In a trio of studies published Sunday, scientists reported that they reversed aging in the muscles and brains of old mice — simply by running the blood of young mice through their veins. Lee Rubin, director of Translational Medicine of the Harvard Stem Cell Institute and professor of stem cell and regenerative biology, led one of the studies. Amy Wagers, professor of stem cell and regenerative biology at FAS and Joslin Diabetes Center, was involved in two of the studies. A study last year by Amy Wagers and Richard T. Lee, professor of medicine at Brigham and Women’s Hospital, is also cited.