Oocyte aging: subcellular morphodynamic

INTRODUCTION: Delayed childbearing may contribute to the increasing number of subfertile couples recurring to assisted reproduction technology (ART). Deterioration of oocyte quality, due to reproductive aging, likely may cause subfertility. Prolonged culture, also called “in vitro aging”, may also damage oocyte functions. Indeed, we previously showed that oocyte ultrastructure integrity is essential for a positive ART outcome. In this study, we evaluated the ultrastructure of oocytes from aged women undergoing to ART procedures. MATERIAL AND METHODS: We used MII oocytes, from women, enrolled in this study after informed consent, under 35 and over 35 years old (assumed as age watershed) fixed at pick up (reproductive aging) or after 24h culture (in vitro aging). We analyzed ultrastructural and morphometric data. RESULTS: Transmission electron microscopy showed several subcellular changes especially in oocytes from aged women and subjected to prolonged culture, as compared to young, fresh oocyte. These changes mainly consisted in increasing of vacuoles, decreasing of mitochondria-smooth endoplasmic reticulum aggregates, increasing of mitochondria-vesicle complexes density, decreasing of cortical granules and microvilli, as well as various alterations of zona pellucida. DISCUSSION: The above subcellular alterations typically reflect an impairment of oocyte developmental competence. Therefore, our data demonstrated that aging affects oocyte quality parameters and that the oocytes from younger women are less sensitive to prolonged culture (in vitro aging) than the oocytes from aged women.