309 ADDITION OF BRAIN-DERIVED NEUROTROPHIC FACTOR IN MATURATION MEDIUM IMPROVED IN VITRO MEIOTIC COMPETENCE OF OVINE OOCYTES AND SUBSEQUENT PARTHENOGENETIC DEVELOPMENT

Abstract

Overall efficiency of in vitro embryo production has remained low despite extensive effort to understand the effects of culture conditions, media composition, and supplementation. Brain-derived neurotrophic factor (BDNF), which is a physiologically important neurotrophin, has been used to enhance oocyte maturation in some previous studies (Lee et al. 2007; Zhang et al. 2010). However, the efficacy of BDNF to improve oocyte competence has not been fully established especially in ovine. Therefore, the present study aimed to evaluate the effect of BDNF during in vitro maturation (IVM) on maturation rate, intracellular glutathione (GSH) content, and embryonic development in sheep oocytes. Cumulus-oocyte complexes (COC) were obtained from ovaries of ewes. The COC were placed in maturation medium supplemented with either 10 (IVM-B10) or 100 (IVM-B100) ng mL^–1 of BDNF (PeproTech, London, UK). Oocytes in control group were incubated in the same maturation medium without BDNF. The IVM was performed in a humidified atmosphere containing 5% CO₂, 5% O₂, and 90% N₂ at 38.5°C for 24 h. After IVM, several oocytes from the IVM-B10 (n = 110), IVM-B100 (n = 124), and control (n = 110) groups were stained with Hoechst and were evaluated in relation to their metaphase-II rate. To measure GSH content, several oocytes from the IVM-B10 (n = 28), IVM-B100 (n = 33), and control (n = 37) groups were incubated in tyrodes medium containing 10 µM Cell Tracker blue for 30 min and transferred under fluorescence microscope, with digital images analysed by image J software. To evaluate the embryonic development, several oocytes from IVM-B10 (n = 145), IVM-B100 (n = 137), and control (n = 143) groups were subjected to parthenogenetic activation by applying 1 min of exposure to 2.5 µM ionomycin followed by 2 mM 6-DMAP treatment for 3 h. After stimulation, oocytes were cultured in CR1aa medium for 7 days under the conditions stated previously. Four replications were performed. The metaphase-II rate, cleavage, and blastocyst rates were compared by x² analysis. The GSH content was analysed by one-way ANOVA. A P-value of less than 0.05 was considered significant. The results showed that metaphase-II rate was higher in the IVM-B100 group (88.7%), as compared with the control group (77.3%), but not significant as compared with that in the IVM-B10 group (84.5%). No difference was also found between the IVM-B10 group and control group in terms of the metaphase-II rate. Oocytes in the IVM-B10 group revealed a higher (96.8%) GSH content than both of the IVM-B100 (86.9%) and control (86.3%) groups. There was, however, no difference in the GSH content between the IVM-B100 group and control group. The proportion of cleaved embryos was not different between the groups; however, the blastocyst rate was higher in both the IVM-B10 (37.9%) and IVM-B100 (39.3%) groups compared with the control group (22.4%). Collectively, the results of this study showed that supplementation of IVM media with BDNF promoted nuclear maturation, increased GSH content, and stimulated in vitro embryonic development in ovine.