Orphan nuclear receptor oestrogen-related receptor γ (ERRγ) plays a key role in hepatic cannabinoid receptor type 1-mediated induction of CYP7A1 gene expression

The roles of nuclear receptors in cholesterol metabolism and reverse cholesterol transport in nonalcoholic fatty liver disease

As the most prevalent chronic liver disease globally, NAFLD encompasses a pathological process that ranges from simple steatosis to NASH, fibrosis, cirrhosis, and HCC, closely associated with numerous extrahepatic diseases. While the initial etiology was believed to be hepatocyte injury caused by lipid toxicity from accumulated triglycerides, recent studies suggest that an imbalance of cholesterol homeostasis is of greater significance. The role of nuclear receptors in regulating liver cholesterol homeostasis has been demonstrated to be crucial. This review summarizes the roles and regulatory mechanisms of nuclear receptors in the 3 main aspects of cholesterol production, excretion, and storage in the liver, as well as their cross talk in reverse cholesterol transport. It is hoped that this review will offer new insights and theoretical foundations for the study of the pathogenesis and progression of NAFLD and provide new research directions for extrahepatic diseases associated with NAFLD.

Sex-Dependent Differences in Cholestasis: Why Estrogen Signaling May Be a Key Pathophysiological Driver

Primary biliary cholangitis (PBC) and primary sclerosing cholangitis (PSC) are cholestatic liver diseases that have significant clinical impact with debilitating symptoms and mortality. While PBC is predominantly seen in perimenopausal and postmenopausal women, men who are diagnosed with PBC have worse clinical outcomes and all-cause mortality. In contrast, 60% to 70% of patients with PSC are men; the data indicate that female sex may be an independent factor against PSC-related complications. These findings suggest a sex-dependent biological basis for these differences. Estrogen has been implicated in the pathogenesis of intrahepatic cholestasis of pregnancy and may induce cholestasis through a variety of interactions. However, it is unclear why some sexual dimorphic features may provide a protective effect despite known estrogen models that induce cholestasis. This article provides a brief introductory background and discusses the sexual dimorphism in clinical presentation in PSC and PBC. It also explores the role of estrogen signaling in pathogenesis and how it relates to intrahepatic cholestasis of pregnancy. Studies have already targeted certain molecules involved in estrogen signaling, and this review discusses these studies that identify estrogen-related receptor, estrogen receptor-α, estrogen receptor-β, farnesoid X receptor, and mast cells as possible targets, in addition to long noncoding RNA H19-induced cholestasis and sexual dimorphism. It also explores these interactions and their role in the pathogenesis of PBC and PSC.

Research progress on tamoxifen and its analogs associated with nuclear receptors

Tamoxifen, a triphenylethylene-based selective estrogen-receptor modulator, is a landmark drug for the treatment of breast cancer and is also used for treating liver cancer and osteoporosis. Structural studies of tamoxifen have led to the synthesis of more than 20 novel tamoxifen analogs as receptor modulators, including 16 ERα modulators 2-17, an ERRβ inverse agonist 19 and six ERRγ inverse agonists 20-25. This paper summarizes the research progress and structure-activity relationships of tamoxifen analogs modulating these three nuclear receptors reported in the literature, and introduces the relationship between these three nuclear receptor-mediated diseases and tamoxifen analogs to guide the research of novel tamoxifen analogs.

Estrogen-related receptor γ (ERRγ) is a key regulator of lysyl oxidase gene expression in mouse hepatocytes

Lysyl oxidase (LOX), the copper-dependent extracellular enzyme, plays a critical role in the regulation of protein cross-linking in the extracellular matrix (ECM). It is also involved in liver regeneration and liver fibrosis. However, the mechanism of LOX regulation in mouse hepatocytes is still unclear. Here, we identify a molecular mechanism showing that orphan nuclear receptor estrogen-related receptor γ (ERRγ) regulates LOX gene expression in the presence of the pro-inflammatory cytokine, interleukin 6 (IL6). IL6 significantly stimulated the expression of ERRγ and LOX in mouse hepatocytes. Overexpression of ERRγ increased LOX mRNA and protein levels. Moreover, knockdown of ERRγ attenuated IL6-mediated LOX gene expression at mRNA and protein levels. Overexpression of ERRγ or IL6 treatment upregulated LOX gene promoter activity, while knockdown of ERRγ decreased the IL6-induced LOX promoter activity. Furthermore, GSK5182, a specific ERRγ inverse agonist, inhibited the induction effect of IL6 on LOX promoter activity and gene expression in mouse hepatocytes. Overall, our study elucidates the mechanism involved in the LOX gene regulation by nuclear receptor ERRγ in response to IL6 in mouse hepatocytes, suggesting that, in conditions such as chronic inflammation, IL6 may contribute to liver fibrosis via inducing LOX gene expression. Thus, LOX gene regulation by the inverse agonist of ERRγ can be applied to improve liver fibrosis.

An Inverse Agonist of Estrogen-Related Receptor Gamma, GSK5182, Enhances Na+/I- Symporter Function in Radioiodine-Refractory Papillary Thyroid Cancer Cells

Previously, we reported that an inverse agonist of estrogen-related receptor gamma (ERRγ), GSK5182, enhances sodium iodide (Na⁺/I^-) symporter (NIS) function through mitogen-activated protein (MAP) kinase signaling in anaplastic thyroid cancer cells. This finding helped us to further investigate the effects of GSK5182 on NIS function in papillary thyroid cancer (PTC) refractory to radioactive iodine (RAI) therapy. Herein, we report the effects of ERRγ on the regulation of NIS function in RAI-resistant PTC cells using GSK5182. RAI-refractory BCPAP cells were treated with GK5182 for 24 h at various concentrations, and radioiodine avidity was determined with or without potassium perchlorate (KClO₄) as an NIS inhibitor. We explored the effects of GSK5182 on ERRγ, the mitogen-activated protein (MAP) kinase pathway, and iodide metabolism-related genes. We examined whether the MAP pathway affected GSK5182-mediated NIS function using U0126, a selective MEK inhibitor. A clonogenic assay was performed to evaluate the cytotoxic effects of I-131. GSK5182 induced an increase in radioiodine avidity in a dose-dependent manner, and the enhanced uptake was completely inhibited by KClO₄ in BCPAP cells. We found that ERRγ was downregulated and phosphorylated extracellular signal-regulated kinase (ERK)1/2 was upregulated in BCPAP cells, with an increase in total and membranous NIS and iodide metabolism-related genes. MEK inhibitors reversed the increase in radioiodine avidity induced by GSK5182. Clonogenic examination revealed the lowest survival in cells treated with a combination of GSK5182 and I-131 compared to those treated with either GSK518 or I-131 alone. We demonstrate that an inverse agonist of ERRγ, GSK5182, enhances the function of NIS protein via the modulation of ERRγ and MAP kinase signaling, thereby leading to increased responsiveness to radioiodine in RAI-refractory papillary thyroid cancer cells.

An Inverse Agonist GSK5182 Increases Protein Stability of the Orphan Nuclear Receptor ERRγ via Inhibition of Ubiquitination

The orphan nuclear receptor, estrogen-related receptor γ (ERRγ) is a constitutively active transcription factor involved in mitochondrial metabolism and energy homeostasis. GSK5182, a specific inverse agonist of ERRγ that inhibits transcriptional activity, induces a conformational change in ERRγ, resulting in a loss of coactivator binding. However, the molecular mechanism underlying the stabilization of the ERRγ protein by its inverse agonist remains largely unknown. In this study, we found that GSK5182 inhibited ubiquitination of ERRγ, thereby stabilizing the ERRγ protein, using cell-based assays and confocal image analysis. Y326 of ERRγ was essential for stabilization by GSK5182, as ligand-induced stabilization of ERRγ was not observed with the ERRγ-Y326A mutant. GSK5182 suppressed ubiquitination of ERRγ by the E3 ligase Parkin and subsequent degradation. The inhibitory activity of GSK5182 was strong even when the ERRγ protein level was elevated, as ERRγ bound to GSK5182 recruited a corepressor, small heterodimer partner-interacting leucine zipper (SMILE), through the activation function 2 (AF-2) domain, without alteration of the nuclear localization or DNA-binding ability of ERRγ. In addition, the AF-2 domain of ERRγ was critical for the regulation of protein stability. Mutants in the AF-2 domain were present at higher levels than the wild type in the absence of GSK5182. Furthermore, the ERRγ-L449A/L451A mutant was no longer susceptible to GSK5182. Thus, the AF-2 domain of ERRγ is responsible for the regulation of transcriptional activity and protein stability by GSK5182. These findings suggest that GSK5182 regulates ERRγ by a unique molecular mechanism, increasing the inactive form of ERRγ via inhibition of ubiquitination.

Hepatic cholesterol transport and its role in non-alcoholic fatty liver disease and atherosclerosis

Non-alcoholic fatty liver disease (NAFLD) is a quickly emerging global health problem representing the most common chronic liver disease in the world. Atherosclerotic cardiovascular disease represents the leading cause of mortality in NAFLD patients. Cholesterol metabolism has a crucial role in the pathogenesis of both NAFLD and atherosclerosis. The liver is the major organ for cholesterol metabolism. Abnormal hepatic cholesterol metabolism not only leads to NAFLD but also drives the development of atherosclerotic dyslipidemia. The cholesterol level in hepatocytes reflects the dynamic balance between endogenous synthesis, uptake, esterification, and export, a process in which cholesterol is converted to neutral cholesteryl esters either for storage in cytosolic lipid droplets or for secretion as a major constituent of plasma lipoproteins, including very-low-density lipoproteins, chylomicrons, high-density lipoproteins, and low-density lipoproteins. In this review, we describe decades of research aimed at identifying key molecules and cellular players involved in each main aspect of hepatic cholesterol metabolism. Furthermore, we summarize the recent advances regarding the biological processes of hepatic cholesterol transport and its role in NAFLD and atherosclerosis.

Estrogen-Related Receptor γ Agonist DY131 Ameliorates Lipopolysaccharide-Induced Acute Liver Injury

Sepsis-associated liver dysfunction remains a challenge in clinical practice with high mortality and limited specific therapies. DY131 is a pharmacological agonist of the orphan receptor estrogen-related receptor (ERR) γ which plays a crucial role in regulating energy generation, oxidative metabolism, cell apoptosis, inflammatory responses, etc. However, its role in acute liver injury is unknown. In this study, we evaluated the effect of DY131 on lipopolysaccharide (LPS)-induced liver injury. Mice were pretreated with DY131 through intraperitoneal injection at a dose of 5 mg/kg/day for 3 days prior to LPS challenge (10 mg/kg). 24 h later, they were anesthetized and sacrificed. Blood and liver tissues were collected for further studies. In a separate experiment, mice were treated with saline (vehicle) or DY131 for 3 days to evaluate the toxicity of DY131. We found that ERRγ was downregulated in the liver tissues from LPS-treated mice. Pretreatment with DY131 ameliorated LPS-induced liver injury as demonstrated by reduced liver enzyme release (ALT, AST, and LDH), improved liver morphological damage, and attenuated oxidative stress, inflammation and apoptosis. Meanwhile, DY131 had no significant side effects on hepatic and renal functions in mice. Finally, transcriptomics analysis revealed that the dysregulated pathways associated with inflammation and metabolism were significantly reversed by DY131 in LPS-treated mice, providing more evidence in favor of the protective effect of DY131 against LPS-induced liver injury. Altogether, these findings highlighted the protective effect of DY131 on LPS-induced hepatotoxicity possibly via suppressing oxidative stress, inflammation, and apoptosis.

Hypolipidemic effect of Alisma orientale (Sam.) Juzep on gut microecology and liver transcriptome in diabetic rats

Alisma orientale (Sam.) Juzep (A. orientale) is a traditional herb that is often used to treat disease including edema and hyperlipidemia. However, the molecular mechanism by which Alisma orientale (Sam.) Juzep exerts its hypolipidemic effects remains unclear. In this study, a diabetic rat model was established by feeding a high-fat and high-sugar diet combined with a low-dose streptozotocin injection (HFS). Then the rats were treated with an A. orientale water extract (AOW), an A. orientale ethanolic extract (AOE) or metform (MET). The gut microflora and liver transcriptome were analyzed by high-throughput next-generation sequencing. Ultra-performance liquid chromatography-triple quadrupole-mass spectrometry was employed to analyze the major compounds in the AOE. The results showed that the serum total cholesterol (TC) and low density lipoprotein cholesterol (LDL-C) levels in rats of the AOE group (2.10 g/kg/day, 14 days) were significantly lower than those in the HFS group (p<0.01). Moreover, AOE treatment altered the gut microecology, particularly modulating the relative abundance of gut microflora involved in lipid metabolism compared with the HFS group. Furthermore, compared with the HFS group, the mRNA expression levels of Fam13a, Mapk7, Mpp7, Chac1, Insig1, Mcpt10, Noct, Greb1l, Fabp12 and Hba-a3 were upregulated after the administration of AOE. In contrast, the mRNA expression levels of Lox, Mybl1, Arrdc3, Cyp4a2, Krt20, Vxn, Ggt1, Nr1d1 and S100a9 were downregulated. Moreover, AOE treatment for two weeks markedly promoted the relative abundance of Lachnospiraceae (p = 0.0013). The triterpenoids contents in AOE were alisol A, alisol A 24-acetate, alisol B, alisol B 23-acetate, alisol C 23-acetate, alisol F, alisol F 24-acetate, and alisol G. Our findings above illustrated that the hypolipidemic effect of the triterpenoids of A. orientale is mediated mainly through alteration of the gut microecology and the regulation of genes involved in cholesterol metabolism, especially Insig1.

ERRγ suppression by Sirt6 alleviates cholestatic liver injury and fibrosis

Orphan nuclear receptor estrogen-related receptor γ (ERRγ) stimulates bile acid production; however, the role and the regulatory mechanism of ERRγ in cholestatic liver disease are largely unknown. This study identifies that Sirt6 is a deacetylase of ERRγ and suggests a potentially novel mechanism by which Sirt6 activation alleviates cholestatic liver damage and fibrosis through regulating ERRγ. We observed that hepatic expression of Sirt6 is repressed, whereas hepatic expression of ERRγ is upregulated in murine cholestasis models. Hepatocyte-specific Sirt6-KO mice were more severely injured after a bile duct ligation (BDL) than WT mice, and adenoviral reexpression of Sirt6 reversed liver damage and fibrosis as demonstrated by biochemical and histological analyses. Mechanistically, Sirt6 deacetylated ERRγ, thereby destabilizing ERRγ and inhibiting its transcriptional activity. Elimination of hepatic ERRγ using Ad-shERRγ abolished the deleterious effects of Sirt6 deficiency, whereas ERRγ overexpression aggravated cholestatic liver injury. Administration of a Sirt6 deacetylase activator prevented BDL-induced liver damage and fibrosis. In patients with cholestasis, Sirt6 expression was decreased, whereas total ERRγ and acetylated ERRγ levels were increased, confirming negative regulation of ERRγ by Sirt6. Thus, Sirt6 activation represents a potentially novel therapeutic strategy for treating cholestatic liver injury.

Sirt6 activation alleviates cholestatic liver damage and fibrosis in murine cholestasis models by deacetylation of ERRγ.

An orally available inverse agonist of estrogen-related receptor gamma showed expanded efficacy for the radioiodine therapy of poorly differentiated thyroid cancer

Estrogen-related receptor gamma (ERRγ) is the NR3B subgroup of associated transcription factors. In this report, a new generation of a potent and selective ERRγ inverse agonist (25) with good biocompatibility was proposed. We also explored the potential of the newly developed compound 25 in the PDTC model to expand the original indications from ATC. In addition, an X-ray crystallographic study of the ligand and ERRγ co-complex showed that 25 completely binds to the target protein (PDB 6KNR). Its medicinal chemistry, including a distinctive structural study to in vivo results, denotes that 25 may be directed towards the development of a pivotal treatment for ERRγ-related cancers.

An inverse agonist of estrogen-related receptor γ regulates 2-arachidonoylglycerol synthesis by modulating diacylglycerol lipase expression in alcohol-intoxicated mice

Chronic alcohol feeding increases the levels of 2-arachidonoylglycerol (2-AG) in the liver, which activates hepatic cannabinoid receptor type 1 (CB1R), leading to oxidative liver injury. 2-AG biosynthesis is catalyzed by diacylglycerol lipase (DAGL). However, the mechanisms regulating hepatic DAGL gene expression and 2-AG production are largely unknown. In this study, we show that CB1R-induced estrogen-related receptor γ (ERRγ) controls hepatic DAGL gene expression and 2-AG levels. Arachidonyl-2'-chloroethylamide (ACEA), a synthetic CB1R agonist, significantly upregulated ERRγ, DAGLα, and DAGLβ, and increased 2-AG levels in the liver (10 mg/kg) and hepatocytes (10 μM) of wild-type (WT) mice. ERRγ overexpression upregulated DAGLα and DAGLβ expressions and increased 2-AG levels, whereas ERRγ knockdown abolished ACEA-induced DAGLα, DAGLβ, and 2-AG in vitro and in vivo. Promoter assays showed that ERRγ positively regulated DAGLα and DAGLβ transcription by binding to the ERR response element in the DAGLα and DAGLβ promoters. Chronic alcohol feeding (27.5% of total calories) induced hepatic steatosis and upregulated ERRγ, leading to increased DAGLα, DAGLβ, or 2-AG in WT mice, whereas these alcohol-induced effects did not occur in hepatocyte-specific CB1R knockout mice or in those treated with the ERRγ inverse agonist GSK5182 (40 mg/kg in mice and 10 μM in vitro). Taken together, these results indicate that suppression of alcohol-induced DAGLα and DAGLβ gene expressions and 2-AG levels by an ERRγ-specific inverse agonist may be a novel and attractive therapeutic approach for the treatment of alcoholic liver disease.

Repression of hepatocyte nuclear factor 4 alpha by AP-1 underlies dyslipidemia associated with retinoic acid

All-trans retinoic acid (atRA) is used to treat certain cancers and dermatologic diseases. A common adverse effect of atRA is hypercholesterolemia; cytochrome P450 (CYP) 7A repression is suggested as a driver. However, the underlying molecular mechanisms remain unclear. We investigated CYP7A1 expression in the presence of atRA in human hepatocytes and hepatic cell lines. In HepaRG cells, atRA increased cholesterol levels dose-dependently alongside dramatic decreases in CYP7A1 expression. Lentiviral-mediated CYP7A1 overexpression reversed atRA-induced cholesterol accumulation, suggesting that CYP7A1 repression mediated cholesterol accumulation. In CYP7A1 promoter reporter assays and gene-knockdown studies, altered binding of hepatocyte nuclear factor 4 α (HNF4α) to the proximal promoter was essential for atRA-mediated CYP7A1 repression. Pharmacologic inhibition of c-Jun N-terminal kinase (JNK) and ERK pathways attenuated atRA-mediated CYP7A1 repression and cholesterol accumulation. Overexpression of AP-1 (c-Jun/c-Fos), a downstream target of JNK and ERK, repressed CYP7A1 expression. In DNA pull-down and chromatin immunoprecipitation assays, AP-1 exhibited sequence-specific binding to the proximal CYP7A1 promoter region overlapping the HNF4α binding site, and atRA increased AP-1 but decreased HNF4α recruitment to the promoter. Collectively, these results indicate that atRA activates JNK and ERK pathways and the downstream target AP-1 represses HNF4α transactivation of the CYP7A1 promoter, potentially responsible for hypercholesterolemia.

Estrogen-related receptor γ regulates hepatic triglyceride metabolism through phospholipase A2 G12B

Hypersecretion of hepatic very LDL (VLDL)-associated triglyceride (TG) is the hallmark of hypertriglyceridemia. The estrogen-related receptor γ (ERRγ), an orphan nuclear receptor, plays crucial roles in the regulation of metabolic homeostasis, including TG formation in the liver. It remains unclear whether ERRγ regulates hepatic VLDL-TG secretion. We demonstrated that knockdown of ERRγ impairs hepatic VLDL-TG secretion in mice, whereas overexpression of ERRγ favors the secretion, indicating a novel role of ERRγ in hepatic TG metabolism. We found that ERRγ transcriptionally regulates the expression of PLA2G12B by binding to the promoter region of the Pla2g12b gene. In Pla2g12b-null mice, ERRγ fails to regulate hepatic VLDL-TG secretion. There is an apparent accumulation of large lipid droplets in the liver of Pla2g12b-null mice. These data suggest that ERRγ is a novel regulator of hepatic VLDL-TG secretion, which is mediated through the action on PLA2G12B.-Chen, L., Wu, M., Zhang, S., Tan, W., Guan, M., Feng, L., Chen, C., Tao, J., Chen, L., Qu, L. Estrogen-related receptor γ regulates hepatic triglyceride metabolism through phospholipase A2 G12B.

Orphan nuclear receptor ERRγ is a key regulator of human fibrinogen gene expression

Fibrinogen, 1 of 13 coagulation factors responsible for normal blood clotting, is synthesized by hepatocytes. Detailed roles of the orphan nuclear receptors regulating fibrinogen gene expression have not yet been fully elucidated. Here, we identified estrogen-related receptor gamma (ERRγ) as a novel transcriptional regulator of human fibrinogen gene expression. Overexpression of ERRγ specially increased fibrinogen expression in human hepatoma cell line. Cannabinoid receptor types 1(CB1R) agonist arachidonyl-2'-chloroethylamide (ACEA) up-regulated transcription of fibrinogen via induction of ERRγ, whereas knockdown of ERRγ attenuated fibrinogen expression. Deletion analyses of the fibrinogen γ (FGG) gene promoter and ChIP assays revealed binding sites of ERRγ on human fibrinogen γ gene promoter. Moreover, overexpression of ERRγ was sufficient to increase fibrinogen gene expression, whereas treatment with GSK5182, a selective inverse agonist of ERRγ led to its attenuation in cell culture. Finally, fibrinogen and ERRγ gene expression were elevated in liver tissue of obese patients suggesting a conservation of this mechanism. Overall, this study elucidates a molecular mechanism linking CB1R signaling, ERRγ expression and fibrinogen gene transcription. GSK5182 may have therapeutic potential to treat hyperfibrinogenemia.

ERRγ: a Junior Orphan with a Senior Role in Metabolism

Estrogen-related receptor (ERR)γ is an orphan nuclear hormone receptor that belongs to the ERR subfamily of transcription factors. No endogenous ligand has been identified to date. ERRγ possesses ligand-independent transcriptional activity that is regulated by co-regulator interactions, and post-translational modifications (PTMs). Recent data from animal models have established ERRγ as a crucial mediator of multiple endocrine and metabolic signals. ERRγ plays important roles in pathological conditions such as insulin resistance, alcoholic liver injury, and cardiac hypertrophy, and controls energy metabolism in the heart, skeletal muscle, and pancreatic β cells. These findings corroborate the importance of ERRγ in metabolic homeostasis, and suggest that ERRγ is a good target for the treatment of metabolic diseases.

Melatonin ameliorates alcohol-induced bile acid synthesis by enhancing miR-497 expression

Alcoholic liver disease is a major cause of chronic liver disease worldwide, and cannabinoid receptor type 1 (CB1R) is involved in a diverse metabolic diseases. B-cell translocation gene 2 (BTG2) and yin yang 1 (YY1) are a potent regulator of biological conditions. Melatonin plays a crucial role in regulating diverse physiological functions and metabolic homeostasis. MicroRNAs are key regulators of various biological processes. Herein, we demonstrate that melatonin improves bile acid synthesis in the liver of alcohol-fed mice by controlling miR-497 expression. The level of bile acid and the expression of Cb1r, Btg2, Yy1, and bile acid synthetic enzymes were significantly elevated in the livers of Lieber-DeCarli alcohol-fed mice. The overexpression of Btg2 enhanced Yy1 gene expression and bile acid production, whereas disrupting the CB1R-BTG2-YY1 cascade protected against the bile acid synthesis caused by alcohol challenge. We identified an alcohol-mediated YY1 binding site on the cholesterol 7α-hydroxylase (Cyp7a1) gene promoter using promoter deletion analysis and chromatin immunoprecipitation assays. Notably, melatonin attenuated the alcohol-stimulated induction of Btg2, Yy1 mRNA levels and bile acid production by promoting miR-497. Overexpression of a miR-497 mimic dramatically diminished the increase of Btg2 and Yy1 gene expression as well as bile acid production by alcohol, whereas this phenomenon was reversed by miR-497 inhibitor. These results demonstrate that the upregulation of miR-497 by melatonin represses alcohol-induced bile acid synthesis by attenuating the BTG2-YY1 signaling pathway. The melatonin-miR497 signaling network may provide novel therapeutic targets for the treatment of hepatic metabolic dysfunction caused by the alcohol-dependent pathway.