E-Poster Presentation ESA-SRB-ANZBMS 2021

Investigating the molecular control of oxygen supply during oocyte maturation (#544)

Megan Lim 1 2 , Hannah Brown 3 , Ryan Rose 2 4 , Jeremy Thompson 1 2 , Kylie Dunning 1 2
  1. Australian Research Council Centre for Nanoscale BioPhotonics, The University of Adelaide, Adelaide, South Australia, Australia
  2. Robinson Research Institute, School of Biomedicine, The University of Adelaide, Adelaide, South Australia, Australia
  3. Monash University, Melbourne, Victoria, VIC, Australia
  4. Fertility SA, St. Andrews Hospital, South Terrace, Adelaide, South Australia, Australia

Oxygen is vital for oocyte maturation, however oxygen regulation within ovarian follicles is not fully understood. The erythrocyte protein haemoglobin is abundant within the in vivo matured oocyte, but significantly reduced following in vitro maturation (IVM)1, indicating potential function as an oxygen regulator. The molecule 2,3-bisphosphoglycerate (2,3-BPG) facilitates the release of oxygen from haemoglobin in erythrocytes. This interplay between 2,3-BPG and haemoglobin has been demonstrated in non-erythroid tissues2,3, suggesting the same might occur in the oocyte4. Towards understanding the role of 2,3-BPG in the oocyte, we characterised the gene expression and protein abundance of bisphosphoglycerate mutase (Bpgm), which synthesizes 2,3-BPG, and whether this is altered under low oxygen or haemoglobin addition during IVM.

We quantified haemoglobin and Bpgm expression within in vivo matured human cumulus cells and mouse cumulus-oocyte complexes (COC) to determine physiological levels of Bpgm. Next, we evaluated whether Bpgm gene expression and protein abundance was dysregulated during standard IVM of mouse COCs at 20% oxygen. Finally, we attempted to normalise Bpgm expression in the presence of low oxygen (2% or 5% oxygen) and/or exogenous haemoglobin, to mimic the in vivo environment.

Our investigation revealed that Bpgm expression was significantly lower than haemoglobin in both in vivo matured human cumulus cells (49-fold, P<0.0001) and mouse COCs (15-fold, P<0.005). Intriguingly, following IVM at 20% oxygen, Bpgm gene expression and protein abundance was significantly elevated compared to in vivo (11-fold, P<0.005). Moreover, in the presence of 2% oxygen, Bpgm expression was further elevated compared to 20% oxygen (2-fold, P<0.05). This was reduced by haemoglobin addition albeit not to in vivo levels (3-fold, P<0.05).

Our study demonstrates that IVM results in dysregulation of Bpgm that cannot be normalised by low oxygen or haemoglobin addition. These findings offer further insight into the potential role of haemoglobin as an oxygen regulator during IVM.

  1. Brown HM, et al. Hemoglobin: a gas transport molecule that is hormonally regulated in the ovarian follicle in mice and humans. Biology of reproduction. 2015;92(1):26. doi:10.1095/biolreprod.114.124594.
  2. Pritlove DC, et al. Novel Placental Expression of 2,3-Bisphosphoglycerate Mutase. Placenta. 2006;27(8):924-7. doi:http://dx.doi.org/10.1016/j.placenta.2005.08.010.
  3. Saha D, et al. Hemoglobin Expression in Nonerythroid Cells: Novel or Ubiquitous? Int J Inflam. 2014;2014:1-8.
  4. Lim M, et al. Hemoglobin: potential roles in the oocyte and early embryo†. Biology of reproduction. 2019;101(2):262-70. doi:10.1093/biolre/ioz078.