Hendrikje van Andel-Schipper died at the ripe old age of 115 in 2005, making her one of the longest lived humans on record. For a woman her age she was also in considerably good health until shortly before she passed away. She was also kind enough to donate her body to science and scientists have been eager to find out more about her, which may help to increase our understanding of ageing. In particular, researchers based at the VU University Medical Center in Amsterdam were keen to know more about the accumulation of mutations in somatic cells as we age.
In the study, which has been published in the journal Genome Research, the team used deep whole-genome sequencing and found 450 somatic mutations within her healthy white blood cells. Furthermore, these mutations were enriched in noncoding regions that are not evolutionarily conserved and appeared to be harmless passenger mutations, unlike those associated with disease.
Mistakes in DNA replication are often made during cell division, but the majority of the time they are removed as mutations can lead to disease. The fact that these mutations were not associated with disease suggests that her body was very efficient at removing harmful mutations, and demonstrates the sheer number of mutations that may be present and tolerated in normal, healthy tissue.
Further investigation led the scientists to discover that the majority of her white blood cells were derived from just two stem cells. This suggested that her pool of stem cells was severely depleted since it is estimated that at birth we have approximately 20,000 blood stem cells.
They also found that the telomeres (protective caps at the ends of chromosomes) on her white blood cells were extremely short; around 17 times shorter than those found on her brain cells, which are more static in comparison to the regularly dividing blood cells. Telomere shortening is a natural, gradual process that occurs as cells divide. However, after a certain point is reached the cells will die; as this occurs in our stem cells we experience something called stem-cell exhaustion.
Taken together these results suggest that, perhaps not surprisingly, one limiting factor in our lifespan is our pool of stem cells; as they slowly diminish, we lose the ability to regenerate tissues.
These results also hint that one day, it may be possible to slow down the process of ageing by replenishing the body with stem cells taken from individuals when they were much younger. “If I took a sample now and gave it back to myself when I’m older, I would have long telomeres again- although it might only be possible with blood, not other tissues,” lead author of the study Henne Holstege told New Scientist.