Effects of C-type natriuretic peptide on meiotic arrest and developmental competence of bovine oocyte derived from small and medium follicles

Effect of biphasic in vitro maturation (CAPA-IVM) on EGF receptor and embryo development of prepubertal goat oocytes according to follicle size

Oocytes spontaneously resume meiosis following their liberation from follicles, preventing full competence acquisition. Biphasic IVM (CAPA-IVM) maintains oocytes in meiotic arrest to improve developmental competence, and it specially affects poorly developed oocytes. We assessed the effect of CAPA-IVM on oocytes from small (<3mm) and large (>3mm) follicles of prepubertal goats. Oocytes were cultured for 6h in pre-IVM with C-type natriuretic peptide (CNP) and estradiol as meiotic inhibitors, and germinal vesicle (GV) rate and chromatin configuration were assessed. Then, oocytes were cultured in conventional IVM (c-IVM) or CAPA-IVM (pre-IVM + c-IVM) and EGF receptor (EGFR) protein expression, intra-oocyte ROS and blastocyst development were assessed. GV rate was higher in CNP groups than control (69% vs 28%, and 67% vs 31%, small and large follicles, respectively), but GV chromatin configuration was similar. In large follicles, EGFR expression was higher in oocytes and cumulus cells after CAPA-IVM, and ROS levels were lower. In small follicles these differences were not observed. c-IVM and CAPA-IVM produced similar blastocyst rates in small (3.7% vs 2.6%, respectively) and large follicles (8.3% vs 2.5%). Overall, CAPA-IVM enhanced EGFR expression for EGF peptide signalling and antioxidant capacity in oocytes from large follicles but oocytes from small follicles were too immature to benefit from it.

Decoding molecular features of bovine oocyte fate during antral follicle growth via single-cell multi-omics analysis†

Antral follicle size is a useful predictive marker of the competency of enclosed oocytes for yielding an embryo following in vitro maturation and fertilization. However, the molecular mechanisms underpinning oocyte developmental potential during bovine antral follicle growth are still unclear. Here, we used a modified single-cell multi-omics approach to analyze the transcriptome, DNA methylome, and chromatin accessibility in parallel for oocytes and cumulus cells collected from bovine antral follicles of different sizes. Transcriptome profiling identified three types of oocytes (small, medium, and large) that underwent different developmental trajectories, with large oocytes exhibiting the largest average follicle size and characteristics resembling metaphase-II oocytes. Differential expression analysis and real-time polymerase chain reaction assay showed that most replication-dependent histone genes were highly expressed in large oocytes. The joint analysis of multi-omics data revealed that the transcription of 20 differentially expressed genes in large oocytes was associated with both DNA methylation and chromatin accessibility. In addition, oocyte-cumulus interaction analysis showed that inflammation, DNA damage, and p53 signaling pathways were active in small oocytes, which had the smallest average follicle sizes. We further confirmed that p53 pathway inhibition in the in vitro maturation experiments using oocytes obtained from small antral follicles could improve the quality of oocytes and increased the blastocyte rate after in vitro fertilization and culture. Our work provides new insights into the intricate orchestration of bovine oocyte fate determination during antral folliculogenesis, which is instrumental for optimizing in vitro maturation techniques to optimize oocyte quality.

C-type natriuretic peptide (CNP): The cardiovascular system and beyond

C-type natriuretic peptide (CNP) represents the 'local' member of the natriuretic peptide family, functioning in an autocrine or paracrine capacity to modulate a hugely diverse portfolio of physiological processes. Whilst the best-characterised of these regulatory roles are in the cardiovascular system, akin to its predominantly endocrine siblings atrial (ANP) and brain (BNP) natriuretic peptides, CNP governs many additional, unrelated mechanisms including bone growth, gamete maturation, auditory processing, and neuronal integrity. Furthermore, there is currently great interest in mimicking the biological activity of CNP for therapeutic gain in many of these disparate organ systems. Herein, we provide an overview of the physiology, pathophysiology and pharmacology of CNP in both cardiovascular and non-cardiovascular settings.

Assessment of differentially expressed genes from in vitro matured human oocytes: A bioinformatics approach

OBJECTIVE

One of the techniques that has gained much attention is the in vitro maturation of oocytes for patients who use assisted reproduction techniques. However, its results are still inferior to controlled ovarian stimulation methodologies. Understanding the maturation mechanisms based on analyses can help improve this methodology's results. The work aims to identify the central genes differentially expressed in oocytes after in vitro maturation in the germinal vesicle and metaphase II stages.

METHODS

This work is a computational analysis. The entire search will be conducted using the Gene Expression Omnibus (GEO) database. To carry out and obtain the data present in the work, an advanced research search was carried out in the GEO database within the period from January 1, 2013, to January 1, 2023. A total of 27 genomic data were available in the GEO database, of which only two were used.

RESULTS

Two datasets were identified on the Gene Expression Omnibus database platform: registration data GSE158802 and GSE95477. From the analysis, we identified five downregulated and thirty-six upregulated genes; the central genes that correlated with the main gene proteins found were CLTA and PANK1.

CONCLUSIONS

There was a differential regulation of gene expression. The most central ones are related to energy capture.

Pre-IVM with C-type natriuretic peptide promotes mitochondrial biogenesis of bovine oocytes via activation of CREB

The aim of this study was to evaluate the effects of C-type natriuretic peptide (CNP) treatment prior to in vitro maturation (IVM) on mitochondria biogenesis in bovine oocyte matured in vitro and explore the related causes. The results showed that treatment with CNP before IVM significantly improved mitochondrial content, elevated the expression of genes related to mitochondria biogenesis, and increased the protein levels of phosphorylation of cAMP-response element binding protein (p-CREB) in bovine oocytes following IVM. However, further studies revealed that treatment with CNP before IVM could not increased the protein levels of p-CREB in bovine oocytes when natriuretic peptide receptor 2 activities was inhibited using the relative specific inhibitor Gö6976. In addition, treatment with CNP before IVM could not improved mitochondrial content or elevated the expression of genes related to mitochondria biogenesis in bovine oocytes when CREB activities was abolished using the specific inhibitor 666-15. In summary, these results provide evidence that treatment of bovine oocytes with CNP before IVM promotes mitochondrial biogenesis in vitro, possibly by activating CREB.

Factors defining developmental competence of bovine oocytes collected for in vitro embryo production†

Despite the currently relatively low effectiveness of producing bovine embryos in vitro, there is a growing interest in applying this laboratory method in the field of reproduction. Many aspects of the procedure need to be improved. One of the main problems is the inferior developmental competence of in vitro matured oocytes that are collected using the ovum pick-up method. The mechanisms of oocyte capacitation and maturation, as well as the in vivo conditions in which they grow and mature, should be carefully analyzed. A deliberate application of the identified mechanisms and beneficial factors affecting the in vitro procedures seems to be essential for achieving higher developmental competence of the oocytes that are subjected to fertilization. The results may be improved by developing and employing a laboratory maturation protocol that corresponds with appropriate preparation of donors before the ovum pick-up, an optimized hormonal treatment program, the appropriate size of ovarian follicles at the time of aspiration, and a fine-tuned coasting period.

NPPC and AREG supplementation in IVM systems alter mRNA translation and decay programs-related gene expression in bovine COC

During oocyte meiosis resumption, a coordinated program of transcript translation and decay machinery promotes a remodeling of mRNA stores, which determines the success of the acquisition of competence and early embryo development. We investigated levels of two genes related to mRNA translation (CPEB1 and CPEB4) and two related to mRNA degradation (CNOT7 and ZFP36L2) machinery and found ZFP36L2 downregulated in in vitro-matured bovine oocytes compared to in vivo counterparts. Thereafter, we tested the effects of a pre-IVM step with NPPC and a modified IVM with AREG on the modulation of members of mRNA translation and degradation pathways in cumulus cells and oocytes. Our data showed a massive upregulation of genes associated with translational and decay processes in cumulus cells, promoted by NPPC and AREG supplementation, up to 9h of IVM. The oocytes were less affected by NPPC and AREG, and even though ZFP36L2 transcript and protein levels were downregulated at 9 and 19h of IVM, only one (KDM4C) from the ten target genes evaluated was differently expressed in these treatments. These data suggest that cumulus cells are more prone to respond to NPPC and AREG supplementation in vitro, regarding translational and mRNA decay programs. Given the important nursing role of these cells, further studies could contribute to a better understanding of the impact of these modulators in maternal mRNA modulation and improve IVM outcomes.

A fresh start for IVM: capacitating the oocyte for development using pre-IVM

BACKGROUND

While oocyte IVM is practiced sporadically it has not achieved widespread clinical practice globally. However, recently there have been some seminal advances in our understanding of basic aspects of oocyte biology and ovulation from animal studies that have led to novel approaches to IVM. A significant recent advance in IVM technology is the use of biphasic IVM approaches. These involve the collection of immature oocytes from small antral follicles from minimally stimulated patients/animals (without hCG-priming) and an ∼24 h pre-culture of oocytes in an advanced culture system ('pre-IVM') prior to IVM, followed by routine IVF procedures. If safe and efficacious, this novel procedure may stand to make a significant impact on human ART practices.

OBJECTIVE AND RATIONALE

The objectives of this review are to examine the major scientific advances in ovarian biology with a unique focus on the development of pre-IVM methodologies, to provide an insight into biphasic IVM procedures, and to report on outcomes from animal and clinical human data, including safety data. The potential future impact of biphasic IVM on ART practice is discussed.

SEARCH METHODS

Peer review original and review articles were selected from PubMed and Web of Science searches for this narrative review. Searches were performed using the following keywords: oocyte IVM, pre-IVM, biphasic IVM, CAPA-IVM, hCG-triggered/primed IVM, natural cycle IVF/M, ex-vivo IVM, OTO-IVM, oocyte maturation, meiotic competence, oocyte developmental competence, oocyte capacitation, follicle size, cumulus cell (CC), granulosa cell, COC, gap-junction communication, trans-zonal process, cAMP and IVM, cGMP and IVM, CNP and IVM, EGF-like peptide and IVM, minimal stimulation ART, PCOS.

OUTCOMES

Minimizing gonadotrophin use means IVM oocytes will be collected from small antral (pre-dominant) follicles containing oocytes that are still developing. Standard IVM yields suboptimal clinical outcomes using such oocytes, whereas pre-IVM aims to continue the oocyte's development ex vivo, prior to IVM. Pre-IVM achieves this by eliciting profound cellular changes in the oocyte's CCs, which continue to meet the oocyte's developmental needs during the pre-IVM phase. The literature contains 25 years of animal research on various pre-IVM and biphasic IVM procedures, which serves as a large knowledge base for new approaches to human IVM. A pre-IVM procedure based on c-type natriuretic peptide (named 'capacitation-IVM' (CAPA-IVM)) has undergone pre-clinical human safety and efficacy trials and its adoption into clinical practice resulted in healthy live birth rates not different from conventional IVF.

WIDER IMPLICATIONS

Over many decades, improvements in clinical IVM have been gradual and incremental but there has likely been a turning of the tide in the past few years, with landmark discoveries in animal oocyte biology finally making their way into clinical practice leading to improved outcomes for patients. Demonstration of favorable clinical results with CAPA-IVM, as the first clinically tested biphasic IVM system, has led to renewed interest in IVM as an alternative, low-intervention, low-cost, safe, patient-friendly ART approach, and especially for patients with PCOS. The same new approach is being used as part of fertility preservation in patients with cancer and holds promise for social oocyte freezing.

C-Type Natriuretic Peptide Pre-Treatment Improves Maturation Rate of Goat Oocytes by Maintaining Transzonal Projections, Spindle Morphology, and Mitochondrial Function

C-type natriuretic peptide (CNP) is a peptide molecule naturally found in follicles and can be used to extend meiotic resumption and enhance the potential for oocytes to develop. However, the mechanism by which CNP improves goat oocyte quality remains unclear. In this study, cumulus-oocyte complexes (COCs) from goats were pre-treated with CNP prior to IVM, and the results showed that pre-treatment with CNP enhanced goat oocyte maturation. First, we discovered that CNP maintained communication between cumulus cells and oocytes by regulating the transzonal projections (TZPs). We then found that CNP treatment reduced abnormal spindle formation and increased the expression of genes associated with spindle assembly and the spindle assembly checkpoint. Moreover, further analysis showed that oocytes exhibited better antioxidant ability in the CNP treatment group, which mainly manifested in higher glutathione (GSH) and lower reactive oxygen species (ROS) concentrations. Enhanced mitochondrial activity was signified via the augmented expression of mitochondrial oxidative metabolism and fusion and fission-related genes, thus diminishing the apoptosis of the oocytes. Overall, these results provide novel insights into the potential mechanism by which CNP treatment before IVM can improve oocyte quality.

Treatment of cattle oocytes with C-type natriuretic peptide before in vitro maturation enhances oocyte mitochondrial function

The present study was conducted to evaluate the effects in vitro on oocyte mitochondrial function of C-type natriuretic peptide (CNP) when treatments were imposed before in vitro maturation (IVM). Immature oocytes were either directly matured in vitro for 24 h (Control, no pre-IVM), or cultured in basic medium not supplemented or supplemented with CNP (100 nM) (Control pre-IVM and CNP pre-IVM, respectively) for 6 h, followed by IVM for 24 h. The results indicated treatment with CNP before IVM affected patterns of distribution of mitochondria, increased the mitochondrial content, membrane potential, and decreased the ROS content in cattle oocytes before and after IVM. Furthermore, treatment of immature cattle oocytes with CNP before IVM induced marked increases in the relative abundance of mRNA transcripts and proteins related to mitochondria development and antioxidative defense mechanisms. Treatment with CNP before oocyte IVM also resulted in an enhanced relative abundance of sirtuin-1 (SIRT1) mRNA transcript in cattle oocytes. Taken together, these results provide evidence that treatment of cattle oocytes with CNP before IVM improved mitochondrial function and antioxidant defense mechanisms in cattle oocytes. Findings in the present study provide insights into the potential mechanisms by which CNP has positive effects on oocyte cytoplasmic organelles, specifically mitochondria.