Lungs are a crucial organ in many animals, including humans. While their function has always seemed pretty straightforward – to take in oxygen, transfer it into blood, and exhale carbon dioxide – scientists have found a previously unrecognized function of the lungs of mice: blood production.
The study, which was published in Nature by researchers at the University of California San Francisco, was performed by inserting fluorescent protein into the mouse’s genome.
The protein caused the platelets (small blood cells that bind together to help create blood clots when a blood vessel is damaged), in the mouse to glow, allowing scientists to trace the platalets’ paths. What they found was a massive number of megakaryocytes, a stem cell that produces in the lungs.
When researched further, scientists found that the lung was producing over 10 million blood-producing platelets per hour, and the platelets produced by the lung accounted for the majority of platelets in the mouse’s circulatory system. Researchers are theorizing that the megakaryocytes are created in the bone marrow, but then travel to the lung to produce platelets.
While it is known that human lungs produce platelets and produce blood, as small amounts of megakaryocytes have been found in lungs before, if these findings are reproduced in humans, it will prove that the sheer amount that lungs produce has been greatly underestimated.
The study also found a reservoir of stem cells with the ability to become blood cells in the lungs. Researchers implanted lungs with the fluorescent megakaryocyte cells into mice that had been engineered to have no blood stem cells in their bone marrow, and found that the fluorescent cells travelled from the lungs to the marrow, and helped to produce platelets and other “ingredients” in blood, including neutrophils. In cases where the bone marrow is dealing with platelet or stem cell deficiency, these stem cells were able to leave the lung and contribute to the “refilling” of platelets in the marrow.
If further research indicates that these findings also apply to humans – which they very well may, considering the genetic and biological similarities between mice and humans – it will not only disprove the current theory that states the bone marrow accounts for most of the human body’s platelet production, but it will also affect how scientists approach treating blood diseases in humans, particularly ones that result in a platelet deficiency, such as thrombocytopenia.