NADPH oxidase 4 promotes endothelial angiogenesis through endothelial nitric oxide synthase activation

The generation of stable microvessels in ischemia is mediated by endothelial cell derived TRAIL

Reversal of ischemia is mediated by neo-angiogenesis requiring endothelial cell (EC) and pericyte interactions to form stable microvascular networks. We describe an unrecognized role for tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) in potentiating neo-angiogenesis and vessel stabilization. We show that the endothelium is a major source of TRAIL in the healthy circulation compromised in peripheral artery disease (PAD). EC deletion of TRAIL in vivo or in vitro inhibited neo-angiogenesis, pericyte recruitment, and vessel stabilization, resulting in reduced lower-limb blood perfusion with ischemia. Activation of the TRAIL receptor (TRAIL-R) restored blood perfusion and stable blood vessel networks in mice. Proof-of-concept studies showed that Conatumumab, an agonistic TRAIL-R2 antibody, promoted vascular sprouts from explanted patient arteries. Single-cell RNA sequencing revealed heparin-binding EGF-like growth factor in mediating EC-pericyte communications dependent on TRAIL. These studies highlight unique TRAIL-dependent mechanisms mediating neo-angiogenesis and vessel stabilization and the potential of repurposing TRAIL-R2 agonists to stimulate stable and functional microvessel networks to treat ischemia in PAD.

Endothelial Reactive Oxygen Species: Key Players in Cardiovascular Health and Disease

Significance: Endothelial cells (ECs) line the entire vasculature system and serve as both barriers and facilitators of intra- and interorgan communication. Positioned to rapidly sense internal and external stressors, ECs dynamically adjust their functionality. Endothelial dysfunction occurs when the ability of ECs to react to stressors is impaired, which precedes many cardiovascular diseases (CVDs). While EC reactive oxygen species (ROS) have historically been implicated as mediators of endothelial dysfunction, more recent studies highlight the central role of ROS in physiological endothelial signaling. Recent Advances: New evidence has uncovered that EC ROS are fundamental in determining how ECs interact with their environment and respond to stress. EC ROS levels are mediated by external factors such as diet and pathogens, as well as inherent characteristics, including sex and location. Changes in EC ROS impact EC function, leading to changes in metabolism, cell communication, and potentially disrupted signaling in CVDs. Critical Issues: Current endothelial biology concepts integrate the dual nature of ROS, emphasizing the importance of EC ROS in physiological stress adaptation and their contribution to CVDs. Understanding the discrete, localized signaling of EC ROS will be critical in preventing adverse cardiovascular outcomes. Future Directions: Exploring how the EC ROS environment alters EC function and cross-cellular communication is critical. Considering the inherent heterogeneity among EC populations and understanding how EC ROS contribute to this diversity and the role of sexual dimorphism in the EC ROS environment will be fundamental for developing new effective cardiovascular treatment strategies.

NADPH Oxidase 4: Crucial for Endothelial Function under Hypoxia-Complementing Prostacyclin

Aim: The primary endothelial NADPH oxidase isoform 4 (NOX4) is notably induced during hypoxia, with emerging evidence suggesting its vasoprotective role through H2O2 production. Therefore, we aimed to elucidate NOX4's significance in endothelial function under hypoxia. Methods: Human vessels, in addition to murine vessels from Nox4-/- mice, were explored. On a functional level, Mulvany myograph experiments were performed. To obtain mechanistical insights, human endothelial cells were cultured under hypoxia with inhibitors of hypoxia-inducible factors. Additionally, endothelial cells were cultured under combined hypoxia and laminar shear stress conditions. Results: In human occluded vessels, NOX4 expression strongly correlated with prostaglandin I2 synthase (PTGIS). Hypoxia significantly elevated NOX4 and PTGIS expression and activity in human endothelial cells. Inhibition of prolyl hydroxylase domain (PHD) enzymes, which stabilize hypoxia-inducible factors (HIFs), increased NOX4 and PTGIS expression even under normoxic conditions. NOX4 mRNA expression was reduced by HIF1a inhibition, while PTGIS mRNA expression was only affected by the inhibition of HIF2a under hypoxia. Endothelial function assessments revealed hypoxia-induced endothelial dysfunction in mesenteric arteries from wild-type mice. Mesenteric arteries from Nox4-/- mice exhibited an altered endothelial function under hypoxia, most prominent in the presence of cyclooxygenase inhibitor diclofenac to exclude the impact of prostacyclin. Restored protective laminar shear stress, as it might occur after thrombolysis, angioplasty, or stenting, attenuated the hypoxic response in endothelial cells, reducing HIF1a expression and its target NOX4 while enhancing eNOS expression. Conclusions: Hypoxia strongly induces NOX4 and PTGIS, with a close correlation between both factors in occluded, hypoxic human vessels. This relationship ensured endothelium-dependent vasodilation under hypoxic conditions. Protective laminar blood flow restores eNOS expression and mitigates the hypoxic response on NOX4 and PTGIS.

Metabolic Responses to Redox Stress in Vascular Cells

Significance: Redox stress underlies numerous vascular disease mechanisms. Metabolic adaptability is essential for vascular cells to preserve energy and redox homeostasis. Recent Advances: Single-cell technologies and multiomic studies demonstrate significant metabolic heterogeneity among vascular cells in health and disease. Increasing evidence shows that reductive or oxidative stress can induce metabolic reprogramming of vascular cells. A recent example is intracellular L-2-hydroxyglutarate accumulation in response to hypoxic reductive stress, which attenuates the glucose flux through glycolysis and mitochondrial respiration in pulmonary vascular cells and provides protection against further reductive stress. Critical Issues: Regulation of cellular redox homeostasis is highly compartmentalized and complex. Vascular cells rely on multiple metabolic pathways, but the precise connectivity among these pathways and their regulatory mechanisms is only partially defined. There is also a critical need to understand better the cross-regulatory mechanisms between the redox system and metabolic pathways as perturbations in either systems or their cross talk can be detrimental. Future Directions: Future studies are needed to define further how multiple metabolic pathways are wired in vascular cells individually and as a network of closely intertwined processes given that a perturbation in one metabolic compartment often affects others. There also needs to be a comprehensive understanding of how different types of redox perturbations are sensed by and regulate different cellular metabolic pathways with specific attention to subcellular compartmentalization. Lastly, integration of dynamic changes occurring in multiple metabolic pathways and their cross talk with the redox system is an important goal in this multiomics era.

Endothelial Drp1 Couples VEGF-induced Redox Signaling with Glycolysis Through Cysteine Oxidation to Drive Angiogenesis

Angiogenesis plays a vital role for postnatal development and tissue repair following ischemia. Reactive oxygen species (ROS) generated by NADPH oxidases (NOXes) and mitochondria act as signaling molecules that promote angiogenesis in endothelial cells (ECs) which mainly relies on aerobic glycolysis for ATP production. However, the connections linking redox signaling with glycolysis are not well understood. The GTPase Drp1 is a member of the dynamin superfamily that moves from cytosol to mitochondria through posttranslational modifications to induce mitochondrial fission. The role of Drp1 in ROS-dependent VEGF signaling and angiogenesis in ECs has not been previously described. Here, we identify an unexpected function of endothelial Drp1 as a redox sensor, transmitting VEGF-induced H 2 O 2 signals to enhance glycolysis and angiogenesis. Loss of Drp1 expression in ECs inhibited VEGF-induced angiogenic responses. Mechanistically, VEGF rapidly induced the NOX4-dependent sulfenylation (CysOH) of Drp1 on Cys 644 , promoting disulfide bond formation with the metabolic kinase AMPK and subsequent sulfenylation of AMPK at Cys 299 / 304 via the mitochondrial fission-mitoROS axis. This cysteine oxidation of AMPK, in turn, enhanced glycolysis and angiogenesis. In vivo , mice with EC-specific Drp1 deficiency or CRISPR/Cas9-engineered "redox-dead" (Cys to Ala) Drp1 knock-in mutations exhibited impaired retinal angiogenesis and post-ischemic neovascularization. Our findings uncover a novel role for endothelial Drp1 in linking VEGF-induced mitochondrial redox signaling to glycolysis through a cysteine oxidation-mediated Drp1-AMPK redox relay, driving both developmental and reparative angiogenesis.

Redox signaling and skeletal muscle adaptation during aerobic exercise

Redox regulation is a fundamental physiological phenomenon related to oxygen-dependent metabolism, and skeletal muscle is mainly regarded as a primary site for oxidative phosphorylation. Several studies have revealed the importance of reactive oxygen and nitrogen species (RONS) in the signaling process relating to muscle adaptation during exercise. To date, improving knowledge of redox signaling in modulating exercise adaptation has been the subject of comprehensive work and scientific inquiry. The primary aim of this review is to elucidate the molecular and biochemical pathways aligned to RONS as activators of skeletal muscle adaptation and to further identify the interconnecting mechanisms controlling redox balance. We also discuss the RONS-mediated pathways during the muscle adaptive process, including mitochondrial biogenesis, muscle remodeling, vascular angiogenesis, neuron regeneration, and the role of exogenous antioxidants.

The Vascular Function of Resistance Arteries Depends on NADPH Oxidase 4 and Is Exacerbated by Perivascular Adipose Tissue

The NADPH oxidase NOX4 that releases H2O2 can mediate vasoprotective mechanisms under pathophysiological conditions in conductive arteries. However, the role of NOX4 in resistance arteries and in perivascular adipose tissue is not well understood. We hypothesized that NOX4 is of functional importance in resistance arteries and perivascular adipose tissue under dyslipidemia conditions. We detected elevated NOX4 expression in murine and human vessels under dyslipidemia. Diminishing Nox4 under these conditions led to endothelial dysfunction in resistance arteries. The mesenteric arteries of Nox4-/-/Ldlr-/- mice revealed decreased eNos mRNA expression. Inhibition of eNOS in those vessels did not affect vascular function, while in Ldlr-/- mice endothelial function was significantly altered. Anticontractile properties of perivascular adipose tissue at resistance arteries were diminished in Nox4-/-/Ldlr-/- compared with Ldlr-/- mice. In addition, the presence of perivascular adipose tissue further worsened endothelial dysfunction in mesenteric arteries under dyslipidemia conditions. Perivascular adipose tissue from mesenteric arteries revealed a higher expression of markers of white adipocytes compared to markers of beige/brown adipocytes. Among those white adipocyte markers, leptin was significantly less expressed in perivascular adipose tissue from Nox4-/-/Ldlr-/- mice compared with Ldlr-/- mice. Furthermore, in human perivascular adipose tissue with a profound pattern of white adipocyte marker genes, we detected a correlation of NOX4 and LEP expression. In addition, incubating arterial vessels with leptin induced nitrite release, indicating increased eNOS activity. In humans, a higher expression of leptin in perivascular adipose tissue correlated with eNOS expression in the corresponding left internal mammary artery. In conclusion, vascular function of resistance arteries was dependent on Nox4-derived H2O2, especially under dyslipidemia conditions. Perivascular adipose tissue of the mesenteric arteries with white adipose tissue characteristics further aggravated endothelial function through reduced leptin-eNOS signaling.

NADPH-oxidases as potential pharmacological targets for thrombosis and depression comorbidity

There is a complex interrelationship between the nervous system and the cardiovascular system. Comorbidities of cardiovascular diseases (CVD) with mental disorders, and vice versa, are prevalent. Adults with mental disorders such as anxiety and depression have a higher risk of developing CVD, and people with CVD have an increased risk of being diagnosed with mental disorders. Oxidative stress is one of the many pathways associated with the pathophysiology of brain and cardiovascular disease. Nicotinamide adenine dinucleotide phosphate oxidase (NOX) is one of the major generators of reactive oxygen species (ROS) in mammalian cells, as it is the enzyme that specifically produces superoxide. This review summarizes recent findings on the consequences of NOX activation in thrombosis and depression. It also discusses the therapeutic effects and pharmacological strategies of NOX inhibitors in CVD and brain disorders. A better comprehension of these processes could facilitate the development of new therapeutic approaches for the prevention and treatment of the comorbidity of thrombosis and depression.

Endothelial Reprogramming in Atherosclerosis

Atherosclerosis (AS) is a severe vascular disease that results in millions of cases of mortality each year. The development of atherosclerosis is associated with vascular structural lesions, characterized by the accumulation of immune cells, mesenchymal cells, lipids, and an extracellular matrix at the intimal resulting in the formation of an atheromatous plaque. AS involves complex interactions among various cell types, including macrophages, endothelial cells (ECs), and smooth muscle cells (SMCs). Endothelial dysfunction plays an essential role in the initiation and progression of AS. Endothelial dysfunction can encompass a constellation of various non-adaptive dynamic alterations of biology and function, termed "endothelial reprogramming". This phenomenon involves transitioning from a quiescent, anti-inflammatory state to a pro-inflammatory and proatherogenic state and alterations in endothelial cell identity, such as endothelial to mesenchymal transition (EndMT) and endothelial-to-immune cell-like transition (EndIT). Targeting these processes to restore endothelial balance and prevent cell identity shifts, alongside modulating epigenetic factors, can attenuate atherosclerosis progression. In the present review, we discuss the role of endothelial cells in AS and summarize studies in endothelial reprogramming associated with the pathogenesis of AS.

Hypoxia stabilizes the H2 O2 -producing oxidase Nox4 in cardiomyocytes via suppressing autophagy-related lysosomal degradation

The hydrogen peroxide (H2 O2 )-producing NADPH oxidase Nox4, forming a heterodimer with p22phox , is expressed in a variety of cells including those in the heart to mediate adaptive responses to cellular stresses such as hypoxia. Since Nox4 is constitutively active, H2 O2 production is controlled by its protein abundance. Hypoxia-induced Nox4 expression is observed in various types of cells and generally thought to be regulated at the transcriptional level. Here we show that hypoxia upregulates the Nox4 protein level and Nox4-catalyzed H2 O2 production without increasing the Nox4 mRNA in rat H9c2 cardiomyocytes. In these cells, the Nox4 protein is stabilized under hypoxic conditions in a manner dependent on the presence of p22phox . Cell treatment with the proteasome inhibitor MG132 results in a marked decrease of the Nox4 protein under both normoxic and hypoxic conditions, indicating that the proteasome pathway does not play a major role in Nox4 degradation. The decrease is partially restored by the autophagy inhibitor 3-methyladenine. Furthermore, the Nox4 protein level is upregulated by the lysosome inhibitors bafilomycin A1 and chloroquine. Thus, in cardiomyocytes, Nox4 appears to be degraded via an autophagy-related pathway, and its suppression by hypoxia likely stabilizes Nox4, leading to upregulation of Nox4-catalyzed H2 O2 production.

Vasoprotective effects of NOX4 are mediated via polymerase and transient receptor potential melastatin 2 cation channels in endothelial cells

BACKGROUND

NOX4 activation has been implicated to have vasoprotective and blood pressure (BP)-lowering effects. Molecular mechanisms underlying this are unclear, but NOX4-induced regulation of the redox-sensitive Ca 2+ channel TRPM2 and effects on endothelial nitric oxide synthase (eNOS)-nitric oxide signalling may be important.

METHOD

Wild-type and LinA3, renin-expressing hypertensive mice, were crossed with NOX4 knockout mice. Vascular function was measured by myography. Generation of superoxide (O 2- ) and hydrogen peroxide (H 2 O 2 ) were assessed by lucigenin and amplex red, respectively, and Ca 2+ influx by Cal-520 fluorescence in rat aortic endothelial cells (RAEC).

RESULTS

BP was increased in NOX4KO, LinA3 and LinA3/NOX4KO mice. This was associated with endothelial dysfunction and vascular remodelling, with exaggerated effects in NOX4KO groups. The TRPM2 activator, ADPR, improved vascular relaxation in LinA3/NOX4KO mice, an effect recapitulated by H 2 O 2 . Inhibition of PARP and TRPM2 with olaparib and 2-APB, respectively, recapitulated endothelial dysfunction in NOX4KO. In endothelial cells, Ang II increased H 2 O 2 generation and Ca 2+ influx, effects reduced by TRPM2 siRNA, TRPM2 inhibitors (8-br-cADPR, 2-APB), olaparib and GKT137831 (NOX4 inhibitor). Ang II-induced eNOS activation was blocked by NOX4 and TRPM2 siRNA, GKT137831, PEG-catalase and 8-br-cADPR.

CONCLUSION

Our findings indicate that NOX4-induced H 2 O 2 production activates PARP/TRPM2, Ca 2+ influx, eNOS activation and nitric oxide release in endothelial cells. NOX4 deficiency impairs Ca 2+ homeostasis leading to endothelial dysfunction, an effect exacerbated in hypertension. We define a novel pathway linking endothelial NOX4/H 2 O 2 to eNOS/nitric oxide through PARP/TRPM2/Ca 2+ . This vasoprotective pathway is perturbed when NOX4 is downregulated and may have significance in conditions associated with endothelial dysfunction, including hypertension.

Deletion of Nox4 enhances remyelination following cuprizone-induced demyelination by increasing phagocytic capacity of microglia and macrophages in mice

NOX4 is a major reactive oxygen species-producing enzyme that modulates cell stress responses. We here examined the effect of Nox4 deletion on demyelination-remyelination, the most common pathological change in the brain. We used a model of cuprizone (CPZ)-associated demyelination-remyelination in wild-type and Nox4-deficient (Nox4^-/- ) mice. While the CPZ-induced demyelination in the corpus callosum after 4 weeks of CPZ intoxication was slightly less pronounced in Nox4^-/- mice than that in wild-type mice, remyelination following CPZ withdrawal was significantly enhanced in Nox4^-/- mice with an increased accumulation of IBA1-positive microglia/macrophages in the demyelinating corpus callosum. Consistently, locomotor function, as assessed by the beam walking test, was significantly better during the remyelination phase in Nox4^-/- mice. Nox4 deletion did not affect autonomous growth of primary-culture oligodendrocyte precursor cells. Although Nox4 expression was higher in cultured macrophages than in microglia, Nox4^-/- microglia and macrophages both showed enhanced phagocytic capacity of myelin debris and produced increased amounts of trophic factors upon phagocytosis. The expression of trophic factors was higher, in parallel with the accumulation of IBA1-positive cells, in the corpus callosum in Nox4^-/- mice than that in wild-type mice. Nox4 deletion suppressed phagocytosis-induced increase in mitochondrial membrane potential, enhancing phagocytic capacity of macrophages. Treatment with culture medium of Nox4^-/- macrophages engulfing myelin debris, but not that of Nox4^-/- astrocytes, enhanced cell growth and expression of myelin-associated proteins in cultured oligodendrocyte precursor cells. Collectively, Nox4 deletion promoted remyelination after CPZ-induced demyelination by enhancing microglia/macrophage-mediated clearance of myelin debris and the production of trophic factors leading to oligodendrogenesis.

Nicotinamide Adenosine Dinucleotide Phosphate Oxidase-Mediated Signaling in Cardiac Remodeling

Significance: Reactive oxygen species (ROS) play a key role in the pathogenesis of cardiac remodeling and the subsequent progression to heart failure (HF). Nicotinamide adenosine dinucleotide phosphate (NADPH) oxidases (NOXs) are one of the major sources of ROS and are expressed in different heart cell types, including cardiomyocytes, endothelial cells, fibroblasts, and inflammatory cells. Recent Advances: NOX-derived ROS are usually produced in a regulated and spatially confined fashion and typically linked to specific signaling. The two main cardiac isoforms, namely nicotinamide adenine dinucleotide phosphate oxidase isoform 2 (NOX2) and nicotinamide adenine dinucleotide phosphate oxidase isoform 4 (NOX4), possess different biochemical and (patho)physiological properties and exert distinct effects on the cardiac phenotype in many settings. Recent work has defined important cell-specific effects of NOX2 that contribute to pathological cardiac remodeling and dysfunction. NOX4, on the other hand, may exert protective effects by stimulating adaptive stress responses, with recent data showing that NOX4-mediated signaling regulates transcription and metabolism in the heart. Critical Issues: The inhibition of NOX2 appears to be a very promising therapeutic target to ameliorate pathological cardiac remodeling. If the beneficial effects of NOX4 can be enhanced, this might be a unique approach to boosting adaptive responses and thereby impact cell survival, activation, contractility, and growth. Future Directions: Increasing knowledge regarding the intricacies of NOX-mediated signaling may yield tractable therapeutic targets, in contrast to the non-specific targeting of oxidative stress. Antioxid. Redox Signal. 38, 371-387.

NOX2 and NOX5 are increased in cardiac microvascular endothelium of deceased COVID-19 patients

BACKGROUND

Cardiac injury and inflammation are common findings in COVID-19 patients. Autopsy studies have revealed cardiac microvascular endothelial damage and thrombosis in COVID-19 patients, indicative of microvascular dysfunction in which reactive oxygen species (ROS) may play a role. We explored whether the ROS producing proteins NOX2, NOX4 and NOX5 are involved in COVID-19-induced cardio-microvascular endothelial dysfunction.

METHODS

Heart tissue were taken from the left (LV) and right (RV) ventricle of COVID-19 patients (n = 15) and the LV of controls (n = 14) at autopsy. The NOX2-, NOX4-, NOX5- and Nitrotyrosine (NT)-positive intramyocardial blood vessels fractions were quantitatively analyzed using immunohistochemistry.

RESULTS

The LV NOX2+, NOX5+ and NT+ blood vessels fractions in COVID-19 patients were significantly higher than in controls. The fraction of NOX4+ blood vessels in COVID-19 patients was comparable with controls. In COVID-19 patients, the fractions of NOX2+, NOX5+ and NT+ vessels did not differ significantly between the LV and RV, and correlated positively between LV and RV in case of NOX5 (r = 0.710; p = 0.006). A negative correlation between NOX5 and NOX2 (r = -0.591; p = 0.029) and between NOX5 and disease time (r = -0.576; p = 0.034) was noted in the LV of COVID-19 patients.

CONCLUSION

We show the induction of NOX2 and NOX5 in the cardiac microvascular endothelium in COVID-19 patients, which may contribute to the previously observed cardio-microvascular dysfunction in COVID-19 patients. The exact roles of these NOXes in pathogenesis of COVID-19 however remain to be elucidated.

Advances in the study of nicotinamide adenine dinucleotide phosphate oxidase in myocardial remodeling

Myocardial remodeling is a key pathophysiological basis of heart failure, which seriously threatens human health and causes a severe economic burden worldwide. During chronic stress, the heart undergoes myocardial remodeling, mainly manifested by cardiomyocyte hypertrophy, apoptosis, interstitial fibrosis, chamber enlargement, and cardiac dysfunction. The NADPH oxidase family (NOXs) are multisubunit transmembrane enzyme complexes involved in the generation of redox signals. Studies have shown that NOXs are highly expressed in the heart and are involved in the pathological development process of myocardial remodeling, which influences the development of heart failure. This review summarizes the progress of research on the pathophysiological processes related to the regulation of myocardial remodeling by NOXs, suggesting that NOXs-dependent regulatory mechanisms of myocardial remodeling are promising new therapeutic targets for the treatment of heart failure.

ROS-triggered endothelial cell death mechanisms: Focus on pyroptosis, parthanatos, and ferroptosis

The endothelium is a single layer of epithelium covering the surface of the vascular system, and it represents a physical barrier between the blood and vessel wall that plays an important role in maintaining intravascular homeostasis. However, endothelial dysfunction or endothelial cell death can cause vascular barrier disruption, vasoconstriction and diastolic dysfunction, vascular smooth muscle cell proliferation and migration, inflammatory responses, and thrombosis, which are closely associated with the progression of several diseases, such as atherosclerosis, hypertension, coronary atherosclerotic heart disease, ischemic stroke, acute lung injury, acute kidney injury, diabetic retinopathy, and Alzheimer's disease. Oxidative stress caused by the overproduction of reactive oxygen species (ROS) is an important mechanism underlying endothelial cell death. Growing evidence suggests that ROS can trigger endothelial cell death in various ways, including pyroptosis, parthanatos, and ferroptosis. Therefore, this review will systematically illustrate the source of ROS in endothelial cells (ECs); reveal the molecular mechanism by which ROS trigger pyroptosis, parthanatos, and ferroptosis in ECs; and provide new ideas for the research and treatment of endothelial dysfunction-related diseases.

NOX4 mRNA correlates with plaque stability in patients with carotid artery stenosis

Carotid artery stenosis (CAS) develops from atherosclerotic lesions and plaques. Plaque rupture or stenosis may result in occlusion of the carotid artery. Accordingly, the asymptomatic disease becomes symptomatic, characterized by ischemic stroke or transient ischemic attacks, indicating an urgent need for better understanding of the underlying molecular mechanisms and eventually prevent symptomatic CAS. NOX4, a member of the NADPH oxidase family, has anti-atherosclerotic and anti-inflammatory properties in animal models of early atherosclerosis. We hypothesized that NOX4 mRNA expression is linked to protective mechanisms in CAS patients with advanced atherosclerotic lesions as well. Indeed, NOX4 mRNA expression is lower in patients with symptomatic CAS. A low NOX4 mRNA expression is associated with an increased risk of the development of clinical symptoms. In fact, NOX4 appears to be linked to plaque stability, apoptosis and plaque hemorrhage. This is supported by cleaved caspase-3 and glycophorin C and correlates inversely with plaque NOX4 mRNA expression. Even healing of a ruptured plaque appears to be connected to NOX4, as NOX4 mRNA expression correlates to fibrous cap collagen and is reciprocally related to MMP9 activity. In conclusion, low intra-plaque NOX4 mRNA expression is associated with an increased risk for symptomatic outcome and with reduced plaque stabilizing mechanisms suggesting protective effects of NOX4 in human advanced atherosclerosis.

S1P (Sphingosine-1-Phosphate)-Induced Vasodilation in Human Resistance Arterioles During Health and Disease

BACKGROUND

Preclinical studies suggest that S1P (sphingosine-1-phosphate) influences blood pressure regulation primarily through NO-induced vasodilation. Because microvascular tone significantly contributes to mean arterial pressure, the mechanism of S1P on human resistance arterioles was investigated. We hypothesized that S1P induces NO-mediated vasodilation in human arterioles from adults without coronary artery disease (non-coronary artery disease) through activation of 2 receptors, S1PR1 (S1P receptor 1) and S1PR3 (S1P receptor 3). Furthermore, we tested whether this mechanism is altered in vessels from patients diagnosed with coronary artery disease.

METHODS

Human arterioles (50-200 µm in luminal diameter) were dissected from otherwise discarded surgical adipose tissue, cannulated, and pressurized. Following equilibration, resistance vessels were preconstricted with ET-1 (endothelin-1) and changes in internal diameter to increasing concentrations of S1P (10-12 to 10-7 M) in the presence or absence of various inhibitors were measured.

RESULTS

S1P resulted in significant dilation that was abolished in vessels treated with S1PR1 and S1PR3 inhibitors and in vessels with reduced expression of each receptor. Dilation to S1P was significantly reduced in the presence of the NOS (NO synthase) inhibitor Nω-nitro-L-arginine methyl ester and the NO scavenger 2-4-(carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide. Interestingly, dilation was also significantly impaired in the presence of PEG-catalase (polyethylene glycol-catalase), apocynin, and specific inhibitors of NOX (NADPH oxidases) 2 and 4. Dilation in vessels from patients diagnosed with coronary artery disease was dependent on H2O2 alone which was only dependent on S1PR3 activation.

CONCLUSIONS

These translational studies highlight the inter-species variation observed in vascular signaling and provide insight into the mechanism by which S1P regulates microvascular resistance and ultimately blood pressure in humans.

Factors and Pathways Modulating Endothelial Cell Senescence in Vascular Aging

Aging causes a progressive decline in the structure and function of organs. With advancing age, an accumulation of senescent endothelial cells (ECs) contributes to the risk of developing vascular dysfunction and cardiovascular diseases, including hypertension, diabetes, atherosclerosis, and neurodegeneration. Senescent ECs undergo phenotypic changes that alter the pattern of expressed proteins, as well as their morphologies and functions, and have been linked to vascular impairments, such as aortic stiffness, enhanced inflammation, and dysregulated vascular tone. Numerous molecules and pathways, including sirtuins, Klotho, RAAS, IGFBP, NRF2, and mTOR, have been implicated in promoting EC senescence. This review summarizes the molecular players and signaling pathways driving EC senescence and identifies targets with possible therapeutic value in age-related vascular diseases.

Nox4 promotes endothelial differentiation through chromatin remodeling

RATIONALE

Nox4 is a constitutively active NADPH oxidase that constantly produces low levels of H2O2. Thereby, Nox4 contributes to cell homeostasis and long-term processes, such as differentiation. The high expression of Nox4 seen in endothelial cells contrasts with the low abundance of Nox4 in stem cells, which are accordingly characterized by low levels of H2O2. We hypothesize that Nox4 is a major contributor to endothelial differentiation, is induced during the process of differentiation, and facilitates homeostasis of the resulting endothelial cells.

OBJECTIVE

To determine the role of No×4 in differentiation of murine inducible pluripotent stem cells (miPSC) into endothelial cells (ECs).

METHODS AND RESULTS

miPSC, generated from mouse embryonic wildtype (WT) and Nox4-/- fibroblasts, were differentiated into endothelial cells (miPSC-EC) by stimulation with BMP4 and VEGF. During this process, Nox4 expression increased and knockout of Nox4 prolonged the abundance of pluripotency markers, while expression of endothelial markers was delayed in differentiating Nox4-depleted iPSCs. Eventually, angiogenic capacity of iPSC-ECs is reduced in Nox4 deficient cells, indicating that an absence of Nox4 diminishes stability of the reached phenotype. As an underlying mechanism, we identified JmjD3 as a redox target of Nox4. iPSC-ECs lacking Nox4 display a lower nuclear abundance of the histone demethylase JmjD3, resulting in an increased triple methylation of histone 3 (H3K27me3), which serves as a repressive mark for several genes involved in differentiation.

CONCLUSIONS

Nox4 promotes differentiation of miPSCs into ECs by oxidation of JmjD3 and subsequent demethylation of H3K27me3, which forced endothelial differentiation and stability.

Effect of bone marrow mesenchymal stem cells-derived exosomes on diabetes-induced retinal injury: Implication of Wnt/ b-catenin signaling pathway

BACKGROUND

Diabetic retinopathy (DR) is a serious microvascular complication of diabetes mellitus. Mesenchymal stem cells are currently studied as therapeutic strategy for management of DR. Exosomes, considered as a promising cell-free therapy option, display biological functions similar to those of their parent cells. In retinal development, Wnt/b-catenin signaling provides key cues for functional progression. The present study aimed to evaluate the potential efficacy of bone marrow-derived mesenchymal stem cell-derived exosomes (BM-MSCs-Ex) in diabetes-induced retinal injury via modulation of the Wnt/ b-catenin signaling pathway.

METHODS

Eighty-one rats were allocated into 6 groups (control, DR, DR + DKK1, DR + exosomes, DR + Wnt3a and DR + exosomes+Wnt3a). Evaluation of each group was via histopathological examination, assessment of gene and/or protein expression concerned with oxidative stress (SOD1, SOD2, Nox2, Nox4, iNOS), inflammation (TNF-α, ICAM-1, NF-κB) and angiogenesis (VEGF, VE-cadherin).

RESULTS

Results demonstrated that exosomes blocked the wnt/b-catenin pathway in diabetic retina concomitant with significant reduction of features of DR as shown by downregulation of retinal oxidants, upregulation of antioxidant enzymes, suppression of retinal inflammatory and angiogenic markers. These results were further confirmed by histopathological results, fundus examination and optical coherence tomography. Additionally, exosomes ameliorative effects abrogated wnt3a-triggered retinal injury in DR.

CONCLUSION

Collectively, these data demonstrated that exosomes ameliorated diabetes-induced retinal injury via suppressing Wnt/ b-catenin signaling with subsequent reduction of oxidative stress, inflammation and angiogenesis.

Role of oxidative stress in calcific aortic valve disease and its therapeutic implications

Calcific aortic valve disease (CAVD) is the end result of active cellular processes that lead to the progressive fibrosis and calcification of aortic valve leaflets. In western populations, CAVD is a significant cause of cardiovascular morbidity and mortality, and in the absence of effective drugs, it will likely represent an increasing disease burden as populations age. As there are currently no pharmacological therapies available for preventing, treating, or slowing the development of CAVD, understanding the mechanisms underlying the initiation and progression of the disease is important for identifying novel therapeutic targets. Recent evidence has emerged of an important causative role for reactive oxygen species (ROS)-mediated oxidative stress in the pathophysiology of CAVD, inducing the differentiation of valve interstitial cells into myofibroblasts and then osteoblasts. In this review, we focus on the roles and sources of ROS driving CAVD and consider their potential as novel therapeutic targets for this debilitating condition.

NADPH oxidase 4 contributes to TRPV4-mediated endothelium-dependent vasodilation in human arterioles by regulating protein phosphorylation of TRPV4 channels

Impaired endothelium-dependent vasodilation has been suggested to be a key component of coronary microvascular dysfunction (CMD). A better understanding of endothelial pathways involved in vasodilation in human arterioles may provide new insight into the mechanisms of CMD. The goal of this study is to investigate the role of TRPV4, NOX4, and their interaction in human arterioles and examine the underlying mechanisms. Arterioles were freshly isolated from adipose and heart tissues obtained from 71 patients without coronary artery disease, and vascular reactivity was studied by videomicroscopy. In human adipose arterioles (HAA), ACh-induced dilation was significantly reduced by TRPV4 inhibitor HC067047 and by NOX 1/4 inhibitor GKT137831, but GKT137831 did not further affect the dilation in the presence of TRPV4 inhibitors. GKT137831 also inhibited TRPV4 agonist GSK1016790A-induced dilation in HAA and human coronary arterioles (HCA). NOX4 transcripts and proteins were detected in endothelial cells of HAA and HCA. Using fura-2 imaging, GKT137831 significantly reduced GSK1016790A-induced Ca²⁺ influx in the primary culture of endothelial cells and TRPV4-WT-overexpressing human coronary artery endothelial cells (HCAEC). However, GKT137831 did not affect TRPV4-mediated Ca²⁺ influx in non-phosphorylatable TRPV4-S823A/S824A-overexpressing HCAEC. In addition, treatment of HCAEC with GKT137831 decreased the phosphorylation level of Ser824 in TRPV4. Finally, proximity ligation assay (PLA) revealed co-localization of NOX4 and TRPV4 proteins. In conclusion, both TRPV4 and NOX4 contribute to ACh-induced dilation in human arterioles from patients without coronary artery disease. NOX4 increases TRPV4 phosphorylation in endothelial cells, which in turn enhances TRPV4-mediated Ca²⁺ entry and subsequent endothelium-dependent dilation in human arterioles.

Cysteine oxidation of copper transporter CTR1 drives VEGFR2 signalling and angiogenesis

VEGFR2 (KDR/Flk1) signaling in endothelial cells (ECs) is essential for developmental and reparative angiogenesis. Reactive oxygen species (ROS) and copper (Cu) are also involved.in these processes. However, their inter-relationship is poorly understood. The role of endothelial Cu importer CTR1 in VEGFR2 signaling and angiogenesis in vivo is hitherto unknown. Here we show that CTR1 functions as a previously unrecognized redox sensor to promote angiogenesis in ECs. CTR1-depleted ECs showed reduced VEGF-induced VEGFR2 signaling and angiogenic responses. Mechanistically, CTR1 was rapidly sulfenylated at Cys189 in cytosolic C-terminus upon VEGF stimulation, which induced CTR1-VEGFR2 disulfide bond formation and their co-internalization to early endosomes, driving sustained VEGFR2 signaling. In vivo, EC-specific Ctr1-deficient mice or CRISPR/Cas9-generated “redox-dead” Cys to Ala Ctr1 knock-in mutant mice had impaired developmental and reparative angiogenesis. Thus, oxidation of CTR1 at Cys189 promotes VEGFR2 internalization and signaling to enhance angiogenesis. Our study uncovers an important mechanism for ROS sensing through CTR1 to drive neovascularization.

NOX4: a potential therapeutic target for pancreatic cancer and its mechanism

Nicotinamide adenine dinucleotide phosphate (NADPH) oxidase 4 (NOX4) is one of the seven isoforms of NOX family, which is upregulated in pancreatic cancer cell, mouse model of pancreatic cancer and human pancreatic cancer tissue. NOX4 is a constitutively active enzyme that primarily produces hydrogen peroxide, which exhibits completely different properties from other subtypes of NOX family. More importantly, recent studies illuminate that NOX4 promotes pancreatic cancer occurrence and development in different ways. This review summarizes the potential roles and its mechanism of NOX4 in pancreatic cancer and explores NOX4 as the potential therapeutic target in pancreatic cancer.

Nicotinamide Adenine Dinucleotide Phosphate Oxidases in Glucose Homeostasis and Diabetes-Related Endothelial Cell Dysfunction

Oxidative stress within the vascular endothelium, due to excess generation of reactive oxygen species (ROS), is thought to be fundamental to the initiation and progression of the cardiovascular complications of type 2 diabetes mellitus. The term ROS encompasses a variety of chemical species including superoxide anion (O₂^•-), hydroxyl radical (OH^-) and hydrogen peroxide (H₂O₂). While constitutive generation of low concentrations of ROS are indispensable for normal cellular function, excess O₂^•- can result in irreversible tissue damage. Excess ROS generation is catalysed by xanthine oxidase, uncoupled nitric oxide synthases, the mitochondrial electron transport chain and the nicotinamide adenine dinucleotide phosphate (NADPH) oxidases. Amongst enzymatic sources of O₂^•- the Nox2 isoform of NADPH oxidase is thought to be critical to the oxidative stress found in type 2 diabetes mellitus. In contrast, the transcriptionally regulated Nox4 isoform, which generates H₂O₂, may fulfil a protective role and contribute to normal glucose homeostasis. This review describes the key roles of Nox2 and Nox4, as well as Nox1 and Nox5, in glucose homeostasis, endothelial function and oxidative stress, with a key focus on how they are regulated in health, and dysregulated in type 2 diabetes mellitus.

Regulation of redox signaling in HIF-1-dependent tumor angiogenesis

Angiogenesis is the process of blood vessel growth. The angiogenic switch consists of new blood vessel formation that, in carcinogenesis, can lead to the transition from a harmless cluster of dormant cells to a large tumorigenic mass with metastatic potential. Hypoxia, that is, the scarcity of oxygen, is a hallmark of solid tumors to which they adapt by activating hypoxia-inducible factor-1 (HIF-1), a transcription factor triggering de novo angiogenesis. HIF-1 and the angiogenic molecules that are expressed upon its activation are modulated by redox status. Modulations of the redox environment can influence the angiogenesis signaling at different levels, thereby impinging on the angiogenic switch. This review provides a molecular overview of the redox-sensitive steps in angiogenic signaling, the main molecular players involved, and their crosstalk with the unfolded protein response. New classes of inhibitors of these modulators which might act as antiangiogenic drugs in cancer are also discussed.

Pyroptosis and Redox Balance in Kidney Diseases

Significance: Kidney diseases remain a worldwide public health problem resulting in millions of deaths each year; they are characterized by progressive destruction of renal function by sustained inflammation. Pyroptosis is a lytic type of programmed cell death involved in inflammation, as well as a key fibrotic mechanism that is critical in the development of kidney pathology. Pyroptosis is induced by the cleavage of Gasdermins by various caspases and is executed by the insertion of the N-terminal fragment of cleaved Gasdermins into the plasma membrane, creating oligomeric pores and allowing the release of diverse proinflammatory products into the extracellular space. Inflammasomes are multiprotein complexes leading to the activation of caspase-1, which will cleave Gasdermin D, releasing several proinflammatory cytokines; this results in the initiation and amplification of the inflammatory response. Recent Advances: The efficacy of Gasdermin D cleavage is reduced by a change in the redox balance. Recently, several studies have shown that the attenuation of reactive oxygen species (ROS) production induced by antioxidant pathways results in a reduction of renal pyroptosis. In this review, we discuss the role of pyroptosis in the pathogenesis of chronic kidney disease (CKD) and acute kidney disease; summarize the clinical outcomes and different molecular mechanisms leading to Gasdermin activation; and examine studies about the capacity of antioxidants, particularly Nrf2 activators, to ameliorate Gasdermin activity. Future Directions: We illustrate the potential influence of the deregulation of redox balance on inflammasome activity and pyroptosis as a novel therapeutic approach for the treatment of kidney diseases. Antioxid. Redox Signal. 35, 40-60.

PRMT4 drives post-ischemic angiogenesis via YB1/VEGF signaling

Angiogenesis is an integral process in many ischemic disorders, and vascular endothelial growth factor (VEGF) plays an important role in it. Protein arginine methyltransferase 4 (PRMT4), a member of the type I PRMT family, is involved in various biological activities, but its role in endothelial cell (EC) remains elusive. Here, we aimed to investigate the role of PRMT4 in ischemic angiogenesis and explore the possible underlying mechanism. We found that PRMT4 was upregulated in ischemic muscles, and VEGF treatment potentiated its expression in ECs. In vitro, adenovirus-mediated PRMT4 overexpression promoted, while its gene disruption inhibited, EC proliferation, migration, and tube formation. In an in vivo hindlimb ischemia model, forced expression of PRMT4 in ECs showed accelerated blood flow recovery and increased capillary density, whereas its knockdown exhibited the opposite effect. Mechanistically, PRMT4 activated the transcription of VEGF via the interaction with Y-box binding protein-1 (YB1), leading to accelerated angiogenesis. Interestingly, the loss of YB1 partially abolished PRMT4-mediated angiogenesis in vitro. Collectively, our data revealed that PRMT4 promoted angiogenesis through interacting with YB1 and the consequential VEGF upregulation, suggesting that PRMT4 may present as a potential therapeutic target in ischemic angiogenesis. KEY MESSAGES: •PRMT4 is induced by VEGF and upregulated in a hindlimb ischemia model. •PRMT4 promotes angiogenesis both in vitro and in vivo. •PRMT4 regulates VEGF expression through interacting with YB1. •YB1 knockdown retards PRMT4-mediated angiogenic effects in vitro.

The hydrogen-peroxide producing NADPH oxidase 4 does not limit neointima development after vascular injury in mice

Objective

The NADPH oxidase Nox4 is an important source of H₂O₂. Nox4-derived H₂O₂ limits vascular inflammation and promotes smooth muscle differentiation. On this basis, the role of Nox4 for restenosis development was determined in the mouse carotid artery injury model.

Methods and results

Genetic deletion of Nox4 by a tamoxifen-activated Cre-Lox-system did not impact on neointima formation in the carotid artery wire injury model. To understand this unexpected finding, time-resolved single-cell RNA-sequencing (scRNAseq) from injured carotid arteries of control mice and massive-analysis-of-cDNA-ends (MACE)-RNAseq from the neointima harvested by laser capture microdissection of control and Nox4 knockout mice was performed. This revealed that resting smooth muscle cells (SMCs) and fibroblasts exhibit high Nox4 expression, but that the proliferating de-differentiated SMCs, which give rise to the neointima, have low Nox4 expression. In line with this, the first weeks after injury, gene expression was unchanged between the carotid artery neointimas of control and Nox4 knockout mice.

Conclusion

Upon vascular injury, Nox4 expression is transiently lost in the cells which comprise the neointima. NADPH oxidase 4 therefore does not interfere with restenosis development after wire-induced vascular injury.

NADPH Oxidases (NOX): An Overview from Discovery, Molecular Mechanisms to Physiology and Pathology

The reactive oxygen species (ROS)-producing enzyme NADPH oxidase (NOX) was first identified in the membrane of phagocytic cells. For many years, its only known role was in immune defense, where its ROS production leads to the destruction of pathogens by the immune cells. NOX from phagocytes catalyzes, via one-electron trans-membrane transfer to molecular oxygen, the production of the superoxide anion. Over the years, six human homologs of the catalytic subunit of the phagocyte NADPH oxidase were found: NOX1, NOX3, NOX4, NOX5, DUOX1, and DUOX2. Together with the NOX2/gp91phox component present in the phagocyte NADPH oxidase assembly itself, the homologs are now referred to as the NOX family of NADPH oxidases. NOX are complex multidomain proteins with varying requirements for assembly with combinations of other proteins for activity. The recent structural insights acquired on both prokaryotic and eukaryotic NOX open new perspectives for the understanding of the molecular mechanisms inherent to NOX regulation and ROS production (superoxide or hydrogen peroxide). This new structural information will certainly inform new investigations of human disease. As specialized ROS producers, NOX enzymes participate in numerous crucial physiological processes, including host defense, the post-translational processing of proteins, cellular signaling, regulation of gene expression, and cell differentiation. These diversities of physiological context will be discussed in this review. We also discuss NOX misregulation, which can contribute to a wide range of severe pathologies, such as atherosclerosis, hypertension, diabetic nephropathy, lung fibrosis, cancer, or neurodegenerative diseases, giving this family of membrane proteins a strong therapeutic interest.

Cellular crosstalk in cardioprotection: Where and when do reactive oxygen species play a role?

A well-balanced intercellular communication between the different cells within the heart is vital for the maintenance of cardiac homeostasis and function. Despite remarkable advances on disease management and treatment, acute myocardial infarction remains the major cause of morbidity and mortality worldwide. Gold standard reperfusion strategies, namely primary percutaneous coronary intervention, are crucial to preserve heart function. However, reestablishment of blood flow and oxygen levels to the infarcted area are also associated with an accumulation of reactive oxygen species (ROS), leading to oxidative damage and cardiomyocyte death, a phenomenon termed myocardial reperfusion injury. In addition, ROS signaling has been demonstrated to regulate multiple biological pathways, including cell differentiation and intercellular communication. Given the importance of cell-cell crosstalk in the coordinated response after cell injury, in this review, we will discuss the impact of ROS in the different forms of inter- and intracellular communication, as well as the role of gap junctions, tunneling nanotubes and extracellular vesicles in the propagation of oxidative damage in cardiac diseases, particularly in the context of ischemia/reperfusion injury.

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.

Bach1 plays an important role in angiogenesis through regulation of oxidative stress

Bach1 is a known transcriptional repressor of the heme oxygenase-1 (HO-1) gene. The purpose of this study was to determine whether angiogenesis is accelerated by genetic ablation of Bach1 in a mouse ischemic hindlimb model. Hindlimb ischemia was surgically induced in wild-type (WT) mice, Bach1-deficient (Bach1-/-) mice, apolipoprotein E-deficient (ApoE-/-) mice, and Bach1/ApoE double-knockout (Bach1-/-/ApoE-/-) mice. Blood flow recovery after hindlimb ischemia showed significant improvement in Bach1-/- mice compared with that in WT mice. Bach1-/-/ApoE-/- mice showed significantly improved blood flow recovery compared with that in ApoE-/- mice to the level of that in WT mice. Migration of endothelial cells in ApoE-/- mice was significantly decreased compared with that in WT mice. Migration of endothelial cells significantly increased in Bach1-/-/ApoE-/- mice compared with that in ApoE-/- mice to the level of that in WT mice. The expression levels of HO-1, peroxisome proliferator-activated receptor γ co-activator-1α, angiopoietin 1, and fibroblast growth factor 2 in endothelial cells isolated from Bach1-/-/ApoE-/- mice were significantly higher than those in ApoE-/- mice. Oxidative stress assessed by anti-acrolein antibody staining in ischemic tissues and urinary 8-isoPGF2α excretion were significantly increased in ApoE-/- mice compared with those in WT and Bach1-/- mice. Oxidative stress was reduced in Bach1-/-/ApoE-/- mice compared with that in ApoE-/- mice. These findings suggest that genetic ablation of Bach1 plays an important role in ischemia-induced angiogenesis under the condition of increased oxidative stress. Bach1 could be a potential therapeutic target to reduce oxidative stress and potentially improve angiogenesis for patients with peripheral arterial disease.

Tubeimoside I promotes angiogenesis via activation of eNOS-VEGF signaling pathway

ETHNOPHARMACOLOGICAL RELEVANCE

Tubeimoside I (TBM) is a triterpenoid saponin purified from tubeimu (tuber of Bolbostemma paniculatum (Maxim.) Franquet). In traditional Chinese medicine, tubeimu had been used to treat acute mastitis, snake bites, detoxication, inflammatory diseases, and tumors for over 1000 years.

AIM OF THE STUDY

This study aimed to investigate whether TBM could promote angiogenesis and how to promote angiogenesis.

MATERIALS AND METHODS

In vivo, the pro-angiogenic effects of TBM were examined using the hindlimb ischemia model. After the ischemia operation, 1 mg/kg/day TBM was given via intraperitoneal injection for 28 days and the recovery of blood flow was monitored by Doppler scanner every 7 days. The capillary density in gastrocnemius muscle was detected by immunofluorescence. Expression of related proteins were determined by western blotting. In vitro, the pro-angiogenic effects of TBM on HUVECs were examined by Cell Counting Kit-8, scratch assay, endothelial cell tube formation assay and western blotting.

RESULTS

TBM improved recovery from hindlimb ischemia in C57BL/6 mice. TBM promoted endothelial cell viability, migration and tube formation in HUVECs. TBM could activate eNOS-VEGF signaling pathway by enhancing expression of eNOS. And TBM's pro-angiogenesis effects could be abolished by L-NAME (an inhibitor of eNOS).

CONCLUSIONS

TBM promoted angiogenesis via the activation of eNOS-VEGF signaling pathway and TBM could be a novel agent for therapeutic angiogenesis in ischemic diseases.

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.

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.

Post-Translational Modification of Cysteines: A Key Determinant of Endoplasmic Reticulum-Mitochondria Contacts (MERCs)

Cells must adjust their redox state to an ever-changing environment that could otherwise result in compromised homeostasis. An obvious way to adapt to changing redox conditions depends on cysteine post-translational modifications (PTMs) to adapt conformation, localization, interactions and catalytic activation of proteins. Such PTMs should occur preferentially in the proximity of oxidative stress sources. A particular concentration of these sources is found near membranes where the endoplasmic reticulum (ER) and the mitochondria interact on domains called MERCs (Mitochondria-Endoplasmic Reticulum Contacts). Here, fine inter-organelle communication controls metabolic homeostasis. MERCs achieve this goal through fluxes of Ca²⁺ ions and inter-organellar lipid exchange. Reactive oxygen species (ROS) that cause PTMs of mitochondria-associated membrane (MAM) proteins determine these intertwined MERC functions. Chronic changes of the pattern of these PTMs not only control physiological processes such as the circadian clock but could also lead to or worsen many human disorders such as cancer and neurodegenerative diseases.

Human in vitro vascularized micro-organ and micro-tumor models are reproducible organ-on-a-chip platforms for studies of anticancer drugs

Angiogenesis is a complex process that is required for development and tissue regeneration and it may be affected by many pathological conditions. Chemicals and drugs can impact formation and maintenance of the vascular networks; these effects may be both desirable (e.g., anti-cancer drugs) or unwanted (e.g., side effects of drugs). A number of in vivo and in vitro models exist for studies of angiogenesis and endothelial cell function, including organ-on-a-chip microphysiological systems. An arrayed organ-on-a-chip platform on a 96-well plate footprint that incorporates perfused microvessels, with and without tumors, was recently developed and it was shown that survival of the surrounding tissue was dependent on delivery of nutrients through the vessels. Here we describe a technology transfer of this complex microphysiological model between laboratories and demonstrate that reproducibility and robustness of these tissue chip-enabled experiments depend primarily on the source of the endothelial cells. The model was highly reproducible between laboratories and was used to demonstrate the advantages of the perfusable vascular networks for drug safety evaluation. As a proof-of-concept, we tested Fluorouracil (1-1,000 μM), Vincristine (1-1,000 nM), and Sorafenib (0.1-100 μM), in the perfusable and non-perfusable micro-organs, and in a colon cancer-containing micro-tumor model. Tissue chip experiments were compared to the traditional monolayer cultures of endothelial or tumor cells. These studies showed that human in vitro vascularized micro-organ and micro-tumor models are reproducible organ-on-a-chip platforms for studies of anticancer drugs. The data from the 3D models confirmed advantages of the physiological environment as compared to 2D cell cultures. We demonstrated how these models can be translated into practice by verifying that the endothelial cell source and passage are critical elements for establishing a perfusable model.

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.

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.

Methylation-dependent antioxidant-redox imbalance regulates hypertensive kidney injury in aging

The prevalence of hypertension increases with age, and oxidative stress is a major contributing factor to the pathogenesis of hypertension-induced kidney damage in aging. The nicotinamide adenine dinucleotide phosphate (NADPH) family is one of the major sources of reactive oxygen species (ROS) generation, and several NADPH oxidase isoforms are highly expressed in the kidney. Although epigenetic protein modification plays a role in organ injury, the methylation of the oxidant-antioxidant defense system and their role in hypertension-induced kidney damage in aging remains underexplored. The present study investigated the role of NADPH oxidase 4, superoxide dismutases (SODs), catalase, and NOS in Ang-II induced kidney damage in aging. Wild type (WT, C57BL/6J) mice aged 12-14 and 75-78 weeks were used and treated with or without Ang-II (1000 ng/kg/min) for 4 weeks with control mice receiving saline. Aged mice with or without Ang-II exhibited higher mean BP, lower renal blood flow, and decreased renal vascular density compared to young mice. While superoxide, 4-HNE, p22^phox, Nox4, iNOS were increased in the aged kidney, the expression of eNOS, MnSOD, CuSOD, catalase, Sirt1, and -3 as well as the ratio of GSH/GSSG, and activities of SODs and catalase were decreased compared to young control mice. The changes further deteriorated with Ang-II treatment. In Ang-II treated aged mice, the expressions of DNMTs were increased and associated with increased methylation of SODs, Sirt1, and Nox4. We conclude that hypermethylation of antioxidant enzymes in the aged kidney during hypertension worsens redox imbalance leading to kidney damage.

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.

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.

Redox basis of exercise physiology

Redox reactions control fundamental processes of human biology. Therefore, it is safe to assume that the responses and adaptations to exercise are, at least in part, mediated by redox reactions. In this review, we are trying to show that redox reactions are the basis of exercise physiology by outlining the redox signaling pathways that regulate four characteristic acute exercise-induced responses (muscle contractile function, glucose uptake, blood flow and bioenergetics) and four chronic exercise-induced adaptations (mitochondrial biogenesis, muscle hypertrophy, angiogenesis and redox homeostasis). Based on our analysis, we argue that redox regulation should be acknowledged as central to exercise physiology.