Paracellular Permeability of Bronchial Epithelium is Controlled by CFTR

Abstract

In normal airway epithelium, the cystic fibrosis transmembrane conductance regulator (CFTR) transports Cl^- ions to the apical surface of the epithelium paralleled by the flow of water through transcellular and paracellular pathways. The hypothesis was tested whether CFTR not only regulates the transcellular but also the paracellular shunt pathway. Therefore, we performed measurements of transepithelial electrical resistance (TER) and paracellular ¹⁴C-mannitol permeability in wtCFTR (16HBE14o^-) and delF508-CFTR (CFBE41o^-) expressing human bronchial epithelial cells. Under resting conditions, CFBE41o^- cell monolayers exhibit a higher paracellular permeability and lower TER as compared to 16HBE14o^- monolayers. Stimulation of CFTR by cAMP induces opposite effects in the two cell lines. 16HBE14o^- monolayers show a sharp decrease of TER, in parallel with a concomitant increase of paracellular permeability. The change in paracellular permeability is mediated by a myosin II dependent mechanism because it can be blocked by the myosin light chain kinase inhibitor ML-7. In contrast, CFBE41o^- cells respond to cAMP stimulation with a decrease of paracellular permeability, paralleled by slight increase of TER. We conclude that stimulation of wtCFTR increases vectorial transcellular salt transport and, simultaneously, the paracellular permeability allowing water to follow through the paracellular pathway. In contrast, in CF epithelium cAMP stimulation increases neither vectorial salt transport nor paracellular permeability which is likely to contribute to the CF pulmonary phenotype. Taken together, our results link CFTR dysfunction to an improper regulation of the paracellular transport route.

CFTR interacts with ZO-1 to regulate tight junction assembly and epithelial differentiation via the ZONAB pathway

“…A previous report showed delayed differentiation and regeneration in non-infected human CF nasal epithelia (Hajj et al, 2007). In the present study, the lower TER that we observed after CFTR inhibition or knockdown in epididymal cells is in agreement with the modulation of paracellular permeability by CFTR previously reported in cultured airway epithelial cells (Castellani et al, 2012;LeSimple et al, 2010;Nilsson et al, 2010;Weiser et al, 2011). In these studies, several mechanisms were proposed to mediate the regulation of the paracellular pathway by apical membranebound CFTR, including the participation of NHERF1, ezrin, the RhoA-ROCK pathway, myosin II and tyrosine kinase phosphorylation.…”

NHERF1 and CFTR restore tight junction organisation and function in cystic fibrosis airway epithelial cells: role of ezrin and the RhoA/ROCK pathway

“…32 While the role of CFTR in the transcellular transport of ions is well known, its the role in paracellular permeability and gate function of the airway epithelium is less known but is at present an intensive field of investigation. [33][34][35] Although we did not analyse here the role of NHERF1 and CFTR in the paracellular permeability to ions, our results are in line with those obtained by LeSimple et al, 33 who demonstrated that the presence of membrane CFTR is required for normal epithelial gate function, and with Weiser et al, 35 who recently showed that CFBE cell monolayers exhibit a higher paracellular permeability and lower TER (as in our study here) as compared with 16HBE monolayers. In particular, LeSimple et al 33 argued that CFTR trafficking is required for the normal organisation and function of TJs, although the increase in gate function upon overexpression of CFTR was not affected by the CFTR inhibitor CFTR inh -172 or lowchloride medium, implying that the effect of CFTR on TJ function was unrelated to its ion channel activity.…”

“…This observation may be coupled with the coaxing of CFTR to the plasma membrane and reduction in its turnover (ie, longer permanence of CFTR at this level) induced by NHERF1 overexpression demonstrated by us, 15 although we do not know the effect of CFTR inhibition on the resumption of TJ permeability defect in CFBE cells upon NHERF1 overexpression. On the same line, Weiser et al 35 showed that while cAMP induced an increase of paracellular permeability Tight junction regulation in cystic fibrosis S Castellani et al in 16HBE cells, in contrast CFBE cells respond to cAMP stimulation with a decrease of paracellular permeability paralleled by slight increase of TER, indicating that there is a link between CFTR dysfunction and an improper regulation of the paracellular transport route. Finally, Nilsson et al 34 tried to link paracellular ion transport, CFTR activity, and cellular cytoskeleton organisation.…”

Transforming Growth Factor-β1 and Cigarette Smoke Inhibit the Ability of β2-Agonists to Enhance Epithelial Permeability

“…The exact mechanism by which CFTR modulates epithelial permeability remains unclear. Weiser and colleagues (7) demonstrated that CFTR modulates phosphorylation of MLCK, and changes in paracellular permeability can be blocked by ML-7. However, ML-7 had no effect on b 2 -agonist-mediated increases of epithelial permeability in our studies.…”

“…These observations point to a significant contribution of the paracellular space for fluid transport. A number of reports have shown that CFTR controls paracellular permeability of bronchial epithelia (5)(6)(7), placing CFTR at a critical juncture in ASL volume regulation. In CF, mutations of the gene encoding CFTR are associated with a significant decrease in epithelial Cl 2 secretion, excessive Na 1 absorption (8), and decreased paracellular permeability (5,6).…”