What does bone marrow actually do

physiology : Surprising orders to the bone marrow

It is a truism that everything in the body is related to everything else. It is also a fact that research is often only possible if one concentrates on individual organs, tissues and cells. The consequence is an increasing specialization in biology and medicine. However, a field called "systems biology" is becoming more and more popular. The aim here is to explicitly research and model how everything is related to everything else. In medicine one speaks of "holistic", although the term has a somewhat esoteric touch. Scientists are always amazed at the connections that emerge. It was no different for Lei Ding, Matthew Decker and their colleagues with their latest discovery, published in the journal "Science".

The knowledge of the liver

In experiments with mice, the immunologists from Columbia University in New York found a vital signal axis between two organs: a molecule from the liver is responsible for the production of blood stem cells in the bone marrow. Up until now it was assumed that the bone marrow regulates itself completely at the level of the stem cells. "It was a surprising find for us," says Ding, "but in retrospect it makes a lot of sense." The liver is the most important metabolic organ of all, it is "predestined to have the best information about the condition of the organism as a whole". In this case, she apparently uses this information to tell another organ how many stem cells it needs.

The signaling molecule in question is called thrombopoietin (TPO). It is the most important factor in platelet formation, a late step in blood formation. It occurs long after they have developed from the original stem cells into special cell lines. This has been known for more than 20 years. Harald Schulze, a biologist at the University of Würzburg, has been researching TPO for almost as long. It was clear from the start that it is not only formed in the bone marrow, but also in the liver and bones. “Most of the TPO is made in the liver,” says Schulze. And erythropoietin for the formation of red blood cells - "also known because it is used for blood doping" - is mainly produced in the kidneys. It has long been known that there are such signals from other organs. What is new, however, is that the so-called stem cell pool is dependent on such remote commands.

Signal gone, stem cells gone

The New York researchers blocked the formation of TPO in the liver of mice. As a result, the amount of blood stem cells, which are precursors to the entire arsenal of blood cells, decreased 24-fold. The same inhibition of TPO in bone cells or in the bone marrow had little effect.

From the point of view of the researchers from Columbia University, the findings generally show that the blood and immune systems not only supply the entire body and protect it in the event of infections, for example, but also that it is dependent on the functioning of other organs.

The Würzburg biologist Schulze therefore finds the findings hardly surprising. "Most of the TPO comes from the liver, so why shouldn't it play a major role in maintaining the stem cell pool?"

Willingness to donate bone marrow is essential

It is unclear whether the results can help improve therapies. Active ingredients that mimic the function of TPO already exist. It is currently being investigated whether they can get the immune system going better after bone marrow transplants. In order for transplants to better help patients with blood cancer, not only more research is needed, but above all volunteers who are willing to donate.

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