News | Study Finds Eggs Deliberately Slow Their Metabolism to Remain Healthy for Decades
Human eggs can remain dormant in the body for decades before being activated to support a pregnancy. A study published in EMBO Journal found that as eggs mature, they deliberately slow their internal waste-disposal systems, lowering metabolism and minimizing damage. The finding reveals a unique minimalist survival strategy that helps eggs remain healthy over the long term.
“By analyzing more than 100 freshly donated human eggs, we discovered an unexpected minimalist strategy that may be key to preserving their integrity for decades,” said corresponding author Elvan Böke, PhD, group leader at the Centre for Genomic Regulation (CRG) in Barcelona.
Women are born with approximately 1 to 2 million immature oocytes. This number declines with age until only a few hundred remain at menopause. Over those decades, each egg must avoid metabolic wear and tear so it can support pregnancy when needed.
The team found that lysosomes and proteasomes, which break down and recycle proteins, are the cell’s main cleaning tools. Yet each round of protein degradation uses energy and may produce damaging reactive oxygen species (ROS), which can harm DNA and cell membranes. The researchers suggest that eggs apply the brakes to keep this degradation at a low level, minimizing ROS production while maintaining enough routine cleaning to survive.
This idea is consistent with a 2022 study by Böke’s team, which found that human oocytes deliberately bypass a basic metabolic step to reduce ROS formation. Together, the studies indicate that human eggs slow down at several levels to remain in a low-damage state for long periods.
The study used more than 100 eggs from 21 healthy donors aged 19–34, including 70 mature eggs capable of fertilization and 30 immature oocytes. Using fluorescent probes, the team tracked lysosome, proteasome, and mitochondrial activity in real time. Activity was about half that of surrounding support cells and declined further as the eggs matured.
More surprisingly, real-time imaging showed that in the final hours before ovulation, eggs expelled some lysosomes into the extracellular fluid while moving mitochondria and proteasomes to the cell’s edge. “This is a major cellular cleanout that has never previously been observed in human eggs,” explained first author Gabriele Zaffagnini, PhD.
This is the largest live-cell study of healthy human eggs to date. Most previous experiments relied on eggs cultured artificially in vitro, which often behave abnormally and are associated with lower in vitro fertilization (IVF) success rates.
The researchers believe the finding may offer new ways to improve outcomes across millions of IVF cycles worldwide. Dr. Böke said: “Fertility patients are often advised to take supplements to improve egg metabolism, but evidence that these approaches improve pregnancy outcomes is limited. Our study suggests that preserving the egg’s naturally low metabolic state may be more helpful for maintaining quality.”
Next, the team plans to study eggs from older donors and unsuccessful IVF cycles to determine whether the egg’s minimalist metabolism is impaired by age or disease.
News | Study Finds Eggs Deliberately Slow Their Metabolism to Remain Healthy for Decades
News | Study Finds Eggs Deliberately Slow Their Metabolism to Remain Healthy for Decades
Human eggs can remain dormant in the body for decades before being activated to support a pregnancy. A study published in EMBO Journal found that as eggs mature, they deliberately slow their internal waste-disposal systems, lowering metabolism and minimizing damage. The finding reveals a unique minimalist survival strategy that helps eggs remain healthy over the long term.
“By analyzing more than 100 freshly donated human eggs, we discovered an unexpected minimalist strategy that may be key to preserving their integrity for decades,” said corresponding author Elvan Böke, PhD, group leader at the Centre for Genomic Regulation (CRG) in Barcelona.
Women are born with approximately 1 to 2 million immature oocytes. This number declines with age until only a few hundred remain at menopause. Over those decades, each egg must avoid metabolic wear and tear so it can support pregnancy when needed.
The team found that lysosomes and proteasomes, which break down and recycle proteins, are the cell’s main cleaning tools. Yet each round of protein degradation uses energy and may produce damaging reactive oxygen species (ROS), which can harm DNA and cell membranes. The researchers suggest that eggs apply the brakes to keep this degradation at a low level, minimizing ROS production while maintaining enough routine cleaning to survive.
This idea is consistent with a 2022 study by Böke’s team, which found that human oocytes deliberately bypass a basic metabolic step to reduce ROS formation. Together, the studies indicate that human eggs slow down at several levels to remain in a low-damage state for long periods.
The study used more than 100 eggs from 21 healthy donors aged 19–34, including 70 mature eggs capable of fertilization and 30 immature oocytes. Using fluorescent probes, the team tracked lysosome, proteasome, and mitochondrial activity in real time. Activity was about half that of surrounding support cells and declined further as the eggs matured.
More surprisingly, real-time imaging showed that in the final hours before ovulation, eggs expelled some lysosomes into the extracellular fluid while moving mitochondria and proteasomes to the cell’s edge. “This is a major cellular cleanout that has never previously been observed in human eggs,” explained first author Gabriele Zaffagnini, PhD.
This is the largest live-cell study of healthy human eggs to date. Most previous experiments relied on eggs cultured artificially in vitro, which often behave abnormally and are associated with lower in vitro fertilization (IVF) success rates.
The researchers believe the finding may offer new ways to improve outcomes across millions of IVF cycles worldwide. Dr. Böke said: “Fertility patients are often advised to take supplements to improve egg metabolism, but evidence that these approaches improve pregnancy outcomes is limited. Our study suggests that preserving the egg’s naturally low metabolic state may be more helpful for maintaining quality.”
Next, the team plans to study eggs from older donors and unsuccessful IVF cycles to determine whether the egg’s minimalist metabolism is impaired by age or disease.
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