01 October 2009

Why do muscles age and how to deal with it

Scientists have figured out how to deal with the natural aging of muscle tissue
Dmitry Safin, CompulentaExperts from the University of California at Berkeley (USA), the University of Southern Denmark and the University of Copenhagen (both Denmark) have identified the main causes of muscle weakness in the elderly and have shown that the natural aging process of muscle tissue can be slowed down.

Slightly less than 30 healthy men took part in the experiments: young (average age – 22.6 years) and elderly (71.3 years). Before starting the study, samples of muscle tissue of the quadriceps femoris were taken from all men. Then the "injured" legs of the subjects were immobilized for two weeks with the help of a special fixing device, simulating muscle atrophy. After removing the device, the volunteers performed a set of exercises aimed at restoring muscle mass; after three days of training, new tissue samples were taken from them, and after another three and a half weeks, the biopsy procedure was repeated.

Analysis of the collected samples showed that at the initial stage of the experiment, the "young" tissue contained twice as many stem cells responsible for muscle renewal as in the tissue of elderly people. At the stage of recovery after artificial atrophy, the gap became fourfold. At the same time, muscle stem cells remained inactive in the elderly study participants; signs of inflammatory reactions and tissue scarring were also noted in this age group (left).

"The results obtained once again remind us that older people should lead an active lifestyle, since long periods of inactivity negatively affect the ability of muscles to recover," summarizes one of the authors of the work Morgan Carlson (Morgan Carlson).

Having completed this stage of the study, the experts decided to find out what factors affect the regeneration of muscle tissue. Previous experiments on mice have shown that the action of muscle stem cells is directly related to the activity of their Notch receptor protein; the receptor of the transforming growth factor TGF-beta has a certain effect, which can interfere with cell division.

In humans, as it turned out, all the described dependencies are preserved; in addition, the authors were able to find a connection between the long-known MAPK enzyme and the activity of the Notch protein.

(The family of mitogenactivated protein kinases – MAPK is one of the links of the signaling pathway that stimulates cell proliferation and migration and their synthesis of physiologically active substances; the Notch signaling pathway plays an important role in the regulation of cell proliferation and the processes of apoptosis and angiogenesis – VM.)

When the action of the MARK was artificially suppressed, the "young" muscle tissue lost its ability to recover. On the contrary, with an increase in its activity, the "old" tissue was renewed much faster and more efficiently than under normal conditions (right).

The full version of the researchers' report will be published in the journal EMBO Molecular Medicine.

Prepared based on the materials of the University of California at Berkeley: Scientists discover clues to what makes human muscle age.

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