Cell division plays an important role in the normal growth, maintenance and repair of human tissue. However, cell division is a limited process in that cells generally divide only 60 to 100 times in the course of their normal lifespans. Once cells reach the end of their replicative capacity, they senesce. Cellular aging or senescence, although influenced by environmental factors, is a genetically determined process. Geron and its collaborators have demonstrated that telomeres, the repeated sequence of DNA at the ends of each chromosome, are key genetic elements in this process.
Telomeres are necessary to protect chromosomes from degradation and fusion .
Each time a normal cell divides, however, telomeres shorten because cells are unable to replicate fully these repeated DNA sequences. Geron has demonstrated that once telomeres reach a certain short length, cell division is halted, which is known as cell senescence. Although senescent cells have stopped dividing, these cells are still metabolically active and demonstrate an altered pattern of gene expression. Specifically, in senescent cells, some genes expressed by young and healthy cells are turned off and other genes are turned on, creating an imbalance of proteins and other cell products that has a direct and potentially destructive effect on the surrounding tissue. Geron believes that this cellular dysfunction, which occurs in numerous tissues throughout the body, causes or contributes to age-related diseases and conditions.