TNFα signaling impairs endothelial calcium signaling and elevates blood pressure in obesity

Abstract

Endothelial dysfunction in small arteries is a hallmark of obesity‐induced hypertension. Recent studies show that endothelial upregulation of inducible nitric oxide synthase (iNOS) and NADPH oxidase 1 (NOX1) plays a critical role in obesity‐induced endothelial dysfunction. Endothelial upregulation of iNOS and NOX1 results in excessive formation of peroxynitrite, a reactive nitrogen species, which impairs endothelium‐dependent vasodilation. It is well‐known that inflammatory mediators elevate cellular iNOS, NOX1, and peroxynitrite levels. In this regard, tumor necrosis factor alpha (TNFa) signaling has been proposed as a key contributor to endothelial dysfunction in obesity. Notably, vascular smooth muscle cells (SMCs) were shown to generate TNFa in heart failure and diabetes. Therefore, we hypothesized that vascular wall‐derived TNFa acts locally to impair endothelial function in obesity. Flow cytometry studies showed an increase in TNFa levels in freshly isolated SMCs from small mesenteric arteries (MAs) of high‐fat diet‐fed (14 weeks) obese mice compared to normal chow‐fed control mice. However, TNFa levels in endothelial cells (ECs) from obese mice were not different from those in ECs from control mice. The levels of two other cytokines, IL‐1b and IL‐6, were not different between in SMCs and ECs from normal and obese mice. Additionally, qPCR studies in endothelium‐denuded MAs provided further evidence that TNFa expression is increased in SMCs from obese mice compared to control mice. The pro‐inflammatory effects of TNFa are mediated mainly through TNFa receptor I activation. Treating the obese mice with a selective inhibitor of TNFa receptor I signaling (R7050, 10 mg/kg, i.p., once a day for 14 days) reduced the blood pressure to normal levels in obese mice, but had no effect on blood pressure in control mice. Treatment with R7050 also abolished obesity‐induced increase in iNOS and NOX1 expression in endothelial cells. Further, R7050 administration restored acetylcholine‐induced, endothelium‐dependent vasodilation of MAs in pressure myography experiments. Previous studies showed that a decrease in Ca2+ influx through endothelial transient receptor potential vanilloid 4 (TRPV4) channels contributes to blood pressure elevation in obese mice. Notably, R7050 administration restored the Ca2+ influx signals through endothelial TRPV4 channels in MAs, as studied using high‐speed confocal Ca2+ imaging. Collectively, our findings indicate that TNFa signaling contributes to the impairment of endothelial calcium signaling and blood pressure elevation in obesity, and highlight the role of SMCs as a source of TNFa in obesity.