The experimental “myografts”, described in Nature Aging on August 26, were made from each animal’s own muscle cells and implanted beneath the skin. The grafts formed mature, vascularised muscle tissue that contracted autonomously for months, while animals carrying them showed gains in lean mass, muscle performance, bone density and metabolic health.
Researchers led by Ng Shyh-Chang at the Chinese Academy of Sciences’ Institute of Zoology tested the approach in adult, aged and diet-induced obese mice. Their results suggest contracting muscle tissue can influence organs well beyond the implant site, mimicking some of the systemic signals normally produced by physical activity.
The work remains preclinical. No comparable exercise-replacement effect has been established in people, and the researchers said the safety and pharmacological profile of autologous myografts must still be determined in human trials. The findings therefore do not show that an implant can substitute for normal exercise in healthy people.
To create the grafts, the team took muscle stem cells from the quadriceps of mice, expanded and differentiated them in the laboratory, then injected the resulting cells beneath the skin of the animals’ backs. Using cells from the same animal reduced the risk of immune rejection.
The transplanted cells organised into muscle-like structures, developed their own blood supply and contracted without conscious movement. Adult mice carrying the grafts developed thicker muscle fibres than untreated controls and showed molecular changes associated with lower inflammation and reduced fat accumulation in muscle.
Effects were also detected in older animals. Mice about 18 months old had a higher proportion of lean body mass eight weeks after transplantation. By 15 weeks, graft-bearing animals also had greater bone density, while physical tests showed improvements in grip strength and running endurance compared with control mice.
The researchers reported broader metabolic effects in mice made obese through a high-fat diet. After 16 weeks, animals with myografts had more lean mass and less fat than untreated counterparts, along with lower blood glucose and smaller increases in cholesterol.
Other measurements indicated reduced systemic inflammation, lower triglycerides, less liver damage and higher energy expenditure. The team also recorded signs of improved cognitive performance in aged mice: animals with grafts spent more time exploring unfamiliar areas during a maze test.
Skeletal muscle is increasingly understood as an endocrine as well as a mechanical organ. Contracting muscle releases signalling molecules that affect metabolism, inflammation and communication with tissues including fat, liver and brain. The researchers’ results indicate that a relatively small implanted muscle mass may be able to trigger some of those body-wide pathways.
Ng said the concept was aimed particularly at people for whom conventional exercise may be difficult or medically unsuitable, including those who are bedridden or weakened by age-related disease. He described the strategy as an attempt to capture beneficial biological effects of muscle activity while avoiding stresses that exercise can place on joints or the cardiovascular system.
Independent physiologist James P. White of Duke University called the premise intriguing but cautioned that translating it to people could be difficult. He noted that humans might need several grafts to reproduce the effects observed in mice, potentially requiring multiple invasive procedures in frail or elderly patients.
The study also explored myografts as delivery platforms for therapeutic proteins. Genetically modified grafts produced compounds including parathyroid hormone and growth hormone, suggesting implanted muscle could eventually function as a living source of medicines targeting bone or muscle loss.
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