Enhancement of 26S proteasome functionality connects oxidative stress and vascular endothelial inflammatory response in diabetes mellitus.
ABSTRACT Although the connection of oxidative stress and inflammation has been long recognized in diabetes mellitus, the underlying mechanisms are not fully elucidated. This study defined the role of 26S proteasomes in promoting vascular inflammatory response in early diabetes mellitus.
The 26S proteasome functionality, markers of autophagy, and unfolded protein response were assessed in (1) cultured 26S proteasome reporter cells and endothelial cells challenged with high glucose, (2) transgenic reporter (Ub(G76V)-green fluorescence protein) and wild-type (C57BL/6J) mice rendered diabetic, and (3) genetically diabetic (Akita and OVE26) mice. In glucose-challenged cells, and also in aortic, renal, and retinal tissues from diabetic mice, enhanced 26S proteasome functionality was observed, evidenced by augmentation of proteasome (chymotrypsin-like) activities and reduction in 26S proteasome reporter proteins, accompanied by increased nitrotyrosine-containing proteins. Also, whereas inhibitor of the nuclear factor κ-light-chain-enhancer of activated B cells α proteins were decreased, an increase was found in nuclear factor κ-light-chain-enhancer of activated B cells (NF-κB) nucleus translocation, which enhanced the NF-κB-mediated proinflammatory response, without affecting markers of autophagy or unfolded protein response. Importantly, the alterations were abolished by MG132 administration, small interfering RNA knockdown of PA700 (proteasome activator protein complex), or superoxide scavenging in vivo.
Early hyperglycemia enhances 26S proteasome functionality, not autophagy or unfolded protein response, through peroxynitrite/superoxide-mediated PA700-dependent proteasomal activation, which elevates NF- ĸB-mediated endothelial inflammatory response in early diabetes mellitus.
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ABSTRACT: Hypoxia induces vascular inflammation by a mechanism not fully understood. Emerging evidence implicates O-GlcNAc transferase (OGT) in inflammation. This study explored the role of OGT in hypoxia-induced vascular endothelial inflammatory response.Methods and ResultsHypoxia was either induced (1% O2 chamber) or mimicked by exposure to hypoxia-mimetic agents in cultured endothelial cells. Hypoxia increased HIF-1α and inflammatory response (gene and protein expression of IL-6, IL-8, MCP-1, and E-selectin) but, surprisingly, reduced OGT protein (not mRNA) levels. Hypoxia-mimetic CoCl2 failed to reduce OGT when proteasome inhibitors were present, suggesting proteasome involvement. Indeed, CoCl2 enhanced 26S proteasome functionality evidenced by diminished reporter (Ub(G76 V)-GFP) proteins in proteasome reporter cells, likely due to increased chymotrypsin-like activities. Mechanistically, β-TrCP1 mediated OGT degradation, since siRNA ablation of this ubiquitin E3 ligase stabilized OGT. Administration of the oxidative stress inhibitors reversed both proteasome activation and OGT degradation. Further, upregulation of OGT by stabilization, overexpression, or activation mitigated CoCl2-elicited inflammatory response. These observations were recapitulated in a mouse (C57BL/6 J) model mimicking hypoxia, in which lung tissues presented higher levels of HIF-1α, proteasome activity, and inflammatory response, but lower levels of OGT (n=5/group, hypoxia vs normoxia, p<0.05). However, administration of an activator of OGT (glucosamine: 1 mg/g/d, vehicle: saline, i.p.5d) abolished the upregulation of proteasome activity and inflammatory response (n= 5/group, the treated vs untreated hypoxia groups, p<0.05). 26S proteasome-mediated OGT reduction contributed to hypoxia-induced vascular endothelial inflammatory response. Modulation of OGT may represent a new approach to treat diseases characterized by hypoxic inflammation.Cardiovascular research 04/2014; · 5.81 Impact Factor
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ABSTRACT: Significance: Atherosclerosis is a vascular disease of worldwide significance with fatal complications such as myocardial infarction, stroke and peripheral artery disease. Atherosclerosis is recognized as a chronic inflammatory disease leading to arterial plaque formation and vessel narrowing in different vascular beds. Besides the strong inflammatory nature of atherosclerosis, it is also characterized by proliferation, apoptosis and enhanced oxidative stress. The ubiquitin-proteasome system (UPS) is the major intracellular degradation system in eukaryotic cells. Besides its essential role in the degradation of dysfunctional and oxidatively damaged proteins, it is involved in many processes which influence disease progression in atherosclerosis. Hence, it is logical to ask whether targeting the proteasome is a reasonable and feasible option for the treatment of atherosclerosis. Recent advances: Several lines of evidence suggest stage-specific dysfunction of the UPS in atherogenesis. Regulation of key processes by the proteasome in atherosclerosis, as well as the modulation of these processes by proteasome inhibitors in vascular cells, is outlined in this review. Treatment of atherosclerotic animal models with proteasome inhibitors yielded partly opposing results; the potentially underlying reasons of which are discussed here. Critical issues and Future directions: Targeting UPS function in atherosclerosis is a promising but challenging option. Limitations of current proteasome inhibitors, dose-dependency and the cell-specificity of effects, as well as the potential of future therapeutics are discussed. Stage-specific in depth exploration of UPS function in atherosclerosis in the future will help identify targets and windows for beneficial intervention.Antioxidants & Redox Signaling 02/2014; · 8.20 Impact Factor
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ABSTRACT: In living organisms, proteins are regularly exposed to 'molecular ageing', which corresponds to a set of non-enzymatic modifications that progressively cause irreversible damage to proteins. This phenomenon is greatly amplified under pathological conditions, such as diabetes mellitus. For their survival and optimal functioning, cells have to maintain protein homeostasis, also called 'proteostasis'. This process acts to maintain a high proportion of functional and undamaged proteins. Different mechanisms are involved in proteostasis, among them degradation systems (the main intracellular proteolytic systems being proteasome and lysosomes), folding systems (including molecular chaperones), and enzymatic mechanisms of protein repair. There is growing evidence that the disruption of proteostasis may constitute a determining event in pathophysiology. The aim of this review is to demonstrate how such a dysregulation may be involved in the pathogenesis of diabetes mellitus and in the onset of its long-term complications.Diabetologia 05/2014; · 6.49 Impact Factor