Glucosamine supplementation during in vitro maturation leads to perturbed developmental capacity of bovine cumulus oocyte complexes

Abstract

Glucose is a primary energy substrate required for successful in vitro oocyte maturation (IVM). However, most maturation media contain more glucose than that seen in follicular fluid (2.3 mM vs. 5.6 mM in TCM199). Glucosamine (Glc) as an alternative substrate for extracellular matrix during cumulus expansion reduced glucose uptake by bovine cumulus oocyte complexes (COCs, Sutton-McDowall et al. 2004 Reproduction 128, 313–319). As this could enable a reduction in glucose concentrations to physiological levels in IVM medium of COCs, the aim of this study was to investigate the influence of Glc supplementation on oocyte developmental capacity. Bovine COCs were matured in synthetic follicular fluid medium (SFFM, a defined medium based on the composition of follicular fluid, plus 5.6 mM glucose, FSH, hCG and BSA, Sutton-McDowall et al. 2004 Reprod. Fertil. Dev. 16 sup, 204) ± 5 mM Glc. After 24 h, either nuclear maturation (rep = 8, n = 160) or blastocyst development 8 days post-fertilization (rep = 5, n = 400) was determined. Data was arcsine transformed and analyzed by ANOVA, followed by Tukey's test. While the presence of Glc did not affect the completion of nuclear maturation and early cleavage, +Glc led to severely perturbed blastocyst development (-Glc, 32.5 ± 1.9% vs. +Glc, 4.7 ± 3.9%, P < 0.001). Glc supplementation in somatic cells is well-known to down-regulate the phosphatidylinositol-3-kinase (PI3K) signalling pathway, reducing protein synthesis and other cell survival mechanisms. Therefore, oocyte protein synthesis (measured by [2,3,4,5,6-³H] phenylalanine incorporation, rep = 5, n = 200) and embryo development (rep = 6, n = 720) following IVM in SFFM ± Glc ± EGF (a PI3K pathway stimulator) was determined. Glc supplementation led to a 40% decrease in protein synthesis compared to -Glc, while the combination of +Glc + EGF significantly increased protein synthesis by 60%. However, IVM + EGF + Glc did not improve blastocyst rates (main effect: -Glc 41.6 ± 6.6% vs. +Glc, 6.6 ± 1.7%, P < 0.001). Additionally, COCs were also cultured in SFFM ± 50 μM LY294002 (a specific PI3K inhibitor) and nuclear maturation (rep = 5, n = 200) or blastocyst development 8 days post-fertilization (rep = 4, n = 200) was determined. Despite the presence of LY294002 leading to 43% less COCs completing nuclear maturation (P < 0.001), blastocyst development was not affected (mean = 38.8 ± 3.2%). These results demonstrate that Glc supplementation during IVM has no effect on nuclear maturation or early development but is detrimental to oocyte developmental capacity by severely perturbing blastocyst development. However, the diminished developmental capacity appears to be independent of the well-characterized Glc down-regulation of the PI3K signalling pathway.