The Role of Telomeres in Cellular Aging and Immortality

During the first half of the twentieth century, it was commonly believed that animal cells had the ability to grow indefinitely. Alexis Carrel, a French-born Nobel Prize-winning surgeon at Rockefeller Institute, conducted an experiment in 1912 where chick heart cells were cultured and remained viable for an astounding thirty-four years, suggesting that cells could be immortal. However, this belief was shattered in 1961 when Leonard Hayflick, an American cell biologist then at the Wistar Institute in Philadelphia, demonstrated that most human cells have a natural limit of reproducing forty to sixty times before they die, known as the Hayflick limit. It is believed that Carrel's cells remained viable due to the accidental addition of fresh cells. While some cells, such as human ova and sperm or cells of perennial plants, sponges, lobsters, hydra, and cancer, are capable of indefinite division, the reason for these differences remains unclear.

The chromosomes containing DNA are located in the nucleus of each of our cells. At the end of each chromosome is a telomere cap that protects the ends of the chromosomes from sticking together and prevents individual DNA strands from linking. However, telomeres also play a role in cellular aging. They act as cellular clocks that determine the rate at which cells age and die. Each time a normal cell undergoes mitosis, its telomeres shorten slightly, and when they become too short, the cell dies. Limiting the number of cell divisions may be beneficial in preventing cancer.

It has been estimated that lobsters can live up to 60 years, and they continue to grow without any decline in fertility or weakening. Unlike the mythical "Fountain of Youth," their longevity is due to their capability to produce telomerase throughout their adult lives.

In contrast, cancer cells grow telomeres after each division, which is attributed to the enzyme telomerase. While normal human cells also have telomerase, the gene responsible for its activity is suppressed. Several fascinating implications arise from this difference, including the potential use of anticancer drugs that prevent cancer cells from producing telomerase. Conversely, telomerase activation might be used as an anti-aging treatment or to treat conditions associated with premature aging. However, this benefit may come with an increased risk of tumor development.