Hypoxic pulmonary vasoconstriction (HPV) optimizes pulmonary ventilation-perfusion matching in regional hypoxia, but promotes pulmonary hypertension in global hypoxia. Ventilation-perfusion mismatch is a major cause of hypoxemia in cystic fibrosis. We hypothesized that cystic fibrosis transmembrane conductance regulator (CFTR) may be critical in HPV, potentially by modulating the response to sphingolipids as mediators of HPV. HPV and ventilation-perfusion mismatch were analyzed in isolated mouse lungs or in vivo. Ca 2+ mobilization and transient receptor potential canonical 6 (TRPC6) translocation were studied in human pulmonary (PASMCs) or coronary (CASMCs) artery smooth muscle cells. CFTR inhibition or deficiency diminished HPV and aggravated ventilation-perfusion mismatch. In PASMCs, hypoxia caused CFTR to interact with TRPC6, whereas CFTR inhibition attenuated hypoxiainduced TRPC6 translocation to caveolae and Ca 2+ mobilization. Ca 2+ mobilization by sphingosine-1-phosphate (S1P) was also attenuated by CFTR inhibition in PASMCs, but amplified in CASMCs. Inhibition of neutral sphingomyelinase (nSMase) blocked HPV, whereas exogenous nSMase caused TRPC6 translocation and vasoconstriction that were blocked by CFTR inhibition. nSMase-and hypoxia-induced vasoconstriction, yet not TRPC6 translocation, were blocked by inhibition or deficiency of sphingosine kinase 1 (SphK1) or antagonism of S1P receptors 2 and 4 (S1P 2/4 ). S1P and nSMase had synergistic effects on pulmonary vasoconstriction that involved TRPC6, phospholipase C, and rho kinase. Our findings demonstrate a central role of CFTR and sphingolipids in HPV. Upon hypoxia, nSMase triggers TRPC6 translocation, which requires its interaction with CFTR. Concomitant SphK1-dependent formation of S1P and activation of S1P 2/4 result in phospholipase C-mediated TRPC6 and rho kinase activation, which conjointly trigger vasoconstriction.

Objective-Neutrophils

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BackgroundHypoxic pulmonary vasoconstriction (HPV) optimizes ventilation‐perfusion matching in the lung. As cystic fibrosis patients suffer from ventilation‐perfusion mismatches, we probed for a potential role of cystic fibrosis transmembrane conductance regulator (CFTR) in HPV.MethodsHPV was quantified in isolated lungs as increase in perfusion pressure in response to hypoxia. In cultured human pulmonary artery smooth muscle cells (PASMC), Ca2+ concentration ([Ca2+]i) was imaged, and caveolae were isolated and probed for translocated Ca2+ entry channels.ResultsHPV was attenuated by CFTR inhibitors or in lungs of CFTR−/− mice. In PASMC, CFTR inhibition blocked the hypoxia‐induced [Ca2+ ]i increase and the caveolar translocation of TRPC6 channels. CFTR's role in HPV was not attributable to Cl− transport, as modulation of extracellular Cl− did not alter HPV. Instead, the role of CFTR was related to sphingolipid signaling in HPV. In isolated lungs, inhibition of either neutral sphingomyelinase (SMase) or sphingosine kinase attenuated HPV. Exogenous SMase mimicked hypoxia, in that it caused pulmonary vasoconstriction, increased PASMC [Ca2+]i, and translocated TRPC6 to caveolae, yet responses to SMase were blocked by CFTR inhibition.ConclusionOur findings identify a critical role for CFTR in HPV that relates to sphingolipid signaling by a mechanism currently under investigation.

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