Impaired iNOS-sGC-cGMP signalling contributes to chronic hypoxic and hypercapnic pulmonary hypertension in rat.
ABSTRACT Nitric oxide (NO) is an important vascular modulator in the development of pulmonary hypertension. NO exerts its regulatory effect mainly by activating soluble guanylate cyclase (sGC) to synthesize cyclic guanosine monophosphate (cGMP). Exposure to hypoxia causes pulmonary hypertension. But in lung disease, hypoxia is commonly accompanied by hypercapnia. The aim of this study was to examine the changes of sGC enzyme activity and cGMP content in lung tissue, as well as the expression of inducible nitric oxide synthase (iNOS) and sGC in rat pulmonary artery after exposure to hypoxia and hypercapnia, and assess the role of iNOS-sGC-cGMP signal pathway in the development of hypoxic and hypercapnic pulmonary hypertension. Male Sprague-Dawley rats were exposed to hypoxia and hypercapnia for 4 weeks to establish model of chronic pulmonary hypertension. Weight-matched rats exposed to normoxia served as control. After exposure to hypoxia and hypercapnia, mean pulmonary artery pressure, the ratio of right ventricle/left ventricle+septum, and the ratio of right ventricle/body weight were significantly increased. iNOS mRNA and protein levels were significantly increased, but sGC α(1) mRNA and protein levels were significantly decreased in small pulmonary arteries of hypoxic and hypercapnic exposed rat. In addition, basal and stimulated sGC enzyme activity and cGMP content in lung tissue were significantly lower after exposure to hypoxia and hypercapnia. These results demonstrate that hypoxia and hypercapnia lead to the upregulation of iNOS expression, downregulation of sGC expression and activity, which then contribute to the development of pulmonary hypertension.
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ABSTRACT: Expression and localization of nitric oxide synthase (NOS) in the lungs of chronically hypoxic and normoxic rats were studied using both immunohistochemistry and NADPH diaphorase (NADPH-d) staining techniques. In the normoxic and in the hypoxic rat, NOS was detected by both methods in the endothelium of large pulmonary vessels and in the epithelium of bronchi and bronchioli. NOS expression was not detected in the endothelium of normoxic pulmonary resistance vessels but was prominently expressed in the endothelium of these vessels after 2-4 wk of chronic hypoxia. In contrast to small pulmonary vessels, the endothelium of small bronchial vessels exhibited NOS immunostaining in both normoxic and hypoxic lungs. Hypoxia was also found to induce de novo NOS expression in the smooth muscle of large and small pulmonary vessels and in bronchial smooth muscle. NOS enzyme activity in lung homogenates was assessed by [3H]arginine to [3H]citrulline conversion. The activity of soluble NOS, but not particulate NOS, was increased in the hypoxic lungs. These results demonstrate chronic hypoxia-induced upregulation of NOS protein expression and activity in the rat lung, suggesting a potentially important role of nitric oxide in adaptation of the pulmonary circulation to chronic hypoxia. The lack of immunostaining in small pulmonary resistance vessels is also consistent with physiological studies suggesting that NO may not be involved in the mechanism for maintaining the normally low pulmonary vascular resistance.The American journal of physiology 01/1995; 267(6 Pt 1):L667-78.
Article: Soluble guanylate cyclase.[show abstract] [hide abstract]
ABSTRACT: Soluble guanylate cyclase (sGC) is a mammalian nitric oxide (NO) sensor. When NO binds to the sGC heme, its GTP cyclase activity markedly increases, thus generating cyclic GMP, which serves to regulate several cell signaling functions. A good deal is known about the kinetics and equilibrium of binding of NO to sGC, leading to a proposed multistep mechanism of sGC activation that involves at least two NO-binding sites. The crystal structure of a member of a recently discovered family of prokaryotic sGC homologues has provided important insights into structure-function relationships within the sGC family of proteins.Current Opinion in Structural Biology 01/2007; 16(6):736-43. · 8.74 Impact Factor
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ABSTRACT: Exposure of rat pulmonary artery smooth muscle cells (rPASMC) to cytokines leads to nitric oxide (NO) production by NO synthase 2 (NOS2). NO stimulates cGMP synthesis by soluble guanylate cyclase (sGC), a heterodimer composed of alpha(1)- and beta(1)-subunits. Prolonged exposure of rPASMC to NO decreases sGC subunit mRNA and protein levels. The objective of this study was to determine whether levels of NO produced endogenously by NOS2 are sufficient to decrease sGC expression in rPASMC. Interleukin-1beta (IL-1beta) and tumor necrosis factor-alpha (TNF-alpha) increased NOS2 mRNA levels and decreased sGC subunit mRNA levels. Exposure of rPASMC to IL-1beta and TNF-alpha for 24 h decreased sGC subunit protein levels and NO-stimulated sGC enzyme activity. L-N(6)-(1-iminoethyl)lysine (NOS2 inhibitor) or 1H-[1,2,4]oxadiazolo-[4,3-a]quinoxalin-1-one (sGC inhibitor) partially prevented the cytokine-mediated decrease in sGC subunit mRNA levels. However, cytokines also decreased sGC subunit mRNA levels in PASMC derived from NOS2-deficient mice. These results demonstrate that levels of NO and cGMP produced in cytokine-exposed PASMC are sufficient to decrease sGC subunit mRNA levels. In addition, cytokines can decrease sGC subunit mRNA levels via NO-independent mechanisms.AJP Lung Cellular and Molecular Physiology 03/2001; 280(2):L272-8. · 3.52 Impact Factor