PGC-1α limits angiotensin II-induced rat vascular smooth muscle cells proliferation via attenuating NOX1-mediated generation of reactive oxygen species

AngII (angiotensin II)-induced excessive ROS (reactive oxygen species) generation and proliferation of VSMCs (vascular smooth muscle cells) is a critical contributor to the pathogenesis of atherosclerosis. PGC-1α [PPARγ (peroxisome-proliferator-activated receptor γ) co-activator-1α] is involved in the regulation of ROS generation, VSMC proliferation and energy metabolism. The aim of the present study was to investigate whether PGC-1α mediates AngII-induced ROS generation and VSMC hyperplasia. Our results showed that the protein content of PGC-1α was negatively correlated with an increase in cell proliferation and migration induced by AngII. Overexpression of PGC-1α inhibited AngII-induced proliferation and migration, ROS generation and NADPH oxidase activity in VSMCs. Conversely, Ad-shPGC-1α (adenovirus-mediated PGC-1α-specific shRNA) led to the opposite effects. Furthermore, the stimulatory effect of Ad-shPGC-1α on VSMC proliferation was significantly attenuated by antioxidant and NADPH oxidase inhibitors. Analysis of several key subunits of NADPH oxidase (Rac1, p22^phox, p40^phox, p47^phox and p67^phox) and mitochondrial ROS revealed that these mechanisms were not responsible for the observed effects of PGC-1α. However, we found that overexpression of PGC-1α promoted NOX1 degradation through the proteasome degradation pathway under AngII stimulation and consequently attenuated NOX1 (NADPH oxidase 1) expression. These alterations underlie the inhibitory effect of PGC-1α on NADPH oxidase activity. Our data support a critical role for PGC-1α in the regulation of proliferation and migration of VSMCs, and provide a useful strategy to protect vessels against atherosclerosis.     

Deletion of Rac1GTPase in the Myeloid Lineage Protects against Inflammation-Mediated Kidney Injury in Mice

Macrophage-mediated inflammation has been implicated in various kidney diseases. We previously reported that Rac1, a Rho family small GTP-binding protein, was overactivated in several chronic kidney disease models, and that Rac1 inhibitors ameliorated renal injury, in part via inhibition of inflammation, but the detailed mechanisms have not been clarified. In the present study, we examined whether Rac1 in macrophages effects cytokine production and the inflammatory mechanisms contributing to kidney derangement. Myeloid-selective Rac1 flox control (M-Rac1 FC) and knockout (M-Rac1 KO) mice were generated using the cre-loxP system. Renal function under basal conditions did not differ between M-Rac1 FC and KO mice. Accordingly, lipopolysaccharide (LPS)-evoked kidney injury model was created. LPS elevated blood urea nitrogen and serum creatinine, enhanced expressions of kidney injury biomarkers, Kim-1 and Ngal, and promoted tubular injury in M-Rac1 FC mice. By contrast, deletion of myeloid Rac1 almost completely prevented the LPS-mediated renal impairment. LPS triggered a marked induction of macrophage-derived inflammatory cytokines, IL-6 and TNFα, in M-Rac1 FC mice, which was accompanied by Rac1 activation, stimulation of reduced nicotinamide-adenine dinucleotide phosphate (NADPH) oxidase, and reactive oxygen species overproduction. These changes were inhibited in M-Rac1 KO mice. LPS evoked F4/80-positive macrophages accumulation in the kidney, which was not affected by myeloid Rac1 deficiency. We further tested the role of Rac1 signaling in cytokine production using macrophage cell line, RAW264.7. Exposure to LPS increased IL-6 and TNFα mRNA expression. The LPS-driven cytokine induction was dose-dependently blocked by the Rac1 inhibitor EHT1864, NADPH oxidase inhibitor diphenyleneiodonium, and NF-κB inhibitor BAY11-7082. In conclusion, genetic ablation of Rac1 in the myeloid lineage protected against LPS-induced renal inflammation and injury, by suppressing macrophage-derived cytokines, IL-6 and TNFα, without blocking recruitment. Our data suggest that Rac1 in macrophage is a novel target for the treatment of kidney disease through inhibition of cytokine production.     

CEACAM1 Negatively Regulates IL-1�� Production in LPS Activated Neutrophils by Recruiting SHP-1 to a SYK-TLR4-CEACAM1 Complex

LPS-activated neutrophils secrete IL-1β by activation of TLR-4. Based on studies in macrophages, it is likely that ROS and lysosomal destabilization regulated by Syk activation may also be involved. Since neutrophils have abundant expression of the ITIM-containing co-receptor CEACAM1 and Gram-negative bacteria such as Neisseria utilize CEACAM1 as a receptor that inhibits inflammation, we hypothesized that the overall production of IL-1β in LPS treated neutrophils may be negatively regulated by CEACAM1. We found that LPS treated neutrophils induced phosphorylation of Syk resulting in the formation of a complex including TLR4, p-Syk, and p-CEACAM1, which in turn, recruited the inhibitory phosphatase SHP-1. LPS treatment leads to ROS production, lysosomal damage, caspase-1 activation and IL-1β secretion in neutrophils. The absence of this regulation in Ceacam1^−/− neutrophils led to hyper production of IL-1β in response to LPS. The hyper production of IL-1β was abrogated by in vivo reconstitution of wild type but not ITIM-mutated CEACAM1 bone marrow stem cells. Blocking Syk activation by kinase inhibitors or RNAi reduced Syk phosphorylation, lysosomal destabilization, ROS production, and caspase-1 activation in Ceacam1^−/− neutrophils. We conclude that LPS treatment of neutrophils triggers formation of a complex of TLR4 with pSyk and pCEACAM1, which upon recruitment of SHP-1 to the ITIMs of pCEACAM1, inhibits IL-1β production by the inflammasome. Thus, CEACAM1 fine-tunes IL-1β production in LPS treated neutrophils, explaining why the additional utilization of CEACAM1 as a pathogen receptor would further inhibit inflammation.     

Annexin Peptide Ac2-26 Suppresses TNFα-Induced Inflammatory Responses via Inhibition of Rac1-Dependent NADPH Oxidase in Human Endothelial Cells

The anti-inflammatory peptide annexin-1 binds to formyl peptide receptors (FPR) but little is known about its mechanism of action in the vasculature. Here we investigate the effect of annexin peptide Ac2-26 on NADPH oxidase activity induced by tumour necrosis factor alpha (TNFα) in human endothelial cells. Superoxide release and intracellular reactive oxygen species (ROS) production from NADPH oxidase was measured with lucigenin-enhanced chemiluminescence and 2′,7′-dichlorodihydrofluorescein diacetate, respectively. Expression of NADPH oxidase subunits and intracellular cell adhesion molecule (ICAM-1) and vascular cell adhesion molecule (VCAM-1) were determined by real-time PCR and Western blot analysis. Promoter activity of nuclear factor kappa B (NFκB) was measured by luciferase activity assay. TNFα stimulated NADPH-dependent superoxide release, total ROS formation and expression of ICAM-1and VCAM-1. Pre-treatment with N-terminal peptide of annexin-1 (Ac2-26, 0.5–1.5 µM) reduced all these effects, and the inhibition was blocked by the FPRL-1 antagonist WRW4. Furthermore, TNFα-induced NFκB promoter activity was attenuated by both Ac2-26 and NADPH oxidase inhibitor diphenyliodonium (DPI). Surprisingly, Nox4 gene expression was reduced by TNFα whilst expression of Nox2, p22phox and p67phox remained unchanged. Inhibition of NADPH oxidase activity by either dominant negative Rac1 (N17Rac1) or DPI significantly attenuated TNFα-induced ICAM-1and VCAM-1 expression. Ac2-26 failed to suppress further TNFα-induced expression of ICAM-1 and VCAM-1 in N17Rac1-transfected cells. Thus, Ac2-26 peptide inhibits TNFα-activated, Rac1-dependent NADPH oxidase derived ROS formation, attenuates NFκB pathways and ICAM-1 and VCAM-1 expression in endothelial cells. This suggests that Ac2-26 peptide blocks NADPH oxidase activity and has anti-inflammatory properties in the vasculature which contributes to modulate in reperfusion injury inflammation and vascular disease.     

Park7 interacts with p47phox to direct NADPH oxidase-dependent ROS production and protect against sepsis

Inappropriate inflammation responses contribute to mortality during sepsis. Through Toll-like receptors (TLRs), reactive oxygen species (ROS) produced by NADPH oxidase could modulate the inflammation responses. Parkinson disease (autosomal recessive, early onset) 7 (Park7) has a cytoprotective role by eliminating ROS. However, whether Park7 could modulate inflammation responses and mortality in sepsis is unclear. Here, we show that, compared with wild-type mice, Park7^−/− mice had significantly increased mortality and bacterial burdens in sepsis model along with markedly decreased systemic and local inflammation, and drastically impaired macrophage phagocytosis and bacterial killing abilities. Surprisingly, LPS and phorbol-12-myristate-13-acetate stimulation failed to induce ROS and proinflammatory cytokine production in Park7^−/− macrophages and Park7-deficient RAW264.7 cells. Through its C-terminus, Park7 binds to p47^phox, a subunit of the NADPH oxidase, to promote NADPH oxidase-dependent production of ROS. Restoration of Park7 expression rescues ROS production and improves survival in LPS-induced sepsis. Together, our study shows that Park7 has a protective role against sepsis by controlling macrophage activation, NADPH oxidase activation and inflammation responses.     

Lipopolysaccharide-mediated reactive oxygen species and signal transduction in the regulation of interleukin-1 gene expression

Lipopolysaccharide (LPS) stimulates macrophages to release inflammatory cytokines, interleukin-1 beta (IL-1), and tumor necrosis factor (TNF). LPS-induced TNF suppresses scavenger receptor functions in macrophages (van Lenten, B. J., and Fogelman, A. M. (1992) J. Immunol. 148, 112-116), which is regulated by TNF-mediated protein kinases (Hsu, H. Y., and Twu, Y. C. (2000) J. Biol. Chem. 275, 41035-41048). To examine the molecular mechanism for LPS induction of IL-1 in macrophages, we demonstrated that LPS quickly stimulated reactive oxygen species (ROS), and 3 h later induced prointerleukin-1 beta (pro-IL-1, precursor of IL-1) production and IL-1 secretion. LPS stimulated pro-IL-1 message/protein between 3 and 10 h; however, there was a 40% reduction of pro-IL-1 in preincubation of the antioxidant, N-acetylcysteine (NAC). Moreover, NAC moderated LPS-induced IL-1 secretion partially via interleukin 1-converting enzyme. The maximal activity of LPS-induced ERK, JNK, and p38 was 12- (30 min), 5- (30 min), and 16-fold (15 min), respectively. In contrast, NAC reduced ERK activity to 60% and decreased p38 activity to the basal level, but JNK activity was induced 2-fold. Furthermore, the pharmacological antagonists LY294002, SB203580, curcumin, calphostin C, and PD98059 revealed the diverse roles of LPS-mediated protein kinases in pro-IL-1. On the other hand, NAC and diphenyleneiodonium chloride partially inhibited LPS-induced Rac activity and protein-tyrosine kinase (PTK), indicating that LPS-mediated ROS and NADPH oxidase correspond to Rac activation and IL-1 expression. Our findings establish for the first time that LPS-mediated PTK/phosphatidylinositol 3-kinase/Rac/p38 pathways play a more important role than pathways of PTK/PKC/MEK/ERK and of PTK/phosphatidylinositol 3-kinase/Rac/JNK in the regulation of pro-IL-1/IL-1. The findings also further elucidate the critical role of LPS-mediated ROS in signal transduction pathways. Our results suggest that understanding LPS-transduced signals in IL-1 induction upon the antibacterial action of macrophages should provide a therapeutic strategy for aberrant inflammatory responses leading to severe cellular injury or concurrent multiorgan septic damage.     

Age‐related sensitivity to endotoxin‐induced liver inflammation: Implication of inflammasome/IL‐1β for steatohepatitis

Aging is associated with increased vulnerability to inflammatory challenge. However, the effects of altered inflammatory response on the metabolic status of tissues or organs are not well documented. In this study, we present evidence demonstrating that lipopolysaccharide (LPS)-induced upregulation of the inflammasome/IL-1β pathway is accompanied with an increased inflammatory response and abnormal lipid accumulation in livers of aged rats. To monitor the effects of aging on LPS-induced inflammation, we administered LPS (2 mg kg⁻¹) to young (6-month old) and aged (24-month old) rats and found abnormal lipid metabolism in only aged rats with increased lipid accumulation in the liver. This lipid accumulation in the liver was due to the dysregulation of PPARα and SREBP1c. We also observed severe liver inflammation in aged rats as indicated by increased ALT levels in serum and increased Kupffer cells in the liver. Importantly, among many inflammation-associated factors, the aged rat liver showed chronically increased IL-1β production. Increased levels of IL-1β were caused by the upregulation of caspase-1 activity and inflammasome activation. In vitro studies with HepG2 cells demonstrated that treatment with IL-1β significantly induced lipid accumulation in hepatocytes through the regulation of PPARα and SREBP1c. In summary, we demonstrated that LPS-induced liver inflammation and lipid accumulation were associated with a chronically overactive inflammasome/IL-1β pathway in aged rat livers. Based on the present findings, we propose a mechanism of aging-associated progression of steatohepatitis induced by endotoxin, delineating a pathogenic role of the inflammasome/IL-1β pathway involved in lipid accumulation in the liver.     

Prevention of CCAAT/Enhancer-binding Protein �� DNA Binding by Hypoxia during Adipogenesis

Upon exposure to adipogenesis-inducing hormones, confluent 3T3-L1 preadipocytes express C/EBPβ (CCAAT/enhancer binding protein β). Early induced C/EBPβ is inactive but, after a lag period, acquires its DNA-binding capability by sequential phosphorylation. During this period, preadipocytes pass the G₁/S checkpoint synchronously. Thr¹⁸⁸ of C/EBPβ is phosphorylated initially to prime the factor for subsequent phosphorylation at Ser¹⁸⁴ or Thr¹⁷⁹ by GSK3β, which translocates into the nuclei during the G₁/S transition. Many events take place during the G₁/S transition, including reduction in p27^Kip1 protein levels, retinoblastoma (Rb) phosphorylation, GSK3β nuclear translocation, and C/EBPβ binding to target promoters. During hypoxia, hypoxia-inducible factor-1α (HIF-1α) is stabilized, thus maintaining expression of p27^Kip1, which inhibits Rb phosphorylation. Even under normoxic conditions, constitutive expression of p27^Kip1 blocks the nuclear translocation of GSK3β and DNA binding capability of C/EBPβ. Hypoxia also blocks nuclear translocation of GSK3β and DNA binding capability of C/EBPβ in HIF-1α knockdown 3T3-L1 cells that fail to induce p27^Kip1. Nonetheless, under hypoxia, these cells can block Rb phosphorylation and the G₁/S transition. Altogether, these findings suggest that hypoxia prevents the nuclear translocation of GSK3β and the DNA binding capability of C/EBPβ by blocking the G₁/S transition through HIF-1α-dependent induction of p27^Kip1 and an HIF-1α/p27-independent mechanism.     

Critical role of NADPH oxidase in neuronal oxidative damage and microglia activation following traumatic brain injury

Background

Oxidative stress is known to play an important role in the pathology of traumatic brain injury. Mitochondria are thought to be the major source of the damaging reactive oxygen species (ROS) following TBI. However, recent work has revealed that the membrane, via the enzyme NADPH oxidase can also generate the superoxide radical (O₂ ⁻), and thereby potentially contribute to the oxidative stress following TBI. The current study thus addressed the potential role of NADPH oxidase in TBI.

Methodology/Principal Findings

The results revealed that NADPH oxidase activity in the cerebral cortex and hippocampal CA1 region increases rapidly following controlled cortical impact in male mice, with an early peak at 1 h, followed by a secondary peak from 24–96 h after TBI. In situ localization using oxidized hydroethidine and the neuronal marker, NeuN, revealed that the O₂ ⁻ induction occurred in neurons at 1 h after TBI. Pre- or post-treatment with the NADPH oxidase inhibitor, apocynin markedly inhibited microglial activation and oxidative stress damage. Apocynin also attenuated TBI-induction of the Alzheimer''s disease proteins β-amyloid and amyloid precursor protein. Finally, both pre- and post-treatment of apocynin was also shown to induce significant neuroprotection against TBI. In addition, a NOX2-specific inhibitor, gp91ds-tat was also shown to exert neuroprotection against TBI.

Conclusions/Significance

As a whole, the study demonstrates that NADPH oxidase activity and superoxide production exhibit a biphasic elevation in the hippocampus and cortex following TBI, which contributes significantly to the pathology of TBI via mediation of oxidative stress damage, microglial activation, and AD protein induction in the brain following TBI.     

Role of Rac1 GTPase in NADPH Oxidase Activation and Cognitive Impairment Following Cerebral Ischemia in the Rat

Background

Recent work by our laboratory and others has implicated NADPH oxidase as having an important role in reactive oxygen species (ROS) generation and neuronal damage following cerebral ischemia, although the mechanisms controlling NADPH oxidase in the brain remain poorly understood. The purpose of the current study was to examine the regulatory and functional role of the Rho GTPase, Rac1 in NADPH oxidase activation, ROS generation and neuronal cell death/cognitive dysfunction following global cerebral ischemia in the male rat.

Methodology/Principal Findings

Our studies revealed that NADPH oxidase activity and superoxide (O₂ ⁻) production in the hippocampal CA1 region increased rapidly after cerebral ischemia to reach a peak at 3 h post-reperfusion, followed by a fall in levels by 24 h post-reperfusion. Administration of a Rac GTPase inhibitor (NSC23766) 15 min before cerebral ischemia significantly attenuated NADPH oxidase activation and O₂ ⁻ production at 3 h after stroke as compared to vehicle-treated controls. NSC23766 also attenuated “in situ” O₂ ⁻ production in the hippocampus after ischemia/reperfusion, as determined by fluorescent oxidized hydroethidine staining. Oxidative stress damage in the hippocampal CA1 after ischemia/reperfusion was also significantly attenuated by NSC23766 treatment, as evidenced by a marked attenuation of immunostaining for the oxidative stress damage markers, 4-HNE, 8-OHdG and H2AX at 24 h in the hippocampal CA1 region following cerebral ischemia. In addition, Morris Water maze testing revealed that Rac GTPase inhibition after ischemic injury significantly improved hippocampal-dependent memory and cognitive spatial abilities at 7–9 d post reperfusion as compared to vehicle-treated animals.

Conclusions/Significance

The results of the study suggest that Rac1 GTPase has a critical role in mediating ischemia/reperfusion injury-induced NADPH oxidase activation, ROS generation and oxidative stress in the hippocampal CA1 region of the rat, and thus contributes significantly to neuronal degeneration and cognitive dysfunction following cerebral ischemia.     

Protein Kinase C�� Mediates Cigarette Smoke/Aldehyde- and Lipopolysaccharide-induced Lung Inflammation and Histone Modifications

Atypical protein kinase C (PKC) ζ is an important regulator of inflammation through activation of the nuclear factor-κB (NF-κB) pathway. Chromatin remodeling on pro-inflammatory genes plays a pivotal role in cigarette smoke (CS)- and lipopolysaccharide (LPS)-induced abnormal lung inflammation. However, the signaling mechanism whereby chromatin remodeling occurs in CS- and LPS-induced lung inflammation is not known. We hypothesized that PKCζ is an important regulator of chromatin remodeling, and down-regulation of PKCζ ameliorates lung inflammation by CS and LPS exposures. We determined the role and molecular mechanism of PKCζ in abnormal lung inflammatory response to CS and LPS exposures in PKCζ-deficient (PKCζ^−/−) and wild-type mice. Lung inflammatory response was decreased in PKCζ^−/− mice compared with WT mice exposed to CS and LPS. Moreover, inhibition of PKCζ by a specific pharmacological PKCζ inhibitor attenuated CS extract-, reactive aldehydes (present in CS)-, and LPS-mediated pro-inflammatory mediator release from macrophages. The mechanism underlying these findings is associated with decreased RelA/p65 phosphorylation (Ser³¹¹) and translocation of the RelA/p65 subunit of NF-κB into the nucleus. Furthermore, CS/reactive aldehydes and LPS exposures led to activation and translocation of PKCζ into the nucleus where it forms a complex with CREB-binding protein (CBP) and acetylated RelA/p65 causing histone phosphorylation and acetylation on promoters of pro-inflammatory genes. Taken together, these data suggest that PKCζ plays an important role in CS/aldehyde- and LPS-induced lung inflammation through acetylation of RelA/p65 and histone modifications via CBP. These data provide new insights into the molecular mechanisms underlying the pathogenesis of chronic inflammatory lung diseases.     

Rac1-NADPH oxidase-regulated generation of reactive oxygen species mediates glutamate-induced apoptosis in SH-SY5Y human neuroblastoma cells

Reactive oxygen species (ROS) are known to play an important role in glutamate-induced neuronal cell death. In the present study, we examined whether NADPH oxidase serves as a source of ROS production and plays a role in glutamate-induced cell death in SH-SY5Y human neuroblastoma cells. Stimulation of the cells with glutamate (100 mM) induced apoptotic cell death and increase in the level of ROS, and these effects of glutamate were significantly suppressed by the inhibitors of the NADPH oxidase, diphenylene iodonium, apocynin, and neopterine. In addition, RT-PCR revealed that SH-SY5Y cells expressed mRNA of gp91^phox, p22^phox and cytosolic p47^phox, p67^phox and p40^phox, the components of the plasma membrane NADPH oxidase. Treatment with glutamate also resulted in activation and translocation of Rac1 to the plasma membrane. Moreover, the expression of Rac1N17, a dominant negative mutant of Rac1, significantly blocked the glutamate-induced ROS generation and cell death. Collectively, these results suggest that the plasma membrane-bound NADPH oxidase complex may play an essential role in the glutamate-induced apoptotic cell death through increased production of ROS.     

Antagonistic cross-talk between Rac and Cdc42 GTPases regulates generation of reactive oxygen species

Cross-talk between Rho GTPase family members (Rho, Rac, and Cdc42) plays important roles in modulating and coordinating downstream cellular responses resulting from Rho GTPase signaling. The NADPH oxidase of phagocytes and nonphagocytic cells is a Rac GTPase-regulated system that generates reactive oxygen species (ROS) for the purposes of innate immunity and intracellular signaling. We recently demonstrated that NADPH oxidase activation involves sequential interactions between Rac and the flavocytochrome b(558) and p67(phox) oxidase components to regulate electron transfer from NADPH to molecular oxygen. Here we identify an antagonistic interaction between Rac and the closely related GTPase Cdc42 at the level of flavocytochrome b(558) that regulates the formation of ROS. Cdc42 is unable to stimulate ROS formation by NADPH oxidase, but Cdc42, like Rac1 and Rac2, was able to specifically bind to flavocytochrome b(558) in vitro. Cdc42 acted as a competitive inhibitor of Rac1- and Rac2-mediated ROS formation in a recombinant cell-free oxidase system. Inhibition was dependent on the Cdc42 insert domain but not the Switch I region. Transient expression of Cdc42Q61L inhibited ROS formation induced by constitutively active Rac1 in an NADPH oxidase-expressing Cos7 cell line. Inhibition of Cdc42 activity by transduction of the Cdc42-binding domain of Wiscott-Aldrich syndrome protein into human neutrophils resulted in an enhanced fMetLeuPhe-induced oxidative response, consistent with inhibitory cross-talk between Rac and Cdc42 in activated neutrophils. We propose here a novel antagonism between Rac and Cdc42 GTPases at the level of the Nox proteins that modulates the generation of ROS used for host defense, cell signaling, and transformation.     

Genetic deficiency of NADPH oxidase does not diminish,but rather enhances,LPS-induced acute inflammatory responses in vivo

Reactive oxygen species (ROS) and oxidative stress are thought to play a central role in the etiology of cell dysfunction and tissue damage in sepsis. However, there is limited and controversial evidence from in vivo studies that ROS mediate cell signaling processes that elicit acute inflammatory responses during sepsis. Because NADPH oxidase is one of the main cellular sources of ROS, we investigated the role of this enzyme in lipopolysaccharide (LPS)-induced acute inflammation in vivo, utilizing mice deficient in the gp91^phox or p47^phox subunits of NADPH oxidase. Age-and body weight-matched C57BL/6J wild-type (WT) and gp91^phox?/? and p47^phox?/? mice were injected ip with 50 μg LPS or saline vehicle and sacrificed at various time points up to 24 h. We found that LPS-induced acute inflammatory responses in serum and tissues were not significantly diminished in gp91^phox?/? and p47^phox?/? mice compared to WT mice. Rather, genetic deficiency of NADPH oxidase was associated with enhanced gene expression of inflammatory mediators and increased neutrophil recruitment to lung and heart. Furthermore, no protection from LPS-induced septic death was observed in either knockout strain. Our findings suggest that NADPH oxidase-mediated ROS production and cellular redox signaling do not promote, but instead limit, LPS-induced acute inflammatory responses in vivo.     

Reactive oxygen species delay control of lymphocytic choriomeningitis virus

Cluster of differentiation (CD)8⁺ T cells are like a double edged sword during chronic viral infections because they not only promote virus elimination but also induce virus-mediated immunopathology. Elevated levels of reactive oxygen species (ROS) have been reported during virus infections. However, the role of ROS in T-cell-mediated immunopathology remains unclear. Here we used the murine lymphocytic choriomeningitis virus to explore the role of ROS during the processes of virus elimination and induction of immunopathology. We found that virus infection led to elevated levels of ROS producing granulocytes and macrophages in virus-infected liver and spleen tissues that were triggered by the nicotinamide adenine dinucleotide phosphate (NADPH) oxidase. Lack of the regulatory subunit p47phox of the NADPH oxidase diminished ROS production in these cells. While CD8⁺ T cells exhibited ROS production that was independent of NADPH oxidase expression, survival and T-cell function was elevated in p47phox-deficient (Ncf1^−/−) mice. In the absence of p47phox, enhanced T-cell immunity promoted virus elimination and blunted corresponding immunopathology. In conclusion, we find that NADPH-mediated production of ROS critically impairs the immune response, impacting elimination of virus and outcome of liver cell damage.