Endothelial sodium channel (EnNaC) activation contributes to mineralocorticoid receptormediated increases in coronary artery and cardiac fibrosis/stiffness leading to diastolic dysfunction in obesity

Abstract

BackgroundWhile obesity, induced by an industrialized or Western diet (WD), has been shown to impact structural and functional properties of both coronary arteries and myocardium, the exact mechanisms by which these interact to cause diastolic dysfunction (DD) are uncertain. We hypothesized that the mineralocorticoid receptor (MR) activation in coronary vascular endothelial cells (ECs) impairs endothelial function via EC Na+ channel, EnNaC, activation. Further, we posited that such coronary dysfunction initiates increased myocyte stiffness and fibrosis ultimately leading to DD. The objective was to demonstrate that WD‐induced DD is dependent on EnNaC activation.MethodsTo cause MR activation, aldosterone was administered to female or male mice (C57BL6) by osmotic minipump for 3 wks. Further, female wild‐type and EC MR deficient mice (2–3 mths of age) or low aldosterone implanted as subcutaneous pellet were fed a WD, high in saturated fat and fructose (16 wks). In an additional experiment, female wild‐type and EnNaC α subunit deficient mice (3–4 mths of age) were fed the WD (12–16 wks). Vascular function was assessed in isolated coronary arteries by pressure myography, cardiac and perivascular fibrosis was evaluated by picosirius red (PSR) staining and diastolic function was assessed by echocardiography. Using in vitro cellular approaches, intrinsic cardiomyocyte stiffness was measured by atomic force microscopy (AFM) and EnNaC activity (Na+ current) determined by whole cell patch clamp.ResultsAldosterone infusion caused impaired endothelium‐dependent relaxation and coronary vascular fibrosis, which were prevented by the MR antagonist, spironolactone (1 mg/kg/day). WD feeding was associated with DD, but not systolic dysfunction, that was prevented by either spironolactone or EC‐specific MR deletion. Furthermore, DD was accompanied by increased vascular EnNaC currents and increased stiffness of both ECs and cardiomyocytes, which were attenuated by EC MR deletion. Finally, WD‐induced increases in activation of coronary EnNaC, EC stiffness and cardiomyocyte stiffness, together with DD, were suppressed in EnNaC α deficient mice.ConclusionsCollectively, these results demonstrate that MR activation (aldosterone infusion and diet‐induced) elicits coronary vascular dysfunction associated with tissue and cellular cardiac changes and DD. Further, activation of EnNaC, a known target of MR signaling, promotes coronary EC‐dependent cardiomyocyte stiffness, cardiac fibrosis and impairs DD. Therapeutic targeting to prevent EnNaC activation may be a viable approach for the management of obesity‐associated diastolic dysfunction.