Reoxygenating microvascular endothelium exhibits temporal dissociation of NF-kappaB and AP-1 activation

ROS Signaling in the Pathogenesis of Acute Lung Injury (ALI) and Acute Respiratory Distress Syndrome (ARDS)

The generation of reactive oxygen species (ROS) plays an important role for the maintenance of cellular processes and functions in the body. However, the excessive generation of oxygen radicals under pathological conditions such as acute lung injury (ALI) and its most severe form acute respiratory distress syndrome (ARDS) leads to increased endothelial permeability. Within this hallmark of ALI and ARDS, vascular microvessels lose their junctional integrity and show increased myosin contractions that promote the migration of polymorphonuclear leukocytes (PMNs) and the transition of solutes and fluids in the alveolar lumen. These processes all have a redox component, and this chapter focuses on the role played by ROS during the development of ALI/ARDS. We discuss the origins of ROS within the cell, cellular defense mechanisms against oxidative damage, the role of ROS in the development of endothelial permeability, and potential therapies targeted at oxidative stress.

Recruitment of the adaptor protein Nck to PECAM-1 couples oxidative stress to canonical NF-κB signaling and inflammation

Oxidative stress stimulates nuclear factor κB (NF-κB) activation and NF-κB-dependent proinflammatory gene expression in endothelial cells during several pathological conditions, including ischemia/reperfusion injury. We found that the Nck family of adaptor proteins linked tyrosine kinase signaling to oxidative stress-induced activation of NF-κB through the classic IκB kinase-dependent pathway. Depletion of Nck prevented oxidative stress induced by exogenous hydrogen peroxide or hypoxia/reoxygenation injury from activating NF-κB in endothelial cells, increasing the abundance of the proinflammatory molecules ICAM-1 (intracellular adhesion molecule-1) and VCAM-1 (vascular cell adhesion molecule-1) and recruiting leukocytes. Nck depletion also attenuated endothelial cell expression of genes encoding proinflammatory factors but not those encoding antioxidants. Nck promoted oxidative stress-induced activation of NF-κB by coupling the tyrosine phosphorylation of PECAM-1 (platelet endothelial cell adhesion molecule-1) to the activation of p21-activated kinase, which mediates oxidative stress-induced NF-κB signaling. Consistent with this mechanism, treatment of mice subjected to ischemia/reperfusion injury in the cremaster muscle with a Nck inhibitory peptide blocked leukocyte adhesion and emigration and the accompanying vascular leak. Together, these data identify Nck as an important mediator of oxidative stress-induced inflammation and a potential therapeutic target for ischemia/reperfusion injury.

Perilla frutescens leaf extract inhibits mite major allergen Der p 2-induced gene expression of pro-allergic and pro-inflammatory cytokines in human bronchial epithelial cell BEAS-2B

Perilla frutescens has been used in traditional medicine for respiratory diseases due to its anti-bacterial and anti-inflammatory activity. This study aimed to investigate effects of Perilla frutescens leaf extract (PFE) on expression of pro-allergic and pro-inflammatory cytokines in airway epithelial cells exposed to mite major allergen Der p 2 (DP2) and the underlying mechanisms. Our results showed that PFE up to 100 µg/mL had no cytotoxic effect on human bronchial epithelial cell BEAS-2B. Further investigations revealed that PFE dose-dependently diminished mRNA expression of pro-allergic cytokine IL-4, IL-5, IL-13 and GM-CSF, as well as pro-inflammatory cytokine IL-6, IL-8 and MCP-1 in BEAS-2B cells treated with DP2. In parallel to mRNA, the DP-2-elevated levels of the tested cytokines were decreased. Further investigation showed that DP2-indued phosphorylation of p38 MAPK (P38) and JNK, but not Erk1/2, was also suppressed by PFE. In addition, PFE elevated cytosolic IκBα level and decreased nuclear NF-κB level in DP2-stimulated BEAS-2B cells. Taken together, these findings revealed that PFE significantly diminished both mRNA expression and protein levels of pro-allergic and pro-inflammatory cytokines in response to DP2 through inhibition of P38/JNK and NK-κB activation. These findings suggest that PFE should be beneficial to alleviate both allergic and inflammatory responses on airway epithelium in response to aeroallergens.

Cezanne regulates inflammatory responses to hypoxia in endothelial cells by targeting TRAF6 for deubiquitination

RATIONALE

Hypoxia followed by reoxygenation promotes inflammation by activating nuclear factor κB transcription factors in endothelial cells (ECs). This process involves modification of the signaling intermediary tumor necrosis factor receptor-associated factor 6 with polyubiquitin chains. Thus, cellular mechanisms that suppress tumor necrosis factor receptor-associated factor 6 ubiquitination are potential therapeutic targets to reduce inflammation in hypoxic tissues.

OBJECTIVE

In this study, we tested the hypothesis that endothelial activation in response to hypoxia-reoxygenation can be influenced by Cezanne, a deubiquitinating enzyme that cleaves ubiquitin from specific modified proteins.

METHODS AND RESULTS

Studies of cultured ECs demonstrated that hypoxia (1% oxygen) induced Cezanne via p38 mitogen-activated protein kinase-dependent transcriptional and post-transcriptional mechanisms. Hypoxia-reoxygenation had minimal effects on proinflammatory signaling in unmanipulated ECs but significantly enhanced Lys63 polyubiquitination of tumor necrosis factor receptor-associated factor 6, activation of nuclear factor κB, and expression of inflammatory genes after silencing of Cezanne. Thus, although hypoxia primed cells for inflammatory activation, it simultaneously induced Cezanne, which impeded signaling to nuclear factor κB by suppressing tumor necrosis factor receptor-associated factor 6 ubiquitination. Similarly, ischemia induced Cezanne in the murine kidney in vascular ECs, glomerular ECs, podocytes, and epithelial cells, and genetic deletion of Cezanne enhanced renal inflammation and injury in murine kidneys exposed to ischemia followed by reperfusion.

CONCLUSIONS

We conclude that inflammatory responses to ischemia are controlled by a balance between ubiquitination and deubiquitination, and that Cezanne is a key regulator of this process. Our observations have important implications for therapeutic targeting of inflammation and injury during ischemia-reperfusion.

Anti-inflammatory activity of Sorbus commixta water extract and its molecular inhibitory mechanism

ETHNOPHARMACOLOGICAL SIGNIFICANCE

Sorbus commixta Hedl. (Rosaceae) is a well known traditionally valuable medicinal plant in Korea, China and Japan. This plant has been prescribed for long time for various inflammatory symptoms such as asthma, bronchitis, gastritis and dropsy.

AIM OF STUDY

Although a number of pharmacological properties have already been demonstrated, the anti-inflammatory effect of this plant and its associated molecular mechanisms has not yet been fully investigated.

MATERIALS AND METHODS

In order to address the anti-inflammatory activity of S. commixta water extract (Sc-WE), lipopolysaccharide (LPS)-stimulated macrophages were employed and production of inflammatory mediators by these cells were evaluated.

RESULTS

Sc-WE significantly suppressed the production of nitric oxide (NO) and prostaglandin (PG)E(2) in a dose-dependent manner and blocked ear edema formation induced by arachidonic acid in mouse. In addition, this extract effectively diminished the mRNA levels of inducible NO synthase (iNOS) and cyclooxygenase (COX)-2, indicating that the inhibition occurs at the transcriptional level. Interestingly, Sc-WE remarkably blocked NF-κB translocation and its upstream signaling events by inhibition of κBα (IκBα), IκBα kinase (IKK), Akt (protein kinase B), phosphoinositide-dependent kinase 1 (PDK1), p85/phosphoinositide-3-kinase (PI3K), as per the results obtained from the reporter gene assay and immunoblotting analysis. More intriguingly, Sc-WE suppressed activities of Src and Syk kinases as well as their phosphorylation levels without altering molecular complex formation between them and toll like receptor (TLR)4 or MyD88, an adaptor protein of TLR4-mediated signaling.

CONCLUSION

Therefore, our results suggest that Sc-WE can be developed as a potent anti-inflammatory remedy, acting by suppressing the inflammatory signaling cascade composed of Src, Syk, and NF-κB.

Reoxygenation attenuates the adhesion of neutrophils to microvascular endothelial cells

In humans, the pathophysiological inflammation response subsequent to hypoxia and reoxygenation often leads to systemic inflammation and multiorgan failure. We applied a newly developed static interaction model using human polymorphonuclear neutrophils and microvascular endothelial cells to clarify the role of hypoxia and hypoxia/reoxygenation in vitro. Human dermal microvascular endothelial cell cultures (n = 7) were exposed to hypoxia and different reoxygenation periods and the adherence rate of neutrophils to the endothelial cells as well as to the protein matrix on the culture slide surface were determined by quantitative microscopy. Hypoxia clearly triggered neutrophil adhesion to human dermal microvascular endothelial cells whereas additional reoxygenation significantly decreased neutrophil adhesion. These in vitro findings suggest that systemic inflammation caused by increased neutrophil adherence to the microvascular endothelium is already initiated by hypoxia rather than by subsequent reoxygenation.

Regulatory effect of cinnamaldehyde on monocyte/macrophage-mediated inflammatory responses

Cinnamaldehyde (CA) has been known to exhibit anti-inflammatory and anticancer effects. Although numerous pharmacological effects have been demonstrated, regulatory effect of CA on the functional activation of monocytes and macrophages has not been fully elucidated yet. To evaluate its monocyte/macrophage-mediated immune responses, macrophages activated by lipopolysaccharide (LPS), and monocytes treated with proaggregative antibodies, and extracellular matrix protein fibronectin were employed. CA was able to suppress both the production of nitric oxide (NO) and upregulation of surface levels of costimulatory molecules (CD80 and CD69) and pattern recognition receptors (toll-like receptor 2 (TLR2) and complement receptor (CR3)). In addition, CA also blocked cell-cell adhesion induced by the activation of CD29 and CD43 but not cell-fibronectin adhesion. Immunoblotting analysis suggested that CA inhibition was due to the inhibition of phosphoinositide-3-kinase (PI3K) and phosphoinositide-dependent kinase (PDK)1 as well as nuclear factor-(NF-) kappaB activation. In particular, thiol compounds with sulphydryl group, L-cysteine and dithiothreitol (DTT), strongly abrogated CA-mediated NO production and NF-kappaB activation. Therefore, our results suggest that CA can act as a strong regulator of monocyte/macrophage-mediated immune responses by thiolation of target cysteine residues in PI3K or PDK1.

Prolyl hydroxylase inhibition attenuates post-ischemic cardiac injury via induction of endoplasmic reticulum stress genes

Ischemia/reperfusion (I/R) unleashes cellular events that threaten organ survival. I/R affects endoplasmic reticulum (ER) integrity and initiates the unfolded protein response (UPR). The adaptive arm of the UPR attenuates ER stress by increasing expression of chaperones promoting proper protein folding. However, failure to resolve ER stress leads to apoptotis. We recently showed that prolyl hydroxylase inhibition (PHI) attenuated post-ischemic cardiac injury. We hypothesized that PHI attenuated myocardial I/R injury through modulation of the UPR. We show for the first time that PHI activates all three regulatory arms of the UPR in murine microvascular endothelial cells and in mouse hearts. Cardiac I/R activated expression of pro-apoptotic CHOP (2.8 fold, n=3, p<0.01). PHI significantly decreased CHOP expression (50%, n=3, p<0.05) in post-ischemic hearts. PHI also induced activating transcription factor 4 (3.5 fold, n=3, p<0.001), glucose-regulated protein 78 (6 fold, n=3, p<0.001) and ER degradation-enhancing alpha-mannosidase-like protein (2.8 fold, n=3, p<0.001) expression in reperfusing hearts. Thus PHI resulted in significant reduction of apoptosis in post-ischemic myocardium. Our studies suggest that PHI induces protective ER stress proteins and attenuates post-ischemic myocardial damage by decreasing the pro-apoptotic components of the UPR.

The A20 gene protects kidneys from ischaemia/reperfusion injury by suppressing pro-inflammatory activation

Ischaemia followed by reperfusion (I/R) can induce inflammation and injury and is a risk factor for delayed graft function and rejection of transplanted kidneys. Inflammation is regulated by NF-kappaB transcription factors which induce pro-inflammatory molecules in endothelial cells (EC). We examined whether A20, a negative regulator of NF-kappaB, can protect kidneys from I/R injury. To mimic the fluctuations in endothelial oxygenation that occur during I/R we exposed cultured human umbilical vein EC (HUVEC) to hypoxia (1% O(2) for 4 h) followed by re-oxygenation (21% O(2) for 1 h-24 h). We observed transient expression of pro-inflammatory molecules (E-selectin, VCAM-1 and IL-8) and sustained expression of A20 in HUVEC exposed to hypoxia/re-oxygenation. The effect of A20 on endothelial responses to hypoxia/re-oxygenation was assessed. We observed that pre-treatment of HUVEC with an adenovirus containing A20 (Ad-A20) suppressed activation of NF-kappaB and induction of pro-inflammatory molecules by hypoxia/re-oxygenation, whereas a control adenovirus had little or no effect. Thus the induction of A20 may form a negative feedback loop in pro-inflammatory signalling in cells exposed to hypoxia/re-oxygenation. To validate our cell culture experiments we examined the role of A20 in renal responses to I/R. We observed that A20 was induced in rat kidneys exposed to I/R. Moreover, pre-treatment of animals with Ad-A20 significantly reduced acute tubular necrosis, renal expression of VCAM-1 and NF-kappaB activation in response to I/R, whereas pre-treatment with control adenovirus did not. Our observations suggest that A20 maintains physiological homeostasis in kidneys exposed to I/R by protecting them from inflammation and injury.

Hypoxia induces protection against etoposide-induced apoptosis: molecular profiling of changes in gene expression and transcription factor activity

Background

it is now well established that hypoxia renders tumor cells resistant to radio- but also chemotherapy. However, few elements are currently available as for the mechanisms underlying this protection.

Results

in this study, physiological hypoxia was shown to inhibit apoptosis induced in HepG2 cells by etoposide. Indeed, hypoxia reduced DNA fragmentation, caspase activation and PARP cleavage. The DNA binding activity of 10 transcription factors was followed while the actual transcriptional activity was measured using specific reporter plasmids. Of note is the inhibition of the etoposide-induced activation of p53 under hypoxia. In parallel, data from low density DNA microarrays indicate that the expression of several pro- and anti-apoptotic genes was modified, among which are Bax and Bak whose expression profile paralleled p53 activity. Cluster analysis of data unravels several possible pathways involved in the hypoxia-induced protection against etoposide-induced apoptosis: one of them could be the inhibition of p53 activity under hypoxia since caspase 3 activity parallels Bax and Bak expression profile. Moreover, specific downregulation of HIF-1α by RNA interference significantly enhanced apoptosis under hypoxia possibly by preventing the hypoxia mediated decrease in Bak expression without altering Bax expression.

Conclusion

these results are a clear demonstration that hypoxia has a direct protective effect on apoptotic cell death. Moreover, molecular profiling points to putative pathways responsible for tumor growth in challenging environmental conditions and cancer cell resistance to chemotherapeutic agents.

Activation of hypoxia-inducible factor-1 via prolyl-4 hydoxylase-2 gene silencing attenuates acute inflammatory responses in postischemic myocardium

Emerging research suggests that oxidant-driven transcription of key cytokine/chemokine networks within the myocardium plays a crucial role in producing ischemia-reperfusion (I/R) injury. We recently showed that activation of hypoxia-inducible factor-1 (HIF-1) attenuated cardiac I/R injury. Diminished injury in these prior studies was associated with significant reductions in circulating interleukin-8 levels, suggesting that HIF-1 may play an important role in modulating postischemic cardiac inflammation. In the current study, we examined the role of HIF-1 activation in modulating proinflammatory chemokine [macrophage inflammatory protein (MIP)-2, cytokine-induced neutrophil chemoattractant factor (KC), and lipopolysaccharide-induced CXC chemokine (LIX)] and adhesion molecule [intercellular adhesion molecule (ICAM)-1] expression in murine cardiomyocytes in vitro (HL-1 cell line) and in intact murine hearts following in vivo I/R injury. Our results show that HIF-1 activation induced both pharmacologically by the prolyl hydroxylase inhibitor dimethyloxallyl glycine and via small-interfering RNA (siRNA)-mediated prolyl-4 hydroxylase-2 (P4HA2) gene silencing significantly attenuated tumor necrosis factor-α-induced chemokine (KC and LIX) and ICAM-1 expression in cardiomyocytes. In vivo, postischemic hearts obtained from animals receiving the P4HA2 siRNA (HIF-1 activation) exhibited significantly reduced CXC chemokine (MIP-2, KC, and LIX), CC chemokine (monocyte chemoattractant protein-1), and ICAM-1 expression when compared with postischemic hearts from either saline I/R controls or postischemic hearts from animals receiving a nontargeting control siRNA (no HIF-1 activation). Diminished chemokine and adhesion molecule expression in HIF-1-activated postischemic hearts was associated with significantly reduced polymorphonuclear leukocyte infiltration and myocardial infarct size (>60% reduction P4HA2 siRNA I/R vs. saline I/R, P < 0.001, n = 6). In conclusion, these results demonstrate for the first time that HIF-1 activation following infusion of siRNA to P4HA2 plays a key role in modulating I/R-associated cardiac inflammatory responses.

Cell passage-associated transient high oxygenation causes a transient decrease in cellular glutathione and affects T cell responses to apoptotic and mitogenic stimuli

Routine cell line maintenance involves removal of waste products and replenishment of nutrients via replacement of cell culture media. Here, we report that routine maintenance of three discrete cell lines (HSB-CCRF-2 and Jurkat T cells, and phaeo-chromocytoma PC12 cells) decreases the principal cellular antioxidant, glutathione, by up to 42% in HSB-CCRF-2 cells between 60 and 120min after media replenishment. However, cellular glutathione levels returned to baseline within 5h after passage. The decrease in glutathione was associated with modulation of the response of Jurkat T cells to apoptotic and mitogenic signals. Methotrexate-induced apoptosis over 16h, measured as accumulation of apoptotic nucleoids, was decreased from 22 to 17% if cells were exposed to cytotoxic agent 30min after passage compared with cells exposed to MTX in the absence of passage. In contrast, interleukin-2 (IL-2) production over 24h in response to the toxin phytohaemagglutinin (PHA), was increased by 34% if cells were challenged 2h after passage compared with PHA treatment in the absence of passage. This research highlights the presence of a window of time after cell passage of non-adherent cells that may lead to over- or under-estimation of subsequent cell responses to toxins, which is dependent on cellular antioxidant capacity or redox state.

Hypoxia inducible factor-1 modulates hemin-induced IL-8 secretion in microvascular endothelium

Ischemia/Reperfusion injury and hemolysis are characterized by erythrocyte lysis and release of free heme into the microcirculation. Following substantial erythrocyte lysis, heme overwhelms circulatory heme-binding protein networks rapidly forming hemin, the oxidized form of iron protoporphyrin IX. Hemin's role in modulating inflammatory responses in microvascular endothelium (MVEC) remains ill-defined. We studied the impact of hemin exposure on human MVEC interleukin-8 (IL-8) expression. Hemin significantly up-regulated MVEC IL-8 secretion and was associated with cellular iron loading. Hemin-induced IL-8 up-regulation was significantly attenuated by increasing environmental serum concentrations. As well, hemin-induced IL-8 secretion was significantly reduced in a concentration-dependent fashion following pyrrolidine dithiocarbamate exposure, suggesting that induction occurred via an oxidant-sensitive mechanism. Interestingly, transfection studies revealed that oxidant-driven transcription factors NF-kappaB and AP-1 played no role in hemin-induced IL-8 transcription. In studies employing actinomycin D, hemin was found to dramatically lengthen IL-8 mRNA half-life. Of major importance in the current report was the finding that hypoxia inducible factor-1 (HIF-1), a powerful transcription factor mediating tissue responses to hypoxia, potently regulated hemin-induced IL-8 secretion in human MVEC. Activation of HIF-1 via the prolyl hydroxylase inhibitor dimethyloxalylglycine attenuated hemin-induced IL-8 secretion. These studies were confirmed via DNA-directed siRNA silencing of HIF-1alpha. In conclusion, hemin induces a serum protein-sensitive pro-inflammatory phenotype in MVEC via an oxidant-sensitive mechanism that is powerfully regulated by HIF-1.

Hypoxia inducible factor-1: regulation by nitric oxide in posthypoxic microvascular endothelium

Microvascular endothelial cells provide a critical regulatory interface between blood constituents and tissue. Hypoxia inducible factor-1 (HIF-1) is a key transcription factor required for expression of hypoxia-dependent genes. We employed a model of hypoxia and reoxygenation (H/R) using the dermal microvascular endothelial cell line HMEC-1 to examine the effects of altered oxygen concentrations on microvascular HIF-1 expression and nitric oxide (NO) formation. Hypoxia increased inducible NO synthase (iNOS) mRNA in a time-dependent manner in HMEC-1. However, endothelial NO synthase mRNA progressively declined during hypoxia. H/R promoted significant increases in cellular nitrite levels that were significantly abrogated by the specific iNOS inhibitor N6-(1-iminoethyl)-L-lysine, di hy drochloride. Exogenous NO promoted stabilization of the alpha subunit of HIF-1 and produced functional DNA binding. Exposure of HMEC-1 to H/R resulted in previously unrecognized biphasic HIF-1alpha stabilization during reoxygenation. When the iNOS gene was silenced through the use of iNOS-specific small interfering RNA, HIF-1alpha stabilization and HIF-1 activation were dramatically diminished, suggesting that inducible NOS-derived NO is a key factor sustaining HIF-1 activation during both hypoxia and reoxygenation.

Comparative effects of IL-1beta and hydrogen peroxide (H2O2) on catabolic and anabolic gene expression in juvenile bovine chondrocytes

OBJECTIVE

To compare the effects of hydrogen peroxide (H(2)O(2)) to those of interleukin-1beta (IL-1beta) on gene expression in juvenile bovine articular chondrocytes (BAC). The study analyses the activation of nuclear factor-kappa B (NF-kappaB) and activator protein-1 (AP-1) transcription factors, and the mRNA steady-state levels of the type II collagen, aggrecan core protein matrix, metalloproteinases (MMP-1, -3), and transforming growth factor-beta1 (TGF-beta1) genes.

METHODS

Confluent BAC cultures were treated for 3 and 24h with IL-1beta and/or different concentrations of H(2)O(2) (Protocol 1). Following initial treatment, a part of the cells was further subjected to another 24h with medium, in the presence of IL-1beta, to determine the effect of the cytokine on H(2)O(2) pre-treated cells (Protocol 2). Total RNA and nuclear protein extractions were performed to study mRNA steady-state levels (real-time polymerase chain reaction) and AP-1/NF-kappaB DNA binding (Electrophoretic Mobility Shift Assays), respectively.

RESULTS

IL-1beta enhanced both AP-1 and NF-kappaB binding, whereas H(2)O(2) only activated AP-1. H(2)O(2) pre-treatment decreased the IL-1beta activation of NF-kappaB. Both H(2)O(2) and IL-1beta down-regulated type II collagen and aggrecan expression and increased that of MMP-1 and -3. When cells were pre-treated with H(2)O(2), followed by IL-1beta, the effects were the same as those observed with H(2)O(2) alone. However, although H(2)O(2) and IL-1beta were capable of increasing TGF-beta1 expression separately, subsequent incubation with both factors led to a partial or total abolition of TGF-beta1 up-regulation.

CONCLUSION

The different regulation of NF-kappaB and AP-1 by H(2)O(2) and IL-1beta underlines the distinct roles played by the two transcription factors in the regulation of gene expression. H(2)O(2) and IL-1beta exert similar effects on matrix, MMPs and TGF-beta1 gene expression. However, the association of H(2)O(2) and IL-1beta does not cause synergic effect, and rather leads, in some cases, to an opposite effect. These data provide further insights into the respective roles of reactive oxygen species and cytokine in the pathophysiology of joint diseases.

Proteomic analysis of the proteins expressed by hydrogen peroxide treated cultured human dermal microvascular endothelial cells

Reactive oxygen species (ROS) have been traditionally regarded as toxic by-products of aerobic metabolism. However, ROS also act as intracellular signaling molecules and can mediate phenotypes in vascular endothelial cells, which may be physiological or pathological in nature. To clarify the molecular mechanisms of ROS signaling, we examined hydrogen peroxide (H(2)O(2))-responsive proteins in cultured human dermal microvascular endothelial cells (HMVEC) using proteomic tools. Protein expression in HMVEC was studied after they had been exposed to low- and high-levels of H(2)O(2) for various times, and intracellular ROS production was examined by flow cytometer and UV spectrophotometer. Proteins obtained from dose- and time-dependent series were separated by two-dimensional gel electrophoresis and tentatively identified by matrix-assisted laser desorption-time of flight mass spectrometry, by matching the tryptic mass maps obtained with entries in the NCBI and Swiss-Prot protein sequence database. At least 163 proteins were changed by H(2)O(2), and 60 proteins were identified. Oxidative stress triggered dramatic change in the expression of proteins in primary microvessel endothelial cells, and their mapping to cellular process provided a view of the ubiquitous cellular changes elicited by H(2)O(2). These results could provide a framework for the understanding of the mechanisms of cellular redox homeostasis and H(2)O(2) metabolism in microendothelium environment in various biological processes as well as pathological conditions.

Transcriptional responses of rat skeletal muscle following hypoxia-reoxygenation and near ischaemia-reperfusion

AIM

The effect of ischaemia/reperfusion or hypoxia/reoxygenation on gene expression has not been extensively studied. We hypothesized that in skeletal muscle, tissue hypoxia of similar magnitude but induced by different mechanisms would lead to different transcriptional responses.

METHODS

Muscle gene transcription was assessed using microarray analysis and reverse transcriptase polymerase chain reaction in 18 rats exposed to regional hind limb near ischaemia/reperfusion (n = 6), hypoxia/reoxygenation (n = 6) or sham operation (n = 6). Hypoxic burden was measured by the area under the PtO(2)-time curve.

RESULTS

PtO(2) was reduced in both the near ischaemia/reperfusion and hypoxia/reoxygenation groups. Although the hypoxic burden was similar, the genomic response was different for each condition. Near ischaemia/reperfusion had a greater effect on gene expression than hypoxia/reoxygenation. Using stringent criteria for changes in gene expression (i.e. more than or equal to twofold change vs. control) unique patterns of gene expression could be identified suggesting individualized transcriptional responses to each of these injuries. Several genes, including insulin-like growth factor 1 (IGF-1) and cyclin-dependent kinase inhibitor (p27(Kip1)) were induced by both injury types and these may have potential clinical application as markers of tissue damage. In contrast, no single gene was downregulated by both injury conditions.

CONCLUSIONS

The mechanism of skeletal muscle hypoxia has a profound effect on its subsequent transcriptional response. We identified several potential candidates as markers of skeletal muscle ischaemic damage.

Multiple Involvement of Oxidative Stress in Werner Syndrome Phenotype

Werner syndrome is a genetic disease characterized by early ageing, excess cancer risk, high incidence of type II diabetes mellitus, early atherosclerosis, ocular cataracts, and osteoporosis. The protein encoded by the defective gene, WRN (WRNp) associates with three activities, that is, a RecQ DNA helicase, 3'-5'-exonuclease and ATPase activities. By highlighting the DNA helicase activity, a widespread consensus in WS-associated defect(s) has been established, pointing toward a deficiency in maintaining DNA integrity. However, a possible involvement of redox pathways in WS may be suggested by several lines of evidence that include: (i) the multiple functions and interactions of WRNp with oxidative stress-related activities and factors; (ii) the pleiotropic WS clinical phenotype encompassing a number of oxidative stress-related pathologies; (iii) redox-related toxicity mechanisms of several xenobiotics exerting excess toxicity in WS cells; (iv) recent in vivo and in vitro findings of redox abnormalities in WS patients and in WS cells. The working hypothesis is raised that a deficiency in WRNp, and the pleiotropic clinical phenotype in WS patients may provide the basis to envision an underlying in vivo prooxidant state, which causes oxidative damage to biomolecules, with multiple oxidative stress-related alterations, resulting in multi-faceted clinical consequences.

HIF-1 activation attenuates postischemic myocardial injury: role for heme oxygenase-1 in modulating microvascular chemokine generation

The CXC chemokine IL-8, which promotes adhesion, activation, and transmigration of polymorphonuclear neutrophils (PMN), has been associated with production of tissue injury in reperfused myocardium. Hypoxia-inducible factor-1 (HIF-1) is a heterodimeric peptide that is a key regulator of genes such as heme oxygenase (HO)-1 expressed under hypoxic conditions. We hypothesized that HO-1 plays an important role in regulating proinflammatory mediator production under conditions of ischemia-reperfusion. HIF-1 was activated in the human microvascular endothelial cell line (HMEC-1) with the prolyl hydroxylase inhibitor dimethyloxalylglycine (DMOG). DMOG significantly attenuated cytokine-induced IL-8 promoter activity and protein secretion and cytokine-induced PMN migration across human microvascular endothelial cell line HMEC-1 monolayers. In vivo studies in a rabbit model of myocardial ischemia-reperfusion showed that rabbits pretreated with a 20 mg/kg DMOG infusion (n = 6) 24 h before study exhibited a 21.58 +/- 1.76% infarct size compared with 35.25 +/- 2.06% in saline-treated ischemia-reperfusion animals (n = 6, change in reduction = 39%; P < 0.001). In DMOG-pretreated (20 mg/kg) animals, plasma IL-8 levels at 3 h after onset of reperfusion were 405 +/- 40 pg/ml vs. 790 +/- 40 pg/ml in saline-treated ischemia-reperfusion animals (P < 0.001). DMOG pretreatment reduced myocardial myeloperoxidase activity, expressed as number of PMN per gram of myocardium, to 1.43 +/- 0.59 vs. 4.86 +/- 1.1 (P = 0.012) in saline-treated ischemia-reperfused hearts. Both in vitro and in vivo DMOG-attenuated IL-8 production was associated with robust HO-1 expression. Thus our data show that HIF-1 activation induces substantial HO-1 expression that is associated with attenuated proinflammatory chemokine production by microvascular endothelium in vitro and in vivo.

Intragraft heme oxygenase-1 and coronary artery disease after heart transplantation

Peri-operative tissue injury triggers the development of Transplant Coronary Artery Disease (TCAD). Animal studies have shown that induction of heme oxygenase (HO)-1 protects the donor organ from the development of TCAD. To investigate the role of HO-1 in TCAD after clinical heart transplantation, we measured intragraft mRNA expression of HO-1, HIF-1alpha, TGF-beta, FLIP, and the Bcl-2/Bax balance. Immunohistochemical staining of HO-1 was performed to determine its origin. Myocardial biopsies taken at the end of the transplantation procedure (time 0), at 1 week and at 10 months after transplantation were studied from recipients with or without angiographic signs of accelerated TCAD, diagnosed after 1 year. At time 0, no differences in mRNA expression for any of the measured parameters were found between TCAD positive and negative patients. At 1 week, mRNA expression of HO-1 and TGF-beta was higher in grafts that developed accelerated TCAD (p=0.001 and p=0.0002). These higher mRNA levels were accompanied by a pro-apoptotic shift in Bcl-2/Bax (p=0.02), suggesting proneness for apoptosis via the mitochondrial pathway. Immunohistochemical staining showed that HO-1 was mainly produced by infiltrating macrophages. At 10 months, again HO-1 and TGF-beta levels were high in TCAD positive patients (p=0.02 and p=0.05), but the expression of apoptotic markers was comparable at this time point. Our results suggest that a higher HO-1 by macrophages in our patient population might be an adaptive response to tissue injury and inflammation, reflecting damage due to the transplantation procedure that finally results in TCAD.

Regulation of hypoxia inducible factor-1 by nitric oxide in contrast to hypoxia in microvascular endothelium

Hypoxia activates the transcription factor, hypoxia inducible factor-1 (HIF-1). Besides hypoxia, HIF-1 can be activated under normoxic conditions by nitric oxide. The signal transduction pathways involved in HIF-1alpha stabilization, HIF-1 DNA binding and transactivation by NO and hypoxia in microvascular endothelium remains unknown. We report that protein phosphorylation is involved in HIF-1 activation during hypoxia and NO. The phosphatidylinositol 3-kinase (PI-3K)/Akt pathway has differential effects on HIF-1 activation by hypoxia and NO. Our data indicate that the PI-3K/Akt pathway is insufficient for HIF-1alpha induction by hypoxia. The lipid and protein phosphatase activities of PTEN also appear to be involved in regulation of HIF-1alpha by NO.

NF-kappa B activation in endothelial cells treated with oxidized high-density lipoprotein

We first determined whether oxidized high-density lipoprotein (ox-HDL) activates transcription factor nuclear factor-kappa B (NF-kappa B) in cultured human umbilical vein endothelial cells (HUVECs). Treatment for 7h with 100 microg/ml ox-HDL elicited a marked downregulation of I kappa B alpha and upregulation of the phosphorylated form of I kappa B alpha in HUVECs in a manner dependent on the dose of ox-HDL. Electrophoretic mobility shift assay in nuclear fraction from HUVECs showed translocation of NF-kappa B to the nucleus and binding of NF-kappa B to NF-kappa B consensus oligonucleotides during ox-HDL exposure for 7h, suggesting that ox-HDL brings about NF-kappa B activation in endothelial cells. To clarify the mechanism of NF-kappa B activation in HUVECs treated with ox-HDL, we investigated the effect of ox-HDL treatment on intracellular production of reactive oxygen species (ROS) in HUVECs. Ox-HDL induced a significant dose-dependent increase in ROS production during 4h incubation and this enhanced production of ROS was inhibited in the presence of probucol or diphenylene iodonium (DPI), an inhibitor of NADPH oxidase. In addition, pretreatment with probucol or DPI suppressed the phosphorylation and degradation of I kappa B alpha protein induced by ox-HDL, demonstrating that increased generation of ROS by ox-HDL may be associated with NF-kappa B activation. Pretreatment with antibody against oxidized low-density lipoprotein receptor-1 (LOX-1) significantly suppressed the ox-HDL-induced downregulation of I kappa B alpha, suggesting that LOX-1 mediates NF-kappa B activation in endothelial cells stimulated with ox-HDL. Taking all of the above findings together, ox-HDL activates NF-kappa B via binding to LOX-1 on the cell surface, followed by enhancement of intracellular ROS production in endothelial cells.

Atypical mechanism of NF-kappaB activation during reoxygenation stress in microvascular endothelium: a role for tyrosine kinases

The transcription factor nuclear factor kappaB (NF-kappaB) regulates genes that contribute to acute inflammatory reactions in cytokine-activated endothelium. Tumor necrosis factor activates NF-kappaB through serine phosphorylation, induced by inhibitor kappaB kinases (IKK), and subsequent degradation of inhibitor kappaB (IkappaB). In contrast to cytokine stress, our studies show that oxidative stress, generated by exposure to hypoxia followed by reoxygenation (H/R), failed to activate IKK in human microvascular endothelial cells (HMEC-1). We report an alternative mechanism for NF-kappaB activation during H/R stress without IkappaBalpha degradation. This mechanism involves activation of protein tyrosine kinases (PTK) that phosphorylate IkappaBalpha with peak phosphorylation occurring after 30 min of reoxygenation. Involvement of PTK was reinforced by the demonstration that the PTK inhibitor, herbimycin A, prevented H/R-mediated NF-kappaB activation. Tyrosine phosphorylation alters the association between IkappaBalpha and NF-kappaB with sufficient intensity to allow transient NF-kappaB translocation to the cell nuclei within 45 min of onset of reoxygenation stress. Immunofluorescence imaging of NF-kappaB protein reveals it to be shuttled between the nucleus and cytoplasm within 90 min of reoxygenation. Furthermore, IkappaBalpha appears to be associated with NF-kappaB during the nucleo-cytoplasmic shuttling and is thus protected from degradation. Overall, these studies suggest that tyrosine phosphorylation of IkappaBalpha represents a proteolysis-independent mechanism of NF-kappaB activation that can be targeted for preventing H/R-mediated injury without affecting normal inflammatory responses.

Hyperbaric oxygen selectively induces angiopoietin-2 in human umbilical vein endothelial cells

One of the biological effects of hyperbaric oxygen (HBO) therapy in enhancing ischemia-related wound healing is the induction of angiogenesis. To elucidate the mechanism(s) underlying the HBO-induced angiogenesis, we studied the expression of several angiogenesis-related genes in human umbilical vein endothelial cells exposed to HBO. Western blot analyses showed that HBO enhanced the expression of angiopoietin-2 (Ang2) with no effect on the expression of Tie2, angiopoietin-1, and VEGF. The induction of Ang2 was further confirmed by immunohistochemistry, quantitative PCR, and Northern blot analyses. Inhibition of endothelial nitric oxide synthase blocked the HBO-induced Ang2 expression, but failed to block hypoxia-induced Ang2 expression. These data indicated that HBO-induced Ang2 expression may be through transcriptional stimulation, and requires the nitric oxide signaling pathway, which may play an important role in HBO-induced angiogenesis.