S Kang

An old mouse hangs on a wire two-thirds longer than a mouse its own age, and after running on a treadmill it doesn't collapse from exhaustion. The difference isn't training or diet: the mice had a single molecule suppressed, and their muscles worked like they did in youth. That molecule is microRNA-128-3p, a short chain of nucleotides that silences entire groups of genes.

The skin of an older person is like an orchestra where the musicians are all in place, the instruments are tuned, but the conductor walks onstage later than he should. Infection with Staphylococcus aureus sets off an elaborate concert of immune cells in the skin, and it used to seem that with age the orchestra simply plays more quietly.