Suppressive effect of microRNA-29b on hepatic stellate cell activation and its crosstalk with TGF-[beta]1/Smad3

The microRNA (miR)-29 family is closely associated with fibrotic processes by virtue of its low expression in many tissues during organ fibrosis. The present study investigated whether miR-29b overexpression suppressed hepatic stellate cell (HSC) activation and its interactions with transforming growth factor (TGF)-[beta]1/mothers against decapentaplegic homolog 3 (Smad3), a classical signal transduction pathway contributing to the activation of HSCs. The results showed that transfection of LX-2 (human HSC) cells with miR-29b mimic or pSUPER-Smad3 silencing (si)RNA resulted in significantly increased expression of miR-29b and decreased expression of Smad3. miR-29b overexpression inhibited proliferation of LX-2 cells 24h after transfection. Both miR-29b overexpression and Smad3 silencing antagonized the effects of TGF-[beta]1 on the expression of [alpha]-smooth muscle actin ([alpha]-SMA) and collagen type I (col-1). Furthermore, infection with miR-29b mimics suppressed Smad3 and TGF-[beta]1 expression, suggesting that miR-29b inhibited LX-2 activation mediated by both Smad3 and TGF-[beta]1. Nevertheless, primary miR-29a/b1, miR-29b2/c and mature miR-29b were downregulated by TGF-[beta]1 and stimulated by Smad3 silencing, suggesting that TGF-[beta]1/Smad3 signalling pathway regulate not just mature miR-29b but also its transcription. In summary, our results show overwhelming evidence corroborating the suppressive effect of miR-29b on TGF-[beta]1-induced LX-2 cell activation. The results also revealed the existence of crosstalk between miR-29b and TGF-[beta]1/Smad3 during LX-2 activation, suggesting a feedback loop between miR-29b and TGF-[beta]1/Smad3 signalling that promotes liver fibrosis. Copyright © 2016 The Authors. Cell Biochemistry and Function published by John Wiley & Sons, Ltd.