Mitochondrial DNA content decreases during in vitro human embryo development: insights into mitochondrial DNA variation in preimplantation embryos donated for research

Abstract

Objective: To assess the mitochondrial DNA (mtDNA) load and variation in human oocytes and during preimplantation embryo development using specimens donated for research. Design: Prospective cohort study. Setting: Not applicable. Patients: A total of 50 in vitro fertilization patients and 11 oocyte donors whose specimens were obtained between July 2017 and July 2018. Interventions: None. Main Outcome Measures: All specimens were separately collected. Quantitative polymerase chain reaction was performed with Sure-Plex DNA Amplification System (Illumina). Primers for the adenosine triphosphate 8 mitochondrial gene and the b-actin were used. Data were statistically analyzed by analysis of variance with the Scheff e multiple pairwise comparison for categorical variables and by linear regression for numerical variables. Results: Human metaphase II (MII) oocytes had significantly more total mtDNA copy number than day 3 embryos, and day 3 embryos had more total and per-cell mtDNA copy number than aneuploid blastocysts. There was a significant decrease in mtDNA content associated with failed-fertilized oocytes compared to noninseminated metaphase II oocytes. Conclusions: During preimplantation development, before implantation, human embryos undergo a significant decrease in total mtDNA content and no increase in mtDNA content at the blastocyst stage. Oocytes need to carry a correct threshold of mitochondrial load in the oocyte in order to successfully fertilize. An active degradation of mtDNA before implantation occurs after fertilization takes place. These findings could be used to improve knowledge about the best embryo culture conditions and would serve as a basis for further studies addressing again the use of mtDNA content as an embryo viability marker.

Mitochondrial DNA Copy Number in Cleavage Stage Human Embryos—Impact on Infertility Outcome

“…Several studies concerned with the correlation of mtDNA content with maternal age have produced opposite results demonstrating positive, negative or no correlation with maternal age [4,9,[11][12][13]17,[21][22][23][24]36]. We evaluated results from 314 cleavage stage embryos derived from patients in different age groups, but no correlation between age and mtDNA could be identified.…”

“…As most of published studies concerning mtDNA copy number in human embryos were conducted using blastocysts from frozen IVF cycles [7][8][9][10][11][12][13]36], we decided to evaluate the end point parameters by assessing blastomeres biopsied at the cleavage stage that were transferred on day 5 of the same cycle. We aimed to evaluate the significance of the energy production process at such an early stage of embryo development.…”

Trophectoderm Mitochondrial DNA Content Associated with Embryo Quality and Day-5 Euploid Blastocyst Transfer Outcomes

“…mtDNA content was also thought to remain nonactive replication during the preimplantation period of human embryogenesis. From MII oocytes to blastocysts, there was a significant decrease in terms of total and per-cell mtDNA content (MII oocytes > day-3 embryos > blastocysts) (Perez- Sanchez et al, 2020).…”

“…More and more studies investigated mtDNA dynamics in human preimplantation embryos. mtDNA copy number significantly decreased in terms of per cell during preimplantation development (MII oocytes > day-3 embryos > blastocysts) (Hashimoto et al, 2017;Perez-Sanchez et al, 2020). There was a high increase in mtDNA content in arrested cleavage-stage embryos compared to not arrested day-3 embryos (Perez-Sanchez et al, 2020).…”

“…This may be due to reduced mitochondrial biological function in immature cytoplasm of oocytes (Reynier et al, 2001;Chan et al, 2005). The recent study found that mtDNA content of failed fertilized oocytes was also significantly lower compared to noninseminated MII oocytes (Perez-Sanchez et al, 2020). It suggested that lower mtDNA content in oocytes was associated with fertilization failure.…”