Targeting mitochondrial reactive oxygen species to modulate hypoxia-induced pulmonary hypertension

Hypoxia-induced pulmonary hypertension in adults and newborns: implications for drug development

Chronic hypoxia-induced pulmonary hypertension (CHPH) presents a complex challenge, characterized by escalating pulmonary vascular resistance and remodeling, threatening both newborns and adults with right heart failure. Despite advances in understanding the pathobiology of CHPH, its molecular intricacies remain elusive, particularly because of the multifaceted nature of arterial remodeling involving the adventitia, media, and intima. Cellular imbalance arises from hypoxia-induced mitochondrial disturbances and oxidative stress, reflecting the diversity in pulmonary hypertension (PH) pathology. In this review, we highlight prominent mechanisms causing CHPH in adults and newborns, and emerging therapeutic targets of potential pharmaceuticals.

Mitochondrial regulation of diabetic endothelial dysfunction: Pathophysiological links

Micro- and macrovascular complications frequently occur in patients with diabetes, with endothelial dysfunction playing a key role in the development and progression of the complications. For the early diagnosis and optimal treatment of vascular complications associated with diabetes, it is imperative to comprehend the cellular and molecular mechanisms governing the function of diabetic endothelial cells. Mitochondria function as crucial sensors of environmental and cellular stress regulating endothelial cell viability, structural integrity and function. Impaired mitochondrial quality control mechanisms and mitochondrial dysfunction are the main features of endothelial damage. Hence, targeted mitochondrial therapy is considered promising novel therapeutic options in vascular complications of diabetes. In this review, we focus on the mitochondrial functions in the vascular endothelial cells and the pathophysiological role of mitochondria in diabetic endothelial dysfunction, aiming to provide a reference for related drug development and clinical diagnosis and treatment.

Lactylation Modification in Cardiometabolic Disorders: Function and Mechanism

Cardiovascular disease (CVD) is recognized as the primary cause of mortality and morbidity on a global scale, and developing a clear treatment is an important tool for improving it. Cardiometabolic disorder (CMD) is a syndrome resulting from the combination of cardiovascular, endocrine, pro-thrombotic, and inflammatory health hazards. Due to their complex pathological mechanisms, there is a lack of effective diagnostic and treatment methods for cardiac metabolic disorders. Lactylation is a type of post-translational modification (PTM) that plays a regulatory role in various cellular physiological processes by inducing changes in the spatial conformation of proteins. Numerous studies have reported that lactylation modification plays a crucial role in post-translational modifications and is closely related to cardiac metabolic diseases. This article discusses the molecular biology of lactylation modifications and outlines the roles and mechanisms of lactylation modifications in cardiometabolic disorders, offering valuable insights for the diagnosis and treatment of such conditions.

Mitochondrial Dynamics in Pulmonary Hypertension

Mitochondria are essential organelles for energy production, calcium homeostasis, redox signaling, and other cellular responses involved in pulmonary vascular biology and disease processes. Mitochondrial homeostasis depends on a balance in mitochondrial fusion and fission (dynamics). Mitochondrial dynamics are regulated by a viable circadian clock. Hypoxia and nicotine exposure can cause dysfunctions in mitochondrial dynamics, increases in mitochondrial reactive oxygen species generation and calcium concentration, and decreases in ATP production. These mitochondrial changes contribute significantly to pulmonary vascular oxidative stress, inflammatory responses, contractile dysfunction, pathologic remodeling, and eventually pulmonary hypertension. In this review article, therefore, we primarily summarize recent advances in basic, translational, and clinical studies of circadian roles in mitochondrial metabolism in the pulmonary vasculature. This knowledge may not only be crucial to fully understanding the development of pulmonary hypertension, but also greatly help to create new therapeutic strategies for treating this devastating disease and other related pulmonary disorders.

Contribution of Mitochondrial Reactive Oxygen Species to Chronic Hypoxia-Induced Pulmonary Hypertension

Pulmonary hypertension (PH) resulting from chronic hypoxia (CH) occurs in patients with chronic obstructive pulmonary diseases, sleep apnea, and restrictive lung diseases, as well as in residents at high altitude. Previous studies from our group and others demonstrate a detrimental role of reactive oxygen species (ROS) in the pathogenesis of CH-induced PH, although the subcellular sources of ROS are not fully understood. We hypothesized that mitochondria-derived ROS (mtROS) contribute to enhanced vasoconstrictor reactivity and PH following CH. To test the hypothesis, we exposed rats to 4 weeks of hypobaric hypoxia (PB ≈ 380 mmHg), with control rats housed in ambient air (PB ≈ 630 mmHg). Chronic oral administration of the mitochondria-targeted antioxidant MitoQ attenuated CH-induced decreases in pulmonary artery (PA) acceleration time, increases in right ventricular systolic pressure, right ventricular hypertrophy, and pulmonary arterial remodeling. In addition, endothelium-intact PAs from CH rats exhibited a significantly greater basal tone compared to those from control animals, as was eliminated via MitoQ. CH also augmented the basal tone in endothelium-disrupted PAs, a response associated with increased mtROS production in primary PA smooth muscle cells (PASMCs) from CH rats. However, we further uncovered an effect of NO synthase inhibition with Nω-nitro-L-arginine (L-NNA) to unmask a potent endothelial vasoconstrictor influence that accentuates mtROS-dependent vasoconstriction following CH. This basal tone augmentation in the presence of L-NNA disappeared following combined endothelin A and B receptor blockade with BQ123 and BQ788. The effects of using CH to augment vasoconstriction and PASMC mtROS production in exogenous endothelin 1 (ET-1) were similarly prevented by MitoQ. We conclude that mtROS participate in the development of CH-induced PH. Furthermore, mtROS signaling in PASMCs is centrally involved in enhanced pulmonary arterial constriction following CH, a response potentiated by endogenous ET-1.

Environmental and behavioral regulation of HIF-mitochondria crosstalk

Reduced oxygen availability (hypoxia) can lead to cell and organ damage. Therefore, aerobic species depend on efficient mechanisms to counteract detrimental consequences of hypoxia. Hypoxia inducible factors (HIFs) and mitochondria are integral components of the cellular response to hypoxia and coordinate both distinct and highly intertwined adaptations. This leads to reduced dependence on oxygen, improved oxygen supply, maintained energy provision by metabolic remodeling and tapping into alternative pathways and increased resilience to hypoxic injuries. On one hand, many pathologies are associated with hypoxia and hypoxia can drive disease progression, for example in many cancer and neurological diseases. But on the other hand, controlled induction of hypoxia responses via HIFs and mitochondria can elicit profound health benefits and increase resilience. To tackle pathological hypoxia conditions or to apply health-promoting hypoxia exposures efficiently, cellular and systemic responses to hypoxia need to be well understood. Here we first summarize the well-established link between HIFs and mitochondria in orchestrating hypoxia-induced adaptations and then outline major environmental and behavioral modulators of their interaction that remain poorly understood.

Mitochondria in hypoxic pulmonary hypertension, roles and the potential targets

Mitochondria are the centrol hub for cellular energy metabolisms. They regulate fuel metabolism by oxygen levels, participate in physiological signaling pathways, and act as oxygen sensors. Once oxygen deprived, the fuel utilizations can be switched from mitochondrial oxidative phosphorylation to glycolysis for ATP production. Notably, mitochondria can also adapt to hypoxia by making various functional and phenotypes changes to meet the demanding of oxygen levels. Hypoxic pulmonary hypertension is a life-threatening disease, but its exact pathgenesis mechanism is still unclear and there is no effective treatment available until now. Ample of evidence indicated that mitochondria play key factor in the development of hypoxic pulmonary hypertension. By hypoxia-inducible factors, multiple cells sense and transmit hypoxia signals, which then control the expression of various metabolic genes. This activation of hypoxia-inducible factors considered associations with crosstalk between hypoxia and altered mitochondrial metabolism, which plays an important role in the development of hypoxic pulmonary hypertension. Here, we review the molecular mechanisms of how hypoxia affects mitochondrial function, including mitochondrial biosynthesis, reactive oxygen homeostasis, and mitochondrial dynamics, to explore the potential of improving mitochondrial function as a strategy for treating hypoxic pulmonary hypertension.

Mitochondrial Dysfunction in Pulmonary Hypertension

Pulmonary hypertension (PH) is a multi-etiological condition with a similar hemodynamic clinical sign and end result of right heart failure. Although its causes vary, a similar link across all the classifications is the presence of mitochondrial dysfunction. Mitochondria, as the powerhouse of the cells, hold a number of vital roles in maintaining normal cellular homeostasis, including the pulmonary vascular cells. As such, any disturbance in the normal functions of mitochondria could lead to major pathological consequences. The Warburg effect has been established as a major finding in PH conditions, but other mitochondria-related metabolic and oxidative stress factors have also been reported, making important contributions to the progression of pulmonary vascular remodeling that is commonly found in PH pathophysiology. In this review, we will discuss the role of the mitochondria in maintaining a normal vasculature, how it could be altered during pulmonary vascular remodeling, and the therapeutic options available that can treat its dysfunction.

Acquired disorders of mitochondrial metabolism and dynamics in pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) is an orphan disease of the cardiopulmonary unit that reflects an obstructive pulmonary vasculopathy and presents with hypertrophy, inflammation, fibrosis, and ultimately failure of the right ventricle (RVF). Despite treatment using pulmonary hypertension (PH)-targeted therapies, persistent functional impairment reduces the quality of life for people with PAH and death from RVF occurs in approximately 40% of patients within 5 years of diagnosis. PH-targeted therapeutics are primarily vasodilators and none, alone or in combination, are curative. This highlights a need to therapeutically explore molecular targets in other pathways that are involved in the pathogenesis of PAH. Several candidate pathways in PAH involve acquired mitochondrial dysfunction. These mitochondrial disorders include: 1) a shift in metabolism related to increased expression of pyruvate dehydrogenase kinase and pyruvate kinase, which together increase uncoupled glycolysis (Warburg metabolism); 2) disruption of oxygen-sensing related to increased expression of hypoxia-inducible factor 1α, resulting in a state of pseudohypoxia; 3) altered mitochondrial calcium homeostasis related to impaired function of the mitochondrial calcium uniporter complex, which elevates cytosolic calcium and reduces intramitochondrial calcium; and 4) abnormal mitochondrial dynamics related to increased expression of dynamin-related protein 1 and its binding partners, such as mitochondrial dynamics proteins of 49 kDa and 51 kDa, and depressed expression of mitofusin 2, resulting in increased mitotic fission. These acquired mitochondrial abnormalities increase proliferation and impair apoptosis in most pulmonary vascular cells (including endothelial cells, smooth muscle cells and fibroblasts). In the RV, Warburg metabolism and induction of glutaminolysis impairs bioenergetics and promotes hypokinesis, hypertrophy, and fibrosis. This review will explore our current knowledge of the causes and consequences of disordered mitochondrial function in PAH.

Specificity Protein 1-Mediated Promotion of CXCL12 Advances Endothelial Cell Metabolism and Proliferation in Pulmonary Hypertension

Pulmonary arterial hypertension (PAH) is a rare yet devastating and incurable disease with few treatment options. The underlying mechanisms of PAH appear to involve substantial cellular proliferation and vascular remodeling, causing right ventricular overload and eventual heart failure. Recent evidence suggests a significant seminal role of the pulmonary endothelium in the initiation and promotion of PAH. Our previous work identified elevated reactive oxygen species (ROS)-producing enzyme NADPH oxidase 1 (NOX1) in human pulmonary artery endothelial cells (HPAECs) of PAH patients promoting endothelial cell proliferation in vitro. In this study, we interrogated chemokine CXCL12's (aka SDF-1) role in EC proliferation under the control of NOX1 and specificity protein 1 (Sp1). We report here that NOX1 can drive hypoxia-induced endothelial CXCL12 expression via the transcription factor Sp1 leading to HPAEC proliferation and migration. Indeed, NOX1 drove hypoxia-induced Sp1 activation, along with an increased capacity of Sp1 to bind cognate promoter regions in the CXCL12 promoter. Sp1 activation induced elevated expression of CXCL12 in hypoxic HPAECs, supporting downstream induction of expression at the CXCL12 promoter via NOX1 activity. Pathological levels of CXCL12 mimicking those reported in human PAH patient serum restored EC proliferation impeded by specific NOX1 inhibitor. The translational relevance of our findings is highlighted by elevated NOX1 activity, Sp1 activation, and CXCL12 expression in explanted lung samples from PAH patients compared to non-PAH controls. Analysis of phosphofructokinase, glucose-6-phosphate dehydrogenase, and glutaminase activity revealed that CXCL12 induces glutamine and glucose metabolism, which are foundational to EC cell proliferation. Indeed, in explanted human PAH lungs, demonstrably higher glutaminase activity was detected compared to healthy controls. Finally, infusion of recombinant CXCL12 into healthy mice amplified pulmonary arterial pressure, right ventricle remodeling, and elevated glucose and glutamine metabolism. Together these data suggest a central role for a novel NOX1-Sp1-CXCL12 pathway in mediating PAH phenotype in the lung endothelium.

PGC-1α activity and mitochondrial dysfunction in preterm infants

Extremely low gestational age neonates (ELGANs) are born in a relatively hyperoxic environment with weak antioxidant defenses, placing them at high risk for mitochondrial dysfunction affecting multiple organ systems including the nervous, respiratory, ocular, and gastrointestinal systems. The brain and lungs are highly affected by mitochondrial dysfunction and dysregulation in the neonate, causing white matter injury (WMI) and bronchopulmonary dysplasia (BPD), respectively. Adequate mitochondrial function is important in providing sufficient energy for organ development as it relates to alveolarization and axonal myelination and decreasing oxidative stress via reactive oxygen species (ROS) and reactive nitrogen species (RNS) detoxification. Peroxisome proliferator-activated receptor gamma coactivator-1 alpha (PGC-1α) is a master regulator of mitochondrial biogenesis and function. Since mitochondrial dysfunction is at the root of WMI and BPD pathobiology, exploring therapies that can regulate PGC-1α activity may be beneficial. This review article describes several promising therapeutic agents that can mitigate mitochondrial dysfunction through direct and indirect activation and upregulation of the PGC-1α pathway. Metformin, resveratrol, omega 3 fatty acids, montelukast, L-citrulline, and adiponectin are promising candidates that require further pre-clinical and clinical studies to understand their efficacy in decreasing the burden of disease from WMI and BPD in preterm infants.

Mitochondrial Regulation of the Hypoxia-Inducible Factor in the Development of Pulmonary Hypertension

Pulmonary hypertension (PH) is a severe progressive lung disorder characterized by pulmonary vasoconstriction and vascular remodeling, culminating in right-sided heart failure and increased mortality. Data from animal models and human subjects demonstrated that hypoxia-inducible factor (HIF)-related signaling is essential in the progression of PH. This review summarizes the regulatory pathways and mechanisms of HIF-mediated signaling, emphasizing the role of mitochondria in HIF regulation and PH pathogenesis. We also try to determine the potential to therapeutically target the components of the HIF system for the management of PH.

Mitochondria-Targeted Compounds to Assess and Improve Human Sperm Function

Significance: Currently 10%-15% of couples in reproductive age face infertility issues. More importantly, male factor contributes to 50% of these cases (either alone or in combination with female causes). Among various reasons, impaired sperm function is the main cause for male infertility. Furthermore, mitochondrial dysfunction and oxidative stress due to increased reactive oxygen species (ROS) production, particularly of mitochondrial origin, are believed to be the main contributors. Recent Advances: Mitochondrial dysfunction, particularly due to increased ROS production, has often been linked to impaired sperm function/quality. For decades, different methods and approaches have been developed to assess mitochondrial features that might correlate with sperm functionality. This connection is now completely accepted, with mitochondrial functionality assessment used more commonly as a readout of sperm functionality. More recently, mitochondria-targeted compounds are on the frontline for both assessment and therapeutic approaches. Critical Issues: In this review, we summarize the current methods for assessing key mitochondrial parameters known to reflect sperm quality as well as therapeutic strategies using mitochondria-targeted antioxidants aiming to improve sperm function in various situations, particularly after sperm cryopreservation. Future Directions: Although more systematic research is needed, mitochondria-targeted compounds definitely represent a promising tool to assess as well as to protect and improve sperm function. Antioxid. Redox Signal. 37, 451-480.

Impact of Zinc on Oxidative Signaling Pathways in the Development of Pulmonary Vasoconstriction Induced by Hypobaric Hypoxia

Hypobaric hypoxia is a condition that occurs at high altitudes (>2500 m) where the partial pressure of gases, particularly oxygen (PO2), decreases. This condition triggers several physiological and molecular responses. One of the principal responses is pulmonary vascular contraction, which seeks to optimize gas exchange under this condition, known as hypoxic pulmonary vasoconstriction (HPV); however, when this physiological response is exacerbated, it contributes to the development of high-altitude pulmonary hypertension (HAPH). Increased levels of zinc (Zn2+) and oxidative stress (known as the “ROS hypothesis”) have been demonstrated in the vasoconstriction process. Therefore, the aim of this review is to determine the relationship between molecular pathways associated with altered Zn2+ levels and oxidative stress in HPV in hypobaric hypoxic conditions. The results indicate an increased level of Zn2+, which is related to increasing mitochondrial ROS (mtROS), alterations in nitric oxide (NO), metallothionein (MT), zinc-regulated, iron-regulated transporter-like protein (ZIP), and nicotinamide adenine dinucleotide phosphate (NADPH) oxidase-induced protein kinase C epsilon (PKCε) activation in the development of HPV. In conclusion, there is an association between elevated Zn2+ levels and oxidative stress in HPV under different models of hypoxia, which contribute to understanding the molecular mechanism involved in HPV to prevent the development of HAPH.

Melatonin Attenuates Dasatinib-Aggravated Hypoxic Pulmonary Hypertension via Inhibiting Pulmonary Vascular Remodeling

Dasatinib treatment is approved as first-line therapy for chronic myeloid leukemia. However, pulmonary hypertension (PH) is a highly morbid and often fatal side-effect of dasatinib, characterized by progressive pulmonary vascular remodeling. Melatonin exerts strong antioxidant capacity against the progression of cardiovascular system diseases. The present work aimed to investigate the effect of melatonin on dasatinib-aggravated hypoxic PH and explore its possible mechanisms. Dasatinib-aggravated rat experimental model of hypoxic PH was established by utilizing dasatinib under hypoxia. The results indicated that melatonin could attenuate dasatinib-aggravated pulmonary pressure and vascular remodeling in rats under hypoxia. Additionally, melatonin attenuated the activity of XO, the content of MDA, the expression of NOX4, and elevated the activity of CAT, GPx, and SOD, the expression of SOD2, which were caused by dasatinib under hypoxia. In vitro, dasatinib led to decreased LDH activity and production of NO in human pulmonary microvascular endothelial cells (HPMECs), moreover increased generation of ROS, and expression of NOX4 both in HPMECs and primary rat pulmonary arterial smooth muscle cells (PASMCs) under hypoxia. Dasatinib up-regulated the expression of cleaved caspase-3 and the ratio of apoptotic cells in HPMECs, and also elevated the percentage of S phase and the expression of Cyclin D1 in primary PASMCs under hypoxia. Melatonin ameliorated dasatinib-aggravated oxidative damage and apoptosis in HPMECs, meanwhile reduced oxidative stress level, proliferation, and repressed the stability of HIF1-α protein in PASMCs under hypoxia. In conclusion, melatonin significantly attenuates dasatinib-aggravated hypoxic PH by inhibiting pulmonary vascular remodeling in rats. The possible mechanisms involved protecting endothelial cells and inhibiting abnormal proliferation of smooth muscle cells. Our findings may suggest that melatonin has potential clinical value as a therapeutic approach to alleviate dasatinib-aggravated hypoxic PH.

Effect of Environmental Stressors, Xenobiotics, and Oxidative Stress on Male Reproductive and Sexual Health

This article examines the environmental factor-induced oxidative stress (OS) and their effects on male reproductive and sexual health. There are several factors that induce OS, i.e. radition, metal contamination, xenobiotic compounds, and cigarette smoke and lead to cause toxicity in the cells through metabolic or bioenergetic processes. These environmental factors may produce free radicals and enhance the reactive oxygen species (ROS). Free radicals are molecules that include oxygen and disbalance the amount of electrons that can create major chemical chains in the body and cause oxidation. Oxidative damage to cells may impair male fertility and lead to abnormal embryonic development. Moreover, it does not only cause a vast number of health issues such as ageing, cancer, atherosclerosis, insulin resistance, diabetes mellitus, cardiovascular diseases, ischemia-reperfusion injury, and neurodegenerative disorders but also decreases the motility of spermatozoa while increasing sperm DNA damage, impairing sperm mitochondrial membrane lipids and protein kinases. This chapter mainly focuses on the environmental stressors with further discussion on the mechanisms causing congenital impairments due to poor sexual health and transmitting altered signal transduction pathways in male gonadal tissues.

Identification of Hypoxia Induced Metabolism Associated Genes in Pulmonary Hypertension

Objective: Pulmonary hypertension (PH) associated with hypoxia and lung disease (Group 3) is the second most common form of PH and associated with increased morbidity and mortality. This study was aimed to identify hypoxia induced metabolism associated genes (MAGs) for better understanding of hypoxic PH.

Methods: Rat pulmonary arterial smooth muscle cells (PASMCs) were isolated and cultured in normoxic or hypoxic condition for 24 h. Cells were harvested for liquid chromatography-mass spectrometry analysis. Functional annotation of distinguishing metabolites was performed using Metaboanalyst. Top 10 enriched metabolite sets were selected for the identification of metabolism associated genes (MAGs) with a relevance score >8 in Genecards. Transcriptomic data from lungs of hypoxic PH in mice/rats or of PH patients were accessed from Gene Expression Omnibus (GEO) database or open-access online platform. Connectivity Map analysis was performed to identify potential compounds to reverse the metabolism associated gene profile under hypoxia stress. The construction and module analysis of the protein-protein interaction (PPI) network was performed. Hub genes were then identified and used to generate LASSO model to determine its accuracy to predict occurrence of PH.

Results: A total of 36 altered metabolites and 1,259 unique MAGs were identified in rat PASMCs under hypoxia. 38 differentially expressed MAGs in mouse lungs of hypoxic PH were revealed, with enrichment in multi-pathways including regulation of glucose metabolic process, which might be reversed by drugs such as blebbistatin. 5 differentially expressed MAGs were displayed in SMCs of Sugen 5416/hypoxia induced PH rats at the single cell resolution. Furthermore, 6 hub genes (Cat, Ephx1, Gpx3, Gstm4, Gstm5, and Gsto1) out of 42 unique hypoxia induced MAGs were identified. Higher Cat, Ephx1 and lower Gsto1 were displayed in mouse lungs under hypoxia (all p < 0.05), in consistent with the alteration in lungs of PH patients. The hub gene-based LASSO model can predict the occurrence of PH (AUC = 0.90).

Conclusion: Our findings revealed six hypoxia-induced metabolism associated hub genes, and shed some light on the molecular mechanism and therapeutic targets in hypoxic PH.

Oxidative Stress, Kinase Activation, and Inflammatory Pathways Involved in Effects on Smooth Muscle Cells During Pulmonary Artery Hypertension Under Hypobaric Hypoxia Exposure

High-altitude exposure results in hypobaric hypoxia, which affects organisms by activating several mechanisms at the physiological, cellular, and molecular levels and triggering the development of several pathologies. One such pathology is high-altitude pulmonary hypertension (HAPH), which is initiated through hypoxic pulmonary vasoconstriction to distribute blood to more adequately ventilated areas of the lungs. Importantly, all layers of the pulmonary artery (adventitia, smooth muscle, and endothelium) contribute to or are involved in the development of HAPH. However, the principal action sites of HAPH are pulmonary artery smooth muscle cells (PASMCs), which interact with several extracellular and intracellular molecules and participate in mechanisms leading to proliferation, apoptosis, and fibrosis. This review summarizes the alterations in molecular pathways related to oxidative stress, inflammation, kinase activation, and other processes that occur in PASMCs during pulmonary hypertension under hypobaric hypoxia and proposes updates to pharmacological treatments to mitigate the pathological changes in PASMCs under such conditions. In general, PASMCs exposed to hypobaric hypoxia undergo oxidative stress mediated by Nox4, inflammation mediated by increases in interleukin-6 levels and inflammatory cell infiltration, and activation of the protein kinase ERK1/2, which lead to the proliferation of PASMCs and contribute to the development of hypobaric hypoxia-induced pulmonary hypertension.

Fluorescent probes for the detection of reactive oxygen species in human spermatozoa

Reactive oxygen species (ROS) production is a by-product of mitochondrial activity and is necessary for the acquisition of the capacitated state, a requirement for functional spermatozoa. However, an increase in oxidative stress, due to an abnormal production of ROS, has been shown to be related to loss of sperm function, highlighting the importance of an accurate detection of sperm ROS, given the specific nature of this cell. In this work, we tested a variety of commercially available fluorescent probes to detect ROS and reactive nitrogen species (RNS) in human sperm, to define their specificity. Using both flow cytometry (FC) and fluorescence microscopy (FM), we confirmed that MitoSOX™ Red and dihydroethidium (DHE) detect superoxide anion (as determined using antimycin A as a positive control), while DAF-2A detects reactive nitrogen species (namely, nitric oxide). For the first time, we also report that RedoxSensor™ Red CC-1, CellROX^® Orange Reagent, and MitoPY1 seem to be mostly sensitive to hydrogen peroxide, but not superoxide. Furthermore, mean fluorescence intensity (and not percentage of labeled cells) is the main parameter that can be reproducibly monitored using this type of methodology.

Hypoxia and the integrated stress response promote pulmonary hypertension and preeclampsia: Implications in drug development

Chronic hypoxia is a common cause of pulmonary hypertension, preeclampsia, and intrauterine growth restriction (IUGR). The molecular mechanisms underlying these diseases are not completely understood. Chronic hypoxia may induce the generation of reactive oxygen species (ROS) in mitochondria, promote endoplasmic reticulum (ER) stress, and result in the integrated stress response (ISR) in the pulmonary artery and uteroplacental tissues. Numerous studies have implicated hypoxia-inducible factors (HIFs), oxidative stress, and ER stress/unfolded protein response (UPR) in the development of pulmonary hypertension, preeclampsia and IUGR. This review highlights the roles of HIFs, mitochondria-derived ROS and UPR, as well as their interplay, in the pathogenesis of pulmonary hypertension and preeclampsia, and their implications in drug development.

Cellular and Molecular Processes in Pulmonary Hypertension

Pulmonary hypertension (PH) is a progressive lung disease characterized by persistent pulmonary vasoconstriction. Another well-recognized characteristic of PH is the muscularization of peripheral pulmonary arteries. This pulmonary vasoremodeling manifests in medial hypertrophy/hyperplasia of smooth muscle cells (SMCs) with possible neointimal formation. The underlying molecular processes for these two major vascular responses remain not fully understood. On the other hand, a series of very recent studies have shown that the increased reactive oxygen species (ROS) seems to be an important player in mediating pulmonary vasoconstriction and vasoremodeling, thereby leading to PH. Mitochondria are a primary site for ROS production in pulmonary artery (PA) SMCs, which subsequently activate NADPH oxidase to induce further ROS generation, i.e., ROS-induced ROS generation. ROS control the activity of multiple ion channels to induce intracellular Ca²⁺ release and extracellular Ca²⁺ influx (ROS-induced Ca²⁺ release and influx) to cause PH. ROS and Ca²⁺ signaling may synergistically trigger an inflammatory cascade to implicate in PH. Accordingly, this paper explores the important roles of ROS, Ca²⁺, and inflammatory signaling in the development of PH, including their reciprocal interactions, key molecules, and possible therapeutic targets.

Riding the tiger - physiological and pathological effects of superoxide and hydrogen peroxide generated in the mitochondrial matrix

Elevated mitochondrial matrix superoxide and/or hydrogen peroxide concentrations drive a wide range of physiological responses and pathologies. Concentrations of superoxide and hydrogen peroxide in the mitochondrial matrix are set mainly by rates of production, the activities of superoxide dismutase-2 (SOD2) and peroxiredoxin-3 (PRDX3), and by diffusion of hydrogen peroxide to the cytosol. These considerations can be used to generate criteria for assessing whether changes in matrix superoxide or hydrogen peroxide are both necessary and sufficient to drive redox signaling and pathology: is a phenotype affected by suppressing superoxide and hydrogen peroxide production; by manipulating the levels of SOD2, PRDX3 or mitochondria-targeted catalase; and by adding mitochondria-targeted SOD/catalase mimetics or mitochondria-targeted antioxidants? Is the pathology associated with variants in SOD2 and PRDX3 genes? Filtering the large literature on mitochondrial redox signaling using these criteria highlights considerable evidence that mitochondrial superoxide and hydrogen peroxide drive physiological responses involved in cellular stress management, including apoptosis, autophagy, propagation of endoplasmic reticulum stress, cellular senescence, HIF1α signaling, and immune responses. They also affect cell proliferation, migration, differentiation, and the cell cycle. Filtering the huge literature on pathologies highlights strong experimental evidence that 30-40 pathologies may be driven by mitochondrial matrix superoxide or hydrogen peroxide. These can be grouped into overlapping and interacting categories: metabolic, cardiovascular, inflammatory, and neurological diseases; cancer; ischemia/reperfusion injury; aging and its diseases; external insults, and genetic diseases. Understanding the involvement of mitochondrial matrix superoxide and hydrogen peroxide concentrations in these diseases can facilitate the rational development of appropriate therapies.

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.

Enhanced Expression of Catalase in Mitochondria Modulates NF-κB-Dependent Lung Inflammation through Alteration of Metabolic Activity in Macrophages

NF-κB is a reduction-oxidation-sensitive transcription factor that plays a key role in regulating the immune response. In these studies, we intended to investigate the role of mitochondrial-derived reactive oxygen species in regulating NF-κB activation by studying transgenic mice that overexpress mitochondrial-targeted human catalase (mCAT). We treated wild-type (WT) and mCAT mice with intratracheal instillation of Escherichia coli LPS and found that mCAT mice had exaggerated NF-κB activation in the lungs, increased neutrophilic alveolitis, and greater lung inflammation/injury compared with WT mice. Additional studies using bone marrow chimeras revealed that this hyperinflammatory phenotype was mediated by immune/inflammatory cells. Mechanistic studies using bone marrow-derived macrophages (BMDMs) showed that LPS treatment induced a sustained increase in NF-κB activation and expression of NF-κB-dependent inflammatory mediators in mCAT BMDMs compared with WT BMDMs. Further investigations showed that cytoplasmic, but not mitochondrial, hydrogen peroxide levels were reduced in LPS-treated mCAT BMDMs. However, mCAT macrophages exhibited increased glycolytic and oxidative metabolism, coupled with increased ATP production and an increased intracellular NADH/NAD+ ratio compared with BMDMs from WT mice. Treatment of BMDMs with lactate increased the intracellular NADH/NAD+ ratio and upregulated NF-κB activation after LPS treatment, whereas treatment with a potent inhibitor of the mitochondrial pyruvate carrier (UK5099) decreased the NADH/NAD+ ratio and reduced NF-κB activation. Taken together, these findings point to an increased availability of reducing equivalents in the form of NADH as an important mechanism by which metabolic activity modulates inflammatory signaling through the NF-κB pathway.

Reactive oxygen species in renal vascular function

Reactive oxygen species (ROS) are produced by the aerobic metabolism. The imbalance between production of ROS and antioxidant defence in any cell compartment is associated with cell damage and may play an important role in the pathogenesis of renal disease. NADPH oxidase (NOX) family is the major ROS source in the vasculature and modulates renal perfusion. Upregulation of Ang II and adenosine activates NOX via AT1R and A1R in renal microvessels, leading to superoxide production. Oxidative stress in the kidney prompts renal vascular remodelling and increases preglomerular resistance. These are key elements in hypertension, acute and chronic kidney injury, as well as diabetic nephropathy. Renal afferent arterioles (Af), the primary resistance vessel in the kidney, fine tune renal hemodynamics and impact on blood pressure. Vice versa, ROS increase hypertension and diabetes, resulting in upregulation of Af vasoconstriction, enhancement of myogenic responses and change of tubuloglomerular feedback (TGF), which further promotes hypertension and diabetic nephropathy. In the following, we highlight oxidative stress in the function and dysfunction of renal hemodynamics. The renal microcirculatory alterations brought about by ROS importantly contribute to the pathophysiology of kidney injury, hypertension and diabetes.

Rats with a Human Mutation of NFU1 Develop Pulmonary Hypertension

NFU1 is a mitochondrial protein that is involved in the biosynthesis of iron-sulfur clusters, and its genetic modification is associated with disorders of mitochondrial energy metabolism. Patients with autosomal-recessive inheritance of the NFU1 mutation G208C have reduced activity of the respiratory chain Complex II and decreased levels of lipoic-acid-dependent enzymes, and develop pulmonary arterial hypertension (PAH) in ∼70% of cases. We investigated whether rats with a human mutation in NFU1 are also predisposed to PAH development. A point mutation in rat NFU1^G206C (human G208C) was introduced through CRISPR/Cas9 genome editing. Hemodynamic data, tissue samples, and fresh mitochondria were collected and analyzed. NFU1^G206C rats showed increased right ventricular pressure, right ventricular hypertrophy, and high levels of pulmonary artery remodeling. Computed tomography and angiography of the pulmonary vasculature indicated severe angioobliterative changes in NFU1^G206C rats. Importantly, the penetrance of the PAH phenotype was found to be more prevalent in females than in males, replicating the established sex difference among patients with PAH. Male and female homozygote rats exhibited decreased expression and activity of mitochondrial Complex II, and markedly decreased pyruvate dehydrogenase activity and lipoate binding. The limited development of PAH in males correlated with the preserved levels of oligomeric NFU1, increased expression of ISCU (an alternative branch of the iron-sulfur assembly system), and increased complex IV activity. Thus, the male sex has additional plasticity to overcome the iron-sulfur cluster deficiency. Our work describes a novel, humanized rat model of NFU1 deficiency that showed mitochondrial dysfunction similar to that observed in patients and developed PAH with the same sex dimorphism.

Bypassing mitochondrial complex III using alternative oxidase inhibits acute pulmonary oxygen sensing

Mitochondria play an important role in sensing both acute and chronic hypoxia in the pulmonary vasculature, but their primary oxygen-sensing mechanism and contribution to stabilization of the hypoxia-inducible factor (HIF) remains elusive. Alteration of the mitochondrial electron flux and increased superoxide release from complex III has been proposed as an essential trigger for hypoxic pulmonary vasoconstriction (HPV). We used mice expressing a tunicate alternative oxidase, AOX, which maintains electron flux when respiratory complexes III and/or IV are inhibited. Respiratory restoration by AOX prevented acute HPV and hypoxic responses of pulmonary arterial smooth muscle cells (PASMC), acute hypoxia-induced redox changes of NADH and cytochrome c, and superoxide production. In contrast, AOX did not affect the development of chronic hypoxia-induced pulmonary hypertension and HIF-1α stabilization. These results indicate that distal inhibition of the mitochondrial electron transport chain in PASMC is an essential initial step for acute but not chronic oxygen sensing.

Antioxidant-Conjugated Peptide Attenuated Metabolic Reprogramming in Pulmonary Hypertension

Pulmonary arterial hypertension (PAH) is a chronic cardiopulmonary disorder instigated by pulmonary vascular cell proliferation. Activation of Akt was previously reported to promote vascular remodeling. Also, the irreversible nitration of Y350 residue in Akt results in its activation. NitroAkt was increased in PAH patients and the SU5416/Hypoxia (SU/Hx) PAH model. This study investigated whether the prevention of Akt nitration in PAH by Akt targeted nitroxide-conjugated peptide (NP) could reverse vascular remodeling and metabolic reprogramming. Treatment of the SU/Hx model with NP significantly decreased nitration of Akt in lungs, attenuated right ventricle (RV) hypertrophy, and reduced RV systolic pressure. In the PAH model, Akt-nitration induces glycolysis by activation of the glucose transporter Glut4 and lactate dehydrogenase-A (LDHA). Decreased G6PD and increased GSK3β in SU/Hx additionally shunted intracellular glucose via glycolysis. The increased glycolytic rate upregulated anaplerosis due to activation of pyruvate carboxylase in a nitroAkt-dependent manner. NP treatment resolved glycolytic switch and activated collateral pentose phosphate and glycogenesis pathways. Prevention of Akt-nitration significantly controlled pyruvate in oxidative phosphorylation by decreasing lactate and increasing pyruvate dehydrogenases activities. Histopathological studies showed significantly reduced pulmonary vascular proliferation. Based on our current observation, preventing Akt-nitration by using an Akt-targeted nitroxide-conjugated peptide could be a useful treatment option for controlling vascular proliferation in PAH.

NADPH oxidase in the vasculature: Expression, regulation and signalling pathways; role in normal cardiovascular physiology and its dysregulation in hypertension

The last 20-25 years have seen an explosion of interest in the role of NADPH oxidase (NOX) in cardiovascular function and disease. In vascular smooth muscle and endothelium, NOX generates reactive oxygen species (ROS) that act as second messengers, contributing to the control of normal vascular function. NOX activity is altered in response to a variety of stimuli, including G-protein coupled receptor agonists, growth-factors, perfusion pressure, flow and hypoxia. NOX-derived ROS are involved in smooth muscle constriction, endothelium-dependent relaxation and smooth muscle growth, proliferation and migration, thus contributing to the fine-tuning of blood flow, arterial wall thickness and vascular resistance. Through reversible oxidative modification of target proteins, ROS regulate the activity of protein tyrosine phosphatases, kinases, G proteins, ion channels, cytoskeletal proteins and transcription factors. There is now considerable, but somewhat contradictory evidence that NOX contributes to the pathogenesis of hypertension through oxidative stress. Specific NOX isoforms have been implicated in endothelial dysfunction, hyper-contractility and vascular remodelling in various animal models of hypertension, pulmonary hypertension and pulmonary arterial hypertension, but also have potential protective effects, particularly NOX4. This review explores the multiplicity of NOX function in the healthy vasculature and the evidence for and against targeting NOX for antihypertensive therapy.

Redox Biology of Peroxisome Proliferator-Activated Receptor-γ in Pulmonary Hypertension

Significance: Peroxisome proliferator-activated receptor-gamma (PPARγ) maintains pulmonary vascular health through coordination of antioxidant defense systems, inflammation, and cellular metabolism. Insufficient PPARγ contributes to pulmonary hypertension (PH) pathogenesis, whereas therapeutic restoration of PPARγ activity attenuates PH in preclinical models. Recent Advances: Numerous studies in the past decade have elucidated the complex mechanisms by which PPARγ in the pulmonary vasculature and right ventricle (RV) protects against PH. The scope of PPARγ-interconnected pathways continues to expand and includes induction of antioxidant genes, transrepression of inflammatory signaling, regulation of mitochondrial biogenesis and bioenergetic integrity, control of cell cycle and proliferation, and regulation of vascular tone through interactions with nitric oxide and endogenous vasoactive molecules. Furthermore, PPARγ interacts with an extensive regulatory network of transcription factors and microRNAs leading to broad impact on cell signaling. Critical Issues: Abundant evidence suggests that targeting PPARγ exerts diverse salutary effects in PH and represents a novel and potentially translatable therapeutic strategy. However, progress has been slowed by an incomplete understanding of how specific PPARγ pathways are critically disrupted across PH disease subtypes and lack of optimal pharmacological ligands. Future Directions: Recent studies indicate that ligand-induced post-translational modifications of the PPARγ receptor differentially induce therapeutic benefits versus adverse side effects of PPARγ receptor activation. Strategies to selectively target PPARγ activity in diseased cells of pulmonary circulation and RV, coupled with development of ligands designed to specifically regulate post-translational PPARγ modifications, may unlock the full therapeutic potential of this versatile master transcriptional and metabolic regulator in PH.

Redox Regulation of Ion Channels and Receptors in Pulmonary Hypertension

Significance: Pulmonary hypertension (PH) is characterized by elevated vascular resistance due to vasoconstriction and remodeling of the normally low-pressure pulmonary vasculature. Redox stress contributes to the pathophysiology of this disease by altering the regulation and activity of membrane receptors, K+ channels, and intracellular Ca2+ homeostasis. Recent Advances: Antioxidant therapies have had limited success in treating PH, leading to a growing appreciation that reductive stress, in addition to oxidative stress, plays a role in metabolic and cell signaling dysfunction in pulmonary vascular cells. Reactive oxygen species generation from mitochondria and NADPH oxidases has substantial effects on K+ conductance and membrane potential, and both receptor-operated and store-operated Ca2+ entry. Critical Issues: Some specific redox changes resulting from oxidation, S-nitrosylation, and S-glutathionylation are known to modulate membrane receptor and ion channel activity in PH. However, many sites of regulation that have been elucidated in nonpulmonary cell types have not been tested in the pulmonary vasculature, and context-specific molecular mechanisms are lacking. Future Directions: Here, we review what is known about redox regulation of membrane receptors and ion channels in PH. Further investigation of the mechanisms involved is needed to better understand the etiology of PH and develop better targeted treatment strategies.

Mitochondrial Dysfunction: Metabolic Drivers of Pulmonary Hypertension

Significance: Pulmonary hypertension (PH) is a progressive disease characterized by pulmonary vascular remodeling and lung vasculopathy. The disease displays progressive dyspnea, pulmonary artery uncoupling and right ventricular (RV) dysfunction. The overall survival rate is ranging from 28-72%. Recent Advances: The molecular events that promote the development of PH are complex and incompletely understood. Metabolic impairment has been proposed to contribute to the pathophysiology of PH with evidence for mitochondrial dysfunction involving the electron transport chain proteins, antioxidant enzymes, apoptosis regulators, and mitochondrial quality control. Critical Issues: It is vital to characterize the mechanisms by which mitochondrial dysfunction contribute to PH pathogenesis. This review focuses on the currently available publications that supports mitochondrial mechanisms in PH pathophysiology. Future Directions: Further studies of these metabolic mitochondrial alterations in PH could be viable targets of diagnostic and therapeutic intervention.

Expression of antioxidant genes in broiler chickens fed nettle (Urtica dioica) and its link with pulmonary hypertension

Nettle (Urtica dioica) contains a wide range of chemical constituents that confer a strong antioxidant capacity to the plant. The present study was to investigate the antioxidant gene expression and pulmonary hypertensive responses of broiler chickens to U. dioica. A total of 240 one-d-old broilers (Ross 308) were randomly assigned to 4 dietary levels of U. dioica (0, 0.5%, 1% and 1.5%). Birds were reared for 6 wk in a high altitude region (2,100 m). The results showed a significant relative overexpression (target gene/β-actin as the arbitrary unit) of catalase (CAT) and superoxide dismutase 1 (SOD1) in the liver and lung of the chickens fed U. dioica. Lipid peroxidation was significantly suppressed, as reflected in reduced circulatory concentrations of malondialdehyde (MDA) in the birds fed U. dioica. These birds also had significantly (P < 0.05) higher serum nitric oxide (NO) concentrations than those in the control group. Feeding U. dioica at 1% and 1.5% also attenuated the right ventricular hypertrophy (reflected in the lower right to total ventricular weight ratio), which was associated with a significant lower rate of mortality from pulmonary hypertension syndrome. Feeding U. dioica led to an upregulation of hepatic and pulmonary antioxidant genes.

Targeting mitochondria-associated membranes as a potential therapy against endothelial injury induced by hypoxia

Mitochondrial dysfunction plays a principal role in hypoxia-induced endothelial injury, which is involved in hypoxic pulmonary hypertension and ischemic cardiovascular diseases. Recent studies have identified mitochondria-associated membranes (MAMs) that modulate mitochondrial function under a variety of pathophysiological conditions such as high-fat diet-mediated insulin resistance, hypoxia reoxygenation-induced myocardial death, and hypoxia-evoked vascular smooth muscle cell proliferation. However, the role of MAMs in hypoxia-induced endothelial injury remains unclear. To explore this further, human umbilical vein endothelial cells and human pulmonary artery endothelial cells were exposed to hypoxia (1% O₂ ) for 24 hours. An increase in MAM formation was uncovered by immunoblotting and immunofluorescence. Then, we performed small interfering RNA transfection targeted to MAM constitutive proteins and explored the biological effects. Knockdown of MAM constitutive proteins attenuated hypoxia-induced elevation of mitochondrial Ca²⁺ and repressed mitochondrial impairment, leading to an increase in mitochondrial membrane potential and ATP production and a decline in reactive oxygen species. Then, we found that MAM disruption mitigated cell apoptosis and promoted cell survival. Next, other protective effects, such as those pertaining to the repression of inflammatory response and the promotion of NO synthesis, were investigated. With the disruption of MAMs under hypoxia, inflammatory molecule expression was repressed, and the eNOS-NO pathway was enhanced. This study demonstrates that the disruption of MAMs might be of therapeutic value for treating endothelial injury under hypoxia, suggesting a novel strategy for preventing hypoxic pulmonary hypertension and ischemic injuries.

Role of Gender in Regulation of Redox Homeostasis in Pulmonary Arterial Hypertension

Pulmonary arterial hypertension (PAH) is one of the diseases with a well-established gender dimorphism. The prevalence of PAH is increased in females with a ratio of 4:1, while poor survival prognosis is associated with the male gender. Nevertheless, the specific contribution of gender in disease development and progression is unclear due to the complex nature of the PAH. Oxidative and nitrosative stresses are important contributors in PAH pathogenesis; however, the role of gender in redox homeostasis has been understudied. This review is aimed to overview the possible sex-specific mechanisms responsible for the regulation of the balance between oxidants and antioxidants in relation to PAH pathobiology.

Regulation of Smooth Muscle Cell Proliferation by NADPH Oxidases in Pulmonary Hypertension

Hyperproliferation of pulmonary arterial smooth muscle cells is a key component of vascular remodeling in the setting of pulmonary hypertension (PH). Numerous studies have explored factors governing the changes in smooth muscle cell phenotype that lead to the increased wall thickness, and have identified various potential candidates. A role for reactive oxygen species (ROS) has been well documented in PH. ROS can be generated from a variety of sources, including mitochondria, uncoupled nitric oxide synthase, xanthine oxidase, and reduced nicotinamide adenine dinucleotide phosphate (NADPH) oxidase. In this article, we will review recent data supporting a role for ROS generated from NADPH oxidases in promoting pulmonary arterial smooth muscle cell proliferation during PH.

Hypoxia-induced pulmonary vasoconstriction of intra-acinar arteries is impaired in NADPH oxidase 4 gene-deficient mice

We show that genetic deficiency of the reactive oxygen species generating enzyme NADPH oxidase 4 (NOX4) impairs hypoxic pulmonary vasoconstriction in small (25–40 µm) intra-acinar, but not pre-acinar, arteries in murine precision cut lung slices. These data suggest an involvement of NOX4 in ventilation-perfusion matching at the acinar level.

NOX4 expression and distal arteriolar remodeling correlate with pulmonary hypertension in COPD

Background

Pulmonary hypertension (PH) in chronic obstructive pulmonary disease (COPD) is suggested as the consequence of emphysematous destruction of vascular bed and hypoxia of pulmonary microenvironment, mechanisms underpinning its pathogenesis however remain elusive. The dysregulated expression of nicotinamide adenine dinucleotide phosphate (NADPH)-oxidases and superoxide generation by pulmonary vasculatures have significant implications in the hypoxia-induced PH.

Methods

In this study, the involvement of NADPH oxidase subunit 4 (NOX4) in pulmonary arteriolar remodeling of PH in COPD was investigated by ascertaining the morphological alteration of pulmonary arteries and pulmonary blood flow using cardiac magnetic resonance imaging (cMRI), and the expression and correlation of NOX4 with pulmonary vascular remodeling and pulmonary functions in COPD lungs.

Results

Results demonstrated that an augmented expression of NOX4 was correlated with the increased volume of pulmonary vascular wall in COPD lung. While the volume of distal pulmonary arteries was inversely correlated with pulmonary functions, despite it was positively associated with the main pulmonary artery distensibility, right ventricular myocardial mass end-systolic and right ventricular myocardial mass end-diastolic in COPD. In addition, an increased malondialdehyde and a decreased superoxide dismutase were observed in sera of COPD patients. Mechanistically, the abundance of NOX4 and production of reactive oxygen species (ROS) in pulmonary artery smooth muscle cells could be dynamically induced by transforming growth factor-beta (TGF-β), which in turn led pulmonary arteriolar remodeling in COPD lungs.

Conclusion

These results suggest that the NOX4-derived ROS production may play a key role in the development of PH in COPD by promoting distal pulmonary vascular remodeling.

Gestational Hypoxia and Developmental Plasticity

Hypoxia is one of the most common and severe challenges to the maintenance of homeostasis. Oxygen sensing is a property of all tissues, and the response to hypoxia is multidimensional involving complicated intracellular networks concerned with the transduction of hypoxia-induced responses. Of all the stresses to which the fetus and newborn infant are subjected, perhaps the most important and clinically relevant is that of hypoxia. Hypoxia during gestation impacts both the mother and fetal development through interactions with an individual's genetic traits acquired over multiple generations by natural selection and changes in gene expression patterns by altering the epigenetic code. Changes in the epigenome determine "genomic plasticity," i.e., the ability of genes to be differentially expressed according to environmental cues. The genomic plasticity defined by epigenomic mechanisms including DNA methylation, histone modifications, and noncoding RNAs during development is the mechanistic substrate for phenotypic programming that determines physiological response and risk for healthy or deleterious outcomes. This review explores the impact of gestational hypoxia on maternal health and fetal development, and epigenetic mechanisms of developmental plasticity with emphasis on the uteroplacental circulation, heart development, cerebral circulation, pulmonary development, and the hypothalamic-pituitary-adrenal axis and adipose tissue. The complex molecular and epigenetic interactions that may impact an individual's physiology and developmental programming of health and disease later in life are discussed.

Recurrent inhibition of mitochondrial complex III induces chronic pulmonary vasoconstriction and glycolytic switch in the rat lung

BACKGROUND

Pulmonary arterial hypertension (PAH) is a fatal disease; however, the mechanisms directly involved in triggering and the progression of PAH are not clear. Based on previous studies that demonstrated a possible role of mitochondrial dysfunction in the pathogenesis of PAH, we investigated the effects of chronic inhibition of mitochondrial function in vivo in healthy rodents.

METHODS

Right ventricle systolic pressure (RVSP) was measured in female rats at baseline and up to 24 days after inhibition of mitochondrial respiratory Complex III, induced by Antimycin A (AA, 0.35 mg/kg, given three times starting at baseline and then days 3 and 6 as a bolus injection into the right atrial chamber).

RESULTS

Rodents exposed to AA demonstrated sustained increases in RVSP from days 6 through 24. AA-exposed rodents also possessed a progressive increase in RV end-diastolic pressure but not RV hypertrophy, which may be attributed to either early stages of PAH development or to reduced RV contractility due to inhibition of myocardial respiration. Protein nitration levels in plasma were positively correlated with PAH development in AA-treated rats. This finding was strongly supported by results obtained from PAH humans where plasma protein nitration levels were correlated with markers of PAH severity in female but not male PAH patients. Based on previously reported associations between increased nitric oxide production levels with female gender, we speculate that in females with PAH mitochondrial dysfunction may represent a more deleterious form, in part, due to an increased nitrosative stress development. Indeed, the histological analysis of AA treated rats revealed a strong perivascular edema, a marker of pulmonary endothelial damage. Finally, AA treatment was accompanied by a severe metabolic shift toward glycolysis, a hallmark of PAH pathology.

CONCLUSIONS

Chronic mitochondrial dysfunction induces the combination of vascular damage and metabolic reprogramming that may be responsible for PAH development. This mechanism may be especially important in females, perhaps due to an increased NO production and nitrosative stress development.

Metabolic Reprogramming and Redox Signaling in Pulmonary Hypertension

Pulmonary hypertension is a complex disease of the pulmonary vasculature, which in severe cases terminates in right heart failure. Complex remodeling of pulmonary arteries comprises the central issue of its pathology. This includes extensive proliferation, apoptotic resistance and inflammation. As such, the molecular and cellular features of pulmonary hypertension resemble hallmark characteristics of cancer cell behavior. The vascular remodeling derives from significant metabolic changes in resident cells, which we describe in detail. It affects not only cells of pulmonary artery wall, but also its immediate microenvironment involving cells of immune system (i.e., macrophages). Thus aberrant metabolism constitutes principle component of the cancer-like theory of pulmonary hypertension. The metabolic changes in pulmonary artery cells resemble the cancer associated Warburg effect, involving incomplete glucose oxidation through aerobic glycolysis with depressed mitochondrial catabolism enabling the fueling of anabolic reactions with amino acids, nucleotides and lipids to sustain proliferation. Macrophages also undergo overlapping but distinct metabolic reprogramming inducing specific activation or polarization states that enable their participation in the vascular remodeling process. Such metabolic synergy drives chronic inflammation further contributing to remodeling. Enhanced glycolytic flux together with suppressed mitochondrial bioenergetics promotes the accumulation of reducing equivalents, NAD(P)H. We discuss the enzymes and reactions involved. The reducing equivalents modulate the regulation of proteins using NAD(P)H as the transcriptional co-repressor C-terminal binding protein 1 cofactor and significantly impact redox status (through GSH, NAD(P)H oxidases, etc.), which together act to control the phenotype of the cells of pulmonary arteries. The altered mitochondrial metabolism changes its redox poise, which together with enhanced NAD(P)H oxidase activity and reduced enzymatic antioxidant activity promotes a pro-oxidative cellular status. Herein we discuss all described metabolic changes along with resultant alterations in redox status, which result in excessive proliferation, apoptotic resistance, and inflammation, further leading to pulmonary arterial wall remodeling and thus establishing pulmonary artery hypertension pathology.

From Physiological Redox Signalling to Oxidant Stress

Oxidant stress is strongly associated with cardiovascular disease, including pulmonary hypertension, but antioxidant therapies have so far proven ineffective. This is partly due to a lack of understanding of the key role played by reactive oxygen species (ROS) in physiological cell signalling, and partly to the complex interrelationships between generators of ROS (e.g. mitochondria and NADPH oxidases, NOX), cellular antioxidant systems and indeed Ca²⁺ signalling. At physiological levels ROS reversibly affect the function of numerous enzymes and transcription factors, most often via oxidation of specific protein thiols. Importantly, they also affect pathways that promote ROS generation by NOX or mitochondria (ROS-induced ROS release), which has an inherent propensity for positive feedback and uncontrolled oxidant production. The reason this does not occur under normal conditions reflects in part a high level of compartmentalisation of ROS signalling within the cell, akin to that for Ca²⁺. This article considers the physiological processes which regulate NOX and mitochondrial ROS production and degradation and their interactions with each other and Ca²⁺ signalling pathways, and discusses how loss of spatiotemporal constraints and activation of positive feedback pathways may impact on their dysregulation in pulmonary hypertension.

Impact of the mitochondria-targeted antioxidant MitoQ on hypoxia-induced pulmonary hypertension

Increased mitochondrial reactive oxygen species (ROS), particularly superoxide have been suggested to mediate hypoxic pulmonary vasoconstriction (HPV), chronic hypoxia-induced pulmonary hypertension (PH) and right ventricular (RV) remodelling.We determined ROS in acute, chronic hypoxia and investigated the effect of the mitochondria-targeted antioxidant MitoQ under these conditions.The effect of MitoQ or its inactive carrier substance, decyltriphenylphosphonium (TPP+), on acute HPV (1% O2 for 10 minutes) was investigated in isolated blood-free perfused mouse lungs. Mice exposed for 4 weeks to chronic hypoxia (10% O2) or after banding of the main pulmonary artery (PAB) were treated with MitoQ or TPP+ (50 mg/kg/day).Total cellular superoxide and mitochondrial ROS levels were increased in pulmonary artery smooth muscle cells (PASMC), but decreased in pulmonary fibroblasts in acute hypoxia. MitoQ significantly inhibited HPV and acute hypoxia-induced rise in superoxide concentration. ROS was decreased in PASMC, while it increased in the RV after chronic hypoxia. Correspondingly, MitoQ did not affect the development of chronic hypoxia-induced PH, but attenuated RV remodelling after chronic hypoxia as well as after PAB.Increased mitochondrial ROS of PASMC mediate acute HPV, but not chronic hypoxia-induced PH. MitoQ may be beneficial under conditions of exaggerated acute HPV.

Hypoxia selectively upregulates cation channels and increases cytosolic [Ca2+] in pulmonary, but not coronary, arterial smooth muscle cells

Ca²⁺ signaling, particularly the mechanism via store-operated Ca²⁺ entry (SOCE) and receptor-operated Ca²⁺ entry (ROCE), plays a critical role in the development of acute hypoxia-induced pulmonary vasoconstriction and chronic hypoxia-induced pulmonary hypertension. This study aimed to test the hypothesis that chronic hypoxia differentially regulates the expression of proteins that mediate SOCE and ROCE [stromal interacting molecule (STIM), Orai, and canonical transient receptor potential channel TRPC6] in pulmonary (PASMC) and coronary (CASMC) artery smooth muscle cells. The resting cytosolic [Ca²⁺] ([Ca²⁺]_cyt) and the stored [Ca²⁺] in the sarcoplasmic reticulum were not different in CASMC and PASMC. Seahorse measurement showed a similar level of mitochondrial bioenergetics (basal respiration and ATP production) between CASMC and PASMC. Glycolysis was significantly higher in PASMC than in CASMC. The amplitudes of cyclopiazonic acid-induced SOCE and OAG-induced ROCE in CASMC are slightly, but significantly, greater than in PASMC. The frequency and the area under the curve of Ca²⁺ oscillations induced by ATP and histamine were also larger in CASMC than in PASMC. Na⁺/Ca²⁺ exchanger-mediated increases in [Ca²⁺]_cyt did not differ significantly between CASMC and PASMC. The basal protein expression levels of STIM1/2, Orai1/2, and TRPC6 were higher in CASMC than in PASMC, but hypoxia (3% O₂ for 72 h) significantly upregulated protein expression levels of STIM1/STIM2, Orai1/Orai2, and TRPC6 and increased the resting [Ca²⁺]_cyt only in PASMC, but not in CASMC. The different response of essential components of store-operated and receptor-operated Ca²⁺ channels to hypoxia is a unique intrinsic property of PASMC, which is likely one of the important explanations why hypoxia causes pulmonary vasoconstriction and induces pulmonary vascular remodeling, but causes coronary vasodilation.

Vascular aging: Molecular mechanisms and potential treatments for vascular rejuvenation

Aging is the main risk factor contributing to vascular dysfunction and the progression of vascular diseases. In this review, we discuss the causes and mechanisms of vascular aging at the tissue and cellular level. We focus on Endothelial Cell (EC) and Smooth Muscle Cell (SMC) aging due to their critical role in mediating the defective vascular phenotype. We elaborate on two categories that contribute to cellular dysfunction: cell extrinsic and intrinsic factors. Extrinsic factors reflect systemic or environmental changes which alter EC and SMC homeostasis compromising vascular function. Intrinsic factors induce EC and SMC transformation resulting in cellular senescence. Replenishing or rejuvenating the aged/dysfunctional vascular cells is critical to the effective repair of the vasculature. As such, this review also elaborates on recent findings which indicate that stem cell and gene therapies may restore the impaired vascular cell function, reverse vascular aging, and prolong lifespan.

Reactive Oxygen and Nitrogen Species in the Development of Pulmonary Hypertension

Pulmonary arterial hypertension (PAH) is a progressive disease of the lung vasculature that involves the loss of endothelial function together with inappropriate smooth muscle cell growth, inflammation, and fibrosis. These changes underlie a progressive remodeling of blood vessels that alters flow and increases pulmonary blood pressure. Elevated pressures in the pulmonary artery imparts a chronic stress on the right ventricle which undergoes compensatory hypertrophy but eventually fails. How PAH develops remains incompletely understood and evidence for the altered production of reactive oxygen and nitrogen species (ROS, RNS respectively) in the pulmonary circulation has been well documented. There are many different types of ROS and RNS, multiple sources, and collective actions and interactions. This review summarizes past and current knowledge of the sources of ROS and RNS and how they may contribute to the loss of endothelial function and changes in smooth muscle proliferation in the pulmonary circulation.

Constitutive Reprogramming of Fibroblast Mitochondrial Metabolism in Pulmonary Hypertension

Remodeling of the distal pulmonary artery wall is a characteristic feature of pulmonary hypertension (PH). In hypoxic PH, the most substantial pathologic changes occur in the adventitia. Here, there is marked fibroblast proliferation and profound macrophage accumulation. These PH fibroblasts (PH-Fibs) maintain a hyperproliferative, apoptotic-resistant, and proinflammatory phenotype in ex vivo culture. Considering that a similar phenotype is observed in cancer cells, where it has been associated, at least in part, with specific alterations in mitochondrial metabolism, we sought to define the state of mitochondrial metabolism in PH-Fibs. In PH-Fibs, pyruvate dehydrogenase was markedly inhibited, resulting in metabolism of pyruvate to lactate, thus consistent with a Warburg-like phenotype. In addition, mitochondrial bioenergetics were suppressed and mitochondrial fragmentation was increased in PH-Fibs. Most importantly, complex I activity was substantially decreased, which was associated with down-regulation of the accessory subunit nicotinamide adenine dinucleotide reduced dehydrogenase (ubiquinone) Fe-S protein 4 (NDUFS4). Owing to less-efficient ATP synthesis, mitochondria were hyperpolarized and mitochondrial superoxide production was increased. This pro-oxidative status was further augmented by simultaneous induction of cytosolic nicotinamide adenine dinucleotide phosphate reduced oxidase 4. Although acute and chronic exposure to hypoxia of adventitial fibroblasts from healthy control vessels induced increased glycolysis, it did not induce complex I deficiency as observed in PH-Fibs. This suggests that hypoxia alone is insufficient to induce NDUFS4 down-regulation and constitutive abnormalities in complex I. In conclusion, our study provides evidence that, in the pathogenesis of vascular remodeling in PH, alterations in fibroblast mitochondrial metabolism drive distinct changes in cellular behavior, which potentially occur independently of hypoxia.

Contribution of reactive oxygen species to the pathogenesis of pulmonary arterial hypertension

Pulmonary arterial hypertension is associated with a decreased antioxidant capacity. However, neither the contribution of reactive oxygen species to pulmonary vasoconstrictor sensitivity, nor the therapeutic efficacy of antioxidant strategies in this setting are known. We hypothesized that reactive oxygen species play a central role in mediating both vasoconstrictor and arterial remodeling components of severe pulmonary arterial hypertension. We examined the effect of the chemical antioxidant, TEMPOL, on right ventricular systolic pressure, vascular remodeling, and enhanced vasoconstrictor reactivity in both chronic hypoxia and hypoxia/SU5416 rat models of pulmonary hypertension. SU5416 is a vascular endothelial growth factor receptor antagonist and the combination of chronic hypoxia/SU5416 produces a model of severe pulmonary arterial hypertension with vascular plexiform lesions/fibrosis that is not present with chronic hypoxia alone. The major findings from this study are: 1) compared to hypoxia alone, hypoxia/SU5416 exposure caused more severe pulmonary hypertension, right ventricular hypertrophy, adventitial lesion formation, and greater vasoconstrictor sensitivity through a superoxide and Rho kinase-dependent Ca2+ sensitization mechanism. 2) Chronic hypoxia increased medial muscularization and superoxide levels, however there was no effect of SU5416 to augment these responses. 3) Treatment with TEMPOL decreased right ventricular systolic pressure in both hypoxia and hypoxia/SU5416 groups. 4) This effect of TEMPOL was associated with normalization of vasoconstrictor responses, but not arterial remodeling. Rather, medial hypertrophy and adventitial fibrotic lesion formation were more pronounced following chronic TEMPOL treatment in hypoxia/SU5416 rats. Our findings support a major role for reactive oxygen species in mediating enhanced vasoconstrictor reactivity and pulmonary hypertension in both chronic hypoxia and hypoxia/SU5416 rat models, despite a paradoxical effect of antioxidant therapy to exacerbate arterial remodeling in animals with severe pulmonary arterial hypertension in the hypoxia/SU5416 model.