CatSper: A Unique Calcium Channel of the Sperm Flagellum

Environmental pollutants and male infertility: Effects on CatSper

Infertility is a growing health concern among many couples worldwide. Men account for half of infertility cases. CatSper, a sperm-specific Ca2+ channel, is expressed on the cell membrane of mammalian sperm. CatSper plays an important role in male fertility because it facilitates the entry of Ca2+ necessary for the rapid change in sperm motility, thereby allowing it to navigate the hurdles of the female reproductive tract and successfully locate the egg. Many pollutants present in the environment have been shown to affect the functions of CatSper and sperm, which is a matter of capital importance to understanding and solving male infertility issues. Environmental pollutants can act as partial agonists or inhibitors of CatSper or exhibit a synergistic effect. In this article, we briefly describe the structure, functions, and regulatory mechanisms of CatSper, and discuss the body of literature covering the effects of environmental pollutants on CatSper.

Factors affecting the success of laparoscopic artificial insemination in sheep

Successful artificial breeding underpins rapid genetic and production gains in animal agriculture. In sheep, artificial insemination with frozen semen is performed via intrauterine laparoscopy as frozen-thawed spermatozoa do not traverse the cervix in sufficient numbers for high fertility and transcervical insemination is anatomically impossible in most ewes. Historically, laparoscopic artificial insemination has always been considered reasonably successful, but recent anecdotal reports of poor fertility place it at risk of warning adoption. Understanding the male, female and environmental factors that influence the fertility of sheep is warranted if the success of artificial insemination is to be improved and genetic progress maximised for the sheep industry. This review details the current practice of laparoscopic AI in sheep. It explores the effects of semen quantity and quality, the ewe, her preparation, and environmental conditions, on the fertility obtained following laparoscopic artificial insemination.

Both protein and non-protein components in extracellular vesicles of human seminal plasma improve human sperm function via CatSper-mediated calcium signaling

STUDY QUESTION

What is the significance and mechanism of human seminal plasma extracellular vesicles (EVs) in regulating human sperm functions?

SUMMARY ANSWER

EV increases the intracellular Ca2+ concentrations [Ca2+]i via extracellular Ca2+ influx by activating CatSper channels, and subsequently modulate human sperm motility, especially hyperactivated motility, which is attributed to both protein and non-protein components in EV.

WHAT IS KNOWN ALREADY

EVs are functional regulators of human sperm function, and EV cargoes from normal and asthenozoospermic seminal plasma are different. Pre-fusion of EV with sperm in the acidic and non-physiological sucrose buffer solution could elevate [Ca2+]i in human sperm. CatSper, a principle Ca2+ channel in human sperm, is responsible for the [Ca2+]i regulation when sperm respond to diverse extracellular stimuli. However, the role of CatSper in EV-evoked calcium signaling and its potential physiological significance remain unclear.

STUDY DESIGN, SIZE, DURATION

EV isolated from the seminal plasma of normal and asthenozoospermic semen were utilized to investigate the mechanism by which EV regulates calcium signal in human sperm, including the involvement of CatSper and the responsible cargoes in EV. In addition, the clinical application potential of EV and EV protein-derived peptides were also evaluated. This is a laboratory study that went on for more than 5 years and involved more than 200 separate experiments.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Semen donors were recruited in accordance with the Institutional Ethics Committee on human subjects of the Affiliated Hospital of Nantong University and Jiangxi Maternal and Child Health Hospital. The Flow NanoAnalyzer, western blotting, and transmission electron microscope were used to systematically characterize seminal plasma EV. Sperm [Ca2+]i responses were examined by fluorimetric measurement. The whole-cell patch-clamp technique was performed to record CatSper currents. Sperm motility parameters were assessed by computer-assisted sperm analysis. Sperm hyperactivation was also evaluated by examining their penetration ability in viscous methylcellulose media. Protein and non-protein components in EV were analyzed by liquid chromatography-mass spectrum. The levels of prostaglandins, reactive oxygen species, malonaldehyde, and DNA integrity were detected by commercial kits.

MAIN RESULTS AND THE ROLE OF CHANCE

EV increased [Ca2+]i via an extracellular Ca2+ influx, which could be suppressed by a CatSper inhibitor. Also, EV potentiated CatSper currents in human sperm. Furthermore, the EV-in [Ca2+]i increase and CatSper currents were absent in a CatSper-deficient sperm, confirming the crucial role of CatSper in EV induced Ca2+ signaling in human sperm. Both proteins and non-protein components of EV contributed to the increase of [Ca2+]i, which were important for the effects of EV on human sperm. Consequently, EV and its cargos promoted sperm hyperactivated motility. In addition, seminal plasma EV protein-derived peptides, such as NAT1-derived peptide (N-P) and THBS-1-derived peptide (T-P), could activate the sperm calcium signal and enhance sperm function. Interestingly, EV derived from asthenozoospermic semen caused a lower increase of [Ca2+]i than that isolated from normal seminal plasma (N-EV), and N-EV significantly improved sperm motility and function in both asthenozoospermic samples and frozen-thawed sperm.

LARGE SCALE DATA

N/A.

LIMITATIONS, REASONS FOR CAUTION

This was an in vitro study and caution must be taken when extrapolating the physiological relevance to in vivo regulation of sperm.

WIDER IMPLICATIONS OF THE FINDINGS

Our findings demonstrate that the CatSper-mediated-Ca2+ signaling is involved in EV-modulated sperm function under near physiological conditions, and EV and their derivates are a novel CatSper and sperm function regulators with potential for clinical application. They may be developed to improve sperm motility resulting from low [Ca2+]i response and/or freezing and thawing.

STUDY FUNDING/COMPETING INTEREST(S)

This research was supported by the National Natural Science Foundation of China (32271167), the Social Development Project of Jiangsu Province (BE2022765), the Nantong Social and People's Livelihood Science and Technology Plan (MS22022087), the Basic Science Research Program of Nantong (JC22022086), and the Jiangsu Innovation and Entrepreneurship Talent Plan (JSSCRC2021543). The authors declare no conflict of interest.

Clinical use of progesterone in human sperm preparation media for increasing IVF success

RESEARCH QUESTION

Can the addition of progesterone and neurotensin, molecular agents found in the female reproductive tract, after sperm washing increase the fertilization potential of human spermatozoa?

DESIGN

(i) Cohort study of 24 men. Spermatozoa selected by swim-up were incubated in either progesterone or neurotensin (0.1-100 µM) for 1-4 h, and hyperactive motility and binding to hyaluronan (0.1-100 µM) were assessed. The effect of progesterone 10 µM on sperm function was assessed in a blinded manner, including: hyperactive motility, binding to hyaluronan, tyrosine phosphorylation, acrosome reaction and oxidative DNA damage. (i) Embryo safety testing [one-cell mouse embryo assay (MEA), endotoxin and sterility counts (n = 3)] in preclinical embryo models of IVF (murine and porcine, n = 7 each model) and a small preliminary human study (n = 4) of couples undergoing standard IVF with oocytes inseminated with spermatozoa ± 10 µM progesterone.

RESULTS

Progesterone 10 µM increased sperm binding to hyaluronan, hyperactive motility and tyrosine phosphorylation (all P < 0.05). Neurotensin had no effect (P > 0.05). Progesterone 10 µM in human embryo culture media passed embryo safety testing (MEA, endotoxin concentration and sterility plate count). In preclinical models of IVF, the exposure of spermatozoa to progesterone 10 µM and oocytes to progesterone 1 µM was not detrimental, and increased the fertilization rate in mice and the blastocyst cell number in mice and pigs (all P ≤ 0.03). In humans, every transferred blastocyst that had been produced from spermatozoa exposed to progesterone resulted in a live birth.

CONCLUSION

The addition of progesterone to sperm preparation media shows promise as an adjunct to current methods for increasing fertilization potential. Randomized controlled trials are required to determine the clinical utility of progesterone for improving IVF outcomes.

Physiological role of potassium channels in mammalian germ cell differentiation, maturation, and capacitation

BACKGROUND

Ion channels are essential for differentiation and maturation of germ cells, and even for fertilization in mammals. Different types of potassium channels have been identified, which are grouped into voltage-gated channels (Kv), ligand-gated channels (Kligand ), inwardly rectifying channels (Kir ), and tandem pore domain channels (K2P ).

MATERIAL-METHODS

The present review includes recent findings on the role of potassium channels in sperm physiology of mammals.

RESULTS-DISCUSSION

While most studies conducted thus far have been focused on the physiological role of voltage- (Kv1, Kv3, and Kv7) and calcium-gated channels (SLO1 and SLO3) during sperm capacitation, especially in humans and rodents, little data about the types of potassium channels present in the plasma membrane of differentiating germ cells exist. In spite of this, recent evidence suggests that the content and regulation mechanisms of these channels vary throughout spermatogenesis. Potassium channels are also essential for the regulation of sperm cell volume during epididymal maturation and for preventing premature membrane hyperpolarization. It is important to highlight that the nature, biochemical properties, localization, and regulation mechanisms of potassium channels are species-specific. In effect, while SLO3 is the main potassium channel involved in the K+ current during sperm capacitation in rodents, different potassium channels are implicated in the K+ outflow and, thus, plasma membrane hyperpolarization during sperm capacitation in other mammalian species, such as humans and pigs.

CONCLUSIONS

Potassium conductance is essential for male fertility, not only during sperm capacitation but throughout the spermiogenesis and epididymal maturation.

Involvement of CATSPER 2 mutation in a familial context of unexplained infertility and fertilization failure associated with hearing loss: a case report

Objective

To explore the functional implications of a homozygous CATSPER 2 (cation channel for sperm) deletion within the acrosome reaction pathway during fertilization in 2 brothers, who have unexplained infertility and hearing loss.

Design

Case report.

Patients

Two twin brothers aged 30 years with hearing loss and unexplained infertility.

Exposure or Intervention

Molecular genetic diagnosis of deafness. Evaluation of the acrosome reaction and calcium mobilization assays after induction by progesterone and ionomycin on spermatozoa of the CATSPER 2-mutated patient and on fertile controls.

Main Outcome Measures

Fertilization rate during conventional in vitro fertilization. Molecular genetic test. Percentage of acrosome-reacted spermatozoa with peanut agglutinin lectin staining. Recording of progesterone and ionomycin-induced intracellular calcium signals with a fluorescent probe.

Results

Mr. S and his brother have normal, conventional sperm parameters. Both brothers have had repeated intrauterine insemination failures and one fertilization failure after conventional in vitro fertilization. Mr. S obtained 2 healthy babies after intracytoplasmic sperm injection. Genetic analysis found a homozygote deletion of the STRC (stereocilin) gene (NM 153700: c.1-? 5328+?del) that removes the CATSPER 2 gene. Mutation of the STRC gene is known to be associated with hearing loss. Sperm functional tests revealed an inability of progesterone to activate intracellular calcium signaling and to induce acrosome reaction.

Conclusion

We demonstrate the absence of a calcium signal and acrosome reaction after progesterone in our patient with a CATSPER 2 mutation. We emphasize the importance of the male medical interview and of the genetic investigation of hearing loss. We show that in vitro fertilization-intracytoplasmic sperm injection is necessary, even where normal sperm parameters are present.

Sperm plasma membrane ion transporters and male fertility potential: A perspective under the prism of cryopreservation

Intracellular calcium homeostasis plays a crucial role in spermatozoa by regulating physiological functions associated with sperm quality and male fertility potential. Intracellular calcium fine balance in the sperm cytoplasm is strictly dependent on sperm surface channels including the CatSper channel. CatSpers' role is to ensure the influx of extracellular calcium, while intracellular pH alkalinization serves as a stimulus for the activation of several channels, including CatSper. Overall, the generation of intracellular calcium spikes through CatSper is essential for fertilization-related processes, such as sperm hyperactivation, acrosome reaction, egg chemotaxis, and zona pellucida penetration. Multiple lines of evidence suggest that disruption in the close interaction among ions, pH, and CatSper could impair male fertility potential. In contemporary times, the growing reliance on Medically Assisted Reproduction procedures underscores the impact of cryopreservation on gametes. In fact, a large body of literature raises concerns about the cryo-damages provoked by the freeze-thawing processes, that can affect the plasma membrane integrity, thus the structure of pivotal ion channels, and the fine regulation of both intracellular calcium and pH. This review aims to provide an overview of the importance of the CatSper channel in sperm quality and further fertilization potential. Additionally, it addresses the emerging issue of cryopreservation's impact on the functionality of this sperm channel.

The Detection of CatSper1 and CatSper3 Expression in Men with Normozoospermia and Asthenoteratozoospermia and Its Association with Sperm Parameters, Fertilization Rate, Embryo Quality

CatSper affects sperm function and male fertilization capacity markers, including sperm motility and egg penetration. The study has aimed to evaluate the mRNA expression of CatSper1, and CatSper3 in the spermatozoa of men with normozoospermia and Asthenoteratozoospermia, and to assess the correlation between genes expression and sperm parameters, fertilization rate, and embryo quality in intracytoplasmic sperm injection (ICSI). Reverse transcription-polymerase chain reaction was utilized to evaluate the mRNA expression of CatSper1 and CatSper3 in sperm in two patient groups: Normozoospermia (NOR; n = 32), and Asthenoteratozoospermia (AT; n = 22). In all patients receiving intracytoplasmic sperm injection, the fertilization rate and embryo quality were evaluated. CatSper1, and CatSper3 mRNA expression in sperm was significantly lower in AT males than in NOR (P < 0.05). Levels of these genes demonstrated a significant positive correlation with sperm motility, mitochondrial membrane potential (MMP), capacitation, fertilization rate, cleavage rate, and embryo quality (P < 0.05) following ICSI. However, a negative correlation was found between mRNA expression of CatSper1, 3 and sperm DNA fragmentation (P < 0.05). Findings indicate low levels of CatSper1 and CatSper3 mRNA expression in men with Asthenoteratozoospermia, which resulted in poor sperm quality and impaired embryo development following ICSI therapy.

CatSper mediates not only chemotactic behavior but also the motility of ascidian sperm

Introduction: Sperm motility, including chemotactic behavior, is regulated by changes in the intracellular Ca2+ concentration, and the sperm-specific Ca2+ channel CatSper has been shown to play an important role in the regulation of intracellular Ca2+. In particular, in mammals, CatSper is the only functional Ca2+ channel in the sperm, and mice deficient in the genes comprising the pore region of the Ca2+ channel are infertile due to the inhibition of sperm hyperactivation. CatSper is also thought to be involved in sea urchin chemotaxis. In contrast, in ascidian Ciona intestinalis, SAAF, a sperm attractant, interacts with Ca2+/ATPase, a Ca2+ pump. Although the existence of CatSper genes has been reported, it is not clear whether CatSper is a functional Ca2+ channel in sperm. Results: We showed that CatSper is present in the sperm flagella of C. intestinalis as in mammalian species, although a small level of gene expression was found in other tissues. The spermatozoa of CatSper3 KO animals were significantly less motile, and some motile sperms did not show any chemotactic behavior. These results suggest that CatSper plays an important role in ascidians and mammals, and is involved in spermatogenesis and basic motility mechanisms.

Architecture and rearrangements of a sperm-specific Na+/H+ exchanger

The sperm-specific sodium hydrogen exchanger, SLC9C1, underlies hyperpolarization and cyclic nucleotide stimulated proton fluxes across sperm membranes and regulates their hyperactivated motility. SLC9C1 is the first known instance of an ion transporter that uses a canonical voltage-sensing domain (VSD) and an evolutionarily conserved cyclic nucleotide binding domain (CNBD) to influence the dynamics of its ion-exchange domain (ED). The structural organization of this 'tripartite transporter' and the mechanisms whereby it integrates physical (membrane voltage) and chemical (cyclic nucleotide) cues are unknown. In this study, we use single particle cryo-electron microscopy to determine structures of a metazoan SLC9C1 in different conformational states. We find that the three structural domains are uniquely organized around a distinct ring-shaped scaffold that we call the 'allosteric ring domain' or ARD. The ARD undergoes coupled proton-dependent rearrangements with the ED and acts as a 'signaling hub' enabling allosteric communication between the key functional modules of sp9C1. We demonstrate that binding of cAMP causes large conformational changes in the cytoplasmic domains and disrupts key ARD-linked interfaces. We propose that these structural changes rescue the transmembrane domains from an auto-inhibited state and facilitate their functional dynamics. Our study provides a structural framework to understand and further probe electrochemical linkage in SLC9C1.

Inhibition of Autophagy in Heat-Stressed Sperm of Adult Mice: A Possible Role of Catsper1, 2 Channel Proteins

Objective

Various phenomena guarantee gamete maturation and formation at all stages of evolution, one of which is autophagy playing a critical role in the final morphology of gametes, particularly sperms. Autophagy is influenced by oxidative stress, disturbances of calcium homeostasis, and hyperthermia conditions. The current study aimed to assess the autophagy-related proteins along with the activity of sperm calcium channel (CatSper) proteins following the induction of heat stress (HS).

Methods

The study sample includes two groups of adult mice: sham and HS groups. In the HS group, the right testis was transferred to the abdominal cavity for 120 hours and then returned to the scrotum where it remained for 7 days. After 7 days, the testis and epididymis were removed to conduct real-time, immunohistochemical studies, sperm parameter evaluation, and seminiferous tubule assessment. In this study, the expression and distribution of autophagy proteins were measured. Plus, CatSper1 and CatSper2 were evaluated as proteins of calcium channels.

Results

The results of the present study demonstrated that the expression intensity of autophagy indices in seminiferous tubules decreased significantly after HS induction, which was associated with a decrease in the distribution of CatSper proteins in the sperms. HS led to morphological changes in sperm, reduced motility and viability of sperm, and decreased spermatogenesis indices.

Conclusion

In this study, following heat stress, the decrease in CatSper protein distribution may lead to the structural disorder of CatSper channels, which could strongly affect autophagic activity. Also, disruption of spermatogenesis and sperm parameters may be the consequence of decreased autophagy activity.

Advances in non-hormonal male contraception targeting sperm motility

BACKGROUND

The high rates of unintended pregnancy and the ever-growing world population impose health, economic, social, and environmental threats to countries. Expanding contraceptive options, including male methods, are urgently needed to tackle these global challenges. Male contraception is limited to condoms and vasectomy, which are unsuitable for many couples. Thus, novel male contraceptive methods may reduce unintended pregnancies, meet the contraceptive needs of couples, and foster gender equality in carrying the contraceptive burden. In this regard, the spermatozoon emerges as a source of druggable targets for on-demand, non-hormonal male contraception based on disrupting sperm motility or fertilization.

OBJECTIVE AND RATIONALE

A better understanding of the molecules governing sperm motility can lead to innovative approaches toward safe and effective male contraceptives. This review discusses cutting-edge knowledge on sperm-specific targets for male contraception, focusing on those with crucial roles in sperm motility. We also highlight challenges and opportunities in male contraceptive drug development targeting spermatozoa.

SEARCH METHODS

We conducted a literature search in the PubMed database using the following keywords: 'spermatozoa', 'sperm motility', 'male contraception', and 'drug targets' in combination with other related terms to the field. Publications until January 2023 written in English were considered.

OUTCOMES

Efforts for developing non-hormonal strategies for male contraception resulted in the identification of candidates specifically expressed or enriched in spermatozoa, including enzymes (PP1γ2, GAPDHS, and sAC), ion channels (CatSper and KSper), transmembrane transporters (sNHE, SLC26A8, and ATP1A4), and surface proteins (EPPIN). These targets are usually located in the sperm flagellum. Their indispensable roles in sperm motility and male fertility were confirmed by genetic or immunological approaches using animal models and gene mutations associated with male infertility due to sperm defects in humans. Their druggability was demonstrated by the identification of drug-like small organic ligands displaying spermiostatic activity in preclinical trials.

WIDER IMPLICATIONS

A wide range of sperm-associated proteins has arisen as key regulators of sperm motility, providing compelling druggable candidates for male contraception. Nevertheless, no pharmacological agent has reached clinical developmental stages. One reason is the slow progress in translating the preclinical and drug discovery findings into a drug-like candidate adequate for clinical development. Thus, intense collaboration among academia, private sectors, governments, and regulatory agencies will be crucial to combine expertise for the development of male contraceptives targeting sperm function by (i) improving target structural characterization and the design of highly selective ligands, (ii) conducting long-term preclinical safety, efficacy, and reversibility evaluation, and (iii) establishing rigorous guidelines and endpoints for clinical trials and regulatory evaluation, thus allowing their testing in humans.

Large-scale growth of C. elegans and isolation of membrane protein complexes

Purification of membrane proteins for biochemical and structural studies is commonly achieved by recombinant overexpression in heterologous cell lines. However, many membrane proteins do not form a functional complex in a heterologous system, and few methods exist to purify sufficient protein from a native source for use in biochemical, biophysical and structural studies. Here, we provide a detailed protocol for the isolation of membrane protein complexes from transgenic Caenorhabditis elegans. We describe how to grow a genetically modified C. elegans line in abundance using standard laboratory equipment, and how to optimize purification conditions on a small scale using fluorescence-detection size-exclusion chromatography. Optimized conditions can then be applied to a large-scale preparation, enabling the purification of adequate quantities of a target protein for structural, biochemical and biophysical studies. Large-scale worm growth can be accomplished in ~9 d, and each optimization experiment can be completed in less than 1 d. We have used these methods to isolate the transmembrane channel-like protein 1 complex, as well as three additional protein complexes (transmembrane-like channel 2, lipid transfer protein and 'Protein S'), from transgenic C. elegans, demonstrating the utility of this approach in purifying challenging, low-abundance membrane protein complexes.

Antioxidant Nanoparticles Restore Cisplatin-Induced Male Fertility Defects by Promoting MDC1-53bp1-Associated Non-Homologous DNA Repair Mechanism and Sperm Intracellular Calcium Influx

Introduction

Cisplatin, a commonly used anticancer compound, exhibits severe off-target organ toxicity. Due to its wide application in cancer treatment, the reduction of its damage to normal tissue is an imminent clinical need. Cisplatin-induced testicular oxidative stress and damage lead to male sub- or infertility. Despite earlier studies showing that the natural polyphenol extracts honokiol serve as the free radical scavenger that reduces the accumulation of intracellular free radicals, whether honokiol exhibits direct effects on the testis and sperm is unclear. Thus, the aim of the current study is to investigate the direct effects of honokiol on testicular recovery and sperm physiology.

Methods

We encapsulated this polyphenol antioxidation compound into liposome-based nanoparticles (nHNK) and gave intraperitoneally to mice at a dosage of 5 mg/kg body mass every other day for consecutive 6 weeks.

Results

We showed that nHNK promotes MDC1-53bp1-associated non-homologous DNA double-strand break repair signaling pathway that minimizes cisplatin-induced DNA damage. This positive effect restores spermatogenesis and allows the restructuring of the multi-spermatogenic layers in the testis. By reducing mitochondrial oxidative damage, nHNK also protects sperm mitochondrial structure and maintains both testicular and sperm ATP production. By a yet-to-identify mechanism, nHNK restores sperm calcium influx at the sperm midpiece and tail, which is essential for sperm hypermotility and their interaction with the oocyte.

Discussion

Taken together, the nanoparticulated antioxidant counteracts cisplatin-induced male fertility defects and benefits patients undertaking cisplatin-based chemotherapy. These data may allow the reintroduction of cisplatin for systemic applications in patients at clinics with reduced testicular toxicity.

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.

A case of hermaphroditism in the gonochoristic sea urchin, Strongylocentrotus purpuratus, reveals key mechanisms of sex determination†

Sea urchins are usually gonochoristic, with all of their five gonads either testes or ovaries. Here, we report an unusual case of hermaphroditism in the purple sea urchin, Strongylocentrotus purpuratus. The hermaphrodite is self-fertile, and one of the gonads is an ovotestis; it is largely an ovary with a small segment containing fully mature sperm. Molecular analysis demonstrated that each gonad producedviable gametes, and we identified for the first time a somatic sex-specific marker in this phylum: Doublesex and mab-3 related transcription factor 1 (DMRT1). This finding also enabled us to analyze the somatic tissues of the hermaphrodite, and we found that the oral tissues (including gut) were out of register with the aboral tissues (including tube feet) enabling a genetic lineage analysis. Results from this study support a genetic basis of sex determination in sea urchins, the viability of hermaphroditism, and distinguish gonad determination from somatic tissue organization in the adult.

Conditioned medium and secretome from epididymal epithelial cell cultures improve sperm kinetics and capacitation

Background and Aim

Sperm maturation occurs in the epididymis through interactions with existing molecules inside the lumen. However, the mechanism of epididymis molecular transfer is currently unclear. This study was aimed to determine the necessity of the epididymal epithelial cells (EECs) in the process of sperm maturation in terms of sperm kinetics and tyrosine phosphorylation.

Materials and Methods

A true experimental research design was used in this study. The medium tested was a primary culture of mice caput epididymal cells (cells and culture medium), conditioned medium (CM) (supernatant of EECs), and secretome (CM filtered at 0.22 μm). Sperm was cocultured in EEC culture, CM, and secretome for 1, 2, 3, or 4 h. The original culture medium was used as the control. Sperm kinetic analysis was performed after the indicated times using computer-assisted sperm analysis, and tyrosine phosphorylation was detected using the Western blot technique.

Results

A primary culture of caput EECs was successfully generated. The results showed increased sperm motility and progressive movement after 3 h of incubation (p < 0.05). There was a significant decrease in the average path velocity (VAP) values after 4 h of incubation (p < 0.05), but there was no significant change in the 1, 2, and 3 h incubation groups. The EEC culture-CM and secretome groups showed a significant increased progressivity and VAP percentage values compared with the control medium (p < 0.05). In terms of percentage motility, the culture and CM groups were significantly different from the control medium, but the secretome group was not.

Conclusion

The sperm kinetics of sperm cultured in CM, secretome, and EEC were significantly increased after 3 h of incubation, suggesting that CM and secretome can be used to replace EECs, especially when analyzing molecules secreted by the epididymal epithelium during sperm maturation. The results of this study highlight the potential of CM and secretome as therapy mediums for sperm kinetic abnormalities.

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

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

High-throughput screening method for discovering CatSper inhibitors using membrane depolarization caused by external calcium chelation and fluorescent cell barcoding

The exclusive expression of CatSper in sperm and its critical role in sperm function makes this channel an attractive target for contraception. The strategy of blocking CatSper as a male, non-hormonal contraceptive has not been fully explored due to the lack of robust screening methods to discover novel and specific inhibitors. The reason for this lack of appropriate methodology is the structural and functional complexity of this channel. We have developed a high-throughput method to screen drugs with the capacity to block CatSper in mammalian sperm. The assay is based on removing external free divalent cations by chelation, inducing CatSper to efficiently conduct monovalent cations. Since Na⁺ is highly concentrated in the extracellular milieu, a sudden influx depolarizes the cell. Using CatSper1 KO sperm we demonstrated that this depolarization depends on CatSper function. A membrane potential (Em) assay was combined with fluorescent cell barcoding (FCB), enabling higher throughput flow cytometry based on unique fluorescent signatures of different sperm samples. These differentially labeled samples incubated in distinct experimental conditions can be combined into one tube for simultaneous acquisition. In this way, acquisition times are highly reduced, which is essential to perform larger screening experiments for drug discovery using live cells. Altogether, a simple strategy for assessing CatSper was validated, and this assay was used to develop a high-throughput drug screening for new CatSper blockers.

Cortisol modulates Ca2+ signaling and acrosome reaction in human sperm

BACKGROUND

Stress and elevated cortisol levels have negative effects on fertility, although there is controversy about the effect of cortisol on human sperm. One study reported that hydrocortisone (HC), the synthetic form of cortisol, does not activate CatSper channel but is able to inhibit its activation by progesterone (Pg). However, subsequent reports showed that HC has an agonist effect on CatSper, producing intracellular Ca²⁺ ([Ca²⁺ ]_i ) increases. These studies were performed using only electrophysiological techniques and fluorometric measurements of Ca²⁺ . Therefore, it is important to evaluate the effects of different HC concentrations on human sperm physiology using other approaches and techniques.

OBJECTIVE

To analyze the effects of different HC concentrations on human sperm physiology and to evaluate the association of perceived stress, anxiety and depression with acrosome reaction (AR), and semen quality.

MATERIALS AND METHODS

In capacitated human sperm, we tested the effects of HC on [Ca²⁺ ]_i mobilization and AR. Furthermore, the perceived stress and symptoms of anxiety and depression were evaluated with standardized psychometric tests.

RESULTS

HC induces a low increase in [Ca²⁺ ]_i compared to Pg response while, at higher concentrations, HC inhibits the Pg-induced Ca²⁺ response. Also, low concentrations of HC induce AR and when co-incubating it with Pg, the percentages of AR are decreased. Finally, the anxiety symptoms are negatively correlated with Pg induced AR and semen quality.

DISCUSSION

HC has an agonist effect on [Ca²⁺ ]_i mobilization and AR. However, our data also suggest that HC may compete for the binding site of Pg. Additionally, the association between anxiety and decreased AR could be explained by high cortisol levels.

CONCLUSION

Our data showed that HC interferes with the Pg action. Therefore, the negative correlation between anxiety symptoms and Pg-induced AR is due to the accompanying high cortisol levels of this condition and its competitive action with Pg.

Differential Distribution and Activity Profile of Acylpeptide Hydrolase in the Rat Seminiferous Epithelium

Acylpeptide hydrolase (APEH) is a serine protease involved in amino acid recycling from acylated peptides (exopeptidase activity) and degradation of oxidized proteins (endoproteinase activity). This enzyme is inhibited by dichlorvos (DDVP), an organophosphate compound used as an insecticide. The role of APEH in spermatogenesis has not been established; therefore, the aim of this study was to characterize the distribution and activity profile of APEH during this process. For this purpose, cryosections of male reproductive tissues (testis and epididymis) and isolated cells (Sertoli cells, germ cells, and spermatozoa) were obtained from adult rats in order to analyze the intracellular localization of APEH by indirect immunofluorescence. In addition, the catalytic activity profiles of APEH in the different male reproductive tissues and isolated cells were quantified. Our results show that APEH is homogeneously distributed in Sertoli cells and early germ cells (spermatocytes and round spermatids), but this pattern changes during spermiogenesis. Specifically, in elongated spermatids and spermatozoa, APEH was localized in the acrosome and the principal piece. The exopeptidase activity was higher in the germ cell pool, compared to sperm and Sertoli cells, while the endoproteinase activity in epididymal homogenates was higher compared to testis homogenates at 24 h of incubation. In isolated cells, this activity was increased in Sertoli and germ cell pools, compared to spermatozoa. Taken together, these results indicate that APEH is differentially distributed in the testicular epithelium and undergoes re-localization during spermiogenesis. A possible role of APEH as a component of a protection system against oxidative stress and during sperm capacitation is discussed.

Reproductive Consequences of Electrolyte Disturbances in Domestic Animals

Electrolyte balance is essential to maintain homeostasis in the body. The most crucial electrolytes are sodium (Na+), potassium (K+), magnesium (Mg2+), chloride (Cl−), and calcium (Ca2+). These ions maintain the volume of body fluids, and blood pressure, participate in muscle contractions, and nerve conduction, and are important in enzymatic reactions. The balance is mainly ensured by the kidneys, which are an important organ that regulates the volume and composition of urine, together with which excess electrolytes are excreted. They are also important in the reproductive system, where they play a key role. In the male reproductive system, electrolytes are important in acrosomal reaction and sperm motility. Sodium, calcium, magnesium, and chloride are related to sperm capacitation. Moreover, Mg2+, Ca2+, and Na+ play a key role in spermatogenesis and the maintenance of morphologically normal spermatozoa. Infertility problems are becoming more common. It is known that disturbances in the electrolyte balance lead to reproductive dysfunction. In men, there is a decrease in sperm motility, loss of sperm capacitation, and male infertility. In the female reproductive system, sodium is associated with estrogen synthesis. In the contraction and relaxation of the uterus, there is sodium, potassium, and calcium. Calcium is associated with oocyte activation. In turn, in women, changes in the composition of the follicular fluid are observed, leading to a restriction of follicular growth. Imbalance of oocyte electrolytes, resulting in a lack of oocyte activation and, consequently, infertility.

A Review on the Role of Bicarbonate and Proton Transporters during Sperm Capacitation in Mammals

Alkalinization of sperm cytosol is essential for plasma membrane hyperpolarization, hyperactivation of motility, and acrosomal exocytosis during sperm capacitation in mammals. The plasma membrane of sperm cells contains different ion channels implicated in the increase of internal pH (pH_i) by favoring either bicarbonate entrance or proton efflux. Bicarbonate transporters belong to the solute carrier families 4 (SLC4) and 26 (SLC26) and are currently grouped into Na⁺/HCO₃⁻ transporters and Cl⁻/HCO₃⁻ exchangers. Na⁺/HCO₃⁻ transporters are reported to be essential for the initial and fast entrance of HCO₃⁻ that triggers sperm capacitation, whereas Cl⁻/HCO₃⁻ exchangers are responsible for the sustained HCO₃⁻ entrance which orchestrates the sequence of changes associated with sperm capacitation. Proton efflux is required for the fast alkalinization of capacitated sperm cells and the activation of pH-dependent proteins; according to the species, this transport can be mediated by Na⁺/H⁺ exchangers (NHE) belonging to the SLC9 family and/or voltage-gated proton channels (HVCN1). Herein, we discuss the involvement of each of these channels in sperm capacitation and the acrosome reaction.

Progesterone-Induced Sperm Release from the Oviduct Sperm Reservoir

In mammalian females, after sperm are deposited in the reproductive tract, a fraction of sperm migrates to the lower oviduct (isthmus) and forms a sperm storage site known as the functional sperm reservoir. The interactions between sperm membrane proteins and oviduct epithelial cells facilitate sperm binding to the oviductal epithelium and retention in the reservoir. Sperm are bound by glycans that contain specific motifs present on isthmic epithelial cells. Capacitated sperm are released from the reservoir and travel further in the oviduct to the ampulla where fertilization occurs. For decades, researchers have been studying the molecules and mechanisms of sperm release from the oviductal sperm reservoir. However, it is still not clear if the release of sperm is triggered by changes in sperm, oviduct cells, oviduct fluid, or a combination of these. While there is a possibility that more than one of these events are involved in the release of sperm from the reservoir, one activator of sperm release has the largest accumulation of supporting evidence. This mechanism involves the steroid hormone, progesterone, as a signal that induces the release of sperm from the reservoir. This review gathers and synthesizes evidence for the role of progesterone in inducing sperm release from the oviduct functional sperm reservoir.

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

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

SOX11-dependent CATSPER1 expression controls colon cancer cell growth through regulation the PI3K/AKT signaling pathway

BACKGROUND

Colorectal cancer (CRC) is one of the most common malignant tumors and the fourth leading cause of cancer death worldwide. Constitutive activation of the PI3K/AKT signaling pathway is a hallmark of colon tumor growth. CATSPER1 gene encodes a pore-forming and pH-sensing subunit of the CatSper Ca²⁺-permeable channel, a sperm-specific calcium channel essential for hyperactivated motility and male fertility. However, the function of CATSPER1 outside the male reproductive system is unclear.

OBJECTIVE

This study was designed to explore whether CatSper exerted its functional role in the progress of CRC, and investigate the possible mechanisms.

METHODS

Microarray data (GSE146587) from 6 patients diagnosed with stage III CRC post-surgery was analyzed by Limma R package. The Kaplan Meier plotter (KM plotter) database was used to assess the relevance of CATSPER1 mRNA expression to the overall survival (OS) rates in CRC. Western blot, real-time PCR and luciferase reporter assays were used to determine the SOX11-CATSPER1 axis in CRC cells. Clustered regularly interspaced short palindromic repeats (CRISPR)-based gene editing was used to generate CATSPER1 knockout (KO) CRC cells. The proliferation of CRC cells was determined by BrdU incorporation and colony formation assays. The effect of CATSPER1 on CRC tumor growth in vivo was investigated in a mice tumor xenograft model.

RESULTS

Here, we show that CATSPER1 expression was significantly up-regulated in CRC and elevated CATSPER1 was associated with poor overall survival (OS). Moreover, the transcription factor SOX11 (SRY-related high-mobility-group (HMG) box 11) activated CATSPER1 transcription in CRC cells. Functionally, we showed that CATSPER1 promoted CRC cells proliferation both in vitro and in vivo. At the molecular level, we demonstrated that CATSPER1 might maintain CRC malignant process partly through the activation of the PI3K/AKT signaling pathway.

CONCLUSION

Increased CATSPER1 expression facilitates CRC cells proliferation, suggesting that targeting CATSPER1 might represent a promising strategy for colon cancer treatment.

[New frontiers in contraception research]

Improving current contraceptives and discover novel methods easy to use with added health benefits would meet the needs of couples who seek alternatives to current methods. New delivery systems target user-controlled, longer-acting options to provide choice, user's autonomy and improve compliance. Self-injections, microarray patches, pod rings able to deliver several molecules aim to prevent both pregnancies and sexually transmitted infections. Improved intrauterine systems and non-surgical permanent methods are also on the research agenda. The search for novel methods must continue, to curb maternal mortality led by multiple pregnancies and unsafe abortion, still a burden in many countries.

Increased mitochondrial activity upon CatSper channel activation is required for mouse sperm capacitation

To fertilize an oocyte, sperm must undergo several biochemical and functional changes known as capacitation. A key event in capacitation is calcium influx through the cation channel of sperm (CatSper). However, the molecular mechanisms of capacitation downstream of this calcium influx are not completely understood. Capacitation is also associated with an increase in mitochondrial oxygen consumption, and several lines of evidence indicate that regulated calcium entry into mitochondria increases the efficiency of oxidative respiration. Thus, we hypothesized that calcium influx through CatSper during capacitation increases mitochondrial calcium concentration and mitochondrial efficiency and thereby contributes to sperm hyperactivation and fertilization capacity. To test this hypothesis, we used high-resolution respirometry to measure mouse sperm mitochondrial activity. We also measured mitochondrial membrane potential, ATP/ADP exchange during capacitation, and mitochondrial calcium concentration in sperm from wild-type and CatSper knockout mice. We show that the increase in mitochondrial activity in capacitated wild-type sperm parallels the increase in mitochondrial calcium concentration. This effect is blunted in sperm from CatSper knockout mice. Importantly, these mechanisms are needed for optimal hyperactivation and fertilization in wild-type mice, as confirmed by using mitochondrial inhibitors. Thus, we describe a novel mechanism of sperm capacitation. This work contributes to our understanding of the role of mitochondria in sperm physiology and opens the possibility of new molecular targets for fertility treatments and male contraception.

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

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

Preclinical contraceptive development for men and women

This manuscript endeavors to present research considerations for the preclinical development of non-hormonal contraceptives. Topics include (1) how advances in genomics and bioinformatics impact the identification of novel targets for non-hormonal contraception, (2) the importance of target validation prior to investment in a contraceptive development campaign, (3) considerations on targeting gametogenesis vs gamete maturation/function, (4) how targets from the male reproductive system are expanding women's options for 'on demand' contraception, and (5) some emerging non-hormonal methods that are not based on a specific molecular target. Also presented are ideas for developing a pipeline of non-hypothalamic-pituitary-gonadal-acting contraceptives for men and women while balancing risk and innovation, and our perspective on the pros and cons of industry and academic environments on contraceptive development. Three product development programs are highlighted that are biologically interesting, innovative, and likely to influence the field of contraceptive development in years to come.

Astaxanthin Induces the Expression of CatSper1 Gene and Protects Sperms in Toxicity Induced by Cadmium in Mice

Cadmium (Cd) as a heavy metal damages testis and decreases fertility, however, antioxidants can improve sperm parameters and decrease male infertility. In this study we investigated the effect of astaxanthin (AST) on sperm parameters, expression levels of CatSper1 and CatSper2 genes in presence of Cd in mice. Thirty adults' mice were divided into 4 groups, sham group received olive oil and saline (olive oil is the solvent of AST and saline is the solvent of Cd), Cd group received 1 mg/kg Cdcl₂, a group received 10 mg/kg AST and 1 mg/kg Cdcl₂ and a group received 10 mg/kg AST. The treatments were done intraperitoneally for 14 days. After 14 days sperm parameters were analyzed. Malondialdehyde level, catalase enzyme activity, the alteration of CatSper1 and CatSper2 genes expression were measured in testis. Results showed that Sperm count, viability, CatSper1 gene expression and catalase activity significantly decreased by Cd compared to sham group. Cd significantly increased sperm DNA fragmentation (SDF), abnormal sperm morphology and malondialdehyd level compared to sham group. AST significantly increased sperm count, viability and CatSper1 gene expression and decreased SDF and abnormal sperm in comparison with Cd group. AST protected testis and decreased oxidative stress induced by Cd. Our findings indicated that AST could protect sperm DNA, enhanced CatSper1 gene expression and sperm quality in presence of Cd. No significant differences were found in CatSper2 expression among treatments. Therefore, AST as a strong antioxidant can help to protect the potential of fertility against Cd toxicity.

A dual-site controlled pH probe revealing the pH of sperm cytoplasm and screening for healthy spermatozoa

A dual-site controlled pH probe, which is composed of gold nanoparticles and modified with rhodamine and fluorescein derivatives, was applied to sensitively monitor intracellular pH changes in sperm. The pH probe revealed the intracellular pH of sperm under different conditions and demonstrated the lower pH in asthenozoospermia patients as compared to healthy individuals. Importantly, the pH probe can help screen for healthy sperm.

Cdc42 localized in the CatSper signaling complex regulates cAMP-dependent pathways in mouse sperm

Sperm acquire the ability to fertilize in a process called capacitation and undergo hyperactivation, a change in the motility pattern, which depends on Ca²⁺ transport by CatSper channels. CatSper is essential for fertilization and it is subjected to a complex regulation that is not fully understood. Here, we report that similar to CatSper, Cdc42 distribution in the principal piece is confined to four linear domains and this localization is disrupted in CatSper1-null sperm. Cdc42 inhibition impaired CatSper activity and other Ca²⁺ -dependent downstream events resulting in a severe compromise of the sperm fertilizing potential. We also demonstrate that Cdc42 is essential for CatSper function by modulating cAMP production by soluble adenylate cyclase (sAC), providing a new regulatory mechanism for the stimulation of CatSper by the cAMP-dependent pathway. These results reveal a broad mechanistic insight into the regulation of Ca²⁺ in mammalian sperm, a matter of critical importance in male infertility as well as in contraception.

Do Seminal Isoprostanes Have a Role in Assisted Reproduction Outcome?

F₂-isoprostanes (F₂-IsoPs), stereoisomers of prostaglandin F2α generated by the free radical-induced oxidation of arachidonic acid, have been associated with different male infertility conditions. This study aimed to evaluate the role of seminal isoprostane levels and sperm characteristics in the reproductive outcome and embryo quality of 49 infertile couples. Semen analysis was performed following WHO guidelines. Sperm chromatin maturity was detected using an aniline blue (AB) assay, and DNA integrity was assessed using the acridine orange (AO) test. Seminal F₂-IsoP levels were quantified by gas chromatography/negative ion chemical ionization tandem mass spectrometry (GC/NICI–MS/MS) analysis. Correlations among variables and their impact on in vitro fertilization (IVF) and intracytoplasmic sperm injection (ICSI) outcome were investigated. F₂-IsoP levels are positively correlated with double-stranded DNA sperm (p < 0.001) and negatively correlated with mature sperm chromatin (p < 0.001). Patients with positive outcomes had an increased percentage of sperm with double-stranded DNA, as did patients producing high-quality embryo, who showed higher F₂-IsoP levels compared to those detected in the low-quality embryo group. An intriguing relationship between a mild increase in F₂-IsoP levels, DNA integrity, and embryo quality seems to indicate that the non-enzymatic oxidation of arachidonic acid can be also a marker of metabolic activity in human semen.

Altered Expression of Ion Channels in White Matter Lesions of Progressive Multiple Sclerosis: What Do We Know About Their Function?

Despite significant advances in our understanding of the pathophysiology of multiple sclerosis (MS), knowledge about contribution of individual ion channels to axonal impairment and remyelination failure in progressive MS remains incomplete. Ion channel families play a fundamental role in maintaining white matter (WM) integrity and in regulating WM activities in axons, interstitial neurons, glia, and vascular cells. Recently, transcriptomic studies have considerably increased insight into the gene expression changes that occur in diverse WM lesions and the gene expression fingerprint of specific WM cells associated with secondary progressive MS. Here, we review the ion channel genes encoding K⁺, Ca²⁺, Na⁺, and Cl^- channels; ryanodine receptors; TRP channels; and others that are significantly and uniquely dysregulated in active, chronic active, inactive, remyelinating WM lesions, and normal-appearing WM of secondary progressive MS brain, based on recently published bulk and single-nuclei RNA-sequencing datasets. We discuss the current state of knowledge about the corresponding ion channels and their implication in the MS brain or in experimental models of MS. This comprehensive review suggests that the intense upregulation of voltage-gated Na⁺ channel genes in WM lesions with ongoing tissue damage may reflect the imbalance of Na⁺ homeostasis that is observed in progressive MS brain, while the upregulation of a large number of voltage-gated K⁺ channel genes may be linked to a protective response to limit neuronal excitability. In addition, the altered chloride homeostasis, revealed by the significant downregulation of voltage-gated Cl^- channels in MS lesions, may contribute to an altered inhibitory neurotransmission and increased excitability.

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.

Progesterone induces porcine sperm release from oviduct glycans in a proteasome-dependent manner

In mammals, the oviduct retains sperm, forming a reservoir from which they are released in synchrony with ovulation. However, the mechanisms underlying sperm release are unclear. Herein, we first examined in greater detail the release of sperm from the oviduct reservoir by sex steroids, and secondly, if the ubiquitin-proteasome system (UPS) mediates this release in vitro. Sperm were allowed to bind to oviductal cells or immobilized oviduct glycans, either bi-SiaLN or a suLeX, and channeled with steroids in the presence or absence of proteasome inhibitors. Previously, we have demonstrated progesterone-induced sperm release from oviduct cells and immobilized glycans in a steroid-specific manner. Herein, we found that the release of sperm from an immobilized oviduct glycan, a six-sialylated branched structure, and from immobilized fibronectin was inhibited by the CatSper blocker NNC 055-0396, akin to the previously reported ability of NNC 055-0396 to inhibit sperm release from another oviduct glycan, sulfated Lewis-X trisaccharide. Thus, CatSper may be required for release of sperm from a variety of adhesion systems. One possible mechanism for sperm release is that glycan receptors on sperm are degraded by proteasomes or shed from the sperm surface by proteasomal degradation. Accordingly, the inhibition of proteasomal degradation blocked sperm release from oviduct cell aggregates both immobilized oviduct glycans as well as fibronectin. In summary, progesterone-induced sperm release requires both active CatSper channels and proteasomal degradation, suggesting that hyperactivation and proteolysis are vital parts of the mechanism by which sperm move from the oviduct reservoir to the site of fertilization.

Genes Regulating Spermatogenesis and Sperm Function Associated With Rare Disorders

Spermatogenesis is a cell differentiation process that ensures the production of fertilizing sperm, which ultimately fuse with an egg to form a zygote. Normal spermatogenesis relies on Sertoli cells, which preserve cell junctions while providing nutrients for mitosis and meiosis of male germ cells. Several genes regulate normal spermatogenesis, some of which are not exclusively expressed in the testis and control multiple physiological processes in an organism. Loss-of-function mutations in some of these genes result in spermatogenesis and sperm functionality defects, potentially leading to the insurgence of rare genetic disorders. To identify genetic intersections between spermatogenesis and rare diseases, we screened public archives of human genetic conditions available on the Genetic and Rare Diseases Information Center (GARD), the Online Mendelian Inheritance in Man (OMIM), and the Clinical Variant (ClinVar), and after an extensive literature search, we identified 22 distinct genes associated with 21 rare genetic conditions and defective spermatogenesis or sperm function. These protein-coding genes regulate Sertoli cell development and function during spermatogenesis, checkpoint signaling pathways at meiosis, cellular organization and shape definition during spermiogenesis, sperm motility, and capacitation at fertilization. A number of these genes regulate folliculogenesis and oogenesis as well. For each gene, we review the genotype–phenotype association together with associative or causative polymorphisms in humans, and provide a description of the shared molecular mechanisms that regulate gametogenesis and fertilization obtained in transgenic animal models.

Long-term segmentation-free assessment of head-flagellum movement and intracellular calcium in swimming human sperm

Human spermatozoa are the archetype of long-term self-organizing transport in nature and are critical for reproductive success. They utilize coordinated head and flagellar movements to swim long distances within the female reproductive tract in order to find and fertilize the egg. However, to date, long-term analysis of the sperm head-flagellar movements, or indeed those of other flagellated microorganisms, remains elusive due to limitations in microscopy and flagellar-tracking techniques. Here, we present a novel methodology based on local orientation and isotropy of bio-images to obtain long-term kinematic and physiological parameters of individual free-swimming spermatozoa without requiring image segmentation (thresholding). This computer-assisted segmentation-free method evaluates, for the first time, characteristics of the head movement and flagellar beating for up to 9.2 min. We demonstrate its powerful use by showing how releasing Ca²⁺ from internal stores significantly alters long-term sperm behavior. The method allows for straightforward generalization to other bio-imaging applications, such as studies of bull sperm and Trypanosoma, or indeed of other flagellated microorganisms - appealing to communities other than those investigating sperm biology.

Cabs1 Maintains Structural Integrity of Mouse Sperm Flagella during Epididymal Transit of Sperm

The calcium-binding protein spermatid-associated 1 (Cabs1) is a novel spermatid-specific protein. However, its function remains largely unknown. In this study, we found that a long noncoding RNA (lncRNA) transcripted from the Cabs1 gene antisense, AntiCabs1, was also exclusively expressed in spermatids. Cabs1 and AntiCabs1 knockout mice were generated separately (using Clustered Regularly Interspaced Short Palindromic Repeat (CRISPR)-Cas9 methods) to investigate their functions in spermatogenesis. The genetic loss of Cabs1 did not affect testicular and epididymal development; however, male mice exhibited significantly impaired sperm tail structure and subfertility. Ultrastructural analysis revealed defects in sperm flagellar differentiation leading to an abnormal annulus and disorganization of the midpiece-principal piece junction, which may explain the high proportion of sperm with a bent tail. Interestingly, the proportion of sperm with a bent tail increased during transit in the epididymis. Furthermore, Western blot and immunofluorescence analyses showed that a genetic loss of Cabs1 decreased Septin 4 and Krt1 and increased cyclin Y-like 1 (Ccnyl1) levels compared with the wild type, suggesting that Cabs1 deficiency disturbed the expression of cytoskeleton-related proteins. By contrast, AntiCabs1^-/- mice were indistinguishable from the wild type regarding testicular and epididymal development, sperm morphology, concentration and motility, and male fertility. This study demonstrates that Cabs1 is an important component of the sperm annulus essential for proper sperm tail assembly and motility.

Roles of CatSper channels in the pathogenesis of asthenozoospermia and the therapeutic effects of acupuncture-like treatment on asthenozoospermia

Rationale: Idiopathic asthenozoospermia (iAZS) is one of the major causes of male infertility and has no effective therapeutic treatment. Understanding the potential mechanisms that cause it may be helpful in seeking novel targets and treatment strategies for overcoming the problem of low sperm motility in iAZS individuals.

Methods: Computer-assisted semen analysis (CASA) was utilized to assess the sperm motility. RT-qPCR, Western blot, immunofluorescence staining, and calcium imaging analysis were performed to examine the expression and function of CatSper channels. Hyperactivation and acrosome reaction were used to evaluate the functional characteristics of epididymal sperm. In vivo fertility assay was applied to determine the fertility of rats. CatSper1 knockdown and overexpression experiments were performed to confirm the roles of CatSper channels in the pathogenesis of iAZS and the therapeutic effects of electroacupuncture (EA) treatment on AZS model rats.

Results: Here, we reported a functional down-regulation of CatSper channel from CatSper1 to CatSper 4 in the sperm of both iAZS patients and ornidazole (ORN)-induced AZS model rats, and an impaired sperm function characterized by a reduction of protein tyrosine phosphorylation, hyperactivation, and acrosome reaction in the epididymal sperm of AZS rats. Knockdown of CatSper1 in the testis tissues is sufficient to induce AZS in normal rats, and this action was validated by the reversal effects of CatSper1 overexpression. Transcutaneous electrical acupoint stimulation (TEAS) and electroacupuncture (EA) at 2 Hz frequency improve the sperm motility via enhancing the functional expression of CatSper channels in the sperm. Gene silencing CatSper1 in the sperm abolishes the therapeutic effects of 2 Hz-EA treatment on AZS rats.

Conclusions: We conclude that a functional down-regulation of CatSper channel in the sperm may be a contributor or a downstream indicator for a portion of AZS, especially iAZS, while 2 Hz-TEAS or EA treatment has a therapeutic effect on iAZS through inducing the functional up-regulation of CatSper channels in the sperm. This study provides a novel mechanism for the pathogenesis of some AZS especially iAZS, and presents a potential therapeutic target of CatSper for iAZS treatment. Acupuncture treatment like TEAS may be used as a promising complementary and alternative medicine (CAM) therapy for male infertility caused by iAZS in clinical practice.

The secrets of success

Imaging sperm as they travel through the female reproductive tract has revealed new details about fertilization at the molecular level.

IP3R Channels in Male Reproduction

As a second messenger in cellular signal transduction, calcium signaling extensively participates in various physiological activities, including spermatogenesis and the regulation of sperm function. Abnormal calcium signaling is highly correlated with male infertility. Calcium signaling is mainly regulated by both extracellular calcium influx and the release of calcium stores. Inositol 1,4,5-trisphosphate receptor (IP3R) is a widely expressed channel for calcium stores. After being activated by inositol 1,4,5-trisphosphate (IP3) and calcium signaling at a lower concentration, IP3R can regulate the release of Ca²⁺ from stores into cytoplasm, and eventually trigger downstream events. The closure of the IP3R channel caused by a rise in intracellular calcium signals and the activation of the calcium pump jointly restores the calcium store to a normal level. In this review, we aim to discuss structural features of IP3R channels and the underlying mechanism of IP3R channel-mediated calcium signaling and further focus on the research progress of IP3R expression and function in the male reproductive system. Finally, we propose key directions and strategies for research of IP3R in spermatogenesis and the regulation of sperm function to provide more understanding of the function and mechanism of IP3R channel actions in male reproduction.

Understanding sperm physiology: Proximate and evolutionary explanations of sperm diversity

Much can be gained from the comprehensive study of a biological system. Based on what is known as Mayr's proximate-ultimate causation and the subsequent expansion to Tinbergen's four questions, biological traits can be understood by taking into account different approximations that try to explain mechanisms, development, adaptive significance or phylogeny. These, in principle, separate areas, can be integrated crossing boundaries, but bearing in mind that answers to one question would not explain a different query. Studies of sperm biology have, until now, not benefited much from this framework and potential integration. Proximate causes (particularly mechanisms) have been the subject of interest for reproductive biologists, and evolutionary explanations have been the domain of behavioural ecologists with interest in adaptive significance of traits in the context of post-copulatory sexual selection. This review will summarize opportunities for research in the different areas, focusing on sperm preparation for fertilization and suggesting possible integration within and between proximate and evolutionary studies.

The Relevance of Aquaporins for the Physiology, Pathology, and Aging of the Female Reproductive System in Mammals

Aquaporins constitute a group of water channel proteins located in numerous cell types. These are pore-forming transmembrane proteins, which mediate the specific passage of water molecules through membranes. It is well-known that water homeostasis plays a crucial role in different reproductive processes, e.g., oocyte transport, hormonal secretion, completion of successful fertilization, blastocyst formation, pregnancy, and birth. Further, aquaporins are involved in the process of spermatogenesis, and they have been reported to be involved during the storage of spermatozoa. It is noteworthy that aquaporins are relevant for the physiological function of specific parts in the female reproductive system, which will be presented in detail in the first section of this review. Moreover, they are relevant in different pathologies in the female reproductive system. The contribution of aquaporins in selected reproductive disorders and aging will be summarized in the second section of this review, followed by a section dedicated to aquaporin-related proteins. Since the relevance of aquaporins for the male reproductive system has been reviewed several times in the recent past, this review aims to provide an update on the distribution and impact of aquaporins only in the female reproductive system. Therefore, this paper seeks to determine the physiological and patho-physiological relevance of aquaporins on female reproduction, and female reproductive aging.

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.

Male Decapacitation Factor SPINK3 Blocks Membrane Hyperpolarization and Calcium Entry in Mouse Sperm

Mammalian sperm acquire ability to fertilize through a process called capacitation, occurring after ejaculation and regulated by both female molecules and male decapacitation factors. Bicarbonate and calcium present in the female reproductive tract trigger capacitation in sperm, leading to acrosomal responsiveness and hyperactivated motility. Male decapacitating factors present in the semen avert premature capacitation, until detached from the sperm surface. However, their mechanism of action remains elusive. Here we describe for the first time the molecular basis for the decapacitating action of the seminal protein SPINK3 in mouse sperm. When present in the capacitating medium, SPINK3 inhibited Src kinase, a modulator of the potassium channel responsible for plasma membrane hyperpolarization. Lack of hyperpolarization affected calcium channels activity, impairing the acquisition of acrosomal responsiveness and blocking hyperactivation. Interestingly, SPINK3 acted only on non-capacitated sperm, as it did not bind to capacitated cells. Binding selectivity allows its decapacitating action only in non-capacitated sperm, without affecting capacitated cells.

Transcriptome analysis of Clarias magur brain and gonads suggests neuro-endocrine inhibition of milt release from captive GnRH-induced males

Transcriptome analysis of Clarias magur brain and gonads at preparatory, mature, 6 and 16 h post-GnRH injection (hpi) stages yielded 9.5 GB data with 39,738 contigs. Sequences of 45 reproductive genes were identified for the first time in C. magur along with unique and differentially expressed genes. The expression of 20 genes was validated by qRT-PCR. Upregulation of Cyp11A1, Cyp17A1 and FTZF1 genes in the 16hpi testis accompanied by the 17β-HSD3 expression indicates testosterone (T) synthesis in response to LH surge, while reduced expression of CYP11B1 suggests a high T: 11-KT ratio. It is evident by the gene expression analysis that the inhibitory neurotransmitter GABA, altered T: 11-KT, increased testicular bile acids, and oxytocin-like neuropeptide in the male brain, appear to be involved in arresting the pulsatile motion of testicular smooth muscles. The work generates important leads for an effective induced breeding strategy for silurid catfish.

Differences and Similarities: The Richness of Comparative Sperm Physiology

Species preservation depends on the success of fertilization. Sperm are uniquely equipped to fulfill this task, and, although several mechanisms are conserved among species, striking functional differences have evolved to contend with particular sperm-egg environmental characteristics. This review highlights similarities and differences in sperm strategies, with examples within internal and external fertilizers, pointing out unresolved issues.

Modular analysis of the control of flagellar Ca2+-spike trains produced by CatSper and CaV channels in sea urchin sperm

Intracellular calcium ([Ca²⁺]_i) is a basic and ubiquitous cellular signal controlling a wide variety of biological processes. A remarkable example is the steering of sea urchin spermatozoa towards the conspecific egg by a spatially and temporally orchestrated series of [Ca²⁺]_i spikes. Although this process has been an experimental paradigm for reproduction and sperm chemotaxis studies, the composition and regulation of the signalling network underlying the cytosolic calcium fluctuations are hitherto not fully understood. Here, we used a differential equations model of the signalling network to assess which set of channels can explain the characteristic envelope and temporal organisation of the [Ca²⁺]_i-spike trains. The signalling network comprises an initial membrane hyperpolarisation produced by an Upstream module triggered by the egg-released chemoattractant peptide, via receptor activation, cGMP synthesis and decay. Followed by downstream modules leading to intraflagellar pH (pH_i), voltage and [Ca²⁺]_i fluctuations. The Upstream module outputs were fitted to kinetic data on cGMP activity and early membrane potential changes measured in bulk cell populations. Two candidate modules featuring voltage-dependent Ca²⁺-channels link these outputs to the downstream dynamics and can independently explain the typical decaying envelope and the progressive spacing of the spikes. In the first module, [Ca²⁺]_i-spike trains require the concerted action of a classical Ca_V-like channel and a potassium channel, BK (Slo1), whereas the second module relies on pH_i-dependent CatSper dynamics articulated with voltage-dependent neutral sodium-proton exchanger (NHE). We analysed the dynamics of these two modules alone and in mixed scenarios. We show that the [Ca²⁺]_i dynamics observed experimentally after sustained alkalinisation can be reproduced by a model featuring the CatSper and NHE module but not by those including the pH-independent Ca_V and BK module or proportionate mixed scenarios. We conclude in favour of the module containing CatSper and NHE and highlight experimentally testable predictions that would corroborate this conclusion.

Fertilisation in marine invertebrates, such as the sea urchin, occurs during broadcast spawning events in which males and females of co-localised species ejaculate sperm and spawn eggs synchronously. During these events, spermatozoa have to find and fertilise conspecific eggs in the midst of all the other ones, which is a remarkable navigation and mating choice achievement. Sperm cells do this by navigating towards the source of species-specific peptides released by the egg, steered by spatial and temporally orchestrated peaks in intracellular calcium concentration that trigger sudden reorientations. How these calcium spikes are regulated and timed remains elusive. Different calcium channels have been implicated by indirect experimental evidence giving rise to a complex network of putative interacting components. We gained insight into the structure and function of this network by modelling it as a set of candidate modules that could be studied separately. By using this ‘divide and conquer’ approach to the complexity of the network, we could characterise the potential dynamics of each module and confront these dynamics with specific quantitative data. Our results indicate that the channel mediating calcium signals in sea urchin sperm is likely CatSper, a calcium channel necessary for human male fertility.