title: Thrombin has biphasic effects on the nitric oxide-cGMP pathway in endothelial cells and contributes to experimental pulmonary hypertension.
abstract: BACKGROUND
  A potential role for coagulation factors in pulmonary arterial hypertension has been recently described, but the mechanism of action is currently not known. Here, we investigated the interactions between thrombin and the nitric oxide-cGMP pathway in pulmonary endothelial cells and experimental pulmonary hypertension.
  
  
  RESULTS
  Chronic treatment with the selective thrombin inhibitor melagatran (0.9 mg/kg daily via implanted minipumps) reduced right ventricular hypertrophy in the rat monocrotaline model of experimental pulmonary hypertension. In vitro, thrombin was found to have biphasic effects on key regulators of the nitric oxide-cGMP pathway in endothelial cells (HUVECs). Acute thrombin stimulation led to increased expression of the cGMP-elevating factors endothelial nitric oxide synthase (eNOS) and soluble guanylate cyclase (sGC) subunits, leading to increased cGMP levels. By contrast, prolonged exposition of pulmonary endothelial cells to thrombin revealed a characteristic pattern of differential expression of the key regulators of the nitric oxide-cGMP pathway, in which specifically the factors contributing to cGMP elevation (eNOS and sGC) were reduced and the cGMP-hydrolyzing PDE5 was elevated (qPCR and Western blot). In line with the differential expression of key regulators of the nitric oxide-cGMP pathway, a reduction of cGMP by prolonged thrombin stimulation was found. The effects of prolonged thrombin exposure were confirmed in endothelial cells of pulmonary origin (HPAECs and HPMECs). Similar effects could be induced by activation of protease-activated receptor-1 (PAR-1).
  
  
  CONCLUSIONS
  These findings suggest a link between thrombin generation and cGMP depletion in lung endothelial cells through negative regulation of the nitric oxide-cGMP pathway, possibly mediated via PAR-1, which could be of relevance in pulmonary arterial hypertension.
authors.affiliation: Cardiology Research, Bayer HealthCare AG, Wuppertal, Germany.
authors.forename: Katrin F
authors.initials: KF
authors.lastname: Nickel
authors.forename: Volker
authors.initials: V
authors.lastname: Laux
authors.forename: Rolf
authors.initials: R
authors.lastname: Heumann
authors.forename: Georges
authors.initials: G
authors.lastname: von Degenfeld
mesh_terms: D000818:Animals; D006152:Cyclic GMP / Q000378:metabolism*; D054706:Cyclic Nucleotide Phosphodiesterases, Type 5 / Q000378:metabolism; D004195:Disease Models, Animal; D042783:Endothelial Cells / Q000187:drug effects / Q000378:metabolism*; D006801:Humans; D006976:Hypertension, Pulmonary / Q000150:complications / Q000188:drug therapy / Q000378:metabolism*; D017380:Hypertrophy, Right Ventricular / Q000188:drug therapy / Q000209:etiology; D008297:Male; D053858:Metabolic Networks and Pathways / Q000187:drug effects; D009569:Nitric Oxide / Q000378:metabolism*; D052250:Nitric Oxide Synthase Type III / Q000378:metabolism; D051381:Rats; D044463:Receptor, PAR-1 / Q000378:metabolism; D013917:Thrombin / Q000008:administration & dosage / Q000378:metabolism* / Q000494:pharmacology
chemical_list: D044463:Receptor, PAR-1; D009569:Nitric Oxide; D052250:Nitric Oxide Synthase Type III; D054706:Cyclic Nucleotide Phosphodiesterases, Type 5; D013917:Thrombin; D006152:Cyclic GMP