Scientists have discovered a new type of cell lurking in the delicate, branching passageways of the human lung. This newly discovered organ plays an important role in keeping the respiratory system functioning properly.
In fact, according to research published in the journal Nature, the organ could also inspire new types of treatment to reverse the effects of certain smoking-related diseases.
The cells, known as respiratory airway secretory (RAS) cells, are found in tiny branching passages known as bronchioles, which end with alveoli, tiny air sacs that exchange oxygen and carbon dioxide with the bloodstream.
The new RAS cells are similar to stem cells, cells that can differentiate into other types of cells in the body, and are able to repair damaged alveolar cells and turn into new cells.
The researchers discovered the RAS cells after growing frustrated with the limitations of relying on mouse lungs as a model for the human respiratory system. However, due to certain differences between the two, scientists are struggling to fill some of the gaps in knowledge about the human lung.
To gain a better understanding of these differences at the cellular level, the team took lung tissue samples from healthy human donors and analyzed the genes in the individual cells, which revealed previously unknown RAS cells.
"It has long been known that the airways of the human lungs are different from those of mice," Edward Morrisey, professor at the Perelman School of Medicine at the University of Pennsylvania, told Live Science.
"However, recent technological developments have allowed us to sample and identify unique cell types," he said.
The team also found the presence of RAS cells in ferrets, whose respiratory systems are more similar to those of humans than mice. As a result, the researchers suspect that most mammals of the same or larger size tend to have RAS cells in their lungs.
RAS cells serve two main functions in the lungs. First, they secrete molecules that maintain a layer of fluid along the bronchioles, helping prevent small airways from collapsing and maximizing lung efficiency.
Second, these cells can act as progenitor cells for type 2 alveolar cells (AT2), a special type of alveoli that secrete chemicals that are partially used to repair other damaged alveoli.
"RAS cells are what we call facultative progenitors, which means they act as progenitor cells and also have an important functional role in maintaining airway health. This means RAS cells play an important role in maintaining lung health," explains Morrisey.
Inspiring new medicine
Researchers think RAS cells may play a key role in smoking-related diseases, such as chronic obstructive pulmonary disease (COPD). COPD is the result of inflammation of the airways within the lungs, which can be caused by smoking and, occasionally, air pollution.
Inflammation of the airways makes it difficult for the lungs to take in enough oxygen properly. As a result, COPD has symptoms similar to those of asthma. COPD can also cause emphysema, in which the alveoli are permanently destroyed, and chronic bronchitis, a long-lasting and intense cough that is usually accompanied by excessive phlegm. Every year, more than 3 million people worldwide die from COPD, according to WHO.
In theory, RAS cells should prevent, or at least mitigate, the effects of COPD by repairing damaged alveoli. However, researchers suspect that smoking can damage, or even completely destroy, new cells, leading to diseases such as COPD.
Patients with COPD are often prescribed anti-inflammatory drugs or oxygen therapy to relieve their symptoms. However, this is only a temporary solution and does nothing to reverse lung damage. Well, RAS cells have the potential to be used to improve treatments or even cure COPD, if researchers can properly harness the regenerative properties of these cells.
"We really don't know if this discovery could lead to a potential treatment for COPD," Morrisey said.
"However, because COPD is a disease of which we know very little, any new insights will help the field start thinking about new therapeutic approaches that can lead to better treatments."