Hypoxic pulmonary vasoconstriction: redox events in oxygen sensing

Mitochondrial ROS-PKCepsilon signaling axis is uniquely involved in hypoxic increase in [Ca2+]i in pulmonary artery smooth muscle cells

The molecular mechanisms underlying hypoxic responses in pulmonary and systemic arteries remain obscure. Here we for the first time report that acute hypoxia significantly increased total PKC and PKCepsilon activity in pulmonary, but not mesenteric arteries, while these two tissues showed comparable PKCepsilon protein expression and activation by the PKC activator phorbol 12-myristate 13-acetate. Hypoxia induced an increase in intracellular reactive oxygen species (ROS) generation in isolated pulmonary artery smooth muscle cells (PASMCs), but not in mesenteric artery SMCs. Inhibition of mitochondrial ROS generation with rotenone, myxothiazol, or glutathione peroxidase-1 overexpression prevented hypoxia-induced increases in total PKC and PKCepsilon activity in pulmonary arteries. The inhibitory effects of rotenone were reversed by exogenous hydrogen peroxide. A PKCepsilon translocation peptide inhibitor or PKCepsilon gene deletion decreased hypoxic increase in [Ca(2+)](i) in PASMCs, whereas the conventional PKC inhibitor GO6976 had no effect. These data suggest that acute hypoxia may specifically increase mitochondrial ROS generation, which subsequently activates PKC, particularly PKCepsilon, contributing to hypoxia-induced increase in [Ca(2+)](i) and contraction in PASMCs.

Response of mitochondrial reactive oxygen species generation to steady-state oxygen tension: implications for hypoxic cell signaling

Mitochondria are proposed to play an important role in hypoxic cell signaling. One currently accepted signaling paradigm is that the mitochondrial generation of reactive oxygen species (ROS) increases in hypoxia. This is paradoxical, because oxygen is a substrate for ROS generation. Although the response of isolated mitochondrial ROS generation to [O(2)] has been examined previously, such investigations did not apply rigorous control over [O(2)] within the hypoxic signaling range. With the use of open-flow respirometry and fluorimetry, the current study determined the response of isolated rat liver mitochondrial ROS generation to defined steady-state [O(2)] as low as 0.1 microM. In mitochondria respiring under state 4 (quiescent) or state 3 (ATP turnover) conditions, decreased ROS generation was always observed at low [O(2)]. It is concluded that the biochemical mechanism to facilitate increased ROS generation in response to hypoxia in cells is not intrinsic to the mitochondrial respiratory chain alone but may involve other factors. The implications for hypoxic cell signaling are discussed.

MYC can induce DNA breaks in vivo and in vitro independent of reactive oxygen species

MYC overexpression is thought to initiate tumorigenesis by inducing cellular proliferation and growth and to be restrained from causing tumorigenesis by inducing cell cycle arrest, cellular senescence, and/or apoptosis. Here we show that MYC can induce DNA breaks both in vitro and in vivo independent of increased production of reactive oxygen species (ROS). We provide an insight into the specific circumstances under which MYC generates ROS in vitro and propose a possible mechanism. We found that MYC induces DNA double-strand breaks (DSBs) independent of ROS production in murine lymphocytes in vivo as well as in normal human foreskin fibroblasts (NHFs) in vitro in normal (10%) serum, as measured by gammaH2AX staining. However, NHFs cultured in vitro in low serum (0.05%) and/or ambient oxygen saturation resulted in ROS-associated oxidative damage and DNA single-strand breaks (SSBs), as measured by Ape-1 staining. In NHFs cultured in low versus normal serum, MYC induced increased expression of CYP2C9, a gene product well known to be associated with ROS production. Specific inhibition of CYP2C9 by small interfering RNA was shown to partially inhibit MYC-induced ROS production. Hence, MYC overexpression can induce ROS and SSBs under some conditions, but generally induces widespread DSBs in vivo and in vitro independent of ROS production.

Molecular Biology of Chronic Thromboembolic Pulmonary Hypertension

Recent efforts have seen major advances in elucidating the mechanisms underlying pulmonary arterial hypertension. However, chronic thromboembolic pulmonary hypertension (CTEPH) often has been excluded from these studies. Consequently, whereas the clinical, radiographic, and hemodynamic characteristics of CTEPH have been well described, there remains a deficit in our understanding of the cellular, molecular, and genetic mechanisms underlying CTEPH. Furthermore, although prior venous thromboembolism may act as the inciting event, it is still unclear what predisposes some patients to develop CTEPH. CTEPH has two major pathogenic components. The first is the primary obstruction of central pulmonary arteries by accumulation of thrombotic material. The second is characterized by severe pulmonary vascular remodeling, similar to that seen in idiopathic pulmonary arterial hypertension. Other articles in this series describe the pathological, surgical, and therapeutic aspects of CTEPH. Here, we review the potential molecular and cellular mechanisms that may contribute to the pathogenesis of CTEPH.

Hypoxic vasoconstriction of partial muscular intra-acinar pulmonary arteries in murine precision cut lung slices

Background

Acute alveolar hypoxia causes pulmonary vasoconstriction (HPV) which serves to match lung perfusion to ventilation. The underlying mechanisms are not fully resolved yet. The major vascular segment contributing to HPV, the intra-acinar artery, is mostly located in that part of the lung that cannot be selectively reached by the presently available techniques, e.g. hemodynamic studies of isolated perfused lungs, recordings from dissected proximal arterial segments or analysis of subpleural vessels. The aim of the present study was to establish a model which allows the investigation of HPV and its underlying mechanisms in small intra-acinar arteries.

Methods

Intra-acinar arteries of the mouse lung were studied in 200 μm thick precision-cut lung slices (PCLS). The organisation of the muscle coat of these vessels was characterized by α-smooth muscle actin immunohistochemistry. Basic features of intra-acinar HPV were characterized, and then the impact of reactive oxygen species (ROS) scavengers, inhibitors of the respiratory chain and Krebs cycle metabolites was analysed.

Results

Intra-acinar arteries are equipped with a discontinuous spiral of α-smooth muscle actin-immunoreactive cells. They exhibit a monophasic HPV (medium gassed with 1% O₂) that started to fade after 40 min and was lost after 80 min. This HPV, but not vasoconstriction induced by the thromboxane analogue U46619, was effectively blocked by nitro blue tetrazolium and diphenyleniodonium, indicating the involvement of ROS and flavoproteins. Inhibition of mitochondrial complexes II (3-nitropropionic acid, thenoyltrifluoroacetone) and III (antimycin A) specifically interfered with HPV, whereas blockade of complex IV (sodium azide) unspecifically inhibited both HPV and U46619-induced constriction. Succinate blocked HPV whereas fumarate had minor effects on vasoconstriction.

Conclusion

This study establishes the first model for investigation of basic characteristics of HPV directly in intra-acinar murine pulmonary vessels. The data are consistent with a critical involvement of ROS, flavoproteins, and of mitochondrial complexes II and III in intra-acinar HPV. In view of the lack of specificity of any of the classical inhibitors used in such types of experiments, validation awaits the use of appropriate knockout strains and siRNA interference, for which the present model represents a well-suited approach.

A central role for ROS in the functional remodelling of L-type Ca2+ channels by hypoxia

Periods of prolonged hypoxia are associated clinically with an increased incidence of dementia, the most common form of which is Alzheimer's disease. Here, we review recent studies aimed at providing a cellular basis for this association. Hypoxia promoted an enhanced secretory response of excitable cells via formation of a novel Ca2+ influx pathway associated with the formation of amyloid peptides of Alzheimer's disease. More strikingly, hypoxia potentiated Ca2+ influx specifically through L-type Ca2+ channels in three distinct cellular systems. This effect was post-transcriptional, and evidence suggests it occurred via increased formation of amyloid peptides which alter Ca2+ channel trafficking via a mechanism involving increased production of reactive oxygen species by mitochondria. This action of hypoxia is likely to contribute to dysregulation of Ca2+ homeostasis, which has been proposed as a mechanism of cell death in Alzheimer's disease. We suggest, therefore, that our data provide a cellular basis to account for the known increased incidence of Alzheimer's disease in patients who have suffered prolonged hypoxic episodes.

Mitochondrial reactive oxygen species and Ca2+ signaling

Mitochondria are an important source of reactive oxygen species (ROS) formed as a side product of oxidative phosphorylation. The main sites of oxidant production are complex I and complex III, where electrons flowing from reduced substrates are occasionally transferred to oxygen to form superoxide anion and derived products. These highly reactive compounds have a well-known role in pathological states and in some cellular responses. However, although their link with Ca(2+) is well studied in cell death, it has been hardly investigated in normal cytosolic calcium concentration ([Ca(2+)](i)) signals. Several Ca(2+) transport systems are modulated by oxidation. Oxidation increases the activity of inositol 1,4,5-trisphosphate and ryanodine receptors, the main channels releasing Ca(2+) from intracellular stores in response to cellular stimulation. On the other hand, mitochondria are known to control [Ca(2+)](i) signals by Ca(2+) uptake and release during cytosolic calcium mobilization, specially in mitochondria situated close to Ca(2+) release channels. Mitochondrial inhibitors modify calcium signals in numerous cell types, including oscillations evoked by physiological stimulus. Although these inhibitors reduce mitochondrial Ca(2+) uptake, they also impair ROS production in several systems. In keeping with this effect, recent reports show that antioxidants or oxidant scavengers also inhibit physiological calcium signals. Furthermore, there is evidence that mitochondria generate ROS in response to cell stimulation, an effect suppressed by mitochondrial inhibitors that simultaneously block [Ca(2+)](i) signals. Together, the data reviewed here indicate that Ca(2+)-mobilizing stimulus generates mitochondrial ROS, which, in turn, facilitate [Ca(2+)](i) signals, a new aspect in the biology of mitochondria. Finally, the potential implications for biological modeling are discussed.

Dietary soy modulates endothelium-dependent relaxation in aged male rats: Increased agonist-induced endothelium-derived hyperpolarising factor and basal nitric oxide activity

We examined the effects of dietary soy on the contributions of endothelium-derived hyperpolarising factor (EDHF), nitric oxide (NO), and oxidative stress to vascular tone in isolated aortic rings and small mesenteric and pulmonary arteries in vitro. Male Wistar rats were either continuously fed a soy-deficient diet (SD) or switched from a soy-deficient diet to a soy-rich one for 6 months (SW). Contractile responses were generally smaller in arteries from SW rats. In mesenteric arteries, this difference was blunted by L-NAME, but not by charybdotoxin and apamin. Preconstricted SW mesenteric arteries were more sensitive to acetylcholine (ACh) than SD ones. This difference was unaffected by L-NAME but was abolished by charybdotoxin and apamin. Exogenous superoxide dismutase (SOD) and catalase induced powerful relaxations in aortic rings, which were smaller in those from SW rats. In mesenteric and pulmonary arteries, however, they partially inhibited ACh-mediated relaxation, and enhanced PGF(2alpha)-mediated contraction, respectively. Our results suggest that feeding aging male rats a soy-rich diet results in improved agonist-mediated EDHF production and a generalized reduction in contractile force, which is partly due to elevated basal NO. Our data also suggest a prorelaxant role for endogenous H(2)O(2) in small arteries, which is modulated by a soy diet.

Oxidative stress at the vascular wall. Mechanistic and pharmacological aspects

During the process of energy production in aerobic respiration, vascular cells produce reactive oxygen species (ROS). A growing body of evidence indicates that oxidative stress refers to a condition in which cells are subjected to excessive levels of ROS. Overall vascular function is dependent upon a fine balance of oxidant and antioxidant mechanisms, which determine endothelial functions. Considerable experimental and clinical data indicate that intracellular oxidant milieu is also involved in several redox-sensitive cellular signaling pathways such as ion transport systems, protein phosphorylation, and gene expression and thus also plays important roles as modulator of vascular cell functions such as cell growth, apoptosis, migration, angiogenesis and cell adhesion. Overproduction of ROS under pathophysiologic conditions is integral in the development of cardiovascular diseases. This fact has raised an intensive search of new pharmacological approaches to improve vascular hemostasis and particularly those intended to decrease oxidative stress or augment the antioxidant defense mechanisms.

Mitochondria as signaling organelles in the vascular endothelium

Vascular endothelial cells are highly glycolytic and consume relatively low amounts of oxygen (O(2)) compared with other cells. We have confirmed that oxidative phosphorylation is not the main source of ATP generation in these cells. We also show that at a low O(2) concentration (<1%) endogenous NO plays a key role in preventing the accumulation of the alpha-subunit of hypoxia-inducible factor 1. At higher O(2) concentrations (1-3%) NO facilitates the production of mitochondrial reactive oxygen species. This production activates the AMP-activated protein kinase by a mechanism independent of nucleotide concentrations. Thus, the primary role of mitochondria in vascular endothelial cells may not be to generate ATP but, under the control of NO, to act as signaling organelles using either O(2) or O(2)-derived species as signaling molecules. Diversion of O(2) away from endothelial cell mitochondria by NO might also facilitate oxygenation of vascular smooth muscle cells.

Role of O2-sensitive K+ and Ca2+ channels in the regulation of the pulmonary circulation: Potential role of caveolae and implications for high altitude pulmonary edema

High altitude pulmonary edema (HAPE) is a potentially fatal complication in response to exposure to low O(2) at high altitudes. Hypoxia, by causing pulmonary vasoconstriction, increases pulmonary vascular resistance and pulmonary arterial pressure, both of which are features in the pathogenesis of HAPE. Uneven hypoxic pulmonary vasoconstriction is thought to be responsible for increased capillary pressure and leakage, resulting in edema. O(2)-sensitive ion channels are known to play pivotal roles in determining vascular tone in response to hypoxia. K(+), Ca(2+) and Na(+) channels are ubiquitously expressed in both endothelial and smooth muscle cells of the pulmonary microvasculature, subfamilies of which are regulated by local changes in P(O(2)). Hypoxia reduces activity of voltage-gated K(+) channels and down-regulates their expression leading to membrane depolarization, Ca(2+) influx in pulmonary artery smooth muscle cells (by activating voltage-dependent Ca(2+) channels) and vasoconstriction. Hypoxia up-regulates transient receptor potential channels (TRPC) leading to enhanced Ca(2+) entry through receptor- and store-operated Ca(2+) channels. Altered enrichment of ion channels in membrane microdomains, in particular in caveolae, may play a role in excitation-contraction coupling and perhaps in O(2)-sensing in the pulmonary circulation and thereby may contribute to the development of HAPE. We review the role of ion channels, in particular those outlined above, in response to low O(2) on vascular tone and pulmonary edema. Advances in the understanding of ion channels involved in the physiological response to hypoxia should lead to a greater understanding of the pathogenesis of HAPE and perhaps in the identification of new therapies.

Red blood cells and hemoglobin in hypoxic pulmonary vasoconstriction

Nitric oxide (NO) plays an important role in the modulation of hypoxic pulmonary vasoconstriction; in turn, red blood cells (RBCs) augment HPV by hemoglobin-mediated oxidation and inactivation of NO. In addition, scavenging of reactive oxygen species by RBCs may play a role in augmentation of HPV. NO delivery and/or production by RBCs does not appear to be important in the control of pulmonary vasomotor tone. This review will discuss regulation of HPV by RBCs with an emphasis on hemoglobin-NO interactions. In addition, the review will discuss how biologic (S-nitrosation) or pharmacologic (cross-linking) modification of hemoglobin may affect pulmonary circulatory-hemoglobin interactions.

Impact of mitochondria and NADPH oxidases on acute and sustained hypoxic pulmonary vasoconstriction

Hypoxic pulmonary vasoconstriction (HPV) matches lung perfusion with ventilation to optimize pulmonary gas exchange. However, it remains unclear whether acute HPV (occurring within seconds) and the vasoconstrictor response to sustained alveolar hypoxia (developing over several hours) are triggered by identical mechanisms. We investigated the effect of mitochondrial and NADPH oxidase inhibitors on both phases of HPV in intact rabbit lungs. These studies revealed that the sustained HPV is largely dependent on mitochondrial complex I and totally dependent on complex IV, whereas NADPH oxidase dependence was only observed for acute HPV. These findings were reinforced by an alternative approach employing lungs from mice deficient in the NADPH oxidase subunit p 47(phox). In these mice (which lack a subunit suggested to be important for the function of most NADPH oxidase isoforms), but not in gp 91(phox)-deficient mice (which represent only one isoform of NADPH oxidases), acute HPV was significantly reduced, while non-hypoxia-induced vasoconstrictions elicited by the thromboxane mimetic U46619 were not affected. We concluded that the acute phase and the sustained phase of HPV are differentially regulated, with NADPH oxidase activity predominating in the acute phase, while a strong dependence on mitochondrial participation was observed for the second phase.

Cloning of the human TASK-2 (KCNK5) promoter and its regulation by chronic hypoxia

The tandem P domain potassium channel family includes five members of the acid-sensing subfamily, TASK. TASK channels are active at resting potential and are inhibited by extracellular protons, suggesting they function as acid sensors and control excitability/ion homeostasis. Indeed, TASK-2 (KCNK5) has been shown to control excitability, volume regulation, bicarbonate handling, and apoptosis in a variety of tissues. With such diverse functions being ascribed to TASK-2, it is important to understand long-term as well as short-term regulation of this important channel. Thus, we have cloned the TASK-2 promoter, demonstrated that its transcriptional activity is dependent upon pO(2), shown that deletion of overlapping consensus binding sites for NF-kappaB/Elk-1 ablates this O(2) sensitivity, and proved that Elk-1 binds preferentially to this site. Furthermore, the consequences of chronic hypoxia on natively expressed TASK-2 are decreased steady-state mRNA and cell depolarization showing that TASK-2 contributes to the excitability of this important lung cell type.

Hypoxic pulmonary vasoconstriction: mechanisms and controversies

The pulmonary circulation differs from the systemic in several important aspects, the most important being that pulmonary arteries constrict to moderate physiological (20-60 mmHg PO2) hypoxia, whereas systemic arteries vasodilate. This phenomenon is called hypoxic pulmonary vasoconstriction (HPV), and is responsible for maintaining the ventilation-perfusion ratio during localized alveolar hypoxia. In disease, however, global hypoxia results in a detrimental increase in total pulmonary vascular resistance, and increased load on the right heart. Despite many years of study, the precise mechanisms underlying HPV remain unresolved. However, as we argue below, there is now overwhelming evidence that hypoxia can stimulate several pathways leading to a rise in the intracellular Ca2+ concentration ([Ca2+]i) in pulmonary artery smooth muscle cells (PASMC). This rise in [Ca2+]i is consistently found to be relatively small, and HPV seems also to require rho kinase-mediated Ca2+ sensitization. There is good evidence that HPV also has an as yet unexplained endothelium dependency. In this brief review, we highlight selected recent findings and ongoing controversies which continue to animate the study of this remarkable and unique response of the pulmonary vasculature to hypoxia.

Acute hypoxia selectively inhibits KCNA5 channels in pulmonary artery smooth muscle cells

Acute hypoxia causes pulmonary vasoconstriction in part by inhibiting voltage-gated K(+) (Kv) channel activity in pulmonary artery smooth muscle cells (PASMC). The hypoxia-mediated decrease in Kv currents [I(K(V))] is selective to PASMC; hypoxia has little effect on I(K(V)) in mesenteric artery smooth muscle cells (MASMC). Functional Kv channels are homo- and/or heterotetramers of pore-forming alpha-subunits and regulatory beta-subunits. KCNA5 is a Kv channel alpha-subunit that forms functional Kv channels in PASMC and regulates resting membrane potential. We have shown that acute hypoxia selectively inhibits I(K(V)) through KCNA5 channels in PASMC. Overexpression of the human KCNA5 gene increased I(K(V)) and caused membrane hyperpolarization in HEK-293, COS-7, and rat MASMC and PASMC. Acute hypoxia did not affect I(K(V)) in KCNA5-transfected HEK-293 and COS-7 cells. However, overexpression of KCNA5 in PASMC conferred its sensitivity to hypoxia. Reduction of Po(2) from 145 to 35 mmHg reduced I(K(V)) by approximately 40% in rat PASMC transfected with human KCNA5 but had no effect on I(K(V)) in KCNA5-transfected rat MASMC (or HEK and COS cells). These results indicate that KCNA5 is an important Kv channel that regulates resting membrane potential and that acute hypoxia selectively reduces KCNA5 channel activity in PASMC relative to MASMC and other cell types. Because Kv channels (including KCNA5) are ubiquitously expressed in PASMC and MASMC, the observation from this study indicates that a hypoxia-sensitive mechanism essential for inhibiting KCNA5 channel activity is exclusively present in PASMC. The divergent effect of hypoxia on I(K(V)) in PASMC and MASMC also may be due to different expression levels of KCNA5 channels.

Hypoxia-induced reactive oxygen species downregulate ETB receptor-mediated contraction of rat pulmonary arteries

Production of reactive oxygen species (ROS) may be increased during hypoxia in pulmonary arteries. In this study, the role of ROS in the effect of hypoxia on endothelin (ET) type B (ETB) receptor-mediated vasocontraction in lungs was determined. In rat intrapulmonary (approximately 0.63 mm ID) arteries, contraction induced by IRL-1620 (a selective ETB receptor agonist) was significantly attenuated after 4 h of hypoxia (30 mmHg Po2) compared with normoxic control (140 mmHg Po2). The effect was abolished by tiron, a scavenger of superoxide anions, but not by polyethylene glycol (PEG)-conjugated catalase, which scavenges H2O2. The hypoxic effect on ETB receptor-mediated vasoconstriction was also abolished by endothelium denudation but not by nitro-L-arginine and indomethacin. Exposure for 4 h to exogenous superoxide anions, but not H2O2, attenuated the vasoconstriction induced by IRL-1620. Confocal study showed that hypoxia increased ROS production in pulmonary arteries that were scavenged by PEG-conjugated SOD. In endothelium-intact pulmonary arteries, the ETB receptor protein was reduced after 4 h of exposure to hypoxia, exogenous superoxide anions, or ET-1. BQ-788, a selective ETB receptor antagonist, prevented these effects. ET-1 production was stimulated in endothelium-intact arteries after 4 h of exposure to hypoxia or exogenous superoxide anions. This effect was blunted by PEG-conjugated SOD. These results demonstrate that exposure to hypoxia attenuates ETB receptor-mediated contraction of rat pulmonary arteries. A hypoxia-induced production of superoxide anions may increase ET-1 release from the endothelium and result in downregulation of ETB receptors on smooth muscle.

Sensing and signalling in response to oxygen deprivation in plants and other organisms

AIMS AND SCOPE

All aerobic organisms require molecular di-oxygen (O2) for efficient production of ATP though oxidative phosphorylation. Cellular depletion of oxygen results in rapid molecular and physiological acclimation. The purpose of this review is to consider the processes of low oxygen sensing and response in diverse organisms, with special consideration of plant cells.

CONCLUSIONS

The sensing of oxygen deprivation in bacteria, fungi, metazoa and plants involves multiple sensors and signal transduction pathways. Cellular responses result in a reprogramming of gene expression and metabolic processes that enhance transient survival and can enable long-term tolerance to sub-optimal oxygen levels. The mechanism of sensing can involve molecules that directly bind or react with oxygen (direct sensing), or recognition of altered cellular homeostasis (indirect sensing). The growing knowledge of the activation of genes in response to oxygen deprivation has provided additional information on the response and acclimation processes. Conservation of calcium fluxes and reactive oxygen species as second messengers in signal transduction pathways in metazoa and plants may reflect the elemental importance of rapid sensing of cellular restriction in oxygen by aerobic organisms.

Oxidant and redox signaling in vascular oxygen sensing mechanisms: basic concepts, current controversies, and potential importance of cytosolic NADPH

Vascular smooth muscle (VSM) derived from pulmonary arteries generally contract to hypoxia, whereas VSM from systemic arteries usually relax, indicating the presence of basic oxygen-sensing mechanisms in VSM that are adapted to the environment from which they are derived. This review considers how fundamental processes associated with the generation of reactive oxygen species (ROS) by oxidase enzymes, the metabolic control of cytosolic NADH, NADPH and glutathione redox systems, and mitochondrial function interact with signaling systems regulating vascular force in a manner that is potentially adapted to be involved in Po2 sensing. Evidence for opposing hypotheses of hypoxia, either decreasing or increasing mitochondrial ROS, is considered together with the Po2 dependence of ROS production by Nox oxidases as sensors potentially contributing to hypoxic pulmonary vasoconstriction. Processes through which ROS and NAD(P)H redox changes potentially control interactive signaling systems, including soluble guanylate cyclase, potassium channels, and intracellular calcium are discussed together with the data supporting their regulation by redox in responses to hypoxia. Evidence for hypothesized potential differences between systemic and pulmonary arteries originating from properties of mitochondrial ROS generation and the redox sensitivity of potassium channels is compared with a new hypothesis in which differences in the control of cytosolic NADPH redox by the pentose phosphate pathway results in increased NADPH and Nox oxidase-derived ROS in pulmonary arteries, whereas lower levels of glucose-6-phosphate dehydrogenase in coronary arteries may permit hypoxia to activate a vasodilator mechanism controlled by oxidation of cytosolic NADPH.

Cobalt chloride, a hypoxia-mimicking agent, modulates redox status and functional parameters of cultured swine granulosa cells

Hypoxia occurs physiologically during ovarian follicle growth; this deprivation represents a triggering stimulus for the production of vascular endothelial growth factor (VEGF) by proliferating granulosa cells, which are mostly responsible for the growth of the follicle. Moreover, the steroidogenic activity of these cells ensures a receptive environment for the implantation and development of the early embryo. The present paper reports the adaptive response of swine granulosa cells to cobalt chloride (CoCl2), a chemical hypoxia-mimicking agent. The effects of the treatment were evaluated on cell proliferation, steroidogenesis and VEGF production. In addition, because mithocondrial reactive oxygen species (ROS) are possibly involved in O2 sensing, ROS levels and scavenging enzyme activity were investigated. In the present study, CoCl2 had no effect on progesterone production, although it significantly reduced oestradiol synthesis. The addition of CoCl2 to granulosa cell culture stimulated VEGF production and the generation of hydrogen peroxide. Chemical hypoxia had different effects on scavenger enzyme activities: the activity of superoxide dismutase was enhanced, that of peroxidase reduced and catalase activity was unaffected. The net result is a ‘pro-oxidant’ state, which appears to be possibly involved in the stimulation of VEGF production, thus inducing follicular angiogenesis.

High altitude pulmonary hypertension: role of K+ and Ca2+ channels

Global alveolar hypoxia, as experienced at high-altitude living, has a serious impact on vascular physiology, particularly on the pulmonary vasculature. The effects of sustained hypoxia on pulmonary arteries include sustained vasoconstriction and enhanced medial hypertrophy. As the major component of the vascular media, pulmonary artery smooth muscle cells (PASMC) are the main effectors of the physiological response(s) induced during or following hypoxic exposure. Endothelial cells, on the other hand, can sense humoral and hemodynamic changes incurred by hypoxia, triggering their production of vasoactive and mitogenic factors that then alter PASMC function and growth. Transmembrane ion flux through channels in the plasma membrane not only modulates excitation- contraction coupling in PASMC, but also regulates cell volume, apoptosis, and proliferation. In this review, we examine the roles of K+ and Ca2+ channels in the pulmonary vasoconstriction and vascular remodeling observed during chronic hypoxia-induced pulmonary hypertension.