Base treatment corrects defects due to misfolding of mutant cystic fibrosis transmembrane conductance regulator

Background & Aims: The most common form of the disease-causing cystic fibrosis transmembrane conductance regulator mutation, ΔF508, leads to a misfolded protein that undergoes endoplasmic reticulum-associated degradation. Retrieval of misfolded protein from the cis-Golgi or pre-Golgi intermediate compartment is a critical factor in endoplasmic reticulum retention and degradation of ΔF508 protein. Therefore, the inhibition of retrograde Golgi-to-endoplasmic reticulum traffic by the alkalinization of Golgi lumen may permit functional ΔF508 protein to reach the cell surface. Methods: Functional and biochemical effects of alkaline treatment on misfolded cystic fibrosis transmembrane conductance regulator-induced defects were measured in CFPAC-1 cells, which endogenously express ΔF508 cystic fibrosis transmembrane conductance regulator, and in CHO cells, which heterologously express ΔF508 cystic fibrosis transmembrane conductance regulator. The animal survival rate and the functional expression of cystic fibrosis transmembrane conductance regulator proteins were analyzed in homozygous ΔF508 mice after chronic treatment with weak base NaHCO₃. Results: In CFPAC-1 and CHO cells, intracellular alkalization by reducing carbon dioxide concentrations in a carbon dioxide incubation chamber or intra-Golgi alkalization by bafilomycin A1 treatment increased the membrane expression of ΔF508 protein and cystic fibrosis transmembrane conductance regulator-dependent anion transport. Notably, chronic administration of NaHCO₃ increased the long-term survival of homozygous ΔF508 mice and induced the functional expression of cystic fibrosis transmembrane conductance regulator in the luminal membrane of intestinal epithelium. Conclusions: We found that base treatments correct misfolded cystic fibrosis transmembrane conductance regulator-induced defects in vitro and in vivo. These results imply that the alkalization of intracellular compartments, in particular, Golgi or pre-Golgi intermediate compartments, can be a potential therapeutic target for the loss-of-function type of conformational diseases.