A Nuclear and Cytoplasmic Characterization of Bovine Oocytes Reveals That Cysteamine Partially Rescues the Embryo Development in a Model of Low Ovarian Reserve

Abstract

Decreased oocyte quality is a major determinant of age-associated fertility decline. Similarly, individuals affected by early ovarian aging carry low-quality oocytes. Using an established bovine model of early ovarian aging, we investigated key features of ‘quality’ oocyte maturation, associated with the onset of egg aneuploidy and reproductive aging, such as histone modifications, mitochondria distribution and activity, reduced glutathione (GSH) content, and gap junction functionality. Bovine ovaries were classified according to the antral follicle count (AFC), and the retrieved oocytes were processed immediately or matured in vitro. We observed alterations in several cellular processes, suggesting a multifactorial etiology of the reduced oocyte quality. Furthermore, we performed a rescue experiment for one of the parameters considered. By adding cysteamine to the maturation medium, we experimentally increased the free radical scavenger ability of the ‘low competence’ oocytes and obtained a higher embryo development. Our findings show that adopting culture conditions that counteract the free radicals has a positive impact on the quality of ‘compromised’ oocytes. Specifically, cysteamine treatment seems to be a promising option for treating aging-related deficiencies in embryo development.

Cytokine-Supplemented Maturation Medium Enhances Cytoplasmic and Nuclear Maturation in Bovine Oocytes

“…Out of all mitochondrial components analyzed in this study, mitochondrial redistribution was the only one that showed a significant difference between FLI or BMM-matured oocytes. Mitochondrial distribution changing from cortical, which presents itself during the GV stage, to diffuse throughout the cytoplasm in metaphase II oocytes during bovine in vitro maturation has been associated with better embryo development [ 27 ]. There was a significantly higher incidence of diffuse and a lower incidence of cortical mitochondrial distribution observed between FLI MII (FM) oocytes and control MII (CM) oocytes after in vitro maturation.…”

“…All images were taken at the same intensity setting. Stained mitochondria within each image were grouped into one of three distributions found throughout bovine IVM: diffuse, aggregates, or cortical [ 27 ]. Mitochondrial mass for each oocyte was calculated by subtracting the average of three background intensity readings from the fluorescent intensity of the oocyte in each image using ImageJ [ 28 , 29 ].…”

An Overview of Reactive Oxygen Species Damage Occurring during In Vitro Bovine Oocyte and Embryo Development and the Efficacy of Antioxidant Use to Limit These Adverse Effects

“…Sovernigo et al (2017) reported that using cysteamine during IVM decreased ROS concentrations and increased GSH concentrations in bovine oocytes [141]. Other studies determined that cysteamine supplementation improved oocyte competency and maturation, increased blastocyst development, improved cryosurvivability, and reduced the adverse effects of prolonged exposure to elevated oxygen tension [9,90,103,135,138,[142][143][144][145].…”

Effect of Season on Oocytes and in Vitro Fertilization by Fresh and Frozen Semen of Cattle

“…The oocyte incubated at 38°C, 5% of CO 2 for 18-20 hours to complete the maturing process. The oocytes were considered as mature when the first polar body was detected and cumulus cells expanded (Lodde et al, 2021).…”