The extragenomic action of progesterone on human spermatozoa is influenced by redox regulated changes in tyrosine phosphorylation during capacitation

De Novo Protein Synthesis Occurs Through the Cytoplasmic Translation Machinery in Mammalian Spermatozoa

The current hypothesis suggests that translation occurs in capacitated spermatozoa through mitochondrial ribosomes. Mitochondrial translation has several particularities, which rise some questions about how mitochondrial ribosomes can ensure sperm translation activity. Here, we aimed to elucidate if cytoplasmic translation occurs in mammalian spermatozoa. A bioinformatic workflow was performed to identify translation-related proteins in human spermatozoa and their association with cytoplasmic translation. The surface sensing of translation (SUnSET) method was used to measure translation activity in capacitated human and bovine spermatozoa. Two translation inhibitors, cycloheximide (CHX, cytoplasmic) and D-chloramphenicol (D-CP, mitochondrial) were used to identify which ribosomes were active in sperm. To spot newly synthesized proteins, puromycin-peptides were immunoprecipitated and analysed by mass spectrometry. A second approach was performed using translation inhibitors and analysing the sperm proteome by mass spectrometry. Bioinformatic analysis revealed that human spermatozoa possess 510 translation proteins, which were enriched for cytoplasmic mRNA translation. CHX decreased translation activity in mammalian sperm, whereas no effect was observed after D-CP treatment. Nine proteins were immunoprecipitated and identified as newly synthesized in capacitated bovine spermatozoa. CHX and D-CP decreased the level of 22 proteins that were replaced, or de novo translated during capacitation. New proteins were associated with relevant processes for sperm physiology. Both translation inhibitors decreased sperm rapid progressive motility and increased sperm immotility. Our results proved sperm translation occurs through cytoplasmic translation machinery in capacitated bovine and human spermatozoa. These results also support that sperm translation is required during capacitation to produce relevant proteins for sperm functions.

MT1/cAMP/PKA Pathway in Melatonin-Regulated Sperm Capacitation

Melatonin is mainly synthesized and secreted by pineal gland, and plays multiple functions, including its regulating effects on reproductive processes. Sperm capacitation is necessary for fertilization, but the effect of melatonin on mouse sperm capacitation remains to be elucidated. We thus investigated the roles of melatonin on capacitation by culturing the sperms from mouse cauda epididymis in the medium with different doses of melatonin. The results showed that 10-7 mol/L melatonin significantly enhanced the sperm capacitation by increasing the sperm tyrosine phosphorylation level, percentage of the capacitated sperms and intracellular calcium concentration. In addition, our in vitro and in vivo results showed that melatonin enhanced the fertilizing capacity by increasing the percentage of oocyte cleavage and the number of the fetuses from receptive females which were mated with melatonin-treated males. Mechanically, melatonin activated cyclic adenosine monophosphate (cAMP)/p-Protein kinase A (p-PKA) pathway. Furthermore, the melatonin-induced tyrosine phosphorylation of sperms was decreased by treatment of MT1 or PKA inhibitor. And the same result was found in the sperms cultured in non-capacitating medium (without bicarbonate and bovine serum albumin). Therefore, all those results indicate that MT1/cAMP/PKA pathway is one of key regulatory factors in melatonin-mediated sperm capacitation. The results here are crucial for understanding the molecular mechanisms by which melatonin regulates sperm capacitation, and providing theoretical support for controlling sperm capacitation during artificial insemination procedures.

A Comparative Analysis of the Antioxidant Profiles Generated by the RoXstaTM System for Diverse Biological Fluids Highlights the Powerful Protective Role of Human Seminal Plasma

(1) Background: The RoXstaTM system has been developed as a rapid, effective means of profiling different types of antioxidant activity. The purpose of this study was to examine its performance utilizing a diverse array of biological fluids including semen, blood plasma, serum, urine, saliva, follicular fluid and plant extracts. (2) Methods: The RoXstaTM system was used to assess the ability of different fluids to suppress free radical formation as well as scavenge a variety of toxic oxygen metabolites including free radicals and both hydrogen and organic peroxides. (3) Results: Human semen was shown to have significantly (p < 0.001) more peroxide scavenging power than any other fluid tested (10-14 mM vitamin C equivalent compared with 1-2 mM for blood serum or plasma), while urine was particularly effective in scavenging free radicals and preventing free radical formation (p < 0.001). The powerful antioxidant properties of human semen were shown to reside within the seminal plasma (SP) fraction, rather than the spermatozoa, and to be resistant to snap freezing in liquid nitrogen. Moreover, comparative studies demonstrated that human SP exhibited significantly (p < 0.001) higher levels of antioxidant potential than any other species examined (stallion, bull, dog) and that this intense activity reflected the relative vulnerability of human spermatozoa to peroxide attack. (4) Conclusions: The RoXstaTM system provides valuable information on the antioxidant profile of complex biological fluids, supporting its diagnostic role in conditions associated with oxidative stress. Based on the results secured in this study, human semen is identified as a particularly rich source of antioxidants capable of scavenging both hydrogen and organic peroxides, in keeping with the high susceptibility of human spermatozoa to peroxide-mediated damage.

Clinical use of progesterone in human sperm preparation media for increasing IVF success

RESEARCH QUESTION

Can the addition of progesterone and neurotensin, molecular agents found in the female reproductive tract, after sperm washing increase the fertilization potential of human spermatozoa?

DESIGN

(i) Cohort study of 24 men. Spermatozoa selected by swim-up were incubated in either progesterone or neurotensin (0.1-100 µM) for 1-4 h, and hyperactive motility and binding to hyaluronan (0.1-100 µM) were assessed. The effect of progesterone 10 µM on sperm function was assessed in a blinded manner, including: hyperactive motility, binding to hyaluronan, tyrosine phosphorylation, acrosome reaction and oxidative DNA damage. (i) Embryo safety testing [one-cell mouse embryo assay (MEA), endotoxin and sterility counts (n = 3)] in preclinical embryo models of IVF (murine and porcine, n = 7 each model) and a small preliminary human study (n = 4) of couples undergoing standard IVF with oocytes inseminated with spermatozoa ± 10 µM progesterone.

RESULTS

Progesterone 10 µM increased sperm binding to hyaluronan, hyperactive motility and tyrosine phosphorylation (all P < 0.05). Neurotensin had no effect (P > 0.05). Progesterone 10 µM in human embryo culture media passed embryo safety testing (MEA, endotoxin concentration and sterility plate count). In preclinical models of IVF, the exposure of spermatozoa to progesterone 10 µM and oocytes to progesterone 1 µM was not detrimental, and increased the fertilization rate in mice and the blastocyst cell number in mice and pigs (all P ≤ 0.03). In humans, every transferred blastocyst that had been produced from spermatozoa exposed to progesterone resulted in a live birth.

CONCLUSION

The addition of progesterone to sperm preparation media shows promise as an adjunct to current methods for increasing fertilization potential. Randomized controlled trials are required to determine the clinical utility of progesterone for improving IVF outcomes.

Influence of Two Widely Used Solvents, Ethanol and Dimethyl Sulfoxide, on Human Sperm Parameters

To study mechanisms involved in fertility, many experimental assays are conducted by incubating spermatozoa in the presence of molecules dissolved in solvents such as ethanol (EtOH) or dimethyl sulfoxide (DMSO). Although a vehicle control group is usually included in such studies, it does not allow to evaluate the intrinsic effect of the solvent on sperm parameters and its potential influence on the outcome of the experiment. In the present study, we incubated human spermatozoa for 4 h in a capacitation medium in the absence or the presence of different concentrations of EtOH and DMSO (0.1, 0.5, 1.0, and 2.0%) to assess the impact of these solvents on sperm motility, vitality, capacitation, and acrosome integrity. The presence of statistically significant relationships between increasing solvent concentrations and the investigated parameters was assessed using linear mixed models. A significant effect was observed with both solvents for total and progressive sperm motilities. We also evaluated the effect of time for these parameters and showed that the influence of the solvents was stable between 0 and 4 h, indicating an almost direct impact of the solvents. While EtOH did not influence sperm vitality and acrosome integrity, a significant effect of increasing DMSO concentrations was observed for these parameters. Finally, regarding capacitation, measured via phosphotyrosine content, although a dose-dependent effect was observed with both solvents, the statistical analysis did not allow to precisely evaluate the intensity of the effect. Based on the results obtained in the present study, and the corresponding linear mixed models, we calculated the concentration of both solvents which would result in a 5% decline in sperm parameters. For EtOH, these concentrations are 0.9, 0.7, and 0.3% for total motility, progressive motility, and capacitation, respectively, while for DMSO they are 1.5, 1.1, >2, 0.3 and >2% for total motility, progressive motility, vitality, capacitation, and acrosome integrity, respectively. We recommend using solvent concentrations below these values to dissolve molecules used to study sperm function in vitro, to limit side effects.

The ribosome inhibitor chloramphenicol induces motility deficits in human spermatozoa: A proteomic approach identifies potentially involved proteins

Mature spermatozoa are almost completely devoid of cytoplasm; as such it has long been believed that they do not contain ribosomes and are therefore not capable of synthesising proteins. However, since the 1950s, various studies have shown translational activity within spermatozoa, particularly during their in vitro capacitation. But the type of ribosomes involved (cytoplasmic or mitochondrial) is still debated. Here, we investigate the presence and activity of the two types of ribosomes in mature human spermatozoa. By targeting ribosomal RNAs and proteins, we show that both types of ribosomes are localized in the midpiece as well as in the neck and the base of the head of the spermatozoa. We assessed the impact of cycloheximide (CHX) and chloramphenicol (CP), inhibitors of cytoplasmic and mitochondrial ribosomes, respectively, on different sperm parameters. Neither CHX, nor CP impacted sperm vitality, mitochondrial activity (measured through the ATP content), or capacitation (measured through the content in phosphotyrosines). However, increasing CP concentrations induced a decrease in total and progressive motilities as well as on some kinematic parameters while no effect was observed with CHX. A quantitative proteomic analysis was performed by mass spectrometry in SWATH mode to compare the proteomes of spermatozoa capacitated in the absence or presence of the two ribosome inhibitors. Among the ∼700 proteins identified in the different tested conditions, 3, 3 and 25 proteins presented a modified abundance in the presence of 1 and 2 mg/ml of CHX, and 1 mg/ml of CP, respectively. The observed abundance variations of some CP-down regulated proteins were validated using Multiple-Reaction Monitoring (MRM). Taken together, our results are in favor of an activity of mitochondrial ribosomes. Their inhibition by CP results in a decrease in the abundance of several proteins, at least FUNDC2 and QRICH2, and consequently induces sperm motility deficits.

Targeted Analysis of HSP70 Isoforms in Human Spermatozoa in the Context of Capacitation and Motility

HSP70s constitute a family of chaperones, some isoforms of which appear to play a role in sperm function. Notably, global proteomic studies analyzing proteins deregulated in asthenozoospermia, a main cause of male infertility characterized by low sperm motility, showed the dysregulation of some HSP70 isoforms. However, to date, no clear trend has been established since the variations in the abundance of HSP70 isoforms differed between studies. The HSPA2 isoform has been reported to play a key role in fertilization, but its dysregulation and possible relocation during capacitation, a maturation process making the spermatozoon capable of fertilizing an oocyte, is debated in the literature. The aim of the present study was to investigate the fate of all sperm HSP70 isoforms during capacitation and in relation to sperm motility. Using Multiple-Reaction Monitoring (MRM) mass spectrometry, we showed that the relative abundance of all detected isoforms was stable between non-capacitated and capacitated spermatozoa. Immunofluorescence using two different antibodies also demonstrated the stability of HSP70 isoform localization during capacitation. We also investigated spermatozoa purified from 20 sperm samples displaying various levels of total and progressive sperm motility. We showed that the abundance of HSP70 isoforms is not correlated to sperm total or progressive motility.

Physiological role of reactive oxygen species in testis and epididymal spermatozoa

The reactive oxygen species (ROS) play an important role in various aspects of male reproductive function, for spermatozoa to acquire the ability to fertilize. However, the increase in ROS generation, both due to internal and external factors, can induce oxidative stress, causing alterations in the structure and function of phospholipids and proteins. In the nucleus, ROS attack DNA, causing its fragmentation and activation of apoptosis, thus altering gene and protein expression. Accumulating evidence also reveals that endogenously produced ROS can act as second messengers in regulating cell signalling pathways and in the transduction of signals that are responsible for regulating spermatogonia self-renewal and proliferation. In the epididymis, they actively participate in the formation of disulphide bridges required for the final condensation of chromatin, as well as in the phosphorylation and dephosphorylation of proteins contained in the fibrous sheath of the flagellum, stimulating the activation of progressive motility in epididymal spermatozoa. In this review, the role of small amounts of ROS during spermatogenesis and epididymal sperm maturation was discussed.

Estrogen Regulates Local Cysteine Metabolism in Mouse Myometrium

Sulfur amino acid metabolism influences reproductive physiology, and transsulfuration in particular may be critical for normal cellular function. The sex hormone estrogen (E2) modulates gene expression and redox balance in some tissues by inducing the transsulfuration enzymes cystathionine β-synthase (CBS) and cystathionine γ-lyase (CSE). The role of sex hormones in sulfur amino acid metabolism by uterine smooth muscle is not known. Here, we show that CBS and CSE proteins increase in the mouse myometrium during estrus and diestrus, respectively, suggesting that E2 reciprocally regulates myometrial CBS and CSE expression. In ovariectomized mice, exogenous E2 upregulates CBS and downregulates CSE levels. E2 promotes CBS mRNA and protein expression but attenuates CSE protein expression without affecting CSE mRNA. This pattern of E2-stimulated changes in transsulfuration enzyme expression is specific to the uterine smooth muscle. E2 does not change vaginal or cervical expression of CBS or CSE significantly, and E2 decreases expression of CSE in the liver without affecting CBS. E2 also downregulates myometrial cysteinesulfinic acid decarboxylase (CSAD) and decreases myometrial biochemical synthesis of the gaso-transmitter hydrogen sulfide (H2S). These findings suggest that myometrial sulfur amino acid metabolism may regulate uterine redox homeostasis, with implications for the source and metabolism of myometrial cysteine in high E2 states such as estrus and pregnancy.

Levels of activity of superoxide dismutase in seminal plasma do not predict fertility of pig AI-semen doses

Superoxide dismutase (SOD) is a major antioxidant enzyme in boar seminal plasma (SP). This study evaluated how SP-SOD affected sperm attributes when semen of boars of various breeds, included in commercial artificial insemination (AI)-programs, was extended and liquid-stored at 17 °C for AI; as well as their in vivo fertility (farrowing rate and litter size of 10,952 AI-sows). SP-SOD-activity was assessed in 311 ejaculates (100 boars) while sperm motility (by CASA), viability and intracellular H₂O₂ generation in viable spermatozoa (by flow cytometry) were measured at 0 and 72 h of liquid storage. SP-SOD activity was not affected by breed but differed (P < 0.001) between boars (n = 50), ranging from 1.16 ± 0.11 to 7.02 ± 0.75 IU/mL. Semen AI-doses (n = 44) hierarchically grouped (P < 0.001) with low SP-SOD activity showed lower (P < 0.05) sperm motility and intracellular H₂O₂ at 72 h of liquid storage. Fertility did not differ between AI-boars (n = 39) hierarchically grouped (P < 0.001) with high or low SP-SOD activity. In conclusion, SP-SOD activity is boar dependent and positively related with sperm functionality of liquid-stored semen AI-doses. However, this positive effect is not reflected on in vivo fertility post-AI.

Use of trehalose in the semen cryopreservation of Amazonian catfish Leiarius marmoratus

The current study assessed a semen cryopreservation protocol in the Amazonian catfish Leiarius marmoratus, a freshwater fish, of rheophilic behavior, and of great importance for Brazilian fish farming. Eight males (n = 8) were stripped and the semen was cryopreserved if total motility in fresh semen was higher than 80%. The external cryoprotectant Trehalose was then diluted in Beltsvile Thawing Solution (BTS) extender in the following concentrations: 50, 100, 150, and 200 mM. Semen samples were diluted in the media (1:9 v/v) being tested, then frozen in a container with nitrogen vapor (dryshipper), and stored in liquid nitrogen at -196 °C. Motility parameters assessed post-thawing were performed by CASA-system and sperm cell integrity analyses (membrane integrity, DNA integrity, and mitochondrial function) were performed through fluorescence microscopy. As a result, no significant statistical difference was observed between treatments, independently of Trehalose concentrations tested in the following post-thawing analysis: membrane integrity, DNA integrity, mitochondrial functionality, and sperm motility duration. As of total and progressive motilities, the treatment containing 50 mM trehalose (15.6 and 9.5%, respectively), exhibited inferior results when compared to treatments with 150 mM (22.9 and 17.7%, respectively) and 200 mM (31.4 and 26.3%, respectively) trehalose concentrations (P < 0.05); however, it did not differ from the treatment with 100 mM trehalose (18.6 and 15.3%, respectively). Therefore, treatments with trehalose at higher concentrations exhibited superior results when compared to other treatments in in vitro motility parameters for L. marmoratus.

Cryopreservation of Atlantic salmon Salmo salar sperm: effects on sperm physiology

The objective of this study was to determine the effect of freezing on the function in Atlantic salmon Salmo salar spermatozoa. The semen was frozen in Cortland's medium + 1.3M dimethyl sulphoxide + 0.3M glucose + 2% bovine serum albumin (final concentration) in a ratio of 1:3 (semen:cryoprotectant) as the treatment (T) and fresh semen as the control (F). Straws of 0·5 ml of sperm suspension were frozen in 4 cm of N2 L. They were thawed in a thermoregulated bath (40° C). After thawing, the percentage of spermatozoa with fragmented DNA [transferase dUTP (deoxyuridine triphosphate) nick-end labelling (TUNEL)], plasma membrane integrity (SYBR-14/PI) and mitochondrial membrane potential (ΔΨMMit, JC-1) were evaluated by flow cytometry and motility was evaluated by optical microscope under stroboscopic light. The fertilization rates of the control and treatment semen were tested at a sperm density of 1·5 × 10(7) spermatozoa oocyte(-1) , by observation of the first cleavages after 16 h incubation at 10° C. In the cryopreserved semen (T), the mean ± s.d. DNA fragmentation was 4·8 ± 2·5%; plasma membrane integrity 75·2 ± 6·3%; mitochondrial membrane potential 51·7 ± 3·6%; motility 58·5 ± 5·3%; curved line velocity (VCL ) 61·2 ± 17·4 µm s(-1) ; average-path velocity (VAP ) 50·1 ± 17·3 µm s(-1) ; straight-line velocity (VSL ) 59·1 ± 18·4 µm s(-1) ; fertilization rate 81·6 ± 1·9%. There were significant differences in the plasma membrane integrity, mitochondrial membrane potential, motility, fertilization rate, VCL , VAP and VSL compared with the controls (P < 0·05). Also the mitochondrial membrane potential correlated with motility, fertilization rate, VCL and VSL (r = 0·75; r = 0·59; r = 0·77 and r = 0·79, respectively; P < 0·05); and the fertilization rate correlated with VCL and VSL (r = 0·59 and r = 0·55, respectively).

Causes and consequences of oxidative stress in spermatozoa

Spermatozoa are highly vulnerable to oxidative attack because they lack significant antioxidant protection due to the limited volume and restricted distribution of cytoplasmic space in which to house an appropriate armoury of defensive enzymes. In particular, sperm membrane lipids are susceptible to oxidative stress because they abound in significant amounts of polyunsaturated fatty acids. Susceptibility to oxidative attack is further exacerbated by the fact that these cells actively generate reactive oxygen species (ROS) in order to drive the increase in tyrosine phosphorylation associated with sperm capacitation. However, this positive role for ROS is reversed when spermatozoa are stressed. Under these conditions, they default to an intrinsic apoptotic pathway characterised by mitochondrial ROS generation, loss of mitochondrial membrane potential, caspase activation, phosphatidylserine exposure and oxidative DNA damage. In responding to oxidative stress, spermatozoa only possess the first enzyme in the base excision repair pathway, 8-oxoguanine DNA glycosylase. This enzyme catalyses the formation of abasic sites, thereby destabilising the DNA backbone and generating strand breaks. Because oxidative damage to sperm DNA is associated with both miscarriage and developmental abnormalities in the offspring, strategies for the amelioration of such stress, including the development of effective antioxidant formulations, are becoming increasingly urgent.

Depletion of Intracellular Thiols and Increased Production of 4-Hydroxynonenal that Occur During Cryopreservation of Stallion Spermatozoa Lead to Caspase Activation, Loss of Motility, and Cell Death

Oxidative stress has been linked to sperm death and the accelerated senescence of cryopreserved spermatozoa. However, the molecular mechanisms behind this phenomenon remain poorly understood. Reactive oxygen species (ROS) are considered relevant signaling molecules for sperm function, only becoming detrimental when ROS homeostasis is lost. We hereby hypothesize that a major component of the alteration of ROS homeostasis in cryopreserved spermatozoa is the exhaustion of intrinsic antioxidant defense mechanisms. To test this hypothesis, semen from seven stallions was frozen using a standard technique. The parameters of sperm quality (motility, velocity, and membrane integrity) and markers of sperm senescence (caspase 3, 4-hydroxynonenal, and mitochondrial membrane potential) were assessed before and after cryopreservation. Changes in the intracellular thiol content were also monitored. Cryopreservation caused significant increases in senescence markers as well as dramatic depletion of intracellular thiols to less than half of the initial values (P < 0.001) postthaw. Interestingly, very high and positive correlations were observed among thiol levels with sperm functionality postthaw: total motility (r = 0.931, P < 0.001), progressive motility (r = 0.904, P < 0.001), and percentage of live spermatozoa without active caspase 3 (r = 0.996, P < 0.001). In contrast, negative correlations were detected between active caspase 3 and thiol content both in living (r = -0.896) and dead (r = -0.940) spermatozoa; additionally, 4-hydroxynonenal levels were negatively correlated with thiol levels (r = -0.856). In conclusion, sperm functionality postthaw correlates with the maintenance of adequate levels of intracellular thiols. The accelerated senescence of thawed spermatozoa is related to oxidative and electrophilic stress induced by increased production of 4-hydroxynoneal in thawed samples once intracellular thiols are depleted.

Differential concentration and time dependent effects of progesterone on kinase activity, hyperactivation and acrosome reaction in human spermatozoa

Progesterone has been identified to be one of the physiological regulators of sperm hyperactivation and acrosome reaction. However, the high sensitivity of human spermatozoa to progesterone implies that many may undergo premature hyperactivation and acrosome reaction thereby compromising their ability to fertilize. We hypothesized that if a spermatozoon has to preclude the occurrence of these events prematurely, there should be differential dose- and time-dependent effects on motility and acrosome reaction. We observed that low concentrations of progesterone (10 and 100 nm) induce sperm motility and activate tyrosine kinase; higher concentrations (1-10 μm) are required to induce extracellular signal regulated kinases 1/2 (Erk1/2), p90 ribosomal S6 kinase (p90RSK), p38 mitogen-activated protein kinase (p38MAPK), c-Jun N-terminal kinase (JNK1) and AKT phosphorylation, hyperactivation and acrosome reaction. The induction of acrosome reaction and tyrosine phosphorylation in response to higher concentration of progesterone is not absolutely dependent on activation of T-type voltage-gated Ca(2+) channel or CatSper as Mibefradil did not completely abrogate progesterone-mediated effects. These results imply that although the spermatozoa are sensitive to low concentrations of progesterone, they only activate motility and tyrosine kinase activation; higher concentrations are required to induce hyperactivation and acrosome reaction probably by activating multiple kinase pathways including the MAPK and AKT.

Role of TRPV1 channels in boar spermatozoa acquisition of fertilizing ability

Recently the transient receptor potential vanilloid type 1 (TRPV1) has been described to be involved in the capacitation, the process leading mammalian spermatozoa to acquire full fertilizing ability within the female genital tract. TRPV1 immunolocalization during capacitation and the effect of TRPV1 inhibition by the capsazepin (CPZ) or activation by the capsaicin (CPS) on membrane resting potential, calcium clearance and actin polymerization have been investigated. It was found that the capacitation promoted the translocation of TRPV1 from the post-acrosomal to the apical region of sperm head. Moreover the CPZ induced the progressive drop in intracellular Ca2+ levels during capacitation and the inhibition of actin polymerization in the acrosomal region. On the contrary, the CPS caused the sperm membrane depolarization due to the Na+ influx and the consequent voltage gated calcium channels (VGCC) opening. In conclusion it was suggested that TRPV1 channels modulate the major pathways involved in capacitation.

Reactive oxygen and nitrogen species in normal physiological processes

Abstract Reactive oxygen species (ROS) and reactive nitrogen species have generally been considered as being highly reactive and cytotoxic molecules. Besides their noxious effects, ROS participate in physiological processes in a carefully regulated manner. By way of example, microbicidal ROS are produced in professional phagocytes, ROS function as short-lived messengers having a role in signal transduction and, among other processes, participate in the synthesis of the iodothyronine hormones, reproduction, apoptosis and necrosis. Because of their ability to mediate a crosstalk between key molecules, their role might be dual (at least in some cases). The levels of ROS increase from a certain age, being associated with various diseases typical of senescence. The aim of this review is to summarize the recent findings on the physiological role of ROS. Other issues addressed are an increase in ROS levels during ageing, and the possibility of the physiological nature of this process.

The spermostatic and microbicidal actions of quinones and maleimides: toward a dual-purpose contraceptive agent

There is an urgent need to develop safe, effective, dual-purpose contraceptive agents that combine the prevention of pregnancy with protection against sexually transmitted diseases. Here we report the identification of a group of compounds that on contact with human spermatozoa induce a state of "spermostasis," characterized by the extremely rapid inhibition of sperm movement without compromising cell viability. These spermostatic agents were more active and significantly less toxic than the reagent in current clinical use, nonoxynol 9, giving therapeutic indices (ratio of spermostatic to cytotoxic activity) that were orders of magnitude greater than this traditional spermicide. Although certain compounds could trigger reactive oxygen species generation by spermatozoa, this activity was not correlated with spermostasis. Rather, the latter was associated with alkylation of two major sperm tail proteins that were identified as A Kinase-Anchoring Proteins (AKAP3 and AKAP4) by mass spectrometry. As a consequence of disrupted AKAP function, the abilities of cAMP to drive protein kinase A-dependent activities in the sperm tail, such as the activation of SRC and the consequent stimulation of tyrosine phosphorylation, were suppressed. Furthermore, analysis of microbicidal activity using Chlamydia muridarum revealed powerful inhibitory effects at the same low micromolar doses that suppressed sperm movement. In this case, the microbicidal action was associated with alkylation of Major Outer Membrane Protein (MOMP), a major chlamydial membrane protein. Taken together, these results have identified for the first time a novel set of cellular targets and chemical principles capable of providing simultaneous defense against both fertility and the spread of sexually transmitted disease.

Cyclic-AMP initiates protein tyrosine phosphorylation independent of cholesterol efflux during ram sperm capacitation

Unlike most other species, ram spermatozoa are difficult to capacitate in vitro. Bicarbonate and Ca(2+) are necessary, whereas bovine serum albumin does not appear to be obligatory. In the present investigation we have assessed (1) the ability of the cholesterol-sequestering agent, methyl-beta-cyclodextrin (M-beta-CD), to initiate protein tyrosine phosphorylation, and (2) the importance of phosphodiesterases (PDEs) in controlling the levels of cAMP. Results show that despite removing significant amounts of membrane cholesterol, as assessed by filipin staining, M-beta-CD treatment did not stimulate major increases in protein tyrosine phosphorylation. Addition of a cocktail of PDE inhibitors (theophylline and caffeine), a phosphatase inhibitor (okadaic acid) and dibutyryl-cAMP (db-cAMP), however, stimulated specific tyrosine phosphorylation of several proteins between 30 and 120 kDa. On their own, none of the above reagents were effective but a combination of db-cAMP + PDE inhibitors was sufficient to achieve a maximal response. H-89, a protein kinase-A inhibitor, suppressed tyrosine phosphorylation significantly. Immunofluorescence revealed that the newly-phosphorylated proteins localised mainly in the sperm tail. These findings suggest that in ram spermatozoa cAMP levels are too low to initiate tyrosine phosphorylation of flagellar proteins that are indicative of the capacitation state and that this is caused by unusually high levels of intracellular PDEs.

Increased activity of the human sperm tyrosine kinase SRC by the cAMP-dependent pathway in the presence of calcium

SRC-related tyrosine kinases are suggested to play a role in the increase of sperm protein phosphotyrosine content that occurs during capacitation. In our laboratory, we previously demonstrated that the SRC-related tyrosine kinase YES1 (also known as c-YES) is present in human spermatozoa. However, since it is negatively regulated by Ca(2+), whose intracellular concentration increases during capacitation, another kinase would most likely be involved in the capacitation-related increase in sperm protein tyrosine phosphorylation. The present study represents the first direct assessment of SRC tyrosine kinase activity in ejaculated mammalian sperm. By immunohistochemistry on human testis sections, it is clearly shown that SRC is expressed during spermatogenesis, mainly in round and elongating spermatids. Using an indirect immunofluorescence approach, SRC is detected in the acrosomal region of the head and in the sperm flagellum of ejaculated sperm. This tyrosine kinase is associated with the plasma membrane and with cytoskeletal elements, as suggested by its partial solubility in nonionic detergents. Despite its partial solubility, SRC kinase activity was assayed after immunoprecipitation using acid-denatured enolase as a substrate. It is clearly demonstrated that SRC activity is inhibited by SU6656 and PP1, selective SRC family tyrosine kinase inhibitors, and activated in a Ca(2+)-dependent manner. Furthermore, it is shown that SRC is activated in a cAMP/PRKA-dependent manner; SRC coimmunoprecipitates with the catalytic subunit of the cAMP-dependent protein kinase (PRKAC) and is phosphorylated by this latter kinase, resulting in an increase in enolase phosphorylation. All these results support the involvement of the tyrosine kinase SRC in the increase in sperm protein phosphotyrosine content observed during capacitation.

Characterization of NADPH oxidase 5 in equine testis and spermatozoa

Reactive oxygen species (ROS) play an important role in normal sperm function, and spermatozoa possess specific mechanisms for ROS generation via an NAD(P)H-dependent oxidase. The aim of this study was to identify the presence of an NADPH oxidase 5 (NOX5) in equine testis and spermatozoa. The mRNA of NOX5 was expressed in equine testis as detected by northern blot probed with human NOX5 cDNA and by RT-PCR. Immunoblotting with affinity purified alpha-NOX5 revealed one major protein in equine testis and other tissues. Immunolocalization of NOX5 showed labeling over the rostral sperm head with some labeling in the equatorial and post-acrosomal regions. In the testis, there was abundant staining in the adluminal region of the seminiferous tubules associated with round and elongating spermatids. The RT-PCR and sequence analysis revealed a high homology with human NOX5. This study demonstrates that NOX5 is present in equine spermatozoa and testes and therefore represents a potential mechanism for ROS generation in equine spermatozoa.

Effects of arachnotoxin on intracellular pH and calcium in human spermatozoa

OBJECTIVE

To determine the effect of arachnotoxin (ATx), a venom extracted from the Chilean spider Latrodectus mactans, on intracellular calcium ([Ca(2+)](i)) and pH (pH(i)) in capacitated human spermatozoa.

DESIGN

Spermatozoa were collected from fertile adult men (n = 8). Mobile spermatozoa were collected by the "swim up" technique and stimulated with the crude extract of ATx and with progesterone (P).

SETTING

Hospital of the Federal University of São Paulo, São Paulo, Brazil.

MAIN OUTCOME MEASURE(S)

[Ca(2+)](i) was measured in fura2-AM-loaded spermatozoa, and pH(i) was measured in spermatozoa loaded with the pH-sensitive dye [(2',7')-bis (carboxymethyl)-(5,6)-carboxyfluorescein]-AM (BCECF).

RESULT(S)

The ATx and P induced a biphasic change in [Ca(2+)](i) consisting of a peak followed by a small but sustained elevation. The response to ATx was greatly reduced by pretreatment with P. The ATx caused intracellular acidification, whereas P induced alkalinization. Blockade of the NA(+)/H(+) exchanger with ethylisopropylamiloride (EIPA) sharply increased ATx-induced acidification.

CONCLUSION(S)

Arachnotoxin increased [Ca(2+)](i) through the opening of calcium channels and release of calcium from intracellular stores. The ATx reduced pH(i) in human sperm, possibly by inhibiting the Na(+)/H(+) exchanger.

Identification of the proteins present in the bull sperm cytosolic fraction enriched in tyrosine kinase activity: a proteomic approach

Numerous sperm proteins have been identified on the basis of their increase in tyrosine phosphorylation during capacitation. However, the tyrosine kinases present in spermatozoa that are responsible for this phosphorylation remain unknown. As spermatozoa are devoid of transcriptional and translational activities, molecular biology approaches might not reflect the transcriptional pattern in mature spermatozoa. Working directly with the proteins present in ejaculated spermatozoa is the most reliable approach to identify the tyrosine kinases potentially involved in the capacitation-associated increase in protein tyrosine phosphorylation. A combination of tyrosine kinase assays and proteomic identification tools were used as an approach to identify sperm protein tyrosine kinases. Fractionation by nitrogen cavitation showed that the majority of tyrosine kinase activity is present in the cytosolic fraction of bovine spermatozoa. By the use of Poly-Glu:Tyr(4:1)-agarose affinity chromatography, we isolated a fraction enriched in tyrosine kinase activity. Proteomics approaches permitted the identification of tyrosine kinases from three families: Src (Lyn), Csk, and Tec (Bmx, Btk). We also identified proteins implicated in different cellular events associated with sperm capacitation and acrosome reaction. These results confirm the implication of tyrosine phosphorylation in some aspects of capacitation/acrosome reaction and reveal the identity of new players potentially involved in these processes.

Sperm DNA fragmentation

Several techniques have been developed to measure the amount of sperm DNA damage in an effort to identify more objective parameters for evaluation of infertile men. The integrity of sperm DNA influences a couple's fertility and helps predict the chances of pregnancy and its successful outcome. The available tests of sperm DNA damage require additional large-scale clinical trails before their integration into routine clinical practice. The physiological/molecular integrity of sperm DNA is a novel parameter of semen quality and a potential fertility predictor. Although DNA integrity assessment appears to be a logical biomarker of sperm quality, it is not being assessed as a routine part of semen analysis by clinical andrologists. Extensive investigation has been conducted for the comparative evolution of these techniques. However, some of these techniques require expensive instrumentation for optimal and unbiased analysis, are labor intensive, or require the use of enzymes whose activity and accessibility to DNA breaks may be irregular. Thus, these techniques are recommended for basic research rather than for routine andrology laboratories. Sperm chromatin structure evaluation is applied to detect male factors that may affect the chance of success with IVF as well as natural fertility. Further research is needed to define the optimal test of sperm chromatin structure. The clinical application of this test will evolve as well.

Photochemistry and Photobiology of Light Absorption by Living Cells

In this review, we summarize a part of our research concerning photobiostimulative effects on cardiomyocytes, sperm cells, and nerve cells. We concentrate on results demonstrating that photobiostimulation can be described by the Arndt-Schultz (A.S.) curve. Results monitoring an increase in reactive oxygen species (ROS) concentration following visible light irradiation describe the ascending part of the A.S. curve, whereas those that describe the antioxidant role of photobiostimulation represent the descending part of the curve.

Changes in spermatozoal chromatin packaging and susceptibility to oxidative challenge during aging

OBJECTIVE

Our goal was to test the hypothesis that spermatozoal chromatin packaging changes with age and that aging affects the susceptibility of spermatozoal DNA to oxidative damage.

DESIGN

Laboratory study.

SETTING

Academic facility.

PATIENT(S)

Young (4 months) and old (21 months) Brown Norway rats.

INTERVENTION(S)

Spermatozoa were collected from the cauda epididymidis and were incubated in saline or H2O2.

MAIN OUTCOME MEASUREMENT(S)

Thiols levels, chromatin condensation, DNA susceptibility to acid-induced DNA denaturation, and DNA damage were evaluated using monobromobimane, chromomycin A3 (CMA3), acridine orange, and polymerase chain reaction, respectively.

RESULT(S)

Spermatozoa from old rats had 25% fewer disulfides but similar levels of free thiols as compared with young. The CMA3 staining was decreased by 13% with age. Levels of chromatin denaturation and DNA damage were similar in control groups. After exposure to oxidant, free thiols became oxidized by about 20% irrespective of age, but CMA3 staining changed little. The acridine orange assay, however, showed a trend for greater chromatin denaturation in spermatozoa from old rats after oxidant treatment. Furthermore, the DNA from spermatozoa of old rats was significantly more susceptible to developing DNA breaks and modification after oxidative challenge.

CONCLUSION(S)

Spermatozoal chromatin packaging changes with aging and vulnerability to oxidative damage increases.

Bicarbonate and bovine serum albumin reversibly ‘switch’ capacitation-induced events in human spermatozoa

We have investigated the reversibility of biochemical and physiological changes that occur upon suspension of ejaculated human spermatozoa during in vitro capacitation. Cells were swum up in a simple HEPES-based saline [lacking bicarbonate and bovine serum albumin (BSA)], then resuspended either in supplemented Earle's balanced salt solution (sEBSS) (25 mM bicarbonate) with 0.3% BSA (for in vitro capacitation) or in medium-lacking bicarbonate and/or BSA. Progesterone-induced acrosome reaction (AR) developed during in vitro capacitation (6 h). A progesterone-induced [Ca2+]i signal was detectable in cells maintained in the simple HEPES-based saline, but upon transfer to sEBSS, the response increased three- to four-fold, saturating within <30 min. Serine/threonine phosphorylation saturated within minutes of resuspension, but tyrosine phosphorylation developed over 3 h. Return of cells to non-capacitating conditions caused reversal of all capacitation-dependent changes. The [Ca2+]i signal reverted to its 'uncapacitated' size within <30 min. Protein phosphorylation reversed gradually and could be reinduced (kinetics resembling the first response) upon resuspension in sEBSS. The ability of cells to undergo progesterone-induced AR fell to levels similar to those in uncapacitated cells within 1 h of resuspension in medium not supporting capacitation. Loss of protein phosphorylation occurred only in the absence of both bicarbonate and BSA, but effects on [Ca2+]i signalling and AR could be seen after removal of only one of these factors. We conclude that key events in the capacitation of human spermatozoa are both reversible and repeatable.

Correlation between tyrosine phosphorylation intensity of a 107 kDa protein band and A23187-induced acrosome reaction in human spermatozoa

This study, performed using semen samples from 10 men, investigated the relationship between sperm protein tyrosine phosphorylation and acrosomal status in conditions supporting in vitro capacitation. Percoll-selected spermatozoa (cells from the 95% fraction) were incubated for 3 h at 37 degrees C under an atmosphere of 5% CO2 in air, in a polyvinyl alcohol (1 mg ml(-1)) containing Biggers-Whitten-Whittingham's medium, nonsupplemented or supplemented with either bovine serum albumin (BSA; fatty acid free, 3 mg ml(-1)) or 2-hydroxy-propyl-beta-cyclodextrin (2-OH-p-beta-CD; 0.5, 1, 2 mmol l(-1)). Sperm suspension in each medium was split into two aliquots. The first was used to evaluate the acrosomal status by staining with the fluorescein isothiocyanate Pisum sativum agglutinin after induction of the acrosome reaction (AR) for 45 min with 10 micromol l(-1) of A23187 calcium ionophore. The second aliquot was used for sodium dodecyl sulphate polyacrylamide gel electrophoresis and immunoblotting, followed by a densitometric analysis. Compared with the nonsupplemented medium, BSA- or 2-OH-p-beta-CD-supplementation induced an increase in both the percentage of live acrosome-reacted sperm and the tyrosine phosphorylation intensity of the main phosphorylated 107 kDa protein. A correlation between the percentage of live acrosome-reacted sperm and the 107-kDa protein phosphotyrosine intensity was observed. Therefore, the 107 kDa protein-phosphotyrosine level measurement would bring additional information to conventional semen parameters in the assessment of the human sperm functionality.

Role of tyrosine phosphorylation in sperm capacitation / acrosome reaction

Capacitation is an important physiological pre-requisite before the sperm cell can acrosome react and fertilize the oocyte. Recent reports from several laboratories have amply documented that the protein phosphorylation especially at tyrosine residues is one of the most important events that occur during capacitation. In this article, we have reviewed the data from our and other laboratories, and have constructed a heuristic model for the mechanisms and molecules involved in capacitation/acrosome reaction.

Regulation of sperm function by reactive oxygen species

Sperm capacitation can be increased by the addition of reactive oxygen species (ROS) and decreased by antioxidants. Broadly consistent results have been achieved with a wide variety of methods and across different species. Exposure to ROS increases protein tyrosine phosphorylation consequent on an increase in cAMP and activation of tyrosine kinase and inhibition of tyrosine phosphatase. The measurement of ROS production by sperm is complicated by contamination of suspensions by leukocytes, laying many studies open to doubt. In human sperm the observation that extracellular NADPH could support superoxide production detected with the chemiluminescent probe lucigenin and had physiological effects similar to hydrogen peroxide led to the suggestion that they contained NADPH oxidase activity to generate ROS to support capacitation. However, the realization that lucigenin can signal superoxide artefactually, combined with failure to detect superoxide production using spin trapping techniques or to detect NADPH oxidase components in mature sperm, and confirmation of old reports that NADPH solution contains substantial amounts of hydrogen peroxide due to autoxidation, have undermined this hypothesis. Although the presence of significant NADPH oxidase activity in mature human sperm now seems less likely, other observations continue to suggest that they can make ROS in some way. There is stronger evidence that animal sperm can make ROS although these may be mainly of mitochondrial origin.

Novel associations between specific sperm morphological defects and leukocytospermia

OBJECTIVE

To examine the relationship between leukocyte concentrations in semen and sperm morphology in a group of infertile men and healthy fertile donors.

DESIGN

A prospective clinical study.

SETTING

Male infertility clinic at a tertiary care teaching hospital and a reproductive medicine unit at a Women's Hospital in the United Kingdom.

PATIENT(S)

Fifty-six infertile men and 13 healthy fertile sperm donors (control).

INTERVENTION(S)

Standard semen analysis, seminal leukocyte concentration, and the assessment of sperm morphology and sperm deformity index (SDI), applying Tygerberg's strict criteria.

MAIN OUTCOME MEASURE(S)

Granulocyte concentrations in semen, percentages of different sperm morphological abnormalities, and SDI scores.

RESULT(S)

Leukocyte concentrations were statistically significantly and negatively correlated with the proportion of sperm with damaged acrosomes, cytoplasmic droplet, tail defects, and SDI scores with normal and borderline morphology. The percentage sperm motility was significantly and negatively correlated with leukocytic concentration in semen. However, the leukocytic concentration was not significantly correlated with sperm concentration.

CONCLUSION(S)

This is the first study to report a significant positive correlation between leukocytospermia and sperm tail defects, acrosomal damage, and high SDI scores. These observations suggest that leukocytospermia is associated with compromised sperm structural integrity.

Analysis of the mechanism by which calcium negatively regulates the tyrosine phosphorylation cascade associated with sperm capacitation

The capacitation of mammalian spermatozoa involves the activation of a cAMP-mediated signal transduction pathway that drives tyrosine phosphorylation via mechanisms that are unique to this cell type. Controversy surrounds the impact of extracellular calcium on this process, with positive and negative effects being recorded in independent publications. We clearly demonstrate that the presence of calcium in the external medium decreases tyrosine phosphorylation in both human and mouse spermatozoa. Under these conditions, a rise in intracellular pH was recorded, however, this event was not responsible for the observed changes in phosphotyrosine expression. Rather, the impact of calcium on tyrosine phosphorylation in these cells was associated with an unexpected change in the intracellular availability of ATP. Thus, the ATP content of both human and mouse spermatozoa fell significantly when these cells were incubated in the presence of external calcium. Furthermore, the removal of glucose, or addition of 2-deoxyglucose, decreased ATP levels within human spermatozoon populations and induced a corresponding decline in phosphotyrosine expression. In contrast, the mitochondrial inhibitor rotenone had no effect on either ATP levels or tyrosine phosphorylation. Addition of the affinity-labeling probe 8-N3 ATP confirmed our prediction that spermatozoa have many calcium-dependent ATPases. Moreover, addition of the ATPase inhibitor thapsigargin, increased intracellular calcium levels, decreased ATP and suppressed tyrosine phosphorylation. Based on these findings, the present study indicates that extracellular calcium suppresses tyrosine phosphorylation by decreasing the availability of intracellular ATP, and not by activating tyrosine phosphatases or inhibiting tyrosine kinases as has been previously suggested.

Cyclic AMP-dependent tyrosine phosphorylation in tammar wallaby (Macropus eugenii) spermatozoa

Despite considerable advances in our understanding of the molecular mechanisms regulating eutherian sperm function, there is a paucity of such knowledge for the Metatheria. In eutherian spermatozoa, the attainment of functional competence is associated with a redox-regulated, cAMP-mediated tyrosine phosphorylation cascade, activated during capacitation. In this report we investigate whether tammar wallaby (Macropus eugenii) spermatozoa possess a similar signal transduction pathway. Western blot analysis of phosphotyrosine expression in caudal and ejaculated populations of tammar spermatozoa revealed that elevation of intracellular cAMP levels, but not exposure to oxidants or NADPH, induced a dramatic increase in the overall level of tyrosine phosphorylation. Washed, ejaculated spermatozoa exhibited more pronounced increases in tyrosine phosphorylation than unwashed sperm populations. Localisation of tyrosine phosphorylation by immunocytochemistry showed that phosphotyrosine residues were principally located along the tammar sperm flagellum, and occasionally at a small region of the sperm head, adjacent to the acrosome. Associated with the tyrosine phosphorylation of tammar spermatozoa, was a change in sperm head conformation to a T-shaped orientation, further implying the importance of these pathways to normal tammar sperm function. Redox activity, as detected by lucigenin-dependent chemiluminescence, was stimulated by NADPH in caudal sperm preparations but not ejaculated spermatozoa. However, neither sperm population responded to treatment with NADPH with changes in intracellular cAMP or tyrosine phosphorylation. In conclusion, tammar spermatozoa possess the same cAMP-mediated, tyrosine phosphorylation-dependent signal transduction cascade that has been associated with capacitation in eutherian spermatozoa. However in Metatherian spermatozoa we could find no evidence that this pathway was redox regulated.

Human spermatozoa capacitated with progesterone or a long incubation show accelerated internalization by an alkyl ether lysophospholipid

OBJECTIVE

To evaluate changes that occur in sperm plasma membranes during capacitation, the internalization of [(3)H]lyso-platelet activating factor ([(3)H]lyso-PAF) across the plasma membrane of human spermatozoa was measured as a function of incubation time or exposure to progesterone (P).

DESIGN

In vitro cell culture study using human spermatozoa.

SETTING

Department of Obstetrics and Gynecology, School of Medicine, the University of Tokushima, Japan.

PATIENT(S)

Semen were obtained from three fertile healthy volunteers.

INTERVENTION(S)

The internalization of [(3)H]lyso-PAF across the plasma membranes of human spermatozoa that were incubated for an extended period or exposed to P was measured at 5, 20, 60, and 120 minutes after the addition of the phospholipid probe using the modified albumin back-exchange method.

MAIN OUTCOME MEASURE(S)

The percentage of capacitated and acrosome-reacted sperm and the proportion of internalization of lyso-PAF across the plasma membrane.

RESULT(S)

A 6-hour incubation period significantly increased the percentage of capacitated spermatozoa and the proportion of internalization of [(3)H]lyso-PAF across the plasma membrane of human spermatozoa compared with controls (capacitated spermatozoa, 20.3 +/- 10.6% vs. 8.5 +/- 1.8%; internalization 120 minutes after the addition of the phospholipid probe, 25.6 +/- 2.5% vs. 11.6 +/- 3.0%) (mean +/- SEM). Exposure to P significantly increased the percentage of capacitated spermatozoa compared with controls (19.6 +/- 6.8% vs. 11.0 +/- 2.4%) and also significantly accelerated the internalization of [(3)H]lyso-PAF compared with controls (internalization 120 minutes after the addition of the phospholipid probe, 26.2 +/- 1.8% vs. 21.4 +/- 1.1%).

CONCLUSION(S)

The administration of P or a long incubation increased the proportion of internalization and consequently induced capacitation in human spermatozoa.

Identification and characterization of a novel splice variant of mouse and rat cytochrome b5/cytochrome b5 reductase

Cytochrome b5/cytochrome b5 reductase (cb5/cb5r) is a cytosolic fusion protein between the hemoprotein cytochrome b5 and the flavoprotein cytochrome b5 reductase. We describe the identification and characterization of a novel splice variant of cb5/cb5r in the mouse and rat and show that expression of the variant is conserved in both species but is not expressed in human tissue. Characterization of the exon structure of cb5/cb5r indicated that the variant was due to the deletion of the whole of exon 12, thus the variant was named cb5/cb5rdelta12. Exon 12 codes for the flavin-adenine dinucleotide binding domain of cb5/cb5r. Expression analysis revealed the transcript of cb5/cb5rdelta12 in mouse and rat testis, brain, and skeletal muscle and also in the male germ line. We postulate that cb5/cb5rdelta12 may function in a dominant negative fashion, limiting the amount of damage caused by the production of reactive oxygen species by cb5/cb5r.

Novel association between sperm reactive oxygen species production, sperm morphological defects, and the sperm deformity index

OBJECTIVE

To examine the relationship between sperm reactive oxygen species (ROS) production and sperm morphology in a group of infertile men and healthy fertile donors.

DESIGN

A prospective clinical study.

SETTING

Male infertility clinic, Glickman Urological Institute, The Cleveland Clinic Foundation, Cleveland, Ohio, and the Reproductive Medicine Unit, Liverpool Women's Hospital, United Kingdom

PATIENT(S)

Thirty-nine infertile men and 13 healthy fertile donors (control).

INTERVENTION(S)

Standard semen analysis, seminal leukocyte concentration, assessment of sperm morphology, and measurement of sperm ROS production.

MAIN OUTCOME MEASURE(S)

Levels of sperm ROS production, percentages of different sperm morphological abnormalities, and the sperm deformity index (SDI) scores.

RESULT(S)

A significant negative correlation was observed between sperm ROS production and the proportion of sperm with normal morphology and borderline morphology. Reactive oxygen species production was positively correlated with the proportion of sperm with amorphous heads, damaged acrosomes, midpiece defects, cytoplasmic droplets, tail defects, and SDI scores. Logistic regression analysis identified a two-variable model including SDI and percentage sperm motility, which correctly identified 84% of individuals with high seminal ROS and 85% of individuals with low seminal ROS. The model had an overall accuracy of 85%.

CONCLUSION(S)

The standard semen analysis to assess sperm motility, sperm morphology, and the SDI scores is a useful tool in identifying infertile men with high seminal ROS in infertility clinics where facilities for measuring levels of seminal ROS are not available.

Requirement of protein tyrosine kinase and phosphatase activities for human sperm exocytosis

The acrosome is a membrane-limited granule that overlies the nucleus of the mature spermatozoon. In response to physiological or pharmacological stimuli, sperm undergo calcium-dependent exocytosis termed the acrosome reaction, which is an absolute prerequisite for fertilization. Protein tyrosine phosphorylation and dephosphorylation are a mechanisms by which multiple cellular events are regulated. Here we report that calcium induces tyrosine phosphorylation in streptolysin O (SLO)-permeabilized human sperm. As expected, pretreatment with tyrphostin A47-a tyrosine kinase inhibitor-abolishes the calcium effect. Interestingly, the calcium-induced increase in tyrosine phosphorylation has a functional correlate in sperm exocytosis. Masking of phosphotyrosyl groups with a specific antibody or inhibition of tyrosine kinases with genistein, tyrphostin A47, and tyrphostin A51 prevent the acrosome reaction. By reversibly sequestering intra-acrosomal calcium with a photo-inhibitable chelator, we show a requirement for protein tyrosine phosphorylation late in the exocytotic pathway, after the efflux of intra-acrosomal calcium. Both mouse and human sperm contain highly active tyrosine phosphatases. Importantly, this activity declines when sperm are incubated under capacitating conditions. Inhibition of tyrosine phosphatases with pervanadate, bis(N,N-dimethylhydroxoamido)hydroxovanadate, ethyl-3,4-dephostatin, and phenylarsine oxide prevents the acrosome reaction. Our results show that both tyrosine kinases and phosphatases play a central role in sperm exocytosis.

Reactive oxygen species promote tyrosine phosphorylation and capacitation in equine spermatozoa

The objective of this study was to examine the influence of reactive oxygen species (ROS) on equine sperm capacitation. Motile equine spermatozoa were separated on a discontinuous Percoll gradient, resuspended at 10 x 10(6)ml in Tyrode's medium supplemented with BSA (0.5%) and polyvinyl alcohol (0.5%) and incubated at 39 degrees C for 2h with or without the xanthine (X; 0.1mM)-xanthine oxidase (XO; 0.01 U/ml) system or NADPH (0.25 mM). The importance of hydrogen peroxide or superoxide for capacitation was determined by the addition of catalase (CAT; 150 U/ml) or superoxide dismutase (SOD; 150 U/ml), respectively. Following incubation, acrosomal exocytosis was induced by a 5 min incubation at 39 degrees C with progesterone (3.18 microM), and sperm viability and acrosomal integrity were then determined by staining with Hoechst 33258 and fluoroisothiocyanate-conjugated Pisum sativum agglutin. To examine tyrosine phosphorylation, treatments were subjected to sodium dodecyl sulfate-polyacrylaminde gel electrophoresis (SDS-PAGE) followed by Western blot analysis with the anti-phosphotyrosine antibody (alpha-PY; clone 4G10). Capacitation with the X-XO system or NADPH led to a significant (P<0.0001) increase in live acrosome-reacted spermatozoa compared to controls. The addition of CAT or SOD prevented the increase in live acrosome-reacted spermatozoa associated with X-XO treatment. Incubation with the X-XO system was also associated with a significant (P<0.005) increase in tyrosine phosphorylation when compared to controls, which could be prevented by the addition of CAT but not SOD. This study indicates that ROS can promote equine sperm capacitation and tyrosine phosphorylation, suggesting a physiological role for ROS generation by equine spermatozoa.