MicroRNA-199a-5p protects hepatocytes from bile acid-induced sustained endoplasmic reticulum stress

B-H Dai,L Geng,R-X Shen,Y Wang,J-M Yang,C-J Sui,F Xie,W-F Shen

doi:10.1038/cddis.2013.134

Abstract

Sustained endoplasmic reticulum (ER) stress has been linked to cell death and the pathogenesis of many liver diseases, including toxic liver, cholestasis, and infectious liver disease. The cellular pathways that attenuate hepatic ER stress have been the focus of many recent studies, but the role of microRNAs (miRNA) in this process remains unknown. Here, we report that one of the most abundant miRNAs in hepatocytes, miR-199a-5p, was elevated in both bile acid- and thapsigargin (TG)-stimulated cultured hepatocytes, as well as in the liver of bile duct-ligated mice. We identify the misfolded protein chaperone GRP78, as well as the unfolded protein response transducers endoplasmic reticulum to nucleus signaling 1 and activating transcription factor 6 as direct targets of miR-199a-5p, and show that endogenous miR-199a-5p represses the 3′ untranslated regions (UTRs) of their mRNAs. Through gain-of-function and loss of function approaches, we demonstrate that the elevated miR-199-5p disrupts sustained ER stress and prevents hepatocytes from undergoing bile acid- or TG-induced cell death. Furthermore, we reveal that the transcription factor AP-1 is a strong positive regulator of miR-199a-5p. In brief, our study demonstrates that AP-1/miR-199a-5p and ER stress mediators form a feedback loop, which shields hepatocytes from sustained ER stress and protects the liver from injury. On the basis of these findings, we also suggest that the miRNA miR-199a-5p is a potential target for clinical approaches aiming to protect hepatocytes in liver disease.

Highlights

Many recent studies have focused on the role of endoplasmic reticulum (ER) stress in various liver diseases, including toxic, metabolic, and infectious liver disease.[5,6,7] Hepatocytes with a high burden of protein synthesis depend on efficient protein folding mechanisms to cope with the protein load within the ER
We found that the apoptosis rate increased 48 h after stimulation in the Dicerknockdown cells, but not in the control cells (Figure 1c)
These results indicated that Dicer knockdown impaired the regression of ER stress and promoted hepatocyte apoptosis during bile acid stimulation, supporting our hypothesis that miRNAs has an essential role in the regulation of hepatic ER stress

Summary

Introduction

Many recent studies have focused on the role of ER stress in various liver diseases, including toxic, metabolic, and infectious liver disease.[5,6,7] Hepatocytes with a high burden of protein synthesis depend on efficient protein folding mechanisms to cope with the protein load within the ER. MiR-199a-5p suppresses sustained hepatic ER stress B-H Dai et al microRNAs (miRNAs) are small noncoding RNAs that can negatively regulate gene expression post-transcriptionally.[19] Hundreds of miRNAs have been identified, and these molecules have important roles in a wide variety of biological processes. We investigated the roles of miRNAs in the direct repression of ER stress genes in hepatocytes. Through expression analysis and computational predictions, we identified endogenous miR-199a-5p is necessary for the modulation of hepatic ER stress progression by negatively regulating the IRE1a-related pathway. Our study uncovered a direct link between a miRNA and hepatic ER stress, and demonstrated that miR-199a-5p repressed sustained ER stress and prevented hepatocyte apoptosis

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Results

Conclusion