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

Abstract

Nonalcoholic 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 (PA) showed increased caspase 3/7 activity and increased levels of cleaved poly (ADP-ribose) polymerase and cleaved caspase 3, demonstrating cholangiocyte lipoapoptosis. Interestingly, treatment with PA significantly increased the levels of microRNA miR-34a, a pro-apoptotic microRNA known to be elevated in NASH. PA induction of miR-34a was abolished in cholangiocytes transduced with forkhead family of transcription factor class O (FoxO)3 shRNA, demonstrating that FoxO3 activation is upstream of miR-34a and suggesting that FoxO3 is a novel transcriptional regulator of miR-34a. Further, anti-miR-34a protected cholangiocytes from PA-induced lipoapoptosis. Direct and indirect targets of miR-34a, such as SIRT1, receptor tyrosine kinase (MET), Kruppel-like factor 4, fibroblast growth factor receptor (FGFR)1, and FGFR4, were all decreased in PA-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 provides evidence for the pro-apoptotic role of miR-34a in PA-induced cholangiocyte lipoapoptosis in culture and in the liver.

Adipocyte-secreted exosomal microRNA-34a inhibits M2 macrophage polarization to promote obesity-induced adipose inflammation

“…Although the precise mechanism whereby obesity induces adipose miR-34a expression remains unknown, both our results and previous studies showed that TNF-α, a proinflammatory cytokine that is elevated at the very early stage of obesity, increases miR-34a expression (40,41). Furthermore, in line with our results, palmitate, a toxic lipid that is increased in obesity, has been reported to induce miR-34a expression through the activation of the transcription factor Foxo3 (42). Therefore, the increased miR-34a expression in obese adipose tissue might be attributed to the synergistic effects of various metabolic stress-induced signaling cascades.…”

To die or not to die: death signaling in nonalcoholic fatty liver disease

“…Cholestatic presentation of NASH has been suggested to develop in a subset of patients [ 119 ] and FFAs induce apoptosis not only in hepatocytes but also in cholangiocytes. Indeed, cholangiocyte lipoapoptosis has been shown to occur in high fat-high sucrose-fed mice [ 117 , 120 ]. Natarajan et al recently found that FFAs induced apoptosis of cholangiocytes through forkhead box O3 (Foxo3)-mediated miR-34a (Fig.…”

The hedgehog pathway in nonalcoholic fatty liver disease

“…In NASH, the primary sources of Hh ligands are the injured hepatic epithelial cells, particularly lipotoxic hepatocytes (Rangwala et al, 2011; Guy et al, 2012) and reactive cholangiocytes (Natarajan et al, 2014; Natarajan et al, 2017). In hepatocytes, fatty acid toxicity provokes ER and apoptotic-stress, resulting in disruption of the cytoskeleton and swelling (a.k.a., ballooning).…”