Augmentation of CFTR function in human bronchial epithelial cells via SLC6A14-dependent amino acid uptake: Implications for treatment of Cystic Fibrosis.
Rationale: SLC6A14 mediated L-arginine transport has been shown to augment the residual anion channel activity of the major mutant, F508del-CFTR, in the murine gastrointestinal tract. It is not yet known if this transporter augments residual and pharmacological corrected F508del-CFTR in primary airway epithelia.
Objective: To determine the role of L-arginine uptake via SLC6A14 in modifying F508del-CFTR channel activity in airway cells from CF patients.
Methods: Human bronchial epithelial cells from lung explants of non-CF (HBE) and CF patients (CF-HBE) were used for H3-flux, airway surface liquid (ASL) and Ussing chamber studies. We used α-methyltryptophan (α-MT) as specific inhibitor for SLC6A14. CFBE41o-, a commonly used CF airway cell line, was employed for studying the mechanism of the functional interaction between SLC6A14 and F508del-CFTR.
Main results: SLC6A14 is functionally expressed in CF-HBE cells. L-arginine uptake via SLC6A14 augmented F508del-CFTR function at baseline and after treatment with lumacaftor. SLC6A14 mediated L-arginine uptake also increased the ASL in CF-HBE cells. Using CFBE41o cells we showed that the positive SLC6A14 effect was mainly dependent on the nitric oxide synthase activity, nitrogen oxides including nitric oxide (NO) and phosphorylation by protein kinase G. These finding were confirmed in CF-HBE as iNOS inhibition abrogated the functional interaction between SLC6A14 and pharmacological corrected F508del-CFTR.
Conclusion: SLC6A14-mediated L-arginine transport augments residual F508del-CFTR channel function via a non-canonical, NO pathway. This effect is enhanced with increasing pharmacological rescue of F508del-CFTR to the membrane. The current study demonstrates how endogenous pathways can be utilized for the development of companion therapy in CF.