Researcher found that the two types of cells at the end of the respiratory tree branches can regenerate to replace each other. File Photo by UPI/Shutterstock/Guzel Studio

PHILADELPHIA, April 13 (UPI) -- A new study suggests lung tissue is more resilient than previously thought, and that lung cells can regenerate to form more than one kind of cell.

There are two main kinds of cells in the alveoli, terminal ends of the respiratory tree that perform the gas-exchange function inside the lungs. Type 1 cells are long and thin and enable the exchange of oxygen and carbon dioxide -- they facilitate the actual breath. Type 2 cells secrete a liquid substance called surfactant, a wetting agent that keeps airways open. Both cells originate from a common stem cell in the embryo.


To study the role of these cells in regeneration, scientists at Duke University and the Perelman School of Medicine at the University of Pennsylvania observed the recovery of mice with parts of their lungs missing.

Previous research showed that Type 2 cells could differentiate into gas-exchanging Type 1 cells in response to injury. But the latest research suggests that the opposite is also possible.

"We decided to test that hypothesis about Type 1 cells," lead researcher Rajan Jain, a cardiologist at Duke, explained in a press release. "We found that Type 1 cells give rise to the Type 2 cells over about three weeks in various models of regeneration. 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."

The scientists were able to coax Type 1 cells into taking on the responsibilities of Type 2 cells, not via petri dish-based transcription processes, but by subjecting the lungs to damages that call for certain types of regeneration.

By understanding how Type 1 and 2 cells revert to early forms and take on new functions can help doctors develop new therapies for lung maladies, as well as for problems like other organs like the heart and intestines.

"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," said lead author Jon Epstein, chair of the department of cell and developmental biology at Pennsylvania. "These aren't classic stem cells that we see regenerating the lung. They are mature lung cells that awaken in response to injury. We want to learn how the lung regenerates so that we can stimulate the process in situations where it is insufficient, such as in patients with COPD [chronic obstructive pulmonary disease]."

The new research was published this week in the journal Nature Communications.