FoxO3 increases miR-34a to cause palmitate-induced cholangiocyte lipoapoptosis.

Natarajan SK, Stringham BA, Mohr AM et al.

University of Nebraska-Lincoln, United States;

Journal of lipid research. Mar 2017.

Non-alcoholic steatohepatitis (NASH) patients have elevated plasma saturated free fatty acid levels. These toxic fatty acids can induce liver cell death and our recent results demonstrated that the biliary epithelium may be susceptible to lipotoxicity. Here, we explored the molecular mechanisms of cholangiocyte lipoapoptosis in cell culture and in an animal model of NASH. Treatment of cholangiocytes with palmitate showed increased caspase-3/7 activity, and increased levels of cleaved PARP and cleaved caspase 3 demonstrating cholangiocyte lipoapoptosis. Interestingly, treatment with palmitate significantly increased the levels of miR-34a, a pro-apoptotic microRNA known to be elevated in NASH. Palmitate induction of miR-34a was abolished in cholangiocytes transduced with FoxO3 shRNA, demonstrating FoxO3 activation is upstream of miR-34a and suggesting that FoxO3 is a novel transcriptional regulator of miR-34a. Further, anti-miR34a protected cholangiocytes from palmitate-induced lipoapoptosis. Direct and indirect targets of miR 34a such as Sirt1, receptor tyrosine kinase (MET), Kruppel like factor 4, fibroblast growth factor receptor-1 and FGFR4 were all decreased in palmitate-treated cholangiocytes. Sirt1 and MET were partially rescued by a miR-34a antagonist. Cholangiocyte apoptosis and miR-34a were dramatically increased in the liver of mice with early histologic features of NASH. Our study provide evidence for the pro-apoptotic role of miR-34a in palmitate-induced cholangiocyte lipoapoptosis in culture and in the liver.