WISP1 promotes non-alcoholic fatty liver disease and skeletal muscle insulin resistance via TLR4/JNK signaling

Wnt1-inducible signaling pathway protein-1 (WISP1) is a Cyr61/CTGF/NOV (CCN) family matricellular protein involved in adipogenesis and low-grade inflammation in obesity. However, the roles of WISP1 in hepatic steatosis and insulin resistance in skeletal muscle remain elusive. Mouse primary hepatocytes and differentiated mouse skeletal muscle cells (C2C12) were treated with various concentrations of WISP1 and the functions and signaling pathways were analyzed by Western blot analysis. In vivo transfection for WISP1 knockdown was also performed to examine the effects of WISP1 on hepatic steatosis and skeletal muscle insulin resistance. Knockdown of WISP1 in high-fat diet-fed C57BL/6 mice significantly reduced (0.45-0.5%; p<0.05) inflammation and JNK phosphorylation (45-50%; P<0.01) and attenuated hepatic steatosis (approximately 55%; p<0.001) and skeletal muscle insulin resistance (30-40%; p<0.05). Treatment with WISP1 significantly induced inflammation (hepatocytes: approximately 500%; p<0.01, C2C12 cells: approximately 500%; p<0.01) and JNK phosphorylation (hepatocytes: approximately 200%; p<0.01, C2C12 cells: approximately 280%; p<0.01) in mouse primary hepatocytes and C2C12 mouse skeletal muscle cells. Moreover, it increased lipogenesis-associated gene expression (200-300%; p<0.01) and accumulation of triglycerides (approximately 320%; p<0.01) in hepatocytes, and suppressed insulin signaling (approximately 50%; p<0.01) in C2C12 cells. These WISP1-induced effects were significantly abrogated in NFB-, JNK-, and TLR4-knockdown hepatocytes (p<0.05) and C2C12 cells (p<0.05). These results indicate that WISP1 contributes to hepatic steatosis and skeletal muscle insulin resistance through a TLR4-activated inflammation/JNK signaling pathway and could be a useful therapeutic target for treatment of non-alcoholic fatty liver disease and type 2 diabetes.