The oocyte microenvironment is altered in adolescents compared to oocyte donors

Abstract

Study question: Do the molecular signatures of cumulus cells (CCs) and follicular fluid (FF) of adolescents undergoing fertility preservation differ from that of oocyte donors?

Summary answer: The microenvironment immediately surrounding the oocyte, including the CCs and FF, is altered in adolescents undergoing fertility preservation compared to oocyte donors.

What is known already: Adolescents experience a period of subfecundity following menarche. Recent evidence suggests that this may be at least partially due to increased oocyte aneuploidy. Reproductive juvenescence in mammals is associated with suboptimal oocyte quality.

Study design size duration: This was a prospective cohort study. Adolescents (10-19 years old, n = 23) and oocyte donors (22-30 years old, n = 31) undergoing ovarian stimulation and oocyte retrieval at a single center between 1 November 2020 and 1 May 2023 were enrolled in this study.

Participants/materials setting methods: Patient demographics, ovarian stimulation, and oocyte retrieval outcomes were collected for all participants. The transcriptome of CCs associated with mature oocytes was compared between adolescents (10-19 years old, n = 19) and oocyte donors (22-30 years old, n = 19) using bulk RNA-sequencing. FF cytokine profiles (10-19 years old, n = 18 vs 25-30 years old, n = 16) were compared using cytokine arrays.

Main results and the role of chance: RNA-seq analysis revealed 581 differentially expressed genes in CCs of adolescents relative to oocyte donors, with 361 genes downregulated and 220 upregulated. Genes enriched in pathways involved in cell cycle and cell division (e.g. GO: 1903047, P = 3.5 × 10^-43; GO: 0051983, P = 4.1 × 10^-30; GO: 0000281, P = 7.7 × 10^-15; GO: 0044839, P = 5.3 × 10^-13) were significantly downregulated, while genes enriched in several pathways involved in cellular and vesicle organization (e.g. GO: 0010256, P = 1.2 × 10^-8; GO: 0051129, P = 6.8 × 10^-7; GO: 0016050, P = 7.4 × 10^-7; GO: 0051640, P = 8.1 × 10^-7) were upregulated in CCs of adolescents compared to oocyte donors. The levels of nine cytokines were significantly increased in FF of adolescents compared to oocyte donors: IL-1 alpha (2-fold), IL-1 beta (1.7-fold), I-309 (2-fold), IL-15 (1.6-fold), TARC (1.9-fold), TPO (2.1-fold), IGFBP-4 (2-fold), IL-12-p40 (1.7-fold), and ENA-78 (1.4-fold). Interestingly, seven of these cytokines have known pro-inflammatory roles. Importantly, neither the CC transcriptomes nor FF cytokine profiles were different in adolescents with or without cancer.

Large scale data: Original high-throughput sequencing data have been deposited in Gene Expression Omnibus (GEO) database with the accession number GSE265995.

Limitations reasons for caution: This study aims to gain insights into the associated gamete quality by studying the immediate oocyte microenvironment. The direct study of oocytes is more challenging due to sample scarcity, as they are cryopreserved for future use, but would provide a more accurate assessment of oocyte reproductive potential.

Wider implications of the findings: Our findings have implications for the adolescent fertility preservation cycles. Understanding the expected quality of cryopreserved eggs in this age group will lead to better counseling of these patients about their reproductive potential and may help to determine the number of eggs that is recommended to be banked to achieve a reasonable chance of future live birth(s).

Study funding/competing interests: This project was supported by Friends of Prentice organization SP0061324 (M.M.L. and E.B.), Gesualdo Family Foundation (Research Scholar: M.M.L.), and NIH/NICHD K12 HD050121 (E.B.). The authors have declared that no conflict of interest exists.

Keywords: RNA-seq; children; cumulus cells; cytokine analysis; egg quality; fertility preservation; follicular fluid.

Figure 1.

Participant age and medical diagnosis, and cumulus cell collection. (A) Distribution of age among adolescents (black bars) and oocyte donors (gray bars). (B) Medical diagnoses of adolescents. (C) Microdissection of cumulus cells from retrieved expanded COCs prior to hyaluronidase treatment: (a) expanded COC before microdissection of cumulus cell masses, (b) trimmed cumulus cell masses (n = 4), (c) COC after microdissection, COC, cumulus–oocyte complex.

Figure 2.

Comparative RNA-seq analysis of cumulus cells collected from adolescents and oocyte donors. (A) Volcano plot with downregulated (n = 361) and upregulated DEGs (n = 220) in adolescents (n = 19) compared to donors (n = 19) (dashed red line—adjusted P < 0.05). (B) Heatmap with the top 50 DEGs with the highest fold change between two age groups. (C) Top 20 significantly downregulated GO terms (biological pathways) in adolescents compared to donors. (D) Top 20 significantly upregulated GO terms (biological pathways) in adolescents compared to donors. DEGs, differentially expressed genes; GO, gene ontology.

Figure 3.

Follicular fluid levels of cytokines in adolescents and oocyte donors. (A) Heatmap of follicular fluid levels of 80 cytokines in adolescents and oocyte donors with nine of them significantly different between the two groups (red boxes). (B) Seven of these nine significantly different cytokines have pro-inflammatory roles (asterisks).