Novel Hemodynamic, Vascular Lesion, and Cytokine/Chemokine Differences Regarding Sex in a Pulmonary Arterial Hypertension Model.

Sex differences are recognized in pulmonary hypertension. However, the progression of disease with regard to vascular lesion formation and circulating cytokines/chemokines is unknown. To determine whether vascular lesion formation, changes in hemodynamics, and alterations in circulating chemokines/cytokines differ between males and females, we used a progressive model of pulmonary arterial hypertension (PAH), Sugen/hypoxia, and analyzed cohorts of male and female rats at time points suggested to indicate worsening disease. Our analysis included echocardiography for hemodynamics, morphometry, immunofluoresecence, and chemokine/cytokine analysis of plasma at each time point in both sexes. We found that male rats had significantly increased Fulton index, compared with those for females at each time point, as well as increased medial artery thickening at 8 weeks of PAH. Furthermore, females exhibited fewer obliterative vascular lesions than males at our latest time point. Our data also show increased IL-4, granulocyte-macrophage colony-stimulating factor, IL-10, and macrophage interacting protein-1α that were not observed in females, whereas females were observed to have increased RANTES (whose name derives from Regulated upon Activation, Normal T Cell Expressed and Presumably Secreted) and CXCL-10 that were not found in males. Males also have increased infiltrating macrophages in vascular lesions, compared with females. We found that development of progressive PAH in hemodynamics, morphology, and chemokine/cytokine circulation differs significantly between males and females. These data suggest a macrophage-driven pathology in males, whereas there may be T cell protection from vascular damage in females with PAH.

Hypoxia and Rho/Rho-kinase signaling. Lung development versus hypoxic pulmonary hypertension.

Intracellular signaling via the small GTP-binding protein RhoA and its downstream effector Rho-kinase plays a role in regulating diverse cellular functions, including cell contraction, migration, gene expression, proliferation, and differentiation. Rho/Rho-kinase signaling has an obligatory role in embryonic cardiac development, and low-level chemical activation of Rho promotes branching morphogenesis in fetal lung explants. Gebb has found that hypoxia markedly augments branching morphogenesis in fetal rat lung explants, and our preliminary results suggest this is associated with activation of RhoA. Whereas hypoxia-induced activation of Rho/Rho-kinase may promote fetal lung development, other evidence indicates it has adverse effects in the lungs of neonates and adults. When exposed at birth to the mild hypoxia of Denver's altitude (5,280 ft), the neonatal fawn-hooded rat (FHR) develops severe pulmonary hypertension (PH) associated with impaired lung alveolarization and vascularization. We have observed that administration via the drinking water of the Rho-kinase inhibitor fasudil to the nursing, Denver FHR mother for the first 2 to 3 weeks, and then directly to the Denver FHR pups for the next 7 to 8 weeks, ameliorates the lung dysplasia and PH. The adult Sprague-Dawley rat develops PH when exposed for 3 to 4 wk to a simulated altitude of 17,000 ft. We have found that this hypoxic PH is associated with activation of pulmonary artery Rho/Rho-kinase and is almost completely reversed by acute intravenous administration of the Rho-kinase inhibitor Y-27632. In addition, chronic in vivo treatment with Y-27632 reduces development of the hypoxic PH. In summary, hypoxic activation of Rho/Rho-kinase signaling may be important for fetal lung morphogenesis, but continued activation of this pathway in the neonate impairs postnatal lung development and re-activation in the adult contributes to development of PH.

Attenuation of acute hypoxic pulmonary vasoconstriction and hypoxic pulmonary hypertension in mice by inhibition of Rho-kinase.

RhoA GTPase mediates a variety of cellular responses, including activation of the contractile apparatus, growth, and gene expression. Acute hypoxia activates RhoA and, in turn, its downstream effector, Rho-kinase, and previous studies in rats have suggested a role for Rho/Rho-kinase signaling in both acute and chronically hypoxic pulmonary vasoconstriction. We therefore hypothesized that activation of Rho/Rho-kinase in the pulmonary circulation of mice contributes to acute hypoxic pulmonary vasoconstriction and chronic hypoxia-induced pulmonary hypertension and vascular remodeling. In isolated, salt solution-perfused mouse lungs, acute administration of the Rho-kinase inhibitor Y-27632 (1 x 10(-5) M) attenuated hypoxic vasoconstriction as well as that due to angiotensin II and KCl. Chronic treatment with Y-27632 (30 mg x kg(-1) x day(-1)) via subcutaneous osmotic pump decreased right ventricular systolic pressure, right ventricular hypertrophy, and neomuscularization of the distal pulmonary vasculature in mice exposed to hypobaric hypoxia for 14 days. Analysis of a small number of proximal pulmonary arteries suggested that Y-27632 treatment reduced the level of phospho-CPI-17, a Rho-kinase target, in hypoxic lungs. We also found that endothelial nitric oxide synthase protein in hypoxic lungs was augmented by Y-27632, suggesting that enhanced nitric oxide production might have played a role in the Y-27632-induced attenuation of chronically hypoxic pulmonary hypertension. In conclusion, Rho/Rho-kinase activation is important in the effects of both acute and chronic hypoxia on the pulmonary circulation of mice, possibly by contributing to both vasoconstriction and vascular remodeling.