Telomeres are important in the aging process, with their shortening increasing the likelihood a cell will induce apoptosis. A telomere is a highly repetitive region at the ends of linear chromosomes, preventing the erosion of genes. This helps to maintain the integrity of a chromosome, with the degradation of telomeric regions occurring after each cell replication event. This is beneficial under normal circumstances, where the Hayflick limit acts as a mitotic clock, inducing apoptosis after a certain number of divisions (usually between 20 to 30).
As there are more than 20 to 30 divisions required in the maintenance of a multi-cellular organism, stem cells contain telomerase. This enzyme enables the extension of telomeres, being activated when a certain length is reached. In some aging-related conditions, telomerase activity can be modified. This may result in premature stem cell death, which can induce aging-related diseases.
Overactive telomerase results in cellular proliferation, as they do not die at the expected rate. This leads to tumour development, and cells with overactive telomerase are frequently used as immortal cell lines (HeLa cells, …).