An aged heart placed in a younger organism can lose some biological signs of aging.
The age recorded on a birth certificate is not the only way to measure aging. Our cells also accumulate molecular changes over time. Some of these can be used to estimate a “biological age,” which may differ from a person’s actual age.
Anatomical illustration of the human heart and the main blood vessels viewed from behind and above.
Credit: OpenStax Anatomy and Physiology / Wikimedia Commons — CC BY 4.0.
Researchers wanted to find out what happens to this biological age when a heart changes bodies. A transplantation creates a special situation: the donor’s organ may be significantly younger or older than the person receiving it. It is then exposed to the blood and physiological environment of its new owner.
The first experiments were conducted in mice. The researchers transplanted hearts between animals of different ages, then analyzed several markers of aging. An aged heart placed in a young mouse quickly showed younger markers. The opposite phenomenon also appeared: a young heart aged faster in an old organism.
To measure these changes, the team notably relied on chemical modifications of DNA. Their distribution changes with age and serves as a true biological clock. The researchers also studied the activity of many genes, another way to observe the biological state of tissues.
An important point emerges from the results: the change mainly affected the transplanted heart. In mice, its new biological age did not lead to an equivalent change in the recipient’s other tissues. The body’s environment therefore appears to act on the transplanted organ, without the organ simply imposing its own age on the rest of the organism.
The question remains whether this phenomenon also occurs in humans. The researchers analyzed heart biopsies from 11 patients with a substantial age gap between themselves and their donors. Several biological clocks then showed a relationship between the age of the transplanted heart and that of its new recipient. The effect was particularly visible in older hearts transplanted into younger people.
It will now be necessary to determine which elements of the younger organism cause these changes and whether they can be reproduced without transplantation.