Abstract-Increased oxidative stress in vascular cells plays a key role in the development of endothelial dysfunction and atherosclerosis. Uncoupling protein 2 (UCP2) is an important regulator of intracellular reactive oxygen species (ROS) production. This study was undertaken to test the hypothesis that, UCP2 functions as an inhibitor of the atherosclerotic process in endothelial cells. Adenovirus-mediated UCP2 (Ad-UCP2) overexpression led to a significant increase in endothelial nitric oxide synthase (eNOS) and decrease in endothelin-1 mRNA expression in human aortic endothelial cells (HAECs). Moreover, UCP2 inhibited the increase in ROS production and NF-B activation, and apoptosis of HAECs induced by lysophophatidylcholine (LPC) and linoleic acid. LPC and linoleic acid caused mitochondrial calcium accumulation and transient mitochondrial membrane hyperpolarization, which was followed by depolarization. UCP2 overexpression prevented these processes. In isolated rat aorta, Ad-UCP2 infection markedly improved impaired vascular relaxation induced by LPC. The data collectively suggest that UCP2, functions as a physiologic regulator of ROS generation in endothelial cells. Thus, measures to increase UCP2 expression in vascular endothelial cells may aid in preventing the development and progression of atherosclerosis in patients with metabolic syndrome. etabolic syndrome is a cluster of simultaneously occurring vascular risk factors, such as central obesity, hypertension, dyslipidemia, and glucose intolerance. 1 Impaired endothelium-dependent vascular relaxation (endothelial dysfunction), generally considered a prerequisite for atherosclerosis, is a frequent finding in metabolic syndrome. 2 Subjects with metabolic syndrome frequently display elevated plasma concentrations of free fatty acid (FFA) and oxidized low-density lipoprotein (LDL). 1,[3][4][5] Lipid emulsion and oxidized LDL induce endothelial dysfunction similar to what is observed in metabolic syndrome. 6,7 It is therefore suggested that endothelial dysfunction in metabolic syndrome is mediated, at least in part, by elevated circulating FFA and oxidized LDL levels.Endothelium is important in the regulation of smooth muscle cell growth, migration, and proliferation. In this regard, endothelial apoptosis is an important early event in the pathogenesis of atherosclerosis. 8 Endothelium also modulates vascular tone through the release of relaxing or contracting substances, including nitric oxide (NO), prostacyclin, endothelium-derived hyperpolarizing factor (EDHF), and endothelin-1 (ET-1). Several lines of evidence have suggested that decreased availability of NO or increased availability of ET-1 in the vasculature are central to the pathogenesis of impaired vascular relaxation observed in the early stages of atherosclerosis. 9 -11 Increased oxidative stress in vascular cells is a key mechanism of endothelial dysfunction and atherosclerosis. 12 Various risk factors for atherosclerosis generate intracellular oxidative stress. A relatively high level of oxida...

The highly developed endoplasmic reticulum (ER) structure of pancreatic beta-cells is a key factor in beta-cell function. Here we examined whether ER stress-induced activation of activating transcription factor (ATF)-6 impairs insulin gene expression via up-regulation of the orphan nuclear receptor small heterodimer partner (SHP; NR0B2), which has been shown to play a role in beta-cell dysfunction. We examined whether ER stress decreases insulin gene expression, and this process is mediated by ATF6. A small interfering RNA that targeted SHP was used to determine whether the effect of ATF6 on insulin gene expression is mediated by SHP. We also measured the expression level of ATF6 in pancreatic islets in Otsuka Long Evans Tokushima Fatty rats, a rodent model of type 2 diabetes. High glucose concentration (30 mmol/liter glucose) increased ER stress in INS-1 cells. ER stress induced by tunicamycin, thapsigargin, or dithiotreitol decreased insulin gene transcription. ATF6 inhibited insulin promoter activity, whereas X-box binding protein-1 and ATF4 did not. Adenovirus-mediated overexpression of active form of ATF6 in INS-1 cells impaired insulin gene expression and secretion. ATF6 also down-regulated pancreatic duodenal homeobox factor-1 and RIPE3b1/MafA gene expression and repressed the cooperative action of pancreatic duodenal homeobox factor-1, RIPE3b1/MafA, and beta-cell E box transactivator 2 in stimulating insulin transcription. The ATF6-induced suppression of insulin gene expression was associated with up-regulation of SHP gene expression. Finally, we found that expression of ATF6 was increased in the pancreatic islets of diabetic Otsuka Long Evans Tokushima Fatty rats, compared with their lean, nondiabetic counterparts, Long-Evans Tokushima Otsuka rats. Collectively, this study shows that ER stress-induced activation of ATF6 plays an important role in the development of beta-cell dysfunction.

Excessive proliferation of vascular smooth muscle cells (VSMCs) and neointimal formation are critical steps in the pathogenesis of atherosclerosis and restenosis after percutaneous transluminal angioplasty. In this study, we investigated the hypothesis that the activator protein-1 (AP-1) plays an important role in neointimal formation after vascular injury. A circular dumbbell AP-1 decoy oligodeoxynucleotide (CDODN) was developed as a novel therapeutic strategy for restenosis after angioplasty. This CDODN was more stable than the conventional phosphorothioate linear decoy ODN (PSODN) and maintained structural integrity on exposure to exonuclease III or serum. Transfection with AP-1 decoy ODNs strongly inhibited VSMC proliferation and migration, as well as glucose- and serum-induced expression of PCNA and cyclin A genes. Administration of AP-1 decoy ODNs in vivo using the hemagglutinating virus of Japan (HVJ)-liposome method virtually abolished neointimal formation after balloon injury to the rat carotid artery. Compared with PSODN, CDODN was more effective in inhibiting the proliferation of VSMCs in vitro and neointimal formation in vivo. Our results collectively indicate that AP-1 activation is crucial for the mediation of VSMC proliferation in response to vascular injury. Moreover, the use of stable CDODN specific for AP-1 activity in combination with the highly effective HVJ-liposome method provides a novel potential therapeutic strategy for the prevention of restenosis after angioplasty in humans.

Objective-Fatty acids increase reactive oxygen species generation and cell apoptosis in endothelial cells. The peroxisome proliferator-activated receptor-␥ coactivator 1-␣ (PGC-1␣) is a transcriptional coactivator that increases mitochondrial biogenesis and fatty acid oxidation in various cells. This study was undertaken to investigate the possible preventive effect of PGC-1␣ on endothelial apoptosis and its molecular mechanism. Methods and Results-Treatment with linoleic acid in cultured human aortic endothelial cells increased reactive oxygen species generation and cell apoptosis. These effects appeared to be mediated by increases in cytosolic fat metabolites, ie, fatty acyl CoA, diacylglycerol, and ceramide, and consequent decreases in ATP/ADP translocase activity of adenine nucleotide translocator. Adenoviral overexpression of PGC-1␣ prevented linoleic acid-induced increases in reactive oxygen species generation and cell apoptosis in human aortic endothelial cells by increasing fatty acid oxidation, decreasing diacylglycerol and ceramide, and increasing ATP/ADP translocase activity. In isolated aorta, PGC-1␣ overexpression prevented linoleic acid-induced decrease in endothelium-dependent vasorelaxation, and this effect was abolished by adenine nucleotide translocator1 shRNA. Key Words: adenine nucleotide translocator Ⅲ peroxisome proliferator-actived receptor-␥ coactivator 1-␣ Ⅲ endothelial apoptosis Ⅲ mitochondrial membrane potential Ⅲ reactive oxygen species C entral obesity is associated with increased cardiovascular morbidity and mortality. 1 Endothelial cell apoptosis and consequent impairment of endothelium-dependent vascular relaxation (endothelial dysfunction) are important early events in the pathogenesis of atherosclerosis. 2 Increased levels of plasma free fatty acids in obesity may lead to endothelial cell apoptosis by increasing the accumulation of lipid metabolites and the generation of reactive oxygen species (ROS). 3,4 Major sites of intracellular ROS generation are mitochondria and cell membrane NAD(P)H oxidase. 4 The mitochondrial respiratory chain generates ROS when the electrochemical gradient between the mitochondrial inner membrane is high and the rate of electron transport is limited. In oxidative phosphorylation, electrons are transferred from electron donors, NADH or FADH, to electron acceptors in the mitochondrial electron transport chain. This transfer releases energy, and most of the energy is captured by proton pumps that build a proton gradient across the mitochondrial inner membrane (⌬ m ), which is the driving force for the phosphorylation of ADP to ATP by ATP synthase. 5,6 However, sustained increase in ⌬ m impairs the flow of electrons through the ETC and increases the accidental transfer of electrons to oxygen to form superoxide. 6,7 ⌬ m is determined by the balance between the export of protons from the mitochondrial matrix into the intermembra- 8 In addition, ANT is responsible for a significant portion of basal uncoupling or proton leak 5,9 independent of its fun...

We examined the effects of high-fat diet (HFD) and exercise training on insulin-stimulated whole body glucose fluxes and several key steps of glucose metabolism in skeletal muscle. Rats were maintained for 3 wk on either low-fat (LFD) or high-fat diet with or without exercise training (swimming for 3 h per day). After the 3-wk diet/exercise treatments, animals underwent hyperinsulinemic euglycemic clamp experiments for measurements of insulin-stimulated whole body glucose fluxes. In addition, muscle samples were taken at the end of the clamps for measurements of glucose 6-phosphate (G-6-P) and GLUT-4 protein contents, hexokinase, and glycogen synthase (GS) activities. Insulin-stimulated glucose uptake was decreased by HFD and increased by exercise training (P < 0.01 for both). The opposite effects of HFD and exercise training on insulin-stimulated glucose uptake were associated with similar increases in muscle G-6-P levels (P < 0.05 for both). However, the increase in G-6-P level was accompanied by decreased GS activity without changes in GLUT-4 protein content and hexokinase activities in the HFD group. In contrast, the increase in G-6-P level in the exercise-trained group was accompanied by increased GLUT-4 protein content and hexokinase II (cytosolic) and GS activities. These results suggest that HFD and exercise training affect insulin sensitivity by acting predominantly on different steps of intracellular glucose metabolism. High-fat feeding appears to induce insulin resistance by affecting predominantly steps distal to G-6-P (e.g., glycolysis and glycogen synthesis). Exercise training affected multiple steps of glucose metabolism both proximal and distal to G-6-P. However, increased muscle G-6-P levels in the face of increased glucose metabolic fluxes suggest that the effect of exercise training is quantitatively more prominent on the steps proximal to G-6-P (i.e., glucose transport and phosphorylation).

Prolonged elevations of glucose concentration have deleterious effects on ␤-cell function. One of the hallmarks of such glucotoxicity is a reduction in insulin gene expression, resulting from decreased insulin promoter activity. Small heterodimer partner (SHP; NR0B2) is an atypical orphan nuclear receptor that inhibits nuclear receptor signaling in diverse metabolic pathways. In this study, we found that sustained culture of INS-1 cells at high glucose concentrations leads to an increase in SHP mRNA expression, followed by a decrease in insulin gene expression. Inhibition of endogenous SHP gene expression by small interfering RNA partially restored high-glucose-induced suppression of the insulin gene. Adenovirus-mediated overexpression of SHP in INS-1 cells impaired glucose-stimulated insulin secretion as well as insulin gene expression. SHP downregulates insulin gene expression via two mechanisms: by downregulating PDX-1 and MafA gene expression and by inhibiting p300-mediated pancreatic duodenal homeobox factor 1-and BETA2-dependent transcriptional activity from the insulin promoter. Finally, the pancreatic islets of diabetic OLETF rats express SHP mRNA at higher levels than the islets from LETO rats. These results collectively suggest that SHP plays an important role in the development of ␤-cell dysfunction induced by glucotoxicity.

Abstract-Neointimal formation, the leading cause of restenosis, is caused by proliferation of vascular smooth muscle cells (VSMCs). Patients with diabetes mellitus have higher restenosis rates after coronary angioplasty than nondiabetic patients. Cilostazol, a selective type 3 phosphodiesterase inhibitor, is currently used to treat patients with diabetic vascular complications. Cilostazol is a potent antiplatelet agent that inhibits VSMC proliferation. In the present study, we examine whether the antiproliferative effect of cilostazol on VSMCs is mediated by inhibition of an important cell cycle transcription factor, E2F. Cilostazol inhibited the proliferation of human VSMCs in response to high glucose in vitro and virtually abolished neointimal formation in rats subjected to carotid artery injury in vivo. Moreover, the compound suppressed high-glucose-induced E2F-DNA binding activity, and the expression of E2F1, E2F2, cyclin A, and PCNA proteins. These data suggest that the beneficial effects of cilostazol on high-glucose-stimulated proliferation of VSMCs are mediated by the downregulation of E2F activity and expression of its downstream target genes, including E2F1, E2F2, cyclin A, and PCNA. The transcription factor, E2F, has been implicated in the periodic regulation of cellular genes required for transition through G1 and entry into the S phase, including dihydrofolate reductase, c-myc, DNA polymerase, cdc2, and proliferating cell nuclear antigen (PCNA). 5-7 E2F activity is regulated by interactions with RB family members. As cells progress toward S phase, RB family proteins are phosphorylated by G1 cyclin-complexes, resulting in the release of transcriptionally active E2F, which then leads to the activation of genes required for cell cycle progression. 8 -10 We recently showed that high glucose activates the DNA-binding activity of E2F, and decoy oligodeoxynucleotides against E2F inhibit the proliferation of VSMCs. 11 These data suggest that downregulation of E2F could constitute a therapeutic target to prevent restenosis after angioplasty in patients with diabetes.Cilostazol increases intracellular cAMP concentrations by selectively blocking phosphodiesterase type III. The clinical implications and pharmacokinetics with respect to the effects and safety of this drug have been well-established, especially in peripheral vascular disease. 12 Cilostazol is a potent antiplatelet agent currently used in clinical practice to treat patients with diabetic vascular complications. [13][14][15] Several lines of evidence indicate that cilostazol additionally inhibits the proliferation of VSMCs, reduces neointimal formation in balloon-injured rat carotid arteries, 16 -18 and inhibits restenosis after percutaneous transluminal coronary angioplasty. 19,20 One mechanism by which cilostazol may inhibit VSMC proliferation is via an increase in intracellular cAMP, because cAMP inhibits the proliferation of VSMCs by induction of p53-mediated and p21-mediated apoptosis. 21 However, Nadri et al demonstrated that increased cAMP...

Mitochondrial dysfunction and endoplasmic reticulum (ER) stress are considered the key determinants of insulin resistance. Impaired mitochondrial function in obese animals was shown to induce the ER stress response, resulting in reduced adiponectin synthesis in adipocytes. The expression of inducible nitric oxide synthase (iNOS) is increased in adipose tissues in genetic and dietary models of obesity. In this study, we examined whether activation of iNOS is responsible for palmitate-induced mitochondrial dysfunction, ER stress, and decreased adiponectin synthesis in 3T3L1 adipocytes. As expected, palmitate increased the expression levels of iNOS and ER stress response markers, and decreased mitochondrial contents. Treatment with iNOS inhibitor increased adiponectin synthesis and reversed the palmitate-induced ER stress response. However, the iNOS inhibitor did not affect the palmitate-induced decrease in mitochondrial contents. Chemicals that inhibit mitochondrial function increased iNOS expression and the ER stress response, whereas measures that increase mitochondrial biogenesis (rosiglitazone and adenoviral overexpression of nuclear respiratory factor-1) reversed them. Inhibition of mitochondrial biogenesis prevented the rosiglitazone-induced decrease in iNOS expression and increase in adiponectin synthesis. These results suggest that palmitate-induced mitochondrial dysfunction is the primary event that leads to iNOS induction, ER stress, and decreased adiponectin synthesis in cultured adipocytes.