The limits of human life


The Danish Hendrikje van Andel-Schipper, who died very lucid in 2005, at 115, left her body to science. Dutch, US and Australian researchers have analyzed its cells and found out why human life cannot go beyond a certain limit.

The working group found, publishing it in the journal Genome Research, that the blood cells of Mrs. van Andel-Schipper have some important characteristics: they are almost all derived from only two stem cells (the last two still active at the time of her death), their genetic material is rich in mutations and the individual chromosomes have very short telomeres (telomeres are the terminal parts of a chromosome, which protect it from possible fraying and deterioration).

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To fully understand the scope of this discovery, we need to understand the biology of human cells in depth. All the cells of an organism derive from a relatively low number of original cells that continuously divide to give rise to blood, brain, liver or other cells.
Scientists estimate that each of us - at the time of birth - has about 20, 000 blood stem cells, of which about 1, 300 are considered "active". From these - by division - all the others develop. The speed of division is different in different areas of the body. For example, in the blood - where there is a greater need for cell turnover - the division is more frequent, while the brain cells live much longer and there is no need to replace them too often. The process of division, however, gives some problems: to each of them a part of the telomeres wear out, and the cells that have suffered more divisions also have shorter telomeres. Those of the Danish lady's blood were 17 times shorter; consequently the chromosomes are always in danger of fraying.
Only two cellulines
In addition to each division the cells can undergo mutations, which change the DNA sequence; and the lady's blood cells were very rich in mutations, which were fortunately not lethal.
Unlike those of the blood, instead, those of the brain (which divide much less) have the telomeres still quite intact and few mutations. Mutations and wear of telomeres finally kill most of the 20, 000 cells with which we are born and from which all blood cells are derived: this is why almost all of Mrs. van Andel-Schipper's derive from only two stem cells. The only two that have passed the harsh age selection.
Young blood
After these reports that seem to silence man's dreams of immortality, the research group thinks that it is possible, however, to remedy some problems caused by aging, at least for blood cells. Setting aside a bit of tissue when one is young, to extract stem cells with few mutations and telomeres intact, could at least rejuvenate the blood.
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