Researchers at the University of Pennsylvania School of Medicine have discovered that an enzyme produced by lung-infecting bacteria further shuts down a protein that is defective in cystic fibrosis patients.
The disruption to this protein that conveys ions from lung cells to airways causes thick mucus to buildup inside the lung. The finding suggests a new therapeutic target for treating lung infections in some cystic fibrosis (CF) patients.
Lung infection, facilitated by CF mutations, is the main cause of death in CF patients. This bacterial component to CF now helps explain why the severity of CF symptoms did not match the pathological effect of the CF mutation alone. The study was published this month in the Proceedings of the National Academy of Sciences.
The research, conducted by Zhe Lu, MD, PhD; Yajamana Ramu, PhD; and Yanping Xu, MD, PhD, of the Department of Physiology, shows that the bacterial enzyme, called sphingomyelinase (SMase), disables a protein in lungs called CFTR, for cystic fibrosis transmembrane conductance regulator. SMase is made by the bacteria that cause pneumonia, some anthrax-causing bacteria, and bacteria that cause opportunistic infections in CF and AIDS patients.
In healthy lungs, CFTR allows the passage of chloride ions (and accompanying water) into airways, creating a thin layer of fluid to keep airways clear. However, SMase, secreted by certain respiratory tract bacteria, breaks down lipids surrounding CFTR and thereby suppresses CFTR's chloride-passing function. To make matters worse, the products of the lipid breakdown are also known to trigger inflammation and cell death.