CGRP induction in cystic fibrosis airways alters the submucosal gland progenitor cell niche in mice

Abstract

In cystic fibrosis (CF), a lack of functional CF transmembrane conductance regulator (CFTR) chloride channels causes defective secretion by submucosal glands (SMGs), leading to persistent bacterial infection that damages airways and necessitates tissue repair. SMGs are also important niches for slow-cycling progenitor cells (SCPCs) in the proximal airways, which may be involved in disease-related airway repair. Here, we report that calcitonin gene-related peptide (CGRP) activates CFTR-dependent SMG secretions and that this signaling pathway is hyperactivated in CF human, pig, ferret, and mouse SMGs. Since CGRP-expressing neuroendocrine cells reside in bronchiolar SCPC niches, we hypothesized that the glandular SCPC niche may be dysfunctional in CF. Consistent with this hypothesis, CFTR-deficient mice failed to maintain glandular SCPCs following airway injury. In wild-type mice, CGRP levels increased following airway injury and functioned as an injury-induced mitogen that stimulated SMG progenitor cell proliferation in vivo and altered the proliferative potential of airway progenitors in vitro. Components of the receptor for CGRP (RAMP1 and CLR) were expressed in a very small subset of SCPCs, suggesting that CGRP indirectly stimulates SCPC proliferation in a non-cell-autonomous manner. These findings demonstrate that CGRP-dependent pathways for CFTR activation are abnormally upregulated in CF SMGs and that this sustained mitogenic signal alters properties of the SMG progenitor cell niche in CF airways. This discovery may have important implications for injury/repair mechanisms in the CF airway.

Lung Phenotype of Juvenile and Adult Cystic Fibrosis Transmembrane Conductance Regulator–Knockout Ferrets

“…Short-circuit current (I SC ) was measured using a VCC MC8 Multichannel voltage/ current clamp (Physiologic Instruments, San Diego, CA) as previously reported (19,20). For more details, see the MATERIALS AND METHODS in the online supplement.…”

Epithelial Cells of Trachea and Bronchi

“…Xie et al demonstrated that calcitonin gene-related peptide (CGRP; see below) activates CFTR-dependent submucosal gland secretion and that the putative CGRP-to-myoepithelial cell signaling pathway is hyperactivated in cystic fibrosis patients and in the pig, ferret, and mouse models of cystic fibrosis (Xie et al, 2011).…”

Bioelectric Characterization of Epithelia from Neonatal CFTR Knockout Ferrets

“…All tissues were harvested into Ringer's solution containing 1 mM indomethacin, and this level of indomethacin was maintained throughout the experiment to eliminate stimulation of cAMP production by endogenous prostaglandins (22,38). I SC and resistances (R) were measured using a VCC MC8 Multichannel voltage/current clamp (Physiologic Instruments) as previously reported (10,39). For more details on electrophysiologic measurements see the online supplement.…”