Poster Presentation The Annual Scientific Meeting of the Endocrine Society of Australia and the Society for Reproductive Biology 2014

Regulated expression of heat shock proteins during ovulation and oocyte maturation (#324)

Macarena Bermudez Gonzalez 1 , Linda L Wu 1 , Rebecca L Robker 1
  1. Robinson Research Institute, School of Paediatrics and Reproductive health, University of Adelaide, Adelaide

Heat Shock Proteins (HSPs) are highly conserved molecular chaperones, which increase during cytoprotective responses against cellular stress. Transcription factor HSF1 directly regulates expression of Hsp70i and Hsp90AA1, which are involved in protein folding, transport and assembly, and maintenance of cell viability. To understand how ovarian cells may respond to various stressors, this study examined expression and localisation of HSF1, Hsp70i and Hsp90AA1 in the mouse ovary during oocyte maturation and ovulation.

Ovaries were obtained from CBAF1 mice treated with PMSG to stimulate folliculogenesis, followed by ovulatory hCG for 0h, 8h, 11.5h or 13h. Paraffin sections were immuno-stained using antibodies against HSF1, Hsp70i and Hsp90AA1 and peroxidase detection methods. Cumulus-oocyte complexes (COCs) and denuded oocytes were stained by immunofluorescence and visualised using confocal microscopy.

HSF1 was highly expressed in granulosa cells of preovulatory follicles, decreasing by 11.5h post-hCG, yet highly expressed in corpora lutea at 13h post-hCG.  In oocytes, HSF1 was highly expressed within the germinal vesicle, and then exhibited diffuse cytoplasmic localisation after hCG co-incident with GVBD and resumption of meiosis. Hsp70i were expressed in granulosa cells in preovulatory follicles, but by 11.5h post-hCG remained only in antral granulosa and cumulus cells. At 13h post-hCG, Hsp70i was expressed in corpora lutea. In oocytes Hsp70i showed strong cytoplasmic expression up to 11’5h post-hCG, then decreased coinciding with ovulation. Hsp90AA1 was expressed in granulosa and cumulus cells of preovulatory follicles, remaining high only in antral granulosa and cumulus cells at 11.5h post-hCG, and localized to corpora lutea at 13h post-hCG. In oocytes, Hsp90AA was intensely localized to the meiotic spindle at 11.5h post-hCG.

These results show that the ovulatory LH surge regulates HSP protein expression levels in granulosa cells and triggers dramatic intracellular re-localization of HSP proteins in oocytes; likely reflective of their important roles in cytoprotection and oocyte developmental competence.