Regular exercise turns back the clock on muscle repair in old mice
A growing body of research is showing us how exercise can help stave off certain effects of aging, including everything from slowing down cognitive decline, to reversing age-related heart damage and boosting our memories. Adding to this pool of knowledge is a team of medical scientists at Stanford University, which has demonstrated how regular exercise can breathe new life into the stem cells responsible for muscle repair in old mice.
The research was carried out by scientists at Stanford’s School of Medicine, who set out to investigate the role that muscle stem cells can play in repairing damaged tissue in older organisms, and how this process could be manipulated for better health outcomes.
Some types of stem cells, such as those of the embryonic or induced pluripotent variety, have the ability to differentiate into any cell in the body. But those related to specific tissues, such as muscle stem cells, already have a future mapped out that involves springing into action when those tissues become damaged. The Stanford team wanted to find out how that ability might be preserved as we age.
“Studies conducted by us and others have shown that tissue regeneration decreases with age, and that this is due to declining function in adult stem cells,” says Thomas Rando, professor of neurology and neurological sciences at Stanford. “Many researchers are looking for a way to restore youthfulness.”
The researchers conducted experiments involving mice around 20 months of age, which equates to an age of 60 to 70 in humans. Over a period of three weeks, the rodents were given access to an exercise wheel and were permitted to run as they saw fit. The outcomes were compared to a group of three- to four-month-old mice (equal to 20 to 30-year-old humans), along with separate groups of young and old mice whose exercise wheels didn’t turn in order to act as controls.
“The animals were exercising at the intensity levels at which they were comfortable, much like what people do for their own health," Rando says. "This is a less stressful situation than resistance training or intense endurance exercise, which may themselves affect muscle stem cell function.”
Following the three-week period, the team examined the abilities of the mice to repair muscle damage. Unsurprisingly, the older mice that had not exercised were far less capable of repairing muscle than the younger, but also sedentary, group. Interestingly, the older group that did exercise exhibited far better muscle repair ability than the older group that didn’t, though this didn't extend to the younger groups of mice, which exhibited no muscle repair benefits compared to their non-exercising youthful counterparts.
“The effect in old animals is very significant,” said Rando. “We found that regular exercise restores youthfulness to tissue repair. Their muscle stem cells start to look and behave like those of much younger animals.”
In a follow-up experiment, where muscle stem cells from the older exercising mice were transplanted into younger mice, the stem cells played a larger role in driving the repair process than stem cells taken from older, sedentary mice. Similar effects were observed when injecting blood taken from older exercising mice into older, sedentary mice.
This indicates that exercise gives rise to certain factors that circulate in the blood and help rejuvenate older stem cells, something that the scientists describe as “fascinating” and are hopeful of replicating. Further investigations zeroed in on a pathway involving a molecule called cyclin D1, which plays a role in spurring resting muscle cells into action when damage occurs.
“If we could develop a drug that mimics this effect, we may be able to experience the benefit without having to do months of exercise,” Rando says.
The research was published in the journal Nature Metabolism.
Source: Stanford University
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