Context: With aging, various problems in the reproductive system emerge, especially in females. However, our understanding of reproductive aging in livestock and humans is limited.
Aims: We aimed to investigate reproductive changes between young and aged mice.
Methods: Eight- to ten-week-old female mice were used as the young group, and 10-month-old mice were studied as the aged group. Reproductive changes were investigated from physiological, histological, cytological, and epigenetic perspectives.
Key results: The estrus cycle was shortened (P <0.0001), and the estradiol (E2) concentration was lower in aged mice (P <0.01), whereas the progesterone (P4) concentration did not differ between young and aged mice (P >0.05). The histological results revealed a lower number of antral follicles in the ovary and disordered epithelial tissue structures in the oviducts in aged mice. During oogenesis, the surrounded nucleolus (SN)-type oocytes in aged mice exhibited increased mitochondrial agglutination (P <0.05) and cellular apoptosis (P <0.01) as well as decreased H3K36 triple-methylation (P <0.001). Although many defects existed, the oocytes from aged mice could normally support cellular reprogramming after somatic cell nuclear transfer.
Conclusions: Our results indicate that the reduced levels of reproductive hormones in aged females lead to shorter estrus cycles and reduced follicular development, leading to abnormal oogenesis, particularly in SN-type immature oocytes.
Implications: These results provide new insight that enhance our understanding and improve the reproductive ability of aged females.