Hypoxia and carbon monoxide in the vasculature.

Department of Medicine, Division of Newborn Medicine, Children's Hospital, Harvard Medical School, Boston, MA 02115, USA.
Antioxidants and Redox Signaling (Impact Factor: 7.67). 05/2002; 4(2):291-9. DOI: 10.1089/152308602753666343
Source: PubMed

ABSTRACT Hypoxia is sensed by all mammalian cells and elicits a variety of adaptive and pathophysiological responses at the molecular and cellular level. For the pulmonary vasculature, hypoxia causes increased vasoconstriction and vessel-wall remodeling. These responses are mediated by complex intracellular cascades leading to altered gene expression and cell-cell interaction. Hypoxia transiently increases the transcriptional rate of the heme oxygenase-1 (HO-1) gene, resulting in increased production of carbon monoxide (CO) and bilirubin. CO has vasodilatory and antiinflammatory properties in the vasculature, whereas bilirubin is an antioxidant. Both enzymatic products could thus modulate the hypoxic cellular response. Accumulating data suggest that CO inhibits the hypoxic induction of genes encoding vasoconstrictors and smooth muscle cell mitogens in the early hypoxic phase. During chronic hypoxia, low CO levels tilt the balance toward increased production of growth factors and vasoconstrictors that promote vessel-wall remodeling. Mice null in the HO-1 gene manifest decreased tolerance to hypoxia with right ventricular dilatation and infarction, whereas targeted lung overexpression of HO-1 prevents hypoxia-induced inflammatory responses and protects against the development of pulmonary hypertension. Such observations point to CO as a critical modulator of the body's adaptive responses to hypoxia.

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    ABSTRACT: Das Ziel der vorliegenden Arbeit war es, die molekularen Mechanismen der hypoxischen pulmonalen Vasokonstriktion in präkapillären pulmonalen arteriellen glatten Muskelzellen (PASMC) sowie des Ischämie-Reperfusionsschadens in den Endothelzellen (LEC) der Säugerlunge zu untersuchen. Da beide fundamentale Mechanismen in TRPC6-defizienten Mäusen nicht mehr auftreten, mussten ihnen eine TRPC6-Aktivierung zugrunde liegen. Zur Aufklärung der Mechanismen auf zellulärer Ebene wurden zuerst PASMC und LEC isoliert und durch Bindung charakteristischer Antikörper identifiziert. Die Identifikation von Signalkomponenten in beiden Zelltypen gelang außerdem durch die Messung der Erhöhung der intrazellulären Ca2+-Konzentration nach Perfusion eines hypoxischen Puffers. Durch Applikation spezifischer pharmakologischer Inhibitoren und Indikatoren gelang es schließlich, Hinweise zum Ablauf der Signaltransduktionskaskaden zu sammeln. In PASMC wird während des sogenannten „priming“ durch eine geringe Rezeptoraktivierung eine basale Konzentration an Diacylglycerin, dem physiologischen Aktivator von TRPC6, gebildet, die jedoch durch die Aktivität von DAG-abbauenden DAG-Kinasen so reduziert wird, dass eine TRPC6-Aktivierung nicht möglich ist. Nach Applikation von Hypoxie führt eine postulierte Erhöhung der reaktiven Sauerstoffradikale in der Zelle jedoch zu einer Inhibition von DAG-Kinasen, zur DAG-Akkumulation und zur TRPC6-Aktivierung. In PASMC werden durch den folgenden Na+-Einstrom spannungsabhängige Ca2+-Kanäle vom L-Typ aktiviert, die den eigentlichen Ca2+-Einstrom zur Zellkontraktion einleiten. In LEC konnte eine ähnliche Signaltransduktionskaskade identifiziert werden, auch wenn hier die Notwendigkeit eines „primings“ nicht geklärt werden konnte und der Ca2+-Einstrom durch TRPC6-Kanäle verläuft, da keine spannungsabhängigen Calciumkanäle vom L-Typ exprimiert werden. Zusammenfassend lässt sich also sagen, dass der TRPC6- Kanal einen wichtigen pharmakologischen Angriffspunkt für beide Signaltransduktionskaskaden darstellt. The aim of this study was to clarify the molecular mechanisms of hypoxic pulmonary vasoconstriction in precapillary arterial pulmonary smooth muscle cells (PASMC) and ischemia-reperfusion injury in lung endothelial cells (LEC). TRPC6-activation is essential for both mechanisms, because they are abolished in TRPC6-deficient mice. To investigate the mechanisms at the cellular level PASMC and LEC were isolated and their identity confirmed by specific antibodies. Components of the signalling cascade in both cell types were identified by monitoring the Ca2+-increase in response to the application of hypoxic solutions. Important key components of the signal transduction cascades in addition to TRPC6 were identified by the application of specific inhibitors and sensors to the cells. In summary, activation of receptors by nanomolar agonist concentrations (priming) results in a low level of diacylglycerol (DAG) production, which is not able to activate TRPC6 channels, but is rapidly degraded by DAG-kinases. After application of hypoxia, however, production of reactive oxygen species results in DAG-kinase inhibition and sufficient DAGaccumulation to induce TRPC6-activation. The bulk of Ca2+ influx in PASMC responsible for contraction enters through L-type voltage gated Ca2+ channels. These are activated by the depolarisation resulting from Na+ influx through TRPC6- channels. A similar signal transduction cascade exists in LEC, although it is unclear whether a priming event is necessary. In these cells, TRPC6 channels mediate the Ca2+ influx, because L-type voltage gated calcium channels are not expressed. Therefore, TRPC6 is an important perspective pharmacological target for acute hypoxic pulmonary vasoconstriction in PASMC and ischemia-reperfusion injury in LEC.
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    ABSTRACT: We determined whether postnatal pulmonary hypertension induced by 70% of pregnancy at high altitude (HA) persists once the offspring return to sea level and investigated pulmonary vascular mechanisms operating under these circumstances. Pregnant ewes were divided into two groups: conception, pregnancy, and delivery at low altitude (580 m, LLL) and conception at low altitude, pregnancy at HA (3,600 m) from 30% of gestation until delivery, and return to lowland (LHL). Pulmonary arterial pressure (PAP) was measured in vivo. Vascular reactivity and morphometry were assessed in small pulmonary arteries (SPA). Protein expression of vascular mediators was determined. LHL lambs had higher basal PAP and a greater increment in PAP after N(G)-nitro-L-arginine methyl ester (20.9 ± 1.1 vs. 13.7 ± 0.5 mmHg; 39.9 ± 5.0 vs. 18.3 ± 1.3 mmHg, respectively). SPA from LHL had a greater maximal contraction to K(+) (1.34 ± 0.05 vs. 1.16 ± 0.05 N/m), higher sensitivity to endothelin-1 and nitroprusside, and persistence of dilatation following blockade of soluble guanylate cyclase. The heart ratio of the right ventricle-to-left ventricle plus septum was higher in the LHL relative to LLL. The muscle area of SPA (29.3 ± 2.9 vs. 21.1 ± 1.7%) and the protein expression of endothelial nitric oxide synthase (1.7 ± 0.1 vs. 1.1 ± 0.2), phosphodiesterase (1.4 ± 0.1 vs. 0.7 ± 0.1), and Ca(2+)-activated K(+) channel (0.76 ± 0.16 vs. 0.30 ± 0.01) were greater in LHL compared with LLL lambs. In contrast, LHL had decreased heme oxygenase-1 expression (0.82 ± 0.26 vs. 2.22 ± 0.44) and carbon monoxide production (all P < 0.05). Postnatal pulmonary hypertension induced by 70% of pregnancy at HA promotes cardiopulmonary remodeling that persists at sea level.
    AJP Regulatory Integrative and Comparative Physiology 09/2010; 299(6):R1676-84. DOI:10.1152/ajpregu.00123.2010 · 3.53 Impact Factor
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    ABSTRACT: Pulmonary arterial hypertension (PAH) is an incurable disease characterized by a progressive increase in pulmonary vascular resistance leading to right heart failure. Carbon monoxide (CO) has emerged as a potently protective, homeostatic molecule that prevents the development of vascular disorders when administered prophylactically. The data presented in this paper demonstrate that CO can also act as a therapeutic (i.e., where exposure to CO is initiated after pathology is established). In three rodent models of PAH, a 1 hour/day exposure to CO reverses established PAH and right ventricular hypertrophy, restoring right ventricular and pulmonary arterial pressures, as well as the pulmonary vascular architecture, to near normal. The ability of CO to reverse PAH requires functional endothelial nitric oxide synthase (eNOS/NOS3) and NO generation, as indicated by the inability of CO to reverse chronic hypoxia-induced PAH in eNOS-deficient (nos3-/-) mice versus wild-type mice. The restorative function of CO was associated with a simultaneous increase in apoptosis and decrease in cellular proliferation of vascular smooth muscle cells, which was regulated in part by the endothelial cells in the hypertrophied vessels. In conclusion, these data demonstrate that CO reverses established PAH dependent on NO generation supporting the use of CO clinically to treat pulmonary hypertension.
    Journal of Experimental Medicine 10/2006; 203(9):2109-19. DOI:10.1084/jem.20052267 · 13.91 Impact Factor