Scientists have grown contracting muscle tissue

Skeletal muscles are not only the driving force of movement but also a kind of endocrine organ, as during exercise they release hundreds of signaling molecules that reduce inflammation and protect other organs from aging. The problem is that people who need these effects the most (due to serious illnesses, injuries, or disabilities) often cannot exercise. The new approach is designed to compensate for this gap.

The researchers took a small sample of muscle tissue from a mouse’s thigh, grew the cells in a laboratory, and turned them into mature muscle cells — myocytes. To ensure the transplant survived (previously, more than 90 % of transplanted cells died within the first 48 hours due to a lack of oxygen and nutrients), the experts did not simply inject the cells; instead, they created a small pocket under the skin on the mouse’s back using a blunt needle and filled it with a mixture of 6 million cells and Matrigel matrix — a special gel‑like scaffold for engraftment. Under these conditions, the cells did not clump together, received nutrition, and developed successfully.

As a result, organized areas of muscle tissue with their own vascular network formed. They not only survived for at least 81 days but also contracted spontaneously, without external influence, continuously, as if they were training on their own.

The effectiveness was tested on four groups of mice: young healthy ones, elderly ones, those with obesity, and those with hormone deficiencies. In elderly and obese animals, the implants slowed the loss of muscle mass, increased the thickness of the natural leg muscles, enhanced grip strength and endurance during running, and also improved bone density. Furthermore, fat burning increased in the test subjects, and the levels of sugar and total cholesterol in the blood decreased.

Cognitive tests proved particularly revealing: mice with implants had fewer degenerating cells in the hippocampus, and they performed noticeably better in tests of spatial learning and memory. This suggests that muscle hormones may protect the brain from age‑related changes.

Another promising direction is the use of implants as a flexible hormone delivery system. When the cells were modified so that they produced a specific hormone, the calcium and phosphate levels in the mice returned to normal. And implants producing growth hormone caused accelerated weight gain and an increase in body length, which suggests that this demonstrates the potential for targeted hormonal intervention.

At the same time, the mini‑muscles remained strictly in the injection site, did not spread throughout the body, and showed no signs of tumor growth.

The authors of the study believe that this approach opens up real prospects for cell and gene therapy for age‑related diseases, especially for those patients for whom conventional physical activity is inaccessible. Of course, the path to human application is still long, as it is necessary to verify the safety, scalability, and effectiveness of the method, as well as to address issues related to immune response and long‑term stability.