Lungs not only breathe, but they also produce blood! A new study published in the journal Nature reveals this unknown role of the lungs.
The established role of lungs is breathing. Through them, the blood is provided with oxygen, and purified from carbon dioxide. The new study extends their intimacy with blood even further: the lungs are not only connected with blood vessels, but they are also the producers of a component of the blood called platelet. Blood-making has, otherwise, been assigned to the bone marrow which contains the cells that produce the life liquid. Up until now, the lungs were not recognised to have any participation at all in blood production.
The ‘new’ role of lungs was discovered when a team of researchers from UC San Francisco analysed a living mouse lung using video microscopy. This revealed that the lungs were the producers of over 50% of the mouse’s blood platelets; the latter are part and parcel of blood, and are necessary for the process of blood clotting. Another surprising finding was the detection of blood stem cells in the lungs that would replenish the blood when the stem cells of the bone marrow were used up. The bone marrow might just have been downgraded! And, the lung elevated!
Senior author, pulmonologist Mark R. Looney, describes their findings as providing a “more sophisticated view of the lungs” because these organs constitute an important contributor to the production of crucial components of the blood in mice. He, therefore, suggests that the human lung might also be playing a comparably essential role in blood formation.
This unprecedented observation was made thanks to a previous work of Looney and his colleague Matthew F. Krummel: the pair developed a refined methodology called two-photon intravital imaging that enabled them to see the individual cells found in the minuscule blood vessels in the lungs of a living mouse.
That was how the researchers saw an abundance of platelet-producing cells, called megakaryocytes, in the vascular system surrounding the lungs. Megakaryocytes in the lungs are not new to the world of science, but their main location was assumed to be the bone marrow where they would produce platelets. However, the team found that the megakaryocytes in the lungs were making over 10 million platelets per hour in the mouse lung vasculature. These figures imply that more than half of the total number of platelets were being produced in the lungs, and not in the bone marrow. Further investigation involving video microscopy showed the occurrence of megakaryocyte progenitor cells together with blood stem cells outside the lung vasculature, a whole 1 million of them in one mouse lung!
Upon tracing the origin of the lung megakaryocytes, the team found that they came from the bone marrow from where they would travel to the lungs to engage in the process of platelet production. Why make the trip to the lungs to form platelets? Co-author Guadalupe Ortiz-Muñoz suggests that the lungs might be providing the ideal conditions, given the mechanical force of the blood.
This research also brings more questions. What is the impact of the blood stem cells of the lungs on lung transplants? How can this relate to diseases like thrombocytopenia whereby sufferers have low levels of platelets?