The importance of redox regulated pathways in sperm cell biology

Reactive oxygen species as an independent marker of male factor infertility

OBJECTIVE

To determine the abnormal patterns of reactive oxygen species (ROS) production in male factor infertility (MFI) patients and to define the ROS reference values in such patients.

DESIGN

A retrospective study.

SETTING

Male infertility clinic at a tertiary healthcare center.

PATIENT(S)

We examined 132 MFI patients (all normal sperm parameters, n = 24, and all abnormal sperm parameters, n = 38) and 34 healthy donors.

INTERVENTION(S)

Routine semen analysis, measurement of ROS.

MAIN OUTCOME MEASURE(S)

Sperm parameters, ROS levels (10(4) cpm/20 x 10(6) sperm).

RESULT(S)

Normal, healthy donors had significantly higher (P<.0001) sperm concentration, motility, and morphology compared with all MFI patients. Univariate analysis indicated a significant association between MFI and log (ROS + 1) (odds ratio [OR] = 3.84), besides sperm parameters and age. A multivariate model using logistic regression analysis also indicated an independent association of log ROS with MFI (OR = 4.25). The ROS cutoff values of 1.2-1.4 had a sensitivity of 0.70-0.78 with a corresponding specificity of 0.82. However, at a cutoff point of 1.2, the OR was 68.6, which increased with an increase in the cutoff.

CONCLUSION(S)

High ROS is an independent marker of MFI, irrespective of whether these patients have normal or abnormal semen parameters. We suggest the inclusion of ROS measurement as part of idiopathic infertility evaluation. Treatment with antioxidants may be beneficial in such patients.

Sperm channel diversity and functional multiplicity

Ion channels are extraordinarily efficient machines that move ions in diversely controlled manners, allowing cells to rapidly exchange information with the outside world and with other cells. Communication is the currency of fertilization, as it is of most fundamental cell signaling events. Ion channels are deeply involved in the dialogue between sperm, its surroundings, and the egg. How sperm swim, find the egg and fertilize it depend on ion permeability changes modulated by environmental cues and components of the egg outer layer. Different ion channels distinctly localized in these tiny, amazing cells perform specific decoding functions that shape the sophisticated behavior of sperm. It is not surprising that certain sperm ion channels are turning out to be unique. New strategies to characterize sperm ion transport have opened exciting possibilities to dissect sperm-egg signaling and unveil novel contraception targets.

Ontogeny of Tyrosine Phosphorylation-Signaling Pathways During Spermatogenesis and Epididymal Maturation in the Mouse1

The objectives of this study were to map the ontogeny of tyrosine phosphorylation signal transduction pathways during germ cell development and to determine their association with the differentiation of a functional gamete. Until testicular germ cells differentiate into spermatozoa, cAMP-induced tyrosine phosphorylation is not detectable. Entry of these cells into the epididymis is accompanied by sudden activation of the tyrosine phosphorylation pathway, initially in the principal piece of the cell and subsequently in the midpiece. In the caput and corpus epididymides, the potential to express this pathway is inhibited by the presence of calcium in the extracellular medium. However, calcium has no effect on the expression of this pathway in caudal epididymal sperm. The competence of these cells to phosphorylate the entire sperm tail, from the neck to the tail-end piece, is accompanied by a capacity to exhibit hyperactivated motility on stimulation with cAMP. A distinctly different pattern of tyrosine phosphorylation, involving the acrosomal domain of the sperm head, is invoked as spermatozoa enter the caput epididymis, and phosphorylation remains high until these cells enter the distal corpus and cauda. The proportion of cells exhibiting this form of tyrosine phosphorylation is not affected by extracellular calcium or cAMP but is negatively correlated (R2 = 0.99) with their ability to acrosome-react. However, this relationship is not causative. Our findings indicate that the development of functional spermatozoa is accompanied by carefully orchestrated changes in tyrosine phosphorylation, controlled by independent regulatory mechanisms in distinct subcellular compartments of these highly specialized cells.

Antioxidant N-acetylcysteine blocks nerve growth factor-induced H2O2/ERK signaling in PC12 cells

We investigated whether H2O2, superoxide, and ERK participate in nerve growth factor (NGF)-induced signaling cascades and whether antioxidant N-acetylcysteine (NAC) regulates these NGF-induced responses. PC12 cells were cultured in medium containing NGF or vehicle with or without NAC pretreatment, and the intracellular H2O2 and superoxide levels and the amount of phosphorylated ERK were evaluated by flow cytometry and Western blotting, respectively. We found that NGF increased intracellular H2O2 concentration and activated ERK but failed to affect intracellular superoxide level. Moreover, NAC counteracted these NGF-induced responses. These findings demonstrate that NAC blocks the NGF-induced H2O2/ERK signaling in PC12 cells.

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.

Modulation of Chlamydomonas reinhardtii flagellar motility by redox poise

Redox-based regulatory systems are essential for many cellular activities. Chlamydomonas reinhardtii exhibits alterations in motile behavior in response to different light conditions (photokinesis). We hypothesized that photokinesis is signaled by variations in cytoplasmic redox poise resulting from changes in chloroplast activity. We found that this effect requires photosystem I, which generates reduced NADPH. We also observed that photokinetic changes in beat frequency and duration of the photophobic response could be obtained by altering oxidative/reductive stress. Analysis of reactivated cell models revealed that this redox poise effect is mediated through the outer dynein arms (ODAs). Although the global redox state of the thioredoxin-related ODA light chains LC3 and LC5 and the redox-sensitive Ca2+ -binding subunit of the docking complex DC3 did not change upon light/dark transitions, we did observe significant alterations in their interactions with other flagellar components via mixed disulfides. These data indicate that redox poise directly affects ODAs and suggest that it may act in the control of flagellar motility.

Detection of superoxide anion generation by equine spermatozoa

OBJECTIVE

To identify the generation of the superoxide anion by equine spermatozoa.

SAMPLE POPULATION

Multiple ejaculates collected from 3 Thoroughbred stallions.

PROCEDURES

Induced superoxide production by reduced nicotinamide adenine dinucleotides (NAD[P]H; ie, reduced nicotinamide adenine dinucleotide [NADH] and reduced nicotinamide adenine dinucleotide phosphate [NADPH]) was measured by use of a nitroblue tetrazolium (NBT) reduction assay on whole spermatozoa and a cytochrome c reduction assay on isolated membrane fractions of spermatozoa. Localization of superoxide generation was determined by use of NBT cytochemistry.

RESULTS

A dose-dependent increase in NBT reduction was found in the presence of NADPH, which was inhibited by superoxide dismutase (SOD). The flavoprotein inhibitor, diphenyleneiodonium (DPI; 5 or 15 microM), significantly decreased NBT reduction. Cytochrome c reduction by plasma membranes of spermatozoa was significantly higher in the presence of NADPH than in its absence. Cytochemical staining of equine spermatozoa in the presence of NADPH and NADH revealed diaphorase labeling in the spermatozoon midpiece and head. This staining was inhibited by DPI and SOD.

CONCLUSIONS AND CLINICAL RELEVANCE

Results of our study indicate that superoxide generation is associated with a membrane-associated NAD(P)H oxidase present in equine spermatozoa, although mitochondrial generation of superoxide is also detected. This oxidase may play a role in cell signaling or may also contribute to cytopathic effects associated with oxidative stress in equine spermatozoa.

The antioxidant glutathione peroxidase family and spermatozoa: a complex story

Oxidative damage is one threat spermatozoa have to face during epididymal maturation and storage. However, it is clear that reactive oxygen species (ROS) are also central for sperm physiology in processes such as sperm maturation and capacitation. It is therefore essential that there exists around sperm cells a fine balance between ROS production and recycling. To do so, sperm cells and epididymal epithelial cells rely on common enzymatic ROS scavengers such as superoxide dismutase (SOD), glutathione peroxidases (GPX) and catalase (CAT) as well as more specific types such as indoleamine dioxygenase (IDO). Among the catalytic triad (SOD/GPX/CAT), the glutathione peroxidase protein family occupies a peculiar position, since several GPX have been found to be present on and around epididymal transiting sperm cells. Here, we will review our present knowledge regarding GPX expression, presence and putative role(s) within the epididymis and on spermatozoa. Taking into account our recent findings regarding the epididymal expression of indoleamine dioxygenase in mouse we will also discuss how we think this superoxide anion recycling enzyme completes the complex ROS generation/recycling balance in this organ.

Heparin- and superoxide anion-dependent capacitation of cryopreserved bovine spermatozoa: requirement of dehydrogenases and protein kinases

Capacitation is part of an oxidative process necessary for bovine spermatozoa to acquire fertilizing capacity. This process includes the generation of reactive oxygen species (ROS) and the participation of protein kinases such as A (PKA), C (PKC) and tyrosine kinase (PTK). A redox status is required to support both sperm motility and capacitation. Our aim was to determine the requirement of lactate dehydrogenase C4 (LDH-C4) and isocitrate dehydrogenase (NADP-ICDH) and of protein kinases in cryopreserved bovine sperm capacitation. The presence of inhibitors of both LDH-C4 and NADP-ICDH prevented the heparin-induced capacitation. H89, GF109203X or genistein blocked capacitation triggered by heparin or the superoxide (O(-*)(2))generator system xanthine-xanthine oxidase-catalase (XXOC) suggesting the requirement of PKA, PKC and PTK in this process. Taken together these results suggest that LDH-C4 and NADP-ICDH contribute with the redox status to support bovine sperm capacitation and that PKA, PKC and PTK are involved in different mechanisms induced by different inducers that lead bovine spermatozoa to be capacitated.

Proteomic identification of Drosophila melanogaster male accessory gland proteins, including a pro-cathepsin and a soluble gamma-glutamyl transpeptidase

BACKGROUND

In Drosophila melanogaster, the male seminal fluid contains proteins that are important for reproductive success. Many of these proteins are synthesised by the male accessory glands and are secreted into the accessory gland lumen, where they are stored until required. Previous studies on the identification of Drosophila accessory gland products have largely focused on characterisation of male-specific accessory gland cDNAs from D. melanogaster and, more recently, Drosophila simulans. In the present study, we have used a proteomics approach without any sex bias to identify proteins in D. melanogaster accessory gland secretions.

RESULTS

Thirteen secreted accessory gland proteins, including seven new accessory gland proteins, were identified by 2D-gel electrophoresis combined with mass spectrometry of tryptic fragments. They included protein-folding and stress-response proteins, a hormone, a lipase, a serpin, a cysteine-rich protein and two peptidases, a pro-enzyme form of a cathepsin K-like cysteine peptidase and a gamma-glutamyl transpeptidase. Enzymatic studies established that accessory gland secretions contain a cysteine peptidase zymogen that can be activated at low pH. This peptidase may have a role in the processing of female and other male-derived proteins, but is unlikely to be involved in the processing of the sex peptide. gamma-Glutamyl transpeptidases are type II integral membrane proteins; however, the identified AG gamma-glutamyl transpeptidase (GGT-1) is unusual in that it is predicted to be a soluble secreted protein, a prediction that is supported by biochemical evidence. GGT-1 is possibly involved in maintaining a protective redox environment for sperm. The strong gamma-glutamyl transpeptidase activity found in the secretions provides an explanation for the observation that glutamic acid is the most abundant free amino acid in accessory gland secretions of D. melanogaster.

CONCLUSION

We have applied biochemical approaches, not used previously, to characterise prominent D. melanogaster accessory gland products. Of the thirteen accessory gland secreted proteins reported in this study, six were represented in a D. simulans male accessory gland EST library that was biased for male-specific genes. Therefore, the present study has identified seven new secreted accessory gland proteins, including GGT-1, which was not recognised previously as a secreted accessory gland product.

Aromatization and antioxidant capacity in the testis of seasonally breeding bank voles: Effects of LH, PRL and IGF-I

Aromatization and antioxidant strategies in the male gonads are important processes, which are involved in control of normal fertility. The objective of this study was to show whether luteinizing hormone (LH), prolactin (PRL), and insulin-like growth factor-I (IGF-I) as well as the length of photoperiod are able to exert an effect on aromatase expression, steroid hormone levels, and antioxidant concentrations in testes of bank voles, seasonally breeding rodents. Mature bank voles that were kept under short light cycles or long light cycles served as the animal model. Testicular sections were used for immunohistochemical visualization of aromatase expression, whereas testicular homogenates were used for radioimmunological measurement of steroids, biochemical determination of superoxide dismutase activity, total antioxidant status (TAS) and protein content. In the testes of hormone-treated voles a stronger immunostaining for aromatase was concurrent with the increase in testosterone and estradiol levels, and total antioxidant status compared with the controls. In contrast, there was a decrease in superoxide dismutase (SOD) activity. The strongest effect on aromatase immunoexpression and steroid hormone levels was detected after combined doses of LH and IGF-I, indicating a stimulatory role of these hormones on estrogen synthesis in the bank vole. An increase in total antioxidant status in testes of hormone-treated bank voles suggests the presence of testicular defense, whereas a decrease in superoxide dismutase activity indicates a protective role of administered hormones against toxic oxygen radicals. The present study also demonstrates a significant, photoperiod-dependent relationship between aromatization and antioxidant capacity in the testis of the bank vole.

Evidence for the involvement of PECAM-1 in a receptor mediated signal-transduction pathway regulating capacitation-associated tyrosine phosphorylation in human spermatozoa

Mammalian spermatozoa must become ;capacitated' in the female reproductive tract before they gain the ability to fertilize the oocyte. The attainment of a capacitated state has been correlated with a number of biochemical changes, the most notable of which is a dramatic increase in the tyrosine phosphorylation status of these cells. Despite its biological importance, the mechanisms responsible for initiating this tyrosine phosphorylation cascade in vivo are unknown. Here, we report that this signalling pathway can be elicited in a rapid, dose-dependent and lectin-specific manner by wheat germ agglutinin (WGA), but none of 18 other lectins assessed. This response was abrogated by prior enzymatic cleavage of either sialic acid or GlcNAc residues from the sperm surface and by treatment with a range of pharmacological inhibitors directed against protein kinase A, protein tyrosine kinases and intermediates including Src. Proteomic analysis of the WGA-binding sites on the sperm surface identified the putative cognate receptor as platelet cell adhesion molecule 1 (PECAM-1/CD31). This conclusion was supported by the following evidence: (i) anti-PECAM-1 antibodies identified a molecule of the correct molecular mass in human spermatozoa, (ii) PECAM-1 could be isolated from a pool of sperm surface proteins using WGA immobilized on a solid phase support, (iii) PECAM-1 and WGA co-localized to the sperm surface and (iv) anti-PECAM-1 antibodies could completely block the ability of WGA to stimulate tyrosine phosphorylation in these cells. Collectively, these data provide the first evidence that a receptor-mediated signal transduction pathway triggers human sperm capacitation and identifies PECAM-1 as the probable initiator of this second messenger cascade.

Ultrastructural Dynamics of Human Reproduction, from Ovulation to Fertilization and Early Embryo Development1

This study describes the updated, fine structure of human gametes, the human fertilization process, and human embryos, mainly derived from assisted reproductive technology (ART). As clearly shown, the ultrastructure of human reproduction is a peculiar multistep process, which differs in part from that of other mammalian models, having some unique features. Particular attention has been devoted to the (1) sperm ultrastructure, likely "Tygerberg (Kruger) strict morphology criteria"; (2) mature oocyte, in which the MII spindle is barrel shaped, anastral, and lacking centrioles; (3) three-dimensional microarchitecture of the zona pellucida with its unique supramolecular filamentous organization; (4) sperm-egg interactions with the peculiarity of the sperm centrosome that activates the egg and organizes the sperm aster and mitotic spindles of the embryo; and (5) presence of viable cumulus cells whose metabolic activity is closely related to egg and embryo behavior in in vitro as well as in vivo conditions, in a sort of extraovarian "microfollicular unit." Even if the ultrastructural morphodynamic features of human fertilization are well understood, our knowledge about in vivo fertilization is still very limited and the complex sequence of in vivo biological steps involved in human reproduction is only partially reproduced in current ART procedures.

Acrosome reaction in bovine spermatozoa: Role of reactive oxygen species and lactate dehydrogenase C4

After capacitation, mammalian spermatozoa accomplish the acrosome reaction (AR), a well-controlled exocytosis process crucial to fertilize mature oocytes that involves several protein kinases such as protein kinase A (PKA), C (PKC), and tyrosine kinase (PTK). Reactive oxygen species (ROS) are involved in both bovine sperm capacitation and AR. Lactate dehydrogenase C4 (LDH-C4) was associated with bovine and mouse sperm capacitation. Our aims were to study the participation of LDH-C4 to contribute with the status redox required for AR and the role of ROS in the regulation of PKA, PKC, and PTK involved in the exocytotic event. Sodium oxamate, an inhibitor of LDH-C4, prevented the AR induced by lysophosphatidylcholine (LPC) or NADH. Hydrogen peroxide promoted and superoxide dismutase (scavenger of superoxide), catalase (scavenger of hydrogen peroxide), diphenyleneiodinum, diphenyliodonium, cibacron blue, and lapachol (inhibitors of NADPH oxidase) prevented the AR, suggesting that ROS and a sperm oxidase are involved in the AR induced by these compounds. Inhibitors of PKA, PKC, and PTK also prevented the AR induced by LPC or NADH, suggesting the involvement of these kinases in the process. These results suggest that LDH-C4 may participate in the regulation of the redox status required to achieve the AR in bovine spermatozoa and that ROS are key elements in the regulation of protein kinases associated with the AR process.

Nitric oxide induces acrosome reaction in cryopreserved bovine spermatozoa

The aim of this work was to study the effect of nitric oxide on acrosome reaction (AR) and the participation of protein kinases and reactive oxygen species in the AR of cryopreserved bovine spermatozoa. Spermatozoa were capacitated in Tyrode's albumin lactate pyruvate medium with heparin (10 IU ml(-1)) and then incubated with different concentrations of sodium nitroprusside (SNP) (1-200 micromol l(-1)). Methylene blue and haemoglobin were used to confirm the role of nitric oxide as an inducer of the AR. The participation of protein kinase A (PKA) , protein kinase C (PKC) and protein tyrosine kinase was evaluated using specific inhibitors of these enzymes (H-89, 50 micromol l(-1); bisindolylmaleimide I, 0.1 micromol l(-1) and genistein, 3 micromol l(-1)). The role of hydrogen peroxide or superoxide anion was evaluated by incubation with catalase or superoxide dismutase respectively. AR percentages were determined by the fluorescence technique with chlortetracycline. The highest levels of AR were obtained in capacitated spermatozoa treated with 5-200 micromol l(-1) SNP (24.8 +/- 1.8%). The presence of PKA, PKC and protein tyrosine kinase inhibitors likewise decreased AR percentages. The addition of superoxide dismutase had no effect on the AR level but catalase completely blocked it. These results indicate that nitric oxide induces AR in capacitated spermatozoa involving hydrogen peroxide and the participation of PKA, PKC and protein tyrosine kinase as part of the signal transduction mechanism which lead to the AR in cryopreserved bovine spermatozoa.

Cell-specific localization of the sulphydryl oxidase QSOX in rat peripheral tissues

Rat quiescin/sulphydryl oxidase (rQSOX) introduces disulphide bridges into peptides and proteins with the reduction of molecular oxygen to hydrogen peroxide. Its occurrence has been previously highlighted in a wide range of organs by reverse transcription-polymerase chain reaction (RT-PCR) and Northern blot analyses, methods that have provided information concerning its expression in whole organs but that do not reveal the cell types expressing this enzyme. In this report, in addition to RT-PCR and Western blot experiments, the cell-specific localization of rQSOX has been investigated in a wide range of male and female adult rat tissues by using in situ hybridization and immunohistochemistry. Labelling was detected in most organs and systems including the immune, endocrine and reproductive systems, the respiratory, digestive and urinary tracts and the skin. No labelling was observed in the heart, blood vessel endothelium, liver or smooth and skeletal muscles. rQSOX expression was mainly localized in epithelial cells specialized in secretion, strengthening the hypothesis that QSOX enzymes play an important role in the mechanism of secretion, notably in the folding of secreted proteins. The intracellular patterns of immunolabelling indicate that the protein usually follows the secretory pathway, which is in accordance with its secreted nature and its presumed involvement in the elaboration of the extracellular matrix. In seminiferous tubules, where a high level of expression was noticed, QSOX might play an important physiological role in sperm function and serve as a marker for the diagnosis of male infertility.

Point Mutations in the Proline-rich Region of p22 Are Dominant Inhibitors of Nox1- and Nox2-dependent Reactive Oxygen Generation

The integral membrane protein p22phox is an indispensable component of the superoxide-generating phagocyte NADPH oxidase, whose catalytic core is the membrane-associated gp91phox (also known as Nox2). p22phox associates with gp91phox and, through its proline-rich C terminus, provides a binding site for the tandem Src homology 3 domains of the activating subunit p47phox. Whereas p22phox is expressed ubiquitously, its participation in regulating the activity of other Nox enzymes is less clear. This study investigates the requirement of p22phox for Nox enzyme activity and explores the role of its proline-rich region (PRR) for regulating activity. Coexpression of specific Nox catalytic subunits (Nox1, Nox2, Nox3, Nox4, or Nox5) along with their corresponding regulatory subunits (NOXO1/NOXA1 for Nox1; p47phox/p67phox/Rac for Nox2; NOXO1 for Nox3; no subunits for Nox4 or Nox5) resulted in marked production of reactive oxygen. Small interfering RNAs decreased endogenous p22phox expression and inhibited reactive oxygen generation from Nox1, Nox2, Nox3, and Nox4 but not Nox5. Truncated forms of p22phox that disrupted the PRR-inhibited reactive oxygen generation from Nox1, Nox2, and Nox3 but not from Nox4 and Nox5. Similarly, p22phox (P156Q), a mutation that disrupts Src homology 3 binding by the PRR, potently inhibited reactive oxygen production from Nox1 and Nox2 but not from Nox4 and Nox5. Expression of p22phox (P156Q) inhibited NOXO1-stimulated Nox3 activity, but co-expression of NOXA1 overcame the inhibitory effect. The P157Q and P160Q mutations of p22phox showed selective inhibition of Nox2/p47phox/p67phox, and selectivity was specific for the organizing subunit (p47phox or NOXO1) rather than the Nox catalytic subunit. These studies stress the importance of p22phox for the function of Nox1, Nox2, Nox3, and Nox4, and emphasize the key role of the PRR for regulating Nox proteins whose activity is dependent upon p47phox or NOXO1.

Capacitation-dependent concentration of lipid rafts in the apical ridge head area of porcine sperm cells

Lipid architecture of the plasma membrane plays an important role in the capacitation process of the sperm cell. During this process, an increase in membrane fluidity takes place, which coincides with a redistribution of cholesterol to the apical region of the head plasma membrane and subsequently an efflux of cholesterol. Cholesterol is also a major player in the formation of lipid rafts or microdomains in the membrane. Lipid rafts favour specific protein-protein interactions by concentrating certain proteins in these microdomains while excluding others. In this study, we investigated the organization of lipid rafts during in vitro capacitation of boar sperm cells. We report on the presence of the lipid raft-specific proteins caveolin-1 and flotillin-1 in sperm cells. Capacitation induced a change in membrane distribution of these proteins. Lipid analysis on detergent-resistant membranes (DRMs) of sperm cells indicated that capacitation induces a lipid raft concentration rather than a disintegration of lipid rafts, because the total amount of lipid in the DRM fraction remained unaltered. Using a proteomic approach, we identified several major DRM proteins, including proteins involved in capacitation-dependent processes and zona pellucida binding. Our data indicate that sperm raft reorganization may facilitate capacitation-specific signalling events and binding to the zona pellucida.

Decline in fertility of mouse sperm with abnormal chromatin during epididymal passage as revealed by ICSI

BACKGROUND

Recent studies showed that ICSI with cauda epididymal or ejaculated sperm of infertile mice or men, respectively, was less effective in fertilization and normal embryo development than ICSI using sperm from the testes. These studies suggested that sperm nuclear quality declined after release from the testis, but the site where this loss of fertility occurs has not been localized.

METHODS

We performed ICSI with testicular, caput, and cauda epididymal sperm from infertile Tnp1-/-Tnp2+/- mutant mice, which have a minimal level of transition nuclear proteins and are sterile by natural mating.

RESULTS

When the heads of motile sperm from the testis or caput epididymis of Tnp1-/-Tnp2+/- males were injected into enucleated mouse oocytes, sperm chromosomes showed no difference from those of wild-type mice, but the chromosomes from sperm taken from the cauda epididymis of mutant males showed increased abnormalities. Injection of testicular or caput epididymal sperm from Tnp1-/-Tnp2+/- males into intact oocytes resulted in normal embryonic and fetal development and yields of liveborn equivalent to wild-type, but cauda sperm from Tnp1-/-Tnp2-/- mice produced lower implantation rates and yields of liveborn than did those from wild-type mice.

CONCLUSIONS

These results demonstrate that in mice with sperm chromatin abnormalities, the decline in fertility of sperm with ICSI occurs after the caput epididymis. The advantage of using caput epididymal sperm for ICSI in certain situations may be considered as an approach to be tested in human assisted reproduction.

The effect of gamete co-incubation time during in vitro fertilization with frozen-thawed unsorted and sex-sorted ram spermatozoa on the development of in vitro matured adult and prepubertal ewe oocytes

In vitro matured adult (Experiment 1) and prepubertal (Experiment 2) ewe oocytes were co-incubated with unsorted or sex-sorted frozen-thawed spermatozoa for 2 to 3 h (short) or 18 to 20 h (long) to determine the effects of reducing the gamete co-incubation time during IVF on subsequent embryonic development in vitro. For oocytes derived from adult ewes, there were no differences in oocyte fertilization and cleavage at 24 h post insemination (hpi) between types of spermatozoa or co-incubation times (P > 0.05). By 48 hpi, oocyte cleavage was higher after a short (390/602, 64.8%) compared with a long (381/617, 61.7%) co-incubation (P < 0.05), and was not significantly different for unsorted (266/372, 71.5%) and sex-sorted (505/849, 59.9%) spermatozoa. Blastocyst formation from cleaved oocytes was similar for unsorted (150/266, 56.4%) and sex-sorted (295/505, 58.4%) spermatozoa, but was higher after a short (240/390, 61.5%) than long (205/381, 53.8%) co-incubation (P < 0.05). Oocyte development to the blastocyst stage was not different for unsorted (150/372; 40.3%) and sex-sorted (295/847; 34.8%) spermatozoa but was significantly increased by a short (240/602, 39.9%) compared with a long (205/617, 33.2%) co-incubation. Fertilization of oocytes from prepubertal ewes was similar for types of spermatozoa and for duration of co-incubation. Oocyte cleavage (48 hpi) was similar for a short (241/377, 63.9%) and long (226/349, 64.8%) co-incubation with unsorted spermatozoa, but was increased (P < 0.05) by a long co-incubation (286/500, 57.2% versus 163/517, 31.5%) with sex-sorted spermatozoa. Blastocyst formation from cleaved oocytes was similar for unsorted (230/467, 49.3%) and sex-sorted (186/449, 41.4%) spermatozoa, and a short (200/404, 49.5%) or long (216/512, 42.1%) co-incubation. However, oocyte development to the blastocyst stage was higher (P < 0.05) after IVF with unsorted (230/726, 37.1%) than sex-sorted (186/1017, 18.3%) spermatozoa. Reducing the duration of gamete co-incubation did not deleteriously affect the in vitro development of adult and prepubertal ewe derived oocytes after IVF with unsorted and sex-sorted spermatozoa. In general, sex-sorting had no substantial influence on fertilization and embryo development rates.

Identification of non-mitochondrial NADPH oxidase and the spatio-temporal organization of its components in mouse spermatozoa

Though the spermatozoa are known to produce superoxide anion radicals, the enzyme system(s) that produce superoxide in these cells are not yet identified. Using Western blot assays and confocal laser scan microscopy, we detected gp91(phox) and p67(phox) associated with spermatozoa from testis and epididymis. We could not detect p22(phox) in any of the sperm samples analyzed. While the expression of gp91(phox) p67(phox) appeared to be constitutive, p47(phox) was detectable only in spermatozoa from testis and vas deferens. Importantly, p40(phox) could be seen in very high quantities in testicular spermatozoa, which also showed the highest levels of NADPH-oxidase activity. Spermatozoa from cauda epididymidis and vas deferens also showed the presence of p40(phox), though the amount was low when compared with that of testicular spermatozoa. The absence of p22(phox) and the striking correlation between the presence of p40(phox) and the NADPH-oxidase activity suggest that the NADPH oxidase associated with spermatozoa is p22(phox)-independent and that its activity is positively modulated by p40(phox). Further, since the confocal imaging detected that the subunits of the NADPH oxidase are located significantly on the head domains, the spermatozoa appear to present a case with dominant non-mitochondrial superoxide anion producing capabilities.

Effects of PNU157706, a Dual 5α-Reductase Inhibitor, on Rat Epididymal Sperm Maturation and Fertility1

Sperm entering the epididymis gain progressive motility and fertilizing ability in a process termed maturation. The functional dependence of the epididymis on dihydrotestosterone (DHT) is well established, yet few studies have examined the consequences on the epididymis of inhibiting DHT formation. We have shown that inhibition of both isoforms of 5alpha-reductase (types 1 and 2), the enzyme that converts testosterone to DHT, has pronounced effects on epididymal gene expression. In the present study, we investigate whether inhibiting 5alpha-reductase has consequences on epididymal sperm maturation. Rats were treated with vehicle or 10 mg/kg/day PNU157706, a dual-type inhibitor, for 28 days. Fertility and several key facets of sperm maturation were analyzed. Changes in sperm motility were assessed by computer-assisted sperm analysis (CASA). Changes in sperm morphology were assessed by CASA and electron microscopy. The motility of spermatozoa from the cauda epididymidis of treated animals showed a significant decrease in both the percentage of motile and progressively motile sperm as well as altered motion parameters. The morphology of cauda epididymal spermatozoa was also adversely affected by the treatment; the most prominent effect was a markedly elevated proportion of sperm that retained their cytoplasmic droplet. Matings with treated males resulted in fewer successful pregnancies and a higher rate of preimplantation loss. Progeny outcome was unaffected. The compromised sperm motility and morphology likely contribute to the subfertility of inhibitor-treated rats. Our results indicate a role for dual 5alpha-reductase inhibitors in further studies of epididymal physiology and as a potential component of a male contraceptive.

Calcium Channels and Ca2+ Fluctuations in Sperm Physiology

Generating new life in animals by sexual reproduction depends on adequate communication between mature and competent male and female gametes. Ion channels are instrumental in the dialogue between sperm, its environment, and the egg. The ability of sperm to swim to the egg and fertilize it is modulated by ion permeability changes induced by environmental cues and components of the egg outer layer. Ca(2+) is probably the key messenger in this information exchange. It is therefore not surprising that different Ca(2+)-permeable channels are distinctly localized in these tiny specialized cells. New approaches to measure sperm currents, intracellular Ca(2+), membrane potential, and intracellular pH with fluorescent probes, patch-clamp recordings, sequence information, and heterologous expression are revealing how sperm channels participate in fertilization. Certain sperm ion channels are turning out to be unique, making them attractive targets for contraception and for the discovery of novel signaling complexes.