K(Ca)3.1 upregulation preserves endothelium‐dependent vasorelaxation during aging and oxidative stress

Endothelial oxidative stress develops with aging and reactive oxygen species impair endothelium‐dependent relaxation (EDR) by decreasing nitric oxide (NO) availability. Endothelial K(Ca)3.1, which contributes to EDR, is upregulated by H(2)O(2). We investigated whether K(Ca)3.1 upregulation compensates for diminished EDR to NO during aging‐related oxidative stress. Previous studies identified that the levels of ceramide synthase 5 (CerS5), sphingosine, and sphingosine 1‐phosphate were increased in aged wild‐type and CerS2 mice. In primary mouse aortic endothelial cells (MAECs) from aged wild‐type and CerS2 null mice, superoxide dismutase (SOD) was upregulated, and catalase and glutathione peroxidase 1 (GPX1) were downregulated, when compared to MAECs from young and age‐matched wild‐type mice. Increased H(2)O(2) levels induced Fyn and extracellular signal‐regulated kinases (ERKs) phosphorylation and K(Ca)3.1 upregulation. Catalase/GPX1 double knockout (catalase(−/−)/GPX1(−/−)) upregulated K(Ca)3.1 in MAECs. NO production was decreased in aged wild‐type, CerS2 null, and catalase(−/−)/GPX1(−/−) MAECs. However, K(Ca)3.1 activation‐induced, N(G)‐nitro‐l‐arginine‐, and indomethacin‐resistant EDR was increased without a change in acetylcholine‐induced EDR in aortic rings from aged wild‐type, CerS2 null, and catalase(−/−)/GPX1(−/−) mice. CerS5 transfection or exogenous application of sphingosine or sphingosine 1‐phosphate induced similar changes in levels of the antioxidant enzymes and upregulated K(Ca)3.1. Our findings suggest that, during aging‐related oxidative stress, SOD upregulation and downregulation of catalase and GPX1, which occur upon altering the sphingolipid composition or acyl chain length, generate H(2)O(2) and thereby upregulate K(Ca)3.1 expression and function via a H(2)O(2)/Fyn‐mediated pathway. Altogether, enhanced K(Ca)3.1 activity may compensate for decreased NO signaling during vascular aging.