A research group including the University of Tokyo discovered in mice that fertilization rates decrease with age due to changes in the structure of the egg's zona pellucida.

 Physical aging is known to decrease female fertility, with fertility declining significantly in humans after age 35. However, the exact reasons why fertility begins to decline with age remain unclear.

 The research group focused on changes in egg morphology and compared eggs from young mice (equivalent to 20-25 years old in humans) with those from aged mice (equivalent to 35-40 years old in humans) to analyze the mechanism behind the decline in fertility.

 As a result, it was found that in aged mice, the interaction between the cumulus cells that cover the egg and the egg was weakened, there was less material transport from the cumulus cells to the egg, and the quality of the eggs was reduced.

 In addition, observations using a scanning electron microscope revealed that the zona pellucida of young eggs exhibits a mesh structure with characteristic irregularities and pores, whereas the zona pellucida of aged eggs has changed to a smooth structure that has lost its irregularities and pores. Perhaps for this reason, sperm have difficulty binding to the zona pellucida of aged eggs, and the fertilization rate of aged eggs in in vitro fertilization was significantly lower than that of young eggs.

 Finally, they confirmed that adding reduced glutathione swells (makes the zona pellucida of aged eggs thinner or more fragile), allowing sperm to pass through more easily, thereby improving fertilization rates.

 These findings provide new insight that the decline in fertility in aged mice is due to inhibition of sperm binding associated with structural changes in the egg zona pellucida. The results of this study have led to a method of restoring fertility that focuses on the zona pellucida, a structure outside the egg, rather than on the gene expression or cytoplasm of the egg. This is expected to contribute to the development of new infertility treatments for the eggs of women with low in vitro fertilization rates and for the eggs of women in the latter stages of reproductive age, when fertility begins to decline.

Paper information:[Communications Biology]Age-associated aberrations of the cumulus-oocyte interaction and in the zona pellucida structure reduce fertility in female mice

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The University of Tokyo was established in 1877 (Meiji 10) by integrating the Tokyo Kaisei School and the Tokyo Medical School.Since its establishment, it has developed education and research in a unique way in the world as a leading university in Japan and an academic center for the fusion of East and West cultures.As a result, many human resources have been produced in a wide range of fields, and many research achievements […]

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