In vitro maturation of porcine oocytes with retinoids improves embryonic development

Retinoic Acid Action in Cumulus Cells: Implications for Oocyte Development and In Vitro Fertilization

In the field of human in vitro fertilization (IVF), selecting the best oocyte for freezing or embryo for transfer remains an important focus of clinical practice. Although several techniques are and have been used for this goal, results have generally not been favorable and/or are invasive such that damage to some embryos occurs, resulting in a reduced number of healthy births. Therefore, the search continues for non-invasive oocyte and embryo quality markers that signal the development of high-quality embryos. Multiple studies indicate the important positive effects of retinoic acid (RA) on oocyte maturation and function. We previously showed that a high follicular fluid (FF) RA concentration at the time of oocyte retrieval in IVF protocols was associated with oocytes, giving rise to the highest quality embryos, and that cumulus granulosa cells (CGCs) are the primary source of follicle RA synthesis. Data also demonstrated that connexin-43 (Cx43), the main connexin that forms gap junctions in CGCs, is regulated by RA and that RA induces a rapid increase in gap junction communication. Here, we hypothesize that CGC RA plays a causal role in oocyte competency through its action on Cx43 and, as such, may serve as a biomarker of oocyte competence. Multiple studies have demonstrated the requirement for Cx43 in CGCs for the normal progression of folliculogenesis, and that the increased expression of this connexin is linked to the improved developmental competence of the oocyte. The data have shown that RA can up-regulate gap junction intercellular communication (GJIC) in the cumulus-oocyte complex via a non-genomic mechanism that results in the dephosphorylation of Cx43 and enhanced GJIC. Recognizing the positive role played by gap junctions in CGCs in oocyte development and the regulation of Cx43 by RA, the findings have highlighted the possibility that CGC RA levels may serve as a non-invasive indicator for selecting high-quality oocytes for IVF procedures. In addition, the data suggest that the manipulation of Cx43 with retinoid compounds could provide new pharmacological approaches to improve IVF outcomes in cases of failed implantation, recurrent miscarriage, or in certain diseases that are characterized by reduced fecundity, such as endometriosis.

The role of acupuncture in women with advanced reproductive age undergoing in vitro fertilization-embryo transfer: A randomized controlled trial and follicular fluid metabolomics study

BACKGROUND

The objective of this study was to determine the efficacy of acupuncture on the outcome of in vitro fertilization (IVF) in elderly infertile patients with kidney qi deficiency, and to explore its possible mechanism from the perspective of pseudo-targeted metabolomics of follicular fluid.

METHODS

Sixty cases of elderly women undergoing IVF were sampled and randomly divided into 2 equal groups: the treatment and the elderly control (HA) group. In the treatment group, routine ovulation induction combined with acupuncture treatment was used. Routine ovulation induction combined with sham acupuncture was used in the HA group. Reproductive outcomes of the 2 groups were compared. The follicular fluid of patients obtained on the day of oocyte retrieval was analyzed by the ultra-high-performance liquid chromatography-mass spectrometry analysis system.

RESULTS

Compared with the HA group, the score of kidney qi deficiency syndrome in the treatment group was significantly decreased, and the 2 PN fertilization rate, high-quality embryo rate and cumulative pregnancy rate were significantly increased (P < .05). Through the identification of target metabolites, 3 metabolic pathways were found to be closely related to the developmental potential of oocytes, namely: Retinol metabolism pathway; Glycine, serine, and threonine metabolism pathway; Glycerophospholipid metabolism pathway.

CONCLUSION

From our findings, acupuncture can improve the quality of oocytes thus bettering the outcome of IVF-assisted pregnancy in elderly patients with kidney qi deficiency.

TRIAL REGISTRATION

ChiCTR1800018329.

The modulator role of Urtica dioica on deleterious effects of retinoic acid high doses on histological parameters and fertilization of rats

Aim

This study purposed to evaluate the modulator and protective role of Urtica dioica (UD) extract against deleterious effects of retinoic acid (RA) high doses on histological parameters and fertilization of rats.

Materials and methods

For the in-vivo phase, 60 female Wistar rats were divided into 6 identical groups as 1) control, 2) 25 mg/kg RA, 3) 25 mg/kg UD extract, 4) 50 mg/kg UD extract, 5) UD extract (25 mg/kg) + RA (25 mg/kg), and 6) UD extract (50 mg/kg) + RA (25 mg/kg). Biochemical parameters, including luteinizing hormone (LH), folliclestimulating hormone (FSH), malondialdehyde (MDA) levels, superoxide dismutase (SOD), and catalase (CAT) activities, were measured. In the in-vitro phase, oocytes were obtained from 10 female rats without injection. In addition to the mentioned parameters, histological parameters (oocytes in various stages) and the results of IVM, IVF, and embryo developments were assessed and compared among the groups with the use of one-way ANOVA and Tukey's post hoc tests.

Results

The high dosage of RA significantly reduced the LH and FSH levels; however, UD alone and with RA increased the hormone levels in rats. Regarding the reactive oxygen species (ROS) activity levels in rats' blood samples, RA increased the MDA and decreased the SOD and CAT levels. Treatment with UD extract (UD + RA groups) significantly improved the parameters mentioned, showing UD's antioxidant effect. The rate of oocyte maturation, 2-cell-4-cell and 4-cell-8-cell embryos, and blastocyst formation increased significantly in the groups in which UD extracts were administered compared to the control and RA groups. Furthermore, the increases were significant in the UD + RA groups compared to the RA group.

Conclusion

UD extract can significantly reduce RA high doses side effects on histological parameters and fertilization of rats and has the protective potential against RA deleterious effects.

Intrafollicular Retinoic Acid Signaling Is Important for Luteinizing Hormone-Induced Oocyte Meiotic Resumption

It has been clear that retinoic acid (RA), the most active vitamin A (VA) derivative, plays a central role in governing oocyte meiosis initiation. However, it has not been functionally determined if RA participates in luteinizing hormone (LH)-induced resumption from long-lasting oocyte meiotic arrest, which is essential for haploid oocyte formation. In the present study, using well-established in vivo and in vitro models, we identified that intrafollicular RA signaling is important for normal oocyte meiotic resumption. A mechanistic study indicated that mural granulosa cells (MGCs) are the indispensable follicular compartment for RA-prompted meiotic resumption. Moreover, retinoic acid receptor (RAR) is essential for mediating RA signaling to regulate meiotic resumption. Furthermore, we found zinc finger protein 36 (ZFP36) is the transcriptional target of RAR. Both RA signaling and epidermal growth factor (EGF) signaling were activated in MGCs in response to LH surge, and two intrafollicular signalings cooperate to induce rapid Zfp36 upregulation and Nppc mRNA decrease, which is critical to LH-induced meiotic resumption. These findings extend our understanding of the role of RA in oocyte meiosis: RA not only governs meiotic initiation but also regulates LH-induced meiotic resumption. We also emphasize the importance of LH-induced metabolic changes in MGCs in this process.

Isolation of female germline stem cells from neonatal piglet ovarian tissue and differentiation into oocyte-like cells

It has been generally accepted that the number of oocyte pool in mammalian ovaries is limited and irreversibly consumed throughout the adulthood until menopause, which has been challenged by the existence of female germline stem cells (FGSCs) and their differentiation potentials into oocytes through mitosis. However, there have been a few reports about the existence of porcine FGSCs (pFGSCs) in the neonatal piglet ovarian tissues. In this study, the pFGSCs were isolated from the one day post partum (1 dpp) piglet ovaries by a differential anchoring velocity method combined with the magnetic cell sorting (MACS) using VASA antibody. The gene expression levels and in vitro differentiation potentials of pFGSCs were subsequently analyzed. The results showed that Oct4, C-kit, Vasa, Stella, Ifitm3 and Dazl were expressed in the pFGSCs. A small portion of pFGSCs (2.81 ± 0.76%) spontaneously differentiated into oocyte-like cells (OLCs) with a mean diameter of 50 μm and gene expressions of Vasa, Ifitm3, Blimp1, Gdf9, Zp3, Dazl and Stella. Compared with that of the spontaneous differentiation system, the differentiation rates of pFGSCs into OLCs were significantly increased after the co-supplementations of porcine follicular fluid (PFF) and retinoic acid (RA). Taken together, these above results revealed the direct evidences for the existence of pFGSCs in 1 dpp piglet ovaries and the in vitro differentiation potential of pFGSCs into OLCs, benefiting future research related to the in vitro establishment of livestock FGSCs and the in vitro differentiation of pFGSCs.

Oviductal Extracellular Vesicles Enhance Porcine In Vitro Embryo Development by Modulating the Embryonic Transcriptome

Oviductal extracellular vesicles (oEVs) have been identified as important components of the oviductal fluid (OF) and have been pointed to as key modulators of gamete/embryo-maternal interactions. Here, we determined the functional impact of oEVs on embryo development and the embryonic transcriptome in porcine. Experiment 1 examined the effect of oEVs and OF on embryo development. In vitro-produced embryos were cultured with oEVs or OF for 2 or 7 days using an in vitro sequential system or without supplementation (control). Experiment 2 analyzed transcriptomic alterations of EV-treated embryos versus control and the oEVs RNA cargo by RNA-sequencing. Two days of EV treatment enhanced embryo development over time when compared to other treatments. Different RNA expression profiles between embryos treated with EVs for two or seven days and untreated controls were obtained, with 54 and 59 differentially expressed (DE) genes and six and seven DE miRNAs, respectively. In oEV RNA cargo, 12,998 RNAs and 163 miRNAs were identified. Integrative analyses pointed to specific oEV components that might act as modulators of the embryonic transcriptome, such as S100A11, ANXA2 or miR-21-5p. Overall, the findings suggested that oEVs could be a potential strategy to improve porcine IVP outcomes, particularly by using two days of EV treatment.

Unveiling how vitrification affects the porcine blastocyst: clues from a transcriptomic study

Background

Currently, there is a high demand for efficient pig embryo cryopreservation procedures in the porcine industry as well as for genetic diversity preservation and research purposes. To date, vitrification (VIT) is the most efficient method for pig embryo cryopreservation. Despite a high number of embryos survives in vitro after vitrification/warming procedures, the in vivo embryo survival rates after embryo transfer are variable among laboratories. So far, most studies have focused on cryoprotective agents and devices, while the VIT effects on porcine embryonic gene expression remained unclear. The few studies performed were based on vitrified/warmed embryos that were cultured in vitro (IVC) to allow them to re–expand. Thus, the specific alterations of VIT, IVC, and the cumulative effect of both remained unknown. To unveil the VIT-specific embryonic alterations, gene expression in VIT versus (vs.) IVC embryos was analyzed. Additionally, changes derived from both VIT and IVC vs. control embryos (CO) were analyzed to confirm the VIT embryonic alterations. Three groups of in vivo embryos at the blastocyst stage were analyzed by RNA–sequencing: (1) VIT embryos (vitrified/warmed and cultured in vitro), (2) IVC embryos and (3) CO embryos.

Results

RNA–sequencing revealed three clearly different mRNA profiles for VIT, IVC and CO embryos. Comparative analysis of mRNA profiles between VIT and IVC identified 321, differentially expressed genes (DEG) (FDR < 0.006). In VIT vs. CO and IVC vs. CO, 1901 and 1519 DEG were found, respectively, with an overlap of 1045 genes. VIT-specific functional alterations were associated to response to osmotic stress, response to hormones, and developmental growth. While alterations in response to hypoxia and mitophagy were related to the sum of VIT and IVC effects.

Conclusions

Our findings revealed new insights into the VIT procedure-specific alterations of embryonic gene expression by first comparing differences in VIT vs. IVC embryos and second by an integrative transcriptome analysis including in vivo control embryos. The identified VIT alterations might reflect the transcriptional signature of the embryo cryodamage but also the embryo healing process overcoming the VIT impacts. Selected validated genes were pointed as potential biomarkers that may help to improve vitrification.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40104-021-00672-1.

Enhancing in vitro oocyte maturation competence and embryo development in farm animals: roles of vitamin-based antioxidants – a review

Oocyte/embryo in vitro culture is one of the most important assisted reproductive technologies used as a tool for maintaining genetic resources biodiversity and the inheritance of valuable genetic resources through generations. The success of such processes affects the final goal of the in vitro culture, getting viable and healthy offspring. In common in vitro oocyte maturation and/or embryo development techniques, the development of oocytes/embryos is carried out at 5% carbon dioxide and roughly 20% atmosphere-borne oxygen ratios in cell culture incubators due to their reduced cost in comparison with low atmospheric oxygen-tension incubators. These conditions are usually accompanying by the emergence of reactive oxygen species (ROS), which can extremely damage cell membrane integrity and other vital cellular organelles, as well as genetic material. The present review mainly focuses on the antioxidant roles of different vitamins on in vitro oocyte maturation competence and embryo development in farm animals. Because, the conditions of in vitro embryo production (IVEP) are usually accompanying by the emergence of reactive oxygen species (ROS), which can extremely damage cell membrane integrity and other vital cellular organelles as well as genetic material. The use of antioxidant agents may prevent the extreme augmentation of ROS generation and enhance in vitro matured oocyte competence and embryo development. Therefore, this review aimed to provide an updated outline of the impact of antioxidant vitamin (Vit) supplementations during in vitro maturation (IVM) and in vitro fertilization (IVF) on oocyte maturation and consequent embryo development, in various domestic animal species. Thus, the enrichment of the culture media with antioxidant agents may prevent and neutralize the extreme augmentation of ROS generation and enhance the in vitro embryo production (IVEP) outcomes.

Retinoic Acid and Germ Cell Development in the Ovary and Testis

Retinoic acid (RA), a derivative of vitamin A, is critical for the production of oocytes and sperm in mammals. These gametes derive from primordial germ cells, which colonize the nascent gonad, and later undertake sexual differentiation to produce oocytes or sperm. During fetal development, germ cells in the ovary initiate meiosis in response to RA, whereas those in the testis do not yet initiate meiosis, as they are insulated from RA, and undergo cell cycle arrest. After birth, male germ cells resume proliferation and undergo a transition to spermatogonia, which are destined to develop into haploid spermatozoa via spermatogenesis. Recent findings indicate that RA levels change periodically in adult testes to direct not only meiotic initiation, but also other key developmental transitions to ensure that spermatogenesis is precisely organized for the prodigious output of sperm. This review focuses on how female and male germ cells develop in the ovary and testis, respectively, and the role of RA in this process.

The Usefulness of Retinoic Acid Supplementation during In Vitro Oocyte Maturation for the In Vitro Embryo Production of Livestock: A Review

Simple Summary

In this review, we provide the previous studies, state-of-the-art practices, and potential implications of retinoic acid for improving in vitro livestock embryo production.

Abstract

Retinoic acid (RA) is an indigenous metabolite and descriptive physiologically functioning constituent of vitamin A. Retinoids were documented as vital regulators for cell development and distinction, embryonic growth, and reproductive function in both male and female livestock. Previously, RA has been shown to have several positive impacts in vivo and in vitro and critically control many reproductive events, such as oocyte development, follicular growth, and early embryonic growth. In addition, RA manages apoptotic signaling and oxidative damages in cells. Recently, RA has been used widely in assisted reproductive technology fields, especially during in vitro embryo development in various mammalian species, including buffaloes, bovine, goats, sheep, pigs, and rabbits. However, the optimum concentration of RA greatly differs based on the condition of maturation media and species. Based on the obtained findings, it was generally accepted that RA enhances nuclear oocyte maturation, cleavage and maturation rates, blastocyst formation, and embryo development. As such, it possesses antioxidant properties against reactive oxygen species (ROS) and an anti-apoptotic effect through enhancing the transcription of some related genes such as superoxide dismutase, prostaglandin synthase, glutathione peroxidase, peroxiredoxins, and heme oxygenase. Therefore, the current review concludes that an addition of RA (up to 50 nM) has the potential to improve the oocyte maturation media of various species of livestock due to its antioxidant activity.

Effects of all-trans retinoic acid on the in vitro maturation of camel (Camelus dromedarius) cumulus-oocyte complexes

All-trans retinoic acid (RA) is a metabolite of vitamin A and has pleiotropic actions on many different biological processes, including cell growth and differentiation, and is involved in different aspects of fertility and developmental biology. In the current study, we investigated the effects of RA on camel (Camelus dromedarius) cumulus-oocyte complex in vitro maturation (IVM). IVM medium was supplemented with 0, 10, 20, and 40 µM RA. Application of 20 µM RA significantly reduced the proportion of degenerated oocytes and significantly improved oocyte meiosis and first polar body extrusion compared to the control and other experimental groups. Retinoic acid significantly reduced the mRNA transcript levels of apoptosis-related genes, including BAX and P53, and reduced the BAX/BCL2 ratio. In addition, RA significantly reduced the expression of the Transforming growth factor beta (TGFβ) pathway-related transcripts associated with the actin cytoskeleton, ACTA2 and TAGLN; however, RA increased TGFβ expression in cumulus cells. The small molecule SB-431542 inhibits the TGFβ pathway by inhibiting the activity of activin receptor-like kinases (ALK-4, ALK-5, and ALK-7); however, combined supplementation with RA during IVM compensated for the inhibitory effect of SB-431542 on cumulus expansion, oocyte meiosis I, and first polar body extrusion in activated oocytes. The current study shows the beneficial effects of RA on camel oocyte IVM and provides a model to study the multifunctional mechanisms involved in cumulus expansion and oocyte meiosis, particularly those involved in the TGFβ pathway.

Retinoic acid improves maturation rate and upregulates the expression of antioxidant-related genes in in vitro matured buffalo (Bubalus bubalis) oocytes

Retinoic acid, vitamin A metabolite, plays a role in oocyte development and maturation in different ways including gene expression alteration and/or prohibiting oxidative stress. The objective of this study was to examine the effect of 9-cis-retinoic acid (9-cisRA) on the quality and maturation rate of buffalo oocytes. Cumulus-oocyte complexes (COCs, n = 460) were collected from ovaries of slaughtered buffalos. Varying concentrations of 9-cisRA (0, 5, 50, and 200 nM) were added to the maturation medium, and the following parameters were analyzed: (i) maturation and cleavage rates, (ii) mitochondrial activity and reactive oxygen species (ROS) levels, (iii) expression level of antioxidant-related genes (PRDX1, SOD1, CAT, HOMX1, and GPX4) using RT-qPCR. Maturation rate was significantly improved in 5 nM 9-cisRA oocyte group (95.8%, P < .05) compared to control and other treatment groups (86.7% in control group). The same oocyte group exhibited significantly higher mitochondrial membrane potential activity and lower ROS accumulation level compared to other treatment groups. Antioxidant-related genes were up-regulated in oocytes matured with 5 or 50 nM 9-cisRA compared to control and 200 nM 9-cisRA groups. In contrast, 200 nM of 9-cisRA showed a clear down-regulation for antioxidant-related genes except for PRDX1. In conclusion, supplementation of 9-cisRA with a lower concentration (5 nM) to the buffalo oocytes maturation media promotes maturation rate through a protection mechanism that maintains adequate levels of antioxidant-related transcripts and improves mitochondrial activity. However, 9-cisRA has no significant effect on the cleavage rate of the treated oocytes.

Antioxidant and developmental capacity of retinol on the in vitro culture of rabbit embryos

Oxidative stress is a major cause of defective embryo development during in vitro culture. Retinoids are recognized as non-enzymatic antioxidants and may have an important role in the regulation of cell differentiation and vertebrate development. However, there are not enough reports discussing the antioxidant and developmental capacity of retinoids, including retinol (RT), on the in vitro development of embryos recovered from livestock animals, particularly in rabbit species. Therefore, morula embryos obtained from nulliparous Red Baladi rabbit does were cultured for 48 h in TCM199 medium in the absence of RT (control group) or in the presence of RT at concentrations of 10, 100 and 1000 nM. The developmental capacity to the hatched blastocyst stage, the antioxidant biomarker assay and the expression of several selected genes were analyzed in each RT group. The data show that RT significantly (P<0.001) promoted the embryo hatchability rate at the concentration of 1000 nM to 69.44% versus 29.71% for the control. The activity of malondialdehyde (MDA) level was significantly (P<0.05) lower in the RT groups than in the control group, while the total antioxidant capacity (TAC), superoxide dismutase (SOD) and glutathione peroxidase (GPx) activities were significantly (P<0.05) higher following treatment with RT. Furthermore, RT treatment considerably upregulated the relative expression of gap junction protein alpha 1 (GJA1), POU class 5 homeobox 1 (POU5F1) and superoxide dismutase 1 (SOD1) genes compared with the control group. The current study highlights the potential effects of RT as antioxidant in the culture medium on the in vitro development of rabbit embryos.

Combined Effect of Retinoic Acid and Basic Fibroblast Growth Factor on Maturation of Mouse Oocyte and Subsequent Fertilization and Development

Background

Many autocrine and paracrine elements that are produced within follicular niche have been the focus of much in vitro maturation (IVM) research. The present study was carried out to compare retinoic acid (RA) and basic fibroblast growth factor (bFGF) efficacy on IVM of mouse oocytes, and their further dual consumption to reach an optimal protocol.

Materials and Methods

In this experimental study, germinal vesicle (GV) oocytes obtained from two-months-old NMRI mice were randomly divided into control, sham and three experimental groups. The basic culture medium was α-MEM supplemented with 10% fetal bovine serum (FBS), 50 mg/l streptomycin, 60 mg/l penicillin and 10 ng/ ml epidermal growth factors. Each of the experimental groups received one of the following treatments: RA (2 µM), bFGF (20 ng/ml) or combination of RA and bFGF with the indicated concentrations. After 24 hours, capacitated spermatozoa were added to in vitro matured oocytes. Five hours later, the oocytes were cultured in fresh droplets of M2 medium for 24 hours and assessed for cleavage to the two-cells stage.

Results

As compared with the control group, the rate of maturation was significantly increased in the RA (P<0.001) and bFGF+RA (P<0.02) groups with 58 ± 10 and 57 ± 3.46, respectively. The rate of maturation was significant in the RA (P<0.02) and bFGF+RA (P<0.03) groups, in comparison with the bFGF group. The bFGF+RA group had higher rate (83 ± 1.52) of two-cells development, than control (33 ± 1, P<0.001).

Conclusion

Our findings showed beneficial effects of 2 µM RA and 20 ng/ml bFGF combination on mouse oocyte IVM.

Retinoic acid enhances progesterone production via the cAMP/PKA signaling pathway in immature rat granulosa cells

Retinoic acid (RA) is a metabolite of vitamin A and has important roles in development, differentiation, and reproduction. Activin has been shown to regulate the RA pathway and affect granulosa cell (GC) proliferation, suggesting that RA is important for early follicle development. However, little is known about the effects of RA on GC functions, particularly steroidogenesis, during the early follicle stage. The aim of this study was to investigate the effects of all-trans-RA (atRA) on progesterone production in immature rat GCs cultured without gonadotropin. Our results demonstrated that atRA enhanced progesterone production by upregulating the levels of steroidogenic acute regulatory protein (StAR) and cytochrome P450scc (Cyp11a1) mRNAs, but not 3β-hydroxysteroid dehydrogenase mRNA in immature rat GCs. Additionally, analysis of the mechanisms through which atRA upregulated StAR and Cyp11a1 mRNAs revealed that atRA enhanced intracellular cAMP accumulation and phosphorylation of cAMP response-element binding protein (CREB). In addition, H-89, an inhibitor of protein kinase A (PKA), abolished the stimulatory effects of atRA, indicating that atRA enhanced progesterone synthesis through cAMP/PKA signaling. In conclusion, our data demonstrated that atRA has a crucial role in progesterone synthesis in rat GCs during the early follicle stage.

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atRA upregulated StAR and Cyp11a1 and enhanced progesterone production.

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atRA enhanced intracellular cAMP accumulation and phosphorylation of CREB.

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Inhibition of PKA abolished the stimulatory effects of atRA.

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atRA mediated progesterone synthesis in rat GCs during the early follicle stage.

A role for retinoids in human oocyte fertilization: regulation of connexin 43 by retinoic acid in cumulus granulosa cells

Retinoids are essential for ovarian steroid production and oocyte maturation in mammals. Oocyte competency is known to positively correlate with efficient gap junction intercellular communication (GJIC) among granulosa cells in the cumulus-oocyte complex. Connexin 43 (C x 43) is the main subunit of gap junction channels in human cumulus granulosa cells (CGC) and is regulated by all-trans retinoic acid (ATRA) in other hormone responsive cell types. The objectives of this study were to quantify retinoid levels in human CGC obtained during IVF oocyte retrievals, to investigate the potential relationship between CGC ATRA levels and successful oocyte fertilization, and to determine the effects of ATRA on C x 43 protein expression in CGC. Results showed that CGC cultures actively metabolize retinol to produce ATRA. Grouped according to fertilization rate tertiles, mean ATRA levels were 2-fold higher in pooled CGC from women in the highest versus the lowest tertile (P < 0.05). ATRA induced a rapid dephosphorylation of C x 43 in CGC and granulosa cell line (KGN) cultures resulting in a >2-fold increase in the expression of the functional non-phosphorylated (P0) species (P < 0.02). Similar enhancement of P0 by ATRA was shown in CGC and KGN cultures co-treated with LH or hCG which, by themselves, enhanced the protein levels of C x 43 without altering its phosphorylation profile. Correspondingly, the combination of ATRA+hCG treatment of KGN caused a significant increase in GJIC compared with single agent treatments (P < 0.025) and a doubling of GJIC from that seen in untreated cells (P < 0.01). These findings indicate that CGC are a primary site of retinoid uptake and ATRA biosynthesis. Regulation of C x 43 by ATRA may serve an important role in folliculogenesis, development of oocyte competency, and successful fertilization by increasing GJIC in CGC.

Analysis of follicular fluid retinoids in women undergoing in vitro fertilization: retinoic acid influences embryo quality and is reduced in women with endometriosis

Retinol (ROL) and its biologically active metabolite, all-trans retinoic acid (ATRA), are essential for a number of reproductive processes. However, there is a paucity of information regarding their roles in ovarian folliculogenesis, oocyte maturation, and early embryogenesis. The objectives of this study were to quantify and compare peripheral plasma (PP) and follicular fluid (FF) retinoid levels, including ATRA in women undergoing in vitro fertilization (IVF) and to investigate the relationship between retinoid levels and embryo quality. Retinoid levels were evaluated in PP and FF from 79 women undergoing IVF at the time of oocyte retrieval and corresponding embryo quality assessed on a daily basis after retrieval for 3 days until uterine transfer. Analysis compared the retinoid levels with day 3 embryo grades and between endometriosis versus control patients. Results demonstrated distinctive levels of retinoid metabolites and isomers in FF versus PP. There was a significantly larger percentage of high-quality grade I embryos derived from the largest versus smallest follicles. An increase in follicle size also correlated with a >50% increase in FF ROL and ATRA concentrations. Independent of follicle size, FF yielding grade I versus nongrade I embryos showed higher mean levels of ATRA but not ROL. In a nested case-control analysis, control participants had 50% higher mean levels of ATRA in their FF and PP than women with endometriosis. These findings strongly support the proposition that ATRA plays a fundamental role in oocyte development and quality, and that reduced ATRA synthesis may contribute to decreased fecundity of participants with endometriosis.

The influence of 9-cis-retinoic acid on nuclear and cytoplasmic maturation and gene expression in canine oocytes during in vitro maturation

Retinoids have important roles in regulation of oocyte nuclear and cytoplasmic maturation. The present study investigated the effects of a retinoid metabolite on nuclear maturation, cytoplasmic maturation, and gene expression in canine oocytes during in vitro maturation (IVM). Cumulus-oocyte complexes (COCs) were harvested from ovaries by slicing. Only oocytes that were >120 μm in diameter, with a homogeneous dark cytoplasm and three or more layers of compact cumulus cells were used. Varying concentrations of 9-cis retinoic acid (9-cis-RA; 0, 5, 50, and 500 nm) were included in the maturation medium, and the following were measured: (i) oocyte nuclear maturation after culture for 48 h; (ii) cytoplasmic granular migration by labeling of oocytes with fluorescein isothiocyanate labeled lectins; and (iii) relative expression of genes related to apoptosis (BAX and BclII) in cumulus cells detached from oocytes, by semiquantitative reverse transcriptase-polymerase chain reaction. After 48 h culture with IVM, the highest percentage of oocytes that had developed to the metaphase II (MII) stage were in the 5 nm 9-cis-RA treatment group (18.3 ± 2.5%; P < 0.05). Complete granular migration was observed in oocytes matured with 5 nm 9-cis-RA, consistent with a commensurate gain in developmental competence. Treatment with 5 nm 9-cis-RA had no effect on BclII gene expression, but downregulated BAX expression. In conclusion, since 5 nm 9-cis-RA was beneficial to nuclear and cytoplasmic maturation of canine oocytes, we inferred an important role for 9-cis-RA during IVM.

Effects of retinoic acid on maturation of immature mouse oocytes in the presence and absence of a granulosa cell co-culture system

PURPOSE

Evaluation of the all-trans retinoic acid (t-RA) effects on in vitro maturation (IVM) and in vitro fertilization (IVF) of immature mouse oocytes in the presence and absence of granulosa cell monolayer.

METHODS

Denuded oocytes isolated from mice ovaries and matured in IVM medium alone (Control I), IVM medium in the presence of granulosa cells (Control II), IVM medium with t-RA (Experimental I) and IVM medium simultaneously with t-RA and granulosa cells (Experimental II). After 24 h, matured oocytes were fertilized in T6 medium and their development was followed until the blastocyst stage. Metaphase II oocytes ploidy were evaluated by chromosome counting.

RESULTS

The t-RA group compared to the control groups showed no obvious abnormalities. Additionally maturation and embryo development rates significantly increased in the t-RA treated granulosa cell co-culture system.

CONCLUSIONS

In conclusion, association of t-RA with granulosa cell co-culture during in vitro maturation increases meiosis resumption, formation of metaphase II oocytes, as well as 2-cell and blastocyst stage embryos.

The 9-cis retinoic acid signaling pathway and its regulation of prostaglandin-endoperoxide synthase 2 during in vitro maturation of pig cumulus cell-oocyte complexes and effects on parthenogenetic embryo production

The addition of 9-cis retinoic acid to the oocyte maturation culture medium has a beneficial effect on in vitro fertilized embryos. However, the mechanism of this activity is not known. Therefore, this study was done to elucidate the effect of 9-cis retinoic acid on parthenogenetic embryo production and its signaling pathway and molecular function during in vitro maturation of porcine cumulus cell-oocyte complexes (COCs). Concentrations of 0, 5, 50, and 500 nM 9-cis retinoic acid were added to the in vitro maturation medium, and the embryos were assessed after parthenogenetic activation. Cumulus cells and oocytes from the in vitro matured COCs were separated and subjected to RT-PCR and real-time RT-PCR for detecting retinoic acid receptors and measuring expression of prostaglandin-endoperoxide synthase1 and 2. The addition of 5 nM 9-cis retinoic acid to the maturation medium was beneficial for parthenogenetic embryo production. The effect of 9-cis retinoic acid was exerted directly through the oocytes via the retinoic acid receptor alpha and retinoid X receptor gamma signaling pathways and indirectly through the cumulus cells by the retinoic acid receptor beta and gamma and retinoid X receptor alpha and beta signaling pathways. The addition of 5 nM 9-cis retinoic acid-stimulated cumulus cells reaches full expansion by suppressing their excessive expression of prostaglandin-endoperoxide synthase 2. This study shows that 9-cis retinoic acid can exert its beneficial effect on parthenogenetic embryo production in pigs by multidimensional pathways affecting oocyte maturation.