New body part found hidden in the lungs

Scientists have discovered a brand-new type of cell hiding inside the delicate, branching passageways of human lungs. The newfound cells play a vital role in keeping the respiratory system functioning properly and could even inspire new treatments 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 are tipped with alveoli, the small air sacs that exchange oxygen and carbon dioxide with the bloodstream. The newfound RAS cells are similar to stem cells – ‘blank canvas’ cells that can differentiate into any other type of cell in the body – and are capable of repairing damaged alveoli cells and transforming into new ones. Researchers discovered RAS cells after becoming increasingly frustrated by the limitations of relying on the lungs of mice as models for the human respiratory system. To get a better understanding of these differences on a cellular level, the team took lung tissue samples from healthy human donors and analysed the genes within individual cells, revealing the previously unknown RAS cells. RAS cells serve two main functions in the lungs. Firstly, they secrete molecules that maintain the fluid lining along bronchioles, helping prevent the tiny airways from collapsing and maximising the efficiency of the lungs. Secondly, they can act as progenitor cells for alveolar type II cells, a special type of alveoli that secrete a chemical that’s used in part to repair other damaged alveoli. A progenitor cell is a cell that has the capacity to differentiate into another type of cell, similar to how stem cells differentiate into other cells.

“RAS cells are what we’ve termed facultative progenitors,” said Edward Morrisey, a professor at the Perelman

School of Medicine at the University of Pennsylvania, “which means they act as both progenitor cells and also have important functional roles in maintaining airway health.” This means RAS cells play a vital role in maintaining healthy lungs, he added.

The 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 airway passages inside the lungs, which can be caused by smoking and occasionally air pollution. The inflammation of the airways makes it harder for the lungs to properly take in enough oxygen; as a result, COPD has similar symptoms to asthma. In theory, RAS cells should prevent, or at least alleviate, the effects of COPD by repairing damaged alveoli. However, the researchers suspect that smoking can damage – or even completely destroy – the newfound cells, leading to the onset of diseases such as COPD.

Patients who have COPD are often prescribed anti-inflammatory drugs or oxygen therapy to ease their symptoms. However, these are only temporary solutions and do nothing to reverse lung damage. RAS cells could potentially be used to improve treatments or even cure COPD if researchers can properly harness these cells’ regenerative properties. “We really don’t know if this discovery could lead to a potential cure for COPD yet,” Morrisey said. “However, since COPD is a disease we know very little about, any new insight should help the field start to think about new therapeutic approaches that could lead to better treatments.”