Platelet-derived growth factor activates production of reactive oxygen species by NAD(P)H oxidase in smooth muscle cells through Gi1,2

NLRP3 inflammasome activation contributes to the development of the pro-fibrotic phenotype of lung fibroblasts

Idiopathic pulmonary fibrosis (IPF) is an irreversible progressive interstitial lung disease of unknown cause. The poorly understood pathophysiology of IPF poses substantial challenges to the development of effective anti-lung fibrotic drugs. The NLRP3 inflammasome, a key component of the innate immune system, has recently been linked to the pathogenesis of lung fibrosis. However, the specific contributions of NLRP3 inflammasomes to determination of the pro-fibrotic phenotype of lung fibroblasts, which play a central role in the production of extracellular matrix protein, remain to be investigated. Therefore, the present study was performed to elucidate the involvement of NLRP3 inflammasome signalling pathways in modulation of lung fibroblast proliferation and differentiation. We found that activation of NLRP3 inflammasomes increased in lung fibroblasts derived from individuals with pulmonary fibrosis and in normal lung fibroblasts stimulated with transforming growth factor β and platelet-derived growth factor. Importantly, blockage of NLRP3 inflammasome signalling, either by gene silencing of NLRP3 or using pharmacological inhibitors of NLRP3, caspase-1, or IL-1 receptor, inhibited the proliferation, differentiation, and extracellular matrix protein synthesis of activated lung fibroblasts. Moreover, induction of the reactive oxygen species/thioredoxin-interacting protein axis, an upstream signalling pathway of NLRP3 inflammasomes, was essential for maintenance of the pro-fibrotic phenotype of lung fibroblasts. Interestingly, treatments with pharmacological inhibitors of NLRP3 inflammasomes prevented the progression of bleomycin-induced pulmonary fibrosis in mice. Collectively, these findings suggest that aberrant activation of NLRP3 inflammasomes is a critical event in the pathogenesis of IPF and that targeting NLRP3 inflammasomes may serve as a therapeutic strategy for IPF.

Redox-Mediated Rewiring of Signalling Pathways: The Role of a Cellular Clock in Brain Health and Disease

Metazoan signalling pathways can be rewired to dampen or amplify the rate of events, such as those that occur in development and aging. Given that a linear network topology restricts the capacity to rewire signalling pathways, such scalability of the pace of biological events suggests the existence of programmable non-linear elements in the underlying signalling pathways. Here, we review the network topology of key signalling pathways with a focus on redox-sensitive proteins, including PTEN and Ras GTPase, that reshape the connectivity profile of signalling pathways in response to an altered redox state. While this network-level impact of redox is achieved by the modulation of individual redox-sensitive proteins, it is the population by these proteins of critical nodes in a network topology of signal transduction pathways that amplifies the impact of redox-mediated reprogramming. We propose that redox-mediated rewiring is essential to regulate the rate of transmission of biological signals, giving rise to a programmable cellular clock that orchestrates the pace of biological phenomena such as development and aging. We further review the evidence that an aberrant redox-mediated modulation of output of the cellular clock contributes to the emergence of pathological conditions affecting the human brain.

Polyphenol Supplementation and Antioxidant Status in Athletes: A Narrative Review

Antioxidants in sports exercise training remain a debated research topic. Plant-derived polyphenol supplements are frequently used by athletes to reduce the negative effects of exercise-induced oxidative stress, accelerate the recovery of muscular function, and enhance performance. These processes can be efficiently modulated by antioxidant supplementation. The existing literature has failed to provide unequivocal evidence that dietary polyphenols should be promoted specifically among athletes. This narrative review summarizes the current knowledge regarding polyphenols' bioavailability, their role in exercise-induced oxidative stress, antioxidant status, and supplementation strategies in athletes. Overall, we draw attention to the paucity of available evidence suggesting that most antioxidant substances are beneficial to athletes. Additional research is necessary to reveal more fully their impact on exercise-induced oxidative stress and athletes' antioxidant status, as well as optimal dosing methods.

Chromatin profiling of cortical neurons identifies individual epigenetic signatures in schizophrenia

Both heritability and environment contribute to risk for schizophrenia. However, the molecular mechanisms of interactions between genetic and non-genetic factors remain unclear. Epigenetic regulation of neuronal genome may be a presumable mechanism in pathogenesis of schizophrenia. Here, we performed analysis of open chromatin landscape of gene promoters in prefrontal cortical (PFC) neurons from schizophrenic patients. We cataloged cell-type-based epigenetic signals of transcriptional start sites (TSS) marked by histone H3-K4 trimethylation (H3K4me3) across the genome in PFC from multiple schizophrenia subjects and age-matched control individuals. One of the top-ranked chromatin alterations was found in the major histocompatibility (MHC) locus on chromosome 6 highlighting the overlap between genetic and epigenetic risk factors in schizophrenia. The chromosome conformation capture (3C) analysis in human brain cells revealed the architecture of multipoint chromatin interactions between the schizophrenia-associated genetic and epigenetic polymorphic sites and distantly located HLA-DRB5 and BTNL2 genes. In addition, schizophrenia-specific chromatin modifications in neurons were particularly prominent for non-coding RNA genes, including an uncharacterized LINC01115 gene and recently identified BNRNA_052780. Notably, protein-coding genes with altered epigenetic state in schizophrenia are enriched for oxidative stress and cell motility pathways. Our results imply the rare individual epigenetic alterations in brain neurons are involved in the pathogenesis of schizophrenia.

Plasma Biomarkers as Potential Predictors of Functional Dependence in Daily Life Activities after Ischemic Stroke: A Single Center Study

Objective:

Despite advances made in the treatment of ischemic stroke, it still remains one of the leading causes of mortality and disability worldwide. The main objective of this study was to identify from a panel of 10 inflammatory markers and chemokines those biomarkers that have a potential predictive role in the evolution of disability and functional dependence in daily activities after an ischemic stroke.

Methods:

The study included 116 patients with ischemic stroke and 40 healthy volunteers matched for gender and age. Stroke severity was assessed by the National Institute of Health Stroke Scale (NIHSS) on admission and during hospitalization and functional mobility in daily activities by Barthel index (BI). Multiplex panel with 10 biomarkers [brain-derived neurotrophic factor (BDNF), platelet-derived growth factor (PDGF)-AA, PDGF-AB/BB, neural cell adhesion molecule (NCAM), cathepsin D, soluble vascular cell adhesion molecule (sVCAM), soluble intercellular cell adhesion molecule (sICAM), myeloperoxidase (MPO), regulated on activation, normal T cell expressed and secreted (RANTES), plasminogen activator inhibitor (PAI)-1] was analyzed on days 1 and 5 after admission using the xMAP technology.

Results:

Plasma concentrations of RANTES and NCAM were significantly lower in patients with ischemic stroke compared with healthy controls, while MPO and sICAM were significantly higher in patients versus controls. Plasma concentrations of sICAM, sVCAM, and RANTES significantly decreased during the analyzed period. For the first-day measurement, the bivariate analysis revealed the association of NIHSS on admission with sVCAM, and on discharge negative association with PDGF-AA, PDGR-AB/BB, BDNF, and RANTES. Plasma levels of PDGF-AA, PDGF-AB/BB, BDNF, and RANTES were found to be significantly lower in patients with BI ≤ 80, on day 5 after disease onset. PDGF-AA, PDGF-AB/BB, and BDNF were univariate and multivariate predictors for functional dependence in daily life activity (BI ≤ 80), having a protective effect (odds ratio < 1).

Conclusion:

Plasma levels of BDNF, PDGF-AA, and PDGF-AB/BB are independent predictors for functional dependency in daily life activities and may be useful prognostic markers in the evaluation of ischemic stroke patients.

Roles of platelet-derived growth factor in vascular calcification

Vascular calcification (VC) is prevalent in aging, and patients with hypertension, chronic kidney disease (CKD), or diabetes. VC is regarded as an active and complex process that involves multiple mechanisms responsible for calcium deposition in vessel wall. In light of the complicated pathogenesis of VC, effective therapy for ameliorating VC is limited. Thus, it is urgent to explore the potential mechanisms and find new targets for the therapy of VC. Platelet-derived growth factor (PDGF), a potent mitogen, and chemoattractant have been found to disturb the vascular homeostasis by inducing inflammation, oxidative stress, and phenotype transition, all of which accelerate the process of VC. The aim of current review is to present a review about the roles of PDGF in affecting VC and to establish a potential target for treating VC.

Phytanic acid activates NADPH oxidase through transactivation of epidermal growth factor receptor in vascular smooth muscle cells

BACKGROUND

Phytanic acid (PA) has been implicated in development of cancer and its defective metabolism is known to cause life-threatening conditions, such as Refsum disease, in children. To explore molecular mechanisms of phytanic acid-induced cellular pathology, we investigated its effect on NADPH oxidase (NOX) and epidermal growth factor receptor (EGFR) in rat aortic smooth muscle cells (RASMC).

METHODS

Smooth muscle cells were isolated from rat aortae using enzymic digestion with collagenase and elastase. Cultured RASMC were treated with varying concentrations (0.5-10 μg/ml) of phytanic acid in the presence/absence of fetal bovine serum (FBS) and/or EGFR inhibitor, AG1478. Following treatment with experimental agents, NOX activity was assayed in RASMC cultures by luminescence method. Gene expression of NOX-1 and p47phox was assessed using RT-PCR. NOX-1, p47phox and, total EGFR protein and its phosphorylated form were measured by Western blotting.

RESULTS

Treatment of RASMC with supraphysiological concentrations (>2.5 μg/ml) of PA significantly (p < 0.01) increased the NOX activity. PA also significantly increased gene/protein expression of NOX-1 and p47phox whereas p22phox and p67phox remained unaffected. Interestingly, PA (2.5-10 μg/ml) markedly (2-3 folds) increased the total and phosphorylated EGFR. Treatment of cells with EGFR inhibitor, AG1478, significantly blocked the PA-induced enhancement of NOX activity.

CONCLUSIONS

Our findings that PA transactivates EGFR and induces NOX activity in vascular smooth muscle cells provide new insights into molecular mechanisms of PA's role in cancer and Refsum disease.

Antioxidant activity of caffeoyl-prolyl-histidine amide and its effects on PDGF-induced proliferation of vascular smooth muscle cells

Caffeic acid (CA) is one of the antioxidants found in plants, which protects vascular cells against vascular injuries from oxidative stress. In our previous study, caffeoyl-prolyl-histidine amide (CA-L-Pro-L-His-NH2; CA-PH; a CA derivative) was synthesized, which exhibited a strong antioxidant activity with sufficient stability. In this study, we investigated the role of CA-PH in vascular smooth muscle cells (VSMCs) and confirmed the enhanced antioxidant activity of CA-PH compared with that of CA. In in vitro tube assays, CA-PH showed a higher free-radical-scavenging activity and lipid-peroxidation-inhibition activity than those of CA. In VSMCs, CA-PH significantly reduced hydrogen peroxide-induced ROS generation and increased the expression of heme oxygenase-1. Moreover, CA-PH effectively inhibited the platelet-derived growth factor-induced cellular proliferation of VSMCs, which was confirmed by a decrease in the expression of the proliferating cell nuclear antigen and the phosphorylation of Akt.

Cyclic stretch stimulates nitric oxide synthase-1-dependent peroxynitrite formation by neonatal rat pulmonary artery smooth muscle

Peroxynitrite, the reaction product of nitric oxide and superoxide, contributes to the pathogenesis of chronic pulmonary hypertension in immature animals by stimulating proliferation of pulmonary arterial smooth muscle cells (PASMCs). Pulmonary vasoconstriction, secondary to hypoxia and other stimuli, leads to enhanced pulsatile stretch of cells in the vascular wall, particularly in smooth muscle, which we hypothesized would cause increased peroxynitrite generation. Our objectives in this study were to determine whether cyclic mechanical stretch, at supraphysiologic levels, would cause increased production of reactive oxygen species (ROS), nitric oxide, and peroxynitrite in vitro. Early passage neonatal rat PASMCs were seeded and grown to subconfluence on collagen-coated elastomer-bottom plates and subjected to cyclic mechanical stretch (10% ("physiologic") or 20% ("supraphysiologic") at 0.5 Hz) for up to 24 h. Compared to nonstretched controls and to cells subjected to 10% stretch, 20% stretch increased H2O2 (stable marker of ROS) and nitrate/nitrite (stable marker of nitric oxide) in conditioned medium. These effects were accompanied by increased peroxynitrite, as evidenced by increased in situ dihydroethidium fluorescence and immunoreactive nitrotyrosine and by increased expression of nitric oxide synthase (NOS)-1 and NADPH oxidase 4 (NOX4), but not NOS-2. Stretch-induced H2O2 release and increased dihydroethidium fluorescence were prevented by pretreatment with a superoxide scavenger, nonspecific inhibitors of NADPH oxidase or NOS, or a peroxynitrite decomposition catalyst. Short-interfering RNA-mediated knockdown of NOS-1 or NOX4 attenuated increased nitric oxide and H2O2 content, respectively, in stretched-cell-conditioned medium. Knockdown of NOS-1 also attenuated increased immunoreactive nitrotyrosine content and stretch-induced proliferation, whereas knockdown of NOS-2 had no effect. We conclude that increased peroxynitrite generation by neonatal rat PASMCs subjected to supraphysiologic levels of cyclic stretch is NOS-1-dependent and that increased ROS production is predominantly mediated by NADPH oxidase, specifically NOX4.

Recruitment of Nox4 to a plasma membrane scaffold is required for localized reactive oxygen species generation and sustained Src activation in response to insulin-like growth factor-I

Nox4-derived ROS is increased in response to hyperglycemia and is required for IGF-I-stimulated Src activation. This study was undertaken to determine the mechanism by which Nox4 mediates sustained Src activation. IGF-I stimulated sustained Src activation, which occurred primarily on the SHPS-1 scaffold protein. In vitro oxidation experiments indicated that Nox4-derived ROS was able to oxidize Src when they are in close proximity, and Src oxidation leads to its activation. Therefore we hypothesized that Nox4 recruitment to the plasma membrane scaffold SHPS-1 allowed localized ROS generation to mediate sustained Src oxidation and activation. To determine the mechanism of Nox4 recruitment, we analyzed the role of Grb2, a component of the SHPS-1 signaling complex. We determined that Nox4 Tyr-491 was phosphorylated after IGF-I stimulation and was responsible for Nox4 binding to the SH2 domain of Grb2. Overexpression of a Nox4 mutant, Y491F, prevented Nox4/Grb2 association. Importantly, it also prevented Nox4 recruitment to SHPS-1. The role of Grb2 was confirmed using a Pyk2 Y881F mutant, which blocked Grb2 recruitment to SHPS-1. Cells expressing this mutant had impaired Nox4 recruitment to SHPS-1. IGF-I-stimulated downstream signaling and biological actions were also significantly impaired in Nox4 Y491F-overexpressing cells. Disruption of Nox4 recruitment to SHPS-1 in aorta from diabetic mice inhibited IGF-I-stimulated Src oxidation and activation as well as cell proliferation. These findings provide insight into the mechanism by which localized Nox4-derived ROS regulates the sustained activity of a tyrosine kinase that is critical for mediating signal transduction and biological actions.

Inhibition of vascular smooth muscle cell proliferation by Gentiana lutea root extracts

Gentiana lutea belonging to the Gentianaceae family of flowering plants are routinely used in traditional Serbian medicine for their beneficial gastro-intestinal and anti-inflammatory properties. The aim of the study was to determine whether aqueous root extracts of Gentiana lutea consisting of gentiopicroside, gentisin, bellidifolin-8-O-glucoside, demethylbellidifolin-8-O-glucoside, isovitexin, swertiamarin and amarogentin prevents proliferation of aortic smooth muscle cells in response to PDGF-BB. Cell proliferation and cell cycle analysis were performed based on alamar blue assay and propidium iodide labeling respectively. In primary cultures of rat aortic smooth muscle cells (RASMCs), PDGF-BB (20 ng/ml) induced a two-fold increase in cell proliferation which was significantly blocked by the root extract (1 mg/ml). The root extract also prevented the S-phase entry of synchronized cells in response to PDGF. Furthermore, PDGF-BB induced ERK1/2 activation and consequent increase in cellular nitric oxide (NO) levels were also blocked by the extract. These effects of extract were due to blockade of PDGF-BB induced expression of iNOS, cyclin D1 and proliferating cell nuclear antigen (PCNA). Docking analysis of the extract components on MEK1, the upstream ERK1/2 activating kinase using AutoDock4, indicated a likely binding of isovitexin to the inhibitor binding site of MEK1. Experiments performed with purified isovitexin demonstrated that it successfully blocks PDGF-induced ERK1/2 activation and proliferation of RASMCs in cell culture. Thus, Gentiana lutea can provide novel candidates for prevention and treatment of atherosclerosis.

Development of the mammalian axial skeleton requires signaling through the Gα(i) subfamily of heterotrimeric G proteins

129/SvEv mice with a loss-of-function mutation in the heterotrimeric G protein α-subunit gene Gnai3 have fusions of ribs and lumbar vertebrae, indicating a requirement for Gα(i) (the "inhibitory" class of α-subunits) in somite derivatives. Mice with mutations of Gnai1 or Gnai2 have neither defect, but loss of both Gnai3 and one of the other two genes increases the number and severity of rib fusions without affecting the lumbar fusions. No myotome defects are observed in Gnai3/Gnai1 double-mutant embryos, and crosses with a conditional allele of Gnai2 indicate that Gα(i) is specifically required in cartilage precursors. Penetrance and expressivity of the rib fusion phenotype is altered in mice with a mixed C57BL/6 × 129/SvEv genetic background. These phenotypes reveal a previously unknown role for G protein-coupled signaling pathways in development of the axial skeleton.

Dietary Nrf2 activators inhibit atherogenic processes

Dietary Nrf2 activators increase expression of phase 2 protein genes in cells undergoing oxidative stress resulting in a lowering of oxidative stress. Oxidative stress promotes atherogenic processes through oxidizing low density lipoproteins and promotion of inflammation through activation of nuclear factor kappa B and activation of mitogen-activated protein kinases. Nrf2 activators by decreasing oxidative stress decrease the probability of developing atherosclerotic lesions.

Tunicamycin inhibits PDGF-BB-induced proliferation and migration of vascular smooth muscle cells through induction of HO-1

The abnormal proliferation and migration of vascular smooth muscle cell (VSMC), which is triggered by various external stimuli, contributes importantly to the pathogenesis of atherosclerosis and restenosis. Recent studies indicate that the endoplasmic reticulum (ER) stress is intensively involved in the pathophysiological changes of VSMCs by various stimuli. However, the direct effects of ER stress on VSMC proliferation and migration remain unknown. In this study, we found that pretreatment with tunicamycin (Tm), an ER stress inducer, significantly inhibited platelet-derived growth factor (PDGF)-BB-induced VSMC proliferation and migration in a dose-dependent manner without causing significant apoptosis. Tm stimulated the expression of the antioxidant gene heme oxygenase-1 (HO-1) both at the transcriptional and translational levels, while reducing phosphorylation and activation of mitogen-activated protein (MAP) kinases. The negative regulative effects of Tm were associated with a decrease in cyclins and cyclin-dependent kinases (CDKs) activation. More importantly, HO-1 siRNA partially abolished the beneficial effects of Tm on VSMCs. These results indicate that Tm-induced ER stress provides protection against the abnormal VSMC activation by PDGF-BB, which may be mediated by the induction of HO-1 and blockade of cell cycle reentry.

Redox control of the survival of healthy and diseased cells

Abstract Cellular redox homeostasis is the first line of defense against diverse stimuli and is crucial for various biological processes. Reactive oxygen species (ROS), byproducts of numerous cellular events, may serve in turn as signaling molecules to regulate cellular processes such as proliferation, differentiation, and apoptosis. However, when overproduced ROS fail to be scavenged by the antioxidant system, they may damage cellular components, giving rise to senescent, degenerative, or fatal lesions in cells. Accordingly, this review not only covers general mechanisms of ROS production under different conditions, but also focuses on various types of ROS-involved diseases, including atherosclerosis, ischemia/reperfusion injury, diabetes mellitus, neurodegenerative diseases, and cancer. In addition, potentially therapeutic agents and approaches are reviewed in a relatively comprehensive manner. However, due to the complexity of ROS and their cellular impacts, we believe that the goal to design more effective approaches or agents may require a better understanding of mechanisms of ROS production, particularly their multifaceted impacts in disease at biochemical, molecular, genetic, and epigenetic levels. Thus, it requires additional tools of omics in systems biology to achieve such a goal. Antioxid. Redox Signal. 15, 2867-2908.

Association of platelet-derived growth factor receptor β accumulation with increased oxidative stress and cellular injury in sestrin 2 silenced human glioblastoma cells

Sestrin 2 (SESN2) is a stress-inducible protein required for maintaining redox homeostasis. However, its mode of action remains to be clarified. In this study, we found that SESN2 is induced in human glioblastoma U87 cells following ionizing radiation (IR). SESN2 silencing not only results in increased oxidative stress but also sensitizes U87 cells to IR. Intriguingly, we found SESN2 silencing significantly increases the expression of platelet-derived growth factor receptor β (PDGFRβ). Using a double knockdown technique, we showed that inhibition of PDGFRβ accumulation in SESN2-silencing cells protects the cells from the deleterious effects induced by SESN2 silencing. Taken together, we revealed that PDGFRβ accumulation is associated with increased oxidative stress and cellular damage in SESN2 silenced human glioblastoma U87 cells.

Pharmacological postconditioning protects against hepatic ischemia/reperfusion injury

Postconditioning is a procedure based on the induction of intracellular protective reactions immediately after the onset of reperfusion. Because of the growing need to prevent ischemia/reperfusion (I/R) injury during liver surgery and transplantation, we investigated the possibility of pharmacologically inducing hepatic postconditioning. The effects of the adenosine A2A receptor agonist 2p-(2-carboxyethyl)-phenyl-amino-5'-N-ethylcarboxyamido-adenosine (CGS21680; 5 μmol/L) and the phosphatase and tensin homologue deleted from chromosome 10 (PTEN) inhibitor dipotassium bisperoxo-(5-hydroxypyridine-2-carboxyl)-oxovanadate [bpV(HOpic); 250 nmol/L] were investigated in primary rat hepatocytes during reoxygenation after 24 hours of cold storage and in an in vivo model of rat liver warm I/R. The addition of CGS21680 at reoxygenation significantly reduced hepatocyte death through the activation of the phosphoinositide 3-kinase (PI3K)-protein kinase B (PKB)/Akt signal pathway and through the reduction of the intracellular level of PTEN. PTEN lowering was associated with the increased generation of reactive oxygen species after A2A receptor-mediated stimulation of β-nicotinamide adenine dinucleotide phosphate oxidase (NOX). The inhibition of PI3K or NOX with wortmannin or diphenyleneiodonium chloride, respectively, and the addition of the antioxidant N,N'-diphenyl-p-phenylenediamine reversed the effects of CGS21680. The PTEN inhibitor bpV(HOpic) mimicked the protection provided by CGS21680 against reoxygenation damage. An in vivo rat treatment with CGS21680 or bpV(HOpic) during reperfusion after 1 hour of partial hepatic ischemia also promoted PKB/Akt activation and ameliorated alanine aminotransferase release and histological lesions induced by 2 hours of reperfusion. We conclude that adenosine A2A receptor agonists and PTEN inhibitors are possibly useful agents for the pharmacological induction of postconditioning in the liver.

Exendin-4 improves hepatocyte injury by decreasing proliferation through blocking NGF/TrkA in diabetic mice

The hepatocytes express nerve growth factor (NGF) and its high affinity receptor tyrosine kinase A (TrkA). However, the link between NGF/TrkA system and hepatocyte proliferation in diabetic animals and the effects of exendin-4, a glucagon like peptide-1 (GLP-1) receptor agonist, on this system are not known. BALB/c male mice were divided into four groups. The first group was given citrate buffer only, the second group was administered exendin-4 alone, the third group received streptozotocin (STZ), and the fourth group was given both STZ and exendin-4. Exendin-4 (3μg/kg) was administered by subcutaneous injection daily for 30 days after the animals were rendered diabetic by administration of STZ (200mg/kg). With treatment of exendin-4 to the diabetic mice the following results were noted (i) NGF, TrkA and proliferating cell nuclear antigen positive hepatocytes were decreased; (ii) p75 neurotrophin receptor and caspase-3 positive hepatocyte could not be detected; (iii) liver alanine transaminase and aspartate transaminase activities, lipid peroxidation, protein carbonyl and myeloperoxidase levels were decreased; (iv) liver catalase, superoxide dismutase, glutathione peroxidase activities and glutathione levels were increased. These data suggest that exendin-4 might exerts its anti-proliferative action through blocking NGF/TrkA system and stimulating oxidative defense system in liver of diabetic mice.

Phagocyte-like NADPH oxidase generates ROS in INS 832/13 cells and rat islets: role of protein prenylation

Recent evidence suggests that an acute increase in the generation of phagocyte-like NADPH-oxidase (Nox)-mediated reactive oxygen species (ROS) may be necessary for glucose-stimulated insulin secretion. Using rat islets and INS 832/13 cells, we tested the hypothesis that activation of specific G proteins is necessary for nutrient-mediated intracellular generation of ROS. Stimulation of β-cells with glucose or a mixture of mitochondrial fuels (mono-methylsuccinate plus α-ketoisocaproic acid) markedly elevated intracellular accumulation of ROS, which was attenuated by selective inhibitors of Nox (e.g., apocynin or diphenyleneiodonium chloride) or short interfering RNA-mediated knockdown of p47(phox), one of the subunits of Nox. Selective inhibitors of protein prenylation (FTI-277 or GGTI-2147) markedly inhibited nutrient-induced ROS generation, suggesting that activation of one (or more) prenylated small G proteins and/or γ-subunits of trimeric G proteins is involved in this signaling axis. Depletion of endogenous GTP levels with mycophenolic acid significantly reduced glucose-induced activation of Rac1 and ROS generation in these cells. Other immunosuppressants, like cyclosporine A or rapamycin, which do not deplete endogenous GTP levels, failed to affect glucose-induced ROS generation, suggesting that endogenous GTP is necessary for glucose-induced Nox activation and ROS generation. Treatment of INS 832/13 cells or rat islets with pertussis toxin (Ptx), which ADP ribosylates and inhibits inhibitory class of trimeric G proteins (i.e., G(i) or G(o)), significantly attenuated glucose-induced ROS generation in these cells, implicating activation of a Ptx-sensitive G protein in these signaling cascade. Together, our findings suggest a prenylated Ptx-sensitive signaling step couples Rac1 activation in the signaling steps necessary for glucose-mediated generation of ROS in the pancreatic β-cells.

Receptor activation of NADPH oxidases

Reactive oxygen species (ROS) have been implicated in many intra- and intercellular processes. High levels of ROS are generated as part of the innate immunity in the respiratory burst of phagocytic cells. Low levels of ROS, however, are generated in a highly controlled manner by various cell types to act as second messengers in redox-sensitive pathways. A NADPH oxidase has been initially described as the respiratory burst enzyme in neutrophils. Stimulation of this complex enzyme system requires specific signaling cascades linking it to membrane-receptor activation. Subsequently, a family of NADPH oxidases has been identified in various nonphagocytic cells. They mainly differ in containing one out of seven homologous catalytic core proteins termed NOX1 to NOX5 and DUOX1 or 2. NADPH oxidase activity is controlled by regulatory subunits, including the NOX regulators p47phox and p67phox, their homologs NOXO1 and NOXA1, or the DUOX1 or 2 regulators DUOXA1 and 2. In addition, the GTPase Rac modulates activity of several of these enzymes. Recently, additional proteins have been identified that seem to have a regulatory function on NADPH oxidase activity under certain conditions. We will thus summarize molecular pathways linking activation of different membrane-bound receptors with increased ROS production of NADPH oxidases.

Reactive oxygen species: A radical role in development?

Reactive oxygen species (ROS), mostly derived from mitochondrial activity, can damage various macromolecules and consequently cause cell death. This ROS activity has been characterized in vitro, and correlative evidence suggests a role in various pathological conditions. In addition to this passive ROS activity, ROS also participate in cell signaling processes, though the relevance of this function in vivo is poorly understood. Throughout development, elevated cell activity is probably accompanied by highly active metabolism and, consequently, the production of large amounts of ROS. To allow proper development, cells must protect themselves from these potentially damaging ROS. However, to what degree ROS could participate as signaling molecules controlling fundamental and developmentally relevant cellular processes such as proliferation, differentiation, and death is an open question. Here we discuss why available data do not yet provide conclusive evidence on the role of ROS in development, and we review recent methods to detect ROS in vivo and genetic strategies that can be exploited specifically to resolve these uncertainties.

Lipid rafts and caveolin-1 coordinate interleukin-1beta (IL-1beta)-dependent activation of NFkappaB by controlling endocytosis of Nox2 and IL-1beta receptor 1 from the plasma membrane

Recent evidence suggests that signaling by the proinflammatory cytokine interleukin-1beta (IL-1beta) is dependent on reactive oxygen species derived from NADPH oxidase. Redox signaling in response to IL-1beta is known to require endocytosis of its cognate receptor (IL-1R1) following ligand binding and the formation of redox-active signaling endosomes that contain Nox2 (also called redoxosomes). The consequent generation of reactive oxygen species by redoxosomes is responsible for the downstream recruitment of IL-1R1 effectors (IRAK, TRAF6, and IkappaB kinase kinases) and ultimately for activation of the transcription factor NFkappaB. Despite this knowledge of the signaling events that occur downstream of redoxosome formation, an understanding of the mechanisms that coordinate the genesis of redoxosomes following IL-1beta stimulation has been lacking. Here, we demonstrate that lipid rafts play an important role in this process. We show that Nox2 and IL-1R1 localize to plasma membrane lipid rafts in the unstimulated state and that IL-1beta signals caveolin-1-dependent endocytosis of both proteins into the redoxosome. We also show that inhibiting lipid raft-mediated endocytosis prevents NFkappaB activation. Finally, we demonstrate that Vav1, a Rac1 guanine exchange factor and activator of Nox2, is recruited to lipid rafts following IL-1beta stimulation and that it is required for NFkappaB activation. Our results fill in an important mechanistic gap in the understanding of early IL-1R1 and Nox2 signaling events that control NFkappaB activation, a redox-dependent process important in inflammation.

Signaling components of redox active endosomes: the redoxosomes

Subcellular compartmentalization of reactive oxygen species (ROS) plays a critical role in transmitting cell signals in response to environmental stimuli. In this regard, signals at the plasma membrane have been shown to trigger NADPH oxidase-dependent ROS production within the endosomal compartment and this step can be required for redox-dependent signal transduction. Unique features of redox-active signaling endosomes can include NADPH oxidase complex components (Nox1, Noxo1, Noxa1, Nox2, p47phox, p67phox, and/or Rac1), ROS processing enzymes (SOD1 and/or peroxiredoxins), chloride channels capable of mediating superoxide transport and/or membrane gradients required for Nox activity, and novel redox-dependent sensors that control Nox activity. This review will discuss the cytokine and growth factor receptors that likely mediate signaling through redox-active endosomes, and the common mechanisms whereby they act. Additionally, the review will cover ligand-independent environmental injuries, such as hypoxia/reoxygenation injury, that also appear to facilitate cell signaling through NADPH oxidase at the level of the endosome. We suggest that redox-active endosomes encompass a subset of signaling endosomes that we have termed redoxosomes. Redoxosomes are uniquely equipped with redox-processing proteins capable of transmitting ROS signals from the endosome interior to redox-sensitive effectors on the endosomal surface. In this manner, redoxosomes can control redox-dependent effector functions through the spatial and temporal regulation of ROS as second messengers.

Silybin, a component of sylimarin, exerts anti-inflammatory and anti-fibrogenic effects on human hepatic stellate cells

BACKGROUND/AIMS

Hepatic fibrogenesis, a consequence of chronic liver tissue damage, is characterized by activation of the hepatic stellate cells (HSC). Silybin has been shown to exert anti-fibrogenic effects in animal models. However, scant information is available on the fine cellular and molecular events responsible for this effect. The aim of this study was to assess the mechanisms regulating the anti-fibrogenic and anti-inflammatory activity of Silybin.

METHODS

Experiments were performed on HSC isolated from human liver and activated by culture on plastic.

RESULTS

Silybin was able to inhibit dose-dependently (25-50 microM) growth factor-induced pro-fibrogenic actions of activated human HSC, including cell proliferation (P < 0.001), cell motility (P < 0.001), and de novo synthesis of extracellular matrix components (P < 0.05). Silybin (25-50 microM), inhibited the IL-1-induced synthesis of MCP-1 (P < 0.01) and IL-8 (P < 0.01) showing a potent anti-inflammatory activity. Silybin exerts its effects by directly inhibiting the ERK, MEK and Raf phosphorylation, reducing the activation of NHE1 (Na+/H+ exchanger, P < 0.05) and the IkBalpha phosphorylation. In addition, Silybin was confirmed to act as a potent anti-oxidant agent.

CONCLUSION

The results of the study provide molecular insights into the potential therapeutic action of Silybin in chronic liver disease. This action seems to be mostly related to a marked inhibition of the production of pro-inflammatory cytokines, a clear anti-oxidant effect and a reduction of the direct and indirect pro-fibrogenic potential of HSC.

Regulation of globular adiponectin-induced apoptosis by reactive oxygen/nitrogen species in RAW264 macrophages

Adiponectin, produced predominantly by differentiating adipocytes, is a protein hormone with antidiabetic and immunosuppressive properties. Here, we report evidence that treatment with globular adiponectin (gAd) induces apoptosis in murine macrophage-like RAW264 cells through the generation of reactive oxygen and/or nitrogen species (ROS/RNS). Treatment with gAd induced apoptosis and enhanced the activities of caspase-3 and -9, but not caspase-8. The gAd stimulation increased ROS generation and significantly reduced the ratio of NADPH to total NADP. Pretreatment with diphenyleneiodonium or apocynin reduced ROS and apoptosis in gAd-treated cells. In addition, transfection with p47(phox)- or gp91(phox)-specific small interfering RNA (siRNA) partially reduced ROS and apoptosis in response to gAd treatment. These results suggest that the administration of gAd induces apoptosis after ROS generation involving activation of NADPH oxidases. The gAd stimulation increased the release of NO into the culture medium, the activity of nitric oxide synthase (NOS), and the expression of inducible NOS (iNOS) mRNA in RAW264 cells. l-NAME reduced gAd-induced apoptotic cell death. In addition, transfection with an iNOS-specific siRNA markedly reduced the generation of NO and the population of apoptotic cells. Taken together, these results demonstrate that the gAd-induced apoptotic process in RAW264 cells involves ROS and RNS, which are generated by NADPH oxidases and iNOS, respectively.

Roles of Oxidants, Nitric Oxide, and Asymmetric Dimethylarginine in Endothelial Function

Vascular endothelium plays a crucial role in ensuring normal function and morphology of blood vessels, and many risk factors of atherosclerosis act via their effects on endothelial cells. However, endothelial dysfunction is induced by very different pathomechanisms. In principle, it is caused by an impaired bioavailability of nitric oxide (NO) due to an inhibited synthesis (eg, by asymmetric dimethylarginine [ADMA]) or increased consumption of formed NO (by reactive oxygen species [ROS]). ROS can be synthesized in the organism (eg, by different enzymes) or can be administered from the environment (eg, by cigarette smoking), whereas ADMA is the subject of endogenous metabolism only. Many studies have elucidated the system of pathomechanisms and targeted some as potential goals for therapeutic interventions. This review demonstrates roles of ROS, NO, ADMA, endothelin, and estrogen in endothelial function and dysfunction focusing on homocysteinemia and diabetes mellitus and provide examples for the medical treatment of endothelial dysfunction.

Protein tyrosine phosphorylation and protein tyrosine nitration in redox signaling

Reversible phosphorylation of protein tyrosine residues by polypeptide growth factor-receptor protein tyrosine kinases is implicated in the control of fundamental cellular processes including the cell cycle, cell adhesion, and cell survival, as well as cell proliferation and differentiation. During the last decade, it has become apparent that receptor protein tyrosine kinases and the signaling pathways they activate belong to a large signaling network. Such a network can be regulated by various extracellular cues, which include cell adhesion, agonists of G protein-coupled receptors, and oxidants. It is well documented that signaling initiated by receptor protein tyrosine kinases is directly dependent on the intracellular production of oxidants, including reactive oxygen and nitrogen species. Accumulated evidence indicates that the intracellular redox environment plays a major role in the mechanisms underlying the actions of growth factors. Oxidation of cysteine thiols and nitration of tyrosine residues on signaling proteins are described as posttranslational modifications that regulate, positively or negatively, protein tyrosine phosphorylation (PTP). Early observations described the inhibition of PTP activities by oxidants, resulting in increased levels of proteins phosphorylated on tyrosine. Therefore, a redox circuitry involving the increasing production of intracellular oxidants associated with growth-factor stimulation/cell adhesion, oxidative reversible inhibition of protein tyrosine phosphatases, and the activation of protein tyrosine kinases can be delineated.

Redox-dependent and ligand-independent trans-activation of insulin receptor by globular adiponectin

Adiponectin/ACRP30 is an adipose tissue-derived hormone with antiatherogenic, antidiabetic, and insulin-sensitizing properties. Although the metabolic effects of adiponectin on glucose and lipid metabolism are well known, the signaling pathways triggered by adiponectin receptors remain to be elucidated. We report evidence that in hepatic cells, adiponectin stimulation produces a transient burst of reactive oxygen species (ROS) through activation of the small GTPase Rac1 and 5-lypoxigenase. Furthermore, adiponectin-induced oxidants cause the oxidation/inhibition of protein-tyrosine phosphatase (PTP) 1B, one of the major phosphotyrosine phosphatases involved in the control of insulin receptor phosphorylation. Adiponectin causes increased association of PTP1B to insulin receptor and the oxidation/inhibition of the phosphatase, ultimately provoking the ligand-independent trans-phosphorylation of insulin receptor. We also report evidence that redox signaling plays a key role in both mitogen-activated protein kinase activation and hepatic glucose consumption induced by adiponectin.

CONCLUSION

These results point to ROS as critical regulators of the cross-talk between adiponectin and insulin pathways and provide a redox-based molecular mechanism for the insulin-sensitizing function of adiponectin.

Protein tyrosine phosphorylation and reversible oxidation: two cross-talking posttranslation modifications

In addition to protein phosphorylation, redox-dependent posttranslational modification of proteins is emerging as a key signaling system, conserved throughout evolution, and influencing many aspects of cellular homeostasis. Recent data have provided new insight about the interplay between phosphorylation- and redox-dependent signaling, and reactive oxygen species have been included among intracellular signal transducers of growth factor and extracellular matrix receptors. Both tyrosine phosphorylation and thiol oxidation are reversible and dynamic, and this review will particularly focus on the cross-talk between these posttranslational protein regulatory means. Although these modifications share their reversibility, their effects on enzymatic activity of protein tyrosine phosphatases (PTPs) and protein tyrosine kinases (PTKs) may be even opposite. Indeed, while tyrosine phosphorylation is frequently correlated to enzyme activation, thiol oxidation leads to inactivation of PTPs and to superactivation of PTKs. Several papers describe that both these modifications occur during the same input, (i.e., cell proliferation and motility induced by numerous growth factors and cytokines). The review will discuss several aspects of phosphorylation\oxidation interplay, describing both convergent and divergent features of the integrated and coordinated function of PTPs and PTKs during signaling.

Reactive oxygen species signaling in vascular smooth muscle cells

Reactive oxygen species (ROS) have been shown to function as important signaling molecules in the cardiovascular system. Vascular smooth muscle cells (VSMCs) contain several sources of ROS, among which the NADPH oxidases are predominant. In VSMCs, ROS mediate many pathophysiological processes, such as growth, migration, apoptosis and secretion of inflammatory cytokines, as well as physiological processes, such as differentiation, by direct and indirect effects at multiple signaling levels. Therefore, it becomes critical to understand the different roles ROS play in the physiology and pathophysiology of VSMCs.

Antagonism of platelet‐derived growth factor by perivascular gene transfer attenuates adventitial cell migration after vascular injury: new tricks for old dogs?

Migration of adventitial fibroblasts contributes to vascular remodeling after angioplasty. This study has used perivascular gene transfer of a truncated platelet-derived growth factor PDGF receptor (PDGFXR) to investigate whether antagonism of PDGF signaling alters adventitial cell migration after balloon injury in rat carotid arteries. Adenoviruses coordinating expression of beta-galactosidase (LacZ) and PDGFXR or LacZ and green fluorescent protein (GFP) were applied to the perivascular surface of arteries and balloon injury performed 4 days later. Vessels were excised at 3, 7, and 14 days to determine morphology and gene expression. Uninjured arteries only expressed LacZ positive cells in the adventitial compartment; however, after injury in LacZ and GFP transfected arteries, LacZ positive cells contributed to the population of cells within the media and neointima at 7-14 days. Overexpression of PDGFXR and LacZ resulted in a significant reduction in the number of LacZ labeled cells in the neointima after vascular injury, concomitant with reduced remodeling, collagen content, expression of matrix metalloproteinase-2, and increased levels of tissue inhibitors of metalloproteinase-1 and -2. We provide evidence that perivascular antagonism of PDGF attenuates remodeling and contribution of adventitial fibroblasts to neointima formation after balloon angioplasty. Perivascular gene transfer may represent a therapeutic strategy to reduce the incidence of restenosis.

Effects of mutagenesis of W343 in human annexin A6 isoform 1 on its interaction with GTP: nucleotide-induced oligomer formation and ion channel activity

Accumulated experimental evidence suggests that annexin A6 (AnxA6) is involved in ion transport in various tissues. Such a biological function is related either to the modulation of ion transport systems by AnxA6 or to the ion channel activity of the protein. While AnxA6 channel activity at low pH seems to be associated with a large conformational transition in the protein, the mechanism of GTP-induced ion channel formation remains obscure. This activity is not accompanied by changes in protein structure. The existence of a domain binding the phosphate groups of GTP in AnxA6 [Bandorowicz-Pikula, J., Kirilenko, A., van Deursen, R., Golczak, M., Kuhnel, M., Lancelin, J. M., Pikula, S., and Buchet, R. (2003) Biochemistry 42, 9137-9146] may provide some clues about the molecular mechanisms of GTP-induced ion channel formation. In addition, we observed that one of the AnxA6 tryptophan residues, W192 or W343, may be involved in GTP binding. Therefore, we created several site-directed mutants of AnxA6 in which selected amino acid residues within a consensus sequence of a putative nucleotide-binding domain of AnxA6 were replaced with other amino acid residues without affecting the overall structure of protein as examined by circular dichroism and infrared spectroscopies. Their properties were analyzed and compared to those of the native protein. In contrast to mutant W192S and wild-type annexin, mutant W343S neither bound GTP nor exhibited GTP-induced ion channel activity. In addition, we detected the likely formation of AnxA6 trimers in the presence of GTP. The ability of mutant W343S to form trimers was significantly impaired. Our findings suggest that W343 participates in the formation of AnxA6 trimers. We hypothesize that such trimers could lead to a functional unit of the GTP-induced ion channels formed by the annexin molecules.

Expression and regulation of antioxidant enzymes in the developing limb support a function of ROS in interdigital cell death

Vertebrate limb development is a well-studied model of apoptosis; however, little is known about the intracellular molecules involved in activating the cell death machinery. We have shown that high levels of reactive oxygen species (ROS) are present in the interdigital 'necrotic' tissue of mouse autopod, and that antioxidants can reduce cell death. Here, we determined the expression pattern of several antioxidant enzymes in order to establish their role in defining the areas with high ROS levels. We found that the genes encoding the superoxide dismutases and catalase are expressed in autopod, but they are downregulated in the interdigital regions at the time ROS levels increased and cell death was first detected. The possible role of superoxide and/or peroxide in activating cell death is supported by the protective effect of a superoxide dismutase/catalase mimetic. Interestingly, we found that peroxidase activity and glutathione peroxidase-4 gene (Gpx4) expression were restricted to the non-apoptotic tissue (e.g., digits) of the developing autopod. Induction of cell death with retinoic acid caused an increase in ROS and decrease in peroxidase activity. Even more inhibition of glutathione peroxidase activity leads to cell death in the digits, suggesting that a decrease in antioxidant activity, likely due to Gpx4, caused an increase in ROS levels, thus triggering apoptosis.

In high glucose protein kinase C-zeta activation is required for mesangial cell generation of reactive oxygen species

BACKGROUND

We postulated that in mesangial cells exposed to high glucose, protein kinase C-zeta (PKC-zeta) is necessary for the generation of reactive oxygen species (ROS) by nicotinamide adenine dinucleotide phosphate (NADPH) oxidase and that the requirement of PKC-zeta for filamentous (F)-actin disassembly may involve ROS. To identify signaling mechanisms relevant to PKC-zeta activation and ROS generation, including phosphoinositide 3 kinase (PI3 kinase), we examined mesangial cell stimulation with platelet-derived growth factor (PDGF).

METHODS

In primary rat mesangial cells cultured in 5.6 mmol/L or 30 mmol/L d-glucose, PKC-zeta expression was identified with immunoblotting and activity was analyzed in cell membrane immunoprecipitates and by confocal immunofluorescence imaging. ROS generation was measured by dichlorofluorescein fluorescence using confocal microscopy and was inhibited by transfection of antisense against NADPH subunits p22(phox) or p47(phox) or with Tempol. F-actin disassembly was observed by dual-channel confocal fluorescence imaging. PI3 kinase activity was detected by immunoblotting of phosphorylated Akt.

RESULTS

In high glucose, generation of NADPH oxidase-dependent ROS was dependent on PKC-zeta. Conversely, sustained PKC-zeta activity was dependent on ROS generation, suggesting a positive feedback. PKC-zeta-dependent F-actin disassembly in high glucose required ROS generation. PDGF stimulated NADPH oxidase generation of ROS through a PKC-zeta mechanism that was independent of Akt phosphorylation and remained unchanged in high glucose.

CONCLUSION

In high glucose, mesangial cell PKC-zeta is required for ROS generation from NADPH oxidase similar to PDGF stimulation of PKC-zeta-dependent ROS generation through a pathway independent of PI3 kinase. F-actin disassembly in high glucose also requires ROS. A positive feedback loop occurs between ROS and the activation of PKC-zeta in high glucose.

Reactive oxygen species as signaling molecules in cardiovascular differentiation of embryonic stem cells and tumor-induced angiogenesis

Besides the well known pathophysiological impact of oxidative stress in cardiovascular disease, reactive oxygen species (ROS) generated at low concentrations exert a role as signaling molecules that are involved in signal transduction cascades of numerous growth factor-, cytokine-, and hormone-mediated pathways, and regulate biological effects such as apoptosis, cell proliferation, and differentiation. Embryonic stem cells have the capacity to differentiate into the cardiovascular cell lineage. Furthermore, upon confrontation culture with tumor tissue, they form blood vessel-like structures that induce tumor-induced angiogenesis within tumor tissues. The role of ROS in cardiovascular differentiation of embryonic stem cells appears to be antagonistic. Whereas continuous exposure to ROS results in inhibition of cardiomyogenesis and vasculogenesis, pulse chase exposure to low-level ROS enhances differentiation toward the cardiomyogenic as well as vascular cell lineage. This review summarizes the current knowledge of ROS-induced cardiovascular differentiation of embryonic stem cells as well as the role of ROS in tumor-induced angiogenesis.

Platelet-derived Growth Factor and Reactive Oxygen Species (ROS) Regulate Ras Protein Levels in Primary Human Fibroblasts via ERK1/2

The levels of Ras proteins in human primary fibroblasts are regulated by PDGF (platelet-derived growth factor). PDGF induced post-transcriptionally Ha-Ras by stimulating reactive oxygen species (ROS) and ERK1/2. Activation of ERK1/2 and high ROS levels stabilize Ha-Ras protein, by inhibiting proteasomal degradation. We found a remarkable example in vivo of amplification of this circuitry in fibroblasts derived from systemic sclerosis (scleroderma) lesions, producing vast excess of ROS and undergoing rapid senescence. High ROS, Ha-Ras, and active ERK1/2 stimulated collagen synthesis, DNA damage, and accelerated senescence. Conversely ROS or Ras inhibition interrupted the signaling cascade and restored the normal phenotype. We conclude that in primary fibroblasts stabilization of Ras protein by ROS and ERK1/2 amplifies the response of the cells to growth factors and in systemic sclerosis represents a critical factor in the onset and progression of the disease.

Hypoxic pulmonary hypertension: role of superoxide and NADPH oxidase (gp91phox)

Chronic exposure to low-O2 tension induces pulmonary arterial hypertension (PAH), which is characterized by vascular remodeling and enhanced vasoreactivity. Recent evidence suggests that reactive oxygen species (ROS) may be involved in both processes. In this study, we critically examine the role superoxide and NADPH oxidase plays in the development of chronic hypoxic PAH. Chronic hypoxia (CH; 10% O2 for 3 wk) caused a significant increase in superoxide production in intrapulmonary arteries (IPA) of wild-type (WT) mice as measured by lucigenin-enhanced chemiluminescence. The CH-induced increase in the generation of ROS was obliterated in NADPH oxidase (gp91phox) knockout (KO) mice, suggesting that NADPH oxidase was the major source of ROS. Importantly, pathological changes associated with CH-induced PAH (mean right ventricular pressure, medial wall thickening of small pulmonary arteries, and right heart hypertrophy) were completely abolished in NADPH oxidase (gp91phox) KO mice. CH potentiated vasoconstrictor responses of isolated IPAs to both 5-hydroxytryptamine (5-HT) and the thromboxane mimetic U-46619. Administration of CuZn superoxide dismutase to isolated IPA significantly reduced CH-enhanced superoxide levels and reduced the CH-enhanced vasoconstriction to 5-HT and U-46619. Additionally, CH-enhanced superoxide production and vasoconstrictor activity seen in WT IPAs were markedly reduced in IPAs isolated from NADPH oxidase (gp91phox) KO mice. These results demonstrate a pivotal role for gp91phox-dependent superoxide production in the pathogenesis of CH-induced PAH.

c-Src is involved in regulating signal transmission from PDGFbeta receptor-GPCR(s) complexes in mammalian cells

We have reported that the platelet-derived growth factor receptor-beta (PDGFbeta) forms a novel signaling complex with G protein-coupled receptors (GPCR) (e.g. S1P(1) receptor) that enables more efficient activation of p42/p44 mitogen-activated protein kinase (MAPK) in response to PDGF and sphingosine 1-phosphate (S1P). We now demonstrate that c-Src participates in regulating the endocytosis of PDGFbeta receptor-GPCR complexes in response to PDGF. This leads to association of cytoplasmic p42/p44 MAPK with the receptor complex in endocytic vesicles. c-Src is regulated by G protein betagamma subunits and can interact with beta-arrestin. Indeed, the PDGF-dependent activation of p42/p44 MAPK was reduced by over-expression of the C-terminal domain of GRK2 (sequesters Gbetagamma subunits), the clathrin-binding domain of beta-arrestin and by inhibitors of c-Src and clathrin-mediated endocytosis. Moreover, PDGF and S1P induce the recruitment of c-Src to the PDGFbeta receptor-S1P(1) receptor complex. This leads to a G protein/c-Src-dependent tyrosine phosphorylation of Gab1 and accumulation of dynamin II at the plasma membrane, a step required for endocytosis of the PDGFbeta receptor-GPCR complex. These findings provide important information concerning the molecular organisation of novel receptor tyrosine kinase (RTK)-GPCR signal relays in mammalian cells.

Mitochondrial-dependent, reactive oxygen species-independent apoptosis by myricetin: roles of protein kinase C, cytochrome c, and caspase cascade

Abrogation of mitochondrial permeability and induction of reactive oxygen species (ROS) production have been observed in chemical-induced apoptosis; however, the relationship between the mitochondria and intracellular ROS levels in apoptosis is still unclear. In the present study, myricetin (ME) but not its respective glycoside, myricitrin (MI; myricetin-3-O-rhamnose) reduced the viability of human leukemia HL-60 cells via apoptosis, characterized by the occurrence of DNA ladders and hypodiploid cells. Results of Western blotting and caspase activity assays showed that activation of caspases 3 and 9 but not caspases 1, 6 or 8 with cleavage of PARP and D4-GDI proteins is involved in ME-induced apoptosis. A reduction in mitochondrial functions characterized by a decrease in the Bcl-2/Bax protein ratio and translocation of cytochrome c (cyt c) from the mitochondria to the cytosol in accordance with a decrease in mitochondrial membrane potential were observed in ME-treated HL-60 cells. No significant induction of intracellular ROS levels by ME was observed by the DCHF-DA assay, DPPH assay or plasmid digestion assay, and antioxidants including N-acetyl-cysteine (NAC), catalase (CAT), superoxide dismutase (SOD), and tiron (TIR) showed no protective effects on ME-induced apoptosis. A PKC activator, 12-O-tetradecaoylphorbol-13-acetate (TPA) significantly attenuated ME-induced apoptosis via preventing cytochrome c release to the cytosol and maintaining the mitochondrial membrane potential by inhibiting the decrease in the Bcl-2/Bax protein ratio; these effects were blocked by protein kinase C (PKC) inhibitors including GF-109203X, H7, and staurosporin. Removing mitochondria by ethidium bromide (EtBr) treatment reduced the apoptotic effect of ME. Results of SAR studies showed that the presence of OH at C3', C4', and C5' is important for the apoptosis-inducing activities of ME, and that ME induces apoptosis in another leukemia cell line, Jurkat cells, but not in primary human polymorphonuclear (PMN) cells or in murine peritoneal macrophages (PMs). The results of the present study suggest that apoptosis induced by ME occurs through a novel mitochondrion-dependent, ROS-independent pathway; TPA protects cells from ME-induced apoptosis via PKC activation which prevents the occurrence of mitochondrial destruction during apoptosis.

Mycophenolic acid inhibits platelet-derived growth factor-induced reactive oxygen species and mitogen-activated protein kinase activation in rat vascular smooth muscle cells

Vascular smooth muscle cell (VSMC) proliferation is the major pathologic feature associated with chronic allograft nephropathy, and mycophenolic acid (MPA) inhibits VSMC proliferation. Since the role of inosine monophosphate dehydrogenase (IMPDH)-dependent de novo guanosine synthesis is limited in VSMCs, we examined the effects of MPA on platelet-derived growth factor (PDGF)-induced cellular ROS and mitogen-activated protein kinases (MAPK) activation in VSMCs. Primary cultured rat VSMCs were stimulated with PDGF-BB in the presence or absence of MPA. Cell proliferation was assessed by [3H]-thymidine incorporation, ROS by flow cytometry and MAPK activation by Western blot analysis. PDGF increased cell proliferation, cellular ROS and extracellular-regulated protein kinase (ERK) 1/2 and p38 MAPK activation by 3.4-, 1.6-, 3.3- and 3.9-fold, respectively. MPA at above 1 muM inhibited PDGF-induced cellular ROS and ERK 1/2 and p38 MAPK activation, as well as proliferation. Structurally different anti-oxidants and inhibitor of ERK or p38 MAPK blocked PDGF-induced proliferation. Anti-oxidants also inhibited ERK 1/2 and p38 MAPK activation. Exogenous guanosine partially recovered the inhibitory effect of MPA on VSMC proliferation. These results suggest that MPA may inhibit PDGF-induced VSMC proliferation partially through inhibiting cellular ROS, and subsequent ERK 1/2 and p38 MAPK activation in addition to inhibiting IMPDH.

Ligand-dependent autophosphorylation of the insulin receptor is positively regulated by Gi-proteins

Previously, we have shown that the human insulin receptor (IR) interacts with G(i)2, independent of tyrosine kinase activity and stimulates NADPH oxidase via the Galpha subunit of G(i)2. We have now investigated the regulatory role of G(i)2-proteins in IR function. For the experiments, isolated IRs from plasma membranes of human fat cells were used. The activation of IR autophosphorylation by insulin was blocked by G-protein inactivation through GDPbetaS (guanosine 5'-[beta-thio]disphosphate). Consistently, activation of G-proteins by micromolar concentrations of GTPgammaS (guanosine 5'-[gamma-thio]triphosphate) induced receptor autophosphorylation 5-fold over baseline and increased insulin-induced autophosphorylation by 3-fold. In the presence of 10 microM GTPgammaS, insulin was active at picomolar concentrations, indicating that insulin acted via its cognate receptor. Pretreatment of the plasma membranes with pertussis toxin prevented insulin- and GTPgammaS-induced autophosphorylation, but did not disrupt the IR-G(i)2 complex. The functional nature of the IR-G(i)2 complex was made evident by insulin's ability to increase association of G(i)2 with the IR. This leads to an augmentation of maximal receptor autophosphorylation induced by insulin and GTPgammaS. The specificity of this mechanism was further demonstrated by the use of isolated preactivated G-proteins. Addition of G(i)2alpha and Gbetagamma mimicked maximal response of insulin, whereas Galphas or Galphao had no stimulatory effect. These results define a novel mechanism by which insulin signalling mediates tyrosine kinase activity and autophosphorylation of the IR through recruitment of G(i)-proteins.

Platelet-derived growth factor induces tissue factor expression in vascular smooth muscle cells via activation of Egr-1

Activation of vascular smooth muscle cells (SMCs) by platelet-derived growth factor (PDGF) is a seminal event in the initiation and progression of the atherosclerotic lesion and may contribute to atherosclerotic plaque instability with plaque rupture and thrombus formation. Tissue factor (TF), a prothrombotic molecule expressed by various cell types within atherosclerotic plaques, is thought to play a major role in thrombus formation after plaque rupture. This study examined intracellular signaling pathways leading to TF expression and Egr-1 activation, a key element in tissue factor transcription, by PDGF-BB in rat SMCs. PDGF-BB induced TF mRNA and protein expression in a time-dependent manner. Early growth response factor-1 (Egr-1) binding activity was also induced by PDGF-BB, as well as phosphorylation of extracellular signal-regulated kinase. PDGF-BB-induced Egr-1 activation was suppressed by inhibitors of 2 upstream activators of Egr-1, extracellular signal-regulated kinase (ERK) and Src family kinases, whereas antioxidants, phosphatidylinositol 3-phosphate kinase, and p38 MAPK inhibitors had no effect. PDGF-BB-stimulated expression of the transcriptional co-repressor NAB2 was time-dependent. Furthermore, transient transfections of SMCs with wild-type and mutated TF promoter constructs showed that the Egr-1 binding region is an important transcriptional regulator of PDGF-BB-induced TF expression. Taken together, the results suggest that PDGF-BB induces TF expression and activity in SMC by a Src family kinases/ERK/Egr-1 signaling pathway and may therefore contribute to thrombus formation in advanced atherosclerosis and restenosis.

SHP2 binds catalase and acquires a hydrogen peroxide-resistant phosphatase activity via integrin-signaling

Here, we examined whether catalase binds SHP2 and alters SHP2 susceptibility to H2O2. Our results indicated that serum and fibrinogen commonly evoked catalase binding to SHP2 in HeLa and A549 cells in a herbimycin-A and TNFalpha sensitive manner. Expression of active catalase nearly 15-fold over control levels in tet-off HeLa cells substantially increased the SHP2 binding, and the catalase-associated SHP2 displayed significantly high phosphatase activities with a H2O2-resistance compared to those with little catalase. Site-directed mutagenesis at 280 abolished the binding capability of catalase to SHP2-SH2 in vitro. These results suggest that catalase-280pYIQV binds SHP2 via integrin-signaling to increase a H2O2-resistant SHP2 activity.

Multi-layered Representation for Cell Signaling Pathways

To understand complex signaling pathways and networks, it is necessary to develop a formal and structured representation of the available information in a format suitable for analysis by software tools. Due to the complexity and incompleteness of the current biological knowledge about cell signaling, such a device must be able to represent cellular pathways at differing levels of details, one level of information abstract enough to convey an essential signaling flow while hiding its details and another level of information detailed enough to explain the underlying mechanisms that account for the signaling flow described at a more abstract level. We have defined a formal ontology for cell-signaling events that allows us to describe these cellular pathways at various levels of abstraction. Using this formal representation, ROSPath (reactive oxygen species-mediated signaling pathway) database system has been implemented and made available on the web (rospath.ewha.ac.kr). ROSPath is a database system for reactive oxygen species (ROS)-mediated cell signaling pathways and signaling processes in molecular detail, which facilitates a comprehensive understanding of the regulatory mechanisms in signaling pathways. ROSPath includes growth factor-, stress-, and cytokine-induced signaling pathways containing about 500 unique proteins (mostly mammalian) and their related protein states, protein complexes, protein complex states, signaling interactions, signaling steps, and pathways. It is a web-based structured repository of information on the signaling pathways of interest and provides a means for managing data produced by large-scale and high-throughput techniques such as proteomics. Also, software tools are provided for querying, displaying, and analyzing pathways, thus furnishing an integrated web environment for visualizing and manipulating ROS-mediated cell-signaling events.

Angioplasty-induced superoxide anions and neointimal hyperplasia in the rabbit carotid artery: suppression by the isoflavone trans-tetrahydrodaidzein

Reactive oxygen species (ROS) may contribute to the development of stenosis in balloon catheter injured arteries. As isoflavones exhibit effects on ROS and cell proliferation In vitro that appear useful in preventing such stenosis, we examined the effects of the isoflavone trans-tetrahydrodaidzein (trans-THD) on development of neointimal lesions in relation to elevations in ROS in balloon catheter injured arteries. Carotid arteries of rabbits treated with either vehicle or trans-THD were injured with an inflated balloon catheter and cell proliferation, collagen content, ROS and vessel structure determined over the ensuing 28 days. Seven days after injury neointimal smooth muscle cell proliferation was reduced by 50% (p < 0.05) whilst medial cell proliferation was largely unaffected (p > 0.10). At this time ROS levels in vehicle-treated rabbits were elevated 3-fold compared to uninjured arteries (p < 0.05). Treatment with trans-THD reduced ROS levels to those seen in uninjured arteries (p > 0.05). The antiproliferative effects of trans-THD on intimal cell proliferation persisted 14 days after the injury, and twenty eight days after injury the size of the lumen in trans-THD-treated animals was 27% greater (p < 0.05) and the intima area: vessel area reduced by 40% (p < 0.05). The small effects of trans-THD on collagen accumulation was not statistically significant, indicating that effects on neointimal cell proliferation was the major mechanism by which this isoflavone attenuated development of the neointima. Intimal smooth muscle cells and ROS represent potentially important targets for the antiproliferative actions of trans-THD in injured arteries. Strategies using such isoflavones may be useful for preventing restenosis after vascular manipulations in humans.