Lung Enzyme Both Friend and Foe

WEDNESDAY June 17, 2009 -- An enzyme involved in the development of emphysema also defends the lungs against bacterial infection, a new study finds.

It had been thought that the only thing macrophage elastase, matrix metalloproteinase-12 (MMP-12), did was degrade lung elasticity as part of the tissue destruction seen in emphysema patients.

"But we found that mice that didn't have the gene to make this enzyme could not clear bacteria well and were more likely to die of infection. They couldn't make this small protein, which kills bacteria by poking holes in cell membranes," study author Dr. A. McGarry Houghton, an assistant professor in the Division of Pulmonary, Allergy and Critical Care Medicine at the University of Pittsburgh School of Medicine, said in a university news release.

The researchers also found that MMP-12's antimicrobial activity comes from a small part of the enzyme that's structurally and sequentially unique.

"Humans, mice, rats and rabbits all have that special sequence and structure in MMP-12, but not in other MMPs," Houghton said.

The study appears in the June 17 issue of Nature.

"While not the initial purpose of this study, finding novel antimicrobial mechanisms is extremely important," senior study author Dr. Steven D. Shapiro, chair of the Department of Medicine at the University of Pittsburgh School of Medicine, said in the same release. "Many microorganisms have adapted to circumvent our current and stagnant arsenal of antibiotics. We must find new weapons so that we don't fall back to the public health problems we had prior to penicillin."

The researchers plan to investigate whether the special sequence and structure in MMP-12 can kill viruses and fungi.

More information

The American Lung Association has more about emphysema.

Posted: June 2009


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