Cumulus cells (CC) surround the oocyte and are coupled metabolically through regulation of nutrient intake. CC removal prior to in vitro maturation (IVM) decreases bovine oocyte developmental competence without affecting nuclear meiotic maturation. Objective was to investigate the influence of CC on oocyte cytoplasmic maturation in relation to energy metabolism. IVM with either cumulus enclosed (CEO) or denuded oocytes (DO) was performed in serum free metabolically optimized medium. Transmission electron microscopy revealed different distribution of membrane bound vesicles and lipid droplets between metaphase-II DO and CEO. By Nile Red staining, a significant reduction in total lipid level was evidenced in DO. Global transcriptomic analysis revealed differential expression of genes regulating energy metabolism, transcription and translation between CEO and DO. By western blot, FAS (fatty acid synthase) and HSL (hormone sensitive phospholipase) proteins were detected in oocytes and in CC indicating a local lipogenesis and lypolysis. FAS protein was significantly less abundant in DO that in CEO and more highly expressed in CC than in the oocytes. On the contrary, HSL protein was more abundant in oocytes than in CC. In addition, active Ser563-phosphorylated HSL was detected in the oocytes only after IVM and its level was similar in CEO and DO. In conclusion, absence of CC during IVM affected lipid metabolism in the oocyte and led to suboptimal cytoplasmic maturation. Thus, CC may influence the oocyte by orienting the consumption of nutritive storages via regulation of local fatty acid synthesis and lipolysis to provide energy for maturation.
- cumulus cells
- in vitro maturation
- lipid metabolism
- Copyright © 2012, American Journal of Physiology - Endocrinology and Metabolism