The surprising impact of pulmonary ionocytes on CF

Mother holding baby with cystic fibrosis during pediatric appointment.
Mother holding baby with cystic fibrosis during pediatric appointment.

A recent study published in The Journal of Clinical Investigation reveals the true function of pulmonary ionocytes—a type of rare lung cells. A research team from the University of Iowa uncovered the cells’ ability to absorb water and salt from the airway surface. This contradicts researchers’ initial theories of the ionocytes’ behavior and demonstrates possible implications for cystic fibrosis (CF). 

The new study builds on a discovery, about five years ago, when investigators found the presence of pulmonary ionocytes in the lining of human lungs and airways. It was previously thought that this type of cells only existed in fish gills and frog skin. This breakthrough was of particular interest to CF researchers. 

Although pulmonary ionocytes represent only 1% of the cells found in humans’ airway lining, they contain nearly half of the total amount of cystic fibrosis transmembrane conductance regulator (CFTR) channels. CFTR is a protein that is defective in people who have CF, which causes a buildup of mucus that leads to infections, blockages and damage to the lungs and other organs. Therefore, the CFTR-rich ionocytes likely play a critical role in the formation and progression of CF.

Typically, CFTR channels increase the volume of airway surface liquid and drive secretion of chloride ions. This thin layer of liquid is vital to helping the lungs defend against harmful germs and dangerous particles. However, when present in the pulmonary ionocytes, the CFTR channels function in the opposite way: they soak up chloride ions and stimulate moisture absorption. 

“The key feature that allows ionocytes to absorb chloride is the ionocyte-specific barttin chloride channel on the opposite membrane of the cell from the CFTR channel,” said Ian Thornell, PhD, who is senior author of the study and a research assistant professor of internal medicine at the University of Iowa. “Together, these two channels form a conduit for chloride through the ionocyte that helps drain the liquid lining of the airways into the body.”

According to Dr. Thornell and his team, the opposing channels and types of airway cells suggest that cystic fibrosis interferes with normal liquid absorption and secretion. This directly impacts lung function in people who have CF as well as how CF drugs work. The study found that pulmonary ionocytes can help to mediate water and chloride absorption. Therefore, CFTR modulator therapies not only treat both absorption and secretion, but also restore CFTR channel function. 

This study was funded by grants from the National Institutes of Health and the Cystic Fibrosis Foundation.

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