Fight Aging!

A few species of hydra are immortal in their normal environmental conditions, meaning that function does not decline over time and mortality risk does not increase over time. Researchers spent a good deal of time taking care of hundreds of hydra some years ago to demonstrate that this is the case. Hydra are lower animals, essentially a bundle of stem cells capable of regenerating and replacing any part of their bodies, somewhat analogous to an ambulatory embryo. It is an open question as to whether anything we can learn from their biochemistry can be useful in human medicine.

In today's open access paper, researchers report on the employment of telomerase by hydra. Telomeres are repeated sequences at the end of chromosomes that shorten with each cell replication, creating a clock that leads to cell death when telomeres are too short. In most species, somatic cells are limited in this way in order to minimize the risk of cancer, while stem cells employ telomerase to maintain long telomeres while delivering a supply of new daughter somatic cells to replace losses. The body is just a temporary vehicle for an immortal population of germline stem cells, in one view. Hydra are obvious very different in terms of the balance between stem cell behavior versus somatic cell behavior in individuals.

Telomerase expression and activity in the immortal cnidarian Hydra

Most living eumetazoan animals are mortal. A fundamental mechanism underlying cellular and organismal aging in many species is the progressive shortening of telomeres - protective nucleoprotein structures at chromosome ends. The finite replicative lifespan of somatic cells is linked to telomere attrition. The discovery of telomerase, a ribonucleoprotein complex with reverse transcriptase activity that synthesizes telomeric repeats, provided a molecular explanation for the unlimited proliferative potential of germlines, stem cells, and most cancer cells. In humans, telomerase is not expressed in most somatic tissues and is active primarily in germ cells, stem cells, and certain rapidly renewing tissues such as blood or intestinal epithelium.

Comparative studies indicate that telomere dynamics correlate with lifespan, with slower shortening rates in long-lived species. Recent cross-species analyses, however, reveal a more complex picture, suggesting that the relationship between telomere maintenance strategies (telomerase activity vs. alternative lengthening) and longevity is not strictly deterministic. Nevertheless, it remains a prevailing hypothesis that biologically immortal organisms must possess robust mechanisms for telomere maintenance. Supporting this, sustained telomerase activity in somatic tissues has been documented in non-senescent invertebrate models such as planarians and long-lived bivalves.

Importantly, several taxa, including some hydras, planarians, and rotifers, have been reported to exhibit negligible or undetectable senescence. In this study, we characterized the telomerase of Hydra vulgaris. The expression pattern of the telomerase catalytic subunit (hyTERT) mRNA correlates with regions exhibiting high proliferative potential and remains unchanged during budding or regeneration. These findings were further corroborated by measurements of telomerase activity. Our data suggest that telomerase may play a role in the immortality of Hydra.