A widely shared fantasy—that replacing old organs with young ones might slow or even reverse aging—has taken a hit. In a study posted on bioRxiv, Jesse Poganik and colleagues at Brigham and Women’s Hospital in Boston transplanted hearts between young and middle-aged mice. Using molecular “aging clocks,” they found that the transplanted hearts soon matched the biological age of the recipient: young hearts aged up, and old hearts aged down. The recipient mice themselves showed no such changes.
The pattern held in human patients. Decades of stored biopsy samples from heart transplant recipients at Brigham and Women’s showed the same result: no matter the donor’s age, the grafted heart quickly adopted the biological age of the person who received it. Poganik, who expected a reciprocal effect, said the environment of the transplanted organ dictates its biological behavior.
Why this happens remains unclear. João Pedro de Magalhães, an aging researcher at the University of Birmingham not involved in the work, suspects immune cells in the recipient’s blood may influence aging markers in the new organ. Poganik speculates that any benefit from a young heart might be diluted by the rest of the aged body—or that a single organ simply isn’t enough to move the needle.
The findings don’t just deflate the immortality theories once floated by world leaders; they have practical implications. Poganik hopes they will encourage surgeons to consider hearts from older donors, which are often discarded. But they also underscore how complex aging is. “There are aspects of biological age that are probably reversible, and there are aspects that are probably not,” Poganik said. Full-scale reversal, he added, would require every damaged cell and tissue to go back in time—an enormous challenge.