Dysregulated macroautophagy and abnormal mitochondria in Cystic Fibrosis

Cystic Fibrosis (CF) is an autosomal recessive genetic disorder, caused by mutations in the CF Transmembrane Conductance Regulator (CFTR) gene, which encodes an ion channel protein that conducts chloride ions, bicarbonate, and regulates the function of other channels. This CFTR protein, when defective, results in excessive pulmonary and systemic inflammation, recurring bacterial infections and progressive lung disease. Autophagy is an essential cellular process by which damaged organelles, as well as misfolded and aggregated proteins, are cleared from the cell. This mechanism is postulated to be defective in CF, as a result of the mutated ΔF508 CFTR protein; however, the current model as to how autophagy is dysregulated remains a subject of debate. In this thesis I have investigated the state of the autophagy-lysosomal axis in CF, using human bronchial epithelial cell lines (HBECs), as well as monocytes and M1 macrophages from patients with
homozygous ΔF508 CFTR mutations. I have also examined the effects of currently available CFTR modulators on modifying this axis. The state of mitochondria was also investigated to establish if dysregulated autophagy leads to an accumulation of damaged mitochondria, thereby exacerbating the NLRP3 inflammasome-driven inflammatory phenotype in CF. The impact of this dysregulation on
metabolism was also investigated.
This study found autophagy to be dysregulated in cells with CF mutations. In CF HBECs, there was an increased turnover of autophagy markers in HBECs homozygous for ΔF508 CFTR. CF monocytes and M1 macrophages, however, showed an increase in a ubiquitin binding protein, p62, with no clearance of the protein via autophagy, but normal clearance of autophagosomes. CFTR modulators, Symdeko and ivacaftor, failed to show an improvement in autophagic function in all cell types. CF monocytes were found to have damaged and damage-prone mitochondria, as well as having an increased metabolic profile. These studies suggest that autophagy is dysregulated in cells that are homozygous for ΔF508 CFTR, and that the mitochondria in these cells are more prone to damage, with an increased metabolic profile.