I am in the laboratory of Juan Carlos Izpisúa Belmonte, a Spaniard who works at the Gene Expression Laboratory at San Diego’s Salk Institute for Biological Studies, and who next shows me something hard to believe. It’s the same mouse, lively and active, after being treated with an age-reversal mixture. “It completely rejuvenates,” Izpisúa Belmonte tells me with a mischievous grin. “If you look inside, obviously, all the organs, all the cells are younger.”
The powerful tool that the researchers applied to the mouse is called “reprogramming.” It’s a way to reset the body’s so-called epigenetic marks: chemical switches in a cell that determine which of its genes are turned on and which are off. Erase these marks and a cell can forget if it was ever a skin or a bone cell, and revert to a much more primitive, embryonic state. The technique is frequently used by laboratories to manufacture stem cells. But Izpisúa Belmonte is in a vanguard of scientists who want to apply reprogramming to whole animals and, if they can control it precisely, to human bodies.
What Izpisúa Belmonte is proposing is to go one step better still, and reverse aging-related aberrations without having to create a new individual. Among these are changes to our epigenetic marks—chemical groups called histones and methylation marks, which wrap around a cell’s DNA and function as on/off switches for genes. The accumulation of these changes causes the cells to function less efficiently as we get older, and some scientists, Izpisúa Belmonte included, think they could be part of why we age in the first place. If so, then reversing these epigenetic changes through reprogramming may enable us to turn back aging itself.
Even skin cells from centenarians, scientists have found, can be rewound to a primitive, youthful state. The artificially reprogrammed cells are called induced pluripotent stem cells, or IPSCs. Like the stem cells in embryos, they can then turn into any kind of body cell—skin, bone, muscle, and so on—if given the right chemical signals.