Involvement of the pentose phosphate pathway and redox regulation in fertilization in the mouse

G6PD lactylation is involved in regulating redox balance of boar sperm in low glucose extender

Glucose metabolism is an essential pathway that indirectly supports cellular redox homeostasis by providing reducing equivalents, such as NADPH, particularly in the highly specialized sperm. Sperm exhibit higher progressive motility in low glucose extender. However, the underlying mechanisms remain unclear. The objective of the present study was to investigate effect of low glucose on sperm metabolism and lactylation modification. After 3 h of incubation, low glucose had an effect on the redox state of boar semen in vitro, particularly in terms of the concentration of reactive oxygen species (ROS) and reductive products. Furthermore, glucose-6-phosphate dehydrogenase (G6PD) activity was significantly increased at low glucose condition, accompanied by increased lactate accumulation extracellularly. Meanwhile, protein lactylation levels were enhanced, with G6PD identified as one of lactylation proteins. In conclusion, low glucose incubation induced lactylation of G6PD, resulting in increased enzymatic activity that enhanced the pentose phosphate pathway (PPP), which in turn increased antioxidant capacity and maintained sperm motility in a low glucose environment. The research results provide valuable insights into the adaptation mechanisms of sperm to their environment and offer new perspectives and opportunities for reproductive biology research.

Redox Regulation and Glucose Metabolism in the Stallion Spermatozoa

Stallion spermatozoa are cells which exhibit intense metabolic activity, where oxidative phosphorylation in the mitochondria is the primary ATP generator. However, metabolism must be viewed as a highly interconnected network of oxidation-reduction reactions that generate the energy necessary for life. An unavoidable side effect of metabolism is the generation of reactive oxygen species, leading to the evolution of sophisticated mechanisms to maintain redox homeostasis. In this paper, we provide an updated overview of glucose metabolism in stallion spermatozoa, highlighting recent evidence on the role of aerobic glycolysis in these cells, and the existence of an intracellular lactate shuttle that may help to explain the particular metabolism of the stallion spermatozoa in the context of their redox regulation.

Manipulation of metabolism to improve liquid preservation of mammalian spermatozoa

Reproductive success in mammals hinges on the ability of sperm to generate sufficient energy through cellular metabolism to perform the energy-intensive processes required for fertilisation, including motility, maturation, and oocyte interactions. It is now widely accepted that sperm exhibit metabolic flexibility, utilising a combination of glycolysis and oxidative phosphorylation (supported by the Krebs cycle and other complementary pathways) to meet their energy demands. However, the preferred pathway for energy production varies significantly among species, making it challenging to map species-specific metabolic strategies, particularly in species with high metabolic flexibility, like the ram. Additionally, differences in methodologies used to measure metabolism have led to biased interpretations of species' metabolic strategies, complicating the development of liquid storage methods aimed at preserving spermatozoa by manipulating energy generation based on species-specific requirements. This review examines sperm energy requirements, current methods for assessing metabolic capacity, and the current research on species-specific metabolism. Future research should focus on establishing a standardised approach for determining metabolic preferences to accurately map species-specific strategies, a critical step before developing effective liquid preservation methods. By identifying species-specific regulatory points, strategies can be designed to temporarily inhibit metabolic pathways, conserving resources and reducing the accumulation of metabolic by-products. Alternatively, supplementation with depleted metabolites can be guided by understanding areas of excessive consumption during prolonged metabolism. Applying this knowledge to develop tailored preservation techniques will help minimise sperm damage and improve survival during in vitro processing and liquid storage, ultimately enhancing the success of artificial breeding programs.

Sperm Metabolism

Bioenergetics plays a crucial role in sperm functions, including motility, capacitation-related protein modifications, oocyte recognition and interaction, all of which are essential for fertilization. Sperm metabolism is recognized as flexible, responding to environmental cues and energetic demands during ejaculation, the journey along the female tract, and until fertilization. Recent studies suggest that sperm metabolic functions are relevant beyond fertilization and may influence zygote and embryo development, impacting paternal-derived effects on offspring development and health. In recent years, sperm metabolic functions and homeostasis have gained increasing interest in male reproduction research. Given the crucial implications of sperm metabolism on fertility-related processes, this field is of interest not only in human male fertility but also in livestock research, semen conservation, and assisted reproductive techniques. Newly developed assessment tools are allowing a better understanding of sperm metabolism under different conditions and identifying species-specific peculiarities. This review aims to discuss the current knowledge of mammalian sperm metabolism, focusing on species-specific features, changes during the sperm journey, and potential contributions to translational research and reproductive biotechnologies. Furthermore, we propose future perspectives on sperm bioenergetics research.

Comparative Proteomics Elucidates the Potential Mechanism of Sperm Capacitation of Chinese Mitten Crabs (Eriocheir sinensis)

Sperm capacitation is broadly defined as a suite of biochemical and biophysical changes resulting from the acquisition of fertilization ability. To gain insights into the regulation mechanism of crustacean sperm capacitation, 4D label-free quantitative proteomics was first applied to analyze the changes of sperm in Eriocheir sinensis under three sequential physiological conditions: seminal vesicles (X2), hatched with the seminal receptacle content (X3), and incubated with egg water (X5). In total, 1536 proteins were identified, among which 880 proteins were quantified, with 82 and 224 proteins significantly altered after incubation with the seminal receptacle contents and egg water. Most differentially expressed proteins were attributed to biological processes by Gene Ontology annotation analysis. As the fundamental bioenergetic metabolism of sperm, the oxidative phosphorylation, glycolysis, and the pentose phosphate pathway presented significant changes under the treatment of seminal receptacle contents, indicating intensive regulation for sperm in the seminal receptacle. Additionally, the seminal receptacle contents also significantly increased the oxidation level of sperm, whereas the enhancement of abundance in superoxide dismutase, peroxiredoxin 1, and glutathione S-transferase after incubation with egg water significantly improved the resistance against oxidation. These results provided a new perspective for reproduction studies in crustaceans.

Pyruvate enhances stallion sperm function in high glucose media improving overall metabolic efficiency

If a mechanism of more efficient glycolysis depending on pyruvate is present in stallion spermatozoa, detrimental effects of higher glucose concentrations that are common in current commercial extenders could be counteracted. To test this hypothesis, spermatozoa were incubated in a 67 mM Glucose modified Tyrode's media in the presence of 1- or 10-mM pyruvate and in the Tyrode's basal media which contains 5 mM glucose. Spermatozoa incubated for 3 h at 37 °C in 67 mM Tyrode's media with 10 mM pyruvate showed increased motility in comparison with aliquots incubated in Tyrode's 5 mM glucose and Tyrode's 67 mM glucose (57.1 ± 3.5 and 58.1 ± 1.9 to 73.0 ± 1.1 %; P < 0.01). Spermatozoa incubated in Tyrode's with 67 mM glucose 10 mM pyruvate maintained the viability along the incubation (64.03 ± 15.4 vs 61.3 ± 10.2), while spermatozoa incubated in 67 mM Glucose-Tyrode's showed a decrease in viability (38.01 ± 11.2, P < 0.01). 40 mM oxamate, an inhibitor of the lactate dehydrogenase LDH, reduced sperm viability (P < 0.05, from 76 ± 5 in 67 mM Glucose/10 mM pyruvate to 68.0 ± 4.3 %, P < 0.05). Apoptotic markers increased in the presence of oxamate. (P < 0.01). UHPLC/MS/MS showed that 10 mM pyruvate increased pyruvate, lactate, ATP and NAD+ while phosphoenolpyruvate decreased. The mechanisms that explain the improvement of in presence of 10 mM pyruvate involve the conversion of lactate to pyruvate and increased NAD+ enhancing the efficiency of the glycolysis.

Type I Diabetes in Zebrafish Reduces Sperm Quality and Increases Insulin and Glucose Transporter Transcripts

Type I diabetes is a prominent human pathology with increasing incidence in the population; however, its cause is still unknown. This disease promotes detrimental effects on reproduction, such as lower sperm motility and DNA integrity. Hence, the investigation of the underlying mechanisms of this metabolic disturbance in reproduction and its transgenerational consequences is of the utmost importance. The zebrafish is a useful model for this research considering its high homology with human genes as well as its fast generation and regeneration abilities. Therefore, we aimed to investigate sperm quality and genes relevant to diabetes in the spermatozoa of Tg(ins:nfsb-mCherry) zebrafish, a model for type I diabetes. Diabetic Tg(ins:nfsb-mCherry) males showed significantly higher expression of transcripts for insulin a (insa) and glucose transporter (slc2a2) compared to controls. Sperm obtained from the same treatment group showed significantly lower sperm motility, plasma membrane viability, and DNA integrity compared to that from the control group. Upon sperm cryopreservation, sperm freezability was reduced, which could be a consequence of poor initial sperm quality. Altogether, the data showed similar detrimental effects related to type I diabetes in zebrafish spermatozoa at the cellular and molecular levels. Therefore, our study validates the zebrafish model for type I diabetes research in germ cells.

An integrated overview on the regulation of sperm metabolism (glycolysis-Krebs cycle-oxidative phosphorylation)

An overview of the sperm metabolism is presented; using the stallion as a model we review glycolysis, Krebs Cycle and oxidative phosphorylation, paying special attention to the interactions among them. In addition, metabolism implies a series of coordinated oxidation-reduction reactions and in the course of these reactions reactive oxygen species (ROS) and reactive oxoaldehydes are produced ; the electron transport chain (ETC) in the mitochondria is the main source of the anion superoxide and hydrogen peroxide, while glycolysis produces 2-oxoaldehydes such as methylglyoxal as byproducts; due to the adjacent carbonyl groups are strong electrophiles (steal electrons oxidizing other compounds). Sophisticated mechanisms exist to maintain redox homeostasis, because ROS under controlled production also have important regulatory functions in the spermatozoa. The interactions between metabolism and production of reactive oxygen species are essential for proper sperm function, and deregulation of these processes rapidly leads to sperm malfunction and finally death. Lastly, we briefly describe two techniques that will expand our knowledge on sperm metabolism in the coming decades, metabolic flow cytometry and the use of the "omics" technologies, proteomics and metabolomics, specifically the micro and nano proteomics/metabolomics. A better understanding of the metabolism of the spermatozoa will lead to big improvements in sperm technologies and the diagnosis and treatment of male factor infertility.

The Stallion Spermatozoa: A Valuable Model to Help Understand the Interplay Between Metabolism and Redox (De)regulation in Sperm Cells

Significance: Proper functionality of the spermatozoa depends on the tight regulation of their redox status; at the same time these cells are highly energy demanding and in the energetic metabolism, principally in the electron transport chain in the mitochondria, reactive oxygen species are continuously produced, in addition to that observed in the Krebs cycle and during the β-oxidation of fatty acids. Recent Advances: In addition, in glycolysis, elimination of phosphate groups from glyceraldehyde 3-phosphate and dihydroxyacetone phosphate results in the byproducts glyoxal (G) and methylglyoxal (MG); these products are 2-oxoaldehydes. The presence of adjacent carbonyl groups makes them strong electrophiles that react with nucleophiles in proteins, lipids, and DNA, forming advanced glycation end products. Critical Issues: This mechanism is behind subfertility in diabetic patients; in the animal breeding industry, commercial extenders for stallion semen contain a supraphysiological concentration of glucose that promotes MG production, constituting a potential model of interest. Future Directions: Increasing our knowledge of sperm metabolism and its interactions with redox regulation may improve current sperm technologies in use, and shall provide new clues to understanding infertility in males. Moreover, stallion spermatozoa due to its accessibility, intense metabolism, and suitability for proteomics/metabolomic studies may constitute a suitable model for studying regulation of metabolism and interactions between metabolism and redox homeostasis. Antioxid. Redox Signal. 37, 521-537.

Sperm Oxidative Stress during In Vitro Manipulation and Its Effects on Sperm Function and Embryo Development

Reactive oxygen species (ROS) generated at low levels during mitochondrial respiration have key roles in several signaling pathways. Oxidative stress (OS) arises when the generation of ROS exceeds the cell's antioxidant scavenging ability and leads to cell damage. Physiological ROS production in spermatozoa regulates essential functional characteristics such as motility, capacitation, acrosome reaction, hyperactivation, and sperm-oocyte fusion. OS can have detrimental effects on sperm function through lipid peroxidation, protein damage, and DNA strand breakage, which can eventually affect the fertility of an individual. Substantial evidence in the literature indicates that spermatozoa experiencing OS during in vitro manipulation procedures in human- and animal-assisted reproduction are increasingly associated with iatrogenic ROS production and eventual impairment of sperm function. Although a direct association between sperm OS and human assisted reproductive techniques (ART) outcomes after in vitro fertilization (IVF) and/or intracytoplasmic sperm injection (ICSI) is still a matter of debate, studies in animal models provide enough evidence on the adverse effects of sperm OS in vitro and defective fertilization and embryo development. This review summarized the literature on sperm OS in vitro, its effects on functional ability and embryo development, and the approaches that have been proposed to reduce iatrogenic sperm damage and altered embryonic development.

Evidence that extrapancreatic insulin production is involved in the mediation of sperm survival

Evidence is presented for expression of the insulin receptor on the surface of mammalian spermatozoa as well as transcripts for the receptor substrate adaptor proteins (IRS1-4) needed to mediate insulin action. Exposure to this hormone resulted in insulin receptor phosphorylation (pTyr972), activation of AKT (pSer473) and the stimulation of sperm motility. Intriguingly, the male germ line is also shown to be capable of generating insulin, possessing the relevant mRNA transcript and expressing strong immunocytochemical signals for both insulin and C-peptide. Insulin could be released from the spermatozoa by sonication in a concentration-dependent manner but was not secreted in response to glucose, fructose or stimulation with progesterone. However, insulin release could be induced by factors present in human uterine lavages. Furthermore, the endometrium was also shown to possess the machinery for insulin production and action (mRNA, insulin, C-peptide, proprotein convertase and insulin receptor), releasing insulin into the uterine lumen prior to ovulation. These studies emphasize the fundamental importance of extra-pancreatic insulin in regulating the reproductive process, particularly in the support of spermatozoa on their perilous voyage to the site of fertilization.

Localisation and function of glucose transporter GLUT1 in chicken (Gallus gallus domesticus) spermatozoa: relationship between ATP production pathways and flagellar motility

Glucose plays an important role in sperm flagellar motility and fertility via glycolysis and oxidative phosphorylation, although the primary mechanisms for ATP generation vary between species. The glucose transporter 1 (GLUT1) is a high-affinity isoform and a major glucose transporter in mammalian spermatozoa. However, in avian spermatozoa, the glucose metabolic pathways are poorly characterised. This study demonstrates that GLUT1 plays a major role in glucose-mediated motility of chicken spermatozoa. Using specific antibodies and ligand, we found that GLUT1 was specifically localised to the midpiece. Sperm motility analysis showed that glucose supported sperm movement during incubation for 0-80min. However, this was abolished by the addition of a GLUT1 inhibitor, concomitant with a substantial decrease in glucose uptake and ATP production, followed by elevated mitochondrial activity in response to glucose addition. More potent inhibition of ATP production and mitochondrial activity was observed in response to treatment with uncouplers of oxidative phosphorylation. Because mitochondrial inhibition only reduced a subset of sperm movements, we investigated the localisation of the glycolytic pathway and showed glyceraldehyde-3-phosphate dehydrogenase and hexokinase I at the midpiece and principal piece of the flagellum. The results of this study provide new insights into the mechanisms involved in ATP production pathways in avian spermatozoa.

Peroxisome proliferator-activated receptor gamma expression along the male genital system and its role in male fertility

Peroxisome proliferator-activated receptor gamma (PPARγ) acts as a ligand activated transcription factor and regulates processes, such as energy homeostasis, cell proliferation and differentiation. PPARγ binds to DNA as a heterodimer with retinoid X receptor and it is activated by polyunsaturated fatty acids and fatty acid derivatives, such as prostaglandins. In addition, the insulin-sensitizing thiazolidinediones, such as rosiglitazone, are potent and specific activators of PPARγ. PPARγ is present along the hypothalamic-pituitary-testis axis and in the testis, where low levels in Leydig cells and higher levels in Sertoli cells as well as in germ cells have been found. High amounts of PPARγ were reported in the normal epididymis and in the prostate, but the receptor was almost undetectable in the seminal vesicles. Interestingly, in the human and in pig, PPARγ protein is highly expressed in ejaculated spermatozoa, suggesting a possible role of PPARγ signaling in the regulation of sperm biology. This implies that both natural and synthetic PPARγ ligands may act directly on sperm improving its performance. Given the close link between energy balance and reproduction, activation of PPARγ may have promising metabolic implications in male reproductive functions. In this review, we first describe PPARγ expression in different compartments of the male reproductive axis. Subsequently, we discuss the role of PPARγ in both physiological and several pathological conditions related to the male fertility.

Role of isoprostanes in human male infertility

One of the major causes of defective sperm function is oxidative stress, which limits the fertilizing potential of these cells as the result of collateral damage to proteins and lipids in the sperm plasma membrane. On this point, a derangement of both generation and neutralization of reactive oxygen species (ROS) is a recognized cause of male infertility. Antioxidant protection in sperm has been widely investigated, as well as the sperm composition of fatty acids (FA), which represents the preferred substrate for ROS, most frequently linked to the disease-related infertility. Isoprostanes are compounds derived from free radical-mediated oxidation of FAs. As such, they are considered an index of lipid oxidative damage and lipid mediators. This article discusses the role of isoprostanes as relevant factors both to sperm FA composition and sperm membrane integrity. Additionally, isoprostane's influence on sperm quality is reviewed. With reference to male reproductive dysfunction, increasing evidence indicates isoprostanes, detectable in biological fluids or sperm membrane, as the specific index of 1) exposure to chemical etiological agents, 2) oxidative damage, 3) reduced antioxidant response, and 4) sperm immaturity.

ABBREVIATIONS

OS: oxidative stress; ROS: reactive oxygen species; PUFAs: polyunsaturated fatty acids; ARA: arachidonic acid, F₂-IsoPs; F₂-isoprostanes, PLA₂: phospholipase A₂; NADPH: nicotinamide adenine dinucleotide phosphate; IVF: in vitro fertilization.

Metabolic changes in mouse sperm during capacitation†

Mammalian sperm are stored in the epididymis in a dormant state. Upon ejaculation, they must immediately start producing sufficient energy to maintain motility and support capacitation. While this increased energy demand during capacitation is well established, it remains unclear how mouse sperm modify their metabolism to meet this need. We now show that capacitating mouse sperm enhance glucose uptake, identifying glucose uptake as a functional marker of capacitation. Using an extracellular flux analyzer, we show that glycolysis and oxidative phosphorylation increase during capacitation. Furthermore, this increase in oxidative phosphorylation is dependent on glycolysis, providing experimental evidence for a link between glycolysis and oxidative phosphorylation in mouse sperm.

Different approaches for assessing sperm function

Different approaches can be used to assess sperm function in different conditions, i.e. sperm storage, freezing-thawing or activation by induction of capacitation and acrosome reaction. In this review we will focus on the assays routinely performed in our laboratories, giving a literature support to critically analyse different approaches. In fact, researchers usually tend to look for the "one shot" parameter that could explain itself a specific process; it is our conviction that a multiparametric approach is still more valid, as some changes in sperm function are very complex and could be explained only by operating in different ways. Sperm motility, the most evident sperm characteristic, should be assessed by computer-aided sperm analysers that permit an objective evaluation of the motility and its kinematic parameters. Commercial and open source instruments are available and could be profitably used together with specific statistical approaches. The use of microscopy, and particularly fluorescent microscopy, could be a very useful tool to assess different parameters in sperm cells both by fluorophores that give indication of a determined function, and by immunolocalization of proteins, that permits the discover of new features or to explain particular sperm functions. The same substrates could be used also in flow cytometry: the difference is that it permits to study wider sperm populations (and their sub-population distribution). Flow cytometry is undergoing a very wide use in spermatology and technical and experimental rigor is needed to obtain reliable results. Metabolic assessment of sperm features, particularly energetic supply, ATP formation and other enzyme activities, could represent a very important challenge to acquire new information and complete/integrate those derived from other techniques. Finally, functional assays such as oocyte binding and in vitro fertilization, represent a very strong tool to assess sperm function in vitro, as they could evidence the functional intactness of some pathways.

L-Glucose: Another Path to Cancer Cells

Cancerous tumors comprise cells showing metabolic heterogeneity. Among numerous efforts to understand this property, little attention has been paid to the possibility that cancer cells take up and utilize otherwise unusable substrates as fuel. Here we discuss this issue by focusing on l-glucose, the mirror image isomer of naturally occurring d-glucose; l-glucose is an unmetabolizable sugar except in some bacteria. By combining relatively small fluorophores with l-glucose, we generated fluorescence-emitting l-glucose tracers (fLGs). To our surprise, 2-NBDLG, one of these fLGs, which we thought to be merely a control substrate for the fluorescent d-glucose tracer 2-NBDG, was specifically taken up into tumor cell aggregates (spheroids) that exhibited nuclear heterogeneity, a major cytological feature of malignancy in cancer diagnosis. Changes in mitochondrial activity were also associated with the spheroids taking up fLG. To better understand these phenomena, we review here the Warburg effect as well as key studies regarding glucose uptake. We also discuss tumor heterogeneity involving aberrant uptake of glucose and mitochondrial changes based on the data obtained by fLG. We then consider the use of fLGs as novel markers for visualization and characterization of malignant tumor cells.

Single-cell RNA sequencing reveals distinct gene expression patterns in glucose metabolism of human preimplantation embryos

Precise regulation of glucose metabolism-related genes is essential for early embryonic development. Although previous research has yielded detailed information on the biochemical processes, little is yet known of the dynamic gene expression profiles in glucose metabolism of preimplantation embryos at a single-cell resolution. In the present study, we performed integrated analysis of single-cell RNA sequencing (scRNA-seq) data of human preimplantation embryos that had been cultured in sequential medium. Different cells in the same embryo have similar gene expression patterns in glucose metabolism. During the switch from the cleavage to morula stage, the expression of glycolysis-related genes, such as glucose transporter genes (solute carrier family 2 (facilitated glucose transporter), member 1 (SLC2A1) and solute carrier family 2 (facilitated glucose transporter), member 3 (SLC2A3) and genes encoding hexokinase, phosphofructokinase, pyruvate kinase and lactate dehydrogenase, is increased. The genes involved in the pentose phosphate pathway are highly expressed at the cleavage stage, generating the reducing power to balance oxidative stress derived from biosynthesis. Expression of the genes involved in the biosynthesis of glycerophospholipids is increased after the morula stage. Nevertheless, the expression of tricarboxylic acid-related genes remains relatively unchanged during the preimplantation stages. In conclusion, we discovered that the gene expression profiles are dynamic according to glucose utilisation in the embryos at different stages, which contributes to our understanding of regulatory mechanisms of glucose metabolism-related genes in human preimplantation embryos.

Energy metabolism of follicular environment during oocyte growth and maturation

Oocyte quality is affected by many factors, among which the environment of growth and maturation seems to be crucial. Studies show that well balanced oocyte energy metabolism has a significant impact on several elements of cytoplasmic and nuclear maturation as well as further embryo developmental competence. Therefore homeostasis between metabolism of glucose and fatty acids in the oocyte is being widely described nowadays. This review aims to discuss the follicular (in vivo) or maturation media (in vitro) environments with regard to glucose and fatty acid metabolism, as the main sources of the energy for the oocyte. A great emphasis is given on the balance between those two metabolic pathways and its further impact on female fertility.

Redox Regulation and Oxidative Stress: The Particular Case of the Stallion Spermatozoa

Redox regulation and oxidative stress have become areas of major interest in spermatology. Alteration of redox homeostasis is recognized as a significant cause of male factor infertility and is behind the damage that spermatozoa experience after freezing and thawing or conservation in a liquid state. While for a long time, oxidative stress was just considered an overproduction of reactive oxygen species, nowadays it is considered as a consequence of redox deregulation. Many essential aspects of spermatozoa functionality are redox regulated, with reversible oxidation of thiols in cysteine residues of key proteins acting as an “on–off” switch controlling sperm function. However, if deregulation occurs, these residues may experience irreversible oxidation and oxidative stress, leading to malfunction and ultimately death of the spermatozoa. Stallion spermatozoa are “professional producers” of reactive oxygen species due to their intense mitochondrial activity, and thus sophisticated systems to control redox homeostasis are also characteristic of the spermatozoa in the horse. As a result, and combined with the fact that embryos can easily be collected in this species, horses are a good model for the study of redox biology in the spermatozoa and its impact on the embryo.

Niacin analogue, 6-Aminonicotinamide, a novel inhibitor of hepatitis B virus replication and HBsAg production

Background: Hepatitis B surface antigen (HBsAg) is one of the important clinical indexes for hepatitis B virus (HBV) infection diagnosis and sustained seroconversion of HBsAg is an indicator for functional cure. However, the level of HBsAg could not be reduced by interferons and nucleoside analogs effectively. Therefore, identification of a new drug targeting HBsAg is urgently needed.

Methods: In this study, 6-AN was screened out from 1500 compounds due to its low cytotoxicity and high antiviral activity. The effect of 6-AN on HBV was examined in HepAD38, HepG2-NTCP and PHHs cells. In addition, the antivirus effect of 6-AN was also identified in mouse model.

Findings: 6-AN treatment resulted in a significant decrease of HBsAg and other viral markers both in vitro and in vivo. Furthermore, we found that 6-AN inhibited the activities of HBV SpI, SpII and core promoter by decreasing transcription factor PPARα, subsequently reduced HBV RNAs transcription and HBsAg production.

Interpretation: We have identified a novel small molecule to inhibit HBV core DNA, HBV RNAs, HBsAg production, as well as cccDNA to a minor degree both in vitro and in vivo. This study may shed light on the development of a novel class of anti-HBV agent.

Dynamic redox balance directs the oocyte-to-embryo transition via developmentally controlled reactive cysteine changes

The metabolic and redox state changes during the transition from an arrested oocyte to a totipotent embryo remain uncharacterized. Here, we applied state-of-the-art, integrated methodologies to dissect these changes in Drosophila We demonstrate that early embryos have a more oxidized state than mature oocytes. We identified specific alterations in reactive cysteines at a proteome-wide scale as a result of this metabolic and developmental transition. Consistent with a requirement for redox change, we demonstrate a role for the ovary-specific thioredoxin Deadhead (DHD). dhd-mutant oocytes are prematurely oxidized and exhibit meiotic defects. Epistatic analyses with redox regulators link dhd function to the distinctive redox-state balance set at the oocyte-to-embryo transition. Crucially, global thiol-redox profiling identified proteins whose cysteines became differentially modified in the absence of DHD. We validated these potential DHD substrates by recovering DHD-interaction partners using multiple approaches. One such target, NO66, is a conserved protein that genetically interacts with DHD, revealing parallel functions. As redox changes also have been observed in mammalian oocytes, we hypothesize a link between developmental control of this cell-cycle transition and regulation by metabolic cues. This link likely operates both by general redox state and by changes in the redox state of specific proteins. The redox proteome defined here is a valuable resource for future investigation of the mechanisms of redox-modulated control at the oocyte-to-embryo transition.

Reactive oxygen species as mediators of sperm capacitation and pathological damage

Oxidative stress plays a major role in the life and death of mammalian spermatozoa. These gametes are professional generators of reactive oxygen species (ROS), which appear to derive from three potential sources: sperm mitochondria, cytosolic L-amino acid oxidases, and plasma membrane Nicotinamide adenine dinucleotide phosphate oxidases. The oxidative stress created via these sources appears to play a significant role in driving the physiological changes associated with sperm capacitation through the stimulation of a cyclic adenosine monophosphate/Protein kinase A phosphorylation cascade, including the activation of Extracellular signal regulated kinase-like proteins, massive up-regulation of tyrosine phosphorylation in the sperm tail, as well as the induction of sterol oxidation. When generated in excess, however, ROS can induce lipid peroxidation that, in turn, disrupts membrane characteristics that are critical for the maintenance of sperm function, including the capacity to fertilize an egg. Furthermore, the lipid aldehydes generated as a consequence of lipid peroxidation bind to proteins in the mitochondrial electron transport chain, triggering yet more ROS generation in a self-perpetuating cycle. The high levels of oxidative stress created as a result of this process ultimately damage the DNA in the sperm nucleus; indeed, DNA damage in the male germ line appears to be predominantly induced oxidatively, reflecting the vulnerability of these cells to such stress. Extensive evaluation of antioxidants that protect the spermatozoa against oxidative stress while permitting the normal reduction-oxidation regulation of sperm capacitation is therefore currently being undertaken, and has already proven efficacious in animal models.

What has passed is prolog: new cellular and physiological roles of G6PD

G6PD deficiency has been the most pervasive inherited disorder in the world since having been discovered. G6PD has an antioxidant role by functioning as a major nicotinamide adenine dinucleotide phosphate (NADPH) provider to reduce excessive oxidative stress. NADPH can produce reactive oxygen species (ROS) and reactive nitrogen species (RNS) mediated by NADPH oxidase (NOX) and nitric oxide synthase (NOS), respectively. Hence, G6PD also has a pro-oxidant role. Research in the past has focused on the enhanced susceptibility of G6PD-deficient cells or individuals to oxidative challenge. The cytoregulatory role of G6PD has largely been overlooked. By using a metabolomic approach, it is noted that upon oxidant challenge, G6PD-deficient cells will reprogram the GSH metabolism from regeneration to synthesis with exhaustive energy consumption. Recently, new cellular/physiologic roles of G6PD have been discovered. By using a proteomic approach, it has been found that G6PD plays a regulatory role in xenobiotic metabolism possibly via NOX and the redox-sensitive Nrf2-signaling pathway to modulate the expression of xenobiotic-metabolizing enzymes. Since G6PD is a key regulator responsible for intracellular redox homeostasis, G6PD deficiency can alter redox balance leading to many abnormal cellular effects such as the cellular inflammatory and immune response against viral infection. G6PD may play an important role in embryogenesis as G6PD-knockdown mouse cannot produce offspring and G6PD-deficient C. elegans with defective egg production and hatching. This array of findings indicates that the cellular and physiologic roles of G6PD, other than the classical role as an antioxidant enzyme, deserve further attention.

Survival of glucose phosphate isomerase null somatic cells and germ cells in adult mouse chimaeras

The mouse Gpi1 gene encodes the glycolytic enzyme glucose phosphate isomerase. Homozygous Gpi1(-/-) null mouse embryos die but a previous study showed that some homozygous Gpi1(-/-) null cells survived when combined with wild-type cells in fetal chimaeras. One adult female Gpi1(-/-)↔Gpi1(c/c) chimaera with functional Gpi1(-/-) null oocytes was also identified in a preliminary study. The aims were to characterise the survival of Gpi1(-/-) null cells in adult Gpi1(-/-)↔Gpi1(c/c) chimaeras and determine if Gpi1(-/-) null germ cells are functional. Analysis of adult Gpi1(-/-)↔Gpi1(c/c) chimaeras with pigment and a reiterated transgenic lineage marker showed that low numbers of homozygous Gpi1(-/-) null cells could survive in many tissues of adult chimaeras, including oocytes. Breeding experiments confirmed that Gpi1(-/-) null oocytes in one female Gpi1(-/-)↔Gpi1(c/c) chimaera were functional and provided preliminary evidence that one male putative Gpi1(-/-)↔Gpi1(c/c) chimaera produced functional spermatozoa from homozygous Gpi1(-/-) null germ cells. Although the male chimaera was almost certainly Gpi1(-/-)↔Gpi1(c/c), this part of the study is considered preliminary because only blood was typed for GPI. Gpi1(-/-) null germ cells should survive in a chimaeric testis if they are supported by wild-type Sertoli cells. It is also feasible that spermatozoa could bypass a block at GPI, but not blocks at some later steps in glycolysis, by using fructose, rather than glucose, as the substrate for glycolysis. Although chimaera analysis proved inefficient for studying the fate of Gpi1(-/-) null germ cells, it successfully identified functional Gpi1(-/-) null oocytes and revealed that some Gpi1(-/-) null cells could survive in many adult tissues.

Are sperm capacitation and apoptosis the opposite ends of a continuum driven by oxidative stress?

This chapter explores the possibility that capacitation and apoptosis are linked processes joined by their common dependence on the continued generation of reactive oxygen species (ROS). According to this model capacitation is initiated in spematozoa following their release into the female reproductive tract as a consequence of intracellular ROS generation, which stimulates intracellular cAMP generation, inhibits tyrosine phosphatase activity and enhances the formation of oxysterols prior to their removal from the sperm surface by albumin. The continued generation of ROS by capacitating populations of spermatozoa eventually overwhelms the limited capacity of these cells to protect themselves from oxidative stress. As a result the over-capacitation of spermatozoa leads to a state of senescence and the activation of a truncated intrinsic apoptotic cascade characterized by enhanced mitochondrial ROS generation, lipid peroxidation, motility loss, caspase activation and phosphatidylserine externalization. The latter may be particularly important in instructing phagocytic leukocytes that the removal of senescent, moribund spermatozoa should be a silent process unaccompanied by the generation of proinflammatory cytokines. These observations reveal the central role played by redox chemistry in defining the life and death of spermatozoa. A knowledge of these mechanisms may help us to engineer novel solutions to both support and preserve the functionality of these highly specialized cells.

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.

Nutrient pathways regulating the nuclear maturation of mammalian oocytes

Oocyte maturation is defined as that phase of development whereby a fully grown oocyte reinitiates meiotic maturation, completes one meiotic division with extrusion of a polar body, then arrests at MII until fertilisation. Completion of maturation depends on many different factors, not the least of which is the proper provision of energy substrates to fuel the process. Interaction of the oocyte and somatic compartment of the follicle is critical and involves numerous signals exchanged between the two cell types in both directions. One of the prominent functions of the cumulus cells is the channelling of metabolites and nutrients to the oocyte to help stimulate germinal vesicle breakdown and direct development to MII. This entails the careful integration and coordination of numerous metabolic pathways, as well as oocyte paracrine signals that direct certain aspects of cumulus cell metabolism. These forces collaborate to produce a mature oocyte that, along with accompanying physiological changes called cytoplasmic maturation, which impart subsequent developmental competence to the oocyte, can be fertilised and develop to term. This review focuses on nuclear maturation and the metabolic interplay that regulates it, with special emphasis on data generated in the mouse.

A TIGAR-regulated metabolic pathway is critical for protection of brain ischemia

TP53-induced glycolysis and apoptosis regulator (TIGAR) inhibits glycolysis and increases the flow of pentose phosphate pathway (PPP), which generates NADPH and pentose. We hypothesized that TIGAR plays a neuroprotective role in brain ischemia as neurons do not rely on glycolysis but are vulnerable to oxidative stress. We found that TIGAR was highly expressed in brain neurons and was rapidly upregulated in response to ischemia/reperfusion insult in a TP53-independent manner. Overexpression of TIGAR in normal mice with lentivirus reduced ischemic neuronal injury, whereas lentivirus-mediated TIGAR knockdown aggravated it. In cultured primary neurons, increasing TIGAR expression reduced oxygen and glucose deprivation (OGD)/reoxygenation-induced injury, whereas decreasing its expression worsened the injury. The glucose 6-phosphate dehydrogenase was upregulated in mouse and cellular models of stroke, and its upregulation was further enhanced by overexpression of TIGAR. Supplementation of NADPH also reduced ischemia/reperfusion brain injury and alleviated TIGAR knockdown-induced aggravation of ischemic injury. In animal and cellular stroke models, ischemia/reperfusion increased mitochondrial localization of TIGAR. OGD/reoxygenation-induced elevation of ROS, reduction of GSH, dysfunction of mitochondria, and activation of caspase-3 were rescued by overexpression of TIGAR or supplementation of NADPH, while knockdown of TIGAR aggravated these changes. Together, our results show that TIGAR protects ischemic brain injury via enhancing PPP flux and preserving mitochondria function, and thus may be a valuable therapeutic target for ischemic brain injury.

A systematic analysis of a deep mouse epididymal sperm proteome

Spermatozoa are highly specialized cells that, when mature, are capable of navigating the female reproductive tract and fertilizing an oocyte. The sperm cell is thought to be largely quiescent in terms of transcriptional and translational activity. As a result, once it has left the male reproductive tract, the sperm cell is essentially operating with a static population of proteins. It therefore is theoretically possible to understand the protein networks contained in a sperm cell and to deduce its cellular function capabilities. To this end, we performed a proteomic analysis of mouse sperm isolated from the cauda epididymis and confidently identified 2850 proteins, which to our knowledge is the most comprehensive sperm proteome for any species reported to date. These proteins comprise many complete cellular pathways, including those for energy production via glycolysis, beta-oxidation and oxidative phosphorylation, protein folding and transport, and cell signaling systems. This proteome should prove a useful tool for assembly and testing of protein networks important for sperm function.

Combination of oocyte and zygote selection by brilliant cresyl blue (BCB) test enhanced prediction of developmental potential to the blastocyst in cattle

The cumulus oocyte complexes (COCs) were obtained from local abattoir. After aspiration, the COCs were allotted into four treatments to evaluation of brilliant cresyl blue (BCB) test. Control treatment (C): oocytes were cultured directly (without exposure to BCB) after recovery in in vitro production (IVP) process. Oocyte treatment (OBCB): immediately after aspiration, COCs were incubated in modified Dulbecco's phosphate-buffered saline (mDPBS) supplemented with 26μM of BCB for 90min and classified into two classes: oocytes with blue cytoplasm coloration (OBCB+: more competent oocytes) and oocytes without blue cytoplasm coloration (OBCB-: low competent oocytes). Directly after classification, the oocytes were maintained undisrupted in the IVP process. Zygote treatment (ZBCB): After oocyte collection, maturation and fertilization, zygotes were stained with BCB for 10min and categorized into three ways, according to whether they were highly stained (ZBCB++: low competent zygotes), moderately stained (ZBCB+: moderate competent zygotes) and unstained (ZBCB-: more competent zygotes). Directly after classification, the zygotes were maintained undisrupted in the culture process. Oocyte and zygote treatments (OBCB/ZBCB): COCs were stained with BCB after recovery and classified into two classes (OBCB+ and OBCB-). After fertilization, the zygotes produced from OBCB+ and OBCB- oocytes were further stained with BCB for 10min and categorized six ways (OBCB+/ZBCB++, OBCB+/ZBCB+, OBCB+/ZBCB-, OBCB-/ZBCB++, OBCB-/ZBCB+ and OBCB-/ZBCB-). Directly after classification, the zygotes were maintained undisrupted in the culture process. The selection rate produced from OBCB treatment (OBCB+; 54.3%) was greater (P<0.05) than ZBCB treatment (ZBCB-; 44.3%). In addition, the selection rate produced from double application (combination of oocyte and zygote selection) of BCB test (OBCB+/ZBCB-: 28.8%) was less (P<0.01) than single application of BCB test (ZBCB-: 44.3%or OBCB+: 54.3%). The percentage of blastocyst production from OBCB+ oocytes (35.7%) and ZBCB- zygotes (36.6%) were greater (P<0.05) than that from C oocytes (25.7%), OBCB- oocytes (16.5%), ZBCB++ (13.5%) and ZBCB+ zygotes (21.3%). However, there were no significant differences (P>0.05) in the percentages of blastocyst production between OBCB+ oocytes (35.7%) and ZBCB- zygotes (36.6%). The proportion of blastocyst production from double application of BCB test (OBCB+/ZBCB-: 48.0%) was greater (P<0.05) than that from single application of BCB test (OBCB+: 35.7% or ZBCB-: 36.6%). In conclusion, current results confirmed that combination of oocyte and zygote selection by BCB test enhanced the efficiency of selecting for high quality embryos, compared to the single BCB test.

Metabolic substrates exhibit differential effects on functional parameters of mouse sperm capacitation

Although substantial evidence exists that sperm ATP production via glycolysis is required for mammalian sperm function and male fertility, conflicting reports involving multiple species have appeared regarding the ability of individual glycolytic or mitochondrial substrates to support the physiological changes that occur during capacitation. Several mouse models with defects in the signaling pathways required for capacitation exhibit reductions in sperm ATP levels, suggesting regulatory interactions between sperm metabolism and signal transduction cascades. To better understand these interactions, we conducted quantitative studies of mouse sperm throughout a 2-h in vitro capacitation period and compared the effects of single substrates assayed under identical conditions. Multiple glycolytic and nonglycolytic substrates maintained sperm ATP levels and comparable percentages of motility, but only glucose and mannose supported hyperactivation. These monosaccharides and fructose supported the full pattern of tyrosine phosphorylation, whereas nonglycolytic substrates supported at least partial tyrosine phosphorylation. Inhibition of glycolysis impaired motility in the presence of glucose, fructose, or pyruvate but not in the presence of hydroxybutyrate. Addition of an uncoupler of oxidative phosphorylation reduced motility with pyruvate or hydroxybutyrate as substrates but unexpectedly stimulated hyperactivation with fructose. Investigating differences between glucose and fructose in more detail, we demonstrated that hyperactivation results from the active metabolism of glucose. Differences between glucose and fructose appeared to be downstream of changes in intracellular pH, which rose to comparable levels during incubation with either substrate. Sperm redox pathways were differentially affected, with higher levels of associated metabolites and reactive oxygen species generated during incubations with fructose than during incubations with glucose.

Function of the pentose phosphate pathway and its key enzyme, transketolase, in the regulation of the meiotic cell cycle in oocytes

Objective

Previously, we identified that transketolase (Tkt), an important enzyme in the pentose phosphate pathway, is highly expressed at 2 hours of spontaneous maturation in oocytes. Therefore, this study was performed to determine the function of Tkt in meiotic cell cycle regulation, especially at the point of germinal vesicle breakdown (GVBD).

Methods

We evaluated the loss-of-function of Tkt by microinjecting Tkt double-stranded RNAs (dsRNAs) into germinal vesicle-stage oocytes, and the oocytes were cultured in vitro to evaluate phenotypic changes during oocyte maturation. In addition to maturation rates, meiotic spindle and chromosome rearrangements, and changes in expression of other enzymes in the pentose phosphate pathway were determined after Tkt RNA interference (RNAi).

Results

Despite the complete and specific knockdown of Tkt expression, GVBD occurred and meiosis was arrested at the metaphase I (MI) stage. The arrested oocytes exhibited spindle loss, chromosomal aggregation, and declined maturation promoting factor and mitogen-activated protein kinase activities. The modified expression of two enzymes in the pentose phosphate pathway, Prps1 and Rbks, after Tkt RNAi and decreased maturation rates were amended when ribose-5-phosphate was supplemented in the culture medium, suggesting that the Tkt and pentose phosphate pathway are important for the maturation process.

Conclusion

We concluded that Tkt and its associated pentose phosphate pathway play an important role in the MI-MII transition of the oocytes' meiotic cell cycle, but not in the process of GVBD.

Developmental competence and expression of the MATER and ZAR1 genes in immature bovine oocytes selected by brilliant cresyl blue

The objective of this work was to evaluate the selection of immature bovine oocytes by brilliant cresyl blue dye (BCB) and expression of transcripts MATER and ZAR1. Cumulus-oocyte complexes (COCs) from slaughterhouse ovaries were exposed to BCB diluted in mDPBS and incubated for 60 min at 38.5 degrees C in humidified air. After exposure those COCs were distributed in two groups, according to their cytoplasm colour: BCB+ (coloured cytoplasm) or BCB- (colourless cytoplasm). The control group was submitted to in vitro maturation (IVM) immediately after morphological selection and holding control group COCs were exposed to mDPBS without BCB but in the same incubation conditions of BCB+ and BCB- group. The COCs of all groups were submitted to IVM, in vitro fertilization (IVF) and in vitro culture (IVC). Cleavage rate (72 h post-insemination) was similar between control (65.3%) and BCB+ (64.4%) groups, but greater than (p < 0.05) holding control (49.8%) and BCB- (51.3%) groups. Blastocyst rate (192 h post-insemination) was not different between BCB+ (18.5%) and control (16.3%) groups, but greater (p < 0.05) than BCB- (8.4%) group. No difference was found for blastocyst rate between holding control group (14.2%), control and BCB+ groups. The relative expression of MATER and ZAR1 genes was evaluated by real-time PCR in immature oocytes collected from the control, holding control, BCB+ and BCB- groups. Despite the relative expression of MATER in holding control, BCB+ and BCB- were down regulated in comparison to control group there was no statistical difference (p > 0.05) in the relative expression of MATER and ZAR1 transcripts among groups. The results indicate that the BCB dye detects immature oocyte populations with different developmental competence, although no improvement in in vitro embryo production using oocytes exposed or not to BCB was observed. Development competence of immature oocytes exposed to BCB does not seem to be associated with variations in the expression of MATER and ZAR1 transcripts.

Oxidative pentose phosphate pathway-dependent sugar sensing as a mechanism for regulation of root ion transporters by photosynthesis

Root ion transport systems are regulated by light and/or sugars, but the signaling mechanisms are unknown. We showed previously that induction of the NRT2.1 NO(3)(-) transporter gene by sugars was dependent on carbon metabolism downstream hexokinase (HXK) in glycolysis. To gain further insights on this signaling pathway and to explore more systematically the mechanisms coordinating root nutrient uptake with photosynthesis, we studied the regulation of 19 light-/sugar-induced ion transporter genes. A combination of sugar, sugar analogs, light, and CO(2) treatments provided evidence that these genes are not regulated by a common mechanism and unraveled at least four different signaling pathways involved: regulation by light per se, by HXK-dependent sugar sensing, and by sugar sensing upstream or downstream HXK, respectively. More specific investigation of sugar-sensing downstream HXK, using NRT2.1 and NRT1.1 NO(3)(-) transporter genes as models, highlighted a correlation between expression of these genes and the concentration of glucose-6-P in the roots. Furthermore, the phosphogluconate dehydrogenase inhibitor 6-aminonicotinamide almost completely prevented induction of NRT2.1 and NRT1.1 by sucrose, indicating that glucose-6-P metabolization within the oxidative pentose phosphate pathway is required for generating the sugar signal. Out of the 19 genes investigated, most of those belonging to the NO(3)(-), NH(4)(+), and SO(4)(2-) transporter families were regulated like NRT2.1 and NRT1.1. These data suggest that a yet-unidentified oxidative pentose phosphate pathway-dependent sugar-sensing pathway governs the regulation of root nitrogen and sulfur acquisition by the carbon status of the plant to coordinate the availability of these three elements for amino acid synthesis.

Regulation of cytosolic and mitochondrial ATP levels in mouse eggs and zygotes

Fertilization activates development by stimulating a plethora of ATP consuming processes that must be provided for by an up-regulation of energy production in the zygote. Sperm-triggered Ca(2+) oscillations are known to be responsible for the stimulation of both ATP consumption and ATP supply but the mechanism of up regulation of energy production at fertilization is still unclear. By measuring [Ca(2+)] and [ATP] in the mitochondria of fertilized mouse eggs we demonstrate that sperm entry triggers Ca(2+) oscillations in the cytosol that are transduced into mitochondrial Ca(2+) oscillations pacing mitochondrial ATP production. This results, during fertilization, in an increase in both [ATP](mito) and [ATP](cyto). We also observe the stimulation of ATP consumption accompanying fertilization by monitoring [Ca(2+)](cyto) and [ATP](cyto) during fertilization of starved eggs. Our observations reveal that lactate, in contrast to pyruvate, does not fuel mitochondrial ATP production in the zygote. Therefore lactate-derived pyruvate is somehow diverted from mitochondrial oxidation and may be channeled to other metabolic routes. Together with our earlier findings, this study confirms the essential role for exogenous pyruvate in the up-regulation of ATP production at the onset of development, and suggests that lactate, which does not fuel energetic metabolism may instead regulate the intracellular redox potential.

Concentrations of monosaccharides and their amino and alcohol derivatives in human preovulatory follicular fluid

The study purpose was to compare sugar and polyol concentrations in preovulatory ovarian follicular fluid (FF) with those in the circulation. Samples of FF and peripheral venous blood were obtained after an overnight fast from 14 women attending an IVF program. High performance liquid chromatography measurements of seven polyols, two aminohexoses and four hexoses were the main outcome measures. Glucose concentrations in FF and plasma were 2781.26 +/- 205.64 and 4431.25 +/- 65.17 microM, respectively (P < 0.001). Mannose concentration in FF was 38.99 +/- 3.33 microM, significantly lower than plasma concentration (55.38 +/- 2.29 microM; P < 0.001). A concentration gradient from plasma to FF was also significant for glycerol (99.41 +/- 8.47 versus 74.32 +/- 6.54 microM; P < 0.002), galactose (31.69 +/- 1.58 versus 26.73 +/- 1.93 microM; P < 0.01) and galactosamine (11.49 +/- 0.69 versus 6.38 +/- 0.59 microM; P < 0.001). The plasma-to-FF concentration difference was greatest for glucose (1649.99 +/- 204.09 microM). There was a significant correlation between plasma and FF concentrations for galactose and glycerol. This study supports a substantial utilization of glucose by the oocyte/granulosa cells complex, and documents a significant concentration gradient from plasma to FF for glycerol, mannose, galactose and galactosamine. These plasma-FF differences may reflect both utilization of these carbohydrates by the cells of the preovulatory ovarian follicle and/or transport characteristics of these cells.

A comparative analysis of metabolism and viability in porcine oocytes during in vitro maturation

The importance of oocyte quality cannot be overstated, because it impacts all subsequent events during development of the embryo, the fetus and even the resulting offspring. Oocyte metabolism plays a critical role in supporting developmental competence via multiple mechanisms. It is beginning to be understood that metabolic pathways not only affect cytoplasmic maturation but may control nuclear maturation as well. A complete understanding of the precise roles that metabolism plays in determining oocyte quality is crucial for developing efficient in vitro maturation systems to support acquisition of oocyte competence. To date, this pursuit has not been entirely successful. Work in our laboratory on porcine oocyte metabolism has elucidated some of the intricate control mechanisms at work within the oocyte, not only for energy production, but also encompassing progression of nuclear maturation, mitochondrial activity and distribution, and oxidative and ionic stresses. We hypothesize that by utilizing oocyte metabolic data, we can develop more appropriate in vitro maturation systems that result in increased oocyte and embryo developmental competence.

Regulation of redox metabolism in the mouse oocyte and embryo

Energy homeostasis of the oocyte is a crucial determinant of fertility. Following ovulation, the oocyte is exposed to the unique environment of the Fallopian tube, and this is reflected in a highly specialised biochemistry. The minute amounts of tissue available have made the physiological analysis of oocyte intermediary metabolism almost impossible. We have therefore used confocal imaging of mitochondrial and cytosolic redox state under a range of conditions to explore the oxidative metabolism of intermediary substrates. It has been known for some time that the early mouse embryo metabolises external pyruvate and lactate but not glucose to produce ATP. We now show at the level of single oocytes, that supplied glucose has no effect on the redox potential of the oocyte. Pyruvate is a cytosolic oxidant but a mitochondrial reductant, while lactate is a strong cytosolic reductant via the activity of lactate dehydrogenase. Unexpectedly, lactate-derived pyruvate appears to be diverted from mitochondrial oxidation. Our approach also reveals that the level of reduced glutathione (GSH) in the oocyte is maintained by glutathione reductase, which oxidises intracellular NADPH to reduce oxidised glutathione. Surprisingly, NADPH does not seem to be supplied by the pentose phosphate pathway in the unfertilised oocyte but rather by cytosolic NADP-dependent isocitrate dehydrogenase. Remarkably, we also found that the oxidant action of pyruvate impairs development, demonstrating the fundamental importance of redox state on early development.