In the human body, most cells have a limited lifespan. The red blood cells survive about 120 days, the cells of the intestine are renewed every five days, and even the neurons, however renowned for their longevity, undergo the outrages of time. However, there is a remarkable exception: female eggs, capable of remaining perfectly preserved for several decades. How do these cells challenge the laws of cellular aging? A team of Barcelona researchers has just lifted the veil on this biological mystery.
A colossal evolutionary challenge
Each woman is born with a stock of immature eggs which must last her all her reproductive life. These precious cells should not only survive, but also keep their ability to bear pregnancy after sometimes having fifty years in the ovaries. This evolutionary feat poses a major scientific challenge: how can a cell avoid deterioration for such a long period?
Dr. Elvan Böke and his team from the Barcelona genomic regulatory center decided to tackle this enigma. Their approach? Directly analyze more than a hundred eggs freshly taken from 21 healthy donors, thus constituting the largest database ever gathered on this subject.
A minimalist revolutionary strategy
The results of this study, published in The Embo Journal, reveal a cellular strategy as elegant as it is unexpected. Unlike other cells that maintain an active metabolism, eggs adopt a resolutely minimalist approach: they voluntarily slow their internal maintenance systems.
Any cell has microscopic “cleaning” teams – lysosomes and proteasomes – which continuously recycle used proteins. This process, although Essents, consumes a lot of energy and produces toxic waste called reactive oxygen species, capable of damaging DNA.
The eggs have found the perfect parade: they reduce the activity of these cleaning systems by around 50% compared to the surrounding cells. This strategy minimizes the production of harmful molecules while keeping just enough activity to keep the cell alive.
Spectacular spring cleaning
The most surprising observation concerns the behavior of eggs just before ovulation. The researchers discovered that these cells then carry out a radical “large household”: they literally expel their lysosomes in the surrounding liquid, while other organelles such as mitochondria migrate to the cellular periphery.
« It is a type of spring cleaning which we did not know that human ovles were capable“, Explains Dr. Gabriele Zaffagnini, first author of the study. This spectacular purge probably prepares the cell for its new mission: fertilization and embryonic development.
Fixed and immunocolorized human oocyte. The mitochondria are represented in orange and the actin actin cytoskeleton. DNA is represented in light blue. Credit: Gabriele Zaffagnini/Centro de Regulación Genómica
A revolution for reproductive medicine
This discovery could transform the approach of in vitro fertilization, a technique used by millions of couples around the world. Currently, protocols often try to stimulate the metabolism of eggs with various supplements, starting from the principle that a high cell activity is synonymous with good health.
The new data suggests the opposite: respecting the naturally “calm” state of the eggs could be the key to preserving their quality. This revolutionary approach could significantly improve the success rates of fertility treatments by working with natural biology rather than trying to force it.
Promising prospects
The Barcelona team now plans to study how this mechanism evolves with maternal age and in cases of infertility. This research could open the way to new therapeutic strategies, offering hope for the millions of couples faced with design difficulties.
This discovery perfectly illustrates how nature has developed solutions of remarkable sophistication to resolve complex biological challenges. The eggs teach us that in terms of cellular longevity, less can sometimes be more.
