When the researchers studied the patterns of aging-associated chemical tags called methyl groups, which serve as an indicator of a cell’s chronological age, they found that the treated cells appeared to be about 1½ to 3½ years younger on average than untreated cells from elderly people, with peaks of 3½ years (in skin cells) and 7½ years (in cells that line blood vessels).

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The study found that inducing old human cells in a lab dish to briefly express these proteins rewinds many of the molecular hallmarks of aging and renders the treated cells nearly indistinguishable from their younger counterparts.

“When iPS cells are made from adult cells, they become both youthful and pluripotent,” says Vittorio Sebastiano, assistant professor of obstetrics and gynecology at Stanford University and senior author of the paper, published in Nature Communications.

“We’ve wondered for some time if it might be possible to simply rewind the aging clock without inducing pluripotency. Now we’ve found that, by tightly controlling the duration of the exposure to these protein factors, we can promote rejuvenation in multiple human cell types.”