They found the actual niche within the bone marrow where the new bone and immune cells are produced. The study, published in Nature, also shows that movement-induced stimulation is required for the upkeep of this niche, as well as the bone and immune-forming cells that it contains.
They suggest the results point to the potential development of the latest therapeutic strategies which may increase bone formation and immune responses, particularly in the elderly.
Researchers from the Morrison laboratory discovered that forces created from any mechanical activity like walking or running are transmitted from bone surfaces along arteriolar blood vessels into the marrow inside bones.
The cells that are present on the surface of the arterioles sense these mechanic-sensitive changes and proliferate to form new bone-forming cells. This not only helps in the formation of the bones but also has lymphopoietic action. It helps in the formation of the latest lymphocytes around the arterioles. The B and T lymphocytes that are thus produced help the system fight infections.
Their studies in laboratory-grown cells and in mice highlighted the very fact that when the ability of those bone-forming cells to sense pressure changes caused due to mechanical activities were inactivated, the formation of the latest bone cells and lymphocytes were reduced, causing bones to become thinner and reducing the power of mice to clear a bacterial infection.
“Past research has shown exercise can improve bone strength and immune function, and our study discovered a new mechanism by which this occurs”, says Sean Morrison, Ph.D., the director of CRI and a Hughes Medical Institute Investigator.
In a previous study at the Morrison laboratory, researchers have discovered the skeletal stem cells that give produce most of the new bone cells that are formed during adulthood within the bone marrow. they’re Leptin Receptor+ (LepR+) found within the lining of blood vessels of bone marrow. A subset of these LepR+ cells forms a protein called Osteolectin, which was previously unknown. This protein commands the LepR+ receptors to make new bone cells.
In the current study, Bo Shen, Ph.D., a postdoctoral fellow in the Morrison laboratory, observed that the amount of Osteolectin-positive cells and lymphoid forming cells decreased with age. Trying to reverse this, Shen put running wheels within the cages in order that the mice could exercise.
He found the bones of those mice became stronger with exercise, while the amount of Osteolectin-positive cells and lymphoid progenitors around the arterioles increased. This was the primary indication that mechanical stimulation regulates a distinct segment within the bone marrow.
He found a receptor on the surface of Osteolectin-positive cells, referred to as Piezo1 that informs the within of the cell in a response to mechanical activity, thus stimulating the lymphoid progenitors, strengthening bones and immune system.
“We think we’ve found a crucial mechanism by which exercise promotes immunity and strengthens bones, on top of other mechanisms previously identified by others,” says Morrison.