In cystic fibrosis (CF) airways, the lack of functional CFTR at the apical epithelial surface leads to decreased mucociliary clearance, chronic airway infection, and inflammation associated with mucus overproduction. Airway disease remains the most common cause of morbidity and mortality in CF. In the US, >90% of CF patients have the ?F508 CFTR mutation, which results in a protein retained in the endoplasmic reticulum (ER). Therapies targeting the mutated CFTR are now available, e.g., correctors support CFTR transfer to the cell surface, while potentiators increase channel activity. The corrector lumacaftor (VX-809) partially restores ?F508 maturation and function in vitro, but is not beneficial in ?F508 homozygous patients. Combination therapy (Orkambi) of VX- 809 with the potentiator ivacaftor (VX-770) is marginally beneficial for these patients. To date, correction of ?F508 by VX-809 or other corrector compounds has not been investigated in vitro under inflammatory conditions found in CF airways in vivo. Moreover, it is unknown whether anti-inflammatory therapies commonly used by CF patients alter the efficacy of ?F508 rescue. These issues are of highest importance because airway inflammation triggers ER stress and activates the unfolded protein response-dependent mRNA splicing of the transcription factor X-box binding protein-1 (XBP-1s) in human bronchial epithelia (HBE). Utilizing a pre-clinical model consisting of HBE exposure to supernatant from mucopurulent material (SMM) from human CF airways, we demonstrated that XBP-1s up-regulates the expression of chaperone proteins, folding enzymes, and lipid constituents of the ER. Our preliminary data indicate that SMM enhances VX-809-induced biochemical and functional correction of ?F508 in HBE. Similar to SMM, sputum from CF children triggers inflammation and increases XBP-1s in HBE, suggesting that the inflammatory airway milieu of the population ultimately targeted for mutant CFTR rescue might also enhance CFTR rescue, further increasing the relevance of our studies. We hypothesize that a) airway inflammation enhances pharmacological correction of ?F508 in HBE and this effect requires XBP-1s, b) inflammation-enhanced CFTR rescue improves mucus hydration and viscoelastic properties in CF airways, and c) decreasing inflammation may reduce ?F508 rescue due to decreased levels of XBP-1s.
Our aims will test in HBE whether: 1) XBP-1s mediates SMM/sputum-enhanced CFTR rescue, 2) SMM/sputum-enhanced CFTR rescue improves mucus hydration and viscoelasticity properties and enhances mucociliary transport and 3) discontinuation of SMM/sputum treatment or anti-inflammatory therapy blunts inflammation-enhanced CFTR rescue. The ultimate goal of these studies is not to advocate airway inflammation to promote CFTR rescue, but to fill a gap regarding the understanding of action of CFTR modulators under conditions relevant to inflamed CF airways. Pre-clinical evaluation of the effects of CFTR modulators in inflamed CF airway epithelia is critical for optimized therapies for CF patients. Addressing the role of XBP-1s in CFTR rescue may lead to novel therapies, based on manipulation of the inflammatory status of CF airways.
Mutations of the CFTR protein cause infection and inflammation in the airways of cystic fibrosis (CF) patients. We will test novel drugs that correct CFTR in models that mimic the native infected/inflamed milieu of CF airways. Our studies will likely improve therapies for CF and benefit CF patients.
