A new study has found that transplanting young organs may not actually help recipients live longer. The researchers discovered that when donated hearts were put into recipients, they rapidly adopted the biological age of the person receiving them, regardless of how young the donor heart originally was.
The finding comes from Jesse Poganik at Brigham and Women’s Hospital in Boston, who led a set of heart transplants in mice. His team also examined data from human heart transplants at Brigham and Women’s, where samples have been stored for decades.
The Experiment With Mice
A team led by Poganik carried out heart transplants in mice, fitting them with a second heart placed in the neck. This arrangement enabled researchers to make comparisons between the new hearts and the original ones. In some cases, young adult mice received hearts from middle-aged donors; in other cases, they received young hearts.
Three “aging clocks” — molecular tools that estimate the biological age of tissues and whole organisms — were employed by the team to measure the mice. The clocks performed well at forecasting the chronological age of mice that didn’t receive new hearts.
Poganik anticipated a two-way exchange, with younger hearts helping older animals in return. His own team’s prior research found that young mice that received aged hearts built up senescent cells in their other organs. These cells are believed to play a part in the aging process.
The findings moved in the opposite direction. Within four to six months following the operation, the donor organs appeared to take on the biological age of their new hosts. The younger hearts grew older, while the older hearts grew younger.
“The environment of the transplanted organ really dictates how it seems to behave biologically.”
Human Data Backs It Up
Support for the mouse findings came from information gathered during human heart transplants, where recipients undergo a series of biopsies after surgery. Small samples of heart tissue taken from those operations at Brigham and Women’s have been preserved over decades.
The team’s tests on the samples showed the same result: the biological age of a new heart changes fast to match the recipient’s age, regardless of how old the donor was.
It’s not clear why this happens. João Pedro de Magalhães, who studies aging at the University of Birmingham in the UK and was not involved in the study, thinks the recipient’s immune system may play a role. He suggests that immune cells circulating in the blood might affect markers of aging in the new organ.
What It Means for Putin’s Idea
Around this time last year, a reporter was at an aging conference in Manchester, listening to a talk about fly aging, when his phone started pinging. News outlets were reporting that a hot mic had caught Russia’s Vladimir Putin and China’s Xi Jinping discussing the possibility of living forever.
“With the developments of biotechnology, human organs can be continuously transplanted, and people can live younger and younger, and even achieve immortality,” Putin reportedly told Jinping.
It appeared he was pointing toward the “replacement” theory of longevity, a notion backed by experiments where young mice were surgically joined to older ones. There was something about the young blood that restored the old mice. The proposal suggested that youthful organs could restore world leaders in their 70s.
The concept has met an obstacle. The latest findings indicate that it is the recipient’s own body, rather than the age of the transplanted organ, that determines the biological age of the graft.
Why Young Hearts May Not Work
Poganik offers several possible explanations for the results. He says that the supposed benefits of a young heart may be weakened by the rest of the old body around it. He also proposes that one organ alone cannot create such an effect.
The research also poses questions about accurate measurement of biological age. When organs appear to be aging by one method yet not by another, how can scientists obtain a complete picture of the biological age of an organ, or a person?
The Practical Payoff
Poganik wants his discovery to prompt surgeons to take a second look at hearts from older donors, many of which are now thrown away because people assume they won’t work well. Machines that keep organs alive before transplantation are already changing that reality, and Poganik has worked on another study showing that these devices appear to rejuvenate donor livers to some extent.
The research underscores how complicated aging is to reverse. Undoing it fully would require fixing DNA damage, structural damage, and every other kind of deterioration that comes with getting older, throughout every cell and tissue in the body.
“There are aspects of biological age that are probably reversible, and there are aspects that are probably not.”
The research fails to resolve whether aging can be halted or turned around. Instead, it demonstrates that the body of the recipient appears to set the biological age of the transplanted organ, rather than the age of the organ itself.
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Source material: “Young organs may not be a fountain of youth for recipients,” MIT Technology Review.
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