Longevity Briefs: Rejuvenating Ageing Muscles With Sound?

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 – the progressive loss of skeletal muscle mass and function – is one of the most important causes of reduced quality of life and frailty in old age. Weaker muscles mean a greater risk of falls and fractures, resulting in long periods of immobility during recovery, more muscle loss and reduced life expectancy. Physical exercise throughout life helps to reduce sarcopenia in old age, but it is hard to rebuild muscle once sarcopenia has already occurred.

Muscle loss with age involves many mechanisms. One of the less studied mechanisms is the ‘gut-muscle axis’. Age-related changes in the composition of the gut microbiota (the population microorganisms that live in the gut) can contribute to chronic low-level inflammation, which in turn can negatively impact skeletal muscle function. Some bacteria also release compounds that are beneficial for muscle health, but populations of said bacteria decline with age. Previous studies show that transplanting the microbiota from a young mouse into an old mouse can improve muscle function. In this study, researchers test this idea using a less conventional, non-invasive approach: ultrasound.

The discovery:

Researchers conducted their study in 92-week-old mice, which are roughly ‘equivalent’ to humans in their early 70s in terms of age. 6 mice were left untreated, while another 6 were treated with Low Intensity Pulsed Ultrasound (LIPUS). LIPUS has previously been found to have a variety of beneficial effects, including suppression of inflammation and the promotion of skeletal muscle regeneration, through a variety of mechanisms that aren’t fully understood. Here, researchers were interested to see if applying LIPUS to the abdomen might have an effect on muscle function via the gut microbiome. In addition to the twelve 92-week-old mice, another six 4-week-old mice were also included as a young control group.

The mice in the treatment group received abdominal LIPUS stimulation daily for 8 weeks. By the end of the treatment period, researchers found that the aged untreated mice had clear sarcopenia-like characteristics, including impaired muscle performance, reduced muscle fibre size and decreased muscle mass. However, the LIPUS-treated mice had significantly improved forelimb strength, hind limb strength and increased muscle mass compared to those that were left untreated. When researchers investigated blood markers, they found a reduction in inflammatory signalling. In the gut, they found that the mice treated with LIPUS had larger populations of bacterial species such as Lactobacillus, Bifidobacterium and Faecalibaculum, which are associated with reduced inflammation and the production of short-chain fatty acids (which are thought to directly benefit muscle tissue).

The implications:

This study suggests that LIPUS may indirectly combat sarcopenia partly by altering the composition of the gut microbiota, at least in mice. LIPUS transmits a mechanical force to tissue, which can trigger a response from cells vie mechano-sensitive proteins (proteins such as channels in the cell membrane that respond to mechanical force). In this case, LIPUS may be triggering a response from the gut bacteria themselves, or it may also be having an effect on gut-resident immune cells.

This was a relatively small mouse study, and there have not yet been any clinical trials to investigate whether LIPUS affects either the gut microbiota or muscle function in humans. LIPUS devices are too expensive for the average person to own, but are still cheap by the standards of medical devices. Given that LIPUS is non-invasive and probably safe, it would be quite an appealing option if it were found to benefit human muscle function.