Overview

Even though all of our cells age with us, it’s unclear why our offspring don’t inherit those changes, effectively aging a child before birth. Scientists once thought that germline cells, such as eggs and sperm, were ageless; however, that notion was dispelled when signs of aging were observed in eggs and sperm. As a result, researchers hypothesized that germline cells could reset their age after conception, and now, a new study has found evidence that supports this hypothesis.

The science and other stuff to know

In a study published in the journal Science Advances, a team of Harvard researchers described evidence that supports the rejuvenation hypothesis of germline cells, showing that both mouse and human germline cells appear to reset their biological age in the early stages of embryo development. A rejuvenation period that occurs after an embryo has attached to the uterus, dubbed “ground zero,” places the growing embryo at its youngest biological age.

Unlike linear chronological ages, the biological age of an embryo determines the health and function of cells. The team of scientists discovered that the age of the mouse embryos remained constant throughout the early stages of cell division, when fertilization had just occurred, while studying these epigenetic changes. The biological age of the embryos dipped around 6.5 to 7.5 days into development, indicating that they underwent some kind of rejuvenation event.

The average biological age of embryos seemed to reverse after 6.5 to 7.5 days, when the embryo becomes attached to the interior lining of the uterus. This indicates that the internal cells were undergoing some sort of rejuvenation process. This “ground zero” for a mouse could be anywhere between 4.5 and 10.5 days after fertilization. Later, the biological age of mouse embryos begins to climb again, but scientists aren’t sure exactly when.

So what?

As of this writing, it is illegal to study human embryos at these early stages of development, which means that scientists could not obtain comparable data from humans. However, some embryos that were slightly more advanced in development than mouse embryos showed no immediate signs of aging, suggesting that human cells also undergo a similar rejuvenation event early in embryonic development.

Understanding how these cells reverse aging could help researchers develop treatments for age-related diseases, such as Parkinson’s, Vittorio Sebastiano, a developmental biologist at Stanford University School of Medicine who wasn’t involved in the study, explained to Science News.

In such diseases, certain cells might become dysfunctional due to damage. Resetting the age of those cells could prevent them from causing problems. It’s also possible that this rejuvenation period “can be leveraged and hijacked somehow to try to promote similar processes of rejuvenation in normal cells,” Sebastiano added.

What’s next?

This isn’t the first demonstration of cells reversing their age. Back in 2016, researchers at Salk Institute showed that activating certain genes associated with embryonic development could “reprogram” the age of cells and help animals, including humans, live longer.