Evidence for a functional glycogen metabolism in mature mammalian spermatozoa

The sperm mitochondria: clues and challenges

Sperm cells rely on different substrates to fulfil thei energy demand for different functions and diverse moments of their life. Species specific mechanism involve both energy substrate transport and their utilization: hexose transporters, a protein family of facilitative passive transporters of glucose and other hexose, have been identified in spermatozoa of different species and, within the species, their localization has been identified and, in some cases, linked to specific glycilitic enzyme presence. The catabolism of hexose sources for energy purposes has been studied in various species, and recent advances has been made in the knowledge of metabolic strategies of sperm cells. In particular, the importance of aerobic metabolism has been defined and described in horse, boar and even mouse spermatozoa; bull sperm cells demonstrate to have a good adaptability and capacity to switch between glycolysis and oxidative phosphorylation; finally, dog sperm cells have been demonstrated to have a great plasticity in energy metabolism management, being also able to activate the anabolic pathway of glycogen syntesis. In conclusion, the study of energy management and mitochondrial function in spermatozoa of different specie furnishes important base knowledge to define new media for preservation as well as newbases for reproductive biotechnologies.

Molecular mechanisms regulating spermatogenesis in vertebrates: Environmental, metabolic, and epigenetic factor effects

The renewal of the natural resources is one of the most concerning aspects of modern farming. In animal production, there are many barriers breeders and researchers have to overcome to develop new practices to improve reproductive potential and hasten sexual maturation of the commercially viable species, while maintaining meat quality and sustainability. With the utilization of molecular biology techniques, there have been relevant advances in the knowledge of spermatogenesis, especially in mammals, resulting in new possibilities to control male fertility and the selection of desirable characteristics. Most of these discoveries have not been implemented in animal production. In this review, recent studies are highlighted on the molecular pathways involved in spermatogenesis in the context of animal production. There is also exploration of the interaction between environmental factors and spermatogenesis and how this knowledge may revolutionize animal production techniques. Furthermore, new insights are described about the inheritance of desired characteristics in mammals and there is a review of nefarious actions of pollutants, nutrition, and metabolism on reproductive potential in subsequent generations. Even though there are these advances in knowledge base, results from recent studies indicate there are previously unrecognized environmental effects on spermatogenesis. The molecular mechanisms underlying this interaction are not well understood. Research in spermatogenesis, therefore, remains pivotal as a pillar of animal production sustainability.

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.

Evaluation of Chilled Dog Semen Extended With Sperm Activator

Within modern biotechnology, different tools and methodologies have been developed to maximize canine semen conservation protocol to optimize reproductive results. In the last decades, the survival of chilled semen has been prolonged from 2 to 3 days with the first basic diluents, to 10–14 days with the modern extenders. However, their main limitation is that sperm quality decreases during cold storage. Sperm activators (SA) have been produced to provide the molecules necessary to maximize the sperm survival and quality with the aim to enhance fertility and prolificacy. In this study, the effect of commercial extender SA (Theriosolution® Canine AI extender -Chile-) was recorded by daily evaluation of chilled semen for 14 days. In this experiment, sperm-rich ejaculate fraction was collected from six adult healthy Neapolitan Mastiff dogs. The semen evaluation started immediately after collection (d0), and after that a next generation extender was added (d0) for every 24 h from d1 (with and without SA) to d14, to determine spermatozoa progressive motility, velocity of forward progression (VFP), morphology, and integrity of the spermatic membrane. The initial sperm concentration of extended semen was 417.3 ± 170.4 x 106/mL (mean ± SEM) with 85.89 ± 4.76% of MNS (morphologically normal sperm), 84.47 ± 5.22 % live sperm, and pH of 6.2 ± 2.8. The initial VFP was 3.83 ± 0.48, but after 1 min with SA, it rises to 4.45 ± 0.45 (P < 0.001). The sperm progressive motility parameter increases significantly (P < 0.05) in experimental trial, respect to control, starting to d2 at finish (except for d7). The VFP analysis significantly increases in experimental trial (P < 0.05) during most days of the study with the exclusion of d3 and d14. To evaluate the seminal characteristics over time, the experiment was divided into T1 (d0–d5), T2 (d6–d10), and T3 (d11–d14) (P < 0.001) in evaluation of morphology and membrane functionality. The MNS reached 70% at d10 and finally 65% at d14, being considered normal and possibly fertile. With Host-s, 65% of MNS were also achieved at d14. The presence of glucose and fructose in the diluents used for refrigeration can exert very important effects given the fact that metabolic routes have been found in both sugars, providing both different and complementing effects. It can be concluded that the use of SA prior to artificial insemination improves the quality of chilled semen significantly, although it does not reverse the effects of deterioration due to cellular metabolism over time.

Energy sources that fuel metabolic processes in protruding finger-like organelles

Cells possess a variety of organelles with characteristic structure and subcellular localization intimately linked to their specific function. While most are intracellular and found in virtually all eukaryotic cells, there is a small group of organelles of elongated cylindrical shapes in highly specialized cells that protrude into the extracellular space, such as cilia, flagella, and microvilli. The ATP required by intracellular organelles is amply available in the cytosol, largely generated by mitochondria. However, such is not the case for cilia and flagella, whose slender structures cannot accommodate mitochondria. These organelles consume massive amounts of ATP to carry out high energy-demanding functions, such as sensory transduction or motility. ATP from the nearest mitochondria or other reactions within the cell body is severely limited by diffusion and generally insufficient to fuel the entire length of cilia and flagella. These organelles overcome this fuel restriction by local generation of ATP, using mechanisms that vary depending on the nutrients that are available in their particular external environment. Here, we review, with emphasis in mammals, the remarkable adaptations that cilia and flagella use to fuel their metabolic needs. Additionally, we discuss how a decrease in nutrients surrounding olfactory cilia might impair olfaction in COVID-19 patients.

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.

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.

Peroxisome proliferator-activated receptor gamma signaling in human sperm physiology

Peroxisome proliferator-activated receptor gamma (PPARγ) is a member of the PPARs, which are transcription factors of the steroid receptor superfamily. PPARγ acts as an important molecule for regulating energy homeostasis, modulates the hypothalamic-pituitary-gonadal (HPG) axis, and is reciprocally regulated by HPG. In the human, PPARγ protein is highly expressed in ejaculated spermatozoa, implying a possible role of PPARγ signaling in regulating sperm energy dissipation. PPARγ protein is also expressed in Sertoli cells and germ cells (spermatocytes). Its activation can be induced during capacitation and the acrosome reaction. This mini-review will focus on how PPARγ signaling may affect fertility and sperm quality and the potential reversibility of these adverse effects.

Glycogen synthase kinase 3 regulates acrosomal exocytosis in mouse spermatozoa via dynamin phosphorylation

The dynamin family of GTPases has been implicated as novel regulators of the acrosome reaction, a unique exocytotic event that is essential for fertilization. Dynamin activity during the acrosome reaction is accompanied by phosphorylation of key serine residues. We now tested the hypothesis that glycogen synthase kinase 3 (GSK3) is the protein kinase responsible for dynamin phosphorylation at these phosphosites in mouse spermatozoa. Pharmacologic inhibition of GSK3 in mature mouse spermatozoa (CHIR99021: IC50 = 6.7 nM) led to a significant reduction in dynamin phosphorylation (10.3% vs. 27.3%; P < 0.001), acrosomal exocytosis (9.7% vs. 25.7%; P < 0.01), and in vitro fertilization (53% vs. 100%; P < 0.01). GSK3 was shown to be present in developing germ cells where it colocalized with dynamin in the peri-acrosomal domain. However, additional GSK3 was acquired by maturing mouse spermatozoa within the male reproductive tract, via a novel mechanism involving direct interaction of sperm heads with extracellular structures known as epididymal dense bodies. These data reveal a novel mode for the cellular acquisition of a protein kinase and identify a key role for GSK3 in the regulation of sperm maturation and acrosomal exocytosis.

Muscle glycogen synthase isoform is responsible for testicular glycogen synthesis: glycogen overproduction induces apoptosis in male germ cells

Glycogen is the main source of glucose for many biological events. However, this molecule may have other functions, including those that have deleterious effects on cells. The rate-limiting enzyme in glycogen synthesis is glycogen synthase (GS). It is encoded by two genes, GYS1, expressed in muscle (muscle glycogen synthase, MGS) and other tissues, and GYS2, primarily expressed in liver (liver glycogen synthase, LGS). Expression of GS and its activity have been widely studied in many tissues. To date, it is not clear which GS isoform is responsible for glycogen synthesis and the role of glycogen in testis. Using RT-PCR, Western blot and immunofluorescence, we have detected expression of MGS but not LGS in mice testis during development. We have also evaluated GS activity and glycogen storage at different days after birth and we show that both GS activity and levels of glycogen are higher during the first days of development. Using RT-PCR, we have also shown that malin and laforin are expressed in testis, key enzymes for regulation of GS activity. These proteins form an active complex that regulates MGS by poly-ubiquitination in both Sertoli cell and male germ cell lines. In addition, PTG overexpression in male germ cell line triggered apoptosis by caspase3 activation, proposing a proapoptotic role of glycogen in testis. These findings suggest that GS activity and glycogen synthesis in testis could be regulated and a disruption of this process may be responsible for the apoptosis and degeneration of seminiferous tubules and possible cause of infertility.

Characterization of 3-hydroxyisobutyrate dehydrogenase, HIBADH, as a sperm-motility marker

PURPOSE

Asthenozoospermia is a major cause of male infertility. However, the molecular mechanisms underlying sperm-motility defects remain largely unknown in the majority of cases. In our previous study, we applied a proteomic approach to identify unknown proteins that were downregulated in spermatozoa with low motility compared to spermatozoa with good motility. Several sperm motility- related proteins have been identified. In this study, 3-hydroxyisobutyrate dehydrogenase (HIBADH), one of the proteins identified using the proteomic tools, is further characterized.

METHODS

Reverse-transcription polymerase chain reactions (RT-PCR), western blotting, and immunofluorescence assays (IFA) were preformed to investigate the expression pattern. The enzymatic activity of HIBADH was evaluated in sperm with good (>50 %), moderate (< 50 %) and lower motility (< 20 %).

RESULTS

Using RT-PCR, we found that transcripts of HIBADH are enriched in the cerebellum, heart, skeletal muscle, uterus, placenta, and testes of male humans. In western blotting, it is expressed in the placenta, testes, and spermatozoa. During spermiogenesis, HIBADH is located at the mid-piece (a specialized development from the mitochondria) of elongating, elongated, and mature sperm. The enzymatic activity of HIBADH in sperm with moderate and lower motility were significantly reduced compared with good motility (P<0.0001 and P<0.05, respectively).

CONCLUSIONS

Our study indicated that HIBADH is involved in the mitochondrial function of spermatozoa, and maintains sperm motility. It may serve as a sperm-motility marker.

Glucose and fructose as functional modulators of overall dog, but not boar sperm function

The main aim of the present work was to test the effects of glucose and fructose on the phosphorylation levels of proteins linked to the control of overall sperm function in two species with very different metabolic characteristics, dog and boar. Incubation of dog spermatozoa with 10mM glucose increased serine phosphorylation of proteins related to cell cycle and signal transduction including cyclins B and E, Cdk2, Cdk6, Cdc6, PYK2, c-kit, Raf-1, TRK and several protein phosphatases. Incubation of dog spermatozoa with 10mM fructose decreased serine phosphorylation levels of cyclins B and D3, Cdk1/Cdc2, Cdk2, Cdk6, Akt, PI3 kinase, ERK-1 and protein kinase C. Incubation of boar spermatozoa with glucose or fructose did not modify any of the phosphorylation patterns studied. Given that one important difference between dog and boar spermatozoa is the presence of glucokinase (GK) in dog but not in boar, GK-transfected COS7 cells were incubated with either 10mM glucose or 10mM fructose. Incubation of GK-transfected cells with fructose decreased serine phosphorylation of cyclin A, ERK-2 and Hsp-70. In contrast, incubation of control COS7 cells with fructose increased serine phosphorylation of Cdk6, Cdk1/Cdc2, protein kinase C and Hsp-70. Incubation with glucose did not induce any significant effect. Our results indicate that monosaccharides act as signalling compounds in dog spermatozoa after ejaculation through changes in the phosphorylation levels of specific proteins. One of the factors that may be related to the action of sugars is the equilibrium of the total sperm hexokinase activity, in which the presence or absence of GK appears to be relevant.

Involvement of mitochondrial activity in mediating ELF-EMF stimulatory effect on human sperm motility

It has recently been reported that the exposure of human spermatozoa to an extremely low frequency (ELF) electromagnetic field (EMF) with a square waveform of 5 mT amplitude and frequency of 50 Hz improves sperm motility. The functional relationship between the energy metabolism and the enhancement of human sperm motility induced by ELF-EMF was investigated. Sperm exposure to ELF-EMF resulted in a progressive and significant increase of mitochondrial membrane potential and levels of ATP, ADP and NAD(+) that was associated with a progressive and significant increase in the sperm kinematic parameters. No significant effects were detected on other parameters such as ATP/ADP ratio and energy charge. When carbamoyl cyanide m-chlorophenylhydrazone (CICCP) was applied to inhibit the oxidative phosphorylation in the mitochondria, the values of energy parameters and motility in the sperm incubated in the presence of glucose and exposed to ELF-EMF did not change, thus indicating that the glycolysis was not involved in mediating ELF-EMF stimulatory effect on motility. By contrast, when pyruvate and lactate were provided instead of glucose, the energy status and motility increased significantly in ELF-EMF-treated sperm. Under these culture conditions, the inhibition of glycolitic metabolism by 2-deoxy-D-glucose (DOG) again resulted in increased values of energy and kinematic parameters, indicating that gluconeogenesis was not involved in producing glucose for use in glycolysis. We concluded that the key role in mediating the stimulatory effects exerted by ELF-EMF on human sperm motility is played by mitochondrial oxidative phosphorylation rather than glycolysis.

Mice lacking the USP2 deubiquitinating enzyme have severe male subfertility associated with defects in fertilization and sperm motility

The ubiquitin-proteasome system plays an important role in spermatogenesis. However, the functions of deubiquitinating enzymes in this process remain poorly characterized. We previously showed that the deubiquitinating enzyme USP2 is induced in late elongating spermatids. To identify its function, we generated mice lacking USP2. Usp2 -/- mice appeared normal, and the weights of major organs, including the testis, did not differ from wild type (Usp2 +/+). However, although the numbers of testicular spermatids and epididymal spermatozoa were normal in Usp2 -/- males, these animals had a severe defect in fertility, yielding only 12% as many offspring as Usp2 +/+ littermates. Spermatogenesis in Usp2 -/- mice was morphologically normal except for the presence of abnormal aggregations of elongating spermatids and formation of multinucleated cells in some tubules. The epididymal epithelium was morphologically normal in Usp2 -/- mice, but some abnormal cells other than sperm were present in the lumen. Usp2 -/- epididymal spermatozoa manifested normal motility when incubated in culture media, but rapidly became immotile when incubated in PBS in contrast to Usp2 +/+ spermatozoa, which largely maintained motility under this condition. Usp2 -/- and +/+ spermatozoa underwent acrosome reactions in vitro with similar frequency. In vitro fertilization assays demonstrated a severe defect in the ability of Usp2 -/- spermatozoa to fertilize eggs. This could be bypassed by intracytoplasmic sperm injection or removal of the zona pellucida, which resulted in fertilization rates similar to that of Usp2 +/+ mice. We demonstrate for the first time, using mouse transgenic approaches, a role for the ubiquitin system in fertilization.

Comparative protein profiles: potential molecular markers from spermatozoa of Acipenseriformes (Chondrostei, Pisces)

Sturgeon and paddlefish (Acipenseriformes), the source of roe consumed as caviar, are a unique and commercially valuable group of ancient fishes. In this study, comparative proteomics was used to analyze protein profiles of spermatozoa from five sturgeon species and one paddlefish: Siberian sturgeon (Acipenser baerii), sterlet (A. ruthenus), Russian sturgeon (A. gueldenstaedtii), starry sturgeon (A. stellatus), beluga (Huso huso), and Mississippi paddlefish (Polyodon spathula). Protein profiles of spermatozoa were determined by isoelectric focusing and two-dimensional electrophoresis (2-DE) high-resolution gels. The peptides, previously selected by 2-DE analysis as potentially species-specific, were obtained by "in-gel" tryptic digestion, followed by matrix-associated laser desorption/ionization time-of-flight/mass spectrometry (MALDI-TOF/MS). Among the 23 protein spots selected, 14 were identified as isoforms of enolase B present in all species, but with different isoelectric points or molecular mass. Exceptions were A. ruthenus and H. huso, species with a close phylogenetic relationship. Glycerol-3-phosphate dehydrogenase was detected exclusively in P. spathula. Phosphoglycerate kinase was detected only in A. ruthenus and H. huso, and 3 additional proteins (fructose bisphosphate aldolase A-2, glycogen phosphorylase type IV and glyceraldehyde-3-phosphate dehydrogenase) were found exclusively in A. gueldenstaedtii and H. huso. This study points to the application of proteomics for differential characterization and comparative studies of acipenseriform species at the molecular level.

Glycolytic enzyme activity is essential for domestic cat (Felis catus) and cheetah (Acinonyx jubatus) sperm motility and viability in a sugar-free medium

We have previously reported a lack of glucose uptake in domestic cat and cheetah spermatozoa, despite observing that these cells produce lactate at rates that correlate positively with sperm function. To elucidate the role of glycolysis in felid sperm energy production, we conducted a comparative study in the domestic cat and cheetah, with the hypothesis that sperm motility and viability are maintained in both species in the absence of glycolytic metabolism and are fueled by endogenous substrates. Washed ejaculates were incubated in chemically defined medium in the presence/absence of glucose and pyruvate. A second set of ejaculates was exposed to a chemical inhibitor of either lactate dehydrogenase (sodium oxamate) or glyceraldehyde-3-phosphate dehydrogenase (alpha-chlorohydrin). Sperm function (motility and acrosomal integrity) and lactate production were assessed, and a subset of spermatozoa was assayed for intracellular glycogen. In both the cat and cheetah, sperm function was maintained without exogenous substrates and following lactate dehydrogenase inhibition. Lactate production occurred in the absence of exogenous hexoses, but only if pyruvate was present. Intracellular glycogen was not detected in spermatozoa from either species. Unexpectedly, glycolytic inhibition by alpha-chlorohydrin resulted in an immediate decline in sperm motility, particularly in the domestic cat. Collectively, our findings reveal an essential role of the glycolytic pathway in felid spermatozoa that is unrelated to hexose metabolism or lactate formation. Instead, glycolytic enzyme activity could be required for the metabolism of endogenous lipid-derived glycerol, with fatty acid oxidation providing the primary energy source in felid spermatozoa.

Cannabinoids and Reproduction: A Lasting and Intriguing History

Starting from an historical overview of lasting Cannabis use over the centuries, we will focus on a description of the cannabinergic system, with a comprehensive analysis of chemical and pharmacological properties of endogenous and synthetic cannabimimetic analogues. The metabolic pathways and the signal transduction mechanisms, activated by cannabinoid receptors stimulation, will also be discussed. In particular, we will point out the action of cannabinoids and endocannabinoids on the different neuronal networks involved in reproductive axis, and locally, on male and female reproductive tracts, by emphasizing the pivotal role played by this system in the control of fertility.

Evidence for compromised metabolic function and limited glucose uptake in spermatozoa from the teratospermic domestic cat (Felis catus) and cheetah (Acinonyx jubatus)

Cheetahs and certain other felids consistently ejaculate high proportions (≥ 60%) of malformed spermatozoa, a condition known as teratospermia, which is prevalent in humans. Even seemingly normal spermatozoa from domestic cat teratospermic ejaculates have reduced fertilizing capacity. To understand the role of sperm metabolism in this phenomenon, we conducted a comparative study in the normospermic domestic cat versus the teratospermic cat and cheetah with the general hypothesis that sperm metabolic function is impaired in males producing predominantly pleiomorphic spermatozoa. Washed ejaculates were incubated in chemically defined medium containing glucose and pyruvate. Uptake of glucose and pyruvate and production of lactate were assessed using enzyme-linked fluorescence assays. Spermatozoa from domestic cats and cheetahs exhibited similar metabolic profiles, with minimal glucose metabolism and approximately equimolar rates of pyruvate uptake and lactate production. Compared to normospermic counterparts, pyruvate and lactate metabolism were reduced in teratospermic cat and cheetah ejaculates, even when controlling for sperm motility. Rates of pyruvate and lactate (but not glucose) metabolism were correlated positively with sperm motility, acrosomal integrity, and normal morphology. Collectively, our findings reveal that pyruvate uptake and lactate production are reliable, quantitative indicators of sperm quality in these two felid species and that metabolic function is impaired in teratospermic ejaculates. Furthermore, patterns of substrate utilization are conserved between these species, including the unexpected lack of exogenous glucose metabolism. Because glycolysis is required to support sperm motility and capacitation in certain other mammals (including dogs), the activity of this pathway in felid spermatozoa is a target for future investigation.

Rimonabant (SR141716) induces metabolism and acquisition of fertilizing ability in human sperm

BACKGROUND AND PURPOSE

The endocannabinoid system and the cannabinoid CB(1) receptor have been identified in human sperm, and it is well known that endocannabinoids have pronounced adverse effects on male and female reproduction. In order to elucidate further the pathophysiological role of the endocannabinoid system in male fertility, we investigated the activity of the CB(1) receptor antagonist rimonabant (SR141716) on the fertilizing ability of human sperm.

EXPERIMENTAL APPROACH

We evaluated in vitro the effects of rimonabant on motility, survival, capacitation, acrosin activity and metabolism of human sperm. Particularly, capacitation was studied by using three different approaches: intracellular free Ca(2+) content assay, cholesterol efflux assay and protein tyrosine phosphorylation analysis.

KEY RESULTS

Rimonabant significantly increased sperm motility and viability through the induction of pAkt and pBcl2, key proteins of cell survival and metabolism, and it induced acrosome reaction and capacitation as well. Rimonabant reduced the triglyceride content of sperm, while enhancing lipase and acyl-CoA dehydrogenase activities, implying an overall lipolytic action in these cells. Rimonabant also affected sperm glucose metabolism by decreasing phosphorylation of glycogen synthase kinase 3 and increasing glucose-6-phosphate dehydrogenase activity, suggesting a role in inducing sperm energy expenditure. Intriguingly, agonism at the CB(1) receptor, with an anandamide analogue or a selective inhibitor of fatty acid amide hydrolase, produced opposing effects on human sperm functions.

CONCLUSIONS AND IMPLICATIONS

Our data suggest that blockade of the CB(1) receptor by rimonabant induces the acquisition of fertilizing ability and stimulates energy expenditure in human sperm.

A new role of anandamide in human sperm: focus on metabolism

The endocannabinoid system and the presence of CB1 receptor (CB1-R) target of the anandamide were identified in human sperm, however the anandamide action in this context needs to be further elucidated. At this purpose we analyzed the effects of anandamide on human sperm capacitation and motility. Afterwards, we focused on lipid and glucose sperm metabolism and also investigated the interrelationship between anandamide and insulin secretion by sperm. By intracellular free Ca(2+) content assay and proteins tyrosine phosphorylation, we evidenced that anandamide did not induce capacitation process and a negative effect was obtained on sperm motility. The blockage of CB1-R by the specific antagonist SR141716 increased both capacitation and sperm motility suggesting an involvement of the CB1-R in the acquisition of sperm fertilizing activity. The evaluation of the triglycerides content, lipase and acyl-CoA dehydrogenase activities, suggest that anandamide exerts a lipogenetic effect on human sperm lipid metabolism. Concerning the glucose metabolism, anandamide increases GSK3 phosphorylation indicating that it is involved in the accumulation of energy substrates. G6PDH activity was not affected by anandamide. Interestingly, AEA is involved in insulin secretion by sperm. As insulin had been demonstrated to be an autocrine factor that triggers capacitation, the endocannabinoid might be inserted in the signaling cascade that induces this process. Altogether these findings highlight a pivotal involvement of the CB1-R in the control of sperm energy homeostasis and propose a new site of action for endocannabinoids in the control of energy metabolism.

Mammalian sperm energy resources management and survival during conservation in refrigeration

The present review has as its main aim to present an overview regarding the mechanisms utilized by mammalian sperm to manage its intracellular energy levels. This management will strongly influence the sperm's ability to maintain its overall function during its entire life span. Thus, the precise knowledge of these mechanisms will be of the utmost interest to optimize the systems utilized to conserve mammalian sperm for a medium-to-long time-lapse. Briefly, utilization of hexoses as energy substrates by mammalian sperm is very finely regulated from the very first step of its metabolization. Furthermore, the equilibrium among the separate, monosaccharide metabolization pathways in mammalian sperm depends on many factors. This prevents the possibility to draw a general vision of sperm energy utilization, which explains the results of all mammalian species in all points of the sperm life-cycle. To complicate the matter further, there are separate energy phenotypes among mammalian spermatozoa. The precise knowledge of these phenotypes is of the greatest importance in order to optimize the design of new extenders for sperm conservation in refrigerated conditions. Moreover, sugars can act on sperm not only as passive metabolic substrates, but also as direct function activators through mechanisms like specific changes in the tyrosine phosphorylation status of distinct proteins. Finally, mammalian sperm utilizes non-glucidic substrates like citrate and lactate to obtain energy in a regular form. This utilization is also finely regulated and of importance to maintain overall sperm function. This implies that the exact proportion of glucidic and non-glucidic energy substrates could be very important to optimize the survival ability of these cells in conservation.

Hexose-specificity of hexokinase and ADP-dependence of pyruvate kinase play important roles in the control of monosaccharide utilization in freshly diluted boar spermatozoa

Incubation of boar sperm from fresh ejaculates in a minimal medium with 10 mM glucose induced a fast and intense activation of glycolysis, as indicated by the observed increases in the intracellular levels of glucose 6-phosphate (G 6-P) and ATP and the rate of formation of extracellular L-lactate. The effect of glucose was much more intense than that induced by fructose, sorbitol, and mannose. The greater utilization of glucose was related to a much greater sensitivity to hexokinase when compared with the other monosaccharides. Thus, the presence of 0.5 mM glucose induced total hexokinase activity in supernatants from sperm extracts of 1.7 +/- 0.1 mIU/mg protein, while the same concentration of both fructose, mannose, and sorbitol induced total hexokinase activity from 0.3 +/- 0.1 mIU/mg protein to 0.60 +/- 1 mIU/mg protein. Kinetic analysis of the total pyruvate kinase activity indicated that this activity was greatly dependent on the presence of ADP and also showed a great affinity for PEP, with an estimated Km in supernatants of 0.15-0.20 mM. Immunological location of proteins closely related to glycolysis, like GLUT-3 hexose transporter and hexokinase-I, indicated that these proteins showed the trend to be distributed around or in the cellular membranes of both head and midpiece in a grouped manner. We conclude that glycolysis is regulated by both the specific availability of a concrete sugar and the internal equilibrium between ATP and ADP levels. Furthermore, localization of proteins involved in the control of monosaccharide uptake and phosphorylation suggests that glycolysis starts at concrete points in the boar-sperm surface.

Utilization of citrate and lactate through a lactate dehydrogenase and ATP-regulated pathway in boar spermatozoa

Incubation of boar spermatozoa in Krebs-Ringer-Henseleit medium with either 10 mM lactate or 10 mM citrate induced a fast and robust increase in the intracellular levels of ATP in both cases, which reached a peak after 30 sec of incubation. Utilization of both citrate and lactate resulted in the export of CO(2) to the extracellular medium, indicating that both substrates were metabolized through the Krebs cycle. Incubation with citrate resulted in the generation of extracellular lactate, which was inhibited in the presence of phenylacetic acid. This indicates that lactate is produced through the pyruvate carboxylase step. In addition, there was also a significant increase in tyrosine phosphorylation induced by both citrate and lactate. Boar sperm has a sperm-specific isoform of lactate dehydrogenase (LDH), mainly located in the principal piece of the tail. Kinetic studies showed that boar sperm has at least two distinct LDH activities. The major activity (with an estimated Km of 0.51 mM) was located in the supernatants of sperm extracts. The minor LDH activity (with an estimated Km of 5.9 mM) was associated with the nonsoluble fraction of sperm extracts. Our results indicate that boar sperm efficiently metabolizes citrate and lactate through a metabolic pathway regulated by LDH.

Glycolysis and sperm motility: does a spoonful of sugar help the flagellum go round?

It is doubtful that diffusion can deliver sufficient ATP from the mitochondria to sustain activity at the distal end of the sperm flagellum. Glycolytic enzymes bound to the fibrous sheath could provide energy along the flagellum at the point it is required. An obligatory role for glycolysis is supported by the lack of progressive motility in sperm from mice where the gene for sperm-specific glyceraldehyde-3-phosphate dehydrogenase (GAPDHs) had been 'knocked out'. Here, I review some evidence against this idea. First, pure diffusion from the mitochondrion is likely to be adequate in species with smaller sperm, and it is possible that rapid ATP delivery required in larger sperm could be achieved by an adenylate kinase shuttle. Second, experience with alpha-chlorohydrin demonstrates that sperm can remain motile with normal ATP concentrations despite inhibition of GAPDHs; adverse effects only occur if glucose is added and high levels of glycolytic intermediates accumulate. These observations undermine the GAPDHs knockout mouse as evidence for an essential role of local glycolysis. Third, sperm from many species can remain motile for long periods in sugar-free media and excepting dog sperm, evidence that gluconeogenesis is a possible explanation, is weak. In most species, it is unlikely that local glycolysis is the only way that ATP can be supplied to the distal flagellum.

Arguments raised by the recent discovery that insulin and leptin are expressed in and secreted by human ejaculated spermatozoa

The recent findings demonstrating that insulin and leptin are expressed in and secreted by human ejaculated spermatozoa raise the controversial issue related to mRNA function in male gamete. Capacitated sperm display an increased metabolism and overall energy expenditure presumably to affect the changes in sperm signaling and function during capacitation. However the relationship between the signaling events associated with capacitation and the change in sperm metabolism energy is poorly understood. It emerges from the findings here reported that both leptin and insulin may be crucial in ejaculated spermatozoa to manage their energy status. Immunoistochemical analysis revealed that in uncapacitated sperm insulin was located at the subacrosomial level, in the midpiece and through the tail while leptin was immunodetected at the equatorial segment and at the midpiece. Capacitated sperm display an overall decrease and a more uniform distribution in the signal for both hormones and this is in agreement with their enhanced release in the medium. Both hormones in ejaculated sperm somehow recapitulate the cross-talk between their signalling transductional pathways in somatic cells, resulting in the increase of phosphoinositide 3-kinase (PI3K) activity, AKT S473 and Glycogen synthase kinase 3 (GSK-3)-S9 phosphorylations. During capacitation GSK-3 phosphorylation was abolished suggesting how in capacitating sperm there is a block in glycogen synthesis. This reasonably indicates how during capacitation glycogen reserve is mobilized and this makes the glucose as energy substrate available. For instance insulin dismissed by ejaculated spermatozoa up-regulates Glucose 6-Phosphate Dehydrogenase (G6PDH), the rate-limiting enzyme in the pentose phosphate pathway (PPP), which has be shown to be crucial in the acquisition of fertilizing capability as well as to mediate gamete fusion. Insulin immunoneutralization or blockage of its release, dramatically down regulated G6PDH. Interestingly, in the presence of a disruptor of insulin signaling wortmannin, an inhibitor of PI3K, the intrinsic activity of G6PDH drops. Leptin appears to play similar action to that of insulin on G6PDH in sperm (data in progress). The enhanced activity of this enzyme induced by both hormones produces an increase of NADPH that is essential for fatty acid synthesis from acetyl CoA. These fatty acids have two possible fates: beta-oxidation to produce ATP or reesterification back into triacylglycerol. Inter-relationships of the classes of substrates of free fatty acids (FFA) and glucose utilized for energy, has been long established [Randle, P.J., 1964. The interrelationships of hormones, fatty acid and glucose in the provision of energy. Postgrad. Med. J. 40, 457-463]. The authors observed in ejaculated spermatozoa what it occurs in somatic cells: FFA beta-oxidation tested utilizing the octanoil-CoA as substrate, appears to be stimulated by leptin and down-regulated by the contemporaneous presence of insulin in uncapacitated sperms. FFA beta-oxidation activity dramatically increases when capacitation starts, so it may be assumed the possibility that leptin may work to stimulate such enzymatic activity providing additional metabolic fuel to triggering capacitation process. The autonomous capability of sperm to release insulin and leptin suggests that they through an autocrine short loop may provide the recruitment of energy substrate according to sperm metabolic needs. This occurs independently by the systemic regulation and may represent a protective mechanism which preserves sperm fertilizing capability by any detrimental effects produced by long calorie restriction or by alterations occurring in the energy homeostasis at systemic level.

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

Glucose metabolism is necessary for successful fertilization in the mouse. Both spermatozoa and oocytes metabolize glucose through the pentose phosphate pathway (PPP), and NADPH appears required for gamete fusion. The aims of this study were to further characterize the utilization of glucose by the fertilizing spermatozoon and the fertilized oocyte, to demonstrate the importance of the PPP in different steps of fertilization, and to examine whether the beneficial effect of glucose could be mediated by a NADPH-dependent enzyme involved in redox regulation. By using a fluorescent analog of 2-deoxyglucose, glucose uptake was evidenced in both the head and flagellum of motile spermatozoa. After sperm-oocyte fusion, an increase in glucose uptake by the fertilized oocyte was observed but not before the formation of the male and female pronuclei. By using a microphotometric technique, activity of glucose 6-phosphate dehydrogenase (G6PDH), the key enzyme of the PPP, was localized to the sperm head and midpiece. When epididymal spermatozoa were released into a glucose-containing medium, the NADPH/NADP ratio increased with capacitation. Sperm-oocyte fusion and meiosis reinitiation of the fertilized oocyte was inhibited by the PPP inhibitor 6-aminonicotinamide (6-AN); inhibition of sperm-oocyte fusion was relieved by NADPH. Sperm-oocyte fusion and meiosis reinitiation were also inhibited by diphenylamine iodonium, which is a flavoenzyme inhibitor reported to prevent reactive oxygen species (ROS) generation in mouse spermatozoa and embryos. These findings indicate that the PPP is involved in different steps of fertilization. Subsequent regulation of a NADPH-dependent flavoenzyme responsible of ROS production is envisaged.

Influence of glucose and fructose in the extender during long-term storage of chilled canine semen

The use of chilled, extended semen in dog breeding is becoming increasingly popular as preparation and transportation is less expensive and regulations are often less complicated than for frozen semen. Sugar is one of the main constituents in semen extenders, and glucose and fructose are metabolized in separate pathways by freshly ejaculated dog sperm. In this study, glucose, fructose or an equal mixture of both were used in an egg-yolk-tris (EYT) extender at two different concentrations (10 and 70 mM). EYT extender without sugar supplementation, providing only the glucose (3-4 mM) originating from the egg-yolk, served as a control. The longevity of the chilled semen at 5 degrees C was 23 days: the quality of physical and functional characteristics decreasing with time. Glucose and fructose had a strong influence on motility and movement patterns of chilled canine semen. The beneficial effect of 70 mM sugar concentrations compared to 10 mM and the control was pronounced, and maintained sperm motility > or = 70% for 8 days of storage, compared to for 4 days in the control extender. Fructose maintained higher sperm motility than did glucose and the mixture. VAP values were higher in sugar-supplemented extenders (P < 0.05). Neither type nor concentration of the two sugars influenced sperm plasma membrane, acrosome integrity or the acrosome reaction following ionophore challenge (ARIC). Sugar consumption by dog sperm varied between the different periods of storage and with sugar concentrations provided in the extenders. Glucose consumption by dog sperm was greater than fructose consumption when both sugars were present in equal amounts, indicating that dog sperm used glucose in preference to fructose. In conclusion, the major influence of the two sugars on chilled semen was to support motility. EYT extender supplemented with fructose at a concentration of 70 mM was found to be the best of the tested extenders for long-term preservation of chilled canine semen.

Gluconeogenesis-Linked Glycogen Metabolism Is Important in the Achievement of In Vitro Capacitation of Dog Spermatozoa in a Medium Without Glucose1

In vitro capacitation of dog spermatozoa in a medium without sugars and with lactate as the metabolic substrate (l-CCM) was accompanied by a progressive increase of intracellular glycogen during the first 2 h of incubation, which was followed by a subsequent decrease of glycogen levels after up to 4 h of incubation. Lactate from the medium is the source for the observed glycogen synthesis, as the presence of [(14)C]glycogen after the addition to l-CCM with [(14)C]lactate was demonstrated. The existence of functional gluconeogenesis in dog sperm was also sustained by the presence of key enzymes of this metabolic pathway, such as fructose 1,6-bisphophatase and aldolase B. On the other hand, glycogen metabolism from gluconeogenic sources was important in the maintenance of a correct in vitro fertilization after incubation in the l-CCM. This was demonstrated after the addition of phenylacetic acid (PAA) to l-CCM. In the presence of PAA, in vitro capacitation of dog spermatozoa suffered alterations, which translated into changes in capacitation functional markers, like the increase in the percentage of altered acrosomes, a distinct motion pattern, decrease or even disappearance of capacitation-induced tyrosine phosphorylation, and increased heterogeneity of the chlorotetracycline pattern in capacitated cells. Thus, this is the first report indicating the existence of a functional glyconeogenesis in mammalian spermatozoa. Moreover, gluconeogenesis-linked glycogen metabolism seems to be of importance in the maintenance of a correct in vitro capacitation in dog sperm in the absence of hexoses in the medium.

The presence of a high-Km hexokinase activity in dog, but not in boar, sperm

The presence of a high-Km hexokinase activity was tested in both dog and boar spermatozoa. Hexokinase kinetics from dog extracts showed the presence of a specific activity (dog-sperm glucokinase-like protein, DSGLP), in the range of glucose concentrations of 4-10 mM, whereas boar sperm did not show any DSGLP activity. Furthermore, dog-sperm cells, but not those of boar, showed the presence of a protein which specifically reacted against a rat-liver anti-glucokinase antibody. This protein also had a molecular weight equal to that observed in rat-liver extracts, suggesting a close similarity between both the proteins. This glucokinase-like protein was distributed in the peri- and post-acrosomal zones of the head, and the midpiece and principal piece of tail of dog spermatozoa. These results indicate that dog spermatozoa have functional high-Km hexokinase activity, which could contribute to a very fine regulation of their hexose metabolism. This strict regulation could ultimately be very important in optimizing dog-sperm function along its life-time.

In vitro Capacitation and Acrosome Reaction of Dog Spermatozoa can be Feasibly Attained in a Defined Medium Without Glucose

Incubation of dog spermatozoa in a medium without glucose and in the presence of lactate and pyruvate (l-CCM) for 4 h at 38.5 degrees C in a 5% CO(2) atmosphere induced in vitro capacitation of these cells. This was verified after the combined specific capacitation-like changes in percentages of viability and altered acrosomes, motility characteristics, sperm location of reactivity against Pisum sativum, Arachis hypogaea and Helix pomatia lectins and the tyrosine phosphorylation pattern. Furthermore, a feasible acrosome reaction (AR) was induced when spermatozoa incubated in l-CCM for 4 h were further co-incubated for 1 h with canine oocytes. This was demonstrated by AR-like changes in percentages of viability, altered acrosomes, motility characteristics and sperm location of reactivity against P. sativum, A. hypogaea and H. pomatia lectins. All these results clearly indicate that in vitro capacitation, and subsequent AR, can be feasibly achieved without the presence of sugars. This ability can be related to the specific characteristics of energy-metabolism regulation reported in dog spermatozoa.

Metabolic strategy of boar spermatozoa revealed by a metabolomic characterization

Metabolomic characteristics in boar spermatozoa were studied using [1,2-(13)C(2)]glucose and mass isotopomer analysis. In boar spermatozoa, glycolysis was the main pathway of glucose utilization producing lactate/pyruvate, whereas no gluconeogenesis was seen. Slight glycogen synthesis through the direct pathway and some incorporation of pyruvate into the Krebs cycle also took place. Neither RNA ribose-5-phosphate nor fatty acid synthesis from glucose occurred despite the detection of pyruvate dehydrogenase activity. In contrast to the known metabolic activities in dog sperm, boar spermatozoa have low levels of energy production and biosynthetic activities suggesting two different metabolic profiles for the two different phenotypes.

Up-regulation of glucose metabolism during male pronucleus formation determines the early onset of the s phase in bovine zygotes

After in vitro fertilization with spermatozoa from bulls with high in vitro fertility, a beneficial paternal effect is manifested during the G1 phase of the first cell cycle. This benefit determines an earlier onset of the first S phase, and then a successful morula-blastocyst transition 7 days later. We hypothesized that the origin of the paternal effect could be a shift of the metabolism of the fertilized oocyte, because in mice, sperm decondensation is responsible for a dramatic increase in glucose metabolism. In this study we investigated the interaction between both pronuclei and compared glycolysis and pentose phosphate pathway (PPP) activities in bovine oocytes fertilized with spermatozoa from bulls of high or low fertility. Here we demonstrate that male pronucleus formation is necessary for the onset of the S phase in the female pronucleus, and that the component promoting an early S phase in both pronuclei is metabolic and linked to an up-regulation of the PPP during the male pronucleus formation. This long-lasting paternal effect is more evidence of the important role of epigenetic control during early embryo development.

Glucose- and fructose-induced dog-sperm glycogen synthesis shows specific changes in the location of the sperm glycogen deposition

Immunocytochemistry of glycogen deposition in dog sperm from fresh ejaculates showed that 53.7% of the population had glycogen at the midpiece, whereas 27.3% of the whole population accumulated glycogen only in the post-acrosomal region of the head. A similar distribution was observed when glycogen synthase, the enzyme which controls glycogen deposition, was studied. Incubation of spermatozoa with fructose increases the intracellular glycogen levels in a time- and concentration-dependent manner. Moreover, after incubation with 2 mM fructose for 30 min, 47.3% of the spermatozoa had glycogen located in both the midpiece and post-acrosomal zone, 25.4% of the population showed the polysaccharide only in the midpiece, and 24.7% of the spermatozoa showed a uniform distribution of glycogen all over the cell. Similar results were observed after incubation with 10-mM fructose. The distribution of glycogen synthase followed a similar pattern to that of glycogen. Incubation with glucose also induced a time- and concentration-dependent increase of glycogen content, whereas incubation with 2 mM glucose for 30 min showed that the majority of the population (81.2%) had the glycogen distributed throughout either the midpiece or the midpiece and the post-acrosomal zones together. There were practically no cells with a uniform glycogen distribution. Similar results were obtained after incubation with 10-mM glucose, whereas glycogen synthase suffered a similar glucose-induced distribution change. These results indicate that dog-sperm glycogen metabolism is modulated by changes in the activity of their controlling enzymes and also by changes in the specific location places where glycogen synthesis is produced.

Expression of a green fluorescence protein-carrier protein into mouse spermatozoa

Intra-testicular inoculation of an adenoviral vector carrying the fusion gene Aequorea victoria green fluorescence protein/rat-liver glycogen synthase (GFP/LGS) resulted in the presence of GFP/GLS in spermatozoa from 7days to, at least, 16days after inoculation. The GFP/LGS was detected in the sperm heads after an "in vitro" fertilization procedure, either before or after the oocyte penetration. Our results indicate that spermatozoa carrying GFP/LGS protein conserved their fertilizing ability and were also detectable after oocyte penetration. This technique will allow to develop an easy system to follow the fate of mature sperm proteins.

Effects of glucose and fructose on motility patterns of dog spermatozoa from fresh ejaculates

This study was performed to gain insight about how fructose and glucose modulate dog spermatozoa motility in the absence of other motility-modulating factors. Incubation of dog spermatozoa from fresh ejaculates in a basal medium without sugars for 60 min at 37 degrees C induced a progressive decrease in the percentage of motile spermatozoa and in some mean motility parameters, such as mean velocity (VAP), linear coefficient (LIN) and dance (DNC), and an increase in the mean frequency of head displacement (BCF). This indicates a progressive loss of linearity and an increase in oscillatory movement. Addition of 10 mM fructose prevented these effects. Incubation in a basal medium with 10 mM glucose for 60 min at 37 degrees C provoked a fast and intense decrease of LIN and a slight increase of DNC, inducing a less linear and more oscillatory mean movement. Neither fructose nor glucose modified the percentage of motile spermatozoa. The response to both sugars was dose-dependent, with differences appearing at concentrations as low as 1 mM. An analysis of the spermatozoa subpopulation placed above the 95th percentile of the whole population and a factorial analysis of the data indicated that the changes in the mean values of the motility parameters were mainly due to a specific motile subpopulation that had a strong reaction to the two sugars. Our results indicate that fructose, at concentrations from 1 to 10 mM, induced a more linear and less oscillatory motility pattern than glucose. Moreover, from our results we suggest the presence of motile dog sperm subpopulations with an increased sensitivity to fructose and glucose.