Loss of Anion Transport without Increased Sodium Absorption Characterizes Newborn Porcine Cystic Fibrosis Airway Epithelia

Abstract

SUMMARY Defective transepithelial electrolyte transport is thought to initiate cystic fibrosis (CF) lung disease. Yet, how loss of CFTR affects electrolyte transport remains uncertain. CFTR−/− pigs spontaneously develop lung disease resembling human CF. At birth, their airways exhibit a bacterial host defense defect, but are not inflamed. Therefore, we studied ion transport in newborn nasal and tracheal/bronchial epithelia in tissue, cultures, and in vivo. CFTR−/− epithelia showed markedly reduced Cl− and HCO3− transport. However, in contrast to a widely held view, lack of CFTR did not increase transepithelial Na+ or liquid absorption or reduce periciliary liquid depth. Like human CF, CFTR−/− pigs showed increased amiloride-sensitive voltage and current, but lack of apical Cl− conductance caused the change, not increased Na+ transport. These results indicate that CFTR provides the predominant transcellular pathway for Cl− and HCO3− in porcine airway epithelia, and reduced anion permeability may initiate CF airway disease.

Relationships among CFTR expression, HCO 3 − secretion, and host defense may inform gene- and cell-based cystic fibrosis therapies

“…2F). These results are consistent with an effect of the Cl − conductance on ΔIsc (amiloride) , rather than changes in ENaC activity (42,43). Those data and that conclusion predicted that removing Cl − would eliminate the relationship between percentage of WT cells and ΔIsc (amiloride).…”

“…In B and D, n = 6 for CFTR ΔF508/ΔF508 , n = 6 for CFTR +/+ , n = 6 for mixtures of CFTR ΔF508/ΔF508 and CFTR +/+ , and n = in viscosity were not due to differences in ASL depth (Fig. 3D) (42).…”

“…Epithelia were generated with varying proportions of CF and WT cells and studied at least 14 d after seeding. Nasal epithelia have electrolyte transport characteristics comparable with tracheal/bronchial epithelia (42). We used standard procedures for quantitative PCR and RT-PCR, Western blots, Ussing chamber analysis of electrolyte transport, fluorescence recovery after photobleaching, measurement of ASL pH, ASL antimicrobial activity, and adenovirus-mediated expression, and GFP quantification.…”

“…In porcine and human epithelia, apical amiloride produces a greater change in Isc in CF than non-CF because of the lack of a Cl − conductance (42,43). Previous studies used gene transfer vectors to overexpress CFTR in human CF epithelia and measured basal transepithelial electrical properties or the amiloride-induced reduction in Isc [ΔIsc (amiloride) ].…”

pH modulates the activity and synergism of the airway surface liquid antimicrobials β-defensin-3 and LL-37

“…Studying a porcine model of cystic fibrosis (CF) (37,38), we found that loss of cystic fibrosis transmembrane conductance regulator (CFTR) anion channels reduced HCO 3 − secretion and decreased ASL pH (39,40), results consistent with earlier findings in human airway epithelia (41)(42)(43)(44). Importantly, the abnormally acidic pH partially inhibited bacterial killing by ASL (40).…”