Hydroxyapatite nanoparticles improve vitrified bovine MII oocyte developmental competence by reducing ultrastructural...

This study aimed to investigate the effects of hydroxyapatite (HA) nanoparticles and cryoprotectant concentrations (CPAs) on ultrastructure, developmental competence and gene expression in bovine metaphase II (MII) oocytes after vitrification. Bovine MII oocytes were vitrified in vitrification solution supplemented with HA nanoparticles sizes (20, 40, or 60 nm) and concentrations (0.01, 0.05, or 0.1%), and the optimal conditions of HA nanoparticles were determined based on survival rate, mitochondrial membrane potential (MMP), and developmental competence. Subsequently, we investigated the synergistic effects of HA and CPAs on ultrastructure, MMP, developmental competence, and related genes expression in bovine MII oocytes. The results showed that 40 nm 0.05% HA group significantly enhanced MMP levels, cleavage and blastocyst rates compared to the control group (P < 0.05). The VS1-HA group (VS1-HA: vitrification solution containing 17.5% EG (v/v) and 17.5% DMSO (v/v) with HA) exhibited the highest cleavage rates (43.67%) and blastocyst rates (15.19%), further reduced ultrastructural damage including mitochondrial swelling, cristae disruption, and microvilli loss, compared with the VS-HA group (VS-HA: vitrification solution containing 20% EG (v/v) and 20% DMSO (v/v) with HA). Furthermore, the relative mRNA levels of mitochondrial genes ND5 and ATPase8, and zona pellucida gene ZP3 (P < 0.05) were significantly higher than those in the VS group, but no difference in KRT8 or COX1 (P > 0.05). In conclusion, HA nanoparticles could reduce the negative effects of cryoinjury on the ultrastructure of certain organelles and the mRNA levels of specific related genes, thereby improving the developmental competence of vitrified bovine MII oocytes.