Ligand-dependent corepressor acts as a novel corepressor of thyroid hormone receptor and represses hepatic lipogenesis in mice

Background & Aims: Transcriptional co-regulators assist nuclear receptors to control the transcription and maintain the metabolic homeostasis. Ligand-dependent corepressor (LCOR) was reported to function as a transcriptional corepressor in vitro. We found LCOR expression decreased in fatty livers of leptin-deficient (ob/ob) mice, diet-induced obese mice, as well as patients, suggesting LCOR may play a role in lipid homeostasis. We sought to investigate the physiological role of LCOR in vivo and elucidate the underlining molecular mechanisms. Methods: The effect of LCOR on hepatic lipid accumulation and thyroid hormone receptor (TR) mediated expression of lipogenic genes was studied in vitro and in vivo. Results: Ectopic expression of LCOR via intravenous infection with LCOR adenovirus decreased the hepatic triglyceride level in wild type, ob/ob, and diet-induced obese mice. Interestingly, overexpression of LCOR repressed the thyroid hormone induced expression of lipogenic genes and non-lipogenic genes, and ame-liorated hepatic steatosis in obese mice, suggesting that LCOR might regulate lipogenesis as a novel TR corepressor. Furthermore, our study revealed that LCOR could interact with TR beta 1 in the presence of the ligand, which resulted in competitive binding and reduced recruitment of steroid receptor coactivator-1/3 (SRC-1/3) to the promoter region of TR target genes. Conclusions: Our data suggest that LCOR is likely to suppress TR beta 1-mediated hepatic lipogenesis by decreasing binding and recruitment of SRCs to TR beta 1. Our study reveals the physiological function of hepatic LCOR in lipid metabolism and the mechanism by which LCOR regulates lipogenesis. Hepatic LCOR may be a potential target for treating hepatic steatosis. (C) 2011 European Association for the Study of the Liver. Published by Elsevier B.V. All rights reserved.