Do Telomeres Adapt to Physiological Stress? Exploring the Effect of Exercise on Telomere Length and Telomere-Related Proteins

Figure 1

Common telomere/telomerase dogma across cell types in humans. Telomeres are located on the ends of linear chromosomes. Over time (i.e., with increased numbers of cell divisions), telomeres shorten due to a number of end-processing events; thus, short telomeres are associated with chronological age and a number of age-related diseases. (A) Telomeres function to mask the ends of chromosomes from being recognized by a cell’s DNA damage response system. When telomeres reach a certain length, they are no longer masked and the cell recognizes the ends of the chromosome as damaged DNA. When the DNA damage signal is initiated, the cell arrests and enters telomere-induced senescence. This occurs in adult human cells lacking the enzyme telomerase, which maintains and elongates telomeres by using reverse transcriptase activity to add telomere repeats to the ends of chromosomes. (B) During development and in certain adult stem cells, telomerase is expressed and slows telomere shortening in these cells, thus maintaining the pool of cells available in a presenescent state. (C) In 85% of tumor cells, telomerase is dysregulated and allows cancer cells to be immortal and divide indefinitely since they do not undergo telomere-driven senescence.