Glucose metabolism characterization during mouse in vitro maturation identifies alterations in cumulus cells

In vitro maturation (IVM) is an assisted reproduction technique with reduced hormone-related side-effects. Several attempts to implement IVM in routine practice have failed, primarily due to its relatively low efficiency compared with conventional in vitro fertilization (IVF). Recently, capacitation (CAPA)-IVM-a novel two-step IVM method-has improved the embryology outcomes through synchronizing the oocyte nuclear and cytoplasmic maturation. However, the efficiency gap between CAPA-IVM and conventional IVF is still noticeable especially in the numerical production of good quality embryos. Considering the importance of glucose for oocyte competence, its metabolization is studied within both in vivo and CAPA-IVM matured mouse cumulus-oocyte-complexes (COCs) through direct measurements in both cellular compartments, from transcriptional and translational perspectives, to reveal metabolic shortcomings within the CAPA-IVM COCs. These results confirmed that within in vivo COC, cumulus cells (CCs) are highly glycolytic, whereas oocytes, with low glycolytic activity, are deviating their glucose towards pentose phosphate pathway. No significant differences were observed in the CAPA-IVM oocytes compared with their in vivo counterparts. However, their CCs exhibited a precocious increase of glycolytic activity during the pre-maturation culture step and activity was decreased during the IVM step. Here, specific alterations in mouse COC glucose metabolism due to CAPA-IVM culture were characterized using direct measurements for the first time. Present data show that, while CAPA-IVM CCs are able to utilize glucose, their ability to support oocytes during final maturation is impaired. Future CAPA-IVM optimization strategies could focus on adjusting culture media energy substrate concentrations and/or implementing co-culture strategies. Summary sentence Pre-maturation culture conditions for immature oocytes from small antral follicles affect glycolytic activity and antioxidant defense capacity in mouse CCs during IVM.

Automated summary

The novel two-step IVM method CAPA-IVM has improved embryology outcomes by synchronizing oocyte nuclear and cytoplasmic maturation, although there is still a noticeable efficiency gap compared with traditional IVF. Glucose metabolism studies have revealed metabolic shortcomings within CAPA-IVM COCs, with specific alterations in mouse COC glucose metabolism characterized for the first time. Future optimization strategies for CAPA-IVM could focus on adjusting culture media energy substrate concentrations and/or implementing co-culture strategies.