MiR-21 Simultaneously Regulates ERK1 Signaling in HSC Activation and Hepatocyte EMT in Hepatic Fibrosis

BACKGROUND MicroRNA-21 (miR-21) plays an important role in the pathogenesis and progression of liver fibrosis. Here, we determined the serum and hepatic content of miR-21 in patients with liver cirrhosis and rats with dimethylnitrosamine-induced hepatic cirrhosis and examined the effects of miR-21 on SPRY2 and HNF4α in modulating ERK1 signaling in hepatic stellate cells (HSCs) and epithelial-mesenchymal transition (EMT) of hepatocytes. METHODS Quantitative RT-PCR was used to determine miR-21 and the expression of SPRY2, HNF4α and other genes. Immunoblotting assay was carried out to examine the expression of relevant proteins. Luciferase reporter assay was performed to assess the effects of miR-21 on its predicted target genes SPRY2 and HNF4α. Primary HSCs and hepatocytes were treated with miR-21 mimics/inhibitors or appropriate adenoviral vectors to examine the relation between miR-21 and SPRY2 or HNF4α. RESULTS The serum and hepatic content of miR-21 was significantly higher in cirrhotic patients and rats. SPRY2 and HNF4α mRNA levels were markedly lower in the cirrhotic liver. MiR-21 overexpression was associated with enhanced ERK1 signaling and EMT in liver fibrosis. Luciferase assay revealed suppressed SPRY2 and HNF4α expression by miR-21. Ectopic miR-21 stimulated ERK1 signaling in HSCs and induced hepatocyte EMT by targeting SPRY2 or HNF4α. Downregulating miR-21 suppressed ERK1 signaling, inhibited HSC activation, and blocked EMT in TGFβ1-treated hepatocytes. CONCLUSIONS MiR-21 modulates ERK1 signaling and EMT in liver fibrosis by regulating SPRY2 and HNF4α expression. MiR-21 may serve as a potentially biomarker as well as intervention target for hepatic cirrhosis.