Intracellular calcium increases with hyperactivation in intact, moving hamster sperm and oscillates with the flagellar beat cycle

Intracellular domain of CATSPER1 could serve as a cytoplasmic platform for redox processes in mammalian sperm

OBJECTIVE

Mammalian sperm acquire fertilizing ability in the female reproductive tract and develop hyperactivated motility, which is indispensable for male fertility. Hyperactivated motility is initiated by Ca2+ influx via the sperm-specific ion channel, CatSper. CATSPER1, a CatSper pore subunit, possesses a long N-terminal intracellular domain and its degradation correlates with unsuccessful sperm migration in the female tract. However, the cellular function and molecular significance of the CATSPER1 N-terminal domain are not well understood. Here, we identify the interactome of the CATSPER1 N-terminal domain and propose a function for the intracellular domain in mammalian sperm.

METHODS

To identify CATSPER1 N-terminus interactome, we produced recombinant CATSPER1-N-terminus in bacterial system. The purified protein was incubated with testicular lysates and eluted together with testicular interacting proteins. The elutes were subjected to proteomic analysis and CATSPER1-N-terminus interactome was profiled. Identified proteins were further analyzed by functional annotation.

RESULTS

We purified the partial CATSPER1 N-terminal domain and identified 57 testicular proteins as domain interactomes using mass spectrometry analysis. Functional annotation analysis revealed that 106 gene ontologies were significantly enriched, 16 of which were related to redox processes. We found that antioxidant enzymes, such as PARK7 and PRDX2, 4, and 6, were included in the enriched redox-related gene ontologies.

CONCLUSION

These results suggest that the CATSPER1 N-terminus could function in defending against oxidative stress to support the successful migration of mammalian sperm to fertilizing sites in the female reproductive tract.

Boar Sperm Motility Assessment Using Computer-Assisted Sperm Analysis: Current Practices, Limitations, and Methodological Challenges

Spermatozoa are highly specialized male cells that are characterized by a unique ability to move, which is a critical factor for successful fertilization. The relative simplicity of motility assessment, especially in livestock, has made it a widely used parameter for evaluating ejaculate quality or cryopreserved semen in the clinical field, and an advanced tool in reproductive physiology and toxicology research. Technological advances in image analysis and computational methods have substantially increased its accuracy through the use of computer-assisted sperm analysis (CASA) to minimize subjective bias in motility assessments. Nevertheless, this more objective method still presents some significant challenges, including variability in the sample preparation, imaging conditions, and analytical parameters. These issues contribute to inconsistency and impair the reproducibility and comparability of data between laboratories. The implementation of standardized protocols, combined with comprehensive training and rigorous evaluation, can serve to mitigate some of the emerging inconsistencies. In addition, the in vitro conditions under which CASA analyses are performed often differ significantly from the natural environment of the female reproductive tract in vivo. This review discusses the methodologies, critical issues, and limitations of sperm motility analyses using CASA, with a particular focus on the boar as an important agricultural and biomedical model species in which this system is widely used.

Manipulation of metabolism to improve liquid preservation of mammalian spermatozoa

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

CABS1 Is Essential for Progressive Motility and the Integrity of Fibrous Sheath in Mouse Epididymal Spermatozoa

The calcium-binding protein spermatid-associated 1 (CABS1) localizes to the principal piece of mature sperm flagella. Deletion of CABS1 results in subfertility in male mice, possibly due to an impaired annulus in the sperm flagella. However, it is unknown whether there are other mechanisms by which CABS1 affects male fertility. Our current investigation has uncovered that CABS1 is located in the midsection of the flagellum in testicular sperm and the principal piece in epididymal sperm. Moreover, male mice lacking CABS1 exhibit a defect in the progressive motility of sperm. Furthermore, the regulation of calcium levels, which has been reported to have a significant impact on sperm motility, capacitation, and the acrosome reaction, is also affected when sperm are exposed to alkalized high-salt buffer (pH 8.0) and progesterone (100 μM) in Cabs1-null spermatozoa. This alteration in calcium response may contribute to changes in the phosphorylation of PKA substrates and subsequent phosphorylation of tyrosine residues. Additionally, the absence of CABS1 leads to a defective fibrous sheath and abnormal configuration of doublet microtubules in post-testicular sperm. These findings indicate that the absence of CABS1 also disrupts the structural integrity of the fibrous sheath, resulting in male subfertility. The highly conserved nature of CABS1 in humans suggests that it could potentially be a contributing factor to asthenozoospermia in men.

Sperm hyperactivation and the CatSper channel: current understanding and future contribution of domestic animals

In female tract, mammalian sperm develop hyperactivated motility which is a key physiological event for sperm to fertilize eggs. This motility change is triggered by Ca2+ influx via the sperm-specific Ca2+ channel, CatSper. Although previous studies in human and mice largely contributed to understanding CatSper and Ca2+ signaling for sperm hyperactivation, the differences on their activation mechanisms are not well understood yet. There are several studies to examine expression and significance of the CatSper channel in non-human and non-mouse models, such as domestic animals. In this review, I summarize key knowledge for the CatSper channel from previous studies and propose future aspects for CatSper study using sperm from domestic animals.

Ca2+ homeostasis and male fertility: a target for a new male contraceptive system

Ca2+ is a key secondary messenger that determines sperm motility patterns. Mammalian sperm undergo capacitation, a process to acquire fertilizing ability, in the female reproductive tract. Capacitated sperm change their flagellar waveform to develop hyperactivated motility, which is crucial for successful sperm navigation to the eggs and fertilization. The sperm-specific channel, CATSPER, and an ATPase transporter, PMCA4, serve as major paths for Ca2+ influx and efflux, respectively, in sperm. The ionic paths coordinate Ca2+ homeostasis in the sperm, and their loss-of-function impairs sperm motility, to cause male infertility. In this review, we summarize the physiological significance of these two Ca2+ gates and suggest their potential applications in novel male contraceptives.

Analysis of Ca2+-mediated sperm motility to evaluate the functional normality of the sperm-specific Ca2+ channel, CatSper

Ca2+ is a key secondary messenger that modulates sperm motility by tuning flagellar movement in various species. The sperm-specific Ca2+ channel, CatSper, is a primary Ca2+ gate that is essential for male fertility in mammals. CatSper-mediated Ca2+ signaling enables sperm to develop hyperactivated motility and fertilize the eggs in the female tract. Therefore, altered CatSper function compromises the entry of Ca2+ into the sperm, followed by impairing hyperactivation and male fertility. However, methods to evaluate the function of the CatSper channel are limited to patch clamping and functional imaging using Ca2+ dye. Previous studies have revealed that various parameters for sperm motility are highly correlated with intracellular Ca2+ levels in mouse. Here, I cover a step-by-step protocol to analyze the change in Ca2+-mediated sperm motility by using computer-assisted semen analysis (CASA) to evaluate the functional normality of the CatSper channel in sperm. This approach analyzes sperm motility parameters during intracellular Ca2+ chelation followed by in vitro capacitation to recover intracellular Ca2+ via the activated CatSper channel. Thus, this Ca2+-handling method is handy and could be broadly applied in reproductive biology labs and clinics that have CASA equipment to examine the functional normality of the CatSper channel.

Identification of differentially expressed genes in human testis biopsies with defective spermatogenesis

Purpose

Sperm morphology and motility are major contributors to male-factor infertility, with many genes predicted to be involved. This study aimed to elucidate differentially expressed transcripts in human testis tissues of normal and abnormal spermatogenesis that could reveal new genes that may regulate sperm morphology and function.

Methods

Human testis biopsies were collected from men with well-characterized phenotypes of normal spermatogenesis, spermatid arrest, and Sertoli cell-only phenotype, and transcriptional differences were quantified by RNA-sequencing (RNA-Seq). Differentially expressed genes (DEGs) were filtered based on predominant expression in spermatids and gene functional annotations relevant to sperm morphology and motility. Selected 10 DEGs were validated by qRT-PCR and the localization of two proteins was determined in testis biopsies.

Results

The analysis revealed 6 genes (SPATA31E1, TEKT3, SLC9C1, PDE4A, CFAP47, and TNC) that are excellent candidates for novel genes enriched in developing human sperm. The immunohistochemical localization of two proteins, ORAI1 and SPATA31E1, in testis biopsies, verified that both are expressed in developing human germ cells, with SPATA31E1 enriched in late spermatocytes and spermatids.

Conclusion

This study identified human germ cell-enriched genes that could play functional roles in spermiogenesis and could thus be important in the development of morphologically normal, motile sperm.

Molecular mechanisms of mammalian sperm capacitation, and its regulation by sodium-dependent secondary active transporters

Background

Mammalian spermatozoa have to be "capacitated" to be fertilization-competent. Capacitation is a collective term for the physiological and biochemical changes in spermatozoa that occur within the female body. However, the regulatory mechanisms underlying capacitation have not been fully elucidated.

Methods

Previously published papers on capacitation, especially from the perspective of ions/channels/transporters, were extracted and summarized.

Results

Capacitation can be divided into two processes: earlier events (membrane potential hyperpolarization, intracellular pH rise, intracellular Ca2+ rise, etc.) and two major later events: hyperactivation and the acrosome reaction. Earlier events are closely interconnected with each other. Various channels/transporters are involved in the regulation of them, which ultimately lead to the later events. Manipulating the extracellular K+ concentration based on the oviductal concentration modifies membrane potential; however, the later events and fertilization are not affected, suggesting the uninvolvement of membrane potential in capacitation. Hyperpolarization is a highly conserved phenomenon among mammalian species, indicating its importance in capacitation. Therefore, the physiological importance of hyperpolarization apart from membrane potential is suggested.

Conclusion

The hypotheses are (1) hyperpolarizing Na+ dynamics (decrease in intracellular Na+) and Na+-driven secondary active transporters play a vital role in capacitation and (2) the sperm-specific potassium channel Slo3 is involved in volume and/or morphological regulation.

A CUG-initiated CATSPERθ functions in the CatSper channel assembly and serves as a checkpoint for flagellar trafficking

Calcium signaling is critical for successful fertilization. In spermatozoa, calcium influx into the sperm flagella mediated by the sperm-specific CatSper calcium channel is necessary for hyperactivated motility and male fertility. CatSper is a macromolecular complex and is repeatedly arranged in zigzag rows within four linear nanodomains along the sperm flagella. Here, we report that the Tmem249-encoded transmembrane (TM) domain-containing protein, CATSPERθ is essential for the CatSper channel assembly during sperm tail formation. CATSPERθ facilitates the channel assembly by serving as a scaffold for a pore-forming subunit CATSPER4. CATSPERθ is specifically localized at the interface of a CatSper dimer and can self-interact, suggesting its potential role in CatSper dimer formation. Male mice lacking CATSPERθ are infertile because the sperm lack the entire CatSper channel from sperm flagella, rendering sperm unable to hyperactivate, regardless of their normal expression in the testis. In contrast, genetic abrogation of any of the other CatSper TM subunits results in loss of CATSPERθ protein in the spermatid cells during spermatogenesis. CATSPERθ might act as a checkpoint for the properly assembled CatSper channel complex to traffic to sperm flagella. This study provides insights into the CatSper channel assembly and elucidates the physiological role of CATSPERθ in sperm motility and male fertility.

Hamster Sperm Possess Functional Na+/Ca2+-Exchanger 1: Its Implication in Hyperactivation

Previous studies demonstrated that hamster sperm hyperactivation is suppressed by extracellular Na⁺ by lowering intracellular Ca²⁺ levels, and Na⁺/Ca²⁺-exchanger (NCX) specific inhibitors canceled the suppressive effects of extracellular Na⁺. These results suggest the involvement of NCX in the regulation of hyperactivation. However, direct evidence of the presence and functionality of NCX in hamster spermatozoa is still lacking. This study aimed to reveal that NCX is present and is functional in hamster spermatozoa. First, NCX1 and NCX2 transcripts were detected via RNA-seq analyses of hamster testis mRNAs, but only the NCX1 protein was detected. Next, NCX activity was determined by measuring the Na⁺-dependent Ca²⁺ influx using the Ca²⁺ indicator Fura-2. The Na⁺-dependent Ca²⁺ influx was detected in hamster spermatozoa, notably in the tail region. The Na⁺-dependent Ca²⁺ influx was inhibited by the NCX inhibitor SEA0400 at NCX1-specific concentrations. NCX1 activity was reduced after 3 h of incubation in capacitating conditions. These results, together with authors' previous study, showed that hamster spermatozoa possesses functional NCX1 and that its activity was downregulated upon capacitation to trigger hyperactivation. This is the first study to successfully reveal the presence of NCX1 and its physiological function as a hyperactivation brake.

CatSper Calcium Channels: 20 Years On

The flagellar-specific Ca2+ channel CatSper is the predominant Ca2+ entry site in mammalian sperm. CatSper-mediated Ca2+ signaling affects nearly every event that regulates sperm to acquire fertilizing capability. In this review, we summarize some of the main findings from 20 years of CatSper research and highlight recent progress and prospects.

A CUG-initiated CATSPERθ functions in the CatSper channel assembly and serves as a checkpoint for flagellar trafficking

Calcium signaling is critical for successful fertilization. In spermatozoa, calcium influx into the sperm flagella mediated by the sperm specific CatSper calcium channel is necessary for hyperactivated motility and male fertility. CatSper is a macromolecular complex and is repeatedly arranged in zigzag rows within four linear nanodomains along the sperm flagella. Here, we report that the Tmem249 -encoded transmembrane domain containing protein, CATSPERθ, is essential for the CatSper channel assembly during sperm tail formation. CATSPERθ facilitates the channel assembly by serving as a scaffold for a pore forming subunit CATSPER4. CATSPERθ is specifically localized at the interface of a CatSper dimer and can self-interact, suggesting its potential role in CatSper dimer formation. Male mice lacking CATSPERθ are infertile because the sperm lack the entire CatSper channel from sperm flagella, rendering sperm unable to hyperactivate, regardless of their normal expression in the testis. In contrast, genetic abrogation of any of the other CatSper transmembrane subunits results in loss of CATSPERθ protein in the spermatid cells during spermatogenesis. CATSPERθ might acts as a checkpoint for the properly assembled CatSper channel complex to traffic to sperm flagella. This study provides insights into the CatSper channel assembly and elucidates the physiological role of CATSPERθ in sperm motility and male fertility.

Antioxidant additive melatonin in tris-based egg yolk extender improves post-thaw sperm attributes in Hariana bull

In the study, melatonin, a known antioxidant pineal peptide was used as an additive in the tris-egg yolk glycerol-based semen extender in Hariana bull semen and post-thaw sperm characters were evaluated. In the study, Group I was a control without melatonin; and Group II, III, and IV were having 0.5 mM, 1 mM, and 2 mM melatonin/80 × 10⁶ spermatozoa, respectively were treatment groups. Thirty-two semen ejaculates from 4 Hariana bulls were processed for freezing and post-thaw sperm characteristics were evaluated. Sperm motility, velocity, the viability with intact membrane, and total antioxidant capacity were markedly (P < 0.05) improved in Group IV compared to all other groups. The lipid peroxidation and total protein carbonylation were substantially (P < 0.05) decreased in Group IV compared to all other groups. The population of cryocapacitated, acrosome-reacted, and apoptotic-like spermatozoa were significantly (P < 0.05) decreased in Group IV. Further, the relative band intensity of 74 kDa protein and percent of spermatozoa showing positive immune reactivity to tyrosine-phosphorylated proteins was decreased in Group IV. The progesterone-receptor ligand binding, in vitro capacitation response, and Vanguard distance were markedly (P < 0.05) improved in Group IV. In summary- Group IV having 2 mM melatonin was found to be optimal in providing cryoprotective effects to Hariana bull spermatozoa after freezing-thawing and can be suitably used as a semen additive during semen cryopreservation.

Motility Assessment of Ram Spermatozoa

For successful fertilisation to occur, spermatozoa need to successfully migrate through the female reproductive tract and penetrate the oocyte. Predictably, poor sperm motility has been associated with low rates of fertilisation in many mammalian species, including the ram. As such, motility is one of the most important parameters used for in vitro evaluation of ram sperm quality and function. This review aims to outline the mechanical and energetic processes which underpin sperm motility, describe changes in motility which occur as a result of differences in sperm structure and the surrounding microenvironment, and assess the effectiveness of the various methods used to assess sperm motility in rams. Methods of subjective motility estimation are convenient, inexpensive methods widely used in the livestock industries, however, the subjective nature of these methods can make them unreliable. Computer-assisted sperm analysis (CASA) technology accurately and objectively measures sperm motility via two-dimensional tracing of sperm head motion, making it a popular method for sperm quality assurance in domesticated animal production laboratories. Newly developed methods of motility assessment including flagellar tracing, three-dimensional sperm tracing, in vivo motility assessment, and molecular assays which quantify motility-associated biomarkers, enable analysis of a new range of sperm motion parameters with the potential to reveal new mechanistic insights and improve ram semen assessment. Experimental application of these technologies is required to fully understand their potential to improve semen quality assessment and prediction of reproductive success in ovine artificial breeding programs.

Understanding sperm motility mechanisms and the implication of sperm surface molecules in promoting motility

Background

It is estimated that approximately 8–12% of couples globally face problems associated with infertility. A large number of men exhibit suboptimal sperm parameters. Sperm motility is one of the factors that is measured when analysing sperm parameters. The indication of several crucial sperm surface molecules, having the ability to modulate motility, has opened new avenues in understanding the complex processes involved in motility.

Main body of the abstract

There are various mechanisms that regulate and enhance sperm motility. Several surface molecules on sperm cells can also regulate motility, thus showing their possible application as a treatment for infertility caused by impaired motility. Sperm motility is regulated by intracellular and extracellular pH, along with calcium ions (Ca2+) and carbonate ion (HCO3−) concentrations. Moreover, sperm cells have an array of surface proteins which play a critical role in their function and motility. The indication of surface molecules presented new opportunities for understanding sperm motility and the possibility of treating infertility caused by impaired sperm function. Infertility and problems associated with conception can cause underlying stress and mental trauma. Although there are several methods for treating infertility, most are complex, invasive, and expensive.

Conclusion

It is important to understand how surface molecules and proteins on the sperm cell regulate motility. This will enable us to treat anomalies associated with proper sperm function. This review highlights the general mechanisms that regulate sperm motility, and it stresses the importance and relevance of sperm surface molecules in regulating sperm motility.

C2cd6-encoded CatSperτ targets sperm calcium channel to Ca2+ signaling domains in the flagellar membrane

In mammalian sperm cells, regulation of spatiotemporal Ca2+ signaling relies on the quadrilinear Ca2+ signaling nanodomains in the flagellar membrane. The sperm-specific, multi-subunit CatSper Ca2+ channel, which is crucial for sperm hyperactivated motility and male fertility, organizes the nanodomains. Here, we report CatSperτ, the C2cd6-encoded membrane-associating C2 domain protein, can independently migrate to the flagella and serve as a major targeting component of the CatSper channel complex. CatSperτ loss of function in mice demonstrates that it is essential for sperm hyperactivated motility and male fertility. CatSperτ targets the CatSper channel into the quadrilinear nanodomains in the flagella of developing spermatids, whereas it is dispensable for functional channel assembly. CatSperτ interacts with ciliary trafficking machinery in a C2-dependent manner. These findings provide insights into the CatSper channel trafficking to the Ca2+ signaling nanodomains and the shared molecular mechanisms of ciliary and flagellar membrane targeting.

Conserved Mechanism of Bicarbonate-Induced Sensitization of CatSper Channels in Human and Mouse Sperm

To fertilize an egg, mammalian sperm must undergo capacitation in the female genital tract. A key contributor to capacitation is the calcium (Ca²⁺) channel CatSper, which is activated by membrane depolarization and intracellular alkalinization. In mouse epididymal sperm, membrane depolarization by exposure to high KCl triggers Ca²⁺ entry through CatSper only in alkaline conditions (pH 8.6) or after in vitro incubation with bicarbonate (HCO₃^–) and bovine serum albumin (capacitating conditions). However, in ejaculated human sperm, membrane depolarization triggers Ca²⁺ entry through CatSper in non-capacitating conditions and at lower pH (< pH 7.4) than is required in mouse sperm. Here, we aimed to determine the mechanism(s) by which CatSper is activated in mouse and human sperm. We exposed ejaculated mouse and human sperm to high KCl to depolarize the membrane and found that intracellular Ca²⁺ concentration increased at pH 7.4 in sperm from both species. Conversely, intracellular Ca²⁺ concentration did not increase under these conditions in mouse epididymal or human epididymal sperm. Furthermore, pre-incubation with HCO₃^– triggered an intracellular Ca²⁺ concentration increase in response to KCl in human epididymal sperm. Treatment with protein kinase A (PKA) inhibitors during exposure to HCO₃^– inhibited Ca²⁺ concentration increases in mouse epididymal sperm and in both mouse and human ejaculated sperm. Finally, we show that soluble adenylyl cyclase and increased intracellular pH are required for the intracellular Ca²⁺ concentration increase in both human and mouse sperm. In summary, our results suggest that a conserved mechanism of activation of CatSper channels is present in both human and mouse sperm. In this mechanism, HCO₃^– in semen activates the soluble adenylyl cyclase/protein kinase A pathway, which leads to increased intracellular pH and sensitizes CatSper channels to respond to membrane depolarization to allow Ca²⁺ influx. This indirect mechanism of CatSper sensitization might be an early event capacitation that occurs as soon as the sperm contact the semen.

Role of calcium oscillations in sperm physiology

Intracellular Ca²⁺ is a key regulator of cell signaling and sperm are not the exception. Cells often use cytoplasmic Ca²⁺ concentration ([Ca²⁺]_i) oscillations as a means to decodify external and internal information. [Ca²⁺]_i oscillations faster than those usually found in other cells and correlated with flagellar beat were the first to be described in sperm in 1993 by Susan Suarez, in the boar. More than 20 years passed before similar [Ca²⁺]_i oscillations were documented in human sperm, simultaneously examining their flagellar beat in three dimensions by Corkidi et al. 2017. On the other hand, 10 years after the discovery of the fast boar [Ca²⁺]_i oscillations, slower ones triggered by compounds from the egg external envelope were found to regulate cell motility and chemotaxis in sperm from marine organisms. Today it is known that sperm display fast and slow spontaneous and agonist triggered [Ca²⁺]_i oscillations. In mammalian sperm these Ca²⁺ transients may act like a multifaceted tool that regulates fundamental functions such as motility and acrosome reaction. This review covers the main sperm species and experimental conditions where [Ca²⁺]_i oscillations have been described and discusses what is known about the transporters involved, their regulation and the physiological purpose of these oscillations. There is a lot to be learned regarding the origin, regulation and physiological relevance of these Ca²⁺ oscillations.

Implications of cryopreservation on structural and functional attributes of bovine spermatozoa: An overview

Sperm cryopreservation is an important adjunct to assisted reproduction techniques (ART) for improving the reproductive efficiency of dairy cattle and buffaloes. Improved understanding of mechanisms and challenges of bovine semen cryopreservation is vital for artificial insemination on a commercial basis. Although cryopreservation of bovine spermatozoa is widely practiced and advanced beyond that of other species, there are still major gaps in the knowledge and technology. Upon cryopreservation, disruption of spermatozoal plasma membrane configuration due to alterations in metabolic pathways, enzymes and antioxidants activity add to lower efficiency with loss of sperm longevity and fertilising ability. Therefore, the effective amalgamation of cryo-variables like ambient temperature, cooling and thawing rates, nucleation temperature, type and concentration of the cryoprotectant, seminal plasma composition, free radicals and antioxidant status are required to optimise cryopreservation. Novel strategies like supplementation of cholesterol-loaded cyclodextrins (CLC), nanovesicles, osteopontin, antioxidants, etc., in an extender and recent techniques like nano-purification and modified packaging have to be optimised to ameliorate the cryodamage. This article is intended to describe the basic facts about the sperm cryopreservation process in bovine and the associated biochemical, biophysical, ultra-structural, molecular and functional alterations.

Synergistic effect of royal jelly in combination with glycerol and dimethyl sulfoxide on cryoprotection of Romanov ram sperm

Sperm fertility decreases significantly after freezing. Providing a suitable and useful diluent compound for freezing ram sperm can increase the efficiency of artificial insemination and consequently, the reproductive performance of sheep. Various biological properties such as antibacterial, anti-cancer, immunosuppressive, antioxidant and reproductive properties of royal jelly (RJ) are well known. The aim of this study was to investigate the possible synergistic effect of royal jelly in combination with glycerol and dimethyl sulfoxide (DMSO) in sperm cryopreservation extender of Romanov ram. The pooled semen samples from 5 Romanov rams were allocated into 3 experiments. The effect of 6% DMSO, 6% glycerol and a combination of 3% DMSO +3% glycerol co-supplemented with 1, 2 and 3% RJ was evaluated in 3 experiments. Samples were frozen by conventional slow freezing method and post-thaw parameters of total motility, progressive motility, plasma membrane integrity, DNA damage, apoptosis, enzyme activity of superoxide dismutase (SOD) and glutathione peroxidase (GPx), total antioxidant capacity (TAC) and malondialdehyde (MDA) were evaluated. The results showed that the percentage of motility, progressive motility, TAC, GPx, SOD and all sperm kinematic parameters except LIN in the group containing 2% RJ + 6% DMSO was higher than the control group (p < 0.05). Some parameters such as progressive motility, sperm membrane integrity, TAC, GPx, VAP, VCL, STR and SRT in the group containing 2% RJ + 6% DMSO were more than (p < 0.05) in the sperm group containing 1% RJ + 6% DMSO. MDA values in sperm groups containing 2% RJ + 6% DMSO were significantly (p < 0.05) lower than the sperm containing 1% royal jelly and the control group. In the sperm group containing 2% RJ + 6% glycerol, sperm membrane integrity, TAC, GPx, SOD, progressive motility and all sperm kinematic parameters except VAP were higher and MDA values and sperm abnormalities were lower than the control group (p < 0.05). The sperm group containing 1% RJ and 3% DMSO +3% glycerol had higher motility, progressive motility, membrane integrity, and all sperm kinematic parameters except VSL; and lower sperm abnormalities, DNA damage, apoptosis and MDA than the control group (p < 0.05). As a general conclusion of this study, the addition of 2% RJ + 3% DMSO and 3% glycerol to the freezing extender improved microscopic and biochemical ram sperm parameters after the freeze-thaw process. Hence, moderate concentrations of royal jelly (2%) are sufficient to protect sperm from freezing damage, and high (3%) and low (1%) concentrations do not have a good cryoprotective effect.

Caffeine induces sperm detachment from sperm head-to-head agglutination in bull

Sperm head-to-head agglutination is a well-known known phenomenon in mammalian and non-mammalian species. Although several factors have been reported to induce sperm agglutination, information on the trigger and process of sperm detachment from the agglutination is scarce. Since hyperactivated motility is involved in bovine sperm detachment from the oviduct, we focused on caffeine, a well-known hyperactivation inducer, and aimed to determine the role of caffeine in sperm detachment from agglutination. Agglutination rate of bovine sperm was significantly decreased upon incubation with caffeine following pre-incubation without caffeine. Additionally, we observed that bovine sperm were detached from agglutination only when the medium contained caffeine. The detached sperm showed more asymmetrical flagellar beating compared to the undetached motile sperm, regardless of whether before or after the detachment. Intriguingly, some sperm that detached from agglutination re-agglutinated with different sperm agglutination. These findings indicated caffeine as a trigger for sperm detachment from the agglutination in bull. Furthermore, another well-known hyperactivation inducer, thimerosal, also significantly reduced the sperm agglutination rate. Overall, the study demonstrated the complete process of sperm detachment from sperm head-to-head agglutination and proposed that hyperactivated motility facilitates sperm detachment from another sperm. These findings would provide a better understanding of sperm physiology and fertilization process in mammals.

Caffeine increased progressive motility of human spermatozoa in normozoospermic and asthenozoospermic semen samples and enhanced activity of seminal creatine kinase

Even though the effect of caffeine on humans' health has been revealed in various research studies, its effect on semen quality has yet to be well explained. Here, we measured the effect of caffeine at 1, 5, 10 and 20 mM on motility of human spermatozoa in normozoospermic and asthenozoospermic semen samples, level of seminal nitric oxide, chelation of seminal calcium ions and activity of seminal creatine kinase. Fifty-one normozoospermic and ten asthenozoospermic semen samples were recruited in this study. Sperm motility was evaluated by Makler counter, and seminal nitric oxide, seminal-free calcium and activity of seminal creatine kinase were measured spectrophotometrically. Caffeine at 10 mM significantly (p < .05) increased progressive motility of spermatozoa in both tested groups. Also, caffeine significantly increased (p < .05) activity of creatine kinase and insignificantly (p > .05) altered nitric oxide and free calcium levels in seminal plasma. In conclusion, progressive motility of human spermatozoa was found to be higher in the presence of caffeine at 10 mM in normozoospermic and asthenozoospermic semen samples; this increase, albeit partially, could be due to increased activity of seminal creatine kinase, but not to increased production of nitric oxide or chelation of free calcium ions.

Sperm ion channels and transporters in male fertility and infertility

Mammalian sperm cells must respond to cues originating from along the female reproductive tract and from the layers of the egg in order to complete their fertilization journey. Dynamic regulation of ion signalling is, therefore, essential for sperm cells to adapt to their constantly changing environment. Over the past 15 years, direct electrophysiological recordings together with genetically modified mouse models and human genetics have confirmed the importance of ion channels, including the principal Ca²⁺-selective plasma membrane ion channel CatSper, for sperm activity. Sperm ion channels and membrane receptors are attractive targets for both the development of contraceptives and infertility treatment drugs. Furthermore, in this era of assisted reproductive technologies, understanding the signalling processes implicated in defective sperm function, particularly those arising from genetic abnormalities, is of the utmost importance not only for the development of infertility treatments but also to assess the overall health of a patient and his children. Future studies to improve reproductive health care and overall health care as a function of the ability to reproduce should include identification and analyses of gene variants that underlie human infertility and research into fertility-related molecules.

The Role of Zinc in Male Fertility

Several studies proposed the importance of zinc ion in male fertility. Here, we describe the properties, roles and cellular mechanisms of action of Zn²⁺ in spermatozoa, focusing on its involvement in sperm motility, capacitation and acrosomal exocytosis, three functions that are crucial for successful fertilization. The impact of zinc supplementation on assisted fertilization techniques is also described. The impact of zinc on sperm motility has been investigated in many vertebrate and invertebrate species. It has been reported that Zn²⁺ in human seminal plasma decreases sperm motility and that Zn²⁺ removal enhances motility. Reduction in the intracellular concentration of Zn²⁺ during epididymal transit allows the development of progressive motility and the subsequent hyper activated motility during sperm capacitation. Extracellular Zn²⁺ affects intracellular signaling pathways through its interaction with the Zn²⁺ sensing receptor (ZnR), also named GPR39. This receptor was found in the sperm tail and the acrosome, suggesting the possible involvement of Zn²⁺ in sperm motility and acrosomal exocytosis. Our studies showed that Zn²⁺ stimulates bovine sperm acrosomal exocytosis, as well as human sperm hyper-activated motility, were both mediated by GPR39. Zn²⁺ binds and activates GPR39, which activates the trans-membrane-adenylyl-cyclase (tmAC) to catalyze cAMP production. The NHE (Na⁺/H⁺-exchanger) is activated by cAMP, leading in increased pHi and activation of the sperm-specific Ca²⁺ channel CatSper, resulting in an increase in [Ca²⁺]_i, which, together with HCO₃⁻, activates the soluble adenylyl-cyclase (sAC). The increase in [cAMP]_i activates protein kinase A (PKA), followed by activation of the Src-epidermal growth factor receptor-Pphospholipase C (Src-EGFR-PLC) cascade, resulting in inositol-triphosphate (IP₃) production, which mobilizes Ca²⁺ from the acrosome, causing a further increase in [Ca²⁺]_i and the development of hyper-activated motility. PKA also activates phospholipase D1 (PLD1), leading to F-actin formation during capacitation. Prior to the acrosomal exocytosis, PLC induces phosphadidylinositol-4,5-bisphosphate (PIP₂) hydrolysis, leading to the release of the actin-severing protein gelsolin to the cytosol, which is activated by Ca²⁺, resulting in F-actin breakdown and the occurrence of acrosomal exocytosis.

Ca2+ signaling in mammalian spermatozoa

Calcium is an essential ion which regulates sperm motility, capacitation and the acrosome reaction (AR), three processes necessary for successful fertilization. The AR enables the spermatozoon to penetrate into the egg. In order to undergo the AR, the spermatozoon must reside in the female reproductive tract for several hours, during which a series of biochemical transformations takes place, collectively called capacitation. An early event in capacitation is relatively small elevation of intracellular Ca²⁺ (in the nM range) and bicarbonate, which collectively activate the soluble adenylyl cyclase to produce cyclic-AMP; c-AMP activates protein kinase A (PKA), leading to indirect tyrosine phosphorylation of proteins. During capacitation, there is an increase in the membrane-bound phospholipase C (PLC) which is activated prior to the AR by relatively high increase in intracellular Ca²⁺ (in the μM range). PLC catalyzes the hydrolysis of phosphatidyl-inositol-4,5-bisphosphate (PIP₂) to diacylglycerol and inositol-trisphosphate (IP₃), leading to activation of protein kinase C (PKC) and the IP₃-receptor. PKC activates a Ca²⁺- channel in the plasma membrane, and IP₃ activates the Ca²⁺- channel in the outer acrosomal membrane, leading to Ca²⁺ depletion from the acrosome. As a result, the plasma-membrane store-operated Ca²⁺ channel (SOCC) is activated to increase cytosolic Ca²⁺ concentration, enabling completion of the acrosome reaction. The hydrolysis of PIP₂ by PLC results in the release and activation of PIP₂-bound gelsolin, leading to F-actin dispersion, an essential step prior to the AR. Ca²⁺ is also involved in the regulation of sperm motility. During capacitation, the sperm develops a unique motility pattern called hyper-activated motility (HAM) which is essential for successful fertilization. The main Ca²⁺-channel that mediates HAM is the sperm-specific CatSper located in the sperm tail.

Na+/K+-ATPase α4 regulates sperm hyperactivation while Na+/K+-ATPase α1 regulates basal motility in hamster spermatozoa

Recently, it was reported that hamster sperm hyperactivation is regulated by extracellular Na⁺. Two types of catalytic Na⁺/K⁺-ATPase (NKA) α subunits (α1 and α4) are present in spermatozoa. In this work, the contribution of these NKA subunits to the regulation of hamster sperm hyperactivation was investigated using the specific inhibitor ouabain. When 10^-6 M ouabain was added to the modified Tyrode's albumin lactate pyruvate medium (mTALP) medium, hyperactivation was significantly inhibited, whereas 10^-5-10^-4 M ouabain was needed to significantly reduce the amount of motile spermatozoa. When a more detailed analysis of flagellar movement was performed, 10^-6 M ouabain suppressed the hyperactivation-associated change in the patterns of flagellar motion without affecting the sliding velocity of microtubules. Since 10^-6 M ouabain specifically inhibits the α4 subunit while 10^-5-10^-4 M ouabain inhibits both the α1 and α4 subunits, these results suggest the α1 subunit is necessary for the maintenance of motility while the α4 subunit is necessary for the hyperactivation-associated change in flagellar movement. Ouabain did not inhibit tyrosine phosphorylation, and activation of tyrosine phosphorylation-dependent signaling had no effect on the inhibition of hyperactivation by ouabain. The immediate recovery of hyperactivation was observed when ouabain was washed out after a 3-h incubation. whereas the administration of ouabain after the onset of hyperactivation significantly inhibited hyperactivation. These results suggest ouabain inhibited hyperactivation in a manner that was independent of time-requiring phosphorylation-mediated signaling.

Effects of digoxin on full-type hyperactivation in bovine ejaculated spermatozoa with relatively lower survivability for incubation with stimulators of cAMP signaling cascades

Previous researches of our laboratory reported that addition of cAMP analog cBiMPS and protein phosphatase inhibitor calyculin A (stimulators of cAMP signaling cascades) improved the capacity of incubation medium to induce full-type hyperactivation in bovine ejaculated spermatozoa. However, this modified medium was valid only for samples with relatively good survivability for incubation with stimulators of cAMP signaling cascades. Thus, it is necessary to make further modified medium for evaluation of potentials to exhibit full-type hyperactivation in bovine sperm samples with relatively lower survivability. Na⁺/K⁺-ATPase is an integral membrane protein and involved with the regulation of rodent sperm motility. To make further modification of the medium, we examined effects of Na⁺/K⁺-ATPase inhibition with digoxin on motility, full-type hyperactivation and protein tyrosine phosphorylation in bovine ejaculated spermatozoa with relatively lower survivability for incubation with stimulators of cAMP signaling cascades and also performed the immunodetection of bovine sperm Na⁺/K⁺-ATPase. The addition of Na⁺/K⁺-ATPase inhibitor digoxin to the incubation medium containing cBiMPS and calyculin A had the tendency to lessen the decreases in the percentages of motile spermatozoa in all of 12 samples after the incubation for 1-3 h and significantly increased the percentages of full-type hyperactivation in one group of 4 samples (Sample-A1) and another group of 4 samples (Sample-A2) after 1 and 2 h respectively, though it had no significant effects on full-type hyperactivation in the other group of 4 samples (Sample-B). In addition, incubation time-related changes in the sperm protein tyrosine phosphorylation (a good marker for sperm capacitation) were correlated with those in the percentages of full-type hyperactivation in Sample-A1 containing digoxin. Immunodetection showed that Na⁺/K⁺-ATPase is present in the middle and principal pieces of the flagella, indicating that Na⁺/K⁺-ATPase has possible relations with sperm motility. These results obtained with bull ejaculated spermatozoa with relatively lower survivability indicate that incubation method using digoxin is useful to evaluate potentials of sperm samples to exhibit full-type hyperactivation, that digoxin has effects on suppressing reduction of sperm motility, and that prolonged incubation with digoxin induces reduction of capacitation state which may suppress the maintenance of full-type hyperactivation.

Update on mammalian sperm capacitation: how much does the horse differ from other species?

In contrast to various other mammalian species, conventional in vitro fertilization (IVF) with horse gametes is not reliably successful. In particular, stallion spermatozoa fails to penetrate the zona pellucida, most likely due to incomplete activation of stallion spermatozoa (capacitation) under in vitro conditions. In other mammalian species, specific capacitation triggers have been described; unfortunately, none of these is able to induce full capacitation in stallion spermatozoa. Nevertheless, knowledge of capacitation pathways and their molecular triggers might improve our understanding of capacitation-related events observed in stallion sperm. When sperm cells are exposed to appropriate capacitation triggers, several molecular and biochemical changes should be induced in the sperm plasma membrane and cytoplasm. At the level of the sperm plasma membrane, (1) an increase in membrane fluidity, (2) cholesterol depletion and (3) lipid raft aggregation should occur consecutively; the cytoplasmic changes consist of protein tyrosine phosphorylation and elevated pH, cAMP and Ca2+ concentrations. These capacitation-related events enable the switch from progressive to hyperactivated motility of the sperm cells, and the induction of the acrosome reaction. These final capacitation triggers are indispensable for sperm cells to migrate through the viscous oviductal environment, penetrate the cumulus cells and zona pellucida and, finally, fuse with the oolemma. This review will focus on molecular aspects of sperm capacitation and known triggers in various mammalian species. Similarities and differences with the horse will be highlighted to improve our understanding of equine sperm capacitation/fertilizing events.

Porcine model for the study of sperm capacitation, fertilization and male fertility

Mammalian fertilization remains a poorly understood event with the vast majority of studies done in the mouse model. The purpose of this review is to revise the current knowledge about semen deposition, sperm transport, sperm capacitation, gamete interactions and early embryonic development with a focus on the porcine model as a relevant, alternative model organism to humans. The review provides a thorough overview of post-ejaculation events inside the sow's reproductive tract including comparisons with humans and implications for human fertilization and assisted reproductive therapy (ART). Porcine methodology for sperm handling, preservation, in vitro capacitation, oocyte in vitro maturation, in vitro fertilization and intra-cytoplasmic sperm injection that are routinely used in pig research laboratories can be successfully translated into ART to treat human infertility. Last, but not least, new knowledge about mitochondrial inheritance in the pig can provide an insight into human mitochondrial diseases and new knowledge on polyspermy defense mechanisms could contribute to the development of new male contraceptives.

Membrane Potential Assessment by Fluorimetry as a Predictor Tool of Human Sperm Fertilizing Capacity

Mammalian sperm acquire the ability to fertilize eggs by undergoing a process known as capacitation. Capacitation is triggered as the sperm travels through the female reproductive tract. This process involves specific physiological changes such as rearrangement of the cell plasma membrane, post-translational modifications of certain proteins, and changes in the cellular permeability to ions - with the subsequent impact on the plasma membrane potential (Em). Capacitation-associated Em hyperpolarization has been well studied in mouse sperm, and shown to be both necessary and sufficient to promote the acrosome reaction (AR) and fertilize the egg. However, the relevance of the sperm Em upon capacitation on human fertility has not been thoroughly characterized. Here, we performed an extensive study of the Em change during capacitation in human sperm samples using a potentiometric dye in a fluorimetric assay. Normospermic donors showed significant Em hyperpolarization after capacitation. Em values from capacitated samples correlated significantly with the sperm ability to undergo induced AR, highlighting the role of hyperpolarization in acrosomal responsiveness, and with successful in vitro fertilization (IVF) rates. These results show that Em hyperpolarization could be an indicator of human sperm fertilizing capacity, setting the basis for the use of Em values as a robust predictor of the success rate of IVF.

Asymmetrically Positioned Flagellar Control Units Regulate Human Sperm Rotation

Ion channels control sperm navigation within the female reproductive tract and, thus, are critical for their ability to find and fertilize an egg. The flagellar calcium channel CatSper controls sperm hyperactivated motility and is dependent on an alkaline cytoplasmic pH. The latter is accomplished by either proton transporters or, in human sperm, via the voltage-gated proton channel Hv1. To provide concerted regulation, ion channels and their regulatory proteins must be compartmentalized. Here, we describe flagellar regulatory nanodomains comprised of Hv1, CatSper, and its regulatory protein ABHD2. Super-resolution microscopy revealed that Hv1 is distributed asymmetrically within bilateral longitudinal lines and that inhibition of this channel leads to a decrease in sperm rotation along the long axis. We suggest that specific distribution of flagellar nanodomains provides a structural basis for the selective activation of CatSper and subsequent flagellar rotation. The latter, together with hyperactivated motility, enhances the fertility of sperm.

pH-dependent effects of procaine on equine gamete activation†

Procaine directly triggers pH-dependent cytokinesis in equine oocytes and induces hypermotility in stallion spermatozoa, an important event during capacitation. However, procaine-induced hyperactivated motility is abolished when sperm is washed to remove the procaine prior to sperm-oocyte co-incubation. To understand how procaine exerts its effects, the external Ca2+ and Na+ and weak base activity dependency of procaine-induced hyperactivation in stallion spermatozoa was assessed using computer-assisted sperm analysis. Percoll-washed stallion spermatozoa exposed to Ca2+-depleted (+2 mM EGTA) procaine-supplemented capacitating medium (CM) still demonstrated hyperactivated motility, whereas CM without NaCl or Na+ did not. Both procaine and NH4Cl, another weak base, were shown to trigger a cytoplasmic pH increase (BCECF-acetoxymethyl (AM)), which is primarily induced by a pH rise in acidic cell organelles (Lysosensor green dnd-189), accompanied by hypermotility in stallion sperm. As for procaine, 25 mM NH4Cl also induced oocyte cytokinesis. Interestingly, hyperactivated motility was reliably induced by 2.5-10 mM procaine, whereas a significant cytoplasmic cAMP increase and tail-associated protein tyrosine phosphorylation were only observed at 10 mM. Moreover, 25 mM NH4Cl did not support the latter capacitation characteristics. Additionally, cAMP levels were more than 10× higher in boar than stallion sperm incubated under similar capacitating conditions. Finally, stallion sperm preincubated with 10 mM procaine did not fertilize equine oocytes. In conclusion, 10 mM procaine causes a cytoplasmic and acidic sperm cell organelle pH rise that simultaneously induces hyperactivated motility, increased levels of cAMP and tail-associated protein tyrosine phosphorylation in stallion spermatozoa. However, procaine-induced hypermotility is independent of the cAMP/protein tyrosine phosphorylation pathway.

Intracellular Ca2+ threshold reversibly switches flagellar beat off and on

Sperm motility is essential for fertilization. The asymmetry of flagellar beat in spermatozoa is finely regulated by intracellular calcium concentration ([Ca2+]i). Recently, we demonstrated that the application of high concentrations (10-20 μM) of the Ca2+ ionophore A23187 promotes sperm immobilization after 10 min, and its removal thereafter allows motility recovery, hyperactivation, and fertilization. In addition, the same ionophore treatment overcomes infertility observed in sperm from Catsper1-/-, Slo3-/-, and Adcy10-/-, but not PMCA4-/-, which strongly suggest that regulation of [Ca2+]i is mandatory for sperm motility and hyperactivation. In this study, we found that prior to inducing sperm immobilization, high A23187 concentrations (10 μM) increase flagellar beat. While 5-10 μM A23187 substantially elevates [Ca2+]i and rapidly immobilizes sperm in a few minutes, smaller concentrations (0.5 and 1 μM) provoke smaller [Ca2+]i increases and sperm hyperactivation, confirming that [Ca2+]i increases act as a motility switch. Until now, the [Ca2+]i thresholds that switch motility on and off were not fully understood. To study the relationship between [Ca2+]i and flagellar beating, we developed an automatic tool that allows the simultaneous measurement of these two parameters. Individual spermatozoa were treated with A23187, which is then washed to evaluate [Ca2+]i and flagellar beat recovery using the implemented method. We observe that [Ca2+]i must decrease below a threshold concentration range to facilitate subsequent flagellar beat recovery and sperm motility.

Induction of sperm hypermotility through membrane progestin receptor alpha (mPRα): A teleost model of rapid, multifaceted, nongenomic progestin signaling

Rapid progestin effects on sperm physiology have been described in a variety of vertebrate species. Here, we briefly review the signaling pathways mediating rapid progestin induction of sperm hypermotility and increased fertility in two teleost species, Atlantic croaker and southern flounder. Acute in vitro treatment of teleost sperm with the progestin hormone, 20β-S, causes activation of progestin membrane receptor alpha (mPRα, or Paqr7) coupled to a stimulatory olfactory G protein (G_olf), resulting in increased cAMP and calcium concentrations and hypermotility upon activation in a hyperosmotic medium. Pharmacological tools were used to investigate the involvement of mPRα and several intracellular signaling pathways in the hypermotility response. Evidence was obtained using the specific mPRα agonist, Org OD 02-0, that this progestin action is mediated through mPRα and not through the nuclear PR. The results indicate that progestins induce hypermotility through activation of a membrane adenylyl cyclase (Acy)/cAMP pathway, an epidermal growth factor receptor (Egfr)/Mapkinase pathway, and a Pi3kinase/Akt/phosphodiesterase (Pde) pathway which result in increased sperm calcium concentrations within 10 s. The finding that inhibition of any one of these pathways is sufficient to prevent hypermotility along with the calcium increase suggests that activation of all of them and the associated calcium increase are required for the progestin hypermotility response. On the basis of these findings a model of progestin induction of sperm hypermotility in teleosts is proposed. As teleosts lack CatSper, the model described here is a non-CatSper mediated one and may therefore be applicable to a wide variety of nonmammalian vertebrates.

Dual Sensing of Physiologic pH and Calcium by EFCAB9 Regulates Sperm Motility

Varying pH of luminal fluid along the female reproductive tract is a physiological cue that modulates sperm motility. CatSper is a sperm-specific, pH-sensitive calcium channel essential for hyperactivated motility and male fertility. Multi-subunit CatSper channel complexes organize linear Ca²⁺ signaling nanodomains along the sperm tail. Here, we identify EF-hand calcium-binding domain-containing protein 9 (EFCAB9) as a bifunctional, cytoplasmic machine modulating the channel activity and the domain organization of CatSper. Knockout mice studies demonstrate that EFCAB9, in complex with the CatSper subunit, CATSPERζ, is essential for pH-dependent and Ca²⁺-sensitive activation of the CatSper channel. In the absence of EFCAB9, sperm motility and fertility is compromised, and the linear arrangement of the Ca²⁺ signaling domains is disrupted. EFCAB9 interacts directly with CATSPERζ in a Ca²⁺-dependent manner and dissociates at elevated pH. These observations suggest that EFCAB9 is a long-sought, intracellular, pH-dependent Ca²⁺ sensor that triggers changes in sperm motility.

Single-cell Motility Analysis of Tethered Human Spermatozoa

Vigorous sperm flagellar motility is essential for fertilization, and so the quantitative measurement of motility is a useful tool to assess the intrinsic fertility potential of sperm cells and explore how various factors can alter sperm's ability to reach the egg and penetrate its protective layers. Human sperm beat their flagella many times each second, and so recording and accurately quantifying this movement requires a high-speed camera. The aim of this protocol is to provide a detailed description of the tools required for quantitative beat frequency measurement of tethered human sperm at the single-cell level and to describe methods for investigating the effects of intracellular or extracellular factors on flagellar motion. This assay complements bulk measurements of sperm parameters using commercially-available systems for computer-assisted sperm analysis (CASA).

Terahertz irradiation-induced motility enhancement and intracellular calcium elevation in human sperm in vitro

To date, there has been limited evidence to reveal the effect of terahertz radiation on sperm. In this study, semen samples were collected from males who had just finished a prepregnancy computer-assisted semen analysis (CASA). The motility, intracellular concentration of free Ca²⁺ and DNA integrity of sperm with or without terahertz (0.1 to 3 THz) irradiation at 60 µW/cm² were assessed. We found that terahertz irradiation for more than 5 minutes significantly increased the progressive motility percentage of sperm, and the DNA integrity was not changed. We also found that the effect of terahertz irradiation on spermatozoa was weakened by reducing the concentration of extracellular calcium ions or by blocking calcium channels.

TRPV4 is the temperature-sensitive ion channel of human sperm

Ion channels control the ability of human sperm to fertilize the egg by triggering hyperactivated motility, which is regulated by membrane potential, intracellular pH, and cytosolic calcium. Previous studies unraveled three essential ion channels that regulate these parameters: (1) the Ca²⁺ channel CatSper, (2) the K⁺ channel KSper, and (3) the H⁺ channel Hv1. However, the molecular identity of the sperm Na⁺ conductance that mediates initial membrane depolarization and, thus, triggers downstream signaling events is yet to be defined. Here, we functionally characterize DSper, the Depolarizing Channel of Sperm, as the temperature-activated channel TRPV4. It is functionally expressed at both mRNA and protein levels, while other temperature-sensitive TRPV channels are not functional in human sperm. DSper currents are activated by warm temperatures and mediate cation conductance, that shares a pharmacological profile reminiscent of TRPV4. Together, these results suggest that TRPV4 activation triggers initial membrane depolarization, facilitating both CatSper and Hv1 gating and, consequently, sperm hyperactivation.

Are there intracellular Ca2+ oscillations correlated with flagellar beating in human sperm? A three vs. two-dimensional analysis

STUDY QUESTION

Are there intracellular Ca2+ ([Ca2+]i) oscillations correlated with flagellar beating in human sperm?

SUMMARY ANSWER

The results reveal statistically significant [Ca2+]i oscillations that are correlated with the human sperm flagellar beating frequency, when measured in three-dimensions (3D).

WHAT IS KNOWN ALREADY

Fast [Ca2+]i oscillations that are correlated to the beating flagellar frequency of cells swimming in a restricted volume have been detected in hamster sperm. To date, such findings have not been confirmed in any other mammalian sperm species. An important question that has remained regarding these observations is whether the fast [Ca2+]i oscillations are real or might they be due to remaining defocusing effects of the Z component arising from the 3D beating of the flagella.

STUDY DESIGN, SIZE, DURATION

Healthy donors whose semen samples fulfill the WHO criteria between the age of 18-28 were selected. Cells from at least six different donors were utilized for analysis. Approximately the same number of experimental and control cells were analyzed.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Motile cells were obtained by the swim-up technique and were loaded with Fluo-4 (Ca2+ sensitive dye) or with Calcein (Ca2+ insensitive dye). Ni2+ was used as a non-specific plasma membrane Ca2+ channel blocker. Fluorescence data and flagella position were acquired in 3D. Each cell was recorded for up to 5.6 s within a depth of 16 microns with a high speed camera (coupled to an image intensifier) acquiring at a rate of 3000 frames per second, while an oscillating objective vibrated at 90 Hz via a piezoelectric device. From these samples, eight experimental and nine control sperm cells were analyzed in both 2D and 3D.

MAIN RESULTS AND THE ROLE OF CHANCE

We have implemented a new system that allows [Ca2+]i measurements of the human sperm flagellum beating in 3D. These measurements reveal statistically significant [Ca2+]i oscillations that correlate with the flagellar beating frequency. These oscillations may arise from intracellular sources and/or Ca2+ transporters, as they were insensitive to external Ni2+, a non-specific plasma membrane Ca2+ channel blocker.

LARGE SCALE DATA

N/A.

LIMITATIONS REASONS FOR CAUTION

Analysis in 3D needs a very fast image acquisition rate to correctly sample a volume containing swimming sperm. This condition requires a very short exposure time per image making it necessary to use an image intensifier which also increases noise. The lengthy analysis time required to obtain reliable results limited the number of cells that could be analyzed.

WIDER IMPLICATIONS OF THE FINDINGS

The possibility of recording flagellar [Ca2+]i oscillations described here may open a new avenue to better understand ciliary and flagellar beating that are fundamental for mucociliary clearance, oocyte transport, fertilization, cerebrospinal fluid pressure regulation and developmental left-right symmetry breaking in the embryonic node.

STUDY FUNDING AND COMPETING INTEREST(S)

This work was supported by Consejo Nacional de Ciencia y Tecnología (CONACyT) (grants 253952 to G.C.; 156667 to F.M.M. and Fronteras 71 39908-Q to A.D. and Post-doctoral scholarships 366844 to P.H.-H. and 291028 to F.M.) and the Dirección General de Asuntos del Personal Académico of the Universidad Nacional Autónoma de México (DGAPA-UNAM) (grants CJIC/CTIC/4898/2016 to F.M. and IN205516 to A.D.). There are no conflicts of interest to declare.

Regulation mechanisms and implications of sperm membrane hyperpolarization

Mammalian sperm are unable to fertilize the egg immediately after ejaculation. In order to gain fertilization competence, they need to undergo a series of biochemical and physiological modifications inside the female reproductive tract, known as capacitation. Capacitation correlates with two essential events for fertilization: hyperactivation, an asymmetric and vigorous flagellar motility, and the ability to undergo the acrosome reaction. At a molecular level, capacitation is associated to: phosphorylation cascades, modification of membrane lipids, alkalinization of the intracellular pH, increase in the intracellular Ca²⁺ concentration and hyperpolarization of the sperm plasma membrane potential. Hyperpolarization is a crucial event in capacitation since it primes the sperm to undergo the exocytosis of the acrosome content, essential to achieve fertilization of the oocyte.

CatSper: A Unique Calcium Channel of the Sperm Flagellum

To overcome egg protective vestments and ensure successful fertilization, mammalian spermatozoa switch symmetrical progressive motility to a powerful, whip-like flagellar motion, known as hyperactivation. The latter is triggered by a calcium influx through the sperm-specific, voltage-dependent, and alkalization-activated calcium channel of sperm - CatSper. The channel comprises nine subunits which together form a heteromeric complex. CatSper-deficient male mice and men with mutations in CatSper genes are infertile. This calcium channel is regulated by various endogenous compounds, such as steroids, prostaglandins, endocannabinoids, and intracellular pH. Being a sperm-specific ion channel that is not expressed anywhere else in the body, CatSper represents an ideal target for the development of female and even male contraceptives. In this review, we discuss the recent advances in studying CatSper functional properties and discuss future steps that are required to take in order to achieve a deep understanding of the molecular basis of CatSper function.

A mosquito sperm's journey from male ejaculate to egg: Mechanisms, molecules, and methods for exploration

The fate of mosquito sperm in the female reproductive tract has been addressed sporadically and incompletely, resulting in significant gaps in our understanding of sperm-female interactions that ultimately lead to fertilization. As with other Diptera, mosquito sperm have a complex journey to their ultimate destination, the egg. After copulation, sperm spend a short time at the site of insemination where they are hyperactivated and quickly congregate near the entrance of the spermathecal ducts. Within minutes, they travel up the narrow ducts to the spermathecae, likely through the combined efforts of female transport and sperm locomotion. The female nourishes sperm and maintains them in these permanent storage organs for her entire life. When she is ready, the female coordinates the release of sperm with ovulation, and the descending egg is fertilized. Although this process has been well studied via microscopy, many questions remain regarding the molecular processes that coordinate sperm motility, movement through the reproductive tract, maintenance, and usage. In this review, we describe the current understanding of a mosquito sperm's journey to the egg, highlighting gaps in our knowledge of mosquito reproductive biology. Where insufficient information is available in mosquitoes, we describe analogous processes in other organisms, such as Drosophila melanogaster, as a basis for comparison, and we suggest future areas of research that will illuminate how sperm successfully traverse the female reproductive tract. Such studies may yield molecular targets that could be manipulated to control populations of vector species. Mol. Reprod. Dev. 83: 897-911, 2016 © 2016 Wiley Periodicals, Inc.

A novel epididymal quiescence factor inhibits sperm motility by modulating NOS activity and intracellular NO-cGMP pathway

Mature and potentially motile spermatozoa stored in cauda epididymis in an inactive state for approximately 30 days; however, during ejaculation they regain motility. To understand the actual molecular mechanism of the sperm quiescence during caudal stay, a proteinaceous quiescence factor (QF) has been purified from caprine epididymal plasma to apparent homogeneity. In the present study complete purification, detailed characterization as well as mechanistic pathway of QF has been described. QF is purified to 215-fold with 45% activity recovery. It is a 59 kDa monomeric protein with isoelectric point 5.8 and optimally active at pH 7.5. Circular dichroism spectroscopy and atomic force microscopy study confirm its α-helical secondary structure and globular tertiary conformation. QF is a thermo-stable protein as higher temperature does not alter its helical structure. N-terminal amino acid sequencing and MALDI analysis of QF did not find 100% similarity with any available protein of the database, proved its novelty. QF at 2 μM dose inhibits sperm progressive forward motility within 10 min. This motility inhibitory activity of QF is mediated by reducing NOS enzyme activity and subsequently decreasing the intracellular NO and cGMP concentration. It does not modulate intracellular Ca⁺⁺ and cAMP concentration. QF has no adverse effect on DNA integrity and morphology of spermatozoa. Motility inhibitory action of QF is reversible. Thus, the role of QF in maintaining energy saving quiescence state of mature cauda spermatozoa and its reactive nitrogen species reducing activity may lead to a new direction for storage of spermatozoa and idiopathic male infertility.

Effect of CatSper and Hv1 Channel Inhibition on Progesterone Stimulated Human Sperm

BACKGROUND

Intracellular calcium and proton concentrations are important factors for activating human sperm. Calcium ion (Ca²⁺) enters sperm through voltage-dependent calcium channel of sperm (CatSper). Proton was extruded from sperm through voltage-gated proton channel (Hv1). In the present study, the selective inhibitors of the CatSper and Hv1 channels, NNC 55-0396 (NNC) and zinc ion, respectively, were used to investigate functions of these channels.

METHODS

Normal semen samples (n=24) were washed and diluted to 20×10⁶sperm/ml. The diluted sample was divided into 8 groups, containing Ham's F-10 (the control group), 2 μM NNC, 1 mM ZnCl₂ and NNC+Zn. The other 4 groups were the same as above, except that they contained 1 μM progesterone. The computer assisted analysis was done by VT-Sperm 3.1 to determine the percentage of motile sperm and sperm velocity. Acrosomal status was monitored by FITC-PSA and viability assessed by Eosin-Y staining. Statistical comparisons were made using ANOVA followed by Tukey post hoc test. The p<0.05 was considered significant.

RESULTS

The percentage of viable and motile sperm, curvilinear velocity and other parameters of motility was reduced in all groups containing NNC, zinc and NNC+ zinc. Progesterone-induced acrosome reaction was abolished by each of these inhibitors. The combination effect of NNC plus zinc on motility and progesterone-induced acrosome reaction was not stronger than NNC by itself.

CONCLUSION

CatSper and Hv1 channels play a critical role in human sperm function and viability. It seems that a functional relationship exists between CatSper and Hv1 channels.

Applications of capacitation status for litter size enhancement in various pig breeds

Objective

Several studies have reported the development of new molecular methods for the prognosis and diagnosis of male fertility based on biomarkers aimed at overcoming the limitations of conventional male fertility analysis tools. However, further studies are needed for the field application of these methods. Therefore, alternative methods based on existing semen analysis methods are required to improve production efficiency in the animal industry.

Methods

we examined the possibility of improving litter size in various pig breeds using combined Hoechst 33258/chlortetracycline fluorescence (H33258/CTC) staining. The correlation between field fertility and capacitation status by combined H33258/CTC staining in different ejaculates spermatozoa (n = 3) from an individual boar (20 Landrace, 20 Yorkshire, and 20 Duroc) was evaluated as well as overall accuracy.

Results

The acrosome reacted (AR) pattern after capacitation (%) was positively correlated with the litter size of Landrace, Yorkshire, and Duroc pigs and the overall accuracy was 75%, 75%, and 70% in Landrace, Yorkshire, and Duroc pigs, respectively. The difference (Δ) in AR pattern before and after capacitation was positively correlated with the litter size of Landrace, Yorkshire, and Duroc pigs and the overall accuracy was 80%, 65%, and 55% in Landrace, Yorkshire, and Duroc pigs, respectively. However, the difference (Δ) in capacitated (B) pattern before and after capacitation was negatively correlated with the litter size of Landrace pigs and the overall accuracy was 75%. Moreover, average litter size was significantly altered according to different combined H33258/CTC staining parameters.

Conclusion

These results show that combined H33258/CTC staining may be used to predict male fertility in various breeds. However, the selection of specific efficiency combined H33258/CTC staining parameters requires further consideration. Taken together, these findings suggest that combined H33258/CTC staining may constitute an alternative method for predicting male fertility until such time as fertility-related biomarkers are further validated.

Expression and localization of relaxin family peptide receptor 4 in human spermatozoa and impact of insulin-like peptide 5 on sperm functions

Insulin-like peptide 5 (INSL5) is a member of the insulin superfamily peptide that interacts with the relaxin family peptide receptor 4 (RXFP4). Numerous recent studies have focused on the functional effects of INSL5 on fat and glucose metabolism. Although there is no evidence that the human sperm may be a candidate target of INSL5, it has been detected in mice testis and sperm. Therefore, the present study sought to analyze the localization and expression of RXFP4 on human sperm and determine the efficiency of INSL5 in human sperm. Normal semen samples were incubated in different doses and exposure time periods of INSL5. We analyzed sperm motility by computer-assisted sperm analysis (CASA) and ROS levels by flow cytometry using the MitoSOX™ Red probe. Localization and expression of RXFP4 were assayed by immunofluorescence and RT-PCR, respectively. The results confirmed the presence of RXFP4 in human spermatozoa, which localized in the neck and midpiece of sperm. Nested PCR showed the expression of RXFP4 in human sperm. INSL5 could attenuate generation of mitochondrial ROS at the 1, 10, 30, and 100nmol/L doses. This result was particularly noted in the 30nmol/L treated samples after 4h incubation. Total motility of sperm was significantly preserved in the 100nmol/L after 2h and in 30nmol/L after 4h incubation period. This study, for the first time, clarified the expression and localization of RXFP4 on human sperm and revealed the role of INSL5 in sperm motility and mitochondrial ROS generation in a dose-dependent manner.

Sperm Sensory Signaling

Fertilization is exceptionally complex and, depending on the species, happens in entirely different environments. External fertilizers in aquatic habitats, like marine invertebrates or fish, release their gametes into the seawater or freshwater, whereas sperm from most internal fertilizers like mammals cross the female genital tract to make their way to the egg. Various chemical and physical cues guide sperm to the egg. Quite generally, these cues enable signaling pathways that ultimately evoke a cellular Ca2+ response that modulates the waveform of the flagellar beat and, hence, the swimming path. To cope with the panoply of challenges to reach and fertilize the egg, sperm from different species have developed their own unique repertoire of signaling molecules and mechanisms. Here, we review the differences and commonalities for sperm sensory signaling in marine invertebrates (sea urchin), fish (zebrafish), and mammals (mouse, human).

Wide-field three-photon excitation in biological samples

Three-photon wide-field depth-resolved excitation is used to overcome some of the limitations in conventional point-scanning two- and three-photon microscopy. Excitation of chromophores as diverse as channelrhodopsins and quantum dots is shown, and a penetration depth of more than 700 μm into fixed scattering brain tissue is achieved, approximately twice as deep as that achieved using two-photon wide-field excitation. Compatibility with live animal experiments is confirmed by imaging the cerebral vasculature of an anesthetized mouse; a complete focal stack was obtained without any evidence of photodamage. As an additional validation of the utility of wide-field three-photon excitation, functional excitation is demonstrated by performing three-photon optogenetic stimulation of cultured mouse hippocampal neurons expressing a channelrhodopsin; action potentials could reliably be excited without causing photodamage.