MITOCHONDRIAL DNA REPLICATION AFTER BLASTOCYST VITRIFICATION: A HEROIC ACT OF SURVIVAL OR AN ALERT FOR THE FUTURE?.

to understand the molecular pathways leading to the increase of the mitochondrial DNA (mtDNA) copy number observed on vitrified-warmed human blastocysts. A prospective cohort study was performed with a total of 18 specimens. An analysis of gene expression profile by RNA sequencing (RNA-seq) in 8 aneuploid blastocysts cultured 0 hours after warming and in 10 aneuploid blastocysts cultured 4,5 hours after warming was performed. Correlation studies, principal component and differential expression analysis were performed with DESeq2 package. Differential gene expression analyses were done using the parametric Wald test, with Benjamini-Hochberg multiple test correction (padj). Finally, Fgsea algorithm was used for enrichment analysis on Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways and Gene ontology (GO) terms. Blastocysts recovered after warming, had similar mitochondrial activity (p>0,05), a significant (p<0,05) upregulated effect on pathways associated with embryo development (blastocyst development, blastocyst growth, in utero embryonic development, etc.) and a significant (p<0,05) upregulated effect on cellular stress responses-related pathways (positive regulation of cell cycle arrest, positive regulation of apoptotic signaling pathway, humoral immune response, etc.) compared to just warmed blastocysts as representation of the pre-vitrification state. We have demonstrated in previous studies that human blastocysts that survive after warming experience a significant increase in their mtDNA content. With this study we have observed that this event coincides with several cellular stress responses-related pathways such as apoptosis, DNA damage, humoral immune responses, cancer, as well as other aspects of embryo growth such as blastocyst development and uterine embryo development but no with an increase in mitochondrial activity and energetic related pathways.