Characterisation and validation of ex vivo nasal epithelial cultures to investigate transmembrane protein 16A as a therapeutic avenue in cystic fibrosis

Abstract

Cystic fibrosis (CF) is the most common genetic life-limiting disease in the UK. Strategies to correct dysfunctional CF transmembrane conductance regulator (CFTR) will not benefit all people with CF and alternative approaches are required. Transmembrane protein 16A (TMEM16A) was recently identified as an essential component of the epithelial calcium activated chloride channel (CaCC) and has potential to bypass effects of faulty CFTR. TMEM16A expression is confirmed in the adult airway, however, its presence in the paediatric airway was previously unknown. Robust experimental models are required to investigate such therapeutic avenues in children. Primary bronchial epithelial cells (PBECs) have been pivotal through their role in CFTR modulator development. Although primary nasal epithelial cells (PNECs) provide a more accessible paediatric model, their characterisation was previously undetermined. To investigate the role of paediatric PNECs as a substitute for PBECs, I established a programme to sample both nasal and bronchial mucosal brushings from children with and without CF. These were used to develop differentiated paediatric cultures using strategies to optimise culture success by improving cell yield, promoting cell attachment and minimising infection. Epithelial properties of paediatric PNECs were confirmed in relation to tight junctional integrity and muco-ciliary differentiation. Ion transport assessment revealed that CFTR and CaCC expression were not different in PNECs versus PBECs in both non-CF and CF cultures. Low levels of TMEM16A expression were identified in the paediatric nasal and bronchial epithelium. Finally, application of a novel TMEM16A activating compound to the PNEC model demonstrated potential to enhance TMEM16A-mediated airway epithelial chloride transport. This characterisation of ex vivo paediatric PNECs has provided evidence to support their role as a tool to investigate the CF airway. Inter-donor variability of PNEC ion transport properties is an important consideration for future investigation of novel therapeutic modulators of CFTR and alternative ‘non-CFTR’ airway epithelial channels.