Coculture with porcine luteal cells during in vitro porcine oocyte maturation affects lipid content, cortical reaction and zona pellucida ultrastructure

Context. In pigs, in vitro fertilisation (IVF) is associated with high polyspermy rates, and for this reason, in vitro embryo production (IVP) is still an inefficient biotechnology. Coculture with somatic cells is an alternative to improve suboptimal in vitro maturation (IVM) conditions. Aim. This study was conducted to test a coculture system of porcine luteal cells (PLC) and cumulus-oocyte complexes (COC) to improve oocyte metabolism. Methods. COC were matured in vitro with PLC. Oocyte lipid content, mitochondrial activity, zona pellucida (ZP) digestibility and pore size, cortical reaction and in vitro embryo development were assessed. Key results. Coculture reduced cytoplasmic lipid content in the oocyte cytoplasm without increasing mitochondrial activity. Although ZP digestibility and ZP pore number were not different between culture systems, ZP pores were smaller in the coculture. Coculture impacted the distribution of cortical granules as they were found immediately under the oolemma, and more of them had released their content in the ZP. Coculture with porcine luteal cells during IVM increased monospermic penetration and embryo development after IVF. Conclusions. The coculture of COC with PLC affects the metabolism of the oocyte and benefits monospermic penetration and embryo development. Implications. The coculture system with PLC could be an alternative for the conventional maturation medium in pigs.