Oral Presentation ESA-SRB-ANZBMS 2021

Oocyte-cumulus cell bidirectional communication impacts oocyte quality (#124)

Dulama Richani 1 , Anne Poljak 2 , Baily Wang 1 , Joanna Biazik 3 , Jared Campbell 4 , Abbas Habibalahi 4 , Saabah B Mahbub 4 , William Stocker 5 6 , David Skerrett-Byrne 7 , Maria Marinova 1 , Sonia Bustamante 2 , Brett Nixon 7 , Ewa Goldys 4 , Craig Harrison 5 6 , Robert B Gilchrist 1
  1. Fertility & Research Centre, School of Women’s and Children’s Health, University of New South Wales Sydney, Australia
  2. Bioanalytical Mass Spectrometry Facility, Mark Wainwright Analytical Centre, University of New South Wales Sydney, Australia
  3. Electron Microscope Unit, Mark Wainwright Analytical Centre, University of New South Wales Sydney, Kensington, NSW, Australia
  4. ARC Centre of Excellence Centre for Nanoscale Biophotonics, Graduate School of Biomedical Engineering, University of New South Wales Sydney, Australia
  5. Biomedicine Discovery Institute, Monash University, Clayton, Victoria, Australia
  6. Department of Physiology, Monash University, Clayton, Victoria, Australia
  7. Priority Research Centre for Reproductive Science, School of Environmental and Life Sciences, College of Engineering, Science and Environment, The University of Newcastle, Australia

Mammalian oocytes grow and mature in a mutually dependent relationship with adjacent somatic cells. The oocyte actively regulates cumulus cell differentiation and function by secreting soluble oocyte-secreted factors which act on cumulus cells in a paracrine manner. Here we investigated the molecular mechanisms by which two oocyte-secreted factors, cumulin and BMP15, regulate oocyte maturation and cumulus-oocyte cooperativity. Immature antral-follicle mouse cumulus-oocyte complexes (COCs) were matured in vitro ± 20ng/mL cumulin or BMP15 (n= 3-8 biological replicate experiments). Thereafter oocytes and cumulus cells were separated and underwent morphological, metabolic, and proteomic analyses. Global analyses (proteomics and hyperspectral analysis of autofluorophores) revealed proteomic and metabolic profiles which discriminate cumulin- and BMP15-treated oocytes/cumulus cells from untreated cells and from each other. In oocytes, proteomic data showed significant upregulation of proteins involved in nuclear function in response to cumulin. In cumulus cells, proteomic data showed marked upregulation of a variety of metabolic processes (mostly anabolic) in response to cumulin and BMP15, including lipid, nucleotide and carbohydrate metabolic processes, while mitochondrial metabolic processes were downregulated. These mitochondrial changes were supported by transmission electron microscopy showing marked morphological changes to cumulus mitochondria and endoplasmic reticulum, while mitotracker staining showed a 17% decrease in mitochondrial content (p<0.05) in cumulin-treated cumulus cells.  In support of reduced mitochondrial number, the hyperspectral unmixed data showed significantly lower NAD(P)H levels and lower REDOX state (p<0.05). Furthermore, cellular and mitochondrial respiration (oxygen consumption rate) was significantly lower (p<0.05) in cumulin-treated COCs. Despite this, mass spectrometry quantification of nucleotides demonstrated that overall energy metabolites were in balance since most cellular energy pathway metabolites, particularly ATP, remained similar in untreated and treated COCs. Collectively, these data demonstrate that oocyte-secreted factors remodel COC metabolism during oocyte maturation in preparation for ensuing fertilization and embryonic development, and this is associated with oocyte developmental competence.