Bar Harbor, Maine —
As people age, muscles naturally lose mass and strength, a condition known as sarcopenia. The decline can make everyday activities harder and increases the risk of falls, disability and early death.
At the moment, the best defense is regular exercise throughout our lives, as effective treatments to slow or prevent muscle atrophy are limited. Progress has been slowed in part because in most vertebrates, aging unfolds over many years, making it difficult for biomedical researchers to study quickly in the laboratory.
Now, MDI Biological Laboratory Associate Professor Romain Madelaine, Ph.D., and his research team in the Kathryn W. Davis Center for Regenerative Biology and Aging have established a new comparative model that dramatically speeds up the process of muscle loss in the zebrafish. Small, transparent and easily managed for research, the zebrafish relies on many of the same genes and molecular pathways that drive human muscle growth, degeneration and repair.
By accelerating the muscle-aging process in an animal whose musculoskeletal systems mimic humans' in many respects, the international team has created a powerful new platform for research on sarcopenia and the search for therapeutic interventions.
The researchers can switch on the expression of a single gene in the fish, Atrogin-1, that in humans and other mammals is known to play a significant role in muscle atrophy. They dubbed the animal the "atrofish".
When Atrogin-1 is activated in skeletal muscle, the fish rapidly develops key features seen in aging humans: thinning muscle fibers, loss of strength, and reduced movement. Processes that normally take years in humans—and years even in naturally aging fish—can now be studied in days to weeks.
"Studies of aging mechanisms have been historically slow because of the unavoidable amount of time required for natural biological aging in animal models," Madelaine says. "Our work shows that we can rapidly model key molecular and cellular processes associated with muscle aging in zebrafish, paving the way for faster discovery and testing of drugs to slow or potentially prevent sarcopenia."
What Fails Inside Aging Muscle
Using live imaging to follow individual muscle cells, the researchers identified one of the earliest failures in aging muscle: the loss of myosin light chains (proteins that are essential for muscle contraction). These proteins disappeared before fibers fully degenerated, pointing to an early structural vulnerability that could be targeted to preserve muscle function. At the same time, aging muscle tissue in atrofish shows other molecular signs linked to human aging: protein breakdown, increased stress signaling and changes in the mesh of tissue that holds muscle cells in position.
A Surprising Link to Nerve Degeneration
One of the most unexpected findings was that muscle loss did not stay strictly confined to muscle cells. As muscle fibers degenerated, the number of connections between the muscles and nerve cells that communicate with the brain — called neuromuscular junctions — were reduced. Even more striking, some related nerve cells within the spinal cord began to disappear.
This ran counter to traditional thinking, which has treated declining muscles only as passive victims of failing nerves, rather than active players that can influence whether nerve cells stay healthy, degrade, or disappear. The findings suggest degenerating muscle may at times actively drive nerve loss, creating a damaging feedback loop of aging.
A Fast New Model for Aging Studies and Drug Development
By recapitulating fundamental drivers of sarcopenia in such a short time frame, the atrofish provides a fast, cost-effective way to study muscle aging in a living vertebrate. It allows researchers to:
- identify early molecular events that trigger muscle weakness;
- explore how muscle health affects the nervous system; and
- rapidly test drugs or interventions aimed at preserving muscle and nerve function.
And by compressing decades of biological aging into a much tighter window, the atrofish opens new possibilities for discovering treatments that could help people stay stronger and more mobile as they grow older.
Madelaine noted that he and the article's first author, doctoral candidate Romain Menard, were joined by 16 colleagues at MDI Bio Lab and the University of Toulouse who contributed their time and expertise to the research.
"This work has been possible thanks to amazing collaborators both internally at MDI Bio Lab and internationally," Madelaine said. "Today more than ever, this is a beautiful reminder that the advancement of science cannot be realized in isolation, but emerges from the collective effort, curiosity and engagement of a global scientific community."
