64 Culture of bovine oocytes and embryos with metabolic hormones concentrations associated with equine metabolic syndrome

Abstract

Maternal metabolic status could affect fertility and early embryo development due to altered concentrations of metabolic hormones. Equine metabolic syndrome (EMS) is a condition in horses associated with obesity and insulin resistance. Equine metabolic syndrome is accompanied by increased concentrations of insulin and leptin and decreased concentrations of adiponectin, in ovarian follicular fluid (FF) and in systemic circulation (SYST). We sought to determine how altered concentrations of insulin, leptin, and adiponectin (ILA), consistent with those in mares with EMS (EMS) or normal mares (normal), would affect blastocyst formation rates, blastocyst gene expression for metabolism and inner cell mass formation (OCT4, SOX2, COX2, DNMT3a1, HK2, LDH, PDH, and GLUT1), and metabolite uptake from culture media. Because equine oocytes are not available for large-scale study, a bovine model was used in this preliminary study to determine the impact of altered ILA on oocytes and embryos. Bovine ovaries were obtained from an abattoir and embryos produced as previously described using chemically defined media (CDM; Barcelo-Fimbres and Seidel 2007 Mol. Reprod. Dev. 74, 1406-1418). Briefly, oocytes were cultured in in vitro maturation medium (IVM), fertilized in FCDM, presumptive zygotes were placed into CDM-1 for ~56 h. Cleavage rates were assessed, and embryos were moved to CDM-2 for ~122 additional hours. Treatments consisted of 5 groups: (1) standard oocyte IVM, FCDM and embryo production (EP) system (control), (2) IVM with normal FF ILA and control FCDM and EP, (3) IVM with normal FF ILA and FCDM and EP with normal SYST ILA, (4) IVM with EMS FF ILA and control FCDM and EP, and (5) IVM with EMS FF ILA and FCDM and EP with EMS SYST ILA. Seven days after fertilization, blastocysts were pooled in groups of 5 and placed into 50 mL of CDM-2 for 24 h. Embryos were removed, and medium was frozen and stored at −80°C to determine metabolite usage via gas chromatography mass spectroscopy. Pooled embryos were washed and placed into RNA lysis solution for relative quantitative PCR. Statistical comparisons were performed using ANOVA with a post-hoc Tukey test. Blastocyst formation rates and gene expression of viability markers were not significantly different among groups. However, aspartate was lower (P = 0.02) in spent media from Group 3 (normal FF and SYST ILA) and tended (P = 0.09) to be lower in media from Group 5 (EMS FF and SYST ILA) when compared with controls (Group 1). The ILA during early embryo development but not oocyte maturation appeared to be associated with increased uptake of aspartate, a nonessential amino acid, thought to be involved in osmoregulation, cellular signalling, and in mouse embryos, facilitate the metabolism of lactate. In conclusion, the addition of ILA in concentrations observed in normal horses and EMS horses did not affect blastocyst formation rates or markers of embryo viability, although embryo metabolism could have been altered.