A major approach to the biology of aging is the study of defective proteins that build up in human or animal cells. In most cases, when the cells divide, the defective proteins are passed on to the new cells. If nothing cleared them, the defects would build up in successive generations, making life impossible. But babies start life without these defects. As one researcher was quoted in The New York Times, "You take humans — they age two, three or four decades, and then they have a baby that’s brand new. There’s some interesting biology there we just don’t understand."
A study in C. elegans, a worm often used in aging research, found one way in which the damage is cleared. When sperm first meets the egg cell, just minutes before fertilization, a network of genes clears the damaged proteins from the egg. This mechanism was also found in frogs, so it is not limited to the worms. It may be active in stem cells as well.[1, 2]
It's a long way from discovering this mechanism in animals to finding treatments that could help people. So practical benefits such as new drugs are probably years away. But defective proteins are found in Alzheimer's and many other disease, and their possible removal is attracting intense scientific and commercial interest.
Growing understanding of the detailed mechanisms involved will likely suggest many opportunities for intervention to remove the damaged proteins that are associated with aging and at least some age-related illnesses. It is suspected (but not known for sure) that these proteins are an important cause of the illnesses. This research was supported by Calico Life Sciences, the company started by Google to conduct aging research.
The process noted above removes damaged proteins from the egg cell just before conception, so that babies start over instead of starting with the cellular age of their parents. Without some way of doing this life could not continue, as each generation would start with worse uncleared damage than the one before.
But it's also necessary to prevent a build-up of errors in the human genome itself (humans have about 20,000 different genes). When DNA reproduces, many of its errors are corrected automatically, but some are not. These uncorrected errors are mutations. If they are in the egg or sperm cells, they can be inherited by future generations. Most mutations are harmful, if they have any important effect; but some can help the animal survive and reproduce in its current environment. What keeps these errors from building up, and preventing the continuation of life?
Evolution is a major force preventing harmful errors from accumulating in the genes. If the genes of a fertilized egg have mutations harmful enough to prevent the animal from surviving and reproducing, then that collection of genes will go nowhere. Much has to work sell for that individual's genes to have any chance of being passed on.
 Pfizer inks protein degradation deal with Arvinas. This is just one of many possible approaches to clearing defective proteins.
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