Inducible nitric oxide synthase and heme oxygenase 1 are expressed in human cumulus cells and may be used as biomarkers of oocyte competence

Bilirubin Concentration in Follicular Fluid Is Increased in Infertile Females, Correlates with Decreased Antioxidant Levels and Increased Nitric Oxide Metabolites, and Negatively Affects Outcome Measures of In Vitro Fertilization

In a previous study, we showed that various low-molecular-weight compounds in follicular fluid (FF) samples of control fertile females (CFF) have different concentrations compared to those found in FF of infertile females (IF), before and after their categorization into different subgroups, according to their clinical diagnosis of infertility. Using the same FF samples of this previous study, we here analyzed the FF concentrations of free and bound bilirubin and compared the results obtained in CFF, IF and the different subgroups of IF (endometriosis, EM, polycystic ovary syndrome, PCOS, age-related reduced ovarian reserve, AR-ROR, reduced ovarian reserve, ROR, genetic infertility, GI and unexplained infertility, UI). The results clearly indicated that CFF had lower values of free, bound and total bilirubin compared to the respective values measured in pooled IF. These differences were observed even when IF were categorized into EM, PCOS, AR-ROR, ROR, GI and UI, with EM and PCOS showing the highest values of free, bound and total bilirubin among the six subgroups. Using previous results of ascorbic acid, GSH and nitrite + nitrate measured in the same FF samples of the same FF donors, we found that total bilirubin in FF increased as a function of decreased values of ascorbic acid and GSH, and increased concentrations of nitrite + nitrate. The values of total bilirubin negatively correlated with the clinical parameters of fertilization procedures (number of retrieved oocytes, mature oocytes, fertilized oocytes, blastocysts, high-quality blastocysts) and with clinical pregnancies and birth rates. Bilirubin concentrations in FF were not linked to those found in serum samples of FF donors, thereby strongly suggesting that its over production was due to higher activity of heme oxygenase-1 (HO-1), the key enzyme responsible for bilirubin formation, in granulosa cells, or cumulus cells or oocytes of IF and ultimately leading to bilirubin accumulation in FF. Since increased activity of HO-1 is one of the main enzymatic intracellular mechanisms of defense towards external insults (oxidative/nitrosative stress, inflammation), and since we found correlations among bilirubin and oxidative/nitrosative stress in these FF samples, it may reasonably be supposed that bilirubin increase in FF of IF is the result of protracted exposures to the aforementioned insults evidently playing relevant roles in female infertility.

The expression levels of NOS2, HMOX1, and VEGFC in cumulus cells are markers of oocyte maturation and fertilization rate

Throughout the reproductive life of women, cumulus cells (CC) protect the dormant oocyte from damage, act as sensors of the follicular microenvironment, and act as a gatekeeper for oocyte developmental potential. One such mechanism relies on the hypoxia-tolerance response, which, with age, decreases systematically, including in the ovary. We aimed to evaluate the association between gene expression related to hypoxia and aging in CC and reproductive results in in vitro fertilization cycles. We recruited 94 women undergoing controlled ovarian stimulation. Total RNA was extracted from pooled CCs collected after oocyte pick-up (OPU) and reverse-transcribed to complementary DNA using random hexamers to test 14 genes related to hypoxia response via HIF1α activation, oxidative stress, and angiogenic responses. The expression of CLU, NOS2, and TXNIP had a positive correlation with age (rs  = 0.25, rs  = 0.24, and rs  = 0.35, respectively). Additionally, NOS2 and HMOX1 expression correlated positively with the retrieval of immature oocytes (rs  = 0.22 and rs  = 0.40, respectively). Moreover, VEGFC levels decreased overall with increasing fertilization rate, independently of age (rs  = -0.29). We found that the fertilization potential of a cohort of oocytes is related to the ability of CC to respond to oxidative stress and hypoxia with age, pointing at NOS2, HMOX1, and VEGFC expression as markers for oocyte maturation and fertilization success.

Cumulus Cell Transcriptome after Cumulus-Oocyte Complex Exposure to Nanomolar Cadmium in an In Vitro Animal Model of Prepubertal and Adult Age

Cadmium (Cd), a highly toxic pollutant, impairs oocyte fertilization, through oxidative damage on cumulus cells (CCs). This study analysed the transcriptomic profile of CCs of cumulus-oocyte complexes (COCs) from adult and prepubertal sheep, exposed to Cd nanomolar concentration during in vitro maturation. In both age-groups, CCs of matured oocytes underwent RNA-seq, data analysis and validation. Differentially expressed genes (DEGs) were identified in adult (n = 99 DEGs) and prepubertal (n = 18 DEGs) CCs upon Cd exposure. Transcriptomes of adult CCs clustered separately between Cd-exposed and control samples, whereas prepubertal ones did not as observed by Principal Component Analysis. The transcriptomic signature of Cd-induced CC toxicity was identified by gene annotation and literature search. Genes associated with previous studies on ovarian functions and/or Cd effects were confirmed and new genes were identified, thus implementing the knowledge on their involvement in such processes. Enrichment and validation analysis showed that, in adult CCs, Cd acted as endocrine disruptor on DEGs involved in hormone biosynthesis, cumulus expansion, regulation of cell signalling, growth and differentiation and oocyte maturation, whereas in prepubertal CCs, Cd affected DEGs involved in CC development and viability and CC-oocyte communications. In conclusion, these DEGs could be used as valuable non-invasive biomarkers for oocyte competence.

Cumulus cell antioxidant system is modulated by patients' clinical characteristics and correlates with embryo development

PURPOSE

To study whether the cumulus cell antioxidant system varies accordingly to patients clinical characteristics' as age, infertility diagnosis, BMI, and stimulation protocol applied and if the antioxidant profile of cumulus cells could be used as a predictor of embryo development.

METHODS

A prospective study including 383 human cumulus samples provided by 191 female patients undergoing intracytoplasmic sperm injection during in vitro fertilization treatments from a local in vitro fertilization center and processed in university laboratories. Catalase (CAT), superoxide dismutase (SOD), glutathione peroxidase (GPx), and glutathione S-transferase (GST) enzyme activity levels and reduced glutathione (GSH) levels were measured in cumulus oophorus cells individually collected from each aspirated cumulus-oocyte complex, and the results of each sample were compared considering the oocytes outcome after ICSI and patients clinical characteristics. A total of 223 other human cumulus samples from previous studies were submitted to a gene expression meta-analysis.

RESULTS

The antioxidant system changes dramatically depending on patients' age, infertility diagnosis, stimulation protocol applied, and oocyte quality. SOD activity in cumulus cells revealed to be predictive of top-quality blastocysts for young patients with male factor infertility (P < 0.05), while GST levels were shown to be extremely influenced by infertility cause (P < 0.0001) and stimulation protocol applied (P < 0.05), but nonetheless, it can be used as a complementary tool for top-quality blastocyst prediction in patients submitted to intracytoplasmic sperm injection technique (ICSI) by male factor infertility (P < 0.05).

CONCLUSION

Through a simple and non-invasive analysis, the evaluation of redox enzymes in cumulus cells could be used to predict embryo development, in a personalized matter in specific patient groups, indicating top-quality oocytes and improving success rates in in vitro fertilization treatments.

TRIAL REGISTRATION

The trial was registered at UFRGS Research Ethics Committee and Plataforma Brasil under approval number 68081017.2.0000.5347 in June 6, 2019.

The Role of Nitric Oxide in Stem Cell Biology

Nitric oxide (NO) is a gaseous biomolecule endogenously synthesized with an essential role in embryonic development and several physiological functions, such as regulating mitochondrial respiration and modulation of the immune response. The dual role of NO in embryonic stem cells (ESCs) has been previously reported, preserving pluripotency and cell survival or inducing differentiation with a dose-dependent pattern. In this line, high doses of NO have been used in vitro cultures to induce focused differentiation toward different cell lineages being a key molecule in the regenerative medicine field. Moreover, optimal conditions to promote pluripotency in vitro are essential for their use in advanced therapies. In this sense, the molecular mechanisms underlying stemness regulation by NO have been studied intensively over the current years. Recently, we have reported the role of low NO as a hypoxia-like inducer in pluripotent stem cells (PSCs), which supports using this molecule to maintain pluripotency under normoxic conditions. In this review, we stress the role of NO levels on stem cells (SCs) fate as a new approach for potential cell therapy strategies. Furthermore, we highlight the recent uses of NO in regenerative medicine due to their properties regulating SCs biology.

Molecular Drivers of Developmental Arrest in the Human Preimplantation Embryo: A Systematic Review and Critical Analysis Leading to Mapping Future Research

Developmental arrest of the preimplantation embryo is a multifactorial condition, characterized by lack of cellular division for at least 24 hours, hindering the in vitro fertilization cycle outcome. This systematic review aims to present the molecular drivers of developmental arrest, focusing on embryonic and parental factors. A systematic search in PubMed/Medline, Embase and Cochrane-Central-Database was performed in January 2021. A total of 76 studies were included. The identified embryonic factors associated with arrest included gene variations, mitochondrial DNA copy number, methylation patterns, chromosomal abnormalities, metabolic profile and morphological features. Parental factors included, gene variation, protein expression levels and infertility etiology. A valuable conclusion emerging through critical analysis indicated that genetic origins of developmental arrest analyzed from the perspective of parental infertility etiology and the embryo itself, share common ground. This is a unique and long-overdue contribution to literature that for the first time presents an all-inclusive methodological report on the molecular drivers leading to preimplantation embryos’ arrested development. The variety and heterogeneity of developmental arrest drivers, along with their inevitable intertwining relationships does not allow for prioritization on the factors playing a more definitive role in arrested development. This systematic review provides the basis for further research in the field.

The effect of carbon monoxide on meiotic maturation of porcine oocytes

Oxidative stress impairs the correct course of meiotic maturation, and it is known that the oocytes are exposed to increased oxidative stress during meiotic maturation in in vitro conditions. Thus, reduction of oxidative stress can lead to improved quality of cultured oocytes. The gasotransmitter carbon monoxide (CO) has a cytoprotective effect in somatic cells. The CO is produced in cells by the enzyme heme oxygenase (HO) and the heme oxygenase/carbon monoxide (HO/CO) pathway has been shown to have an antioxidant effect in somatic cells. It has not yet been investigated whether the CO has an antioxidant effect in oocytes as well. We assessed the level of expression of HO mRNA, using reverse transcription polymerase chain reaction. The HO protein localization was evaluated by the immunocytochemical method. The influence of CO or HO inhibition on meiotic maturation was evaluated in oocytes cultured in a culture medium containing CO donor (CORM-2 or CORM-A1) or HO inhibitor Zn-protoporphyrin IX (Zn-PP IX). Detection of reactive oxygen species (ROS) was performed using the oxidant-sensing probe 2′,7′-dichlorodihydrofluorescein diacetate. We demonstrated the expression of mRNA and proteins of both HO isoforms in porcine oocytes during meiotic maturation. The inhibition of HO enzymes by Zn-PP IX did not affect meiotic maturation. CO delivered by CORM-2 or CORM-A1 donors led to a reduction in the level of ROS in the oocytes during meiotic maturation. However, exogenously delivered CO also inhibited meiotic maturation, especially at higher concentrations. In summary, the CO signaling molecule has antioxidant properties in porcine oocytes and may also be involved in the regulation of meiotic maturation.

Novel Insights on the Role of Nitric Oxide in the Ovary: A Review of the Literature

Nitric oxide (NO) is formed during the oxidation of L-arginine to L-citrulline by the action of multiple isoenzymes of NO synthase (NOS): neuronal NOS (nNOS), endotelial NOS (eNOS), and inducible NOS (iNOS). NO plays a relevant role in the vascular endothelium, in central and peripheral neurons, and in immunity and inflammatory systems. In addition, several authors showed a consistent contribution of NO to different aspects of the reproductive physiology. The aim of the present review is to analyse the published data on the role of NO within the ovary. It has been demonstrated that the multiple isoenzymes of NOS are expressed and localized in the ovary of different species. More to the point, a consistent role was ascribed to NO in the processes of steroidogenesis, folliculogenesis, and oocyte meiotic maturation in in vitro and in vivo studies using animal models. Unfortunately, there are few nitric oxide data for humans; there are preliminary data on the implication of nitric oxide for oocyte/embryo quality and in-vitro fertilization/embryo transfer (IVF/ET) parameters. NO plays a remarkable role in the ovary, but more investigation is needed, in particular in the context of human ovarian physiology.

Effect of a Combination of Myo-Inositol, Alpha-Lipoic Acid, and Folic Acid on Oocyte Morphology and Embryo Morphokinetics in non-PCOS Overweight/Obese Patients Undergoing IVF: A Pilot, Prospective, Randomized Study

Herein we aimed at assessing whether Myo-Inositol (MI), Alpha–Lipoic acid (ALA), and Folic acid (FA) could improve oocyte quality and embryo development in non-PCOS overweight/obese women undergoing IVF. Three hundred and twenty-four mature oocytes were obtained from non-PCOS overweight/obese patients, randomized to receive either MI, ALA, and FA (MI + ALA + FA group, n = 155 oocytes) or FA alone (FA-only group, n = 169 oocytes). Oocytes were examined using Polarized Light Microscopy to assess morphological features of zona pellucida (ZP) and meiotic spindle (MS). One hundred and seventy-six embryos (n = 84 in the MI + ALA + FA group, n = 92 in the FA-only group) were assessed by conventional morphology on days 2 and 5, as well as using the Time-Lapse System morphokinetic analysis. A significantly higher ZP retardance, area, and thickness (p < 0.05), and a shorter MS axis (p < 0.05) were observed in the MI + ALA + FA group, suggesting a positive effect on oocyte quality. Conventional morphology evaluation on day 2 showed a higher mean embryo score in the MI + ALA + FA group, whereas embryo morphokinetic was comparable in the two groups. Overall, our data show a possible beneficial effect of the combination of MI, ALA, and FA on oocyte and embryo morphology, encouraging testing of this combination in adequately powered randomized trials to assess their impact of clinical IVF results.

Human recombinant FSH induces chemoresistance in human breast cancer cells via HIF-1α activation†

Breast cancer patients under 40 years of age who are candidate to chemotherapy with alkylating drugs may undergo controlled ovarian stimulation (COS) with recombinant human follicle-stimulating hormone (rhFSH) in order to get fertility preservation by mature oocyte cryostorage. The direct effect(s) of exogenous rhFSH on the chemosensitivity of breast cancer is currently unknown. To clarify this issue, we incubated four different breast cancer cell lines with rhFSH (10 IU/L, 24 h) and then we exposed them to doxorubicin (DOX) or cyclophosphamide (CPA). The effect(s) of rhFSH on human breast cancer cells treated with DOX or CPA was measured in terms of (1) cell viability, (2) cytotoxicity, (3) multidrug resistance (MDR) genes and proteins expression and activities, and (4) hypoxia-inducible factor 1-alpha (HIF-1α) activation. Pretreatment with rhFSH significantly increased the viability of breast cancer cells after treatment with DOX or CPA, and reduced the lactate dehydrogenase leakage and reactive oxygen species production. Moreover, after preincubation with rhFSH, the MDR proteins (Pgp, MPR1, and BCRP) expression and activity resulted upregulated and the HIF-1α pathway activated. In addition, the use of a widely used HIF-1α inhibitor, the 3-(5'-hydroxymethyl-2'-furyl)-1-benzylindazole (YC-1), prevented the rhFSH effect on the onset of MDR. Taken together, these observations suggest that a short exposure to rhFSH induces chemoresistance to DOX and CPA in human breast cancer cells via HIF-1α activation.

Melatonin Inhibits Oxidative Stress and Apoptosis in Cryopreserved Ovarian Tissues via Nrf2/HO-1 Signaling Pathway

In the field of assisted reproductive technology, female fertility preservation, particularly ovarian tissue cryopreservation in adolescent cancer patients, has attracted much attention. Melatonin (MLT) is well known for its antioxidative and anti-apoptotic properties; however, whether it can ameliorate the cryoinjury and inhibit the generation of reactive oxygen species (ROS) in cryopreserved ovarian tissues (OTs) has not yet been reported. Here, we demonstrated that MLT could protect follicular integrity; prevent cell apoptosis; decrease ROS, malondialdehyde (MDA), and nitric oxide (NO) levels; and increase activities of glutathione peroxidases (GSH-Px), glutathione (GSH), catalase (CAT), and superoxide dismutase (SOD) in cryopreserved OTs. Furthermore, these effects may be related with the activation of the nuclear factor erythroid 2-related factor 2 (Nrf2) signaling pathway, as evidenced by increased mRNA levels of Nrf2 downstream genes, including heme oxygenase-1 (HO-1), glutathione S-transferase M1 (GSTM1), SOD, and CAT. In summary, MLT can not only directly scavenge ROS but also significantly induce the activation of antioxidative enzymes via the Nrf2 signaling pathway, which is a new mechanism underlying the protection effects of MLT on cryopreserved OTs.

Induction of oxidative stress does not increase the cryotolerance of vitrified embryos

Short-term treatment of mammalian oocytes with different stressors induces stress tolerance of embryos derived from these oocytes. The aims of this study were to evaluate effects on embryo development when there was treatment of oocyte complexes (COCs) used to derive the embryos with hydrogen peroxide (H₂O₂).The COCs were not incubated with H₂O₂: control (0 μM), or were incubated with 25, 50, 75, or 100 μM concentrations of H₂O₂ for 1 h prior to in vitro fertilization, and presumptive zygotes were cultured until day 7. Blastocysts at day 7 of development derived from H₂O₂-treated (25 μM treatment concentration) COCs were vitrified. Percentage of embryos undergoing cleavage was not affected by any treatment, while percentage of embryos developing to the blastocyst stage was less when there was treatment of COCs with 100 μM of H₂O₂. Embryo quality was less when COCs used to derive blastocysts were treated with 50, 75, or 100 μM concentrations of H₂O₂. There were lesser relative abundances of some mRNA transcripts of interest in blastocysts when there was treatment of COCs with H₂O₂. After vitrification, there were no differences in embryo re-expansion and hatching rates compared with fresh and vitrified blastocysts of the control group and those derived from COCs treated with 25 μM H₂O₂. In conclusion, treatment of COCs used to derive blastocysts with H₂O₂ does not induce stress tolerance in vitrified embryos of cattle; however, the viability of these blastocysts is similar to those of the control group.

Morphokinetic analysis of cleavage stage embryos and assessment of specific gene expression in cumulus cells independently predict human embryo development to expanded blastocyst: a preliminary study

To assess whether morphokinetic features at the cleavage stage together with specific gene expression in cumulus cells (CCs) may be used to predict whether human embryos are able to achieve the expanded blastocyst stage on day 5. Eighty-one embryos were cultured using the Geri plus® time-lapse system. Twenty-seven embryos progressing to the expanded blastocyst stage (BL group) were compared with thirty-five embryos showing developmental arrest (AR group) and nineteen reaching the stage of early or not fully expanded blastocyst (nBL group). The analyzed morphokinetic variables were pronuclear appearance (tPNa), pronuclear fading (tPNf), and completion of cleavage to two, three, four, and eight cells (t2, t3, t4, and t8). CCs were analyzed by RT-qPCR for bone morphogenetic protein 15 (BMP15), cytochrome c oxidase subunit II (COXII), ATP synthase subunit 6 (MT-ATP6), connexin 43 (Cx43), and heme oxygenase-1 (HO-1). Embryos of BL group showed a significantly faster kinetic. BMP15, COXII, and MT-ATP6 mRNA expression was significantly higher in CCs of BL group embryos, whereas Cx43 and HO-1 mRNA levels were higher in AR group. Kinetic parameters and gene expression were not significantly different between either the BL and nBL groups or the AR and nBL groups. ROC curves showed that the most predictive cut-offs were t2 < 26.25 for morphokinetics and COXII > 0.3 for gene expression. Multivariable logistic regression analysis showed that morphokinetic variables and gene expression were both valuable, independent predictors of embryo development to expanded blastocyst. Our results suggest the possibility of developing integrated prediction models for early embryo selection at the cleavage stage.

Redox Biology of Human Cumulus Cells: Basic Concepts, Impact on Oocyte Quality, and Potential Clinical Use

Significance: Four decades have passed since the first successful human embryo conceived from a fertilization in vitro. Despite all advances, success rates in assisted reproduction techniques still remain unsatisfactory and it is well established that oxidative stress can be one of the major factors causing failure in in vitro fertilization (IVF) techniques. Recent Advances: In the past years, researchers have been shown details of the supportive role CCs play along oocyte maturation, development, and fertilization processes. Regarding redox metabolism, it is now evident that the synergism between gamete and somatic CCs is fundamental to further support a healthy embryo, since the oocyte lacks several defense mechanisms that are provided by the CCs. Critical Issues: There are many sources of reactive oxygen species (ROS) in the female reproductive tract in vivo that can be exacerbated (or aggravated) by pathological features. While an imbalance between ROS and antioxidants can result in oxidative damage, physiological levels of ROS are essential for oocyte maturation, ovulation, and early embryonic growth where they act as signaling molecules. At the event of an assisted reproduction procedure, the cumulus/oophorus complex is exposed to additional sources of oxidative stress in vitro. The cumulus cells (CCs) play essential roles in protecting the oocytes from oxidative damage. Future Directions: More studies are needed to elucidate redox biology in human CCs and oocyte. Also, randomized controlled trials will identify possible benefits of in vivo or in vitro administration of antioxidants for patients seeking IVF procedure.

Contributions from the ovarian follicular environment to oocyte function

The magnitude of oocyte's role for embryo development is categorical. This unique cell contains the machineries and cellular components necessary to remodel male and female chromatin, to sustain early development and to, ultimately, generate a complete and complex individual. However, to gain these competences before fertilization, the oocyte undergoes several morphological, cellular and molecular changes during its lifetime enclosed in the ovarian follicle. This review will briefly revisit how the oocyte orchestrate the follicular cells, and how molecules transit to the oocyte from the innermost (cumulus) and outermost (antrum and granulosa cells) layers surrounding the follicle-enclosed oocyte. Finally, we will discuss the interferences of in vitro culture conditions in the communication of the oocyte with its surrounding cells and the potential strategies to modulate these communication systems to increase oocyte competence.

Genomic study and Medical Subject Headings enrichment analysis of early pregnancy rate and antral follicle numbers in Nelore heifers

Zebu animals () are known to take longer to reach puberty compared with taurine animals (), limiting the supply of animals for harvest or breeding and impacting profitability. Genomic information can be a helpful tool to better understand complex traits and improve genetic gains. In this study, we performed a genomewide association study (GWAS) to identify genetic variants associated with reproductive traits in Nelore beef cattle. Heifer pregnancy (HP) was recorded for 1,267 genotyped animals distributed in 12 contemporary groups (CG) with an average pregnancy rate of 0.35 (±0.01). Disregarding one of these CG, the number of antral follicles (NF) was also collected for 937 of these animals, with an average of 11.53 (±4.43). The animals were organized in CG: 12 and 11 for HP and NF, respectively. Genes in linkage disequilibrium (LD) with the associated variants can be considered in a functional enrichment analysis to identify biological mechanisms involved in fertility. Medical Subject Headings (MeSH) were detected using the MESHR package, allowing the extraction of broad meanings from the gene lists provided by the GWAS. The estimated heritability for HP was 0.28 ± 0.07 and for NF was 0.49 ± 0.09, with the genomic correlation being -0.21 ± 0.29. The average LD between adjacent markers was 0.23 ± 0.01, and GWAS identified genomic windows that accounted for >1% of total genetic variance on chromosomes 5, 14, and 18 for HP and on chromosomes 2, 8, 11, 14, 15, 16, and 22 for NF. The MeSH enrichment analyses revealed significant ( < 0.05) terms associated with HP-"Munc18 Proteins," "Fucose," and "Hemoglobins"-and with NF-"Cathepsin B," "Receptors, Neuropeptide," and "Palmitic Acid." This is the first study in Nelore cattle introducing the concept of MeSH analysis. The genomic analyses contributed to a better understanding of the genetic control of the reproductive traits HP and NF and provide new selection strategies to improve beef production.

Oocyte polarized light microscopy, assay of specific follicular fluid metabolites, and gene expression in cumulus cells as different approaches to predict fertilization efficiency after ICSI

BACKGROUND

The complex relationship between oocyte morphology, specific follicular fluid metabolites, gene expression in cumulus granulosa cells, and oocyte competence toward fertilization and embryo development still needs further clarification.

METHODS

Forty-six oocytes retrieved from the largest pre-ovulatory follicle of patients undergoing intra-cytoplasmic sperm injection (ICSI) were considered assessing: (a) oocyte morphological characteristics at polarized light microscopy (PLM), (b) specific follicular fluid (FF) metabolites previously suggested to influence oocyte competence (AMH, markers of redox status and of cytotoxicity), (c) transcription of AMH and AMH type II receptor genes in cumulus cells. Data were analyzed using mono-parametric tests and multivariable logistic analysis in order to correlate morphological and biochemical data with fertilization.

RESULTS

Comparing normally fertilized oocytes (n = 29, F group) with unfertilized (n = 17, nF group) we observed that: (a) the meiotic spindle area and major axis were significantly higher in nF group and in fertilized oocytes undergoing an early embryo development arrest; (b) AMH level in FF was comparable in F and nF groups; (c) the FF of nF group contained significantly higher levels of cytotoxicity (lactate dehydrogenase) and oxidative stress (Cu,Zn-superoxide dismutase, catalase, 4-hydroxynonenal-protein conjugates) markers; (d) cumulus cells of nF group showed significantly higher AMH receptor type II gene expression.

CONCLUSIONS

Taken together, these observations suggest that an excessive cytotoxicity level can alter AMH signal transduction within cumulus cells, in turn leading to partial inhibition of aromatase activity, altered cytoplasmic maturation and increased oxidative stress, factors able to impair oocyte fertilization competence and embryo growth.

Effect of short-term exposure of cumulus-oocyte complex to 3-morpholinosydnonimine on in vitro embryo development and gene expression in cattle

Short-term exposure of gametes to different types of stress might induce stress tolerance in mammalian embryos. The aim of this study was to evaluate the effect of short-term exposure of bovine mature cumulus-oocyte complex (COC) to 3-morpholinosydnonimine (SIN-1) on subsequent in vitro embryo development, embryo quality and relative gene expression. Matured COCs were incubated with SIN-1 (0, 0.1, 1, 10 and 100 μM SIN-1) for 1 hr before in vitro fertilization and zygotes were cultured until Day 7. The cleavage rate at 72 hr did not show any differences among groups. However, the blastocyst rate on Day 7 decreased with all treatments evaluated, with the embryos generated with 10 μM SIN-1 showing the lowest embryo production rate. Embryo quality analysis did not show any differences in total cell number (TCN) or inner cell mass (ICM) among groups. Relative gene expression analysis showed a downregulation of eNOS expression and an upregulation of nNOS expression in all treatments evaluated compared to the control group. Also, a downregulation was observed in some treatments: SOD2 at 0.1 μM; SOD1 at 0.1 and 100 μM; PRDX5 at 0.1, 10 and 100 μM; and NANOG at 10 and 100 μM; and an upregulation of CDX2 expression was observed at 100 μM. The other genes (OCT4, HIF1A, HSPA1A, BCL2A and iNOS) did not show any differences in the relative gene expression. These results suggest that the short-term exposure of mature bovine COCs to SIN-1 does not induce stress tolerance and has no beneficial effect on bovine in vitro embryo production.

Transcriptome analysis of human cumulus cells reveals hypoxia as the main determinant of follicular senescence

STUDY QUESTION

Can RNA sequencing of human cumulus cells (CC) reveal molecular pathways involved in the physiology of reproductive aging?

STUDY FINDING

Senescent but not young CC activate gene pathways associated with hypoxia and oxidative stress.

WHAT IS KNOWN ALREADY

Shifts in socioeconomic norms are resulting in larger numbers of women postponing childbearing. The reproductive potential is sharply decreased with aging, and the reasons are poorly understood. Since CCs play an integral role in oocyte maturation and direct access to human oocytes is limited, we used whole transcriptome analysis of these somatic cells to gain insights into the molecular mechanisms playing a role in follicular senescence.

STUDY DESIGN, SAMPLES/MATERIALS, METHODS

Twenty CC samples (from a total of 15 patients) were obtained from oocytes of either male factor or egg donor patients. RNA sequencing and bioinformatic tools were used to identify differentially expressed genes between CCs from seven aged and eight young patients (<35 (years old) y.o. vs >40 y.o.). Quantitative-PCR and immunoflourescent staining were used for validation.

MAIN RESULTS AND THE ROLE OF CHANCE

RNA sequencing identified 11 572 genes expressed in CC of both age cohorts, 45 of which were differentially expressed. In CC collected from patients >40 y.o., genes involved in the hypoxia stress response (NOS2, RORA and NR4A3), vasculature development (NR2F2, PTHLH), glycolysis (RALGAPA2 and TBC1D4) and cAMP turnover (PDE4D) were significantly overexpressed when compared with CC of patients younger than 35 y.o.

LIMITATIONS, REASONS FOR CAUTION

This study focused almost exclusively on assessing the genetic differences in CC transcriptome between young and older women. These genetic findings were not fully correlated with embryonic development and clinical outcome.

WIDER IMPLICATIONS OF THE FINDINGS

Our data provide a new hypothesis-follicular hypoxia-as the main mechanism leading to ovarian follicular senescence and suggest a link between cumulus cell aging and oocyte quality decay. If specific molecular findings of hypoxia would be confirmed also in oocytes, genetic platforms could screen CC for hypoxic damage and identify healthier oocytes. Protocols of ovarian stimulation in older patients could also be adjusted to diminish oocyte exposure time to hypoxic follicles.

LARGE SCALE DATA

GEO accession number: GSE81579 STUDY FUNDING AND COMPETING INTERESTS: Funded in part by EMD Serono Grant for Fertility Innovation (GFI).

Nitric oxide in follicle development and oocyte competence

Apart from its well-known role in regulating endothelial function, in mammals, nitric oxide (NO) is an important signaling molecule involved in many processes, regulating different biological functions. It has been demonstrated that NO plays a role in the physiology of the reproductive system, where it acts in controlling the activity of reproductive organs in both sexes. In the female of several animal species, experimental data suggest the presence of an intraovarian NO-generating system, which could be involved in the control of follicular development. The role of NO in regulating follicular atresia by apoptosis is still controversial, as a dual action depending mostly on its concentration has been documented. NO also displays positive effects on follicle development and selection related to angiogenic events and it could also play a modulatory role in steroidogenesis in ovarian cells. Both in monovulatory and poliovulatory species, the increase in PGE2production induced by NO via a stimulatory effect on COX-2 activity appears to be a common ovulatory mechanism. Considerable evidence also exists to support an involvement of the NO/NO synthase system in the control of meiotic maturation of cumulus–oocyte complexes.

Oocyte environment: follicular fluid and cumulus cells are critical for oocyte health

Bidirectional somatic cell-oocyte signaling is essential to create a changing intrafollicular microenvironment that controls primordial follicle growth into a cohort of growing follicles, from which one antral follicle is selected to ovulate a healthy oocyte. Such intercellular communications allow the oocyte to determine its own fate by influencing the intrafollicular microenvironment, which in turn provides the necessary cellular functions for oocyte developmental competence, which is defined as the ability of the oocyte to complete meiosis and undergo fertilization, embryogenesis, and term development. These coordinated somatic cell-oocyte interactions attempt to balance cellular metabolism with energy requirements during folliculogenesis, including changing energy utilization during meiotic resumption. If these cellular mechanisms are perturbed by metabolic disease and/or maternal aging, molecular damage of the oocyte can alter macromolecules, induce mitochondrial mutations, and reduce adenosine triphosphate production, all of which can harm the oocyte. Recent technologies are now exploring transcriptional, translational, and post-translational events within the human follicle with the goal of identifying biomarkers that reliably predict oocyte quality in the clinical setting.