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.

Supplementation of Beltsville extender with quercetin improves the quality of frozen-thawed rooster semen

1. Excessive reactive oxygen species (ROS) production during the sperm freeze-thawing process leads to membrane lipid peroxidation, DNA damage, and motility loss.2. This study examined the effect of supplementation of Beltsville poultry semen extender with different concentrations of quercetin (and antioxidants) on the cryopreservation of rooster sperm.3. Semen samples were collected from six Ross broiler breeders via abdominal massage twice a week for 4 weeks (eight replicates), and were divided into five equal aliquots to be diluted in Beltsville extenders that contained different concentrations of quercetin: 0, 5, 10, 15, and 20 mM. Motility, membrane functionality, abnormal morphology, lipid peroxidation, mitochondrial activity, viability, apoptosis status, and fertility potential were assessed post thaw.4. The addition of 10 and 15 mM quercetin to the semen extender significantly increased the total motility, straight-line velocity (VSL), and sperm membrane functionality compared with the other groups (P ≤ 0.05). Moreover, 10 mM quercetin caused higher progressive motility (34.86 ± 3.80%), curvilinear velocity (VCL; 175.11 ± 3.20 µm/s), average path velocity (VAP; 44.35 ± 11.06 µm/s), viability (59.14 ± 1.36%), mitochondrial activity (80.14 ± 2.07%), lower abnormal morphology (19.21 ± 0.45%), and lower lipid peroxidation (2.7 ± 0.13 nmol/ml) compared with the other groups (P < 0.05). The rate of fertility and hatchability after artificial insemination was not affected by experimental groups.5. In conclusion, supplementation of Beltsville extender with 10 mM quercetin could be a suitable method to improve post-thawed rooster sperm quality resulting in better freeze/thaw characteristics.

GH Overexpression Alters Spermatic Cells MicroRNAome Profile in Transgenic Zebrafish

Overexpression of growth hormone (GH) in gh-transgenic zebrafish of a highly studied lineage F0104 has earlier been reported to cause increased muscle growth. In addition to this, GH affects a broad range of cellular processes in transgenic fish, such as morphology, physiology, and behavior. Reports show changes such as decreased sperm quality and reduced reproductive performance in transgenic males. It is hypothesized that microRNAs are directly involved in the regulation of fertility potential during spermatogenesis. The primary aim of our study was to verify whether gh overexpression disturbs the sperm miRNA profile and influences the sperm quality in transgenic zebrafish. We report a significant increase in body weight of gh-transgenic males along with associated reduced sperm motility and other kinetic parameters in comparison to the non-transgenic group. MicroRNA transcriptome sequencing of gh-transgenic zebrafish sperms revealed expressions of 186 miRNAs, among which six miRNA were up-regulated (miR-146b, miR-200a-5p, miR-146a, miR-726, miR-184, and miR-738) and sixteen were down-regulated (miR-19d-3p, miR-126a-5p, miR-126b-5p, miR-22a-5p, miR-16c-5p, miR-20a-5p, miR-126b-3p, miR-107a-3p, miR-93, miR-2189, miR-202–5p, miR-221–3p, miR-125a, miR-125b-5p, miR-126a-3p, and miR-30c-5p) in comparison to non-transgenic zebrafish. Some of the dysregulated miRNAs were previously reported to be related to abnormalities in sperm quality and reduced reproduction ability in other species. In this study, an average of 134 differentially expressed miRNAs-targeted genes were predicted using the in silico approach. Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analysis demonstrated that the genes of affected pathways were primarily related to spermatogenesis, sperm motility, and cell apoptosis. Our results suggested that excess GH caused a detrimental effect on sperm microRNAome, consequently reducing the sperm quality and reproductive potential of zebrafish males.

S100A4 promotes the progression of lipopolysaccharide-induced acute epididymitis in mice†

S100A4 has been suggested to be a critical regulator of tumor metastasis and is implicated in the progression of inflammation. The aim of this study is to investigate the expression and possible role of S100A4 in epididymitis. Using a mouse model of epididymitis induced by the injection of lipopolysaccharide (LPS) in the deferent duct, we found that LPS administration induced an upregulation of S100a4 transcription (P < 0.05) and a recruitment of S100A4 positive cells in the epididymal interstitium of wild type (WT) mice. Co-immunofluorescence showed that S100A4 was mainly expressed by granulocytes, CD4 lymphocytes, and macrophages. Deficiency of S100A4 reduced epididymal pathological reaction and the mRNA levels of the pro-inflammatory cytokines IL-1β and TNF-α (P < 0.01), suggesting that S100A4 promotes the progression of epididymitis. Furthermore, S100A4 deficiency alleviated the decline of sperm motility and rectified the abnormal expression of sperm membrane protein AMAD3, which suggested that in the progression of epididymitis, S100A4 aggravates the damage to sperm vitality. In addition, both Ki-67 marked cell proliferation and transferase-mediated dUTP-biotin nick end labeling detected cell apoptosis were reduced in S100a4-/- mice compared with WT mice after LPS treatment, indicating that S100A4 promotes both cell proliferation and cell apoptosis in epididymitis. Overall, these results demonstrate that S100A4 promotes the progression of LPS-induced epididymitis and facilitates a decline in sperm vitality, and its function may be related to the process of cell proliferation and apoptosis during inflammation.

The motor domain of testis-enriched kinesin KIF9 is essential for its localization in the mouse flagellum

Kinesin is a molecular motor that moves along microtubules. Testis-enriched kinesin KIF9 (Kinesin family member 9) is localized in the mouse sperm flagellum and is important for normal sperm motility and male fertility; however, it is unclear if the motor domain of KIF9 is involved in these processes. In this study, we substituted threonine of the ATP binding motif in the KIF9 motor domain to asparagine (T100N) in mice using the CRISPR/Cas9 system, which is known to impair kinesin motor activity. T100N mutant mice exhibit reduced sperm motility and male fertility consistent with Kif9 knockout mice. Further, KIF9 was depleted in the spermatozoa of T100N mutant mice although the amounts of KIF9 were comparable between wild-type and T100N mutant testes. These results indicate that the motor domain of KIF9 is essential for its localization in the sperm flagellum.

Aurora a kinase (AURKA) is required for male germline maintenance and regulates sperm motility in the mouse

Aurora A kinase (AURKA) is an important regulator of cell division and is required for assembly of the mitotic spindle. We recently reported the unusual finding that this mitotic kinase is also found on the sperm flagellum. To determine its requirement in spermatogenesis, we generated conditional knockout animals with deletion of the Aurka gene in either spermatogonia or spermatocytes to assess its role in mitotic and postmitotic cells, respectively. Deletion of Aurka in spermatogonia resulted in disappearance of all developing germ cells in the testis, as expected given its vital role in mitotic cell division. Deletion of Aurka in spermatocytes reduced testis size, sperm count, and fertility, indicating disruption of meiosis or an effect on spermiogenesis in developing mice. Interestingly, deletion of Aurka in spermatocytes increased apoptosis in spermatocytes along with an increase in the percentage of sperm with abnormal morphology. Despite the increase in abnormal sperm, sperm from spermatocyte Aurka knockout mice displayed increased progressive motility. In addition, sperm lysate prepared from Aurka knockout animals had decreased protein phosphatase 1 (PP1) activity. Together, our results show that AURKA plays multiple roles in spermatogenesis, from mitotic divisions of spermatogonia to sperm morphology and motility.

Sperm production and quality in European eel (Anguilla anguilla) in relation to hormonal treatment

Aquaculture production relies on controlled management of gametogenesis, especially in species where assisted reproduction is needed for obtaining gametes in captivity. The present study used human chorionic gonadotropin (hCG) treatments to induce and sustain spermatogenesis in European eel (Anguilla anguilla). The aim was to evaluate effects of strip-spawning timing (12 vs. 24 hr) after weekly administration of hCG and the necessity of a primer dose (in addition to weekly hormonal treatment) prior to strip spawning (primer vs. no-primer) on sperm quality parameters. Sperm parameters included milt production (weight), density and sperm kinematics at Week 9, 11 and 13 after onset of treatment. Spermiation commenced in 11.5% of males in Week 5 and by Week 9, and all males produced milt. Male weight, milt production, sperm density and spermatocrit did not differ among hormonal treatments during the experimental period. Overall, male weight decreased from 106.3 to 93.0 g, milt weight increased from 3.5 to 5.4 g, sperm density counts decreased from 11.7 × 10⁹ to 10.5 × 10⁹  cells/ml, and spermatocrit decreased from 46.5% to 40.5%. Furthermore, spermatocrit was positively related to haemocytometer counts (R²  = .86, p < .001), providing a reliable indicator of sperm density. Differences in sperm kinematics were observed depending on strip-spawning timing after hormonal injection (12 vs. 24 hr) but with no consistent pattern. These sperm quality parameters also did not consistently differ between the no-primer and primer treatments. Considering that each male may be stripped 4-5 times over the 2-3 months spawning season, omitting the primer would reduce animal handling, material costs and labour intensity, while sustaining high-quality sperm production.

Comparison of 3- and 6-Month Outcomes of Combined Oral L-Carnitine Fumarate and Acetyl-L-Carnitine Therapy, Included in an Antioxidant Formulation, in Patients with Idiopathic Infertility

The male factor is responsible for infertility in about 35-40% of all cases. Idiopathic oligo- and/or astheno- and/or therato-zoospermia is one of the most common male fertility disorders and remains a significant therapeutic challenge. The primary cause of idiopathic male infertility remains unknown but seems to be associated with oxidative stress. Objective: The use of antioxidative formulation to improve qualitative and quantitative deficiencies in the male gametes.In total, 78 subjects were treated with a combination of 1,725 mg L-carnitine fumarate, 500 mg acetyl-L-carnitine, 90 mg vitamin C, 20 mg coenzyme Q10, 10 mg zinc, 200 µg folic acid, 50 µg selenium, and 1.5 µg vitamin B12 (Proxeed® Plus, Sigma-Tau, Italy) for 6 months; the preparation was taken twice daily from the time idiopathic infertility was diagnosed. Basic seminal parameters were evaluated by a European Society of Human Reproduction and Embryology (ESHRE) -certified embryologist following the fifth edition of the World Health Organisation (2010) guidelines at three time points: at baseline and 3 and 6 months of treatment.Improvements in semen parameters (differing in terms of dynamics) were evident at 3 months and gradually improved over the 6 months of treatment. Each parameter: sperm concentration, total sperm count, sperm total and progressive motility improved significantly after treatment except for the percentage of sperm of abnormal morphology and ejaculate volume.Proxeed Plus was effective for patients with idiopathic infertility; however, a long treatment period is needed to achieve optimal results.

Does the Rainbow Trout Ovarian Fluid Promote the Spermatozoon on Its Way to the Egg?

The fertilization of freshwater fish occurs in an environment that may negatively affect the gametes; therefore, the specific mechanisms triggering the encounters of gametes would be highly expedient. The egg and ovarian fluid are likely the major sources of these triggers, which we confirmed here for rainbow trout (Oncorhynchus mykiss). The ovarian fluid affected significantly spermatozoa performance: it supported high velocity for a longer period and changed the motility pattern from tumbling in water to straightforward moving in the ovarian fluid. Rainbow trout ovarian fluid induced a trapping chemotaxis-like effect on activated male gametes, and this effect depended on the properties of the activating medium. The interaction of the spermatozoa with the attracting agents was accompanied by the "turn-and-run" behavior involving asymmetric flagellar beating and Ca²⁺ concentration bursts in the bent flagellum segment, which are characteristic of the chemotactic response. Ovarian fluid created the optimal environment for rainbow trout spermatozoa performance, and the individual peculiarities of the egg (ovarian fluid)-sperm interaction reflect the specific features of the spawning process in this species.

Ultra-acute exposure to cadmium does not impair whitefish sperm motility

Cadmium (Cd) exposure can impair the traits of aquatic animals associated with reproduction. In natural lakes Cd is typically detected at concentrations below 0.001 mg l^-1 . The authors investigated the impact of ultra-acute Cd exposure on sperm motility in European whitefish (Coregonus lavaretus). They activated sperm with water containing various nominal concentrations of Cd and recorded sperm motility parameters. Only the highest Cd concentration (500 mg l^-1 ) was associated with decreased sperm swimming velocity and increases in both the percentage of static cells and curvature of the sperm swimming trajectory. The results indicate that environmentally realistic concentrations of Cd during the sperm motility activation are not critically harmful to male C. lavaretus fertilization potential.

Semen parameters in men recovered from COVID-19

The novel coronavirus disease (COVID-19) pandemic is emerging as a global health threat and shows a higher risk for men than women. Thus far, the studies on andrological consequences of COVID-19 are limited. To ascertain the consequences of COVID-19 on sperm parameters after recovery, we recruited 41 reproductive-aged male patients who had recovered from COVID-19, and analyzed their semen parameters and serum sex hormones at a median time of 56 days after hospital discharge. For longitudinal analysis, a second sampling was obtained from 22 of the 41 patients after a median time interval of 29 days from first sampling. Compared with controls who had not suffered from COVID-19, the total sperm count, sperm concentration, and percentages of motile and progressively motile spermatozoa in the patients were significantly lower at first sampling, while sperm vitality and morphology were not affected. The total sperm count, sperm concentration, and number of motile spermatozoa per ejaculate were significantly increased and the percentage of morphologically abnormal sperm was reduced at the second sampling compared with those at first in the 22 patients examined. Though there were higher prolactin and lower progesterone levels in patients at first sampling than those in controls, no significant alterations were detected for any sex hormones examined over time following COVID-19 recovery in the 22 patients. Although it should be interpreted carefully, these findings indicate an adverse but potentially reversible consequence of COVID-19 on sperm quality.

Soluble adenylyl cyclase inhibition prevents human sperm functions essential for fertilization

Soluble adenylyl cyclase (sAC: ADCY10) has been genetically confirmed to be essential for male fertility in mice and humans. In mice, ex vivo studies of dormant, caudal epididymal sperm demonstrated that sAC is required for initiating capacitation and activating motility. We now use an improved sAC inhibitor, TDI-10229, for a comprehensive analysis of sAC function in mouse and human sperm. In contrast to caudal epididymal mouse sperm, human sperm are collected post-ejaculation, after sAC activity has already been stimulated. In addition to preventing the capacitation-induced stimulation of sAC and protein kinase A activities, tyrosine phosphorylation, alkalinization, beat frequency and acrosome reaction in dormant mouse sperm, sAC inhibitors interrupt each of these capacitation-induced changes in ejaculated human sperm. Furthermore, we show for the first time that sAC is required during acrosomal exocytosis in mouse and human sperm. These data define sAC inhibitors as candidates for non-hormonal, on-demand contraceptives suitable for delivery via intravaginal devices in women.

Apical Sperm Hook Morphology Is Linked to Sperm Swimming Performance and Sperm Aggregation in Peromyscus Mice

Mammals exhibit a tremendous amount of variation in sperm morphology and despite the acknowledgement of sperm structural diversity across taxa, its functional significance remains poorly understood. Of particular interest is the sperm of rodents. While most Eutherian mammal spermatozoa are relatively simple cells with round or paddle-shaped heads, rodent sperm are often more complex and, in many species, display a striking apical hook. The function of the sperm hook remains largely unknown, but it has been hypothesized to have evolved as an adaptation to inter-male sperm competition and thus has been implicated in increased swimming efficiency or in the formation of collective sperm movements. Here we empirically test these hypotheses within a single lineage of Peromyscus rodents, in which closely related species naturally vary in their mating systems, sperm head shapes, and propensity to form sperm aggregates of varying sizes. We performed sperm morphological analyses as well as in vitro analyses of sperm aggregation and motility to examine whether the sperm hook (i) morphologically varies across these species and (ii) associates with sperm competition, aggregation, or motility. We demonstrate inter-specific variation in the sperm hook and then show that hook width negatively associates with sperm aggregation and sperm swimming speed, signifying that larger hooks may be a hindrance to sperm movement within this group of mice. Finally, we confirmed that the sperm hook hinders motility within a subset of Peromyscus leucopus mice that spontaneously produced sperm with no or highly abnormal hooks. Taken together, our findings suggest that any adaptive value of the sperm hook is likely associated with a function other than inter-male sperm competition, such as interaction with ova or cumulous cells during fertilization, or migration through the complex female reproductive tract.

SPATA33 localizes calcineurin to the mitochondria and regulates sperm motility in mice

Calcineurin is a target of immunosuppressive drugs such as cyclosporine A and tacrolimus. In the immune system, calcineurin interacts with NFAT via the PxIxIT motif to activate T cells. In contrast, little is known about the proteins that interact with a testis-enriched calcineurin that is essential for sperm motility and male fertility. Here, we discovered that calcineurin interacts with SPATA33 via a PQIIIT sequence in the testis. Further analyses reveal that SPATA33 plays critical roles in sperm motility and male fertility. Our finding sheds new light on the molecular mechanisms of sperm motility regulation and the etiology of human male fertility. Furthermore, it may help us not only understand reproductive toxicities but also develop nonhormonal male contraceptives.

Calcineurin is a calcium-dependent phosphatase that plays roles in a variety of biological processes including immune responses. In spermatozoa, there is a testis-enriched calcineurin composed of PPP3CC and PPP3R2 (sperm calcineurin) that is essential for sperm motility and male fertility. Because sperm calcineurin has been proposed as a target for reversible male contraceptives, identifying proteins that interact with sperm calcineurin widens the choice for developing specific inhibitors. Here, by screening the calcineurin-interacting PxIxIT consensus motif in silico and analyzing the function of candidate proteins through the generation of gene-modified mice, we discovered that SPATA33 interacts with sperm calcineurin via a PQIIIT sequence. Spata33 knockout mice exhibit reduced sperm motility because of an inflexible midpiece, leading to impaired male fertility, which phenocopies Ppp3cc and Ppp3r2 knockout mice. Further analysis reveals that sperm calcineurin disappears from the mitochondria in the Spata33 knockout testis. In addition, immunoprecipitation analysis indicates that sperm calcineurin interacts with not only SPATA33 but also the mitochondrial protein VDAC2. These results indicate that SPATA33 localizes calcineurin to the mitochondria and regulates sperm motility.

Elevated seminal protein carbonyl concentration is correlated with asthenozoospermia and affects adversely the laboratory intracytoplasmic sperm injection (ICSI) outcomes

Elevated concentrations of reactive oxygen species (ROS) in the semen can lead to oxidative protein damage as they react with the amino acids' side chains in the protein, leading to the generation of carbonyl groups. This study aimed to investigate the effect of protein carbonyl (PC) concentration on sperm motility and the laboratory intracytoplasmic sperm injection (ICSI) outcomes. A total of 150 couples from the ICSI cycle were enrolled in this study and were divided into three groups (G) according to the PC concentration as following, G1 included samples with PC concentrations <0.65 nmol/mg, G2 included samples with 0.65≤PC≤2.23 nmol/mg and G3 included samples with PC>2.23 (nmol/mg). PC concentrations were measured in all semen samples, and the laboratory ICSI outcomes were evaluated for all injected oocytes. The Kruskal-Wallis p-values for the differences in the medians of sperm motility, fertilisation rate, embryo cleavage score and embryo quality score were <0.05. Furthermore, Dunn's post hoc test showed a significant difference between all groups, p-values <0.05, except for the medians of embryo quality score between G2 and G3. In conclusion, our results showed that sperm motility and laboratory ICSI outcomes are affected negatively by higher concentrations of PC in the semen.

ZDHHC19 Is Dispensable for Spermatogenesis, but Is Essential for Sperm Functions in Mice

Spermatogenesis is a complicated process involving mitotically proliferating spermatogonial cells, meiotically dividing spermatocytes, and spermatid going through maturation into spermatozoa. The post-translational modifications of proteins play important roles in this biological process. S-palmitoylation is one type of protein modifications catalyzed by zinc finger Asp-His-His-Cys (ZDHHC)-family palmitoyl S-acyltransferases. There are 23 mammalian ZDHHCs that have been identified in mouse. Among them, Zdhhc19 is highly expressed in adult testis. However, the in vivo function of Zdhhc19 in mouse spermatogenesis and fertility remains unknown. In this study, we knocked out the Zdhhc19 gene by generating a 2609 bp deletion from exon 3 to exon 6 in mice. No differences were found in testis morphology and testis/body weight ratios upon Zdhhc19 deletion. Spermatogenesis was not disrupted in Zdhhc19 knockout mice, in which properly developed TRA98+ germ cells, SYCP3+ spermatocytes, and TNP1+ spermatids/spermatozoa were detected in seminiferous tubules. Nevertheless, Zdhhc19 knockout mice were male infertile. Zdhhc19 deficient spermatozoa exhibited multiple defects including abnormal morphology of sperm tails and heads, decreased motility, and disturbed acrosome reaction. All of these led to the inability of Zdhhc19 mutant sperm to fertilize oocytes in IVF assays. Taken together, our results support the fact that Zdhhc19 is a testis enriched gene dispensable for spermatogenesis, but is essential for sperm functions in mice.

Differences of Extracellular Cues and Ca2+ Permeable Channels in the Signaling Pathways for Inducing Amphibian Sperm Motility

Low osmolality of freshwater and/or sperm motility-initiating substance (SMIS) induce amphibian sperm motility through increases in intracellular Ca²⁺. In the internally fertilizing newt Cynops pyrrhogaster, the sperm motility-initiating substance engages T type voltage-dependent Ca² + channels and N-methyl D-aspartate-type glutamate receptors to initiate sperm motility and L type voltage-dependent Ca²⁺ channels to enhance motility. In the present study, differences in the usages of SMIS and Ca²⁺ permeable channels for sperm motility regulation were examined in amphibians that undergo different reproductive modes. Proteins of 14-17 kDa were detected by antibody against the active site peptide of SMIS in the oviduct secretion of internal fertilizers (C. pyrrhogaster, Cynops ensicauda, and Ambystoma mexicanum) and arboreal fertilizers (Rhacophorus arboreus and Rhacophorus schlegelii), but not in Buergeria japonica, an external fertilizer in freshwater. In the pharmacological study, a blocker of some transient receptor potential channels (RN1734) additionally suppressed enhancement of sperm motility in C. pyrrhogaster. In R. schlegelii, blockers of four types of channels differently suppressed sperm motility induced by low osmolality with or without the active site peptide of SMIS. Notably, blockers of L type voltage-dependent Ca²⁺ channels (nifedipine) and N-methyl D-aspartate-type glutamate receptors (MK801) suppressed sperm motility in the presence and the absence of the peptide, respectively. Low osmolality-induced sperm motility was suppressed by RN1734 and MK801 in B. japonica, but not in Xenopus laevis. These results reveal complex differences in the signaling pathways for inducing sperm motility that may be partly related to reproductive modes in amphibians.

Dependence of sperm structural and functional integrity on testicular calcineurin isoform PPP3R2 expression

After leaving the testis, mammalian sperm undergo a sequential maturation process in the epididymis followed by capacitation during their movement through the female reproductive tract. These phenotypic changes are associated with modification of protein phosphorylation and membrane remodeling, which is requisite for sperm to acquire forward motility and induce fertilization. However, the molecular mechanisms underlying sperm maturation and capacitation are still not fully understood. Herein, we show that PPP3R2, a testis-specific regulatory subunit of protein phosphatase 3 (an isoform of calcineurin in the testis), is essential for sperm maturation and capacitation. Knockout of Ppp3r2 in mice leads to male sterility due to sperm motility impairment and morphological defects. One very noteworthy change includes increases in sperm membrane stiffness. Moreover, PPP3R2 regulates sperm maturation and capacitation via (i) modulation of membrane diffusion barrier function at the annulus and (ii) facilitation of cholesterol efflux during sperm capacitation. Taken together, PPP3R2 plays a critical role in modulating cholesterol efflux and mediating the dynamic control of membrane remodeling during sperm maturation and capacitation.

Semen parameter thresholds and time-to-conception in subfertile couples: how high is high enough?

STUDY QUESTION

What thresholds for total sperm count, sperm concentration, progressive motility, and total progressive motile sperm count (TPMC) are associated with earlier time-to-conception in couples undergoing fertility evaluation?

SUMMARY ANSWER

Values well above the World Health Organization (WHO) references for total sperm count, concentration, and progressive motility, and values up to 100 million for TPMC were consistently associated with earlier time-to-conception and higher conception rates.

WHAT IS KNOWN ALREADY

Although individual semen parameters are generally not able to distinguish between fertile and infertile men, they can provide clinically useful information on time-to-pregnancy for counseling patients seeking fertility treatment. Compared to the conventional semen parameters, TPMC might be a better index for evaluating the severity of male infertility.

STUDY DESIGN, SIZE, DURATION

We used data from a longitudinal cohort study on subfertile men from 2002 to 2017 and included 6061 men with initial semen analysis (SA) in the study.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Men from subfertile couples who underwent a SA within the study period were included, and 5-year follow-up data were collected to capture conception data. Couples were further categorized into two subgroups: natural conception (n = 5126), after separating those who achieved conception using ART or IUI; natural conception without major female factor (n = 3753), after separating those with severe female factor infertility diagnoses. TPMC was calculated by multiplying the semen volume (ml) by sperm concentration (million/ml) and the percentage of progressively motile sperm (%). Cox proportional hazard models were used to report hazard ratios (HRs) with 95% CIs before and after adjusting for male age, the number of previous children before the first SA, and income. Using the regression tree method, we calculated thresholds for total sperm count, sperm concentration, progressive motility, and TPMC to best differentiate those who were more likely to conceive within 5 years after first SA from those less likely to conceive. We also plotted continuous values of semen parameters in predicting 5-year conception rates and time-to-conception.

MAIN RESULTS AND THE ROLE OF CHANCE

Overall, the median time to conception was 22 months (95% CI: 21-23). A total of 3957 (65%) couples were known to have achieved conception within 5 years of the first SA. These patients were younger and had higher values of sperm concentration, progressive motility, and TPMC. In the overall cohort, a TPMC of 50 million best differentiated men who were more likely to father a child within 5 years. Partners of men with TPMC ≥50 million had a 45% greater chance of conception within 5 years in the adjusted model (HR: 1.45; 95% CI: 1.34-1.58) and achieved pregnancy earlier compared to those men with TPMC < 50 million (median 19 months (95% CI: 18-20) versus 36 months (95% CI: 32-41)). Similar results were observed in the natural conception cohort. For the natural conception cohort without major female factor, the TPMC cut-off was 20 million. In the visual assessment of the graphs for the continuous semen parameter values, 5-year conception rates and time-to-conception consistently plateaued at higher values of sperm concentration, total sperm count, progressive motility, and TPMC compared to the WHO reference levels and our calculated thresholds. For TPMC, values up to 100-150 million were still associated with a better conception rate and time-to-conception in the visual assessment of the curves.

LIMITATIONS, REASONS FOR CAUTION

There was limited information on female partners and potential for inaccuracies in capturing less severe female infertility diagnoses. Also we lacked details on assisted pregnancies achieved outside of our healthcare network (with possible miscoding as 'natural conception' in our cohort). We only used the initial SA and sperm morphology, another potentially important parameter, was not included in the analyses. We had no information on continuity of pregnancy attempts/intention, which could affect the time-to-conception data. Finally, most couples had been attempting conception for >12 months prior to initiating fertility treatment, so it is likely that we are underestimating time to conception. Importantly, our data might lack the generalizability to other populations.

WIDER IMPLICATIONS OF THE FINDINGS

Our results suggest that a TPMC threshold of 50 million sperm provided the best predictive power to estimate earlier time-to-conception in couples evaluated for male factor infertility. Higher values of sperm count, concentration and progressive motility beyond the WHO references were still associated with better conception rates and time-to-conception. This provides an opportunity to optimize semen parameters in those with semen values that are low but not abnormal according to the WHO reference values. These data can be used to better inform patients regarding their chances of conception per year when SA results are used for patient counseling.

STUDY FUNDING/COMPETING INTEREST(S)

None.

TRIAL REGISTRATION NUMBER

N/A.

Bioenergetic Pathways in the Sperm of an Under-Ice Spawning Fish, Burbot (Lota lota): The Role of Mitochondrial Respiration in a Varying Thermal Environment

Regarding the sperm of cold-water fish, the contributions of different bioenergetic pathways, including mitochondrial respiration, to energy production at the spawning temperature and its adaptation at the maximum critical temperature (CTmax) are unclear. The roles of glycolysis, fatty acid oxidation, oxidative phosphorylation (OXPHOS) at 4 °C, and OXPHOS at 15 °C for energy production in burbot (Lota lota) spermatozoa were studied by motility and the oxygen consumption rate (OCR) (with and without pathway inhibitors and the OXPHOS uncoupler). At both temperatures, the effects of the inhibitors and the uncoupler on the motility duration, curvilinear velocity, and track linearity were insignificant; in addition, the OCRs in activation and non-activation media differed insignificantly and were not enhanced after uncoupler treatment. After inhibitor treatment in both media, OXPHOS was insignificantly different at the 2, 30, and 60 s time points at 4 °C but was reduced significantly at the 30 and 60 s time points after treatment with sodium azide at 15 °C. In conclusion, for burbot sperm at both the spawning temperature and the CTmax, the energy synthesized via OXPHOS during motility was insufficient. Therefore, the majority of the energy required to sustain motility was derived from pre-accumulated energy produced and stored during the quiescent state of the spermatozoa.

Sperm adaptation in relation to salinity in three goby species

In externally fertilizing species, the gametes of both males and females are exposed to the influences of the environment into which they are released. Sperm are sensitive to abiotic factors such as salinity, but they are also affected by biotic factors such as sperm competition. In this study, the authors compared the performance of sperm of three goby species, the painted goby, Pomatoschistus pictus, the two-spotted goby, Pomatoschistus flavescens, and the sand goby, Pomatoschistus minutus. These species differ in their distributions, with painted goby having the narrowest salinity range and sand goby the widest. Moreover, data from paternity show that the two-spotted goby experiences the least sperm competition, whereas in the sand goby sperm competition is ubiquitous. The authors took sperm samples from dissected males and exposed them to high salinity water (31 PSU) representing the North Sea and low salinity water (6 PSU) representing the brackish Baltic Sea Proper. They then used computer-assisted sperm analysis to measure the proportion of motile sperm and sperm swimming speed 10 min and 20 h after sperm activation. The authors found that sperm performance depended on salinity, but there seemed to be no relationship to the species' geographical distribution in relation to salinity range. The species differed in the proportion of motile sperm, but there was no significant decrease in sperm motility during 20 h. The sand goby was the only species with motile sperm after 72 h.

CRISP2, CATSPER1 and PATE1 Expression in Human Asthenozoospermic Semen

The etiology of human asthenozoospermia is multifactorial. The need to unveil molecular mechanisms underlying this state of infertility is, thus, impelling. Circular RNAs (circRNAs) are involved in microRNA (miRNA) inhibition by a sponge activity to protect mRNA targets. All together they form the competitive endogenous RNA network (ceRNET). Recently, we have identified differentially expressed circRNAs (DE-circRNAs) in normozoospermic and asthenozoospermic patients, associated with high-quality (A-spermatozoa) and low-quality (B-spermatozoa) sperm. Here, we carried out a differential analysis of CRISP2, CATSPER1 and PATE1 mRNA expression in good quality (A-spermatozoa) and low quality (B-spermatozoa) sperm fractions collected from both normozoospermic volunteers and asthenozoospermic patients. These sperm fractions are usually separated on the basis of morphology and motility parameters by a density gradient centrifugation. B-spermatozoa showed low levels of mRNAs. Thus, we identified the possible ceRNET responsible for regulating their expression by focusing on circTRIM2, circEPS15 and circRERE. With the idea that motility perturbations could be rooted in quantitative changes of transcripts in sperm, we evaluated circRNA and mRNA modulation in A-spermatozoa and B-spermatozoa after an oral amino acid supplementation known to improve sperm motility. The profiles of CRISP2, CATSPER1 and PATE1 proteins in the same fractions of sperm well matched with the transcript levels. Our data may strengthen the role of circRNAs in asthenozoospermia and shed light on the molecular pathways linked to sperm motility regulation.

Mitochondria Content and Activity Are Crucial Parameters for Bull Sperm Quality Evaluation

Standard sperm evaluation parameters do not enable predicting their ability to survive cryopreservation. Mitochondria are highly prone to suffer injuries during freezing, and any abnormalities in their morphology or function are reflected by a decline of sperm quality. Our work focused on describing a link between the number and the activity of mitochondria, with an aim to validate its applicability as a biomarker of bovine sperm quality. Cryopreserved sperm collected from bulls with high (group 1) and low (group 2) semen quality was separated by swim up. The spermatozoa of group 1 overall retained more mitochondria (MitoTrackerGreen) and mtDNA copies, irrespective of the fraction. Regardless of the initial ejaculate quality, the motile sperm contained significantly more mitochondria and mtDNA copies. The same trend was observed for mitochondrial membrane potential (ΔΨm, JC-1), where motile sperm displayed high ΔΨm. These results stay in agreement with transcript-level evaluation (real-time polymerase chain reaction, PCR) of antioxidant enzymes (PRDX1, SOD1, GSS), which protect cells from the reactive oxygen species. An overall higher level of glutathione synthetase (GSS) mRNA was noted in group 1 bulls, suggesting higher ability to counteract free radicals. No differences were noted between basal oxygen consumption rate (OCR) (Seahorse XF Agilent) and ATP-linked respiration for group 1 and 2 bulls. In conclusion, mitochondrial content and activity may be used as reliable markers for bovine sperm quality evaluation.

Associations of serum estradiol level, serum estrogen receptor-alpha level, and estrogen receptor-alpha polymorphism with male infertility: A retrospective study

Estradiol regulates spermatogenesis partly via estrogen receptor-alpha (ESRα). This study aimed to analyze the associations of serum estradiol level, serum ESRα level, and ESRα gene polymorphisms with sperm quality.This retrospective study included infertile men attending the Reproductive Center, Affiliated Hospital of Youjiang Medical University for Nationalities, and a control group without a history of fertility (October, 2016 to March, 2017). Data regarding sperm quality, serum levels of estradiol and ESRα, and rs2234693C/T genotype were extracted from the medical records. Pearson/Spearman correlations (as appropriate) between estradiol level, ESRα level, and sperm quality parameters were evaluated.The analysis included 215 men with infertility and 83 healthy controls. The infertile group had higher serum levels of estradiol (147.57 ± 35.3 vs 129.62 ± 49.11 pg/mL, P < .05) and ESRα (3.02 ± 2.62 vs 1.33 ± 0.56 pg/mL, P < .05) than the control group. For the infertile group, serum estradiol level was negatively correlated with sperm concentration, percentage of progressively motile sperm, and percentage of sperm with normal morphology (r = 0.309, 0.211, and 0.246, respectively; all P < .05). Serum estradiol and ESRα levels were lower in infertile men with normozoospermia than in those with azoospermia, oligozoospermia, mild azoospermia, or malformed spermatozoa (all P < .05). Sperm concentration, percentage of progressively motile sperm, serum ESRα level, and serum estradiol level did not differ significantly among the rs2234693 CC, CT, and TT genotypes.Elevated serum levels of estradiol and possibly ESRα might have a negative impact on sperm quality and fertility, whereas single nucleotide polymorphisms at rs2234693 of the ESRα gene had little or no effect.

Protective effects of selenium on Bisphenol A-induced oxidative stress in mouse testicular mitochondria and sperm motility

OBJECTIVE

This study aimed to explore the impact of selenium (SE) on Bisphenol-A (BPA)-exposed sperm and isolated testicular mitochondria of mice.

METHODS

Mouse sperm and isolated mitochondria were exposed to BPA (0.8 mM) and different concentrations of SE (50, 100, and 200 μM) for four hours. The viability of sperm and isolated mitochondria as well as the mitochondrial membrane potential (MMP) were evaluated. SOD (superoxide dismutase), GSH (glutathione), MDA (malondialdehyde), and ROS (reactive oxygen species) levels in testicular mitochondria were also examined.

RESULTS

BPA concentration-dependently enhanced ROS and MDA levels in isolated mitochondria, while MMP and acclivity of GSH and SOD significantly reduced. BPA also considerably impaired spermatozoa survival and motility. SE concentration-dependently reduced mitochondrial oxidative stress, MMP, sperm survival, and total sperm motility.

CONCLUSIONS

Our findings collectively suggested that SE concentration-dependently reversed BPA-caused mitochondrial toxicity and reduced sperm motility by suppressing oxidative stress.