Cigarette smoke activates CFTR through ROS-stimulated cAMP signaling in human bronchial epithelial cells

Abstract

Air pollution stimulates airway epithelial secretion through a cholinergic reflex that is unaffected in cystic fibrosis (CF), yet a strong correlation is observed between passive smoke exposure in the home and impaired lung function in CF children. Our aim was to study the effects of low smoke concentrations on cystic fibrosis transmembrane conductance regulator (CFTR) function in vitro. Cigarette smoke extract stimulated robust anion secretion that was transient, mediated by CFTR, and dependent on cAMP-dependent protein kinase activation. Secretion was initiated by reactive oxygen species (ROS) and mediated by at least two distinct pathways: autocrine activation of EP4 prostanoid receptors and stimulation of Ca store-operated cAMP signaling. The response was absent in cells expressing the most common disease-causing mutant F508del-CFTR. In addition to the initial secretion, prolonged exposure of non-CF bronchial epithelial cells to low levels of smoke also caused a gradual decline in CFTR functional expression. F508del-CFTR channels that had been rescued by the CF drug combination VX-809 (lumacaftor) + VX-770 (ivacaftor) were more sensitive to this downregulation than wild-type CFTR. The results suggest that CFTR-mediated secretion during acute cigarette smoke exposure initially protects the airway epithelium while prolonged exposure reduces CFTR functional expression and reduces the efficacy of CF drugs.

Oxidative stress, autophagy and airway ion transport

“…These results were consistent with an earlier study showing that oxidative stress induced by H 2 O 2 stimulated the synthesis and rapid release of prostaglandin E 2 from Calu-3 cells, which activated EP 4 receptors and increased CFTR-dependent anion secretion (99). Persistent low-dose CSE exposure, however, caused a gradual decrease in CFTR expression and function (233). This result was similar to previously reported effects of CSE on airway epithelial cells that caused CFTR internalization and a reduction in CFTR-C22 OXIDATIVE STRESS, AUTOPHAGY AND AIRWAY ION TRANSPORT dependent anion secretion (33,203).…”

“…Recently, experiments examining the effects of low concentrations of CS extract (CSE) on human bronchial epithelial cells showed transient stimulation of CFTR-mediated anion secretion that was dependent on activation of AMPK (233). Acute activation of anion transport was similar to the effects of H 2 O 2 and blocked by pretreatment with a ROS scavenger, indicating that the increased secretion was induced by oxidative stress.…”

“…Airborne pollutants, tobacco smoke, and various environmental allergens are known to induce oxidative stress and alter the ion transport properties of the airway epithelium. A direct effect of tobacco smoke, for example, at low concentrations was a biphasic effect on ion transport, initially stimulating anion secretion, while chronic exposure or higher dosages inhibit apical expression of ion channels (e.g., CFTR and C25 OXIDATIVE STRESS, AUTOPHAGY AND AIRWAY ION TRANSPORT KCa1.1/KCNMA1) that directly participate in production of ASL (33,187,203,233). The acute increase in anion secretion was shown to be ROS-dependent and to stimulate autocrine signaling, similar to the effects of oxidative stress following allergen exposure, although different signaling molecules are involved.…”

Agonists that stimulate secretion promote the recruitment of CFTR into membrane lipid microdomains

“…To measure short-circuit current (I sc ), cells were seeded on fibronectin-coated polyester membrane inserts (0.4 µM pore diameter, 6.5 mm diameter; Corning Costar) and kept submerged until the transepithelial electrical resistance reached >400 Ω⋅cm 2 as measured using an epithelial volt-ohmmeter (World Precision Instruments). Apical medium was then aspirated and cultures were maintained at the air-liquid interface for another 7 d (CFBE41o − ) or >21 d (pHBE) as described previously (Wong et al, 2018).…”

Increases in cytosolic Ca2+ induce dynamin- and calcineurin-dependent internalisation of CFTR

“…Wong and colleagues have recently found cigarette smoke extract (CSE) caused a reactive oxygen species-dependent increase in CFTR activity. This increase in activity was followed by a decline after prolonged exposure to CSE [55]. However, the researchers used CSE which captures a different phase of smoke than our preparation.…”