Transplanted hearts shift their biological age toward the host: mouse grafts and 11 human transplants show donor hearts ageing or rejuvenating

Transplanted hearts shift their biological age toward that of the host: young hearts age rapidly in older bodies, and old hearts are rejuvenated in young recipients. Earlier evidence that organ ageing can be reshaped by the systemic environment came mainly from heterochronic parabiosis, in which two living animals share one circulatory system; this work tests that logic directly in solid-organ transplantation. In mice, hearts from three-month-old, one-year-old and 1.5-1.67-year-old donors were grafted into recipients in all three age groups so that each animal carried both the graft and its native heart; four to six months after surgery, tissue was sampled and DNA methylation measured in about 320,000 genetic regions, comparing ageing-linked methylation in the graft against the animal's original heart.

Human historical transplant samples showed the same direction of effect as the mice. It extends the mouse finding into a real clinical transplant setting and deliberately selects cases with a substantial donor-recipient age gap, making host age easier to observe. The researchers identified 11 transplants at Brigham and Women's Hospital with a substantial age gap (8 to 24 years for older hearts grafted into younger people, and 38 to 50 years for younger hearts into older people) and ran DNA-methylation tests on biopsy samples they could access; the researcher describes the effects as exactly the same as those seen in mice.

Some cardiac functional measures tracked recipient age rather than donor age, though not all of them did. It places molecular biological-age change alongside how the transplanted heart actually performs, rather than stopping at methylation readings. The researchers examined electronic medical records of hundreds of heart-transplant recipients one year after surgery and found that measures such as heart rate, the thickness of the heart's posterior wall and exercise capacity were associated with the recipient's age rather than the donor's; the researcher notes that some but not all functional measures matched the prediction that older hearts in younger individuals functioned as if biologically younger, and that some things are probably simply irreversible.

The result points to a practical implication: organs for transplant might be sourced from older donors than current practice allows. Donors younger than 45 are generally recommended, with older ones considered only when they show no signs of significant coronary artery disease; this study offers a biological-age rationale for revisiting that boundary. The background figures given are that there were 4,636 heart transplants in the United States in 2024, 81.5% more than in 2013, while hundreds of people worldwide still die each year on waiting lists. These are context statistics, not efficacy evidence from the study itself.

The result applies to the specific setting of heart transplantation, with evidence from a mouse allograft heart model and from historical transplant biopsies and medical records at Brigham and Women's Hospital. For clinical practice and organ allocation, it suggests that a donor organ's biological age may not be a fixed property but can adjust to the host environment, so donor quality assessment may need to consider recipient age as well. For research, it carries the systemic-environment effect revealed by heterochronic parabiosis down to the level of a single transplanted organ. The human portion described in the coverage rests on 11 transplants with large age gaps, within the range of biopsy samples that could be accessed.

The study was posted as a preprint and has not yet been peer reviewed, so the stability of the conclusions awaits formal review and replication. The human portion rests on 11 biopsy samples, a limited sample size, and the researcher states that only some functional measures matched the prediction and that some things are probably simply irreversible, indicating that molecular age change and organ function do not map one-to-one. In addition, this evidence bundle contains only the external coverage and no paper text, so the specific methylation assay, statistical approach and effect sizes cannot be checked; whether donor age criteria can be relaxed on this basis still needs larger studies with longer follow-up.