86 Effect of in vitro culture conditions on mitochondria functions in mouse embryos

Abstract

Mitochondria provide the energy for oocyte maturation, fertilisation, and embryo formation via oxidative phosphorylation. Consequently, any adverse influence on mitochondrial function may negatively affect the development of pre-implantation embryos especially because there is no mitochondrial DNA (mtDNA) replication until post-implantation. Studies in the field of mitochondrial dynamics have identified an intriguing link between energy demand/supply balance and mitochondrial architecture, which may suggest that inappropriate culture conditions may inhibit mitochondrial functions, which may negatively affect embryo development. We wanted to check whether in vitro culture (IVC) conditions of mouse embryos affect mitochondrial functionality. The IVC as well as naturally matted (NM) mouse embryos at the 2-cell and blastocyst stage were subjected to mitochondrial analysis (distribution, organisation, and mitochondrial membrane potential), and expression of mRNA and proteins involved in regulation of mitochondria functions, as well as number of mtDNA copies, were evaluated. Significance level was set at 0.05. We observed that the mitochondria in 2-cell IVC embryos were less numerous and localised mainly in the pericortical region of the cytoplasm, whereas mitochondria in NM embryos were numerous and homogeneously distributed in both blastomeres. Drastic differences were observed in blastocysts. Mitochondria in the IVC group were fragmented, rounded, and aggregated mainly in the perinuclear region of the cells, whereas mitochondria of NM blastocysts were numerous and created an elongated mitochondrial network along the cells. Time-lapse analysis showed reduced mitochondrial and mitochondrial membrane activity in IVC blastocysts. Moreover, our results indicate the IVC group had reduced mRNA expression of mitofusin 1, mitofusin 2, and optic atrophy 1 responsible for mitochondrial fusion. Additionally, mtDNA copy number for IVC blastocysts (398 887.45 ± 30 608.65) was significantly lower than that of NM blastocysts (593 367.12 ± 66 540.32; P < 0.02). Furthermore, no significant differences were found in mtDNA copy number of IVC 2-cell embryos when compared with NM embryos. The results obtained clearly showed that IVC conditions affect proper mitochondrial functionality and hence embryo development.