Old muscle stem cells can act young again but there’s a catch

 

Growing older often means recovering more slowly from muscle injuries, but scientists may have uncovered an important reason why.

A new study from UCLA, conducted in mice, found that aging muscle stem cells build up high levels of a protein that slows their ability to spring into action and repair damaged tissue. At the same time, that protein appears to help the cells endure the challenging conditions found in aging muscle.

The research, published in the journal Science, suggests that some biological changes linked to aging may not simply be signs of decline. Instead, they may serve as protective adaptations that help cells survive.

"This has led us to a new way of thinking about aging," said Dr. Thomas Rando, senior author of the study and director of the Eli and Edythe Broad Center of Regenerative Medicine and Stem Cell Research at UCLA.

"It's counterintuitive, but the stem cells that make it through aging may actually be the least functional ones. They survive not because they're the best at their job, but because they're the best at surviving. That gives us a completely different lens for understanding why tissues decline with age."

Protein Linked to Slower Muscle Repair

The researchers, led by postdoctoral scholars Jengmin Kang and Daniel Benjamin, compared muscle stem cells taken from young and old mice. They found that levels of a protein known as NDRG1 rose dramatically with age, reaching concentrations 3.5 times higher in older cells.

NDRG1 functions like a brake inside the cell. It suppresses a signaling pathway called mTOR, which normally helps drive cell activation and growth.

To determine whether NDRG1 was contributing to slower muscle recovery, the scientists studied mice that had aged naturally to roughly the equivalent of 75 human years. When they blocked NDRG1 activity, the older muscle stem cells quickly regained youthful behavior, becoming more active and improving muscle repair after injury.

The improvement, however, came with a drawback. Without the protective effects provided by NDRG1, fewer stem cells remained alive over time. As a result, the tissue became less capable of regenerating after repeated injuries.

Survival Versus Performance

"Think of it like a marathon runner versus a sprinter," said Rando, who is also a professor of neurology at the David Geffen School of Medicine at UCLA. "The stem cells in young animals are hyper-functioning -- really good at what they do, namely sprinting, but they're not good for the long term. They can make it through the 100-yard dash, but they can't make it even halfway through the marathon. By contrast, aged stem cells are like marathon runners -- slower to respond, but better equipped for the long haul. However, what makes them so proficient over long distances is exactly what renders them poor at sprinting."

The researchers confirmed their results using several different methods. They examined muscle stem cells from both young and old mice in laboratory cultures as well as in living tissue.

Across these experiments, the pattern remained consistent. Higher levels of NDRG1 reduced the cells' ability to rapidly activate and repair muscle, while also increasing their resilience and long-term survival.

A Cellular Survivorship Bias

According to the researchers, the rise in NDRG1 may be driven by what they describe as a "cellular survivorship bias" -- stem cells with insufficient NDRG1 gradually disappear over time, leaving behind a population that survives better but functions more slowly.

"Some age-related changes that look detrimental -- like slower tissue repair -- may actually be necessary compromises that prevent something worse: the complete depletion of the stem cell pool," Rando said.

The researchers compare this phenomenon to trade-offs seen throughout nature. During difficult conditions such as drought, famine, or extreme cold, animals often shift resources toward survival mechanisms like hibernation rather than reproduction. Muscle stem cells may be doing something similar as they age, directing resources away from their reproductive role (making more cells) and toward survival.

"Species survive because they reproduce, but in times of deprivation, animals turn on their own resilience programs," Rando said. "There are a lot of examples in nature of allocating resources to survival under times of stress. It's exactly aligned with what we're seeing at the cellular level."

Implications for Future Aging Therapies

The findings could help guide future efforts to develop therapies that improve tissue repair while preserving stem cell survival. However, Rando cautions that enhancing one aspect of stem cell function may come with unintended consequences.

"There's no free lunch. We can improve the function of aged cells for a period of time, for certain tissues, but every time we do this, there's going to be a potential cost and a potential downside."

The team plans to continue studying the molecular mechanisms that determine how stem cells balance survival and performance during aging.

"This gene is almost like our doorway that we've opened into understanding what controls these trade-offs that are so critical, not only for evolution of species but also for the aging of tissues within an individual," Rando said.

Funding for the study came from the National Institutes of Health, the NOMIS Foundation, the Milky Way Research Foundation, the Hevolution Foundation, and the National Research Foundation of Korea.

Journal Reference:

1. Jengmin Kang, Daniel I. Benjamin, Qiqi Guo, Chauncey Evangelista, Soochi Kim, Marina Arjona, Pieter Both, Mingyu Chung, Ananya K. Krishnan, Gurkamal Dhaliwal, Richard Lam, Thomas A. Rando. Cellular survivorship bias as a mechanistic driver of muscle stem cell aging. Science, 2026; 391 (6784): 517 DOI: 10.1126/science.ads9175

Courtesy:
University of California - Los Angeles Health Sciences. "Old muscle stem cells can act young again but there’s a catch." ScienceDaily. ScienceDaily, 3 July 2026. <www.sciencedaily.com/releases/2026/06/260622014315.htm>. 

 

 

 

 

Melanoma's secret to cheating death has finally been revealed

 

Scientists at the University of Pittsburgh School of Medicine have identified a crucial missing piece in the long standing mystery of how melanoma tumors avoid death and continue growing.

Writing this week in Science, Jonathan Alder, Ph.D., and colleagues describe a combination of genetic changes that allows melanoma cells to dramatically extend their lifespan while fueling rapid tumor growth. The discovery could reshape how researchers understand melanoma and may point to new treatment strategies.

"We did something that was, in essence, obvious based on previous basic research and connected back to something that is happening in patients," said Alder, assistant professor in the Division of Pulmonary, Allergy and Critical Care Medicine at Pitt's School of Medicine.

Telomeres Help Control a Cell's Lifespan

Telomeres are protective caps located at the ends of chromosomes that help keep DNA from breaking down. Every time a healthy cell divides, its telomeres become a little shorter. Eventually, they shrink to the point where the cell can no longer divide.

Keeping telomeres at the proper length is critical for health. Telomeres that become too short can cause disorders linked to premature aging and early death. On the other hand, unusually long telomeres are often associated with cancer.

Scientists have long known that melanoma tumors contain exceptionally long telomeres, especially compared with many other types of cancer.

"There's some special link between melanoma and telomere maintenance," said Alder. "For a melanocyte to transform into cancer, one of the biggest hurdles is to immortalize itself. Once it can do that, it's well on its way to cancer."

The Missing Genetic Link Behind Melanoma

The enzyme telomerase lengthens telomeres, helping protect chromosomes and preventing cells from dying. In most healthy cells, telomerase remains inactive. Many cancers, however, activate the enzyme through mutations in the telomerase gene known as TERT, allowing cancer cells to keep dividing.

Melanoma is particularly dependent on this strategy. Roughly 75% of melanoma tumors carry TERT mutations that increase telomerase production and activity.

Yet there was a mystery. Even after researchers introduced TERT mutations into melanocytes, they still could not recreate the unusually long telomeres found in melanoma tumors. That suggested another important factor was missing.

Pattra Chun-on, M.D., an internist pursuing her Ph.D. in Alder's lab, set out to uncover that missing link. Drawing on her background in cancer biology and growing interest in telomeres, she investigated why TERT mutations alone were not enough.

The fun part of this story is when Pattra joined my lab," Alder said. "She contacted me and told me that she was interested in studying cancer. I told her that I study short telomeres and not long telomeres. This went on until I realized that Pattra would never take 'no' for an answer."

TPP1 Completes the Puzzle

Earlier work from Alder's laboratory had identified frequent mutations in a telomere binding protein called TPP1 while analyzing cancer mutation databases.

Chun-on discovered that these TPP1 mutations closely resembled the TERT mutations. They occurred in the newly annotated promoter region of TPP1 and boosted production of the protein. That finding immediately caught Alder's attention because scientists had already shown that TPP1 enhances telomerase activity.

"Biochemists more than a decade before us showed that TPP1 increases the activity of telomerase in a test tube, but we never knew that this actually happened clinically," he said.

Chun-on, who is also enrolled in a Ph.D. program in the Department of Environmental and Occupational Health at Pitt's School of Public Health, then introduced the mutated forms of both TERT and TPP1 into cells. Working together, the two proteins produced the exceptionally long telomeres that characterize melanoma tumors.

The results revealed that TPP1 was the long sought missing factor, one that had been hidden in plain sight.

New Target for Future Melanoma Treatments

The findings offer a new explanation for how melanoma develops and survives. They also identify a cancer specific telomere maintenance system that could become a promising target for future therapies.

Additional authors of the study are Angela M. Hinchie, Agustin A. Gil Silva, Ph.D., Elizabeth Rush, Cindy Sander, Brittani K.N. Seynnaeve, M.D., M.S., John M. Kirkwood, M.D., all of Pitt, UPMC or both; Holly C. Beale, Ph.D., and Olena M. Vaske, Ph.D., both of the University of California, Santa Cruz; Carla J. Connelly, of Johns Hopkins University; and Carol W. Greider, Ph.D., of the University of California, Santa Cruz and Johns Hopkins University.

The research was supported by National Institutes of Health grants R35CA209974 and R01HL135062.

Journal Reference:

1. Pattra Chun-on, Angela M. Hinchie, Holly C. Beale, Agustin A Gil Silva, Elizabeth Rush, Cindy Sander, Carla J. Connelly, Brittani K.N. Seynnaeve, John M. Kirkwood, Olena M. Vaske, Carol W. Greider, Jonathan K. Alder. TPP1 promoter mutations cooperate with TERT promoter mutations to lengthen telomeres in melanoma. Science, 2022; 378 (6620): 664 DOI: 10.1126/science.abq0607

Courtesy:

University of Pittsburgh. "Melanoma's secret to cheating death has finally been revealed." ScienceDaily. ScienceDaily, 30 June 2026. <www.sciencedaily.com/releases/2026/06/260625014833.htm>.