Time-lapse confocal imaging-induced calcium ion discharge from the cumulus-oocyte complex at the time of cattle oocyte activation

Oocyte activation, the dynamic transformation of an oocyte into an embryo, is largely driven by Ca2+ oscillations that vary in duration and amplitude across species. Previous studies have analysed intraoocyte Ca2+ oscillations in the absence of the oocyte's supporting cumulus cells. Therefore, it is unknown whether cumulus cells also produce an ionic signal that reflects fertilisation success. Time-lapse confocal microscopy and image analysis on abattoir-derived cattle cumulus-oocyte complexes coincubated with spermatozoa revealed a distinct discharge of fluorescence from the cumulus vestment. This study demonstrated that this Ca2+ fluorescence discharge was an artefact induced by the imaging procedure independently of oocyte activation success. The fluorescence discharge was a direct result of cumulus cell membrane integrity loss, and future studies should consider the long-term effect of fluorescent labels on cells in time-lapse imaging. However, this study also demonstrated that the distinctive pattern of a coordinated fluorescence discharge was associated with both the presence of spermatozoa and subsequent embryo development to the morula stage, which was affected by Ca2+ chelation and a reduction in the active efflux of the fluorophore. This indicates that the cumulus vestment may have a relationship with oocyte activation at and beyond fertilisation that requires further investigation.

Quantitative non-invasive cell characterisation and discrimination based on multispectral autofluorescence features

Automated and unbiased methods of non-invasive cell monitoring able to deal with complex biological heterogeneity are fundamentally important for biology and medicine. Label-free cell imaging provides information about endogenous autofluorescent metabolites, enzymes and cofactors in cells. However extracting high content information from autofluorescence imaging has been hitherto impossible. Here, we quantitatively characterise cell populations in different tissue types, live or fixed, by using novel image processing and a simple multispectral upgrade of a wide-field fluorescence microscope. Our optimal discrimination approach enables statistical hypothesis testing and intuitive visualisations where previously undetectable differences become clearly apparent. Label-free classifications are validated by the analysis of Classification Determinant (CD) antigen expression. The versatility of our method is illustrated by detecting genetic mutations in cancer, non-invasive monitoring of CD90 expression, label-free tracking of stem cell differentiation, identifying stem cell subpopulations with varying functional characteristics, tissue diagnostics in diabetes, and assessing the condition of preimplantation embryos.

Extending prematuration with cAMP modulators enhances the cumulus contribution to oocyte antioxidant defence and oocyte quality via gap junctions

STUDY QUESTION

Can bovine oocyte antioxidant defence and oocyte quality be improved by extending the duration of pre-in vitro maturation (IVM) with cyclic adenosine mono-phosphate (cAMP) modulators?

SUMMARY ANSWER

Lengthening the duration of cAMP-modulated pre-IVM elevates intra-oocyte reduced glutathione (GSH) content and reduces hydrogen peroxide (H2O2) via increased cumulus cell-oocyte gap-junctional communication (GJC), associated with an improvement in subsequent embryo development and quality.

WHAT IS KNOWN ALREADY

Oocytes are susceptible to oxidative stress and the oocyte's most important antioxidant glutathione is supplied, at least in part, by cumulus cells. A temporary inhibition of spontaneous meiotic resumption in oocytes can be achieved by preventing a fall in cAMP, and cyclic AMP-modulated pre-IVM maintains cumulus-oocyte GJC and improves subsequent embryo development.

STUDY DESIGN, SIZE, DURATION

This study consisted of a series of 10 experiments using bovine oocytes in vitro, each with multiple replicates. A range of pre-IVM durations were examined as the key study treatments which were compared with a control. The study was designed to examine if one of the oocyte's major antioxidant defences can be enhanced by pre-IVM with cAMP modulators, and to examine the contribution of cumulus-oocyte GJC on these processes.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Immature bovine cumulus-oocyte complexes were treated in vitro without (control) or with the cAMP modulators; 100 µM forskolin (FSK) and 500 µM 3-isobutyl-1-methyxanthine (IBMX), for 0, 2, 4 or 6 h (pre-IVM phase) prior to IVM. Oocyte developmental competence was assessed by embryo development and quality post-IVM/IVF. Cumulus-oocyte GJC, intra-oocyte GSH and H2O2 were quantified at various time points during pre-IVM and IVM, in the presence and the absence of functional inhibitors: carbenoxolone (CBX) to block GJC and buthionine sulfoximide (BSO) to inhibit glutathione synthesis.

MAIN RESULTS AND THE ROLE OF CHANCE

Pre-IVM with FSK + IBMX increased subsequent blastocyst formation rate and quality compared with standard IVM (P < 0.05), regardless of pre-IVM duration. The final blastocyst yields (proportion of blastocysts/immature oocyte) were 26.3% for the control, compared with 39.2, 35.2 and 34.2%, for the 2, 4 and 6 h pre-IVM FSK + IBMX treatments, respectively. In contrast to standard IVM (control), pre-IVM with cAMP modulators maintained open gap junctions between cumulus cells and oocytes for the duration (6 h) of pre-IVM examined, and persisted for a further 8 h in the IVM phase. Cyclic AMP-modulated pre-IVM increased intra-oocyte GSH levels at the completion of both pre-IVM and IVM, in a pre-IVM duration-dependent manner (P < 0.05), which was ablated when GJC was blocked using CBX (P < 0.05). By 4 h of pre-IVM treatment with cAMP modulators, oocyte H2O2 levels were reduced compared the control (P < 0.05), although this beneficial effect was lost when oocytes were co-treated with BSO. Inhibiting glutathione synthesis with BSO during pre-IVM ablated any positive benefits of cAMP-mediated pre-IVM on oocyte developmental competence (P < 0.01).

LIMITATIONS, REASONS FOR CAUTION

It is unclear if the improvement in oocyte antioxidant defence and developmental competence reported here is due to direct transfer of total and/or reduced glutathione from cumulus cells to the oocyte via gap junctions, or whether a GSH synthesis signal and/or amino acid substrates are supplied to the oocyte via gap junctions. Embryo transfer experiments are required to determine if the cAMP-mediated improvement in blastocyst rates leads to improved live birth rates.

WIDER IMPLICATIONS OF THE FINDINGS

IVM offers significant benefits to infertile and cancer patients and has the potential to significantly alter ART practice, if IVM efficiency in embryo production could be improved closer to that of conventional IVF (using ovarian hyperstimulation). Pre-IVM with cAMP modulators is a simple and reliable means to improve IVM outcomes.

STUDY FUNDING/COMPETING INTERESTS

This work was supported by grants and fellowships from the National Health and Medical Research Council of Australia (1007551, 627007, 1008137, 1023210) and by scholarships from the Chinese Scholarship Council (CSC) awarded to H.J.L. and the Japanese Society for the Promotion of Science Postdoctoral Fellowship for Research Abroad awarded to S.S. The Fluoview FV10i confocal microscope was purchased as part of the Sensing Technologies for Advanced Reproductive Research (STARR) facility, funded by the South Australian Premier's Science and Research Fund. We acknowledge partial support from the Australian Research Council Centre of Excellence for Nanoscale BioPhotonics (CE140100003). We declare that there is no conflict of interest that could be perceived as prejudicing the impartiality of the research reported.

Measuring embryo metabolism to predict embryo quality

Measuring the metabolism of early embryos has the potential to be used as a prospective marker for post-transfer development, either alone or in conjunction with other embryo quality assessment tools. This is necessary to maximise the opportunity of couples to have a healthy child from assisted reproduction technology (ART) and for livestock breeders to efficiently improve the genetics of their animals. Nevertheless, although many promising candidate substrates (e.g. glucose uptake) and methods (e.g. metabolomics using different spectroscopic techniques) have been promoted as viability markers, none has yet been widely used clinically or in livestock production. Herein we review the major techniques that have been reported; these are divided into indirect techniques, where measurements are made from the embryo’s immediate microenvironment, or direct techniques that measure intracellular metabolic activity. Both have strengths and weaknesses, the latter ruling out some from contention for use in human ART, but not necessarily for use in livestock embryo assessment. We also introduce a new method, namely multi- (or hyper-) spectral analysis, which measures naturally occurring autofluorescence. Several metabolically important molecules have fluorescent properties, which we are pursuing in conjunction with improved image analysis as a viable embryo quality assessment methodology.

Nonesterified Fatty Acid-Induced Endoplasmic Reticulum Stress in Cattle Cumulus Oocyte Complexes Alters Cell Metabolism and Developmental Competence

Reduced oocyte quality has been associated with poor fertility of high-performance dairy cows during peak lactation, due to negative energy balance. We examined the role of nonesterified fatty acids (NEFAs), known to accumulate within follicular fluid during under- and overnutrition scenarios, in causing endoplasmic reticulum (ER) stress of in vitro maturated cattle cumulus-oocyte complexes (COCs). NEFA concentrations were: palmitic acid (150 μM), oleic acid (200 μM), and steric acid (75 μM). Abattoir-derived COCs were randomly matured for 24 h in the presence of NEFAs and/or an ER stress inhibitor, salubrinal. Total and hatched blastocyst yields were negatively impacted by NEFA treatment compared with controls, but this was reversed by salubrinal. ER stress markers, activating transcription factor 4 (Atf4) and heat shock protein 5 (Hspa5), but not Atf6, were significantly up-regulated by NEFA treatment within whole COCs but reversed by coincubation with salubrinal. Likewise, glucose uptake and lactate production, measured in spent medium samples, showed a similar pattern, suggesting that cumulus cell metabolism is sensitive to NEFAs via an ER stress-mediated process. In contrast, while mitochondrial DNA copy number was recovered in NEFA-treated oocytes, oocyte autofluorescence of the respiratory chain cofactor, FAD, was lower following NEFA treatment of COCs, and this was not reversed by salubrinal, suggesting the negative impact was via reduced mitochondrial function. These results reveal the significance of NEFA-induced ER stress on bovine COC developmental competence, revealing a potential therapeutic target for improving oocyte quality during peak lactation.

Redox and anti-oxidant state within cattle oocytes following in vitro maturation with bone morphogenetic protein 15 and follicle stimulating hormone

The developmental competence of cumulus oocyte complexes (COCs) can be increased during in vitro oocyte maturation with the addition of exogenous oocyte-secreted factors, such as bone morphogenetic protein 15 (BMP15), in combination with hormones. FSH and BMP15, for example, induce different metabolic profiles within COCs-namely, FSH increases glycolysis while BMP15 stimulates FAD and NAD(P)H accumulation within oocytes, without changing the redox ratio. The aim of this study was to investigate if this BMP15-induced NAD(P)H increase was due to de novo NADPH production. Cattle COCs were cultured with FSH and/or recombinant human BMP15, resulting in a significant decrease in glucose-6-phosphate dehydrogenase activity (P < 0.05). Inhibition of isocitrate dehydrogenase (IDH) during this process decreased NAD(P)H intensity threefold in BMP15-treated oocytes, suggesting that BMP15 stimulates IDH and NADPH production via the tricarboxylic acid cycle. As NADPH is a reducing agent, reduced glutathione (GSH), H2O2, and mitochondrial activity were also measured to assess the general redox status of the oocyte. FSH alone decreased GSH levels whereas the combination of BMP15 and FSH sustained higher levels. Expression of genes encoding glutathione-reducing enzymes were also lower in oocytes cultured in the presence of FSH alone. BMP15 supplementation further promoted mitochondrial localization patterns that are consistent with enhanced developmental competence. Metabolomics revealed significant consumption of glutamine and production of alanine by COCs matured with both FSH and BMP15 compared to the control (P < 0.05). Hence, BMP15 supplementation differentially modulates reductive metabolism and mitochondrial localization within the oocyte. In comparison, FSH-stimulation alone decreases the oocytes' ability to regulate cellular stress, and therefore utilizes other mechanisms to improve developmental competence.

Bone morphogenetic protein 15 in the pro-mature complex form enhances bovine oocyte developmental competence

Developmental competence of in vitro matured (IVM) oocytes needs to be improved and this can potentially be achieved by adding recombinant bone morphogenetic protein 15 (BMP15) or growth differentiation factor (GDF9) to IVM. The aim of this study was to determine the effect of a purified pro-mature complex form of recombinant human BMP15 versus the commercially available bioactive forms of BMP15 and GDF9 (both isolated mature regions) during IVM on bovine embryo development and metabolic activity. Bovine cumulus oocyte complexes (COCs) were matured in vitro in control medium or treated with 100 ng/ml pro-mature BMP15, mature BMP15 or mature GDF9 +/− FSH. Metabolic measures of glucose uptake and lactate production from COCs and autofluorescence of NAD(P)H, FAD and GSH were measured in oocytes after IVM. Following in vitro fertilisation and embryo culture, day 8 blastocysts were stained for cell numbers. COCs matured in medium +/− FSH containing pro-mature BMP15 displayed significantly improved blastocyst development (57.7±3.9%, 43.5±4.2%) compared to controls (43.3±2.4%, 28.9±3.7%) and to mature GDF9+FSH (36.1±3.0%). The mature form of BMP15 produced intermediate levels of blastocyst development; not significantly different to control or pro-mature BMP15 levels. Pro-mature BMP15 increased intra-oocyte NAD(P)H, and reduced glutathione (GSH) levels were increased by both forms of BMP15 in the absence of FSH. Exogenous BMP15 in its pro-mature form during IVM provides a functional source of oocyte-secreted factors to improve bovine blastocyst development. This form of BMP15 may prove useful for improving cattle and human artificial reproductive technologies.

Prematuration with cyclic adenosine monophosphate modulators alters cumulus cell and oocyte metabolism and enhances developmental competence of in vitro-matured mouse oocytes

Oocyte in vitro maturation (IVM) is an important assisted reproductive technology and research tool. The adoption of IVM into routine clinical practice has been hindered by its significantly lower success rates compared to conventional in vitro fertilization. Cyclic AMP (cAMP) modulation and follicle-stimulating hormone (FSH), independently, have long been known to improve IVM oocyte developmental competence. This study comprehensively examined the effects of FSH and cAMP/cGMP modulation, alone and in combination, on IVM oocyte metabolism and developmental outcomes. Mouse cumulus-oocyte complexes (COCs) were subjected to a 1 h prematuration phase ± the cAMP modulator forskolin and cAMP/cGMP modulator 3-isobutyl-1-methylxanthine followed by IVM ± FSH. Prematuration with these cyclic nucleotide modulators or IVM with FSH significantly improved oocyte developmental competence and reduced spindle abnormalities compared to spontaneous IVM (no treatment); however, these two treatments in combination endowed even greater developmental competence (improved subsequent blastocyst rates and quality; P < 0.05), albeit blastocyst yield and quality remained significantly lower than that of oocytes matured in vivo. A significant additive effect of combined IVM treatments was evident as increased COC lactate production and oxygen consumption and enhanced oocyte oxidative metabolism, ATP production, ATP:ADP ratio, and glutathione levels (P < 0.05). Nevertheless, IVM increased reactive oxygen species production, particularly as a consequence of FSH addition, relative to in vivo matured oocytes. In conclusion, improvements in the embryo yield following IVM is associated with increased COC oxygen consumption and oocyte oxidative metabolism, but these remain metabolically and developmentally less competent relative to in vivo derived oocytes.

Effect of epidermal growth factor-like peptides on the metabolism of in vitro- matured mouse oocytes and cumulus cells

Oocyte in vitro maturation (IVM) is an assisted reproductive technology that involves the maturation of cumulus-oocyte complexes (COCs) that are then capable of normal development. We have shown that epidermal growth factor (EGF)-like peptide signaling is perturbed in mouse COCs undergoing IVM when matured with follicle-stimulating hormone (FSH) and/or EGF, but supplementation of IVM with EGF-like peptides amphiregulin or epiregulin improves oocyte developmental competence. Here we aimed to determine whether EGF-like peptides regulate COC metabolism. Immature 129/Sv mouse COCs underwent IVM with FSH, EGF, amphiregulin, epiregulin, betacellulin, or no treatment (control). Epiregulin significantly increased intraoocyte flavin adenine dinucleotide (FAD) and REDOX (reduction and oxidation) ratio compared to FSH and control. Amphiregulin and epiregulin significantly increased the proportion of J aggregates (from JC-1) in oocyte mitochondria compared to control, FSH, or EGF, and this coupled with FAD and REDOX measures indicates greater mitochondrial activity. There were no differences in glucose consumption, lactate production, or glycolysis between COCs matured with FSH, EGF, and EGF-like peptides. COCs matured with EGF or EGF-like peptides exhibited significantly higher mRNA expression of the hexosamine biosynthesis pathway (HBP) rate-limiting enzyme gene Gfpt2, Has2 expression, and global beta-O-linked glycosylation of proteins, compared to control or FSH, suggesting greater HBP activity. Our findings suggest that 1) EGF-like peptides, particularly epiregulin, induce more oocyte mitochondrial activity than EGF or FSH and 2) EGF-like peptides and EGF induce greater HBP activity, enabling more hyaluronic acid synthesis and protein beta-O-linked glycosylation. These metabolic alterations may be a mechanism by which EGF-like peptides increase oocyte developmental competence.

Bone morphogenetic protein 15 and fibroblast growth factor 10 enhance cumulus expansion, glucose uptake, and expression of genes in the ovulatory cascade during in vitro maturation of bovine cumulus-oocyte complexes

Oocyte-secreted factors (OSFs) regulate differentiation of cumulus cells and are of pivotal relevance for fertility. Bone morphogenetic protein 15 (BMP15) and fibroblast growth factor 10 (FGF10) are OSFs and enhance oocyte competence by unknown mechanisms. We tested the hypothesis that BMP15 and FGF10, alone or combined in the maturation medium, enhance cumulus expansion and expression of genes in the preovulatory cascade and regulate glucose metabolism favouring hyaluronic acid production in bovine cumulus-oocyte complexes (COCs). BMP15 or FGF10 increased the percentage of fully expanded COCs, but the combination did not further stimulate it. BMP15 increased cumulus cell levels of mRNA encoding a disintegrin and metalloprotease 10 (ADAM10), ADAM17, amphiregulin (AREG), and epiregulin (EREG) at 12 h of culture and of prostaglandin (PG)-endoperoxide synthase 2 (PTGS2), pentraxin 3 (PTX3) and tumor necrosis factor alpha-induced protein 6 (TNFAIP6 (TSG6)) at 22 h of culture. FGF10 did not alter the expression of epidermal growth factor-like factors but enhanced the mRNA expression of PTGS2 at 4 h, PTX3 at 12 h, and TNFAIP6 at 22 h. FGF10 and BMP15 stimulated glucose consumption by cumulus cells but did not affect lactate production or levels of mRNA encoding glycolytic enzymes phosphofructokinase and lactate dehydrogenase A. Each growth factor increased mRNA encoding glucosamine:fructose-6-PO4 transaminases, key enzymes in the hexosamine pathway leading to hyaluronic acid production, and BMP15 also stimulated hyaluronan synthase 2 (HAS2) mRNA expression. This study provides evidence that BMP15 and FGF10 stimulate expansion of in vitro-matured bovine COCs by driving glucose metabolism toward hyaluronic acid production and controlling the expression of genes in the ovulatory cascade, the first acting upon ADAM10, ADAM17, AREG, and EREG and the second on downstream genes, particularly PTGS2.

Regulation of sheep oocyte maturation using cAMP modulators

Physical removal of mammalian cumulus-oocyte complexes (COCs) from ovarian follicles results in spontaneous resumption of meiosis, largely because of a decrease in cAMP concentrations, causing asynchrony between cytoplasmic and nuclear maturation and decreased oocyte developmental competence. The aim of this study was to modulate cAMP concentrations within ovine COCs to delay spontaneous nuclear maturation and improve developmental competence. Abattoir-derived sheep COCs were cultured for 2 hours (pre-IVM) in 100 μM forskolin (FSK) plus 500 μM 3-isobutyl-1-methylxanthine (IBMX). Pre-IVM (100 μM FSK and 500 μM IBMX) culture increased COC cAMP concentrations 10-fold compared with controls (P < 0.05). With regard to nuclear maturation, with FSK and IBMX and/or with FSH and cilostamide delayed completion of meiosis (metaphase II) by 3 to 4 hours compared with standard IVM (FSH-stimulated induction of meiosis). In this study, pre-IVM (with FSK and IBMX) followed by IVM (with FSH and cilostamide), increased ovine COC cAMP concentrations and delayed, but did not inhibit, completion of nuclear maturation. This did not affect embryo development rates, but increased total cell number of blastocysts compared with IVM with FSH alone (103 ± 6 vs. 66 ± 4 cells, respectively; mean ± SEM; P < 0.05). We inferred that regulation of ovine oocyte cAMP concentrations during IVM improved embryo quality compared with embryos produced by standard IVM methods.

Utilization of endogenous fatty acid stores for energy production in bovine preimplantation embryos

Although current embryo culture media are based on carbohydrate metabolism of embryos, little is known about metabolism of endogenous lipids. L-carnitine is a β-oxidation cofactor absent in most culture media. The objective was to investigate the influence of L-carnitine supplementation on bovine embryo development. Abattoir-derived bovine cumulus oocyte complexes were cultured and fertilized. Post-fertilization, presumptive zygotes were transferred into a basic cleavage medium ± carbohydrates (glucose, lactate and pyruvate) ± 5 mm L-carnitine and cultured for 4 days in vitro. In the absence of carbohydrates during culture, embryos arrested at the 2- and 4-cell stages. Remarkably, +L-carnitine increased development to the morula stage compared to +carbohydrates alone (P < 0.001). The beneficial effects of L-carnitine were further demonstrated by inclusion of carbohydrates, with 14-fold more embryos reaching the morula stage after culture in the +carbohydrates +L-carnitine group compared to the +carbohydrates group (P < 0.05). Whereas there was a trend for +L-carnitine to increase ATP (P = 0.09), ADP levels were higher and ATP: ADP ratio were 1.9-fold lower (main effect, P < 0.05) compared to embryos cultured in -L-carnitine. Therefore, we inferred that +L-carnitine embryos were more metabolically active, with higher rates of ATP-ADP conversion. In conclusion, L-carnitine supplementation supported precompaction embryo development and there was an additive effect of +L-carnitine +carbohydrates on early embryo development, most likely through increased β-oxidation within embryos.

Temporal effects of exogenous oocyte-secreted factors on bovine oocyte developmental competence during IVM

We investigated whether paracrine signalling between the bovine oocyte and cumulus cells is altered during the course of in vitro maturation (IVM). Bovine COCs were cocultured with denuded oocytes or treated with specific oocyte-secreted factors, namely recombinant bone morphogenetic protein (BMP)-15 or growth differentiation factor (GDF)-9, beginning from 0 or 9 h IVM. To generate a 9-h denuded oocyte (DO) group, COCs were cultured intact for the first 9 h of IVM and then denuded. Coculturing intact COCs with DOs denuded immediately after collection or following 9 h of maturation did not affect cleavage rate, but improved blastocyst yield (P < 0.05) on Day 8 (51 and 61%, respectively; P < 0.05) and cell number compared with COCs cultured alone (41%). Significantly, we observed higher levels of endogenous GDF-9 and BMP-15 protein in oocytes of COCs matured for 9 h compared with no incubation. The addition of 175 ng mL–1 GDF-9 or 10% v/v BMP-15 from partially purified transfected 293H cell supernatant for 24 h IVM significantly enhanced development to the blastocyst stage from 40% (control) to 51 and 47%, respectively (P < 0.05). However, treatment of COCs with GDF-9 or BMP-15 between 9 and 24 h of IVM did not increase blastocyst yield. These results provide evidence of quantitative and possibly qualitative temporal changes in oocyte paracrine factor production during IVM.

The pivotal role of glucose metabolism in determining oocyte developmental competence

The environment that the cumulus oocyte complex (COC) is exposed to during either in vivo or in vitro maturation (IVM) can have profound effects on the success of fertilisation and subsequent embryo development. Glucose is a pivotal metabolite for the COC and is metabolised by glycolysis, the pentose phosphate pathway (PPP), the hexosamine biosynthesis pathway (HBP) and the polyol pathway. Over the course of oocyte maturation, a large proportion of total glucose is metabolised via the glycolytic pathway to provide substrates such as pyruvate for energy production. Glucose is also the substrate for many cellular functions during oocyte maturation, including regulation of nuclear maturation and redox state via the PPP and for the synthesis of substrates of extracellular matrices (cumulus expansion) and O-linked glycosylation (cell signalling) via the HBP. However, the oocyte is susceptible to glucose concentration-dependent perturbations in nuclear and cytoplasmic maturation, leading to poor embryonic development post-fertilisation. For example, glucose concentrations either too high or too low result in precocious resumption of nuclear maturation. This review will discuss the relevant pathways of glucose metabolism by COCs during in vivo maturation and IVM, including the relative contribution of the somatic and gamete compartments of the COC to glucose metabolism. The consequences of exposing COCs to abnormal glucose concentrations will also be examined, either during IVM or by altered maternal environments, such as during hyperglycaemia induced by diabetes and obesity.

Glucosamine Supplementation During In Vitro Maturation Inhibits Subsequent Embryo Development: Possible Role of the Hexosamine Pathway as a Regulator of Developmental Competence1

Glucose concentration during cumulus-oocyte complex (COC) maturation influences several functions, including progression of oocyte meiosis, oocyte developmental competence, and cumulus mucification. Glucosamine (GlcN) is an alternative hexose substrate, specifically metabolized through the hexosamine biosynthesis pathway, which provides the intermediates for extracellular matrix formation during cumulus cell mucification. The aim of this study was to determine the influence of GlcN on meiotic progression and oocyte developmental competence following in vitro maturation (IVM). The presence of GlcN during bovine IVM did not affect the completion of nuclear maturation and early cleavage, but severely perturbed blastocyst development. This effect was subsequently shown to be dose-dependent and was also observed for porcine oocytes matured in vitro. Hexosamine biosynthesis upregulation using GlcN supplementation is well known to increase O-linked glycosylation of many intracellular signaling molecules, the best-characterized being the phosphoinositol-3-kinase (PI3K) signaling pathway. We observed extensive O-linked glycosylation in bovine cumulus cells, but not oocytes, following IVM in either the presence or the absence of GlcN. Inhibition of O-linked glycosylation significantly reversed the effect of GlcN-induced reduction in developmental competence, but inhibition of PI3K signaling had no effect. Our data are the first to link hexosamine biosynthesis, involved in cumulus cell mucification, to oocyte developmental competence during in vitro maturation.

Effect of hexoses and gonadotrophin supplementation on bovine oocyte nuclear maturation during in vitro maturation in a synthetic follicle fluid medium

In vitro oocyte maturation (IVM) culture conditions have been relatively unchanged over the past few decades and remain suboptimal. In contrast, studies of the in vivo environment have led to significant improvements to in vitro embryo culture technologies. The aim of the present study was to determine the effect of maturing bovine cumulus–oocyte complexes (COCs) in medium based on the composition of bovine follicular fluid (Bovine VitroMat; Cook Australia, Eight Mile Plain, Qld, Australia). In particular, the effect of different glucose concentrations and glucosamine supplementation on meiotic maturation was determined. Culturing COCs in the presence of gonadotrophins in Bovine VitroMat, containing either physiological glucose concentrations (2.3 mm) or 5.6 mm (equivalent to levels in Tissue Culture Medium 199 (TCM199)) supplemented with glucosamine resulted in comparable cumulus expansion to COCs cultured in TCM199 plus gonadotrophins. However, nuclear maturation was 1.3-fold lower in Bovine VitroMat cultures containing 2.3 mm glucose compared with 5.6 mm glucose and this effect was independent of glucosamine supplementation. Investigations into the effects of different glucose concentrations and gonadotrophin supplementation during the initial 6 h of maturation demonstrated that COCs cultured in Bovine VitroMat with 5.6 mm glucose without gonadotrophins had a twofold acceleration of the rate of meiotic resumption, yet the rate of polar body formation was decreased by approximately 20% compared with cultures in 2.3 mm glucose and TCM199. However, this effect was not seen when COCs were cultured for the initial 16 h in Bovine VitroMat + 5.6 mm minus gonadotrophins or in Bovine VitroMat + 2.3 mm glucose ± gonadotrophins. These data demonstrate that glucose concentrations and the timing of the introduction of gonadotrophin during IVM have variable effects on nuclear maturation. Manipulation of glucose concentrations may be a mechanism to influence oocyte meiotic progression and may lead to the development of improved IVM systems, allowing for an increased developmental capacity of bovine oocytes.

Cumulus expansion and glucose utilisation by bovine cumulus–oocyte complexes during in vitro maturation: the influence of glucosamine and follicle-stimulating hormone

Glucose is an important metabolite and its presence duringin vitrooocyte maturation (IVM) can have profound effects on the oocyte’s developmental capacity. We have demonstrated that glucose uptake increases over a 24 h IVM period, with most accounted for asl-lactate production. However, as maturation proceeds,l-lactate production remains constant, suggesting an alternative role for glucose metabolism. We hypothesised that in the latter stages of oocyte maturation, glucose not accounted for byl-lactate production is utilised for FSH-stimulated extracellular matrix (ECM) synthesis. To examine precursor utilisation for synthesis of ECM, bovine cumulus–oocyte complexes (COCs) were matured in ± FSH and/or glucosamine (an alternative substrate of matrix components). Measurements included COC diameters, glucose consumption andl-lactate production in spent media and [U-14C]glucose incorporation into ECM. FSH significantly stimulated both diameter and glucose consumption during 20–24 h maturation compared with unstimulated complexes, although co-incubation with glucosamine and FSH decreased total glucose consumption 1.7-fold compared with FSH alone (P< 0.05). Furthermore, there was a linear relationship between glucose andl-lactate metabolism in the presence of glucosamine, suggesting that the majority of glucose was being utilised forl-lactate production via glycolysis. In the presence of glucosamine, twofold less [U-14C]glucose was incorporated into matrix compared with COCs cultured without glucosamine. These results support the hypothesis that there is a link between glucose and glucosamine uptake in FSH-stimulated ECM synthesis. Furthermore, glucose has multiple fates within the COC during maturation and levels of utilisation are dependent on the composition of the maturation environment.

Seminal plasma regulates corpora lutea macrophage populations during early pregnancy in mice

In mice, exposure of the uterus to seminal plasma at mating initiates an inflammatory response within the endometrium, which is characterized by production of cytokines that recruit and activate leukocytes. We hypothesized that this seminal plasma-induced inflammatory response would extend to the ovary, increasing leukocyte abundance within corpora lutea and potentially enhancing progesterone synthesis. Female mice mated to males with their seminal vesicles surgically removed exhibited fewer macrophages within corpora lutea on the day after mating, compared with females mated to vasectomized or normal, intact males. The mean number of F4/80-positive macrophages and major histocompatibility complex (MHC) class II-positive activated macrophages was approximately 2-fold fewer in the absence of seminal vesicle fluid. The effects of seminal plasma on macrophage abundance subsided by Day 4 and were not accompanied by a change in serum progesterone levels during luteinization (Days 1, 2, or 4 after mating) or luteolysis (Days 6 or 9). In vitro secretion of progesterone from corpora lutea cultured with or without LH also did not differ between treatment groups. There was no effect of seminal plasma deficiency in males on the number of ovulated ova or corpora lutea in females. These results imply that seminal plasma exposure of the female reproductive tract at mating augments the macrophage population of newly formed corpora lutea, although these additional macrophages seem not to play a role in steroidogenesis and may instead be involved in tissue remodeling within corpora lutea.