A recent study investigated the effect of a single treatment of prostaglandin E2 on improving muscle strength and rejuvenating muscle stem cells in mice. The researchers explored the molecular and epigenetic aspects underlying this rejuvenation [1].
Aging muscle stem cells
Sarcopenia, a loss of skeletal muscle mass and strength, is an age-related disorder that leads to increased risks of other conditions such as osteoporosis, heart failure, and cognitive decline.
Its sources include significant decreases in both the number and function of muscle stem cells, which are typically needed to regenerate skeletal muscles. Aging also causes changes in the microenvironment of muscle stem cells, leading to disrupted signaling that results in reduced self-renewal and increased senescence. Identifying ways to reverse these processes would be a promising avenue for both ameliorating sarcopenia and accelerating recovery after injury.
In a previous study, this study’s researchers reported that a lipid-derived metabolite, prostaglandin E2 (PGE2), which is located in membranes, responds to muscle injury [2], and a transient increase in PGE2 signaling is necessary for muscle stem cells to regenerate muscles.
Muscle repair is also delayed in mice that do not have either a functioning PGE2 receptor called EP4 or sufficient levels of PGE2, and PGE2 levels decrease in skeletal muscles with age. Increased levels of 15-hydroxylprostaglandin dehydrogenase (15-PGDH) cause this age-related in PGE2 levels.
Overcoming muscle loss with PGE2 and exercise
For their first experiment, the researchers used genetically engineered young and aged mice that lacked EP4 receptors in muscle stem cells. Those mice exhibited approximately 20% reduced muscle strength and muscle mass compared to control animals.
Aged, genetically engineered mice were treated for five days with a non-hydrolyzable PGE2 analog. This form of PGE2 is resistant to degradation by 15-PGDH, whose activity is increased in aged muscle. The same mice were subjected to daily downhill running. Two weeks from the start of the experiment, the researchers observed an increase in the mice’s muscle strength, suggesting that even such short treatment with PGE2, when combined with exercise, can partially overcome sarcopenia.
Lasting consequences
Next, they simulated muscle injury by injecting a toxin called notexin (NTX), which causes damage to muscles, into old mice. Two days later, these mice received a single, high dose of non-hydrolyzable PGE2 to simulate the PGE2 surge that happens after injury in young mice. Assessing the mice two weeks after the toxin and PGE2 treatment, the researchers noted a significant increase in muscle stem cells expressing Pax7, a transcription factor essential for muscle development and regeneration. A single PGE2 treatment helped to regenerate muscle, increase muscle mass, and enhance strength in aged mice.
This and subsequent experiments, in which aged PGE-2-treated cells are engrafted into young animals and then treated with toxin, suggest that PGE-2 has a positive long-term effect on the regenerative capacity of muscle stem cells that persist in the progeny of the treated cells.
Those observations were confirmed by cell culture experiments using isolated aged muscle stem cells treated with PGE2. Those cells showed a significant increase in cell proliferation compared to untreated aged muscle stem cells. The researchers observed that cell numbers increased by approximately 60%, which they believe “overcomes the deficit in proliferative capacity” of aged muscle stem cells. Apart from increased proliferation, PGE2-treated aged stem cells also showed a threefold reduction in cell death.
“What amazes me most is that a single dose of treatment is sufficient to restore muscle stem cell function, and that the benefit lasts far beyond the duration of the drug,” said Yu Xin (Will) Wang, Ph.D., an assistant professor at the Center for Cardiovascular and Muscle Diseases, Center for Data Sciences, and Cancer Metabolism and Microenvironment Program at Sanford Burnham Prebys. “In addition to making new muscle, the stem cells stay in the tissue, where they sustain the effect of the PGE2 and instill the muscle with further capacity to regenerate.”
Sleeping through regeneration
After observing the positive impact of PGE2 treatment, the researchers investigated age-related changes in PGE2-EP4 signaling. They isolated the myofibers (individual muscle cells) with their associated muscle stem cells from young (2-4 months) and aged (over 18 months) mice.
They observed a substantial reduction in the expression of the PGE2 receptor EP4 in the Pax7-positive muscle stem cells isolated from aged mice compared to those isolated from young mice (70% of aged cells expressed EP4 compared to nearly 100% of young cells). Even among the aged muscle stem cells that expressed this EP4 receptor, the levels of expression were lower by roughly 50% compared to cells from young animals.
“PGE2 levels in muscle also decline with age, so we see blunted signaling from reductions in both the messenger and receiver,” said Wang. “PGE2 is an alarm clock to wake up the stem cells and repair the damage. Aging essentially reduces the volume of the alarm and the stem cells have also put on ear plugs.”
Further analysis of single-cell levels in young and aged muscle stem cells and myogenic progenitors showed that diminished PGE2 signaling changes gene expression during regeneration in aged muscle stem cells. The results also suggested that PGE2 signaling starts in stem cells and is propagated to their cellular progeny.
The researchers identified that the transcription factor family known as AP1, which includes transcription factors such as JUN and FOS, was persistently activated in aged muscle stem cells. AP1 is involved in various processes including cell growth, differentiation, and apoptosis. Persistent activation of AP1 family members was also observed in human muscle biopsies, suggesting conservation across species.
PGE2 treatment of aged muscle stem cells suppressed age-dependent AP1 activation. It significantly impacted gene expression levels, leading to more rejuvenated gene expression patterns.
“The genes that are upregulated during the aging process are downregulated after treatment, and vice versa,” Wang said.
Molecular memory
The regenerative effects of PGE2 treatment are observed even weeks afterwards. The researchers hypothesized that some kind of “molecular memory” must be driving those changes. Most likely, this kind of memory is caused by epigenetic changes in the chromatin landscape that are propagated to the muscle stem cells’ progeny.
To test this hypothesis, the researchers analyzed chromatin accessibility and correlated it with a gene expression analysis. They found differences between chromatin regions that were more accessible (open) or less accessible (closed) in aged compared to young muscle stem cells. The distribution of those differences suggested that, with aging, the activity of genes involved in muscle stem cell expansion during injury is decreased. In contrast, the activity of other regions, including AP1, is increased.
PGE2 treatment rejuvenated the aged muscle stem cells, altering the accessibility pattern of chromatin.
Beyond muscle
Overall, the researchers demonstrated that a single injection of PGE2 into aged muscles has a long-term rejuvenating effect, and when combined with exercise, it increases muscle strength and mass. Such results are promising for patients suffering from sarcopenia, but whether those results translate to humans is still unexplored.
However, the authors believe in PGE2’s therapeutic potential, and they think it can extend beyond rejuvenating muscle cells.
“We’ve previously shown that PGE2 can also benefit the muscle fiber and neurons that innervate the muscle. PGE2 has been implicated in the regenerative process and signaling for the intestine, liver, and several other tissues, potentially opening up an approach that could restore the renewing capacity of other aged tissues,” elaborated Wang. “The ultimate goal is to improve people’s quality of life by reversing the effects of aging.”
Literature
[1] Wang, Y. X., Palla, A. R., Ho, A. T. V., Robinson, D. C. L., Ravichandran, M., Markov, G. J., Mai, T., Still, C., 2nd, Balsubramani, A., Nair, S., Holbrook, C. A., Yang, A. V., Kraft, P. E., Su, S., Burns, D. M., Yucel, N. D., Qi, L. S., Kundaje, A., & Blau, H. M. (2025). Multiomic profiling reveals that prostaglandin E2 reverses aged muscle stem cell dysfunction, leading to increased regeneration and strength. Cell stem cell, S1934-5909(25)00192-4. Advance online publication.
[2] Ho, A. T. V., Palla, A. R., Blake, M. R., Yucel, N. D., Wang, Y. X., Magnusson, K. E. G., Holbrook, C. A., Kraft, P. E., Delp, S. L., & Blau, H. M. (2017). Prostaglandin E2 is essential for efficacious skeletal muscle stem-cell function, augmenting regeneration and strength. Proceedings of the National Academy of Sciences of the United States of America, 114(26), 6675–6684.
