According to University of Minnesota Medical School researchers, estrogen is essential in females for muscle stem cell maintenance and function. It is well known that skeletal muscle mass, strength, and regenerative capacity decline with age, especially when estrogen levels decrease at menopause, but this new research also found that estrogen deficiency severely compromises the maintenance of muscle stem cells (i.e., satellite cells).
In a Cell Reports paper published earlier this month, the team described their study in mice whose ovaries were surgically removed as well as mice without the estrogen receptor in their muscle stem cells. They found that the loss of estrogen or genetic deletion of the estrogen receptor in muscle stem cells led to a 30 to 60 percent drop in muscle stem cell numbers across five different muscles. The surviving cells had severe difficulty reproducing and generating new muscle after injury.
The study also included a collaboration with scientists in Finland who performed muscle biopsies in women shortly before and after the transition to menopause. This showed that in humans, the number of satellite cells correlated strongly with changing serum estrogen levels. "This is the first work to show that estrogen deficiency affects the number as well as the function of satellite cells," said Dawn Lowe, one of the lead authors of the paper.
Estrogen replacement therapy has been shown to help maintain muscle health, but it also raises the risk of cancer due to estrogen's effects on tissues, such as those of the breast and endometrium. The team showed that a new class of drug, known to interact with estrogen receptors in a way that doesn't affect breast or endometrial tissue, was able to stimulate the estrogen signal in muscle stem cells and could potentially shield aging women from muscle stem cell decline due to menopause, without the risks associated with conventional hormone replacement therapy.