Transient reprogramming, mediated by transient expression of mRNAs, promotes a rapid reversal of both cellular aging and of epigenetic clock in human fibroblasts and endothelial cells, reduces the inflammatory profile in human chondrocytes, and restores youthful regenerative response to aged, human muscle stem cells, in each case without abolishing cellular identity.

Old human cells can become more youthful by coaxing them to briefly express proteins used to make induced pluripotent cells, Stanford researchers and their colleagues have found. The finding may have implications for aging research. Elderly mice regained youthful strength after their existing muscle stem cells were subjected to the rejuvenating protein treatment and transplanted back into their bodies.

The proteins, known as Yamanaka factors, are commonly used to transform adult cells into induced pluripotent stem cells, or iPS cells. Induced pluripotent stem cells can become nearly any type of cell in the body, regardless of the cell from which they originated. They've become important in regenerative medicine and drug discovery.

By making old human cells in a lab dish to briefly express Yamanak proteins rewinds many of the molecular hallmarks of aging and renders the treated cells nearly indistinguishable from their younger counterparts.