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mechanism by which exercise strengthens bones and immunity

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Researchers identify mechanism by which exercise strengthens bones and immunity

[There is a] specialized environment, known as a niche, in the bone marrow where new bone and immune cells are produced.

movement-induced stimulation is required for the maintenance of this niche, as well as the bone and immune-forming cells that it contains.

forces created from walking or running are transmitted from bone surfaces along arteriolar blood vessels into the marrow inside bones. Bone-forming cells that line the outside of the arterioles sense these forces and are induced to proliferate. This not only allows the formation of new bone cells, which helps to thicken bones, but the bone-forming cells also secrete a growth factor that increases the frequency of cells that form lymphocytes around the arterioles.

When the ability of the bone-forming cells to sense pressure caused by movement, also known as mechanical forces, was inactivated, it reduced the formation of new bone cells and lymphocytes, causing bones to become thinner and reducing the ability of mice to clear a bacterial infection.

The Morrison lab also found that a subset of LepR+ cells synthesize a previously undiscovered bone-forming growth factor called Osteolectin. Osteolectin promotes the maintenance of the adult skeleton by causing LepR+ to form new bone cells.

discovered that these cells [the subset of LepR+ cells that make Osteolectin] reside exclusively around arteriolar blood vessels in the bone marrow and that they maintain nearby lymphoid progenitors by synthesizing stem cell factor (SCF)—a growth factor on which those cells depend. Deleting SCF from Osteolectin-positive cells depleted lymphoid progenitors and undermined the ability of mice to mount an immune response to bacterial infection.

Shen found that the number of Osteolectin-positive cells and lymphoid progenitors decreased with age. Curious if he could reverse this trend, Shen put running wheels in the cages so that the mice could exercise. He found the bones of these mice became stronger with exercise, while the number of Osteolectin-positive cells and lymphoid progenitors around the arterioles increased. This was the first indication that mechanical stimulation regulates a niche in the bone marrow.

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Very interesting. Mechanical stimulation has been found of course to govern skeletal muscle growth, following certain laws. To govern tendon growth and repair, following different laws. 

Edited by mccoy

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