• The singular proteus challenges our understanding of longevity in animals, according to our partner The Conversation.
  • This urodele of about twenty centimeters, white, without eyes and with red external gills can indeed live for more than 100 years and reproduces only every 7 years on average.
  • This analysis was conducted by Yann Voituron, professor and researcher in physiology at the French National Research Institute for Agriculture, Food and the Environment (INRAE).

What is aging? Biologically speaking, aging means undergoing a continuous and progressive process of natural impairment of both survival and reproductive performance.

Scientists have long sought reliable measures of aging. If it can be measured thanks to different markers such as muscle strength, lung function, hormonal levels, telomere length remains a recognized standard.

We have just published a study that focuses on this variable in the proteus, a small amphibian that challenges our understanding of longevity in animals with respect to these telomeres.

Discovered in the 1930s, these particular DNA sequences are like caps at the ends of chromosomes. These pieces of DNA are made up of repeats of non-coding sequences (they are not the basis for protein production).

DNA is composed of 4 bases named Adenosine (A), Thymine (T), Cytosine (C) and Guanine (G). Telomere sequences are different depending on the groups of organisms (TTAGG in arthropods, TTAGGG in vertebrates and TTTAGGG in plants) and the number of repeats is also variable. In humans, for example, the TTAGGG sequence is repeated on about 1,000 base pairs.

In humans, telomeres shorten with age

It is now clear that telomere length decreases with age and shorter telomeres are associated with an increased risk of mortality. What for? Because with each cell division, 25 to 200 bases are lost at the ends of the telomeres of each chromosome but, thanks to telomeres, without affecting the coding sequences (serving as the basis for the formation of proteins).

Without telomeres, sequences of this coding DNA would be lost each time a cell divides (usually about 50 to 70 times) and this would eventually lead to mutations and/or the loss of entire genes.

When the telomere has become too short, the chromosome reaches a "critical length" and can no longer be replicated; Apoptosis (or programmed cell death) is then triggered.

Conversely, if telomerase (the enzyme that synthesizes telomeres) has strong activity, telomere length is maintained, and cell aging is delayed, for example in germline cells (eggs and sperm) and in cancer cells.

This relationship being general and repeatedly demonstrated in mammals and birds, telomeres have become a kind of universal molecular clock.

In the proteus, telomeres lengthen with age

However, in ectotherms (reptiles, amphibians, insects, molluscs, etc.) which are animals that grow continuously and generally retain important "telomerase" activities in all cells, even somatic (all cells of an organism apart from egg or spermatozoa) throughout life.

The decreases in telomeres with age in these animals become much less clear, or even non-existent as in some molluscs.

Such variability among ectothermic species has often been attributed to environmental temperature effects that determine metabolism, growth, and even mortality in these animals. Indeed, lower temperatures generally lead to lower growth rates in ectotherms but larger adult sizes and longer longevities.

However, there are some species of ectothermic animals living naturally at stable temperatures throughout their lives. Among these particular species is the proteus (Proteus anguinus) which is a cave amphibian.

In a cave with a constant temperature, this urodele of about twenty centimeters, white, without eyes and with red external gills can live for more than 100 years and reproduces only every 7 years on average.

These data come from the only breeding in the world started just after the Second World War in a cave in the Pyrenees (in Moulis, France) equipped with multiple basins supplied with running water at 12 ° C of a natural underground river faithfully reproducing the natural habitat of this animal.

So here is an organism that lives a long time and with which there is no effect of temperature! So we measured telomere length on proteas ranging from 4 to 41 years old and they... increase with age, in both females and males!

Is this the key to its longevity? In any case, it shows that some organisms have selected mechanisms that break the classic pattern of age-related telomere shortening.

Small in size but long-lasting

Interestingly, the proteus, such as the mole rat, some deep-sea fish and some Arctic mollusks, seem to belong to a small group of organisms that are small in size but with very long lifetimes.

The mole rat (Heterocephalus glaber) weighs 35 grams and lives more than 30 years; one of the champions of longevity being the mollusk called Icelandic meadow (Arctica islandica) which can live up to 400 years weighing only a few hundred grams.

The extreme longevity of these small organisms is partly explained by their generally very stable habitat and their ability to reduce the risk of predation, but telomeres that remain of the same length that would increase with age could also be one of their signatures.

But it would also have surprising consequences. Indeed, if long telomeres protect against cell senescence, overuse of telomere maintenance processes could increase the risk of cell immortalization and therefore cancer. This could explain why specific anticancer mechanisms have been shown in mole-rats.

OUR "AGING" DOSSIER

Is this the case with the proteus? This remains an open question, but studying the biology of long-lived animals that remain healthy and able to maintain high levels of reproduction until late in life will contribute to our better understanding of how aging processes have evolved in response to environmental factors.

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This article is produced by The Conversation and hosted by 20 Minutes.

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