Effect of leptin supplementation during in vitro oocyte maturation and embryo culture on bovine embryo development and gene expression patterns

New aspect on the regulation of in vitro oocyte maturation: role of the obesity, neuropeptides and adipokines

Oocyte quality determinants and nuclear and cytoplasmic maturation establish essential processes for fertilization and further development of the conceptus. Moreover, female fertility is strongly dependent on the metabolic status of the organism. Numerous sources indicate that obesity impairs ovarian function including oocyte physiology by inhibiting nuclear maturation, stimulating lipotoxicity and inflammation, enabling cumulus cells apoptosis, promoting reactive oxygen species formation and ultimately imposing pathogenic effects on mitochondria leading to infertility. Whereas, the number of overweight and obese individuals has reached alarming levels over the past decades, what is more, by 2030, the prevalence of overweight and obesity might reach 65.3% in adults in China and 78% in the USA. Thus, relationships between reproduction and metabolism are being intensively studied to prevent obesity-induced infertility. The metabolic markers of oocyte condition and function are adipokines and neuropeptides, which regulate food intake, lipid and glucose metabolism, insulin resistance and impart significant influences on reproduction. Thus, in this review, we focus on interrelationships between obesity, oocyte maturation and the role of selected neuropeptides and adipokines including leptin, adiponectin, kisspeptin, nesfatin-1, phoenixin, visfatin, chemerin and vaspin.

Cell specification and functional interactions in the pig blastocyst inferred from single-cell transcriptomics and uterine fluids proteomics

The embryonic development of the pig comprises a long in utero pre- and peri-implantation development, which dramatically differs from mice and humans. During this peri-implantation period, a complex series of paracrine signals establishes an intimate dialogue between the embryo and the uterus. To better understand the biology of the pig blastocyst during this period, we generated a large dataset of single-cell RNAseq from early and hatched blastocysts, spheroid and ovoid conceptus and proteomic datasets from corresponding uterine fluids. Our results confirm the molecular specificity and functionality of the three main cell populations. We also discovered two previously unknown subpopulations of the trophectoderm, one characterised by the expression of LRP2, which could represent progenitor cells, and the other, expressing pro-apoptotic markers, which could correspond to the Rauber's layer. Our work provides new insights into the biology of these populations, their reciprocal functional interactions, and the molecular dialogue with the maternal uterine environment.

The effects of obesity and insulin dysregulation on mare reproduction, pregnancy, and foal health: a review

Obesity is a growing welfare concern in modern equine populations and predisposes horses to disturbances in energy metabolism such as insulin dysregulation. However, equine metabolic syndrome has only been recognized in recent decades. Functioning energy metabolism is pivotal to normal body homeostasis and affects essentially all organ systems, including reproduction. Previous literature suggests that obesity has an effect not only on the reproductive processes in mares but also on offspring health, predisposing the offspring to later-onset orthopedic and metabolic problems. This review focuses on the effects of obesity, insulin dysregulation and hyperinsulinemia on the reproductive functions of mares and the implications on foal health before and after birth. The points of interest are the cyclicity and ovarian function, uterine environment, gestation, the postpartum period, and the newborn foal. The aim is to review the current state of knowledge, and identify outstanding questions that could stimulate future research. This topic is important not only from the equine industry and production perspective but is also relevant for the welfare of future populations and individuals.

Relationships between placental adiponectin, leptin, visfatin and resistin and birthweight in cattle

Adipokines can affect intrauterine development while calf birthweight (CBW) is a breeding standard of calves, which reflects the status of fetal intrauterine development. To explore the correlation between placental adipokines and CBW, 54 healthy Chinese Holstein cows were used in the present study. The cows were grouped according to the CBW of their calves. Placentas were collected immediately after delivery and enzyme-linked immunosorbent assay and reverse transcription-polymerase chain reaction were used to detect the placental expression levels of adiponectin, leptin, visfatin and resistin. Our results show that the mRNA transcription and blood placental content of adiponectin, leptin, visfatin and resistin increased with increasing CBW. The analysis showed that the mRNA transcription levels of placental adiponectin, leptin and resistin were positively correlated with CBW. The mRNA and protein expression levels of adiponectin, leptin and visfatin between the three groups were significantly correlated. Placental resistin mRNA levels correlated positively with adiponectin mRNA, but not leptin or visfatin. The protein expression levels of resistin were significantly positively correlated with those of adiponectin, leptin and visfatin. These results suggest that placental adipokines play important roles in regulating calf intrauterine growth.

Anethole Supplementation During Oocyte Maturation Improves In Vitro Production of Bovine Embryos

Oxidative stress is one of the most detrimental factors that affect oocyte developmental competence and embryo development in vitro. The impact of anethole supplementation to in vitro maturation (IVM) media on oocyte maturation and further bovine in vitro embryo production was investigated. Oocytes of slaughterhouse-derived bovine ovaries were placed in IVM with anethole at different concentrations of 30 (AN30), 300 (AN300), and 2000 μg/mL (AN2000), or without (control treatment). The oocytes were assessed for maturation rates, and for reactive oxygen species (ROS) and ferric reducing antioxidant power (FRAP) levels, and mitochondrial membrane potential. Embryo development was assessed by cleavage and blastocyst rates, and embryo cell number. The percentage of metaphase II oocytes were similar among the treatments (range, 77%-96%). Anethole at 300 μg/mL was the only treatment that yielded higher cleavage and embryo development (morula and blastocyst) rates compared to the control treatment. The ROS production in the oocytes after maturation did not differ among treatments. However, oocytes treated with anethole at 300 μg/mL had higher (P < .05) FRAP and mitochondrial membrane potential compared to the control treatment. Furthermore, AN300 treatment increased (P < .05) the average number of total cells in blastocysts compared to the control and AN30 treatments. The use of anethole at 300 μg/mL during IVM is suggested to improve the quantity and quality of bovine embryos produced in vitro. The beneficial effects of anethole on embryonic developmental competence in vitro seems to be related to its capacity to regulate the redox balance and improve mitochondrial function in oocytes and embryos.

Expression and Impact of Vaspin on In Vitro Oocyte Maturation through MAP3/1 and PRKAA1 Signalling Pathways

Oocyte maturation is a critical stage in embryo production and female reproduction. The aims of this study were to determine: (i) the mRNA and protein expression of vaspin and its receptor 78-kDa glucose-regulated (GRP78) in porcine cumulus-oocyte complexes (COCs) by real-time PCR and Western blot analysis, respectively, and their localisation by immunofluorescence; and (ii) the effects of vaspin on in vitro oocyte maturation (IVM) and the involvement of mitogen ERK1/2 (MAP3/1)- and AMPKα (PRKAA1)-activated kinases in the studied processes. Porcine COCs were matured in vitro for 22 h or 44 h with vaspin at a dose of 1 ng/mL and nuclear maturation assessed by Hoechst 33342 or DAPI staining and the measurement of progesterone (P4) level in the maturation medium. We showed that vaspin and GRP78 protein expression increased in oocytes and cumulus cells after IVM. Moreover, vaspin enhanced significantly porcine oocyte IVM and P4 concentration, as well as MAP3/1 phosphorylation, while decreasing PRKAA1. Using pharmacological inhibitors of MAP3/1 (PD98059) and PRKAA1 (Compound C), we observed that the effect of vaspin was reversed to the control level by all studied parameters. In conclusion, vaspin, by improving in vitro oocyte maturation via MAP3/1 and PRKAA1 kinase pathways, can be a new factor to improve in vitro fertilisation protocols.

Adipokines Expression and Effects in Oocyte Maturation, Fertilization and Early Embryo Development: Lessons from Mammals and Birds

Some evidence shows that body mass index in humans and extreme weights in animal models, including avian species, are associated with low in vitro fertilization, bad oocyte quality, and embryo development failures. Adipokines are hormones mainly produced and released by white adipose tissue. They play a key role in the regulation of energy metabolism. However, they are also involved in many other physiological processes including reproductive functions. Indeed, leptin and adiponectin, the most studied adipokines, but also novel adipokines including visfatin and chemerin, are expressed within the reproductive tract and modulate female fertility. Much of the literature has focused on the physiological and pathological roles of these adipokines in ovary, placenta, and uterine functions. The purpose of this review is to summarize the current knowledge regarding the involvement of leptin, adiponectin, visfatin, and chemerin in the oocyte maturation, fertilization, and embryo development in both mammals and birds.

BOARD INVITED REVIEW: Post-transfer consequences of in vitro-produced embryos in cattle

In vitro embryo production (IVP) in cattle has gained worldwide interest in recent years, but the efficiency of using IVP embryos for calf production is far from optimal. This review will examine the pregnancy retention rates of IVP embryos and explore causes for pregnancy failures. Based on work completed over the past 25 yr, only 27% of cattle receiving IVP embryos will produce a live calf. Approximately 60% of these pregnancies fail during the first 6 wk of gestation. When compared with embryos generated by superovulation, pregnancy rates are 10% to 40% lower for cattle carrying IVP embryos, exemplifying that IVP embryos are consistently less competent than in vivo-generated embryos. Several abnormalities have been observed in the morphology of IVP conceptuses. After transfer, IVP embryos are less likely to undergo conceptus elongation, have reduced embryonic disk diameter, and have compromised yolk sac development. Marginal binucleate cell development, cotyledon development, and placental vascularization have also been documented, and these abnormalities are associated with altered fetal growth trajectories. Additionally, in vitro culture conditions increase the risk of large offspring syndrome. Further work is needed to decipher how the embryo culture environment alters post-transfer embryo development and survival. The risk of these neonatal disorders has been reduced by the use of serum-free synthetic oviductal fluid media formations and culture in low oxygen tension. However, alterations are still evident in IVP oocyte and embryo transcript abundances, timing of embryonic cleavage events and blastulation, incidence of aneuploidy, and embryonic methylation status. The inclusion of oviductal and uterine-derived embryokines in culture media is being examined as one way to improve the competency of IVP embryos. To conclude, the evidence presented herein clearly shows that bovine IVP systems still must be refined to make it an economical technology in cattle production systems. However, the current shortcomings do not negate its current value for certain embryo production needs and for investigating early embryonic development in cattle.

Anethole Supplementation During Oocyte Maturation Improves In Vitro Production of Bovine Embryos

Oxidative stress is one of the most detrimental factors that affect oocyte developmental competence and embryo development in vitro. The impact of anethole supplementation to in vitro maturation (IVM) media on oocyte maturation and further bovine in vitro embryo production was investigated. Oocytes of slaughterhouse-derived bovine ovaries were placed in IVM with anethole at different concentrations of 30 (AN30), 300 (AN300), and 2000 μg/mL (AN2000), or without (control treatment). The oocytes were assessed for maturation rates, and for reactive oxygen species (ROS) and ferric reducing antioxidant power (FRAP) levels, and mitochondrial membrane potential. Embryo development was assessed by cleavage and blastocyst rates, and embryo cell number. The percentage of metaphase II oocytes were similar among the treatments (range, 77%-96%). Anethole at 300 µg/mL was the only treatment that yielded higher cleavage and embryo development (morula and blastocyst) rates compared to the control treatment. The ROS production in the oocytes after maturation did not differ among treatments. However, oocytes treated with anethole at 300 µg/mL had higher ( P < .05) FRAP and mitochondrial membrane potential compared to the control treatment. Furthermore, AN300 treatment increased ( P < .05) the average number of total cells in blastocysts compared to the control and AN30 treatments. The use of anethole at 300 μg/mL during IVM is suggested to improve the quantity and quality of bovine embryos produced in vitro. The beneficial effects of anethole on embryonic developmental competence in vitro seems to be related to its capacity to regulate the redox balance and improve mitochondrial function in oocytes and embryos.

Inflammatory markers in human follicular fluid correlate with lipid levels and Body Mass Index

The detrimental consequences of obesity on female fertility are well known, but the functional changes that occur in the ovary in response to elevated BMI are not clear. Obesity induces multiple components of a systemic inflammatory state that is a key pathway by which it initiates tissue dysfunction in adipose, liver and muscle; however whether obesity induces similar inflammatory changes in the ovary has not been fully investigated. This is important to understand because it is increasingly clear that obesity at conception impacts not only pregnancy rates but also influences pre-implantation embryo development. To further understand the characteristics of inflammation in the ovaries of obese women we analysed a panel of cytokines (IL6, IL10 and TNFα), adipokines (adiponectin, leptin and monocyte chemotactic factor 1 (MCP-1)) and acute phase proteins (C-Reactive Protein (CRP) and sICAM-1) in the ovarian follicular fluid obtained at oocyte aspiration from women (n = 48) who were lean, overweight or obese. We hypothesised that adipokines and pro-inflammatory cytokines would be correlated with and/or dysregulated by increasing Body Mass Index (BMI). Surprisingly however, the majority were not related to BMI but instead were positively correlated with lipid levels in follicular fluid, namely triglycerides and free fatty acids. Further, as is typical of metabolic inflammation, the inflammatory markers that were associated with intra-follicular lipids included both pro-inflammatory (CRP, IL6, TNFα) and anti-inflammatory (adiponectin, IL10) mediators. The direct consequences of an ovarian microenvironment containing high levels of lipids and inflammatory mediators are not known but could impact luteinisation, ovulation and/or oocyte developmental competence.

Early sex-dependent differences in response to environmental stress

Developmental plasticity enables the appearance of long-term effects in offspring caused by exposure to environmental stressors during embryonic and foetal life. These long-term effects can be traced to pre- and post-implantation development, and in both cases, the effects are usually sex specific. During preimplantation development, male and female embryos exhibit an extensive transcriptional dimorphism mainly driven by incomplete X chromosome inactivation. These early developmental stages are crucial for the establishment of epigenetic marks that will be conserved throughout development, making it a particularly susceptible period for the appearance of long-term epigenetic-based phenotypes. Later in development, gonadal formation generates hormonal differences between the sexes, and male and female placentae exhibit different responses to environmental stressors. The maternal environment, including hormones and environmental insults during pregnancy, contributes to sex-specific placental development that controls genetic and epigenetic programming during foetal development, regulating sex-specific differences, including sex-specific epigenetic responses to environmental hazards, leading to long-term effects. This review summarizes several human and animal studies examining sex-specific responses to environmental stressors during both the periconception period (caused by differences in sex chromosome dosage) and placental development (caused by both sex chromosomes and hormones). The identification of relevant sex-dependent trajectories caused by sex chromosomes and/or sex hormones is essential to define diagnostic markers and prevention/intervention protocols.

The Responses of Mouse Preimplantation Embryos to Leptin In Vitro in a Transgenerational Model for Obesity

The aim of the present study was to test the hypothesis that leptin can directly mediate the negative effect of maternal obesity on preimplantation embryos. As previously shown, maternal obesity retards early embryonic development in vivo and increases the incidence of apoptosis in blastocysts. When two-cell embryos isolated from control and obese mice were transferred to identical (leptin free) conditions in vitro, no differences in any growth or quality parameters were recorded, including apoptosis incidence in blastocysts. Embryos isolated from control mice responded to transfer to environments with a high concentration of leptin (10 ng/mL) with a significant increase in arrest at the first or subsequent cell cycle. However, the majority of non-arrested embryos developed into blastocysts, showing morphology comparable to those cultured in the leptin-free group. On the other hand, the exposure of embryos isolated from obese mice to high leptin concentration in vitro did not retard their development. Furthermore, these embryos developed into blastocysts, showing a lower incidence of apoptosis. In vivo-developed blastocysts recovered from obese mice showed elevated expression levels of the proapoptotic gene BAX and the insulin-responsive glucose transporter gene SLC2A4. In conclusion, elevated leptin levels have both positive and negative effects on preimplantation embryo development in vitro, a response that likely depends on the body condition of the embryo donor. Moreover, these results suggest that leptin acts as a survival factor rather than an apoptotic inductor in embryonic cells. Since no elevations in the expression of the leptin receptor gene (LEPR) or fat metabolism-associated genes (PLIN2, SLC27A4) were recorded in blastocysts recovered from obese mice, the role of leptin in mediating the effects of obesity on embryos at the peripheral level is likely lower than expected.

Activities for leptin in bovine trophoblast cells

Leptin is involved in various reproductive processes in humans and rodents, including placental development and function. The specific ways that leptin influences placental development and function in cattle are poorly understood. This work was completed to explore how leptin regulates hormone, cytokine and metalloprotease transcript abundance, and cell proliferation in cultured bovine trophoblast cells. In the first set of studies, cells were cultured in the presence of graded recombinant bovine leptin concentrations (0, 10, 50, 250 ng/mL) for 6 or 24 h. Transcript profiles were examined from extracted RNA. Leptin supplementation did not affect abundance of the maternal recognition of pregnancy factor, interferon-tau (IFNT), but leptin increased (P < 0.05) abundance of chorionic somatomammotropin hormone 2 (CSH2; ie, placental lactogen) at both 6 and 24 h at each concentration tested. At 24 h, the greatest CSH2 abundance (P < 0.05) was detected in cells supplemented with 50 ng/mL leptin. Transcript abundance of the remodeling factor, metalloprotease 2 (MMP2), was greater (P < 0.05) in leptin-treated cells at 24 h but not at 6 h. The 24 h MMP2 response was greatest (P < 0.05) at 250 ng/mL. Transcript abundance for MMP9 was not altered by leptin treatment. In a separate set of studies, cell proliferation assays were completed. Leptin supplementation did not affect bovine trophoblast cell line proliferation at any dose tested. In conclusion, leptin supplementation did not affect bovine trophoblast cell proliferation or IFNT expression, but leptin increases CSH2 and MMP2 transcript abundance. Both of these factors are involved with peri-implantation and postimplantation placental development and function, and this implicates leptin as a potential mediator of early placental development and function in cattle.

Design and synthesis of polyhydroxy steroids as selective inhibitors against AKR1B10 and molecular docking

AKR1B10 is a member of the human aldo-keto reductase superfamily which is highly expressed in several types of cancers, and has been regarded as a promising cancer therapeutic target. In this paper, a series of polyhydroxy steroids were designed and synthesized to selectively inhibit AKR1B10 activity. The most selective compound, novel compound 6, has an IC50 of 0.83±0.07μM and a selectivity of more than 120-fold for AKR1B10/AKR1B1. Structure-activity relation analyses indicate that hydroxyl at C-19 can significantly improve the selective inhibition of AKR1B10. The binding mode of AKR1B10 and its inhibitors were studied.

Effect of high fat diet on artificial oocyte activation following superovulation in mice

The aim of the present study was to determine the effects of increased dietary intake and high fat diet (HFD) in mice on artificial oocyte activation by using puromycin or roscovitine. Six-week-old mice were fed as either a control diet group, an increased dietary intake group or an HFD group for 4 weeks. Oocytes were obtained following superovulation and were divided into three treatment groups (no activation treatment, calcium ionophore and puromycin treatment, and calcium ionophore and roscovitine treatment) and were incubated for 4 h. Retrieved oocytes and numbers of oocytes activated as assessed by morphological changes were compared among the three treatment groups. The proportion of degenerated oocytes in HFD mice was significantly higher than that in control diet mice. The rates of activation in oocytes treated with roscovitine were 90.3% in control diet mice, 89.8% in increased dietary intake mice and 67.9% in HFD mice. The rate of activation in oocytes treated with roscovitine in HFD mice was significantly lower than the rates in control diet mice and increased dietary intake mice. The rates of activation in oocytes treated with puromycin were 90.6% in control diet mice, 94.0% in increased dietary intake mice and 71.4% in HFD mice, and the rate of activation in oocytes treated with puromycin in HFD mice was significantly lower than the rates in control diet mice and increased dietary intake mice. HFD-induced obesity deteriorated induction of oocyte activation by roscovitine or puromycin in mice.

Impact of maternal malnutrition during the periconceptional period on mammalian preimplantation embryo development

During episodes of undernutrition and overnutrition the mammalian preimplantation embryo undergoes molecular and metabolic adaptations to cope with nutrient deficits or excesses. Maternal adaptations also take place to keep a nutritional microenvironment favorable for oocyte development and embryo formation. This maternal-embryo communication takes place via several nutritional mediators. Although adaptive responses to malnutrition by both the mother and the embryo may ensure blastocyst formation, the resultant quality of the embryo can be compromised, leading to early pregnancy failure. Still, studies have shown that, although early embryonic mortality can be induced during malnutrition, the preimplantation embryo possesses an enormous plasticity that allows it to implant and achieve a full-term pregnancy under nutritional stress, even in extreme cases of malnutrition. This developmental strategy, however, may come with a price, as shown by the adverse developmental programming induced by even subtle nutritional challenges exerted exclusively during folliculogenesis and the preimplantation period, resulting in offspring with a higher risk of developing deleterious phenotypes in adulthood. Overall, current evidence indicates that malnutrition during the periconceptional period can induce cellular and molecular alterations in preimplantation embryos with repercussions for fertility and postnatal health.

Effect of Glycosaminoglycans on In vitro Fertilizing Ability and In vitro Developmental Potential of Bovine Embryos

The glycosaminoglycans (GAGs) present in the female reproductive tract promote sperm capacitation. When bovine sperm were exposed to 10 μg/ml of one of four GAGs (Chondroitin sulfate, CS; Dermatan sulfate, DS; Hyaluronic acid, HA; Heparin, HP) for 5 h, the total motility (TM), straight-line velocity (VSL), and curvilinear velocity (VCL) were higher in the HP- or HA-treated sperm, relative to control and CS- or DS-treated sperm. HP and HA treatments increased the levels of capacitated and acrosome-reacted sperm over time, compared to other treatment groups (p<0.05). In addition, sperm exposed to HP or HA for 1 h before IVF exhibited significantly improved fertilizing ability, as assessed by 2 pronucleus (PN) formation and cleavage rates at d 2. Exposure to these GAGs also enhanced in vitro embryo development rates and embryo quality, and increased the ICM and total blastocyst cell numbers at d 8 after IVF (p<0.05). A real-time PCR analysis showed that the expression levels of pluripotency (Oct 4), cell growth (Glut 5), and anti-apoptosis (Bax inhibitor) genes were significantly higher in embryos derived from HA- or HP-treated sperm than in control or other treatment groups, while pro-apoptotic gene expression (caspase-3) was significantly lower in all GAG treatment groups (p<0.05). These results demonstrated that exposure of bovine sperm to HP or HA positively correlates with in vitro fertilizing ability, in vitro embryo developmental potential, and embryonic gene expression.

Expression and potential roles of HLA-G in human spermatogenesis and early embryonic development

As one of the non-classical major histocompatibility complex(MHC)-1 antigens, Human Leukocyte Antigen G (HLA-G), has been suggested as a prognostic marker to identify the embryo developmental potential. In the present study, we investigated the potential roles of HLA-G in human spermatogenesis and early embryonic development. Quantitative real-time PCR analysis revealed that HLA-G's expression was increased with increased Johnsen score in testicular tissues. There was no significant difference in HLA-G mRNA expression between testicular tissues with Johnsen score of 8–9 and normal sperm from ejaculated semen. HLA-G mRNA expression was detected in human zygotes, embryos and blastocysts but not in unfertilized oocytes. In testicular tissues where sperm was obtained by testicular sperm extraction (Johnsen score was 8 to 9), there were no correlations between HLA-G mRNA expression and fertilization, cleavage and high-quality embryo rates. At 48–72 h post-fertilization, HLA-G expression was higher in fast growing embryos. HLA-G specific siRNA injection into zygotes not only slowed down embryonic cleavage rate at 48 h post-fertilization, but also down-regulated the expression of embryo metabolism related gene (SLC2A1) and cell cycle-regulated gene (CCND2). Taken together, our findings suggested that HLA-G plays significant roles in human spermatogenesis and early embryonic development.

Characterization of foamy epithelial surface cells in the canine endometrium

In mature bitches, endometrial epithelial surface cells modify function and corresponding morphology during the oestrous cycle. During late metoestrous, endometrial epithelial surface cells frequently accumulate fat and thereby adopt a foamy morphology. This cyclic appearance of foamy endometrial epithelial cells (fEECs) seems to be physiological in the dog, whereas in other species, it indicates pathological changes. Function of these fEECs has not been identified until now. Therefore, the aim of the study was to characterize the fEECs by means of transmission electron microscopy and immunohistochemistry. Different manifestations of fEECs were observed and analysed with regard to proliferative activity and presence of different epithelial adhesion molecules including PLEKHA7, β-catenin and E-cadherin. PLEKHA7 was restricted to the apical regions of the fEECs, whereas E-cadherin and β-catenin were demonstrated basolateral. The immunohistochemical detection of steroid hormone receptors demonstrated the responsiveness of the fEECs to steroid hormones. Intense progesterone receptor expression was observed in the fEECs indicating a high responsiveness to this hormone. Considering a potential function of the fEECs, we hypothesized that leptin, a hormone produced by other lipid-accumulating cells and described to be involved in reproduction, in particular during implantation, might also originate from the fEECs which was confirmed by immunohistochemical methods. Moreover, leptin receptor was found in fEECs indicating the fEECs as both, source and target for leptin. Therefore, we conclude that fEECs in the canine uterus have a potential role in early pregnancy events and that the different observed manifestations might simply reflect the variations of signs of pseudopregnancy among bitches.

Defined media optimization for in vitro culture of bovine somatic cell nuclear transfer (SCNT) embryos

The objective was to establish an efficient defined culture medium for bovine somatic cell nuclear transfer (SCNT) embryos. In this study, modified synthetic oviductal fluid (mSOF) without bovine serum albumin (BSA) was used as the basic culture medium (BCM), whereas the control medium was BCM with BSA. In Experiment 1, adding polyvinyl alcohol (PVA) to BCM supported development of SCNT embryos to blastocyst stage, but blastocyst formation rate and blastocyst cell number were both lower (P < 0.05) compared to the undefined group (6.1 vs. 32.6% and 67.3 ± 3.4 vs. 109.3 ± 4.5, respectively). In Experiment 2, myo-inositol, a combination of insulin, transferrin and selenium (ITS), and epidermal growth factor (EGF) were added separately to PVA-supplemented BCM. The blastocyst formation rate and blastocyst cell number of those three groups were dramatically improved compared with that of PVA-supplemented group in Experiment 1 (18.5, 23.0, 24.1 vs. 6.1% and 82.7 ± 2.0, 84.3 ± 4.2, 95.3 ± 3.8 vs. 67.3 ± 3.4, respectively, P < 0.05), but were still lower compared with that of undefined group (33.7% and 113.8 ± 3.4, P < 0.05). In Experiment 3, when a combination of myo-inositol, ITS and EGF were added to PVA-supplemented BCM, blastocyst formation rate and blastocyst cell number were similar to that of undefined group (30.4 vs. 31.1% and 109.3 ± 4.4 vs. 112.0 ± 3.6, P > 0.05). In Experiment 4, when blastocysts were cryopreserved and subsequently thawed, there were no significant differences between the optimized defined group (Experiment 3) and undefined group in survival rate and 24 and 48 h hatching blastocyst rates. Furthermore, there were no significant differences in expression levels of H19, HSP70 and BAX in blastocysts derived from optimized defined medium and undefined medium, although the relative expression abundance of IGF-2 was significantly decreased in the former. In conclusion, a defined culture medium containing PVA, myo-inositol, ITS, and EGF supported in vitro development of bovine SCNT embryos.

Effect of maternal obesity on estrous cyclicity, embryo development and blastocyst gene expression in a mouse model

STUDY QUESTION

Does maternal obesity affect estrous cyclicity, embryo development and blastocyst gene expression in mice?

SUMMARY ANSWER

Maternal obesity alters estrous cyclicity and causes the down-regulation of two key metabolite receptors (Slc2a1 and Ldlr) in blastocysts recovered from diet-induced obese females, but embryo development is not affected.

WHAT IS KNOWN ALREADY

Maternal obesity reduces fertility because of effects in the periconception period, but its negative influence is on estrous cyclicity, oocyte quality or embryo development.

STUDY DESIGN, SIZE AND DURATION

This was a randomized study based on a mouse model for obesity. Twenty-one outbred NIH Swiss mice were used and obesity was induced by a diet high in fat administered for 12 weeks prior to breeding to control males.

MATERIAL, SETTING AND METHODS

Females were fed either a control diet (C, n = 9) or a diet high in fat [diet-induced obesity (DiO), n = 12] for 12 weeks, and were then co-housed with fertile males. Mice that failed to breed during 20 consecutive days were considered infertile. Control and diet-induced obese females that demonstrated vaginal plugs were euthanized 3.5 days after mating, blood was sampled for glucose and hormone measurements, corpora lutea counted and embryos recovered; the relative mRNA abundance of 11 candidate genes was determined in blastocysts by qPCR.

MAIN RESULTS AND THE ROLE OF CHANCE

Five DiO females failed to breed and displayed anovulatory ovaries (DiOI), whereas the other seven DiO females (DiOF) could breed, albeit over an extended period compared with controls. DiOF weighed significantly less than DiOI. Both groups had elevated serum insulin compared with C, although blood glucose level was only significantly higher than that in controls in the infertile DiOI group. Adiponectin was lower in the DiOI and leptin higher in both the DiOI and DiOF mice than in C. DiOF ovulated the same number of oocytes as C, and embryo development to blastocyst was normal. The expression of genes encoding metabolic hormone receptors (Insr, Igf1r, Igf2r, Adipor1, Adipor2 and Lepr) and key metabolic enzymes (Gapdh, Cpt1a and Sod2) did not differ between DiOF and C blastocysts, but that of metabolite receptors (Slc2a1 and Ldr) was down-regulated in DiOF. To limit the role of chance, the experiments were conducted in a defined laboratory setting with the proper controls, and the animals were randomly assigned to each experimental group. Moreover, a P-value of < 0.05 was chosen to determine whether the differences observed between the groups were statistically significant.

LIMITATIONS AND REASONS FOR CAUTION

The results obtained may not fully extrapolate to humans. Also, as follicular activity was not monitored while breeding, so the extended breeding period for DiOF group might be explained by behavioral abnormalities occurring in normal cycling animals.

WIDER IMPLICATIONS OF THE FINDINGS

DiO alters the estrous cycle in the mouse model and demonstrates a role of obesity in infertility. The data also suggest that in an outbred, genetically diverse population, such as the human, individual susceptibility to obesity and associated infertility induced by diet exists. The apparently normal development to blastocyst observed in fertile, obese females suggests that preimplantation embryos can resist potentially adverse outcomes caused by an oversupply of fatty acids and glucose under in vivo conditions. This metabolic plasticity may, in part, be due to an ability to down-regulate metabolite transporters, thereby preventing excessive nutrient uptake.

STUDY FUNDING/COMPETING INTEREST(S)

The research was supported by funds from the University of Missouri, grants from the National Institutes of Health and by a fellowship from the Lalor Foundation. There were no competing interests.

TRIAL REGISTRATION NUMBER

Not applicable.

The impact of obesity on egg quality

Obesity in women is a concern in many countries. This causes numerous health issues; however, this review focuses on the impact of obesity on women's reproduction, and in particular the oocyte. Data from infertility clinics and experimental animal models that address the effects of obesity are presented. Bidirectional communication and metabolic support from the surrounding cumulus cells are critical for oocyte development, and the impact of obesity on these cells is also addressed. Both oocyte maturation and metabolism are impaired due to obesity, negatively impacting further development. In addition to reproductive hormones, obesity induced elevations in insulin, glucose, or free fatty acids, and changes in adipokines appear to impact the developmental competence of the oocyte. The data indicate that any one of these hormones or metabolites can impair oocyte developmental competence in vivo, and the combination of all of these factors and their interactions are the subject of ongoing investigations.