Hepatic Reduction in Cholesterol 25-Hydroxylase Aggravates Diet-induced Steatosis

BACKGROUND & AIMS: Cholesterol 25-hydroxylase (Ch25h), converting cholesterol to 25-hydroxycholesterol (25-HC), is critical in modulating cellular lipid metabolism and anti-inflammatory and antiviral activities. However, its role in nonalcoholic fatty liver disease remains unclear.& nbsp;METHODS: Ch25h expression was detected in livers of ob/ob mice and E3 rats fed a high-fat diet (HFD). Gain-or loss-of-function of Ch25h was performed using Ch25h(+/+) (wild type [WT]) mice receiving AAV8-Ch25h or Ch25h knockout (Ch25h(-/-)) mice. WT mice fed an HFD were administered with 25-HC. The Ch25h-LXRa-CYP axis was measured in primary hepatocytes isolated from WT and Ch25h(-/-) mice.& nbsp;RESULTS: We found that Ch25h level was decreased in livers of ob/ob mice and E3 rats fed an HFD. Ch25h(-/- )mice fed an HFD showed aggravated fatty liver and decreased level of cytochrome P450 7A1 (CYP7A1), in comparison with their WT littermates. RNA-seq analysis revealed that the differentially expressed genes in livers of HFD-fed Ch25h(-/- )mice were involved in pathways of positive regulation of lipid metabolic process, steroid metabolic process, cholesterol metabolic process, and bile acid biosynthetic process. As gain-of-function experiments, WT mice receiving AAV8-Ch25h or 25-HC showed alleviated NAFLD, when compared with the control group receiving AAV8-control or vehicle control. Consistently, Ch25h overexpression significantly elevated the levels of primary and secondary bile acids and CYP7A1 but decreased those of small heterodimer partner and FGFR4.& nbsp;CONCLUSIONS: Elevated levels of Ch25h and its enzymatic product 25-HC alleviate HFD-induced hepatic steatosis via regulating enterohepatic circulation of bile acids. The underlying mechanism involves 25-HC activation of CYP7A1 via liver X receptor. These data suggest that targeting Ch25h or 25-HC may have therapeutic advantages against nonalcoholic fatty liver disease.