Nox4 is a protective reactive oxygen species generating vascular NADPH oxidase

The Skeletal Effects of Tanshinones: A Review

Background: Osteoporosis results from excessive bone resorption and reduced bone formation, triggered by sex hormone deficiency, oxidative stress and inflammation. Tanshinones are a class of lipophilic phenanthrene compounds found in the roots of Salvia miltiorrhiza with antioxidant and anti-inflammatory activities, which contribute to its anti-osteoporosis effects. This systematic review aims to provide an overview of the skeletal beneficial effects of tanshinones. Methods: A systematic literature search was conducted in January 2021 using Pubmed, Scopus and Web of Science from the inception of these databases. Original studies reporting the effects of tanshinones on bone through cell cultures, animal models and human clinical trials were considered. Results: The literature search found 158 unique articles on this topic, but only 20 articles met the inclusion criteria and were included in this review. The available evidence showed that tanshinones promoted osteoblastogenesis and bone formation while reducing osteoclastogenesis and bone resorption. Conclusions: Tanshinones modulates bone remodelling by inhibiting osteoclastogenesis and osteoblast apoptosis and stimulating osteoblastogenesis. Therefore, it might complement existing strategies to prevent bone loss.

Oxidative Stress and Hypertension

A link between oxidative stress and hypertension has been firmly established in multiple animal models of hypertension but remains elusive in humans. While initial studies focused on inactivation of nitric oxide by superoxide, our understanding of relevant reactive oxygen species (superoxide, hydrogen peroxide, and peroxynitrite) and how they modify complex signaling pathways to promote hypertension has expanded significantly. In this review, we summarize recent advances in delineating the primary and secondary sources of reactive oxygen species (nicotinamide adenine dinucleotide phosphate oxidases, uncoupled endothelial nitric oxide synthase, endoplasmic reticulum, and mitochondria), the posttranslational oxidative modifications they induce on protein targets important for redox signaling, their interplay with endogenous antioxidant systems, and the role of inflammasome activation and endoplasmic reticular stress in the development of hypertension. We highlight how oxidative stress in different organ systems contributes to hypertension, describe new animal models that have clarified the importance of specific proteins, and discuss clinical studies that shed light on how these processes and pathways are altered in human hypertension. Finally, we focus on the promise of redox proteomics and systems biology to help us fully understand the relationship between ROS and hypertension and their potential for designing and evaluating novel antihypertensive therapies.

AMP-activated protein kinase: A remarkable contributor to preserve a healthy heart against ROS injury

Heart failure is one of the leading causes of death and disability worldwide. Left ventricle remodeling, fibrosis, and ischemia/reperfusion injury all contribute to the deterioration of cardiac function and predispose to the onset of heart failure. Adenosine monophosphate-activated protein kinase (AMPK) is the universally recognized energy sensor which responds to low ATP levels and restores cellular metabolism. AMPK activation controls numerous cellular processes and, in the heart, it plays a pivotal role in preventing onset and progression of disease. Excessive reactive oxygen species (ROS) generation, known as oxidative stress, can activate AMPK, conferring an additional role of AMPK as a redox-sensor. In this review, we discuss recent insights into the crosstalk between ROS and AMPK. We describe the molecular mechanisms by which ROS activate AMPK and how AMPK signaling can further prevent heart failure progression. Ultimately, we review the potential therapeutic approaches to target AMPK for the treatment of cardiovascular disease and prevention of heart failure.

Endothelium-restricted endothelin-1 overexpression in type 1 diabetes worsens atherosclerosis and immune cell infiltration via NOX1

AIMS

NADPH oxidase (NOX) 1 but not NOX4-dependent oxidative stress plays a role in diabetic vascular disease, including atherosclerosis. Endothelin (ET)-1 has been implicated in diabetes-induced vascular complications. We showed that crossing mice overexpressing human ET-1 selectively in endothelium (eET-1) with apolipoprotein E knockout (Apoe-/-) mice enhanced high-fat diet-induced atherosclerosis in part by increasing oxidative stress. We tested the hypothesis that ET-1 overexpression in the endothelium would worsen atherosclerosis in type 1 diabetes through a mechanism involving NOX1 but not NOX4.

METHODS AND RESULTS

Six-week-old male Apoe-/- and eET-1/Apoe-/- mice with or without Nox1 (Nox1-/y) or Nox4 knockout (Nox4-/-) were injected intraperitoneally with either vehicle or streptozotocin (55 mg/kg/day) for 5 days to induce type 1 diabetes and were studied 14 weeks later. ET-1 overexpression increased 2.5-fold and five-fold the atherosclerotic lesion area in the aortic sinus and arch of diabetic Apoe-/- mice, respectively. Deletion of Nox1 reduced aortic arch plaque size by 60%; in contrast, Nox4 knockout increased lesion size by 1.5-fold. ET-1 overexpression decreased aortic sinus and arch plaque alpha smooth muscle cell content by ∼35% and ∼50%, respectively, which was blunted by Nox1 but not Nox4 knockout. Reactive oxygen species production was increased two-fold in aortic arch perivascular fat of diabetic eET-1/Apoe-/- and eET-1/Apoe-/-/Nox4-/- mice but not eET-1/Apoe-/-/Nox1y/- mice. ET-1 overexpression enhanced monocyte/macrophage and CD3+ T-cell infiltration ∼2.7-fold in the aortic arch perivascular fat of diabetic Apoe-/- mice. Both Nox1 and Nox4 knockout blunted CD3+ T-cell infiltration whereas only Nox1 knockout prevented the monocyte/macrophage infiltration in diabetic eET-1/Apoe-/- mice.

CONCLUSION

Endothelium ET-1 overexpression enhances the progression of atherosclerosis in type 1 diabetes, perivascular oxidative stress, and inflammation through NOX1.

Reactive Oxygen Species and Antioxidants in Carcinogenesis and Tumor Therapy

Strictly regulated balance between the formation and utilization of reactive oxygen species (ROS) is the basis of normal functioning of organisms. ROS play an important role in the regulation of many metabolic processes; however, excessive content of ROS leads to the development of various disorders, including oncological diseases, as a result of ROS-induced mutations in DNA. In tumors, high levels of oxygen radicals promote cell proliferation and metastasis. On the other hand, high content of ROS can trigger cell death, a phenomenon used in the antitumor therapy. Water- and lipid-soluble antioxidants, as well as antioxidant enzyme systems, can inhibit ROS generation; however, they should be used with caution. Antioxidants can suppress ROS-dependent cell proliferation and metastasis, but at the same time, they may inhibit the death of tumor cells if the antitumor therapeutic agents stimulate oxidative stress. The data on the role of antioxidants in the death of tumor cells and on the effects of antioxidants taken as dietary supplements during antitumor therapy, are contradictory. This review focuses on the mechanisms by which antioxidants can affect tumor and healthy cells.

Genetic deletion of Nox4 enhances cancerogen-induced formation of solid tumors

The stereotype of ROS produced by NADPH oxidases as cause of malignant diseases persists in a generalized manner. In fact, high levels of ROS formation could be harmful in the context of a disease process. This study demonstrates that loss of the NADPH oxidase Nox4, as a constitutive source of ROS, promotes cancerogen-induced formation of solid tumors. Accordingly, a certain tonic, constitutive low level of Nox4-derived hydrogen peroxide appears to reduce the risk of cancerogen-induced tumor formation.

Reactive oxygen species (ROS) can cause cellular damage and promote cancer development. Besides such harmful consequences of overproduction of ROS, all cells utilize ROS for signaling purposes and stabilization of cell homeostasis. In particular, the latter is supported by the NADPH oxidase 4 (Nox4) that constitutively produces low amounts of H₂O₂. By that mechanism, Nox4 forces differentiation of cells and prevents inflammation. We hypothesize a constitutive low level of H₂O₂ maintains basal activity of cellular surveillance systems and is unlikely to be cancerogenic. Utilizing two different murine models of cancerogen-induced solid tumors, we found that deletion of Nox4 promotes tumor formation and lowers recognition of DNA damage. Nox4 supports phosphorylation of H2AX (γH2AX), a prerequisite of DNA damage recognition, by retaining a sufficiently low abundance of the phosphatase PP2A in the nucleus. The underlying mechanism is continuous oxidation of AKT by Nox4. Interaction of oxidized AKT and PP2A captures the phosphatase in the cytosol. Absence of Nox4 facilitates nuclear PP2A translocation and dephosphorylation of γH2AX. Simultaneously AKT is left phosphorylated. Thus, in the absence of Nox4, DNA damage is not recognized and the increased activity of AKT supports proliferation. The combination of both events results in genomic instability and promotes tumor formation. By identifying Nox4 as a protective source of ROS in cancerogen-induced cancer, we provide a piece of knowledge for understanding the role of moderate production of ROS in preventing the initiation of malignancies.

Oxidative Stress Triggers Defective Autophagy in Endothelial Cells: Role in Atherothrombosis Development

Atherothrombosis, a multifactorial and multistep artery disorder, represents one of the main causes of morbidity and mortality worldwide. The development and progression of atherothrombosis is closely associated with age, gender and a complex relationship between unhealthy lifestyle habits and several genetic risk factors. The imbalance between oxidative stress and antioxidant defenses is the main biological event leading to the development of a pro-oxidant phenotype, triggering cellular and molecular mechanisms associated with the atherothrombotic process. The pathogenesis of atherosclerosis and its late thrombotic complications involve multiple cellular events such as inflammation, endothelial dysfunction, proliferation of vascular smooth muscle cells (SMCs), extracellular matrix (ECM) alterations, and platelet activation, contributing to chronic pathological remodeling of the vascular wall, atheromatous plague formation, vascular stenosis, and eventually, thrombus growth and propagation. Emerging studies suggest that clotting activation and endothelial cell (EC) dysfunction play key roles in the pathogenesis of atherothrombosis. Furthermore, a growing body of evidence indicates that defective autophagy is closely linked to the overproduction of reactive oxygen species (ROS) which, in turn, are involved in the development and progression of atherosclerotic disease. This topic represents a large field of study aimed at identifying new potential therapeutic targets. In this review, we focus on the major role played by the autophagic pathway induced by oxidative stress in the modulation of EC dysfunction as a background to understand its potential role in the development of atherothrombosis.

Discovery of new therapeutic redox targets for cardioprotection against ischemia/reperfusion injury and heart failure

Global epidemiological studies reported a shift from maternal/infectious communicable diseases to chronic non-communicable diseases and a major part is attributable to atherosclerosis and metabolic disorders. Accordingly, ischemic heart disease was identified as a leading risk factor for global mortality and morbidity with a prevalence of 128 million people. Almost 9 million premature deaths can be attributed to ischemic heart disease and subsequent acute myocardial infarction and heart failure, also representing a substantial socioeconomic burden. As evidenced by typical oxidative stress markers such as lipid peroxidation products or oxidized DNA/RNA bases, the formation of reactive oxygen species by various sources (NADPH oxidases, xanthine oxidase and mitochondrial resperatory chain) plays a central role for the severity of ischemia/reperfusion damage. The underlying mechanisms comprise direct oxidative damage but also adverse redox-regulation of kinase and calcium signaling, inflammation and cardiac remodeling among others. These processes and the role of reactive oxygen species are discussed in the present review. We also present and discuss potential targets for redox-based therapies that are either already established in the clinics (e.g. guanylyl cyclase activators and stimulators) or at least successfully tested in preclinical models of myocardial infarction and heart failure (mitochondria-targeted antioxidants). However, reactive oxygen species have not only detrimental effects but are also involved in essential cellular signaling and may even act protective as seen by ischemic pre- and post-conditioning or eustress - which makes redox therapy quite challenging.

Mitochondrial Ca2+, redox environment and ROS emission in heart failure: Two sides of the same coin?

Heart failure (HF) is a progressive, debilitating condition characterized, in part, by altered ionic equilibria, increased ROS production and impaired cellular energy metabolism, contributing to variable profiles of systolic and diastolic dysfunction with significant functional limitations and risk of premature death. We summarize current knowledge concerning changes of intracellular Na+ and Ca2+ control mechanisms during the disease progression and their consequences on mitochondrial Ca2+ homeostasis and the shift in redox balance. Absent existing biological data, our computational modeling studies advance a new 'in silico' analysis to reconcile existing opposing views, based on different experimental HF models, regarding variations in mitochondrial Ca2+ concentration that participate in triggering and perpetuating oxidative stress in the failing heart and their impact on cardiac energetics. In agreement with our hypothesis and the literature, model simulations demonstrate the possibility that the heart's redox status together with cytoplasmic Na+ concentrations act as regulators of mitochondrial Ca2+ levels in HF and of the bioenergetics response that will ultimately drive ATP supply and oxidative stress. The resulting model predictions propose future directions to study the evolution of HF as well as other types of heart disease, and to develop novel testable mechanistic hypotheses that may lead to improved therapeutics.

Endothelial NADPH oxidase 4 protects against angiotensin II-induced cardiac fibrosis and inflammation

Aims

Endothelial activation and inflammatory cell infiltration have important roles in the development of cardiac fibrosis induced by renin–angiotensin system activation. NADPH oxidases (Nox proteins) are expressed in endothelial cells (ECs) and alter their function. Previous studies indicated that Nox2 in ECs contributes to angiotensin II (AngII)‐induced cardiac fibrosis. However, the effects of EC Nox4 on cardiac fibrosis are unknown.

Methods and results

Transgenic (TG) mice overexpressing endothelial‐restricted Nox4 were studied alongside wild‐type (WT) littermates as controls. At baseline, Nox4 TG mice had significantly enlarged hearts compared with WT, with elongated cardiomyocytes (increased by 18.5%, P < 0.01) and eccentric hypertrophy but well‐preserved cardiac function by echocardiography and in vivo pressure–volume analysis. Animals were subjected to a chronic AngII infusion (AngII, 1.1 mg/kg/day) for 14 days. Whereas WT/AngII developed a 2.1‐fold increase in interstitial cardiac fibrosis as compared with WT/saline controls (P < 0.01), TG/AngII mice developed significant less fibrosis (1.4‐fold increase, P > 0.05), but there were no differences in cardiac hypertrophy or contractile function between the two groups. TG hearts displayed significantly decreased inflammatory cell infiltration with reduced levels of vascular cell adhesion molecule 1 in both the vasculature and myocardium compared with WT after AngII treatment. TG microvascular ECs stimulated with AngII in vitro supported significantly less leukocyte adhesion than WT ECs.

Conclusions

A chronic increase in endothelial Nox4 stimulates physiological cardiac hypertrophy and protects against AngII‐induced cardiac fibrosis by inhibiting EC activation and the recruitment of inflammatory cells.

Mice with endothelium‐specific overexpression of Nox4 (EndoNox4 TG) exhibit eccentric hypertrophy with well‐preserved cardiac function at baseline.

EndoNox4 TG mice develop significantly less interstitial cardiac fibrosis in response to chronic pressure AngII stimulation, independent of cardiac hypertrophy.

Overexpression of Nox4 in endothelial cells reduces AngII‐induced endothelial activation.

An increase in endothelial Nox4 inhibits AngII‐induced recruitment of inflammatory cells in the heart.

Nox4 mediates skeletal muscle metabolic responses to exercise

OBJECTIVE

The immediate signals that couple exercise to metabolic adaptations are incompletely understood. Nicotinamide adenine dinucleotide phosphate oxidase 4 (Nox4) produces reactive oxygen species (ROS) and plays a significant role in metabolic and vascular adaptation during stress conditions. Our objective was to determine the role of Nox4 in exercise-induced skeletal muscle metabolism.

METHODS

Mice were subjected to acute exercise to assess their immediate responses. mRNA and protein expression responses to Nox4 and hydrogen peroxide (H₂O₂) were measured by qPCR and immunoblotting. Functional metabolic flux was measured via ex vivo fatty acid and glucose oxidation assays using ¹⁴C-labeled palmitate and glucose, respectively. A chronic exercise regimen was also utilized and the time to exhaustion along with key markers of exercise adaptation (skeletal muscle citrate synthase and beta-hydroxyacyl-coA-dehydrogenase activity) were measured. Endothelial-specific Nox4-deficient mice were then subjected to the same acute exercise regimen and their subsequent substrate oxidation was measured.

RESULTS

We identified key exercise-responsive metabolic genes that depend on H₂O₂ and Nox4 using catalase and Nox4-deficient mice. Nox4 was required for the expression of uncoupling protein 3 (Ucp3), hexokinase 2 (Hk2), and pyruvate dehydrogenase kinase 4 (Pdk4), but not the expression of peroxisome proliferator-activated receptor gamma coactivator 1-alpha (Pgc-1α). Global Nox4 deletion resulted in decreased UCP3 protein expression and impaired glucose and fatty acid oxidization in response to acute exercise. Furthermore, Nox4-deficient mice demonstrated impaired adaptation to chronic exercise as measured by the time to exhaustion and activity of skeletal muscle citrate synthase and beta-hydroxyacyl-coA-dehydrogenase. Importantly, mice deficient in endothelial-Nox4 similarly demonstrated attenuated glucose and fatty acid oxidation following acute exercise.

CONCLUSIONS

We report that H₂O₂ and Nox4 promote immediate responses to exercise in skeletal muscle. Glucose and fatty acid oxidation were blunted in the Nox4-deficient mice post-exercise, potentially through regulation of UCP3 expression. Our data demonstrate that endothelial-Nox4 is required for glucose and fatty acid oxidation, suggesting inter-tissue cross-talk between the endothelium and skeletal muscle in response to exercise.

The homeostatic role of hydrogen peroxide, superoxide anion and nitric oxide in the vasculature

Reactive oxygen and nitrogen species are produced in a wide range of physiological reactions that, at low concentrations, play essential roles in living organisms. There is a delicate equilibrium between formation and degradation of these mediators in a healthy vascular system, which contributes to maintaining these species under non-pathological levels to preserve normal vascular functions. Antioxidants scavenge reactive oxygen and nitrogen species to prevent or reduce damage caused by excessive oxidation. However, an excessive reductive environment induced by exogenous antioxidants may disrupt redox balance and lead to vascular pathology. This review summarizes the main aspects of free radical biochemistry (formation, sources and elimination) and the crucial actions of some of the most biologically relevant and well-characterized reactive oxygen and nitrogen species (hydrogen peroxide, superoxide anion and nitric oxide) in the physiological regulation of vascular function, structure and angiogenesis. Furthermore, current preclinical and clinical evidence is discussed on how excessive removal of these crucial responses by exogenous antioxidants (vitamins and related compounds, polyphenols) may perturb vascular homeostasis. The aim of this review is to provide information of the crucial physiological roles of oxidation in the endothelium, vascular smooth muscle cells and perivascular adipose tissue for developing safer and more effective vascular interventions with antioxidants.

Lipid Peroxidation in Atherosclerotic Cardiovascular Diseases

Significance: Atherosclerotic cardiovascular diseases (ACVDs) continue to be a primary cause of mortality worldwide in adults aged 35-70 years, occurring more often in countries with lower economic development, and they constitute an ever-growing global burden that has a considerable socioeconomic impact on society. The ACVDs encompass diverse pathologies such as coronary artery disease and heart failure (HF), among others. Recent Advances: It is known that oxidative stress plays a relevant role in ACVDs and some of its effects are mediated by lipid oxidation. In particular, lipid peroxidation (LPO) is a process under which oxidants such as reactive oxygen species attack unsaturated lipids, generating a wide array of oxidation products. These molecules can interact with circulating lipoproteins, to diffuse inside the cell and even to cross biological membranes, modifying target nucleophilic sites within biomolecules such as DNA, lipids, and proteins, and resulting in a plethora of biological effects. Critical Issues: This review summarizes the evidence of the effect of LPO in the development and progression of atherosclerosis-based diseases, HF, and other cardiovascular diseases, highlighting the role of protein adduct formation. Moreover, potential therapeutic strategies targeted at lipoxidation in ACVDs are also discussed. Future Directions: The identification of valid biomarkers for the detection of lipoxidation products and adducts may provide insights into the improvement of the cardiovascular risk stratification of patients and the development of therapeutic strategies against the oxidative effects that can then be applied within a clinical setting.

Galectin-3 Promotes ROS, Inflammation, and Vascular Fibrosis in Pulmonary Arterial Hypertension

Pulmonary Arterial Hypertension (PAH) is a progressive vascular disease arising from the narrowing of pulmonary arteries (PA) resulting in high pulmonary arterial blood pressure and ultimately right ventricular (RV) failure. A defining characteristic of PAH is the excessive remodeling of PA that includes increased proliferation, inflammation, and fibrosis. There is no cure for PAH nor interventions that effectively impede or reverse PA remodeling, and research over the past several decades has sought to identify novel molecular mechanisms of therapeutic benefit. Galectin-3 (Gal-3; Mac-2) is a carbohydrate-binding lectin that is remarkable for its chimeric structure, comprised of an N-terminal oligomerization domain and a C-terminal carbohydrate-recognition domain. Gal-3 is a regulator of changes in cell behavior that contribute to aberrant PA remodeling including cell proliferation, inflammation, and fibrosis, but its role in PAH is poorly understood. Herein, we summarize the recent literature on the role of Gal-3 in the development of PAH and provide experimental evidence supporting the ability of Gal-3 to influence reactive oxygen species (ROS) production, NOX enzyme expression, inflammation, and fibrosis, which contributes to PA remodeling. Finally, we address the clinical significance of Gal-3 as a target in the development of therapeutic agents as a treatment for PAH.

NADPH oxidase-4 promotes eccentric cardiac hypertrophy in response to volume overload

AIMS

Chronic pressure or volume overload induce concentric vs. eccentric left ventricular (LV) remodelling, respectively. Previous studies suggest that distinct signalling pathways are involved in these responses. NADPH oxidase-4 (Nox4) is a reactive oxygen species-generating enzyme that can limit detrimental cardiac remodelling in response to pressure overload. This study aimed to assess its role in volume overload-induced remodelling.

METHODS AND RESULTS

We compared the responses to creation of an aortocaval fistula (Shunt) to induce volume overload in Nox4-null mice (Nox4-/-) vs. wild-type (WT) littermates. Induction of Shunt resulted in a significant increase in cardiac Nox4 mRNA and protein levels in WT mice as compared to Sham controls. Nox4-/- mice developed less eccentric LV remodelling than WT mice (echocardiographic relative wall thickness: 0.30 vs. 0.27, P < 0.05), with less LV hypertrophy at organ level (increase in LV weight/tibia length ratio of 25% vs. 43%, P < 0.01) and cellular level (cardiomyocyte cross-sectional area: 323 µm2 vs. 379 μm2, P < 0.01). LV ejection fraction, foetal gene expression, interstitial fibrosis, myocardial capillary density, and levels of myocyte apoptosis after Shunt were similar in the two genotypes. Myocardial phospho-Akt levels were increased after induction of Shunt in WT mice, whereas levels decreased in Nox4-/- mice (+29% vs. -21%, P < 0.05), associated with a higher level of phosphorylation of the S6 ribosomal protein (S6) and the eIF4E-binding protein 1 (4E-BP1) in WT compared to Nox4-/- mice. We identified that Akt activation in cardiac cells is augmented by Nox4 via a Src kinase-dependent inactivation of protein phosphatase 2A.

CONCLUSION

Endogenous Nox4 is required for the full development of eccentric cardiac hypertrophy and remodelling during chronic volume overload. Nox4-dependent activation of Akt and its downstream targets S6 and 4E-BP1 may be involved in this effect.

NOX Inhibitors: From Bench to Naxibs to Bedside

Reactive oxygen species (ROS) are ubiquitous metabolic products and important cellular signaling molecules that contribute to several biological functions. Pathophysiology arises when ROS are generated either in excess or in cell types or subcellular locations that normally do not produce ROS or when non-physiological types of ROS (e.g., superoxide instead of hydrogen peroxide) are formed. In the latter scenario, antioxidants were considered as the apparent remedy but, clinically, have consistently failed and even sometimes induced harm. The obvious reason for that is the non-selective ROS scavenging effects of antioxidants which interfere with both qualities of ROS, physiological and pathological. Therefore, it is essential to overcome this "antidote or neutralizer" strategy. We here review the most promising alternative approach by identifying the disease-relevant enzymatic sources of ROS, target these selectively, but leave physiological ROS signaling through other sources intact. Among all ROS sources, NADPH oxidases (NOX1-5 and DUOX1-2) stand out as their sole function is to produce ROS, whereas most other enzymatic sources only produce ROS as a by-product or upon biochemical uncoupling or damage. This qualifies NOXs as the main potential drug-target candidates in diseases associated with dysfunction in ROS signaling. As a reflection of this, the development of several NOX inhibitors has taken place. Recently, the WHO approved a new stem, "naxib," which refers to NADPH oxidase inhibitors, and thereby recognized NOX inhibitors as a new therapeutic class. This has been announced while clinical trials with the first-in-class compound, setanaxib (initially known as GKT137831) had been initiated. We also review the differences between the seven NOX family members in terms of structure and function in health and disease and then focus on the most advanced NOX inhibitors with an exclusive focus on clinically relevant validations and applications. Therapeutically relevant NADPH oxidase isoforms type 1, 2, 4, and 5 (NOX1, NOX2, NOX4, NOX5). Of note, NOX5 is not present in mice and rats and thus pre-clinically less studied. NOX2, formerly termed gp91^phox, has been correlated with many, too many, diseases and is rather relevant as genetic deficiency in chronic granulomatous disease (CGD), treated by gene therapy. Overproduction of ROS through NOX1, NOX4, and NOX5 leads to the indicated diseases states including atherosclerosis (red), a condition where NOX4 is surprisingly protective.

Adult Renal Stem/Progenitor Cells Can Modulate T Regulatory Cells and Double Negative T Cells

Adult Renal Stem/Progenitor Cells (ARPCs) have been recently identified in the human kidney and several studies show their active role in kidney repair processes during acute or chronic injury. However, little is known about their immunomodulatory properties and their capacity to regulate specific T cell subpopulations. We co-cultured ARPCs activated by triggering Toll-Like Receptor 2 (TLR2) with human peripheral blood mononuclear cells for 5 days and 15 days and studied their immunomodulatory capacity on T cell subpopulations. We found that activated-ARPCs were able to decrease T cell proliferation but did not affect CD8⁺ and CD4⁺ T cells. Instead, Tregs and CD3⁺ CD4^- CD8^- double-negative (DN) T cells decreased after 5 days and increased after 15 days of co-culture. In addition, we found that PAI1, MCP1, GM-CSF, and CXCL1 were significantly expressed by TLR2-activated ARPCs alone and were up-regulated in T cells co-cultured with activated ARPCs. The exogenous cocktail of cytokines was able to reproduce the immunomodulatory effects of the co-culture with activated ARPCs. These data showed that ARPCs can regulate immune response by inducing Tregs and DN T cells cell modulation, which are involved in the balance between immune tolerance and autoimmunity.

Molecular Mechanisms in Early Diabetic Kidney Disease: Glomerular Endothelial Cell Dysfunction

Diabetic kidney disease (DKD) is the leading cause of end-stage renal disease (ESRD), with prevalence increasing at an alarming rate worldwide and today, there are no known cures. The pathogenesis of DKD is complex, influenced by genetics and the environment. However, the underlying molecular mechanisms that contribute to DKD risk in about one-third of diabetics are still poorly understood. The early stage of DKD is characterized by glomerular hyperfiltration, hypertrophy, podocyte injury and depletion. Recent evidence of glomerular endothelial cell injury at the early stage of DKD has been suggested to be critical in the pathological process and has highlighted the importance of glomerular intercellular crosstalk. A potential mechanism may include reactive oxygen species (ROS), which play a direct role in diabetes and its complications. In this review, we discuss different cellular sources of ROS in diabetes and a new emerging paradigm of endothelial cell dysfunction as a key event in the pathogenesis of DKD.

The Relationship Between Reactive Oxygen Species and Endothelial Cell Metabolism

Cardiovascular disease (CVD) has been the leading cause of death for many decades, highlighting the importance of new research and treatments in the field. The role of hypoxia and subsequent free radical production [reactive oxygen species (ROS)] have become an area of particular interest in CVD. Interestingly, our laboratory and other laboratories have recently reported positive roles of subcellular ROS in modulating endothelial cell (EC) metabolism, proliferation, and angiogenesis. This bidirectional relationship between ROS and EC metabolism, as well as functional changes, continues to be an area of active research. Interestingly, ECs have been shown to rely on anaerobic processes for ATP generation, despite their direct access to oxygen. This paradox has proven to be beneficial as the major reliance on glycolysis produces ATP faster, preserves oxygen, and results in reduced ROS levels in contrast to oxidative phosphorylation. This review will address the relationship between ROS and carbohydrate, lipid, and nitrogen metabolism in ECs, and their effects on EC phenotype such as sprouting angiogenesis.

Oxidative Stress and Preeclampsia-Associated Prothrombotic State

Preeclampsia (PE) is a common obstetric disease characterized by hypertension, proteinuria, and multi-system dysfunction. It endangers both maternal and fetal health. Although hemostasis is critical for preventing bleeding complications during pregnancy, delivery, and post-partum, PE patients often develop a severe prothrombotic state, potentially resulting in life-threatening thrombosis and thromboembolism. The cause of this thrombotic complication is multi-factorial, involving endothelial cells, platelets, adhesive ligands, coagulation, and fibrinolysis. Increasing evidence has shown that hemostatic cells and factors undergo oxidative modifications during the systemic inflammation found in PE patients. However, it is largely unknown how these oxidative modifications of hemostasis contribute to development of the PE-associated prothrombotic state. This knowledge gap has significantly hindered the development of predictive markers, preventive measures, and therapeutic agents to protect women during pregnancy. Here we summarize reports in the literature regarding the effects of oxidative stress and antioxidants on systemic hemostasis, with emphasis on the condition of PE.

NOX5-induced uncoupling of endothelial NO synthase is a causal mechanism and theragnostic target of an age-related hypertension endotype

Hypertension is the most important cause of death and disability in the elderly. In 9 out of 10 cases, the molecular cause, however, is unknown. One mechanistic hypothesis involves impaired endothelium-dependent vasodilation through reactive oxygen species (ROS) formation. Indeed, ROS forming NADPH oxidase (Nox) genes associate with hypertension, yet target validation has been negative. We re-investigate this association by molecular network analysis and identify NOX5, not present in rodents, as a sole neighbor to human vasodilatory endothelial nitric oxide (NO) signaling. In hypertensive patients, endothelial microparticles indeed contained higher levels of NOX5—but not NOX1, NOX2, or NOX4—with a bimodal distribution correlating with disease severity. Mechanistically, mice expressing human Nox5 in endothelial cells developed—upon aging—severe systolic hypertension and impaired endothelium-dependent vasodilation due to uncoupled NO synthase (NOS). We conclude that NOX5-induced uncoupling of endothelial NOS is a causal mechanism and theragnostic target of an age-related hypertension endotype. Nox5 knock-in (KI) mice represent the first mechanism-based animal model of hypertension.

The causes of hypertension are not understood; treatments are symptomatic and prevent only few of the associated risks. This study applies network medicine to identify a subgroup of patients with NADPH oxidase 5-induced uncoupling of nitric oxide synthase as the cause of age-related hypertension, enabling a first-in-class mechanism-based treatment of hypertension.

Myeloperoxidase: A versatile mediator of endothelial dysfunction and therapeutic target during cardiovascular disease

Myeloperoxidase (MPO) is a prominent mammalian heme peroxidase and a fundamental component of the innate immune response against microbial pathogens. In recent times, MPO has received considerable attention as a key oxidative enzyme capable of impairing the bioactivity of nitric oxide (NO) and promoting endothelial dysfunction; a clinically relevant event that manifests throughout the development of inflammatory cardiovascular disease. Increasing evidence indicates that during cardiovascular disease, MPO is released intravascularly by activated leukocytes resulting in its transport and sequestration within the vascular endothelium. At this site, MPO catalyzes various oxidative reactions that are capable of promoting vascular inflammation and impairing NO bioactivity and endothelial function. In particular, MPO catalyzes the production of the potent oxidant hypochlorous acid (HOCl) and the catalytic consumption of NO via the enzyme's NO oxidase activity. An emerging paradigm is the ability of MPO to also influence endothelial function via non-catalytic, cytokine-like activities. In this review article we discuss the implications of our increasing knowledge of the versatility of MPO's actions as a mediator of cardiovascular disease and endothelial dysfunction for the development of new pharmacological agents capable of effectively combating MPO's pathogenic activities. More specifically, we will (i) discuss the various transport mechanisms by which MPO accumulates into the endothelium of inflamed or diseased arteries, (ii) detail the clinical and basic scientific evidence identifying MPO as a significant cause of endothelial dysfunction and cardiovascular disease, (iii) provide an up-to-date coverage on the different oxidative mechanisms by which MPO can impair endothelial function during cardiovascular disease including an evaluation of the contributions of MPO-catalyzed HOCl production and NO oxidation, and (iv) outline the novel non-enzymatic mechanisms of MPO and their potential contribution to endothelial dysfunction. Finally, we deliver a detailed appraisal of the different pharmacological strategies available for targeting the catalytic and non-catalytic modes-of-action of MPO in order to protect against endothelial dysfunction in cardiovascular disease.

Nox1/4 inhibition exacerbates age dependent perivascular inflammation and fibrosis in a model of spontaneous hypertension

Hypertension is associated with oxidative stress and perivascular inflammation, critical contributors to perivascular fibrosis and accelerated vascular ageing. Oxidative stress can promote vascular inflammation, creating options for potential use of NADPH oxidase inhibitors in pharmacological targeting of perivascular inflammation and its consequences.

Accordingly, we characterized age-related changes in oxidative stress and immune cell infiltration in normotensive (WKY) and spontaneously hypertensive rats (SHRs). Subsequently, we used pharmacological inhibitors of Nox1 (ML171) and Nox1/Nox4 (GKT137831; 60 mg/kg), to modulate NADPH oxidase activity at the early stage of spontaneous hypertension and investigated their effects on perivascular inflammation and fibrosis.

Results

Ageing was associated with a progressive increase of blood pressure as well as an elevation of the total number of leukocytes, macrophages and NK cells infiltrating perivascular adipose tissue (PVAT) in SHRs but not in WKY. At 1 month of age, when blood pressure was not yet different, only perivascular NK cells were significantly higher in SHR. Spontaneous hypertension was also accompanied by the higher perivascular T cell accumulation, although this increase was age independent. Aortic Nox1 and Nox2 mRNA expression increased with age only in SHR but not in WKY, while age-related increase of Nox4 mRNA in the vessels has been observed in both groups, it was more pronounced in SHRs. At early stage of hypertension (3-months) the most pronounced differences were observed in Nox1 and Nox4. Surprisingly, GKT137831, dual inhibitor of Nox1/4, therapy increased both blood pressure and perivascular macrophage infiltration. Mechanistically, this was linked to increased expression of proinflammatory chemokines expression (CCL2 and CCL5) in PVAT. This inflammatory response translated to increased perivascular fibrosis. This effect was likely Nox4 dependent as the Nox1 inhibitor ML171 did not affect the development of spontaneous hypertension, perivascular macrophage accumulation, chemokine expression nor adventitial collagen deposition.

In summary, spontaneous hypertension promotes ageing-associated perivascular inflammation which is exacerbated by Nox4 but not Nox1 pharmacological inhibition.

Importance of cholesterol-rich microdomains in the regulation of Nox isoforms and redox signaling in human vascular smooth muscle cells

Vascular smooth muscle cell (VSMC) function is regulated by Nox-derived reactive oxygen species (ROS) and redox-dependent signaling in discrete cellular compartments. Whether cholesterol-rich microdomains (lipid rafts/caveolae) are involved in these processes is unclear. Here we examined the sub-cellular compartmentalization of Nox isoforms in lipid rafts/caveolae and assessed the role of these microdomains in VSMC ROS production and pro-contractile and growth signaling. Intact small arteries and primary VSMCs from humans were studied. Vessels from Cav-1^-/- mice were used to test proof of concept. Human VSMCs express Nox1, Nox4, Nox5 and Cav-1. Cell fractionation studies showed that Nox1 and Nox5 but not Nox4, localize in cholesterol-rich fractions in VSMCs. Angiotensin II (Ang II) stimulation induced trafficking into and out of lipid rafts/caveolae for Nox1 and Nox5 respectively. Co-immunoprecipitation studies showed interactions between Cav-1/Nox1 but not Cav-1/Nox5. Lipid raft/caveolae disruptors (methyl-β-cyclodextrin (MCD) and Nystatin) and Ang II stimulation variably increased O₂^- generation and phosphorylation of MLC20, Ezrin-Radixin-Moesin (ERM) and p53 but not ERK1/2, effects recapitulated in Cav-1 silenced (siRNA) VSMCs. Nox inhibition prevented Ang II-induced phosphorylation of signaling molecules, specifically, ERK1/2 phosphorylation was attenuated by mellitin (Nox5 inhibitor) and Nox5 siRNA, while p53 phosphorylation was inhibited by NoxA1ds (Nox1 inhibitor). Ang II increased oxidation of DJ1, dual anti-oxidant and signaling molecule, through lipid raft/caveolae-dependent processes. Vessels from Cav-1^-/- mice exhibited increased O₂^- generation and phosphorylation of ERM. We identify an important role for lipid rafts/caveolae that act as signaling platforms for Nox1 and Nox5 but not Nox4, in human VSMCs. Disruption of these microdomains promotes oxidative stress and Nox isoform-specific redox signalling important in vascular dysfunction associated with cardiovascular diseases.

Reactive Oxygen Species and Oxidative Stress in the Pathogenesis and Progression of Genetic Diseases of the Connective Tissue

Connective tissue is known to provide structural and functional “glue” properties to other tissues. It contains cellular and molecular components that are arranged in several dynamic organizations. Connective tissue is the focus of numerous genetic and nongenetic diseases. Genetic diseases of the connective tissue are minority or rare, but no less important than the nongenetic diseases. Here we review the impact of reactive oxygen species (ROS) and oxidative stress on the onset and/or progression of diseases that directly affect connective tissue and have a genetic origin. It is important to consider that ROS and oxidative stress are not synonymous, although they are often closely linked. In a normal range, ROS have a relevant physiological role, whose levels result from a fine balance between ROS producers and ROS scavenge enzymatic systems. However, pathology arises or worsens when such balance is lost, like when ROS production is abnormally and constantly high and/or when ROS scavenge (enzymatic) systems are impaired. These concepts apply to numerous diseases, and connective tissue is no exception. We have organized this review around the two basic structural molecular components of connective tissue: The ground substance and fibers (collagen and elastic fibers).

Vasoconstrictor Mechanisms in Chronic Hypoxia-Induced Pulmonary Hypertension: Role of Oxidant Signaling

Elevated resistance of pulmonary circulation after chronic hypoxia exposure leads to pulmonary hypertension. Contributing to this pathological process is enhanced pulmonary vasoconstriction through both calcium-dependent and calcium sensitization mechanisms. Reactive oxygen species (ROS), as a result of increased enzymatic production and/or decreased scavenging, participate in augmentation of pulmonary arterial constriction by potentiating calcium influx as well as activation of myofilament sensitization, therefore mediating the development of pulmonary hypertension. Here, we review the effects of chronic hypoxia on sources of ROS within the pulmonary vasculature including NADPH oxidases, mitochondria, uncoupled endothelial nitric oxide synthase, xanthine oxidase, monoamine oxidases and dysfunctional superoxide dismutases. We also summarize the ROS-induced functional alterations of various Ca2+ and K+ channels involved in regulating Ca2+ influx, and of Rho kinase that is responsible for myofilament Ca2+ sensitivity. A variety of antioxidants have been shown to have beneficial therapeutic effects in animal models of pulmonary hypertension, supporting the role of ROS in the development of pulmonary hypertension. A better understanding of the mechanisms by which ROS enhance vasoconstriction will be useful in evaluating the efficacy of antioxidants for the treatment of pulmonary hypertension.

NADPH oxidase 4 is protective and not fibrogenic in intestinal inflammation

Dysregulated redox signaling and oxidative injury are associated with inflammatory processes and fibrosis. H₂O₂ generation by NOX4 has been suggested as a key driver in the development of fibrosis and a small molecule drug is under evaluation in clinical trials for idiopathic pulmonary fibrosis and primary biliary cholangitis. Fibrosis is a common complication in Crohn's disease (CD) leading to stricture formation in 35-40% of patients, who require surgical interventions in the absence of therapeutic options. Here we assess NOX4 expression in CD patients with inflammatory or stricturing disease and examine whether loss of NOX4 is beneficial in acute and fibrotic intestinal disease. NOX4 was upregulated in inflamed mucosal tissue of CD and ulcerative colitis (UC) patients, in CD ileal strictures, and in mice with intestinal inflammation. Nox4 deficiency in mice promoted pathogen colonization and exacerbated tissue injury in acute bacterial and chemical colitis. In contrast, in two chronic injury models aberrant tissue remodeling and fibrosis-related gene expression did not differ substantially between Nox4^-/- mice and wildtype mice, suggesting that Nox4 is dispensable in TGF-β1-driven intestinal fibrogenesis. While animal models do not recapitulate all the hallmarks of CD fibrosis, the tissue-protective role of Nox4 warrants a cautious approach to pharmacological inhibitors.

Nox4 regulates InsP3 receptor-dependent Ca2+ release into mitochondria to promote cell survival

Cells subjected to environmental stresses undergo regulated cell death (RCD) when homeostatic programs fail to maintain viability. A major mechanism of RCD is the excessive calcium loading of mitochondria and consequent triggering of the mitochondrial permeability transition (mPT), which is especially important in post-mitotic cells such as cardiomyocytes and neurons. Here, we show that stress-induced upregulation of the ROS-generating protein Nox4 at the ER-mitochondria contact sites (MAMs) is a pro-survival mechanism that inhibits calcium transfer through InsP3 receptors (InsP3 R). Nox4 mediates redox signaling at the MAM of stressed cells to augment Akt-dependent phosphorylation of InsP3 R, thereby inhibiting calcium flux and mPT-dependent necrosis. In hearts subjected to ischemia-reperfusion, Nox4 limits infarct size through this mechanism. These results uncover a hitherto unrecognized stress pathway, whereby a ROS-generating protein mediates pro-survival effects through spatially confined signaling at the MAM to regulate ER to mitochondria calcium flux and triggering of the mPT.

Oxidative stress mitigation by antioxidants - An overview on their chemistry and influences on health status

The present review paper focuses on the chemistry of oxidative stress mitigation by antioxidants. Oxidative stress is understood as a lack of balance between the pro-oxidant and the antioxidant species. Reactive oxygen species in limited amounts are necessary for cell homeostasis and redox signaling. Excessive reactive oxygenated/nitrogenated species production, which counteracts the organism's defense systems, is known as oxidative stress. Sustained attack of endogenous and exogenous ROS results in conformational and oxidative alterations in key biomolecules. Chronic oxidative stress is associated with oxidative modifications occurring in key biomolecules: lipid peroxidation, protein carbonylation, carbonyl (aldehyde/ketone) adduct formation, nitration, sulfoxidation, DNA impairment such strand breaks or nucleobase oxidation. Oxidative stress is tightly linked to the development of cancer, diabetes, neurodegeneration, cardiovascular diseases, rheumatoid arthritis, kidney disease, eye disease. The deleterious action of reactive oxygenated species and their role in the onset and progression of pathologies are discussed. The results of oxidative attack become themselves sources of oxidative stress, becoming part of a vicious cycle that amplifies oxidative impairment. The term antioxidant refers to a compound that is able to impede or retard oxidation, acting at a lower concentration compared to that of the protected substrate. Antioxidant intervention against the radicalic lipid peroxidation can involve different mechanisms. Chain breaking antioxidants are called primary antioxidants, acting by scavenging radical species, converting them into more stable radicals or non-radical species. Secondary antioxidants quench singlet oxygen, decompose peroxides, chelate prooxidative metal ions, inhibit oxidative enzymes. Moreover, four reactivity-based lines of defense have been identified: preventative antioxidants, radical scavengers, repair antioxidants, and those relying on adaptation mechanisms. The specific mechanism of a series of endogenous and exogenous antioxidants in particular aspects of oxidative stress, is detailed. The final section resumes critical conclusions regarding antioxidant supplementation.

The correlation of IRE1α oxidation with Nox4 activation in aging-associated vascular dysfunction

Oxidative stress attributable to the activation of a Nox4-containing NADPH oxidase is involved in aging-associated vascular dysfunction. However, the Nox4-induced signaling mechanism for the vascular alteration in aging remains unclear. In an aged aorta, the expression of Nox4 mRNA and protein by Nox family of genes was markedly increased compared with a young aorta. Nox4 localization mainly to ER was also established. In the aorta of Nox4 WT mice aged 23–24 months (aged), reactive oxygen species (ROS) and endoplasmic reticulum (ER)/oxidative stress were markedly increased compared with the counter KO mice. Furthermore, endothelial functions including eNOS coupling process and acetylcholine-induced vasodilation were significantly disturbed in the aged WT, slightly affected in the counter KO aorta. Consistently, in d-galactose-induced in vitro aging condition, ER-ROS and its associated ER Nox4 expression and activity were highly increased. Also, in chronic d-galactose-treated condition, IRE1α phosphorylation and XBP-1 splicing and were transiently increased, but IRE1α sulfonation was robustly increased in the aging Nox4 WT condition when compared to the counter KO condition. In vitro D-gal-induced aging study, the phenomenon were abrogated with Nox4 knock-down condition and was significantly decreased in GKT, Nox4 inhibitor and 4-PBA, ER chemical chaperone-treated human umbilical vein endothelial cells. The state of Nox4-based ER redox imbalance/ROS accumulation is suggested to determine the pathway “the UPR; IRE1α phosphorylation and XBP-1 splicing and the UPR failure; IRE1α cysteine-based oxidation, especially sulfonation, finally controlling aging-associated vascular dysfunction.

NADPH oxidases in the differentiation of endothelial cells

The differentiation of stem cells into endothelial cells involves the modulation of highly interconnected metabolic and epigenetic processes. Therefore, the differentiation of endothelial cells is a tightly controlled process, which is adjusted at multiple levels, meaning that even the smallest variation can result in major consequences. Reactive oxygen species (ROS) represent a group of second messengers that can interfere with both metabolic and epigenetic processes. Besides their generation by mitochondria, ROS are produced in a controlled manner by the family of NADPH oxidases. The different members of the NADPH oxidase family produce superoxide anions or hydrogen peroxide. Due to the specific sub-cellular localization of the different NADPH oxidases, ROS are produced at diverse sites in the cell, such as the plasma membrane or the endoplasmic reticulum. Once produced, ROS interfere with proteins, lipids, and DNA to modulate intracellular signal cascades. Accordingly, ROS represent a group of readily available and specifically localized modulators of the highly sophisticated signalling network that eventually leads to the differentiation of stem cells into endothelial cells. This review focuses on the role of NADPH oxidases in the differentiation of stem cells into endothelial cells.

MicroRNAs and obesity-induced endothelial dysfunction: key paradigms in molecular therapy

The endothelium plays a pivotal role in maintaining vascular health. Obesity is a global epidemic that has seen dramatic increases in both adult and pediatric populations. Obesity perturbs the integrity of normal endothelium, leading to endothelial dysfunction which predisposes the patient to cardiovascular diseases. MicroRNAs (miRNAs) are short, single-stranded, non-coding RNA molecules that play important roles in a variety of cellular processes such as differentiation, proliferation, apoptosis, and stress response; their alteration contributes to the development of many pathologies including obesity. Mediators of obesity-induced endothelial dysfunction include altered endothelial nitric oxide synthase (eNOS), Sirtuin 1 (SIRT1), oxidative stress, autophagy machinery and endoplasmic reticulum (ER) stress. All of these factors have been shown to be either directly or indirectly caused by gene regulatory mechanisms of miRNAs. In this review, we aim to provide a comprehensive description of the therapeutic potential of miRNAs to treat obesity-induced endothelial dysfunction. This may lead to the identification of new targets for interventions that may prevent or delay the development of obesity-related cardiovascular disease.

Revisiting pharmacology of oxidative stress and endothelial dysfunction in cardiovascular disease: Evidence for redox-based therapies

According to the latest Global Burden of Disease Study data, non-communicable diseases in general and cardiovascular disease (CVD) in particular are the leading cause of premature death and reduced quality of life. Demographic shifts, unhealthy lifestyles and a higher burden of adverse environmental factors provide an explanation for these findings. The expected growing prevalence of CVD requires enhanced research efforts for identification and characterisation of novel therapeutic targets and strategies. Cardiovascular risk factors including classical (e.g. hypertension, diabetes, hypercholesterolaemia) and non-classical (e.g. environmental stress) factors induce the development of endothelial dysfunction, which is closely associated with oxidant stress and vascular inflammation and results in CVD, particularly in older adults. Most classically successful therapies for CVD display vasoprotective, antioxidant and anti-inflammatory effects, but were originally designed with other therapeutic aims. So far, only a few 'redox drugs' are in clinical use and many antioxidant strategies have not met expectations. With the present review, we summarise the actual knowledge on CVD pathomechanisms, with special emphasis on endothelial dysfunction, adverse redox signalling and oxidative stress, highlighting the preclinical and clinical evidence. In addition, we provide a brief overview of established CVD therapies and their relation to endothelial dysfunction and oxidative stress. Finally, we discuss novel strategies for redox-based CVD therapies trying to explain why, despite a clear link between endothelial dysfunction and adverse redox signalling and oxidative stress, redox- and oxidative stress-based therapies have not yet provided a breakthrough in the treatment of endothelial dysfunction and CVD.

NOX4 is a major regulator of cord blood-derived endothelial colony-forming cells which promotes post-ischaemic revascularization

AIMS

Cord blood-derived endothelial colony-forming cells (CB-ECFCs) are a defined progenitor population with established roles in vascular homeostasis and angiogenesis, which possess low immunogenicity and high potential for allogeneic therapy and are highly sensitive to regulation by reactive oxygen species (ROS). The aim of this study was to define the precise role of the major ROS-producing enzyme, NOX4 NADPH oxidase, in CB-ECFC vasoreparative function.

METHODS AND RESULTS

In vitro CB-ECFC migration (scratch-wound assay) and tubulogenesis (tube length, branch number) was enhanced by phorbol 12-myristate 13-acetate (PMA)-induced superoxide in a NOX-dependent manner. CB-ECFCs highly-expressed NOX4, which was further induced by PMA, whilst NOX4 siRNA and plasmid overexpression reduced and potentiated in vitro function, respectively. Increased ROS generation in NOX4-overexpressing CB-ECFCs (DCF fluorescence, flow cytometry) was specifically reduced by superoxide dismutase, highlighting induction of ROS-specific signalling. Laser Doppler imaging of mouse ischaemic hindlimbs at 7 days indicated that NOX4-knockdown CB-ECFCs inhibited blood flow recovery, which was enhanced by NOX4-overexpressing CB-ECFCs. Tissue analysis at 14 days revealed consistent alterations in vascular density (lectin expression) and eNOS protein despite clearance of injected CB-ECFCs, suggesting NOX4-mediated modulation of host tissue. Indeed, proteome array analysis indicated that NOX4-knockdown CB-ECFCs largely suppressed tissue angiogenesis, whilst NOX4-overexpressing CB-ECFCs up-regulated a number of pro-angiogenic factors specifically-linked with eNOS signalling, in parallel with equivalent modulation of NOX-dependent ROS generation, suggesting that CB-ECFC NOX4 signalling may promote host vascular repair.

CONCLUSION

Taken together, these findings indicate a key role for NOX4 in CB-ECFCs, thereby highlighting its potential as a target for enhancing their reparative function through therapeutic priming to support creation of a pro-reparative microenvironment and effective post-ischaemic revascularization.

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.

Cross-Talk between NADPH Oxidase and Mitochondria: Role in ROS Signaling and Angiogenesis

Angiogenesis, a new vessel formation from the pre-existing ones, is essential for embryonic development, wound repair and treatment of ischemic heart and limb diseases. However, dysregulated angiogenesis contributes to various pathologies such as diabetic retinopathy, atherosclerosis and cancer. Reactive oxygen species (ROS) derived from NADPH oxidase (NOX) as well as mitochondria play an important role in promoting the angiogenic switch from quiescent endothelial cells (ECs). However, how highly diffusible ROS produced from different sources and location can communicate with each other to regulate angiogenesis remains unclear. To detect a localized ROS signal in distinct subcellular compartments in real time in situ, compartment-specific genetically encoded redox-sensitive fluorescence biosensors have been developed. Recently, the intercellular communication, “cross-talk”, between ROS derived from NOX and mitochondria, termed “ROS-induced ROS release”, has been proposed as a mechanism for ROS amplification at distinct subcellular compartments, which are essential for activation of redox signaling. This “ROS-induced ROS release” may represent a feed-forward mechanism of localized ROS production to maintain sustained signaling, which can be targeted under pathological conditions with oxidative stress or enhanced to promote therapeutic angiogenesis. In this review, we summarize the recent knowledge regarding the role of the cross-talk between NOX and mitochondria organizing the sustained ROS signaling involved in VEGF signaling, neovascularization and tissue repair.

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.

Dynamic regulation of NADPH oxidase 5 by intracellular heme levels and cellular chaperones

NADPH oxidase 5 (NOX5) is a transmembrane signaling enzyme that produces superoxide in response to elevated cytosolic calcium. In addition to its association with numerous human diseases, NOX5 has recently been discovered to play crucial roles in the immune response and cardiovascular system. Details of NOX5 maturation, and specifically its response to changes in intracellular heme levels have remained unclear. Here we establish an experimental system in mammalian cells that allows us to probe the influence of heme availability on ROS production by NOX5. We identified a mode of dynamic regulatory control over NOX5 activity through modulation of its heme saturation and oligomeric state by intracellular heme levels and Hsp90 binding. This regulatory mechanism allows for fine-tuning and reversible modulation of NOX5 activity in response to stimuli.

Blockade of the TLR4-MD2 complex lowers blood pressure and improves vascular function in a murine model of type 1 diabetes

While the pathogenesis of diabetes-induced high blood pressure (BP) is not entirely clear, current evidence suggests that Toll-like receptor 4 (TLR4) is a key player in the mechanisms associated with hypertension. However, it is unknown whether this receptor affects BP under type 1 diabetes. Likewise, there is insufficient knowledge about the role of TLR4 in diabetes-associated vascular dysfunction of large arteries. To narrow these gaps, in this study, we investigated if blockade of the TLR4-MD2 complex impacts BP and vascular function in diabetic rats. We injected streptozotocin in male Sprague Dawley rats and treated them with a neutralizing anti-TLR4 antibody for 14 days. BP was directly measured in conscious animals at the end of the treatment. In another set of experiments, we excised the aorta from control and diabetic animals, and measured TLR4 and MD2—a co-receptor that confers functionality to TLR4—levels by Western blotting. We also performed functional studies and evaluated ROS levels with and without a pharmacological inhibitor for TLR4 as well as for MD2. Additionally, we scrutinized a large human RNA-Seq dataset of aortic tissue to assess the co-expression of TLR4, MD2, and subunits of the vascular NADPH oxidases under diabetes and hypertension. We report that (a) chronic blockade of the TLR4–MD2 complex lowers BP in diabetic animals; that (b) type 1 diabetes modulates the levels of MD2 expression in the aorta, but not TLR4, at least in the conditions evaluated in this study; and, that (c) acute inhibition of TLR4 or MD2 diminishes vascular contractility and reduces oxidative stress in the aorta of these animals. In summary, we show evidence that the TLR4–MD2 complex is involved in the mechanisms linking type 1 diabetes and hypertension.

Ca2+-Dependent NOX5 (NADPH Oxidase 5) Exaggerates Cardiac Hypertrophy Through Reactive Oxygen Species Production

NOX5 (NADPH oxidase 5) is a homolog of the gp91^phox subunit of the phagocyte NOX, which generates reactive oxygen species. NOX5 is involved in sperm motility and vascular contraction and has been implicated in diabetic nephropathy, atherosclerosis, and stroke. The function of NOX5 in the cardiac hypertrophy is unknown. Because NOX5 is a Ca²⁺-sensitive, procontractile NOX isoform, we questioned whether it plays a role in cardiac hypertrophy. Studies were performed in (1) cardiac tissue from patients undergoing heart transplant for cardiomyopathy and heart failure, (2) NOX5-expressing rat cardiomyocytes, and (3) mice expressing human NOX5 in a cardiomyocyte-specific manner. Cardiac hypertrophy was induced in mice by transverse aorta coarctation and Ang II (angiotensin II) infusion. NOX5 expression was increased in human failing hearts. Rat cardiomyocytes infected with adenoviral vector encoding human NOX5 cDNA exhibited elevated reactive oxygen species levels with significant enlargement and associated increased expression of ANP (atrial natriuretic peptides) and β-MHC (β-myosin heavy chain) and prohypertrophic genes (Nppa, Nppb, and Myh7) under Ang II stimulation. These effects were reduced by N-acetylcysteine and diltiazem. Pressure overload and Ang II infusion induced left ventricular hypertrophy, interstitial fibrosis, and contractile dysfunction, responses that were exaggerated in cardiac-specific NOX5 trangenic mice. These phenomena were associated with increased reactive oxygen species levels and activation of redox-sensitive MAPK (mitogen-activated protein kinase). N-acetylcysteine treatment reduced cardiac oxidative stress and attenuated cardiac hypertrophy in NOX5 trangenic. Our study defines Ca²⁺-regulated NOX5 as an important NOX isoform involved in oxidative stress- and MAPK-mediated cardiac hypertrophy and contractile dysfunction.

NADPH Oxidases and Their Role in Atherosclerosis

The current view on atherosclerosis positions it as a multifactorial disorder that results from the interplay between lipid metabolism disturbances and inflammatory processes. Oxidative stress is proven to be one of the initiating factors in atherosclerosis development, being implicated both in the inflammatory response and in atherogenic modifications of lipoproteins that facilitate lipid accumulation in the arterial wall. The hallmark of oxidative stress is the elevated level of reactive oxygen species (ROS). Correspondingly, the activity of major ROS-generating enzymes, including nicotinamide adenine dinucleotide phosphate (NADPH) oxidases, xanthine oxidases, and cyclooxygenases, is an important element in atherosclerosis development. In particular, the role of NADPH oxidases in atherosclerosis development has become a subject of intensive research. Aberrant activity of NADPH oxidases was shown to be associated with cardiovascular disease in humans. With regard to atherosclerosis, several important pathological components of the disease development, including endothelial dysfunction, inflammation, and vascular remodeling, involve aberrations in NADPH oxidases functioning. In humans, NADPH oxidases are represented by four isoforms expressed in vascular tissues, where they serve as the main source of ROS during atherogenesis. Moreover, recent studies have demonstrated their impact on vascular remodeling processes. Interestingly, one of the NADPH oxidase isoforms, NOX4, was shown to have an atheroprotective effect. Despite the growing evidence of the crucial involvement of NADPH oxidases in atherosclerosis pathogenesis, the available data still remains controversial. In this narrative review, we summarize the current knowledge of the role of NADPH oxidases in atherosclerosis and outline the future directions of research.

The NADPH Oxidase Isoform 1 Contributes to Angiotensin II-Mediated DNA Damage in the Kidney

In higher concentrations, the blood pressure regulating hormone angiotensin II leads to vasoconstriction, hypertension, and oxidative stress by activating NADPH oxidases which are a major enzymatic source of reactive oxygen species (ROS). With the help of knockout animals, the impact of the three predominant NADPH oxidases present in the kidney, i.e., Nox1, Nox2 and Nox4 on angiotensin II-induced oxidative damage was studied. Male wildtype (WT) C57BL/6 mice, Nox1-, Nox2- and Nox4-deficient mice were equipped with osmotic minipumps, delivering either vehicle (PBS) or angiotensin II, for 28 days. Angiotensin II increased blood pressure and urinary albumin levels significantly in all treated mouse strains. In Nox1 knockout mice these increases were significantly lower than in WT, or Nox2 knockout mice. In WT mice, angiotensin II also raised systemic oxidative stress, ROS formation and DNA lesions in the kidney. A local significantly increased ROS production was also found in Nox2 and Nox4 knockout mice but not in Nox1 knockout mice who further had significantly lower systemic oxidative stress and DNA damage than WT animals. Nox2 and Nox4 knockout mice had increased basal DNA damage, concealing possible angiotensin II-induced increases. In conclusion, in the kidney, Nox1 seemed to play a role in angiotensin II-induced DNA damage.

The role of NADPH oxidases in neuronal development

Reactive oxygen species (ROS) are critical for maintaining cellular homeostasis and function when produced in physiological ranges. Important sources of cellular ROS include NADPH oxidases (Nox), which are evolutionary conserved multi-subunit transmembrane proteins. Nox-mediated ROS regulate variety of biological processes including hormone synthesis, calcium signaling, cell migration, and immunity. ROS participate in intracellular signaling by introducing post-translational modifications to proteins and thereby altering their functions. The central nervous system (CNS) expresses different Nox isoforms during both development and adulthood. Here, we review the role of Nox-mediated ROS during CNS development. Specifically, we focus on how individual Nox isoforms contribute to signaling in neural stem cell maintenance and neuronal differentiation, as well as neurite outgrowth and guidance. We also discuss how ROS regulates the organization and dynamics of the actin cytoskeleton in the neuronal growth cone. Finally, we review recent evidence that Nox-derived ROS modulate axonal regeneration upon nervous system injury.

Glucose-Stimulated Insulin Secretion Fundamentally Requires H2O2 Signaling by NADPH Oxidase 4

NADPH facilitates glucose-stimulated insulin secretion (GSIS) in pancreatic islets (PIs) of β-cells through an as yet unknown mechanism. We found NADPH oxidase isoform 4 (NOX4) to be the main producer of cytosolic H₂O₂, which is essential for GSIS; an increase in ATP alone was insufficient for GSIS. The fast GSIS phase was absent from PIs from NOX4-null, β-cell-specific knockout mice (NOX4βKO) (though not from NOX2 knockout mice) and from NOX4-silenced or catalase-overexpressing INS-1E cells. Lentiviral NOX4 overexpression or H₂O₂ rescued GSIS in PIs from NOX4βKO mice. NOX4 silencing suppressed Ca²⁺ oscillations, and the patch-clamped K_ATP channel opened more frequently when glucose was high. Mitochondrial H₂O₂, decreasing upon GSIS, provided alternative redox signaling when 2-oxo-isocaproate or fatty acid oxidation formed superoxides through electron-transfer flavoprotein:Q-oxidoreductase. Unlike GSIS, such insulin secretion was blocked with mitochondrial antioxidant SkQ1. Both NOX4 knockout and NOX4βKO mice exhibited impaired glucose tolerance and peripheral insulin resistance. Thus, the redox signaling previously suggested to cause β-cells to self-check hypothetically induces insulin resistance when it is absent. In conclusion, increases in ATP and H₂O₂ constitute an essential signal that switches on insulin exocytosis for glucose and branched-chain oxoacids as secretagogues (it does so partially for fatty acids). Redox signaling could be impaired by cytosolic antioxidants; hence, those targeting mitochondria should be preferred for clinical applications to treat (pre)diabetes at any stage.

Activation of NADPH/ROS pathway contributes to angiogenesis through JNK signaling in brain endothelial cells

Recent evidences have shown that reactive oxygen species (ROS) are involved in regulating angiogenesis and preventing tissue injury. However, the precise molecular mechanisms behind ROS-induced angiogenesis are still unknown. The aim of the present study was to investigate the effects of ROS-induced angiogenesis in rat brain microvessel endothelial cells (rBMECs) and identify involving the signal pathways. For initial experiments, the rBMECs were incubated with different concentrations of hydrogen peroxide (H₂O₂). For the second experiments, the rBMECs were respectively treated with ROS scavenger dimethylthiourea (DMTU), NADPH oxidase (Nox) inhibitor apocynin, small interfering RNAs-mediated knock down Nox2 or Nox4, or pretreated with c-Jun N-terminal kinase (JNK) inhibitor SP600125. The cell proliferation, migration, tube formation, and the expressions of several important neuroangiogenic factors including vascular endothelial growth factor (VEGF), brain derived neurotrophic factor (BDNF), matrix metalloproteinase (MMP) -9 and phos-JNK were measured. Low level of H₂O₂ significantly promoted endothelial cell (EC) proliferation, migration and tube formation and upregulated levels of VEGF, BDNF, MMP-9 and phos-JNK. DMTU and apocynin significantly inhibited endothelial angiogenesis and downregulated these protein levels. As expected, knockdown of Nox2 or Nox4 expression blocked endothelial angiogenesis and downregulated the expressions of pro-neuroangiogenic factors. Furthermore, H₂O₂-induced endothelial angiogenesis and high expressions of pro-neuroangiogenic factors were decreased by SP600125. In conclusion, Nox-derived ROS were required for endothelial angiogenesis. Low level of ROS may activate JNK signaling pathway and upregulate pro-neuroangiogenic factors, ultimately mediating endothelial angiogenesis.

Inhibiting thrombin improves motor function and decreases oxidative stress in the LRRK2 transgenic Drosophila melanogaster model of Parkinson's disease

Parkinson's disease (PD) is a complex neurodegenerative disease characterized by the presence of tremors, loss of dopaminergic neurons and accumulation of α-synuclein. While there is no single direct cause of PD, genetic mutations, exposure to pesticides, diet and traumatic brain injury have been identified as risk factors. Increasing evidence suggests that oxidative stress and neuroinflammation contribute to the pathogenesis of neuronal injury in neurodegenerative diseases such as PD and Alzheimer's disease (AD). We have previously documented that the multifunctional inflammatory mediator thrombin contributes to oxidative stress and neuroinflammation in AD. Here, for the first time, we explore the role of thrombin in a transgenic PD model, the LRRK2 mutant Drosophila melanogaster. Transgenic flies were treated with the direct thrombin inhibitor dabigatran for 7 days and locomotor activity and indices of oxidative stress evaluated. Our data show that dabigatran treatment significantly (p < 0.05) improved climbing activity, a measurement of locomotor ability, in male but had no effect on locomotor performance in female flies. Dabigatran treatment had no effect on tyrosine hydroxylase levels. Analysis of oxidative stress in male flies showed that dabigatran was able to significantly (p < 0.01) lower reactive oxygen species levels. Furthermore, Western blot analysis showed that the pro-oxidant proteins iNOS and NOX4 are elevated in LRRK2 male flies compared to wildtype and that treatment with dabigatran reduced expression of these proteins. Our results indicate that dabigatran treatment could improve motor function in PD by reducing oxidative stress. These data suggest that targeting thrombin may improve oxidative stress related pathologies in PD.

Vascular Cardio-Oncology: Vascular Endothelial Growth Factor inhibitors and hypertension

Since the formation of new blood vessels is essential for tumour growth and metastatic spread, inhibition of angiogenesis by targeting the vascular endothelial growth factor (VEGF) pathway is an effective strategy for various types of cancer, most importantly renal cell carcinoma, thyroid cancer, and hepatocellular carcinoma. However, VEGF inhibitors have serious side effects, most importantly hypertension and nephropathy. In case of fulminant hypertension, this may only be handled by lowering the dosage since the blood pressure rise is proportional to the amount of VEGF inhibition. These effects pathophysiologically and clinically resemble the most severe complication of pregnancy, preeclampsia, in which case an insufficient placenta leads to a rise in sFlt-1 levels causing a decrease in VEGF availability. Due to this overlap, studies in preeclampsia may provide important information for VEGF inhibitor-induced toxicity and vice versa. In both VEGF inhibitor-induced toxicity and preeclampsia, endothelin (ET)-1 appears to be a pivotal player. In this review, after briefly summarizing the anticancer effects, we discuss the mechanisms that potentially underlie the unwanted effects of VEGF inhibitors, focusing on ET-1, nitric oxide and oxidative stress, the renin-angiotensin-aldosterone system, and rarefaction. Given the salt sensitivity of this phenomenon, as well as the beneficial effects of aspirin in preeclampsia and cancer, we next provide novel treatment options for VEGF inhibitor-induced toxicity, including salt restriction, ET receptor blockade, and cyclo-oxygenase inhibition, in addition to classical antihypertensive and renoprotective drugs. We conclude with the recommendation of therapeutic drug monitoring to improve patient outcome.

Reduced Sirtuin1 signalling exacerbates diabetic mice hindlimb ischaemia injury and inhibits the protective effect of a liver X receptor agonist

Diabetes mellitus causes endothelial dysfunction, which further exacerbates peripheral arterial disease (PAD). Improving endothelial function via reducing endothelial oxidative stress (OS) may be a promising therapy for diabetic PAD. Activation of liver X receptor (LXR) inhibits excessive OS and provides protective effects on endothelial cells in diabetic individuals. Therefore, we investigated the effects of LXR agonist treatment on diabetic PAD with a focus on modulating endothelial OS. We used a streptozotocin‐induced diabetes mouse model combined with a hindlimb ischaemia (HLI) injury to mimic diabetic PAD, which was followed by LXR agonist treatment. In our study, the LXR agonist T0901317 protected against HLI injury in diabetic mice by attenuating endothelial OS and stimulating angiogenesis. However, a deficiency in endothelial Sirtuin1 (SIRT1) largely inhibited the therapeutic effects of T0901317. Furthermore, we found that the underlying therapeutic mechanisms of T0901317 were related to SIRT1 and non‐SIRT1 signalling, and the isoform LXRβ was involved in LXR agonist‐elicited SIRT1 regulation. In conclusion, LXR agonist treatment protected against HLI injury in diabetic mice via mitigating endothelial OS and stimulating cellular viability and angiogenesis by LXRβ, which elicited both SIRT1‐mediated and non‐SIRT1‐mediated signalling pathways. Therefore, LXR agonist treatment may be a promising therapeutic strategy for diabetic PAD.

The NADPH oxidase 4 protects vascular endothelial cells from copper oxide nanoparticles-induced oxidative stress and cell death

AIMS

Nanoparticles (NPs) exposure is associated with increased risk of cardiovascular diseases, but the underlying mechanism is still obscure. In this study, we investigated the role of NADPH oxidase 4 (NOX4) in copper oxide nanoparticles (CuONPs)-induced cytotoxicity in human umbilical vein endothelial cells (HUVECs).

MATERIALS AND METHODS

Morphology changes were examined under the microscope. Cell viability was determined by MTS assay and Calcein AM assay. Apoptosis and the levels of superoxide anion (O₂^-) and hydrogen peroxide (H₂O₂) were measured by fluorescence activated cell sorting (FACS). Oxidative stress was detected by assaying the levels of glutathione/glutathione disulfide (GSH/GSSG) and malondialdehyde (MDA). Protein expression levels were determined by western blotting.

KEY FINDINGS

We revealed that O₂^- rather than H₂O₂ was the major component of reactive oxygen species (ROS) in CuONPs-treated HUVECs. Meanwhile, CuONPs downregulated expression of O₂^--eliminating enzyme NOX4 both at mRNA and protein levels, but did not affect the expression of SOD2 and catalase. NOX4 knockdown caused more accumulation of O₂^-, and a further decrease of H₂O₂ in CuONPs-treated HUVECs, suggesting that NOX4 regulates the conversion of O₂^- to H₂O₂ in CuONPs-treated HUVECs. Furthermore, we revealed that NOX4 knockdown aggravated CuONPs-induced oxidative stress, characterized by a decrease of GSH/GSSG ratio, an increase of MDA level, and upregulation of HSPA5 and γH2AX. Finally, we showed that NOX4 knockdown exacerbated CuONPs-induced apoptotic cell death in HUVECs, indicating that NOX4 could protect ECs from CuONPs-induced cell death.

SIGNIFICANCE

Our study provides the evidence that NOX4 protects vascular endothelial cells from CuONPs-induced oxidative stress and cell death.