Cystic fibrosis transmembrane conductance regulator and sphingolipids regulate hypoxic pulmonary vasoconstriction

Abstract

Background: Gene mutations of cystic fibrosis transmembrane conductance regulator (CFTR) cause cystic fibrosis, which is associated with profound pulmonary ventilation-perfusion (V_A/Q) mismatches. Hypoxic pulmonary vasoconstriction (HPV) minimizes V_A/Q inequalities. However, chronic hypoxemia-associated lung diseases frequently result in pulmonary hypertension (PH).

Aims and objectives: We hypothesized that CFTR may mediate HPV potentially by modulating the response to sphingolipids as mediators of HPV.

Methods: HPV and V_A/Q mismatch were analyzed in isolated mouse lungs or in vivo. Ca²⁺ mobilization, transient receptor potential canonical 6 (TRPC6) translocation to caveolae and the interaction between CFTR and TRPC6 were studied in pulmonary arterial smooth muscle cells (PASMC). The role of CFTR in long-term vascular adaptation to chronic hypoxia was analyzed in CFTR^-/- mice.

Results: CFTR deficiency diminished HPV, aggravated V_A/Q mismatch and partially protected from hypoxic PH. In PASMC, hypoxia caused CFTR/TRPC6 complex formation, while CFTR inhibition attenuated hypoxia-induced TRPC6 translocation to caveolae and Ca²⁺ mobilization. Inhibition of neutral sphingomyelinase (nSMase) blocked HPV, while exogenous nSMase caused CFTR-dependent TRPC6 translocation and vasoconstriction. 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 vasoconstriction that involved TRPC6, phospholipase C, and rho kinase.

Conclusions: These findings demonstrate a central role of CFTR and sphingolipids in HPV.