Relationship between bovine oocytes developmental competence and mRNA expression of apoptotic and mitochondrial genes following the change of vitrification temperatures and cryoprotectant concentrations

The present study analyzed the relationship between bovine oocytes developmental competence and mRNA expression of apoptotic and mitochondrial genes following the change of vitrification temperatures (VTs) and cryoprotectant agent concentrations (CPAs). Cumulus oocyte complexes were randomly divided into five groups: control, vitrified in liquid nitrogen (LN; -196 °C) with 5.6 M CPAs (LN 5.6 M), LN with 6.6 M CPAs (LN 6.6 M), liquid helium (LHe; -269 °C) with 5.6 M CPAs (LHe 5.6 M), and LHe with 6.6 M CPAs (LHe 6.6 M). After vitrification and warming, oocytes of vitrified and control groups were subjected to in vitro maturation (IVM), in vitro fertilization and in vitro culture. The blastocyst rate in LHe 5.6 M group was the highest among the four vitrified groups (13.7% vs. 9.4%, 1.3%, and 8.4%; P 0.05). The mRNA expression level of 8 apoptotic- and 12 mitochondria-related genes were detected through qRT-PCR after IVM. Lower VT (LHe, -269 °C) positively affected the mRNA expression levels of apoptotic genes (BAD, BID, BTK, TP53, and TP53I3) and mitochondrial genes (COX6B1, DERA, FIS1, NDUFA1, NDUFA4, PRDX2, SLC25A5, TFB1M, and UQCRB), and reduced oxidative stress from freezing. Decreased CPAs (5.6 M) positively affected mRNA expression levels of apoptotic genes (BAD, BCL2A1, BID, and CASP3) in LHe vitrification but negatively affected apoptotic genes (BAD, BAX, BID, BTK, and BCL2A1) in LN vitrification. In conclusion, decreased VTs and CPAs in LHe vitrification may increase the blastocyst rate by changing the mRNA expression levels of these apoptotic and mitochondrial genes for the vitrified oocytes.