MiR-17 family-mediated regulation of Pknox1 influences hepatic steatosis and insulin signaling

The aberrant expression of Pknox1 is associated with hepatic glucose and lipid dysmetabolism status of type 2 diabetes mellitus (T2DM) and nonalcoholic fatty liver disease (NAFLD). However, the underlying mechanism causing Pknox1 overexpression in this pathological status remains unclear. By using miRNA target prediction programs, we found that the 3 '-UTR of the Pknox1 mRNA sequence contains highly conserved target sites of miR-17 family. In a rat model of streptozotocin and high-fat diet-induced T2DM and NAFLD complication, the increased hepatic expression of Pknox1 was consistent with decreased expressions of miR-17 family, especially miR-17 and miR-20a. Furthermore, an inverse correlation was observed between Pknox1 and miR-17 and miR-20a in free fatty acids-induced hepatocyte steatosis. Dual-luciferase reporter assay further showed that Pknox1 was a valid target gene of miR-17 family. The ectopic expression of miR-17 or miR-20a could markedly suppress Pknox1 expression in hepatocytes. MiR-17 or miR-20a overexpression also resulted in significantly enhanced insulin sensitivity and reduced hepatocyte steatosis in HepG2 and L02 cells, which were determined by altered phosphorylation on insulin receptor signaling pathway proteins and decreased intracellular triglyceride and lipid accumulation, respectively. These data implicate the upregulated hepatic expression of Pknox1 in T2DM complicated with NAFLD may be caused by the reduced expression of miR-17 family, indicating that developing miRNA-mediated regulation strategies on Pknox1 may provide new therapeutic options for metabolic disease.