No abstract

Bile acids are primarily synthesized from cholesterol in the liver and have important roles in dietary lipid absorption and cholesterol homoeostasis. Detailed roles of the orphan nuclear receptors regulating cholesterol 7α-hydroxylase (CYP7A1), the rate-limiting enzyme in bile acid synthesis, have not yet been fully elucidated. In the present study, we report that oestrogen-related receptor γ (ERRγ) is a novel transcriptional regulator of CYP7A1 expression. Activation of cannabinoid receptor type 1 (CB1 receptor) signalling induced ERRγ-mediated transcription of the CYP7A1 gene. Overexpression of ERRγ increased CYP7A1 expression in vitro and in vivo, whereas knockdown of ERRγ attenuated CYP7A1 expression. Deletion analysis of the CYP7A1 gene promoter and a ChIP assay revealed an ERRγ -binding site on the CYP7A1 gene promoter. Small heterodimer partner (SHP) inhibited the transcriptional activity of ERRγ and thus regulated CYP7A1 expression. Overexpression of ERRγ led to increased bile acid levels, whereas an inverse agonist of ERRγ, GSK5182, reduced CYP7A1 expression and bile acid synthesis. Finally, GSK5182 significantly reduced hepatic CB1 receptor-mediated induction of CYP7A1 expression and bile acid synthesis in alcohol-treated mice. These results provide the molecular mechanism linking ERRγ and bile acid metabolism.

No abstract

Upon liver intoxication with malnutrition or high-fat diet feeding, fibrinogen is synthesized by hepatocytes and secreted into the blood in human and mouse. Its primary function is to occlude blood vessels upon damage and thereby stop excessive bleeding. High fibrinogen levels may contribute to the development of pathological thrombosis, which is one mechanism linking fatty liver disease with cardiovascular disease. Our previous results present ERRγ as key regulator of hepatocytic fibrinogen gene expression in human. In a therapeutic approach, we now tested ERRγ inverse agonist GSK5182 as regulator of fibrinogen levels in mouse hyperfibrinogenemia caused by diet-induced obesity and in mouse hepatocytes. ACEA, a CB1R agonist, up-regulated transcription of mouse fibrinogen via induction of ERRγ, whereas knockdown of ERRγ attenuated the effect of ACEA (10 µM) on fibrinogen expression in AML12 mouse hepatocytes. Deletion analyses of the mouse fibrinogen γ (FGG) gene promoter and ChIP assays revealed binding sites for ERRγ on the mouse FGG promoter. ACEA or adenovirus ERRγ injection induced FGA, FGB and FGG mRNA and protein expression in mouse liver, while ERRγ knockdown with Ad-shERRγ attenuated ACEA-mediated induction of fibrinogen gene expression. Moreover, mice maintained on a high-fat diet (HFD) expressed higher levels of fibrinogen, whereas cannabinoid receptor type 1 (CB1R)-KO mice fed an HFD had nearly normal fibrinogen levels. Finally, GSK5182 (40 mg/kg) strongly inhibits the ACEA (10 mg/kg) or HFD-mediated induction of fibrinogen level in mice. Taken together, targeting ERRγ with its inverse agonist GSK5182 represents a promising therapeutic strategy for ameliorating hyperfibrinogenemia.