BACKGROUND Fertility loss during female ageing is associated with increasing basal FSH and decreasing anti-Müllerian hormone (AMH) concentrations, together with compromised oocyte quality, presumably due to increased oxidative stress (OS) and DNA damage, as well as reduced metabolic and meiotic competences. Basal FSH and AMH circulatory concentrations have been broadly utilized as IVF success predictors, regardless of fluctuations in prognostic accuracy; basal FSH and AMH perform better in pre-advanced maternal age (AMA: >35 years) and AMA patients, respectively. The relationships between FSH and AMH intrafollicular levels and IVF outcomes suggest, nevertheless, that both hormones regulate oocyte competence, supporting the hypothesis that changes in FSH/AMH levels cause, at least in part, oocyte quality degradation during ageing. To understand the reasons behind the fluctuations in FSH and AMH prognostic accuracies and to clarify their participation in mechanisms determining oocyte competence and age-related subfertility, a deeper knowledge of the regulation of FSH and AMH intrafollicular signalling during the female reproductive lifespan, and of their effects on the cumulus–oocyte complex, is required. OBJECTIVE AND RATIONALE An extensive body of information on the regulation of FSH and AMH intrafollicular availability and signalling, as well as on the control of folliculogenesis and oocyte metabolism, has been accumulated. However, these datasets have been explored within the relatively narrow boundaries of their specific subjects. Given the aforementioned gaps in knowledge and their clinical relevance, herein we integrate clinical and basic data, within a wide biological perspective, aiming to shed light on (i) the reasons for the variability in the accuracy of serum FSH and AMH as fertility markers, and on (ii) the potential roles of these hormones in mechanisms regulating oocyte quality, particularly those associated with ageing. SEARCH METHODS The PubMed database encompassing the period between 1960 and 2021 was searched. Principal search terms were FSH, FSH receptor, AMH, oocyte, maternal age, cumulus, transzonal projections (TZPs), actin, OS, redox, reactive oxygen species, mitochondria, DNA damage, DNA repair, aneuploidy, spindle, meiosis, gene expression, transcription, translation, oocyte secreted factors (OSFs), cAMP, cyclic guanosine monophosphate, natriuretic peptide C, growth differentiation factor 9, bone morphogenetic protein 15 and fibroblast growth factor. OUTCOMES Our analysis suggests that variations in the accuracy of fertility prognosis reflect a modest association between circulatory AMH levels and oocyte quality as well as increasing basal FSH inter-cycle variability with age. In addition, the basic and clinical data articulated herein support the hypothesis that increased intrafollicular FSH levels, as maternal age advances, may override the physiological protective influences of AMH and OSFs against excessive FSH signalling in cumulus cells. This would result in the disruption of oocyte homeostasis via reduced TZP-mediated transfer of cumulus-derived molecules essential for meiotic competence, gene expression, redox activity and DNA repair. WIDER IMPLICATIONS In-depth data analysis, encompassing a wide biological perspective has revealed potential causative mechanisms of age-related subfertility triggered by alterations in FSH/AMH signalling during the female reproductive life. Insights from new mechanistic models arising from this analysis should contribute to advancing our comprehension of oocyte biology in humans and serve as a valuable reference for novel AMA subfertility treatments aimed at improving oocyte quality through the modulation of AMH/FSH action.

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In vitro maturation (IVM) has been applied in numerous different contexts and strategies in humans and animals, but in both cases it represents a challenge still far from being overcome. Despite the large dataset produced over the last two decades on the mechanisms that govern antral follicular development and oocyte metabolism and differentiation, IVM outcomes are still unsatisfactory. This review specifically focuses on data concerning the potential consequences of using supraphysiological levels of FSH during IVM, as well as on the regulation of oocyte chromatin dynamics and its utility as a potential marker of oocyte developmental competence. Taken together, the data revisited herein indicate that a significant improvement in IVM efficacy may be provided by the integration of pre-OPU patient-specific protocols preparing the oocyte population for IVM and more physiological culture systems mimicking more precisely the follicular environment that would be experienced by the recovered oocytes until completion of metaphase II.

Study question Does the oocyte control the expression of genes regulating the ovulatory cascade and the formation of the extracellular matrix in cumulus cells? Summary answer Oocyte secreted factors (OSFs) suppress the expression of prostaglandin synthase-2 (PTGS2) in cumulus cells, a key mediator of the maturation cascade. What is known already Oocyte quality depends on cytoplasmic and nuclear maturation synchrony. OSFs modulate maturation dynamics by inhibiting the expression of AREG (amphiregulin) and EREG (epiregulin), key mediators of the ovulatory cascade. AREG and EREG stimulate PTGS2 expression in cumulus cells, which catalyses the synthesis of prostaglandins, that amplify and translate AREG/EREG signals leading to meiotic completion and expression of genes required for cumulus expansion, among which HAS2 (hyaluronan synthase-2), essential for the synthesis of hyaluronan, the backbone of cumulus extracellular matrix, as well as PTX3 (pentraxin 3) and TNFAIP6 (tumor necrosis factor alpha-induced protein 6), genes encoding for matrix structural proteins. Study design, size, duration Relative mRNA levels of PTGS2, HAS2, PTX3 and TNFAIP6 were compared in cumulus cells from 3 treatment-groups: 1-COC: Intact cumulus-oocyte complexes subjected to in vitro maturation (IVM); 2-OOX: oocytectomized COC subjected to IVM; 3-OOX+DO: OOX subjected to IVM with the addition of denuded oocytes (1 DO/µL). Four experimental replicates including all three treatment-groups were performed. The inclusion of OOX+DO aimed to assess whether the effects of the oocyte on gene expression are mediated by OSFs. Participants/materials, setting, methods COC were aspirated from 3-8mm follicles of bovine ovaries. Oocytectomy was achieved by ooplasm aspiration with a micromanipulator. Pools of 20 COCs/OOX/OOX+DO were cultured for 22 hours in TCM199 with 100ng/mL AREG and 0.4% BSA. Subsequently, cumulus cells were separated, total RNA extracted, and mRNA abundance assessed by real-time RT-PCR with oligo-dT primers and two internal controls for relative quantification. Treatment effects were tested by ANOVA and groups were compared with the Tukey test. Main results and the role of chance Oocyctectomy drastically increased PTGS2 mRNA abundance, which was reversed by the addition of denuded oocytes (DO) to culture. Relative PTGS2 mRNA levels (mean ± EPM) were 1.02 ± 0.12, 10.40 ± 1.65 and 0.88 ± 0.08 for COC, OOX and OOX+DO, respectively (P = 0.02). Consistently, although in a lower magnitude, oocytectomy increased mRNA levels of PTX3(1.00 ± 0.04, 2.50 ± 0.18 and 0.75 ± 0.15 for COC, OOX and OOX+DO, respectively. P < 0.001) and TNFAIP6 (1.00 ± 0.07, 2.04 ± 0.17 and 0.67 ± 0.04 for COC, OOX and OOX+DO, respectively. P < 0.001), an effect again reversed by the presence of DO in culture. In contrast, oocytectomy decreased the expression of HAS2, which was neutralised in the presence of DO (1.01 ± 0.09, 0.69 ± 0.02 and 1.11 ± 0.08 for COC, OOX and OOX+DO, respectively. P = 0.005). Our data indicate that the oocyte modulates its own maturation pace by inhibiting the expression of PTGS2, which is accompanied by similar negative impacts on genes that strongly respond to prostaglandin signalling such as PTX3 and TNFAIP6. In parallel, our data suggest that OSFs exert a potent stimulatory effect on HAS2 transcription, capable to overcome their concomitant inhibitory influence via supressed AREG/EREG and PTGS2 expression. Limitations, reasons for caution Our study utilised animal and culture models that may not exactly represent human COC physiological maturation. In addition, our data are restricted to mRNA levels. Nevertheless, somatic cells predominantly transcribe poly A-mRNA that is promptly exported and translated. Accordingly, our RT-PCR strategy utilised poly-A reverse transcription with oligo-dT primers. Wider implications of the findings Our data indicate that OSFs inhibit the expression of PTGS2, a key gene for activation and amplification of the maturation cascade in cumulus cells. We speculate that this may represent an effort of the oocyte to prevent precocious meiotic resumption, thus favouring nuclear and cytoplasmic maturation synchrony and developmental competence. Trial registration number Not applicable

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