MiRNA-21 mediates the antiangiogenic activity of metformin through targeting PTEN and SMAD7 expression and PI3K/AKT pathway

Metformin, an anti-diabetic drug commonly used for type 2 diabetes therapy, is associated with antiangiogenic effects in conditions beyond diabetes. miR-21 has been reported to be involved in the process of angiogenesis. However, the precise regulatory mechanisms by which the metformin-induced endothelial suppression and its effects on miR-21-dependent pathways are still unclear. Bioinformatic analysis and identification of miR-21 and its targets and their effects on metformin-induced antiangiogenic activity were assessed using luciferase assays, quantitative real-time PCR, western blots, scratch assays, CCK-8 assays and tubule formation assays. In this study, miR-21 was strikingly downregulated by metformin in a time-and dose-dependent manner. miR-21 directly targeted the 3'-UTR of PTEN and SMAD7, and negatively regulated their expression. Overexpression of miR-21 abrogated the metformin-mediated inhibition of endothelial cells proliferation, migration, tubule formation and the TGF-beta-induced AKT, SMAD-and ERK-dependent phosphorylations, and conversely, down-regulation of miR-21 aggravated metformin's action and revealed significant promotion effects. Our study broadens our understanding of the regulatory mechanism of miR-21 mediating metformin-induced anti-angiogenic effects, providing important implications regarding the design of novel miRNA-based therapeutic strategies against angiogenesis.