Abstract
The F508del-CFTR mutation, responsible for Cystic Fibrosis (CF), leads to the retention of the protein in the endoplasmic reticulum (ER). The mistrafficking of this mutant form can be corrected by pharmacological chaperones, but these molecules showed limitations in clinical trials. We therefore hypothesized that important factors in CF patients may have not been considered in the in vitro assays. CF has also been associated with an altered lipid homeostasis, i. e. a decrease in polyunsaturated fatty acid levels in plasma and tissues. However, the precise fatty acyl content of membrane phospholipids from human CF bronchial epithelial cells had not been studied to date. Since the saturation level of phospholipids can modulate crucial membrane properties, with potential impacts on membrane protein folding/trafficking, we analyzed this parameter for freshly isolated bronchial epithelial cells from CF patients. Interestingly, we could show that Palmitate, a saturated fatty acid, accumulates within Phosphatidylcholine (PC) in CF freshly isolated cells, in a process that could result from hypoxia. The observed PC pattern can be recapitulated in the CFBE41o− cell line by incubation with 100 µM Palmitate. At this concentration, Palmitate induces an ER stress, impacts calcium homeostasis and leads to a decrease in the activity of the corrected F508del-CFTR. Overall, these data suggest that bronchial epithelial cells are lipointoxicated by hypoxia-related Palmitate accumulation in CF patients. We propose that this phenomenon could be an important bottleneck for F508del-CFTR trafficking correction by pharmacological agents in clinical trials.
Highlights
Cystic fibrosis (CF) is a genetic disease caused by mutations in the CFTR (CF Transmembrane conductance Regulator) gene, encoding a plasma-membrane chloride channel
We show that a Palmitate accumulation occurs within CF patient bronchial epithelial cells with, as a corollary, an increase of the PC saturation rates
We formulated the hypothesis that Palmitate accumulation could be the consequence of hypoxia, which relates to the thick layer of mucus obstructing the lungs [30], because fatty acid desaturases are oxygendependent [31]
Summary
Cystic fibrosis (CF) is a genetic disease caused by mutations in the CFTR (CF Transmembrane conductance Regulator) gene, encoding a plasma-membrane chloride channel. Some molecules were found to act as pharmacological chaperones or as proteostasis modulators during the F508del-CFTR folding process in the ER, restoring its trafficking to the plasma membrane. Among these correctors, 4-PBA (sodium 4-phenylbutyrate) [8], CPX (8-cyclopentyl-1,3-dipropylxanthine) [8], VX809 [9] and miglustat [10] have been tested in clinical trials but, until now, they appeared to be less efficient in vivo than in vitro [11,12,13,14]. We hypothesized that important factors in CF patients may have not been taken into consideration in the in vitro assays, accounting for the clinical trial failure
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