Physiological volume regulation by spermatozoa

Clustering of spermatozoa examined through flow cytometry provides more information than the conventional assessment: a resilience to osmotic stress example

Context Conventional sperm quality tests may not be sufficient to predict the fertilising ability of a given ejaculate; thus, rapid, reliable and sensitive tests are necessary to measure sperm function. Aims This study sought to address whether a cluster analysis approach based on flow cytometry variables could provide more information about sperm function. Methods Spermatozoa were exposed to either isotonic (300mOsm/kg) or hypotonic (180mOsm/kg) media for 5 and 20min, and were then stained with SYBR14 and propidium iodide (PI). Based on flow cytometry dot plots, spermatozoa were classified as either viable (SYBR14+ /PI- ) or with different degrees of plasma membrane alteration (SYBR14+ /PI+ and SYBR14- /PI+ ). Moreover, individual values of electronic volume (EV), side scattering (SS), green (FL1) and red (FL3) fluorescence were recorded and used to classify sperm cells through cluster analysis. Two strategies of this approach were run. The first one was based on EV and the FL3/FL1 quotient, and the second was based on EV, SS and the FL3/FL1 quotient. Key results The two strategies led to the identification of more than three sperm populations. In the first strategy, EV did not differ between membrane-intact and membrane-damaged sperm, but it was significantly (P P P Conclusions Cluster analysis based on flow cytometry variables provides more information about sperm function than conventional assessment does. Implications Combining flow cytometry with cluster analysis is a more robust approach for sperm evaluation.

Physiological Functions of the Volume-Regulated Anion Channel VRAC/LRRC8 and the Proton-Activated Chloride Channel ASOR/TMEM206

Volume-regulated anion channels (VRACs) and the acid-sensitive outwardly rectifying anion channel (ASOR) mediate flux of chloride and small organic anions. Although known for a long time, they were only recently identified at the molecular level. VRACs are heteromers consisting of LRRC8 proteins A to E. Combining the essential LRRC8A with different LRRC8 paralogues changes key properties of VRAC such as conductance or substrate selectivity, which is how VRACs are involved in multiple physiological functions including regulatory volume decrease, cell proliferation and migration, cell death, purinergic signalling, fat and glucose metabolism, insulin signalling, and spermiogenesis. VRACs are also involved in pathological conditions, such as the neurotoxic release of glutamate and aspartate. Certain VRACs are also permeable to larger, organic anions, including antibiotics and anti-cancer drugs, making them an interesting therapeutic target. ASOR, also named proton-activated chloride channel (PAC), is formed by TMEM206 homotrimers on the plasma membrane and on endosomal compartments where it mediates chloride flux in response to extracytosolic acidification and plays a role in the shrinking and maturation of macropinosomes. ASOR has been shown to underlie neuronal swelling which causes cell death after stroke as well as promoting the metastasis of certain cancers, making them intriguing therapeutic targets as well.

Lactobacillus plantarum secretions may exert a cryoprotective effect on human sperm motility: A prospective in vitro study

BACKGROUND

Semen cryopreservation is a widely used procedure for fertility preservation, despite some level of cryodamage that may occur in spermatozoa after thawing. However, there is some evidence that lactobacilli, one of the bacteria found in semen, might benefit sperm quality.

OBJECTIVES

This study aims to determine whether the addition of Lactobacillus plantarum secretions to sperm freezing medium has an impact on sperm motility, morphology, and DNA fragmentation.

MATERIALS AND METHODS

This is a prospective auto-controlled study. It was conducted on 30 raw semen samples from 30 infertile men attending a fertility center for semen analysis. Before freezing, all the samples were analyzed for motility, morphology, and DNA fragmentation percentages. Each sample was then divided equally into three aliquots. Cryopreservation was performed on each aliquot using one of the following three media: without Lactobacillus plantarum secretions (control group) or with 107 or 108 colony-forming units/mL Lactobacillus plantarum secretions. Sperm motility, morphology, and DNA integrity were evaluated after the cryopreservation media were added and after semen thawing.

RESULTS

The results of this study indicated that after thawing, no statistically significant decrease in progressive motility and non-progressive percentages were detected in the sperm freezing medium supplemented with 108 colony-forming units/mL Lactobacillus plantarum secretions than the fresh raw semen. Moreover, multivariate linear regression model analyses showed that the progressive motility (p = 0.02), non-progressive motility (p = 0.016), and non-motile spermatozoa (p = 0.012) percentages were significantly decreased in the freezing medium (without Lactobacillus plantarum secretions) compared to the fresh raw semen.

DISCUSSION AND CONCLUSION

To the best of our knowledge, this is the first study showing that Lactobacillus plantarum secretions had a cryoprotective effect on sperm motility when added to the sperm freezing medium. Furthermore, Lactobacillus plantarum secretions were found to protect sperm DNA integrity more effectively than the freezing medium without Lactobacillus plantarum secretions in non-normozoospermia group. Cryopreservation procedures must therefore be optimized to minimize any iatrogenically induced sperm DNA damage, given the correlation between sperm DNA damage and increased mutation loads in progeny.

Signaling Roleplay between Ion Channels during Mammalian Sperm Capacitation

In order to accomplish their primary goal, mammalian spermatozoa must undergo a series of physiological, biochemical, and functional changes crucial for the acquisition of fertilization ability. Spermatozoa are highly polarized cells, which must swiftly respond to ionic changes on their passage through the female reproductive tract, and which are necessary for male gametes to acquire their functional competence. This review summarizes the current knowledge about specific ion channels and transporters located in the mammalian sperm plasma membrane, which are intricately involved in the initiation of changes within the ionic milieu of the sperm cell, leading to variations in the sperm membrane potential, membrane depolarization and hyperpolarization, changes in sperm motility and capacitation to further lead to the acrosome reaction and sperm-egg fusion. We also discuss the functionality of selected ion channels in male reproductive health and/or disease since these may become promising targets for clinical management of infertility in the future.

Aquaporin-7-Mediated Glycerol Permeability Is Linked to Human Sperm Motility in Asthenozoospermia and during Sperm Capacitation

Osmoregulation plays a vital role in sperm function, encompassing spermatogenesis, maturation, and fertilization. Aquaglyceroporins, a subclass of aquaporins (AQPs), facilitate the transport of water and glycerol across the sperm membrane, with glycerol serving as an important substrate for sperm bioenergetics. This study aimed to elucidate the significance of AQP-mediated glycerol permeability in sperm motility. The presence and localization of AQP3 and AQP7 in human sperm were assessed using immunofluorescence. Subsequently, the glycerol permeability of spermatozoa obtained from normozoospermic individuals (n = 30) was measured, using stopped-flow light scattering, after incubation with specific aquaporin inhibitors targeting AQP3 (DFP00173), AQP7 (Z433927330), or general aquaglyceroporin (phloretin). Sperm from asthenozoospermic men (n = 30) were utilized to evaluate the AQP7-mediated glycerol permeability, and to compare it with that of normozoospermic men. Furthermore, hypermotile capacitated sperm cells were examined, to determine the AQP7 expression and membrane glycerol permeability. AQP3 was predominantly observed in the tail region, while AQP7 was present in the head, midpiece, and tail of human sperm. Our findings indicate that AQP7 plays a key role in glycerol permeability, as the inhibition of AQP7 resulted in a 55% decrease in glycerol diffusion across the sperm membrane. Importantly, this glycerol permeability impairment was evident in spermatozoa from asthenozoospermic individuals, suggesting the dysregulation of AQP7-mediated glycerol transport, despite similar AQP7 levels. Conversely, the AQP7 expression increased in capacitated sperm, compared to non-capacitated sperm. Hence, AQP7-mediated permeability may serve as a valuable indicator of sperm motility, and be crucial in sperm function.

Male Sex Hormones, Metabolic Syndrome, and Aquaporins: A Triad of Players in Male (in)Fertility

Infertility is becoming a chronic and emerging problem in the world. There is a resistant stigma that this health condition is mostly due to the female, although the literature supports that the responsibility for the onset of infertility is equally shared between both sexes in more or less equal proportions. Nevertheless, male sex hormones, particularly testosterone (T), are key players in male-related infertility. Indeed, hypogonadism, which is also characterized by changes in T levels, is one of the most common causes of male infertility and its incidence has been interconnected to the increased prevalence of metabolic diseases. Recent data also highlight the role of aquaporin (AQP)-mediated water and solute diffusion and the metabolic homeostasis in testicular cells suggesting a strong correlation between AQPs function, metabolism of testicular cells, and infertility. Indeed, recent studies showed that both metabolic and sexual hormone concentrations can change the expression pattern and function of AQPs. Herein, we review up-to-date information on the involvement of AQP-mediated function and permeability in men with metabolic syndrome and testosterone deficit, highlighting the putative mechanisms that show an interaction between sex hormones, AQPs, and metabolic syndrome that may contribute to male infertility.

Extend the Survival of Human Sperm In Vitro in Non-Freezing Conditions: Damage Mechanisms, Preservation Technologies, and Clinical Applications

Preservation of human spermatozoa in vitro at normothermia or hypothermia maintaining their functions and fertility for several days plays a significant role in reproductive biology and medicine. However, it is well known that human spermatozoa left in vitro deteriorate over time irreversibly as the consequence of various stresses such as the change of osmolarity, energy deficiency, and oxidative damage, leading to substantial limitations including the need for semen examinations, fertility preservation, and assisted reproductive technology. These problems may be addressed with the aid of non-freezing storage techniques. The main and most effective preservation strategies are the partial or total replacement of seminal plasma with culture medium, named as extenders, and temperature-induced metabolic restriction. Semen extenders consist of buffers, osmolytes, and antioxidants, etc. to protect spermatozoa against the above-mentioned adverse factors. Extended preservation of human spermatozoa in vitro has a negative effect on sperm parameters, whereas its effect on ART outcomes remains inconsistent. The storage duration, temperature, and pre-treatment of semen should be determined according to the aims of preservation. Advanced techniques such as nanotechnology and omics have been introduced and show great potential in the lifespan extension of human sperm. It is certain that more patients will benefit from it in the near future. This review provided an overview of the current knowledge and prospects of prolonged non-freezing storage of human sperm in vitro.

Electrophysiology of Human Gametes: A Systematic Review

PURPOSE

Oocytes and spermatozoa are electrogenic cells with the ability to respond to electrical stimuli and modulate their electrical properties accordingly. Determination of the ionic events during the gamete maturation helps to design suitable culture media for gametes in assisted reproductive technology (ART). The present systematic review focuses on the electrophysiology of human gametes during different stages of maturation and also during fertilization.

MATERIALS AND METHODS

The reports published in the English language between January 2000 and July 2021 were extracted from various electronic scientific databases following the PRISMA checklist using specific MeSH keywords.

RESULTS

Subsequent to the screening process with defined inclusion and exclusion criteria, 60 articles have been included in this review. Among them, 11 articles were directly related to the electrophysiology of human oocytes and 49 physiology department to the electrophysiology of human spermatozoa.

CONCLUSIONS

Gametes generate electrical currents by ionic exchange, particularly Na+, K+, Cl-, H+, Zn2+, Cu2+, Se2+, Mg2+, HCO3-, and Ca2+ through specific ion channels in different stages of gamete maturation. The ionic concentrations, pH, and other physicochemical variables are modulated during the gametogenesis, maturation, activation, and the fertilization process following gamete function and metabolism. The electrical properties of human gametes change during different stages of maturation. Although it is demonstrated that the electrical properties are significant regulators of cell signaling and are fundamental to gamete maturation and fertilization, their exact roles in these processes are still poorly understood. Further research is required to unveil the intricate electrophysiological processes of human gamete maturation.

New Insight on the In Vitro Effects of Melatonin in Preserving Human Sperm Quality

Spermatozoa (SPZ) are sensitive to stressful conditions, particularly oxidative stress, which alters their quality; thus, the use of protective molecules as an antioxidant is encouraged. Herein, we used melatonin (MLT) to investigate its in vitro effects on human sperm parameters under conditions of oxidative stress induced by cadmium (Cd). Fifteen human semen samples were divided into control, Cd-treated, MLT-treated, and Cd+MLT-treated groups and analyzed after 30 min, 6 h, and 24 h of exposure. Results showed a time-dependent decrease in SPZ motility, DNA integrity, and increased apoptosis induced by oxidative stress, and these effects were counteracted by MLT co-treatment. Based on these data, we further explored additional parameters just at 24 h. The induced oxidative stress, highlighted by the increased lipid peroxidation, reduced the percentage of SPZ able to undertake acrosome reaction and altered the levels and localization of some protein markers of motility (PREP, RSPH6A), morphology (DAAM1), and acrosome membrane (PTMA, IAM38); all these effects were counteracted by MLT co-treatment. Interestingly, MLT alone was able to ameliorate motility at 30 min of incubation compared to the control, while at 24 h, it prevented the physiological alteration in terms of motility, DNA integrity, and apoptosis. Collectively, the data encourage MLT use as an integrative molecule to ameliorate human gamete quality when compromised by stressful conditions.

Sperm Ion Transporters and Channels in Human Asthenozoospermia: Genetic Etiology, Lessons from Animal Models, and Clinical Perspectives

In mammals, sperm fertilization potential relies on efficient progression within the female genital tract to reach and fertilize the oocyte. This fundamental property is supported by the flagellum, an evolutionarily conserved organelle that provides the mechanical force for sperm propulsion and motility. Importantly several functional maturation events that occur during the journey of the sperm cells through the genital tracts are necessary for the activation of flagellar beating and the acquisition of fertilization potential. Ion transporters and channels located at the surface of the sperm cells have been demonstrated to be involved in these processes, in particular, through the activation of downstream signaling pathways and the promotion of novel biochemical and electrophysiological properties in the sperm cells. We performed a systematic literature review to describe the currently known genetic alterations in humans that affect sperm ion transporters and channels and result in asthenozoospermia, a pathophysiological condition defined by reduced or absent sperm motility and observed in nearly 80% of infertile men. We also present the physiological relevance and functional mechanisms of additional ion channels identified in the mouse. Finally, considering the state-of-the art, we discuss future perspectives in terms of therapeutics of asthenozoospermia and male contraception.

Relevance of Aquaporins for Gamete Function and Cryopreservation

Simple Summary

The interaction between cells and the extracellular medium is of great importance; changes in medium composition can drive water movement across plasma membranes. Aquaporins (AQPs) are membrane channels involved in the transport of water and some solutes across membranes. When sperm enter the female reproductive tract after ejaculation, they encounter a drastic change in extracellular composition, which leads to water flowing across the plasma membrane. This triggers a series of events that are crucial to allowing fertilization to take place, such as regulation of sperm motility. In the context of assisted reproduction techniques (ART), long-term storage of gametes is sometimes required, and, during cryopreservation, these cells undergo drastic changes in extracellular medium composition. As a result, AQPs are crucial in both sperm and oocytes during this process. Cryopreservation is of considerable importance for fertility preservation in livestock, endangered species and for individuals undergoing certain medical treatments that compromise their fertility. Further research to fully elucidate the roles and underlying mechanisms of AQPs in mammalian sperm is therefore warranted.

Abstract

The interaction between cells and the extracellular medium is of great importance, and drastic changes in extracellular solute concentrations drive water movement across the plasma membrane. Aquaporins (AQPs) are a family of transmembrane channels that allow the transport of water and small solutes across cell membranes. Different members of this family have been identified in gametes. In sperm, they are relevant to osmoadaptation after entering the female reproductive tract, which is crucial for sperm motility activation and capacitation and, thus, for their fertilizing ability. In addition, they are relevant during the cryopreservation process, since some members of this family are also permeable to glycerol, one of the most frequently used cryoprotective agents in livestock. Regarding oocytes, AQPs are very important in their maturation but also during cryopreservation. Further research to define the exact sets of AQPs that are present in oocytes from different species is needed, since the available literature envisages certain AQPs and their roles but does not provide complete information on the whole set of AQPs. This is of considerable importance because, in sperm, specific AQPs are known to compensate the role of non-functional members.

Osmoregulation in fish sperm

In most fish exhibiting external fertilization, spermatozoa become motile after release into water, triggered by differences between intracellular and extracellular conditions such as osmotic pressure, ion composition, and pH. The rapid change in osmolarity initiating spermatozoon motility induces osmotic pressure, resulting in active water movement across the cell membrane. Mechanisms of ion and water transport across the plasma membrane and cell volume regulation are important in maintaining structure and functional integrity of the cell. The capacity of the fish spermatozoon plasma membrane to adapt to dramatic environmental changes is an essential prerequisite for motility and successful fertilization. Adaptation to change in external osmolality may be the basis of spermatozoon function and an indicator of sperm quality. The involvement of specific water channels (aquaporins) in cell volume regulation and motility is highly likely. The goal of this review is to describe basic mechanisms of water transport and their role in fish spermatozoon physiology, focusing on osmoresistance, cell volume regulation, motility, and survival.

Na,K-ATPase Atp1a4 isoform is important for maintaining sperm flagellar shape

PURPOSE

The aim of this study is to investigate the mechanisms by which the testis specific Na,K-ATPase ion transport system (Atp1a4) controls sperm morphology and shape.

METHODS

Sperm from wild-type (WT) and Atp1a4 knockout (Atp1a4 KO) mice were analyzed morphologically, using light, transmission, and scanning electron microscopy; and functionally, applying sperm osmotic challenge and viability tests. In addition, a sperm proteomic study was performed.

RESULTS

Light microscopy confirmed that sperm lacking Atp1a4 present a bend at the junction of the mid- and principal piece of the flagellum. This bend had different degrees of angulation, reaching occasionally a complete flagellar retroflexion. The defect appeared in sperm collected from the cauda epididymis, but not the epididymal caput or the testis. Transmission and scanning electron microscopy revealed a dilation of the cytoplasm at the site of the bend, with fusion of the plasma membrane in overlapping segments of the flagellum. This was accompanied by defects in the axoneme and peri-axonemal structures. Sperm from Atp1a4 KO mice showed an abnormal response to hypoosmotic challenge with decreased viability, suggesting reduced capacity for volume regulation. Exposure to Triton X-100 only partially recovered the flagellar bend of Atp1a4 KO sperm, showing that factors other than osmotic regulation contribute to the flagellar defect. Interestingly, several key sperm structural proteins were expressed in lower amounts in Atp1a4 KO sperm, with no changes in their localization.

CONCLUSIONS

Altogether, our results show that Atp1a4 plays an important role in maintaining the proper shape of the sperm flagellum through both osmotic control and structurally related mechanisms.

Assessment of the Morphometry of Heads of Normal Sperm and Sperm with the Dag Defect in the Semen of Duroc Boars

Introduction

The Dag defect is one of the primary morphological defects in sperm correlating with reduced fertility. This defect is found in the spermatozoa of many livestock species. The aim of the study was to assess the morphometry of the heads of normal sperm and sperm with the Dag defect in the semen of Duroc breeding boars.

Material and Methods

Sperm morphology was examined in ten ejaculates each from 12 Duroc boars. In total, 3,600 morphologically normal sperm and 838 sperm with the Dag defect were evaluated. The area, perimeter, length and width of the sperm head were measured and these basic morphometric parameters were used to calculate four additional shape indices characterising the sperm head, i.e. ellipticity, elongation, roughness and regularity.

Results

Sperm with this defect had markedly smaller heads, 0.32 μm shorter and 0.19 μm narrower than the heads of sperm with normal morphological structure. The heads of sperm with the Dag defect also had a 1.1μm smaller perimeter and a 2.5 μm² smaller surface area than the heads of morphologically normal sperm.

Conclusions

The Dag defect is found in boar sperm irrespective of the age of the individual. It affects the morphology of the sperm head.

Observations on Dag-like defect of spermatozoa induced by treatment of the phytotherapeutic Quassia amara/quassin in the mouse model

Gross alterations in the morphology of spermatozoa, teratozoospermia, invariably render them incapable of fertilisation. One of the contributory factors to teratozoospermia is failure of spermatozoon to shed the cytoplasmic droplet even after their arrival at epididymis. Quassia amara and quassin are of medicinal value with special reference to malaria. Nevertheless, there are also reports implicating Quassia/quassin in male reproductive toxicity. We were interested in finding if its therapeutic application would jeopardise male fertility. So, we tested it for male reproductive toxicity by analysing, among other aspects, abnormal sperm morphologies, and made a systematic analysis of the spermatozoa of treated mice before they are spermiated and until they arrive at the cauda epididymis. The spermatozoa not only failed to shed the cytoplasmic droplet during epididymal transit but swell to a very large size and were angulated, resulting in Dag-like defect or lasso shape. A link between cytoplasmic droplet that was retained and lasso shape of tail was indicated. This article traces the structural changes in spermatozoa that lead to angulation, flexion and coiling of the tail, caused due to retention of cytoplasmic droplet, and explains one of the mechanisms of toxicant-induced teratozoospermia.

Hypotonic challenge reduces human sperm motility through coiling and folding of the tail

Human ejaculates collected for in vitro procedures show variably rapid increases in osmolality, depending on enzymatic degradation of compounds. Changes in osmolality can affect cell functions due to the energy consuming processes needed to control cell volume. The aim was to examine the effects of a hypotonic challenge for spermatozoa exposed to increased osmolality. Spermatozoa were selected by density gradient centrifugation and washed in media with different osmolalities. Osmolality was measured by freezing‐point depression and sperm velocities by CASA. Swimming pattern observations and assessments of tail morphology of fixed spermatozoa were done with phase contrast microscopy. Increased osmolality did not change the curvilinear velocity (VCL), while decreased osmolality reduced or abolished VCL nonreversibly. For spermatozoa first exposed to 400 mOsm/kg, reversal of osmolality to 290 mOsm/kg reduced the VCL and the average path velocity (VAP) permanently. Hypotonic challenges increased sperm tail coiling and folding in a dose‐response pattern. Spermatozoa once adjusted to high osmolality in the liquefied ejaculate are likely to suffer if exposed to a medium with a lower osmolality. For improved success of Assisted Reproductive Technologies (ART), it appears to be important to minimise the duration of sperm exposure to the ejaculate, by early dilution or sperm preparation.

DAAM1 and PREP are involved in human spermatogenesis

During differentiation of the male gamete, there is a massive remodelling in the shape and architecture of all the cells in the seminiferous epithelium. The cytoskeleton, as well as many associated proteins, plays a pivotal role in this process. To better characterise the factors involved, we analysed two proteins: the formin, dishevelled-associated activator of morphogenesis 1 (DAAM1), which participates in the regulation of actin polymerisation, and the protease, prolyl endopeptidase (PREP), engaged in microtubule-associated processes. In our previous studies we demonstrated their involvement in cytoskeletal dynamics necessary for correct postnatal development of the rat testis. Here, we used samples of testicular tissue obtained from infertile men by testicular sperm extraction and the spermatozoa of asthenoteratozoospermic patients. By western blot and immunofluorescent analysis, we found that DAAM1 and PREP expression and localisation were impaired in both the testis and spermatozoa, and in particular in the midpiece as well as in the principal and end-pieces of the flagella, as compared with spermatozoa of normospermic men. Our results provide new knowledge of the dynamics of spermatogenesis, raising the possibility of using DAAM1 and PREP as new markers of normal fertility.

More than just a pressure relief valve: physiological roles of volume-regulated LRRC8 anion channels

The volume-regulated anion channel (VRAC) is a key player in the volume regulation of vertebrate cells. This ubiquitously expressed channel opens upon osmotic cell swelling and potentially other cues and releases chloride and organic osmolytes, which contributes to regulatory volume decrease (RVD). A plethora of studies have proposed a wide range of physiological roles for VRAC beyond volume regulation including cell proliferation, differentiation and migration, apoptosis, intercellular communication by direct release of signaling molecules and by supporting the exocytosis of insulin. VRAC was additionally implicated in pathological states such as cancer therapy resistance and excitotoxicity under ischemic conditions. Following extensive investigations, 5 years ago leucine-rich repeat-containing family 8 (LRRC8) heteromers containing LRRC8A were identified as the pore-forming components of VRAC. Since then, molecular biological approaches have allowed further insight into the biophysical properties and structure of VRAC. Heterologous expression, siRNA-mediated downregulation and genome editing in cells, as well as the use of animal models have enabled the assessment of the proposed physiological roles, together with the identification of new functions including spermatogenesis and the uptake of antibiotics and platinum-based cancer drugs. This review discusses the recent molecular biological insights into the physiology of VRAC in relation to its previously proposed roles.

Post-ejaculatory increase in human semen osmolality in vitro

Spermatozoa prepared in vitro for assisted reproductive technology (ART) encounter other challenges than in vivo. One could be to survive and function despite varying extracellular osmolality. There is a lack of consistent knowledge of human semen osmolality and changes after liquefaction. The aim of this study was to investigate changes in semen osmolality that may occur in vitro after ejaculation and during sperm handling for ART. Osmolality was measured in 86 semen samples by freezing-point depression during storage in vitro at various times and temperatures. The freezing-point depression method was robust and reliable for measuring the osmolality of whole semen as shown by a low variability between repeats. At ejaculation, the osmolality was isotonic to cervical mucus and body fluids. There was a marked increase in osmolality after liquefaction, and the degree of increase varied greatly between samples. Osmolality rose with increasing temperature, and the progressive increase was blocked by denaturising temperature. Spermatozoa in each individual semen sample experienced a highly variable environment in vitro with respect to osmolality. This may be of importance regarding the handling of semen samples for the outcome of ART.

Sperm motility and lipid composition in internally fertilizing ocellate river stingray Potamotrygon motoro

All extant groups of Elasmobranches have internal fertilization and the structure of the male reproductive organs is very specific: sperm passes from the internal organs via the cloaca, but the male copulating organ (clasper) is distant from the cloaca. This suggests that sperm can contact the surrounding medium before fertilization. Because of this involvement with the environment, external signaling in sperm motility activation could occur in these species even though their fertilization mode is internal. In this case, spermatozoa of Elasmobranches should hypothetically possess a specific structure and membrane lipid composition which supports physiological functions of the sperm associated with environmental tonicity changes occurring at fertilization. Additionally, sperm motility properties in these taxa are poorly understood. The current study examined sperm lipid composition and motility under different environmental conditions for the ocellate river stingray, Potamotrygon motoro, an endemic South America freshwater species. Sperm samples were collected from six mature males during the natural spawning period. Sperm motility was examined in seminal fluid and fresh water by light video microscopy. Helical flagellar motion was observed in seminal fluid and resulted in spermatozoon progression; however, when diluted in fresh water, spermatozoa were immotile and had compromised structure. Lipid class and fatty acid (FA) composition of spermatozoa was analyzed by thin layer and gas chromatography. Spermatozoa FAs consisted of 33 ± 1% saturated FAs, 28 ± 1% monounsaturated FAs (MUFAs), and 41 ± 1% polyunsaturated FAs (PUFAs), and a high content of n-6 FAs (32 ± 2%) was measured. These results allowed us to conclude that sperm transfer from P. motoro male into female should occur without coming into contact with the hypotonic environment so as to preserve potent motility. In addition, this unusual reproductive strategy is associated with specific spermatozoa structure and lipid composition. Low level of docosahexaenoic acid and relatively low PUFA/MUFA ratio probably account for the relatively low fluidity of freshwater stingray membrane and can be the main reason for its low tolerance to hypotonicity.

Epididymal approaches to male contraception

Today, a vast arsenal of contraceptive methods interfering at different levels of the female reproductive axis is available. This is not the case for men for whom, until now, there is no reliable male reversible method and for whom vasectomy, condom and withdrawal are the only options available. Despite this limited supply, more than one third of all contraceptive methods used worldwide rely on the cooperation of the male partner. Besides developing hormonal approaches to stop sperm production, there may be attractive approaches that will interfere with sperm functions rather than production. Sperm functions are primarily established during post-testicular maturation, with the epididymis accounting for the majority. The purpose of this review is to present some of the promising and/or already abandoned leads that emerge from research efforts targeting the epididymis and its activities as potential means to achieve male post-meiotic contraception.

Slc26a3 deficiency is associated with epididymis dysplasia and impaired sperm fertilization potential in the mouse

Members of the solute carrier 26 (SLC26) family have emerged as important players in mediating anions fluxes across the plasma membrane of epithelial cells, in cooperation with the cystic fibrosis transmembrane conductance regulator (CFTR) chloride channel. Among them, SLC26A3 acts as a chloride/bicarbonate exchanger, highly expressed in the gastrointestinal, pancreatic and renal tissues. In humans, mutations in the SLC26A3 gene were shown to induce congenital chloride-losing diarrhea (CLD), a rare autosomal recessive disorder characterized by life-long secretory diarrhea. In view of some reports indicating subfertility in some male CLD patients together with SLC26-A3 and -A6 expression in the male genital tract and sperm cells, we analyzed the male reproductive parameters and functions of SLC26A3 deficient mice, which were previously reported to display CLD gastro-intestinal features. We show that in contrast to Slc26a6, deletion of Slc26a3 is associated with severe lesions and abnormal cytoarchitecture of the epididymis, together with sperm quantitative, morphological and functional defects, which altogether compromised male fertility. Overall, our work provides new insight into the pathophysiological mechanisms that may alter the reproductive functions and lead to male subfertility in CLD patients, with a phenotype reminiscent of that induced by CFTR deficiency in the male genital tract.

Deficient LRRC8A-dependent volume-regulated anion channel activity is associated with male infertility in mice

Ion channel-controlled cell volume regulation is of fundamental significance to the physiological function of sperm. In addition to volume regulation, LRRC8A-dependent volume-regulated anion channel (VRAC) activity is involved in cell cycle progression, insulin signaling, and cisplatin resistance. Nevertheless, the contribution of LRRC8A and its dependent VRAC activity in the germ cell lineage remain unknown. By utilizing a spontaneous Lrrc8a mouse mutation (c.1325delTG, p.F443*) and genetically engineered mouse models, we demonstrate that LRRC8A-dependent VRAC activity is essential for male germ cell development and fertility. Lrrc8a-null male germ cells undergo progressive degeneration independent of the apoptotic pathway during postnatal testicular development. Lrrc8a-deficient mouse sperm exhibit multiple morphological abnormalities of the flagella (MMAF), a feature commonly observed in the sperm of infertile human patients. Importantly, we identified a human patient with a rare LRRC8A hypomorphic mutation (c.1634G>A, p.Arg545His) possibly linked to Sertoli cell-only syndrome (SCOS), a male sterility disorder characterized by the loss of germ cells. Thus, LRRC8A is a critical factor required for germ cell development and volume regulation in the mouse, and it might serve as a novel diagnostic and therapeutic target for SCOS patients.

Cryopreservation media differentially affect sperm motility, morphology and DNA integrity

INTRODUCTION

Human sperm freezing is very widely used for male fertility preservation. This procedure consists in adding cryoprotectants to the spermatozoa followed by cooling and storing the spermatozoa at a subzero temperature. Many standardized cryopreservation media are available on the market. However, these media differ in their chemical composition and there are no sufficient data to optimize their classification. Therefore, the aim of this study was to compare five commercially available sperm cryopreservation media, which have not been compared together, in terms of motility, morphology and DNA integrity.

MATERIALS AND METHODS

One-hundred semen samples were obtained from 10 fertile participants and 90 infertile men. Each sample was evaluated before freezing for motility, morphology and DNA fragmentation index (DFI). Then, it was equally divided into five aliquots. Each aliquot was cryopreserved using one of the five media (A, B, C, D, and E). The same parameters were re-evaluated after the addition of the cryopreservation media in the fertile group, and after sperm thawing in fertile and infertile groups.

RESULTS

The results showed that the five selected cryopreservation media had negative effects on sperm motility and morphology per se. In the infertile group, the cryosurvival factor was significantly lower in cryomedium A when compared to the four other media (p < 0.001). In addition, a significantly higher percentage of sperm with coiled tail was detected in cryomedium E compared to cryomedium A (p < 0.05) and to cryomedium B (p < 0.001) after thawing, in the infertile group. Furthermore, the sperm DFI was significantly higher in cryomedia A (p < 0.001), B (p < 0.001), C (p < 0.01), D (p < 0.01) and E (p < 0.05) compared to that of the fresh semen derived from infertile participants.

CONCLUSION

This study indicates that the recovery rate of competent spermatozoa, after cryopreservation, is still critical in infertile men. Therefore, frozen semen sample should be used only when necessary.

LRRC8/VRAC anion channels are required for late stages of spermatid development in mice

Spermatogenesis is a highly complex developmental process that occurs primarily in seminiferous tubules of the testes and requires additional maturation steps in the epididymis and beyond. Mutations in many different genes can lead to defective spermatozoa and hence to male infertility. Some of these genes encode for ion channels and transporters that play roles in various processes such as cellular ion homeostasis, signal transduction, sperm motility, and the acrosome reaction. Here we show that germ cell–specific, but not Sertoli cell–specific, disruption of Lrrc8a leads to abnormal sperm and male infertility in mice. LRRC8A (leucine-rich repeat containing 8A) is the only obligatory subunit of heteromeric volume-regulated anion channels (VRACs). Its ablation severely compromises cell volume regulation by completely abolishing the transport of anions and osmolytes through VRACs. Consistent with impaired volume regulation, the cytoplasm of late spermatids appeared swollen. These cells failed to properly reduce their cytoplasm during further development into spermatozoa and later displayed severely disorganized mitochondrial sheaths in the midpiece region, as well as angulated or coiled flagella. These changes, which progressed in severity on the way to the epididymis, resulted in dramatically reduced sperm motility. Our work shows that VRAC, probably through its role in cell volume regulation, is required in a cell-autonomous manner for proper sperm development and explains the male infertility of Lrrc8a^−/− mice and the spontaneous mouse mutant ébouriffé.

Seminal plasma differentially alters the resistance of dog, ram and boar spermatozoa to hypotonic stress

During ejaculation and the deposition in the female genital tract, spermatozoa undergo hypo-osmotic stress and need to withstand it for optimal fertility. Resistance to hypo-osmotic stress may be affected by the interaction of the spermatozoa with seminal fluid components. The hypo-osmotic resistance of epididymal and ejaculated spermatozoa from dogs, rams and boars was assessed by flow cytometric measurement of sperm viability after incubation in NaCl solutions with osmolalities ranging from 0 to 300 mmol/kg. The hypotonic resistance of epididymal spermatozoa was greater than those of ejaculated spermatozoa in all three species. Among species comparison revealed that ejaculated spermatozoa from dogs were much more resistant than those from rams and boars as 80.4 ± 5.3%, 56.7 ± 4.7 and 9.6 ± 3.6% of live spermatozoa were observed following exposure to an osmolality of 90 mmol/kg in dogs, rams and boars respectively. This can be explained by the fact that dog, ram and boar differ markedly in composition of the seminal plasma owing to the presence (ram, boar) or absence (dog) of seminal vesicles. Hypotonic resistance of epididymal and ejaculated dog spermatozoa was similar whereas ram and boar spermatozoa showed a marked drop in resistance after ejaculation. The in vitro incubation of boar epididymal spermatozoa with raw seminal plasma or the seminal plasma protein fraction induced a similar loss of resistance, suggesting that seminal proteins are involved in the lack of resistance to hypotonic stress of boar ejaculated spermatozoa.

Major regulatory mechanisms involved in sperm motility

The genetic bases and molecular mechanisms involved in the assembly and function of the flagellum components as well as in the regulation of the flagellar movement are not fully understood, especially in humans. There are several causes for sperm immotility, of which some can be avoided and corrected, whereas other are related to genetic defects and deserve full investigation to give a diagnosis to patients. This review was performed after an extensive literature search on the online databases PubMed, ScienceDirect, and Web of Science. Here, we review the involvement of regulatory pathways responsible for sperm motility, indicating possible causes for sperm immotility. These included the calcium pathway, the cAMP-dependent protein kinase pathway, the importance of kinases and phosphatases, the function of reactive oxygen species, and how the regulation of cell volume and osmolarity are also fundamental components. We then discuss main gene defects associated with specific morphological abnormalities. Finally, we slightly discuss some preventive and treatments approaches to avoid development of conditions that are associated with unspecified sperm immotility. We believe that in the near future, with the development of more powerful techniques, the genetic causes of sperm immotility and the regulatory mechanisms of sperm motility will be better understand, thus enabling to perform a full diagnosis and uncover new therapies.

Aquaporins in boar spermatozoa. Part II: detection and localisation of aquaglyceroporin 3

The proteins belonging to the aquaporin family play a fundamental role in water and solute transport across biological membranes. While the presence of these proteins has been extensively studied in somatic cells, their function in mammalian spermatozoa has been studied less. The present study was designed to identify and localise aquaglyceroporin 3 (AQP3) in boar spermatozoa. With this purpose, 29 fresh ejaculates from post-pubertal Piétrain boars were classified into two groups based upon their sperm quality and subsequently evaluated through western blot and immunofluorescence assessments. Western blotting showed the specific signal band of AQP3 at 25 kDa, whereas immunofluorescence assessments allowed us to identify two different AQP3 localisation patterns: (1) spermatozoa presenting a clear labelling located only in the mid-piece and (2) spermatozoa exhibiting a distribution pattern in the head and along the entire tail. The first staining pattern was predominant in all studied ejaculates. Despite individual differences in AQP3 content and localisation between boar ejaculates, these differences were not correlated with sperm quality. In conclusion, although AQP3 is present in boar spermatozoa in two different localisation patterns, neither the AQP3 content nor its localisation have been found to be associated with conventional sperm parameters.

Mitigation of sperm tail abnormalities using demembranation approach in the clouded leopard (Neofelis nebulosa)

Clouded leopards (Neofelis nebulosa) produced high proportion of abnormal spermatozoa (mainly tail defects) that can limit sperm movement and conception. The study aimed to better identify the origin of those defects using a demembranation approach. Ejaculates (1-2 ejaculations/male; n = 9) were allocated to simple washing (control; resulting in 11.7% ± 1.9% coiled tails) and processed through colloid centrifugation to reduce the number of sperm with tail defects (treatment, resulting in 5.9% ± 0.9% coiled tails). Aliquots of semen were incubated in hypo-osmotic solution (HOS, 60 mOsm fructose solution) containing 5 mM dithiothreitol (DTT) (a reducing agent) to prevent oxidation of sperm membrane. Thereafter, 20% Triton X-100 (TX) (a detergent) was added to the HOS/DTT-treated samples. After HOS/DTT incubation, the control samples and sperm-selected samples presented 73.4% ± 3.1% and 73.9% ± 2.5% swollen sperm (bent and coiled) indicating membrane intact, respectively. Most of the coiled tail in the raw ejaculates could not be opened by TX indicating that the cause of coiled sperm tails may be from testicular origin. The proportion of sperm with tightly coiled tail tended to be lower in the sperm-selected group than control group (18.8% ± 3.8% and 26.5% ± 3.4%; p = .1), whereas the sperm opened up by TX tended to be higher in the sperm-selected group (53.6% ± 10.4% and 21.1% ± 7.9%; p = .06). The results indicated TX was able to uncoil half of the tightly coiled sperm in the semen undergone preparation. In conclusion, the coiled sperm in the clouded leopard semen were likely not a defect of sperm volume regulation during post-ejaculate (osmotic swelling) but pre-ejaculate origin. Semen preparation demonstrated its ability to lessen the primary sperm defects and selected spermatozoa that were prone to be mitigated after demembranation.

Regulation of hamster sperm hyperactivation by extracellular Na+

Mammalian sperm motility has to be hyperactivated to be fertilization-competent. Hyperactivation is regulated by extracellular environment. Osmolality of mammalian semen is higher than that in female reproductive tract; however, the effect of them on hyperactivation has not been investigated. So we investigated the effect of osmotic environment on hyperactivation using hamster spermatozoa at first. Increase in the osmolality of the media (∼370 mOsm) by increasing the concentration of NaCl (∼150 mmol/L) caused the delay of the expression of hyperactivation. When NaCl concentration varied in the same range (75–150 mmol/L) whereas the osmolality was fixed at 370 mOsm by adding mannitol, the delay of hyperactivation occurred dependent on NaCl concentration. Increase in NaCl concentration also caused suppression of curvilinear velocity, bend angle, and sliding velocity of the flagellum at the onset of incubation, suggesting that NaCl concentration affect both activation and hyperactivation in hamster spermatozoa. Hamster sperm intracellular Ca2+ concentration decreased as extracellular NaCl concentration increased, whereas membrane potential and intracellular pH were unaffected by extracellular NaCl concentration. SN-6 and SEA0400, inhibitors of Na+-Ca2+ exchanger (NCX), increased intracellular Ca2+ and accelerated hyperactivation in the presence of 150 mmol/L NaCl. Tyrosine phosphorylation on fibrous sheath proteins was unaffected by extracellular NaCl concentration. These results suggest that extracellular Na+ suppresses hamster sperm hyperactivation by reducing intracellular Ca2+ via an action of NCX in a tyrosine phosphorylation-independent manner. It seems that the removal of suppression by extracellular Na+ leads to the expression of hyperactivated motility.

First Evidence of DAAM1 Localization During the Post-Natal Development of Rat Testis and in Mammalian Sperm

Dishevelled-associated activator of morphogenesis 1 (DAAM1) is a formin-family protein involved in nucleation of unbranched actin filaments and in cytoskeletal organization through Wnt-Dishevelled PCP pathway, which participates in essential biological processes, such as cell polarity, movement, and adhesion during morphogenesis and organogenesis. While its role has been investigated during development and in somatic cells, its potential association with the germinal compartment and reproduction is still unexplored. In this work, we assessed the possible association of DAAM1 with the morphogenesis of rat testis. We studied its expression and profiled its localization versus actin and tubulin, during the first wave of spermatogenesis and in the adult gonad (from 7 to 60 dpp). We show that, in mitotic phases, DAAM1 shares its localization with actin in Sertoli cells, gonocytes, and spermatogonia. Later, during meiosis, both proteins are found in spermatocytes, while only actin is detectable at the forming blood-testis barrier. DAAM1, then, follows the development of the acrosome system throughout spermiogenesis, and it is finally retained inside the cytoplasmic droplet in mature gametes, as corroborated by additional immunolocalization data on both rat and human sperm. Unlike the DAAM1, actin keeps its localization in Sertoli cells, and tubulin is associated with their protruding cytoplasm during the process. Our data support, for the first time, the hypothesis of a role for DAAM1 in cytoskeletal organization during Mammalian testis morphogenesis and gamete progression, while also hinting at its possible investigation as a morphological marker of germ cell and sperm physiology. J. Cell. Physiol. 231: 2172-2184, 2016. © 2016 Wiley Periodicals, Inc.

An Ecology of Sperm: Sperm Diversification by Natural Selection

Using basic ecological concepts, we introduce sperm ecology as a framework to study sperm cells. First, we describe environmental effects on sperm and conclude that evolutionary and ecological research should not neglect the overwhelming evidence presented here (both in external and internal fertilizers and in terrestrial and aquatic habitats) that sperm function is altered by many environments, including the male environment. Second, we determine that the evidence for sperm phenotypic plasticity is overwhelming. Third, we find that genotype-by-environment interaction effects on sperm function exist, but their general adaptive significance (e.g., local adaptation) awaits further research. It remains unresolved whether sperm diversification occurs by natural selection acting on sperm function or by selection on male and female microenvironments that enable optimal plastic performance of sperm (sperm niches). Environmental effects reduce fitness predictability under sperm competition, predict species distributions under global change, explain adaptive behavior, and highlight the role of natural selection in behavioral ecology and reproductive medicine.

Morphological study of boar sperm during their passage through the female genital tract

Once deposited in the female tract, sperm face a series of challenges that must be overcome to ensure the presence of an adequate normal sperm population close to the site of fertilization. Our aim was to evaluate the influence of the uterine milieu on boar sperm morphology. In experiment 1, sperm morphology was evaluated in the backflow (60 min after insemination) and within the uterotubal junction (UTJ) (collected ~24 h after insemination) following intrauterine sperm deposition (n = 6) and compared with the morphology of the sperm in the insemination dose. In experiment 2, the influence of the uterine fluid (UF) on sperm morphological modifications was evaluated. For this purpose, ejaculated (n = 4) and epididymal (n = 4) sperm were in vitro incubated with or without UF for 2 and 24 h. In both experiments, sperm were classified as normal, having a cytoplasmic droplet (proximal or distal) or having tail defects. The results of experiment 1 pointed to an increase in morphologically abnormal sperm collected in the backflow (27.70%) and a reduction of the same in the UTJ (2.12%) compared with the insemination dose (17.75%) (P < 0.05). In experiment 2, incubation of ejaculated sperm with UF did not provoke any morphological modifications; however, when epididymal sperm were incubated with UF, a pronounced increase in the percentage of normal sperm was evident after 24 h compared with the initial dose (from 25.77% to 53.58%, P < 0.05), mainly due to distal cytoplasmatic droplet shedding (53.22 vs. 20.20%). In conclusion, almost all the sperm that colonize the UTJ had a normal morphology, with part of the abnormal sperm having been discarded in the backflow and part selected/modified on their way to the oviduct. UF seems to influence cytoplasmic distal droplet removal, as demonstrated previously in seminal plasma.

Morphometry of boar sperm head and flagellum in semen backflow after insemination

Once deposited in the female reproductive system, sperm begin their competition and undergo a selection to reach the site of fertilization. Little is known about the special characteristics of sperm that reach the oviduct and are able to fertilize, with even less information on the role of sperm dimension and shape in transport and fertilization. Here, we examine whether sperm morphometry could be involved in their journey within the uterus. For this purpose, sperm head dimension (length, width, area, and perimeter) and shape (shape factor, ellipticity, elongation, and regularity), and flagellum length were analyzed in the backflow at different times after insemination (0-15, 16-30, and 31-60 minutes). Sperm morphometry in the backflow was also analyzed taking into account the site of semen deposition (cervical vs. intrauterine). Finally, flagellum length was measured at the uterotubal junction. Sperm analyzed in the backflow were small (head and flagellum) with different head shapes compared with sperm observed in the dose before insemination. The site of deposition influenced head morphometry and tail size both being smaller in the backflow after cervical insemination compared with intrauterine insemination. Mean tail length of sperm collected in the backflow was smaller than that in the insemination dose and at the uterotubal junction. Overall, our results suggest that sperm size may be involved in sperm transport either because of environment or through sperm selection and competence on their way to encounter the female gamete.

Deep sequencing analysis of microRNAs in bovine sperm

microRNAs (miRNAs) are small non-coding RNAs that participates in the regulation of many physiological pathways, but a role for spermatozoon-delivered miRNAs in fertilization and embryonic development remains controversial. A library of miRNAs in bovine sperm was constructed using Illumina high-throughput sequencing technology, along with the predication and the pathway analysis of target genes. miRNAs in mammalian spermatozoon were systematically investigated, and a protocol for RNA isolation from the cauda region of an epididymal biopsy was established. Unique sequences that were 18-26 nucleotides in length were mapped to specific precursors in miRBase 20.0 using BLAST. A total of 951 known miRNAs and 8 novel, highly expressed miRNA candidates were identified. The search for endogenous sperm miRNAs will contribute to a preliminary database for functional and molecular mechanistic studies in embryonic development and sperm epigenetic programming.

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.

An investigation of excess residual cytoplasm in human spermatozoa and its distinction from the cytoplasmic droplet

Recent studies have shown cytoplasmic droplets to be normal morphological occurrences in human male spermatozoa. When the cytoplasm around the sperm midpiece is present in large amounts, however, pathological effects may transpire. The cytoplasmic droplet then becomes known as excess residual cytoplasm, which can impair overall sperm function and produce higher levels of reactive oxygen species, potentially leading to male infertility. Though the distinction between cytoplasmic droplets and excess residual cytoplasm has been made, some studies fail to recognize the difference and incorrectly label the latter as a cytoplasmic droplet. This review attempts to clarify excess residual cytoplasm's effect on fertility, examine the enzymes responsible, and suggest tests and possible treatment options for those affected by this defect.

Les approches épididymaires de la contraception masculine

L’offre en matière de moyens contraceptifs masculins est limitée et, en particulier, à ce jour il n’existe pas de contraception hormonale masculine sur le marché. L’épididyme, dans lequel les spermatozoïdes acquièrent leurs capacités fécondantes et où ils sont stockés, s’avère être un site intéressant à cibler. Cette revue vise à présenter de façon synthétique les quelques pistes prometteuses qui ont émergé ces dernières années.

Changes in rat spermatozoa function after cooling, cryopreservation and centrifugation processes

Rat sperm cryopreservation is an effective method of archiving valuable strains for biomedical research and handling of rat spermatozoa is very important for successful cryopreservation. The aim of this study was to evaluate changes in rat sperm function during cryopreservation and centrifugation. Epididymal rat spermatozoa were subjected to cooling and freezing-thawing processes and then motility, plasma membrane integrity (PMI), mitochondrial membrane potential (MMP) and reactive oxygen species (ROS) were compared before and after minimum centrifugation force (200×g). Cryopreservation decreased sperm motility, PMI, and MMP (P<0.05). Basal (without ROS inducer, tert-butyl hydroperoxide [TBHP] treatment) and stimulated ROS (with TBHP treatment) were increased in viable cooled spermatozoa compared to viable fresh spermatozoa (P<0.01), with equal susceptibility to TBHP among fresh, cooled, and frozen-thawed spermatozoa. Centrifugation decreased motility and PMI of frozen-thawed spermatozoa (P<0.05). Centrifugation decreased basal ROS of all spermatozoa (P<0.01), while it led to higher susceptibility to TBHP in viable cooled spermatozoa, showing higher increased fold in ROS and decreased rate in viability by TBHP in viable cooled spermatozoa (P<0.05). Cooling process was the major step of ROS generation, with loss in sperm motility, PMI, and MMP. Centrifugation affected function of cryopreserved spermatozoa. These data suggest that centrifugation makes rat spermatozoa susceptible to external ROS source, in particular during cooling process. Thus, protection from ROS damage and minimizing centrifugation should be considered during cryopreservation and post-thaw use of cryopreserved epididymal rat spermatozoa.

Epididymis response partly compensates for spermatozoa oxidative defects in snGPx4 and GPx5 double mutant mice

We report here that spermatozoa of mice lacking both the sperm nucleaus glutathione peroxidase 4 (snGPx4) and the epididymal glutathione peroxidase 5 (GPx5) activities display sperm nucleus structural abnormalities including delayed and defective nuclear compaction, nuclear instability and DNA damage. We show that to counteract the GPx activity losses, the epididymis of the double KO animals mounted an antioxydant response resulting in a strong increase in the global H₂O₂-scavenger activity especially in the cauda epididymis. Quantitative RT-PCR data show that together with the up-regulation of epididymal scavengers (of the thioredoxin/peroxiredoxin system as well as glutathione-S-transferases) the epididymis of double mutant animals increased the expression of several disulfide isomerases in an attempt to recover normal disulfide-bridging activity. Despite these compensatory mechanisms cauda-stored spermatozoa of double mutant animals show high levels of DNA oxidation, increased fragmentation and greater susceptibility to nuclear decondensation. Nevertheless, the enzymatic epididymal salvage response is sufficient to maintain full fertility of double KO males whatever their age, crossed with young WT female mice.

[Post-testicular protection of male gametes from oxidative damage. The role of the epididymis]

Spermatozoa leave the testis in an immature functional state and are devoid of self defense mechanisms. They will become motile and ready to fertilize only after their descent and their progressive maturation within the epididymal tubule. The epididymis also ensures the survival and the protection of male gametes while they go through the epididymis and during their storage in between two ejaculations. Amongst common stresses that concern spermatozoa, oxidative stress occupies a peculiar and dual position. While the events of epididymal sperm maturation necessitate a given level of oxidation, spermatozoa are particularly sensitive to oxidative damage. A fine balance between beneficial oxidation versus detrimental oxidative damage has to be maintained in the epididymal environment. Antioxidant enzymes of the glutathione peroxidase family play a key role in controling such a situation in the epididymis.

Sperm preparation: state-of-the-art--physiological aspects and application of advanced sperm preparation methods

For assisted reproduction technologies (ART), numerous techniques were developed to isolate spermatozoa capable of fertilizing oocytes. While early methodologies only focused on isolating viable, motile spermatozoa, with progress of ART, particularly intracytoplasmic sperm injection (ICSI), it became clear that these parameters are insufficient for the identification of the most suitable spermatozoon for fertilization. Conventional sperm preparation techniques, namely, swim-up, density gradient centrifugation and glass wool filtration, are not efficient enough to produce sperm populations free of DNA damage, because these techniques are not physiological and not modeled on the stringent sperm selection processes taking place in the female genital tract. These processes only allow one male germ cell out of tens of millions to fuse with the oocyte. Sites of sperm selection in the female genital tract are the cervix, uterus, uterotubal junction, oviduct, cumulus oophorus and the zona pellucida. Newer strategies of sperm preparation are founded on: (i) morphological assessment by means of 'motile sperm organelle morphological examination (MSOME)'; (ii) electrical charge; and (iii) molecular binding characteristics of the sperm cell. Whereas separation methods based on electrical charge take advantage of the sperm's adherence to a test tube surface or separate in an electrophoresis, molecular binding techniques use Annexin V or hyaluronic acid (HA) as substrates. Techniques in this category are magnet-activated cell sorting, Annexin V-activated glass wool filtration, flow cytometry and picked spermatozoa for ICSI (PICSI) from HA-coated dishes and HA-containing media. Future developments may include Raman microspectrometry, confocal light absorption and scattering spectroscopic microscopy and polarization microscopy.

Calcium Channels in the Development, Maturation, and Function of Spermatozoa

A proper dialogue between spermatozoa and the egg is essential for conception of a new individual in sexually reproducing animals. Ca2+ is crucial in orchestrating this unique event leading to a new life. No wonder that nature has devised different Ca2+-permeable channels and located them at distinct sites in spermatozoa so that they can help fertilize the egg. New tools to study sperm ionic currents, and image intracellular Ca2+ with better spatial and temporal resolution even in swimming spermatozoa, are revealing how sperm ion channels participate in fertilization. This review critically examines the involvement of Ca2+ channels in multiple signaling processes needed for spermatozoa to mature, travel towards the egg, and fertilize it. Remarkably, these tiny specialized cells can express exclusive channels like CatSper for Ca2+ and SLO3 for K+, which are attractive targets for contraception and for the discovery of novel signaling complexes. Learning more about fertilization is a matter of capital importance; societies face growing pressure to counteract rising male infertility rates, provide safe male gamete-based contraceptives, and preserve biodiversity through improved captive breeding and assisted conception initiatives.

Aquaporins in sperm osmoadaptation: an emerging role for volume regulation

Upon ejaculation, mammalian sperm experience a natural osmotic decrease during male to female reproductive tract transition. This hypo-osmotic exposure not only activates sperm motility, but also poses potential harm to sperm structure and function by inducing unwanted cell swelling. In this physiological context, regulatory volume decrease (RVD) is the major mechanism that protects cells from detrimental swelling, and is essential to sperm survival and normal function. Aquaporins are selective water channels that enable rapid water transport across cell membranes. Aquaporins have been implicated in sperm osmoregulation. Recent discoveries show that Aquaporin-3 (AQP3), a water channel protein, is localized in sperm tail membranes and that AQP3 mutant sperm show defects in volume regulation and excessive cell swelling upon physiological hypotonic stress in the female reproductive tract, thereby highlighting the importance of AQP3 in the postcopulatory sperm RVD process. In this paper, we discuss current knowledge, remaining questions and hypotheses about the function and mechanismic basis of aquaporins for volume regulation in sperm and other cell types.