It never ceases to amaze me that in 2017 we are still discovering significant things about the body. Last week a paper was published that discovered the lungs were acting as a living Petri dish for the cells that make your platelets. Before this discovery, doctors and scientists assumed that the cells that made your platelets lived only in the bone marrow. So meet your newly discovered lungs, which now handle respiration and act as a place where your cells come to grow up!
Platelet Function and Manufacture
Platelets are minuscule fragments of a larger cell that clot your blood. They have no nucleus (command center) like other cells, and their main function is to clot your blood and heal injuries. To do the former, they are involved in an intricate dance, and the latter is why they are used in platelet rich plasma.
First, platelets attach to chemicals on broken blood vessels: adhesion. Second, they morph their shape and secrete chemical messengers: activation. Third, they connect to each other through small bridges, like Lego blocks: aggregation. At this point, they form a platelet plug and activate the coagulation cascade, which causes fibrinogen to make fibrin (the mortar between the Lego bricks). All of this makes up a blood clot.
Platelets are also chock-full of growth factors (GFs), which are like espresso shots for the local repair cells (they kick them into high gear). So after a clot is formed, the platelets secrete these GFs, which help in healing. These are on a timed-release program, where certain GFs are released early and others come later.
Platelets are made by megakaryocytes, which are huge cells that are 10–15 times the size of a red blood cell. These cells are made in the bone marrow from hematopoietic stem cells and then break apart to form platelets. We thought that all of this happened in the bone marrow, but this new study suggests the last part likely occurs in the lungs.
The Study That Revealed a New Function for Our Lungs
The researchers who authored the new study were trying to determine how platelets traveled around the body. They labeled the platelets and the megakaryocytes in mice with a green fluorescent protein and saw the usual stock in the bone marrow. What they did not expect to see was an extensive collection of megakaryocytes parked just outside the lungs. When they ran further experiments, they saw the cells traveling from the bone marrow to the lungs to spawn platelets, turning upside down our assumption that this happened in the bone marrow. Even stranger, when they transplanted healthy lungs into mice with bad bone marrow cells, megakaryocytes and other stem cells traveled from the lungs to repopulate the dying bone marrow!
Implications for PRP Use
So how does this impact platelets? While more research needs to be performed to confirm that all of this happens in humans the same way it happens in mice, the possible implications for PRP therapies are obvious. If you have a patient with lung disease, you may have defective platelets being produced. Alternatively, does the bone marrow take over that function so this does not happen? We won’t know for sure until someone measures the growth-factor release of platelets from patients with lung disease and compares that to similar patients without that problem.
The upshot? It is absolutely amazing that in 2017 we’re still discovering major things about the body that we did not know. This one continues to show what we have learned over the last decade about how flexible the body’s systems can be. For example, if your bone marrow has problems, your lungs can recuse the cell factory by sending in the stem cell calvary parked there! How much more is there to learn about the body? I bet there’s quite a bit!