P-129 single human oocyte and cumulus cells transcriptome analyses reveal the stage-dependent energy metabolism dynamics during oocyte maturation before ovulation
Authors: Hu Y , Zhang R 
Published: June 2022

Abstract

Study question
What is the energy metabolic crosstalk between the oocyte and cumulus cells (CCs) during oocyte maturation before ovulation?

Summary answer
Cumulus cells provide local high progesterone to assist fertilization and lipids to support oocyte and embryo development during the late stage of oocyte maturation.

What is known already
There is increasing evidence showing that the maturation of oocytes relies on the materials and energy provided by CCs. In the absence of CCs, bovine oocytes exhibit metabolic disturbances, and similarly, in the absence of an oocyte, the metabolically driven function of CCs is also inhibited. However, their fundamental energy metabolic interactions and crosstalk, especially in the late stage of human oocyte maturation, are poorly understood.

Study design, size, duration
A total of 33 human oocytes (GV:22, MI:11) and 97 corresponding CCs (GV:35, MI:30, MII:32) were collected from 47 preimplantation genetic testing for aneuploidy patients.10 cells were randomly selected from individually cumulus-oocyte complex (COC) per CC sample to avoid bias due to the different number of CCs in each follicle. The samples were collected within a time frame of 3 months. RNA was isolated and performed transcriptome sequencing.

Participants/materials, setting, methods
The oocytes removed from CGCs were quickly transferred to the operating dish for marking, the maturation stage was assessed and recorded by observing the nucleus of oocytes, the CCs were mechanically isolated. Isolated RNA from oocytes and CCs underwent library preparation using an oligo deoxy-thymidine(dT) priming approach followed by deep sequencing. Data processing and bioinformatics analysis were performed using software, mainly including FASTP, STAR, String Tie, and DESeq2 along with functional annotation analysis.

Main results and the role of chance
Following deep sequencing of the single human oocyte (GV; MI) and corresponding CCs (GV; MI; MII), we found cholesterol and lipid metabolism-related transcripts of CCs are increasingly expressed during the late stage of oocyte maturation, the expression of progesterone synthesis-related transcripts was also increased. Our results suggest that cholesterol produced by CCs provides local high progesterone for mature oocytes in preparation for fertilization, while lipids from CCs serve as a more efficient energy source for oocyte and embryo development. Moreover, we found that oocyte maturation is a dynamic process and MI oocytes may be subdivided into early MI oocytes and late MI oocytes.

Limitations, reasons for caution
Since the MII oocytes from patients were used for clinical assisted reproduction, only MII-CCs were obtained, the data of MII oocytes were downloaded from the GEO database and merged with our data, further improvement in the future is needed.

Wider implications of the findings
This study may provide insights into how to intervene in natural conception and new ideas for promoting oocyte maturation in vitro through fatty acids supplementation in clinically assisted reproduction.

Trial registration number
not applicable