The scenario is likely. Today, centenarians are no longer an exception and, if the mechanisms of aging have not yet revealed all their secrets, research is advancing. As a result, life expectancy continues to increase. If it first grew, since the beginning of the 20th century, thanks to the gradual collapse of infant mortality, it is now at the other end of life, in old age, that the gains are made. The tracks followed by the researchers suggest that the lengthening of life is still far from having reached a ceiling.
A few months ago, the start-up Altos Labs, financed in particular by Jeff Bezos, the former CEO of Amazon, raised 3 billion dollars to work on the subject. Delirium of billionaires fed on science fiction or credible scientific ambition
contributes to polluting research by getting lost in scientifically unproven tracks , ”says geneticist Hugo Aguilaniu. In reality, the challenge is not to chase after eternal life, but to improve aging. Die later, okay, provided you enjoy the extra years while staying healthy.
Better known mechanisms
As strange as it may seem, we don’t know exactly how the human body ages. “There are many avenues of research on aging. It’s a very complex mechanism,” says Bertrand Friguet, professor at the Sorbonne University and director of the SU-CNRS joint research unit on biological adaptation and aging, and of Inserm unit 1164 at the Institute of biology of Paris Seine.
Let’s start from the observation: beyond wrinkles and brown spots on the skin, age is above all associated with a significant prevalence of diseases, such as cancer , cardiovascular or neurodegenerative pathologies. One of the explanations for this decline in physiological functions is cell senescence, in other words ” our limited ability to repair, regenerate and replace damaged cells“, specifies the biologist. One of the markers of this cellular alteration is the shortening of telomeres, stretches of DNA located at the ends of chromosomes. Throughout an organism’s life, healthy cells divide to replicate. This replicative faculty is exhausted over time. Two choices are then offered to the cells: enter into apoptosis, which amounts to dying, or into senescence. In the latter case, the cells retain metabolic activity, but in another form. ” We find these senescent cells in a number of aged organs and they most often show a shortening of telomeres which lose a little of their length with each replication “, reports Bertrand Friguet, who sees in this cellular senescence a kind of escape. “It prevents cells that have reached the end of their race from proliferating uncontrollably to turn into cancerous cells ,” he explains.
If the anarchic multiplication of malignant tumors is spared us, the senescence of the cells nevertheless leads to a low noise inflammation, combined with the secretion of pro-inflammatory cytokines. However, when they are too abundant, these molecules create lesions. In the end, the combination of the deficiency of cellular protection tools and the occurrence of morbid phenomena contributes to weakening the organs. Bertrand Friguet observes, however, that “ the repair capacities of cells vary not only from one organism to another, but also from one organ to another ”. In fact, if advancing age is accompanied by a form of both physical and psychological vulnerability, the organs do not deteriorate all at once. ” Some are getting old and some are less“, confirms Professor Nathalie Salles, head of the gerontology center at the Bordeaux University Hospital. Muscle is a good example.
With senescence, the muscle phenotype changes. The lean mass is gradually replaced by adipose tissue which, by a succession of mechanisms, will slow down the synthesis of the proteins which the muscle needs to maintain itself. Fast-twitch muscle fibers (type 2) gradually give way to slow-twitch fibers (type 1). As a result, muscle strength also decreases, leading to a loss of functional mobility, especially in sedentary people. Cartilage and bone mineral density also tend to thin quite early, due to the decline in cartilage cells and hormones, especially in women over 50, following menopause. Side arteries, elastin, a protein that gives elasticity to tissues, like the skin, is rare. Result,hence the risk of high blood pressure, past a certain age, to circulate the blood , ”adds Professor Salles, also president of the French Society of Geriatrics and Gerontology (SFGG).
Among the most valiant organs, the prize goes to the digestive tract. “ The stomach does not change, its acidity remains the same whether you are 20 or 90 years old. Only the muscles of the digestive tract slow down, including that of the colon ,” continues the specialist. The respiratory system is also maintained quite well, enough in any case to carry out daily activities without discomfort. Same observation for the brain: ” Even if cerebral performance is a little slower, aging does not affect the brain, and in particular its memory capacities “, notes the geriatrician. In addition, if aging results in a decrease in reserve capacities, both of cells and organs, it varies greatly from one person to another, at the same age.
If the hope of living forever or, at the very least, of significantly postponing the hour of death, has always fed the imagination of novelists, science has only recently taken hold of the subject seriously.