting that primary MASLD is the hepatic manifestation of the metabolic syndrome.2 There is extensive guidance for the clinical management of MASLD3; however, current therapeutic approaches are limited to lifestyle interventions and treatment of common comorbidities, such as obesity, dyslipidemia, and insulin resistance. There are multiple drugs in clinical trials that use chemical or genetic approaches against metabolic dysfunction–associated steatohepatitis by targeting a diverse range of pathways from hepatic thyroid hormone and PPARα signaling to the inhibition of genetic risk factors, such as PNPLA3 and HSD17B13, using RNA interference. However, no drugs have received regulatory approval.4–6 The development of safe and effective therapies for MASLD/metabolic dysfunction–associated steatohepatitis thus remains of fundamental importance.

See accompanying article on page 1086

In this issue of Arteriosclerosis, Thrombosis, and Vascular Biology, Pennisi et al7 investigate the role of ANGPTL3 (angiopoietin-like protein 3) in hepatic lipid metabolism and demonstrate that its inhibition results in increased steatosis. Previous studies showed that inhibition of ANGPTL3 increases glucose uptake and insulin resistance in white adipose tissue8 and reduces hepatic VLDL (very-low-density lipoprotein) secretion.9 Moreover, in the DiscovEHR study with 58 335 participants, genetic loss-of-function variants in ANGPTL3 were significantly associated with reduced coronary artery disease risk.10 However, while antibody-based inhibition of ANGPTL3 reduced triglyceride and LDL (low-density lipoprotein) cholesterol levels,10,11 a clinical trial of hepatic ANGPTL3 inhibition using the antisense oligonucleotide drug vupanorsen had to be stopped due to dose-dependent hepatotoxicity and increases in hepatic steatosis.12

To identify the underlying mechanisms, Pennisi et al first replicated the clinical findings that hepatic ANGPTL3 inhibition increased steatosis using different hepatic cell lines and primary human hepatocytes. Specifically, they used 2-dimensional spheroid cultures of the hepatoma cell lines HepG2, Hep3B2, and Huh7, as well as 3-dimensional spheroid cultures of HepG2 and primary human hepatocytes, and demonstrated that siRNA-mediated knockdown of ANGPTL3 increased intracellular lipid levels. These effects were caused by the downregulation of both mitochondrial β-oxidation and peroxisomal fatty acid degradation. Using RNA sequencing, the authors found that DIO1, the enzyme bioactivating the thyroid hormone T4 to its active form T3, was significantly downregulated upon ANGPTL3 inhibition. Strikingly, incubation of liver spheroids in which ANGPTL3 was inhibited with T3 was sufficient to blunt the increased steatosis seen upon ANGPTL3 knockdown. These results thus convincingly demonstrate that ANGPTL3 inhibition increases steatosis and reduces thyroid hormone availability, effects that can be rescued via external supply of T3 (Figure). As such, the findings are consistent with the view that the different pools of ANGPTL3 have differing roles. The circulating ANGPTL3 pool acts as a hepatokine regulating LPL activity and glucose uptake in extrahepatic tissues, whereas the intracellular pool in hepatocytes regulates VLDL secretion. Thus, antibody-based neutralization of ANGPTL3 only affects extrahepatic functions, whereas hepatic silencing via antisense oligonucleotides would reduce VLDL secretion, thereby providing a possible explanation for the increased steatosis seen in the latter. However, multiple questions remain:

Figure.

Figure. Schematic depiction of the diverse roles of ANGPTL3 (angiopoietin-like protein 3) in liver metabolism. While inhibition of circulating ANGPTL3 increases glucose uptake in peripheral tissues without adverse liver effects, inhibition of hepatic ANGPTL3 results in liver injury and steatosis, at least in part via inhibition of thyroid hormone signaling and β-oxidation. THR-β indicates thyroid hormone receptor-beta.

  1. Previous results indicated in both mice and hepatoma cells that hepatic ablation of ANGPTL3 reduced secretion of ApoB-containing lipoproteins,13 whereas results by Pennisi et al show the opposite. Further investigations into the molecular basis of this discrepancy could reveal interesting new findings about the interface between ANGPTL3 and lipoprotein processing. Of particular interest in this regard is that ANGPTL3 is an LXR target gene.14 LXR is activated by cholesterol, raising the possibility that effects on VLDL secretion might be indirect and drastically different between in vivo (where cholesterol is present) and in vitro conditions without cholesterol.

  2. The NCoR nuclear receptor is an important mediator of T3 signaling and can modulate its interaction with PPARα.15 Deciphering this coregulatory network in different liver models might explain model-specific differences of ANGPTL3 modulation and provide new opportunities to refine context-specific therapies.

  3. Indeed, thyroid hormones are well known to induce β-oxidation and stimulate the reverse transport of cholesterol to the liver where it is converted into bile acids,16 and hypothyroidism is linked to dyslipidemia, hypertriglyceridemia, and MASLD.17 Multiple thyroid hormone signaling agonists are currently in clinical development.18 Recently (February 2024), results of a randomized controlled phase III trial for the selective thyroid hormone receptor-β agonist resmetirom were published and showed significant effects on metabolic dysfunction–associated steatohepatitis resolution and improvement in liver fibrosis.19 Given the results from the study by Pennisi et al, it is thus important to understand whether findings are translatable, and, if so, this might suggest that the hepatic adverse effects of ANGPTL3 inhibitors might be overcome by selective coactivation of hepatic thyroid signaling.

Combined, the interesting findings published by Pennisi et al provide convincing orthogonal support for the importance of thyroid hormone signaling in MASLD and incentivize further investigations into ANGPTL3 biology in health and disease.

ARTICLE INFORMATION

Disclosures V.M. Lauschke is the Chief Executive Officer and shareholder of HepaPredict AB, as well as cofounder and shareholder of Shanghai Hepo Biotechnology, Ltd. The other author reports no conflicts.

Footnotes

For Sources of Funding and Disclosures, see page 1100.

The opinions expressed in this article are not necessarily those of the editors or of the American Heart Association.

Correspondence to: Prof Volker M. Lauschke, Dr. Margarete Fischer-Bosch Institute of Clinical Pharmacology, Stuttgart, Germany. Email

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