Activation of members of the mitogen-activated protein kinase family by glucose in endothelial cells

Pathophysiological Impact of the MEK5/ERK5 Pathway in Oxidative Stress

Oxidative stress regulates many physiological and pathological processes. Indeed, a low increase in the basal level of reactive oxygen species (ROS) is essential for various cellular functions, including signal transduction, gene expression, cell survival or death, as well as antioxidant capacity. However, if the amount of generated ROS overcomes the antioxidant capacity, excessive ROS results in cellular dysfunctions as a consequence of damage to cellular components, including DNA, lipids and proteins, and may eventually lead to cell death or carcinogenesis. Both in vitro and in vivo investigations have shown that activation of the mitogen-activated protein kinase kinase 5/extracellular signal-regulated kinase 5 (MEK5/ERK5) pathway is frequently involved in oxidative stress-elicited effects. In particular, accumulating evidence identified a prominent role of this pathway in the anti-oxidative response. In this respect, activation of krüppel-like factor 2/4 and nuclear factor erythroid 2-related factor 2 emerged among the most frequent events in ERK5-mediated response to oxidative stress. This review summarizes what is known about the role of the MEK5/ERK5 pathway in the response to oxidative stress in pathophysiological contexts within the cardiovascular, respiratory, lymphohematopoietic, urinary and central nervous systems. The possible beneficial or detrimental effects exerted by the MEK5/ERK5 pathway in the above systems are also discussed.

Distinct Mechanisms of Human Retinal Endothelial Barrier Modulation In Vitro by Mediators of Diabetes and Uveitis

Ocular diseases such as diabetic retinopathy (DR) and uveitis are associated with injury to the blood–retinal barrier (BRB). Whereas high glucose (HG) and advanced glycation end products (AGE) contribute to DR, bacterial infections causing uveitis are triggered by endotoxins such as lipopolysaccharide (LPS). It is unclear how HG, AGE, and LPS affect human retinal endothelial cell (HREC) junctions. Moreover, tumor necrosis factor-α (TNFα) is elevated in both DR and ocular infections. In the current study, we determined the direct effects of HG, AGE, TNFα, and LPS on the expression and intracellular distribution of claudin-5, VE-cadherin, and β-catenin in HRECs and how these mediators affect Akt and P38 MAP kinase that have been implicated in ocular pathologies. In our results, whereas HG, AGE, and TNFα activated both Akt and P38 MAPK, LPS treatment suppressed Akt but increased P38 MAPK phosphorylation. Furthermore, while treatment with AGE and HG increased cell-junction protein expression in HRECs, LPS elicited a paradoxical effect. By contrast, when HG treatment increased HREC-barrier resistance, AGE and LPS stimulation compromised it, and TNFα had no effect. Together, our results demonstrated the differential effects of the mediators of diabetes and infection on HREC-barrier modulation leading to BRB injury.

Molecular Mechanisms of Glucose Fluctuations on Diabetic Complications

Accumulating evidence indicates the occurrence and development of diabetic complications relates to not only constant high plasma glucose, but also glucose fluctuations which affect various kinds of molecular mechanisms in various target cells and tissues. In this review, we detail reactive oxygen species and their potentially damaging effects upon glucose fluctuations and resultant downstream regulation of protein signaling pathways, including protein kinase C, protein kinase B, nuclear factor-κB, and the mitogen-activated protein kinase signaling pathway. A deeper understanding of glucose-fluctuation-related molecular mechanisms in the development of diabetic complications may enable more potential target therapies in future.

Molecular regulation of ERK5 in development of diabetic retinopathy

Diabetic retinopathy (DR) is a major complication of diabetes, and causes pathological changes in retina blood vessels, as the most common cause of vision loss. Extracellular-signal-regulated kinase 5 (ERK5) is the newest discovered member in the mitogen-activated protein kinases (MAPKs) family, and recent evidence demonstrates an essential role of ERK5 signaling in the angiogenesis. However, whether ERK5 signaling may regulate DR development is unknown. Here, we used a streptozocin (STZ)-induce mouse DR model to investigate this question. We detected significant increases in the phosphorylation of ERK5, a signature of ERK5 activation in the purified retinal endothelial cells in DR mice, compared to control mice. In vivo suppression of ERK5 phosphorylation through administration of a specific inhibitor of ERK5 activation, BIX02189, did not prevent the occurrence of STZ-induced diabetes in mice, but significantly alleviated the severity of DR, seemingly through attenuating the retina neovascularization. Thus, our study suggests a previously unappreciated role of ERK5 signaling in DR development.

High-density lipoproteins attenuate high glucose-impaired endothelial cell signaling and functions: potential implications for improved vascular repair in diabetes

Background

Abnormalities of endothelial cell function are proposed to be a critical factor underlying adverse cardiovascular outcomes in the setting of hyperglycaemia. While high-density lipoproteins (HDL) have been demonstrated to be cardioprotective, the impact on the endothelium in hyperglycaemia has not been fully elucidated.

Methods

Human umbilical vein endothelial cells (HUVECs) were exposed to high-glucose conditions using dextrose, the main isoform of glucose, and native HDL. HUVEC proliferation and migration were determined. The key signalling pathways that regulate endothelial cell function were also characterized.

Results

Increasing concentrations of dextrose resulted in significant reductions in HUVEC proliferation, this was attenuated by coincubation with HDL. In support of this, HDL was also found to rescue dextrose impaired expression of PCNA and the activation (phosphorylation) of the key transcription factor for proliferation ERK. Dextrose also dose-dependently inhibited HUVEC migration, which was mitigated by co-incubation with HDL. Consistent with this, HDL prevented dextrose-induced inhibition of p38 phosphorylation, responsible for cell migration. Finally, phosphorylation of the pro-survival transcription factor Akt was dose-dependently inhibited by dextrose, however, this was completely rescued by co-administration with HDL.

Conclusion

Dextrose-induced hyperglycaemia causes the impairment of endothelial cell proliferation and migration and inhibits the activation of ERK, p38 and Akt pathways. The protective effects of HDL in this milieu highlights the potential for HDL to improve vascular repair in patients with impaired glucose homeostasis.

Role of the PKCβII/JNK signaling pathway in acute glucose fluctuation-induced apoptosis of rat vascular endothelial cells

AIMS

The purpose of this study was to investigate the mechanism of vascular endothelial cell apoptosis induced by acute blood glucose fluctuation.

METHODS

Thirty rats were assigned to three groups: normal saline (SAL group), constant high glucose (CHG group) and acute blood glucose fluctuation (AFG) group. Other forty rats were assigned to SAL group, AFG group, LY group (PKCβ inhibitor LY333531 was injected intragastrically to the rats who were under acute blood glucose fluctuation) and SP group (JNK inhibitor SP600125 was injected intraperitoneally to the rats who were under acute blood glucose fluctuation). Oxidative stress and inflammatory cytokines were detected. TUNEL was performed to detect apoptosis. Pro-caspase-3, caspase-3 p17, JNK, PKC-βII and insulin signaling-related protein expression were tested by Western blotting.

RESULTS

After administration of LY333531, AFG-induced membrane translocation of PKCβII protein was inhibited, but SP600125 failed to affect AFG-induced PKCβII membrane translocation. After administration of LY333531, the AFG-induced increase in JNK activity was significantly compromised. LY333531 inhibited AFG-induced oxidative stress. However, SP600125 only slightly inhibited AFG-induced oxidative stress reaction (P > 0.05). Both LY333531 and SP600125 can reverse AFG-induced endothelial cell apoptosis increase, inflammatory cytokines levels rise and insulin signaling impairment.

CONCLUSIONS

It is necessary to actively control blood glucose and avoid significant glucose fluctuation. PKCβII/JNK may serve as a target, and inhibitors of PKCβII/JNK may be used to help prevent cardiovascular diseases in patients with poor glucose control or significant glucose fluctuation.

Ursodeoxycholic Acid (UDCA) Exerts Anti-Atherogenic Effects by Inhibiting RAGE Signaling in Diabetic Atherosclerosis

A naturally occurring bile acid, ursodeoxycholic acid (UDCA), is known to alleviate endoplasmic reticulum (ER) stress at the cellular level. However, the detailed action mechanisms of UDCA in atherosclerosis are not fully understood. In this study, we demonstrated whether UDCA exerts anti-atherogenic activity in diabetic atherosclerosis by targeting ER stress and “receptor for advanced glycation endproduct” (RAGE) signaling. UDCA markedly reduced ER stress, RAGE expression, and pro-inflammatory responses [including NF-κB activation and reactive oxygen species (ROS) production] induced in endothelial cells (ECs) by high glucose (HG). In particular, UDCA inhibited HG-induced ROS production by increasing the Nrf2 level. In macrophages, UDCA also blocked HG-induced RAGE and pro-inflammatory cytokine expression and inhibited foam cell formation via upregulation of the ATP-binding cassette (ABC) transporters, ABCA1 and ABCG1. In the diabetic mouse model, UDCA inhibited atheromatous plaque formation by decreasing ER stress, and the levels of RAGE and adhesion molecules. In conclusion, UDCA exerts an anti-atherogenic activity in diabetic atherosclerosis by targeting both ER stress and RAGE signaling. Our work implicates UDCA as a potential therapeutic agent for prevention or treatment of diabetic atherosclerosis.

Heme oxygenase-1-derived bilirubin protects endothelial cells against high glucose-induced damage

Hyperglycemia and diabetes are associated with endothelial cell dysfunction arising from enhanced oxidative injury, leading to the progression of diabetic vascular pathologies. The redox-sensitive transcription factor nuclear factor-E2-related factor 2 (Nrf2) is a master regulator of antioxidant genes, such as heme oxygenase-1 (HO-1), involved in cellular defenses against oxidative stress. We have investigated the pathways involved in high glucose-induced activation of HO-1 in endothelial cells and examined the molecular mechanisms underlying cytoprotection. Elevated d-glucose increased intracellular generation of reactive oxygen species (ROS), leading to nuclear translocation of Nrf2 and HO-1 expression in bovine aortic endothelial cells, with no changes in cell viability. Superoxide scavenging and inhibition of endothelial nitric oxide synthase (eNOS) abrogated upregulation of HO-1 expression by elevated glucose. Inhibition of HO-1 increased the sensitivity of endothelial cells to high glucose-mediated damage, while addition of bilirubin restored cell viability. Our findings establish that exposure of endothelial cells to high glucose leads to activation of endogenous antioxidant defense genes via the Nrf2/ARE pathway. Upregulation of HO-1 provides cytoprotection against high glucose-induced oxidative stress through the antioxidant properties of bilirubin. Modulation of the Nrf2 pathway in the early stages of diabetes may thus protect against sustained damage by hyperglycemia during progression of the disease.

Hyperbranched polyglycerol as a colloid in cold organ preservation solutions

Hydroxyethyl starch (HES) is a common colloid in organ preservation solutions, such as in University of Wisconsin (UW) solution, for preventing graft interstitial edema and cell swelling during cold preservation of donor organs. However, HES has undesirable characteristics, such as high viscosity, causing kidney injury and aggregation of erythrocytes. Hyperbranched polyglycerol (HPG) is a branched compact polymer that has low intrinsic viscosity. This study investigated HPG (MW-0.5 to 119 kDa) as a potential alternative to HES for cold organ preservation. HPG was synthesized by ring-opening multibranching polymerization of glycidol. Both rat myocardiocytes and human endothelial cells were used as an in vitro model, and heart transplantation in mice as an in vivo model. Tissue damage or cell death was determined by both biochemical and histological analysis. HPG polymers were more compact with relatively low polydispersity index than HES in UW solution. Cold preservation of mouse hearts ex vivo in HPG solutions reduced organ damage in comparison to those in HES-based UW solution. Both size and concentration of HPGs contributed to the protection of the donor organs; 1 kDa HPG at 3 wt% solution was superior to HES-based UW solution and other HPGs. Heart transplants preserved with HPG solution (1 kDa, 3%) as compared with those with UW solution had a better functional recovery, less tissue injury and neutrophil infiltration in syngeneic recipients, and survived longer in allogeneic recipients. In cultured myocardiocytes or endothelial cells, significantly more cells survived after cold preservation with the HPG solution than those with the UW solution, which was positively correlated with the maintenance of intracellular adenosine triphosphate and cell membrane fluidity. In conclusion, HPG solution significantly enhanced the protection of hearts or cells during cold storage, suggesting that HPG is a promising colloid for the cold storage of donor organs and cells in transplantation.

Effects of a novel curcumin derivative on insulin synthesis and secretion in streptozotocin-treated rat pancreatic islets in vitro

Background

Hyperglycemia induces activation of the c-Jun N-terminal kinase (JNK) pathway, which suppresses insulin gene expression and reduces DNA binding of pancreatic and duodenal homeobox factor (PDX)-1. This study aims to investigate the effects of a novel curcumin derivative (NCD) on JNK signaling pathway on insulin synthesis and secretion in streptozotocin (STZ)-treated rat pancreatic islets in vitro.

Methods

Isolated rat pancreatic islets were divided into five groups: untreated control group; group treated with NCD (10 μM); group exposed to STZ (5 mM); group treated with NCD (10 μM) and then exposed to STZ (5 mM); and group exposed to STZ (5 mM) and then treated with NCD (10 μM). The pancreatic islets from all groups were used for DNA fragmentation assays and quantitative assessments of the JNK, Pdx1, glucose transporter-2 (GLUT2), heme oxygenase (HO)-1, transcription factor 7-like 2 (TCF7L2), and glucagon-like peptide (GLP)-1 gene expression levels. The intracellular calcium, zinc, and the phosphorylated and total JNK protein levels were assessed. The insulin (secreted/total) and C-peptide levels were examined in islet culture medium.

Results

NCD protected pancreatic islets against STZ-induced DNA damage, improved total insulin (P = 0.001), secreted insulin (P = 0.001), and C-peptide levels (P = 0.001), normalized mRNA expressions of insulin, Pdx1, and GLUT2 (P = 0.0001), and significantly elevated calcium and zinc levels (P = 0.0001). All effects were significant when islets were treated with NCD before STZ (P = 0.05). JNK gene overexpression and JNK protein levels induced by STZ were significantly inhibited after NCD treatment of islets ( P = 0.0001). NCD-treated islets showed significantly elevated gene expressions of HO-1, TCF7L2, and GLP-1 (P = 0.0001), and these upregulated gene expressions were more significantly elevated with NCD treatment before STZ than after STZ (P = 0.05).

Conclusions

NCD improved insulin synthesis and secretion in vitro in isolated pancreatic islets treated with STZ through inhibition of the JNK pathway, up-regulation of the gene expressions of HO-1, TCF7L2, and GLP-1 and enhancing effects on calcium and zinc levels.

IGFBP5 mediates high glucose-induced cardiac fibroblast activation

This study examined whether IGF-binding protein 5 (IGFBP5) is involved in the high glucose-induced deteriorating effects in cardiac cells. Cardiac fibroblasts and cardiomyocytes were isolated from the hearts of 1- to 3-day-old Sprague Dawley rats. Treatment of fibroblasts with 25 mM glucose increased the number of cells and the mRNA levels of collagen III, matrix metalloproteinase 2 (MMP2), and MMP9. High glucose increased ERK1/2 activity, and the ERK1/2 inhibitor PD98059 suppressed high glucose-mediated fibroblast proliferation and increased collagen III mRNA levels. Whereas high glucose increased both mRNA and protein levels of IGFBP5 in fibroblasts, high glucose did not affect IGFBP5 protein levels in cardiomyocytes. The high glucose-induced increase in IGFBP5 protein levels was inhibited by PD98059 in fibroblasts. While recombinant IGFBP5 increased ERK phosphorylation, cell proliferation, and the mRNA levels of collagen III, MMP2, and MMP9 in fibroblasts, IGFBP5 increased c-Jun N-terminal kinase phosphorylation and induced apoptosis in cardiomyocytes. The knockdown of IGFBP5 inhibited high glucose-induced cell proliferation and collagen III mRNA levels in fibroblasts. Although high glucose increased IGF1 levels, IGF1 did not increase IGFBP5 levels in fibroblasts. The hearts of Otsuka Long-Evans Tokushima Fatty rats and the cardiac fibroblasts of streptozotocin-induced diabetic rats showed increased IGFBP5 expression. These results suggest that IGFBP5 mediates high glucose-induced profibrotic effects in cardiac fibroblasts.

Activation of JNK/c-Jun is required for the proliferation, survival, and angiogenesis induced by EET in pulmonary artery endothelial cells

Pulmonary artery endothelial plexiform lesion is responsible for pulmonary vascular remodeling (PVR), a basic pathological change of pulmonary arterial hypertension (PAH). Recent evidence suggests that epoxyeicosatrienoic acid (EET), which is derived from arachidonic acid by cytochrome p450 (CYP) epoxygenase, has an essential role in PAH. However, until now, most research has focused on pulmonary vasoconstriction; it is unclear whether EET produces mitogenic and angiogenic effects in pulmonary artery endothelial cells (PAEC). Here we found that 500 nM/l 8,9-EET, 11,12-EET, and 14,15-EET markedly augmented JNK and c-Jun activation in PAECs and that the activation of c-Jun was mediated by JNK, but not the ERK or p38 MPAK pathway. Moreover, treatment with 8,9-EET, 11,12-EET, and 14,15-EET promoted cell proliferation and cell-cycle transition from the G0/G1 phase to S phase and stimulated tube formation in vitro. All these effects were reversed after blocking JNK with Sp600125 (a JNK inhibitor) or JNK1/2 siRNA. In addition, the apoptotic process was alleviated by three EET region isomers through the JNK/c-Jun pathway. These observations suggest that 8,9-EET, 11,12-EET, and 14,15-EET stimulate PAEC proliferation and angiogenesis, as well as protect the cells from apoptosis, via the JNK/c-Jun pathway, an important underlying mechanism that may promote PAEC growth and angiogenesis during PAH.

Role of differential signaling pathways and oxidative stress in diabetic cardiomyopathy

Diabetes mellitus increases the risk of heart failure independently of underlying coronary artery disease, and many believe that diabetes leads to cardiomyopathy. The underlying pathogenesis is partially understood. Several factors may contribute to the development of cardiac dysfunction in the absence of coronary artery disease in diabetes mellitus. There is growing evidence that excess generation of highly reactive free radicals, largely due to hyperglycemia, causes oxidative stress, which further exacerbates the development and progression of diabetes and its complications. Hyperglycemia-induced oxidative stress is a major risk factor for the development of micro-vascular pathogenesis in the diabetic myocardium, which results in myocardial cell death, hypertrophy, fibrosis, abnormalities of calcium homeostasis and endothelial dysfunction. Diabetes-mediated biochemical changes show cross-interaction and complex interplay culminating in the activation of several intracellular signaling molecules. Diabetic cardiomyopathy is characterized by morphologic and structural changes in the myocardium and coronary vasculature mediated by the activation of various signaling pathways. This review focuses on the oxidative stress and signaling pathways in the pathogenesis of the cardiovascular complications of diabetes, which underlie the development and progression of diabetic cardiomyopathy.

O-linked β-N-acetylglucosamine supports p38 MAPK activation by high glucose in glomerular mesangial cells

Hyperglycemia augments flux through the hexosamine biosynthetic pathway and subsequent O-linkage of single β-N-acetyl-d-glucosamine moieties to serine and threonine residues on cytoplasmic and nuclear proteins (O-GlcNAcylation). Perturbations in this posttranslational modification have been proposed to promote glomerular matrix accumulation in diabetic nephropathy, but clear evidence and mechanism are lacking. We tested the hypothesis that O-GlcNAcylation enhances profibrotic signaling in rat mesangial cells. An adenovirus expressing shRNA directed against O-GlcNAc transferase (OGT) markedly reduced basal and high-glucose-stimulated O-GlcNAcylation. Interestingly, O-GlcNAc depletion prevented high-glucose-induced p38 mitogen-activated protein kinase (MAPK) and c-Jun NH(2)-terminal kinase phosphorylation. Downstream of p38, O-GlcNAc controlled the expression of plasminogen activator inhibitor-1, fibronectin, and transforming growth factor-β, important factors in matrix accumulation in diabetic nephropathy. Treating mesangial cells with thiamet-G, a highly selective inhibitor of O-GlcNAc-specific hexosaminidase (O-GlcNAcase), increased O-GlcNAcylation and p38 phosphorylation. The high-glucose-stimulated kinase activity of apoptosis signal-regulating kinase 1 (ASK1), an upstream MAPK kinase kinase for p38 that is negatively regulated by Akt, was inhibited by OGT shRNA. Akt Thr(308) and Ser(473) phosphorylation were enhanced following OGT shRNA expression in high-glucose-exposed mesangial cells, but high-glucose-induced p38 phosphorylation was not attenuated by OGT shRNA in cells pretreated with the phosphatidylinositol 3-kinase inhibitor LY-294002. OGT shRNA also reduced high-glucose-stimulated reactive oxygen species (ROS) formation. In contrast, diminished O-GlcNAcylation caused elevated ERK phosphorylation and PKCδ membrane translocation. Thus, O-GlcNAcylation is coupled to profibrotic p38 MAPK signaling by high glucose in part through Akt and possibly through ROS.

Glucose-induced endothelin-1 expression is regulated by ERK5 in the endothelial cells and retina of diabetic rats

Upregulation of endothelin 1 (ET-1) causing blood flow alteration and increased extracellular matrix production are characteristic features of diabetic angiopathy. Several glucose-induced signaling mechanisms cause ET-1 upregulation in diabetic angiopathy. Extracellular signal-regulated kinase 5 (ERK5) is a member of the MAPK family, which plays a key role in cardiovascular development. ERK kinase (MEK) 5 is the specific MEK for ERK5 activation. In this study we examined the role of glucose-induced ERK5 signaling in mediating ET-1 expression in diabetic angiopathy. We investigated retinas from 1-month STZ-induced diabetic rats and human macro- and microvascular endothelial cells to study ERK5-dependent ET-1 alterations. Glucose (25 mmol/L) caused significant upregulation of ET-1 mRNA and downregulation of ERK5 and Kruppel-like factor 2 (KLF2) after 24 h treatment in the endothelial cells. Simultaneously, phospho-ERK5 proteins were reduced. Activation of ERK5 by constitutively active MEK5 (caMEK5) upregulated KLF2 and suppressed ET-1 expression in both cell lines, whereas ERK5 siRNA transfection resulted in decreased ERK5 and KLF2 and increased ET-1 mRNA expression. In addition, caMEK5 prevented glucose-induced upregulation of ET-1. Furthermore, 1 month of diabetes caused a significant increase in retinal ET-1 mRNA and decrease in ERK5 mRNA expression. These data indicate that ERK5 signaling regulates glucose-induced ET-1 expression in diabetes. The ERK5/ET-1 pathway may provide a potential novel target for the treatment of diabetic angiopathy.

ERK5 Contributes to VEGF Alteration in Diabetic Retinopathy

Diabetic retinopathy is one of the most common causes of blindness in North America. Several signaling mechanisms are activated secondary to hyperglycemia in diabetes, leading to activation of vasoactive factors. We investigated a novel pathway, namely extracellular signal regulated kinase 5 (ERK5) mediated signaling, in modulating glucose-induced vascular endothelial growth factor (VEGF) expression. Human microvascular endothelial cells (HMVEC) were exposed to glucose. In parallel, retinal tissues from streptozotocin-induced diabetic rats were examined after 4 months of follow-up. In HMVECs, glucose caused initial activation followed by deactivation of ERK5 and its downstream mediators myocyte enhancing factor 2C (MEF2C) and Kruppel-like factor 2 (KLF2) mRNA expression. ERK5 inactivation further led to augmented VEGF mRNA expression. Furthermore, siRNA mediated ERK5 gene knockdown suppressed MEF2C and KLF2 expression and increased VEGF expression and angiogenesis. On the other hand, constitutively active MEK5, an activator of ERK5, increased ERK5 activation and ERK5 and KLF2 mRNA expression and attenuated basal- and glucose-induced VEGF mRNA expression. In the retina of diabetic rats, depletion of ERK5, KLF2 and upregulation of VEGF mRNA were demonstrated. These results indicated that ERK5 depletion contributes to glucose induced increased VEGF production and angiogenesis. Hence, ERK5 may be a putative therapeutic target to modulate VEGF expression in diabetic retinopathy.

Inflammation determines the pro-adhesive properties of high extracellular d-glucose in human endothelial cells in vitro and rat microvessels in vivo

Background

Hyperglycemia is acknowledged as an independent risk factor for developing diabetes-associated atherosclerosis. At present, most therapeutic approaches are targeted at a tight glycemic control in diabetic patients, although this fails to prevent macrovascular complications of the disease. Indeed, it remains highly controversial whether or not the mere elevation of extracellular D-glucose can directly promote vascular inflammation, which favors early pro-atherosclerotic events.

Methods and Findings

In the present work, increasing extracellular D-glucose from 5.5 to 22 mmol/L was neither sufficient to induce intercellular adhesion molecule-1 (ICAM-1) and vascular cell adhesion molecule-1 (VCAM-1) expression, analyzed by flow cytometry, nor to promote leukocyte adhesion to human umbilical vein endothelial cells (HUVEC) in vitro, measured by flow chamber assays. Interestingly, the elevation of D-glucose levels potentiated ICAM-1 and VCAM-1 expression and leukocyte adhesion induced by a pro-inflammatory stimulus, such as interleukin (IL)-1β (5 ng/mL). In HUVEC, high D-glucose augmented the activation of extracellular signal-regulated kinase 1/2 (ERK 1/2) and nuclear transcription factor-κB (NF-κB) elicited by IL-1β, measured by Western blot and electromobility shift assay (EMSA), respectively, but had no effect by itself. Both ERK 1/2 and NF-κB were necessary for VCAM-1 expression, but not for ICAM-1 expression. In vivo, leukocyte trafficking was evaluated in the rat mesenteric microcirculation by intravital microscopy. In accordance with the in vitro data, the acute intraperitoneal injection of D-glucose increased leukocyte rolling flux, adhesion and migration, but only when IL-1β was co-administered.

Conclusions

These results indicate that the elevation of extracellular D-glucose levels is not sufficient to promote vascular inflammation, and they highlight the pivotal role of a pro-inflammatory environment in diabetes, as a critical factor conditioning the early pro-atherosclerotic actions of hyperglycemia.

Beneficial effect of the oligomerized polyphenol oligonol on high glucose-induced changes in eNOS phosphorylation and dephosphorylation in endothelial cells

BACKGROUND AND PURPOSE

Hyperglycaemia is known to reduce nitric oxide (NO) bioavailability by modulating endothelial NO synthase (eNOS) activity, and polyphenols are believed to have cardiovascular benefit. One possible mechanism could be through interaction with eNOS.

EXPERIMENTAL APPROACH

The effects of the oligomerized polyphenol oligonol on eNOS phosphorylation status and activity were examined in porcine aortic endothelial cells cultured in high glucose concentrations.

KEY RESULTS

Exposure to high glucose concentrations strongly inhibited eNOS phosphorylation at Ser-1177 and dephosphorylation at Thr-495 in bradykinin (BK)-stimulated cells. These inhibitory effects of high glucose were significantly prevented by treatment with oligonol. Akt and p38 mitogen-activated protein kinase (MAPK) were activated in BK-stimulated cells. High glucose inhibited Akt activation but enhanced p38 MAPK activation, both of which were reversed by oligonol treatment. The phosphatidylinositol 3-kinase inhibitor wortmannin blocked the reversal by oligonol of phosphorylation at Ser-1177, but not dephosphorylation at Thr-495, in BK-stimulated cells exposed to high glucose. The effect of oligonol on BK dephosphorylation under high glucose was mimicked by protein kinase C (PKC) epsilon-neutralizing peptides. These data suggest that the effects of oligonol on high glucose-induced attenuation of eNOS Ser-1177 phosphorylation and Thr-495 dephosphorylation may be regulated by Akt activation and PKCepsilon inhibition respectively. Oligonol also prevented high glucose-induced attenuation of BK-stimulated NO production.

CONCLUSIONS AND IMPLICATIONS

Oligonol prevented the impairment of eNOS activity induced by high glucose through reversing altered eNOS phosphorylation status. This mechanism may underlie the beneficial cardiovascular health effects of this oligomerized polyphenol.

Role of 14-3-3 protein and oxidative stress in diabetic cardiomyopathy

Cardiovascular disease is a leading cause of death worldwide. Diabetes mellitus is a well-known and important risk factor for cardiovascular diseases. The occurrence of diabetic cardiomyopathy is independent of hypertension, coronary artery disease, or any other known cardiac diseases. There is growing evidence that excess generation of highly reactive free radicals, largely due to hyperglycemia, causes oxidative stress, which further exacerbates the development and progression of diabetes and its complications. Diabetic cardiomyopathy is characterized by morphologic and structural changes in the myocardium and coronary vasculature mediated by the activation of various signaling pathways. Myocardial apoptosis, hypertrophy and fibrosis are the most frequently proposed mechanisms to explain cardiac changes in diabetic cardiomyopathy. Mammalian 14-3-3 proteins are dimeric phosphoserine-binding proteins that participate in signal transduction and regulate several aspects of cellular biochemistry. 14-3-3 protein regulates diabetic cardiomyopathy via multiple signaling pathways. This review focuses on emerging evidence suggesting that 14-3-3 protein plays a key role in the pathogenesis of the cardiovascular complications of diabetes, which underlie the development and progression of diabetic cardiomyopathy.

Synergy research: vitamins and secondary plant components in the maintenance of the redox-homeostasis and in cell signaling

The maintenance of the redox-homeostasis is an essential task of antioxidants. Reactive oxygen species (ROS) formed during oxidative stress can potentially damage the normal cellular functions and support pathological processes like atherosclerosis in vessels or malignant growth in other tissues, but also the aging process. However, recent findings link ROS also to cell survival and/or proliferation, which revolutionises the age-old dogmatic view of ROS being exclusively involved in cell damage and death. Low concentrations of hydrogenperoxide e.g. are involved in cell signaling and can activate mitogen-activated kinases (MAPK) to initiate cell growth. Nutritional antioxidants like vitamin C or E can promote endothelial cell growth, but can also inhibit growth of muscle cells, and influence MAPK. Thus, keeping the redox-homeostasis in a steady state especially in the context of tissue regeneration appears to be more important than previously known and seems to be a controlled synergistic action of antioxidants and ROS. The present review summarizes the properties and functions of ROS and nutritional antioxidants like the vitamins C and E, and polyphenols in redox-homeostasis. Their relevance in the treatment of various diseases is discussed in the context of a multitarget therapy with nutraceuticals and phytotherapeutic drugs.

High glucose promotes retinal endothelial cell migration through activation of Src, PI3K/Akt1/eNOS, and ERKs

Hyperglycemia impacts retinal vascular function and promotes the development and progression of diabetic retinopathy, which ultimately results in growth of new blood vessels and loss of vision. How high glucose affects retinal endothelial cell (EC) properties requires further investigation. Here we determined the impact of high glucose on mouse retinal EC function in vitro. High glucose significantly enhanced the migration of retinal EC without impacting their proliferation, apoptosis, adhesion, and capillary morphogenesis. The enhanced migration of retinal EC under high glucose was reversed in the presence of the antioxidant N-acetylcysteine, suggesting increased oxidative stress under high-glucose conditions. Retinal EC under high-glucose conditions also expressed increased levels of fibronectin, osteopontin, and alpha(v)beta(3)-integrin, and reduced levels of thrombospondin-1. These changes were concomitant with sustained activation of the downstream prosurvival and promigratory signaling pathways, including Src kinase, phosphatidylinositol 3-kinase/Akt1/endothelial nitric oxide synthase, and ERKs. The sustained activation of these signaling pathways was essential for enhanced migration of retinal EC under high-glucose conditions. Together, our results indicate the exposure of retinal EC to high glucose promotes a promigratory phenotype. Thus alterations in the proangiogenic properties of retinal EC during diabetes may contribute to the development and pathogenesis of diabetic retinopathy.

The deleterious effect of high concentrations of D-glucose requires pro-inflammatory preconditioning

OBJECTIVES

The present study investigated whether high concentrations of D-glucose can trigger pro-inflammatory mechanisms in human aortic smooth muscle cells.

METHODS

The expression and/or the activity of inducible nitric oxide synthase (iNOS), the extracellular signal-regulated kinase (ERK) 1/2 and nuclear factor (NF)-kappaB were studied in cultured human aortic smooth muscle cells (HASMC) in response to increasing concentrations of D-glucose and/or the inflammatory cytokine interleukin (IL)-1beta.

RESULTS

Increasing D-glucose in the medium from 5.5 to 22 mmol/l had no effect on any of these parameters. However, the high concentration of D-glucose did increase iNOS expression in response to low concentrations of IL-1beta (2.5 and 5 ng/ml), as well as the IL-1beta-induced activation of both ERK 1/2 and NF-kappaB. D-glucose also enhanced, concentration-dependently, the expression and activity of iNOS induced by co-incubation with IL-1beta (10 ng/ml). Pretreatment with IL-1beta sensitized the cells to the subsequent effects of high D-glucose.

CONCLUSIONS

The results indicate that high concentrations of D-glucose exacerbate the pro-inflammatory effects of IL-1beta. We suggest that the observed association between inflammation and diabetes is the result of elevated D-glucose enhancing a pre-existing inflammatory condition, rather than a direct effect of D-glucose on the production of inflammatory mediators.

Cellular signaling and potential new treatment targets in diabetic retinopathy

Dysfunction and death of microvascular cells and imbalance between the production and the degradation of extracellular matrix (ECM) proteins are a characteristic feature of diabetic retinopathy (DR). Glucose-induced biochemical alterations in the vascular endothelial cells may activate a cascade of signaling pathways leading to increased production of ECM proteins and cellular dysfunction/death. Chronic diabetes leads to the activation of a number of signaling proteins including protein kinase C, protein kinase B, and mitogen-activated protein kinases. These signaling cascades are activated in response to hyperglycemia-induced oxidative stress, polyol pathway, and advanced glycation end product formation among others. The aberrant signaling pathways ultimately lead to activation of transcription factors such as nuclear factor-κB and activating protein-1. The activity of these transcription factors is also regulated by epigenetic mechanisms through transcriptional coactivator p300. These complex signaling pathways may be involved in glucose-induced alterations of endothelial cell phenotype leading to the production of increased ECM proteins and vasoactive effector molecules causing functional and structural changes in the microvasculature. Understanding of such mechanistic pathways will help to develop future adjuvant therapies for diabetic retinopathy.

Vitamin C promotes human endothelial cell growth via the ERK-signaling pathway

BACKGROUND

Epidemiological, secondary prevention and small interventional trials suggest a preventive role of vitamin C for cardiovascular diseases (CAD), especially through improving endothelial dysfunction. Large primary prevention trials failed to confirm this. Mechanistic studies may contribute to resolve this discrepancy.

AIM OF THE STUDY

We examined whether vitamin C activates mitogen-activated protein kinases (MAPK) in human umbilical cord venous endothelial cells (HUVECs) and whether reactive oxygen species (ROS) play a role in this process.

METHODS

Subconfluent quiescent HUVECs were incubated with vitamin C alone or in combination with catalase (CAT) and/or hydrogenperoxide (H2O2). Intracellular MAPK were determined by Western blot, proliferation by cell count and DNA-synthesis by [3H]-thymidine-uptake.

RESULTS

HUVECs were incubated with vitamin C (60 microM) for 5-60 min or for 20 min (30-90 microM). A dose-dependent phosphorylation of extracellular signal-regulated-kinases (ERKs)-1 and -2 with a maximum of phosphorylation at 15-20 min was observed and inhibitable by MEK1/2-inhibitor U0126 (5-10 microM). Vitamin C (60 microM) stimulated phosphorylation of ERK5, but not of p38 and c-Jun, demonstrating a different MAPK-activation pattern compared to H2O2. Vitamin C (60 microM) induced proliferation and a dose-dependent [3H]-thymidine-uptake (30-120 microM) within 20 h. CAT (0.3 U/ml) did neither suppress the vitamin C induced [3H]-thymidine-uptake nor ERK1/2-phosphorylation. CAT (0.3 U/ml), but not vitamin C (60 microM) abrogated the inhibitory effects of H2O2 (100 microM) on [3H]-thymidine-uptake.

CONCLUSION

Physiological vitamin C-concentrations promote proliferation of subconfluent ECs by activating an ERK1/2 controlled pathway. Targeting MAPK by vitamin C may improve, besides antioxidant mechanisms, endothelial dysfunction by promoting a fast regeneration of the endothelium after tissue injury, particularly required during secondary prevention and early development.

Effects of Edaravone in Heart of Aged Rats after Cerebral Ischemia-Reperfusion Injury

Edaravone (3-methyl-1-phenyl-2-pyrazolin-5-one) has potent effects in the brain as a free radical scavenger in ischemia-reperfusion (IR) injuries. However, whether this free radical scavenger can prevent myocardial injury after cerebral IR is not clear. The aim of the present study was to investigate the effect of edaravone against oxidative damage in brain-to-heart signaling triggered by IR injury and its possible mechanism. In this study, the expression of glutathione peroxidase (GSHPx) and protein carbonyl content was examined to evaluate oxidative stress. The activation of mitogen-activated protein kinases (MAPKs) was also examined. Terminal deoxynucleotidyl transferase nick-end labeling (TUNEL) analysis was performed to estimate cardiomyocytes cell death. After edaravone treatment there was a mild increase in activities of GSHPx in cardiomyocytes; however, there was a decrease in protein carbonyl content. p38 MAPK activity was inhibited by edaravone treatment in comparison with the vehicle group in myocardium. These results were further complemented by a significant reduction of TUNEL-positive cells in the heart sections. Our results demonstrate that edaravone provides ameliorative effects in the myocardium after cerebral IR injury by differentially modulating MAPK's activity, thus reducing the oxidative stress state.

Prediction of postprandial glycemic exposure: utility of fasting and 2-h glucose measurements alone and in combination with assessment of body composition, fitness, and strength

OBJECTIVE

To determine the best predictors of total postprandial glycemic exposure and peak glucose concentrations in nondiabetic humans.

RESEARCH DESIGN AND METHODS

Data from 203 nondiabetic volunteers who ingested a carbohydrate-containing mixed meal were analyzed.

RESULTS

Fasting glucose and insulin concentrations were poor predictors of postprandial glucose area above basal (R2 = approximately 0.07, P < 0.001). The correlation was stronger for 2-h glucose concentration (R2 = 0.55, P < 0.001) and improved slightly but significantly (P < 0.001) with the addition of fasting glucose, insulin, age, sex, and body weight to the model (r2 = 0.58). The 2-h glucose concentration also predicted the peak glucose concentration (R2 = 0.37, P < 0.001) with strength of the prediction increasing (P < 0.001) modestly with the addition of fasting glucose, insulin, age, sex, and body weight to the model (R2 = 0.48, P < 0.001). On the other hand, addition of measures of body function and composition did not improve prediction of total glycemic exposure or peak glucose concentration.

CONCLUSIONS

Isolated measures of fasting or 2-h glucose concentrations alone or in combination with more complex measures of body composition and function are poor predictors of postprandial glycemic exposure or peak glucose concentration. This may explain, at least in part, the weak and at times inconsistent relationship between these parameters and cardiovascular risk.

Hyperglycemia alters PI3k and Akt signaling and leads to endothelial cell proliferative dysfunction

Diabetes mellitus is a major risk factor for the development of vascular complications. We hypothesized that hyperglycemia decreases endothelial cell (EC) proliferation and survival via phosphatidylinositol 3-kinase (PI3k) and Akt signaling pathways. We cultured human umbilical vein ECs (HUVEC) in 5, 20, or 40 mM d-glucose. Cells grown in 5, 20, and 40 mM mannitol served as a control for osmotic effects. We measured EC proliferation for up to 15 days. We assessed apoptosis by annexin V and propidium iodide staining and flow cytometry, analyzed cell lysates obtained on culture day 8 for total and phosphorylated PI3k and Akt by Western blot analysis, and measured Akt kinase activity using a GSK fusion protein. HUVEC proliferation was also tested in the presence of pharmacological inhibitors of PI3k-Akt (wortmannin and LY294002) and after transfection with a constitutively active Akt mutant. ECs in media containing 5 mM d-glucose (control) exhibited log-phase growth on days 7-10. d-Glucose at 20 and 40 mM significantly decreased proliferation versus control (P < 0.05 for both), whereas mannitol did not impair EC proliferation. Apoptosis increased significantly in HUVEC exposed to 40 mM d-glucose. d-Glucose at 40 mM significantly decreased tyrosine-phosphorylated PI3k, threonine 308-phosphorylated-Akt, and Akt activity relative to control 5 mM d-glucose. Pharmacological inhibition of PI3k-Akt resulted in a dose-dependent decrease in EC proliferation. Transfection with a constitutively active Akt mutant protected ECs by enhancing proliferation when grown in 20 and 40 mM d-glucose. We conclude that d-glucose regulates Akt signaling through threonine phosphorylation of Akt and that hyperglycemia-impaired PI3k-Akt signaling may promote EC proliferative dysfunction in diabetes.

Reduced insulin and IGF-I signaling, not hyperglycemia, underlies the diabetes-associated depletion of interstitial cells of Cajal in the murine stomach

Damage to interstitial cells of Cajal (ICC), pacemakers, and mediators of neuromuscular neurotransmission in the gastrointestinal tract contributes to the pathogenesis of diabetic gastroenteropathy in both patients and animal models. ICC depletion in diabetes may result from chronic hyperglycemia or lost/ineffective insulin signaling. Because independent control of insulin and glucose concentrations is difficult in chronic in vivo studies, we used long-term organotypic cultures to address this problem. Murine gastric muscles were cultured in normoglycemic or hyperglycemic basal media with or without insulin or IGF-I for 1-3 months, the time required for gastroparesis and ICC damage to develop in diabetic mice. ICC were assessed by c-Kit immunohistochemistry and quantitative analysis of c-kit expression. Electrical pacemaking was studied by intracellular recording of slow waves. ICC survived for at least 34 days in unsupplemented normoglycemic media, but their networks, c-kit expression, and slow waves were profoundly reduced after 68 days. These changes could be entirely prevented by insulin or IGF-I supplementation. ICC networks were completely resistant to hyperglycemia for at least 72 days. Thus, hyperglycemia is unlikely to be responsible for the diabetes-associated depletion of ICC. In contrast, maintenance of ICC requires insulin or IGF-I, which are reduced or ineffective in diabetes.

The interaction between HIF-1 and AP-1 transcription factors in response to low oxygen

Hypoxia-inducible factor-1 (HIF-1) is a critical regulator of the transcriptional response to low oxygen conditions (hypoxia/anoxia) experienced by mammalian cells in both physiological and pathophysiological circumstances. As our understanding of the biology and biochemistry of HIF-1 has grown, it has become apparent that cells adapt to signals generated by low oxygen through a network of stress responsive transcription factors or complexes, which are influenced by HIF-1 activity. This review summarizes our current understanding of the interaction of HIF-1 with AP-1, a classic example of a family of pleiotropic transcription factors that impact on diverse cellular processes and phenotypes, including the adaptation to low oxygen stress. The review focuses on experimental studies involving cultured cells exposed to hypoxia/anoxia, and describes both established and possible interactions between HIF-1 and AP-1 at different levels of cellular organization.

Protective effects of a free radical scavenger, MCI-186, on high-glucose-induced dysfunction of human dermal microvascular endothelial cells

Functional damage to microvascular endothelial cells by hyperglycemia is thought to be one of the critical risk factors in the impaired wound healing seen with diabetes mellitus. It is also thought that free radical stress plays a significant role in this endothelial cell dysfunction. In the present study, the effect of a free radical scavenger, MCI 186, on the endothelial cell dysfunction of cultured cells induced by high-glucose conditions was studied. Human dermal microvascular endothelial cells were cultured with high-glucose medium (50 mM) with or without MCI-186 (10 microM) for 7 days. Fifty mM mannitol was used as an osmotic control in this study. After this treatment, cell proliferation, activation of mitogen-activated protein kinase (MAPK), the level of apoptosis, and caspase-3 activation induced by removal of growth factors or tumor necrosis factor-alpha treatment were studied. High-glucose conditions significantly decreased cell proliferation and increased apoptosis levels with the activation of caspase-3 induced by growth factor removal. The high-glucose condition significantly activated MAPK. MCI-186 treatment improved cellular proliferation and reduced apoptosis and caspase-3 activation induced by high-glucose conditions. MCI-186 also inhibited the activation of MAPK. On the other hand, MCI-186 did not alter the level of apoptosis and caspase-3 activation induced by TNF-alpha treatment. In conclusion, we suggest that MCI-186 may be beneficial for improving the endothelial cell dysfunction induced by hyperglycemia.

Cytosolic NADH redox and thiol oxidation regulate pulmonary arterial force through ERK MAP kinase

An ERK MAP kinase-mediated contractile mechanism previously reported to be activated by peroxide and stretch in bovine coronary arteries is shown in this study to be present in endothelium-denuded bovine pulmonary arteries and subject to regulation by modulation of cytosolic NAD(H) redox through the lactate dehydrogenase reaction. Although our previous work identified an acute PO2-dependent peroxide-mediated relaxation of bovine pulmonary arteries on exposure to lactate, a 30-min treatment with 10 mM lactate enhanced ERK phosphorylation and increased force generation to 30 mM KCl. Hypoxia inhibited these responses to lactate. Increases in ERK phosphorylation and the enhancement of force generation by lactate and stretch are attenuated in the presence of inhibitors of Nox oxidase (0.1 mM apocynin) or ERK activation (10 microM PD-98059) and by 0.1 mM ebselen. Additionally, incubation of pulmonary arteries with 10 mM pyruvate lowered basal levels of ERK phosphorylation, and it inhibited both the ERK phosphorylation and the enhancement in force generation to 30 mM KCl caused by stretch. Treatment of pulmonary arteries with the thiol oxidant diamide (1 microM) elicited what appears to be a peroxide-independent increase in force and ERK phosphorylation that were both attenuated by PD-98059. Thus pulmonary arteries possess a peroxide-elicited contractile mechanism involving ERK MAP kinase, which is stimulated by stretch and regulated through the control of Nox oxidase activity by the availability of cytosolic NADH.

High expression of PKC-MAPK pathway mRNAs correlates with glomerular lesions in human diabetic nephropathy

BACKGROUND

Activation of protein kinase C (PKC) is a major signaling pathway for transforming growth factor (TGF)-beta to induce extracellular matrix (ECM) production in diabetic nephropathy (DN). PKC also activates mitogen-activated protein kinase (MAPK), which is called the PKC-MAPK pathway. The PKC-MAPK pathway is probably responsible for PKC-related abnormalities in diabetic glomeruli. To confirm the involvement of this pathway, we determined the localization and expression of mRNAs in glomeruli by in situ hybridization method.

METHODS

In the present study, we examined expression of PKCbeta1, MAPK/ERK kinase (MEK) 1, MEK2, extracellular signal-regulated protein kinase (ERK) 1, ERK2, and TGF-beta1 mRNAs using renal tissue samples from kidneys affected by DN (N= 21) and from normal human kidney (NHK; N= 6). We also performed an immunohistochemical study using anti-phosphorylated MEK1/2 (P-MEK) and ERK1/2 (P-ERK) antibodies. The glomerular severity of DN was classified into three groups according to mesangial expansion: D1 (N= 4), D2 (N= 13), and D3 (N= 4). We analyzed differences and correlations between variables.

RESULTS

In the glomeruli, the number of cells that stained for these mRNAs in DN was significantly higher than in NHK. The expression of PKC-MAPK pathway mRNAs tended to be inversely proportional to the degree of mesangial expansion. The P-MEK and P-ERK signal intensity were parallel to its mRNA expression pattern. Furthermore, there were significant correlations among the P-MEK, P-ERK signal intensity, PKCbeta1 mRNA expression.

CONCLUSION

Our results suggest that high expression of PKC-MAPK pathway mRNAs plays an important role in the development and/or progression of early tissue damage in DN.

Glucose-Potentiated Chemotaxis in Human Vascular Smooth Muscle Is Dependent on Cross-Talk Between the PI3K and MAPK Signaling Pathways

Atheroma formation involves the movement of vascular smooth muscle cells (VSMC) into the subendothelial space. The aim of this study was to determine the involvement of PI3K and MAPK pathways and the importance of cross-talk between these pathways, in glucose-potentiated VSMC chemotaxis to serum factors. VSMC chemotaxis occurred in a serum gradient in 25 mmol/L glucose (but not in 5 mmol/L glucose) in association with increased phosphorylation (activation) of Akt and ERK1/2 in PI3K and MAPK pathways, respectively. Inhibitors of these pathways blocked chemotaxis, as did an mTOR inhibitor. VSMC expressed all class IA PI3K isoforms, but microinjection experiments demonstrated that only the p110β isoform was involved in chemotaxis. ERK1/2 phosphorylation was reduced not only by MAPK pathway inhibitors but also by PI3K and mTOR inhibitors; when PI3K was inhibited, ERK phosphorylation could be induced by microinjected activated Akt, indicating important cross-talk between the PI3K and ERK1/2 pathways. Glucose-potentiated phosphorylation of molecules in the p38 and JNK MAPK pathways inhibited these pathways but did not affect chemotaxis. The statin, mevinolin, blocked chemotaxis through its effects on the MAPK pathway. Mevinolin-inhibited chemotaxis was restored by farnesylpyrophosphate but not by geranylgeranylpyrophosphate; in the absence of mevinolin, inhibition of farnesyltransferase reduced ERK phosphorylation and blocked chemotaxis, indicating a role for the Ras family of GTPases (MAPK pathway) under these conditions. In conclusion, glucose sensitizes VSMC to serum, inducing chemotaxis via pathways involving p110β-PI3K, Akt, mTOR, and ERK1/2 MAPK. Cross-talk between the PI3K and MAPK pathways is necessary for VSMC chemotaxis under these conditions.

Dominant negative 14-3-3 promotes cardiomyocyte apoptosis in early stage of type I diabetes mellitus through activation of JNK

14-3-3 family members are dimeric, phosphoserine binding proteins that regulate signal transduction, apoptotic, and checkpoint control pathways. Recently, cardiomyocyte apoptosis has been characterized in type I diabetes mellitus. In order to study the molecular mechanism underlying diabetes-induced cardiomyocyte apoptosis, we examined the role of 14-3-3 protein and MAPK pathways in transgenic mice with cardiac specific expression of dominant negative 14-3-3eta (DN-14-3-3). p38 MAPK was highly activated 1, 28, and 56 days after diabetes induction by streptozotocin, whereas peak JNK activation was found on day 3 and decreased afterwards. In contrast, ERK1/2 were not activated in diabetic myocardium. Cardiomyocyte apoptosis was peaked on day 3 and decreased on 7, 28, and 56 days. p38 MAPK and JNK activation as well as cardiomyocyte apoptosis were greatly increased in DN-14-3-3 mice relative to non-transgenic mice. Moreover, we found a significant correlation between JNK activation and apoptosis in diabetic myocardium. These results indicate for the first time that 14-3-3 protein plays a critical anti-apoptotic role in diabetic myocardium by inhibiting the JNK pathway.

Direct effects of high glucose and insulin on protein synthesis in cultured cardiac myocytes and DNA and collagen synthesis in cardiac fibroblasts

The present study examined the direct effects of high glucose and insulin on protein synthesis in cardiac myocytes and DNA and collagen synthesis in cardiac fibroblasts. Cultured rat cardiac myocytes and fibroblasts were grown in media containing normal glucose, high glucose, or osmotic control, and incubated with or without insulin. In cardiac myocytes, high glucose had no effect, but insulin increased protein synthesis and atrial natriuretic peptide (ANP) secretion and gene expression. The extracellular signal-regulated protein kinase (ERK)/mitogen-activated protein kinase (MAPK) inhibitor and the protein kinase C (PKC) inhibitor blocked insulin-induced protein synthesis. In cardiac fibroblasts, high glucose and osmotic control media increased DNA synthesis. Collagen synthesis and fibronectin and transforming growth factor-beta1 (TGF-beta1) mRNA expression were stimulated by high glucose, but not by osmotic control. Insulin increased DNA and collagen synthesis in fibroblasts, and the insulin-induced increase in DNA synthesis was blocked by the phosphatidylinositol 3 kinase (PI3K) inhibitor. Our findings suggest that cardiomyocyte protein synthesis is mainly regulated by insulin rather than high glucose and both high glucose and insulin contribute to fibroblast DNA and collagen synthesis. High glucose accelerates fibroblast DNA synthesis and collagen synthesis, and fibronectin and TGF-beta1 mRNA expression, dependent or independent of osmotic stress. Insulin regulates myocyte protein synthesis and fibroblast DNA synthesis through different intracellular mechanisms.

Activation of the hexosamine pathway leads to phosphorylation of insulin receptor substrate-1 on Ser307 and Ser612 and impairs the phosphatidylinositol 3-kinase/Akt/mammalian target of rapamycin insulin biosynthetic pathway in RIN pancreatic beta-cells

Many adverse effects of glucose were attributed to its increased routing through the hexosamine pathway (HBP). There is evidence for an autocrine role of the insulin signaling in beta-cell function. We tested the hypothesis that activation of the HBP induces defects in insulin biosynthesis by affecting the insulin-mediated protein translation signaling. Exposure of human pancreatic islets and RIN beta-cells to glucosamine resulted in reduction in glucose- and insulin-stimulated insulin biosynthesis, which in RIN beta-cells was associated with impairment in insulin-stimulated insulin receptor substrate-1 (IRS-1) phosphorylation at Tyr(608) and Tyr(628), which are essential for engaging phosphatidylinositol 3-kinase (PI 3-kinase). These changes were accompanied by impaired activation of PI 3-kinase, and activation of Akt/mammalian target of rapamycin/phosphorylated heat- and acid-stable protein-1/p70S6 kinase pathway. RIN beta-cells exposed to high glucose exhibited increased c-Jun N-terminal kinase (JNK) and ERK1/2 activity, which was associated with increased IRS-1 phosphorylation at serine (Ser)(307) and Ser(612), respectively, that inhibits coupling of IRS-1 to the insulin receptor and is upstream of the inhibition of IRS-1 tyrosine phosphorylation. Azaserine reverted the stimulatory effects of high glucose on JNK and ERK1/2 activity and IRS-1 phosphorylation at Ser(307) and Ser(612). Glucosamine mimicked the stimulatory effects of high glucose on JNK and ERK1/2 activity and IRS-1 phosphorylation at Ser(307) and Ser(612). Inhibition of JNK and MAPK kinase-1 activity reverted the negative effects of glucosamine on insulin-mediated protein synthesis. These results suggest that activation of the HBP accounts, in part, for glucose-induced phosphorylation at Ser(307) and Ser(612) of IRS-1 mediated by JNK and ERK1/2, respectively. These changes result in impaired coupling of IRS-1 and PI 3-kinase, and activation of the Akt/mammalian target of rapamycin/phosphorylated heat- and acid-stable protein-1/p70S6 kinase pathway.

BMK1 is activated in glomeruli of diabetic rats and in mesangial cells by high glucose conditions

BACKGROUND

High glucose causes renal cell injury through various signal transduction pathways, including mitogen-activated protein (MAP) kinases cascades. Big MAP kinase 1 (BMK1), also known as extracellular signal-regulated kinase 5 (ERK5), is a recently identified MAP kinase family member and was reported to be sensitive to osmotic and oxidative stress. However, the role of BMK1 in diabetic nephropathy has not been elucidated yet.

METHODS

We investigated whether BMK1 is activated in the glomeruli of Otsuka Long Evans Tokushima Fatty (OLETF) rats, a model of type 2 diabetes mellitus in comparison with the control Long Evans Tokushima Otsuka (LETO) rats. We also examined the effect of high glucose on BMK1 activity in cultured rat mesangial cells.

RESULTS

BMK1 and ERK1/2 but not p38 were activated in the glomeruli of OLETF rats, which showed diabetic nephropathy at 52 weeks of age. High glucose, in addition to a high concentration of raffinose, caused rapid and significant activation of BMK1 in rat mesangial cells. MAP kinase/ERK kinase (MEK) inhibitors, U0126 and PD98059, both inhibited BMK1 activation by high glucose in a concentration-dependent manner. Protein kinase C (PKC) inhibition by GF109203X and PKC down-regulation with long-time phorbol myristate acetate (PMA) treatment both inhibited BMK1 and Src kinase activation. Src kinase inhibitors, herbimycin A and PP2, also inhibited high glucose-induced BMK1 activation. PKC inhibitors, Src inhibitors and MEK inhibitors, all inhibited cell proliferation by high glucose. Finally, transfection of dominant-negative MEK5, which is an upstream regulator of BMK1, abolished the BMK1-mediated rat mesangial cell proliferation stimulated by high glucose.

CONCLUSION

In the present study, we demonstrated that high glucose activates BMK1 both in vivo and in vitro. It was suggested that high glucose induces PKC- and c-Src-dependent BMK1 activation. It could not be denied that BMK1 activation is induced through an osmotic stress-sensitive mechanism. BMK1-mediated mesangial cell growth may be involved in the pathogenesis of diabetic nephropathy.

High glucose-mediated effects on endothelial cell proliferation occur via p38 MAP kinase

The mitogen-activated protein (MAP) kinases contribute to altered cell growth and function in a variety of disease states. However, their role in the endothelial complications of diabetes mellitus remains unclear. Human endothelial cells were exposed for 72 h to 5 mM (control) or 25 mM (high) glucose or 5 mM glucose plus 20 mM mannitol (osmotic control). The roles of p38 and p42/44 MAP kinases in the high glucose-induced growth effects were determined by assessment of phosphorylated MAP kinases and their downstream activators by Western blot and by pharmacological inhibition of these MAP kinases. Results were expressed as a percentage (means +/- SE) of control. High glucose increased the activity of total and phosphorylated p38 MAP kinase (P < 0.001) and p42/44 MAP kinase (P < 0.001). Coexposure of p38 MAP kinase blocker with high glucose reversed the antiproliferative but not the hypertrophic effects associated with high-glucose conditions. Transforming growth factor (TGF)-beta1 increased the levels of phosphorylated p38 MAP kinase, and p38 MAP kinase blockade reversed the antiproliferative effects of this cytokine. The high glucose-induced increase in phosphorylated p38 MAP kinase was reversed in the presence of TGF-beta1 neutralizing antibody. Although hyperosmolarity also induced antiproliferation (P < 0.0001) and cell hypertrophy (P < 0.05), there was no change in p38 activity, and therefore inhibition of p38 MAP kinase had no influence on these growth responses. Blockade of p42/44 MAP kinase had no effect on the changes in endothelial cell growth induced by either high glucose or hyperosmolarity. High glucose increased p42/44 and p38 MAP kinase activity in human endothelial cells, but only p38 MAP kinase mediated the antiproliferative growth response through the effects of autocrine TGF-beta1. High glucose-induced endothelial cell hypertrophy was independent of activation of the MAP kinases studied. In addition, these effects were independent of any increase in osmolarity associated with high-glucose exposure.

Regulation of amino acid and glucose transporters in endothelial and smooth muscle cells

While transport processes for amino acids and glucose have long been known to be expressed in the luminal and abluminal membranes of the endothelium comprising the blood-brain and blood-retinal barriers, it is only within the last decades that endothelial and smooth muscle cells derived from peripheral vascular beds have been recognized to rapidly transport and metabolize these nutrients. This review focuses principally on the mechanisms regulating amino acid and glucose transporters in vascular endothelial cells, although we also summarize recent advances in the understanding of the mechanisms controlling membrane transport activity and expression in vascular smooth muscle cells. We compare the specificity, ionic dependence, and kinetic properties of amino acid and glucose transport systems identified in endothelial cells derived from cerebral, retinal, and peripheral vascular beds and review the regulation of transport by vasoactive agonists, nitric oxide (NO), substrate deprivation, hypoxia, hyperglycemia, diabetes, insulin, steroid hormones, and development. In view of the importance of NO as a modulator of vascular tone under basal conditions and in disease and chronic inflammation, we critically review the evidence that transport of L-arginine and glucose in endothelial and smooth muscle cells is modulated by bacterial endotoxin, proinflammatory cytokines, and atherogenic lipids. The recent colocalization of the cationic amino acid transporter CAT-1 (system y(+)), nitric oxide synthase (eNOS), and caveolin-1 in endothelial plasmalemmal caveolae provides a novel mechanism for the regulation of NO production by L-arginine delivery and circulating hormones such insulin and 17beta-estradiol.

Hyperglycemia reduces nitric oxide synthase and glycogen synthase activity in endothelial cells

Hyperglycemia is considered a primary cause of diabetic vascular complications. A hallmark of vascular disease is endothelial cell dysfunction characterized by diminished nitric-oxide (NO)-dependent phenomena such as vasodilation, angiogenesis, and vascular maintenance. This study was designed to investigate the effects of a high level of D-glucose on endothelial NO response, oxidative stress, and glucose metabolism. Bovine aortic endothelial cells (BAECs) were pretreated with a high concentration of glucose (HG) (22 mmol/L) for at least 2 weeks and compared with control cells exposed to 5 mmol/L glucose (NG). The effect of chronic hyperglycemia on endothelial NO-synthase (eNOS) activity and expression, glycogen synthase (GS) activity, extracellular-signal-regulated kinase (ERK 1,2), p38, Akt expression, and Cu/Zn superoxide-dismutse (SOD-1) activity and expression were determined. Western blot analysis showed that eNOS protein expression decreased in HG cells and was accompanied by diminished eNOS activity. The activity of GS was also significantly lower in the HG cells than in NG cells, 25.0+/-17.4 and 89+/-22.5 nmol UDP-glucose.mg protein(-1)x min(-1), respectively. Western blot analysis revealed a 40-60% decrease in ERK 1,2 and p38 protein levels, small modification of phosphorylated Akt expression, and a 30% increase in SOD-1 protein expression in HG cells. Although SOD expression was increased, no change was observed in SOD activity. These results support the findings that vascular dysfunction due to exposure to pathologically high D-glucose concentrations may be caused by impairment of the NO pathway and increased oxidative stress accompanied by altered glucose metabolism.

Glutamine and its relationship with intracellular redox status, oxidative stress and cell proliferation/death

Glutamine is a multifaceted amino acid used for hepatic urea synthesis, renal ammoniagenesis, gluconeogenesis in both liver and kidney, and as a major respiratory fuel for many cells. Decreased glutamine concentrations are found during catabolic stress and are related to susceptibility to infections. Besides, glutamine is not only an important energy source in mitochondria, but is also a precursor of the brain neurotransmitter glutamate, which is likewise used for biosynthesis of the cellular antioxidant glutathione. Reactive oxygen species, such as superoxide anions and hydrogen peroxide, function as intracellular second messengers activating, among others, apoptosis, whereas glutamine is an apoptosis suppressor. In fact, it could contribute to block apoptosis induced by exogenous agents or by intracellular stimuli. In conclusion, this article shows evidences for the important role of glutamine in the regulation of the cellular redox balance, including brain oxidative metabolism, apoptosis and tumour cell proliferation.

Hyperglycemia activates p53 and p53-regulated genes leading to myocyte cell death

To determine whether enzymatic p53 glycosylation leads to angiotensin II formation followed by p53 phosphorylation, prolonged activation of the renin-angiotensin system, and apoptosis, ventricular myocytes were exposed to levels of glucose mimicking diabetic hyperglycemia. At a high glucose concentration, O-glycosylation of p53 occurred between 10 and 20 min, reached its peak at 1 h, and then decreased with time. Angiotensin II synthesis increased at 45 min and 1 h, resulting in p38 mitogen-activated protein (MAP) kinase-driven p53 phosphorylation at Ser 390. p53 phosphorylation was absent at the early time points, becoming evident at 1 h, and increasing progressively from 3 h to 4 days. Phosphorylated p53 at Ser 18 and activated c-Jun NH(2)-terminal kinases were identified with hyperglycemia, whereas extracellular signal-regulated kinase was not phosphorylated. Upregulation of p53 was associated with an accumulation of angiotensinogen and AT(1) and enhanced production of angiotensin II. Bax quantity also increased. These multiple adaptations paralleled the concentrations of glucose in the medium and the duration of the culture. Myocyte death by apoptosis directly correlated with glucose and angiotensin II levels. Inhibition of O-glycosylation prevented the initial synthesis of angiotensin II, p53, and p38-MAP kinase (MAPK) phosphorylation and apoptosis. AT(1) blockade had no influence on O-glycosylation of p53, but it interfered with p53 phosphorylation; losartan also prevented phosphorylation of p38-MAPK by angiotensin II. Inhibition of p38-MAPK mimicked at a more distal level the consequences of losartan. In conclusion, these in vitro results support the notion that hyperglycemia with diabetes promotes myocyte apoptosis mediated by activation of p53 and effector responses involving the local renin-angiotensin system.