Oocyte in-vitro maturation: BCL2 mRNA content in cumulus cells reflects oocyte competency

Circular RNAs: Emerging Modulators in the Pathophysiology of Polycystic Ovary Syndrome and their Clinical Implications

Polycystic ovary syndrome (PCOS) is a prevalent endocrine/metabolic disorder in women of reproductive age. PCOS is characterized by hyperandrogenism, polycystic ovary morphology, and ovulatory dysfunction/anovulation. It involves multiple effects in patients, including granulosa/theca cell hyperplasia, menstrual disturbances, infertility, acne, obesity, insulin resistance, and cardiovascular disorders. Biochemical analyses and the results of RNA sequencing studies in recent years have shown a type of non-coding RNAs as a splicing product known as circular RNAs (circRNAs). Several biological functions have been identified in relation to circRNAs, including a role in miRNA sponge, protein sequestration, increased parental gene expression, and translation leading to polypeptides. These circular molecules are more plentiful and specialized than other types of RNAs. For this reason, they are referred to as potential biomarkers in different diseases. Evidence suggests that circRNAs may have regulatory potentials through different signaling pathways, such as the miRNA network. Probably most experts in the field of obstetricians are not aware of circRNAs as a useful biomarker. Therefore, this review focused on the researches that have been done on the involvement of circRNAs in PCOS and summarized recent supportive evidence, and evaluated the circRNA association and mechanisms involved in PCOS.

Effect of Passage Number of Conditioned Medium Collected from Equine Amniotic Fluid Mesenchymal Stem Cells: Porcine Oocyte Maturation and Embryo Development

Oocyte in vitro maturation (IVM) is the most important first step in in vitro embryo production. One prerequisite for the success of IVM in oocytes is to provide a rich culture microenvironment that meets the nutritional needs of developing oocytes. We applied different equine amniotic fluid mesenchymal stem cell conditioned medium (eAFMSC-CM) from passages 7, 18, and 27 to porcine oocytes during IVM to determine its effects on oocyte development and subsequent embryo development, specifically. The eAFMSC-CM from passage 7 (eAFMSC-CMp7) has a considerable impact on 9 genes: BAX, BCL2, SOD2, NRF2, TNFAIP6, PTGS2, HAS2, Cx37, and Cx43, which are associated with cumulus cell mediated oocyte maturation. GSH levels and distribution of mitochondrial and cortical granules were significantly increased in oocytes incubated with eAFMSC-CMp7. In addition, catalase and superoxide dismutase activities were high after IVM 44 h with eAFMSC-CMp7. After in vitro fertilization, blastocyst quality was significantly increased in the eAFMSC-CMp7 group compared to control. Lastly, the antioxidant effect of eAFMSC-CMp7 substantially regulated the expression of apoptosis, pluripotency related genes and decreased autophagy activity in blastocysts. Taken together, this study demonstrated that the eAFMSC-CMp7 enhanced the cytoplasmic maturation of oocytes and subsequent embryonic development by generating high antioxidant activity.

The boosting effects of melatonin on the expression of related genes to oocyte maturation and antioxidant pathways: a polycystic ovary syndrome- mouse model

Background

Melatonin, as a free radical scavenger exhibiting genomic actions, regulates the antioxidant genes expression and apoptosis mechanisms. In polycystic ovary syndrome (PCOS) patients, an imbalance between free radicals and antioxidants in follicular fluid leads to oxidative stress, aberrant folliculogenesis, and intrinsic defects in PCOS oocytes. In this experimental mouse model study, oocytes of PCOS and the control groups were cultured in different melatonin concentrations (10− 5, 10− 6, and 10− 7 M) to investigate the expression of oocyte maturation-related genes (Gdf9/Bmp15), antioxidant-related genes (Gpx1/Sod1), apoptotic biomarkers (Bcl2/Bax) and total intracellular ROS levels.

Results

Gdf9 and Bmp15, Gpx1 and Sod1 were up-regulated in PCOS and control oocytes cultured in all melatonin concentrations compared to those cultured in IVM basal medium (P < 0.05). A significant decrease in the total ROS level was observed in all groups cultured in the supplemented cultures. Melatonin increased Bcl2 and decreased Bax gene expression in PCOS and control oocytes compared to non-treated oocytes.

Conclusions

Melatonin increased antioxidant gene expression and regulated the apoptosis pathway, effectively reducing the adverse effects of culture conditions on PCOS oocytes. Furthermore, it influenced the expression of oocyte maturation-related genes in PCOS, providing valuable support during the IVM process.

The brominated flame retardant, TBCO, impairs oocyte maturation in zebrafish (Danio rerio)

The brominated flame retardant, 1,2,5,6-tetrabromocyclooctane (TBCO), has been shown to decrease fecundity in Japanese medaka (Oryzias latipes) and there is indirect evidence from analysis of the transcriptome and proteome that this effect might be due to impaired oogenesis. An assay for disruption of oocyte maturation by chemical stressors has not been developed in Japanese medaka. Thus, using zebrafish (Danio rerio) as a model, objectives of the present study were to determine whether exposure to TBCO has effects on maturation of oocytes and to investigate potential mechanisms. Sexually mature female zebrafish were given a diet of 35.3 or 628.8 μg TBCO / g food for 14 days after which, stage IV oocytes were isolated to assess maturation in response to maturation inducing hormone. To explore potential molecular mechanisms, abundances of mRNAs of a suite of genes that regulate oocyte maturation were quantified by use of quantitative real-time PCR, and abundances of microRNAs were determined by use of miRNAseq. Ex vivo maturation of oocytes from fish exposed to TBCO was significantly less than maturation of oocytes from control fish. The percentage of oocytes which matured from control fish and those exposed to low and high TBCO were 89, 71, and 67%, respectively. Among the suite of genes known to regulate oocyte maturation, mRNA abundance of insulin like growth factor-3 was decreased by 1.64- and 3.44-fold in stage IV oocytes from females given the low and high concentrations of TBCO, respectively, compared to the control group. Abundances of microRNAs regulating the expression of proteins that regulate oocyte maturation, including processes related to insulin-like growth factor, were significantly different in stage IV oocytes from fish exposed to TBCO. Overall, results of this study indicated that impaired oocyte maturation might be a mechanism of reduced reproductive performance in TBCO-exposed fish. Results also suggested that effects of TBCO on oocyte maturation might be due to molecular perturbations on insulin-like growth factor signaling and expression of microRNAs.

Heat Shock Protein 70 Improves In Vitro Embryo Yield and Quality from Heat Stressed Bovine Oocytes

Heat shock protein 70 (HSP70) is a chaperon that stabilizes unfolded or partially folded proteins, preventing inappropriate inter- and intramolecular interactions. Here, we examined the developmental competence of in vitro matured oocytes exposed to heat stress with or without HSP70. Bovine oocytes were matured for 24 h at 39 °C without (group C39) or with HSP70 (group H39) and at 41 °C for the first 6 h, followed by 16 h at 39 °C with (group H41) or without HSP70 (group C41). After insemination, zygotes were cultured for 9 days at 39 °C. Cleavage and embryo yield were assessed 48 h post insemination and on days 7, 8, 9, respectively. Gene expression was assessed by RT-PCR in oocytes, cumulus cells and blastocysts. In C41, blastocysts formation rate was lower than in C39 and on day 9 it was lower than in H41. In oocytes, HSP70 enhanced the expression of three HSP genes regardless of incubation temperature. HSP70 at 39 °C led to tight coordination of gene expression in oocytes and blastocysts, but not in cumulus cells. Our results imply that HSP70, by preventing apoptosis, supporting signal transduction, and increasing antioxidant protection of the embryo, protects heat stressed maturing bovine oocyte and restores its developmental competence.

MiRNA-155 regulates cumulus cells function, oocyte maturation, and blastocyst formation

Numerous oocytes are retrieved during in vitro fertilization from patients with polycystic ovary syndrome (PCOS). The poor quality of these oocytes leads to lower fertilization and decreases in cleavage and implantation. MiR-155 is one of the microRNA (miRNA) that is increased in serum and granulosa cells of PCOS patients. In this study, we investigate the effects of miR-155 expression and its target genes on oocyte maturation and embryo development. We used the calcium phosphate protocol to transfect vectors that contained miR-155 or miR-off 155 and alone eGFP into cumulus oophorus complex (COCs) of B6D2F1 female mice for in vitro maturation. Cumulus expansion, nuclear, and cytoplasmic maturation, as well as cleavage rates were determined in groups transfected and compared with the control groups. Quantitative real-time polymerase chain reaction was performed to analyze expression levels of miR-155 and the target genes in the cumulus cells, oocytes, and blastocysts. MiR-155 overexpression in COCs suppressed cumulus expansion, oocyte maturation, and inhibition of endogenous miR-155 by miR-off 155 improved cumulus expansion and oocyte maturation by downregulation and expression increase of the Smad2 and Bcl2 genes. On the other hand, overexpression and downregulation of miR-155 in the COCs led to increase and decrease in cleavage rates by changes in expressions of the Mecp2, Jarid2, and Notch1 genes, respectively (P &lt; 0.05). These results suggested that miR-155 overexpression in granulosa cells of PCOS patients can negatively affect nuclear and cytoplasmic maturation, but this miRNA expression has a positive impact on embryo development.

Hyperandrogen enhances apoptosis of human ovarian granulosa cells via up-regulation and demethylation of PDCD4

Apoptosis of granulosa cells (GCs) induced by hyperandrogen plays a key role in the pathogenesis of polycystic ovary syndrome (PCOS). However, the mechanism of androgen-induced apoptosis of GCs has not been clarified to date. Recent studies have reported that PDCD4 expression is higher in PCOS patients and might be a key factor in PCOS progression. In this study, we aimed to investigate the role of PDCD4 in regulating apoptosis of human GCs and whether hyperandrogen regulate PDCD4 expression through DNA methylation. Overexpression of PDCD4 in human ovarian granulosa cell line KGN cells promoted cells apoptosis. Meanwhile, expression of caspase-3 and caspase-9 were significantly elevated. High concentration of testosterone treatment resulted in up-regulation of PDCD4 and a significant increase of apoptosis in KGN cells. In addition, knockdown of PDCD4 in KGN cells treated with high concentration of testosterone abolished the hyperandrogen-induced apoptosis. Furthermore, high concentration of testosterone down-regulated DNMT1, DNMT3A and DNMT3B expression and the methylation level in the promoter region of PDCD4 was decreased. In conclusion, PDCD4 can promote apoptosis of human ovarian GCs. The mechanism of hyperandrogen-induced apoptosis may be mediated by PDCD4. Furthermore, the up-regulation of PDCD4 induced by hyperandrogen may through demethylation of its promoter regions.

Mitochondrial dysfunction: An emerging link in the pathophysiology of polycystic ovary syndrome

Polycystic ovary syndrome (PCOS) is a common endocrine disorder characterized by irregular menstrual cycles, hyperandrogenism and subfertility. Due to its complex manifestation, the pathogenic mechanism of PCOS is not well defined. Cumulative effect of altered genetic and epigenetic factors along with environmental factors may play a role in the manifestation of PCOS leading to systemic malfunction. With failure of genome-wide association study (GWAS) and other studies performed on nuclear genome to provide any clue for precise mechanism of PCOS pathogenesis, attention has been diverted to mitochondria. Mitochondrion plays an important role in cellular metabolic functions and is linked to Insulin Resistance (IR). Recently, increasing reports suggest that mitochondrial dysfunction may be a contributing factor in the pathogenesis of PCOS. Hence, in this review, we have discussed mitochondrial biology in brief and emphasizes on genetic and epigenetic aspects of mitochondrial dysfunction studied in PCOS women and PCOS-like animal models. We also highlight underlying mechanism behind mitochondrial dysfunction contributing to PCOS and its related complications such as obesity, diabetes, cardiovascular diseases, metabolic syndrome, non-alcoholic fatty liver disease (NAFLD) and cancer. Furthermore, contrasting remarks against involvement of mitochondrial dysfunction in PCOS pathophysiology have also been presented. This review enhances our understanding in relation to mitochondrial dysfunction in the etiology of PCOS and stimulates further research to explore a clear link between mitochondrial dysfunction and PCOS pathogenesis and progression. Understanding pathogenic mechanisms underlying PCOS will open new windows to develop promising therapeutic strategies against PCOS.

Oocyte Aging: The Role of Cellular and Environmental Factors and Impact on Female Fertility

Female aging is one of the most important factors that impacts human reproduction. With aging, there is a natural decline in female fertility. The decrease in fertility is slow and steady in women aged 30-35 years; however, this decline is accelerated after the age of 35 due to decreases in the ovarian reserve and oocyte quality. Human oocyte aging is affected by different environmental factors, such as dietary habits and lifestyle. The ovarian microenvironment contributes to oocyte aging and longevity. The immediate oocyte microenvironment consists of the surrounding cells. Crosstalk between the oocyte and microenvironment is mediated by direct contact with surrounding cells, the extracellular matrix, and signalling molecules, including hormones, growth factors, and metabolic products. In this review, we highlight the different microenvironmental factors that accelerate human oocyte aging and decrease oocyte function. The ovarian microenvironment and the stress that is induced by environmental pollutants and a poor diet, along with other factors, impact oocyte quality and function and contribute to accelerated oocyte aging and diseases of infertility.

Gonadotropin-Dependent Neuregulin-1 Signaling Regulates Female Rat Ovarian Granulosa Cell Survival

Mammalian ovarian follicular development and maturation of an oocyte competent to be fertilized and develop into an embryo depends on tightly regulated, spatiotemporally orchestrated crosstalk among cell death, survival, and differentiation signals through extra- and intraovarian signals, as well as on a permissive ovarian follicular microenvironment. Neuregulin-1 (NRG1) is a member of the epidermal growth factor-like factor family that mediates its effects by binding to a member of the erythroblastoma (ErbB) family. Our experimental results suggest gonadotropins promote differential expression of NRG1 and erbB receptors in granulosa cells (GCs), and NRG1 in theca cells during follicular development, and promote NRG1 secretions in the follicular fluid (FF) of rat ovaries. During the estrous cycle of rat, NRG1 and erbB receptors are differentially expressed in GCs and correlate positively with serum gonadotropins and steroid hormones. Moreover, in vitro experimental studies suggest that the protein kinase C inhibitor staurosporine (STS) causes the physical destruction of GCs by the activation of caspase-3. Exogenous NRG1 treatment of GCs delayed onset of STS-induced apoptosis and inhibited cleaved caspase-3 expressions. Moreover, exogenous NRG1 treatment of GCs alters STS-induced death by maintaining the expression of ErbB2, ErbB3, pAkt, Bcl2, and BclxL proteins. Taken together, these studies demonstrate that NRG1 is gonadotropin dependent, differentially regulated in GCs and theca cells, and secreted in ovarian FF as an intracellular survival factor that may govern follicular maturation.

Temporal expression of cumulus cell marker genes during in vitro maturation and oocyte developmental competence

PURPOSE

Cumulus cells (CC) play important roles in oocyte development and cumulus expressed genes can be used as markers for oocyte quality. This study aimed to investigate temporal changes in the expression of cumulus marker genes during oocyte maturation as possible biomarkers of embryo developmental competence in ovine.

METHODS

Gene expression was assessed in the CC of the BCB+ (developmentally competent) and BCB- (developmentally poor) oocytes at 0, 12, and 24 h of in vitro maturation (IVM). Further, the association between the temporal cumulus gene expression and in vitro oocyte and embryo development was assessed.

RESULTS

The maturation and blastocyst formation rates were found significantly greater for the BCB+ than the BCB- oocytes. At the 0 h of IVM, a significant upregulation in the expression of PTGS2, STAR, SDC2, LHR, FGF2, BCL2, IL7RA, HSPA1A, and IFNT was observed in the CC of the poor (BCB-) as compared to the competent (BCB+) oocytes. In contrast, it was observed that as maturation progressed, the cumulus expression of most of the favorable genes was reduced and was found significantly downregulated at the completion of IVM in the poor as compared to the competent oocytes.

CONCLUSIONS

The study revealed noticeable differences in the cumulus gene expression profile at different stages of IVM between ovine oocytes of differential developmental ability. The results indicated that the loss of cumulus gene expression along the maturation period in the poor oocytes was related to their intrinsic poor quality in the ovarian follicle.

Follicle-stimulating hormone-induced rescue of cumulus cell apoptosis and enhanced development ability of buffalo oocytes

The effect of follicle-stimulating hormone (FSH) on apoptotic status of cumulus cells, expression of proapoptotic and antiapoptotic genes, and development rate of in vitro fertilization-produced buffalo embryos were investigated. FSH supplementation in in vitro maturation-medium resulted in a dose-dependent reduction in the expression of proapoptotic genes namely, BCL2-associated X protein (BAX), cytochrome c, and caspase-3 and increase in the expression of antiapoptotic genes such as B-cell lymphoma 2 (BCL2) and X-linked inhibitor of apoptosis protein (XIAP) in cumulus cells of mature oocyte. Cumulus expansion, oocyte maturation, cleavage, and blastocyst development rates were significantly higher (P < 0.05) in 5 and 10-μg/mL FSH-supplemented groups as compared with control. Significant increase in the expression of FSH receptor messenger RNA was also found with 5 and 10-μg/mL FSH (P < 0.05). Terminal deoxynucleotidyl transferase dUTP nick end labeling assay confirmed that the population of apoptotic cumulus cells of matured oocytes was reduced in the FSH-treated groups as compared with control (P < 0.05). In conclusion, our data suggest that FSH may attenuate apoptosis in cumulus cells via mitochondria-dependent apoptotic pathway by increasing XIAP expression, resulting in a more favorable ratio of BCL2/BAX expression and decreasing the cytochrome c and caspase-3 expression, eventually contributing to developmental competence of oocytes. The information generated will help in improving the in vitro embryo production program in buffalo.

Viability of cumulus cells is associated with basal AMH levels in assisted reproduction

OBJECTIVE(S)

An interesting non-invasive approach to select embryos for transfer is analyzing the health state of somatic granulosa cells surrounding the oocyte addressing their mutual dependence. This prospective study was set up to analyse whether the DNA integrity of cumulus cells correlates with preimplantation development and basal AMH levels.

STUDY DESIGN

Therefore, 56 patients who gave written consent were enrolled. Sequential denudation of the cumulus-oocyte-complexes was performed in order to separate corona radiata from outer cumulus cells. DNA integrity of both cell types was analysed using a modified chromatin dispersion test.

RESULTS

The percentage of viable corona radiata cells per patient showed a linear correlation to blastulation (P<0.05). These innermost cells showed significantly lower rates of strand breaks (P<0.01) as compared to outer cumulus cells. Age-corrected AMH was significantly associated with the DNA integrity of outer cumulus cells (P<0.05).

CONCLUSION(S)

For the first time it could be shown that in fact clinical embryologists deal with two different entities of cumulus cells, inner and outer ones. It seems that any protective mechanism of the female gamete follows an outward gradient, so that negative effects, e.g. apoptosis, may impair outer cumulus cells first. Age-corrected AMH reflects quality of these outer cumulus cells.

KEYWORDS

AMH; Corona radiata cells; DNA fragmentation; Outer cumulus cells; SCD test.

In vitro maturation of oocytes alters gene expression and signaling pathways in bovine cumulus cells

In vitro maturation (IVM) of immature oocytes is widely used in assisted reproduction technologies in cattle, and is increasingly used to treat human infertility. The development competence of IVM oocytes, however, is lower than preovulatory, in vivo-matured oocytes. During maturation, cumulus cells (CC) are metabolically coupled with an oocyte and support the acquisition of its developmental potential. Our objective was to identify genes and pathways that were affected by IVM in bovine CC. Microarray transcriptomic analysis of CC enclosing in vitro- or in vivo-mature oocytes revealed 472 differentially expressed genes, including 28% related to apoptosis, correlating with twofold higher cell death after IVM than in vivo, as detected by TUNEL. Genes overexpressed after IVM were significantly enriched in functions involved in cell movement, focal adhesion, extracellular matrix function, and TGF-beta signaling, whereas under-expressed genes were enriched in regulating gene expression, energy metabolism, stress response, and MAP kinases pathway functions. Differential expression of 15 genes, including PAG11 (increased) and TXNIP (decreased), which were never detected in CC before, was validated by real-time RT-PCR. Moreover, protein quantification confirmed the lower abundance of glutathione S-transferase A1 and prostaglandin G/H synthase 2, and the higher abundance of hyaluronan synthase 2 and SMAD4, a member of TGF-beta pathway, in CC after IVM. Phosphorylation levels of SMAD2, MAPK3/1, and MAPK14, but not MAPK8, were higher after IVM that in vivo. In conclusion, IVM provokes the hyper-activation of TGF-beta and MAPK signaling components, modifies gene expression, leads to increased apoptosis in CC, and thus affects oocyte quality.

Incidence of apoptosis and transcript abundance in bovine follicular cells is associated with the quality of the enclosed oocyte

The close contact and interaction between the oocyte and the follicular environment influence the establishment of oocyte developmental competence. Moreover, it is assumed that apoptosis in the follicular cells has a beneficial influence on the developmental competence of oocytes. The aim of this study was to investigate whether bovine oocytes with varied developmental competence show differences in the degree of apoptosis and gene expression pattern in their surrounding follicular cells (cumulus and granulosa cells). Oocytes and follicular cells from follicles of 3 to 5 mm in diameter were grouped as brilliant cresyl blue (BCB)+ and BCB- based on glucose-6-phosphate dehydrogenase (G6PDH) activity in the ooplasm by BCB staining. In the follicular cells initial, early and late apoptotic events were assessed by analyzing caspase-3 activity, annexin-V and TUNEL, respectively. Global gene expression was investigated in immature oocytes and corresponding follicular cells. BCB+ oocytes resulted in a higher blastocyst rate (19.3%) compared to the BCB- group (7.4%, P < 0.05). Moreover, the analysis of apoptosis showed a higher caspase-3 activity in the follicular cells and an increased degree of late apoptotic events in granulosa cells in the BCB+ compared with the BCB- group. Additionally, the global gene expression profile revealed a total of 34 and 37 differentially expressed genes between BCB+ and BCB- cumulus cells and granulosa cells, respectively, whereas 207 genes showed an altered transcript abundance between BCB+ and BCB- oocytes. Among these, EIF3F, RARRES2, RNF34, ACTA1, GSTA1, EIF3A, VIM and CS gene transcripts were most highly enriched in the BCB+ oocytes, whereas OLFM1, LINGO1, ALDH1A3, PTHLH, BTN3A3, MRPS2 and PPM1K were most significantly reduced in these cells. Therefore, the follicular cells enclosing developmentally competent oocytes show a higher level of apoptosis and a different pattern of gene expression compared to follicular cells enclosing non-competent bovine oocytes.

Expression of apoptotic genes in immature and in vitro matured equine oocytes and cumulus cells

The gene expression of Bax, Bcl-2, survivin and p53, following in vitro maturation of equine oocytes, was compared in morphologically distinct oocytes and cumulus cells. Cumulus-oocyte complexes (COC) were harvested and divided into two groups: G1 - morphologically healthy cells; and G2 - less viable cells or cells with some degree of atresia. Total RNA was isolated from both immature and in vitro matured COC and real-time reverse transcription polymerase chain reaction (qRT-PCR) was used to quantify gene expression. Our results showed there was significantly higher expression of survivin (P < 0.05) and lower expression of p53 (P < 0.01) in oocytes compared with cumulus cells in G1. No significant difference in gene expression was observed following in vitro maturation or in COC derived from G1 and G2. However, expression of the Bax gene was significantly higher in cumulus cells from G1 (P < 0.02).