This is early phase research, but Researchers at UC Berkeley have discovered a drug that rejuvenates old stems in the brains and muscles of mice.
You can read about this on Science Alert: Scientists have identified a drug that rejuvenates ageing muscle and brain tissue
Or the UC Berkeley Press release: Drug perks up old muscles and aging brains
Or from the journal article itself in Oncotarget: Systemic attenuation of the TGF-β pathway by a single drug simultaneously rejuvenates hippocampal neurogenesis and myogenesis in the same old mammal
From the press release:
We established that you can use a single small molecule to rescue essential function in not only aged brain tissue but aged muscle,” said co-author David Schaffer, director of the Berkeley Stem Cell Center and a professor of chemical and biomolecular engineering. “That is good news, because if every tissue had a different molecular mechanism for aging, we wouldn’t be able to have a single intervention that rescues the function of multiple tissues.