Stem Cells and Aging
Dennis M. Lox M.D.
Stem cells are naturally suppose to rejuvenate our bodies tissue, whether that is skin, brain or heart muscle. Stem cells are also necessary to keep healthy tissue functioning properly. This is through the process of differentiation to create new cells, or the action of cell signaling to orchestrate proper cell functioning. Stem cells and the aging environment in which they live, or the area in which they are implanted into to create a regenerative effect, has long been the source of troubling discord for researchers. As we age many processes are effected, including stem cells.
The number of stem cells are reduced in humans as we age. The effective repair processes of the body are also reduced. This involves many systems besides just stem cells. It is sufficient to say that every body part is aging, including the stem cell and the surrounding microenviorment known as the stem cell niche. This is why we age and our joints develop arthritis and are skin looses its youthful vitality. Some individuals are blessed with the genetics to remain youthful far longer than others, while others age at a more rapid rate. Environmental and disease factors can sharply accelerate this effect.
As the microenviroment of the stem cell is altered, so to is the stem cell itself. Proper stem cell functioning requires cell surface receptors that respond to cell signaling from the environment. Aging creates alterations in the cell surface which impairs proper functioning and homing to direct repair. Improper repair responses results in environmental breakdown and the resulting effect is apparent in what we take for granted as signs of aging. If the overall total stem cell population is decreased as we age, and the effectiveness of the stem cell is reduced, we have an inability to correct tissue repair processes. These processes are widespread throughout the body. The joints develop degenerative arthritis, the skin sags as collagen is lost, cardiac functioning is impaired as muscle tissue is ineffective, and list goes on in every body part or organ.
Every body tissue has cells that keep tissue healthy. Stem cells can make more new cells. In Spanish stem cells are referred to as cellulas madre, or mother cell. When cells of the body are dying they send warning signals to the stem cell to turn on a genetic switch that prevents the cells from dying. This is an inherent warning signal for cellular death or attack. DNA damage may be be repaired by stem cells in such a fashion. In aging, this process is impaired. Excessive DNA damage from external toxins may be beyond the capacity for the stem cell to exert a reparative effect. Conversely, these same mechanisms may allow cancer cells to thrive, and targeting stem cell receptors to not aid the cancerous cells may be another aging factor for stem cell science.
Research has lead to aging of cells and telomere shortening as cells continue to self divide through the aging process. Direct cell injury through oxidative stress from free radicals, toxins, environmental harm. Radiation and chemotherapy are direct examples of harm placed on all cells, cancerous and stem cells. No cell is spared from these harmful effects. The practice of a healthy lifestyle applies to the entire body, including the stem cell. Recent research has focused on making stem cells younger again. A normal tissue signaling molecule known as TGF-B is similar in some ways to building new tissue as the active from of tissue growth hormone (IGF-1). TGF-B is elevated in older tissues. Scientists at the University of California, Berkeley, found that a drug which blocks the action of TGF-1B reversed the effects of aging, and made the stem cells function like their younger versions, whether it was brain or heart tissue. This was well demonstrated in mice, and is currently in clinical trials. Stem cells are master conductors of the complex array of cell signaling. As with rheumatoid arthritis blocking one aspect of this complex molecular cascade of cell signaling may not always be effective. The aging process will undoubtedly be as complex, as each human is an individual with many different sets of circumstances beyond just their chronological age that is responsible for the aging process. Further methods to aid in keeping stem cells youthful as we age will undoubtedly be a key strategy.