Lungs try to repair damaged elastic fibers

The lungs of patients suffering chronic obstructive pulmonary disease (COPD) attempt to repair damaged elastic fibers, a new finding that contradicts the conventional wisdom on the capabilities of the adult lung.

The study "Evidence for attempted regional elastic fiber repair in severe emphysema," was done by Jason Woods, Kristin Castillo, Alexander Patterson and Richard Pierce of Washington University, St. Louis, Mo.; Joel Cooper of the University of Pennsylvania, Philadelphia; and James Hogg of St. Paul's Hospital, Vancouver, British Columbia. The authors will be present their findings Nov. 3 at The American Physiological Society conference "Physiological Genomics and Proteomics of Lung Disease."

The researchers found that synthesis of elastin, a gene linked to elastic fiber growth, is increased in the moderately diseased tissue of COPD patients. Elastic fibers allow the lung to expand and contract with breathing.

"We've found elastin synthesis to increase in the air sacs (alveoli) and airways of the lungs of patients suffering severe or end-stage COPD," Woods explained. "This shows that the lung may be attempting to repair itself."

The finding is important because it could pave the way to develop a drug to 'turn on' key genes to allow the lung to grow new alveoli, he said. Alveoli play a role in the exchange of oxygen and carbon dioxide between the lungs and the circulatory system.

A 2-year-old could do it

Very young children who suffer lung injuries increase elastin expression and produce new elastic fibers inside the alveoli, Woods said. Adults do not have that ability and that has led physiologists to conclude that the elastin gene must shut off after we reach a certain age, ending elastin fiber production.

Physiologists want to understand this process in the hope that it could be harnessed to repair the diseased adult lung. In particular, Woods and his colleagues looked at three genes associated with elastic fiber assembly: Emilin-1, MFAP2 and elastin. They found the expression of elastin consistently increased in the diseased lungs they studied.

In a preliminary study, the researchers examined two diseased lungs removed from end-stage COPD patients undergoing lung transplants. COPD develops as a result of exposure to toxins such as cigarette smoke, resulting in inflammation to the small airways and destruction of elastic fibers within alveoli. The patients suffered from emphysema.

The team used hyperpolarized magnetic resonance imaging (MRI) to characterize the regions of the lung showing moderate emphysema and regions showing severe emphysema. They found that new elastin synthesis was initiated in moderately diseased specimens.

The researchers did a second study using 10 lungs from end-stage COPD patients who had undergone transplants. Again, they found the greatest amount of elastin gene expression in the moderately diseased areas of the lungs, Woods said. There was no variability in elastin levels within the control lungs.

Further, the team found that the increase in elastin expression occurred on the alveolar walls, the same area where elastin occurs during the lung's development in children. This shows the lung is attempting to repair the elastic fibers in end-stage emphysema, the authors concluded. Source : American Physiological Society