Cholesterol efflux-mediated signal transduction in mammalian sperm: cholesterol release signals an increase in protein tyrosine phosphorylation during mouse sperm capacitation

Bovine serum albumin-induced calcium influx triggers soluble adenylyl cyclase activation and cyclic AMP signalling pathways in mouse sperm capacitation

Sperm capacitation involves a series of biochemical and physiological changes essential for fertilization. A critical regulator of capacitation, the soluble adenylyl cyclase (sAC; ADCY10)-dependent production of the second messenger cyclic AMP (cAMP), drives key downstream events such as protein kinase A (PKA) substrate phosphorylation. sAC activity is directly stimulated by bicarbonate (HCO3 -) and calcium (Ca2+). CatSper, a sperm-specific Ca2+ channel, is considered the primary pathway for Ca2+ influx during capacitation; however, emerging evidence suggests additional pathways exist. This study reveals that bovine serum albumin (BSA) influences the dynamics of intracellular Ca2+ concentration ([Ca2+]i) in CatSper1 knockout (KO) sperm and plays a novel role in sAC activation. Using single-cell live imaging and flow cytometry, we observed a rapid [Ca2+]i rise in the head of CatSper1 KO sperm under capacitating conditions, indicating an alternative Ca2+ entry mechanism. BSA alone, in the absence of HCO3 -, triggered a significant [Ca2+]i rise. Removal of extracellular Ca2+ abolished this [Ca2+]i rise, confirming the necessity of Ca2+ influx. This BSA-induced [Ca2+]i rise was upstream of sAC activation, since it was not affected by sAC inhibitors and led to increased cAMP production and PKA substrate phosphorylation. Our findings provide new insights into the regulatory mechanisms of sAC, highlighting the existence of a CatSper-independent Ca2+ entry pathway activated by BSA during sperm capacitation. This rapid [Ca2+]i rise is initiated in the sperm head and propagates throughout the cell, and is sufficient to activate sAC and stimulate cAMP synthesis independently of HCO3 -. KEY POINTS: Sperm capacitation, essential for fertilization, is regulated by sAC, which produces cAMP in response to HCO3 - and Ca2+, driving key events like protein kinase A substrate phosphorylation. We demonstrate the existence of a CatSper-independent Ca2+ entry pathway that initiates in the sperm head and propagates throughout the cell, occurring rapidly after sperm encounters albumin, a critical component of the capacitation medium used in in vitro fertilization procedures in mammals. This albumin-induced Ca2+ influx is sufficient to activate sAC and stimulate cAMP synthesis independently of HCO3 -. We further reveal a novel role for albumin, beyond its well-established function as a cholesterol acceptor, in triggering this rapid Ca2+ influx and downstream signalling events essential for sperm capacitation. By demonstrating a CatSper-independent regulatory pathway, we expand the current paradigm of Ca2+ signalling in sperm physiology.

Role of PI3K/AKT signaling pathway during capacitation

Spermatozoa must undergo a complex maturation process within the female genital tract known as capacitation. This process entails the phosphorylation or dephosphorylation of various proteins, and multiple signaling pathways are recognized to play a role. The present study aims to identify alterations in the expression of proteins related to the phosphatidylinositol-3 kinase (PI3K)/protein kinase B (AKT) signaling pathway and assess sperm functions during capacitation. Mouse spermatozoa were incubated in a medium supplemented with bovine serum albumin to induce capacitation. Subsequently, we evaluated sperm motility, cell viability, capacitation status, and acrosome reaction. Consequently, we observed a significant increase in several kinematic parameters. Additionally, the capacitation status and acrosome reaction exhibited a time-dependent manner. Furthermore, we confirmed a significant increase in the phosphorylation of PI3K, PDK1, and p-AKT (Thr308), along with activation of PKA and tyrosine phosphorylation. These alterations in protein expression were found to correlate with capacitation status, acrosome reaction, and various kinematic parameters. Therefore, our findings show that the phosphorylation of PKA and PI3K/AKT pathway-related proteins during capacitation may plays a crucial role in regulating sperm function. These findings contribute to a better understanding of the molecular mechanisms and interactions of the PI3K/AKT signaling pathway in the capacitation process.

Bicarbonate, calcium ions, hydrogen peroxide and trypsin modulate activation of Anopheles gambiae sperm motility and protein tyrosine phosphorylation

With the increasing concern of potential loss of transgenic mosquitoes which are candidates as new tools for mosquito-borne disease control, methods for cryopreservation are actively under investigation. Methods to cryopreserve Anopheles gambiae sperm have recently been developed, but there are no artificial insemination or in vitro fertilization tools available. As a step to achieve this, we sought to identify a suitable medium for in vitro incubation of An. gambiae sperm and to tease out critical components that are involved in the sperm motility activation process. Using two cell viability assays, we identified the Biggers-Whitten-Whittingham (BWW) medium as suitable for in vitro incubation of An. gambiae sperm isolated from testes. We then modified the medium for motility assays by testing different HCO3- and Ca2+ concentrations. Our results show that there is an HCO3- and Ca2+ concentration-dependent activation of An. gambiae sperm motility. We further demonstrated that H2O2 can be produced by the testes in vitro and that the addition of 5.3 μM of H2O2 to the medium improves sperm motility and increases protein tyrosine phosphorylation in An. gambiae. Finally, we show a dose-dependent activation of sperm motility by the addition of trypsin to the medium and more than a 2-fold increase in sperm motility when modified BWW (mBWW) medium is supplemented with H2O2 and trypsin. Our in vitro results suggest that protein tyrosine phosphorylation, intracellular ionic influx, intrinsic production of H2O2 and trypsin-like proteases play a vital role in signal transduction that leads to the activation of An. gambiae sperm motility.

Role of lipid binding protein, Niemann pick type C-2, in enhancing shrimp sperm physiological function

Sperm activation occurring in both male and female reproductive tract involves a highly complex series of biomolecular dynamics, particularly on membrane lipids and proteins. In mammals, the universal anticipation in cholesterol (CHO) sequestration plays a role in mammalian sperm maturation/capacitation, subsequently enhancing sperm fertilizing ability. In shrimp, we have previously shown that the level of cholesterol (CHO) is significantly reduced in vas deferens sperm when compared with sperm in the testes, presumably due to the sequestering action of the lipid-binding protein, one of which is Niemann-Pick Type C-2 (NPC2). Here, we used recombinant MrNPC2 protein to treat testicular sperm (Tsp) and quantitatively compared the amount of CHO with non-treated or 2-OH-β-CD treated sperm. HPTLC of the extracted lipids from Macrobrachium rosenbergii sperm revealed the presence of major phospholipids and CHO. Tsp treated with 2-OH-β-CD or MrNPC2 showed lower CHO levels, which was comparable to that of the vas deferens sperm as verified by the Amplex Red assay. Finally, the enhanced levels of protein tyrosine phosphorylation and ionophore-induced AR levels in the MrNPC2 treated Tsp significantly increased in a concentration-dependent manner, similar to that of the Vsp sperm. Altogether, our results indicated the importance of MrNPC2 as CHO moderator in sperm membrane, leading to an enhancement in sperm fertilizing ability.

Advancements in cyclodextrin-based controlled drug delivery: Insights into pharmacokinetic and pharmacodynamic profiles

This article discusses and summarizes some fascinating outcomes and applications of cyclodextrins (CDs) and their derivatives in drug delivery. These applications include the administration of protein, peptide medications, and gene delivery. Several innovative drug delivery systems, including NPs, microspheres, microcapsules, and liposomes, are designed with the help of CD, which is highlighted in this article. The use of these compounds as excipients in medicine formulation is reviewed, in addition to their well-known effects on drug solubility and dissolution, as well as their bioavailability, safety, and stability. Furthermore, the article focuses on many factors that influence the development of inclusion complexes, as having this information is necessary to manage these diverse materials effectively. An overview of the commercial availability, regulatory status, and patent status of CDs for pharmaceutical formulation is also presented. Due to the fact that CDs can discover new uses in drug delivery consistently, it is predicted that they will solve a wide range of issues related to the distribution of a variety of unique medications through various delivery channels.

Metabolic Shift in Porcine Spermatozoa during Sperm Capacitation-Induced Zinc Flux

Mammalian spermatozoa rely on glycolysis and mitochondrial oxidative phosphorylation for energy leading up to fertilization. Sperm capacitation involves a series of well-regulated biochemical steps that are necessary to give spermatozoa the ability to fertilize the oocyte. Additionally, zinc ion (Zn2+) fluxes have recently been shown to occur during mammalian sperm capacitation. Semen from seven commercial boars was collected and analyzed using image-based flow cytometry before, after, and with the inclusion of 2 mM Zn2+ containing in vitro capacitation (IVC) media. Metabolites were extracted and analyzed via Gas Chromatography-Mass Spectrometry (GC-MS), identifying 175 metabolites, with 79 differentially abundant across treatments (p < 0.05). Non-capacitated samples showed high levels of respiration-associated metabolites including glucose, fructose, citric acid, and pyruvic acid. After 4 h IVC, these metabolites significantly decreased, while phosphate, lactic acid, and glucitol increased (p < 0.05). With zinc inclusion, we observed an increase in metabolites such as lactic acid, glucitol, glucose, fructose, myo-inositol, citric acid, and succinic acid, while saturated fatty acids including palmitic, dodecanoic, and myristic acid decreased compared to 4 h IVC, indicating regulatory shifts in metabolic pathways and fatty acid composition during capacitation. These findings underscore the importance of metabolic changes in improving artificial insemination and fertility treatments in livestock and humans.

Differential role of bovine serum albumin and HCO3- in the regulation of GSK3 alpha during mouse sperm capacitation

To become fertile, mammalian sperm are required to undergo capacitation in the female tract or in vitro in defined media containing ions (e.g. HCO3 -, Ca2+, Na+, and Cl-), energy sources (e.g. glucose, pyruvate) and serum albumin (e.g. bovine serum albumin (BSA)). These different molecules initiate sequential and concomitant signaling pathways, leading to capacitation. Physiologically, capacitation induces changes in the sperm motility pattern (e.g. hyperactivation) and prepares sperm for the acrosomal reaction (AR), two events required for fertilization. Molecularly, HCO3 - activates the atypical adenylyl cyclase Adcy10 (aka sAC), increasing cAMP and downstream cAMP-dependent pathways. BSA, on the other hand, induces sperm cholesterol release as well as other signaling pathways. How these signaling events, occurring in different sperm compartments and with different kinetics, coordinate among themselves is not well established. Regarding the AR, recent work has proposed a role for glycogen synthase kinases (GSK3α and GSK3β). GSK3α and GSK3β are inactivated by phosphorylation of residues Ser21 and Ser9, respectively, in their N-terminal domain. Here, we present evidence that GSK3α (but not GSK3β) is present in the anterior head and that it is regulated during capacitation. Interestingly, BSA and HCO3 - regulate GSK3α in opposite directions. While BSA induces a fast GSK3α Ser21 phosphorylation, HCO3 - and cAMP-dependent pathways dephosphorylate this residue. We also show that the HCO3--induced Ser21 dephosphorylation is mediated by hyperpolarization of the sperm plasma membrane potential (Em) and by intracellular pH alkalinization. Previous reports indicate that GSK3 kinases mediate the progesterone-induced AR. Here, we show that GSK3 inhibition also blocks the Ca2+ ionophore ionomycin-induced AR, suggesting a role for GSK3 kinases downstream of the increase in intracellular Ca2+ needed for this exocytotic event. Altogether, our data indicate a temporal and biphasic GSK3α regulation with opposite actions of BSA and HCO3 -. Our results also suggest that this regulation is needed to orchestrate the AR during sperm capacitation.

Lipidomic Profile of Human Sperm Membrane Identifies a Clustering of Lipids Associated with Semen Quality and Function

Reduced sperm motility and/or count are among the major causes of reduced fertility in men, and sperm membranes play an important role in the spermatogenesis and fertilization processes. However, the impact of sperm lipid composition on male fertility remains under-investigated. The aim of the present study was to perform a lipidomic analysis of human sperm membranes: we performed an untargeted analysis of membrane lipid composition in fertile (N = 33) and infertile subjects (N = 29). In parallel, we evaluated their serum lipid levels. Twenty-one lipids were identified by their mass/charge ratio and post-source decay spectra. Sulfogalactosylglycerolipid (SGG, seminolipid) was the most abundant lipid component in the membranes. In addition, we observed a significant proportion of PUFAs. Important differences have emerged between the fertile and infertile groups, leading to the identification of a lipid cluster that was associated with semen parameters. Among these, cholesterol sulfate, SGG, and PUFAs represented the most important predictors of semen quality. No association was found between the serum and sperm lipids. Dietary PUFAs and SGG have acknowledged antioxidant functions and could, therefore, represent sensitive markers of sperm quality and testicular function. Altogether, these results underline the important role of sperm membrane lipids, which act independently of serum lipids levels and may rather represent an independent marker of reproductive function.

Lactate-induced spontaneous acrosomal exocytosis as a method to study acrosome function in stallion sperm

Evaluation of acrosome function in stallion sperm is mostly based on the use of inducers of acrosomal exocytosis (AE), such as the calcium ionophore A23187 or progesterone. Recently, it has been reported that incubation of stallion sperm under presumed capacitating conditions (i.e., medium formulated with calcium, bicarbonate, and bovine serum albumin) using a lactate-only containing medium (Lac-MW) results in a high rate of spontaneous AE in viable sperm (AE/Viable). In the current study, we developed an alternative assay of acrosome function for stallion sperm following the incubation of sperm in a medium formulated only with lactate as an energy substrate (Lac-MW). In Experiment 1, freshly ejaculated stallion sperm was incubated with 10 μM A23187, Lac-MW, or Control, for up to 6 h under capacitating conditions. The percentages of motile sperm, viable sperm, total AE (Total AE), and AE in viable sperm (AE/Viable) were compared among treatment groups. Incubation in Lac-MW, but not with Control or A23187, resulted in a time-dependent increase in the percentage of AE/Viable, as determined by flow cytometry, particularly at 4 and 6 h of incubation (P < 0.05). In Experiment 2, freshly ejaculated sperm was incubated in Lac-MW for up to 6 h, and the occurrence of protein tyrosine phosphorylation and AE/Viable were determined. At 4h and 6h of incubation in Lac-MW, ∼40% of the sperm displayed a protein tyrosine phosphorylation immunofluorescence pattern that coincides with that recently associated with stallion sperm capacitation (i.e., immunofluorescence signal at the acrosome and midpiece). In Experiment 3, the rate of AE/Viable sperm was compared among freshly ejaculated, cool-stored, and frozen/thawed stallion sperm. Except at 2h incubation in Lac-MW, differences in mean AE/Viable among fresh, cool-stored, and frozen/thawed sperm were not observed (P > 0.05). In Experiment 4, the relationship between Total AE (A23187), or AE/Viable (Lac-MW), and in vivo fertility of 5 stallions was determined. A linear relationship was observed between mean AE/Viable and the per-cycle (r = 0.93; P < 0.05) and seasonal (r = 0.66; P < 0.05) pregnancy rates of five stallions used for artificial insemination with cool-stored semen. In Experiment 5, frozen/thawed sperm from subfertile Thoroughbred (TB) stallions, known to carry the susceptibility genotype for Impaired Acrosomal Exocytosis (IAE; FKBP6 A/A-A/A) was evaluated following incubation in Lac-MW. Sperm from subfertile TB stallions with IAE had lower mean AE/Viable, at both 4h and 6h incubation in Lac-MW, when compared to that of fertile control stallions (P < 0.05). Overall, the Lac-MW model validated in the current study may be a useful complementary assay to evaluate the ability of stallion sperm to physiologically undergo AE and to study stallion fertility potential. This acrosome function assay can be used to evaluate fresh, cool-stored, or frozen/thawed stallion sperm, and describes a strong linear relationship with in vivo-fertility of stallions used in artificial insemination programs.

Spermiogenesis in Caenorhabditis elegans: An Excellent Model to Explore the Molecular Basis for Sperm Activation

C. elegans spermiogenesis converts non-motile spermatids into motile, fertilization-competent spermatozoa. Two major events include the building of a pseudopod required for motility and fusion of membranous organelles (MOs)-intracellular secretory vesicles-with the spermatid plasma membrane required for the proper distribution of sperm molecules in mature spermatozoa. The mouse sperm acrosome reaction-a sperm activation event occurring during capacitation-is similar to MO fusion in terms of cytological features and biological significance. Moreover, C. elegans fer-1 and mouse Fer1l5, both encoding members of the ferlin family, are indispensable for MO fusion and acrosome reaction, respectively. Genetics-based studies have identified many C. elegans genes involved in spermiogenesis pathways; however, it is unclear whether mouse orthologs of these genes are involved in the acrosome reaction. One significant advantage of using C. elegans for studying sperm activation is the availability of in vitro spermiogenesis, which enables combining pharmacology and genetics for the assay. If certain drugs can activate both C. elegans and mouse spermatozoa, these drugs would be useful probes to explore the mechanism underlying sperm activation in these two species. By analyzing C. elegans mutants whose spermatids are insensitive to the drugs, genes functionally relevant to the drugs' effects can be identified.

A new role of H89: Reduces capacitation-like changes through inhibition of cholesterol efflux, calcium influx, and proteins tyrosine phosphorylation during sperm cryopreservation in buffalo

It is a known fact that cryopreservation initiates premature capacitation in spermatozoa during the cryopreservation process. Protein tyrosine phosphorylation is a landmark of cascade reaction accountable for capacitation or capacitation-like changes in spermatozoa. Therefore, our hypothesis was to test an inhibitor (H89) that reversibly inhibits the cascade reaction responsible for capacitation during the cryopreservation process but does not hamper normal capacitation and fertilizing ability of sperm. For this, sixteen ejaculates were collected from Murrah buffalo bulls (n = 4). Each ejaculate was divided into four equal aliquots and diluted in an egg yolk-based semen dilutor supplemented with 0, 2, 10, and 30 μM concentrations of H89 and cryopreserved. Interestingly, H89 reduces cholesterol efflux from spermatozoa and protects spermatozoa from membrane damage during the cryopreservation process. H89 did not prevent lipid peroxidation of the sperm membrane. H89 reduced intracellular calcium concentration in spermatozoa in a dose-dependent manner, but tyrosine phosphorylation reduction was observed in the 2 and 10 μM H89 groups. The CTC assay revealed that the percentage of uncapacitated spermatozoa in different treatment groups increases in a dose-dependent manner. In the in vitro capacitation medium, the effect of H89 is abolished and spermatozoa underwent normal capacitation, but H89-treated spermatozoa attached to zona pellucida in large numbers compared to untreated spermatozoa. In conclusion, H89 does not only inhibit tyrosine phosphorylation of spermatozoa but it reduces cholesterol efflux and calcium influx, and ultimately reduces capacitation-like changes during the cryopreservation process.

The stallion sperm acrosome: Considerations from a research and clinical perspective

During the fertilization process, the interaction between the sperm and the oocyte is mediated by a process known as acrosomal exocytosis (AE). Although the role of the sperm acrosome on fertilization has been studied extensively over the last 70 years, little is known about the molecular mechanisms that govern acrosomal function, particularly in species other than mice or humans. Even though subfertility due to acrosomal dysfunction is less common in large animals than in humans, the evaluation of sperm acrosomal function should be considered not only as a complementary but a routine test when individuals are selected for breeding potential. This certainly holds true for stallions, which might display lower levels of fertility in the face of "acceptable" sperm quality parameters determined by conventional sperm assays. Nowadays, the use of high throughput technologies such as flow cytometry or mass spectrometry-based proteomic analysis is commonplace in the research arena. Such techniques can also be implemented in clinical scenarios of males with "idiopathic" subfertility. The current review focuses on the sperm acrosome, with particular emphasis on the stallion. We aim to describe the physiological events that lead to the acrosome formation within the testis, the role of very specific acrosomal proteins during AE, the methods to study the occurrence of AE under in vitro conditions, and the potential use of molecular biology techniques to discover new markers of acrosomal function and subfertility associated with acrosomal dysfunction in stallions.

Bioenergetic changes in response to sperm capacitation and two-way metabolic compensation in a new murine model

The acquisition of fertilizing ability by mammalian spermatozoa, known as "capacitation," includes processes that depend on particular metabolic pathways. This has led to the hypothesis that ATP demands might differ between capacitated and non-capacitated cells. Mouse sperm can produce ATP via OXPHOS and aerobic glycolysis, an advantageous characteristic considering that these cells have to function in the complex and variable environment of the female reproductive tract. Nonetheless, despite evidence showing that both metabolic pathways play a role in events associated with mouse sperm capacitation, there is contradictory evidence regarding changes promoted by capacitation in this species. In addition, the vast majority of studies regarding murine sperm metabolism use Mus musculus laboratory strains as model, thus neglecting the wide diversity of sperm traits of other species of Mus. Focus on closely related species with distinct evolutionary histories, which may be the result of different selective pressures, could shed light on diversity of metabolic processes. Here, we analyzed variations in sperm bioenergetics associated with capacitation in spermatozoa of the steppe mouse, Mus spicilegus, a species with high sperm performance. Furthermore, we compared sperm metabolic traits of this species with similar traits previously characterized in M. musculus. We found that the metabolism of M. spicilegus sperm responded to capacitation in a manner similar to that of M. musculus sperm. However, M. spicilegus sperm showed distinct metabolic features, including the ability to perform cross-pathway metabolic compensation in response to either respiratory or glycolytic inhibition, thus revealing a delicate fine-tuning of its metabolic capacities.

Capacitation promotes a shift in energy metabolism in murine sperm

In mammals, sperm acquire fertilization ability after a series of physiological and biochemical changes, collectively known as capacitation, that occur inside the female reproductive tract. In addition to other requirements, sperm bioenergetic metabolism has been identified as a fundamental component in the acquisition of capacitation. Mammalian sperm produce ATP through two main metabolic processes, oxidative phosphorylation (OXPHOS) and aerobic glycolysis that are localized to two different flagellar compartments, the midpiece, and the principal piece, respectively. In mouse sperm, the occurrence of many events associated with capacitation relies on the activity of these two energy-producing pathways, leading to the hypothesis that some of these events may impose changes in sperm energetic demands. In the present study, we used extracellular flux analysis to evaluate changes in glycolytic and respiratory parameters of murine sperm that occur as a consequence of capacitation. Furthermore, we examined whether these variations affect sperm ATP sustainability. Our results show that capacitation promotes a shift in the usage ratio of the two main metabolic pathways, from oxidative to glycolytic. However, this metabolic rewiring does not seem to affect the rate at which the sperm consume ATP. We conclude that the probable function of the metabolic switch is to increase the ATP supply in the distal flagellar regions, thus sustaining the energetic demands that arise from capacitation.

Functional significance of mouse seminal vesicle sulfhydryl oxidase on sperm capacitation in vitro

During ejaculation, cauda epididymal spermatozoa are suspended in a protein-rich solution of seminal plasma which is composed of proteins mostly secreted from the seminal vesicle. These seminal proteins interact with the sperm cells and bring about changes in their physiology, so that they can become capacitated in order for the fertilization to take place. Sulfhydryl oxidase (SOX) is a member of the QSOX family and its expression is found to be high in the seminal vesicle secretion of mouse. Previously, it has been reported to cross-link thiol containing amino acids among major seminal vesicle secretion (SVS) proteins. However, its role in male reproduction is unclear. In this study, we determined the role of SOX on epididymal sperm maturation and also disclosed the binding effect of SOX on the sperm fertilizing ability in vitro. In order to achieve the above two objectives, we constructed a Sox clone (1.7 kb) using a pET-30a vector. His-tagged recombinant Sox was over expressed in Shuffle Escherichia coli cells and purified using His-Trap column affinity chromatography along with hydrophobic interaction chromatography. The purified SOX was confirmed by Western blot analysis and by its activity with DTT as a substrate. Results obtained from immunocytochemical staining clearly indicated that SOX possesses a binding site on the sperm acrosome. The influence of SOX on oxidation of sperm sulfhydryl to disulfides during epididymal sperm maturation was evaluated by a thiol labelling agent, mBBr. The SOX protein binds on to the sperm cells and increases their progressive motility. The effect of SOX binding on reducing the [Ca2+]i concentration in sperm head, was determined using a calcium probe, Fluo-3 AM. The inhibitory influence of SOX on sperm acrosome reaction was shown by using calcium ionophore A32187 to induce the acrosome reaction. The acrosome-reacted sperm were examined by staining with FITC-conjugated Arachis hypogaea (peanut) lectin. Furthermore, immunocytochemical analysis revealed that SOX remains bound to the sperm cells in the uterus but disappears in the oviduct during their transit in the female reproductive tract. The results from the above experiment revealed that SOX binding on to the sperm acrosome prevents sperm capacitation by affecting the [Ca2+]i concentration in the sperm head and the ionophore-induced acrosome reaction. Thus, the binding of SOX on to the sperm acrosome may possibly serve as a decapacitation factor in the uterus to prevent premature capacitation and acrosome reaction, thus preserving their fertilizing ability.

Calcium chloride dihydrate supplementation at ICSI improves fertilization and pregnancy rates in patients with previous low fertilization: a retrospective paired treatment cycle study

PURPOSE

To determine if 5mM calcium chloride dihydrate supplementation of the Polyvinylpyrrolidone (PVP) media at the time of ICSI (ICSI-Ca) improves fertilization, utilization, and clinical pregnancy rates compared to ICSI alone, particularly in patients with a history of low fertilization (< 50%).

METHODS

Retrospective study between 2016 and 2021 at Monash IVF Victoria on a paired cohort of patients (n = 178 patients) where an ICSI cycle was analyzed coupled with the subsequent ICSI-Ca cycle. The paired cohort was further subdivided into a low-fertilization cohort (< 50% fertilization on previous cycles: n = 66 patients) compared to the remaining patients with fertilization ≥ 50% (n = 122). Exclusion criteria included donor cycles, PGT patients, surgical sperm retrieval, women ≥ 45 years old, patients with > 6 cycles, and patients with ≤ 5 inseminated oocytes.

RESULTS

Calcium supplementation significantly increased both fertilization (28.8% ICSI vs 49.7% ICSI-Ca, P < 0.0001) and clinical pregnancy rate (4.9% ICSI vs 25.0% ICSI-Ca: P < 0.05) in the low-fertilization cohort but not in the normal-fertilization cohort. Interestingly, utilization rate significantly increased in the normal-fertilization cohort (32.6% ICSI vs ICSI-Ca: 44.9%, P < 0.01) but not in the low-fertilization cohort, although the number of embryos utilized per patient after ICSI-Ca increased in both groups.

CONCLUSION

Calcium supplementation does not appear to be a detrimental addition to ICSI and may improve IVF outcomes, particularly for patients with a history of low fertilization. Further investigations including prospective case-matched studies or a RCT are required to confirm these findings.

Energy Metabolism and Hyperactivation of Spermatozoa from Three Mouse Species under Capacitating Conditions

Mammalian sperm differ widely in sperm morphology, and several explanations have been presented to account for this diversity. Less is known about variation in sperm physiology and cellular processes that can give sperm cells an advantage when competing to fertilize oocytes. Capacitation of spermatozoa, a process essential for mammalian fertilization, correlates with changes in motility that result in a characteristic swimming pattern known as hyperactivation. Previous studies revealed that sperm motility and velocity depend on the amount of ATP available and, therefore, changes in sperm movement occurring during capacitation and hyperactivation may involve changes in sperm bioenergetics. Here, we examine differences in ATP levels of sperm from three mouse species (genus Mus), differing in sperm competition levels, incubated under non-capacitating and capacitating conditions, to analyse relationships between energetics, capacitation, and swimming patterns. We found that, in general terms, the amount of sperm ATP decreased more rapidly under capacitating conditions. This descent was related to the development of a hyperactivated pattern of movement in two species (M. musculus and M. spicilegus) but not in the other (M. spretus), suggesting that, in the latter, temporal dynamics and energetic demands of capacitation and hyperactivation may be decoupled or that the hyperactivation pattern differs. The decrease in ATP levels during capacitation was steeper in species with higher levels of sperm competition than in those with lower levels. Our results suggest that, during capacitation, sperm consume more ATP than under non-capacitating conditions. This higher ATP consumption may be linked to higher velocity and lateral head displacement, which are associated with hyperactivated motility.

Exogenous gamma-aminobutyric acid addition enhances porcine sperm acrosome reaction

The widely used porcine artificial insemination procedure involves the use of liquid‐stored semen because it is difficult to control the quality of frozen–thawed porcine sperm. Therefore, there is a high demand for porcine semen. The control and enhancement of sperm function are required for the efficient reproduction of pigs. We previously reported that gamma‐aminobutyric acid (GABA) enhanced sperm capacitation and acrosome reaction in mice. In this study, we demonstrated the presence of GABA_A receptors in porcine sperm acrosome. Furthermore, we investigated the GABA effects on porcine sperm function. We did not detect any marked effect of GABA on sperm motility and tyrosine phosphorylation of sperm proteins. However, GABA promoted acrosome reaction, which was suppressed by a selective GABA_A receptor antagonist. GABA binds to GABA_A receptors, resulting in chloride ion influx. We found that treatment with 1 μM GABA increased the intracellular concentration of chloride ion in the sperm. In addition, the GABA concentration effective in the acrosome reaction was correlated with the porcine sperm concentration. These results indicate that GABA and its receptors can act as modulators of acrosome reaction. This study is the first to report the effects of GABA on porcine sperm function.

Polyvinyl alcohol, but not bovine serum albumin, promotes the induction of full‐type hyperactivation in boar cyclic AMP analog‐treated spermatozoa

This study aimed to verify the effects of polyvinyl alcohol (PVA) and bovine serum albumin (BSA) on the induction of full-type hyperactivation in boar spermatozoa treated with a cyclic AMP analog (cBiMPS). Washed spermatozoa were treated with cBiMPS (100 μM) for 180 min. As shown in the assessment of sperm motility, PVA (0.05%-0.4%) significantly promoted the induction of full-type hyperactivation, whereas BSA (0.025%-0.4%) did not affect the induction. In comparative experiments, BSA (0.4%) effectively promoted the induction of full-type hyperactivation in bovine spermatozoa treated with cBiMPS, calyculin A (a protein phosphatase inhibitor), and digoxin (a Na⁺ /K⁺ -ATPase inhibitor), while PVA (0.1%) did not affect the induction. Western blotting showed that protein tyrosine phosphorylation states of >50 kDa sperm proteins were effectively enhanced by treatment with cBiMPS in the PVA/BSA-free medium and not affected by the addition of PVA (0.1%). The assessment of plasma membrane integrity indicated that BSA (0.4%) significantly decreased spermatozoa with intact plasma membranes. These results indicate that PVA (0.1%) promotes the induction of full-type hyperactivation and does not influence the protein tyrosine phosphorylation states in boar cBiMPS-treated spermatozoa. They also suggest that BSA should not be added to medium containing cBiMPS for boar spermatozoa.

HDL mediates reverse cholesterol transport from ram spermatozoa and induces hyperactivated motility

Reverse cholesterol transport or cholesterol efflux is part of an extensive plasma membrane remodeling process in spermatozoa that is imperative for fertilization. For ram spermatozoa, sheep serum is well known to support in vitro fertilization (IVF), but knowledge of its explicit role is limited. Though, it is postulated to elicit cholesterol efflux owing to the presence of high-density lipoproteins (HDLs) that interact with transmembrane cholesterol transporters, such as adenosinetriphosphate (ATP)-binding cassette transporter A1 (ABCA1) and scavenger receptor class B, type I (SR-BI). In this study, we report that both sheep serum and HDLs were able to elicit cholesterol efflux alone by up to 20–40% (as measured by the boron dipyrromethene (BODIPY)-cholesterol assay). Furthermore, when the antagonists glibenclamide and valspodar were used to inhibit the function of ABCA1 and SR-BI or ABCA1 alone, respectively, cholesterol efflux was only marginally reduced (8–15%). Nevertheless, it is likely that in ram spermatozoa, a specific facilitated pathway of cholesterol efflux is involved in the interaction between cholesterol acceptors and transporters. Interestingly, exposure to HDLs also induced hyperactivated motility, another critical event required for successful fertilization. Taken together, this study details the first report of the dual action of HDLs on ram spermatozoa, providing both an insight into the intricacy of events leading up to fertilization in vivo as well as demonstrating the possible application of HDL supplementation in media for IVF.

Expression and Possible Role of Nicotinic Acetylcholine Receptor ε Subunit (AChRe) in Mouse Sperm

The nicotinic acetylcholine receptor (nAChR) is one of the receptors of acetylcholine (ACh), and nicotine (NIC) acts as an agonist of this receptor. Among the nAChR subunits, we found that the ε subunit (AChRe) had approximately 10 to 1000 times higher level of mRNA expression in mouse testes than the other subunits. In this study, we aimed to elucidate the expression and localization of AChRe in the testes and spermatozoa of mice and clarify the effect of AChRe on sperm function. Immunocytochemistry showed that AChRe was expressed in the murine testes and spermatozoa. We found that AChRe was localized only in elongated spermatids from step 12 onwards in the testes. In spermatozoa, AChRe was localized in the head, especially in the anterior region of the acrosome, but only approximately 50% of spermatozoa showed this immunoreactivity. Additionally, we analyzed the effects of ACh and NIC on sperm acrosome reaction (AR) and found that both ACh and NIC suppressed the AR rate, which was restored by an AChRe-specific antagonist. These results suggest that AChRe may be a regulator of mammalian sperm AR.

Cholesterol-cyclodextrin complex as a replacement for egg yolk in bull semen extender: sperm characteristics post-thawing and in vivo fertility

Egg yolk, a major semen extender constituent, lacks a defined composition, therefore, there are biosecurity concerns with use of egg yolk. Cryopreservation of bull semen without inclusion of animal protein in the semen extender, therefore, is an important consideration. Cholesterol may be delivered and incorporated into the sperm plasma membrane by cyclodextrins to protect sperm during cryopreservation. The aim of this study was to determine suitability of a cholesterol-cyclodextrin semen extender, without inclusion of egg yolk, for cryopreservation of bull semen. Bull semen was collected and cryopreserved in either egg yolk or with inclusions of three different concentrations of cholesterol-cyclodextrin complex (0.5, 1 or 2 mg/mL semen) in Tris-glycerol (TG) extender. Sperm motion characteristics examined using the computer-assisted sperm analysis, and plasma membrane and acrosome integrity examined using flow cytometry, were similar for all extenders. The inclusion of the greatest concentration of cholesterol-cyclodextrin complex (2 mg/mL semen) followed by dilution in TG extender resulted in lesser pregnancy rates (P <  0.05). There was a pregnancy rate of as great as 56 % when sperm cryopreserved in 0.5 mg/mL cholesterol-cyclodextrin Tris-glycerol extender were used for artificial insemination following imposing of a hormonal treatment regimen for synchrony of timing of ovarian functions among cows for conducting fixed-time artificial insemination (FTAI). Results indicate cholesterol-cyclodextrin Tris-glycerol extender, with a chemically defined composition and without inclusion of egg yolk, may be used to cryopreserve bull sperm with there being acceptable pregnancy rates when this semen is used for FTAI.

A decrease of docosahexaenoic acid in testes of mice fed a high-fat diet is associated with impaired sperm acrosome reaction and fertility

Obesity is a major worldwide health problem that is related to most chronic diseases, including male infertility. Owing to its wide impact on health, mechanisms underlying obesity-related infertility remain unknown. In this study, we report that mice fed a high-fat diet (HFD) for over 2 months showed reduced fertility rates and increased germ cell apoptosis, seminiferous tubule degeneration, and decreased intratesticular estradiol (E2) and E2-to-testosterone ratio. Interestingly, we also detected a decrease in testicular fatty acid levels, behenic acid (C22:0), and docosahexaenoic acid (DHA, 22:6n-3), which may be related to the production of dysfunctional spermatozoa. Overall, we did not detect any changes in the frequency of seminiferous tubule stages, sperm count, or rate of in vitro capacitation. However, there was an increase in spontaneous and progesterone-induced acrosomal exocytosis (acrosome reaction) in spermatozoa from HFD-fed mice. These data suggest that a decrease in E2 and fatty acid levels influences spermatogenesis and some steps of acrosome biogenesis that will have consequences for fertilization. Thus, our results add new evidence about the adverse effect of obesity in male reproduction and suggest that the acrosomal reaction can also be affected under this condition.

Involvement of nitric oxide during in vitro oocyte maturation, sperm capacitation and in vitro fertilization in pig

The importance of porcine species for meat production is undeniable. Due to the genetic, anatomical, and physiological similarities with humans, from a biomedical point of view, pig is considered an ideal animal model for the study and development of new therapies for human diseases. The in vitro production (IVP) of porcine embryos has become widespread as a result of these qualities and there is significant demand for these embryos for research purposes. However, the efficiency of porcine embryo IVP remains very low, which hinders its use as a model for research. The high degree of polyspermic fertilization is the main problem that affects in vitro fertilization (IVF) in porcine species. Furthermore, oocyte in vitro maturation (IVM) is another important step that could be related to polyspermic fertilization and low embryo production. The presence of nitric oxide synthase (NOS), the enzyme that produces nitric oxide (NO), has been detected in the oviduct, the ovary, the oocyte and the sperm cell of porcine species. Its functions include regulating oviductal activity, ovulation, acquisition of meiotic competence, oocyte activation, sperm capacitation, and gamete interaction. Therefore, in this review, we summarize the current knowledge on the role of NO/NOS system in each of the steps that lead to the production of porcine embryos in an in vitro environment, i.e. IVM, sperm capacitation, IVF, and embryo culture. We also discuss the possible ways in which the NO/NOS system could be used to enhance IVP of porcine embryos.

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.

3D in situ imaging of the female reproductive tract reveals molecular signatures of fertilizing spermatozoa in mice

Out of millions of ejaculated sperm, a few reach the fertilization site in mammals. Flagellar Ca²⁺ signaling nanodomains, organized by multi-subunit CatSper calcium channel complexes, are pivotal for sperm migration in the female tract, implicating CatSper-dependent mechanisms in sperm selection. Here using biochemical and pharmacological studies, we demonstrate that CatSper1 is an O-linked glycosylated protein, undergoing capacitation-induced processing dependent on Ca²⁺ and phosphorylation cascades. CatSper1 processing correlates with protein tyrosine phosphorylation (pY) development in sperm cells capacitated in vitro and in vivo. Using 3D in situ molecular imaging and ANN-based automatic detection of sperm distributed along the cleared female tract, we demonstrate that spermatozoa past the utero-tubal junction possess the intact CatSper1 signals. Together, we reveal that fertilizing mouse spermatozoa in situ are characterized by intact CatSper channel, lack of pY, and reacted acrosomes. These findings provide molecular insight into sperm selection for successful fertilization in the female reproductive tract.

Capacitation increases glucose consumption in murine sperm

Mammalian sperm acquire fertilization capacity in the female reproductive tract in a process known as capacitation. During capacitation, sperm change their motility pattern (i.e., hyperactivation) and become competent to undergo the acrosome reaction. We have recently shown that, in the mouse, sperm capacitation is associated with increased uptake of fluorescently labeled deoxyglucose and with extracellular acidification suggesting enhanced glycolysis. Consistently, in the present work we showed that glucose consumption is enhanced in media that support mouse sperm capacitation suggesting upregulation of glucose metabolic pathways. The increase in glucose consumption was modulated by bicarbonate and blocked by protein kinase A and soluble adenylyl cyclase inhibitors. Moreover, permeable cyclic adenosine monophosphate (cAMP) agonists increase glucose consumption in sperm incubated in conditions that do not support capacitation. Also, the increase in glucose consumption was reduced when sperm were incubated in low calcium conditions. Interestingly, this reduction was not overcome with cAMP agonists. Despite these findings, glucose consumption of sperm from Catsper1 knockout mice was similar to the one from wild type suggesting that other sources of calcium are also relevant. Altogether, these results suggest that cAMP and calcium pathways are involved in the regulation of glycolytic energy pathways during murine sperm capacitation.

Pantoprazole, a proton-pump inhibitor, impairs human sperm motility and capacitation in vitro

BACKGROUND

The effects of PPIs on human sperm fertilizing capacity were poorly investigated although these drugs are widely over-used. Two publications retrospectively studied relationships between any PPI intake and sperm parameters from patients consulting at infertility clinics, but the conclusions of these reports were contradictory. Only two reports investigated the effects of lansoprazole and omeprazole on sperm motility and found lansoprazole to be deleterious and omeprazole to be neutral for sperm motility. The inconsistency of the PPI effect in the previous reports emphasizes the need for more basic research on human spermatozoa, taking into account the hypothesis that the different PPI drugs may have different effects on sperm physiology.

OBJECTIVES

Do PPIs, which are among the most widely sold drug in the word, impact negatively human sperm capacitation and sperm motility?

MATERIALS AND METHODS

The effects of PPIs on human sperm maturation and motility were analyzed by CASA, flow cytometry, and Western blot.

RESULTS

We tested the impact of 6 different PPIs on human sperm motility and capacitation. We showed that pantoprazole, but not the other PPIs, decreased sperm progressive motility and capacitation-induced sperm hyperactivation. We therefore investigated further the effects of pantoprazole on sperm capacitation, and we observed that it had a significant deleterious effect on the capacitation-induced hyperpolarization of the membrane potential and capacitation-associated protein phosphorylation.

DISCUSSION AND CONCLUSION

Our results indicate that exposure to pantoprazole has an adverse effect on the physiological competence of human spermatozoa. As the capacitation process takes place within the female tract, our results suggest that PPIs intake by the female partner may impair in vivo sperm maturation and possibly fertilization. Moreover, the absence of adverse effect by PPIs on mouse sperm emphasizes the need to develop reprotox assays using human material to better assess the effects of medication intake on sperm physiology.

The activation of the chymotrypsin-like activity of the proteasome is regulated by soluble adenyl cyclase/cAMP/protein kinase A pathway and required for human sperm capacitation

One of the first events of mammalian sperm capacitation is the activation of the soluble adenyl cyclase/cAMP/protein kinase A (SACY/cAMP/PKA) pathway. Here, we evaluated whether the increase in PKA activity at the onset of human sperm capacitation is responsible for the activation of the sperm proteasome and whether this activation is required for capacitation progress. Viable human sperm were incubated with inhibitors of the SACY/cAMP/PKA pathway. The chymotrypsin-like activity of the sperm proteasome was evaluated using a fluorogenic substrate. Sperm capacitation status was evaluated using the chlortetracycline assay and tyrosine phosphorylation. To determine whether proteasomal subunits were phosphorylated by PKA, the proteasome was immunoprecipitated and tested on a western blot using an antibody against phosphorylated PKA substrates. Immunofluorescence microscopy analysis and co-immunoprecipitation (IPP) were used to investigate an association between the catalytic subunit alpha of PKA (PKA-Cα) and the proteasome. The chymotrypsin-like activity of the sperm proteasome significantly increased after 5 min of capacitation (P < 0.001) and remained high for the remaining incubation time. Treatment with H89, KT5720 or KH7 significantly decreased the chymotrypsin-like activity of the proteasome (P < 0.001). IPP experiments indicated that PKA inhibition significantly modified phosphorylation of proteasome subunits. In addition, PKA-Cα colocalized with the proteasome in the equatorial segment and in the connecting piece, and co-immunoprecipitated with the proteasome. This is the first demonstration of sperm proteasome activity being directly regulated by SACY/PKA-Cα. This novel discovery extends our current knowledge of sperm physiology and may be used to manage sperm capacitation during assisted reproductive technology procedures.

Existence and distribution of Niemann-Pick type 2C (NPC2) in prawn reproductive tract and its putative role as a cholesterol modulator during sperm transit in the vas deferens

Sequestering of cholesterol (CHO) is a hallmark molecular event that is known to be associated with sperm gaining their fertilizing ability in a broad array of animals. We have shown previously that the level of CHO declines in the Macrobrachium rosenbergii sperm membrane when they are migrating into the vas deferens, prompting us to search for CHO transporters, one of which is Niemann-Pick type 2C (NPC2), within the prawn male reproductive tract. Sequence comparison of MrNPC2 with other NPC2, from crustaceans to mammals, revealed its conserved features in the hydrophobic cavity with 3 amino acids forming a CHO lid that is identical in all species analyzed. Expressions of MrNPC2 transcript and protein were detected in testicular supporting and interstitial cells and along the epithelial cells of the vas deferens. As confirmed by live cell staining, the testicular sperm (Tsp) surface was devoid of MrNPC2 but it first existed on the vas deferens sperm, suggesting its acquisition from the luminal fluid, possibly through trafficking of multi-lamellar vesicles during sperm transit in the vas deferens. We further showed that recombinant MrNPC2 had a high affinity towards CHO in the lipid extracts, either from Tsp or from lipid vesicles in the vas deferens. Together, our results indicated the presence of MrNPC2 in the male reproductive tract, which may play an important role as a CHO modulator between the sperm membrane and vas deferens epithelial communication.

Cholesterol and desmosterol incorporation into ram sperm membrane before cryopreservation: Effects on membrane biophysical properties and sperm quality

Ram sperm are particularly sensitive to freeze-thawing mainly due to their lipid composition, limiting their use in artificial insemination programs. We evaluated the extent of cholesterol and desmosterol incorporation into ram sperm through incubation with increasing concentrations of methyl-β-cyclodextrin (MβCD)-sterol complexes, and its effect on membrane biophysical properties, membrane lateral organization and cryopreservation outcome. Sterols were effectively incorporated into the sperm membrane at 10 and 25 mM MβCD-sterols, similarly increasing membrane lipid order at physiological temperature and during temperature decrease. Differential ordering effect of sterols in ternary-mixture model membranes revealed a reduced tendency of desmosterol of segregating into ordered domains. Live cell imaging of fluorescent cholesterol showed sterol incorporation and evidenced the presence of sperm sub-populations compatible with different sterol contents and a high concentration of sterol rich-ordered domains mainly at the acrosome plasma membrane. Lateral organization of the plasma membrane, assessed by identification of GM1-related rafts, was preserved after sterol incorporation except when high levels of sterols (25 mM MβCD-desmosterol) were incorporated. Ram sperm incubation with 10 mM MβCD-sterols prior to cryopreservation in a cholesterol-free extender improved sperm quality parameters after cooling and freezing. While treatment with 10 mM MβCD-cholesterol increased sperm motility, membrane integrity and tolerance to osmotic stress after thawing, incorporation of desmosterol increased the ability of ram sperm to overcome osmotic stress. Our research provides evidence on the effective incorporation and biophysical behavior of cholesterol and desmosterol in ram sperm membranes and on their consequences in improving functional parameters of sperm after temperature decrease and freezing.

Cryopreservation of bison semen without exogenous protein in extender and its fertility potential in vitro and in vivo following fixed-time artificial insemination

Successful cryopreservation of bison semen is fundamental for restoration of genetic diversity in Canada's wood bison. Conventional bovine semen extenders contain animal products, such as egg yolk and milk, which are undesirable because of biosecurity risks and undefined composition. In this study, we examined the efficacy of an exogenous protein-free extender containing cholesterol-cyclodextrin complex (CC) to cryopreserve bison semen. The study also provided an opportunity to determine the effectiveness of different ovulation synchronization protocols for fixed-time artificial insemination in bison. Semen was collected from wood bison bulls via electroejaculation and cryopreserved in either Tris-egg yolk-glycerol (called 'TEYG') extender or pretreated with CC (2 mg/mL semen) and diluted in Tris-glycerol (collectively called 'CC-TG') extender. Post-thaw sperm motion characteristics and in vitro fertilization of cattle oocytes confirmed that CC alone without egg yolk protected bison sperm during cryopreservation process. In the first fertility trial, however, no pregnancy was obtained following fixed-time artificial insemination of bison cows with CC-TG extender. In a follow-up trial, low concentration of CC (1 mg/mL semen) resulted in better post-thaw sperm motion characteristics, fertility rate, and birth of live calves following fixed-time artificial insemination. Results showed that 1 mg CC/mL semen completely replaced egg yolk in bison semen extender. In addition, both follicular ablation and steroid treatment protocols provided ovulation synchrony to permit successful application of fixed-time artificial insemination in bison. This is the first report on the birth of live bison calves following fixed-time artificial insemination using semen cryopreserved in a defined extender.

Periovulatory oviductal fluid decreases sperm protein kinase A activity, tyrosine phosphorylation, and in vitro fertilization in pig

BACKGROUND

Molecules from the female reproductive tract modulate capacitation and function of sperm cells in vivo. These molecules vary in a quantitative and qualitative manner throughout the estrous cycle.

OBJECTIVES

This work evaluates the effect of using various female reproductive fluids on capacitation and fertilization of pig spermatozoa in vitro.

MATERIAL AND METHODS

The effects of culturing spermatozoa in different fluids on the levels of sperm protein kinase A (pPKA), tyrosine phosphorylation, acrosome reaction, and in vitro fertilization (IVF) were evaluated. The fluids tested were as follows: oviductal fluid (OF) from five phases of the estrous cycle, namely early and late follicular (OF-EF, OF-LF), early and late luteal (OF-EL, OF-LL) and periovulatory (pOF), follicular fluid from medium-sized follicles, and secretions of cumulus-oocyte complexes (conditioned medium).

RESULTS

The pPKAs and tyrosine phosphorylation were decreased by OF-EF, OF-LF, OF-EL, and pOF but not by follicular fluid and conditioned medium. OF-EF, OF-LF, and pOF also decreased the sperm acrosome reaction. Moreover, the effect of pOF on pPKAs and tyrosine phosphorylation was reversible. In in vitro fertilization, OF-EF, OF-LF, OF-EL, and pOF reduced the percentage of penetrated oocytes, the mean number of spermatozoa per penetrated oocyte, and increased monospermy.

CONCLUSION

OF from follicular, early luteal, and periovulatory phases of the estrous cycle modulates the sperm protein phosphorylation as well as the acrosome reaction involved in capacitation and increases monospermic fertilization in in vitro fertilization. Our findings suggest that fluids from the female reproductive tract could be used as additives in porcine IVF systems to modulate sperm-oocyte interaction.

Isoform-specific requirement for GSK3α in sperm for male fertility

Glycogen synthase kinase 3 (GSK3) is a highly conserved protein kinase regulating key cellular functions. Its two isoforms, GSK3α and GSK3β, are encoded by distinct genes. In most tissues the two isoforms are functionally interchangeable, except in the developing embryo where GSK3β is essential. One functional allele of either of the two isoforms is sufficient to maintain normal tissue functions. Both GSK3 isoforms, present in sperm from several species including human, are suggested to play a role in epididymal initiation of sperm motility. Using genetic approaches, we have tested requirement for each of the two GSK3 isoforms in testis and sperm. Both GSK3 isoforms are expressed at high levels during the onset of spermatogenesis. Conditional knockout of GSK3α, but not GSK3β, in developing testicular germ cells in mice results in male infertility. Mice lacking one allele each of GSK3α and GSK3β are fertile. Despite overlapping expression and localization in differentiating spermatids, GSK3β does not substitute for GSK3α. Loss of GSK3α impairs sperm hexokinase activity resulting in low ATP levels. Net adenine nucleotide levels in caudal sperm lacking GSK3α resemble immature caput epididymal sperm. Changes in the association of the protein phosphatase PP1γ2 with its protein interactors occurring during epididymal sperm maturation is impaired in sperm lacking GSK3α. The isoform-specific requirement for GSK3α is likely due to its specific binding partners in the sperm principal piece. Testis and sperm are unique in their specific requirement of GSK3α for normal function and male fertility.

BODIPY-cholesterol can be reliably used to monitor cholesterol efflux from capacitating mammalian spermatozoa

Capacitation is the final maturation step spermatozoa undergo prior to fertilisation. The efflux of cholesterol from the sperm membrane to the extracellular environment is a crucial step during capacitation but current methods to quantify this process are suboptimal. In this study, we validate the use of a BODIPY-cholesterol assay to quantify cholesterol efflux from spermatozoa during in vitro capacitation, using the boar as a model species. The novel flow cytometric BODIPY-cholesterol assay was validated with endogenous cholesterol loss as measured by mass spectrometry and compared to filipin labelling. Following exposure to a range of conditions, the BODIPY-cholesterol assay was able to detect and quantify cholesterol efflux akin to that measured with mass spectrometry. The ability to counterstain for viability is a unique feature of this assay that allowed us to highlight the importance of isolating viable cells only for a reliable measure of cholesterol efflux. Finally, the BODIPY-cholesterol assay proved to be the superior method to quantify cholesterol efflux relative to filipin labelling, though filipin remains useful for assessing cholesterol redistribution. Taken together, the BODIPY-cholesterol assay is a simple, inexpensive and reliable flow cytometric method for the measurement of cholesterol efflux from spermatozoa during in vitro capacitation.

Capacitation of mouse sperm is modulated by gamma-aminobutyric acid (GABA) concentration

In mammals, ejaculated sperm acquire their fertilizing ability during migration through the female reproductive tract, which secretes several factors that contribute to sperm capacitation. Gamma-aminobutyric acid (GABA) is a well-known neurotransmitter in the central nervous system, but additionally enhances the sperm acrosome reaction in the rat and cow. However, the detailed effects of GABA concentration on sperm function remain unclear. In this study, we detected the presence of the GABA type A receptor (GABA A) in mouse epididymal sperm by western blot analysis and in the sperm acrosome by immunocytochemistry. We also investigated the effects of GABA on sperm fertilizing ability. We found that GABA facilitated the tyrosine phosphorylation of sperm proteins, which is an index of sperm capacitation. GABA also promoted the acrosome reaction, which was suppressed by a selective GABA A receptor antagonist. We then found that the effective GABA concentration for the acrosome reaction corresponds to sperm concentration, but we did not detect any marked effect of GABA on sperm motility using a computer-assisted sperm analysis system. Using immunohistochemistry, we also detected GABA expression in the epithelia of the mouse uterus and oviduct. Furthermore, we found that the mRNA levels of glutamate decarboxylase (Gad), which generates GABA from L-glutamate, were higher in the oviduct than in the uterus, and that Gad mRNA levels were higher at estrus than at the diestrus stage. These results indicate that the GABA concentration can act as a modulator of the acrosome reaction and sperm capacitation in the female reproductive tract.

Impairment of sperm maturation and capacitation due to diet-dependent cholesterol overload

BACKGROUND

Lipid metabolic disorders (dyslipidemia) are constantly increasing in occidental societies and lead to the development of pathologies such as obesity, diabetes, and metabolic syndrome. It has been demonstrated that dyslipidemia can alter the reproductive function. Animal models have recently been used to show that the offspring of dyslipidemic males could also develop such pathologies and that the transgenerational transmission involved post-testicular sperm maturation. These data targeted the essential role of male gamete epididymal maturation and its importance for the health of the offspring.

OBJECTIVES

This publication summarizes in the first place experimental data obtained using a mouse model of dyslipidemia-induced post-testicular infertility, knockout mice for the two isoforms of the 'Liver X Receptors' (Lxrα;β^-/- ), the major regulators of cholesterol homeostasis. The impact of a high cholesterol diet (HCD) on the protein YWHAZ (14-3-3 ζ or tyrosine 3-monooxygenase/tryptophan 5-monooxygenase activation protein Zeta) was also investigated in our model.

MATERIALS AND METHODS

In our mouse model, when young fertile Lxrα;β^-/- males aged three months were fed four weeks with a HCD, they developed an epididymal phenotype leading to infertility. The level of sperm YWHAZ was evaluated by Western blot and its tyrosine phosphorylation state by immunoprecipitation followed by Western blot.

RESULTS

Our data revealed that sperm lipid composition and structure were altered, leading to defects of the capacitation-associated signaling pathway. They also showed that both the level and the tyrosine phosphorylation state of YWHAZ were affected by the HCD in sperm cells from Lxrα;β^-/- males.

DISCUSSION AND CONCLUSION

YWHAZ could be a new important regulator of capacitation-associated tyrosine phosphorylation and a marker of dyslipidemia-induced infertility.

Novel methods to detect capacitation-related changes in spermatozoa

Prior to interaction with the oocyte, spermatozoa must undergo capacitation, which involves a series of physio-chemical transformations that occur in the female tract. As capacitation is a pre-requisite for successful fertilisation, it is a topic of great interest for sperm biologists, but the complexity of the numerous biochemical and biophysical processes involved make it difficult to measure. Capacitation is an extremely complex event that encompasses numerous integrated processes that can occur concurrently during this window of time. The identification of techniques to accurately assess and quantify capacitation is therefore crucial to gain a meaningful insight into this fascinating sperm maturation event. Whilst there are extensive reviews in the literature that focus on the functional changes to spermatozoa during capacitation, few have examined the methods required to measure these changes. The aim of this review is to highlight frequently used methods to quantify different stages of capacitation and identify promising novel techniques. Factors that are able to modulate various capacitation processes will also be discussed. The overall outcome is to provide researchers with a toolbox of methods that can be used to gain a deeper understanding of the intricacies of capacitation in spermatozoa.

Tyrosine phosphorylation signaling regulates Ca2+ entry by affecting intracellular pH during human sperm capacitation

Capacitation is a mandatory process for the acquisition of mammalian sperm fertilization competence and involves the activation of a complex and still not fully understood system of signaling pathways. Under in vitro conditions, there is an increase in both protein tyrosine phosphorylation (pTyr) and intracellular Ca²⁺ levels in several species. In human sperm, results from our group revealed that pTyr signaling can be blocked by inhibiting proline-rich tyrosine kinase 2 (PYK2). Based on the role of PYK2 in other cell types, we investigated whether the PYK2-dependent pTyr cascade serves as a sensor for Ca ²⁺ signaling during human sperm capacitation. Flow cytometry studies showed that exposure of sperm to the PYK2 inhibitor N-[2-[[[2-[(2,3-dihydro-2-oxo-1 H-indol-5-yl)amino]-5-(trifluoromethyl)-4-pyrimidinyl]amino]methyl]phenyl]- N-methyl-methanesulfonamide hydrate (PF431396) produced a significant and concentration-dependent reduction in intracellular Ca ²⁺ levels during capacitation. Further studies revealed that PF431396-treated sperm exhibited a decrease in the activity of CatSper, a key sperm Ca ²⁺ channel. In addition, time course studies during capacitation in the presence of PF431396 showed a significant and sustained decrease in both intracellular Ca ²⁺ and pH levels after 2 hr of incubation, temporarily coincident with the activation of PYK2 during capacitation. Interestingly, decreases in Ca ²⁺ levels and progressive motility caused by PF431396 were reverted by inducing intracellular alkalinization with NH ₄ Cl, without affecting the pTyr blockage. Altogether, these observations support pTyr as an intracellular sensor for Ca ²⁺ entry in human sperm through regulation of cytoplasmic pH. These results contribute to a better understanding of the modulation of the polymodal CatSper and signaling pathways involved in human sperm capacitation.

Molecular Basis of Human Sperm Capacitation

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

Factors and pathways involved in capacitation: how are they regulated?

In mammals, fertilization occurs via a comprehensive progression of events. Freshly ejaculated sperm have yet to acquire progressive motility or fertilization ability. They must first undergo a series of biochemical and physiological changes, collectively known as capacitation. Capacitation is a significant prerequisite to fertilization. During the process of capacitation, changes in membrane properties, intracellular ion concentration and the activities of enzymes, together with other protein modifications, induce multiple signaling events and pathways in defined media in vitro or in the female reproductive tract in vivo. These, in turn, stimulate the acrosome reaction and prepare spermatozoa for penetration of the egg zona pellucida prior to fertilization. In the present review, we conclude all mainstream factors and pathways regulate capacitation and highlight their crosstalk. We also summarize the relationship between capacitation and assisted reproductive technology or human disease. In the end, we sum up the open questions and future avenues in this field.

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.

Dyslipidemia alters sperm maturation and capacitation in LXR-null mice

Lipid metabolism disorders (dyslipidemia) are causes of male infertility, but little is known about their impact on male gametes when considering post-testicular maturation events, given that studies concentrate most often on endocrine dysfunctions and testicular consequences. In this study, three-month-old wild-type (wt) and Liver-X-Receptors knock out (Lxrα;β−/−) males were fed four weeks with a control or a lipid-enriched diet containing 1.25% cholesterol (high cholesterol diet (HCD)). The HCD triggered a dyslipidemia leading to sperm post-testicular alterations and infertility. Sperm lipids were analyzed by LC–MS and those fromLxrα;β−/−males fed the HCD showed higher chol/PL and PC/PE ratios compared towt-HCD (P < 0.05) and lower oxysterol contents compared to wt (P < 0.05) orLxrα;β−/−(P < 0.05). These modifications impaired membrane-associated events triggering the tyrosine phosphorylation normally occurring during the capacitation process, as shown by phosphotyrosine Western blots. Using flow cytometry, we showed that a smaller subpopulation of spermatozoa fromLxrα;β−/−-HCD males could raise their membrane fluidity during capacitation (P < 0.05 vswtorwt-HCD) as well as their intracellular calcium concentration (P < 0.05 vsLxrα;β−/−andP < 0.001 vswt). The accumulation of the major sperm calcium efflux pump (PMCA4) was decreased inLxrα;β−/−males fed the HCD (P < 0.05 vsLxrα;β−/−andP < 0.001 vswt). This study is the first showing an impact of dyslipidemia on post-testicular sperm maturation with consequences on the capacitation signaling cascade. It may lead to the identification of fertility prognostic markers in this pathophysiological situation, which could help clinicians to better understand male infertilities which are thus far classified as idiopathic.

Neuronal signaling repertoire in the mammalian sperm functionality

The common embryonic origin has been a recurrent explanation to understand the presence of "neural receptors" in sperm. However, this designation has conditioned a bias marked by the classical neurotransmission model, dismissing the possibility that neurotransmitters can play specific roles in the sperm function by themselves. For instance, the launching of acrosome reaction, a fundamental sperm function, includes several steps that recall the process of presynaptic secretion. Unlike of postsynaptic neuron, whose activation is mediated by molecular interaction between neurotransmitter and postsynaptic receptors, the oocyte activation is not mediated by receptors, but by cytosolic translocation of sperm phospholipase (PLCζ). Thus, the sperm has a cellular design to access and activate the oocyte and restore the ploidy of the species by an "allogenic pronuclear fusion." At subcellular level, the events controlling sperm function, particularly the capacitation process, are activated by chemical signals that trigger ion fluxes, sterol oxidation, synthesis of cyclic adenosine monophosphate, protein kinase A activation, tyrosine phosphorylations and calcium signaling, which correspond to second messengers similar to those associated with exocytosis and growth cone guidance in neurons. Classically, the sperm function associated with neural signals has been analyzed as a unidimensional approach (single ligand-receptor effect). However, the in vivo sperm are exposed to multidimensional signaling context, for example, the GABAergic, monoaminergic, purinergic, cholinergic, and melatoninergic, to name a few. The aim of this review is to present an overview of sperm functionality associated with "neuronal signaling" and possible cellular and molecular mechanisms involved in their regulation.

Localization patterns of the ganglioside GM1 in human sperm are indicative of male fertility and independent of traditional semen measures

Semen analysis lacks a functional component and best identifies extreme cases of infertility. The ganglioside G_M1 is known to have functional roles during capacitation and acrosome exocytosis. Here, we assessed whether G_M1 localization patterns (Cap‐Score™) correspond with male fertility in different settings: Study 1 involved couples pursuing assisted reproduction in a tertiary care fertility clinic, while Study 2 involved men with known fertility versus those questioning their fertility at a local urology center. In Study 1, we examined various thresholds versus clinical history for 42 patients; 13 had Cap‐Scores ≥39.5%, with 12 of these (92.3%) achieving clinical pregnancy by natural conception or ≤3 intrauterine insemination cycles. Of the 29 patients scoring <39.5%, only six (20.7%) attained clinical pregnancy by natural conception or ≤3 intrauterine insemination cycles. In Study 2, Cap‐Scores were obtained from 76 fertile men (Cohort 1, pregnant partner or recent father) and compared to 122 men seeking fertility assessment (Cohort 2). Cap‐Score values were normally distributed in Cohort 1, with 13.2% having Cap‐Scores more than one standard deviation below the mean (35.3 ± 7.7%). Significantly, more men in Cohort 2 had Cap‐Scores greater than one standard deviation below the normal mean (33.6%; p = 0.001). Minimal/no relationship was found between Cap‐Score and sperm concentration, morphology, or motility. Together, these data demonstrate that Cap‐Score provides novel, clinically relevant insights into sperm function and male fertility that complement traditional semen analysis. Furthermore, the data provide normal reference ranges for fertile men that can help clinicians counsel couples toward the most appropriate fertility treatment.

Improving porcine in vitro fertilization output by simulating the oviductal environment

Differences between the in vitro and in vivo environment in which fertilization occurs seem to play a key role in the low efficiency of porcine in vitro fertilization (IVF). This work proposes an IVF system based on the in vivo oviductal periovulatory environment. The combined use of an IVF medium at the pH found in the oviduct in the periovulatory stage (pH_e 8.0), a mixture of oviductal components (cumulus-oocyte complex secretions, follicular fluid and oviductal periovulatory fluid, OFCM) and a device that interposes a physical barrier between gametes (an inverted screw cap of a Falcon tube, S) was compared with the classical system at pH_e 7.4, in a 4-well multidish (W) lacking oviduct biological components. The results showed that the new IVF system reduced polyspermy and increased the final efficiency by more than 48%. This higher efficiency seems to be a direct consequence of a reduced sperm motility and lower capacitating status and it could be related to the action of OFCM components over gametes and to the increase in the sperm intracellular pH (pH_i) caused by the higher pH_e used. In conclusion, a medium at pH 8.0 supplemented with OFCM reduces polyspermy and improves porcine IVF output.

Redistribution of soluble N-ethylmaleimide-sensitive-factor attachment protein receptors in mouse sperm membranes prior to the acrosome reaction

Formation of complexes between soluble N-ethylmaleimide-sensitive-factor attachment protein receptor (SNARE) proteins on opposing membranes is the minimal requirement for intracellular membrane fusion. The SNARE, syntaxin 2, is found on the sperm plasma membrane and a second SNARE, vesicle associated membrane protein 2 (VAMP2, also known as synaptobrevin 2, SYB2), is on the apposing outer acrosomal membrane. During the acrosome reaction, the outer acrosomal membrane fuses at hundreds of points with the plasma membrane. We hypothesized that syntaxin 2 and VAMP2 redistribute within their respective membranes prior to the acrosome reaction to form trans-SNARE complexes and promote membrane fusion. Immunofluorescence and superresolution structured illumination microscopy were used to localize syntaxin 2 and VAMP2 in mouse sperm during capacitation. Initially, syntaxin 2 was found in puncta throughout the acrosomal region. At 60 and 120 min of capacitation, syntaxin 2 was localized in puncta primarily in the apical ridge. Although deletion of bicarbonate during incubation had no effect, syntaxin 2 puncta were relocated in the restricted region in less than 20% of sperm incubated without albumin. In contrast, VAMP2 was already found in puncta within the apical ridge prior to capacitation. The puncta containing syntaxin 2 and VAMP2 did not precisely co-localize at 0 or 60 min of capacitation time. In summary, syntaxin 2 shifted its location to the apical ridge on the plasma membrane during capacitation in an albumin-dependent manner but VAMP2 was already localized to the apical ridge. Puncta containing VAMP2 did not co-localize with those containing syntaxin 2 during capacitation; therefore, formation of trans-SNARE complexes containing these SNAREs does not occur until after capacitation, immediately prior to acrosomal exocytosis.

Expression and alteration of BKCa channels in the sphincter of Oddi's from rabbits with hypercholesterolemia

This study aimed to investigate the expression and function of BK_Ca channels in the Sphincter of Oddi (SO) in a rabbit model of hypercholesterolemia (HC). New Zealand white rabbits were randomly divided into 2 groups: the control group was fed standard chow (n = 18) whereas the high-cholesterol group was fed cholesterol-enriched chow containing 1.5% cholesterol (n = 18). The serum cholesterol level was significantly greater in the HC groups than in the control group, but there was no significant difference in body weight between the control and HC groups. Although the total protein expression of BK_Ca α- and β₁-subunit was not significantly different between the control and HC groups, the Tyr-phosphorylation of BK_Ca α-subunit was significantly decreased in the HC group than in the control group. In addition, hypercholesterolemia significantly increased Acetylcholine (ACh)-induced contraction of the SO rings. Pretreatment with 30 μM NS1619, a BK_Ca channel agonist, significantly reduced ACh-induced contraction of the SO rings in HC rabbits. Moreover, pretreatment with 100 μM Na₃OV₄, a protein tyrosine phosphatase inhibitor, significantly reduced ACh-induced contraction of the SO rings in HC rabbits, whereas it significantly increased upon pretreating with 10 μM Genistein, a tyrosine kinase inhibitor. Whole-cell patch clamp recordings showed that BK_Ca current density was significantly lower in SOSMCs from HC group than that from control group. Our findings suggest that hypercholesterolemia-induced downregulation of BK_Ca channel, and Tyr-phosphorylation of BK_Ca α-subunit may contribute to the hyperresponsiveness of the SO ring in HC rabbits.