The story starts with an observation, made a few years ago, that senescent cells often produce a molecule called P16INK4A. Most body cells have an upper limit on the number of times they can divide—and thus multiply in number. P16INK4A is part of the control mechanism that brings cell division to a halt when this limit is reached.
The extra tweak he added to the DNA of these mice was a way of killing cells that produce P16INK4A. He did this by inserting into the animals’ DNA, near the gene for P16INK4A, a second gene that was, because of this proximity, controlled by the same genetic switch. This second gene, activated whenever the gene for P16INK4A was active, produced a protein that was harmless in itself, but which could be made deadly by the presence of a particular drug. Giving a mouse this drug, then, would kill cells which had reached their Hayflick limits while leaving other cells untouched. Dr Baker raised his mice, administered the drug, and watched.
The drug, Dr Baker found, produced some benefit even if it was administered to a mouse only later in life. Though it could not clear cataracts that had already formed, it partly reversed muscle-wasting and fatty-tissue loss. Such mice were thus healthier than their untreated confrères.
Regardless of the biochemical details, the most intriguing thing Dr Baker’s result provides is a new way of thinking about how to slow the process of ageing—and one that works with the grain of nature, rather than against it. Existing lines of inquiry into prolonging lifespan are based either on removing the Hayflick limit, which would have all sorts of untoward consequences, or suppressing production of the oxidative chemicals that are believed to cause much of the cellular damage which is bracketed together and labelled as senescence. But these chemicals are a by-product of the metabolic activity that powers the body. If 4 billion years of natural selection have not dealt with them it suggests that suppressing them may have worse consequences than not suppressing them.
By contrast, actually eliminating senescent cells may be a logical extension of the process of shutting them down (they certainly cannot cause cancer if they are dead), and thus may not have adverse consequences. It is not an elixir of life, for eventually the body will run out of cells, as more and more of them reach their Hayflick limits. But it could be a way of providing a healthier and more robust old age than people currently enjoy.
A real breakthrough in life that Chinese emperors dreamed about for centuries!!!