Telomere Attrition

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title: Telomere Attrition slug: telomere-attrition category: hallmarks summary: Progressive shortening of chromosomal end-caps with each cell division, triggering senescence or apoptosis. lastUpdated: 2026-05-17 tags: [telomeres, telomerase, replicative senescence] references:

• "Blackburn, E. H., Epel, E. S. & Lin, J. Human telomere biology. Science 350, 1193–1198 (2015)."
• "Aubert, G. & Lansdorp, P. M. Telomeres and aging. Physiol. Rev. 88, 557–579 (2008)."

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What it is

Telomeres are repetitive (TTAGGG)_n DNA–protein caps at chromosome ends. They protect coding DNA from being degraded or fused. Because DNA polymerase cannot fully replicate the lagging strand at chromosome termini, telomeres shorten by ~50–100 base pairs with each somatic cell division. After roughly 50–70 divisions (the Hayflick limit) telomeres become critically short and the cell triggers replicative senescence or apoptosis.

Why it matters in aging

Short telomeres correlate with shorter healthspan and higher all-cause mortality in epidemiological studies. Inherited telomere-biology disorders (dyskeratosis congenita) cause bone-marrow failure, pulmonary fibrosis, and liver cirrhosis — tissues highly dependent on stem-cell renewal.

Mechanisms

• End-replication problem depletes telomeres on dividing cells.
• Telomerase (TERT + TERC) can extend telomeres but is largely silenced in adult somatic cells; it is active in germ-line, stem, and many cancer cells.
• Shelterin complex (TRF1, TRF2, POT1, TIN2, TPP1, RAP1) suppresses spurious DNA-damage response at chromosome ends.
• Oxidative damage accelerates telomere loss independent of replication.

What’s being studied

Telomerase activators (e.g. TA-65) have weak human evidence. AAV-mediated telomerase gene therapy extended mouse lifespan in early proof-of-concept work; human trials are early. Telomere length itself is a noisy biomarker — population averages are useful, but a single individual’s measurement is hard to act on.

Related entries

See also: Cellular senescence, Stem cell exhaustion, Epigenetic clocks.