Progesterone influences cytoplasmic maturation in porcine oocytes developing in vitro

Progesterone and Androstenedione Are Important Follicular Fluid Factors Regulating Porcine Oocyte Maturation Quality

Oocytes matured in vitro are useful for assisted human and farm animal reproduction. However, the quality of in vitro matured oocytes is usually lower than that of in vivo matured oocytes, possibly due to the absence of some important signal regulators in vitro. In this study, untargeted metabolomics was used to detect the changes in the metabolites in the follicular fluid (FF) during in vivo pig oocyte maturation and in the culture medium during in vitro maturation. Our results showed that the total metabolite changing profile of the in vivo FF was different from that of the in vitro maturation medium, but the levels of 23 differentially expressed metabolites (DEMs) changed by following the same trend during both in vivo and in vitro pig oocyte maturation. These 23 metabolites may be important regulators of porcine oocyte maturation. We found that progesterone and androstenedione, two factors in the ovarian steroidogenesis pathway enriched from the DEMs, were upregulated in the FF during in vivo pig oocyte maturation. The levels of these two factors were 31 and 20 fold, respectively, and they were higher in the FF than in the culture medium at the oocyte mature stage. The supplementation of progesterone and androstenedione during in vitro maturation significantly improved the pig oocyte maturation rate and subsequent embryo developmental competence. Our finding suggests that a metabolic abnormality during in vitro pig oocyte maturation affects the quality of the matured oocytes. This study identified some important metabolites that regulate oocyte maturation and their developmental potential, which will be helpful to improve assisted animal and human reproduction.

Effects of cumulus cells on the in vitro cytoplasmic maturation of immature oocytes in pigs

The exposure of cumulus cells to nuclear matured oocytes can be regulated through the forced delay of nuclear maturation or the alteration of in vitro maturation (IVM) time in cumulus-oocyte complexes (COCs). However, to date, no evidence has been presented for the enhancement of cytoplasmic maturation by them, indicating irrelevance of cumulus cells in cytoplasmic maturation. Therefore, in order to identify the requirement of cumulus cells in achieving the cytoplasmic maturation of immature oocytes, this study investigated the effects of cumulus cells on the in vitro cytoplasmic maturation of oocytes within COCs derived from porcine medium antral follicles (MAFs) post-the completion of nuclear maturation. For these, with IVM of COCs for 44 h (control), cumulus cell-free oocytes with completed nuclear maturation were in-vitro-matured additionally for 0, 6, or 12 h, and then a variety of factors representing the cytoplasmic maturation of oocytes were analyzed and compared. As the results, the IVM of COCs for 32 h showed complete nuclear maturation and incomplete cytoplasmic maturation. Moreover, after the removal of cumulus cells from COCs with the completion of nuclear maturation, IVM for an additional 6 or 12 h resulted in significant increases in the size of the perivitelline space, the proportion of oocytes with a normal intracellular mitochondrial distribution and a normal round first polar body, and the preimplantation development into the 2-cell and blastocyst stages after parthenogenetic activation. Simultaneously, they showed significant reduction in the level of intracellular reactive oxygen species and no significant differences in the total number of blastocysts. Furthermore, oocytes obtained by this approach did not significantly differ from control oocytes produced by IVM of COCs for 44 h. Our results demonstrate that the cumulus cells enclosing COCs derived from porcine MAFs are not essential for the completion of cytoplasmic maturation after complete nuclear maturation by COCs.

Effect of progesterone on in vitro meiotic maturation of canine oocytes associated with Cx37 and Cx43 gene expression

Progesterone (P4) concentrations in canines are exceptionally high in the periovulatory period. However, the mechanisms by which P4 modulates final oocyte development in dogs remain to be characterized. The aim of this study was to evaluate the effect of P4 on meiotic development related to the gene expression of connexin 37 (Cx37) and connexin 43 (Cx43) in the canine cumlus oocyte complexes (COCs). COCs were isolated from 120 canine ovaries after a routine ovariohysterectomy. In each experiment, groups of COCs retrieved from the antral follicles were subjected to in vitro maturation (IVM) for 72 h without (control) or with P4 (50 μg/mL and 100 μg/mL) or the P4 receptor antagonist, aglepristone (RU534 at 1 μM and 10 μM). Some of the COCs recovered (from each group) after 72 h of IVM were subjected to meiotic evaluation; the remaining COCs, and those not subjected to IVM, were used to analyze the gene expression of Cx37 and Cx43 by qPCR. The results were evaluated using ANOVA. The addition of P4 increased (P < 0.05) the meiotic development compared to that in the control or aglepristone groups. The highest (P < 0.05) percentage of oocytes in the MII stage was observed upon P4 supplementation. In contrast, the highest percentage (P < 0.05) of oocytes arrested in the GV stage and the lowest (P < 0.05) percentages in the MII stage were observed for COCs cultured with aglepristone. Although a significant decrease in the mRNA levels of both connexins was observed after culturing, no effect on Cx37 and Cx43 gene expression was observed when exogenous P4 was added compared to those of the control group. However, COCs cultured with aglepristone exhibited higher (P < 0.05) expression of Cx37 and Cx43 than COCs in the control IVM-group, regardless of the concentration. In conclusion, our results suggest that a high dosage of P4 during IVM enhances the nuclear maturation of canine oocytes without altering the gene expression levels of Cx37 and Cx43. However, the increase in their expression upon treatment with a P4 antagonist indicates an in vivo role for this hormone in the endogenous modulation of both Cx37 and Cx43.

Follicular fluid steroid profile in sows: relationship to follicle size and oocyte quality†

Identification of reliable characteristics of follicle quality and developmental competence has been pursued in numerous studies, but with inconsistent outcomes. Here, we aimed to identify these characteristics by analysis of the follicular fluid (FF) steroid profile in relation to cumulus-oocyte complex (COC) morphology and follicle size, followed by molecular substantiation. Multiparous sows at weaning were used to facilitate analysis at the start of the follicular phase of the oestrus cycle. Sows with a higher average follicle size (≥5 mm vs. < 5 mm) had a higher follicular fluid β-estradiol concentration, but did not differ in other measured steroids. Sows with high compared to low percentage high-quality COCs (<70% vs. ≥70% high-quality) had follicular fluid with a higher concentration of β-estradiol, 19-norandrostenedione, progesterone, and α-testosterone, while the concentration of cortisol was lower. Transcriptome analysis of granulosa cells of healthy follicles of sows with a high percentage high-quality COCs showed higher abundance of transcripts involved in ovarian steroidogenesis (e.g., CYP19A2 and 3, POR, VEGFA) and growth (IGF1) and differential abundance of transcripts involved in granulosa cell apoptosis (e.g., GADD45A, INHBB). Differences in aromatase transcript abundance (CYP19A1, 2 and 3) were confirmed at the protein level. In addition, sows with a high percentage high-quality COCs lost less weight during lactation and had higher plasma IGF1 concentration at weaning, which may have affected COC quality. To the best of our knowledge, this study is also the first to report the relation between FF steroid profile and COC quality.

Consequences of negative energy balance on follicular development and oocyte quality in primiparous sows†

Metabolic demands of modern hybrid sows have increased over the years, which increases the chance that sows enter a substantial negative energy balance (NEB) during lactation. This NEB can influence the development of follicles and oocytes that will give rise to the next litter. To study effects of a lactational NEB on follicular development, we used 36 primiparous sows of which 18 were subjected to feed restriction (3.25 kg/day) and 18 were full-fed (6.5 kg/day) during the last 2 weeks of a 24.1 ± 0.3 day lactation. Feed restriction resulted in a 70% larger lactational body weight loss and 76% higher longissimus dorsi depth loss, but similar amounts of backfat loss compared to the full fed sows. These changes were accompanied by lower plasma insulin-like growth factor 1 (IGF1) and higher plasma creatinine levels in the restricted sows from the last week of lactation onward. Ovaries were collected 48 h after weaning. Restricted sows had a lower average size of the 15 largest follicles (−26%) and cumulus–oocyte complexes showed less expansion after 22 h in vitro maturation (−26%). Less zygotes of restricted sows reached the metaphase stage 24 h after in vitro fertilization and showed a higher incidence of polyspermy (+89%). This shows that feed restriction had severe consequences on oocyte developmental competence. Follicular fluid of restricted sows had lower IGF1 (−56%) and steroid levels (e.g., β-estradiol, progestins, and androgens), which indicated that follicles of restricted sows were less competent to produce steroids and growth factors needed for oocytes to obtain full developmental competence.

Hydroxyurea affects in vitro porcine oocyte maturation through increased apoptosis and oxidative stress

Hydroxyurea (HU) is an FDA-approved drug used to treat a variety of diseases, especially malignancies, but is harmful to fertility. We used porcine oocytes as an experimental model to study the effect of HU during oocyte maturation. Exposure of cumulus–oocyte complexes (COCs) to 20 µM (P<0.01) and 50 µM (P<0.001) HU reduced oocyte maturation. Exposure to 20 µM HU induced approximately 1.5- and 2-fold increases in Caspase-3 (P<0.001) and P53 (P<0.01) gene expression levels in cumulus cells, respectively, increased Caspase-3 (P<0.01) and P53 (P<0.001) protein expression levels in metaphase II (MII) oocytes and increased the percentage of apoptotic cumulus cells (P<0.001). In addition, HU decreased the mitochondrial membrane potential (Δφm) (P<0.01 and P<0.001) and glutathione (GSH) levels (P<0.01 and P<0.001) of both cumulus cells and MII oocytes, while increasing their reactive oxygen species (ROS) levels (P<0.001). Following parthenogenetic activation of embryos derived from MII oocytes, exposure to 20 µM HU significantly reduced total blastocyst cell numbers (P<0.001) and increased apoptosis of blastocyst cells (P<0.001). Moreover, HU exposure reduced the rate of development of two-celled, four- to eight-celled, blastocyst, and hatching stages after parthenogenetic activation (P<0.05). Our findings indicate that exposure to 20 µM HU caused significant oxidative stress and apoptosis of MII oocytes during maturation, which affected their developmental ability. These results provide valuable information for safety assessments of HU.

Mifepristone and PGF2α activate phosphatidylinositol hydrolysis in the ovine corpus luteum

Two experiments were conducted to determine whether mifepristone (RU486) and PGF2α activate the phosphatidylinositol hydrolysis pathway during the midluteal phase of the ovine estrous cycle. In experiment 1, ewes on day 8 of the cycle were given 10 μg RU486 or vehicle into the ovarian artery with removal of the corpus luteum (CL) after 10 min. Blood collected prior to and after treatment was analyzed for progesterone. Aliquots of CL were incubated with 10 μCi of 3H-inositol and in the presence and absence of PGF2α (10 nM) for 15 min. Exposure of CL to RU486 and PGF2α increased phosphatidylinositol hydrolysis (p < 0.05). Serum progesterone was reduced in both control and RU486-treated ewes (p < 0.05) compared to concentrations before treatments. In experiment 2, aliquots of CL collected from ewes on day 8 of the cycle were incubated with 3H-inositol and exposed to RU486 (2 μM) in the presence and absence of PGF2α (1 μM) for 15 min. Treatments stimulated phosphatidylinositol hydrolysis as in Exp 1 (p < 0.05). Progesterone concentrations in incubation medium were increased in response to RU486 and PGF2α (p < 0.05). Collectively, these data suggest that RU486 and PGF2α act to stimulate phosphatidylinositol hydrolysis in the mature ovine CL.

Transcriptome Analysis of Porcine Granulosa Cells in Healthy and Atretic Follicles: Role of Steroidogenesis and Oxidative Stress

One of the main causes of female infertility is a deregulated antral follicular atresia, a process of which the underlying molecular mechanisms are largely unknown. Our objective was therefore to characterize the complex transcriptome changes in porcine granulosa cells of healthy antral (HA) and advanced antral atretic (AA) follicles, using ELISA and RNA-Seq followed by qRT-PCR and immunohistochemistry. Granulosa cell RNA-Seq data revealed 2160 differentially expressed genes, 1483 with higher and 677 with lower mRNA concentrations in AA follicles. Bioinformatic analysis showed that the upregulated genes in AA follicles were highly enriched in inflammation and apoptosis processes, while the downregulated transcripts were mainly highlighted in the steroid biosynthesis pathway and response to oxidative stress processes including antioxidant genes (e.g., GSTA1, GCLC, GCLM, IDH1, GPX8) involved in the glutathione metabolism pathway and other redox-related genes (e.g., RRM2B, NDUFS4). These observations were confirmed by RT-qPCR and immunohistochemistry. Additionally, the granulosa cells of AA follicles express significantly stronger 8-OHdG immunostaining, a marker of oxidative DNA damage, implicating that oxidative stress may participate in follicular atresia. We hypothesize that the decrease in anti-apoptotic factors and steroid hormones coincides with increased oxidative stress markers and the expression of pro-apoptotic factors, all contributing to antral follicular atresia.

Procyanidin B1 promotes in vitro maturation of pig oocytes by reducing oxidative stress

Oxidative stress negatively affects the in vitro maturation (IVM) of oocytes. Procyanidin B1 (PB1) is a natural polyphenolic compound that has antioxidant properties. In this study, we investigated the effect of PB1 supplementation during IVM of porcine oocytes. Treatment with 100 μM PB1 significantly increased the MII oocytes rate (p <0.05), the parthenogenetic (PA) blastocyst rate (p <0.01) and the total cell number in the PA blastocyst (p < 0.01) which were cultured in regular in vitro culture (IVC) medium. The PA blastocyst rate of regular MII oocytes activated and cultured in IVC medium supplemented with 100 and 150 μM PB1 significantly increased compared with control (p < 0.01 and p < 0.05). We also evaluated the reactive oxygen species (ROS) levels, mitochondrial membrane potential (Δψm) levels, glutathione (GSH) levels, and apoptotic levels in MII oocytes and cumulus cells following 100 μM PB1 treatment. The results showed that the PB1 supplementation decreased ROS production and apoptotic levels. In addition, PB1 was found to increase Δψm levels and GSH levels. In conclusion, PB1 inhibited apoptosis of oocytes and cumulus cells by reducing oxidative stress. Moreover, PB1 improved the quality of oocytes and promoted PA embryo development. Taken together, our results suggest that PB1 is a promising antioxidant additive for IVM of oocytes.

Glyphosate and its formulation Roundup impair pig oocyte maturation

Glyphosate, formulated as glyphosate-based herbicides (GBHs) including the best-known formulation Roundup, is the world's most widely used herbicide. During the last years, the growing and widespread use of GBHs has raised a great concern about the impact of environmental contamination on animal and human health including potential effect on reproductive systems. Using an in vitro model of pig oocyte maturation, we examined the biological impact of both glyphosate and Roundup on female gamete evaluating nuclear maturation, cytoplasmic maturation and developmental competence of oocytes, steroidogenic activity of cumulus cells as well as intracellular levels of glutathione (GSH) and ROS of oocytes. Our results indicate that although exposure to glyphosate and Roundup during in vitro maturation does not affect nuclear maturation and embryo cleavage, it does impair oocyte developmental competence in terms of blastocyst rate and cellularity. Moreover, Roundup at the same glyphosate-equivalent concentrations was shown to be more toxic than pure glyphosate, altering steroidogenesis and increasing oocyte ROS levels, thus confirming that Roundup adjuvants enhance glyphosate toxic effects and/or are biologically active in their side-effect and therefore should be considered and tested as active ingredients.

Effect of Frozen Embryo Transfer and Progestin-primed Ovary Stimulation on IVF outcomes in women with high body mass index

Among women undergoing IVF, high BMI negatively affects pregnancy outcomes when using the conventional ovary stimulating protocols combined with fresh embryo transfer. Therefore, finding a proper treatment for these high BMI women is more important and urgent when obesity is prevalent. In our study, we reported a retrospective study of 4457 women who were divided into normal BMI group (18.5 kg/m²–24.9 kg/m²) and high BMI group (≥25 kg/m²) undergoing 4611 IVF treatment cycles with frozen embryo transfer (FET). We found the high BMI group originally had the poor oocytes performance, but after FET they got the similar pregnancy outcomes as the normal BMI group. Then under FET we analyzed the IVF outcomes of our new progestin-primed ovary stimulation (PPOS) protocol, indicating that the hMG + MPA (4 or 10 mg/d) groups had the obvious better pregnancy results than the conventional short group in the high BMI group, and binary logistic regression analysis showed the hMG + MPA (10 mg/d) group was associated with better pregnancy outcomes than the hMG + MPA (4 mg/d) group. These results indicate PPOS - hMG + MPA (10 mg/d) combined with FET might be a new potential treatment choice for the high BMI women undergoing IVF treatments.

Toxic effects of atrazine on porcine oocytes and possible mechanisms of action

Because atrazine is a widely used herbicide, its adverse effects on the reproductive system have been extensively researched. In this study, we investigated the effects of atrazine exposure on porcine oocyte maturation and the possible mechanisms. Our results showed that the rates of oocyte maturation significantly decreased after treatment with 200 μM atrazine in vitro. Atrazine treatment resulted in abnormal spindle morphology but did not affect actin distribution. Atrazine exposure not only triggered a DNA damage response but also decreased MPF levels in porcine oocytes. Our results also revealed that atrazine worsened porcine oocyte quality by causing excessive accumulation of superoxide radicals, increasing cathepsin B activity, and decreasing the GSH level and mitochondrial membrane potential. Furthermore, atrazine decreased developmental competence of porcine oocytes up to the blastocyst stage and changed some properties: cell numbers, apoptosis, and related gene expression levels. Collectively, our results indicate that porcine oocyte maturation is defective after atrazine treatment at least through disruption of spindle morphology, MPF activity, and mitochondrial function and via induction of DNA damage, which probably reduces developmental competence.

The Role of Glucose Metabolism on Porcine Oocyte Cytoplasmic Maturation and Its Possible Mechanisms

In the present study, we investigated the potential role of glucose and pyruvate in the cytoplasmic maturation of porcine oocytes by investigating the effect of glucose and/or pyruvate supplementation, in the presence or absence of 10% porcine follicular fluid (PFF), on meiotic maturation and subsequent embryo development. In the absence of 10% PFF, without exogenous addition of glucose and pyruvate, the medium seemed unable to support maturation. In the presence of 10% PFF, the addition of 5.6 mM glucose and/or 2 mM pyruvate during in vitro maturation of cumulus enclosed oocytes increased MII oocyte and blastocyst rates. In contrast, oocytes denuded of cumulus cells were not able to take full advantage of the glucose in the medium, as only pyruvate was able to increase the MII rate and the subsequent early embryo developmental ability. Treatment of cumulus enclosed oocytes undergoing maturation with 200 μM dehydroepiandrosterone (DHEA), a pentose phosphate pathway inhibitor, or 2 μM iodoacetate (IA), a glycolysis inhibitor, significantly reduced GHS, intra-oocyte ATP, maternal gene expression, and MPF activity levels. DHEA was also able to increase ROS and reduce the levels of NADPH. Moreover, blastocysts of the DHEA- or IA-treated groups presented higher apoptosis rates and markedly lower cell proliferation cell rates than those of the non-treated group. In conclusion, our results suggest that oocytes maturing in the presence of 10% PFF can make full use of energy sources through glucose metabolism only when they are accompanied by cumulus cells, and that pentose phosphate pathway (PPP) and glycolysis promote porcine oocyte cytoplasmic maturation by supplying energy, regulating maternal gene expression, and controlling MPF activity.