Transient receptor potential canonical channel 6 links Ca2+ mishandling to cystic fibrosis transmembrane conductance regulator channel dysfunction in cystic fibrosis.

In cystic fibrosis (CF), abnormal control of cellular Ca(2+) homeostasis is observed. We hypothesized that transient receptor potential canonical (TRPC) channels could be a link between the abnormal Ca(2+) concentrations in CF cells and cystic fibrosis transmembrane conductance regulator (CFTR) dysfunction. We measured the TRPC and CFTR activities (using patch clamp and fluorescent probes) and interactions (using Western blotting and co-immunoprecipitation) in CF and non-CF human epithelial cells treated with specific and scrambled small interfering RNA (siRNA). The TRPC6-mediated Ca(2+) influx was abnormally increased in CF compared with non-CF cells. After correction of abnormal F508 deletion (del)-CFTR trafficking in CF cells, the level of TRPC6-dependent Ca(2+) influx was also normalized. In CF cells, siRNA-TRPC6 reduced this abnormal Ca(2+) influx. In non-CF cells, siRNA-TRPC6 reduced the Ca(2+) influx and activity wild-type (wt)-CFTR. Co-immunoprecipitation experiments revealed TRPC6/CFTR and TRPC6/F508 del-CFTR interactions in CF or non-CF epithelial cells. Although siRNA-CFTR reduced the activity of wt-CFTR in non-CF cells and of F508 del-CFTR in corrected CF cells, it also enhanced TRPC6-dependent Ca(2+) influx in non-CF cells, mimicking the results obtained in CF cells. Finally, this functional and reciprocal coupling between CFTR and TRPC6 was also detected in non-CF ciliated human epithelial cells freshly isolated from lung samples. These data indicate that TRPC6 and CFTR are functionally and reciprocally coupled within a molecular complex in airway epithelial human cells. Because this functional coupling is lost in CF cells, the TRPC6-dependent Ca(2+) influx is abnormal.

Dysfunction of mitochondria Ca2+ uptake in cystic fibrosis airway epithelial cells.

In the genetic disease cystic fibrosis (CF), the most common mutation F508del promotes the endoplasmic reticulum (ER) retention of misfolded CF proteins. Furthermore, in homozygous F508del-CFTR airway epithelial cells, the histamine Ca(2+) mobilization is abnormally increased. Because the uptake of Ca(2+) by mitochondria during Ca(2+) influx or Ca(2+) release from ER stores may be crucial for maintaining a normal Ca(2+) homeostasis, we compared the mitochondria morphology and distribution by transmission electron microscopy technique and the mitochondria membrane potential variation (DeltaPsi(mit)) using a fluorescent probe (TMRE) on human CF (CF-KM4) and non-CF (MM39) tracheal serous gland cell lines. Confocal imaging of Rhod-2-AM-loaded or of the mitochondrial targeted cameleon 4mtD3cpv-transfected human CF and non-CF cells, were used to examine the ability of mitochondria to sequester intracellular Ca(2+). The present study reveals that (i) the mitochondria network is fragmented in F508del-CFTR cells, (ii) the DeltaPsi(mit) of CF mitochondria is depolarized compared non-CF mitochondria, and (iii) the CF mitochondria Ca(2+) uptake is reduced compared non-CF cells. We propose that these defects in airway epithelial F508del-CFTR cells are the consequence of mitochondrial membrane depolarization leading to a deficient mitochondrial Ca(2+) uptake.