P–217 The mitochondrial DNA copy number of cumulus granulosa cells is associated with the symmetry of cleavage embryo but not blastocyst quality
Authors: Ji Y , Hu L 
Published: August 2021

Abstract

Study question
To study the relationship between mitochondrial DNA copy number of cumulus granulosa cells (CGCs-mtDNA) and the quality of early embryos.

Summary answer
CGCs-mtDNA was related to the symmetry of cleavage. However, CGCs-mtDNA was not associated with fertilization, blastocysts quality, or blastocysts euploidy.

What is known already
The potential of early embryonic development mainly depends on the quality of oocytes to a large extent. Mitochondria of CGCs are directly involved in the establishment of oocytes capacitation during oocytes maturation and development.

Study design, size, duration
This is a retrospective study from December 2018 to January 2019, involving a total of 283 CGCs surrounding Metaphase II oocytes from 49 patients who underwent preimplantation genetic testing for aneuploidy (PGT-A) at the Reproductive and Genetic Hospital of CITIC-Xiangya.

Participants/materials, setting, methods
We used the TaqMan probes to quantitatively detect mitochondrial DNA copy number of per CGCs by quantitative PCR in mitochondrial genes (MT-ND1 and MT-CO1) and a nuclear gene (β-globin). Besides, according to the nature of the dependent variable, the binary logistic regression model and the logistic regression analysis model of ordered multi-classification were used for multivariate statistical analysis.

Main results and the role of chance
The CGCs-mtDNA corresponding to fertilized eggs was not different from that of unfertilized eggs in MT-ND1 gene and MT-CO1 gene (MT-ND1: fertilized vs. unfertilized, 600±337 vs. 604±367, P = 0.593; MT-CO1: fertilized vs. unfertilized, 1336±531 vs. 1329±478, P = 0.938). Interestingly, we found that the CGCs-mtDNA of D3 embryos with good quality was statistically higher than that of D3 embryos with fair or poor quality for MT-ND1 gene and MT-CO1 gene (MT-ND1: good quality vs. fair/poor quality, 803±627 vs. 587±307, P = 0.028; MT-CO1: good quality vs. fair/poor quality, 1682±554 vs. 1374±702, P = 0.025). Moreover, the CGCs-mtDNA corresponding to D3 embryos with even cleavage was higher than that of D3 embryos with uneven cleavage (MT-ND1: even cleavage vs. uneven cleavage, 803±627 vs. 590±309, P = 0.036; MT-CO1: even cleavage vs. uneven cleavage, 1562±552 vs. 1316±525, P = 0.037). Besides, we investigated the difference among the CGCs-mtDNA in blastocysts with the good quality, blastocysts with fair or poor quality, and the developmental blocked embryos before the blastocyst stage. But we didn’t found any difference among the above three groups (MT-ND1: P = 0.531; MT-CO1: P = 0.609). In the study of the relationship between CGCs-mtDNA and blastocysts euploidy, we got similar results (MT-ND1: P = 0.602; MT-CO1: P = 0.570).

Limitations, reasons for caution
The sample size of this study was relatively small.
Wider implications of the findings: Although the sample size of this study is limited, our results indicated the importance of mitochondria in CGCs in early embryo development, especially in the first three days. The investigation of mitochondrial function in CGCs may shed light on the mechanism of CGCs-oocyte crosstalk.

Trial registration number
LL-SC–2019–005