MicroRNA-9 limits hepatic fibrosis by suppressing the activation and proliferation of hepatic stellate cells by directly targeting MRP1/ABCC1.

Liver fibrosis is a chronic liver disease characterized by the proliferation and activation of hepatic stellate cells (HSCs) and excessive deposition of extracellular matrix (ECM). Research suggests that microRNAs (miRNAs) are a new type of regulator of liver fibrosis. In the present study, we investigated the role of microRNA-9 (miR-9) in the process of liver fibrosis, as well as the underlying mechanism of action. Downregulated levels of miR-9 were found in fibrotic liver tissues and activated HSCs as detected by qRT-PCR; whereas, expression of multidrug resistance‑associated protein 1 (MRP1/ABCC1) was upregulated in the fibrotic liver tissues and activated HSCs. CCK-8 and BrdU assays revealed that miR-9 reduced the proliferative ability of the HSCs. In addition, expression levels of ECM-related genes (α-SMA, Col-1 and Timp-1), which are markers of HSC activation, were downregulated by miR-9. Conversely, an miR-9 inhibitor promoted cell proliferation and HSC activation. In addition, a luciferase reporter assay indicated that miR-9 targets the 3'-untranslated region (3'-UTR) of MRP1 and causes a significant decrease in MRP1. miR-9 inhibited the activation of the Hedgehog (Hh) pathway and the expression of MRP1, while this suppression was rescued by the overexpression of MRP1. Finally, a CCl4-induced mouse model of liver fibrosis was used to investigate the effects of miR-9 on liver fibrosis in vivo. The results showed that miR-9 abrogated hepatic fibrosis by suppressing the expression of MRP1 in CCl4-induced liver fibrotic mice. In conclusion, the present study demonstrated that miR-9 suppresses the proliferation and activation of HSCs through the Hh pathway by targeting MRP1, which suggests that miR-9 has therapeutic potential for liver fibrosis.