There is a saying, "muscle over pension." It means muscle matters more than money for a happy old age. When aging accelerates abnormally and frailty sets in, muscle drops sharply, making one prone to illness and slow to recover. Scientists have found a way to accumulate the natural pension called muscle: a rejuvenation therapy that restores the function of muscle stem cells.
A research team led by James White at Duke University School of Medicine said in Nature Aging on the 15th that "when we rejuvenated the muscle stem cells of aged mice outside the body and reintroduced them into old mice, we confirmed that the muscle regenerated like that of young mice."
When muscle is damaged, stem cells in the muscle sheath regenerate cells. But as people age, muscle stem cells decline and their regenerative capacity drops. The Duke team induced reprogramming, that is, dedifferentiation, to turn back the biological clock of muscle stem cells and rejuvenate muscle.
◇ Boosting fatty acid production to increase muscle cells
The team found that aging of muscle stem cells stems from a decrease in glutamine catabolic enzymes. They extracted muscle stem cells from 24-month-old mice, roughly equivalent to humans in their 70s, and compared them with those from 6-month-old mice, roughly equivalent to those in their 30s. Aged muscle stem cells had 51% less glutamine catabolic enzymes.
Glutamine catabolic enzymes play a decisive role in muscle regeneration. For stem cells to grow into muscle cells, their size must increase severalfold. That requires many fatty acids to form cell membranes and serve as an energy source. Glutamine catabolic enzymes produce fatty acids such as palmitic acid and oleic acid.
The team succeeded in reversing the aging of muscle stem cells. Using a harmless virus, they added a gene that produces glutamine catabolic enzymes to muscle stem cells extracted from 24-month-old mice. When these stem cells were injected back into mice of the same age, the cross-sectional area of muscle fibers increased by 45%. Even without adding genes, supplementing aged mice's muscle stem cells with palmitic acid and oleic acid produced the same muscle-regenerating effect.
In other words, if the sharply reduced enzyme gene in aged muscle stem cells is delivered via a virus, the cells break down glutamine to make fatty acids like palmitic acid and oleic acid more effectively. Once muscle stem cells are rejuvenated this way, muscles grow, improving athletic performance, and injuries heal quickly. The muscle pension builds up.
That does not mean one can build muscle by eating fatty acids, the team emphasized. Fatty acids supplemented through food rarely reach muscle stem cells. The team warned instead that excessive intake of fatty acids could have the opposite effect by feeding cancer cells.
They added that stem cell rejuvenation is effective for people whose aging has accelerated abnormally and become frail, but those like athletes, who already have abundant muscle stem cells, cannot use this method to build more muscle. In other words, stem cell rejuvenation cannot serve as a doping tool for athletes to temporarily boost physical performance.
◇ Muscle rejuvenation effects in stem cell clinical trials
The anti-aging of stem cells has shown effects in animal experiments, but its efficacy and safety have not yet been tested in humans. Instead, therapy that injects muscle stem cells has already shown muscle-regenerating effects in human clinical trials.
Joshua Hare of the University of Miami Miller School of Medicine said in Cell Stem Cell in Feb. that when bone marrow stem cells that form muscle were injected into frail patients, their walking distance increased by 20%. Mesenchymal stem cells in bone marrow are adult stem cells that can grow into various tissue cells, including muscle, cartilage, bone, and fat.
Longeveron, a biotech corporations founded by Hare, extracted stem cells from the bone marrow of healthy adults ages 18–45. The cells were cultured outside the body, expanding their number to hundreds of millions, and then administered by intravenous injection to elderly patients diagnosed with frailty. After nine months, patients who received the stem cell injections walked 60 meters more in six minutes than the control group that received a placebo. Muscle strength improved as muscle cells regenerated.
Hare said, "When frailty was rated on a 1 (very healthy) to 9 (severely frail) scale, one-third of patients who received stem cell therapy recovered to 2–3," adding, "which means they are no longer frail." According to the British Geriatrics Society, patients with severe frailty are five times more likely to die within a year than others. The muscle pension gained through stem cells can save lives.
References
Nature Aging (2026), DOI: https://doi.org/10.1038/s43587-026-01120-3
Cell Stem Cell (2026), DOI: https://doi.org/10.1016/j.stem.2026.01.017