Lung tissue is better at regenerating itself after injury than previously thought, a discovery that could improve the treatment of some lung and breathing disorders, researchers say.

In addition, lung cells -- which come in two distinct types in the alveoli, where lungs perform their gas-exchange function -- can be regenerated from more than one kind of cell, scientists at Duke University and the University of Pennsylvania report.

Long, thin Type 1 cells are where the gases oxygen and carbon dioxide are exchanged during breathing. Type 2 cells secrete surfactant, a slippery substance that helps keep airways open.

Both types grow from common stem cells in the embryo.

While previous research has demonstrated that Type 2 cells can differentiate into gas-exchanging Type 1 cells in response to injury, the new study suggests the opposite -- Type 1 cells becoming Type 2 cells -- is also possible, the scientists say.

"It's as if the lung cells can regenerate from one another as needed to repair missing tissue, suggesting that there is much more flexibility in the system than we have previously appreciated," says Penn's Jon Epstein, chair of the university's department of Cell and Developmental Biology "These aren't classic stem cells that we see regenerating the lung. They are mature lung cells that awaken in response to injury."

Learning just exactly how lungs go about regenerating cells could lead to the ability of stimulate the repair process in patients with lung conditions such as chronic obstructive pulmonary disease (COPD,) he says.

The researches say their study, published in Nature Communications, is one of the first to demonstrate that a specialized cell type considered to be at the end of its period of ability to differentiate can modify itself back to an earlier state under the right conditions.

In experiments with mice, the scientists were able to observe Type 1 cells taking on the role of Type 2 cells in response to kinds of damages to the lungs that call for certain types of regeneration.

"We found that Type 1 cells give rise to the Type 2 cells over about three weeks in various models of regeneration," says Penn cardiologist Rajan Jain. "We saw new cells growing back into these new areas of the lung. It's as if the lung knows it has to grow back and can call into action some Type 1 cells to help in that process."

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