Serine 1179 Phosphorylation of Endothelial Nitric Oxide Synthase Increases Superoxide Generation and Alters Cofactor Regulation

Novel Role of GPR35 (G-Protein-Coupled Receptor 35) in the Regulation of Endothelial Cell Function and Blood Pressure

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GPR35 (G-protein–coupled receptor 35) is a poorly characterized receptor that has garnered increased interest as a therapeutic target through its implications in a range of inflammatory and cardiovascular diseases, but its biological functions stay largely unknown. The current study evaluated the effect of GPR35 on endothelial cell (EC) functions and hemodynamic homeostasis. In primary human aortic ECs, the expression of GPR35 was manipulated by transfections of adenovirus carrying either GPR35 cDNA or shRNA against GPR35, using adenovirus carrying β-gal as control. Mouse aortic ECs were isolated and cultured from GPR35 knockout and wild-type control mice. Our results indicated that genetic inhibition of GPR35 in human and mouse ECs significantly promoted cell proliferation, migration, and tube formation in vitro. The GCH1 (guanosine triphosphate cyclohydrolase I)-mediated biosynthesis of tetrahydrobiopterin was enhanced, reducing intracellular superoxide. Knocking down GCH1 or eNOS (endothelial nitric oxide synthase) significantly blunted the robust angiogenesis induced by GPR35 suppression. Male GPR35 knockout mice demonstrated reduced basal arterial blood pressure and an attenuated onset of hypertension in deoxycorticosterone acetate-salt induced hypertensive model compared with male GPR35 wild-type control mice in vivo, with concomitant improved endothelium-dependent vasodilation and decreased superoxide in isolated aortas. The difference in arterial blood pressure was absent between female GPR35 wild-type control and female GPR35 knockout mice. Our study provides novel insights into the roles of GPR35 in endothelial function and vascular tone modulation that critically contribute to the pathophysiology of blood pressure elevation. Antagonizing GPR35 activity might represent a potentially effective therapeutic approach to restore EC function and hemodynamic homeostasis.

mTORc1 activity is necessary and sufficient for phosphorylation of eNOSS1177

Nitric oxide, produced by eNOS, plays critical roles in the regulation of vascular function and maintenance. Chronic PI3K signaling has recently been associated with vascular malformations. A well described substrate downstream of PI3K signaling is eNOS. Another critical downstream target of PI3K is the metabolic regulator, mTORc1. The relationship between mTORc1 and eNOS regulation, has not been determined. We generated cells with manipulated PI3K signaling by expressing the activating mutation, PIK3CAH1047R , or knocking down PTEN expression. We investigated eNOSS1177 phosphorylation, a major activating regulatory site, following mTORC1 inhibition. We also tested the sufficiency of mTORc1 activation to stimulate eNOSS1177 phosphorylation. Our data indicate mTORc1 activity is required for the phosphorylation of eNOSS1177 , even in the presence of robust AKT activation. Moreover, we found that expression of RHEB, which functions in the absence of AKT activation to activate mTORc1, is sufficient to phosphorylate this site. Our data indicate that mTORc1, rather than AKT, may be the critical determinant of eNOSS1177 phosphorylation. As mTORc1 is a central regulator of cellular metabolism, the finding that this regulatory complex can directly participate in the regulation of eNOS provides new insights into metabolic uncoupling and vascular disease that often accompanies diabetes, high fat diets, and aging.

Differential effects of heat shock protein 90 and serine 1179 phosphorylation on endothelial nitric oxide synthase activity and on its cofactors

Endothelial nitric oxide synthase (eNOS) is responsible for maintaining systemic blood pressure, vascular remodeling and angiogenesis. Previous studies showed that bovine eNOS serine 1179 (Serine 1177 for human eNOS) phosphorylation enhanced NO synthesis. Meanwhile, heat shock protein 90 (Hsp90) plays a critical role in maintenance of eNOS structure and function. However, the regulatory difference and importance between Serine 1179 phosphorylation and Hsp90 on eNOS activity have not been evaluated. In current studies, S1179D eNOS was employed to mimic phospho-eNOS and exhibited markedly increased enzyme activity than wild type eNOS (WT eNOS). Hsp90 showed a dose-dependent increase for both WT eNOS and S1179D eNOS activity at the presence of all eNOS cofactors, such as Calcium/Calmodulin (Ca2+ /CaM), BH4, and NADPH etc. The enhancement effects were abolished by dominant-negative mutant Hsp 90 protein. ENOS-cofactors dynamic assay showed that Hsp90 enhanced WT eNOS affinity to NADPH, L-arginine, and CaM but not to Ca2+ and BH4. The impact of eNOS Serine 1179 phosphorylation and Hsp90 on eNOS affinity to cofactors has also been compared. Different from the effect of Hsp90 on eNOS affinity to specific cofactors, Serine 1179 phosphorylation significantly increased eNOS affinity to all cofactors. Moreover, VEGF-induced eNOS phosphorylation in bovine aortic endothelial cells (BAECs) and more NO generation from eNOS compared to control. Inhibition of Hsp90 by geldanamycin decreased eNOS activity and decreased endothelial viability. In conclusion, by changing eNOS structure, Hsp90 profoundly affected eNOS functions, including change of affinity of eNOS to cofactors like Ca2+, L-arginine, BH4 and further affecting NO generation capability. These specific cofactors regulated by Hsp 90 could become potential therapeutic targets of the eNOS-related diseases in future.