Assisted reproductive technologies (ARTs) have significantly advanced, yet the definition and assessment of oocyte quality remain pivotal for successful embryo development. Oocyte quality is influenced by various factors, including lifestyle, age, metabolic status, and exposure to pollutants or medications. Non-invasive techniques to evaluate oocyte quality are limited, and invasive methods are commonly used in research. In vitro maturation (IVM) of oocytes from cows and pigs offers valuable models for human ART due to various similarities, though there are species-specific differences. These IVM and in vitro embryo production (IVEP) systems offer valuable insights into oocyte maturation and early embryo development without use of experimental animals. While bovine IVEP is well established, porcine IVEP has great potential for improvement. The models can be crucial for reproductive biology and biomedical research and can contribute to advancements in areas such as human fertility treatments and toxicity testing. Apart from oocyte quality assessment, there are challenges, such as variability in oocyte quality from slaughterhouse ovaries and the difficulty in mimicking the complex in vivo environment. Emerging technologies, like gene-expression analysis tools, and non-invasive -omics approaches hold promise for overcoming some obstacles by improving precision, sensitivity, and reproducibility in IVEP studies. In this review, we discuss the model in simulating various conditions but with main focus on metabolic challenges and in toxicity screening and aim to give an overview of the current and possible future use of IVM in cows and pigs as a model for the same or other mammalian species, as well as the limitations.

IntroductionSince boar spermatozoa show a marked deterioration in sperm quality when cooled, insemination doses are usually stored at 16–18 °C. However, maintaining this temperature during transport of semen doses is challenging, particularly during the summer months. An alternative could be to store the doses at 4 °C if cold-shock to the sperm could be prevented. The objective of this study was to evaluate boar sperm quality and fertility in in vitro fertilization after storage in AndroStar Premium at 4 °C for 1 week.MethodsInsemination doses (n = 9) in AndroStar Premium from a commercial boar semen collection station were transported to the laboratory at approximately 20 °C. At the laboratory, sperm quality evaluation and was preformed and each dose was split; half of each ejaculate was stored in a climate-controlled box at 16–18 °C, the other was slowly cooled to 4 °C. Both samples were stored for 1 week before further sperm quality evaluation and in vitro fertilization (IVF) were performed. Mean values were tested using generalized linear regression, with treatment and boar as fixed factors; p ≤ 0.05 was considered significant.ResultsSperm membrane integrity (mean ± sem: 91 ± 0.05 and 83 ± 0.09% for 16 and 4 °C, respectively) and superoxide production (6.79 ± 2.37 and 13.54 ± 6.23% for 16 and 4 °C, respectively), were different between treatments. The DNA fragmentation index was lower in cold-stored samples than in conventionally stored samples (3.74 ± 2.25 and 7.40 ± 3.36% for 4 and 16 °C, respectively). The numbers of oocytes developing to blastocyst on Day 6 (mean ± sd: 9.0 ± 8.0 and 6.0 ± 5.0%, for storage at 16 and 4 °C, respectively) were not different between treatments.DiscussionTherefore, storage of boar semen doses in AndroStar Premium at 4 °C for up to 7 days would be a viable alternative to current praxis.

Knowledge on the effects of perfluorohexane sulfonate (PFHxS) on ovarian function is limited. In the current study, we investigated the sensitivity of oocytes to PFHxS during in vitro maturation (IVM), including consequences on embryo development at the morphological, transcriptomic, and epigenomic levels. Bovine cumulus-oocyte complexes (COCs) were exposed to PFHxS during 22 h IVM. Following fertilisation, developmental competence was recorded until day 8 of culture. Two experiments were conducted: 1) exposure of COCs to 0.01 µg mL-1 - 100 µg mL-1 PFHxS followed by confocal imaging to detect neutral lipids and nuclei, and 2) exposure of COCs to 0.1 µg mL-1 PFHxS followed by analysis of transcriptomic and DNA methylation changes in blastocysts. Decreased oocyte developmental competence was observed upon exposure to ≥ 40 µg mL-1 PFHxS and altered lipid distribution was observed in the blastocysts upon exposure to 1-10 µg mL-1 PFHxS (not observed at lower or higher concentrations). Transcriptomic data showed that genes affected by 0.1 µg mL-1 PFHxS were enriched for pathways related to increased synthesis and production of reactive oxygen species. Enrichment for peroxisome proliferator-activated receptor-γ and oestrogen pathways was also observed. Genes linked to DNA methylation changes were enriched for similar pathways. In conclusion, exposure of the bovine oocyte to PFHxS during the narrow window of IVM affected subsequent embryonic development, as reflected by morphological and molecular changes. This suggests that PFHxS interferes with the final nuclear and cytoplasmic maturation of the oocyte leading to decreased developmental competence to blastocyst stage.

Insulin is a key hormone with important functions in energy metabolism and is involved in the regulation of reproduction. Hyperinsulinaemia is known to impair fertility (for example, in obese mothers); therefore, we aimed to investigate the impact of elevated insulin concentrations during the sensitive period of oocyte maturation on gene expression and lipid profiles of the bovine Day-8 embryo. Two different insulin concentrations were used during in vitro oocyte maturation (INS10=10µgmL-1 and INS0.1=0.1µgmL-1) in order to observe possible dose-dependent effects or thresholds for hyperinsulinaemia in vitro. By investigating gene expression patterns by an mRNA microarray in combination with lipid profile analysis by desorption electrospray ionisation-mass spectrometry (DESI-MS) of embryos derived from insulin-treated oocytes, we gained further insights regarding molecular responses of embryos to insulin provocation during the first days of development. Lipid metabolism appeared to be influenced on multiple levels according to gene expression results but the profiles collected in positive-ion mode by DESI-MS (showing mostly ubiquinone, cholesteryl esters and triacylglycerols) did not differ significantly from controls. There are parallels in follicular development of ruminants and humans that make this bovine model relevant for comparative research on early human embryonic development during hyperinsulinaemia.

Insulin functions as a regulator of metabolism and plays an important role in reproduction. Hyperinsulinemia is often observed in patients with obesity and diabetes type 2 and is known to impair fertility, but the underlying molecular mechanisms are only partly understood. Metabolic programming through epigenetic mechanisms such as DNA methylation during embryonic development can lead to health implications for the offspring later in life. Our aim was to study the potential effect of hyperinsulinemia on gene expression and DNA methylation of embryos by adding insulin (0.1 µg/ml = INS0.1 or 10 µg/ml = INS10) during in vitro oocyte maturation by using the EmbryoGENE DNA methylation array for a study of the bovine epigenome. Our results showed significant differences between blastocysts originating from insulin-treated oocytes compared with untreated control blastocysts. In total, 13,658 and 12,418 probes were differentially methylated (DM) in INS0.1 and INS10, respectively, with an overlap of 3,233 probes in the DM regions (DMR) for both insulin groups. Genes related to pathways such as lipid metabolism, growth and proliferation, mitochondrial function, and oxidative stress responses were influenced at both the epigenetic and transcriptomic levels. In addition, imprinted genes and genes with functions in the epigenetic machinery were among the DMRs. This study identified DMRs correlated to differential expression of genes involved in metabolic regulation and should help to improve our knowledge of the underlying molecular mechanisms of metabolic imbalance.

Insulin is a key metabolic hormone that controls energy homeostasis in the body, including playing a specific role in regulating reproductive functions. Conditions associated with hyperinsulinemia can lower developmental rates in bovine in vitro embryo production and are linked to decreased fertility in humans, as in cases of obesity or type 2 diabetes. Embryo quality is important for fertility outcome and it can be assessed by choosing scoring standards for various characteristics, such as developmental stage, quality grade, cell number, mitochondrial pattern or actin cytoskeleton structure. Changes in the embryo's gene expression can reflect environmental impacts during maturation and may explain morphological differences. Together with morphological evaluation, this could enable better assessment and possibly prediction of the developmental potential of the embryo. The aim of this study was to use a bovine model to identify potential gene signatures of insulin-induced changes in the embryo by combining gene expression data and confocal microscopy evaluation. Bovine embryos were derived from oocytes matured in two different insulin concentrations (10 mu g mL(-1) and 0.1 mu g mL(-1)), then stained to distinguish f-Actin, DNA and active mitochondria. The total cell number of the embryo, quality of the actin cytoskeleton and mitochondrial distribution were assessed and compared to an insulin-free control group. A microarray-based transcriptome analysis was used to investigate key genes involved in cell structure, mitochondrial function and cell division. Our results indicate that insulin supplementation during oocyte maturation leads to lower blastocyst rates and a different phenotype, characterised by an increased cell number and different actin and mitochondrial distribution patterns. These changes were reflected by an up-regulation of genes involved in cell division (MAP2K2; DHCR7), cell structure (LMNA; VIM; TUBB2B; TUBB3; TUBB4B) and mitochondrial activation (ATP5D; CYP11A1; NDUFB7; NDUFB10; NDUFS8). Taken together, we hypothesise that the increased proliferation in the insulin-treated groups might impair the developmental potential of the embryos by inducing metabolic stress on the molecular level, which could be detrimental for the survival of the embryo. (C) 2017 Elsevier Inc. All rights reserved.

Metabolic imbalance impairs fertility, because changes in concentrations of metabolites and hormones in the blood and follicular fluid create an unfavourable environment for early embryonic development. Insulin is a key metabolic hormone known for its effects on fertility: insulin concentrations are increased during energy balance disturbances in diabetes or metabolic syndrome. Still, insulin is frequently used at supraphysiological concentrations for embryo in vitro culture with unknown consequences for the developmental potential of the offspring. In the present study we investigated the effects of insulin exposure during in vitro bovine oocyte maturation on developmental rates, embryo quality and gene expression. Supplementation of the maturation media with insulin at 10 or 0.1 µg mL-1 decreased blastocyst rates compared with an insulin-free control (19.8 ± 1.3% and 20.4 ± 1.3% vs 23.8 ± 1.3%, respectively; P < 0.05) and led to increased cell numbers (nearly 10% more cells on Day 8 compared with control; P < 0.05). Transcriptome analysis revealed significant upregulation of genes involved in lipid metabolism, nuclear factor (erythroid-derived 2)-like 2 (NRF2) stress response and cell differentiation, validated by quantitative polymerase chain reaction. To conclude, the results of the present study demonstrate that insulin exposure during in vitro oocyte maturation has a lasting effect on the embryo until the blastocyst stage, with a potential negative effect in the form of specific gene expression perturbations.

Obesity and overfeeding are common causes for female infertility, leading to insulin resistance and hyperinsulinemia and associated with an increased risk for type 2 diabetes mellitus (Pasquali et al., http://dx.doi.org/10.1093/humupd/dmg024). We investigated here the effect of insulin during in vitro oocyte maturation on methylation changes in bovine Day 8 blastocysts (BC8) and focused on methylation patterns of candidate genes associated with metabolism and steroidogenesis (Day 0 = day of oocyte collection). Abattoir-derived oocytes (n = 882) were in vitro matured for 22 h with 2 different insulin concentrations, INS10 (10 µg mL−1) and INS0.1 (0.1 µg mL−1) or without insulin (INS0, control). Subsequently, IVF and IVC were performed to equal standardized conditions for all groups. Parallel genomic DNA and total RNA extraction (AllPrepDNA/RNA micro kit, cat no. 80284, Qiagen®, Valencia, CA, USA) from pools of 10 frozen (−80°C) BC8 was followed by transcriptome and epigenome analysis (Laskowski et al., http://dx.doi.org/10.1071/RD15315). An empirical Bayes moderated t-test and the ‘limma’ package in R (www.r-project.org) were used to search for differentially expressed genes between the control and the insulin groups. Analysis of the epigenome by using a specific pipeline, described by Shojaei Saadi et al. (2014 BMC Genomics 15, 451), showed that 7632 and 3914 regions were hypomethylated in the INS0.1 and INS10 v. INS0, whereas 6026 and 8504 regions were hypermethylated in INS0.1 and INS10 v. INS0. Combining epigenetic and transcriptomic data, we found that high methylation and low expression or the reverse (low methylation and high expression) were observed for a set of 14 and 11 genes for INS0.1 and INS10 respectively. Most of these genes are associated with lipid metabolism, steroid synthesis, and oxidative stress. Further investigation of the localization of differentially methylated regions (DMR) in genes showed that the conservation odds (methylation) was in general higher in coding regions and CpG islands than in noncoding regions. We observed a large overlap of DMR in the 2 insulin groups compared with controls (3233 common DMR). These numerous changes illustrate the potential unfavourable effects of elevated insulin during maturation leading to alteration of the methylation patterns of the early embryo. This model may help us better understand the mechanisms by which metabolic disorders observed pre-conception can affect embryonic development and subsequent health of the offspring. Our results based on changes in transcriptome or epigenome did show that insulin challenge during maturation leads to postponed effects associated with steroidogenesis, lipid metabolism and oxidative stress in the BC8. By this early stage, if persistent, specific changes in the expression and methylation patterns of genes associated to hyperinsulinemia may decrease the developmental potential of early embryos or could be responsible for subsequent pathologies. This study was funded by FORMAS.

Insulin has been used as a stimulatory factor for in vitro cell culture since many years. Even for routine in vitro embryo production (IVP), insulin is added to the media during different steps. There is a strong difference in concentrations used in vitro compared to what is measured in vivo in follicular fluid or serum. We performed a pilot study on insulin stability to explain possible reasons for that variation.

Insulin is a key metabolic hormone that plays a crucial role in regulating energy homeostasis in the body. In addition, insulin-dependent signaling has important functions in reproduction and early embryo development. As metabolism and reproduction are closely linked, metabolic challenges may be the source of reproductive disorders and decreased fertility. This is known for the dairy cow and for other species including the human. Although metabolic disorders in the dairy cow often derive from a failure to adapt to a high milk production, the situation in the human is often linked to emerging conditions and associated diseases in our modern society such as obesity and diabetes, where an excess energy intake causes decreased fertility in women. Both energy excess and energy deficit are associated with a deviation of insulin concentrations in serum and follicular fluid from normal levels. Although many studies have shown that extreme variation in energy supply can negatively influence early embryo development by inducing changes in circulating concentrations of several metabolites or hormones like insulin, several in vitro culture media are still supplemented with insulin in high concentrations. In this review, direct and indirect effects of insulin on fertility will be described. Differences between the in vivo and in vitro situations will also be discussed. (C) 2016 Elsevier Inc. All rights reserved.

Insulin is a key metabolic hormone that plays a crucial role in regulating energy homeostasis in the body. In addition, insulin-dependent signaling has important functions in reproduction and early embryo development. As metabolism and reproduction are closely linked, metabolic challenges may be the source of reproductive disorders and decreased fertility. This is known for the dairy cow and for other species including the human. Although metabolic disorders in the dairy cow often derive from a failure to adapt to a high milk production, the situation in the human is often linked to emerging conditions and associated diseases in our modern society such as obesity and diabetes, where an excess energy intake causes decreased fertility in women. Both energy excess and energy deficit are associated with a deviation of insulin concentrations in serum and follicular fluid from normal levels. Although many studies have shown that extreme variation in energy supply can negatively influence early embryo development by inducing changes in circulating concentrations of several metabolites or hormones like insulin, several in vitro culture media are still supplemented with insulin in high concentrations. In this review, direct and indirect effects of insulin on fertility will be described. Differences between the in vivo and in vitro situations will also be discussed.

Insulin has frequently been used as a stimulatory factor in routine in vitro embryo production (IVP) and is added in supra-physiological concentrations to different media. Meanwhile, insulin as a key metabolic hormone is elevated in patients with metabolic syndrome or diabetes, syndromes known to impair fertility.

The aim of this study was to characterize the lipid profile of bovine blastocysts produced from oocytes exposed to different insulin concentrations during maturation by DESI-MS. Insulin is a key metabolic hormone and its concentration in blood and follicular fluid changes in situations of metabolic imbalance as obesity, diabetes or negative energy balance (NEB). The impact of insulin on the lipid profile of blastocysts can provide important insights on the metabolic changes induced by this hormone on early development. Blastocysts were produced from abattoir derived oocytes according to standardized IVP-protocols in our laboratory. Insulin treatment was performed during 22 h of maturation using 0 (INS0); 0.1 (INS0.1) or 10 (INS10) µg/ml bovine insulin. After maturation, all treatment groups were submitted to equal conditions during fertilization and culture. On day 8, blastocysts were separately frozen at -80oC in PBS with 0.1% PVA and individually transferred to glass sides in randomized order. A total of 63 blastocysts were used for DESI-MS lipid profile analysis. Lipids such as diacylglycerols (DAG), triacylglycerols (TAG) cholesteryl esters (CE), squalene and ubiquinone were detected in positive ion mode as silver adducts. Average full scan mass spectra of the three different treatment groups indicated few changes in the lipid profiles. Multivariate statistics by PCA (Principal Component Analysis) was used to comprehensively explore the chemical information of the full mass spectral dataset and visualize the grouping of samples resulting from chemical similarity. PCA showed some extent of discrimination between INS0 and INS10 whereas the discrimination between INS0 and INS0.1 was less evident. Data suggests down-regulated mitochondrial metabolism (indicated by ubiquinone abundance) in INS10 as well as few changes in TAG- and cholesterol metabolism comparing the treated groups (INS10 and INS0.1) with the control (INS0). Overall, the low extension of changes observed in the DESIMS lipid profiles indicates minimal impact of insulin exposure during oocyte maturation on lipid content during preimplantation embryo development. The results of the lipid profile analysis shows that the lipid profile was not significantly different in the day 8 blastocyst after exposure of insulin during maturation. Possible explanations could be that the insulin exposure during the IVM period is not sufficient to promote extensive end-point metabolism changes in the lipids detected during preimplantation development, or that the early embryo strongly compensates for the impact of a metabolic stressor as insulin during oocyte maturation by a subsequent change in gene expression, leading to compensating mechanisms to obtain balance in the chemical profile and permitting a viable phenotype.

The obesity-metabolic-syndrome-complex is a growing problem in humans as in other species and known to be associated with decreased fertility. Insulin concentrations differ from physiological levels during periods of metabolic imbalance. The dairy cow suffers from metabolic disturbances due to a stressed metabolism caused by high milk-production.

Dairy cow fertility has decreased during the last decades, and much evidence indicates that metabolic disorders are an important part of this decline. Insulin is a key factor in the metabolic challenge during the transition period that coincides with the oocyte maturation and may therefore have an impact on the early embryo development. The aim of this study was to test the effect of insulin during oocyte maturation on early embryo development by adding insulin during the oocyte maturation in vitro. In this study, abattoir-derived bovine ovaries were used and cumulus-oocyte complexes (n = 991) were in vitro matured for 22 h according to standard protocols. Insulin was added during maturation in vitro as follows: H (10 µg mL–1 of insulin), L (0.1 µg mL–1 of insulin), or Z (0 µg mL–1 of insulin). After maturation, oocytes were removed and fixed in paraformaldehyde before staining. Click-it TUNEL assay (Invitrogen, Stockholm, Sweden) was used for apoptotic staining and DRAQ5 (BioNordika, Stockholm, Sweden) for nuclear staining (n = 132). Cumulus-oocyte complexes were evaluated using laser scanning confocal microscope (Zeiss LSM 510, Zeiss, Oberkochen, Germany). Five levels of scans were used to assess oocyte maturation (MII stage) and apoptosis. Because of incomplete penetration of the TUNEL stain (3–5 layers of cumulus cells), only the outer 2 layers of the cumulus complex were investigated regarding apoptosis. Apoptotic index was calculated as apoptotic cells/total cells visualised. Remaining oocytes were fertilized and cultured in vitro until Day 8. Day 7 and Day 8 blastocyst formation was assessed as well as blastocyst stage and grade. Effect of insulin treatment on variables was analysed by ANOVA following arc sin √p transformation. Post-ANOVA comparisons between H+L group v. Z were performed by using the contrast option under GLM (Scheffé test). Results are presented as least squares means ± s.e. P-values ≤ 0.05 were considered as statistically significant. Insulin treatment during oocyte maturation in vitro had no significant effect on oocyte nuclear maturation or apoptotic index of the cumulus cells (Z: 0.052 ± 0.025, L: 0.039 ± 0.016, H: 0.077 ± 0.044, P > 0.05). No effect was seen on cleavage rates (Z: 0.85 ± 0.02, L: 0.85 ± 0.02, H: 0.89 ± 0.03, P > 0.05), but insulin treatment significantly decreased Day 7 rates from fertilized oocytes (Z: 0.19 ± 0.02, L: 0.14 ± 0.02, H: 0.12 ± 0.02, P < 0.05). This study also showed a significantly retarded developmental stage and decreased grade of blastocysts in insulin-treated groups taken together when compared with the control group (P < 0.05). In this study, no effect of insulin supplementation during in vitro maturation was seen on bovine oocyte maturation and apoptosis of cumulus cells, but blastocyst formation and development were negatively affected. Further studies are needed for understanding the relationship between the addition of insulin during maturation in vitro and impaired blastocyst formation. Insulin is a common supplement in the first phase of the first in vitro maturation medium for pig oocytes and is believed to have a beneficial effect on this species.Funding was received from Stiftelsen Nils Lagerlöfs Fond H12–0051-NLA.

Insulin as a key metabolic hormone has crucial functions in metabolic regulation in all mammals. Deviation of its physiological concentration occurs in metabolic disorders as obesity and diabetes in humans or negative energy balance and overfeeding in the cow. As these metabolic disorders are strongly correlated with reproductive disturbances, we investigated the effect of insulin during oocyte maturation on gene expression of bovine Day 8 blastocysts (BC8) by transcriptome analysis. Abattoir-derived oocytes (n = 882) were divided into 3 groups and in vitro matured for 22 h by adding insulin (H: High 10 µg mL–1; L: Low 0.1 µg mL–1 and Z: Zero, control). This was followed by standard in vitro production (IVP) and evaluation of developmental rates up to blastocyst stage. BC8 (n = 120) were pooled in groups of 10 and total RNA was extracted by parallel gDNA and total RNA-extraction (AllPrepDNA/RNA micro kit, cat no. 80284, Qiagen®, Valencia, CA, USA) for analyses of the transcriptome. All samples (4 biological replicates/group) resulted in RIN-values >7.5. RNA amplification, cDNA synthesis, purification, and labelling were performed and 825 ng of Cy3- and Cy5-labelled linearly amplified aRNA was hybridized on the Agilent-manufactured EmbryoGENE-slides in a 2-colour dye swap design. An empirical Bayes moderated t-test was applied to search for the differentially expressed transcripts (DET) between control and insulin-treated groups, using the ‘limma’ package in R (www.r-project.org). The DET were defined as having a 1.5-fold change difference between treatment and control and P < 0.05. Pathways and molecular functions influenced by insulin treatment were analysed by using Ingenuity Pathway Analysis (IPA; Ingenuity® Systems, www.ingenuity.com). As a global pattern, insulin treatment induced an up-regulation of genes. In total, 202 DET in the H and 142 DET in the L group were found where 104 DET were common in both insulin groups. Fifteen selected candidate genes chosen for qPCR validation and 12 (80%) showed similar expression patterns as the microarray data. DET relevant for following cellular functions were found in H: Cell Cycle, Cellular Compromise, Lipid Metabolism, Molecular Transport, Small Molecule Biochemistry respective L: Cell Morphology, Cellular Growth and Proliferation, Cell Cycle, Carbohydrate Metabolism and Cellular Assembly and Organization. The top canonical pathways influenced were Epithelial Adherens Junction Signalling and Remodelling, Germ Cell Sertoli Cell Junction Signalling and NRF2-mediated Oxidative Stress Response. Correlatively, blastocyst rates on Day 8 were significantly lower in H and L v. Z (P < 0.05). The transcriptome data could explain the mechanisms behind the impaired development, as genes involved in cellular growth and energy metabolism in Day 8 blastocysts were affected. The fact that transcripts related to NRF2-mediated oxidative stress response and lipid metabolism are up-regulated suggests that insulin induces dysregulation of cellular functions and energy metabolism leading to impaired embryo developmental potential.Funded by FORMAS.