Apelin/APJ increased renal blood flow through endothelial BKCa channel induced p-eNOS and ET-1 in diabetic conditions.

Renal hemodynamics damage, an important driving mechanism of diabetic nephropathy (DN), is related to many abnormal endothelial released molecules, such as endothelial nitrogen monoxide synthase (eNOS) and endothelin-1 (ET-1), caused by glomerular endothelial cells dysfunction. Apelin, as the endogenous ligand for APJ, was reported to be associated with endothelial cell dysfunction in diabetes. Therefore, it is hypothesized that apelin/APJ increased renal perfusion in DN through regulating endothelial released molecules. Diabetic models were replicated via injecting STZ intraperitoneally (40 mg/kg/day) for 5 consecutive days. Apelin-13 was infused with micro-osmotic pump at 30 μg/kg/day for 4 weeks. The results showed that apelin increased renal blood flow by increasing phosphorylated eNOS and decreasing ET-1 in diabetic mice, which were cancelled in endothelial-specific APJ knockout mice or whole-body large conductance Ca^2 +-activated K⁺ (BKCa) channel knockout rats. Additionally, apelin/APJ activated BKCa channel via increasing expression of BKCa subunits through PI3K/AKT/GSK-3β/Nrf2 pathway but not increasing intracellular Ca²⁺ concentration under high glucose conditions. In conclusion, this study revealed that apelin/APJ increased renal blood flow in early phase of DN via increasing p-eNOS and decreasing ET-1 in glomerular endothelial cells dependent on PI3K/AKT/GSK-3β/Nrf2 pathway induced expression of BKCa subunits.