Angiotensin II Downregulates MicroRNA-145 to Regulate Kruppel-like Factor 4 and Myocardin Expression in Human Coronary Arterial Smooth Muscle Cells under High Glucose Conditions

MicroRNA (miR)-145 is the most abundant miR in vascular smooth muscle cells (VSMCs). However, the effect of hyperglycemia on the regulation of miR-145 is unknown. We hypothesized that the hyperglycemic condition activates a proinflammatory response that mediates the expression of miR-145 in VSMCs. We investigated whether miR-145 serves as a critical regulator to regulate the downstream proliferation factors (including Kruppel-like factor 4 [Klf4] and myocardin) in VSMCs under hyperglycemic conditions. Human coronary artery smooth muscle cells (HCASMCs) were cultured under high glucose conditions. Sustained high glucose at 25 mmol/L significantly decreased the expression of miR-145 in HCASMCs. High glucose significantly increased angiotensin II (Ang II) secretion from HCASMCs and Ang II suppressed miR-145 expression in HCASMCs. Ang II repression of miR145 expression resulted in increased Klf4 and decreased myocardin expression under conditions of high glucose. Overexpression of miR-145 significantly decreased Klf4 and increased myocardin expression and inhibited HCASMC proliferation and migration induced by a high glucose state. Balloon injury of the carotid artery in diabetic rats was performed to investigate miR-145, Klf and myocardin expression. The expression of miR-145 was maximally increased at 7 d after carotid injury and gradually declined thereafter. Overexpression of miR-145 and treatment with valsartan reversed Klf4 and myocardin protein expression induced by balloon injury and improved vascular injury. In conclusion, our study reveals that Ang II downregulates miR-145 to regulate Klf4 and myocardin expression in HCASMCs under high glucose conditions. Ang II plays a critical role in the regulation of miR-145 under hyperglycemic conditions.