Transcriptional and metabolic characterization for optimization of capacitation-in vitro maturation

Research output: ThesisPhD Thesis

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In vitro oocyte maturation (IVM) is an assisted reproductive technology (ART) alternative to conventional IVF. IVM refers to in vitro maturation of immature cumulus-oocyte-complexes (COCs) collected from small-/mid- antral follicles following minimal (or no) exogenous gonadotropin administration and without ovulatory stimulus. Compared to conventional IVF that requires several days of gonadotropin priming and ovulatory stimulus prior to oocyte pick-up (OPU), IVM cycles are shorter, cheaper and hormone related side-effects are minimal. Thus, IVM is a patient friendly approach and a convenient choice for a certain group of patients such as women with polycystic ovarian syndrome (PCOS) and/or high antral follicle count. Despite of its advantages, utilization of IVM has been limited due to lower success rates in the number of good quality embryos and live births compared to conventional IVF. Development of bi phasic IVM systems with an added pre-maturation (pre-IVM)step, including a maturation inhibitory factor, prior to IVM have improved the developmental competence of IVM oocytes through synchronizing cytoplasmic and nuclear oocyte maturation. Capacitation (CAPA) – IVM is a successful example of a bi-phasic IVM systems with improved maturation and clinical pregnancy rates compared to standard IVM systems. As the efficiency gap between conventional IVF and CAPA-IVM still exists, current research is aiming to further improve the oocyte competence to eliminate the high attrition rate from mature oocyte to good quality embryo, to make CAPA-IVM a potent alternative for conventional IVF. Hence, this thesis focused on several important molecular mechanisms with known roles in acquisition of oocyte developmental competence (such as epidermal growth factor (EGF) network, oocyte secreted factors and glucose metabolism) with an attempt to improve current CAPA-IVM system to obtain in vitro matured oocytes with the best quality.
Following the use of the EGF ligand amphiregulin as meiotic trigger (compared to standard human chorionic gonadotropin and growth hormone mix) in human CAPA-IVM medium, we obtained improved oocyte maturation rates and identified the gene targets of amphiregulin in cumulus cells (CCs). Furthermore, we suggested new CC biomarkers for CAPA-IVM oocyte competence.
Next, we explored the potential roles of oocyte secreted factors’ cumulin and super-GDF9 in mouse CAPA-IVM. This multicentral study tested cumulin and super-GDF9 in stimulated, minimally stimulated and unstimulated mice models, out of which the last one was performed at Vrije Universiteit Brussel. We observed regulated CC expression of ovulatory cascade genes and improved COC mucification, which are bringing us one step closer to the good quality in vivo matured COC morphology.
Finally, focusing on glucose metabolism, first we characterized the metabolism of mouse CAPA-IVM COCs compared to in vivo matured counterparts and discovered that CAPA-IVM CCs exhibit an increased glycolytic activity already at the end of the pre-IVM step. During the follow-up study, we analyzed the bioenergetic profiles of COCs with and without lactate and/or super-GDF9, and culturing under low oxygen concentrations during pre-IVM. We showed that basal respiration of COCs increase dramatically during pre-IVM compared to in vivo conditions and neither of the supplements is successful to restore this boost during the pre-IVM. On the other hand, reducing the pre-IVM culture oxygen concentration normalized the bioenergetic profiles of CAPA-IVM COCs without altering oocyte developmental competence.
In conclusion, through studying several important drivers of oocyte maturation, we collected data from both human and mouse CAPA-IVM models which revealed insights for future CAPA-IVM optimization strategies and contributed to our knowledge of oocyte biology.
Original languageEnglish
QualificationDoctor in Medical Sciences
Awarding Institution
  • Vrije Universiteit Brussel
  • Anckaert, Ellen, Supervisor
  • Smitz, Johan, Co-Supervisor
Award date16 Feb 2023
Place of PublicationBrussel
Print ISBNs9789464443516
Publication statusPublished - 2023


  • vitro oocyte maturation
  • assisted reproductive technology
  • conventional IVF


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