The extracellular calcium-sensing receptor regulates human fetal lung development via CFTR

Sarah C Brennan,Samantha Quilliam,Brenda Finney,Bethan Monk,Holly Dibble,Paul J Kemp,David Warburton,Hsiu-Er Tseng,William J Wilkinson,Daniela Riccardi,Luis J Galietta

doi:10.1038/srep21975

Abstract

Optimal fetal lung growth requires anion-driven fluid secretion into the lumen of the developing organ. The fetus is hypercalcemic compared to the mother and here we show that in the developing human lung this hypercalcaemia acts on the extracellular calcium-sensing receptor, CaSR, to promote fluid-driven lung expansion through activation of the cystic fibrosis transmembrane conductance regulator, CFTR. Several chloride channels including TMEM16, bestrophin, CFTR, CLCN2 and CLCA1, are also expressed in the developing human fetal lung at gestational stages when CaSR expression is maximal. Measurements of Cl−-driven fluid secretion in organ explant cultures show that pharmacological CaSR activation by calcimimetics stimulates lung fluid secretion through CFTR, an effect which in humans, but not mice, was also mimicked by fetal hypercalcemic conditions, demonstrating that the physiological relevance of such a mechanism appears to be species-specific. Calcimimetics promote CFTR opening by activating adenylate cyclase and we show that Ca2+-stimulated type I adenylate cyclase is expressed in the developing human lung. Together, these observations suggest that physiological fetal hypercalcemia, acting on the CaSR, promotes human fetal lung development via cAMP-dependent opening of CFTR. Disturbances in this process would be expected to permanently impact lung structure and might predispose to certain postnatal respiratory diseases.

Highlights

During gestation, the developing lung goes from a fluid-filled organ in the fetus to a fully formed, highly mature structure equipped for optimal gaseous exchange from the moment of birth[1,2,3]
A number of different chloride channels have been shown to be expressed in fluid-secreting fetal alveolar epithelial cells including members of the chloride channel (CLC) family[19,20], the Ca2+-activated chloride channel TMEM16A21,22, bestrophin-123 and the cystic fibrosis transmembrane conductance regulator (CFTR)[24], but the exact mechanism by which activation of the calcium-sensing receptor (CaSR) leads to chloride-driven fluid secretion in the fetal lung lumen is currently unknown[1]
We have shown previously that, in intact mouse pseudoglandular lungs, CaSR activation leads to Cl−-driven fluid secretion by unknown mechanisms[10]

Summary

Introduction

The developing lung goes from a fluid-filled organ in the fetus to a fully formed, highly mature structure equipped for optimal gaseous exchange from the moment of birth[1,2,3]. During the pseudoglandular stage (E11.5–16.5 in mice, weeks 5–17 in humans) there is a rapid expansion of the conducting airways when the developing lung undergoes stereotypic branching and budding[5], a process which is driven by fluid secreted into the lung lumen to generate the distending pressure required for normal expansion[6,7]. We have demonstrated that this relative fetal hypercalcaemia is necessary for optimal prenatal lung fluid secretion[10], an effect which is mediated by the extracellular calcium-sensing receptor (CaSR)[10,16], a G protein-coupled receptor (GPCR) whose expression is developmentally regulated and confined to the prenatal www.nature.com/scientificreports/. Because much of the work aimed at testing the contribution of each Cl− channel to lung fluid secretion has been done using genetically modified mice, initially we compared the expression of a variety of chloride channels in the developing mouse and human fetal lungs using immunohistochemistry. The signalling machinery involved in CaSR-driven fluid secretion was examined using live imaging in an in vitro cell reporter system

Methods

Results

Conclusion