Insulin- and Aldosterone-Mediated Signaling in Endothelial Cells Converge on SGK1 to Promote Endothelial Sodium Channel Activation

Abstract

Background: Abnormal cardiovascular (CV) stiffening precedes overt tissue fibrosis and dysfunction. Although CV stiffening normally occurs with ageing it is accelerated in states of hyperinsulinemia/insulin (INS) resistance including obesity and Type 2 diabetes. While questions remain regarding the underlying cellular mechanisms, heightened activation of endothelial cell (EC) mineralocorticoid receptors (MRs) and INS receptors occur in hyperinsulinemic/INS resistance states. Further, EC sodium (Na+) channel (EnNaC) activation has recently been identified as a key determinant of endothelial dysfunction, CV fibrosis and stiffening in diet-induced obesity and associated INS resistance . As renal epithelial Na+ channels are known to be regulated via sodium glucocorticoid kinase (SGK-1) through INS and MR-dependent mechanisms this study aimed to determine whether vascular EnNaC is similarly regulated. Methods: Lung ECs were isolated from SGK-1 -/- mice and littermate control and maintained under short-term tissue culture conditions. EnNaC activity was determined as Na+ current measured by whole cell patch clamp. Results: The SGK-1 inhibitor, GSK 650394 suppressed amiloride-sensitive Na+ currents in isolated ECs, consistent with an effect on EnNaC activity. Under similar conditions INS caused concentration (0 – 100nM)-dependent stimulation of EnNaC currents. MR activation with aldosterone (24 hrs) caused an increase in EnNaC current which was absent in cells from the SGK-1 -/- mice. INS stimulated EnNaC currents were decreased in cells from SGK-1 -/- mice compared to littermate control.