Researchers at Johns Hopkins Children’s Center have discovered that a protein involved in cystic fibrosis (CF) also regulates inflammation and cell death in emphysema and may be responsible for other chronic lung diseases, using flow cytometry and microscopy to determine the relationship.
The study indicates that the cystic fibrosis transmembrane conductance regulator (CFTR) protein, well known for its role in transporting chloride in and out of cells, is involved in immune regulation and immune response on a far wider scale. The research—conducted in mice and using lung tissue from people with and without emphysema—shows that those with lung damage from emphysema had less CFTR on the cell surface and that changes in the level of CFTR corresponded directly to disease severity. Decreases in CFTR also corresponded to increased buildup in the lung cells of a fatty molecule called ceramide, a well-known trigger of inflammation and cell death. So by regulating ceramide’s inflammation-causing activity, CFTR appears to be a watchdog for inflammation and cell death.
To elucidate the role played by cigarette smoking—the leading cause of emphysema—the researchers analyzed CFTR and ceramide levels in lung tissue obtained from non-smokers and from light and heavy former or current smokers. To further explore the link between cigarette smoke, CFTR and ceramide, the researchers compared lung tissue from mice with lungs never exposed to smoke to tissue from the lungs of mice exposed to cigarette smoke for five hours a day over five days. The lungs of smoke-exposed mice had decreased CFTR expression and increased ceramide levels, thus confirming the role of cigarette smoke in lung damage. The heavier the smoking, the greater the lung damage, the lower the CFTR expression and the higher the ceramide accumulation, the researchers noted, clearly linking CFTR and ceramide levels to smoking history and disease severity.
The Hopkins team also explained just how CFTR causes ceramide to trigger lung-damaging inflammation. Analyzing lung cells from people and mice lacking CFTR in their cell membrane under a microscope and using flow cytometry, the scientists noticed increased clustering of ceramide molecules on sections of the cell membrane called lipid rafts, known to be hot spots where inflammatory signaling proteins congregate. This clustering, the researchers said, leads to increased inflammatory signaling, greater inflammation and cell damage, but cells with normal CFTR had no such clustering. Apparently, the researchers say, when functioning properly CFTR keeps a lid on the signaling activity of inflammatory receptors by preventing them from clustering, thus warding off inflammation and lung damage.
To further test their hypothesis, the researchers used two types of ceramide inhibitors to treat mice with lung damage caused by a bacterial infection. One of the inhibitors, FB1, successfully decreased ceramide buildup in mice with intact CFTR, but failed to stop ceramide accumulation in mice with absent CFTR, as is the case in CF. However, the other type of inhibitor, AMT, curbed ceramide activity in the mice with the absent CFTR, while failing to do so in those with decreased CFTR.
The findings were published online in the December 2010 issue of The Journal of Immunology, and the National Institutes of Health and the Flight Attendant Medical Research Institute supported this work.
Source: Johns Hopkins Children's Center
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Posted by Lee Mather
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