miR-194 Up-Regulates Cholesterol 7 Alpha-Hydroxylase Expression via ß-Catenin Signaling and Aggravates Cholestatic Liver Diseases.

miR-194 is abundantly expressed in hepatocytes, and its depletion increases hepatic resistance to acetaminophen-induced acute injuries. In this study, the biological role of miR-194 in cholestatic liver injury was investigated by using miR-194/miR-192 cluster liver-specific knockout (LKO) mice, in which no liver injuries or metabolic disorders were predisposed. Bile duct ligation (BDL) and 1-naphthyl isothiocyanate (ANIT) were applied to LKO and matched control wild-type (WT) mice to induce hepatic cholestasis. Periportal liver damage, mortality rate, and liver injury biomarkers in LKO mice were significantly less than in WT mice after BDL and ANIT injection. Intrahepatic bile acid level was significantly lower in the LKO liver within 48 hours of BDL- and ANIT-induced cholestasis compared with WT. Western blot analysis showed that ß-catenin (CTNNB1) signaling and genes involved in cellular proliferation were activated in BDL- and ANIT-treated mice. The expression levels of cholesterol 7 alpha-hydroxylase (CYP7A1), pivotal in bile synthesis, and its upstream regulator hepatocyte nuclear factor 4α were reduced in primary LKO hepatocytes and liver tissues compared with WT. The knockdown of miR-194 using miRNA inhibitors reduced CYP7A1 expression in WT hepatocytes. In contrast, the knockdown of CTNNB1 and overexpression of miR-194, but not miR-192, in LKO hepatocytes and AML12 cells increased CYP7A1 expression. In conclusion, the results suggest that the loss of miR-194 ameliorates cholestatic liver injury and may suppress CYP7A1 expression via activation of CTNNB1 signaling.

Loss of hepatic miR-194 promotes liver regeneration and protects from acetaminophen-induced acute liver injury.

The two microRNAs miR-192 and miR-194 are abundantly expressed in the liver and are considered serum biomarkers of liver injury. However, their role in the development of liver injury has not yet been determined. In this study, we generated miR-192/194 mutant mice and determined the effect of miR-192/194 loss on acetaminophen (APAP)-induced acute liver injury. With genetic depletion of miR-192/194, mutant mice were fertile and normally developed. No spontaneous liver injuries were observed in mutant mice. After APAP administration, mutant mice developed less severe liver damage than control mice. Specifically, mutant mice exhibited significantly lower serum alanine transaminase (ALT) levels and pericentral necrosis/apoptosis than control mice receiving APAP. ß-catenin signaling was activated during the early phase of liver injury. Activated ß-catenin signaling led to faster cellular proliferation and higher expression of AXIN2 and glutamine synthetases. After partial hepatectomy, the miR-192/194 mutant hepatocytes were more regenerative than control hepatocytes (as shown by BrdU incorporation). Moreover, in vitro experiments indicated that miR-194, but not miR-192, specifically repressed ß-catenin signaling, while animal experiments revealed that chemical-mediated knockdown of ß-catenin signaling compromised APAP resistance that liver protected from miR-192/194 genetic depletion. Collectively, our data indicated that the loss of miR-194 promoted liver regeneration and protected the liver from APAP-induced injury.