New Delhi: For now, the average human lifespan is 79 years, but if scientists could get rid of every cause of aging, would humans be immortal? A recent study found that even then, humans would only live up to 150 years because of one unavoidable reason — the slow damage to DNA, also known as somatic mutations.
The study, titled ‘Somatic mutations impose an entropic upper bound on human lifespan’ was published in NPJ Aging in June by researchers at the Skolkovo Institute of Science and Technology, and the Artificial Intelligence Research Institute, both in Moscow. However, their estimate of 150 years is purely theoretical and does not mean that humans are likely to soon live up to 150 years.
“We can now not just say that mutations are harmful, but quantify exactly how much they shorten life and compare their contribution with other aging processes,” the study’s principal investigator Ekaterina Khrameeva, an associate professor at the Skoltech Biomed Technologies Center, said in a press release. “This work is important for understanding which aging mechanisms deserve the most attention and resources.”
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What are somatic mutations?
Aging has several causes. Sometimes the proteins within the body get damaged. Sometimes the telomeres, the DNA sequences at the ends of chromosomes, become shorter. Every time a cell copies itself to divide, it cannot quite reach the very end of the DNA strand, leaving a tiny piece behind. Often the mitochondria, or the powerhouse of cells, stops working as efficiently. In addition there is DNA damage, or somatic mutations.
These mutations are like typos in the instruction manual within the cells. Every time cells divide or repair themselves they pick up these typos and while most of them are harmless, over decades they can either kill off cells or make them malfunction.
When researchers built a mathematical model to estimate the maximum human lifespan they found that DNA damage alone would be enough to limit the lifespan even if every other cause of aging could be eliminated. The two main organs behind this would be the brain and the heart which cannot replace lost cells. In contrast, the liver can keep renewing itself using stem cells.
“The key finding of the study is the discovery of substantial differences between tissue types. Neurons and cardiomyocytes (cells of the brain and the heart) which lack the ability to divide, turned out to be the main limiting factor: when all other causes of aging are eliminated, somatic mutations alone reduce the theoretical median lifespan from 1,759 years (for a hypothetical non‑aging human organism) to 156 years. At the same time, tissues with high regenerative capacity — such as the liver — can maintain their function for thousands of years through continuous cell renewal,” said Evgeny Efimov, one of the key authors of the study, a research intern at the Skoltech Biomed Technologies Center and a researcher at AIRI.