Bones don’t just support the body. They may also influence the pace of aging. During exercise, they release substances that benefit other organs. In experiments on mice, mechanical stimulation of the bones extended the animals’ lives by nearly 80 days.
The results of the study, conducted by researchers at Southern Medical University in China, were published in the journal Cell Metabolism.
As the authors noted, it has long been known that physical activity helps maintain health in old age, lowers the risk of many diseases and promotes longevity. But it is not entirely clear which mechanisms are responsible for these benefits. Until now, scientists have attributed them mainly to muscles, which release substances into the blood during exertion that affect the functioning of other organs.
The authors of the new study decided to test whether bones might play a similar role. During walking, running or lifting weights, bones are subjected to various mechanical loads. Osteocytes, the cells of bone tissue, use special proteins (such as PIEZO1) to detect the forces acting on bones and trigger the appropriate biological responses.
To test whether this matters for the aging of the body, the researchers conducted an experiment on mice. The animals were 10 months old, meaning they were middle-aged.
Using genetic modification, the scientists switched off the gene responsible for producing the PIEZO1 protein in the rodents’ osteocytes. After five months, these mice showed significantly more signs of aging than those in the control group. They had poorer memory, weaker motor coordination and lower fitness. More aging cells and signs of inflammation were found in their brains, livers, bones and other organs. Their ability to regulate blood glucose levels also worsened.
These changes also affected lifespan. Males lacking the PIEZO1 protein in their osteocytes lived 13.2 percent shorter lives than mice in the control group, and females lived 10.7 percent shorter lives.
In a further experiment, the authors tested whether stimulating the bones could have the opposite effect, that is, slow the aging of the body. This time they used old mice, aged 20 months. For four months, twice a week, they subjected the animals’ tibias (shinbones) to controlled loading (pressure).
After that time, the animals in this group turned out to perform better in tests of memory, motor fitness and muscle strength. They also had stronger bones, better glucose tolerance, fewer signs of aging in various organs and less inflammation.
Most importantly, they lived nearly 80 days longer than the animals in the control group. This applied to both males and females.
The researchers determined how pressing on the tibias can affect organs as distant as the brain or liver. They found that mechanically stimulated osteocytes release substances into the blood that reach other parts of the body and limit the aging processes taking place there. One of the most important is the protein PEDF, which is involved in anti-inflammatory and protective processes.
Further experiments confirmed that bone stimulation increased the concentration of PEDF in the mice’s blood. In turn, administering the protein intravenously to old animals produced effects similar to those seen after loading the bones.
It also turned out that stimulating osteocytes had a beneficial effect on the immune system. In the bone marrow of old mice, more immune cells typical of young animals began to form, and fewer of those that promote the chronic inflammation associated with aging.
The researchers also carried out preliminary analyses involving humans. They found that the concentration of PEDF in our blood decreases with age and is particularly low in people with osteoporosis. In experiments on a model of human cartilage, the protein reduced signs of cell aging and protected the tissue from damage.
The authors hope their discovery will help in the future to develop methods of slowing aging, mainly in people who cannot exercise regularly because of illness, disability or advanced age. One option would be mechanical stimulation of their bones; another would be the use of PEDF.
The scientists cautioned, however, that so far the lifespan extension from such stimulation has been shown only in mice. It is not known whether similar results can be achieved in humans.
Katarzyna Czechowicz (PAP)
