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: The precise link between hyperglycemia and its deleterious effects on retinal and kidney microvasculature, and more specifically loss of retinal perivascular supporting cells including smooth muscle cell/pericytes (SMC/PC), in diabetes are not completely understood. We hypothesized that differential cellular proteasome activity contributes to sensitivity of PC to high glucose-mediated oxidative stress and vascular rarefaction. Here we show that retinal endothelial cells (EC) have significantly higher proteasome peptidase activity compared to PC. High glucose treatment (HGT) increased the level of total ubiquitin-conjugated proteins in cultured retinal PC and EC, but not photoreceptor cells. In addition, in vitro proteasome activity assays showed significant impairment of proteasome chymotrypsin-like peptidase activity in PC, but not EC. The PA28-α/-β and PA28-β/-γ protein levels were also higher in the retina and kidney glomeruli of diabetic mice, respectively. Our results demonstrate, for the first time, that high glucose has direct biological effects on cellular proteasome function, and this modulation might be protective against cellular stress or damage induced by high glucose.Biochemical and Biophysical Research Communications 02/2013; · 2.28 Impact Factor
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ABSTRACT: Advanced age is associated with a disproportionate prevalence of cardiovascular disease (CVD). Intrinsic alterations in the heart and the vasculature occurring over the life course render the cardiovascular system more vulnerable to various stressors in late life, ultimately favoring the development of CVD. Several lines of evidence indicate mitochondrial dysfunction as a major contributor to cardiovascular senescence. Besides being less bioenergetically efficient, damaged mitochondria also produce increased amounts of reactive oxygen species, with detrimental structural and functional consequences for the cardiovascular system. The age-related accumulation of dysfunctional mitochondrial likely results from the combination of impaired clearance of damaged organelles by autophagy and inadequate replenishment of the cellular mitochondrial pool by mitochondriogenesis. In this review, we summarize the current knowledge about relevant mechanisms and consequences of age-related mitochondrial decay and alterations in mitochondrial quality control in the cardiovascular system. The involvement of mitochondrial dysfunction in the pathogenesis of cardiovascular conditions especially prevalent in late life and the emerging connections with neurodegeneration are also illustrated. Special emphasis is placed on recent discoveries of the role played by alterations in mitochondrial dynamics (fusion and fission), mitophagy and their interconnections in the context of age-related CVD and endothelial dysfunction. Finally, we discuss pharmacological interventions targeting mitochondrial dysfunction to delay cardiovascular aging and manage CVD.AJP Heart and Circulatory Physiology 06/2013; · 4.01 Impact Factor
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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