Identification Of The Role Of Cystic Fibrosis Transmembrane Conductance Regulator Cftr In The Autophagy And Lysosomal Dysfunction In Cf Macrophages

Cystic fibrosis (CF) is an autosomal recessive disease that mainly affects the Caucasian population with no definitive available cure. CF is caused by specific mutations in the Cystic fibrosis transmembrane conductance regulator (CFTR) gene that encodes an ion channel which has been mostly studied in epithelial cells. CFTR F508del mutation is the most common mutation which, in epithelial cells, prevents the CFTR protein from reaching the plasma membrane due to misfolding. People with CF (pwCF) are more prone to infections by opportunistic pathogens such as Burkholderia cenocepacia (B. cenocepacia) resulting in fatal respiratory infections. Macrophages play critical roles in the process of clearance of lung pathogens, the locations and functions of CFTR in macrophages are unclear. In CF, human and mouse macrophages expressing F508del CFTR are defective in their ability to kill bacteria. Furthermore, the autophagy process in CF macrophages is halted, and the underlying mechanism remains to be elucidated. Using 3D reconstruction and confocal microscopy, we demonstrate that CFTR protein is expressed in the macrophage and on the autophagosome. We identified that CFTR is recruited to LC3-labeled autophagosomes harboring B. cenocepacia, but not to vacuoles enclosing Escherichia coli (E. coli). Using several complementary approaches, we found that F508del CFTR macrophages display defective lysosomal acidification as well as impaired degradative function for cargos destined to autophagosomes such as B. cenocepacia, whereas non-autophagosomal cargos such as E. coli are effectively degraded. CFTR modulators are used for treating CF patients, via correction of misfolded CFTR, and improving its function in epithelial cells. Yet, their effect on macrophages is still unclear. Here, we show that treatment of CF macrophages with CFTR modulators increased F508del CFTR localization to B. cenocepacia containing vacuoles, improved the autophagy flux, and lysosomal function. Additionally, CFTR modulators enhanced B. cenocepacia clearance in CF macrophages. These effects are achieved when the modulators are present before, but not after B. cenocepacia infection. An efficient autophagy process is required for B. cenocepacia clearance in vivo and in vitro in macrophages. The effect of CFTR modulators on improving autophagic mediated bacterial clearance is dependent on CFTR function in the autophagy process. In conclusion, CFTR plays an important role in autophagy-mediated bacterial clearance in macrophages by regulating acidification of the autophago-lysosomes. Therefore, our study describes a new biological location and function for CFTR in the autophagy pathway in macrophages.