Stem Cells and Aging
The stem cells found within the average adult human are capable of restoring dying cells while also fixing damaged tissue. Nothing is safe from the aging process, though, and as we get older we begin to lose the very same stem cells that once kept our bodies in functional condition. But there could be a way around that: new stem cell research has revealed a nutrient sensing pathway called TOR can be subdued in order to prevent such loses. TOR plays a key role in the aging process and is largely responsible for the loss of stem cells in the human body.
The research examining the relationship between stem cells and TOR, published in the journal Cell Stem Cell, was carried out at the Buck Institute for Research on Aging in California, as well as at Stanford University. Samantha Haller, Ph.D. led the work at Buck Institute, which started with the intestines of fruit flies before advancing to the tracheas of mice; a move made due to the similar traits shared by both. At Stanford, meanwhile, researchers experimented on mouse muscles.
The mice at Buck Institute were put on varying schedules of rapamycin treatment. Rapamycin, also known as Sirolimus, is a drug used to prevent the rejection of kidney transplants. In this study, it was used to suppress the effects of TOR. According to Buck professor and senior author Heinrich Jasper, Ph.D., rapamycin was able to successfully maintain and restore stem cells regardless of the age of the mouse. One mouse in the study was around 15 months old, which roughly equates to a 50-year-old human.
"In every case we saw a decline in the number of stem cells, and rapamycin would bring it back," said Jasper.
A Steady Supply of Stem Cells?
When stem cell division occurs, a "daughter" cell is created that then proliferates into new cells that can repair the damaged tissue. The process is always asymmetrical, meaning one cell will become a repair cell while the other remains a stem cell. When rapamycin is introduced, the stem cells are recovered — though Jasper notes the current work done by Buck and Stanford is unable to confirm how, exactly, the cells are restored. It could be a simple replenishment of cells, or that the stem cells are creating two daughter cells instead of one during the division process. It could be another process altogether that the researchers have yet to uncover.
"It's all about maintaining a balance between stem cell renewal and differentiation," said Jasper. "It's easy to see how a loss of adult stem cells might accrue over a lifetime and accelerate with aging. We are excited to have a means of rescuing stem cells, boosting their ability to maintain healthy tissue."
Going forward, Jasper explains that researchers will be focusing on better understanding TOR and how it governs stem cells, specifically asking questions like "Is there a chronic increase in TOR over a lifetime, or is activation stronger in aging animals? What happens downstream of TOR?"
It was an exciting year for research involving stem cells and aging: back in July, scientists were able to slow the aging process in mice using stem cells. The Cedars-Sinai Heart Institute revealed in August that stem cells from younger hearts could reverse the aging process in humans. The applications for stem cells go far beyond aging: they could also be used to one day cure balding and Parkinson's Disease.
Some, like SENS Research Foundation co-founder Aubrey de Grey, believe we're on the verge of fully understanding aging, and it's becoming increasingly likely that stem cells will play a key role in that enlightenment.