Longevity Briefs: An Injection Of Muscle Cells That Exercise For You?

Longevity briefs provides a short summary of novel research in biology, medicine, or biotechnology that caught the attention of our researchers in Oxford, due to its potential to improve our health, wellbeing, and longevity.

The problem:

Sarcopenia is the age-related loss of muscle mass and strength, leading to an increased risk of falls, fractures, and even death amongst the elderly. Physical exercise – especially resistance training – can help preserve muscle mass in old age but cannot completely prevent muscle loss. Once somebody has lost a lot of muscle strength, it becomes challenging for them to exercise, locking them out of the other health benefits of physical activity and preventing them from rebuilding their muscle tissue.

For the reasons above, scientists are looking for ways to mimic some of the benefits of exercise and improve muscle function in the elderly. While unlikely to completely replicate all the benefits of exercise any time soon, such a treatment could be extremely valuable for reducing frailty in old age. Most of these efforts involve trying to mimic the beneficial chemical signals produced during physical activity, but in this study researchers stumble upon a different approach – the introduction of exercising muscle tissue into the body.

The discovery:

Researchers’ original intention was to see if they could increase muscle mass in mice by injecting them with new myocytes (muscle cells) derived from those mice’s own muscle stem cells. After these cells were injected into the mice’s backs, they formed a patch of muscle tissue with its own blood supply. However, researchers noticed that this patch of muscle was regularly contracting spontaneously, even while the mice were asleep – researchers had essentially created a new, constantly exercising piece of muscle tissue. They decided to investigate whether this had any broader effects on the mice’s health.

Groups of 8 one-and-a-half year-old mice (roughly ‘equivalent’ to humans in their 50s) were given either the muscle cell injection or a control injection and were then followed up over 15 weeks. Researchers found that treated mice gained widespread benefits, including many that were not directly related to muscle mass. For example, they could run significantly further and had significantly better grip strength compared to control mice, but also had significantly improved bone density and immune system function. Mice even appeared to gain some cognitive benefits – in a Y-maze test, which measures mice’s tendency to explore new arms of a Y-shaped maze as a test of exploratory behaviour, treated mice performed better.

Researchers also investigated the effects of this treatment in groups of 5 mice that were fed a high-fat diet in order to induce obesity. They found that the treatment significantly slowed down weight gain compared to obese mice given a control injection, and also improved their physical performance (running distance and grip strength).

The implications:

This study suggests that introducing a continuously contracting patch of muscle cells could have widespread health benefits. This makes sense given that we already know that physical exercise has wide ranging benefits (including on cognitive function), many of which seem to come from beneficial signalling molecules released by muscle tissue. Rather than mimicking the benefits of exercise by introducing specific signalling molecules, this technique actually introduces muscle tissue that constantly exercises. It remains to be seen how practical this would be in humans – how large would the grafts need to be to produce meaningful benefits, and would it feel unpleasant to have a continuously contracting piece of muscle under your skin? One also has to consider the risk of cancer when introducing stem cell-derived products, though no tumours formed in any of the mice in this study.