Rescue in vitro maturation using ovarian support cells of human oocytes from conventional stimulation cycles yields oocytes with improved nuclear maturation and transcriptomic resemblance to in vivo matured oocytes

Abstract

Purpose: Determine if the gene expression profiles of ovarian support cells (OSCs) and cumulus-free oocytes are bidirectionally influenced by co-culture during in vitro maturation (IVM).

Methods: Fertility patients aged 25 to 45 years old undergoing conventional ovarian stimulation donated denuded immature oocytes for research. Oocytes were randomly allocated to either OSC-IVM culture (intervention) or Media-IVM culture (control) for 24-28 h. The OSC-IVM culture condition was composed of 100,000 OSCs in suspension culture with human chorionic gonadotropin (hCG), recombinant follicle stimulating hormone (rFSH), androstenedione, and doxycycline supplementation. The Media-IVM control lacked OSCs and contained the same supplementation. A limited set of in vivo matured MII oocytes were donated for comparative evaluation. Endpoints consisted of MII formation rate, morphological and spindle quality assessment, and gene expression analysis compared to in vitro and in vivo controls.

Results: OSC-IVM resulted in a statistically significant improvement in MII formation rate compared to the Media-IVM control, with no apparent effect on morphology or spindle assembly. OSC-IVM MII oocytes displayed a closer transcriptomic maturity signature to IVF-MII controls than Media-IVM control MII oocytes. The gene expression profile of OSCs was modulated in the presence of oocytes, displaying culture- and time-dependent differential gene expression during IVM.

Conclusion: The OSC-IVM platform is a novel tool for rescue maturation of human oocytes, yielding oocytes with improved nuclear maturation and a closer transcriptomic resemblance to in vivo matured oocytes, indicating a potential enhancement in oocyte cytoplasmic maturation. These improvements on oocyte quality after OSC-IVM are possibly occurring through bidirectional crosstalk of cumulus-free oocytes and ovarian support cells.

Keywords: Granulosa cells; In vitro maturation; Oocyte transcriptomics; Ovarian support cells; Stem cells.

Fig. 1

Treatment with OSC-IVM improves maturation rate of human denuded oocytes compared to an IVM media-matched control. A Schematic of the experimental co-culture IVM approach. hiPSCs were differentiated using inducible transcription factor overexpression to form ovarian support cells (OSCs). Human oocytes were obtained from patients in the clinic after standard gonadotropin stimulation, and immature oocytes (GV and MI) identified after denuding were allocated between the experimental OSC-IVM condition (OSC-IVM) or the control IVM media condition (Media-IVM) for IVM co-culture. Oocyte maturation and health were assessed after 24–28 h IVM co-culture, and oocytes were frozen for further analyses. The figure was created with BioRender.com. B Representative image of co-culture containing immature human oocytes (n = 3) and OSCs. Scale bar: 200 µm. Denuded GV oocytes are seen with surrounding OSCs in suspension culture. C Maturation rate of oocytes after 24–28 h IVM experiments, including oocyte co-culture with OSCs (OSC-IVM), or in media control (Media-IVM). n indicates the number of individual oocytes in each culture condition. Error bars indicate mean ± SEM. The p-value is derived from unpaired t-test comparing experimental OSC-IVM to control Media-IVM. Due to low numbers of retrieved oocytes per donor, each group contains oocytes from predominantly non-overlapping donor groups, and pairwise comparisons are not utilized

Fig. 2

Transcriptomics analysis reveals that oocytes matured under the OSC-IVM condition are transcriptionally closer to IVF MII oocytes than those oocytes matured in Media-IVM, despite no changes in morphological features. A Total Oocyte Scores (TOS) generated from imaging analysis of MII oocytes after 24–28 h IVM experiments and IVF-MII oocytes. n indicates the number of individual MII oocytes analyzed. Median (dashed lines) and quartiles (dotted lines) are indicated. ANOVA indicated no significant (p = 0.5274) difference between the means of each condition. B Quantification of the angle between the first polar body (PB1) and spindle apparatus, derived from oocyte fluorescent imaging analysis (See Supplementary Fig. 2), of oocytes co-cultured with OSCs (OSC-IVM) or in media control (Media-IVM), and IVF-MII oocytes. n indicates the number of individual oocytes analyzed from each condition. Number and percentage (%) of MII oocytes with no spindle assembly observed are also indicated below the axis labels in the dashed box. Median (dashed line) and quartiles (dotted line) are indicated. ANOVA statistical analysis found no significant difference (ns, p = 0.1155) between the means of each condition. C Scatterplot projections of oocyte transcriptomes generated from the GV fail-to-mature Signature Score (X axis) and IVF MII Signature Score (Y axis). Symbols are color-coded based on the experimental condition (OSC-IVM, Media-IVM, IVF-MII), and symbol shapes represent oocyte maturation stages (GV, MI, and MII). Each symbol represents one oocyte. Histograms on top depict distribution of MII oocytes across the GV fail-to-mature Signature Score axis. Histograms on the right depict distribution of MII oocytes across the IVF MII Signature Score axis. Histograms are color-coded based on the experimental condition. n = 114 oocytes. D BoxPlot of distribution of MII oocytes across IVF MII Signature Score (left) and GV fail-to-mature Signature Score (right). ANOVA statistical analysis found a significant difference between the OSC-IVM-MII oocytes and Media-IVM MII oocytes (**p = 0.0003) and between the IVF-MII oocytes and Media-IVM oocytes (****p < 0.0001), as well as between the OSC-IVM-MII oocytes and the IVF-MII oocytes (**p < 0.0026)

Fig. 3

MII oocytes treated with OSC-IVM are enriched for genes related to oocyte maturation and embryo development. A Graphical illustration of the strategy to identify transcriptomic profile enrichment during the progression from the germinal vesicle (GV) to MII oocyte. Differentially expressed genes (DEG) were identified by comparing GVs to MII oocytes. B Venn diagram illustrating the gene enrichment in successfully matured MII versus fail-to-mature GVs treated with OSC-IVM versus Media-IVM oocytes. Numbers display the total number of genes identified. Selected functional enrichment analysis terms are shown for each subgroup. See Supplementary Fig. 5 for extended details. C Venn diagram illustrating the gene depletion in successfully matured MII versus fail-to-mature GVs treated with OSC-IVM versus Media-IVM oocytes. Numbers display the total number of genes identified. Selected functional enrichment analysis terms are shown for each subgroup. See Supplementary Fig. 5 for extended details

Fig. 4

Pathway enrichment analysis reveals similarities between MII oocytes rescued from OSC-IVM and IVF-MII oocytes. A Dotplot displaying gene enrichment among Media-IVM MII oocytes, OSC-IVM MII oocytes, and IVF-MII oocytes. The bottom panel shows enrichment of Gene Ontology (GO) terms and KEGG and REACTOME pathways (see an extended version in Supplementary Fig. 7). GO, gene ontology; MF, molecular function; BP, biological process; CC, cellular component; KEGG, KEGG pathway; REAC, Reactome pathway. B Heatmap of Gene Set Enrichment Analysis (GSEA) hallmarks among Media-IVM MII oocytes, OSC-IVM MII oocytes, and IVF-MII oocytes. Heatmap represents row-normalized gene expression using a color gradients scale ranging from higher (red) to lower (blue) relative levels