Calcium signalling in human spermatozoa: a specialized 'toolkit' of channels, transporters and stores

Characterization of acrosin and acrosin binding protein as novel CRISP2 interacting proteins in boar spermatozoa

BACKGROUND

Previously, we reported that cysteine-rich secretory protein 2 is involved in high molecular weight complexes in boar spermatozoa. These cysteine-rich secretory protein 2protein complexes are formed at the last phase of sperm formation in the testis and play a role in sperm shaping and functioning.

OBJECTIVES

This study aimed to identify cysteine-rich secretory protein 2 interacting partners. These binding partner interactions were investigated under different conditions, namely, non-capacitating conditions, after the induction of in vitro sperm capacitation and subsequently during an ionophore A23187-induced acrosome reaction.

MATERIALS AND METHODS

The incubated pig sperm samples were subjected to protein extraction. Extracted proteins were subjected to blue native gel electrophoresis and native immunoblots. Immunoreactive gel bands were excised and subjected to liquid chromatography-mass spectrometry (LC-MS) analysis for protein identification. Protein extracts were also subjected to CRISP2 immunoprecipitation and analyzed by LC-MS for protein identification. The most prominent cystein-rich secretory protein 2 interacting proteins that appeared in both independent LC-MS analyses were studied with a functional in situ proximity interaction assay to validate their property to interact with cystein-rich secretory protein 2 in pig sperm.

RESULTS

Blue native gel electrophoresis and native immunoblots revealed that cystein-rich secretory protein 2 was present within a ∼150 kDa protein complex under all three conditions. Interrogation of cystein-rich secretory-protein 2-immunoreactive bands from blue native gels as well as cystein-rich secretory protein 2 immunoprecipitated products using mass spectrometry consistently revealed that, beyond cystein-rich secretory protein 2, acrosin and acrosin binding protein were among the most abundant interacting proteins and did interact under all three conditions. Co-immunoprecipitation and immunoblotting indicated that cystein-rich secretory protein 2 interacted with pro-acrosin (∼53 kDa) and Aacrosin binding protein under all three conditions and additionally to acrosin (∼35 kDa) after capacitation and the acrosome reaction. The colocalization of these interacting proteins with cystein-rich secretory protein 2 was assessed via in situ proximity ligation assays. The colocalization signal of cystein-rich secretory protein 2 and acrosin in the acrosome seemed dispersed after capacitation but was consistently present in the sperm tail under all conditions. The fluorescent foci of cystein-rich secretory protein 2 and acrsin binding protein colocalization appeared to be redistributed within the sperm head from the anterior acrosome to the post-acrosomal sheath region upon capacitation.

DISCUSSION AND CONCLUSION

These results suggest that CRISP2 may act as a scaffold for protein complex formation and dissociation to ensure the correct positioning of proteins required for the acrosome reaction and zona pellucida penetration.

The Role of Sperm Membrane Potential and Ion Channels in Regulating Sperm Function

During the last seventy years, studies on mammalian sperm cells have demonstrated the essential role of capacitation, hyperactivation and the acrosome reaction in the acquisition of fertilization ability. These studies revealed the important biochemical and physiological changes that sperm undergo in their travel throughout the female genital tract, including changes in membrane fluidity, the activation of soluble adenylate cyclase, increases in intracellular pH and Ca2+ and the development of motility. Sperm are highly polarized cells, with a resting membrane potential of about -40 mV, which must rapidly adapt to the ionic changes occurring through the sperm membrane. This review summarizes the current knowledge about the relationship between variations in the sperm potential membrane, including depolarization and hyperpolarization, and their correlation with changes in sperm motility and capacitation to further lead to the acrosome reaction, a calcium-dependent exocytosis process. We also review the functionality of different ion channels that are present in spermatozoa in order to understand their association with human infertility.

TRPV1 channel in spermatozoa is a molecular target for ROS-mediated sperm dysfunction and differentially expressed in both natural and ART pregnancy failure

Bi-directional crosstalk between Ca2+ signaling and ROS modulates physiological processes as a part of a regulatory circuit including sperm function. The role of transient receptor potential vanilloid 1 (TRPV1) in this regard cannot be undermined. This is the first report demonstrating the Ca2+-sensitive TRPV1 channel to be under-expressed in spermatozoa of subfertile men, idiopathic infertile men, and normozoospermic infertile males with high ROS (idiopathic infertility and unilateral varicocele). To study the effect of TRPV1 in determining the fertility outcome, we compared the expression profile of TRPV1 in spermatozoa of male partners who achieved pregnancy by natural conception (NC+, n = 10), IVF (IVF+, n = 23), or ICSI (ICSI +, n = 9) and their respective counterparts with failed pregnancy NC (n = 7), IVF (n = 23), or ICSI (n = 10), by both immunocytochemistry and flow-cytometry. Reduced expression of TRPV1 in sperm of IVF ± and ICSI ± men with respect to that NC+ men imply its role in mediating successful fertilization. Unsuccessful pregnancy outcome with an underexpression of TRPV1 in sperm of NC-/IVF-/ICSI-men suggests its role in conception and maintenance of pregnancy. Since ROS is regarded as one of the major contributors to sperm dysfunction, the effect of H2O2 +/- TRPV1 modulators (RTX/iRTX) on acrosomal reaction and calcium influx was evaluated to confirm TRPV1 as a redox sensor in human sperm. A significant increment in the percentage of acrosome reacted spermatozoa along with augmented Ca2+-influx was observed after H2O2 treatment, both in the presence or absence of TRPV1 agonist resiniferatoxin (RTX). The effect was attenuated by the TRPV1 antagonist iodoresiniferatoxin (iRTX), indicating the involvement of TRPV1 in mediating H2O2 response. Enhancement of motility and triggering of acrosomal reaction post TRPV1 activation suggested that disruption of these signaling cascades in vivo, possibly due to down-regulation of TRPV1 in these subfertile males. Bioinformatic analysis of the crosstalk between TRPV1 with fertility candidate proteins (reported to influence IVF outcome) revealed cell death and survival, cellular compromise, and embryonic development to be the primary networks affected by anomalous TRPV1 expression. We therefore postulate that TRPV1 can act as a redox sensor, and its expression in spermatozoa may serve as a fertility marker.

Thermotaxis of mammalian sperm

Sperm are guided through the female reproductive tract. A temperature difference of about 2 °C exists between the storage site and fertilization site of the mammalian oviduct, leading to the hypothesis that sperm can sense and swim towards the oocyte along a rising temperature gradient, known as thermotaxis. Research over the past two decades has reported that sperm feature a sophisticated thermal detection system to detect and track ambient temperature gradients. More recently, thermotaxis is expected to be added to the microfluidic isolation method based on sperm tactic responses for sperm selection. In this paper, mammalian sperm thermotaxis is discussed, explaining the underlying behavioral mechanisms and molecular basis, according to the latest research. Finally, this paper explores the possible application of sperm thermotaxis in assisted reproductive technologies.

In vitro storage of boar spermatozoa increases the demand of ATP for reactivation of motility

BACKGROUND

Prolonging the shelf-life of liquid-preserved semen without compromising its fertilizing capacity may increase the efficiency of artificial insemination in pigs. Many fertilization-relevant processes are ATP dependent. The impact of semen storage and rewarming to body temperature on the energy status of sperm are as yet unknown.

OBJECTIVES

To investigate the energy status of boar spermatozoa during storage and subsequent rewarming, and to reveal the potential role of mitochondrial function for reactivation and maintenance of sperm motility.

MATERIALS AND METHODS

Extended semen samples (n = 7 boars) were used. Spermatozoa were challenged by storage at 17°C for seven days and incubation at 38°C for 180 minutes. The ATP concentration and energy charge (EC) in semen samples and lactate concentration in the extracellular medium were assessed. Viability and mitochondrial activity were determined by flow cytometry, and clustered single cell analysis of motility parameters were performed.

RESULTS

The energy status was not affected by semen storage (p>0.05). Rewarming resulted in a net reduction in ATP concentration which increased with storage time (maximum Day 5: -24.2±10.3 %), but was not accompanied by a loss in viability, motility or mitochondrial activity. Blocking glycolysis with 2-Deoxy-D-glucose prevented re-establishing of motility and mitochondrial activity after rewarming. Mitochondrial activity gradually subsided in virtually all spermatozoa during incubation at 38°C, while ATP and EC remained high. Concomitantly, extracellular lactate levels rose and sperm populations with lower velocity, increased linearity, and low lateral head-displacement grew larger. Size changes for major sperm subpopulations correlated with the percentage of viable sperm with high mitochondrial activity (r = 0.44 to 0.70 for individual subpopulations, p<0.01).

CONCLUSION

Storage of boar spermatozoa increases the demand of ATP for reactivation of sperm towards fast, non-linear and hyperactivation-like motility patterns upon rewarming. Maintenance of glycolysis seems to be decisive for sperm function after long-term storage in vitro. This article is protected by copyright. All rights reserved.

G protein-coupled estrogen receptor promotes acrosome reaction via regulation of Ca2+ signaling in mouse sperm

G protein-coupled estrogen receptor (GPER), a seven-transmembrane G protein-coupled receptor, mediates the rapid pre-genomic signaling actions of estrogen and derivatives thereof. The expression of GPER is extensive in mammal male reproductive system. However, the functional role of GPER in mouse sperm has not yet been well recognized. This study revealed that GPER was expressed at the acrosome and the mid-flagellum of the mouse sperm. The endogenous GPER ligand 17β-estradiol and the selective GPER agonist G1 increased intracellular Ca2+ concentration ([Ca2+]i) in mouse sperm, which could be abolished by G15, an antagonist of GPER. In addition, the G1-stimulated Ca2+ response was attenuated by interference with the phospholipase C (PLC) signaling pathways or by blocking the cation sperm channel (CatSper). Chlortetracycline staining assay showed that the activation of GPER increased the incidence of acrosome-reacted sperm. Conclusively, GPER was located at the acrosome and mid-flagellum of the mouse sperm. Activation of GPER triggered the elevation of [Ca2+]i through PLC-dependent Ca2+ mobilization and CatSper-mediated Ca2+ influx, which promoted the acrosome reaction in mouse sperm.

Involvement of Ca2+-ATPase in suppressing the appearance of bovine helically motile spermatozoa with intense force prior to cryopreservation

In cattle, cryopreserved spermatozoa are generally used for artificial insemination (AI). Many of these specimens exhibit helical movement, although the molecular mechanisms underlying this phenomenon remain unclear. This study aimed to characterize helically motile spermatozoa, investigate the involvement of Ca²⁺-ATPase in suppressing the appearance of these spermatozoa prior to cryopreservation, and examine the potential of helical movement as an index of sperm quality. In the cryopreserved semen, approximately 50% of spermatozoa were helically motile, whereas approximately 25% were planarly motile. The helically motile samples swam significantly faster than those with planar movement, in both non-viscous medium and viscous medium containing polyvinylpyrrolidone. In contrast, in non-cryopreserved semen, planarly motile spermatozoa outnumbered those that were helically motile. Fluorescence microscopy with Fluo-3/AM and propidium iodide showed that flagellar [Ca²⁺]_i was significantly higher in cryopreserved live spermatozoa than in non-cryopreserved live ones. The percentage of non-cryopreserved helically motile spermatozoa was approximately 25% after washing, and this increased significantly to approximately 50% after treatment with an inhibitor of sarcoplasmic reticulum Ca²⁺-ATPases (SERCAs), “thapsigargin.” Immunostaining showed the presence of SERCAs in sperm necks. Additionally, the percentages of cryopreserved helically motile spermatozoa showed large inter-bull differences and a significantly positive correlation with post-AI conception rates, indicating that helical movement has the potential to serve as a predictor of the fertilizing ability of these spermatozoa. These results suggest that SERCAs in the neck suppress the cytoplasmic Ca²⁺-dependent appearance of helically motile spermatozoa with intense force in semen prior to cryopreservation.

Mitochondria: their role in spermatozoa and in male infertility

BACKGROUND

The best-known role of spermatozoa is to fertilize the oocyte and to transmit the paternal genome to offspring. These highly specialized cells have a unique structure consisting of all the elements absolutely necessary to each stage of fertilization and to embryonic development. Mature spermatozoa are made up of a head with the nucleus, a neck, and a flagellum that allows motility and that contains a midpiece with a mitochondrial helix. Mitochondria are central to cellular energy production but they also have various other functions. Although mitochondria are recognized as essential to spermatozoa, their exact pathophysiological role and their functioning are complex. Available literature relative to mitochondria in spermatozoa is dense and contradictory in some cases. Furthermore, mitochondria are only indirectly involved in cytoplasmic heredity as their DNA, the paternal mitochondrial DNA, is not transmitted to descendants.

OBJECTIVE AND RATIONAL

This review aims to summarize available literature on mitochondria in spermatozoa, and, in particular, that with respect to humans, with the perspective of better understanding the anomalies that could be implicated in male infertility.

SEARCH METHODS

PubMed was used to search the MEDLINE database for peer-reviewed original articles and reviews pertaining to human spermatozoa and mitochondria. Searches were performed using keywords belonging to three groups: 'mitochondria' or 'mitochondrial DNA', 'spermatozoa' or 'sperm' and 'reactive oxygen species' or 'calcium' or 'apoptosis' or signaling pathways'. These keywords were combined with other relevant search phrases. References from these articles were used to obtain additional articles.

OUTCOMES

Mitochondria are central to the metabolism of spermatozoa and they are implicated in energy production, redox equilibrium and calcium regulation, as well as apoptotic pathways, all of which are necessary for flagellar motility, capacitation, acrosome reaction and gametic fusion. In numerous cases, alterations in one of the aforementioned functions could be linked to a decline in sperm quality and/or infertility. The link between the mitochondrial genome and the quality of spermatozoa appears to be more complex. Although the quantity of mtDNA, and the existence of large-scale deletions therein, are inversely correlated to sperm quality, the effects of mutations seem to be heterogeneous and particularly related to their pathogenicity.

WIDER IMPLICATIONS

The importance of the role of mitochondria in reproduction, and particularly in gamete quality, has recently emerged following numerous publications. Better understanding of male infertility is of great interest in the current context where a significant decline in sperm quality has been observed.

Mode of Action of Farnesol, the "Noble Unknown" in Particular in Ca2+ Homeostasis, and Its Juvenile Hormone-Esters in Evolutionary Retrospect

Farnesol, the sesquiterpenoid precursor of insect juvenile hormones (JH) that itself has JH activity, existed already long before animals and their hormones came into being. Although it is omnipresent in all eukaryotes, this molecule remains a "noble unknown" in cell physiology. It is neither documented as a hormone nor as another type of signaling molecule. To date, its function as an intermediate in the synthesis of squalene-cholesterol-steroids in chordates/vertebrates, and of the insect/arthropod JHs, esters of farnesol, in the mevalonate biosynthetic pathway is assumed to be the only one. This assumption neglects that already two decades ago, farnesol has been shown to be a potent endogenous inhibitor of N-type voltage-gated Ca²⁺ channels in some mammalian cell types. The tandem mevalonate pathway and Ca²⁺ channels originated early in eukaryotic evolution, and has since been well conserved, "promoting" it as a ubiquitous player in Ca²⁺ homeostasis in all eukaryotes. This paper accentuates how this drastic change in thinking gained momentum after the discovery by Paroulek and Sláma that the huge amounts of JH I in male accessory glands of the Cecropia moth, are actually synthesized in these glands themselves and not in the corpora allata, the hitherto assumed unique synthesis site of such compounds. In addition, MAG-JHs have no hormonal- but an exocrine function. Here we hypothesize that MAG-JHs may function in protecting the spermatozoa against toxic Ca²⁺ concentrations, and in enabling their flagellum to undulate. They may do so by acting through membrane receptors. Our novel paradigm assigns to farnesol/JHs a function of flexible hydrophobic molecular valves for restricting untimely Ca²⁺-passage through some types of canonical Ca²⁺channels, using covalently bound farnesyl- or geranyl-geranyl group attachment as well as GPCRs-G proteins all containing a prenyl group. The high rotatable bond count, and their horseshoe-shape are instrumental to their valve function. In our paradigm, Met/Tai and Gce, to date generally thought to be the (only) functional (nuclear) receptors for JHs, are classified as probable Ca²⁺-sensitive transcription factors. Some theoretical and practical considerations for possible applications in a medical context will be discussed.

Molecular Basis of Human Sperm Capacitation

In the early 1950s, Austin and Chang independently described the changes that are required for the sperm to fertilize oocytes in vivo. These changes were originally grouped under name of “capacitation” and were the first step in the development of in vitro fertilization (IVF) in humans. Following these initial and fundamental findings, a remarkable number of observations led to characterization of the molecular steps behind this process. The discovery of certain sperm-specific molecules and the possibility to record ion currents through patch-clamp approaches helped to integrate the initial biochemical observation with the activity of ion channels. This is of particular importance in the male gamete due to the fact that sperm are transcriptionally inactive. Therefore, sperm must control all these changes that occur during their transit through the male and female reproductive tracts by complex signaling cascades that include post-translational modifications. This review is focused on the principal molecular mechanisms that govern human sperm capacitation with particular emphasis on comparing all the reported pieces of evidence with the mouse model.

Copy number variation of functional RBMY1 is associated with sperm motility: an azoospermia factor-linked candidate for asthenozoospermia

STUDY QUESTION

What is the influence of copy number variation (CNV) in functional RNA binding motif protein Y-linked family 1 (RBMY1) on spermatogenic phenotypes?

SUMMARY ANSWER

The RBMY1 functional copy dosage is positively correlated with sperm motility, and dosage insufficiency is an independent risk factor for asthenozoospermia.

WHAT IS KNOWN ALREADY

RBMY1, a multi-copy gene expressed exclusively in the adult testis, is one of the most important candidates for male infertility in the azoospermia factor (AZF) region of the Y-chromosome. RBMY1 encodes an RNA-binding protein that serves as a pre-mRNA splicing regulator during spermatogenesis, and male mice deficient in Rbmy are sterile.

STUDY DESIGN, SIZE, DURATION

A total of 3127 adult males were recruited from 2009 to 2016; of this group, the dosage of RBMY1 functional copy were investigated in 486 fertile males. In the remaining 2641 males with known spermatogenesis status, 1070 Y-chromosome haplogroup (Y-hg) O3* or O3e carriers without chromosomal aberration or known AZF structure mutations responsible for spermatogenic impairment, including 506 men with normozoospermia and 564 men with oligozoospermia or/and asthenozoospermia, were screened, and the RBMY1 functional copy dosage and copy conversion were determined to explore their associations with sperm phenotypes. The correlation between RBMY1 dosage and its mRNA level or RBMY1 protein level and the correlation between sperm RBMY1 level and motility were analysed in 15 testis tissue samples and eight semen samples. Ten additional semen samples were used to confirm the subcellular localization of RBMY1 in individual sperm.

PARTICIPANTS/MATERIALS, SETTING, METHODS

All the Han volunteers donating whole blood, semen and testis tissue were from southwest China. RBMY1 copy number, copy conversion, mRNA/protein amount and protein location in sperm were detected using the AccuCopy® assay method, paralog ratio test, quantitative PCR, western blotting and immunofluorescence staining methods, respectively.

MAIN RESULTS AND THE ROLE OF CHANCE

This study identified Y-hg-independent CNV of functional RBMY1 in the enrolled population. A difference in the distribution of RBMY1 copy number was observed between the group with normal sperm motility and the group with asthenozoospermia. A positive correlation between the RBMY1 copy dosage and sperm motility was identified, and the males with fewer than six copies of RBMY1 showed an elevated risk for asthenozoospermia relative to those with six RBMY1 copies, the most common dosage in the population. The RBMY1 copy dosage was positively correlated with its mRNA and protein level in the testis. Sperm with high motility were found to carry more RBMY1 protein than those with relatively low motility. The RBMY1 protein was confirmed to predominantly localize in the neck and mid-piece region of sperm as well as the principal piece of the sperm tail. Our population study completes a chain of evidence suggesting that RBMY1 influences the susceptibility of males to asthenozoospermia by modulating sperm motility.

LIMITATIONS REASONS FOR CAUTION

High sequence similarity between the RBMY1 functional copies and a large number of pseudogenes potentially reduces the accuracy of the copy number detection. The mechanism underlying the CNV in RBMY1 is still unclear, and the effect of the structural variations in the RBMY1 copy cluster on the copy dosage of other protein-coding genes located in the region cannot be excluded, which may potentially bias our observations.

WIDER IMPLICATIONS OF THE FINDINGS

Asthenozoospermia is a multi-factor complex disease with a limited number of proven susceptibility genes. This study identified a novel genomic candidate independently contributing to the condition, enriching our understanding of the role of AZF-linked genes in male reproduction. Our finding provides insight into the physiological and pathological characteristics of RBMY1 in terms of sperm motility, supplies persuasive evidence of the significance of RBMY1 copy number analysis in the clinical counselling of male infertility resulting from asthenozoospermia.

STUDY FUNDING/COMPETING INTEREST(S)

This work was funded by the National Natural Science Foundation of China (Nos. 81370748 and 30971598). The authors have no conflicts of interest.

Is transcription in sperm stationary or dynamic?

Transcriptional activity is repressed due to the packaging of sperm chromatins during spermiogenesis. The detection of numerous transcripts in sperm, however, raises the question whether transcriptional events exist in sperm, which has been the central focus of the recent studies. To summarize the transcriptional activity during spermiogenesis and in sperm, we reviewed the documents on transcript differences during spermiogenesis, in sperm with differential motility, before and after capacitation and cryopreservation. This will lay a theoretical foundation for studying the mechanism(s) of gene expression in sperm, and would be invaluable in making better use of animal sires and developing reproductive control technologies.

Interactions between oestrogen and 1α,25(OH)2-vitamin D3 signalling and their roles in spermatogenesis and spermatozoa functions

Oestrogens and 1α,25(OH)₂-vitamin D₃ (1,25-D₃) are steroids that can provide effects by binding to their receptors localised in the cytoplasm and in the nucleus or the plasma membrane respectively inducing genomic and non-genomic effects. As confirmed notably by invalidation of the genes, coding for their receptors as tested with mice with in vivo and in vitro treatments, oestrogens and 1,25-D₃ are regulators of spermatogenesis. Moreover, some functions of ejaculated spermatozoa as viability, DNA integrity, motility, capacitation, acrosome reaction and fertilizing ability are targets for these hormones. The studies conducted on their mechanisms of action, even though not completely elicited, have allowed the demonstration of putative interactions between their signalling pathways that are worth examining more closely. The present review focuses on the elements regulated by oestrogens and 1,25-D₃ in the testis and spermatozoa as well as the interactions between the signalling pathways of both hormones.

The beneficial effect of repaglinide on in vitro maturation and development ability of immature mouse oocytes

Repaglinide is a hypoglycemic drug, causing depolarization of the cell membrane, opening the voltage-gated calcium channels, and then increasing intracellular calcium in the pancreatic B cells by inhibition of the K-ATP-sensitive channels. Oocyte in vitro maturation (IVM) is influenced by different factors such as calcium signaling. In this study, we examined the effects of repaglinide on in vitro maturation and fertilization ability of mouse oocyte. Immature oocytes were isolated from female Naval Medical Research Institute mice which are 6-8 wk old mechanically and then cultured in 30 μl droplets of T6 medium with different concentrations of repaglinide. The control group did not receive repaglinide (R₀). Treatment groups received different concentrations (5, 10, and 100 nM and 1 and 10 μM) of repaglinide (R₁, R₂, R₃, R₄, and R₅, respectively). Oocyte in vitro maturation rate was assessed after 24 h. In vitro fertilization was performed using metaphase II oocytes obtained from R₀ and R₄ treatments. Embryo cleavage rate was calculated at 48 h post-IVF. Chi-square test was used for evaluating difference between control and treatment groups (p < 0.05). Oocyte maturation rate after 24 h in treatment groups R₂, R₃, R₄, and R₅ was significantly higher than that in the control (p < 0.05). Supplementation of medium with 1 μM of repaglinide (R₄) during IVM significantly improved outcome of embryo cleavage rate than control at 48 h post-IVF (p < 0.05). In conclusion, repaglinide can be considered as an effective agent for in vitro oocyte maturation and embryo cleavage.

Luteinizing hormone modulates intracellular calcium, protein tyrosine phosphorylation and motility during human sperm capacitation

In order to fertilize, spermatozoa must undergo physiological and biochemical changes during their transit along the female reproductive tract before reaching and fusing with the oocyte, process known as capacitation. Sperm modifications associated with capacitation are modulated by their interaction with molecules present in the female reproductive tract. During the woman fertile window, some reproductive hormones reach their maximum concentrations in serum, such as the luteinizing hormone (LH). Since spermatozoa preparing to fertilize may be exposed to LH, the purpose of this work was to study the effects of this hormone on intracellular Ca²⁺ concentrations ([Ca²⁺]_i), protein tyrosine phosphorylation, sperm motility and acrosome reaction under capacitating conditions. The results showed that LH increases the duration and amplitude of Ca²⁺ oscillations. Furthermore, motility analysis indicated that LH decreases rapid progressive motility and that sperm hyperactivation as well as several kinetic parameters augment in the presence of 0.5 and 1 μg/ml of the hormone. In addition, these two hormone concentrations also consistently promoted protein tyrosine phosphorylation. However, no effects on acrosome reaction were observed. In conclusion, the evidence indicates that LH modulates several sperm function variables involved in capacitation, suggesting that may have an important and unexplored role during human fertilization.

Heat Sensing Receptor TRPV1 Is a Mediator of Thermotaxis in Human Spermatozoa

The molecular bases of sperm thermotaxis, the temperature-oriented cell motility, are currently under investigation. Thermal perception relies on a subclass of the transient receptor potential [TRP] channels, whose member TRPV1 is acknowledged as the heat sensing receptor. Here we investigated the involvement of TRPV1 in human sperm thermotaxis. We obtained semen samples from 16 normozoospermic subjects attending an infertility survey programme, testis biopsies from 6 patients with testicular germ cell cancer and testis fine needle aspirates from 6 patients with obstructive azoospermia undergoing assisted reproductive technologies. Expression of TRPV1 mRNA was assessed by RT-PCR. Protein expression of TRPV1 was determined by western blot, flow cytometry and immunofluorescence. Sperm motility was assessed by Sperm Class Analyser. Acrosome reaction, apoptosis and intracellular-Ca²⁺ content were assessed by flow cytometry. We found that TRPV1 mRNA and protein were highly expressed in the testis, in both Sertoli cells and germ-line cells. Moreover, compared to no-gradient controls at 31°C or 37°C (Ctrl 31°C and Ctrl 37°C respectively), sperm migration towards a temperature gradient of 31–37°C (T gradient) in non-capacitated conditions selected a higher number of cells (14,9 ± 4,2×10⁶ cells T gradient vs 5,1± 0,3×10⁶ cells Ctrl 31°C and 5,71±0,74×10⁶ cells Ctrl 37°C; P = 0,039). Capacitation amplified the migrating capability towards the T gradient. Sperms migrated towards the T gradient showed enriched levels of both TRPV1 protein and mRNA. In addition, sperm cells were able to migrate toward a gradient of capsaicin, a specific agonist of TRPV1, whilst capsazepine, a specific agonist of TRPV1, blocked this effect. Finally, capsazepine severely blunted migration towards T gradient without abolishing. These results suggest that TRPV1 may represent a facilitating mediator of sperm thermotaxis.

Sperm Release From the Oviductal Epithelium Depends on Ca(2+) Influx Upon Activation of CB1 and TRPV1 by Anandamide

The oviduct acts as a functional sperm reservoir in many mammalian species. Both binding and release of spermatozoa from the oviductal epithelium are mainly modulated by sperm capacitation. Several molecules from oviductal fluid are involved in the regulation of sperm function. Anandamide is a lipid mediator involved in reproductive physiology. Previously, we demonstrated that anandamide, through activation of the cannabinoid receptor type 1 (CB1), promotes sperm release from bovine oviductal epithelial cells, and through CB1 and the transient receptor potential vanilloid 1 (TRPV1), induces sperm capacitation. Herein we investigate co-activation between CB1 and TRPV1, and Ca(2+) influx as part of the mechanism of action of anandamide during sperm release from oviductal cells. Our results indicate that in the absence of Ca(2+) anandamide failed to release spermatozoa from oviductal epithelial cells. Additionally, sperm release promoted by cannabinoid and vanilloid agonists was abolished when the spermatozoa were preloaded with BAPTA-AM, a Ca(2+) chelator. We also determined Ca(2+) levels in spermatozoa preloaded with FURA2-AM co-cultured with oviductal cells and incubated with different cannabinoid and vanilloid agonists. The incubation with different agonists induced Ca(2+) influx, which was abolished by CB1 or TRPV1 antagonists. Our results also suggest that a phospholypase C (PLC) might mediate the activation of CB1 and TRPV1 in sperm release from the bovine oviduct. Therefore, our findings indicate that anandamide, through CB1 and TRPV1 activation, is involved in sperm release from the oviductal reservoir. An increase of sperm Ca(2+) levels and the PLC activation might be involved in anandamide signaling pathway.

Participation of protein kinases and phosphatases in the progesterone-induced acrosome reaction and calcium influx in human spermatozoa

In human spermatozoa, protein kinases have a role in the acrosome reaction (AR) induced by a variety of stimuli. However, there is disagreement or a lack of information regarding the role of protein kinases and phosphatases in the progesterone (P)-induced increase in intracellular calcium concentration ([Ca²⁺ ]_i ). In addition, there are no studies regarding the role of Ser/Thr and Tyr phosphatases and there are contradictory results regarding the role of Tyr kinases in the P-induced acrosome reaction. Here, we performed a simultaneous evaluation of the involvement of protein kinases and phosphatases in the P-induced acrosome reaction and in the P-induced calcium influx. Motile spermatozoa were capacitated for 18 h and different aliquots were allocated to treated or control groups and then evaluated for their ability to undergo the acrosome reaction and to increase [Ca²⁺ ]_i in response to P. The acrosome reaction was evaluated using Pisum sativum agglutinin (PSA)-FITC, and [Ca²⁺ ]_i was evaluated using fura 2AM. At all of the concentrations tested, PKA inhibitors significantly reduced the percentage of the P-induced acrosome reaction (p < 0.001). However, only the highest concentrations of PKA inhibitors reduced the P-induced calcium influx; lower concentrations of PKA inhibitors did not affect it. Similar results were apparent for PKC inhibitors and for tyrosine kinase inhibitors. None of the Ser/Thr phosphatase inhibitors affected the P-induced acrosome reaction or the P-induced calcium influx, except for the PP2B inhibitors that significantly reduced the P-induced acrosome reaction without affecting calcium influx. Finally, the protein tyrosine phosphatase inhibitors significantly blocked the P-induced acrosome reaction and reduced the amplitude of the P-induced calcium transient (p < 0.001) as well as the amplitude of the plateau phase (p < 0.01). The data suggest that protein kinases and possibly PP2B have a role on the acrosome reaction at some point downstream of calcium entry and that Tyr phosphatases have a role on the acrosome reaction upstream of calcium entry.

Calcium channels in chicken sperm regulate motility and the acrosome reaction

Intracellular cytoplasmic calcium ([Ca(2+) ]i ) has an important regulatory role in gamete functions. However, the biochemical components involved in Ca(2+) transport are still unknown in birds, an animal class that has lost functional sperm-specific CatSper channels. Here, we provide evidence for the presence and expression of various Ca(2+) channels in chicken sperm, including high voltage-activated channels (L and R types), the store-operated Ca(2+) channel (SOC) component Orai1, the transient receptor potential channel (TRPC1) and inositol-1,4,5-trisphosphate receptors (IP3 R1). L- and R-type channels were mainly localized in the acrosome and the midpiece, and T-type channels were not detected in chicken sperm. Orai1 was found in all compartments, but with a weak, diffuse signal in the flagellum. TRCP1 was mainly localized in the acrosome and the midpiece, but a weak diffuse signal was also observed in the nucleus and the flagellum. IP3 R1 was mainly detected in the nucleus. The L-type channel inhibitor nifedipine, the R-type channel inhibitor SNX-482 and the SOC inhibitors MRS-1845, 2-APB and YM-58483 decreased [Ca(2+) ]i sperm motility and acrosome reaction capability, with the SOC inhibitors inhibiting these functions most efficiently. Furthermore, we showed that Ca(2+) -mediated induction of AMP-activated protein kinase (AMPK) phosphorylation was blocked by SOC inhibition. Our identification of important regulators of Ca(2+) signaling in avian sperm suggests that SOCs play a predominant role in gamete function, whereas T-type channels may not be involved. In addition, Ca(2+) entry via SOCs appears to be the most likely pathway for AMPK activation and energy-requiring sperm functions such as motility and the acrosome reaction.

CABCOCO1, a novel coiled-coil protein With calcium-binding activity, is localized in the sperm flagellum

The gene 1700040L02Rik (GenBank accession number NM_028491, NP_082767.1) was selected by in silico screening as candidate that encodes a calcium-binding protein in sperm from a database of predicted mouse cilia-related genes. The predicted amino acid sequence revealed the presence of coiled-coil domain at the C-terminus and a CLAMP motif containing a leucine zipper domain in the middle of the protein. Assessment of a recombinant version of this protein by Stains-all and ruthenium red staining and by direct measurement of terbium binding revealed its calcium-binding activities. We therefore named this protein CABCOCO1 for calcium-binding coiled-coil protein-1. Immunohistochemical analyses showed its localization in spermatogenic cells of mouse testis. CABCOCO1 was first observed in the cytoplasm of murine spermatocytes, concentrated around centrioles of spermatids and co-localized with the centrosomal protein pericentrin. During the stage when centrosome number is reduced, CABCOCO1 relocalized to the murine sperm flagellum. On the other hand, in porcine sperm, whose proximal centriole remains intact while the distal centriole degenerates during spermiogenesis, CABCOCO1 localized both in the basal body and the flagellum. These results suggested that CABCOCO1 is involved in the control of sperm flagellar movement. Mol. Reprod. Dev. 83: 912-926, 2016 © 2016 Wiley Periodicals, Inc.

Identification, localization, and functional analysis of the homologues of mouse CABS1 protein in porcine testis

Previously, we have identified a calcium-binding protein that is specifically expressed in spermatids and localized to the flagella of the mature sperm in mouse, so-called mCABS1. However, the physiological roles of CABS1 in the male reproductive system have not been fully elucidated yet. In the current study, we aimed to localize and clarify the role of CABS1 in porcine (pCABS1). We determined for the first time the full nucleotides sequence of pCABS1 mRNA. pCABS1 protein was detected on SDS-PAGE gel as two bands at 75 kDa and 70 kDa in adult porcine testis, whereas one band at 70 kDa in epididymal sperm. pCABS1 immunoreactivity in seminiferous tubules was detected in the elongated spermatids, and that in the epididymal sperm was found in the acrosome as well as flagellum. The immunoreactivity of pCABS1 in the acrosomai region disappeared during acrosome reaction. We also identified that pCABS1 has a transmembrane domain using computational prediction of the amino acids sequence. The treatment of porcine capacitated sperm with anti-pCABS1 antiserum significantly decreased acrosome reactions. These results suggest that pCABS1 plays an important role in controlling calcium ion signaling during the acrosome reaction.

The non-genomic effects of endocrine-disrupting chemicals on mammalian sperm

Exposure to toxicants present in the environment, especially the so-called endocrine-disrupting chemicals (EDCs), has been associated with decreased sperm quality and increased anomalies in male reproductive organs over the past decades. Both human and animal populations are continuously exposed to ubiquitous synthetic and natural-occurring EDCs through diet, dermal contact and/or inhalation, therefore potentially compromising male reproductive health. Although the effects of EDC are likely induced via multiple genomic-based pathways, their non-genomic effects may also be relevant. Furthermore, spermatozoa are transcriptionally inactive cells that can come in direct contact with EDCs in reproductive fluids and secretions and are therefore a good model to address non-genomic effects. This review thus focuses on the non-genomic effects of several important EDCs relevant to mammalian exposure. Notably, EDCs were found to interfere with pre-existing pathways inducing a panoply of deleterious effects to sperm function that included altered intracellular Ca2+oscillations, induction of oxidative stress, mitochondrial dysfunction, increased DNA damage and decreased sperm motility and viability, among others, potentially jeopardizing male fertility. Although many studies have used non-environmentally relevant concentrations of only one compound for mechanistic studies, it is important to remember that mammals are not exposed to one, but rather to a multitude of environmental EDCs, and synergistic effects may occur. Furthermore, some effects have been detected with single compounds at environmentally relevant concentrations.

Plasma membrane Ca2+-ATPase 4: interaction with constitutive nitric oxide synthases in human sperm and prostasomes which carry Ca2+/CaM-dependent serine kinase

Deletion of the gene encoding the widely conserved plasma membrane calcium ATPase 4 (PMCA4), a major Ca(2+) efflux pump, leads to loss of sperm motility and male infertility in mice. PMCA4's partners in sperm and how its absence exerts its effect on fertility are unknown. We hypothesize that in sperm PMCA4 interacts with endothelial nitric oxide synthase (eNOS) and neuronal nitric oxide synthase (nNOS) which are rapidly activated by Ca(2+), and that these fertility-modulating proteins are present in prostasomes, which deliver them to sperm. We show that in human sperm PMCA4 is present on the acrosome, inner acrosomal membrane, posterior head, neck, midpiece and the proximal principal piece. PMCA4 localization showed inter- and intra-individual variation and was most abundant at the posterior head/neck junction, co-localizing with NOSs. Co-immunoprecipitations (Co-IP) revealed a close association of PMCA4 and the NOSs in Ca(2+) ionophore-treated sperm but much less so in uncapacitated untreated sperm. Fluorescence resonance energy transfer (FRET) showed a similar Ca(2+)-related association: PMCA4 and the NOSs are within 10 nm apart, and preferentially so in capacitated, compared with uncapacitated, sperm. FRET efficiencies varied, being significantly (P < 0.001) higher at high cytosolic Ca(2+) concentration ([Ca(2+)]c) in capacitated sperm than at low [Ca(2+)]c in uncapacitated sperm for the PMCA4-eNOS complex. These dynamic interactions were not seen for PMCA4-nNOS complexes, which had the highest FRET efficiencies. Further, along with Ca(2+)/CaM-dependent serine kinase (CASK), PMCA4 and the NOSs are present in the seminal plasma, specifically in prostasomes where Co-IP showed complexes similar to those in sperm. Finally, flow cytometry demonstrated that following co-incubation of sperm and seminal plasma, PMCA4 and the NOSs can be delivered in vitro to sperm via prostasomes. Our findings indicate that PMCA4 interacts simultaneously with the NOSs preferentially at high [Ca(2+)]c in sperm to down-regulate them, and thus prevent elevated levels of NO, known to induce asthenozoospermia via oxidative stress. Our studies point to the potential underlying cause of infertility in PMCA4's absence, and suggest that inactivating mutations of PMCA4 could lead to asthenozoospermia and human infertility. Screening for these mutations may serve both diagnostic and therapeutic purposes.

ATPases, ion exchangers and human sperm motility

Human sperm has several mechanisms to control its ionic milieu, such as the Na,K-ATPase (NKA), the Ca-ATPase of the plasma membrane (PMCA), the Na+/Ca2+-exchanger (NCX) and the Na+/H+-exchanger (NHE). On the other hand, the dynein-ATPase is the intracellular motor for sperm motility. In this work, we evaluated NKA, PMCA, NHE, NCX and dynein-ATPase activities in human sperm and investigated their correlation with sperm motility. Sperm motility was measured by Computer Assisted Semen Analysis. It was found that the NKA activity is inhibited by ouabain with twoKi(7.9×10−9and 9.8×10−5 M), which is consistent with the presence of two isoforms of α subunit of the NKA in the sperm plasma membranes (α1 and α4), being α4 more sensitive to ouabain. The decrease in NKA activity is associated with a reduction in sperm motility. In addition, sperm motility was evaluated in the presence of known inhibitors of NHE, PMCA and NCX, such as amiloride, eosin, and KB-R7943, respectively, as well as in the presence of nigericin after incubation with ouabain. Amiloride, eosin and KB-R7943 significantly reduced sperm motility. Nigericin reversed the effect of ouabain and amiloride on sperm motility. Dynein-ATPase activity was inhibited by acidic pH and micromolar concentrations of Ca2+. We explain our results in terms of inhibition of the dynein-ATPase in the presence of higher cytosolic H+and Ca2+, and therefore inhibition of sperm motility.

Transient receptor potential-canonical 3 modulates sperm motility and capacitation-associated protein tyrosine phosphorylation via [Ca2+]i mobilization

Ca(2+) signaling is pivotal for sperm maturation, including the processes of motility, capacitation, and the acrosome reaction. As a Ca(2+) conductor, transient receptor potential-canonical 3 (TRPC3) plays an important role in somatic cells. However, the function of TRPC3 in sperm is not well understood. Here, a pharmacological approach was used to investigate the role and mechanism of TPRC3 in sperm function. The TRPC3 antagonist Pyr3 could inhibit sperm motility and accelerate capacitation-associated protein tyrosine phosphorylation in a time- and dose-dependent manner, regardless of the presence or absence of Ca(2+) in the incubation medium. Further investigation revealed that sperm [Ca(2+)]i fell immediately once Pyr3 was added to Ca(2+)-free medium, and then gradually increased and returned to baseline levels. Moreover, the [Ca(2+)]i levels markedly elevated when sperm were incubated for 30 min in the presence of Pyr3; this change was subsequently accompanied by a significant reduction in sperm mitochondrial membrane potential. This study suggested that TRPC3 can modulate sperm function via mobilization of sperm [Ca(2+)]i.

Improving fertilization rate in ICSI cycles by adding myoinositol to the semen preparation procedures: a prospective, bicentric, randomized trial on sibling oocytes

PURPOSE

To evaluate whether the in vitro incubation of spermatozoa with myoinositol may improve the fertilization rate in ICSI cycles.

METHODS

This is a prospective, bicentric, randomized study on 500 MII sibling oocytes injected in 78 ICSI cycles performed between March and October 2013. Randomization of the oocytes into two groups was performed at the time of the denudation. Fertilization rates (per oocyte injected with spermatozoa treated with myoinositol versus per oocyte injected with spermatozoa treated with placebo) were measured as primary outcome and embryo morphology as secondary outcome. Clinical outcomes were also documented.

RESULT (S)

Fertilization rate (78.9 ± 28.6% vs 63.2 ± 36.7, P = 0.002) and percentage of grade A embryos on day 3 (59.8 ± 35.6% vs 43.5 ± 41.5, P = 0.019) were significantly higher when spermatozoa were treated in vitro with myoinositol versus placebo. No differences were found for the expanded blastocyst formation rate.

CONCLUSION (S)

In vitro treatment of spermatozoa with myoinositol may optimize ICSI outcomes by improving the fertilization rate and embryo quality on day 3. The improvement of the number and the quality of embryos available in an ICSI cycle may have clinical utility if these findings can be confirmed.

Kinetics of human sperm acrosomal exocytosis

The acrosome reaction is a unique event in the lifespan of sperm characterized by the exocytosis of the acrosomal content and the release of hybrid vesicles formed by patches of the outer acrosomal membrane and the plasma membrane. This unique regulated exocytosis is mediated by essentially the same membrane fusion machinery present in neuroendocrine cells. However, whereas secretion in neuroendocrine cells occurs in less than a second, the acrosome reaction is normally assessed after several minutes of incubation with inducers. In this report, we measured the kinetics of human sperm exocytosis triggered by two stimuli (calcium ionophore and progesterone) by using electron microscopy and three different approaches based on the incorporation of fluorescent Pisum sativum agglutinin into the acrosome upon opening of fusion pores connecting the extracellular medium with the acrosomal lumen. The results with the different methods are consistent with a slow kinetics (t½ = 14 min). We also manipulated the system to measure different steps of the process. We observed that cytosolic calcium increased with a relatively fast kinetics (t½ = 0.1 min). In contrast, the swelling of the acrosomal granule that precedes exocytosis was a slow process (t½ = 13 min). When swelling was completed, the fusion pore opening was fast (t½ = 0.2 min). The results indicate that acrosomal swelling is the slowest step and it determines the kinetics of the acrosome reaction. After the swelling is completed, the efflux of calcium from intracellular stores triggers fusion pores opening and the release of hybrid vesicles in seconds.

Proteogenomics of Gammarus fossarum to document the reproductive system of amphipods

Because of their ecological importance, amphipod crustacea are employed worldwide as test species in environmental risk assessment. Although proteomics allows new insights into the molecular mechanisms related to the stress response, such investigations are rare for these organisms because of the lack of comprehensive protein sequence databases. Here, we propose a proteogenomic approach for identifying specific proteins of the freshwater amphipod Gammarus fossarum, a keystone species in European freshwater ecosystems. After deep RNA sequencing, we created a comprehensive ORF database. We identified and annotated the most relevant proteins detected through a shotgun tandem mass spectrometry analysis carried out on the proteomes from three major tissues involved in the organism's reproductive function: the male and female reproductive systems, and the cephalon, where different neuroendocrine glands are present. The 1,873 mass-spectrometry-certified proteins represent the largest crustacean proteomic resource to date, with 218 proteins being lineage specific. Comparative proteomics between the male and female reproductive systems indicated key proteins with strong sexual dimorphism. Protein expression profiles during spermatogenesis at seven different stages highlighted the major gammarid proteins involved in the different facets of reproduction.

Evidence for the involvement of proline-rich tyrosine kinase 2 in tyrosine phosphorylation downstream of protein kinase A activation during human sperm capacitation

Sperm capacitation involves an increase in intracellular Ca(2+) concentration as well as in protein kinase A (PKA)-dependent protein tyrosine (Tyr) phosphorylation. Interestingly, in humans, a decrease in extracellular Ca(2+) concentration ([Ca(2+)]e) during capacitation induces an increase in Tyr phosphorylation indicating the complexity of Ca(2+) signaling during this process. In view of this, in the present study we further investigated the Ca(2+)-mediated signaling pathways implicated in Tyr phosphorylation during human sperm capacitation. Results revealed that sperm incubation in a medium without added Ca(2+) (⊖ Ca(2+)) increased Tyr phosphorylation but did not modify PKA-mediated phosphorylation. Moreover, inhibition of either PKA or Src family kinase signaling cascades in ⊖ Ca(2+) down-regulated both PKA substrate and Tyr phosphorylations, indicating that the [Ca(2+)]e effects on Tyr phosphorylation depend on PKA targets. Inhibition of calmodulin or Ser/Thr protein phosphatase 2B also increased Tyr phosphorylation without affecting PKA-mediated phosphorylation, supporting the potential role of these Ca(2+) downstream effectors in the increase in Tyr phosphorylation observed in ⊖ Ca(2+). Experiments aimed to identify the kinase responsible for these observations revealed the presence of proline-rich tyrosine kinase 2 (PYK2), a focal adhesion kinase (FAK) family member, in human sperm, and the use of PF431396, an FAK inhibitor, supported the involvement of PYK2 in Tyr phosphorylation downstream of PKA activation. Results also showed that PYK2 was activated in ⊖ Ca(2+) as well as during capacitation and that PF431396 affected capacitated sperm motility, acrosome reaction and ability to penetrate both mouse cumulus matrix and zona-free hamster eggs. Together, our observations support PYK2 as an intermediary component of Ca(2+) signaling between PKA-mediated and Tyr phosphorylations that is required for achieving functional human sperm capacitation.

Real-time calcium measurements of live optically trapped microorganisms

A system has been developed that allows for the real-time measurement of calcium dynamics in swimming sperm. Specifically, the ratiometric dye Indo-I is used as a fluorescent indicator of intracellular calcium dynamics. The dual emissions are collected by a high-sensitivity back-illuminated CCD camera coupled to a Dual-View imaging system. From the CCD, the images are sent to a custom developed algorithm which processes the images and outputs the calcium measurements in real-time. Additionally, sperm velocity and position data are processed and outputted in real-time. The velocity and position data are obtained using a separate coupled red light (>670 nm) phase contrast imaging setup that does not optically interfere with the fluorescent imaging. Using this system the effects of optical trapping on calcium dynamics was determined. Optical trapping of sperm with a decaying focused laser power of 510 mW to 3 mW over 8 seconds causes a statistically insignificant change in calcium dynamics between in-trap and out-of-trap conditions. Progesterone, a calcium activator, was added and sperm were trapped under the 8 second power decay conditions. Progesterone treated sperm has a statistically higher average calcium level than untreated sperm, but shows no statistical difference between progesterone treated in-trap and out-of-trap conditions. Trapping at 16 seconds at 510 mW without decay, which have been shown to decrease sperm motility, shows a statistical difference between baseline pre-trap and in-trap intracellular calcium levels.

Effect of mitochondrial calcium uniporter blocking on human spermatozoa

Calcium (Ca(2+) ) regulates a number of essential processes in spermatozoa. Ca(2+) is taken up by mitochondria via the mitochondrial calcium uniporter (mCU). Oxygen-bridged dinuclear ruthenium amine complex (Ru360) has been used to study mCU because it is a potent and specific inhibitor of this channel. In bovine spermatozoa, it has been demonstrated that mitochondrial calcium uptake inhibition adversely affects the capacitation process. It has been demonstrated in human spermatozoa that mCU blocking, through Ru360, prevents apoptosis; however, the contribution of the mCU to normal human sperm function has not been studied. Therefore, the aim of this study was to evaluate the effect of mCU blocking on human sperm function. Spermatozoa obtained from apparently healthy donors were incubated with 5 and 10 μm Ru360 for 4 h at 37 °C. Viability was assessed using propidium iodide staining; motility was determined by computer-aided sperm analysis, adenosine triphosphate (ATP) levels using a luminescence-based method, mitochondrial membrane potential (ΔΨm) using JC-1 staining and reactive oxygen species (ROS) production using dihydroethidium dye. Our results show that mCU blocking significantly reduced total sperm motility and ATP levels without affecting sperm viability, ΔΨm and ROS production. In conclusion, mCU contributes to the maintenance of sperm motility and ATP levels in human spermatozoa.

Effects of frozen and liquid hypothermic storage and extender type on calcium homeostasis in relation to viability and ATP content in striped bass (Morone saxatilis) sperm

The effect of hypothermic storage on striped bass sperm calcium homeostasis was determined by Fluo-3 flow cytometry. Calcium homeostasis was defined as the ability of cells to maintain a low concentration of intracellular free calcium as measured by Fluo-3 fluorescence. Sperm were stored frozen in striped bass extender (SBE) and Tris-NaCl medium (T350) modified with 50 mM glycine and 7.5% dimethylsulfoxide and in nonfrozen form diluted 1:3 (vol/vol) in SBE and T350 for 1, 24, and 48 hours at 4 °C in an oxygen atmosphere. Fluo-3 fluorescence was detected in less than 5% of fresh viable sperm cells indicating maintenance of calcium homeostasis. In contrast to sperm in fresh semen, frozen-thawed and nonfrozen sperm cells lost to a considerable extent the ability to maintain low intracellular free calcium even in the absence of exogenous calcium; positive Fluo-3 fluorescence was found in 26% and 39% of thawed sperm frozen in SBE- and T350-based freezing diluents, respectively, and increased (P < 0.05) to 67% during nonfrozen storage in SBE and T350 at 24 and 48 hours. Sperm viability measured by exclusion of propidium iodide by flow cytometry was 99% in fresh milt and maintained at 86% (P > 0.05) in SBE after 48 hours of nonfrozen storage but decreased (P < 0.05) to 55.7% after 48 hours in T350. Energy status in terms of ATP content, determined by luciferin-luciferase bioluminescence assay, was higher (P < 0.05) in sperm frozen in SBE than in T350 during the first 5 minutes post-thaw and decreased to essentially zero by 15 minutes post-thaw and did not differ among nonfrozen storage treatments. In conclusion, sperm cells impervious to propidium iodide after frozen or nonfrozen storage were unable to maintain low intracellular calcium content. SBE is a better medium than T350 for frozen or nonfrozen storage of striped bass sperm. The inability to regulate intracellular calcium in striped bass sperm may be associated with poor activation of motility after 4 °C storage and cryopreservation.

Characterization of NAADP-mediated calcium signaling in human spermatozoa

Ca(2+) signaling in spermatozoa plays a crucial role during processes such as capacitation and release of the acrosome, but the underlying molecular mechanisms still remain unclear. Nicotinic acid adenine dinucleotide phosphate (NAADP) is a potent Ca(2+)-releasing second messenger in a variety of cellular processes. The presence of a NAADP synthesizing enzyme in sea urchin sperm has been previously reported, suggesting a possible role of NAADP in sperm Ca(2+) signaling. In this work we used in vitro enzyme assays to show the presence of a novel NAADP synthesizing enzyme in human sperm, and to characterize its sensitivity to Ca(2+) and pH. Ca(2+) fluorescence imaging studies demonstrated that the permeable form of NAADP (NAADP-AM) induces intracellular [Ca(2+)] increases in human sperm even in the absence of extracellular Ca(2+). Using LysoTracker, a fluorescent probe that selectively accumulates in acidic compartments, we identified two such stores in human sperm cells. Their acidic nature was further confirmed by the reduction in staining intensity observed upon inhibition of the endo-lysosomal proton pump with Bafilomycin, or after lysosomal bursting with glycyl-l-phenylalanine-2-naphthylamide. The selective fluorescent NAADP analog, Ned-19, stained the same subcellular regions as LysoTracker, suggesting that these stores are the targets of NAADP action.

IFN-gamma alters the human sperm membrane permeability to Ca(2+)

Inflammation in the male genitourinary tract has been associated with the release of pro-inflammatory cytokines such as interferon-gamma (IFN-γ) and elevated reactive oxygen species, which affects spermatozoa capacitation, motility, and the acrosome reaction, along with functions regulated by the concentration of cytoplasmic Ca(2+) ([Ca(2+)]cyto). Though Ca(2+) signaling is of particular significance in sperm, the effect of IFN-γ intracellular calcium on these cells is still unknown. The present study evaluated the effect of IFN-γ on the [Ca(2+)]cyto and Ca(2+) permeability on human sperm. A cell suspension loaded with fura-2 was incubated with or without IFN-γ (from 0 to 2000 pg/ml) for 0, 30, 60, and 120 minutes, and the [Ca(2+)]cyto was measured. The permeability to Ca(2+) was evaluated by the change of the intracellular concentration following an extracellular Ca(2+) pulse. IFN-γ at low concentrations (≤ 500  pg/ml) did not affect the [Ca(2+)]cyto and Ca(2+) permeability of sperm. At a high concentration (2000  pg/ml), IFN-γ did not alter the [Ca(2+)](cyto), but significantly decreased the magnitude and velocity of Ca(2+) entry into the cell. This effect was dependent on incubation time and IFN-γ concentration. This alteration induced by IFN-γ was prevented by the simultaneous incubation of sperm with the antioxidant butylhydroxytoluene (BHT). In conclusion, in vitro, IFN-γ modifies Ca(2+) sperm membrane permeability, probably via lipid peroxidation. IFN-γ in high concentration, as observed in inflammation/infection, can affect [Ca(2+)](cyto) regulation and alter sperm fertilizing capacity.

p,p'-DDE activates CatSper and compromises human sperm function at environmentally relevant concentrations

STUDY QUESTION

Is the environmental endocrine disruptor p,p′-dichlorodiphenyldichloroethylene (p,p′-DDE) able to induce non-genomic changes in human sperm and consequently affect functional sperm parameters?

SUMMARY ANSWER

p,p′-DDE promoted Ca²⁺ flux into human sperm by activating CatSper channels even at doses found in human reproductive fluids, ultimately compromising sperm parameters important for fertilization.

WHAT IS KNOWN ALREADY

p,p′-DDE may promote non-genomic actions and interact directly with pre-existing signaling pathways, as already observed in other cell types. However, although often found in both male and female reproductive fluids, its effects on human spermatozoa function are not known.

STUDY DESIGN, SIZE, DURATION

Normozoospermic sperm samples from healthy individuals were included in this study. Samples were exposed to several p,p′-DDE concentrations for 3 days at 37°C and 5% CO₂in vitro to mimic the putative continuous exposure to this toxicant in the female reproductive tract in vivo. Shorter p,p′-DDE incubation periods were also performed in order to monitor sperm rapid Ca²⁺ responses. All experiments were repeated on a minimum of five sperm samples from different individuals.

PARTICIPANTS/MATERIALS, SETTING, METHODS

All healthy individuals were recruited at the Biosciences School, University of Birmingham, the Medical Research Institute, University of Dundee and in the Human Reproduction Service at University Hospitals of Coimbra. Intracellular Ca²⁺ concentration ([Ca²⁺]_i) was monitored by imaging single spermatozoa loaded with Oregon Green BAPTA-1AM and further whole-cell patch-clamp recordings were performed to validate our results. Sperm viability and acrosomal integrity were assessed using the LIVE/DEAD sperm vitality kit and the acrosomal content marker PSA-FITC, respectively.

MAIN RESULTS AND THE ROLE OF CHANCE

p,p′-DDE rapidly increased [Ca²⁺]_i (P < 0.05) even at extremely low doses (1 pM and 1 nM), with magnitudes of response up to 200%, without affecting sperm viability, except after 3 days of continuous exposure to the highest concentration tested (P < 0.05). Furthermore, experiments performed in a low Ca²⁺ medium demonstrated that extracellular Ca²⁺ influx was responsible for this Ca²⁺ increase (P < 0.01). Mibefradil and NNC 55-0396, both inhibitors of the sperm-specific CatSper channel, reversed the p,p′-DDE-induced [Ca²⁺]_i rise, suggesting the participation of CatSper in this process (P < 0.05). In fact, whole-cell patch-clamp recordings confirmed CatSper as a target of p,p′-DDE action by monitoring an increase in CatSper currents of >100% (P < 0.01). Finally, acrosomal integrity was adversely affected after 2 days of exposure to p,p′-DDE concentrations, suggesting that [Ca²⁺]_i rise may cause premature acrosome reaction (P < 0.05).

LIMITATIONS, REASONS FOR CAUTION

This is an in vitro study, and caution must be taken when extrapolating the results.

WIDER IMPLICATIONS OF THE FINDINGS

A novel non-genomic p,p′-DDE mechanism specific to sperm is shown in this study. p,p′-DDE was able to induce [Ca²⁺]_i rise in human sperm through the opening of CatSper consequently compromising male fertility. The promiscuous nature of CatSper activation may predispose human sperm to the action of some persistent endocrine disruptors.

STUDY FUNDING/COMPETING INTEREST(S)

The study was supported by both the Portuguese National Science Foundation (FCT; PEst-C/SAU/LA0001/2011) and the UK Wellcome Trust (Grant #86470). SM was supported by the Infertility Research Trust. RST is a recipient of a PhD fellowship from FCT (SFRH/BD/46002/2008). None of the authors has any conflict of interest to declare.

K+ and Cl- channels and transporters in sperm function

To succeed in fertilization, spermatozoa must decode environmental cues which require a set of ion channels. Recent findings have revealed that K(+) and Cl(-) channels participate in some of the main sperm functions. This work reviews the evidence indicating the involvement of K(+) and Cl(-) channels in motility, maturation, and the acrosome reaction, and the advancement in identifying their molecular identity and modes of regulation. Improving our insight on how these channels operate will strengthen our ability to surmount some infertility problems, improve animal breeding, preserve biodiversity, and develop selective and secure male contraceptives.

Non-genomic effects of vitamin D in human spermatozoa

The spectrum for vitamin D (VD) mediated effects has expanded in recent years. Activated VD (1,25(OH)(2)D(3)) binds to the VD receptor (VDR) and mediates non-genomic effects through the alternative ligand binding-pocket (VDR-ap) or regulates gene transcription through the genomic binding-pocket. VDR and VD-metabolizing enzymes are expressed in human testis, male reproductive tract and mature spermatozoa, and VD is considered important for male reproduction. Expression of the VD-inactivating enzyme CYP24A1 at the annulus of human spermatozoa distinguish normal and infertile men with high specificity, and CYP24A1 expression is positively correlated with all semen variables and suggested as a marker for both semen quality and VD responsiveness. Moreover, spermatozoa are transcriptionally silent and are therefore a unique model to study non-genomic effects. 1,25(OH)(2)D(3) induced a rapid increase in intracellular calcium concentration [Ca(2+)](i) in human spermatozoa. The [Ca(2+)](i) increase was abrogated by the non-genomic VDR antagonist 1β,25(OH)(2)D(3), while the specific agonist for VDR-ap (JN) increased [Ca(2+)](i) with similar kinetics as 1,25(OH)(2)D(3). The rise in [Ca(2+)](i) originated as a Ca(2+)-release from intracellular stores since inhibition of phospholipase-C diminished the 1,25(OH)(2)D(3) mediated Ca(2+) response, while suspending spermatozoa in a nominally Ca(2+)-free medium did not affect the VD mediated Ca(2+) rise. The spatio-temporal kinetics of the VD-response differed from the progesterone-mediated increase in [Ca(2+)](i) as the VD-mediated Ca(2+) rise was not observed in the tail region and was independent of extracellular Ca(2+). A functional role of the VD-mediated Ca(2+) increase was supported by showing that 1,25(OH)(2)D(3) increased sperm motility and induced the acrosome reaction in vitro.

Vitamin D metabolism, sex hormones, and male reproductive function

The spectrum of vitamin D (VD)-mediated effects has expanded in recent years, and VD is now recognized as a versatile signaling molecule rather than being solely a regulator of bone health and calcium homeostasis. One of the recently identified target areas of VD is male reproductive function. The VD receptor (VDR) and the VD metabolizing enzyme expression studies documented the presence of this system in the testes, mature spermatozoa, and ejaculatory tract, suggesting that both systemic and local VD metabolism may influence male reproductive function. However, it is still debated which cell is the main VD target in the testis and to what extent VD is important for sex hormone production and function of spermatozoa. This review summarizes descriptive studies on testicular VD metabolism and spatial distribution of VDR and the VD metabolizing enzymes in the mammalian testes and discusses mechanistic and association studies conducted in animals and humans. The reviewed evidence suggests some effects of VD on estrogen and testosterone biosynthesis and implicates involvement of both systemic and local VD metabolism in the regulation of male fertility potential.

Sperm epidermal growth factor receptor (EGFR) mediates α7 acetylcholine receptor (AChR) activation to promote fertilization

To attain fertilization the spermatozoon binds to the egg zona pellucida (ZP) via sperm receptor(s) and undergoes an acrosome reaction (AR). Several sperm receptors have been described in the literature; however, the identity of this receptor is not yet certain. In this study, we suggest that the α7 nicotinic acetylcholine receptor (α7nAChR) might be a sperm receptor activated by ZP to induce epidermal growth factor receptor (EGFR)-mediated AR. We found that isolated ZP or α7 agonists induced the AR in sperm from WT but not α7-null spermatozoa, and the induced AR was inhibited by α7 or EGFR antagonists. Moreover, α7-null sperm showed very little binding to the egg, and microfluidic affinity in vitro assay clearly showed that α7nAChR, as well as EGFR, interacted with ZP3. Induction of EGFR activation and the AR by an α7 agonist was inhibited by a Src family kinase (SFK) inhibitor. In conclusion we suggest that activation of α7 by ZP leads to SFK-dependent EGFR activation, Ca(2+) influx, and the acrosome reaction.

Con A-binding protein Zn-α2-glycoprotein on human sperm membrane is related to acrosome reaction and sperm fertility

Fertilization, the recognition and fusion between spermatozoa and oocyte, involves various molecules on the spermatozoa and oocyte membranes. Concanavalin A (ConA)-binding proteins may be one of the molecules involved in mammal spermatozoa fertilization; however, their structure and function remain largely unknown. Here, we initially identified a ConA-binding protein, Zn-α2-glycoprotein (ZAG), involved in regulating the acrosome reaction (AR) of human spermatozoa. ZAG is localized on the pre-equatorial region covering the acrosome, neck and tail (some parts of middle piece and principal piece respectively) regions of the acrosome intact human spermatozoa, and disappears in the acrosomal region of the acrosome-reacted spermatozoa. Polyclonal antibodies against human recombinant ZAG significantly reduced the AR and sperm capability binding to human zona pellucida or penetration into zona-free hamster oocytes. Furthermore, assessment of the signaling pathways regulated by ZAG revealed that ZAG affects sperm AR through both the cAMP/PKA and PKC pathways. These results indicate that ZAG, which is present on the human sperm membrane, plays a critical role in the AR and subsequently, may be involved in sperm fertility.

Mathematical modeling of calcium signaling during sperm hyperactivation

Mammalian sperm must hyperactivate in order to fertilize oocytes. Hyperactivation is characterized by highly asymmetrical flagellar bending. It serves to move sperm out of the oviductal reservoir and to penetrate viscoelastic fluids, such as the cumulus matrix. It is absolutely required for sperm penetration of the oocyte zona pellucida. In order for sperm to hyperactivate, cytoplasmic Ca(2+) levels in the flagellum must increase. The major mechanism for providing Ca(2+) to the flagellum, at least in mice, are CatSper channels in the plasma membrane of the principal piece of the flagellum, because sperm from CatSper null males are unable to hyperactivate. There is some evidence for the existence of other types of Ca(2+) channels in sperm, but their roles in hyperactivation have not been clearly established. Another Ca(2+) source for hyperactivation is the store in the redundant nuclear envelope of sperm. To stabilize levels of cytoplasmic Ca(2+), sperm contain Ca(2+) ATPase and exchangers. The interactions between channels, Ca(2+) ATPases, and exchangers are poorly understood; however, mathematical modeling can help to elucidate how they work together to produce the patterns of changes in Ca(2+) levels that have been observed in sperm. Mathematical models can reveal interesting and unexpected relationships, suggesting experiments to be performed in the laboratory. Mathematical analysis of Ca(2+) dynamics has been used to develop a model for Ca(2+) clearance and for CatSper-mediated Ca(2+) dynamics. Models may also be used to understand how Ca(2+) patterns produce flagellar bending patterns of sperm in fluids of low and high viscosity and elasticity.

Chemosensory Ca2+ dynamics correlate with diverse behavioral phenotypes in human sperm

In the female reproductive tract, mammalian sperm undergo a regulated sequence of prefusion changes that "prime" sperm for fertilization. Among the least understood of these complex processes are the molecular mechanisms that underlie sperm guidance by environmental chemical cues. A "hard-wired" Ca(2+) signaling strategy that orchestrates specific motility patterns according to given functional requirements is an emerging concept for regulation of sperm swimming behavior. The molecular players involved, the spatiotemporal characteristics of such motility-associated Ca(2+) dynamics, and the relation between a distinct Ca(2+) signaling pattern and a behavioral sperm phenotype, however, remain largely unclear. Here, we report the functional characterization of two human sperm chemoreceptors. Using complementary molecular, physiological, and behavioral approaches, we comparatively describe sperm Ca(2+) responses to specific agonists of these novel receptors and bourgeonal, a known sperm chemoattractant. We further show that individual receptor activation induces specific Ca(2+) signaling patterns with unique spatiotemporal dynamics. These distinct Ca(2+) dynamics are correlated to a set of stimulus-specific stereotyped behavioral responses that could play vital roles during various stages of prefusion sperm-egg chemical communication.