Impairment of integrin-mediated cell-matrix adhesion in oxidant-stressed PC12 cells

Origin of Elevated S-Glutathionylated GAPDH in Chronic Neurodegenerative Diseases

H2O2-oxidized glyceraldehyde-3-phosphate dehydrogenase (GAPDH) catalytic cysteine residues (Cc(SH) undergo rapid S-glutathionylation. Restoration of the enzyme activity is accomplished by thiol/disulfide SN2 displacement (directly or enzymatically) forming glutathione disulfide (G(SS)G) and active enzyme, a process that should be facile as Cc(SH) reside on the subunit surface. As S-glutathionylated GAPDH accumulates following ischemic and/or oxidative stress, in vitro/silico approaches have been employed to address this paradox. Cc(SH) residues were selectively oxidized and S-glutathionylated. Kinetics of GAPDH dehydrogenase recovery demonstrated that glutathione is an ineffective reactivator of S-glutathionylated GAPDH compared to dithiothreitol. Molecular dynamic simulations (MDS) demonstrated strong binding interactions between local residues and S-glutathione. A second glutathione was accommodated for thiol/disulfide exchange forming a tightly bound glutathione disulfide G(SS)G. The proximal sulfur centers of G(SS)G and Cc(SH) remained within covalent bonding distance for thiol/disulfide exchange resonance. Both these factors predict inhibition of dissociation of G(SS)G, which was verified by biochemical analysis. MDS also revealed that both S-glutathionylation and bound G(SS)G significantly perturbed subunit secondary structure particularly within the S-loop, region which interacts with other cellular proteins and mediates NAD(P)+ binding specificity. Our data provides a molecular rationale for how oxidative stress elevates S-glutathionylated GAPDH in neurodegenerative diseases and implicates novel targets for therapeutic intervention.

Allogeneic/xenogeneic transplantation of peptide-labeled mitochondria in Parkinson's disease: restoration of mitochondria functions and attenuation of 6-hydroxydopamine-induced neurotoxicity

Although restoration of mitochondrial function in mitochondrial diseases through peptide-mediated allogeneic mitochondrial delivery (PMD) has been demonstrated in vitro, the in vivo therapeutic efficacy of PMD in Parkinson's disease (PD) has yet to be determined. In this study, we compared the functionality of mitochondrial transfer with or without Pep-1 conjugation in neurotoxin (6-hydroxydopamine, 6-OHDA)-induced PC12 cells and PD rat models. We injected mitochondria into the medial forebrain bundle (MFB) of the PD rats after subjecting the nigrostriatal pathway to a unilateral 6-OHDA lesion for 21 days, and we verified the effectiveness of the mitochondrial graft in enhancing mitochondrial function in the soma of the substantia nigra (SN) neuron through mitochondrial transport dynamics in the nigrostriatal circuit. The result demonstrated that only PMD with allogeneic and xenogeneic sources significantly sustained mitochondrial function to resist the neurotoxin-induced oxidative stress and apoptotic death in the rat PC12 cells. The remaining cells exhibited a greater capability of neurite outgrowth. Furthermore, allogeneic and xenogeneic transplantation of peptide-labeled mitochondria after 3 months improved the locomotive activity in the PD rats. This increase was accompanied by a marked decrease in dopaminergic neuron loss in the substantia nigra pars compacta (SNc) and consistent enhancement of tyrosine hydroxylase-positive immunoreaction of dopaminergic neurons in the SNc and striatum. We also observed that in the SN dopaminergic neuron in the treated PD rats, mitochondrial complex I protein and mitochondrial dynamics were restored, thus ameliorating the oxidative DNA damage. Moreover, we determined signal translocation of graft allogeneic mitochondria from the MFB to the calbindin-positive SN neuron, which demonstrated the regulatory role of mitochondrial transport in alleviating 6-OHDA-induced degeneration of dopaminergic neurons.

Graphene oxide flakes as a cellular adhesive: prevention of reactive oxygen species mediated death of implanted cells for cardiac repair

Mesenchymal stem cell (MSC) implantation has emerged as a potential therapy for myocardial infarction (MI). However, the poor survival of MSCs implanted to treat MI has significantly limited the therapeutic efficacy of this approach. This poor survival is primarily due to reactive oxygen species (ROS) generated in the ischemic myocardium after the restoration of blood flow. ROS primarily causes the death of implanted MSCs by inhibiting the adhesion of the MSCs to extracellular matrices at the lesion site (i.e., anoikis). In this study, we proposed the use of graphene oxide (GO) flakes to protect the implanted MSCs from ROS-mediated death and thereby improve the therapeutic efficacy of the MSCs. GO can adsorb extracellular matrix (ECM) proteins. The survival of MSCs, which had adhered to ECM protein-adsorbed GO flakes and were subsequently exposed to ROS in vitro or implanted into the ischemia-damaged and reperfused myocardium, significantly exceeded that of unmodified MSCs. Furthermore, the MSC engraftment improved by the adhesion of MSCs to GO flakes prior to implantation enhanced the paracrine secretion from the MSCs following MSC implantation, which in turn promoted cardiac tissue repair and cardiac function restoration. This study demonstrates that GO can effectively improve the engraftment and therapeutic efficacy of MSCs used to repair the injury of ROS-abundant ischemia and reperfusion by protecting implanted cells from anoikis.

Toxicity induced by cumene hydroperoxide in PC12 cells: protective role of thiol donors

Oxidative shock and production of reactive oxygen species are known to play a major role in situations leading to neuron degeneration, but the precise mechanisms responsible for cell degeneration remain uncertain. In the present article, we have studied in PC 12 cells the effect of cumene hydroxyperoxide on both cell metabolism and morphology. We observed that relatively low concentrations of the drug (100 μM) led to a significant decrease in the cellular content of ATP and reduced glutathione as well as to a decreased mitochondrial potential. These metabolic alterations were followed by an important increase in intracellular free calcium and membrane disruption and death. In parallel, we observed profound changes in cell morphology with a shortening of cell extensions, the formation of ruffles and blebs at the cell surface, and a progressive detachment of the cells from the surface of the culture flasks. We also showed that addition of thiol donors such as N-acetylcysteine or β-mercaptoethanol, which were able to enhance cell glutathione content, almost completely protected PC 12 cells from the toxic action of cumene hydroperoxide whereas pretreatment by buthionine sulfoximine, a selective inhibitor of GSH synthesis, enhanced its action.

Angiopoietin-1 reduces H(2)O(2)-induced increases in reactive oxygen species and oxidative damage to skin cells

UV light-based damage to skin cells can cause photoaging and skin cancer. A major cause of UV light-induced damage to skin is increased free radicals, such as superoxides. Increased superoxides can cause oxidative and nitrative damage to cell components. Thus, agents that counteract these damages may have therapeutic value. Herein, we show that angiopoietin-1 (ang1) prevented and blocked H(2)O(2)-induced increases in superoxides in human spontaneously immortalized keratinocyte line, HaCaT, and primary melanocytes (HeMn). Ang1 prevented H(2)O(2)-induced increases in damage to DNA (8-hydroxy-2'-deoxyguanosine) and proteins (nitrotyrosinylation). Ang1 promoted skin cell metabolism/viability, adhesion, and akt and MAPK(p42/44) activations. Using multi-gene transcriptional profiling, we found that skin cells express integrin subunits {(beta(1), beta(4-6), beta(8), alpha(v), alpha(2), alpha(3), alpha(6) (HaCaT)), (beta(1), beta(3), beta(5), beta(8), alpha(v), alpha(3) (HeMn))} and lack tie2 receptor mRNA. Integrin antibodies (alpha(v), beta(1)) disrupted skin cell adhesion to ang1 and ang1-induced decreases in superoxides. Our findings show that ang1 blocks free radical damage to skin cells and may be clinically useful to prevent and/or reduce photoaging and skin cancer.

Cellular mechanisms underlying temperature-induced bleaching in the tropical sea anemone Aiptasia pulchella

Temperature-induced bleaching in symbiotic cnidarians is a result of the detachment and loss of host cells containing symbiotic algae. We tested the hypothesis that host cell detachment is evoked through a membrane thermotropic event causing an increase in intracellular calcium concentration, [Ca2+]i, which could then cause collapse of the cytoskeleton and perturb cell adhesion. Electron paramagnetic resonance measurements of plasma membranes from the tropical sea anemone Aiptasia pulchella and the Hawaiian coral Pocillopora damicornis labeled with 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) revealed no membrane thermotropic event. In addition, intracellular imaging using Fura-2AM as well as labeling anemones with 45Ca revealed no significant change in [Ca2+]i. However, bleaching could be evoked at ambient temperature with 25 mmol l–1 caffeine without affecting [Ca2+]i. [Ca2+]i could be altered with ionomycin in isolated host cells, but ionomycin could not induce bleaching in A. pulchella. As caffeine can affect levels of intracellular protein phosphorylation, the ability of other agents that alter intracellular levels of protein phosphorylation to evoke bleaching was investigated. The protein phosphatase inhibitor vanadate could induce bleaching in A. pulchella. Two-dimensional gels of 32P-labeled proteins from cold-shocked, caffeine-treated and control anemones show that both temperature shock and caffeine alter the array of phosphorylated host soluble proteins. We conclude that cnidarian bleaching is linked to a temperature-induced alteration in protein phosphorylation.

Hydrogen peroxide induces Src family tyrosine kinase-dependent activation of Xenopus eggs

Fertilization is accompanied by a rapid and transient calcium release in eggs, which is required for the onset of zygotic developmental program or 'egg activation'. Recently, it was found that Src family tyrosine kinase (SFK)-dependent phospholipase C (PLC) activity is necessary for the calcium transience in fertilized Xenopus eggs. The present study demonstrates that hydrogen peroxide (H2O2) stimulates protein-tyrosine phosphorylation in Xenopus eggs, which occurs primarily in the egg cortex of the animal hemisphere as revealed by indirect immunofluorescence study. Egg SFK was found to be upregulated by H2O2 while the SFK-specific inhibitor PP1 effectively blocked H2O2-induced tyrosine phosphorylation. As in fertilized eggs, PLCgamma, but not Shc, was tyrosine-phosphorylated in H2O2-treated eggs. H2O2 also caused inositol 1,4,5-trisphosphate (IP3) production and sustained calcium release. After limited application of H2O2, elevated SFK activity and tyrosine phosphorylation were quickly reversed. Under such conditions, eggs showed cortical contraction and dephosphorylation of p42 MAP kinase, both of which are indicative of egg activation. These egg activation events, as well as H2O2-induced IP3 production and calcium release, were sensitive to PP1 and PLC inhibitor U-73122. Together, the present study demonstrated that H2O2 can mimic, at least in part, early events of Xenopus egg activation that require an SFK-dependent PLC pathway.

Oxidative stress affects cytoskeletal structure and cell-matrix interactions in cells from an ocular tissue: the trabecular meshwork

The trabecular meshwork (TM) is a specialized eye tissue that regulates the aqueous humor outflow and controls intraocular pressure. Cells in this tissue are essential for maintenance of the outflow system. Disturbance of the TM cell status by insults such as oxidative stress may lead to elevation of the intraocular pressure and development of glaucoma. In the present study, we investigated the effect of oxidative stress on the adhesion of human TM cells to extracellular matrix (ECM) proteins. Treatment with 1 mM of H2O2 for 10 or 30 min did not affect cell viability, whereas the adhesion of TM cells to fibronectin, laminin, and collagen types I and IV was significantly reduced. Phalloidin and immunostaining also revealed reorganization of actin and vimentin structures. The level of integrins alpha5beta1, alphavbeta3, and beta1 was not altered, although the distribution of paxillin and focal adhesion kinase in focal contacts was reduced. Concomitantly, the level of transcription factor NF-kappaB was enhanced by the H2O2 treatment. Nuclear extracts of the treated cells also contained a heightened NF-kappaB binding activity. These changes persisted for up to 6 h after the H2O2 treatment but were partially recovered by 24 h. We concluded that under sublethal oxidative stress conditions, the TM cell adhesion to the ECM was impaired. The short-term loss of cell-matrix adhesiveness may be related to the rearrangement of cytoskeletal structures. Extensive and repeated oxidative stress in vivo may result in reduced TM cell adhesion, leading to cell loss, compromised TM integrity, and pathologic consequences.

BPD-MA-mediated photosensitization in vitro and in vivo: cellular adhesion and beta1 integrin expression in ovarian cancer cells

Benzoporphyrin derivative monoacid (BPD-MA) photosensitization was examined for its effects on cellular adhesion of a human ovarian cancer cell line, OVCAR 3, to extracellular matrix (ECM) components. Mild BPD-MA photosensitization (approximately 85% cell survival) of OVCAR 3 transiently decreased adhesion to collagen IV, fibronectin, laminin and vitronectin to a greater extent than could be attributed to cell death. The loss in adhesiveness was accompanied by a loss of beta1 integrin-containing focal adhesion plaques (FAPs), although beta1 subunits were still recognized by monoclonal antibody directed against human beta1 subunits. In vivo BPD-MA photosensitization decreased OVCAR 3 adhesiveness as well. Photosensitized adhesion was reduced in the presence of sodium azide and enhanced in deuterium oxide, suggesting mediation by singlet oxygen. Co-localization studies of BPD-MA and Rhodamine 123 showed that the photosensitizer was largely mitochondrial, but also exhibited extramitochondrial, intracellullar, diffuse cytosolic fluorescence. Taken together, these data show that intracellular damage mediated by BPD-PDT remote from the FAP site can affect cellular-ECM interactions and result in loss of FAP formation. This may have an impact on long-term effects of photodynamic therapy. The topic merits further investigation.

The antioxidant N-acetylcysteine induces mesangial cells to create three-dimensional cytoarchitecture that underlies cellular differentiation

Prolonged culture of mesangial cells produces multifocal nodular structures, i.e., "hillocks," consisting of cells and extracellular matrix. Hillock formation is associated with induction of a differentiated phenotype of mesangial cells, with suppressed mitogenesis and downregulation of alpha-smooth muscle actin (alpha-SMA). Currently, little is understood regarding physiologically relevant factors that facilitate this cytodifferentiation. This study explores whether and how the cellular redox state modulates hillock formation. Exposure of confluent rat mesangial cells to the antioxidant N-acetylcysteine (NAC), an inducer of glutathione, dramatically facilitated hillock formation. This effect was mimicked by external addition of the reduced form of glutathione ethyl ester. In contrast, the oxidizing agents diamide and menadione inhibited the development of hillocks triggered by either NAC, glutathione, or prolonged culture. The induction of hillocks by NAC was correlated with downregulation of alpha-SMA as well as attenuated activity of the CArG box element (the cis-element relevant to the expression of the alpha-SMA gene and growth-associated genes). These results indicate that, by a redox-sensitive mechanism, NAC induces mesangial cells to create three-dimensional cytoarchitecture that underlies cellular differentiation.

Hydrogen peroxide decreases pHi in human aortic endothelial cells by inhibiting Na+/H+ exchange

Postischemic endothelial dysfunction may occur as a result of the effects of endogenous oxidants like hydrogen peroxide. Since endothelium-dependent vasodilator function may be affected by pHi, the effect of hydrogen peroxide on endothelial pHi was examined. Hydrogen peroxide (100 micromol/L for 10 minutes) decreased pHi from 7.24+/-0.01 to 7.02+/-0.02 and inhibited recovery from an ammonium chloride-induced intracellular acid load in carboxy SNARF 1 (c-SNARF 1)-loaded human aortic endothelial cells in bicarbonate-free solution. Prior inhibition of Na+/H+ exchange with 5-(N-ethyl-N-isopropyl)amiloride (10 micromol/L), by removal of extracellular Na+, or by glycolytic inhibition with iodoacetic acid blocked the subsequent effect of hydrogen peroxide on pHi. A 2-minute exposure to 100 micromol/L H2O2 decreased intracellular ATP levels by approximately 40%; this was prevented by 3-aminobenzamide and nicotinamide (1 mmol/L each), inhibitors of the DNA repair enzyme poly(ADP-ribose) polymerase. Both 3-aminobenzamide and nicotinamide significantly inhibited the hydrogen peroxide-induced intracellular acidification and the effect of hydrogen peroxide on recovery from an intracellular acid load. Hydrogen peroxide decreases pHi in human endothelial cells by inhibiting Na+/H+ exchange. This appears to be mediated by activation of the DNA repair enzyme poly(ADP-ribose) polymerase and subsequent depletion of intracellular ATP. Since a decrease in pHi in this range may alter the activity of NO synthase or affect the synthesis of vasodilator prostaglandins, the effect of hydrogen peroxide on the endothelial Na+/H+ exchanger may be important in the pathogenesis of postischemic endothelial dysfunction.

Importance of glucose-6-phosphate dehydrogenase activity for cell growth

The intracellular redox potential, which is determined by the level of oxidants and reductants, has been shown to play an important role in the regulation of cell growth. The principal intracellular reductant is NADPH, which is mainly produced by the pentose phosphate pathway through the actions of glucose-6-phosphate dehydrogenase (G6PD), the rate-limiting enzyme of the pentose phosphate pathway, and by 6-phosphogluconate dehydrogenase. Previous research has suggested that an increase in G6PD activity is important for cell growth. In this article, we suggest that G6PD activity plays a critical role in cell growth by providing NADPH for redox regulation. The results show the following: 1) inhibition of G6PD activity abrogated growth factor stimulation of [3H]thymidine incorporation in all cell lines tested; 2) overexpression of G6PD stimulated cell growth, as measured by an increase in [3H]thymidine incorporations as compared with cells transfected with vector alone; 3) inhibition of G6PD caused cells to be more susceptible to the growth inhibitory effects of H2O2; 4) inhibition of G6PD led to a 30-40% decrease in the NADPH/NADP ratio; and 5) inhibition of G6PD inhibited cell anchorage and significantly decreased the growth-related stimulation of tyrosine phosphorylation.

Photodynamic therapy inhibits cell adhesion without altering integrin expression

Adhesion is a primordial cell function that, among others, regulates inflammation, metastasis, and tissue repair. To understand how these events could be affected by photodynamic therapy (PDT), we studied the effects of PDT on human foreskin fibroblast (HFF) adhesion to bovine collagen type I, human vitronectin or fibronectin. PDT, using benzoporphyrin derivative monoacid ring A (verteporfin) as the photosensitizer, inhibited cell adhesion in a drug dose-dependent manner, with no significant difference among matrices. The drug dose that killed 90% of cells within 20 h post-treatment inhibited HFF adhesion by 55%-68%. However, 45 min following PDT, a time period corresponding to that of the adhesion assay, HFF membrane integrity remained unaltered. In addition, cell surface expression of integrins was not modified for at least 2h following PDT. Western blots of cell lysates, using the anti-phosphotyrosine 4G10 monoclonal antibody, revealed that PDT prevented the adhesion-induced phosphorylation of 110-130 kDa proteins. Immunoblots of cell lysates immunoprecipitated with antibodies to focal adhesion kinase suggested that its phosphorylation was suppressed by PDT. These results demonstrate that PDT inhibits cell adhesion and affects integrin signalling without modifying cell membrane integrity or integrin expression.

Measurement of striatal H2O2 by microdialysis following global forebrain ischemia and reperfusion in the rat: correlation with the cytotoxic potential of H2O2 in vitro

Toxic reactive oxygen species have been implicated as important mediators of tissue injury after reperfusion of ischemic organs. When rats are subject to 30 min global forebrain ischemia, 24 h following this insult, there is substantial loss of medium-sized neurones as revealed by histological sectioning of the striatal region of the forebrain. The goal of this study was to utilize microdialysis to directly measure one of the more stable intermediates of reduced molecular oxygen, H2O2 in the rat striatum following 4-vessel occlusion and reperfusion, and to correlate these levels with H2O2 toxicity to neurones grown in culture. A significant rise in striatal H2O2 levels was observed for about 1 h during reperfusion, amounting to an increase of approximately 100 microM at the peak. In control experiments where the dialysis probe was embedded in cortical regions surrounding the striatum (where there is no neuronal loss due to the ischemic episode), there was no measurable increase in tissue H2O2 levels. H2O2 has been previously shown to be neurotoxic to PC12 cells as well as rat primary hippocampal neurones at comparable concentrations striatal neurones experience during reperfusion. We demonstrate that H2O2 is also neurotoxic to the human cortical neuronal cell line, HCN-1A. These experiments establish an important link between oxidant generation and neuronal loss in this tissue following global forebrain ischemia.