Hypoxic pulmonary vasoconstriction: redox events in oxygen sensing

Mitochondrial oxygen sensing of acute hypoxia in specialized cells - Is there a unifying mechanism?

Acclimation to acute hypoxia through cardiorespiratory responses is mediated by specialized cells in the carotid body and pulmonary vasculature to optimize systemic arterial oxygenation and thus oxygen supply to the tissues. Acute oxygen sensing by these cells triggers hyperventilation and hypoxic pulmonary vasoconstriction which limits pulmonary blood flow through areas of low alveolar oxygen content. Oxygen sensing of acute hypoxia by specialized cells thus is a fundamental pre-requisite for aerobic life and maintains systemic oxygen supply. However, the primary oxygen sensing mechanism and the question of a common mechanism in different specialized oxygen sensing cells remains unresolved. Recent studies unraveled basic oxygen sensing mechanisms involving the mitochondrial cytochrome c oxidase subunit 4 isoform 2 that is essential for the hypoxia-induced release of mitochondrial reactive oxygen species and subsequent acute hypoxic responses in both, the carotid body and pulmonary vasculature. This review compares basic mitochondrial oxygen sensing mechanisms in the pulmonary vasculature and the carotid body.

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.

Induced pluripotent stem cells can improve thrombolytic effect of low-dose rt-PA after acute carotid thrombosis in rat

Background

Intravenous thrombolysis using recombinant tissue plasminogen activator (rt-PA) is the standard treatment for acute ischemic stroke. Standard-dose rt-PA (0.9 mg/kg) is known to achieve good recanalization but carries a high bleeding risk. Lower dose of rt-PA has less bleeding risk but carries a high re-occlusion rate. We investigate if induced pluripotent stem cells (iPSCs) can improve the thrombolytic effect of low-dose rt-PA (0.45 mg/kg).

Methods

Single irradiation with 6 mW/cm² light-emitting diode (LED) for 4 h at rat common carotid artery was used as thrombosis model according to our previous report. Endothelin-1 (ET-1), intercellular adhesion molecule-1 (ICAM-1), and interleukin 1 beta (IL-1 beta) were used as the inflammatory markers for artery endothelial injury. Angiopoietin-2 (AP-2), brain-derived neurotrophic factor (BDNF) and vascular endothelial growth factor (VEGF) were examined in artery wall and iPSCs culture. Animal ultrasound was used to evaluate the stenosis degree of common carotid artery before and at 2 h, 24 h, 4 days and 7 days after LED irradiation.

Results

After LED irradiation alone, there was a persistent occlusion from 2 h to 7 days. Standard-dose rt-PA alone could recanalize the occluded artery from 24 h to 7 days to stenotic degree ≤ 50%. Low-dose rt-PA or 1 × 10⁶ mouse iPSCs alone could not recanalize the occluded arteries from 2 h to 7 days. Combination use of low-dose rt-PA plus 1 × 10⁶ mouse iPSCs caused better recanalization from 24 h to 7 days. ET-1, ICAM-1 and IL-1 beta were strongly expressed after LED irradiation but reduced after iPSCs treatment. AP-2, BDNF and VEGF were rarely induced after LED irradiation but strongly expressed after iPSCs treatment. In vitro study showed iPSCs could express AP-2, BDNF and VEGF.

Conclusion

The adjuvant use of iPSCs may help improving the thrombolytic effect of low-dose rt-PA by suppressing inflammatory factors and inducing angiogenic trophic factors. Stem cells could be a potential regimen in acute thrombolytic therapy to improve recanalization and reduce complications.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13287-021-02615-z.

Chronic Obstructive Pulmonary Disease and the Cardiovascular System: Vascular Repair and Regeneration as a Therapeutic Target

Chronic obstructive pulmonary disease (COPD) is a major cause of morbidity and mortality worldwide and encompasses chronic bronchitis and emphysema. It has been shown that vascular wall remodeling and pulmonary hypertension (PH) can occur not only in patients with COPD but also in smokers with normal lung function, suggesting a causal role for vascular alterations in the development of emphysema. Mechanistically, abnormalities in the vasculature, such as inflammation, endothelial dysfunction, imbalances in cellular apoptosis/proliferation, and increased oxidative/nitrosative stress promote development of PH, cor pulmonale, and most probably pulmonary emphysema. Hypoxemia in the pulmonary chamber modulates the activation of key transcription factors and signaling cascades, which propagates inflammation and infiltration of neutrophils, resulting in vascular remodeling. Endothelial progenitor cells have angiogenesis capabilities, resulting in transdifferentiation of the smooth muscle cells via aberrant activation of several cytokines, growth factors, and chemokines. The vascular endothelium influences the balance between vaso-constriction and -dilation in the heart. Targeting key players affecting the vasculature might help in the development of new treatment strategies for both PH and COPD. The present review aims to summarize current knowledge about vascular alterations and production of reactive oxygen species in COPD. The present review emphasizes on the importance of the vasculature for the usually parenchyma-focused view of the pathobiology of COPD.

Cardiac autonomic recovery following traditional and augmented remote ischemic preconditioning

PURPOSE

While the possible ergogenic benefits of remote ischemic preconditioning (RIPC) make it an attractive training modality, the mechanisms of action remain unclear. Alterations in neural tone have been demonstrated in conjunction with circulatory occlusion, yet investigation of the autonomic nervous system following RIPC treatment has received little attention. We sought to characterize alterations in autonomic balance to both RIPC and augmented RIPC (RIPC_aug) performed while cycling, using acute and sustained autonomic indices.

METHODS

Thirteen participants (8M:5F) recorded baseline waking heart rate variability (HRV) for 5 days prior to treatment. Participants then completed control exercise (CON), RIPC, and RIPC_aug interventions in a randomized cross-over design. Cardiovascular measurements were recorded immediately before and after each intervention at rest, and during an orthostatic challenge. Waking HRV was repeated the morning after each intervention.

RESULTS

RIPC resulted in acutely reduced resting heart rates (HR) (∆ - 4 ± 6 bpm, P = 0.02) and suppressed HR 30 s following the orthostatic challenge compared to CON (64 ± 10 vs 74 ± 9 bpm, P = 0.003). RIPC_aug yielded elevated HRs compared to CON and RIPC prior to (P = 0.003) and during the orthostatic challenge (P = 0.002). RIPC_aug reduced LnSDNN (Baseline 4.39 ± 0.27; CON 4.44 ± 0.39; RIPC 4.41 ± 0.34; RIPC_aug 4.22 ± 0.29, P = 0.02) and LnHfa power (Baseline 7.82 ± 0.54; CON 7.73 ± 1.11; RIPC 7.89 ± 0.78; RIPC_aug 7.23 ± 0.87, P = 0.04) the morning after treatment compared to all other conditions.

CONCLUSIONS

Our data suggest that RIPC may influence HR acutely, possibly through a reduction in cardiac sympathetic activity, and that RIPC_aug reduces HRV through cardiac vagal withdrawal or increased cardiac sympathetic modulation, with alterations persisting until the following morning. These findings imply a dose-response relationship with potential for optimization of performance.

Mitochondria in the Pulmonary Vasculature in Health and Disease: Oxygen-Sensing, Metabolism, and Dynamics

In lung vascular cells, mitochondria serve a canonical metabolic role, governing energy homeostasis. In addition, mitochondria exist in dynamic networks, which serve noncanonical functions, including regulation of redox signaling, cell cycle, apoptosis, and mitochondrial quality control. Mitochondria in pulmonary artery smooth muscle cells (PASMC) are oxygen sensors and initiate hypoxic pulmonary vasoconstriction. Acquired dysfunction of mitochondrial metabolism and dynamics contribute to a cancer-like phenotype in pulmonary arterial hypertension (PAH). Acquired mitochondrial abnormalities, such as increased pyruvate dehydrogenase kinase (PDK) and pyruvate kinase muscle isoform 2 (PKM2) expression, which increase uncoupled glycolysis (the Warburg phenomenon), are implicated in PAH. Warburg metabolism sustains energy homeostasis by the inhibition of oxidative metabolism that reduces mitochondrial apoptosis, allowing unchecked cell accumulation. Warburg metabolism is initiated by the induction of a pseudohypoxic state, in which DNA methyltransferase (DNMT)-mediated changes in redox signaling cause normoxic activation of HIF-1α and increase PDK expression. Furthermore, mitochondrial division is coordinated with nuclear division through a process called mitotic fission. Increased mitotic fission in PAH, driven by increased fission and reduced fusion favors rapid cell cycle progression and apoptosis resistance. Downregulation of the mitochondrial calcium uniporter complex (MCUC) occurs in PAH and is one potential unifying mechanism linking Warburg metabolism and mitochondrial fission. Mitochondrial metabolic and dynamic disorders combine to promote the hyperproliferative, apoptosis-resistant, phenotype in PAH PASMC, endothelial cells, and fibroblasts. Understanding the molecular mechanism regulating mitochondrial metabolism and dynamics has permitted identification of new biomarkers, nuclear and CT imaging modalities, and new therapeutic targets for PAH. © 2020 American Physiological Society. Compr Physiol 10:713-765, 2020.

Metabolism and Redox in Pulmonary Vascular Physiology and Pathophysiology

Significance: This review considers how some systems controlling pulmonary vascular function are potentially regulated by redox processes to examine how and why conditions such as prolonged hypoxia, pathological mediators, and other factors promoting vascular remodeling contribute to the development of pulmonary hypertension (PH). Recent Advances and Critical Issues: Aspects of vascular remodeling induction mechanisms described are associated with shifts in glucose metabolism through the pentose phosphate pathway and increased cytosolic NADPH generation by glucose-6-phosphate dehydrogenase, increased glycolysis generation of cytosolic NADH and lactate, mitochondrial dysfunction associated with superoxide dismutase-2 depletion, changes in reactive oxygen species and iron metabolism, and redox signaling. Future Directions: The regulation and impact of hypoxia-inducible factor and the function of cGMP-dependent and redox regulation of protein kinase G are considered for their potential roles as key sensors and coordinators of redox and metabolic processes controlling the progression of vascular pathophysiology in PH, and how modulating aspects of metabolic and redox regulatory systems potentially function in beneficial therapeutic approaches.

Blood flow restricted resistance exercise and reductions in oxygen tension attenuate mitochondrial H2 O2 emission rates in human skeletal muscle

KEY POINTS

Blood flow restricted resistance exercise (BFR-RE) is capable of inducing comparable adaptations to traditional resistance exercise (RE), despite a lower total exercise volume. It has been suggested that an increase in reactive oxygen species (ROS) production may be involved in this response; however, oxygen partial pressure ( P O 2 ) is reduced during BFR-RE, and the influence of P O 2 on mitochondrial redox balance remains poorly understood. In human skeletal muscle tissue, we demonstrate that both maximal and submaximal mitochondrial ROS emission rates are acutely decreased 2 h following BFR-RE, but not RE, occurring along with a reduction in tissue oxygenation during BFR-RE. We further suggest that P O 2 is involved in this response because an in vitro analysis revealed that reducing P O 2 dramatically decreased mitochondrial ROS emissions and electron leak to ROS. Altogether, these data indicate that mitochondrial ROS emission rates are attenuated following BFR-RE, and such a response is likely influenced by reductions in P O 2 .

ABSTRACT

Low-load blood flow restricted resistance exercise (BFR-RE) training has been proposed to induce comparable adaptations to traditional resistance exercise (RE) training, however, the acute signalling events remain unknown. Although a suggested mechanism of BFR-RE is an increase in reactive oxygen species (ROS) production, oxygen partial pressure ( P O 2 ) is reduced during BFR-RE, and the influence of O₂ tension on mitochondrial redox balance remains ambiguous. We therefore aimed to determine whether skeletal muscle mitochondrial bioenergetics were altered following an acute bout of BFR-RE or RE, and to further examine the role of P O 2 in this response. Accordingly, muscle biopsies were obtained from 10 males at rest and 2 h after performing three sets of single-leg squats (RE or BFR-RE) to failure at 30% one-repetition maximum. We determined that mitochondrial respiratory capacity and ADP sensitivity were not altered in response to RE or BFR-RE. Although maximal (succinate) and submaximal (non-saturating ADP) mitochondrial ROS emission rates were unchanged following RE, BFR-RE attenuated these responses by ∼30% compared to pre-exercise, occurring along with a reduction in skeletal muscle tissue oxygenation during BFR-RE (P < 0.01 vs. RE). In a separate cohort of participants, evaluation of mitochondrial bioenergetics in vitro revealed that mild O₂ restriction (50 µm) dramatically attenuated maximal (∼4-fold) and submaximal (∼50-fold) mitochondrial ROS emission rates and the fraction of electron leak to ROS compared to room air (200 µm). Combined, these data demonstrate that mitochondrial ROS emissions are attenuated following BFR-RE, a response which may be mediated by a reduction in skeletal muscle P O 2 .

Mitochondrial bioenergetics and pulmonary dysfunction: Current progress and future directions

This review summarizes current understanding of mitochondrial bioenergetic dysfunction applicable to mechanisms of lung diseases and outlines challenges and future directions in this rapidly emerging field. Although the role of mitochondria extends beyond the term of cellular "powerhouse", energy generation remains the most fundamental function of these organelles. It is not counterintuitive to propose that intact energy supply is important for favorable cellular fate following pulmonary insult. In this review, the discussion of mitochondrial dysfunction focuses on those molecular mechanisms that alter cellular bioenergetics in the lungs: (a) inhibition of mitochondrial respiratory chain, (b) mitochondrial leak and uncoupling, (c) alteration of mitochondrial Ca²⁺ handling, (d) mitochondrial production of reactive oxygen species and self-oxidation. The discussed lung diseases were selected according to their pathological nature and relevance to pediatrics: Acute lung injury (ALI), defined as acute parenchymal lung disease associated with cellular demise and inflammation (Acute Respiratory Distress Syndrome, ARDS, Pneumonia), alveolar developmental failure (Bronchopulmonary Dysplasia, BPD or chronic lung disease in premature infants), obstructive airway diseases (Bronchial asthma) and vascular remodeling affecting pulmonary circulation (Pulmonary Hypertension, PH). The analysis highlights primary mechanisms of mitochondrial bioenergetic dysfunction contributing to the disease-specific pulmonary insufficiency and proposes potential therapeutic targets.

Ceramide and Regulation of Vascular Tone

In addition to playing a role as a structural component of cellular membranes, ceramide is now clearly recognized as a bioactive lipid implicated in a variety of physiological functions. This review aims to provide updated information on the role of ceramide in the regulation of vascular tone. Ceramide may induce vasodilator or vasoconstrictor effects by interacting with several signaling pathways in endothelial and smooth muscle cells. There is a clear, albeit complex, interaction between ceramide and redox signaling. In fact, reactive oxygen species (ROS) activate different ceramide generating pathways and, conversely, ceramide is known to increase ROS production. In recent years, ceramide has emerged as a novel key player in oxygen sensing in vascular cells and mediating vascular responses of crucial physiological relevance such as hypoxic pulmonary vasoconstriction (HPV) or normoxic ductus arteriosus constriction. Likewise, a growing body of evidence over the last years suggests that exaggerated production of vascular ceramide may have detrimental effects in a number of pathological processes including cardiovascular and lung diseases.

The Theoretical Basis for Using Apnoeic Oxygenation via the Non-ventilated Lung during One-lung Ventilation to Delay the Onset of Arterial Hypoxaemia

At the time one-lung ventilation is initiated, nitrogen from the atmosphere may enter the non-ventilated lung via a double-lumen tube connector that has been left open to air, even momentarily. Ongoing oxygen uptake from the non-ventilated lung raises the partial pressure of nitrogen. This should lead to activation of hypoxic pulmonary vasoconstriction and a reduction in intra-pulmonary shunting. However, in spite of this, some patients still become hypoxaemic. In such cases, it may be advantageous to have excluded nitrogen from the non-ventilated lung by connecting it to an oxygen source at ambient pressure. Ongoing apnoeic oxygenation, while the airways are patent, and as the lung collapses, should delay the onset of arterial desaturation. In this paper we review the theoretical basis for apnoeic oxygenation during one-lung ventilation, and in particular on oxygen uptake by the non-ventilated lung prior to and during its subsequent collapse.

Redox Signaling and Persistent Pulmonary Hypertension of the Newborn

Reactive oxygen species (ROS) are redox-signaling molecules that are critically involved in regulating endothelial cell functions, host defense, aging, and cellular adaptation. Mitochondria are the major sources of ROS and important sources of redox signaling in pulmonary circulation. It is becoming increasingly evident that increased mitochondrial oxidative stress and aberrant signaling through redox-sensitive pathways play a direct causative role in the pathogenesis of many cardiopulmonary disorders including persistent pulmonary hypertension of the newborn (PPHN). This chapter highlights redox signaling in endothelial cells, antioxidant defense mechanism, cell responses to oxidative stress, and their contributions to disease pathogenesis.

Endothelial Cell Reactive Oxygen Species and Ca2+ Signaling in Pulmonary Hypertension

Pulmonary hypertension (PH) refers to a disorder characterized by elevated pulmonary arterial pressure, leading to right ventricular overload and eventually right ventricular failure, which results in high morbidity and mortality. PH is associated with heterogeneous etiologies and distinct molecular mechanisms, including abnormal migration and proliferation of endothelial and smooth muscle cells. Although the exact details are not fully elucidated, reactive oxygen species (ROS) have been shown to play a key role in promoting abnormal function in pulmonary arterial smooth muscle and endothelial cells in PH. In endothelial cells, ROS can be generated from sources such as NADPH oxidase and mitochondria, which in turn can serve as signaling molecules in a wide variety of processes including posttranslational modification of proteins involved in Ca²⁺ homeostasis. In this chapter, we discuss the role of ROS in promoting abnormal vasoreactivity and endothelial migration and proliferation in various models of PH. Furthermore, we draw particular attention to the role of ROS-induced increases in intracellular Ca²⁺ concentration in the pathobiology of PH.

Thin Air Resulting in High Pressure: Mountain Sickness and Hypoxia-Induced Pulmonary Hypertension

With rising altitude the partial pressure of oxygen falls. This phenomenon leads to hypobaric hypoxia at high altitude. Since more than 140 million people permanently live at heights above 2500 m and more than 35 million travel to these heights each year, understanding the mechanisms resulting in acute or chronic maladaptation of the human body to these circumstances is crucial. This review summarizes current knowledge of the body's acute response to these circumstances, possible complications and their treatment, and health care issues resulting from long-term exposure to high altitude. It furthermore describes the characteristic mechanisms of adaptation to life in hypobaric hypoxia expressed by the three major ethnic groups permanently dwelling at high altitude. We additionally summarize current knowledge regarding possible treatment options for hypoxia-induced pulmonary hypertension by reviewing in vitro, rodent, and human studies in this area of research.

Hypoxic Pulmonary Vasoconstriction in Humans: Tale or Myth

Hypoxic Pulmonary vasoconstriction (HPV) describes the physiological adaptive process of lungs to preserves systemic oxygenation. It has clinical implications in the development of pulmonary hypertension which impacts on outcomes of patients undergoing cardiothoracic surgery. This review examines both acute and chronic hypoxic vasoconstriction focusing on the distinct clinical implications and highlights the role of calcium and mitochondria in acute versus the role of reactive oxygen species and Rho GTPases in chronic HPV. Furthermore it identifies gaps of knowledge and need for further research in humans to clearly define this phenomenon and the underlying mechanism.

Hypoxia-induced contraction of chicken embryo mesenteric arteries: mechanisms and developmental changes

The fetal cardiovascular responses to acute hypoxia include a redistribution of the cardiac output toward the heart and the brain at the expense of other organs, such as the intestine. We hypothesized that hypoxia exerts a direct effect on the mesenteric artery (MA) that may contribute to this response. Using wire myography, we investigated the response to hypoxia (Po2 ~2.5 kPa for 20 min) of isolated MAs from 15- to 21-day chicken embryos (E15, E19, E21), and 1- to 45-day-old chickens (P1, P3, P14, P45). Agonist-induced pretone or an intact endothelium were not required to obtain a consistent and reproducible response to hypoxia, which showed a pattern of initial rapid phasic contraction followed by a sustained tonic contraction. Phasic contraction was reduced by elimination of extracellular Ca2+ or by presence of the neurotoxin tetrodotoxin, the α1-adrenoceptor antagonist prazosin, or inhibitors of L-type voltage-gated Ca2+ channels (nifedipine), mitochondrial electron transport chain (rotenone and antimycin A), and NADPH oxidase (VAS2870). The Rho-kinase inhibitor Y27632 impaired both phasic and tonic contraction and, when combined with elimination of extracellular Ca2+, hypoxia-induced contraction was virtually abolished. Hypoxic MA contraction was absent at E15 but present from E19 and increased toward the first days posthatching. It then decreased during the first weeks of life and P45 MAs were unable to sustain hypoxia-induced contraction over time. In conclusion, the results of the present study demonstrate that hypoxic vasoconstriction is an intrinsic feature of chicken MA vascular smooth muscle cells during late embryogenesis and the perinatal period.

Effect of protein arginine methyltransferase-1 inhibition on hypoxia-induced vasoconstriction

Hypoxia is defined as a decrease in the oxygen supply to a level below physiological levels which is insufficient to maintain cellular function, in the presence of unrestricted coronary inflow. It is one of the leading causes of global mortality and morbidity, due to its association with the pathology of cancer, cardiovascular disease and stroke. The common feature in these pathologies is the limitation of oxygen availability that participates in the development of these conditions. The pulmonary response to hypoxia, when hypoxia is localized, is hypoxic pulmonary vasoconstriction (HPV). HPV is a physiological and self-regulatory mechanism by which pulmonary capillary blood flow is automatically adjusted to alveolar ventilation for maintaining the optimal balance of ventilation and perfusion. In pathological conditions, HPV occurs as an acute episode during progressive critical illness or as a sustained response with vascular remodeling and pulmonary hypertension. Inspite of the hypoxia-induced shift in the redox status to a more oxidized state, the endothelium-dependent mediators of HPV that cause vasoconstrictor response to hypoxia include nitric oxide (NO), endothelin-1 and angiotensin-II. Indeed, in chronic hypoxia, due to the enhanced reactive oxygen species (ROS) generation, inhibition of endothelial nitric oxide synthase (eNOS) activity and reduced nitric oxide (NO) production there is an imbalance in the vasoconstriction-vasodilation status toward constriction. It is our hypothesis that, in hypoxic stress, a key player in initiating this imbalance is the enzyme, protein arginine methyltransferase-1 (PRMT1) which indirectly affects eNOS activity by increased production of asymmetric dimethylarginine (ADMA), a NOS-inhibitor. Thus, pharmacological inhibition of PRMT1 should restore the cellular and vascular homeostasis in hypoxic conditions.

Oxygen sensing and signal transduction in hypoxic pulmonary vasoconstriction

Hypoxic pulmonary vasoconstriction (HPV), also known as the von Euler-Liljestrand mechanism, is an essential response of the pulmonary vasculature to acute and sustained alveolar hypoxia. During local alveolar hypoxia, HPV matches perfusion to ventilation to maintain optimal arterial oxygenation. In contrast, during global alveolar hypoxia, HPV leads to pulmonary hypertension. The oxygen sensing and signal transduction machinery is located in the pulmonary arterial smooth muscle cells (PASMCs) of the pre-capillary vessels, albeit the physiological response may be modulated in vivo by the endothelium. While factors such as nitric oxide modulate HPV, reactive oxygen species (ROS) have been suggested to act as essential mediators in HPV. ROS may originate from mitochondria and/or NADPH oxidases but the exact oxygen sensing mechanisms, as well as the question of whether increased or decreased ROS cause HPV, are under debate. ROS may induce intracellular calcium increase and subsequent contraction of PASMCs via direct or indirect interactions with protein kinases, phospholipases, sarcoplasmic calcium channels, transient receptor potential channels, voltage-dependent potassium channels and L-type calcium channels, whose relevance may vary under different experimental conditions. Successful identification of factors regulating HPV may allow development of novel therapeutic approaches for conditions of disturbed HPV.

ROS Scavenger Decreases Basal Perfusion Pressure, Vasoconstriction and NO Synthase Activity in Pulmonary Circulation During Pulmonary Microembolism

Two mechanisms contribute in the development of pulmonary hypertension in pulmonary embolism (PE) – obstruction of pulmonary blood vessels and vasoconstriction. We hypothesize that hypoxia, increased shear stress and/or activation of gathered leukocytes in the PE may cause a release of reactive oxygen species (ROS). Therefore our aim was to determine the influence of the ROS scavenger Tempol on pulmonary hypertension and to describe NO synthase activity and production of NO oxidative products (NOx) after PE. In general anesthesia sephadex microspheres suspended in PSS were applied in right jugular vein as the pulmonary microembolism. Than we measured in isolated salt solution-perfused lungs the changes in perfusion pressure, activity of NO synthase and NOx plasma concentration in 7 groups of rats: C: control group (n=5), CN: C + sodium nitroprusside (SN) (n=5), EN: PE + SN (n=5), ETN: Tempol + PE + SN (n=5), CL: C + L-NAME (n=5), EL: PE + L-NAME (n=5), ETL: Tempol + PE + L-NAME (n=5). Tempol was applied intraperitoneally before PE. Animals that received Tempol (groups TN, TL) had significantly lower basal perfusion pressure than those which did not receive Tempol (EN, EL). Overall we measured a higher decrease of perfusion pressure than in the control group (C) after application of SN. Administration of L NAME after PE (EL) increased the pressure more than in the control group (NL). NOx concentration was higher after PE. We found that preventive administration of Tempol decreases the increase in perfusion pressure after PE. PE increased NO release and concentration of NOx.

Potassium channels in pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) is a devastating cardiopulmonary disorder with various origins. All forms of PAH share a common pulmonary arteriopathy characterised by vasoconstriction, remodelling of the pre-capillary pulmonary vessel wall, and in situ thrombosis. Although the pathogenesis of PAH is recognised as a complex and multifactorial process, there is growing evidence that potassium channels dysfunction in pulmonary artery smooth muscle cells is a hallmark of PAH. Besides regulating many physiological functions, reduced potassium channels expression and/or activity have significant effects on PAH establishment and progression. This review describes the molecular mechanisms and physiological consequences of potassium channel modulation. Special emphasis is placed on KCNA5 (Kv1.5) and KCNK3 (TASK1), which are considered to play a central role in determining pulmonary vascular tone and may represent attractive therapeutic targets in the treatment of PAH.

Molecular Connections between Cancer Cell Metabolism and the Tumor Microenvironment

Cancer cells preferentially utilize glycolysis, instead of oxidative phosphorylation, for metabolism even in the presence of oxygen. This phenomenon of aerobic glycolysis, referred to as the “Warburg effect”, commonly exists in a variety of tumors. Recent studies further demonstrate that both genetic factors such as oncogenes and tumor suppressors and microenvironmental factors such as spatial hypoxia and acidosis can regulate the glycolytic metabolism of cancer cells. Reciprocally, altered cancer cell metabolism can modulate the tumor microenvironment which plays important roles in cancer cell somatic evolution, metastasis, and therapeutic response. In this article, we review the progression of current understandings on the molecular interaction between cancer cell metabolism and the tumor microenvironment. In addition, we discuss the implications of these interactions in cancer therapy and chemoprevention.

Redox regulation of ion channels in the pulmonary circulation

SIGNIFICANCE

The pulmonary circulation is a low-pressure, low-resistance, highly compliant vasculature. In contrast to the systemic circulation, it is not primarily regulated by a central nervous control mechanism. The regulation of resting membrane potential due to ion channels is of integral importance in the physiology and pathophysiology of the pulmonary vasculature.

RECENT ADVANCES

Redox-driven ion conductance changes initiated by direct oxidation, nitration, and S-nitrosylation of the cysteine thiols and indirect phosphorylation of the threonine and serine residues directly affect pulmonary vascular tone.

CRITICAL ISSUES

Molecular mechanisms of changes in ion channel conductance, especially the identification of the sites of action, are still not fully elucidated.

FUTURE DIRECTIONS

Further investigation of the interaction between redox status and ion channel gating, especially the physiological significance of S-glutathionylation and S-nitrosylation, could result in a better understanding of the physiological and pathophysiological importance of these mediators in general and the implications of such modifications in cellular functions and related diseases and their importance for targeted treatment strategies.

Resveratrol regulates mitochondrial reactive oxygen species homeostasis through Sirt3 signaling pathway in human vascular endothelial cells

Mitochondrial reactive oxygen species (mtROS) homeostasis plays an essential role in preventing oxidative injury in endothelial cells, an initial step in atherogenesis. Resveratrol (RSV) possesses a variety of cardioprotective activities, however, little is known regarding the effects of RSV on mtROS homeostasis in endothelial cells. Sirt3 is a mitochondrial deacetylase, which plays a key role in mitochondrial bioenergetics and is closely associated with oxidative stress. The goal of the study is to investigate whether RSV could attenuate oxidative injury in endothelial cells via mtROS homeostasis regulation through Sirt3 signaling pathway. We found that pretreatment with RSV suppressed tert-butyl hydroperoxide (t-BHP)-induced oxidative damage in human umbilical vein endothelial cells (HUVECs) by increasing cell viability, inhibiting cell apoptosis, repressing collapse of mitochondrial membrane potential and decreasing mtROS generation. Moreover, the enzymatic activities of isocitrate dehydrogenase 2 (IDH2), glutathione peroxidase (GSH-Px) and manganese superoxide dismutase (SOD2) as well as deacetylation of SOD2 were increased by RSV pretreatment, suggesting RSV notably enhanced mtROS scavenging in t-BHP-induced endothelial cells. Meanwhile, RSV remarkably reduced mtROS generation by promoting Sirt3 enrichment within the mitochondria and subsequent upregulation of forkhead box O3A (FoxO3A)-mediated mitochondria-encoded gene expression of ATP6, CO1, Cytb, ND2 and ND5, thereby leading to increased complex I activity and ATP synthesis. Furthermore, RSV activated the expressions of phosphorylated adenosine monophosphate-activated protein kinase (p-AMPK), peroxisome proliferator-activated receptor gamma coactivator-1α (PGC-1α) and Sirt3, as well as estrogen-related receptor-α (ERRα)-dependent Sirt3 mRNA transcription, which were abolished in the presence of AMPK inhibitor and AMPK, PGC-1α or Sirt3 siRNA transfection, indicating the effects of RSV on mtROS homeostasis regulation were dependent on AMPK-PGC-1α-ERRα-Sirt3 signaling pathway. Our findings indicated a novel mechanism that RSV-attenuated oxidative injury in endothelial cells through the regulation of mtROS homeostasis, which, in part, was mediated through the activation of the Sirt3 signaling pathway.

A synthetic steroid 5α-androst-3β,5,6β-triol blocks hypoxia/reoxygenation-induced neuronal injuries via protection of mitochondrial function

Ischemic stroke is a leading cause of death worldwide, yet therapies are limited. During periods of ischemia following reperfusion in ischemic stroke, not only loss of energy supply, but a few other factors including mitochondrial dysfunction and oxidative stress also make vital contribution to neuronal injury. Here we synthesized a steroid compound 5α-androst-3β,5,6β-triol by 3 steps starting from dehydroepiandrosterone and examined its effect on mitochondrial function and oxidative stress in primary cultured cortical neurons exposed to hypoxia followed by reoxygenation. 5α-Androst-3β,5,6β-triol dose-dependently protected cortical neurons from hypoxia/reoxygenation exposure. Rates of reduction in neuronal viability, loss of mitochondrial membrane potential, disruption of ATP production and oxidative stress were ameliorated in 5α-androst-3β,5,6β-triol pretreated cultures. In summary, these results suggest that 5α-androst-3β,5,6β-triol is neuroprotective against hypoxia/reoxygenation induced neuronal injuries through mediation of mitochondrial function and oxidative stress.

Uncoupling protein 2 deficiency mimics the effects of hypoxia and endoplasmic reticulum stress on mitochondria and triggers pseudohypoxic pulmonary vascular remodeling and pulmonary hypertension

RATIONALE

Mitochondrial signaling regulates both the acute and the chronic response of the pulmonary circulation to hypoxia, and suppressed mitochondrial glucose oxidation contributes to the apoptosis-resistance and proliferative diathesis in the vascular remodeling in pulmonary hypertension. Hypoxia directly inhibits glucose oxidation, whereas endoplasmic reticulum (ER)-stress can indirectly inhibit glucose oxidation by decreasing mitochondrial calcium (Ca²⁺m levels). Both hypoxia and ER stress promote proliferative pulmonary vascular remodeling. Uncoupling protein 2 (UCP2) has been shown to conduct calcium from the ER to mitochondria and suppress mitochondrial function.

OBJECTIVE

We hypothesized that UCP2 deficiency reduces Ca²⁺m in pulmonary artery smooth muscle cells (PASMCs), mimicking the effects of hypoxia and ER stress on mitochondria in vitro and in vivo, promoting normoxic hypoxia inducible factor-1α activation and pulmonary hypertension.

METHODS AND RESULTS

Ucp2 knockout (KO)-PASMCs had lower mitochondrial calcium than Ucp2 wildtype (WT)-PASMCs at baseline and during histamine-stimulated ER-Ca²⁺ release. Normoxic Ucp2KO-PASMCs had mitochondrial hyperpolarization, lower Ca²⁺-sensitive mitochondrial enzyme activity, reduced levels of mitochondrial reactive oxygen species and Krebs' cycle intermediates, and increased resistance to apoptosis, mimicking the hypoxia-induced changes in Ucp2WT-PASMC. Ucp2KO mice spontaneously developed pulmonary vascular remodeling and pulmonary hypertension and exhibited a pseudohypoxic state with pulmonary vascular and systemic hypoxia inducible factor-1α activation (increased hematocrit), not exacerbated further by chronic hypoxia.

CONCLUSIONS

This first description of the role of UCP2 in oxygen sensing and in pulmonary hypertension vascular remodeling may open a new window in biomarker and therapeutic strategies.

Evolution of air breathing: oxygen homeostasis and the transitions from water to land and sky

Life originated in anoxia, but many organisms came to depend upon oxygen for survival, independently evolving diverse respiratory systems for acquiring oxygen from the environment. Ambient oxygen tension (PO2) fluctuated through the ages in correlation with biodiversity and body size, enabling organisms to migrate from water to land and air and sometimes in the opposite direction. Habitat expansion compels the use of different gas exchangers, for example, skin, gills, tracheae, lungs, and their intermediate stages, that may coexist within the same species; coexistence may be temporally disjunct (e.g., larval gills vs. adult lungs) or simultaneous (e.g., skin, gills, and lungs in some salamanders). Disparate systems exhibit similar directions of adaptation: toward larger diffusion interfaces, thinner barriers, finer dynamic regulation, and reduced cost of breathing. Efficient respiratory gas exchange, coupled to downstream convective and diffusive resistances, comprise the "oxygen cascade"-step-down of PO2 that balances supply against toxicity. Here, we review the origin of oxygen homeostasis, a primal selection factor for all respiratory systems, which in turn function as gatekeepers of the cascade. Within an organism's lifespan, the respiratory apparatus adapts in various ways to upregulate oxygen uptake in hypoxia and restrict uptake in hyperoxia. In an evolutionary context, certain species also become adapted to environmental conditions or habitual organismic demands. We, therefore, survey the comparative anatomy and physiology of respiratory systems from invertebrates to vertebrates, water to air breathers, and terrestrial to aerial inhabitants. Through the evolutionary directions and variety of gas exchangers, their shared features and individual compromises may be appreciated.

Photooxidation of Amplex Red to resorufin: implications of exposing the Amplex Red assay to light

The Amplex Red assay, a fluorescent assay for the detection of H(2)O(2), relies on the reaction of H(2)O(2) and colorless, nonfluorescent Amplex Red with a 1:1 stoichiometry to form colored, fluorescent resorufin, catalyzed by horseradish peroxidase (HRP). We have found that resorufin is artifactually formed when Amplex Red is exposed to light. In the absence of H(2)O(2) and HRP, the absorption and fluorescence spectra of Amplex Red changed during exposure to ambient room light or instrumental excitation light, clearly indicating that the fluorescent product resorufin had formed. This photochemistry was initiated by trace amounts of resorufin that are present in Amplex Red stock solutions. ESR spin-trapping studies demonstrated that superoxide radical was an intermediate in this process. Oxygen consumption measurements further confirmed that superoxide and H(2)O(2) were artifactually produced by the photooxidation of Amplex Red. The artifactual formation of resorufin was also significantly increased by the presence of superoxide dismutase or HRP. This photooxidation process will result in a less sensitive assay for H(2)O(2) under ambient light exposure and potentially invalid measurements under high energy exposure such as UVA irradiation. In general, precautions should be taken to minimize exposure to light during measurement of oxidative stress with Amplex Red.

Chronic hypoxia impairs cytochrome oxidase activity via oxidative stress in selected fetal Guinea pig organs

We hypothesized that chronic hypoxia disrupts mitochondrial function via oxidative stress in fetal organs. Pregnant guinea pig sows were exposed to either normoxia or hypoxia (10.5% O2, 14 days) in the presence or absence of the antioxidant, N-acetylcysteine (NAC). Near-term anesthetized fetuses were delivered via hysterotomy, and fetal livers, hearts, lungs, and forebrains harvested. We quantified the effects of chronic hypoxia on cytochrome oxidase (CCO) activity and 2 factors known to regulate CCO activity: malondialdehyde (MDA) and CCO subunit 4 (COX4). Hypoxia increased the MDA levels in fetal liver, heart, and lung with a corresponding reduction in CCO activity, prevented by prenatal NAC. The COX4 expression paralleled CCO activity in fetal liver and lung, but was unaltered in fetal hearts due to hypoxia. Hypoxia reduced the brain COX4 expression despite having no effect on CCO activity. This study identifies the mitochondrion as an important target site in tissue-specific oxidative stress for the induction of fetal hypoxic injury.

Effect of Yifei Huoxue Granule on the proliferation of rat pulmonary artery smooth muscle cells upon exposure to chronic hypoxic conditions in vitro

OBJECTIVE

To investigate the inhibitory effect of Yifei Huoxue Granule (, YFHXG) on the hypoxia-induced proliferation of rat pulmonary artery smooth muscle cells (PASMCs) and its mechanism of decreasing pulmonary arterial pressure.

METHODS

Twenty male Sprague-Dawley (SD) rats were randomly divided into four groups: saline, and 0.66, 3.30 and 16.50 g/kg of YFHXG groups, the saline and different concentrations of YFHXG were given twice daily for 7 days, respectively. Serum-pharmacology method was used in the preparation of YFHXG serum. Tissue block anchorage was employed in the primary culture of rat PASMCs. The PASMCs were randomly divided into normoxia group, hypoxia group, and hypoxia+YFHXG group (0.66, 3.30 and 16.50 g/kg doses of YFHXG-treated serum groups, exposed to hypoxic condition). PASMCs in normoxia and hypoxia group were cultured with saline serum, hypoxia+YFHXG groups were cultured with different concentrations of YFHXG serum. Cell viability was assessed with 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. Cell cycle was analyzed using flow cytometry. In addition, hypoxia inducible factor-1-alpha (HIF-1α) protein expression was evaluated by immunocytochemistry analysis, the concentration of intracellular reactive oxygen species (ROS) and Ca(2+) were determined by laser scanning confocal microscopy (LSCM).

RESULTS

MTT assay and flow cytometry showed that hypoxia could directly activate the proliferation of PASMCs, while YFHXG dose-dependently inhibited hypoxia-induced proliferation of rat PASMCs. Immunocytochemistry showed that hypoxia enhanced HIF-1α protein expression, and LSCM showed that hypoxia significantly increased intracellular ROS and Ca(2+), while YFHXG decreased the expression of HIF- 1α and attenuated the hypoxia-induced increase in intracellular concentration of ROS and Ca(2+).

CONCLUSIONS

YFHXG could inhibit hypoxia-induced proliferation of rat PASMCs, which may decrease pulmonary arterial pressure and vascular remodeling. The anti-hypoxia effect of YFHXG may be explained by its regulation of HIF-1α expression and of the levels of intracellular ROS and Ca(2+).

Characterization of miRNAs in response to short-term waterlogging in three inbred lines of Zea mays

Waterlogging of plants leads to low oxygen levels (hypoxia) in the roots and causes a metabolic switch from aerobic respiration to anaerobic fermentation that results in rapid changes in gene transcription and protein synthesis. Our research seeks to characterize the microRNA-mediated gene regulatory networks associated with short-term waterlogging. MicroRNAs (miRNAs) are small non-coding RNAs that regulate many genes involved in growth, development and various biotic and abiotic stress responses. To characterize the involvement of miRNAs and their targets in response to short-term hypoxia conditions, a quantitative real time PCR (qRT-PCR) assay was used to quantify the expression of the 24 candidate mature miRNA signatures (22 known and 2 novel mature miRNAs, representing 66 miRNA loci) and their 92 predicted targets in three inbred Zea mays lines (waterlogging tolerant Hz32, mid-tolerant B73, and sensitive Mo17). Based on our studies, miR159, miR164, miR167, miR393, miR408 and miR528, which are mainly involved in root development and stress responses, were found to be key regulators in the post-transcriptional regulatory mechanisms under short-term waterlogging conditions in three inbred lines. Further, computational approaches were used to predict the stress and development related cis-regulatory elements on the promoters of these miRNAs; and a probable miRNA-mediated gene regulatory network in response to short-term waterlogging stress was constructed. The differential expression patterns of miRNAs and their targets in these three inbred lines suggest that the miRNAs are active participants in the signal transduction at the early stage of hypoxia conditions via a gene regulatory network; and crosstalk occurs between different biochemical pathways.

Hypoxia induces Kv channel current inhibition by increased NADPH oxidase-derived reactive oxygen species

There is current discussion whether reactive oxygen species are up- or downregulated in the pulmonary circulation during hypoxia, from which sources (i.e., mitochondria or NADPH oxidases) they are derived, and what the downstream targets of ROS are. We recently showed that the NADPH oxidase homolog NOX4 is upregulated in hypoxia-induced pulmonary hypertension in mice and contributes to the vascular remodeling in pulmonary hypertension. We here tested the hypothesis that NOX4 regulates K(v) channels via an increased ROS formation after prolonged hypoxia. We showed that (1) NOX4 is upregulated in hypoxia-induced pulmonary hypertension in rats and isolated rat pulmonary arterial smooth muscle cells (PASMC) after 3days of hypoxia, and (2) that NOX4 is a major contributor to increased reactive oxygen species (ROS) after hypoxia. Our data indicate colocalization of K(v)1.5 and NOX4 in isolated PASMC. The NADPH oxidase inhibitor and ROS scavenger apocynin as well as NOX4 siRNA reversed the hypoxia-induced decrease in K(v) current density whereas the protein levels of the channels remain unaffected by siNOX4 treatment. Determination of cysteine oxidation revealed increased NOX4-mediated K(v)1.5 channel oxidation. We conclude that sustained hypoxia decreases K(v) channel currents by a direct effect of a NOX4-derived increase in ROS.

Hypoxic Pulmonary Vasoconstriction

It has been known for more than 60 years, and suspected for over 100, that alveolar hypoxia causes pulmonary vasoconstriction by means of mechanisms local to the lung. For the last 20 years, it has been clear that the essential sensor, transduction, and effector mechanisms responsible for hypoxic pulmonary vasoconstriction (HPV) reside in the pulmonary arterial smooth muscle cell. The main focus of this review is the cellular and molecular work performed to clarify these intrinsic mechanisms and to determine how they are facilitated and inhibited by the extrinsic influences of other cells. Because the interaction of intrinsic and extrinsic mechanisms is likely to shape expression of HPV in vivo, we relate results obtained in cells to HPV in more intact preparations, such as intact and isolated lungs and isolated pulmonary vessels. Finally, we evaluate evidence regarding the contribution of HPV to the physiological and pathophysiological processes involved in the transition from fetal to neonatal life, pulmonary gas exchange, high-altitude pulmonary edema, and pulmonary hypertension. Although understanding of HPV has advanced significantly, major areas of ignorance and uncertainty await resolution.

Peripheral chemoreceptors: function and plasticity of the carotid body

The discovery of the sensory nature of the carotid body dates back to the beginning of the 20th century. Following these seminal discoveries, research into carotid body mechanisms moved forward progressively through the 20th century, with many descriptions of the ultrastructure of the organ and stimulus-response measurements at the level of the whole organ. The later part of 20th century witnessed the first descriptions of the cellular responses and electrophysiology of isolated and cultured type I and type II cells, and there now exist a number of testable hypotheses of chemotransduction. The goal of this article is to provide a comprehensive review of current concepts on sensory transduction and transmission of the hypoxic stimulus at the carotid body with an emphasis on integrating cellular mechanisms with the whole organ responses and highlighting the gaps or discrepancies in our knowledge. It is increasingly evident that in addition to hypoxia, the carotid body responds to a wide variety of blood-borne stimuli, including reduced glucose and immune-related cytokines and we therefore also consider the evidence for a polymodal function of the carotid body and its implications. It is clear that the sensory function of the carotid body exhibits considerable plasticity in response to the chronic perturbations in environmental O2 that is associated with many physiological and pathological conditions. The mechanisms and consequences of carotid body plasticity in health and disease are discussed in the final sections of this article.

Oxygen matters: tissue culture oxygen levels affect mitochondrial function and structure as well as responses to HIV viroproteins

Mitochondrial dysfunction is implicated in a majority of neurodegenerative disorders and much study of neurodegenerative disease is done on cultured neurons. In traditional tissue culture, the oxygen level that cells experience is dramatically higher (21%) than in vivo conditions (1-11%). These differences can alter experimental results, especially, pertaining to mitochondria and oxidative metabolism. Our results show that primary neurons cultured at physiological oxygen levels found in the brain showed higher polarization, lower rates of ROS production, larger mitochondrial networks, greater cytoplasmic fractions of mitochondria and larger mitochondrial perimeters than those cultured at higher oxygen levels. Although neurons cultured in either physiological oxygen or atmospheric oxygen exhibit significant increases in mitochondrial reactive oxygen species (ROS) production when treated with the human immunodeficiency virus (HIV) virotoxin trans-activator of transcription, mitochondria of neurons cultured at physiological oxygen underwent depolarization with dramatically increased cell death, whereas those cultured at atmospheric oxygen became hyperpolarized with no increase in cell death. Studies with a second HIV virotoxin, negative regulation factor (Nef), revealed that Nef treatment also increased mitochondrial ROS production for both the oxygen conditions, but resulted in mitochondrial depolarization and increased death only in neurons cultured in physiological oxygen. These results indicate a role for oxidative metabolism in a mechanism of neurotoxicity during HIV infection and demonstrate the importance of choosing the correct, physiological, culture oxygen in mitochondrial studies performed in neurons.

Roles for redox mechanisms controlling protein kinase G in pulmonary and coronary artery responses to hypoxia

We previously reported that isolated endothelium-removed bovine pulmonary arteries (BPAs) contract to hypoxia associated with removal of peroxide- and cGMP-mediated relaxation. In contrast, bovine coronary arteries (BCAs) relax to hypoxia associated with cytosolic NADPH oxidation coordinating multiple relaxing mechanisms. Since we recently found that H(2)O(2) relaxes BPAs through PKG activation by both soluble guanylate cyclase (sGC)/cGMP-dependent and cGMP-independent thiol oxidation/subunit dimerization mechanisms, we investigated if these mechanisms participate in BPA contraction and BCA relaxation to hypoxia. The contraction of BPA (precontracted with 20 mM KCl) to hypoxia was associated with decreased PKG dimerization and PKG-mediated vasodilator-stimulated phosphoprotein (VASP) phosphorylation. In contrast, exposure of 20 mM KCl-precontracted endothelium-removed BCAs to hypoxia caused relaxation and increased dimerization and VASP phosphorylation. Depletion of sGC by organoid culture of BPAs with an oxidant of the sGC heme (10 μM 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one) increased aerobic force generation, decreased VASP phosphorylation, and inhibited further contraction to hypoxia and changes in VASP phosphorylation. Thiol reduction with dithiothreitol increased aerobic force in BPAs and decreased PKG dimerization, VASP phosphorylation, and the contraction to hypoxia. Furthermore, PKG-1α and sGC β(1)-subunit small interfering RNA-transfected BPAs demonstrated increased aerobic K(+) force and inhibition of further contraction to hypoxia, associated with an attenuation of H(2)O(2)-elicited relaxation and VASP phosphorylation. Thus, decreases in both a sGC/cGMP-dependent and a dimerization-dependent activation of PKG by H(2)O(2) appear to contribute to the contraction of BPAs elicited by hypoxia. In addition, stimulation of PKG activation by dimerization may be important in the relaxation of coronary arteries to hypoxia.

Reactive oxygen species production and discontinuous gas exchange in insects

While biochemical mechanisms are typically used by animals to reduce oxidative damage, insects are suspected to employ a higher organizational level, discontinuous gas exchange mechanism to do so. Using a combination of real-time, flow-through respirometry and live-cell fluorescence microscopy, we show that spiracular control associated with the discontinuous gas exchange cycle (DGC) in Samia cynthia pupae is related to reactive oxygen species (ROS). Hyperoxia fails to increase mean ROS production, although minima are elevated above normoxic levels. Furthermore, a negative relationship between mean and mean ROS production indicates that higher ROS production is generally associated with lower . Our results, therefore, suggest a possible signalling role for ROS in DGC, rather than supporting the idea that DGC acts to reduce oxidative damage by regulating ROS production.

Pulmonary arterial responses to reactive oxygen species are altered in newborn piglets with chronic hypoxia-induced pulmonary hypertension

Reactive oxygen species (ROS) have been implicated in the pathogenesis of pulmonary hypertension. ROS might mediate vascular responses, at least in part, by stimulating prostanoid production. Our goals were to determine whether the effect of ROS on vascular tone is altered in resistance pulmonary arteries (PRAs) of newborn piglets with chronic hypoxia-induced pulmonary hypertension and the role, if any, of prostanoids in ROS-mediated responses. In cannulated, pressurized PRA, ROS generated by xanthine (X) plus xanthine oxidase (XO) had minimal effect on vascular tone in control piglets but caused significant vasoconstriction in hypoxic piglets. Both cyclooxygenase inhibition with indomethacin and thromboxane synthase inhibition with dazoxiben significantly blunted constriction to X+XO in hypoxic PRA. X+XO increased prostacyclin production (70 ± 8%) by a greater degree than thromboxane production (50 ± 6%) in control PRA; this was not the case in hypoxic PRA where the increases in prostacyclin and thromboxane production were not statistically different (78 ± 13% versus 216 ± 93%, respectively). Thromboxane synthase expression was increased in PRA from hypoxic piglets, whereas prostacyclin synthase expression was similar in PRA from hypoxic and control piglets. Under conditions of chronic hypoxia, altered vascular responses to ROS may contribute to pulmonary hypertension by a mechanism that involves the prostanoid vasoconstrictor, thromboxane.

Intermittent hypoxia augments pulmonary vascular smooth muscle reactivity to NO: regulation by reactive oxygen species

Intermittent hypoxia (IH) resulting from sleep apnea can lead to pulmonary hypertension. IH causes oxidative stress that may limit bioavailability of the endothelium-derived vasodilator nitric oxide (NO) and thus contribute to this hypertensive response. We therefore hypothesized that increased vascular superoxide anion (O(2)(-)) generation reduces NO-dependent pulmonary vasodilation following IH. To test this hypothesis, we examined effects of the O(2)(-) scavenger tiron on vasodilatory responses to the endothelium-dependent vasodilator ionomycin and the NO donor S-nitroso-N-acetylpenicillamine in isolated lungs from hypocapnic-IH (H-IH; 3 min cycles of 5% O(2)/air flush, 7 h/day, 4 wk), eucapnic-IH (E-IH; cycles of 5% O(2), 5% CO(2)/air flush), and sham-treated (air/air cycled) rats. Next, we assessed effects of endogenous O(2)(-) on NO- and cGMP-dependent vasoreactivity and measured O(2)(-) levels using the fluorescent indicator dihydroethidium (DHE) in isolated, endothelium-disrupted small pulmonary arteries from each group. Both E-IH and H-IH augmented NO-dependent vasodilation; however, enhanced vascular smooth muscle (VSM) reactivity to NO following H-IH was masked by an effect of endogenous O(2)(-). Furthermore, H-IH and E-IH similarly increased VSM sensitivity to cGMP, but this response was independent of either O(2)(-) generation or altered arterial protein kinase G expression. Finally, both H-IH and E-IH increased arterial O(2)(-) levels, although this response was more pronounced following H-IH, and H-IH exposure resulted in greater protein tyrosine nitration indicative of increased NO scavenging by O(2)(-). We conclude that IH increases pulmonary VSM sensitivity to NO and cGMP. Furthermore, endogenous O(2)(-) limits NO-dependent vasodilation following H-IH through an apparent reduction in bioavailable NO.

Hypoxia. 4. Hypoxia and ion channel function

The ability to sense and respond to oxygen deprivation is required for survival; thus, understanding the mechanisms by which changes in oxygen are linked to cell viability and function is of great importance. Ion channels play a critical role in regulating cell function in a wide variety of biological processes, including neuronal transmission, control of ventilation, cardiac contractility, and control of vasomotor tone. Since the 1988 discovery of oxygen-sensitive potassium channels in chemoreceptors, the effect of hypoxia on an assortment of ion channels has been studied in an array of cell types. In this review, we describe the effects of both acute and sustained hypoxia (continuous and intermittent) on mammalian ion channels in several tissues, the mode of action, and their contribution to diverse cellular processes.

Oxidant-redox regulation of pulmonary vascular responses to hypoxia and nitric oxide-cGMP signaling

Most current theories for the mechanism of hypoxic pulmonary vasoconstriction (HPV) include a role for reactive oxygen species and/or changes in redox regulation, but extreme controversy exists regarding which systems and redox changes mediate the HPV response. Nitric oxide (NO) appears to help to maintain low pulmonary arterial pressure, suppress HPV, and prevent the development of pulmonary hypertension. Our studies have found a key role for glucose-6-phosphate dehydrogenase in bovine pulmonary arterial smooth muscle functioning to maintain elevated levels of cytosolic NADPH which fuels the generation of vasodilator levels of hydrogen peroxide. HPV results from hypoxia removing vasodilation by peroxide. Decreased superoxide generation by Nox4 oxidase and its conversion to peroxide by Cu,Zn-SOD appear to be potential factors in sensing hypoxia, and decreased cGMP-associated vasodilation and removal of redox controlled vasodilator mechanisms by increased cytosolic NADPH may be key coordinators of the HPV response. Oxidant generation associated with vascular disease processes, including the removal of NO by superoxide, and attenuation of its ability to stimulate cGMP production by oxidation of the heme and thiols of soluble guanylate cyclase attenuate potential beneficial actions of NO on pulmonary arterial function. While pulmonary hypertension appears to have multiple poorly understood effects on redox-associated processes, potentially influencing responses to hypoxia and NO-cGMP signaling, much remains to be elucidated regarding how these processes may be important factors in the progression, expression and therapeutic treatment of pulmonary hypertension.

Diacylglycerol regulates acute hypoxic pulmonary vasoconstriction via TRPC6

Background

Hypoxic pulmonary vasoconstriction (HPV) is an essential mechanism of the lung that matches blood perfusion to alveolar ventilation to optimize gas exchange. Recently we have demonstrated that acute but not sustained HPV is critically dependent on the classical transient receptor potential 6 (TRPC6) channel. However, the mechanism of TRPC6 activation during acute HPV remains elusive. We hypothesize that a diacylglycerol (DAG)-dependent activation of TRPC6 regulates acute HPV.

Methods

We investigated the effect of the DAG analog 1-oleoyl-2-acetyl-sn-glycerol (OAG) on normoxic vascular tone in isolated perfused and ventilated mouse lungs from TRPC6-deficient and wild-type mice. Moreover, the effects of OAG, the DAG kinase inhibitor R59949 and the phospholipase C inhibitor U73122 on the strength of HPV were investigated compared to those on non-hypoxia-induced vasoconstriction elicited by the thromboxane mimeticum U46619.

Results

OAG increased normoxic vascular tone in lungs from wild-type mice, but not in lungs from TRPC6-deficient mice. Under conditions of repetitive hypoxic ventilation, OAG as well as R59949 dose-dependently attenuated the strength of acute HPV whereas U46619-induced vasoconstrictions were not reduced. Like OAG, R59949 mimicked HPV, since it induced a dose-dependent vasoconstriction during normoxic ventilation. In contrast, U73122, a blocker of DAG synthesis, inhibited acute HPV whereas U73343, the inactive form of U73122, had no effect on HPV.

Conclusion

These findings support the conclusion that the TRPC6-dependency of acute HPV is induced via DAG.

Redox regulation of guanylate cyclase and protein kinase G in vascular responses to hypoxia

The production of cGMP by the soluble form of guanylate cyclase (sGC) in bovine pulmonary arteries (BPA) is controlled by cytosolic NADPH maintaining reduced thiol and heme sites on sGC needed for activation by NO, and the levels of Nox oxidase-derived superoxide and peroxide that influence pathways regulating sGC activity. Our recent studies in BPA suggest that the activities of peroxide metabolizing pathways in vascular smooth muscle potentially determine the balance between sGC stimulation by peroxide and a cGMP-independent activation of cGMP-dependent protein kinase (PKG) by a disulfide-mediated subunit dimerization. Cytosolic NADPH oxidation also appears to function in BPA through its influence on protein thiol redox control as an additional mechanism promoting vascular relaxation through PKG activation. These processes regulating PKG may participate in decreases in peroxide and increases in NADPH associated with contraction of BPA to hypoxia and in cytosolic NADPH oxidation potentially mediating bovine coronary artery relaxation to hypoxia.

Mitochondrial superoxide anion radicals mediate induction of apoptosis in cardiac myoblasts exposed to chronic hypoxia

Both reactive oxygen species (ROS) and ATP depletion may be significant in hypoxia-induced damage and death, either collectively or independently, with high energy requiring, metabolically active cells being the most susceptible to damage. We investigated the kinetics and effects of ROS production in cardiac myoblasts, H9C2 cells, under 2%, 10% and 21% O₂ in the presence or absence of apocynin, rotenone and carbonyl cyanide p-(trifluoromethoxy) phenylhydrazone. H9C2 cells showed significant loss of viability within 30 min of culture at 2% oxygen which was not due to apoptosis, but was associated with an increase in protein oxidation. However, after 4 h, apoptosis induction was observed at 2% oxygen and also to a lesser extent at 10% oxygen; this was dependent on the levels of mitochondrial superoxide anion radicals determined using dihydroethidine. Hypoxia-induced ROS production and cell death could be rescued by the mitochondrial complex I inhibitor, rotenone, despite further depletion of ATP. In conclusion, a change to superoxide anion radical steady state level was not detectable after 30 min but was evident after 4 h of mild or severe hypoxia. Superoxide anion radicals from the mitochondrion and not ATP depletion is the major cause of apoptotic cell death in cardiac myoblasts under chronic, severe hypoxia.

A revisit to O2 sensing and transduction in the carotid body chemoreceptors in the context of reactive oxygen species biology

Oxygen-sensing and transduction in purposeful responses in cells and organisms is of great physiological and medical interest. All animals, including humans, encounter in their lifespan many situations in which oxygen availability might be insufficient, whether acutely or chronically, physiologically or pathologically. Therefore to trace at the molecular level the sequence of events or steps connecting the oxygen deficit with the cell responses is of interest in itself as an achievement of science. In addition, it is also of great medical interest as such knowledge might facilitate the therapeutical approach to patients and to design strategies to minimize hypoxic damage. In our article we define the concepts of sensors and transducers, the steps of the hypoxic transduction cascade in the carotid body chemoreceptor cells and also discuss current models of oxygen- sensing (bioenergetic, biosynthetic and conformational) with their supportive and unsupportive data from updated literature. We envision oxygen-sensing in carotid body chemoreceptor cells as a process initiated at the level of plasma membrane and performed by a hemoprotein, which might be NOX4 or a hemoprotein not yet chemically identified. Upon oxygen-desaturation, the sensor would experience conformational changes allosterically transmitted to oxygen regulated K+ channels, the initial effectors in the transduction cascade. A decrease in their opening probability would produce cell depolarization, activation of voltage dependent calcium channels and release of neurotransmitters. Neurotransmitters would activate the nerve endings of the carotid body sensory nerve to convey the information of the hypoxic situation to the central nervous system that would command ventilation to fight hypoxia.

Redox regulation of responses to hypoxia and NO-cGMP signaling in pulmonary vascular pathophysiology

Pulmonary vascular responses elicited by hypoxia and NO-cGMP signaling are potentially influenced by ROS and redox mechanisms that change during the progression of disease processes. Our studies in endothelium-rubbed bovine pulmonary arteries suggest increased glucose-6-phosphate dehydrogenase levels (compared to coronary arteries) seem to maintain a tonic peroxide-mediated relaxation removed by hypoxia through NADPH fueling superoxide generation from Nox oxidase. The activities of glucose-6-phosphate dehydrogenase, oxidases (i.e., Nox4), and systems metabolizing superoxide and peroxide markedly influence hypoxic pulmonary vasoconstriction (HPV). Activation of soluble guanylate cyclase and cGMP protein kinase seems to participate in peroxide-elicited relaxation. Endogenous NO helps maintain low pulmonary arterial pressure and suppresses HPV. Multiple redox processes potentially occurring during the progression of pulmonary hypertension may also attenuate NO-mediated relaxation beyond its scavenging by superoxide, including oxidation of guanylate cyclase heme and thiols normally maintained by cytosolic NADPH redox control.