microRNA-29b prevents liver fibrosis by attenuating hepatic stellate cell activation and inducing apoptosis through targeting PI3K/AKT pathway

Abstract

// Jia Wang 1,2 , Eagle S.H. Chu 1,2 , Hai-Yong Chen 1 , Kwan Man 3 , Minnie Y.Y. Go 1 , Xiao Ru Huang 1 , Hui Yao Lan 1 , Joseph J.Y. Sung 1 , 2 and Jun Yu 1,2 1 Institute of Digestive Disease and The Department of Medicine and Therapeutics, State Key Laboratory of Digestive Disease, Li Ka Shing Institute of Health Sciences, The Chinese University of Hong Kong, Hong Kong 2 Gastrointestinal Cancer Biology & Therapeutics Laboratory, CUHK-Shenzhen Research Institute, Shenzhen, China 3 Department of Surgery, LKS Faculty of Medicine, The University of Hong Kong, Hong Kong Correspondence to: Jun Yu, email: // Keywords : miR-29b, hepatic stellate cell, liver fibrosis, AKT3 Received : August 25, 2014 Accepted : October 22, 2014 Published : October 22, 2014 Abstract microRNA-29b (miR-29b) is known to be associated with TGF-β-mediated fibrosis, but the mechanistic action of miR-29b in liver fibrosis remains unclear and is warranted for investigation. We found that miR-29b was significantly downregulated in human and mice fibrotic liver tissues and in primary activated HSCs. miR-29b downregulation was directly mediated by Smad3 through binding to the promoter of miR-29b in hepatic stellate cell (HSC) line LX1, whilst miR-29b could in turn suppress Smad3 expression. miR-29b transduction in the liver of mice prevented CCl 4 induced-fibrogenesis, concomitant with decreased expression of α-SMA, collagen I and TIMP-1. Ectopic expression of miR-29b in activated HSCs (LX-1, HSC-T6) inhibited cell viability and colony formation, and caused cell cycle arrest in G1 phase by downregulating cyclin D1 and p21 cip1 . Further, miR-29b induced apoptosis in HSCs mediated by caspase-9 and PARP. miR-29b inhibited its downstream effectors of PIK3R1 and AKT3 through direct targeting their 3’UTR regions. Moreover, knockdown of PIK3R1 or AKT3 suppressed α-SMA and collagen I and induced apoptosis in both HSCs and in mice. In conclusion, miR-29b prevents liver fibrogenesis by inhibiting HSC activation and inducing HSC apoptosis through inhibiting PI3K/AKT pathway. These results provide novel mechanistic insights for the anti-fibrotic effect of miR-29b.