Phox activity of differentiated PLB-985 cells is enhanced, in an agonist specific manner, by the PLA2 activity of Prdx6-PLA2

Orosomucoid 2 as a biomarker of carotid artery atherosclerosis plaque vulnerability through its generation of reactive oxygen species and lipid accumulation in vascular smooth muscle cells

BACKGROUND

Orosomucoid (ORM) has been reported as a biomarker of carotid atherosclerosis, but the role of ORM 2, a subtype of ORM, in carotid atherosclerotic plaque formation and the underlying mechanism have not been established.

METHODS

Plasma was collected from patients with carotid artery stenosis (CAS) and healthy participants and assessed using mass spectrometry coupled with isobaric tags for relative and absolute quantification (iTRAQ) technology to identify differentially expressed proteins. The key proteins and related pathways were identified via western blotting, immunohistochemistry, and polymerase chain reaction of carotid artery plaque tissues and in vitro experiments involving vascular smooth muscle cells (VSMCs).

RESULTS

We screened 33 differentially expressed proteins out of 535 proteins in the plasma. Seventeen proteins showed increased expressions in the CAS groups relative to the healthy groups, while 16 proteins showed decreased expressions during iTRAQ and bioinformatic analysis. The reactive oxygen species metabolic process was the most common enrichment pathway identified by Gene Ontology analysis, while ORM2, PRDX2, GPX3, HP, HBB, ANXA5, PFN1, CFL1, and S100A11 were key proteins identified by STRING and MCODE analysis. ORM2 showed increased expression in patients with CAS plaques, and ORM2 was accumulated in smooth muscle cells. Oleic acid increased the lipid accumulation and ORM2 and PRDX6 expressions in the VSMCs. The recombinant-ORM2 also increased the lipid accumulation and reactive oxygen species (ROS) in the VSMCs. The expressions of ORM2 and PRDX-6 were correlated, and MJ33 (an inhibitor of PRDX6-PLA2) decreased ROS production and lipid accumulation in VSMCs.

CONCLUSION

ORM2 may be a biomarker for CAS; it induced lipid accumulation and ROS production in VSMCs during atherosclerosis plaque formation. However, the relationships between ORM2 and PRDX-6 underlying lipid accumulation-induced plaque vulnerability require further research.

NOX1 and PRDX6 synergistically support migration and invasiveness of hepatocellular carcinoma cells through enhanced NADPH oxidase activity

The NADPH oxidase 1 (NOX1) complex formed by proteins NOX1, p22phox, NOXO1, NOXA1, and RAC1 plays an important role in the generation of superoxide and other reactive oxygen species (ROS) which are involved in normal and pathological cell functions due to their effects on diverse cell signaling pathways. Cell migration and invasiveness are at the origin of tumor metastasis during cancer progression which involves a process of cellular de-differentiation known as the epithelial-mesenchymal transition (EMT). During EMT cells lose their polarized epithelial phenotype and express mesenchymal marker proteins that enable cytoskeletal rearrangements promoting cell migration, expression and activation of matrix metalloproteinases (MMPs), tissue remodeling, and cell invasion during metastasis. In this work, we explored the importance of the peroxiredoxin 6 (PRDX6)-NOX1 enzyme interaction leading to NOXA1 protein stabilization and increased levels of superoxide produced by NOX in hepatocarcinoma cells. This increase was accompanied by higher levels of N-cadherin and MMP2, correlating with a greater capacity for cell migration and invasiveness of SNU475 hepatocarcinoma cells. The increase in superoxide and the associated downstream effects on cancer progression were suppressed when phospholipase A2 or peroxidase activities of PRDX6 were abolished by site-directed mutagenesis, reinforcing the importance of these catalytic activities in supporting NOX1-based superoxide generation. Overall, these results demonstrate a clear functional cooperation between NOX1 and PRDX6 catalytic activities which generate higher levels of ROS production, resulting in a more aggressive tumor phenotype.

Peroxiredoxin 6 Regulates Glutathione Peroxidase 1-Medited Glutamine Synthase Preservation in the Hippocampus of Chronic Epilepsy Rats

Clasmatodendrosis (an autophagic astroglial degeneration) plays an important role in the regulation of spontaneous seizure duration but not seizure frequency or behavioral seizure severity in chronic epilepsy rats. Recently, it has been reported that N-acetylcysteine (NAC), a precursor to glutathione (GSH), attenuates clasmatodendritic degeneration and shortens spontaneous seizure duration in chronic epilepsy rats, although the underlying mechanisms of its anti-convulsive effects are not fully understood. To elucidate this, the present study was designed to investigate whether NAC affects astroglial glutamine synthase (GS) expression mediated by GSH peroxidase 1 (GPx1) and/or peroxiredoxin 6 (Prdx6) in the epileptic hippocampus. As compared to control animals, GS and GPx1 expressions were upregulated in reactive CA1 astrocytes of chronic epilepsy rats, while their expressions were significantly decreased in clasmatodendritic CA1 astrocytes and reactive astrocytes within the molecular layer of the dentate gyrus. Prdx6 expression was increased in reactive CA1 astrocytes as well as clasmatodendritic CA1 astrocytes. In the molecular layer of the dentate gyrus, Prdx6 expression levels were similar to those in control animals. NAC ameliorated clasmatodendrosis through the increment of GS and GPx1 expressions, while it abolished Prdx6 upregulation. 1-hexadecyl-3-(trifluoroethgl)-sn-glycerol-2 phosphomethanol (MJ33, a selective inhibitor of aiPLA2 activity of Prdx6) alleviated clasmatodendrosis by enhancing GPx1 and GS expressions in clasmatodendritic CA1 astrocytes without changing the Prdx6 level. NAC or MJ33 did not affect GS, GPx1 and Prdx6 expression in astrocytes within the molecular layer of the dentate gyrus. These findings indicate that upregulated aiPLA2 activity of Prdx6 may abolish GPx1-mediated GS preservation and lead to clasmatodendrosis in CA1 astrocytes, which would extend spontaneous seizure duration due to impaired glutamate-glutamine conversion regulated by GS. Therefore, the present data suggest that aiPLA2 activity of Prdx6 in astrocytes may be one of the upstream effectors of seizure duration in the epileptic hippocampus.

Sp1-Mediated Prdx6 Upregulation Leads to Clasmatodendrosis by Increasing Its aiPLA2 Activity in the CA1 Astrocytes in Chronic Epilepsy Rats

Clasmatodendrosis is an autophagic astroglial degeneration (a non-apoptotic (type II) programmed cell death) whose underlying mechanisms are fully understood. Peroxiredoxin-6 (Prdx6), the “non-selenium glutathione peroxidase (NSGPx)”, is the only member of the 1-cysteine peroxiredoxin family. Unlike the other Prdx family, Prdx6 has multiple functions as glutathione peroxidase (GPx) and acidic calcium-independent phospholipase (aiPLA2). The present study shows that Prdx6 was upregulated in CA1 astrocytes in chronic epilepsy rats. 2-Cyano-3,12-dioxo-oleana-1,9(11)-dien-28-oic acid methyl ester (CDDO-Me) and N-acetylcysteine (NAC, a precursor of glutathione) ameliorated clasmatodendrosis accompanied by reduced Prdx6 level in CA1 astrocytes. Specificity protein 1 (Sp1) expression was upregulated in CA1 astrocyte, which was inhibited by mithramycin A (MMA). MMA alleviated clasmatodendrosis and Prdx6 upregulation. Sp1 expression was also downregulated by CDDO-Me and NAC. Furthermore, 1-hexadecyl-3-(trifluoroethgl)-sn-glycerol-2 phosphomethanol (MJ33, a selective inhibitor of aiPLA2 activity of Prdx6) attenuated clasmatodendrosis without affecting Prdx6 expression. All chemicals shortened spontaneous seizure duration but not seizure frequency and behavioral seizure severity in chronic epilepsy rats. Therefore, our findings suggest that Sp1 activation may upregulate Prdx6, whose aiPLA2 activity would dominate over GPx activity in CA1 astrocytes and may lead to prolonged seizure activity due to autophagic astroglial degeneration.

A Peptide Inhibitor of Peroxiredoxin 6 Phospholipase A2 Activity Significantly Protects against Lung Injury in a Mouse Model of Ventilator Induced Lung Injury (VILI)

Ventilator induced lung injury (VILI) is a lung injury syndrome associated with mechanical ventilation, most frequently for treatment of Acute Lung Injury (ALI), and generally secondary to the use of greater than physiologic tidal volumes. To reproduce this syndrome experimentally, C57Bl/6 mice were intubated and ventilated with low (4 mL/Kg body weight) or high (12 mL/Kg) tidal volume for 6 h. Lung parameters with low volume ventilation were unchanged from non-ventilated (control) mice. High tidal volume ventilation resulted in marked lung injury with increased neutrophils in the bronchoalveolar lavage fluid (BALf) indicating lung inflammation, increase in both protein in BALf and lung dry/wet weight indicating lung edema, increased lung thiobarbituric acid reactive substances (TBARS) and 8-isoprostanes indicating lung lipid peroxidation, and increased lung protein carbonyls indicating protein oxidation. Either intratracheal or intravenous pretreatment of mice with a 9 amino acid peptide called peroxiredoxin 6 inhibitor peptide-2 (PIP-2) significantly reduced all parameters of lung injury by ~50–80%. PIP-2 inhibits NADPH oxidase type 2 (NOX2) activation. We propose that PIP-2 does not affect the mechanically induced lung damage component of VILI but does significantly reduce the secondary inflammatory component.

Metabolic abnormalities in G6PC3-deficient human neutrophils result in severe functional defects

Severe congenital neutropenia type 4 (SCN-4) is an autosomal recessive condition in which mutations in the G6PC3 gene encoding for the catalytic 3 subunit of glucose-6-phosphatase-β result in neutropenia, neutrophil dysfunction, and other syndromic features. We report a child with SCN-4 caused by compound heterozygous mutations in G6PC3, a previously identified missense mutation in exon 6 (c.758G>A[p.R235H]), and a novel missense mutation in exon 2 (c.325G>A[p.G109S]). The patient had recurrent bacterial infections, inflammatory bowel disease, neutropenia, and intermittent thrombocytopenia. Administration of granulocyte colony-stimulating factor (G-CSF) resolved the neutropenia and allowed for detailed evaluation of human neutrophil function. Random and directed migration by the patient's neutrophils was severely diminished. Associated with this were defects in CD11b expression and F-actin assembly. Bactericidal activity at bacteria/neutrophil ratios >1:1 was also diminished and was associated with attenuated ingestion. Superoxide anion generation was <25% of control values, but phox proteins appeared quantitatively normal. Extensive metabolomics analysis at steady state and upon incubation with stable isotope-labeled tracers (U-13C-glucose, 13C,15N-glutamine, and U-13C-fructose) demonstrated dramatic impairments in early glycolysis (hexose phosphate levels), hexosemonophosphate shunt (required for the generation of the NADPH), and the total adenylate pool, which could explain the dramatic cell dysfunction displayed by the patient's neutrophils. Preliminary experiments with fructose supplementation to bypass the enzyme block demonstrated that the metabolic profile could be reversed, but was not sustained long enough for functional improvement. In human deficiency of G6PC3, metabolic defects resulting from the enzyme deficiency account for diverse neutrophil functional defects and present a major risk of infection.

Redox signalling and regulation of the blood-brain barrier

Neurological disorders are associated with increased oxidative stress. Reactive oxidants damage tissue and promote cell death, but it is apparent that oxidants can have more subtle effects on cell function through the modulation of redox-sensitive signalling pathways. Cells of the blood-brain barrier regulate the brain microenvironment but become dysfunctional during neurological disease. The blood-brain barrier is maintained by many cell types, and is modulated by redox-sensitive pathways, ranging from the cytoskeletal elements responsible for establishing a barrier, to growth factor and cytokine signalling pathways that influence neurovascular cells. During neurological disease, blood-brain barrier cells are exposed to exogenously generated oxidants from immune cells, as well as increasing endogenously oxidant production. These oxidants impair the function of the blood-brain barrier, leading to increased leakage and reduced blood flow. Reducing the impact of oxidants on the function of blood-brain barrier cells may provide new strategies for delaying the progression of neurological disease.

The Role of Peroxiredoxin 6 in Cell Signaling

Peroxiredoxin 6 (Prdx6, 1-cys peroxiredoxin) is a unique member of the peroxiredoxin family that, in contrast to other mammalian peroxiredoxins, lacks a resolving cysteine and uses glutathione and π glutathione S-transferase to complete its catalytic cycle. Prdx6 is also the only peroxiredoxin capable of reducing phospholipid hydroperoxides through its glutathione peroxidase (Gpx) activity. In addition to its peroxidase activity, Prdx6 expresses acidic calcium-independent phospholipase A₂ (aiPLA₂) and lysophosphatidylcholine acyl transferase (LPCAT) activities in separate catalytic sites. Prdx6 plays crucial roles in lung phospholipid metabolism, lipid peroxidation repair, and inflammatory signaling. Here, we review how the distinct activities of Prdx6 are regulated during physiological and pathological conditions, in addition to the role of Prdx6 in cellular signaling and disease.

Functional role of peroxiredoxin 6 in the eye

Peroxiredoxin 6 (Prdx6) is the only mammalian 1-Cys member of the Prdx family, a group of enzymes which share the ability to reduce peroxides. In addition to its peroxidase function, Prdx6 also demonstrates phospholipase A₂ and lysophosphatidylcholine acyl transferase (LPCAT) activities. These enzymatic activities play an important role in regenerating oxidized membrane phospholipids and maintaining an appropriate balance of intracellular reactive oxygen species. Development of clinical pathologies, including those within the eye, have been linked to dysregulation of Prdx6 function. Interplay between external stressors like exposure to UV light, transforming growth factor β (TGF-β), and hyperglycemia in conjunction with diminished Prdx6 levels and loss of redox balance is associated with cellular changes in a variety of ophthalmic pathologies including cataracts, glaucoma, and retinal degeneration. Many of these cellular abnormalities can be rescued through supplementation with exogenous Prdx6. Additionally, corneal endothelial cells have been found to express high levels of Prdx6 in the plasma membrane. These findings highlight the importance of Prdx6 as an essential regulator of oxidative stress in the eye.

Microglia antioxidant systems and redox signalling

For many years, microglia, the resident CNS macrophages, have been considered only in the context of pathology, but microglia are also glial cells with important physiological functions. Microglia-derived oxidant production by NADPH oxidase (NOX2) is implicated in many CNS disorders. Oxidants do not stand alone, however, and are not always pernicious. We discuss in general terms, and where available in microglia, GSH synthesis and relation to cystine import and glutamate export, and the thioredoxin system as the most important antioxidative defence mechanism, and further, we discuss in the context of protein thiolation of target redox proteins the necessity for tightly localized, timed and confined oxidant production to work in concert with antioxidant proteins to promote redox signalling. NOX2-mediated redox signalling modulates the acquisition of the classical or alternative microglia activation phenotypes by regulating major transcriptional programs mediated through NF-κB and Nrf2, major regulators of the inflammatory and antioxidant response respectively. As both antioxidants and NOX-derived oxidants are co-secreted, in some instances redox signalling may extend to neighboring cells through modification of surface or cytosolic target proteins. We consider a role for microglia NOX-derived oxidants in paracrine modification of synaptic function through long term depression and in the communication with the adaptive immune system. There is little doubt that a continued foray into the functions of the antioxidant response in microglia will reveal antioxidant proteins as dynamic players in redox signalling, which in concert with NOX-derived oxidants fulfil important roles in the autocrine or paracrine regulation of essential enzymes or transcriptional programs.

LINKED ARTICLES

This article is part of a themed section on Redox Biology and Oxidative Stress in Health and Disease. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v174.12/issuetoc.

Phospholipase A2 of Peroxiredoxin 6 Plays a Critical Role in Cerebral Ischemia/Reperfusion Inflammatory Injury

Microglia-mediated inflammation is an important step in the progression of cerebral ischemia/reperfusion injury and the associated production of receptors of immunomoudulation, including Toll-like receptors (TLRs). Peroxiredoxin 6 (Prdx6) has been demonstrated as the endogenous antioxidant protein for its peroxidase properties. However, the role of the independent phospholipase A2 (iPLA2) activity of Prdx6 in stroke has not been well studied. In this study, we evaluated whether blocking the calcium-iPLA2 activity of Prdx6 using siRNA and inhibitors (1-hexadecyl-3-(trifluoroethgl)-sn-glycerol-2 phosphomethanol, MJ33) would have a critical effect on inflammatory brain damage. We conducted oxygen-glucose deprivation (OGD)/recovery (R) in vitro and middle cerebral artery occlusion (MCAO) in vivo in a microglia/neuron co-culture system and in rats. In vitro, we found that Prdx6-iPLA2 activity was associated with the secretion of neurotoxic inflammatory mediators interleukin1β (IL-1β), interleukin-17 (IL-17) and interleukin-23 (IL-23) and elevated expression of Toll-like receptor 2/4 (TLR2/4), leading to the formation of nuclear factor-kappa B (NF-κB), inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2) in microglial cells. In vivo, combined treatment with Prdx6-iPLA2 activity inhibitor MJ33 showed a greater diminution in neurologic deficits, cerebral infarction, brain water content and inflammatory molecules than Prdx6-siRNA treatment alone. Our findings provide new insight into Prdx6-iPLA2 function in the brain. Inhibition of Prdx6-iPLA2 activity by gene therapy and/or pharmacology may constitute a promising new therapeutic approach to the treatment of stroke.

Peroxiredoxin 6 in the repair of peroxidized cell membranes and cell signaling

Peroxiredoxin 6 represents a widely distributed group of peroxiredoxins that contain a single conserved cysteine in the protein monomer (1-cys Prdx). The cys when oxidized to the sulfenic form is reduced with glutathione (GSH) catalyzed by the π isoform of GSH-S-transferase. Three enzymatic activities of the protein have been described:1) peroxidase with H2O2, short chain hydroperoxides, and phospholipid hydroperoxides as substrates; 2) phospholipase A2 (PLA2); and 3) lysophosphatidylcholine acyl transferase (LPCAT). These activities have important physiological roles in antioxidant defense, turnover of cellular phospholipids, and the generation of superoxide anion via initiation of the signaling cascade for activation of NADPH oxidase (type 2). The ability of Prdx6 to reduce peroxidized cell membrane phospholipids (peroxidase activity) and also to replace the oxidized sn-2 fatty acyl group through hydrolysis/reacylation (PLA2 and LPCAT activities) provides a complete system for the repair of peroxidized cell membranes.

Neutrophil function in children following allogeneic hematopoietic stem cell transplant

HSCT is a lifesaving procedure for children with malignant and non-malignant conditions. The conditioning regimen renders the patient severely immunocompromised and recovery starts with neutrophil (PMN) engraftment. We hypothesize that children demonstrate minimal PMN dysfunction at engraftment and beyond, which is influenced by the stem cell source and the conditioning regimen. Peripheral blood was serially collected from children at 1 to 12 months following allogeneic HSCT. PMN superoxide (O2-) production, degranulation (elastase), CD11b surface expression, and phagocytosis were assessed. Twenty-five patients, mean age of 10.5 yr with 65% males, comprised the study and transplant types included: 14 unrelated cord blood stem cells (cords), seven matched related bone marrow donors, three matched unrelated bone marrow donors, and one peripheral blood progenitor cells. Engraftment occurred at 24 days. There were no significant differences between controls and patients in PMN O2- production, phagocytosis, CD11b surface expression, and total PMN elastase. Elastase release was significantly decreased <6 months vs. controls (p < 0.05) and showed normalization by six months for cords only. The conditioning regimen did not affect PMN function. PMN function returns with engraftment, save elastase release, which occurs later related to the graft source utilized, and its clinical significance is unknown.

Peroxiredoxin 6 (Prdx6) supports NADPH oxidase1 (Nox1)-based superoxide generation and cell migration

Nox1 is an abundant source of reactive oxygen species (ROS) in colon epithelium recently shown to function in wound healing and epithelial homeostasis. We identified Peroxiredoxin 6 (Prdx6) as a novel binding partner of Nox activator 1 (Noxa1) in yeast two-hybrid screening experiments using the Noxa1 SH3 domain as bait. Prdx6 is a unique member of the Prdx antioxidant enzyme family exhibiting both glutathione peroxidase and phospholipase A2 activities. We confirmed this interaction in cells overexpressing both proteins, showing Prdx6 binds to and stabilizes wild type Noxa1, but not the SH3 domain mutant form, Noxa1 W436R. We demonstrated in several cell models that Prdx6 knockdown suppresses Nox1 activity, whereas enhanced Prdx6 expression supports higher Nox1-derived superoxide production. Both peroxidase- and lipase-deficient mutant forms of Prdx6 (Prdx6 C47S and S32A, respectively) failed to bind to or stabilize Nox1 components or support Nox1-mediated superoxide generation. Furthermore, the transition-state substrate analogue inhibitor of Prdx6 phospholipase A2 activity (MJ-33) was shown to suppress Nox1 activity, suggesting Nox1 activity is regulated by the phospholipase activity of Prdx6. Finally, wild type Prdx6, but not lipase or peroxidase mutant forms, supports Nox1-mediated cell migration in the HCT-116 colon epithelial cell model of wound closure. These findings highlight a novel pathway in which this antioxidant enzyme positively regulates an oxidant-generating system to support cell migration and wound healing.

Peroxiredoxin 5 Protects TGF-β Induced Fibrosis by Inhibiting Stat3 Activation in Rat Kidney Interstitial Fibroblast Cells

Renal fibrosis is a common final pathway of end-stage kidney disease which is induced by aberrant accumulation of myofibroblasts. This process is triggered by reactive oxygen species (ROS) and proinflammatory cytokines generated by various source of injured kidney cells. Peroxiredoxin 5 (Prdx5) is a thiol-dependent peroxidase that reduces oxidative stress by catalyzing intramolecular disulfide bonds. Along with its antioxidant effects, expression level of Prdx5 also was involved in inflammatory regulation by immune stimuli. However, the physiological effects and the underlying mechanisms of Prdx5 in renal fibrosis have not been fully characterized. Sprague-Dawley rats were subjected to unilateral ureteral obstruction (UUO) for 1 or 7 days. For the in vitro model, NRK49F cells, a rat kidney interstitial fibroblast cell lines, were treated with transforming growth factor β (TGF-β) for 0, 1, 3, or 5 days. To access the involvement of its peroxidase activity in TGF-β induced renal fibrosis, wild type Prdx5 (WT) and double mutant Prdx5 (DM), converted two active site cysteines at Cys 48 and Cys 152 residue to serine, were transiently expressed in NRK49F cells. The protein expression of Prdx5 was reduced in UUO kidneys. Upregulation of fibrotic markers, such as fibronectin and alpha-smooth muscle actin (α-SMA), declined at 5 days in time point of higher Prdx5 expression in TGF-β treated NRK49F cells. The overexpression of wild type Prdx5 by transient transfection in NRK49F cells attenuated the TGF-β induced upregulation of fibronectin and α-SMA. On the other hand, the transient transfection of double mutant Prdx5 did not prevent the activation of fibrotic markers. Overexpression of Prdx5 also suppressed the TGF-β induced upregulation of Stat3 phosphorylation, while phosphorylation of Smad 2/3 was unchanged. In conclusion, Prdx5 protects TGF-β induced fibrosis in NRK49F cells by modulating Stat3 activation in a peroxidase activity dependent manner.

Inactivation of Peroxiredoxin 6 by the Pla Protease of Yersinia pestis

Pneumonic plague represents the most severe form of disease caused by Yersinia pestis due to its ease of transmission, rapid progression, and high mortality rate. The Y. pestis outer membrane Pla protease is essential for the development of pneumonic plague; however, the complete repertoire of substrates cleaved by Pla in the lungs is not known. In this study, we describe a proteomic screen to identify host proteins contained within the bronchoalveolar lavage fluid of mice that are cleaved and/or processed by Y. pestis in a Pla-dependent manner. We identified peroxiredoxin 6 (Prdx6), a host factor that contributes to pulmonary surfactant metabolism and lung defense against oxidative stress, as a previously unknown substrate of Pla. Pla cleaves Prdx6 at three distinct sites, and these cleavages disrupt both the peroxidase and phospholipase A2 activities of Prdx6. In addition, we found that infection with wild-type Y. pestis reduces the abundance of extracellular Prdx6 in the lungs compared to that after infection with Δpla Y. pestis, suggesting that Pla cleaves Prdx6 in the pulmonary compartment. However, following infection with either wild-type or Δpla Y. pestis, Prdx6-deficient mice exhibit no differences in bacterial burden, host immune response, or lung damage from wild-type mice. Thus, while Pla is able to disrupt Prdx6 function in vitro and reduce Prdx6 levels in vivo, the cleavage of Prdx6 has little detectable impact on the progression or outcome of pneumonic plague.

ExoU-induced redox imbalance and oxidative stress in airway epithelial cells during Pseudomonas aeruginosa pneumosepsis

ExoU is a potent proinflammatory toxin produced by Pseudomonas aeruginosa, a major agent of severe lung infection and sepsis. Because inflammation is usually associated with oxidative stress, we investigated the effect of ExoU on free radical production and antioxidant defense mechanisms during the course of P. aeruginosa infection. In an experimental model of acute pneumonia, ExoU accounted for increased lipid peroxidation in mice lungs as soon as 3 h after intratracheal instillation of PA103 P. aeruginosa strain. The contribution of airway cells to the generation of a redox imbalance was assessed by in vitro tests carried out with A549 airway epithelial cells. Cultures infected with the ExoU-producing PA103 P. aeruginosa strain produced significantly increased concentrations of lipid hydroperoxides, 8-isoprostane, reactive oxygen intermediates, peroxynitrite and nitric oxide (NO), when compared to cells infected with exoU-deficient mutants. Overproduction of NO by PA103-infected cells likely resulted from overexpression of both inducible and endothelial NO synthase isoforms. PA103 infection was also associated with a significantly increased activity of superoxide dismutase (SOD) and decreased levels of reduced glutathione (GSH), a major antioxidant compound. Our findings unveil another potential mechanism of tissue damage during infection by ExoU-producing P. aeruginosa strains.

Bioinformatic and mass spectrometry identification of Anaplasma phagocytophilum proteins translocated into host cell nuclei

Obligate intracellular bacteria have an arsenal of proteins that alter host cells to establish and maintain a hospitable environment for replication. Anaplasma phagocytophilum secrets Ankyrin A (AnkA), via a type IV secretion system, which translocates to the nucleus of its host cell, human neutrophils. A. phagocytophilum-infected neutrophils have dramatically altered phenotypes in part explained by AnkA-induced transcriptional alterations. However, it is unlikely that AnkA is the sole effector to account for infection-induced transcriptional changes. We developed a simple method combining bioinformatics and iTRAQ protein profiling to identify potential bacterial-derived nuclear-translocated proteins that could impact transcriptional programming in host cells. This approach identified 50 A. phagocytophilum candidate genes or proteins. The encoding genes were cloned to create GFP fusion protein-expressing clones that were transfected into HEK-293T cells. We confirmed nuclear translocation of six proteins: APH_0062, RplE, Hup, APH_0382, APH_0385, and APH_0455. Of the six, APH_0455 was identified as a type IV secretion substrate and is now under investigation as a potential nucleomodulin. Additionally, application of this approach to other intracellular bacteria such as Mycobacterium tuberculosis, Chlamydia trachomatis and other intracellular bacteria identified multiple candidate genes to be investigated.

A novel nontoxic inhibitor of the activation of NADPH oxidase reduces reactive oxygen species production in mouse lung

1-Hexadecyl-3-trifluoroethylglycero-sn-2-phosphomethanol (MJ33) is a fluorinated phospholipid analog that inhibits the phospholipase A2 (PLA2) activity of peroxiredoxin 6 (Prdx6). Prdx6 PLA2 activity is required for activation of NADPH oxidase 2 and subsequent generation of reactive oxygen species (ROS). In vitro, MJ33 inhibited agonist-stimulated production of ROS by the isolated perfused mouse lung, lung microvascular endothelial cells, and polymorphonuclear leukocytes. MJ33 (0.02-0.5 µmol MJ33/kg body weight) in mixed unilamellar liposomes was administered to C57BL/6 mice by either intratracheal (i.t.) or i.v. routes. Lung MJ33 content, measured by liquid chromatography/mass spectroscopy, showed uptake of 67-87% of the injected dose for i.t. and 23-42% for i.v. administration at 4 hours postinjection. PLA2 activity of lung homogenates was markedly inhibited (>85%) at 4 hours postadministration. Both MJ33 content and PLA2 activity gradually returned to near control levels over the subsequent 24-72 hours. Mice treated with MJ33 at 12.5-25 µmol/kg did not show changes (compared with control) in clinical symptomatology, body weight, hematocrit, and histology of lung, liver, and kidney during a 30- to 50-day observation period. Thus, the toxic dose of MJ33 was >25 µmol/kg, whereas the PLA2 inhibitory dose was approximately 0.02 µmol/kg, indicating a high margin of safety. MJ33 administered to mice prior to lung isolation markedly reduced ROS production and tissue lipid and protein oxidation during ischemia followed by reperfusion. Thus, MJ33 could be useful as a therapeutic agent to prevent ROS-mediated tissue injury associated with lung inflammation or in harvested lungs prior to transplantation.

p67(phox) terminates the phospholipase A(2)-derived signal for activation of NADPH oxidase (NOX2)

The phospholipase A2 (PLA2)activity of phosphorylated peroxiredoxin 6 (Prdx6) is required for activation of NADPH oxidase (NOX2). We investigated the interaction of Prdx6 with p67(phox) and its effect on NOX2 activity. With the use of specific antibodies, coimmunoprecipitation of p67(phox) and phosphorylated Prdx6 was demonstrated with lysates of mouse pulmonary microvascular endothelial cells (MPMVECs) that were stimulated with angiotensin II; the interaction of p67(phox) with nonphosphorylated Prdx6 was relatively weak. Association of p67(phox) and phosphoPrdx6 in intact MPMVECs after angiotensin II stimulation was demonstrated by proximity ligation assay and was abolished by U0126, a MAP kinase inhibitor. By isothermal titration calorimetry, p67(phox) bound strongly to phosphoPrdx6 but bound poorly to Prdx6; phosphorylated p67(phox) did not bind to either Prdx6 or phosphoPrdx6. PLA2 activity of recombinant phosphoPrdx6 was decreased by >98% in the presence of p67(phox); the calculated dissociation constant (Kd) of the p67(phox): phosphoPrdx6 complex was 65 nM. PLA2 activity (MJ33 sensitive) in cell lysates following angiotensin II treatment of MPMVECs was increased by 85% following knockdown of p67(phox) with siRNA. These data indicate that p67(phox) binds to phosphoPrdx6 and inhibits its PLA2 activity, an interaction that could function to terminate the PLA2-mediated NOX2 activation signal.-Krishnaiah, S. Y., Dodia, C., Feinstein, S. I., and Fisher, A. B. p67(phox) terminates the phospholipase A2-derived signal for activation of NADPH oxidase (NOX2).

Peroxiredoxin-6 and NADPH oxidase activity

Peroxiredoxins (Prdxs) are a family of proteins which catalyze the reduction of H2O2 through the interaction of active site cysteine residues. Conserved within all plant and animal kingdoms, the function of these proteins is related to protection from oxidation or participation of signaling through degradation of H2O2. Peroxiredoxin 6 (Prdx6), a protein belonging to the class of 1-cys Prdxs, was identified in polymorphonuclear leukocytes or neutrophils, defined by amino acid sequence and activity, and found associated with a component of the NADPH oxidase (Nox2), p67(phox). Prdx6 plays an important role in neutrophil function and supports the optimal activity of Nox2. In this chapter, methods are described for determining the Prdx activity of Prdx6. In addition, the approach for assessing the effect of Prdx6 on Nox2 in the SDS-activated, cell-free system of NADPH oxidase activity is presented. Finally, the techniques for suppressing Prdx6 expression in phox-competent K562 cells and cultured myeloid cells with siRNA and shRNA methods are described. With these approaches, the role of Prdx6 in Nox2 activity can be explored with intact cells. The biochemical mechanisms of the Prdx6 effect on the NADPH oxidase can be investigated with the experimental strategies described.