Accumulation of unwanted/misfolded proteins in aggregates has been observed in airways of patients with cystic fibrosis (CF), a life-threatening genetic disorder caused by mutations in the gene encoding the cystic fibrosis transmembrane conductance regulator (CFTR). Here we show how the defective CFTR results in defective autophagy and decreases the clearance of aggresomes. Defective CFTR-induced upregulation of reactive oxygen species (ROS) and tissue transglutaminase (TG2) drive the crosslinking of beclin 1, leading to sequestration of phosphatidylinositol-3-kinase (PI(3)K) complex III and accumulation of p62, which regulates aggresome formation. Both CFTR knockdown and the overexpression of green fluorescent protein (GFP)-tagged-CFTR(F508del) induce beclin 1 downregulation and defective autophagy in non-CF airway epithelia through the ROS-TG2 pathway. Restoration of beclin 1 and autophagy by either beclin 1 overexpression, cystamine or antioxidants rescues the localization of the beclin 1 interactome to the endoplasmic reticulum and reverts the CF airway phenotype in vitro, in vivo in Scnn1b-transgenic and Cftr(F508del) homozygous mice, and in human CF nasal biopsies. Restoring beclin 1 or knocking down p62 rescued the trafficking of CFTR(F508del) to the cell surface. These data link the CFTR defect to autophagy deficiency, leading to the accumulation of protein aggregates and to lung inflammation.

These authors equally contributed to this work.Keywords: cystic fibrosis, CFTR, autophagy, cysteamine, epigallocatechin gallate, sweat chloride Abbreviations: BECN1/Beclin 1, autophagy-related; CF, cystic fibrosis; CFTR, cystic fibrosis transmembrane conductance regulator; CHX, cycloheximide; CSNK2, casein kinase 2; CXCL2, chemokine (C-X-C motif) ligand 2; CXCL8, chemokine (C-X-C motif) ligand 8; EGCG, epigallocatechin gallate; FEV, forced expiratory volume; PM, plasma membrane; RPD, rectal potential difference; SQSTM1, sequestosome 1; TGM2, transglutaminase 2; TNF, tumor necrosis factor.Restoration of BECN1/Beclin 1-dependent autophagy and depletion of SQSTM1/p62 by genetic manipulation or autophagy-stimulatory proteostasis regulators, such as cystamine, have positive effects on mouse models of human cystic fibrosis (CF). These measures rescue the functional expression of the most frequent pathogenic CFTR mutant, F508del, at the respiratory epithelial surface and reduce lung inflammation in Cftr F508del homozygous mice. Cysteamine, the reduced form of cystamine, is an FDA-approved drug. Here, we report that oral treatment with cysteamine greatly reduces the mortality rate and improves the phenotype of newborn mice bearing the F508del-CFTR mutation. Cysteamine was also able to increase the plasma membrane expression of the F508del-CFTR protein in nasal epithelial cells from F508del homozygous CF patients, and these effects persisted for 24 h after cysteamine withdrawal. Importantly, this cysteamine effect after washout was further sustained by the sequential administration of epigallocatechin gallate (EGCG), a green tea flavonoid, both in vivo, in mice, and in vitro, in primary epithelial cells from CF patients. In a pilot clinical trial involving 10 F508del-CFTR homozygous CF patients, the combination of cysteamine and EGCG restored BECN1, reduced SQSTM1 levels and improved CFTR function from nasal epithelial cells in vivo, correlating with a decrease of chloride concentrations in sweat, as well as with a reduction of the abundance of TNF/ TNF-alpha (tumor necrosis factor) and CXCL8 (chemokine [C-X-C motif] ligand 8) transcripts in nasal brushing and TNF and CXCL8 protein levels in the sputum. Altogether, these results suggest that optimal schedules of cysteamine plus EGCG might be used for the treatment of CF caused by the F508del-CFTR mutation.

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