Increased O-GlcNAcylation of Endothelial Nitric Oxide Synthase Compromises the Anti-contractile Properties of Perivascular Adipose Tissue in Metabolic Syndrome.

Rafael M Da Costa,Diane M Rassi,Rita C Tostes,Josiane F Da Silva,Thiago B Dias,Juliano V Alves,Luis V Garcia,Núbia De Souza Lobato

doi:10.3389/fphys.2018.00341

Abstract

Under physiological conditions, the perivascular adipose tissue (PVAT) negatively modulates vascular contractility. This property is lost in experimental and human obesity and in the metabolic syndrome, indicating that changes in PVAT function may contribute to vascular dysfunction associated with increased body weight and hyperglycemia. The O-linked β-N-acetylglucosamine (O-GlcNAc) modification of proteins (O-GlcNAcylation) is a unique posttranslational process that integrates glucose metabolism with intracellular protein activity. Increased flux of glucose through the hexosamine biosynthetic pathway and the consequent increase in tissue-specific O-GlcNAc modification of proteins have been linked to multiple facets of vascular dysfunction in diabetes and other pathological conditions. We hypothesized that chronic consumption of glucose, a condition that progresses to metabolic syndrome, leads to increased O-GlcNAc modification of proteins in the PVAT, decreasing its anti-contractile effects. Therefore, the current study was devised to determine whether a high-sugar diet increases O-GlcNAcylation in the PVAT and how increased O-GlcNAc interferes with PVAT vasorelaxant function. To assess molecular mechanisms by which O-GlcNAc contributes to PVAT dysfunction, thoracic aortas surrounded by PVAT were isolated from Wistar rats fed either a control or high sugar diet, for 10 and 12 weeks. Rats chronically fed a high sugar diet exhibited metabolic syndrome features, increased O-GlcNAcylated-proteins in the PVAT and loss of PVAT anti-contractile effect. PVAT from high sugar diet-fed rats for 12 weeks exhibited decreased NO formation, reduced expression of endothelial nitric oxide synthase (eNOS) and increased O-GlcNAcylation of eNOS. High sugar diet also decreased OGA activity and increased superoxide anion generation in the PVAT. Visceral adipose tissue samples from hyperglycemic patients showed increased levels of O-GlcNAc-modified proteins, increased ROS generation and decreased OGA activity. These data indicate that O-GlcNAcylation contributes to metabolic syndrome-induced PVAT dysfunction and that O-GlcNAcylation of eNOS may be targeted in the development of novel therapies for vascular dysfunction in conditions associated with hyperglycemia.

Highlights

The perivascular adipose tissue (PVAT) is a highly active endocrine organ that releases a wide variety of adipokines that control vascular smooth muscle tone in veins, conductance arteries, and vessels of smaller caliber (Szasz and Webb, 2012)
These data indicate that the high sugar diet decreases PVAT anticontractile effect by reducing NO bioavailability (Figures 4G,H). Consistent with these results, the expression of endothelial nitric oxide synthase was significantly reduced in the PVAT from high sugar-fed rats (Figure 5A) and this change was accompanied by increased eNOS O-GlcNAcylation (Figure 5B). These results indicate that O-GlcNAcylation of eNOS impairs the activity of this enzyme and decreases NO production in PVAT
The present study demonstrates that OGlcNAcylation plays a key role on high-sugar diet-induced PVAT dysfunction

Summary

Introduction

The perivascular adipose tissue (PVAT) is a highly active endocrine organ that releases a wide variety of adipokines that control vascular smooth muscle tone in veins, conductance arteries, and vessels of smaller caliber (Szasz and Webb, 2012). The vasoactive factors released by the PVAT (AdventitiumDerived Relaxing Factors—ADRF) under physiological conditions include adiponectin, angiotensin- (1-7), hydrogen peroxide, leptin, nitric oxide (NO), and other agents that negatively modulate vascular contraction, that is, the PVAT exerts an anti-contractile effect and is essential for the maintenance of vascular function (Fernandez-Alfonso et al, 2013; Xia and Li, 2017). In obesity and metabolic syndrome, there is an increase in the amount of PVAT accompanied by changes in the PVAT pattern of adipokines expression, infiltration, and activation of circulating inflammatory cells (Lumeng et al, 2007), hypoxia, and oxidative stress (Gao, 2007). The predominant mechanisms leading to a dysfunctional PVAT in obesity and metabolic syndrome have not been identified so far. Post-translational modifications of intrinsic components of PVAT seem to contribute to the loss of its anti-contractile effect in metabolic and cardiovascular diseases. As an example, reduced NO synthase phosphorylation in the serine activation residue (Ser1177) and decreased phosphorylation of adenosine monophosphate-activated protein kinases, which positively regulate NO synthase activity, have been reported in the PVAT of animals fed a high fat diet for 6 months (Ma et al, 2010)

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