[Ca2+]i signalling in sperm — making the most of what you've got

The Olfactory Receptor Olfr25 Mediates Sperm Dysfunction Induced by Low-Dose Bisphenol A through the CatSper-Ca2+ Signaling Pathway

Bisphenol A (BPA), a typical endocrine disruptor, is known to have various adverse effects on the male reproductive system. However, the toxic effects and mechanisms of low-dose BPA have not yet been fully explored. In this study, male Kunming mice were orally administered low-dose BPA (0.03, 0.3 and 3 mg/kg/d) for ten consecutive weeks. Pathological sections of testicular tissue showed no significant morphological differences after BPA exposure. An analysis of the functional parameters of sperm revealed that exposure to low-dose BPA significantly decreased sperm motility, chemotaxis, and the acrosome reaction. An in vitro BPA exposure model combined with an omics data analysis showed that the olfactory receptor-related pathway was significantly enriched after BPA treatment. Subsequent experiments verified the reduced mRNA level of a novel olfactory receptor gene, Olfr25, in vivo and in vitro exposure models. Meanwhile, exposure to low-dose BPA reduced the intracellular calcium ion concentration and the mRNA levels of pore-forming subunits of the CatSper channel in sperm. Importantly, the knockdown of Olfr25 inhibited calcium ion levels and CatSper subunit expression in GC-2 cells. Olfr25 overexpression attenuated the BPA-induced downregulation of CatSper subunit expression in GC-2 cells. These findings indicate that Olfr25 might participate in low-dose BPA-induced sperm dysfunction by affecting the CatSper-Ca2+ signaling pathway. This study reveals a new mechanism underlying the effects of low-dose BPA on sperm function and provides a reference for assessing the safety of low-dose BPA exposure.

The neonicotinoid, imidacloprid, disrupt the chicken sperm quality through calcium efflux

Imidacloprid (IMI), an insecticide from the neonicotinoid group widely used in agriculture, has drawn attention due to its potential harmful effects on non-target species, including bird populations. In the present work, we investigated the effect of IMI on avian semen by in vitro exposure of rooster spermatozoa to this pesticide. The semen was collected twice a week. Samples collected on one day were pooled and incubated with the following IMI concentrations: 0 mM, 0.5 mM, 5 mM, 10 mM, and 50 mM at 36°C for 3 h. Comprehensive semen analysis was carried out after 1 h and 3 h of incubation, evaluating sperm motility parameters with the CASA system and using flow cytometry to assess membrane integrity, mitochondrial activity, acrosome integrity, chromatin structure, intracellular calcium level and apoptosis markers such as: early apoptosis and caspase activation and lipid peroxidation. The results of the first experiment suggest that low concentrations of IMI have a different effect on sperm motility compared to higher concentrations. In IMI samples, we also observed a lower percentage of cells with a high level of calcium ions compared to the control, and a lower level of lipid peroxidation. We concluded that IMI may act as a blocker of calcium channels, preventing the influx of these ions into the cell. To confirm this mechanism, we conducted a second experiment with calcium channel blockers: SNX 325, MRS-1845, and Nifedipine. The results of this experiment confirmed that the mechanism of action of IMI largely relies on the blockade of calcium channels in rooster sperm. Blocking the influx of calcium ions into the cell prevents the formation of Ca²⁺-dependent pores, thereby preventing an increase in cell membrane permeability, ultimately blocking early apoptosis and lipid peroxidation in chicken spermatozoa.

Calcium and vitamin D homoeostasis in male fertility

Calcium and vitamin D have well-established roles in maintaining calcium balance and bone health. Decades of research in human subjects and animals have revealed that calcium and vitamin D also have effects on many other organs including male reproductive organs. The presence of calcium-sensing receptor, vitamin D receptor, vitamin D activating and inactivating enzymes and calcium channels in the testes, male reproductive tract and human spermatozoa suggests that vitamin D and calcium may modify male reproductive function. Functional animal models have shown that vitamin D deficiency in male rodents leads to a decrease in successful mating and fewer pregnancies, often caused by impaired sperm motility and poor sperm morphology. Human studies have to a lesser extent validated these findings; however, newer studies suggest a positive effect of vitamin D supplementation on semen quality in cases with vitamin D deficiency, which highlights the need for initiatives to prevent vitamin D deficiency. Calcium channels in male reproductive organs and spermatozoa contribute to the regulation of sperm motility and capacitation, both essential for successful fertilisation, which supports a need to avoid calcium deficiency. Studies have demonstrated that vitamin D, as a regulator of calcium homoeostasis, influences calcium influx in the testis and spermatozoa. Emerging evidence suggests a potential link between vitamin D deficiency and male infertility, although further investigation is needed to establish a definitive causal relationship. Understanding the interplay between vitamin D, calcium and male reproductive health may open new avenues for improving fertility outcomes in men.

MAPKs signaling is obligatory for male reproductive function in a development-specific manner

Mitogen-activated protein kinases (MAPKs) represent widely expressed and evolutionarily conserved proteins crucial for governing signaling pathways and playing essential roles in mammalian male reproductive processes. These proteins facilitate the transmission of signals through phosphorylation cascades, regulating diverse intracellular functions encompassing germ cell development in testis, physiological maturation of spermatozoa within the epididymis, and motility regulation at ejaculation in the female reproductive tract. The conservation of these mechanisms appears prevalent across species, including humans, mice, and, to a limited extent, livestock species such as bovines. In Sertoli cells (SCs), MAPK signaling not only regulates the proliferation of immature SCs but also determines the appropriate number of SCs in the testes at puberty, thereby maintaining male fertility by ensuring the capacity for sperm cell production. In germ cells, MAPKs play a crucial role in dynamically regulating testicular cell-cell junctions, supporting germ cell proliferation and differentiation. Throughout spermatogenesis, MAPK signaling ensures the appropriate Sertoli-to-germ cell ratio by regulating apoptosis, controlling the metabolism of developing germ cells, and facilitating the maturation of spermatozoa within the cauda epididymis. During ejaculation in the female reproductive tract, MAPKs regulate two pivotal events-capacitation and the acrosome reaction essential for maintaining the fertility potential of sperm cells. Any disruptions in MAPK pathway signaling possibly may disturb the testicular microenvironment homeostasis, sperm physiology in the male body before ejaculation and in the female reproductive tract during fertilization, ultimately compromising male fertility. Despite decades of research, the physiological function of MAPK pathways in male reproductive health remains inadequately understood. The current review attempts to combine recent findings to elucidate the impact of MAPK signaling on male fertility and proposes future directions to enhance our understanding of male reproductive functions.

Identification of ITPR1 gene as a novel target for hsa-miR-34b-5p in non-obstructive azoospermia: a Ca2+/apoptosis pathway cross-talk

MiR-34b-5p has been reported as a non-invasive diagnostic biomarker for infertility. However, no gene targets regulating the mechanism of cation of this miRNA are known. In this study, using gene set enrichment analysis the Inositol 1,4,5-Trisphosphate Receptor Type 1 (ITPR1) gene was identified as the sole target for hsa-miR-34b-5p, and found significantly overexpressed in non-obstructive azoospermia (NOA) patients. This finding was confirmed by qRT-PCR on fresh testicular tissues from NOA patients. Then, pathway enrichment analysis as well as the diagnostic value analysis of hsa-miR-34b-5p/ITPR1 indicated ITPR1 as a hub gene in the calcium (Ca2+)-apoptosis pathway, and a valuable predictive biomarker for NOA. Moreover, gene expression and histological assays showed the association of the effects of ITPR1's increased expression on spermatogenesis failure through induction of apoptosis in NOA patients. These data suggested that the hsa-miR-34b-5p/ITPR1 axis could serve as a potential regulatory predictive biomarker for human spermatogenesis through the Ca2+-apoptosis pathway cross-talk.

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

BACKGROUND

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

OBJECTIVES

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

MATERIALS AND METHODS

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

RESULTS

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

DISCUSSION AND CONCLUSION

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

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.

The action of physiological and synthetic steroids on the calcium channel CatSper in human sperm

The sperm-specific channel CatSper (cation channel of sperm) controls the intracellular Ca2+ concentration ([Ca2+]i) and plays an essential role in sperm function. It is mainly activated by the steroid progesterone (P4) but is also promiscuously activated by a wide range of synthetic and physiological compounds. These compounds include diverse steroids whose action on the channel is so far still controversial. To investigate the effect of these compounds on CatSper and sperm function, we developed a high-throughput screening (HTS) assay to measure changes in [Ca2+]i in human sperm and screened 1,280 approved and off-patent drugs including 90 steroids from the Prestwick chemical library. More than half of the steroids tested (53%) induced an increase in [Ca2+]i and reduced the P4-induced Ca2+ influx in human sperm in a dose-dependent manner. Ten of the most potent steroids (activating and P4-inhibiting) were selected for a detailed analysis of their action on CatSper and their ability to act on sperm acrosome reaction (AR) and penetration in viscous media. We found that these steroids show an inhibitory effect on P4 but not on prostaglandin E1-induced CatSper activation, suggesting that they compete for the same binding site as P4. Pregnenolone, dydrogesterone, epiandrosterone, nandrolone, and dehydroepiandrosterone acetate (DHEA) were found to activate CatSper at physiologically relevant concentrations within the nanomolar range. Like P4, most tested steroids did not significantly affect the AR while stanozolol and estropipate slightly increased sperm penetration into viscous medium. Furthermore, using a hybrid approach integrating pharmacophore analysis and statistical modelling, we were able to screen in silico for steroids that can activate the channel and define the physicochemical and structural properties required for a steroid to exhibit agonist activity against CatSper. Overall, our results indicate that not only physiological but also synthetic steroids can modulate the activity of CatSper with varying potency and if bound to CatSper prior to P4, could impair the timely CatSper activation necessary for proper fertilization to occur.

Capacitation induces changes in metabolic pathways supporting motility of epididymal and ejaculated sperm

Mammalian sperm require sufficient energy to support motility and capacitation for successful fertilization. Previous studies cataloging the changes to metabolism in sperm explored ejaculated human sperm or dormant mouse sperm surgically extracted from the cauda epididymis. Due to the differences in methods of collection, it remains unclear whether any observed differences between mouse and human sperm represent species differences or reflect the distinct maturation states of the sperm under study. Here we compare the metabolic changes during capacitation of epididymal versus ejaculated mouse sperm and relate these changes to ejaculated human sperm. Using extracellular flux analysis and targeted metabolic profiling, we show that capacitation-induced changes lead to increased flux through both glycolysis and oxidative phosphorylation in mouse and human sperm. Ejaculation leads to greater flexibility in the ability to use different carbon sources. While epididymal sperm are dependent upon glucose, ejaculated mouse and human sperm gain the ability to also leverage non-glycolytic energy sources such as pyruvate and citrate.

Reproductive toxicity of combined effects of endocrine disruptors on human reproduction

Confluence of environmental, genetic, and lifestyle variables is responsible for deterioration of human fecundity. Endocrine disruptors or endocrine disrupting chemicals (EDCs) may be found in a variety of foods, water, air, beverages, and tobacco smoke. It has been demonstrated in experimental investigations that a wide range of endocrine disrupting chemicals have negative effects on human reproductive function. However, evidence on the reproductive consequences of human exposure to endocrine disrupting chemicals is sparse and/or conflicting in the scientific literature. The combined toxicological assessment is a practical method for assessing the hazards of cocktails of chemicals, co-existing in the environment. The current review provides a comprehensive overview of studies emphasizing the combined toxicity of endocrine disrupting chemicals on human reproduction. Endocrine disrupting chemicals interact with each other to disrupt the different endocrine axes, resulting in severe gonadal dysfunctions. Transgenerational epigenetic effects have also been induced in germ cells, mostly through DNA methylation and epimutations. Similarly, after acute or chronic exposure to endocrine disrupting chemicals combinations, increased oxidative stress (OS), elevated antioxidant enzymatic activity, disrupted reproductive cycle, and reduced steroidogenesis are often reported consequences. The article also discusses the concentration addition (CA) and independent action (IA) prediction models, which reveal the importance of various synergistic actions of endocrine disrupting chemicals mixtures. More crucially, this evidence-based study addresses the research limitations and information gaps, as well as particularly presents the future research views on combined endocrine disrupting chemicals toxicity on human reproduction.

Microfluidics facilitating the use of small extracellular vesicles in innovative approaches to male infertility

Sperm are transcriptionally and translationally quiescent and, therefore, rely on the seminal plasma microenvironment for function, survival and fertilization of the oocyte in the oviduct. The male reproductive system influences sperm function via the binding and fusion of secreted epididymal (epididymosomes) and prostatic (prostasomes) small extracellular vesicles (S-EVs) that facilitate the transfer of proteins, lipids and nucleic acids to sperm. Seminal plasma S-EVs have important roles in sperm maturation, immune and oxidative stress protection, capacitation, fertilization and endometrial implantation and receptivity. Supplementing asthenozoospermic samples with normospermic-derived S-EVs can improve sperm motility and S-EV microRNAs can be used to predict non-obstructive azoospermia. Thus, S-EV influence on sperm physiology might have both therapeutic and diagnostic potential; however, the isolation of pure populations of S-EVs from bodily fluids with current conventional methods presents a substantial hurdle. Many conventional techniques lack accuracy, effectiveness, and practicality; yet microfluidic technology has the potential to simplify and improve S-EV isolation and detection.

Escaping Behavior of Sperms on the Biomimetic Oviductal Surface

Before fertilization, sperms adhere to oviductal epithelium cells, and only a restrictive number of winner sperms can escape to reach the egg. To study the sperm escape behavior from the oviductal surface, we developed a microfluidic chip to fabricate an adhesive surface and to create a gradient of progesterone (P₄) for mimicking the oviduct microenvironment in vivo. We identified three sperm motion patterns in such a microenvironment─anchored spin, run-and-spin, and escaped mode. By using kinetic analysis, we verified the hypothesis that the responsive rotation energy anchored with the adhered sperm head determines whether the sperm is trapped or detaching, which is defined as the hammer flying strategy of successful escape after accumulating energy in the process of rotating. Intriguingly, this hammer-throw escaping is able to be triggered by the P₄ biochemical stimulation. Our results revealed the tangled process of sperm escape before fertilization in the ingenious microfluidic system.

Organic food consumption and fecundability in a preconception cohort study of Danish couples trying to conceive

BACKGROUND

Little is known about potential health effects of eating organic food in relation to reproduction.

OBJECTIVE

We examined associations between organic food consumption and fecundability.

METHODS

Data were derived from a preconception cohort study of Danish couples trying to conceive (SnartForaeldre.dk, SF). Participants completed a baseline questionnaire on socio-demographics, anthropometrics and lifestyle and a validated food-frequency questionnaire, which included questions on proportions of organic food consumed within six food groups. Participants were followed up with bimonthly questionnaires for up to 12 months or until pregnancy. Analyses were restricted to 2061 participants attempting pregnancy for ≤6 cycles at enrollment and 1303 with <3 cycles. Fecundability ratios (FRs) and 95% confidence intervals (CI) were estimated by proportional probabilities regression models adjusted for potential confounders including age, lifestyle and socioeconomic factors. Associations were examined for vegetables, fruits, cereals, dairy products, eggs and meat, separately, and for the overall pattern of organic food consumption (organic sum score).

RESULTS

The final analytic sample comprised 2069 participants. In the full cohort, organic food consumption was not meaningfully associated with fecundability. Among participants <3 cycles of pregnancy attempt at study entry (n = 1303), the FR was 1.11 (95% CI 0.93, 1.33) for the category 'less than half', for 'more than half' the FR was 1.17 (95% CI 0.99, 1.38) and for 'almost everything' the FR was 1.12 (95% CI 0.97, 1.28).

CONCLUSION

Higher consumption of organic foods was not meaningfully associated with fecundability, although slightly greater fecundability was seen among participants with <3 cycles of pregnancy attempt time.

In vitro investigation of endocrine disrupting effects of pesticides on Ca2+-signaling in human sperm cells through actions on the sperm-specific and steroid-activated CatSper Ca2+-channel

BACKGROUND

Ca²⁺-signaling controls sperm cell functions necessary for successful fertilization. Multiple endocrine disrupting chemicals have been found to interfere with normal Ca²⁺-signaling in human sperm cells through an activation of the sperm-specific CatSper Ca²⁺-channel, which is vital for normal male fertility.

OBJECTIVES

We investigated 53 pesticides for their ability to interfere with CatSper mediated Ca²⁺-signaling and function in human sperm cells.

METHODS

Effects of the pesticides on Ca²⁺-signaling in human sperm cells were evaluated using a Ca²⁺-fluorometric assay. Effects via CatSper were assessed using the specific CatSper inhibitor RU1968. Effects on human sperm function and viability were assessed using an image cytometry-based acrosome reaction assay and the modified Kremer's sperm-mucus penetration assay.

RESULTS

28 of 53 pesticides were found to induce Ca²⁺-signals in human sperm cells at 10 µM. The majority of these 28 active pesticides induced Ca²⁺-signals through CatSper and interfered with subsequent Ca²⁺-signals induced by the two endogenous CatSper ligands progesterone and prostaglandin E₁. Multiple active pesticides were found to affect Ca²⁺-mediated sperm functions and viability at 10 µM. Low nM dose mixtures of the active pesticides alone or in combination with other environmental chemicals were found to significantly induce Ca²⁺-signals and inhibit Ca²⁺-signals induced subsequently by progesterone and prostaglandin E₁.

CONCLUSIONS

Our results show that pesticides, both alone and in low nM dose mixtures, interfere with normal Ca²⁺-signaling in human sperm cells in vitro in low nM concentrations. Biomonitoring of the active pesticides in relevant matrices such as blood and reproductive fluids is very limited and the effects of real time human pesticide exposure on human sperm cells and fertility thus remains largely unknown. To which extent human pesticide exposure affects the chances of a successful fertilization in humans in vivo needs further research.

Competitive CatSper Activators of Progesterone from Rhynchosia volubilis

The root Rhynchosia volubilis was widely used for contraception in folk medicine, although its molecular mechanism on antifertility has not yet been revealed. In human sperm, it was reported that the cation channel of sperm, an indispensable cation channel for the fertilization process, could be regulated by various steroid-like compounds in plants. Interestingly, these nonphysiological ligands would also disturb the activation of the cation channel of sperm induced by progesterone. Therefore, this study aimed to explore whether the compounds in R. volubilis affect the physiological regulation of the cation channel of sperm. The bioguided isolation of the whole herb of R. volubilis has resulted in the novel discovery of five new prenylated isoflavonoids, rhynchones A - E (1:  - 5: ), a new natural product, 5'-O-methylphaseolinisoflavan (6: ) (¹H and ¹³C NMR data, Supporting Information), together with twelve known compounds (7:  - 18: ). Their structures were established by extensive spectroscopic analyses and drawing a comparison with literature data, while their absolute configurations were determined by electronic circular dichroism calculations. The experiments of intracellular Ca²⁺ signals and patch clamping recordings showed that rhynchone A (1: ) significantly reduced cation channel of sperm activation by competing with progesterone. In conclusion, our findings indicat that rhynchone A might act as a contraceptive compound by impairing the activation of the cation channel of sperm and thus prevent fertilization.

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

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

A Sea Anemone Lebrunia neglecta Venom Fraction Decreases Boar Sperm Cells Capacitation: Possible Involvement of HVA Calcium Channels

Sea anemones produce venoms characterized by a complex mixture of low molecular weight compounds, proteins and peptides acting on voltage-gated ion channels. Mammal sperm cells, like neurons, are characterized by their ion channels. Calcium channels seem to be implicated in pivotal roles such as motility and capacitation. In this study, we evaluated the effect of a low molecular weight fraction from the venom of the sea anemone Lebrunia neglecta on boar sperm cells and in HVA calcium channels from rat chromaffin cells. Spermatozoa viability seemed unaffected by the fraction whereas motility and sperm capacitation were notoriously impaired. The sea anemone fraction inhibited the HVA calcium current with partial recovery and no changes in chromaffin cells’ current kinetics and current–voltage relationship. These findings might be relevant to the pharmacological characterization of cnidarian venoms and toxins on voltage-gated calcium channels.

Decoding the Bell-Shaped Calcium Spikes in Phosphorylation Cycles of Flagella

We investigate the messenger role of calcium ions implicated in the regulation of wave-like bending dynamics of flagella. The emphasis is on microtubules of flagellar axoneme serving as nonlinear transmission lines for bell-shaped spikes of calcium ions. The calcium sensitive proteins, such as calmodulin, exhibit activation dependence on the spike train frequency and amplitude. Here, we analyze a Ca²⁺ decoding module IDA-I1 whose activity is controlled by Ca²⁺ activated kinase. We find that trains of Ca²⁺ spikes are advantageous compared to a constant rise in Ca²⁺ concentration as being more efficient and much less prone to noisy fluctuations.

The influence of the female reproductive tract and sperm features on the design of microfluidic sperm-sorting devices

Although medical advancements have successfully helped a lot of couples with their infertility by assisted reproductive technologies (ART), sperm selection, a crucial stage in ART, has remained challenging. Therefore, we aimed to investigate novel sperm separation methods, specifically microfluidic systems, as they do sperm selection based on sperm and/or the female reproductive tract (FRT) features without inflicting any damage to the selected sperm during the process. In this review, after an exhaustive studying of FRT features, which can implement by microfluidics devices, the focus was centered on sperm selection and investigation devices. During this study, we tried not to only point to the deficiencies of these systems, but to put forth suggestions for their improvement as well.

Prostate secretory protein 94 (PSP94) inhibits sterol-binding and export by the mammalian CAP protein CRISP2 in a calcium-sensitive manner

Members of the CAP protein superfamily are present in all kingdoms of life and have been implicated in many different processes, including pathogen defense, immune evasion, sperm maturation, and cancer progression. Most CAP proteins are secreted glycoproteins and share a unique conserved αβα sandwich fold. The precise mode of action of this class of proteins, however, has remained elusive. Saccharomyces cerevisiae has three CAP family members, termed pathogen related in yeast (Pry). We have previously shown that Pry1 and Pry2 export sterols in vivo and that they bind sterols in vitro. This sterol binding and export function of yeast Pry proteins is conserved in the mammalian CRISP proteins and other CAP superfamily members. CRISP3 is an abundant protein of the human seminal plasma and interacts with prostate secretory protein of 94 amino acids (PSP94), another major protein component in the seminal plasma. Here we examine whether the interaction between CRISP proteins and PSP94 affects the sterol binding function of CAP family members. We show that coexpression of PSP94 with CAP proteins in yeast abolished their sterol export function and the interaction between PSP94 and CAP proteins inhibits sterol binding in vitro. In addition, mutations that affect the formation of the PSP94–CRISP2 heteromeric complex restore sterol binding. Of interest, we found the interaction of PSP94 with CRISP2 is sensitive to high calcium concentrations. The observation that PSP94 modulates the sterol binding function of CRISP2 in a calcium-dependent manner has potential implications for the role of PSP94 and CRISP2 in prostate physiology and progression of prostate cancer.

OUP accepted manuscript

BACKGROUND

Oocyte activation deficiency (OAD) is attributed to the majority of cases underlying failure of ICSI cycles, the standard treatment for male factor infertility. Oocyte activation encompasses a series of concerted events, triggered by sperm-specific phospholipase C zeta (PLCζ), which elicits increases in free cytoplasmic calcium (Ca²⁺) in spatially and temporally specific oscillations. Defects in this specific pattern of Ca²⁺ release are directly attributable to most cases of OAD. Ca²⁺ release can be clinically mediated via assisted oocyte activation (AOA), a combination of mechanical, electrical and/or chemical stimuli which artificially promote an increase in the levels of intra-cytoplasmic Ca²⁺. However, concerns regarding safety and efficacy underlie potential risks that must be addressed before such methods can be safely widely used.

OBJECTIVE AND RATIONALE

Recent advances in current AOA techniques warrant a review of the safety and efficacy of these practices, to determine the extent to which AOA may be implemented in the clinic. Importantly, the primary challenges to obtaining data on the safety and efficacy of AOA must be determined. Such questions require urgent attention before widespread clinical utilization of such protocols can be advocated.

SEARCH METHODS

A literature review was performed using databases including PubMed, Web of Science, Medline, etc. using AOA, OAD, calcium ionophores, ICSI, PLCζ, oocyte activation, failed fertilization and fertilization failure as keywords. Relevant articles published until June 2019 were analysed and included in the review, with an emphasis on studies assessing large-scale efficacy and safety.

OUTCOMES

Contradictory studies on the safety and efficacy of AOA do not yet allow for the establishment of AOA as standard practice in the clinic. Heterogeneity in study methodology, inconsistent sample inclusion criteria, non-standardized outcome assessments, restricted sample size and animal model limitations render AOA strictly experimental. The main scientific concern impeding AOA utilization in the clinic is the non-physiological method of Ca²⁺ release mediated by most AOA agents, coupled with a lack of holistic understanding regarding the physiological mechanism(s) underlying Ca²⁺ release at oocyte activation.

LIMITATIONS, REASONS FOR CAUTION

The number of studies with clinical relevance using AOA remains significantly low. A much wider range of studies examining outcomes using multiple AOA agents are required.

WIDER IMPLICATIONS

In addition to addressing the five main challenges of studies assessing AOA safety and efficacy, more standardized, large-scale, multi-centre studies of AOA, as well as long-term follow-up studies of children born from AOA, would provide evidence for establishing AOA as a treatment for infertility. The delivery of an activating agent that can more accurately recapitulate physiological fertilization, such as recombinant PLCζ, is a promising prospect for the future of AOA. Further to PLCζ, many other avenues of physiological oocyte activation also require urgent investigation to assess other potential physiological avenues of AOA.

STUDY FUNDING/COMPETING INTERESTS

D.G. was supported by Stanford University’s Bing Overseas Study Program. J.K. was supported by a Healthcare Research Fellowship Award (HF-14-16) made by Health and Care Research Wales (HCRW), alongside a National Science, Technology, and Innovation plan (NSTIP) project grant (15-MED4186-20) awarded by the King Abdulaziz City for Science and Technology (KACST). The authors have no competing interests to declare.

N-Methyl-d-aspartic Acid (NMDA) Receptor Is Involved in the Inhibitory Effect of Ketamine on Human Sperm Functions

Ketamine, which used to be widely applied in human and animal medicine as a dissociative anesthetic, has become a popular recreational drug because of its hallucinogenic effect. Our previous study preliminarily proved that ketamine could inhibit human sperm function by affecting intracellular calcium concentration ([Ca²⁺]_i). However, the specific signaling pathway of [Ca²⁺]_i induced by ketamine in human sperm is still not clear yet. Here, the N-methyl-d-aspartic acid (NMDA) receptor was detected in the tail region of human sperm. Its physiological ligand, NMDA (50 μM), could reverse ketamine's inhibitory effect on human sperm function, and its antagonist, MK801 (100 μM), could restrain the effect of NMDA. The inhibitory effect caused by 4 mM ketamine or 100 μM MK801 on [Ca²⁺]_i, which is a central factor in the regulation of human sperm function, could also be recovered by 50 μM NMDA. The results suggest that the NMDA receptor is probably involved in the inhibitory effect of ketamine on human sperm functions.

Cyclic FEE Peptide Improves Human Sperm Movement Parameters without Modification of Their Energy Metabolism

Cyclic fertilin peptide (cFEE: phenylalanine, glutamic acid; glutamic acid) improves gamete interaction in humans. We investigate whether it could be via improvement of sperm movement parameters and their mitochondrial ATP production. Sperm movement parameters were studied using computer-assisted sperm analysis (CASA) in sperm samples from 38 patients with normal sperm in medium supplemented with cyclic fertilin against a control group. Sperm mitochondrial functions were studied using donor’s sperm, incubated or not with cFEE. It was evaluated by the measurement of their ATP production using bioluminescence, their respiration by high resolution oxygraphy, and of mitochondrial membrane potential (MMP) using potentiometric dyes and flow cytometry. cFEE significantly improved sperm movement parameters and percentage of hyperactivated sperm. Impact of inhibitors showed OXPHOS as the predominant energy source for sperm movement. However, cFEE had no significant impact on any of the analyzed mitochondrial bioenergetic parameters, suggesting that it could act via a more efficient use of its energy resources.

Structure-based redesigning of pentoxifylline analogs against selective phosphodiesterases to modulate sperm functional competence for assisted reproductive technologies

Phosphodiesterase (PDE) inhibitors, such as pentoxifylline (PTX), are used as pharmacological agents to enhance sperm motility in assisted reproductive technology (ART), mainly to aid the selection of viable sperm in asthenozoospermic ejaculates and testicular spermatozoa, prior to intracytoplasmic sperm injection (ICSI). However, PTX is reported to induce premature acrosome reaction (AR) and, exert toxic effects on oocyte function and early embryo development. Additionally, in vitro binding studies as well as computational binding free energy (ΔG_bind) suggest that PTX exhibits weak binding to sperm PDEs, indicating room for improvement. Aiming to reduce the adverse effects and to enhance the sperm motility, we designed and studied PTX analogues. Using structure-guided in silico approach and by considering the physico-chemical properties of the binding pocket of the PDEs, designed analogues of PTX. In silico assessments indicated that PTX analogues bind more tightly to PDEs and form stable complexes. Particularly, ex vivo evaluation of sperm treated with one of the PTX analogues (PTXm-1), showed comparable beneficial effect at much lower concentration-slower AR, higher DNA integrity and extended longevity of  spermatozoa and  superior embryo quality. PTXm-1 is proposed to be a better pharmacological agent for ART than PTX for sperm function enhancement.

Brain and testis: more alike than previously thought?

Several strands of evidence indicate the presence of marked similarities between human brain and testis. Understanding these similarities and their implications has become a topic of interest among the scientific community. Indeed, an association of intelligence with some semen quality parameters has been reported and a relation between dysfunctions of the human brain and testis has also been evident. Numerous common molecular features are evident when these tissues are compared, which is reflected in the huge number of common proteins. At the functional level, human neurons and sperm share a number of characteristics, including the importance of the exocytotic process and the presence of similar receptors and signalling pathways. The common proteins are mainly involved in exocytosis, tissue development and neuron/brain-associated biological processes. With this analysis, we conclude that human brain and testis share several biochemical characteristics which, in addition to their involvement in the speciation process, could, at least in part, be responsible for the expression of a huge number of common proteins. Nonetheless, this is an underexplored topic, and the connection between these tissues needs to be clarified, which could help to understand the dysfunctions affecting brain and testis, as well as to develop improved therapeutic strategies.

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

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

[Ca2+]i oscillations in human sperm are triggered in the flagellum by membrane potential-sensitive activity of CatSper

STUDY QUESTION

How are progesterone (P4)-induced repetitive intracellular Ca2+ concentration ([Ca2+]i) signals (oscillations) in human sperm generated?

SUMMARY ANSWER

P4-induced [Ca2+]i oscillations are generated in the flagellum by membrane potential (Vm)-sensitive Ca2+-influx through CatSper channels.

WHAT IS KNOWN ALREADY

A subset of human sperm display [Ca2+]i oscillations that regulate flagellar beating and acrosome reaction. Although pharmacological manipulations indicate involvement of stored Ca2+ in these oscillations, influx of extracellular Ca2+ is also required.

STUDY DESIGN, SIZE, DURATION

This was a laboratory study that used >20 sperm donors and involved more than 100 separate experiments and analysis of more than 1000 individual cells over a period of 2 years.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Semen donors and patients were recruited in accordance with local ethics approval from Birmingham University and Tayside ethics committees. [Ca2+]i responses and Vm of individual cells were examined by fluorescence imaging and whole-cell current clamp.

MAIN RESULTS AND THE ROLE OF CHANCE

P4-induced [Ca2+]i oscillations originated in the flagellum, spreading to the neck and head (latency of 1-2 s). K+-ionophore valinomycin (1 µM) was used to investigate the role of membrane potential (Vm). Direct assessment by whole-cell current-clamp confirmed that Vm in valinomycin-exposed cells was determined primarily by K+ equilibrium potential (EK) and was rapidly 'reset' upon manipulation of [K+]o. Pre-treatment of sperm with valinomycin ([K+]o = 5.4 mM) had no effect on the P4-induced [Ca2+] transient (P = 0.95; eight experiments), but application of valinomycin to P4-pretreated sperm suppressed activity in 82% of oscillating cells (n = 257; P = 5 × 10-55 compared to control) and significantly reduced both the amplitude and frequency of persisting oscillations (P = 0.0001). Upon valinomycin washout, oscillations re-started in most cells. When valinomycin was applied in saline with elevated [K+], the inhibitory effect of valinomycin was reduced and was dependent on EK (P = 10-25). Amplitude and frequency of [Ca2+]i oscillations that persisted in the presence of valinomycin showed similar sensitivity to EK (P < 0.01). The CatSper inhibitor RU1968 (4.8 and 11 µM) caused immediate and reversible arrest of activity in 36% and 96% of oscillating cells, respectively (P < 10-10). Quinidine (300 µM) which blocks the sperm K+ current (IKsper) completely, inhibited [Ca2+]i oscillations.

LARGE SCALE DATA

N/A.

LIMITATIONS, REASONS FOR CAUTION

This was an in-vitro study and caution must be taken when extrapolating these results to in-vivo regulation of sperm.

WIDER IMPLICATIONS OF THE FINDINGS

[Ca2+]i oscillations in human sperm are functionally important and their absence is associated with failed fertilisation at IVF. The data reported here provide new understanding of the mechanisms that underlie the regulation and generation (or failure) of these oscillations.

STUDY FUNDING/COMPETING INTEREST(S)

E.T.-N. was in receipt of a postgraduate scholarship from the CAPES Foundation (Ministry of Education, Brazil). E.M-M received travel funds from the Programa de Apoyo a los Estudios de Posgrado (Maestria y Doctorado en Ciencias Bioquimicas-Universidad Autonoma de Mexico). SGB and CLRB are recipients of a Chief Scientist Office (NHS Scotland) grant TCS/17/28. The authors have no conflicts of interest.

Transcriptomic and metabolomic insights into the variety of sperm storage in oviduct of egg layers

In birds, the sperm storage tubules (SST) are dispersed in uterovaginal junction (UVJ) and highly correlated with differential capacity of sperm storage (SS) in and among species with unspecified mechanisms. Here, the SS duration of 252 egg layer breeders was evaluated in 5 rounds with 3 phenotypic traits to screen high- and low-SS individuals, respectively, followed with transcriptome of UVJ tissues and metabolome of serum (high-SS vs. low-SS) to decipher the candidate genes and biochemical markers correlated with differential SS capacity. Histological characterization suggested slightly higher density of SST in UVJ (high-SS vs. low-SS). Transcriptome analyses identified 596 differentially expressed genes (336 upregulated vs. 260 downregulated), which were mainly enriched in gene ontology terms of homeostasis, steroid and lipid metabolism and hormone activity, and 12 significant pathways (P < 0.05) represented by calcium, steroid, and lipid metabolism. Immunohistochemical staining of GNAQ, ST6GAL1, ADFP, and PCNA showed similar distribution in UVJ tissues between 2 groups. Several candidates (HSD11B2, DIO2, AQP3, GNAQ, NANS, ST6GAL1) combined with 4 (11β-prostaglandin F2α, prostaglandin B1, 7α-hydroxytestosterone, and N-acetylneuraminic acid) of 40 differential metabolites enriched in serum metabolome were considered as regulators and biomarkers of SS duration in egg layer breeders. The integrated transcriptome and metabolome analyses of chicken breeder hens will provide novel insights for exploration and improvement of differential SS capacity in birds.

Characterization and biological role of cysteine-rich venom protein belonging to CRISPs from turkey seminal plasma†

Turkey semen contains cysteine-rich secretory proteins (CRISPs) that belong to the dominant seminal plasma proteins. We aimed to isolate and characterize CRISP from turkey seminal plasma and evaluate its possible involvement in yellow semen syndrome (YSS). YSS, which is well characterized, causes reduced fertility and hatchability. The protein was purified using hydrophobic interaction, gel filtration, and reverse phase chromatography. It then was subjected to identification by mass spectrometry, analysis of physicochemical properties, and specific antibody production. The biological function of the isolated protein was tested and included its effects on sperm motility and migration and sperm-egg interactions. Sperm motility was measured with the CASA system using Hobson Sperm Tracker. The reproductive tract of turkey toms was analyzed for gene expression; immunohistochemistry was used for protein localization in the male reproductive tract, spermatozoa, and inner perivitelline layer. The isolated protein was identified as cysteine-rich venom protein-like isoform X2 (CRVP X2; XP_010706464.1) and contained feature motifs of CRISP family proteins. Turkey CRVP X2 was present in both spermatozoa and seminal plasma. The extensive secretion of CRVP X2 by the epithelial cells of the epididymis and ductus deferens suggests its involvement in post-testicular sperm maturation. The internally localized CRVP X2 in the proximal part of the sperm tail might be responsible for stimulation of sperm motility. CRVP X2 on the sperm head might be involved in several events prior to fusion and may also participate in gamete fusion itself. Although the mechanisms by which CRVP X2 mediates fertilization are still unknown, the involvement of complementary sites cannot be excluded. The disturbance of CRVP X2 expression can serve as an etiologic factor of YSS in the turkey. This study expands the understanding of the detailed mechanism of fertilization in birds by clarifying the specific role of CRVP X2.

UV filters in matched seminal fluid-, urine-, and serum samples from young men

Recent in vitro studies have shown that some chemical UV filters mimic the effect of progesterone in the activation of the CatSper Ca2⁺ channel in human spermatozoa. However, so far, the extent of exposure of human spermatozoa to chemical UV filters via the presence of these chemicals in seminal fluid has been unknown. Here, we present levels of UV filters measured in human seminal fluid and comparisons to levels measured in concurrently collected urine and serum samples. In total nine UV filters were analysed by TurboFlow-LC-MS/MS in paired urine, serum, and seminal fluid samples from 300 young Danish men from the general population; each man collected one of each sample type within 1 h. The samples were collected during February-December 2013 and only six of the men reported having used sunscreen during the 48 h preceding the sample collection. Four of the examined UV filters could be detected in seminal fluid samples at levels above LOD in more than 10% of the samples. Benzophenone (BP), benzophenone-1 (BP-1), and benzophenone-3 (BP-3) were most frequently detected in, respectively, 18%, 19%, and 27% of the seminal fluid samples albeit at levels one to two orders of magnitude lower than the levels observed in urine. 4-methyl-benzophenone (4-MBP) was detectable in 11% of the seminal fluid samples while in <5% of the urine samples. Overall 45% of the men had at least one of the UV filters present in their seminal fluid at detectable levels. For BP-1 and BP-3 individual levels in urine and seminal fluid were significantly correlated, while this was not evident for BP nor 4-MBP. In conclusion, chemical UV filters are present in men's seminal fluid; some of which can activate the human sperm-specific CatSper Ca²⁺ channel and thereby potentially interfere with the fertilisation process.

Inhibition of Potassium Channels Affects the Ability of Pig Spermatozoa to Elicit Capacitation and Trigger the Acrosome Exocytosis Induced by Progesterone

During capacitation, sperm undergo a myriad of changes, including remodeling of plasma membrane, modification of sperm motility and kinematic parameters, membrane hyperpolarization, increase in intracellular calcium levels, and tyrosine phosphorylation of certain sperm proteins. While potassium channels have been reported to be crucial for capacitation of mouse and human sperm, their role in pigs has not been investigated. With this purpose, sperm samples from 15 boars were incubated in capacitation medium for 300 min with quinine, a general blocker of potassium channels (including voltage-gated potassium channels, calcium-activated potassium channels, and tandem pore domain potassium channels), and paxilline (PAX), a specific inhibitor of calcium-activated potassium channels. In all samples, acrosome exocytosis was induced after 240 min of incubation with progesterone. Plasma membrane and acrosome integrity, membrane lipid disorder, intracellular calcium levels, mitochondrial membrane potential, and total and progressive sperm motility were evaluated after 0, 120, and 240 min of incubation, and after 5, 30, and 60 min of progesterone addition. Although blocking potassium channels with quinine and PAX prevented sperm to elicit in vitro capacitation by impairing motility and mitochondrial function, as well as reducing intracellular calcium levels, the extent of that inhibition was larger with quinine than with PAX. Therefore, while our data support that calcium-activated potassium channels are essential for sperm capacitation in pigs, they also suggest that other potassium channels, such as the voltage-gated, tandem pore domain, and mitochondrial ATP-regulated ones, are involved in that process. Thus, further research is needed to elucidate the specific functions of these channels and the mechanisms underlying its regulation during sperm capacitation.

Mitochondria: their role in spermatozoa and in male infertility

BACKGROUND

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

OBJECTIVE AND RATIONAL

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

SEARCH METHODS

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

OUTCOMES

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

WIDER IMPLICATIONS

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

Na+/H+ Exchangers Involve in Regulating the pH-Sensitive Ion Channels in Mouse Sperm

Sperm-specific K⁺ ion channel (KSper) and Ca²⁺ ion channel (CatSper), whose elimination causes male infertility in mice, determine the membrane potential and Ca²⁺ influx, respectively. KSper and CatSper can be activated by cytosolic alkalization, which occurs during sperm going through the alkaline environment of the female reproductive tract. However, which intracellular pH (pH_i) regulator functionally couples to the activation of KSper/CatSper remains obscure. Although Na⁺/H⁺ exchangers (NHEs) have been implicated to mediate pH_i in sperm, there is a lack of direct evidence confirming the functional coupling between NHEs and KSper/CatSper. Here, 5-(N,N-dimethyl)-amiloride (DMA), an NHEs inhibitor that firstly proved not to affect KSper/CatSper directly, was chosen to examine NHEs function on KSper/CatSper in mouse sperm. The results of patch clamping recordings showed that, when extracellular pH was at the physiological level of 7.4, DMA application caused KSper inhibition and the depolarization of membrane potential when pipette solutions were not pH-buffered. In contrast, these effects were minimized when pipette solutions were pH-buffered, indicating that they solely resulted from pH_i acidification caused by NHEs inhibition. Similarly, DMA treatment reduced CatSper current and intracellular Ca²⁺, effects also dependent on the buffer capacity of pH in pipette solutions. The impairment of sperm motility was also observed after DMA incubation. These results manifested that NHEs activity is coupled to the activation of KSper/CatSper under physiological conditions.

A systems biology framework integrating GWAS and RNA-seq to shed light on the molecular basis of sperm quality in swine

BACKGROUND

Genetic pressure in animal breeding is sparking the interest of breeders for selecting elite boars with higher sperm quality to optimize ejaculate doses and fertility rates. However, the molecular basis of sperm quality is not yet fully understood. Our aim was to identify candidate genes, pathways and DNA variants associated to sperm quality in swine by analysing 25 sperm-related phenotypes and integrating genome-wide association studies (GWAS) and RNA-seq under a systems biology framework.

RESULTS

By GWAS, we identified 12 quantitative trait loci (QTL) associated to the percentage of head and neck abnormalities, abnormal acrosomes and motile spermatozoa. Candidate genes included CHD2, KATNAL2, SLC14A2 and ABCA1. By RNA-seq, we identified a wide repertoire of mRNAs (e.g. PRM1, OAZ3, DNAJB8, TPPP2 and TNP1) and miRNAs (e.g. ssc-miR-30d, ssc-miR-34c, ssc-miR-30c-5p, ssc-miR-191, members of the let-7 family and ssc-miR-425-5p) with functions related to sperm biology. We detected 6128 significant correlations (P-value ≤ 0.05) between sperm traits and mRNA abundances. By expression (e)GWAS, we identified three trans-expression QTL involving the genes IQCJ, ACTR2 and HARS. Using the GWAS and RNA-seq data, we built a gene interaction network. We considered that the genes and interactions that were present in both the GWAS and RNA-seq networks had a higher probability of being actually involved in sperm quality and used them to build a robust gene interaction network. In addition, in the final network we included genes with RNA abundances correlated with more than four semen traits and miRNAs interacting with the genes on the network. The final network was enriched for genes involved in gamete generation and development, meiotic cell cycle, DNA repair or embryo implantation. Finally, we designed a panel of 73 SNPs based on the GWAS, eGWAS and final network data, that explains between 5% (for sperm cell concentration) and 36% (for percentage of neck abnormalities) of the phenotypic variance of the sperm traits.

CONCLUSIONS

By applying a systems biology approach, we identified genes that potentially affect sperm quality and constructed a SNP panel that explains a substantial part of the phenotypic variance for semen quality in our study and that should be tested in other swine populations to evaluate its relevance for the pig breeding sector.

CatSper: The complex main gate of calcium entry in mammalian spermatozoa

Calcium ions (Ca²⁺) are involved in nearly every aspect of cellular life. They are one of the most abundant elements in mammals and play a vital role in physiological and biochemical processes acting mainly as intracellular messengers. In spermatozoa, several key functions are regulated by cytoplasmic Ca²⁺ concentration such as sperm capacitation, chemotaxis, hyperactive motility, and acrosome reaction. The sperm-specific ion channel CatSper is the principal calcium channel in sperm mediating the calcium influx into the sperm flagellum and acting as an essential modulator of downstream mechanisms involved in fertilization. This review aims to provide insights into the structure, localization, and function of the mammalian CatSper channel, primarily human and mice. The activation of CatSper by progesterone and prostaglandins, as well as the ligand-independent regulation of the channel by a change in the membrane voltage and intracellular pH are going to be addressed. Finally, major questions, challenges, and perspectives are discussed.

Implications of ram sperm rheotaxis analysed by microfluidics for fertility

Rheotaxis of sperm using a microfluidic device was explored in human, mice and bull. However, the rheotaxis of ram sperm and its role in fertility are unknown. Herein, we described the sperm rheotaxis in ram using microfluidic devices and focused on rheotaxis as potential markers of in vivo fertility. Computer-assisted sperm analysis (CASA) with controlled flow velocity was used to explore the kinematic parameters of sperm, total motility and positive rheotaxis (PR). The percentage of PR was defined as the number of PR sperm cells over the number of motile sperm cells. Then, according to the percentage of PR sperm, rams were classified into two groups; sperm with ≥40% PR and <40% PR, although the two ram groups showed similar total motility and kinematic values of sperm evaluated by CASA (p > .05). Two groups of rams mated one hundred thirty ewes naturally (10 ewes/ram). In the results, the pregnancy rate was higher in ≥40% PR (94.4%) than in <40% PR (42.5%, p < .05) after natural mating. Besides, the pregnancy loss was higher in <40% PR (33.3%) than in >40% PR group (8.1%, p < .05). In conclusion, the PR examination in semen can contribute to evaluate the reproductive performance of ram that will provide valuable insights into the semen evaluation.

Effects of the methanol root extract of Carpolobia lutea on sperm indices, acrosome reaction, and sperm DNA integrity in cadmium-induced reproductive toxicity in male Wistar rats

OBJECTIVE

Oxidative stress is a mechanism of cadmium-induced reproductive dysfunction. Carpolobia lutea is a free radical scavenger. Our study investigated the potential protective effects of Carpolobia lutea root methanol extract against cadmium-induced reproductive toxicity.

METHODS

We obtained the Carpolobia lutea root in Akure, and it was authenticated at the Forestry Research Institute of Nigeria (FRIN) herbarium, Ibadan, Nigeria, with FHI number 109784. We used Soxhlet extraction to obtain its methanol extract. We used thirty male Wistar rats (150-170g) in this study, (n=5 per group), and treated them as follows: Control (1 ml/kg normal saline), Cd (2 mg/kg), Cd+MCL (2 mg/kg+100 mg/kg), Cd+MCL (2 mg/kg+200 mg/kg), MCL (100 mg/kg), MCL (200 mg/kg). We administered Carpolobia lutea orally for 8 weeks. We administered a single dose of 2 mg/kg of cadmium intraperitoneally. We assessed the sperm profile using a computer-aided sperm analyzer. Under microscopy, we determined the sperm acrosome reaction and the DNA damage. We measured the seminal fructose level using spectrophotometry, and the data were analyzed using ANOVA at p<0.05.

RESULTS

Cd+MCL (2mg/kg+200 mg/kg) significantly increased sperm count (339.0±25.0 vs. 29.0±4.5 million/mL), motility (80.0±0.2 vs. 55.0±4.9%), viability (68.7±2.7 vs. 31.3±2.9%) and decreased abnormal sperm (28.3±1.7 vs. 43.3±2.5%), relative to the cadmium group. Cd+MCL (2mg/kg+200 mg/kg) significantly increased acrosome reaction (68.0±7.5 vs. 15.2±2.4%) and seminal fructose level (0.49±0.06 vs. 0.28±0.06 mmol/L) relative to the cadmium group. Cd+MCL (2mg/kg+200 mg/kg) significantly decreased sperm DNA damage (14.1±1.6 vs. 35.9±5.3%) in relation to the cadmium group.

CONCLUSIONS

Carpolobia lutea root extract improves the sperm variables of rats exposed to cadmium.

Ca2+ signaling in mammalian spermatozoa

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

Exosome Composition and Seminal Plasma Proteome: A Promising Source of Biomarkers of Male Infertility

Infertility has become a global health issue, with approximately 50% of infertility cases generated by disorders in male reproduction. Spermatozoa are conveyed towards female genital tracts in a safe surrounding provided by the seminal plasma. Interestingly, this dynamically changing medium is a rich source of proteins, essential not only for sperm transport, but also for its protection and maturation. Most of the seminal proteins are acquired by spermatozoa in transit through exosomes (epididymosomes and prostasomes). The high number of seminal proteins, the increasing knowledge of their origins and biological functions and their differential expression in the case of azoospermia, asthenozoospermia, oligozoospermia and teratozoospermia or other conditions of male infertility have allowed the identification of a wide variety of biomarker candidates and their involvement in biological pathways, thus to strongly suggest that the proteomic landscape of seminal plasma may be a potential indicator of sperm dysfunction. This review summarizes the current knowledge in seminal plasma proteomics and its potentiality as a diagnostic tool in different degrees of male infertility.

Adhesion to oviduct glycans regulates porcine sperm Ca2+ influx and viability

Before fertilization, sperm bind to epithelial cells of the oviduct isthmus to form a reservoir that regulates sperm viability and capacitation. The sperm reservoir maintains optimum fertility in species, like swine, in which semen deposition and ovulation may not be well synchronized. We demonstrated previously that porcine sperm bind to two oviductal glycan motifs, a biantennary 6-sialylated N-acetyllactosamine (bi-SiaLN) oligosaccharide and 3-O-sulfated Lewis X trisaccharide (suLe^X). Here, we assessed the ability of these glycans to regulate sperm Ca²⁺ influx, capacitation and affect sperm lifespan. After 24 h, the viability of sperm bound to immobilized bi-SiaLN and suLe^X was higher (46% and 41% respectively) compared to viability of free-swimming sperm (10–12%). Ca²⁺ is a central regulator of sperm function so we assessed whether oviduct glycans could affect the Ca²⁺ influx that occurs during capacitation. Using a fluorescent intracellular Ca²⁺ probe, we observed that both oviduct glycans suppressed the Ca²⁺ increase that occurs during capacitation. Thus, specific oviduct glycans can regulate intracellular Ca²⁺. Because the increase in intracellular Ca²⁺ was suppressed by oviduct glycans, we examined whether glycans affected capacitation, as determined by protein tyrosine phosphorylation and the ability to undergo a Ca²⁺ ionophore-induced acrosome reaction. We found no discernable suppression of capacitation in sperm bound to oviduct glycans. We also detected no effect of oviduct glycans on sperm motility during capacitation. In summary, Le^X and bi-SiaLN glycan motifs found on oviduct oligosaccharides suppress the Ca²⁺ influx that occurs during capacitation and extend sperm lifespan but do not affect sperm capacitation or motility.

A novel copy number variation in CATSPER2 causes idiopathic male infertility with normal semen parameters

STUDY QUESTION

Are genetic abnormalities in CATSPER (cation channel of sperm) genes associated with idiopathic male infertility with normal semen parameters and, if so, how do they affect male fertility?

SUMMARY ANSWER

A novel copy number variation (CNV) in CATSPER2 causes idiopathic male infertility with normal semen parameters by disrupting the ability of sperm to penetrate viscous media, undergo hyperactivation and respond to progesterone.

WHAT IS KNOWN ALREADY

CATSPER is the principle Ca2+ channel mediating extracellular Ca2+ influx into spermatozoa. Although several case reports have suggested a causal relationship between CATSPER disruption and human male infertility, whether genetic abnormalities in CATSPER genes are associated with idiopathic male infertility with normal semen parameters remains unclear.

STUDY DESIGN, SIZE, DURATION

Spermatozoa were obtained from men attending the reproductive medical center at Jiangxi Provincial Maternal and Child Health Hospital, Nanchang, Jiangxi, China between January 2014 and June 2016. In total, 120 men from infertile couples and 20 healthy male donors were selected to take part in the study, based on their normal semen parameters.

PARTICIPANTS/MATERIALS, SETTING, METHODS

CATSPER and KSPER currents were assessed using the whole-cell patch-clamp technique. Whole-genome sequencing and TaqMan® CNV assays were performed to identify genetic variations. The expression levels of genes encoding the CATSPER complex were measured by quantitative real-time PCR and Western blot. Sperm motion characteristics and hyperactivation were examined with a computer-aided sperm analysis (CASA) system. Sperm responses to progesterone, assessed as increases in CATSPER current and intercellular Ca2+ concentrations ([Ca2+]i), as well as inducement of penetration ability and acrosome reaction, were examined by means of whole-cell patch-clamp technique, single-sperm [Ca2+]i imaging, penetration into methylcellulose assay and chlortetracycline staining, respectively.

MAIN RESULTS AND THE ROLE OF CHANCE

An infertile man with complete disruption of CATSPER current was identified. This individual has a novel CNV which disrupts one gene copy in the region 43894500-43950000 in chromosome 15 (GRCh37.p13 Primary Assembly, nsv3067119), containing the whole DNA sequence of CATSPER2. This CNV affected the expression of CATSPER2, resulting in dramatically reduced levels of CATSPER2 proteins in the individual's spermatozoa. Although this individual exhibited normal semen parameters, his spermatozoa showed impaired penetration ability, deficient hyperactivation, and did not respond to progesterone, in terms of monovalent current potentiation, [Ca2+]i increase, penetration ability enhancement and acrosome reaction inducement, which may explain the individual's idiopathic infertility.

LARGE SCALE DATA

N/A.

LIMITATIONS, REASONS FOR CAUTION

Our novel findings require more cases to support the CATSPER2 CNV identified in this study as a common cause of idiopathic male infertility in patients with normal semen parameters. Therefore, caution must be taken when extrapolating the use of this CNV as a potential biomarker for idiopathic male infertility.

WIDER IMPLICATIONS OF THE FINDINGS

The findings from the unique human CATSPER 'knockout' model in this study not only confirm the essential roles of CATSPER in mediating progesterone response and regulating hyperactivation in human spermatozoa but also reveal that disruption of CATSPER current is a significant factor causing idiopathic male infertility.

STUDY FUNDING/COMPETING INTEREST(S)

This study was funded by National Natural Science Foundation of China (81771644 and 31400996 to T.L.; 31230034 to X.Z.); National Basic Research Program of China (973 Program, 2015CB943003 to X.Z.); National Key Research and Development Program of China (2016YFC1000905 to T.L.); Natural Science Foundation of Jiangxi, China (20121BBG70021 and GJJ12015 to X.Z.; 20161BAB204167 and 20171ACB21006 to T.L.) and the open project of National Population and Family Planning Key Laboratory of Contraceptives and Devices Research (No. 2016KF07 to T.L.). The authors have no conflicts of interest to declare.

Continuous behavioural 'switching' in human spermatozoa and its regulation by Ca2+-mobilising stimuli

Human sperm show a variety of different behaviours (types of motility) that have different functional roles. Previous reports suggest that sperm may reversibly switch between these behaviours. We have recorded and analysed the behaviour of individual human sperm (180 cells in total), each cell monitored continuously for 3–3.5 min either under control conditions or in the presence of Ca²⁺-mobilising stimuli. Switching between different behaviours was assessed visually (1 s bins using four behaviour categories), and was verified by fractal dimension analysis of sperm head tracks. In the absence of stimuli, ~90% of cells showed at least one behavioural transition (mean rate under control conditions = 6.4 ± 0.8 transitions.min⁻¹). Type 1 behaviour (progressive, activated-like motility) was most common, but the majority of cells (>70%) displayed at least three behaviour types. Treatment of sperm with Ca²⁺-mobilising agonists had negligible effects on the rate of switching but increased the time spent in type 2 and type 3 (hyperactivation-like) behaviours (P < 2^*10⁻⁸; chi-square). Treatment with 4-aminopyridine under alkaline conditions (pH_o = 8.5), a highly-potent Ca²⁺-mobilising stimulus, was the most effective in increasing the proportion of type 3 behaviour, biasing switching away from type 1 (P < 0.005) and dramatically extending the duration of type 3 events (P < 10⁻¹⁶). Other stimuli, including 300 nM progesterone and 1% human follicular fluid, had qualitatively similar effects but were less potent. We conclude that human sperm observed in vitro constitutively display a range of behaviours and regulation of motility by [Ca²⁺]_i, at the level of the single cell, is achieved not by causing cells to adopt a ‘new’ behaviour but by changing the relative contributions of those behaviours.

The 2020 motile active matter roadmap

Activity and autonomous motion are fundamental in living and engineering systems. This has stimulated the new field of 'active matter' in recent years, which focuses on the physical aspects of propulsion mechanisms, and on motility-induced emergent collective behavior of a larger number of identical agents. The scale of agents ranges from nanomotors and microswimmers, to cells, fish, birds, and people. Inspired by biological microswimmers, various designs of autonomous synthetic nano- and micromachines have been proposed. Such machines provide the basis for multifunctional, highly responsive, intelligent (artificial) active materials, which exhibit emergent behavior and the ability to perform tasks in response to external stimuli. A major challenge for understanding and designing active matter is their inherent nonequilibrium nature due to persistent energy consumption, which invalidates equilibrium concepts such as free energy, detailed balance, and time-reversal symmetry. Unraveling, predicting, and controlling the behavior of active matter is a truly interdisciplinary endeavor at the interface of biology, chemistry, ecology, engineering, mathematics, and physics. The vast complexity of phenomena and mechanisms involved in the self-organization and dynamics of motile active matter comprises a major challenge. Hence, to advance, and eventually reach a comprehensive understanding, this important research area requires a concerted, synergetic approach of the various disciplines. The 2020 motile active matter roadmap of Journal of Physics: Condensed Matter addresses the current state of the art of the field and provides guidance for both students as well as established scientists in their efforts to advance this fascinating area.

HVCN1 Channels Are Relevant for the Maintenance of Sperm Motility During In Vitro Capacitation of Pig Spermatozoa

The objective of the present study was to determine the physiological role of voltage-gated hydrogen channels 1 (HVCN1 channels) during in vitro capacitation of pig spermatozoa. Sperm samples from 20 boars were incubated in capacitating medium for 300 minutes (min) in the presence of 2-guanidino benzimidazole (2-GBI), a specific HVCN1-channel blocker, added either at 0 min or after 240 min of incubation. Control samples were incubated in capacitating medium without the inhibitor. In all samples, acrosomal exocytosis was triggered with progesterone after 240 min of incubation. Sperm viability, sperm motility and kinematics, acrosomal exocytosis, membrane lipid disorder, intracellular calcium levels and mitochondrial membrane potential were evaluated after 0, 60, 120, 180, 240, 250, 270 and 300 min of incubation. While HVCN1-blockage resulted in altered sperm viability, sperm motility and kinematics and reduced mitochondrial membrane potential as compared to control samples, at any blocker concentration and incubation time, it had a non-significant effect on intracellular Ca²⁺ levels determined through Fluo3-staining. The effects on acrosomal exocytosis were only significant in blocked samples at 0 min, and were associated with increased membrane lipid disorder and Ca²⁺ levels of the sperm head determined through Rhod5-staining. In conclusion, HVCN1 channels play a crucial role in the modulation of sperm motility and kinematics, and in Ca²⁺ entrance to the sperm head.

A genome-wide single nucleotide polymorphism scan reveals genetic markers associated with fertility rate in Chinese Jing Hong chicken

The function of the sperm storage tubules is directly correlated with the fertility of laying hens. However, little is known about the molecular mechanisms regulating the fertility traits in chicken. To identify genetic markers associated with reproductive traits, we calculated fertility rate at 61 to 69 wk (51 D) of Jing Hong chickens parent generation as the phenotype and the genotype were detected by the chicken 600K Affymetrix Axiom High Density single nucleotide polymorphisms (SNP)-array. The genome-wide association study using 190 Jing Hong hens showed that the 20 SNP in chromosomes 3 and 13 were significantly associated with fertility rate. To verify these results, a total of 1900 Jing Hong laying hens from 2 populations (P1 and P2) were further genotyped by polymerase chain reaction-restriction fragments length polymorphisms method. The association analysis results revealed that 12 polymorphisms (AX-75769978, AX-76582632, AX-75730546, AX-75730496, AX-75730588, AX-76530282, AX-76530329, AX-76529310, AX-75769906, AX-75755394, AX-80813697 and AX-76582809) out of 20 showed highly significant effects (P < 0.0001) on fertility rate in P1, P2 and P1+P2. Six haplotypes (TTAA, TTGG, TTAG, CTAA, CTGG, and CTAG) were inferred based on significant loci (AX-75730546 and AX-76530282) also showed significant association with fertility rate, where haplotype CTAG was shown to be markedly associated with the significantly highest (P < 0.0001) fertility rate (in P1, 86.42 ± 0.59; P2, 85.98 ± 0.59 and P1+P2, 86.16 ± 0.42) followed by other haplotypes for the irrespective of population studied. Collectively, we report for the first time that 12 SNP in the chromosomes 3 and 13 were significantly associated with fertility rate during the later stage of egg production, which could be used as the potential genetic markers that would be able to facilitate in the selection and improvement of fertility rate through chicken breeding.

Missing Information from the Estrogen Receptor Puzzle: Where Are They Localized in Bull Reproductive Tissues and Spermatozoa?

Estrogens are steroid hormones that affect a wide range of physiological functions. The effect of estrogens on male reproductive tissues and sperm cells through specific receptors is essential for sperm development, maturation, and function. Although estrogen receptors (ERs) have been studied in several mammalian species, including humans, they have not yet been described in bull spermatozoa and reproductive tissues. In this study, we analyzed the presence of all types of ERs (ESR1, ESR2, and GPER1) in bull testicular and epididymal tissues and epididymal and ejaculated spermatozoa, and we characterize them here for the first time. We observed different localizations of each type of ER in the sperm head by immunofluorescent microscopy. Additionally, using a selected polyclonal antibody, we found that each type of ER in bull sperm extracts had two isoforms with different molecular masses. The detailed detection of ERs is a prerequisite not only for understanding the effect of estrogen on all reproductive events but also for further studying the negative effect of environmental estrogens (endocrine disruptors) on processes that lead to fertilization.

Bisphenol A Diglycidyl Ether (BADGE) and Bisphenol Analogs, but Not Bisphenol A (BPA), Activate the CatSper Ca2+ Channel in Human Sperm

Aim: Evidence suggests that bisphenol A diglycidyl ether (BADGE), bisphenol A (BPA), and BPA analogs can interfere with human male fertility. However, the effect directly on human sperm function is not known. The CatSper Ca²⁺ channel in human sperm controls important sperm functions and is necessary for normal male fertility. Environmental chemicals have been shown to activate CatSper and thereby affect Ca²⁺ signaling in human sperm. BPA has previously been investigated for effects on Ca²⁺ signaling human sperm, whereas the effects of other BPA analogs are currently unknown. The aim of this study is thus to characterize the effect of BADGE, BPA, and the eight analogs BPG, BPAF, BPC, BPB, BPBP, BPE, BPF, BPS on Ca²⁺ signaling, and CatSper in human sperm. Methods: Direct effects of the bisphenols on Ca²⁺ signaling in human sperm cells were evaluated using a Ca²⁺ fluorimetric assay measuring changes in intracellular Ca²⁺. Effects via CatSper were assessed using the specific CatSper inhibitor RU1968. Effects on human sperm function was assessed using an image cytometry-based acrosome reaction assay and the modified Kremer's sperm-mucus penetration assay. Results: At 10 μM the bisphenols BPG, BPAF, BPC, BADGE, BPB, and BPBP induced Ca²⁺ signals in human sperm cells, whereas BPE, BPF, BPS, and BPA had no effect. The efficacy of the chemicals at 10 μM is BPG > BPAF > BPC > BADGE > BPB > BPBP. Dose-response relations of BPG, BPAF, BPC, BADGE, BPB, and BPBP yielded EC50-values in the nM-μM range. The induced Ca²⁺ signals were almost completely abolished using the CatSper inhibitor RU1968, indicating an effect of the bisphenols on CatSper. All bisphenols, except BPBP, were found to dose-dependently inhibit progesterone-induced Ca²⁺ signals, with BPG and BPAF displaying inhibition even in low μM doses. BPG and BPAF were shown to affect human sperm function in a progesterone-like manner. Conclusion: Our results show that the bisphenols BPG, BPAF, BPC, BADGE, BPB, and BPBP can affect Ca²⁺ signaling in human sperm cells through activation of CatSper. This could potentially disrupt human sperm function by interfering with normal CatSper-signaling and thus be a contributing factor in human infertility, either alone or in mixtures with other chemicals.

Elucidating the Role of K+ Channels during In Vitro Capacitation of Boar Spermatozoa: Do SLO1 Channels Play a Crucial Role?

This study sought to identify and localize SLO1 channels in boar spermatozoa by immunoblotting and immunofluorescence, and to determine their physiological role during in vitro sperm capacitation. Sperm samples from 14 boars were incubated in a capacitation medium for 300 min in the presence of paxilline (PAX), a specific SLO1-channel blocker, added either at 0 min or after 240 min of incubation. Negative controls were incubated in capacitation medium, and positive controls in capacitation medium plus tetraethyl ammonium (TEA), a general K+-channel blocker, also added at 0 min or after 240 min of incubation. In all samples, acrosome exocytosis was triggered with progesterone after 240 min of incubation. Sperm motility and kinematics, integrity of plasma and acrosome membranes, membrane lipid disorder, intracellular calcium levels and acrosin activity were evaluated after 0, 60, 120, 180, 240, 250, 270 and 300 min of incubation. In boar spermatozoa, SLO1 channels were found to have 80 kDa and be localized in the anterior postacrosomal region and the mid and principal piece of the tail; their specific blockage through PAX resulted in altered calcium levels and acrosome exocytosis. As expected, TEA blocker impaired in vitro sperm capacitation, by altering sperm motility and kinematics and calcium levels. In conclusion, SLO1 channels are crucial for the acrosome exocytosis induced by progesterone in in vitro capacitated boar spermatozoa.