Exception to the rule
Scientists have discovered an organ that grows younger with the onset of old age
Observations of the life of elderly mice revealed an interesting fact – their skin heals cuts and other wounds faster and "better" than in young individuals. This conclusion was reached by biologists who published an article in the journal Cell Reports (Nishiguchi et al., Aging Suppresses Skin-Derived Circulating SDF1 to Promote Full-Thickness Tissue Regeneration).
Embryo cells and embryonic stem cells are virtually immortal from the point of view of biology – they can live almost indefinitely in an adequate habitat, and divide an unlimited number of times. In contrast, adult body cells gradually lose their ability to divide after 40-50 division cycles, entering the aging phase, which presumably reduces the chances of developing cancer.
Why do cells do this? As scientists believe today, in this way cells protect themselves and the body as a whole from the development of cancer, stopping division at a time when the probability of mutations in their genome reaches a certain critical point. The decrepitude of the body, in turn, is a side effect of this process associated with the accumulation of "aged" cells in organs.
Thomas Leung from the University of Pennsylvania in Philadelphia (USA) and his colleagues discovered a big exception to this rule by observing how the skin of young and elderly mice heals small cuts, and how their cells behave when such damage occurs.
"Plastic surgeons and dermatologists often notice that scars are less likely to occur on the skin of older people, but the causes and mechanisms of this unusual phenomenon remained a mystery to us. Understanding why this is happening will pave the way for the creation of skin regeneration technologies," says Leung.
To answer this question, scientists have acted in an unusual way. They "stitched" the circulatory systems of two mice – an elderly and a young rodent, and traced the work of which genes and signaling molecules present in their skin changed the most and how these changes affected the regeneration process when piercing holes in their ears.
Piercing the ear of "ordinary" young mice, not connected with elderly companions, led to the formation of scar tissue at the edges of the wound and the formation of a permanent "hole" in their shell. If they were "connected" to the circulatory system of elderly rodents, this did not happen – the hole was slowly but tightened and the damage disappeared without a trace.
Figure from an article in Cell Reports – VM.
The reason for this, as Leung and his colleagues discovered, was that the blood of young mice contained large amounts of the substance SDF1, special signaling molecules responsible, as biologists previously believed, for the regeneration of the liver, kidneys and some other organs.
This protein is practically absent in the body of elderly rodents, since its work is blocked by changes in the structure of the DNA envelope containing "instructions" for the synthesis of SDF1, and increased activity of the EZH2 gene, which controls the application of such labels on the protein wrapper of DNA. Its shutdown in the cells of elderly rodents dramatically worsened its regeneration, causing it to form scars and scars more often.
Having discovered this unusual phenomenon, scientists have tested whether human skin works in a similar way. As observations of wounds on the skin of young and elderly volunteers, aging similarly changed the behavior of their cells, which suggests that the skin really begins to work "better" with the onset of old age.
"Such behavior of the skin makes sense from the point of view of evolution. The faster the wound is healed, the easier it will be for a young animal to survive, even if the treatment process is not too high–quality," the geneticist concludes.
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