N Daei-Farshbaf - Department of Anatomy, School of Medicine, Iran University of Medical Sciences, Tehran, Iran
FS Amjadi - Department of Anatomy, School of Medicine, Iran University of Medical Sciences, Tehran, Iran
S Taleahmad - Department of Molecular Systems Biology, Cell Science Research Center, Royan Institute for Stem Cell, Tehran, Iran
M Ashrafi - Department of Anatomy, School of Medicine, Iran University of Medical Sciences, Tehran, Iran

Background: Morphological changes during meiotic division are indicative of simultaneous cytoplasmic and nuclear maturation of oocyte which will determine its final quality and fertilization outcome. Although several molecules are involved in these phenomena, it has been proven that the calcium fluctuation plays vital role in oocyte maturation. There is evidence that mainly intercellular sources release their calcium, but extracellular calcium participation rate is less known.Objective: We analyze the proteome profiling of cumulus cells (CCs), in order to discover proteins which support oocyte maturation and provide fertilization competency by managing extracellular calcium trafficking in CCs.Materials and Methods: Proteomics were conducted on cumulus cells of oocytes at different maturation stages of metaphase I (MI), unfertilized metaphase II (Uf-MII) and fertilized metaphase II (F-MII). These cumulus cells were obtained from tubal factors and donors with normal oogenesis using GnRH agonists. Three-step analysis were performed: as the first step, proteomic data were analyzed, proteins were organized in related biological pathways, and olfactory transduction pathway was selected due to its role in calcium trafficking. Second, western blot and qRT PCR were conducted on olfactory marker protein (OMP) and adenylyl cyclase 3 (AC3) -as olfactory neuron biomarkers- proteins and genes respectively to confirm the function of olfactory pathway in cumulus cells. Since in several studies, it is demonstrated that olfactory receptors (ORs) have specified expression pattern in brain of a young and healthy person which could be altered due to ageing and some disorders such as Alzheimer and Parkinson diseases, in final step, eight olfactory receptors were selected from ORs expressed ectopically in cumulus cells and after performing qRT PCR, special expression patterns of these 8 ORs were analyzed in all 3 groups.Results: The results demonstrate increased expression of OMP and AC3 proteins and related genes in the cumulus cells of F-MII oocytes. Moreover, drawn patterns of selected ORs show that oocytes at different maturation stages, depending on their maturation level and fertilization potential, have specific expression pattern of ORs in related CCs.Conclusion: The present study strongly supports a functional role of olfactory receptors in cytoplasmic and nuclear oocyte maturation by impacting on calcium trafficking. However, ectopic expression and specific pattern of ORs in human cumulus cells were confirmed by this study, but how ORs are regulated by gonadotropins or other factors remains to be determined.

Cumulus cells, Proteomics, Olfactory receptors, Oocyte maturation, Calcium