C-Type Natriuretic Peptide Pre-Treatment Improves Maturation Rate of Goat Oocytes by Maintaining Transzonal Projections, Spindle Morphology, and Mitochondrial Function

Simple Summary C-type natriuretic peptide (CNP) is a member of a family of natriuretic peptides that are expressed in mammals and have an important role in the recovery of meiosis. The aim of this research was to examine the effect of CNP on meiosis of goat oocytes. The results showed that pre-treatment of a goat cumulus–oocytes complex with CNP before maturation culture promoted the maturation of goat oocytes. Experiments revealed that CNP can control transzonal projection (TZPs) in order to maintain communication between cumulus cells and oocytes, and it can also control the assembly of the oocyte meiosis spindle apparatus. Further analysis showed that pre-treatment of goat cumulus–oocytes complex with CNP had an improved antioxidant capacity and increased mitochondrial activity. In conclusion, these findings shed new light on the potential mechanism of CNP treatment to enhance oocyte quality before fertilization. Abstract C-type natriuretic peptide (CNP) is a peptide molecule naturally found in follicles and can be used to extend meiotic resumption and enhance the potential for oocytes to develop. However, the mechanism by which CNP improves goat oocyte quality remains unclear. In this study, cumulus–oocyte complexes (COCs) from goats were pre-treated with CNP prior to IVM, and the results showed that pre-treatment with CNP enhanced goat oocyte maturation. First, we discovered that CNP maintained communication between cumulus cells and oocytes by regulating the transzonal projections (TZPs). We then found that CNP treatment reduced abnormal spindle formation and increased the expression of genes associated with spindle assembly and the spindle assembly checkpoint. Moreover, further analysis showed that oocytes exhibited better antioxidant ability in the CNP treatment group, which mainly manifested in higher glutathione (GSH) and lower reactive oxygen species (ROS) concentrations. Enhanced mitochondrial activity was signified via the augmented expression of mitochondrial oxidative metabolism and fusion and fission-related genes, thus diminishing the apoptosis of the oocytes. Overall, these results provide novel insights into the potential mechanism by which CNP treatment before IVM can improve oocyte quality.