Transplanted human and animal hearts adjust biological age to match recipients

Transplanted hearts adjust their biological age to match the bodies they enter, according to a recent scientific study. Researchers found that young donor hearts age quickly inside older recipients, while older hearts grow younger inside younger hosts. Heart transplants are limited worldwide because donor organs are in short supply. In the United States, 4,636 heart transplants took place in 2024, marking an 81.5% increase compared to 2013. Even with this growth, hundreds of people die each year while waiting for a new organ. This shortage has prompted alternative methods like pig-to-human heart transplants and led many places to change their guidelines to expand the human donor pool. Donors are generally recommended to be under 45 years old, though older donors without significant coronary artery disease are also considered. To study how transplanted hearts change, Jesse Poganik and his colleagues at Harvard University in Boston, Massachusetts, examined mice and human tissue. They grafted extra hearts from young mice at three months old, middle-aged mice at one year old, and old mice at 1.5 to 1.67 years old into mice across all three age groups. Four to six months later, the team tested tissue samples for DNA methylation levels across about 320,000 genetic regions to measure cellular damage from ageing. The biological ages of the donated hearts had shifted to match the recipients. Next, the team studied historical heart transplants at Brigham and Women's Hospital in Boston by reviewing biopsy samples from 11 transplants with a large age gap between donor and recipient. The age gaps ranged from 8 to 24 years for older hearts placed in younger people, and 38 to 50 years for younger hearts placed in older people. Jesse Poganik noted that the team found the exact same effects in humans as they saw in the mice. Researchers also reviewed electronic medical records of hundreds of heart-transplant recipients one year after surgery. Measures like heart rate, posterior wall thickness, and exercise capacity tracked with the recipient's age rather than the donor's age.

Context

Organ transplants require careful matching between donors and recipients to reduce the risk of organ rejection by the immune system. Studies on biological aging help scientists understand how cells accumulate damage over time and how different environments influence tissue health. These findings could eventually help medical professionals use healthy organs from older donors safely.