LPS-Induced Acute Kidney Injury Is Mediated by Nox4-SH3YL1

Cytosolic proteins are required for regulation of NADPH (nicotinamide adenine dinucleotide phosphate) oxidase (Nox) isozymes. Here we show that Src homology 3 (SH3) domain-containing YSC84-like 1 (SH3YL1), as a Nox4 cytosolic regulator, mediates lipopolysaccharide (LPS)-induced H₂O₂ generation, leading to acute kidney injury. The SH3YL1, Ysc84p/Lsb4p, Lsb3p, and plant FYVE proteins (SYLF) region and SH3 domain of SH3YL1 contribute to formation of a complex with Nox4-p22^phox. Interaction of p22^phox with SH3YL1 is triggered by LPS, and the complex induces H₂O₂ generation and pro-inflammatory cytokine expression in mouse tubular epithelial cells. After LPS injection, SH3YL1 knockout mice show lower levels of acute kidney injury biomarkers, decreased secretion of pro-inflammatory cytokines, decreased infiltration of macrophages, and reduced tubular damage compared with wild-type (WT) mice. The results strongly suggest that SH3YL1 is involved in renal failure in LPS-induced acute kidney injury (AKI) mice. We demonstrate that formation of a ternary complex of p22^phox-SH3YL1-Nox4, leading to H₂O₂ generation, induces severe renal failure in the LPS-induced AKI model.

Beneficial Effect of Chloroquine and Amodiaquine on Type 1 Diabetic Tubulopathy by Attenuating Mitochondrial Nox4 and Endoplasmic Reticulum Stress

BACKGROUND

Oxidative stress induced by chronic hyperglycemia is recognized as a significant mechanistic contributor to the development of diabetic kidney disease (DKD). Nonphagocytic nicotinamide adenine dinucleotide phosphate oxidase 4 (Nox4) is a major source of reactive oxygen species (ROS) in many cell types and in the kidney tissue of diabetic animals. We designed this study to explore the therapeutic potential of chloroquine (CQ) and amodiaquine (AQ) for inhibiting mitochondrial Nox4 and diabetic tubular injury.

METHODS

Human renal proximal tubular epithelial cells (hRPTCs) were cultured in high-glucose media (30 mM D-glucose), and diabetes was induced with streptozotocin (STZ, 50 mg/kg i.p. for 5 days) in male C57BL/6J mice. CQ and AQ were administered to the mice via intraperitoneal injection for 14 weeks.

RESULTS

CQ and AQ inhibited mitochondrial Nox4 and increased mitochondrial mass in hRPTCs under high-glucose conditions. Reduced mitochondrial ROS production after treatment with the drugs resulted in decreased endoplasmic reticulum (ER) stress, suppressed inflammatory protein expression and reduced cell apoptosis in hRPTCs under high-glucose conditions. Notably, CQ and AQ treatment diminished Nox4 activation and ER stress in the kidneys of STZ-induced diabetic mice. In addition, we observed attenuated inflammatory protein expression and albuminuria in STZ-induced diabetic mice after CQ and AQ treatment.

CONCLUSION

We substantiated the protective actions of CQ and AQ in diabetic tubulopathy associated with reduced mitochondrial Nox4 activation and ER stress alleviation. Further studies exploring the roles of mitochondrial Nox4 in the pathogenesis of DKD could suggest new therapeutic targets for patients with DKD.

The early effects of uninephrectomy on rat kidney metabolic state using optical imaging

Uninephrectomy (UNX) is known to result in structural and metabolic changes to the remaining kidney, although it is uncertain if this alters the mitochondrial redox state and how soon such changes may occur. A custom-designed fluorescence cryo-imaging technique was used to quantitatively assess the effect of UNX by measuring the levels of nicotinamide adenine dinucleotide (NADH) and flavin adenine dinucleotide (FAD) in the remaining kidney. Kidneys were snap-frozen 3 days following UNX, and the intrinsic fluorescence of NADH and FAD were optically acquired. The 3D images were created to characterize the NADH/FAD redox ratios (RR) of the right kidneys, which underwent UNX and the remaining kidneys 3 days following UNX. Both the NADPH-oxidases (Nox2 and Nox4) and the mitochondria are the main sources of reactive oxygen species (ROS) production in tubular epithelial cells. Responses to the UNX were obtained in kidneys of normal Sprague Dawley (SD) rats, Dahl salt-sensitive (SS) rats and SS rats in which NADPH-oxidase isoform 4 (Nox4) was knocked out (SS^Nox4-/- ). The results found that each of the strains exhibited similar increase in kidney weights averaging 17% after 3 days of UNX. SD and SS^Nox4-/- rats both exhibited global reductions of the RR (P < .05) with a similar tendency observed in SS rats (P < .08), indicating increased ROS production. The unexpected reduction of the RR in the remnant kidneys of SS^Nox4-/- rats indicates that mechanisms independent of H₂ O₂ produced from Nox4 may be responsible for this global increase of ROS. We propose that the reduced RR was largely a consequence of enhanced mitochondrial bioenergetics due to increased tubular workload of the remaining kidney. The data indicate that mitochondria become the dominant source of increased ROS following UNX and could represent an important hypertrophic signaling mechanism.

The NADPH oxidase NOX4 promotes the directed migration of endothelial cells by stabilizing vascular endothelial growth factor receptor 2 protein

Directed migration of endothelial cells (ECs) is an important process during both physiological and pathological angiogenesis. The binding of vascular endothelial growth factor (VEGF) to VEGF receptor-2 (VEGFR-2) on the EC surface is necessary for directed migration of these cells. Here, we used TAXIScan, an optically accessible real-time horizontal cell dynamics assay approach, and demonstrate that reactive oxygen species (ROS)-producing NADPH oxidase 4 (NOX4), which is abundantly expressed in ECs, mediates VEGF/VEGFR-2-dependent directed migration. We noted that a continuous supply of endoplasmic reticulum (ER)-retained VEGFR-2 to the plasma membrane is required to maintain VEGFR-2 at the cell surface. siRNA-mediated NOX4 silencing decreased the ER-retained form of VEGFR-2, resulting in decreased cell surface expression levels of the receptor. We also found that ER-localized NOX4 interacts with ER-retained VEGFR-2 and thereby stabilizes this ER-retained form at the protein level in the ER. We conclude that NOX4 contributes to the directed migration of ECs by maintaining VEGFR-2 levels at their surface.

Oxidation of HDAC4 by Nox4-derived H2O2 maintains tube formation by endothelial cells

NADPH oxidases produce reactive oxygen species that differ in localization, type and concentration. Within the Nox family only Nox4 produces H₂O₂ which can directly oxidize cysteine residues. With this post-translational modification, activity, stability, localization and protein-protein interactions of the affected protein is altered. Nox4 controls differentiation, cellular homeostasis and prevents inflammation. Therefore, is likely that epigenetic mechanisms contribute to the effects of Nox4. One group of epigenetic modifiers are class IIa histone deacetylases (HDACs). We hypothesize that Nox4-derived H₂O₂ oxidizes HDACs and analyzed whether HDACs can be differentially oxidized by Nox4. As an artificial system, we utilized HEK293 cells, overexpressing Nox4 in a tetracycline-inducible manner. HDAC4 was oxidized upon Nox4 overexpression. Additionally, Nox4 overexpression increased HDAC4 phosphorylation on Ser632. H₂O₂ disrupted HDAC4/Mef2A complex, which de-represses Mef2A. In endothelial cells such as HUVECs and HMECs, overexpression of HDAC4 significantly reduced tube formation. Overexpression of a redox insensitive HDAC4 had no effect on endothelial tube formation. Treatment with H₂O₂, induction of Nox4 expression by treatment of the cells with TGFβ and co-overexpression of Nox4 not only induced phosphorylation of HDAC4, but also restored the repressive effect of HDAC4 for tube formation, while overexpression of a redox dead mutant of Nox4 did not. Taken together, Nox4 oxidizes HDAC4, increases its phosphorylation, and eventually ensures proper tube formation by endothelial cells.

Selenoprotein T protects against cisplatin-induced acute kidney injury through suppression of oxidative stress and apoptosis

Previously, selenoprotein T (SelT) expression was shown to be induced in nervous, endocrine, and metabolic tissues during ontogenetic and regenerative processes. However, whether SelT plays a critical role in renal diseases remains unclear. Here, we explored the role of SelT in cisplatin-induced acute kidney injury (AKI). Results revealed that SelT was highly expressed in renal tubules, but its expression was significantly reduced in cisplatin-induced AKI. Importantly, knocking down of SelT expression in kidney cells in vitro resulted in cisplatin-induced cell apoptosis, as indicated by the elevation of cleaved-PARP and Bax expression, Caspase-3 activity, and number of TUNEL-positive cells. Moreover, SelT silencing-induced reactive oxygen species (ROS) production, accompanied by a decrease in intracellular superoxide dismutase (SOD) and catalase (CAT) activity and increase in malondialdehyde (MDA) content. Notably, the protein and mRNA levels of Nox4 were increased in response to SelT downregulation. Furthermore, suppression of Nox4 expression by GKT137831 partially alleviated SelT knockdown-induced ROS generation and cell apoptosis in cisplatin-treated kidney cells. Taken together, our findings provide the first evidence that SelT protects against cisplatin-induced AKI by suppression of oxidative stress and apoptosis.

Nox4 - RyR1 - Nox2: Regulators of micro-domain signaling in skeletal muscle

The ability for skeletal muscle to perform optimally can be affected by the regulation of Ca²⁺ within the triadic junctional space at rest. Reactive oxygen species impact muscle performance due to changes in oxidative stress, damage and redox regulation of signaling cascades. The interplay between ROS and Ca²⁺ signaling at the triad of skeletal muscle is therefore important to understand as it can impact the performance of healthy and diseased muscle. Here, we aimed to examine how changes in Ca²⁺ and redox signaling within the junctional space micro-domain of the mouse skeletal muscle fibre alters the homeostasis of these complexes. The dystrophic mdx mouse model displays increased RyR1 Ca²⁺ leak and increased NAD(P)H Oxidase 2 ROS. These alterations make the mdx mouse an ideal model for understanding how ROS and Ca²⁺ handling impact each other. We hypothesised that elevated t-tubular Nox2 ROS increases RyR1 Ca²⁺ leak contributing to an increase in cytoplasmic Ca²⁺, which could then initiate protein degradation and impaired cellular functions such as autophagy and ER stress. We found that inhibiting Nox2 ROS did not decrease RyR1 Ca²⁺ leak observed in dystrophin-deficient skeletal muscle. Intriguingly, another NAD(P)H isoform, Nox4, is upregulated in mice unable to produce Nox2 ROS and when inhibited reduced RyR1 Ca²⁺ leak. Our findings support a model in which Nox4 ROS induces RyR1 Ca²⁺ leak and the increased junctional space [Ca²⁺] exacerbates Nox2 ROS; with the cumulative effect of disruption of downstream cellular processes that would ultimately contribute to reduced muscle or cellular performance.

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Nox2 ROS does not influence RyR1 Ca²⁺ leak in skeletal muscle.

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Lack of Nox2 ROS increases Nox4 expression.

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Nox4 ROS induces RyR1 Ca²⁺ leak via S-nitrosylation.

Inhibition of vascular adventitial remodeling by netrin-1 in diabetic rats

Cardiovascular complications of type 2 diabetes mellitus (T2DM) are associated with vascular remodeling in the arteries. Perivascular sympathetic neurons release an abundance of trophic factors to regulate vascular function via a paracrine signaling. Netrin-1, a diffusible protein that can be secreted outside the cell, is one of common signals of 'conversation' between nerve and vessel. The present study investigated whether netrin-1 is a novel modulator of sympathetic neurons paracrine signaling and played a critical role in vascular adventitial remodeling under T2DM. Vascular adventitial remodeling was observed in adventitial fibroblasts (AFs) responding to netrin-1 deficiency in the supernatant from primary rat superior cervical ganglia (SCG) neurons, shown as AFs proliferation, migration, and collagen deposition. Conditioned medium from the high glucose (HG)-treated SCG neurons contributed to AFs remodeling, which was effectively alleviated by exogenous netrin-1 supplementation. Further, it was found that uncoordinated-5-B (Unc5b) was mainly expressed in AFs among netrin-1 specific receptors. Treatment of netrin-1 inhibited H2O2 production derived from NADPH oxidase 4 (NOX4) through the UNC5b/CAMP/PKA signal pathway in AFs remodeling. In vivo, aorta adventitial remodeling was accompanied with the downregulation of netrin-1 in the perivascular sympathetic nerve in T2DM rats. Such abnormalities were restored by netrin-1 intervention, which was associated with the inhibition of NOX4 expression in the aorta adventitia. In conclusion, netrin-1 is a novel modulator of sympathetic neurons paracrine signaling to maintain AFs function. Vascular adventitial remodeling was aggravated by sympathetic neurons paracrine signaling under hyperglycemia, which was ameliorated by netrin-1 treatment through the UNC5b/CAMP/PKA/NOX4 pathway.

Farrerol alleviates high glucose-induced renal mesangial cell injury through the ROS/Nox4/ERK1/2 pathway

Hyperproliferation and oxidative stress induced by hyperglycemia in mesangial cells plays crucial roles in the pathological process of diabetic nephropathy. Farrerol, isolated from rhododendron leaves, possesses broad anti-oxidative and anti-inflammatory properties towards several diseases, but its role in diabetic neuropathy remains unclear. The aim of this study was to evaluate the effects of farrerol in high glucose induced mesangial cell injury, and to explore underlying molecular mechanisms. Our results showed that high glucose in vitro conditions significantly stimulated cell proliferation, inflammatory cytokine secretion, extracellular matrix deposition, excessive oxidative stress, and NADPH oxidase activity in mesangial cells. Levels of NADPH oxidase 4 (Nox4) expression, ERK1/2 phosphorylation, and TGF-β1/Smad2 activation were significantly induced by high glucose conditions in mesangial cells. Inversely, farrerol treatments at 40, 60, and 80 μM concentrations, dose-dependently alleviated this molecular damage by high glucose in mesangial cells. We also found that restoration of Nox4 expression abolished the protective effects of farrerol on high glucose-induced proliferation and reactive oxygen species generation. Furthermore, pretreatment with the Nox4 inhibitor diphenyliodonium or the ERK1/2 pathway inhibitor PD98059, displayed similar ameliorated effects of farrerol on high glucose-induced mesangial cell damage. Taken together, these data suggest that farrerol displays protective effects on high glucose induced mesangial cell injury, partly through the Nox4-mediated ROS/ERK1/2 signaling pathway. These observations may provide novel insights into the application of farrerol as a diabetic neuropathy treatment.

Nox4-mediated ROS production is involved, but not essential for TGFβ-induced lens EMT leading to cataract

The reactive oxygen species (ROS) producing enzyme, NADPH oxidase 4 (Nox4), is upregulated in response to TGFβ in lens epithelial cells in vitro, and its selective inhibition was shown to block aspects of TGFβ-induced epithelial-mesenchymal transition (EMT). In the present in situ study we validate the role(s) of Nox4 in TGFβ-induced lens EMT leading to anterior subcapsular cataract (ASC) formation. Mice overexpressing TGFβ in the lens, that develop ASC, were crossed to Nox4-deficient mice. When comparing mice overexpressing TGFβ in lens, to mice that were also deficient for Nox4, we see the delayed onset of cataract, along with a delay in EMT protein markers normally associated with TGFβ-induced fibrotic cataracts. In the absence of Nox4, we also see elevated levels of ERK1/2 activity that was shown to be required for TGFβ/Smad2/3-signaling. qRT-PCR revealed upregulation of Nox2 and its regulatory subunit in TGFβ-overexpressing lens epithelial cells devoid of Nox4. Taken together, these findings provide an improved platform to delineate putative Nox4 (and ROS) interactions with Smad2/3 and/or ERK1/2, in particular in the development of fibrotic diseases, such as specific forms of cataract.

Oxidative Stress-Related Gene Polymorphisms Are Associated With Hepatitis B Virus-Induced Liver Disease in the Northern Chinese Han Population

Oxidative stress is closely related to the occurrence and development of various diseases such as cancer, diabetes, and cardiovascular and infectious diseases. We identified six critical genetic variants related to oxidative stress, and evaluated their main effects and their interaction effects on hepatitis B virus (HBV)-induced liver diseases. We enrolled 3,128 Han Chinese subjects into five groups: healthy controls, chronic hepatitis B (CHB), liver cirrhosis (LC), hepatocellular carcinoma (HCC), and natural clearance. We then determined the genotypes in each group for CYBA-rs4673, NCF4-rs1883112, NOX4-rs1836882, rs3017887, SOD2-rs4880, and GCLM-rs41303970, and evaluated the association between these variants and HBV-induced liver diseases. Gene-gene interactions were evaluated using generalized multifactor dimensionality reduction, logistic regression, and four-by-two tables. Significant associations were observed between healthy controls and the CIB group (CHB+LC+HCC). The CYBA-rs4673AG genotype was associated with a 1.356 rate of susceptibility of HBV-induced liver disease compared to the wild type GG genotype. The NCF4-rs1883112G allele occurred more frequently in healthy controls than in the CIB group in all three models (dominant, codominant, and recessive). Nox4-rs1836882 TC showed a protective association, being more frequent in healthy controls compared to the wild type TT genotype. GCLM-rs41303970A was associated with HBV-induced liver disease. The overall best model by multifactor dimensionality reduction was a five factor interaction model that had the highest cross validation consistency (10/10) and test accuracy (0.5669), P= 0.001. Oxidative stress-related gene polymorphisms are likely to be associated with HBV-induced liver disease, suggesting that information on these variations is useful for risk assessment of HBV-induced liver disease.

Nox2 and Nox4 Participate in ROS-Induced Neuronal Apoptosis and Brain Injury During Ischemia-Reperfusion in Rats

BACKGROUND

Previously studies have shown that Nox2 and Nox4, as members of nicotinamide adenine dinucleotide phosphate oxidase (NADPH oxidase, Nox), participate in brain damage caused by ischemia-reperfusion (I/R). The aim of this study is to investigate the effects of specific chemical inhibitors of Nox2 and Nox4 on cerebral I/R-induced brain injury in rats.

METHODS

At 0.5 h before MCAO surgery, the rats were pretreated with vehicle, Nox2 inhibitor (gp91ds-tat), and Nox4 inhibitor (GKT137831), respectively. After reperfusion for 24 h, the infarct sizes of brain tissues in rats in various groups are determined. The penumbra (ischemic) tissues are collected to measure ROS levels, neuronal apoptosis, and degeneration, as well as the integrity of the blood-brain barrier (BBB) in brain tissues of rats.

RESULTS

gp91ds-tat and GKT137831 pretreatment significantly reduced the infarct sizes in brain tissues of rats, effectively suppressed I/R-induced increase in ROS levels, neuronal apoptosis and degeneration, and obviously alleviated BBB damage.

CONCLUSION

Under cerebral I/R conditions, Nox2 inhibitor (gp91ds-tat) and Nox4 inhibitor (GKT137831) can effectively play a protective role in the brain tissues of rats.

Protective effects of acarbose against vascular endothelial dysfunction through inhibiting Nox4/NLRP3 inflammasome pathway in diabetic rats

The cardiovascular efficacy of glucose-lowering drugs is needed due to the cardiovascular complication in type 2 diabetes mellitus (T2DM). Acarbose is an α-glucosidase inhibitor that suppresses postprandial hyperglycemia, however, the cardiovascular protection of acarbose has still remained controversial. NLRP3 inflammasome activation mediated tight junction disruption, a hallmark event of endothelial barrier dysfunction leading to endothelial hyperpermeability in diabetes. Given the anti-inflammatory property of acarbose, it was investigated that acarbose protected against vascular endothelial barrier dysfunction through inhibiting NLRP3 inflammasome in vascular endothelial cells in T2DM rats. The rat aortic endothelial cells (RAECs) were incubated with high glucose (HG, 30 mM) for 24 h in vitro. It was found that HG significantly induced the formation and activation of NLRP3 inflammasome, which was markedly blocked by acarbose treatment. Furthermore, acarbose blocked the Nox4-dependent superoxide (O₂^.-) generation, which regulated NLRP3 inflammasome in RAECs. Importantly, we found that acarbose remarkably enhanced the junction protein expression of ZO-1 and VE-Cadherin and consequently abolished vascular hyperpermeability, which was associated with inhibiting NLRP3 inflammasome in RAECs. In vivo, acarbose intervention relieved vascular leakage in the heart of diabetic rats injected with Evans blue dye and the vasodilatory response to acetylcholine, which was accompanied with the restoration of ZO-1, VE-Cadherin, Nox4 and NLRP3 inflammasome in the aortal endothelium of diabetic rats. Taken together, our data indicated that acarbose ameliorated endothelial barrier dysfunction by directly inhibiting NLRP3 inflammasome which was dependent on inhibiting Nox4 oxidase-dependent O₂^.- production. These properties might carry a potential significance for acarbose in cardiovascular protection in diabetic patients.

Enhancer of zeste homolog 2 modulates oxidative stress-mediated pyroptosis in vitro and in a mouse kidney ischemia-reperfusion injury model

Enhancer of zeste homolog 2 (EZH2), a well-known methyltransferase, mediates histone H3 lysine 27 trimethylation (H3K27me3) and plays a crucial role in several kidney disease models. However, its role in renal ischemia/reperfusion (I/R) injury still remains unclear. In this study, we found that EZH2 was positively related to renal I/R injury and inhibition of EZH2 with DZNeP alleviated I/R injury and blocked the activation of oxidative stress and pyroptosis in vivo. Similarly, inhibition of EZH2 with either DZNeP or si-RNA also exerted an inhibitory effect on hypoxia/reoxygenation (H/R)-induced oxidative stress and pyroptosis in vitro. Moreover, further study revealed that ablation of reactive oxygen species (ROS) with N-acetyl-cysteine (NAC) suppressed pyroptosis in human renal proximal tubular epithelial cell line cells exposed to H/R stimulation. Furthermore, Nox4, which was positively related to the generation of ROS, was upregulated during H/R process, while it could be reversed by EZH2 inhibition. Consistently, Nox4-mediated ROS generation was attenuated upon inhibition of EZH2 with DZNeP or si-RNA. Additionally, the transcriptional activity of Nox4 was enhanced by the activation of ALK5/Smad2/3 signaling pathway, which was abolished by ALK5 knockdown in vitro. Finally, EZH2 inhibition blocked H/R and I/R-activated ALK5/Smad2/3 pathway and also resulted in an obvious decrease in the transcriptional activity and protein expression levels of Nox4. In conclusion, our results proved that EZH2 inhibition alleviated renal pyroptosis by blocking Nox4-dependent ROS generation through ALK5/Smad2/3 signaling pathway, indicating that EZH2 could be a potential therapeutic target for renal I/R injury.

Nuclear Nox4 interaction with prelamin A is associated with nuclear redox control of stem cell aging

Mesenchymal stem cells have emerged as an important tool that can be used for tissue regeneration thanks to their easy preparation, differentiation potential and immunomodulatory activity. However, an extensive culture of stem cells in vitro prior to clinical use can lead to oxidative stress that can modulate different stem cells properties, such as self-renewal, proliferation, differentiation and senescence. The aim of this study was to investigate the aging process occurring during in vitro expansion of stem cells, obtained from amniotic fluids (AFSC) at similar gestational age.

The analysis of 21 AFSC samples allowed to classify them in groups with different levels of stemness properties. In summary, the expression of pluripotency genes and the proliferation rate were inversely correlated with the content of reactive oxygen species (ROS), DNA damage signs and the onset premature aging markers, including accumulation of prelamin A, the lamin A immature form. Interestingly, a specific source of ROS, the NADPH oxidase isoform 4 (Nox4), can localize into PML nuclear bodies (PML-NB), where it associates to prelamin A. Besides, Nox4 post translational modification, involved in PML-NB localization, is linked to its degradation pathway, as it is also for prelamin A, thus possibly modulating the premature aging phenotype occurrence.

Acute Changes in NADPH Oxidase 4 in Early Post-Traumatic Osteoarthritis

Knee injuries cause structural damage and acute inflammation that initiates the development of post-traumatic osteoarthritis (PTOA). NADPH oxidase 4 (Nox4), a member of a family of enzymes that generates reactive oxygen species (ROS), plays a pivotal role in normal development of the musculoskeletal system, but may increase ROS production to harmful levels after joint injury. The role of ROS in both normal joint homeostasis and injury is poorly understood, but inhibition of excessive ROS production by Nox4 after joint injury could be protective to the joint, decreasing oxidative stress, and initiation of PTOA. Knee injuries were simulated using inflammatory cytokines in cultured primary human chondrocytes and a non-invasive mouse model of PTOA in C57BL/6N and Nox4 knockout mice. There is an acute decrease in Nox4 activity within 24 h after injury in both systems, followed by a subsequent sustained low-level increase, a novel finding not seen in any other system. Inhibition of Nox4 activity by GKT137831 was protective against early structural changes after non-invasive knee injury in a mouse model. Nox4 knockout mice had significant differences in structural and mechanical properties of bone, providing further evidence for the role of Nox4 in development of joint tissues and biochemical response after joint injury. Nox4 plays a significant role in the acute phase after joint injury, and targeted inhibition of inflammation caused by Nox4 may be protective against early joint changes in the pathogenesis of PTOA. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 37:2429-2436, 2019.

Inhibition of neointima hyperplasia by the combined therapy of linagliptin and metformin via AMPK/Nox4 signaling in diabetic rats

BACKGROUND

Neointima hyperplasia is the pathological basis of atherosclerosis and restenosis which have been associated with diabetes mellitus (DM). It is controversial for linagliptin and metformin to protect against vascular neointimal hyperplasia caused by DM. Given the combined therapy of linagliptin and metformin in clinical practice, we investigated whether the combination therapy inhibited neointimal hyperplasia in the carotid artery in diabetic rats.

METHODS AND RESULTS

Neointima hyperplasia in the carotid artery was induced by balloon-injury in the rats fed with high fat diet (HFD) combined with low dose streptozotocin (STZ) administration. In vitro, vascular smooth muscle cells (VSMCs) were incubated with high glucose (HG, 30 mM) and the proliferation, migration, apoptosis and collagen deposition were analyzed in VSMCs. We found that the combined therapy, not the monotherapy of linagliptin and metformin significantly inhibited the neointima hyperplasia and improved the endothelium-independent contraction in the balloon-injured cardia artery of diabetic rats, which was associated with the inhibition of superoxide (O₂^-.) production in the cardia artery. In vitro, HG-induced VSMC remodeling was shown as the remarkable upregulation of PCNA, collagan1, MMP-9, Bcl-2 and migration rate as well as the decreased apoptosis rate. Such abnormal changes were dramatically reversed by the combined use of linagliptin and metformin. Moreover, the AMP-activated protein kinase (AMPK)/Nox4 signal pathway was found to mediate VSMC remodeling responding to HG. Linagliptin and metformin were synergistical to target AMPK/Nox4 signal pathway in VSMCs incubated with HG and in the cardia artery of diabetic rats, which was superior to the monotherapy.

CONCLUSIONS

We demonstrated that the potential protection of the combined use of linagliptin and metformin on VSMC remodeling through AMPK/Nox4 signal pathway, resulting in the improvement of neointima hyperplasia in diabetic rats. This study provided new therapeutic strategies for vascular stenosis associated with diabetes.

Differential contribution of Nox1, Nox2 and Nox4 to kidney vascular oxidative stress and endothelial dysfunction in obesity

Oxidative stress-associated endothelial dysfunction is a key pathogenic factor underlying the microvascular complications of metabolic disease. NADPH oxidase (Nox) is a major source of oxidative stress in diabetic nephropathy and chronic kidney disease, despite Nox4 and Nox2 have been identified as relevant sources of vasodilator endothelial H₂O₂.The present study was sought to investigate the role of Nox enzymes in renal vascular oxidative stress and endothelial dysfunction in a rat model of genetic obesity. Endothelial function was assessed in intrarenal arteries of obese Zucker rats (OZR) and their counterparts lean Zucker rats (LZR) mounted in microvascular myographs, and superoxide (O₂^.-) and H₂O₂ production were measured. Impaired endothelium-dependent relaxations to acetylcholine (ACh) were associated to augmented O₂^.- generation, but neither ROS scavengers nor the Nox inhibitor apocynin significantly improved these relaxant responses in renal arteries of OZR. Whereas NO contribution to endothelial relaxations was blunted, catalase-sensitive non-NO non-prostanoid relaxations were enhanced in obese rats. Interestingly, NADPH-dependent O₂^.- production was augmented while NADPH-dependent H₂O₂ generation was reduced, and cytosolic and mitochondrial SOD were up-regulated in kidney of obese rats. Nox4 was down-regulated in renal arteries and Nox4-dependent H₂O₂ generation and endothelial relaxation were reduced in OZR. Up-regulation of both Nox2 and Nox1 was associated with augmented O₂^.- production but reduced H₂O₂ generation and blunted endothelial Nox2-derived H₂O₂-mediated in obese rats. Moreover, increased Nox1-derived O₂^.- contributed to renal endothelial dysfunction in OZR. In summary, the current data support a main role for Nox1-derived O₂^.- in kidney vascular oxidative stress and renal endothelial dysfunction in obesity, while reduced endothelial Nox4 expression associated to decreased H₂O₂ generation and H₂O₂-mediated vasodilatation might hinder Nox4 protective renal effects thus contributing to kidney injury. This suggests that effective therapies to counteract oxidative stress and prevent microvascular complications must identify the specific Nox subunits involved in metabolic disease.

Protective effects of catalpol on diabetes mellitus-induced male reproductive damage via suppression of the AGEs/RAGE/Nox4 signaling pathway

AIMS

Diabetes mellitus (DM)-induced reproductive damage is an important cause of infertility for male DM patients, we herein evaluated the effects of catalpol on diabetic reproductive damage through the suppression of the AGEs/RAGE/Nox4 signaling pathway.

METHODS

KK-Ay diabetic reproductive damage mice were administered with catalpol for 8 weeks, the testis/body weight ratio, testicular histopathology, the levels of endogenous hormone and the activity of testicular marker enzymes were determined. In vitro, the GC-2 cell injury model was induced by advanced glycation end-products (AGEs) and pretreated with catalpol. Cell viability, apoptosis, and oxidative stress markers were detected and the mechanism based on the AGEs/RAGE/Nox4 pathway was explored.

KEY FINDINGS

Catalpol showed remarkable capacity on protecting diabetic reproductive damage by improving the histomorphology of the testes, increasing the testis/body weight ratio and activity of acid phosphatase (ACP), lactate dehydrogenase (LDH), gamma-glutamyl transferase (γ-GT). The reduced testosterone (T), luteinizing hormone (LH) and follicle-stimulating hormone (FSH) levels in DM mice were also reversed with catalpol intervention. Moreover, catalpol showed markedly effects of anti-oxidative in vivo and in vitro, which significantly down-regulated reactive oxygen species (ROS) levels and restored superoxide dismutase (SOD) activity, meanwhile decreased GC-2 cell apoptosis and Bax/Bcl-2 ratio. Moreover, the over-expression of receptors for AGEs (RAGE), NADPH oxidase type 4 (Nox4) and phosphorylation of nuclear transcription factor-κB p65 (NF-κB p65) were suppressed by catalpol.

SIGNIFICANCE

Catalpol could alleviate DM-induced male reproductive damage by inhibiting oxidative stress-induced apoptosis and inflammation mediated by AGEs/RAGE/Nox4 signaling pathway.

Catalpol Inhibits Homocysteine-induced Oxidation and Inflammation via Inhibiting Nox4/NF-κB and GRP78/PERK Pathways in Human Aorta Endothelial Cells

Hyperhomocysteinemia (HHCY) has been recognized as an independent risk factor for atherosclerosis and plays a vital role in the development of atherosclerosis. Catalpol, an iridoid glucoside extracted from the root of Rehmannia glutinosa, can produce anti-inflammatory, anti-oxidant, anti-tumor, and dopaminergic neurons protecting effects. This study aimed to determine the protecting effects of catalpol against homocysteine (HCY)-induced injuries in human aortic endothelial cells (HAECs) and uncover the underlying mechanisms: 1. HAECs were cultured with different concentrations of HCY (3 mM) and catalpol (7.5 μΜ, 15 μΜ, 30 μΜ) for 24 h. (1) The level of MDA and GSH as well as LDH release was measured with colorimetric assay. (2) Reactive oxygen species (ROS) were detected by flow cytometry analysis. (3) Western blotting analysis was performed to detect the expression of Nox4, p22^phox, ICAM-1, MCP-1, VCAM-1, IκB, nucleus p65, p65 phosphorylation, caspase-3, −9, bax, bcl-2, and ER stress-related proteins. (4) The expressions of CHOP, ATF4 were measured by qRT-PCR. (5) Mitochondrial membrane potential in HCY-treated HAECs was measured by rhodamine 123 staining, and the samples were observed by confocal laser scanning microscopy. 2. DPI, PDTC, and TUDCA were used to determine the interaction among Nox4/ROS, NF-κB, and endoplasmic reticulum stress. 3. TUDCA or Nox4 siRNA were used to investigate whether the effect of catalpol inhibiting the over-production of ROS were associated with inhibiting ER stress and Nox4 expression. Catalpol significantly suppressed LDH release, MDA level, and the reduction of GSH. Catalpol reduced HCY-stimulated ROS over-generation, inhibited the NF-κB transcriptional activation as well as the protein over-expressions of Nox4, ICAM-1, VCAM-1, and MCP-1. Catalpol elevated bcl-2 protein expression and reduced bax, caspase-3, −9 protein expressions in the HCY-treated HAECs. Simultaneously, catalpol could also inhibit the activation of ER stress-associated sensors GRP78, IRE1α, ATF6, P-PERK, P-eIF2α, CHOP, and ATF4 induced by HCY. In addition, the extent of catalpol inhibiting ROS over-generation and NF-κB signaling pathway was reduced after inhibiting Nox4 or ER stress with DPI or TUDCA. The inhibitor of NF-κB PDTC also reduced the effects of catalpol inhibiting the expressions of Nox4 and GRP78. Furthermore, the effect of catalpol inhibiting the over-generation of ROS was reduced by Nox4 siRNA. Catalpol could ameliorate HCY-induced oxidation, cells apoptosis and inflammation in HAECs possibly by inhibiting Nox4/NF-κB and ER stress.

Tanshinone IIA Activates Nuclear Factor-Erythroid 2-Related Factor 2 to Restrain Pulmonary Fibrosis via Regulation of Redox Homeostasis and Glutaminolysis

AIMS

Pulmonary fibrosis (PF) is characterized by myofibroblast activation through oxidative stress. However, the precise regulation of myofibroblast transdifferentiation remains largely uncharacterized.

RESULTS

In this study, we found that tanshinone IIA (Tan-IIA), an active component in the root of Salvia miltiorrhiza Bunge, can suppress reactive oxygen species (ROS)-mediated activation of myofibroblast and reduce extracellular matrix deposition in bleomycin (BLM)-challenged mice through the regulation of nuclear factor-erythroid 2-related factor 2 (Nrf2). Additionally, Tan-IIA restored redox homeostasis by upregulating Nrf2 with NADPH oxidase 4 suppression and effectively prevented myofibroblast activation by blocking ROS-mediated protein kinase C delta (PKCδ)/Smad3 signaling. Nrf2 knockdown in the fibroblasts and the lungs of BLM-treated mice reduced the inhibitory effects of Tan-IIA, indicating the essential role of Nrf2 in the Tan-IIA activity. Tan-IIA impaired the binding of kelch-like ECH-associated protein 1 (Keap1) to Nrf2 by promoting the degradation of Keap1 and thereby increasing Nrf2 induction by protecting Nrf2 stability against ubiquitination and proteasomal degradation. Importantly, we also found that the glutamate anaplerotic pathway was involved in energy generation and biosynthesis in activated myofibroblasts and their proliferation. Tan-IIA shunted glutaminolysis into glutathione (GSH) production by activating Nrf2, resulting in the reduction of glutamate availability for tricarboxylic acid cycle. Ultimately, myofibroblast activation was prevented by impairing cell proliferation. Innovation and Conclusion: In addition to the regulation of redox homeostasis, our work showed that Tan-IIA activated Nrf2/GSH signaling pathway to limit glutaminolysis in myofibroblast proliferation, which provided further insight into the critical function of Nrf2 in PF.

NADPH oxidase-derived reactive oxygen species: Dosis facit venenum

New Findings

What is the topic of this review?

Within this review, the role of reactive oxygen species in cellular homeostasis, physiology and pathophysiology is discussed.

What advances does it highlight?

The review provides new concepts of how reactive oxygen species influence gene expression, energy consumption and other aspects of the life of a cell. Furthermore, a model is provided to illustrate how reactive oxygen species elicit specific oxidation of target molecules.

Abstract

Reactive oxygen species (ROS) have a long history of bad reputation. They are needed and effective in host defense, but on the contrary may induce situations of oxidative stress. Besides that, within recent years several soft functions (functions that may occur and are not directly connected to an effect, but may influence signaling in an indirect manner) of NADPH oxidases have been discovered, which are slowly eroding the image of the solely dangerous ROS. NADPH oxidase‐derived ROS serve to ease or enable signal transduction and to maintain homeostasis. However, there is still an enormous lag in the knowledge concerning target proteins and how ROS can elicit specific signalling in different cells and tissues. The present review summarizes some important functions of Nox2 and Nox4. Furthermore, although highly speculative, a model is provided of how those NADPH oxidases might be able to oxidize target proteins in a specific way. Many concepts mentioned in this review represent my personal view and are supported only in part by published studies.

Redox-Dependent Regulation of Sulfur Metabolism in Biomolecules: Implications for Cardiovascular Health

SIGNIFICANCE

Sulfur-containing amino acids are integral to the molecular mechanisms that underlie many aspects of cellular function and homeostasis, facilitated by reversible changes in the oxidation states of sulfur atoms. Sulfur-containing amino acids are metabolically linked by interacting pathways that impact the one-carbon metabolic cycle and generation of methyl groups, the folate cycle, and maintenance of the major cellular redox buffer; glutathione. Dysregulation of these pathways is associated with diverse pathologies, notably of the cardiovascular (CV) system, which are typically characterized by inappropriate plasma levels of sulfur-containing amino acids. Recent Advances: Perhaps not surprisingly, the cellular redox state has emerged as a major regulator of many enzymatic processes within these metabolic cycles. The metabolism of cysteine can also result in the production of hydrogen sulfide (H₂S), a signaling molecule whose activity is potentially linked to intracellular levels of both reactive oxygen species (ROS) and molecular oxygen.

CRITICAL ISSUES

In most cases, the endogenous physiological sources of ROS that might mediate the interlinked metabolic pathways of sulfur-containing biomolecules remain unknown. However, the family of NADPH oxidases, and Nox4 in particular, is emerging as a likely candidate.

FUTURE DIRECTIONS

This review focuses on the current knowledge of key aspects of sulfur metabolism, which are regulated by redox-based chemical reactions, and the likely intracellular oxidant sources that might mediate this regulation. This knowledge will be important to guide future targeted therapeutic interventions in diverse CV disorders.

BIAM switch assay coupled to mass spectrometry identifies novel redox targets of NADPH oxidase 4

Aim

NADPH oxidase (Nox) -derived reactive oxygen species have been implicated in redox signaling via cysteine oxidation in target proteins. Although the importance of oxidation of target proteins is well known, the specificity of such events is often debated. Only a limited number of Nox-oxidized proteins have been identified thus far; especially little is known concerning redox-targets of the constitutively active NADPH oxidase Nox4.

In this study, HEK293 cells with tetracycline-inducible Nox4 overexpression (HEK-tet-Nox4), as well as podocytes of WT and Nox4-/- mice, were utilized to identify Nox4-dependent redox-modified proteins.

Results

TGFβ1 induced an elevation in Nox4 expression in podocytes from WT but not Nox4-/- mice. Using BIAM based redox switch assay in combination with mass spectrometry and western blot analysis, 142 proteins were identified as differentially oxidized in podocytes from wild type vs. Nox4-/- mice and 131 proteins were differentially oxidized in HEK-tet-Nox4 cells upon Nox4 overexpression. A predominant overlap was found for peroxiredoxins and thioredoxins, as expected. More interestingly, the GRB2-associated-binding protein 1 (Gab1) was identified as being differentially oxidized in both approaches. Further analysis using mass spectrometry-coupled BIAM switch assay and site directed mutagenesis, revealed Cys374 and Cys405 as the major Nox4 targeted oxidation sites in Gab1.

Innovation & conclusion

BIAM switch assay coupled to mass spectrometry is a powerful and versatile tool to identify differentially oxidized proteins in a global untargeted way. Nox4, as a source of hydrogen peroxide, changes the redox-state of numerous proteins. Of those, we identified Gab1 as a novel redox target of Nox4.

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BIAM switch assay coupled to MS is a powerful tool to identify oxidized proteins.

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Stable Nox4 overexpression oxidized Prx and Trx in presence of Auranofin only.

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Gab1 was identified as novel redox-target of Nox4.

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Cys374 and Cys405 were identified as the major oxidized cysteines in Gab1.

Participation of NADPH 4 oxidase in thyroid regulation

Different factors are involved in thyroid function and proliferation such as thyrotropin (TSH), insulin, growth factors, iodide, etc. TSH and IGF1/insulin increase proliferation rate and stimulate genes involved in thyroid differentiation. In the present study, we analyse the physiological regulation of NOX4 expression by TSH, insulin and iodine, and the role of NOX4 on thyroid genes expression. Differentiated rat thyroid cells (FRTL-5) were incubated in the presence or absence of TSH/insulin and TTF2, PAX8, TPO, NIS, NOX4, TGFβ1, FOXO1/3 mRNA levels were examined by Real Time PCR. We showed that TSH and insulin repress NOX4 expression and appears to be inversely correlated with some thyroid genes. SiRNA targeted knockdown of NOX4 increased mRNA levels of TGFβ1, TPO, PAX8, TTF2, FOXO1 and FOXO3. A PI3K inhibitor (LY294002), increases the expression of NIS, TTF2 and FOXO1/3, however PI3K/AKT pathway does not regulate NOX4 expression. We observed that iodine increased NOX4 expression and knockdown of NOX4 reduced ROS and reversed the inhibitory effect of iodine on NIS, TPO, PAX8 and TTF2 expression. Our findings provide strong evidence that NOX4 could be a novel signaling modulator of TSH/insulin pathway and would have a critical role in the autoregulatory mechanism induced by iodine.

Nox4 and soluble epoxide hydrolase synergistically mediate homocysteine-induced inflammation in vascular smooth muscle cells

BACKGROUND

Hyperhomocysteinemia leads to a vascular smooth muscle cell (VSMC) inflammatory response. Meanwhile, Nox4 dependent reactive oxygen species (ROS) signaling and soluble epoxide hydrolase (sEH)/epoxyeicosatrienoic acids (EETs) are both involved in vascular inflammation. Herein, we hypothesized that Nox4 and soluble epoxide hydrolase cross regulated during homocysteine-induced VSMC inflammation.

METHODS AND RESULTS

In cultured VSMCs, the expression of the inflammatory factors VCAM1 and ICAM1 was measured by real-time PCR and Western blotting, while supernatant MCP1 was measured by ELISA. Upon VSMC stimulation with 50 μΜ homocysteine, we observed the VCAM1 and ICAM1 mRNA levels were increased by 1.15 and 1.0 folds, respectively. The MCP1 levels in the supernatant of cultured VSMCs treated with 100 μΜ increased to 1.76 folds. As expected, homocysteine induced Nox4 expression and Nox4-dependent ROS generation. The sEH expression was also upregulated in the presence of homocysteine in a dose-dependent manner. Furthermore, we knocked down Nox4 with siRNA. Knockdown of Nox4 decreased ROS generation and homocysteine-induced sEH expression. Overexpression of Nox4 with an adenovirus stimulated sEH expression. Similarly, knockdown or chemical inhibition of sEH blunted the upregulation of Nox4 by homocysteine. In vivo, in homocysteine-fed mice, concomitant upregulation of Nox4 and sEH was associated with increased VCAM1 and ICAM1 expression in the aortic wall.

CONCLUSIONS

The inflammatory response induced by homocysteine in VSMCs was accompanied by Nox4 and sEH upregulation. Nox4 and soluble epoxide hydrolase synergistically contribute to homocysteine-induced inflammation.

Myocardial NADPH oxidase-4 regulates the physiological response to acute exercise

Regular exercise has widespread health benefits. Fundamental to these beneficial effects is the ability of the heart to intermittently and substantially increase its performance without incurring damage, but the underlying homeostatic mechanisms are unclear. We identify the ROS-generating NADPH oxidase-4 (Nox4) as an essential regulator of exercise performance in mice. Myocardial Nox4 levels increase during acute exercise and trigger activation of the transcription factor Nrf2, with the induction of multiple endogenous antioxidants. Cardiomyocyte-specific Nox4-deficient (csNox4KO) mice display a loss of exercise-induced Nrf2 activation, cardiac oxidative stress and reduced exercise performance. Cardiomyocyte-specific Nrf2-deficient (csNrf2KO) mice exhibit similar compromised exercise capacity, with mitochondrial and cardiac dysfunction. Supplementation with an Nrf2 activator or a mitochondria-targeted antioxidant effectively restores cardiac performance and exercise capacity in csNox4KO and csNrf2KO mice respectively. The Nox4/Nrf2 axis therefore drives a hormetic response that is required for optimal cardiac mitochondrial and contractile function during physiological exercise.

Uric acid and angiotensin II additively promote inflammation and oxidative stress in human proximal tubule cells by activation of toll-like receptor 4

Renal proximal tubular cells (PTECs) participate in several mechanisms of innate immunity, express toll-like receptors (TLRs), and proinflammatory cytokines. Hyperuricemia may be a promoter of inflammation and renal damage. Angiotensin II (Ang II) modulate immune and inflammatory responses in renal tubular cells. With the aim to evaluate the effect of uric acid (UA) and Ang II on oxidative stress and inflammation mediated by toll-like receptor 4 (TLR4) activation in human PTECs, human kidney 2 (HK2) were incubated for 24 hr with UA (12 mg/dl) and Ang II (10 ^-7  M). HK2 were pretreated with an antagonist of TLR4 (TAK 242), valsartan or losartan. The genic expression of TLR4, monocyte chemoattractant protein-1 (MCP1), and Nox4 was quantified with reverse transcription polymerase chain reaction, proteins were evaluated with Western blot. The incubation of HK2 either with UA or with Ang II determines an increased expression of TLR4, production of proinflammatory cytokines as MCP1 and pro-oxidants as Nox4 ( p < 0.05). TAK 242 attenuates the expression of MCP1 induced both by UA and Ang II. Valsartan attenuated all the effects we described after exposure to Ang II but not those observed after UA exposure. At variance, pretreatment with losartan, which inhibits UA internalization, attenuates the expression of TLR4, MCP1, and Nox4 in cells previously treated with UA, Ang II, and UA plus Ang II. Proinflammatory pathways are induced in an additive manner by UA and Ang II ( p < 0.05) and might be mediated by TLR4 in PTECs. Renin-angiotensin-aldosterone system (RAAS) activation, hyperuricemia, and innate immunity interplay in the development of chronic tubular damage and the interaction of several nephrotoxic mechanisms blunt the protective effect of RAAS inhibition.

Nox4 Overexpression as a Poor Prognostic Factor in Patients with Oral Tongue Squamous Cell Carcinoma Receiving Surgical Resection

BACKGROUND

Nox4 has been reported to promote tumor progression of various types of cancer through many different pathways. The current study was designed to evaluate the prognostic significance of Nox4 in patients with oral tongue squamous cell carcinoma (OTSCC) receiving surgical resection.

METHODS

We retrospectively analyzed the 161 patients with OTSCC treated with surgical resection, including 81 patients with high expression of Nox4 and 80 patients with low expression of Nox4. Two OTSCC cell lines, SAS and SCC4, were used to investigate the proliferation activity.

RESULTS

The univariate and multivariable analyses showed that negative nodal metastasis and low expression of Nox4 were significantly associated with superior disease-free survival (DFS) and overall survival (OS). Western blotting analysis indicated that Nox4 was highly expressed in these two OTSCC cell lines and knockdown of Nox4 was successful by transfecting with Nox4 shRNA. In addition, these cell lines were also treated with a Nox4 inhibitor (GKT-137831) and the results showed GKT-137831 could inhibit the proliferation of OTSCC tumor cells in a dose-dependent manner.

CONCLUSION

Our study suggests that Nox4 plays an important role in disease progression of OTSCC and Nox4 overexpression is a poor prognostic factor for patients with OTSCC who received surgical resection.

TRPC1 Deficiency Exacerbates Cerebral Ischemia/Reperfusion-Induced Neurological Injury by Potentiating Nox4-Derived Reactive Oxygen Species Generation

BACKGROUND/AIMS

Transient receptor potential cation channel 1 (TRPC1)-mediated the calcium (Ca2+) influx plays an important role in several brain disorders. However, the function of TRPC1 in ischemia/reperfusion (I/R)-induced neurological injury is unclear.

METHODS

Wild-type or TRPC1 knockout mice underwent middle cerebral artery occlusion for 90 min followed by 24 h of reperfusion. In an in vitro study, neuronal cells were treated with oxygen-glucose deprivation and reoxygenation (OGD/R) to mimic I/R. The intracellular Ca2+ concentration [Ca2+]i was measured by Fura 2-AM under a microscope. Cerebral infarct volume was measured by triphenyltetrazolium chloride staining. Neurological function was examined by neurological severity score, Morris water maze test, rotarod test and string test. Oxidative parameters were detected by malondialdehyde, glutathione peroxidase, and superoxide dismutase commercially available kits. The protein expression levels of TRPC1, Nox4, p22phox, p47phox, and p67phox were analyzed by western blotting.

RESULTS

Brain tissues from cerebral I/R mice showed decreased TRPC1 expression. Similarly, TRPC1 expression was reduced in HT22 cells upon exposure to OGD/R treatment, followed by decreased Ca2+ influx. However, TRPC1 overexpression reversed the OGD/R-induced decrease in [Ca2+]i. TRPC1 knockout significantly exacerbated I/R-induced brain infarction, edema, neurological severity score, memory impairment, neurological deficits, and oxidative stress. In contrast, TRPC1 upregulation inhibited the increase in reactive oxygen species (ROS) generation induced by OGD/R. Analysis of key subunits of the Nox family and mitochondrial ROS revealed that the effects of TRPC1 downregulation on oxidative stress were associated with activation of Nox4-containing NADPH oxidase. TRPC1 interacted with Nox4 and facilitated Nox4 protein degradation under OGD/R conditions. In addition, TRPC1 inhibition potentiated the OGD/R-induced translocation of p47phox and p67phox as well as the interaction between Nox4 and p47phox or p67phox, whereas TRPC1 overexpression had the opposite effects.

CONCLUSION

TRPC1 deficiency potentiates ROS generation via Nox4-containing NADPH oxidase, which exacerbates cerebral I/R injury. TRPC1 may be a promising molecular target for the treatment of stroke.

Oxidative activation of type III CD38 by NADPH oxidase-derived hydrogen peroxide in Ca2+ signaling

Reactive oxygen species (ROS) derived from NADPH oxidase (Nox) has been shown to activate ADP-ribosyl cyclase (ARC), which produces the Ca²⁺ mobilizing second messenger, cyclic ADP-ribose (cADPR). In the present study, we examined how ROS activates cluster of differentiation (CD)38, a mammalian prototype of ARC. CD38 exists in type II and III forms with opposing membrane orientation. This study showed the coexpression of type II and III CD38 in lymphokine-activated killer (LAK) cells. The catalytic site of the constitutively active type II CD38 faces the outside of the cell or the inside of early endosomes (EEs), whereas the basally inactive type III CD38 faces the cytosol. Type III CD38 interacted with Nox4/phosphorylated-p22phox (p-p22phox) in EEs of LAK cells upon IL-8 treatment. H₂O₂ derived from Nox4 activated type III CD38 by forming a disulfide bond between Cys164 and Cys177, resulting in increased cADPR formation. Our study identified the mechanism by which type III CD38 is activated in an immune cell (LAK), in which H₂O₂ generated by Nox4 oxidizes and activates type III CD38 to generate cADPR. These findings provide a novel model of cross-talk between ROS and Ca²⁺ signaling.-Park, D.-R., Nam, T.-S., Kim, Y.-W., Bae, Y. S., Kim, U.-H. Oxidative activation of type III CD38 by NADPH oxidase-derived hydrogen peroxide in Ca²⁺ signaling.

miR-423-5p suppresses high-glucose-induced podocyte injury by targeting Nox4

Podocyte injury plays crucial roles in the pathogenesis of diabetic nephropathy (DN). Aberrant microRNAs (miRNAs) have been suggested to contribute to podocyte injury. However, whether miR-423-5p could alleviate high glucose (HG)-mediated podocyte injury and the underlying mechanisms remains unclear. In this study, we found that patients with DN have reduced miR-423-5p and elevated Nicotinamide adenine dinucleotide phosphate oxidase 4 (Nox4) expressions in clinical renal tissues, and HG induced Nox4 but suppressed miR-423-5p expressions in cultured podocytes in a time-dependent manner. Moreover, overexpression of miR-423-5p antagonized HG-stimulated podocyte injury by enhancing cell viability, inhibiting reactive oxygen species (ROS) production, suppressing cell apoptosis, reducing inflammatory activity, and repressing cytoskeleton damage accompanied with alternations of podocyte specific proteins. Furthermore, functional assays substantiated that Nox4 was a direct target and negatively regulated by miR-423-5p. Additionally, restoration of Nox4 impeded the protective effect of miR-423-5p on podocyte injury via activation of p38 MAPK pathway. Therefore, this study manifested that miR-423-5p overexpression protected HG-induced podocyte damage by inhibiting ROS generation via targeting Nox4, providing a potential therapeutic strategy against DN.

The involvement of Nox4 in fine particulate matter exposure-induced cardiac injury in mice

Epidemiological studies have confirmed that ambient fine particulate matter (PM_2.5) exposure is associated with cardiovascular disease (CVD). However, the underlying mechanisms in PM_2.5 exposure-induced heart injury are largely unknown. It has been acknowledged that NADPH oxidase (Nox) 4 plays a critical role in CVD development. To investigate the acute effects of PM_2.5 on the mouse heart and the role of Nox4 in PM_2.5 exposure-induced cardiac injury, C57BL/6J mice were instilled with saline or 1.5, 3.0, 6.0 mg/kg BW PM_2.5 suspension for two weeks (five days per week). The levels of malondialdehyde (MDA), super oxide dismutase (SOD), inducible nitric oxide synthase (iNOS), tumor necrosis factor-α (TNF-α) and interleukin (IL)-1β in heart supernatants were determined using related kits. The expression of Nox4, p67^phox, p47^phox and p22^phox in heart tissue was evaluated by immunofluorescence staining or Western blotting, respectively. Protein levels of p53, Bax, Bcl-2 and Caspase-3 in the heart were examined using immunohistochemical staining and Western blotting. TUNEL assay was used to measure myocardial apoptosis. PM_2.5 exposure leads to obvious cardiac injury. PM_2.5 exposure increases MDA level and iNOS activity, and decreases activity of SOD in heart supernatants of mice. High levels of TNF-α and IL-1β in heart supernatants of mice with PM_2.5 instillation were determined. Nox4 and Nox-associated subunits such as p67^phox, p47^phox and p22^phox expression levels were increased in heart tissue of mice after PM_2.5 exposure. Additionally, PM_2.5 exposure causes myocardial apoptosis in the mouse heart. This study suggested that Nox4 is involved in PM_2.5 exposure-induced cardiac injury in mice.

Hydrogen peroxide derived from NADPH oxidase 4- and 2 contributes to the endothelium-dependent vasodilatation of intrarenal arteries

The role of NADPH oxidase (Nox)-derived reactive oxygen species in kidney vascular function has extensively been investigated in the harmful context of oxidative stress in diabetes and obesity-associated kidney disease. Since hydrogen peroxide (H₂O₂) has recently been involved in the non-nitric oxide (NO) non-prostanoid relaxations of intrarenal arteries, the present study was sought to investigate whether NADPH oxidases may be functional sources of vasodilator H₂O₂ in the kidney and to assess their role in the endothelium-dependent relaxations of human and rat intrarenal arteries. Renal interlobar arteries isolated from the kidney of renal tumor patients who underwent nephrectomy, and from the kidney of Wistar rats, were mounted in microvascular myographs to assess function. Superoxide (O₂^.-) and H₂O₂ production was measured by chemiluminescence and Amplex Red fluorescence, and Nox2 and Nox4 enzymes were detected by Western blotting and by double inmunolabeling along with eNOS. Nox2 and Nox4 proteins were expressed in the endothelium of renal arterioles and glomeruli co-localized with eNOS, levels of expression of both enzymes being higher in the cortex than in isolated arteries. Pharmacological inhibition of Nox with apocynin and of CYP 2C epoxygenases with sulfaphenazol, but not of the NO synthase (NOS), reduced renal NADPH-stimulated O₂^.- and H₂O₂ production. Under conditions of cyclooxygenase and NOS blockade, acetylcholine induced endothelium-dependent relaxations that were blunted by the non-selective Nox inhibitor apocynin and by the Nox2 or the Nox1/4 inhibitors gp91ds-tat and GKT136901, respectively. Acetylcholine stimulated H₂O₂ production that was reduced by gp91ds-tat and by GKT136901. These results suggest the specific involvement of Nox4 and Nox2 subunits as physiologically relevant endothelial sources of H₂O₂ generation that contribute to the endothelium-dependent vasodilatation of renal arteries and therefore have a protective role in kidney vasculature.

Nox4-dependent ROS production is involved in CVB3-induced myocardial apoptosis

Viral myocarditis is a cardiovascular disease that seriously affects human health. Its mechanism is not clear. Coxsackievirus B3 (CVB3) is a member of the picornavirus family and is the leading cause of viral myocarditis. Our group tested the genes in a mouse model of CVB3 virus infection and confirmed that the NADPH oxidase gene had a high expression trend in the acute phase of infection. Whether Nox4, the homologue of NADPH oxidase, participates in the process of viral myocarditis has not been reported. In this study, we found increased expression of Nox4 in viral myocarditis in vivo and in vitro. DPI is a non-specific inhibitor of Nox4 that improved CVB3-induced myocarditis after injection in vivo. DPI also inhibited intracellular ROS release and apoptosis in vitro. Our data indicated that Nox4-dependent ROS production was involved in CVB3-induced myocardial apoptosis.

NADPH Oxidases and Mitochondria in Vascular Senescence

Aging is the major risk factor in the development of cardiovascular diseases (CVDs), including hypertension, atherosclerosis, and myocardial infarction. Oxidative stress caused by overproduction of reactive oxygen species (ROS) and/or by reduced expression of antioxidant enzymes is a major contributor to the progression of vascular senescence, pathologic remodeling of the vascular wall, and disease. Both oxidative stress and inflammation promote the development of senescence, a process by which cells stop proliferating and become dysfunctional. This review focuses on the role of the mitochondria and the nicotinamide adenine dinucleotide phosphate (NADPH) oxidases Nox1 and Nox4 in vascular senescence, and their contribution to the development of atherosclerosis. Recent findings are reviewed, supporting a critical role of the mitochondrial regulator peroxisome proliferator-activated receptor gamma (PPARγ) coactivator-1α (PGC-1α), the inflammatory gene nuclear factor κB (NF-κB), zinc, the zinc transporters (ZnTs) ZnT3 and ZnT10, and angiotensin II (Ang II) in mitochondrial function, and their role in telomere stability, which provides new mechanistic insights into a previously proposed unified theory of aging.

ROS signaling and ER stress in cardiovascular disease

The endoplasmic reticulum (ER) produces the vast majority of all proteins secreted into the extracellular space, including hormones and cytokines, as well as cell surface receptors and other proteins which interact with the environment. Accordingly, this organelle controls essentially all vital links to a cell's external milieu, responding to systemic metabolic, inflammatory, endocrine, and mechanical stimuli. The central role the ER plays in meeting protein synthetic and quality control requirements in the face of such demands is matched by an extensive and versatile ER stress response signaling network. ROS mediate several critical aspects of this response. Nox4, an ER resident capable of producing ROS, acts as a proximal signaling intermediate to transduce ER stress-related conditions to the unfolded protein response, a homeostatic corrective mechanism. However, chronic ER stress caused by unrelenting internal or external demands produces a secondary rise in ROS, generally resulting in cell death. Sorting out the involvement of ROS at different levels of the ER stress response in specific cell types is key to understanding the molecular basis for chronic diseases such as atherosclerosis, hypertension, and diabetes. Here, we provide an overview of ER stress signaling with an emphasis on the role of ROS.

Design, synthesis, and biological evaluation of inhibitors of the NADPH oxidase, Nox4

NADPH oxidases (Nox enzymes) are critical mediators of both physiologic and pathophysiologic processes. Nox enzymes catalyze NADPH-dependent generation of reactive oxygen species (ROS), including superoxide and hydrogen peroxide. Until recently, Nox4 was proposed to be involved exclusively in normal physiologic functions. Compelling evidence, however, suggests that Nox4 plays a critical role in fibrosis, as well as a host of pathologies and diseases. These considerations led to a search for novel, small molecule inhibitors of this important enzyme. Ultimately, a series of novel tertiary sulfonylureas (23-25) was designed using pharmacophore modeling, synthesized, and evaluated for inhibition of Nox4-dependent signaling.

Interaction between p22phox and Nox4 in the endoplasmic reticulum suggests a unique mechanism of NADPH oxidase complex formation

The p22^phox protein is an essential component of the phagocytic- and inner ear NADPH oxidases but its relationship to other Nox proteins is less clear. We have studied the role of p22^phox in the TGF-β1-stimulated H₂O₂ production of primary human and murine fibroblasts. TGF-β1 induced H₂O₂ release of the examined cells, and the response was dependent on the expression of both Nox4 and p22^phox. Interestingly, the p22^phox protein was present in the absence of any detectable Nox/Duox expression, and the p22^phox level was unaffected by TGF-β1. On the other hand, Nox4 expression was dependent on the presence of p22^phox, establishing an asymmetrical relationship between the two proteins. Nox4 and p22^phox proteins localized to the endoplasmic reticulum and their distribution was unaffected by TGF-β1. We used a chemically induced protein dimerization method to study the orientation of p22^phox and Nox4 in the endoplasmic reticulum membrane. This technique is based on the rapamycin-mediated heterodimerization of the mammalian FRB domain with the FK506 binding protein. The results of these experiments suggest that the enzyme complex produces H₂O₂ into the lumen of the endoplasmic reticulum, indicating that Nox4 contributes to the development of the oxidative milieu within this organelle.

Blockage of endoplasmic reticulum stress attenuates nilotinib-induced cardiotoxicity by inhibition of the Akt-GSK3β-Nox4 signaling

Cardiotoxicity is a critical side-effect of nilotinib during treatment for cancer, such as chronic myeloid leukemia, while the potential signaling mechanisms remain unclear. The role of and the relationship between endoplasmic reticulum (ER) stress and mitochondrial dysfunction was investigated in nilotinib-induced cardiac H9C2 injury as a suitable cell model. Our results showed that ER stress was persistently induced in nilotinib-treated cells, evidenced by increase of GRP78, CHOP, ATF4 and XBP1 as well as phospho-PERK^Thr980. The results from 4-phenylbutyrate (PBA, an ER stress inhibitor) and SC79 (a specific Akt activator) suggested that ER stress increased activity of glycogen synthase kinase-3 beta (GSK3β) that is reflected by decrease of phospho-GSK3β^Ser9, through downregulation of phospho-Akt^Ser473, and that prolonged ER stress and activated GSK3β involved nilotinib-induced apoptosis. In addition, the data from JNK inhibition using SP600125 showed that over-activated JNK was responsible for Akt de-phosphorylation. Moreover, the abundance of NADPH oxidase (Nox4) was significantly increased following nilotinib treatment, which was prevented by SB216763 (a specific GSK3β inhibitor). Additionally, mitochondrial dysfunction was indicated by reduced mitochondrial membrane potential (MMP) level and increased reactive oxygen species level. In nilotinib-treated cells, knockdown of Nox4 preserved MMP level, abrogated reactive oxygen species production, and decreased apoptosis. Accordingly, our data demonstrated that inhibition of ER stress may protect cardiomyocytes against nilotinib toxicity potentially through inactivation of Akt-GSK3β-Nox4 signaling. These findings may provide an attractive therapeutic target for treatment of nilotinib-related cardiotoxicity.

Astragaloside IV protects rat retinal capillary endothelial cells against high glucose-induced oxidative injury

Aim

Diabetic retinopathy is a microvascular complication of diabetes that leads to blindness. Hyperglycemia causes oxidative stress, which is an important cause in the pathogenesis of microangiopathy. The aim of this study was to investigate the potential protective effects of astragaloside IV (AS-IV) in retinal capillary endothelial cells (RCECs) incubated with high glucose conditions.

Methods and results

Based on rat RCECs cultured with high glucose (30 mM) in vitro, a significant increase in cell viability in rat RCECs incubated with both AS-IV and high glucose for 48 or 72 h by MTT assay. The increased viability was accompanied by decreased glucose transporter-1 expression using immunofluorescent assay. Meanwhile, AS-IV reduced intracellular hydrogen peroxide and superoxide, decreased mitochondrial reactive oxygen species in rat RCECs with high glucose by the fluorescent probes, and lowered malondialdehyde levels. In addition, AS-IV increased the activities of total superoxide dismutase, MnSOD, catalase, and glutathione peroxidase. The glutathione content also increased after AS-IV treatment. Furthermore, AS-IV reduced NADPH oxidase 4 expression by western blot method.

Conclusion

These results suggest that the main mechanism underlying the protective effects of AS-IV in high glucose-injured RCECs may be related to its antioxidative function.

Nox4 regulates the eNOS uncoupling process in aging endothelial cells

ROS and its associated signaling contribute to vascular aging-associated endothelial disturbance. Since the non-effective endothelial nitric oxide synthase (eNOS) coupling status is related to vascular aging-related phenotypes, eNOS coupled/uncoupled system signaling was studied in human umbilical vein endothelial cells (HUVEC). Nitric oxide (NO) and eNOS Ser1177 were significantly decreased, whereas O₂^- (superoxide anion radical) increased with passage number. In aging cells, NADPH oxidase 4 (Nox4), one of the main superoxide generating enzymes, and its associated protein disulfide isomerase (PDI) chaperone were highly activated, and the resultant ER redox imbalance leads to disturbance of protein folding capability, namely endoplasmic reticulum (ER) stress, ultimately inducing dissociation between HSP90 and IRE-1α or PERK, decreasing HSP90 stability and dissociating the binding of eNOS from the HSP90 and leading to eNOS uncoupling. Through chemical and Nox4 siRNA approaches, Nox4 and its linked ER stress were shown to mainly contribute to eNOS uncoupling and its associated signaling, suggesting that Nox4 and its related ER stress signaling are key signals of the aging process in endothelial cells.

Responses to reductive stress in the cardiovascular system

There is a growing appreciation that reductive stress represents a disturbance in the redox state that is harmful to biological systems. On a cellular level, the presence of increased reducing equivalents and the lack of beneficial fluxes of reactive oxygen species can prevent growth factor-mediated signaling, promote mitochondrial dysfunction, increase apoptosis, and decrease cell survival. In this review, we highlight the importance of redox balance in maintaining cardiovascular homeostasis and consider the tenuous balance between oxidative and reductive stress. We explain the role of reductive stress in models of protein aggregation-induced cardiomyopathies, such as those caused by mutations in αB-crystallin. In addition, we discuss the role of NADPH oxidases in models of heart failure and ischemia-reperfusion to illustrate how oxidants may mediate the adaptive responses to injury. NADPH oxidase 4, a hydrogen peroxide generator, also has a major role in promoting vascular homeostasis through its regulation of vascular tone, angiogenic responses, and effects on atherogenesis. In contrast, the lack of antioxidant enzymes that reduce hydrogen peroxide, such as glutathione peroxidase 1, promotes vascular remodeling and is deleterious to endothelial function. Thus, we consider the role of oxidants as necessary signals to promote adaptive responses, such as the activation of Nrf2 and eNOS, and the stabilization of Hif1. In addition, we discuss the adaptive metabolic reprogramming in hypoxia that lead to a reductive state, and the subsequent cellular redistribution of reducing equivalents from NADH to other metabolites. Finally, we discuss the paradoxical ability of excess reducing equivalents to stimulate oxidative stress and promote injury.

Dual-Specificity Phosphatase 4 Overexpression in Cells Prevents Hypoxia/Reoxygenation-Induced Apoptosis via the Upregulation of eNOS

Mitogen-activated protein kinases (MAPKs) signaling cascades regulate several cellular functions, including differentiation, proliferation, survival, and apoptosis. The duration and magnitude of phosphorylation of these MAPKs are decisive determinants of their physiological functions. Dual-specificity phosphatases exert kinetic control over these signaling cascades. Previously, we demonstrated that DUSP4^−/− hearts sustain a larger infarct and have poor functional recovery, when isolated hearts were subjected to ischemia/reperfusion. Uncontrolled p38 activation and upregulation of Nox4 expression are the main effectors for this functional alteration. Here, dual-specificity phosphatase 4 (DUSP4) overexpression in endothelial cells was used to investigate the role of DUSP4 on the modulation of reactive oxygen species (ROS) generation and vascular function, when cells were subjected to hypoxia/reoxygenation (H/R) insult. Immunostaining with cleaved caspase-3 revealed that DUSP4 overexpression prevents caspase-3 activation and apoptosis after H/R. The beneficial effects occur via modulating p38 activity, increased NO bioavailability, and reduced oxidative stress. More importantly, DUSP4 overexpression upregulates eNOS protein expression (1.62 ± 0.33 versus 0.65 ± 0.16) during H/R-induced stress. NO is a critical small molecule involved in regulating vascular tone, vascular growth, platelet aggregation, and modulation of inflammation. The level of NO generation determined using DAF-2 fluorescence demonstrated that DUSP4 overexpression augments NO production and thus improves vascular function. The level of superoxide generated from cells after being subjected to H/R was determined using dihydroethidium-HPLC method. The results suggested that DUSP4 overexpression in cells decreases H/R-induced superoxide generation (1.56 ± 0.14 versus 1.19 ± 0.05) and thus reduces oxidant stress. This also correlates with the reduction in the total protein S-glutathionylation, an indicator of protein oxidation. These results further support our hypothesis that DUSP4 is an antioxidant gene and a key phosphatase in modulating MAPKs, especially p38, during oxidative stress, which regulates ROS generation and eNOS expression and thus protects against oxidant-induced injury or apoptosis. Overall, DUSP4 may serve as an excellent molecular target for the treatment of ischemic heart disease.

Knock out of the NADPH oxidase Nox4 has no impact on life span in mice

The free radical theory of aging suggests reactive oxygen species as a main reason for accumulation of damage events eventually leading to aging. Nox4, a member of the family of NADPH oxidases constitutively produces ROS and therefore has the potential to be a main driver of aging. Herein we analyzed the life span of Nox4 deficient mice and found no difference when compared to their wildtype littermates. Accordingly neither Tert expression nor telomere length was different in cells isolated from those animals. In fact, Nox4 mRNA expression in lungs of wildtype mice dropped with age. We conclude that Nox4 has no influence on lifespan of healthy mice.

Spinal Cord Injury Leads to Hyperoxidation and Nitrosylation of Skeletal Muscle Ryanodine Receptor-1 Associated with Upregulation of Nicotinamide Adenine Dinucleotide Phosphate Oxidase 4

Spinal cord injury (SCI) results in marked atrophy and dysfunction of skeletal muscle. There are currently no effective treatments for SCI-induced muscle atrophy or the dysfunction of the remaining muscle tissue. Nicotinamide adenine dinucleotide phosphate (NADPH) oxidase-4 (Nox4) produces reactive oxygen species (ROS) in sarcoplasmic reticulum (SR) and has been identified as an important O₂ sensor in skeletal muscle. Ryanodine receptors (RyRs) are calcium (Ca²⁺) channels that are responsible for Ca²⁺ release from SR. In skeletal muscle, type1 RyR (RyR1) is predominantly functional. RyR1 is regulated by multiple proteins, including calstabin1, which assures that they close appropriately once contraction has ceased. RyR1 function is also regulated by oxidation and redox-dependent cysteine nitrosylation. Excessive oxidation/nitrosylation of RyR1 is associated with dissociation of calstabin1 and reduced muscle force generation. However, whether Nox4 levels in skeletal muscle are elevated or whether RyR1 is oxidized or nitrosylated after SCI has not been determined. In this study, we examined Nox4 expression, oxidation/nitrolysation status, and association of calstabin1 with RyR1 in skeletal muscle derived from rats that were subjected to T4 complete transection (SCI), and observed elevated expression of Nox4 messenger RNA and protein in muscle after SCI associated with enhanced binding of Nox4 to RyR1, increased oxidation and nitrosylation of RyR1, and dissociation of calstabin1 from RyR1 in SCI rat muscle. Our data suggest that RyR1 dysfunction resulting from excessive oxidation/nitrosylation may contribute to reduced specific force after SCI and suggest that Nox4 may be the source of ROS responsible for increased oxidation and nitrosylation of RyR1.

ZYZ-772 Prevents Cardiomyocyte Injury by Suppressing Nox4-Derived ROS Production and Apoptosis

Nox-dependent signaling plays critical roles in the development of heart failure, cardiac hypertrophy, and myocardial infarction. NADPH oxidase 4 (Nox4) as a major source of oxidative stress in the heart offers a new therapeutic target in cardiovascular disease. In the present work, a novel flavonoid was isolated from Zanthoxylum bungeanum. Its structure was elucidated as Quercetin-3-O-(6′′-O-α-l-rhamnopyransoyl)-β-d-glucopyranoside-7-O-β-d-glucopyranoside (ZYZ-772) for the first time. ZYZ-772 exhibited significant cardio-protective property against CoCl₂ induced H9c2 cardiomyocyte cells injury. In CoCl₂ stimulated cardiomyocyte injury, ZYZ-772 inhibited expression of Nox4, and alleviated ROS overproduction. Importantly, ROS triggered MAPKs phosphorylation and P53 signaling mediated apoptosis were restored by ZYZ-772. Our findings present the first piece of evidence for the therapeutic properties of ZYZ-772 in preventing cardiomyocyte injury, which could be attributed to the suppression of Nox4/MAPKs/P53 axis. This will offer a novel therapeutic strategy for the treatment of cardiac ischemia disease.

Endothelial Nox4-based NADPH oxidase regulates atherosclerosis via soluble epoxide hydrolase

Nox4-based NADPH oxidase is a major reactive oxygen species-generating enzyme in the vasculature, but its role in atherosclerosis remains controversial.

OBJECTIVE

Our goal was to investigate the mechanisms of endothelial Nox4 in regulating atherosclerosis.

APPROACH AND RESULTS

Atherosclerosis-prone conditions (disturbed blood flow, type I diabetes, and Western diet) downregulated endothelial Nox4 mRNA in arteries. To address whether the downregulated endothelial Nox4 was directly involved in the development of atherosclerosis, we generated mice carrying a human Nox4 P437H dominant negative mutation (Nox4DN), driven by the endothelial specific promoter Tie-2, on atherosclerosis-prone genetic background (ApoE deficient mice) to mimic the effect of decreased endothelial Nox4. Nox4DN significantly increased type I diabetes-induced aortic stiffness and atherosclerotic lesions. Gene analysis indicated that soluble epoxide hydrolase 2 (sEH) was significantly upregulated in Nox4DN endothelial cells (EC). Inhibition of sEH activity in Nox4DN EC suppressed inflammation and macrophage adhesion to EC. On the contrary, overexpression of endothelial wild type Nox4 suppressed sEH, ameliorated Western diet-induced atherosclerosis and decreased aortic stiffness.

CONCLUSIONS

Atherosclerosis-prone conditions downregulated endothelial Nox4 to accelerate the progress of atherosclerosis, at least in part, by upregulating sEH to enhance inflammation.

Dysregulated Nox4 ubiquitination contributes to redox imbalance and age-related severity of acute lung injury

Acute respiratory distress syndrome (ARDS) is a devastating critical illness disproportionately affecting the elderly population, with both higher incidence and mortality. The integrity of the lung endothelial cell (EC) monolayer is critical for preservation of lung function. However, mechanisms mediating EC barrier regulation in the context of aging remain unclear. We assessed the severity of acute lung injury (ALI) in young (2 mo) and aged (18 mo) mice using a two-hit preclinical model. Compared with young cohorts, aged mice exhibited increased ALI severity, with greater vascular permeability characterized by elevated albumin influx and levels of bronchoalveolar lavage (BAL) cells (neutrophils) and protein. Aged/injured mice also demonstrated elevated levels of reactive oxygen species (ROS) in the BAL, which was associated with upregulation of the ROS-generating enzyme, Nox4. We evaluated the role of aging in human lung EC barrier regulation utilizing a cellular model of replicative senescence. Senescent EC populations were defined by increases in β-galactosidase activity and p16 levels. In response to lipopolysaccharide (LPS) challenge, senescent ECs demonstrate exacerbated permeability responses compared with control "young" ECs. LPS challenge led to a rapid induction of Nox4 expression in both control and senescent ECs, which was posttranslationally mediated via the proteasome/ubiquitin system. However, senescent ECs demonstrated deficient Nox4 ubiquitination, resulting in sustained expression of Nox4 and alterations in cellular redox homeostasis. Pharmacological inhibition of Nox4 in senescent ECs reduced LPS-induced alterations in permeability. These studies provide insight into the roles of Nox4/senescence in EC barrier responses and offer a mechanistic link to the increased incidence and mortality of ARDS associated with aging.

Adventitial Fibroblast Nox4 Expression and ROS Signaling in Pulmonary Arterial Hypertension

Pulmonary arterial hypertension (PAH) is a progressive disease arising from remodeling and narrowing of pulmonary arteries (PA) resulting in high pulmonary arterial blood pressure and ultimately right ventricular failure. Elevated production of reactive oxygen species (ROS) by NADPH oxidase 4 (Nox4), a constitutively active enzyme, has been associated with oxygen sensing, vasomotor control, cellular proliferation, differentiation, migration, apoptosis, senescence, fibrosis, and angiogenesis. Further, elevated expression of Nox4 has been reported in a number of cardiovascular diseases, including atherosclerosis, hypertension, cardiac failure, ischemic stroke, and PAH. However, the cellular location of Nox4 and its contribution to aberrant vascular remodeling in PAH remains poorly understood. The goal of this review is to summarize the recent literature on the enzymatic regulation of Nox4 in the production of ROS in PAH. In the vascular wall, Nox4 is present in fibroblasts, a primary cell of the adventitia, and matches the adventitial location of ROS production in PAH. Further, in adventitial fibroblasts, Nox4 overexpression stimulates migration and proliferation as well as matrix gene expression. Collectively, reports indicate that Nox4 contributes to altered fibroblast behavior, ROS production leading to hypertensive vascular remodeling and the development of PAH. Finally, we address the functional significance of Nox4 in fibroblasts, and also suggest an "outside in" (adventitial) process of vascular remodeling that is mediated by Nox4, which although has physiological roles in the intimal layer (i.e., endothelium), may also have pathologic importance in the adventitial layer of the vascular wall through signaling in fibroblasts.