Reproduction Abstracts

Introduction: Cystine-glutamate transporter (xCT) regulates cysteine levels by limiting uptake of cystine and consequently determines glutathione (GSH) contents in the cells. This study was performed to clarify effects of xCT deficiency (KO) on oocyte quality and ovarian function during maternal aging.

Materials and methods: Ovaries and plasma were collected from young (2 months) and aged (12 months) C57BL/6 xCT-KO and WT mice at 44 h after PMSG treatments. Follicle numbers at each classification stage were counted, and the estradiol levels were quantified by ELISA. The ovulated oocytes from each group were fertilized and cultured under 2% O₂/5% CO₂/93% N₂. Contents of ATP and GSH in the MII oocytes were measured. Also mRNA expressions of genes related to GSH synthesis, antioxidation, and aging were evaluated by real-time RT-PCR.

Results and discussion: The number of primordial follicles from young xCT-KO was significantly higher than that from WT (WT: 378.9±26.0, xCT-KO: 471.7±45.7). The number of total follicles from xCT-KO also tended to be higher than that from WT. The estradiol levels were not significantly different among the experimental groups. The fertilization rate of aged xCT-KO oocytes was lower than that of WT oocytes. However developmental potency of the fertilized oocytes to blastocysts was the same between the aged xCT-KO oocytes and the young WT oocytes. Both ATP and GSH contents were higher in the aged xCT-KO oocytes than the aged WT oocytes. Expression of several antioxidant-related genes was enhanced by aging. These results suggest that long-term deficiency of xCT does not affect oocyte quality from aged mice but unexpectedly raises potential to maintain the primordial follicle number.