ABSTRACT
L-Carnitine (LC) is known to play key roles in lipid metabolism and antioxidative activity, implicating enhanced cryotolerance of bovine blastocysts. However, sustainability of LC supplementation during culture period on preimplantation development beyond the blastocyst stage has not been investigated so far. Therefore, all embryos were cultured under fatty acid free conditions, one group with LC (LC-Embryos) and the control group without LC (Control) supplementation. Transfer to recipients was conducted on day 6. Elongation-stage embryos were recovered on day 14; metrics of embryo recollection, developmental rates to early elongation-stage as well as mean embryo length did not differ between the groups. Gene expression analysis via NGS revealed 341 genes to be differentially regulated between elongation-stage embryos derived from LC supplementation compared to controls. These played mainly a role in molecular functions and biological processes like oxidoreductase activity, ATP dependent activity, cellular stress and respiration. Pathways like oxidative phosphorylation and thermogenesis, ECM receptor signaling, PI3K-Akt and focal adhesion were affected by differentially regulated genes. Moreover, all DEGs located on the mitochondria were significantly downregulated in the LC-Embryos, being in line with lower mitochondrial copy number and mtDNA integrity compared to the control group. Finally, we uncovered alterations of the bioenergetic profile on day 7 as a consequence of LC supplementation for the first time, revealing significantly higher oxygen consumption rates, ATP linked respiration and spare capacity for LC-embryos. Conclusively, we uncovered direct effects of LC supplementation during the culture period on the bioenergetic profile going along with sustainable effects on mtDNA copy numbers and transcriptome profile of bovine day 14 embryos.
ABSTRACT
The major limitation of the widespread use of IVP derived embryos is their consistent deficiencies in vitality when compared with their ex vivo derived counterparts. Although embryo metabolism is considered a useful metric of embryo quality, research connecting mitochondrial function with the developmental capacity of embryos is still lacking. Therefore, the aim of the present study was to analyse bovine embryo respiration signatures in relation to developmental capacity. This was achieved by taking advantage of two generally accepted metrics for developmental capacity: (I) environmental conditions during development (vivo vs. vitro) and (II) developmental kinetics (day 7 vs. day 8 blastocysts). Our study showed that the developmental environment affected total embryo oxygen consumption while different morphokinetics illustrating the embryo qualities correlate with maximal mitochondrial respiration, mitochondrial spare capacity, ATP-linked respiration as well as efficiency of ATP generation. This respiration fingerprint for high embryo quality is reflected by relatively lower lipid contents and relatively higher ROS contents. In summary, the results of the present study extend the existing knowledge on the relationship between bovine embryo quality and the signature of mitochondrial respiration by considering contrasting developmental environments as well as different embryo morphokinetics.
