Part 2: The causes of aging - Telomere shortening

Previously, we covered DNA degradation and its impact on aging. We will now address a second identified cause of aging, the shortening of telomeres, which we often consider to be the biological clock of our cells.

Telomeres – Definition

But what are telomeres? At the end of each of the four ends of the chromosome is a small DNA cap called a telomere, which protects the chromosome. Unfortunately, they are eaten away with each cell division, until they disappear and leave the DNA exposed. When this happens, the DNA is no longer able to replicate without making errors, and this causes the cell to die.

So what's going on? When a cell divides, it replicates its DNA in order to transfer the genetic information to the new cells created. In fact, with each cell division, a molecule called DNA polymerase duplicates our genetic code. But DNA polymerases “forget” to reproduce the end of the DNA structure, in this case, the telomeres.

Telomeres – Telomerase

This function is exclusively carried out by a special enzyme known as telomerase. But it would be great if all our cells expressed telomerase, they would be almost immortal! This enzyme is only present in certain cells. First of all in our stem cells, that is to say the cells capable of creating all our specialized cells, liver cells, muscle cells, fat cells, etc.

Telomerase is also present in our so-called 'germinal' cells, that is to say the cells allowing our reproduction, finally it is also present in some fortunate classic cells called 'somatic', such as the cells of hair follicles. For others, it is a programmed death that awaits them, defined by Hayflick's limit. This Dr. Hayflick discovered that there was a maximum number of divisions that a cell could carry out... and that above all this number depended on the length of its telomeres: in fact, in the absence of telomerase, cells are not capable to rebuild their telomeres and the cell will decide to die rather than replicate its DNA with missing information.

Unfortunately for us, another type of cell has telomerase: cancer cells. 90% of these cells express telomerase, which makes them almost immortal and capable of dividing infinitely. And these cancer cells clearly highlight the dilemma of telomerase and telomeres: their shortening causes our cells to die and our tissues to age, but protects us against the appearance of cancer.

Telomeres – State of research

So obviously, as you can imagine, some researchers have tried to evaluate the possibility of using telomerase to rejuvenate our tissues.

In old mice, a Harvard team activated the genes responsible for telomerase production. These experiments gave good results, with rejuvenation of the mice and good regeneration of damaged tissues.

Another study was carried out on skin cells. In culture, these cells can divide between 40 and 60 times during their life. By genetically modifying them to activate the production of telomerase, these same cells were able to divide up to 300 times.

These two experiments show the importance that telomeres have in the life expectancy of a cell, but the associated risks, such as the development of cancer, are very present and no study has been conducted in humans at this time. day.

This did not prevent Liz Parrish, CEO of Bioviva, from carrying out an experimental gene therapy on herself in 2016 aimed at activating her telomerase expression gene. For now, the results are encouraging, as she says she has rejuvenated her telomeres by 20 years. But for the moment it remains difficult to conclude on the reality of an increase in his life expectancy, which we wish him with all our hearts however.

Moreover, for those who are interested in the metrology of aging, telomeres can be used as a means of partially measuring your physiological age and some companies or clinics offer to measure the size of your telomeres on samples of your cells. .

In summary: telomere shrinkage can be seen as a biological clock of each cell. This mechanism limits the life expectancy of our cells, which is why it has a very important place in current research against aging.

SOURCES:

Dr. Guilhem Velvé Casquillas on http://www.longlonglife.org/