Stem Cells and Aging – What Happens When Our Stem Cells Get Old and Tired?
Aging is an inevitable, unnerving process that confronts us all. Eventually our muscles and immune systems will weaken, our hair will thin, and our minds won’t be as sharp as they once were. But what is the biology that underlies this process? And what if advances in the field of regenerative medicine could counteract this decline and alleviate the symptoms of old age?
Do Our Stem Cells Age as We Do?
Consider the body not as a single entity but as a dynamic multitude of cells growing, changing, dying, and being born. These cells make up and replenish the bodies’ tissues and organs, acting in concert and communicating in fascinating ways to keep the body in good working order. In many tissues, adult stem cells are at the root of this process, tasked with supplying cells to maintain normal tissue function and facilitating regeneration in response to injury. It is logical then to assume that, as our bodies grow older and our organs and faculties begin to degenerate, our stem cells must be failing us.
In fact, much research has gone into uncovering what happens to our stem cells as they age. For example, hematopoietic stem cells, which produce all the cells of the blood and immune system, actually increase in number in aging adults. Unfortunately, the expansion in cell numbers is to compensate for their overall loss in functionality. Ultimately, fewer white blood cells are produced, which contributes to a deficient immune system and diminished resistance to disease and infections in the elderly.
What About Stem Cells in Our Brains?
One fascinating avenue of research focuses on what happens to stem cells in the brain as we age. Until the 1960s it was believed that we are born with our lifetime’s supply of brain cells. This dogma was broken by the discovery of neural stem cells (NSCs), which reside in certain regions of the brain. Now we know that NSCs do have the ability to produce glia and some types of neurons in certain conditions. As NSCs age, however, their ability to regenerate lost or damaged brain cells decreases and they have a significant reduction in the number of neurons they can generate.
Fortunately, the advent of technology to identify and isolate these NSCs means we can study how they change as they age and, armed with this knowledge, begin to innovate ways to halt or reverse the aging process. Recently published research from a group at Stanford University provides fascinating new insights. Using a mouse model, the team investigated the differences in NSCs between young and old mice and found that as NSCs age they do a poor job of clearing away broken proteins that can interfere with the normal functions of the cells. Aged NSCs have an increased accumulation of protein aggregates, or clumps of broken proteins. This is striking as a number of age-related neurodegenerative diseases, such as Alzheimer’s and Parkinson’s disease, are linked to a build-up of proteins that can clog up brain cells and cause them to malfunction or die.
The researchers discovered that the inability of aged NSCs to clear broken proteins impairs their activation and production of new neurons. In the study they found that artificially stimulating the protein clearing system in aged NSCs gave them a new lease on life, restoring their ability to generate neurons, and increasing the number of active NSCs in elderly mouse brains. This type of fundamental research enhances our understanding of the biology of aging and provides the scientific underpinning for potential new treatments that could improve people’s health into old age.
Can We Treat Aging?
Although most research is far from the clinic, new drugs are being developed with the potential to treat degenerative age-related diseases, some by potentially promoting stem cell regeneration. It will take time and controlled clinical trials to determine the safety and efficacy of these treatments. In the meantime, some companies are harvesting and freezing young stem cells, with the hope that the cells will be useful in the future and will be able to delay or reverse aging. While this may sound appealing, at the moment, “[t]here is no way to extend anybody’s life with stem cells,” as former ISSCR President Sean Morrison said in a recent interview, and consumers should be wary until further studies have been done.
The study of stem cell aging is a field of research at the cutting edge of biomedical innovation. With incremental progress, research groups around the world are uncovering the biology of why and how stem cell function declines with age. The hope is that one day this fundamental research will be translated into treatments that enhance the health and quality of life for future generations.
Special thanks to Edie Crosse, PhD student at the MRC Centre for Regenerative Medicine, University of Edinburgh, for this guest blog post.