Static magnetic field halves cryoinjuries of vitrified mouse COCs, improves their functions and modulates pluripotency of derived blastocysts.

This study was performed with the aim of evaluating the influence of static magnetic field (SMF) of 60 mT on mouse Cumulus Oocytes Complexes (COCs) vitrification. The COCs were vitrified in the presence (Vit_SMF+) and absence of SMF (Vit_SMF-). Along with these groups, non-vitrified or fresh COCS, which exposed (nVit_SMF+) and non-exposed (nVit_SMF-) to magnetic field, were also considered. Survival and viability rates and mitochondrial activity as well as ultrastructure of oocytes were examined by trypan blue Staining (TBS), Annexin-PI Staining, JC1 staining and transition electron microscopy, respectively. Following in vitro fertilization (IVF) and embryo development, gene expression was carried out through qRT-PCR at blastocyst (BL) stage. The survival rate in Vit_SMF+ and Vit_SMF- decreased meaningfully in comparison with nVit_SMF- (P < 0.05), but there was no significant difference between SMF+ and SMF- groups. The mitochondrial activity in Vit_SMF- was significantly reduced compared to the nVit_SMF- group (P < 0.05), however its value in Vit_SMF+ returned to the control level. Ultrastructural study demonstrated that SMF could protect the COCs from cryoinjuries and reduced damaged features in ooplasm of the vitrified oocytes. There was no significant difference in fertilization rate. Although, BL formation was the highest rate in the Vit_SMF+ group, it was just substantially higher than the non-vitrified groups (P < 0.05). The significant changes of Oct4, Cdx2 and Nanog genes expression due to vitrification (Vit_SMF-) or SMF (nVit_SMF+) treatments (P < 0.05) as compared to control (nVit_SMF-), returned to the natural level after using SMF in vitrified derived blastocysts (Vit_SMF+). Totally based on the results, it is clear that static magnetic field improves mitochondrial potential activity and ultrastructure of mouse vitrified COCs. In addition, SMF enhances the embryo cleavage rate to blastocyst stage and modulates pluripotency in blastocyst embryos derived from vitrified COCs.