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Therapeutically robust correction, in vitro, of the most common cystic fibrosis mutation

In experiments with isolated cystic fibrosis lung cells, University of Alabama at Birmingham researchers and colleagues from two other institutions have partially restored the lost function of those cells.

The work is proof-of-concept for using a yeast genetic model to find therapeutic targets, in this case for people with the most common cystic fibrosis mutation, called deltaF508-CFTR. This mutation affects close to 90 percent of patients with cystic fibrosis, and half of those have two copies of the mutation.

“The research is the first preclinical study, to our knowledge, that demonstrates therapeutic levels of deltaF508-CFTR function in primary patient cells,” said John L. Hartman IV, M.D., associate professor in the UAB Department of Genetics and the Gregory Fleming James Cystic Fibrosis Research Center.

The work was recently published in PLOS Biology, and it will next be tested in animal models of cystic fibrosis, says Kathryn Oliver, the graduate student who did the laboratory work at UAB.

Cystic fibrosis is a progressive genetic disease marked by persistent lung infections that lead to lung damage and severe difficulty in breathing. The lungs of healthy people produce about two quarts of mucus a day. This mucus is transported up to the throat by the waving motion of hair-like cilia on the cells that line the respiratory tract, a conveyor-belt-like activity that removes bacteria, viruses and small particles that were inhaled into the lungs.

The defective gene in cystic fibrosis results in a thick, viscous mucus that resists transport. The gene product, called CFTR, is a tiny channel that pushes chloride ions across the cell membrane of secretory epithelial cells. Water moves along with those ions to lubricate the extracellular cilia and, consequently, the mucus. In cystic fibrosis patients, the channel is broken, so the cilia and mucus do not get hydrated.

UAB researchers, along with colleagues at McGill University, Montreal, Canada, and Emory University, Atlanta, restored the chloride channel by the additive effects of suppressing a ribosomal protein called Rpl12 and use of the investigational drug VX-809, or Lumacaftor. Together, these two treatments were able to restore CFTR chloride transport to 50 percent of the normal activity in bronchial epithelial cells. This level, if achieved in patients, could be enough to produce healthy lung function.

This work is proof-of-concept for discovering novel therapeutic targets for patients, using genomewide gene interaction analysis with a yeast homolog. The common ancestor of yeast and humans diverged about a billion years ago, but there is still enough functional conservation between some pairs of yeast and human genes that they can be substituted for each other.

“We are curious about the extent to which yeast genetic models can reveal gene interaction networks relevant to human disease,” Hartman said. “For cystic fibrosis, this yeast phenomics approach appears to be very useful.”