MicroRNA-17-5p activates hepatic stellate cells through targeting of Smad7

A considerable amount of research has focused on the roles of microRNAs (miRNA) in the pathophysiology of liver fibrosis in view of their regulatory effects on hepatic stellate cell (HSC) functions, including proliferation, differentiation, and apoptosis. Recently, miR-17-5p was shown to promote cell proliferation and migration in liver. Transforming growth factor-beta 1 (TGF-beta 1) has been characterized as the master fibrogenic cytokine that stimulates HSC activation and promotes progression of liver fibrosis. The issue of whether miR-17-5p plays a role in TGF-beta 1-induced hepatic fibrogenesis remains to be established. In this study, we demonstrated a dose-/time-dependent increase in miR-17-5p expression in TGF-beta 1-treated HSCs. Enhanced miR-17-5p expression was additionally observed in CCl4-induced rat liver fibrosis. Inhibition of miR-17-5p led to suppression of HSC proliferation induced by TGF-beta 1 without affecting cellular apoptosis. Notably, miR-17-5p was significantly associated with TGF-beta 1-induced expression of type I collagen and alpha-SMA in HSC. Furthermore, Smad7, a negative regulator of the TGF-beta/Smad pathway, was confirmed as a direct target of miR-17-5p. Serum miR-17-5p levels were significantly higher in patients with cirrhosis, compared to healthy controls. Our results collectively indicate that miR-17-5p promotes HSC proliferation and activation, at least in part, via reduction of Smad7, supporting its potential utility as a novel therapeutic target for liver fibrosis.