Acrosome Reaction Research Articles

P-354 Advanced Paternal Age (APA) amplifies cryopreservation-induced stress in human spermatozoa

Abstract Study question Does paternal age intensify the negative effects of cryopreservation on sperm quality? Summary answer Paternal age exacerbates the adverse impact of cryopreservation on sperm quality. What is known already Despite mounting evidence indicating age-related declines in sperm quality, the impact of APA on male fertility remains unclear. APA raises questions about DNA fragmentation and mitochondrial activity, a robust indicator of sperm functionality. While sperm cryopreservation is extensively employed in fertility preservation and assisted reproductive technology (ART), its potentially detrimental effects on cells compartments, including mitochondria, persist. The mechanisms of APA on sperm susceptibility to cryopreservation-induced cellular damage still need to be addressed. Study design, size, duration This prospective multicentric study, conducted between January and October 2023, comprised 200 men. Only normozoospermic samples were included in the research (n = 81). Then, based on their age, the participants were categorised into two groups: ages ≤35 (non-APA, n = 40) and ages ≥42 (APA, n = 41). The cohorts were stratified into distinct subgroups, encompassing both fresh and frozen/thawed specimens of APA and non-APA sperm, and subjected to evaluations encompassing mitochondrial functionality, acrosomal reaction, DNA fragmentation and Tyrosine phosphorylation. Participants/materials, setting, methods Semen samples were collected after 2-7 days abstinence and analysed according to WHO 2021 guidelines. Acrosomal status was determined using FITC-conjugate PSA. DNA fragmentation was examined with the Halosperm kit. Mitochondrial functionality was gauged using MitoTracker Red CMXRos through the percentage of stained cells and fluorescence intensity and PCR for mitochondrial DNA copy number (mtDNAcn). Tyrosine phosphorylation was assessed through immunofluorescence and Western Blotting. Main results and the role of chance Non-APA group exhibited significantly superior fresh semen characteristics. DNA fragmentation was notably elevated in fresh semen from APA group, reaching 21.7%, compared to 15.4% non-APA individuals. After cryopreservation, the DNA fragmentation index further increased in men over 42 years to 26.7%. Mitochondrial functionality analysis indicated a significant decrease in staining intensity in cryopreserved sperm, notably in the APA group, with mean fluorescence intensity decreasing from 3.35±1.5 to 1.8±0.5. In contrast, the non-APA group experienced a drop from 3.33±1.6 to 2.53±1.6. Additionally, in the APA group, a significant increase in mtDNAcn was observed in both fresh and frozen/thawed sperm compared to the younger counterparts, indicative of poor mitochondrial quality. Cryopreservation negatively impacted acrosome integrity in both age groups, with a significant decrease observed in unreacted acrosomes from 71.5% to 57.7% in the non-APA group and from 75% to 63% in the APA group. Furthermore, exploration of capacitation-like changes, like tyrosine phosphorylation, demonstrated a significant decrease with age and a negative impact of cryopreservation on tyrosine phosphorylation in sperm from young males. Limitations, reasons for caution Main limitations are the small number of examined samples and the inclusion of only normozoospermic patients. Therefore, future investigations are needed to provide a more comprehensive understanding of the impact of paternal age on cryopreservation-induced stress in human spermatozoa. Wider implications of the findings Our research sheds light on the influence of paternal age on sperm cryopreservation, revealing higher vulnerability of mitochondria and elevated DNA fragmentation in APA. These findings should be considered when advising older men on choosing cryopreservation techniques in assisted reproductive treatments. Trial registration number Not applicable

P-091 The Dopamine Transporter (DAT) and it’s role in male fertility- an in vitro investigation

Abstract Study question Does Ritalin (DAT antagonist) and dopamine (DAT agonist), influence human sperm parameters, and do these act via the DAT protein? Summary answer DAT is positively expressed on human sperm membranes with dopamine regulating sperm functions through mechanisms involving DAT whereas Ritalin does not affect sperm parameters. What is known already Spermatozoa exhibit a biphasic dose-response to dopamine: low concentrations enhance key sperm functions such as motility and viability, while high concentrations impair them. This biphasic response suggests the presence of a dopamine transporter (DAT), however its role in human sperm function remains under-investigated. Concerns regarding the unprescribed use of Ritalin, a dopamine reuptake inhibitor, are growing among men of reproductive age, given its potential to mimic dopamine’s negative effects on sperm function. Further research is crucial to elucidate the mechanisms and potential consequences of Ritalin exposure on male fertility. Study design, size, duration Twenty samples were collected and utilized to identify and localize DAT via indirect Immunofluorescence (IF) assays. Thirty samples were collected and sperm were treated at 37 °C to 100 nM, 10 μM, and 1 mM dopamine concentrations for 1, 3 and 6 hours; similarly sperm were exposed to 4 ng/mL, 30 ng/mL, and 100 ng/mL Ritalin concentrations for 1, 2 and 3 hours, whereafter the effects on basic and advanced sperm parameters were investigated. Participants/materials, setting, methods Participants were recruited from the Faculty of Medicine and Health Sciences at Stellenbosch University, Cape Town, South Africa. Male students aged 18-29 years donated a semen sample via masturbation. An indirect IF assay, adapted from Ramírez et al. (2009), was utilized to identify DAT. Computer-Aided Sperm Analysis (CASA) was employed to determine motility parameters. Viability was assessed via a dye-exclusion staining technique and the acrosome reaction was assessed via fluorescent microscopy. Main results and the role of chance Immunofluorescence confirmed the presence of the Dopamine Transporter (DAT) on human sperm, primarily localized in the mid-piece and tail regions. Interestingly, dopamine exhibited a biphasic effect on sperm function. Low doses offered protection, while high doses (1 mM) negatively impacted motility (total and progressive motility) and kinematic parameters (Curvilinear Velocity (VCL) and Average Path Velocity (VAP)) as early as 60 minutes, and significantly decreased viability after 3 hours. Additionally, the high dose prematurely triggered the acrosome reaction. Conversely, Ritalin, even at supraphysiological concentrations (100 ng/mL), showed no significant impact on basic or advanced sperm parameters. This suggests that, unlike high-dose dopamine, Ritalin exposure might not negatively affect sperm function within the tested parameters. This study highlights the complex role of dopamine in sperm function and emphasizes the need for further research to clarify potential consequences of high dopamine exposure or dopaminergic drugs such as Ritalin. Limitations, reasons for caution Ejaculated spermatozoa are transcriptionally and translationally silent, therefore the in vitro nature of this study is a limitation. The physiological relevance needs to be assessed in an in vivo system, additionally the treatments (dopamine plus Ritalin) should be investigated in combination to demonstrate their concurrent existence within a system. Wider implications of the findings These findings suggest a possible regulatory role for DAT inhibitory drugs on sperm parameters and cautions users thereof. Dopamine may be utilized as a physiological regulator of in vivo fertilization and should be further investigated with regards to Assisted Reproductive Techniques (ART’s). Trial registration number not applicable

P-014 Extracellular vesicles (EVs) from female reproductive tracts positively affect sperm capacitation and progressive motility

Abstract Study question Do EVs from human follicular fluid (FF-EVs), cervicovaginal fluid (CVF-EVs), and endometrial stromal cells spent medium (ESCs-EVs) induce sperm capacitation and enhance sperm motility? Summary answer In humans, EVs from different female reproductive tracts actively contribute to sperm maturation by inducing capacitation and enhancing sperm progressive motility. What is known already In the human body, EVs represent crucial players in cell-to-cell communication. EVs presence has been detected also in the female and male reproductive systems, specifically in seminal, follicular, oviductal, endometrial and vaginal fluid, as well as in embryo secretions. Moreover, EVs have been shown to be of pivotal importance in the fertilization process, as they support the maturation of spermatozoa and oocytes, as well as embryos in their development and endometrial implantation. The majority of these studies, though, have been conducted in animal models, underscoring the necessity to replicate analogous investigations also in humans. Study design, size, duration Follicular fluid (FF, n = 8), cervicovaginal fluid (CVF, n = 20) and endometrial tissue (n = 8) samples were collected from women undergoing assisted reproductive technology (ART) cycles at San Raffaele Hospital Fertility Centre (Milan). CVF were collected 2 and 7 days after the LH peak (CVF LH + 2 and CVF LH + 7, respectively). ESCs-EVs were isolated from both decidualized (dESCs-EVs) and not decidualized (eESCs-EVs) endometrial cells. Semen samples (n = 15) were collected from normozoospermic men. Participants/materials, setting, methods EVs were isolated using differential centrifugations and characterized using Transmission Electron Microscopy (TEM), Nanoparticle Tracking Analysis (NTA), and western blotting (WB). EVs capture by spermatozoa was assessed using flow cytometry. EVs impact on sperm progressive motility was evaluated following WHO guidelines. EVs potential to induce sperm capacitation was examined through sperm acrosome reaction (AR) induction using a Ca2+ ionophore, followed by Coomassie blue staining. All experiments were performed using EVs at 50 and 100 μg/mL. Main results and the role of chance Isolated EVs displayed comparable size, with mean diameters ranging from 147,9±11,6 nm to 168,1±6,2 nm (mean ± SEM) and average concentrations from 9,53E+10 ± 8,11E+09 to 2,70E+11 ± 3,49E+10 particles/ml (mean ± SEM). TEM analysis confirmed their round-shaped morphology and structural integrity, while WB confirmed their positivity for EVs markers (Alix, TSG101, CD63, CD9). Spermatozoa efficiency in capturing these fluorescently-labeled EVs, measured as the percentage of fluorescence-positive spermatozoa, reached up to 3,6±1,1% for FF-EVs, 12,1±3,7% for CVF-EVs and 9,4±1,9% for ESCs-EVs (mean ± SEM). Sperm cells co-incubated with any EVs group maintained unaffected vitality. Following a 4-hour incubation with EVs, a rise in the proportion of progressively motile spermatozoa was observed, with percentages of progressively motile spermatozoa ranging from a minimum of 45,4±3,8% for CVF-EVs LH + 7 to a maximum of 52,7±2,7% for dESCs-EVs (mean ± SEM). This increase resulted to be statistically significant (p < 0.05 and p < 0.01, respectively) compared to the untreated (UT) condition, which exhibited 26,2±0,7% of progressively motile sperm cells. Spermatozoa that completed the AR, indicating capacitation, after 4-hour incubation with EVs resulted to be up to 25,8±3,2% for FF-EVs, 35,0±6,6% for CVF-EVs and 26,9±3,0% for ESCs-EVs, compared to an average of 13% in the UT control. Limitations, reasons for caution This study constitutes a pilot investigation characterized by a limited sample size, necessitating larger cohorts to validate results. Wider implications of the findings Studied EVs may exert beneficial effects on capacitation and progressive motility also on asthenozoospermic (AS) men’s spermatozoa. Therefore, they could be used in ART cycles to prime spermatozoa from AS men and increase the percentage of sperm cells displaying progressive motility, potentially favouring fertilization via classical IVF instead of ICSI. Trial registration number not applicable

P-017 DNA fragmentation Index before and after density gradient centrifugation using flow cytometry, its reflection in sperm ultrastructure and its association with clinical outcome

Abstract Study question Is DNA fragmentation Index (DFI) affected by Density Gradient Centrifugation (DGC), reflected in sperm ultrastructure and associated with clinical outcome? Summary answer DFI was not affected by DGC, nor associated with clinical outcome, but it was negatively correlated with sperm concentration/motility and positively correlated with ultrastructural anomalies. What is known already Oxidative stress induces DNA fragmentation during sperm transit through the male genital tract and it is suggested to be the main mechanism causing DNA breaks after ejaculation during in vitro manipulation and sperm selection for injection/insemination. High levels of sperm DNA fragmentation have been linked to lower fertilization rates, poor embryo quality and delayed cleavage. Limited studies, have investigated in detail the effects of DGC on DFI and the reflection in sperm ultrastructure, while the predictive value of DFI on clinical outcome still remains controversial. Study design, size, duration Semen samples were collected on the day of the female partener’s oocyte collection and analysed before and after DGC for standard characteristics by light microscopy, according to World Health Organization (WHO) criteria (n = 120), for DNA Fragmentation by Flow Cytometry and for ultrastructure by Transmission Electron Microscopy (TEM). The predictive value of DFI for clinical outcome was also assessed. Participants/materials, setting, methods Standard semen analysis and DGC using the Sil-Select 40%/ 80 % layers were performed at an IVF Laboratory of an academic Hospital. Sperm DFI before and after DGC was assessed by Flow Cytometry at the Department of Immunology and Histocompatibility of the same academic Hospital. Ultrastructure analysis by TEM was carried out at an academic Histology/Embryology Laboratory following fixation in 3% glutaraldehyde, 1% osmium tetroxide, washes in PBS and staining with 1% aqueous uranyl acetate. Main results and the role of chance DGC did not alter DFI significantly (p = 0.052), but lead to a statistically significant increase in Progressive Motility (p < 0.001). DFI was higher in men with a male factor infertility compared to men without a male factor (p = 0.032) and Oligoasthenoteratospermia (OAT) exhibited the highest DFI levels (36.38% ± 5.36). DFI was negatively correlated with sperm concentration (rho = -0.361, p < 0.01) and sperm motility (rho = -0.301, p < 0.05). No significant association was observed between DFI and clinical outcome, but statistically significant differences were observed both in the age of men (37.54±1.33 vs 42.8±1.27 p = 0.017) and the age of women (35.77±1.25 vs 40.17±0.78 p = 0.007) in the group of patients who achieved a pregmamcy and those that did not. TEM showed that DGC did not lead to an increase in ultrastructural anomalies of spermatozoa, but DFI was positively correlated with ultrastructural anomalies. In teratozoospermic men TEM revealed head, neck and tail defects, including elongated forms, axonemal defects and premature initiation of the acrosome reaction. Limitations, reasons for caution The ultrastructure analysis was not possible to be performed in severely oligospermic samples. Wider implications of the findings This study shows that sperm ultrastructure and DFI are not adversely affected by DGC confirming the safety of the preparation method for sperm selection prior to insemination/injection. Larger-scale studies are needed, to elucidate any potential correlations between DFI and the probability of pregnancy. Trial registration number not applicable

Effect of Glutathione Supplementation in Cryoprotectant Modification on Tyrosine Phosphorylation, Acrosin Expression and Acrosome Reaction of Post-Thawing Spermatozoa Quality

Effect of Glutathione Supplementation in Cryoprotectant Modification on Tyrosine Phosphorylation, Acrosin Expression and Acrosome Reaction of Post-Thawing Spermatozoa Quality

Spermatogenic cell-specific type 1 hexokinase (HK1S) is essential for capacitation-associated increase in tyrosine phosphorylation and male fertility in mice.

Hexokinase (HK) catalyzes the first irreversible rate-limiting step in glycolysis that converts glucose to glucose-6-phosphate. HK1 is ubiquitously expressed in the brain, erythrocytes, and other tissues where glycolysis serves as the major source of ATP production. Spermatogenic cell-specific type 1 hexokinase (HK1S) is expressed in sperm but its physiological role in male mice is still unknown. In this study, we generate Hk1s knockout mice using the CRISPR/Cas9 system to study the gene function in vivo. Hk1s mRNA is exclusively expressed in testes starting from postnatal day 18 and continuing to adulthood. HK1S protein is specifically localized in the outer surface of the sperm fibrous sheath (FS). Depletion of Hk1s leads to infertility in male mice and reduces sperm glycolytic pathway activity, yet they have normal motile parameters and ATP levels. In addition, by using in vitro fertilization (IVF), Hk1s deficient sperms are unable to fertilize cumulus-intact or cumulus-free oocytes, but can normally fertilize zona pellucida-free oocytes. Moreover, Hk1s deficiency impairs sperm migration into the oviduct, reduces acrosome reaction, and prevents capacitation-associated increases in tyrosine phosphorylation, which are probable causes of infertility. Taken together, our results reveal that HK1S plays a critical role in sperm function and male fertility in mice.

Characterization of expression patterns and dynamic relocation of Notch proteins during acrosome reaction of bull spermatozoa

Notch is a conserved cell-signaling pathway involved in spermatogenesis regulation. This study firstly evaluated the presence, localization patterns, acquisition origin and relation to acrosome reaction of Notch proteins in bull sperm. Western Blot analysis detected all Notch proteins in ejaculated bull sperm, and immunostaining described their specific sperm localization. Recovery of sperm from different segments showed that Notch proteins have testicular origin (NOTCH1, NOTCH2, DLL4), are sequentially acquired during sperm maturation along epididymal transit (NOTCH3, DLL3, JAGGED1-2), or post-ejaculation (DLL1, NOTCH4). Testis NOTCH2 is ubiquitously expressed in all germ-cell lines, whereas DLL4 is expressed in round and elongated spermatids during the Golgi, Cap, Acrosome and Maturation phases. In vitro spontaneous and induced sperm acrosome reaction induce consistent sperm regional relocation of NOTCH2, DLL4 and JAGGED1, and these relocation patterns are significantly associated to sperm acrosome status. NOTCH2 and JAGGED1 are relocated from the head apical to the post-equatorial regions, whereas DLL4 is lost along with the acrosome, evidencing that sperm spatial redistribution of NOTCH2 and JAGGED1 is linked to acrosome reaction onset, whereas DLL4 loss is linked to AR completion. Overall, results prompt for a relevant Notch role in bull sperm acrosome testicular development, epididymal maturation and acrosome reaction.

The Role of Tubulin Polymerization-Promoting Protein2 (TPPP2) in Spermatogenesis: A Narrative Review.

Tubulin polymerization-promoting protein2 (TPPP2) is one of the three paralogs of mammalian TPPP proteins. Its possible role in spermatogenesis is described in this narrative review. TPPP2 is expressed specifically in the male reproductive system, mainly in testes and sperm, and also in the epididymis. In testes, TPPP2 is exclusively expressed in elongating spermatids; in the epididymis, it is located in the middle piece of the sperm tail. TPPP2 is involved in spermiogenesis, in steps which are determinative for the formation and morphology of spermatids. The inhibition of TPPP2 decreases sperm motility (the curvilinear velocity of sperms), probably due to influencing mitochondrial energy production since TPPP2 knockout mice possess an impaired mitochondrial structure. There are data on the role of TPPP2 in various mammalian species: human, mouse, swine, and various ruminants; there is a significant homology among TPPP2s from different species. Experiments with Tppp2-/--mice show that the absence of TPPP2 results in decreased sperm count and serious dysfunction of sperm, including decreased motility; however, the in vitro capacitation and acrosome reaction are not influenced. The symptoms show that Tppp2-/--mice may be considered as a model for oligoasthenozoospermia.

Dual role of valosin-containing protein (VCP/p97) in mouse sperm during capacitation.

Valosin-containing protein (VCP; aka p97), a member of the AAA (ATPases Associated with various cellular Activities) family, has been associated with a wide range of cellular functions. While previous evidence has shown its presence in mammalian sperm, our study unveils its function in mouse sperm. Notably, we found that mouse VCP does not undergo tyrosine phosphorylation during capacitation and exhibits distinct localization patterns. In the sperm head, it resides within the equatorial segment and, following acrosomal exocytosis, it is released and cleaved. In the flagellum, VCP is observed in the principal and midpiece. Furthermore, our research highlights a unique role for VCP in the cAMP/PKA pathway during capacitation. Pharmacological inhibition of sperm VCP led to reduced intracellular cAMP levels that resulted in decreased phosphorylation in PKA substrates and tyrosine residues and diminished fertilization competence. Our results show that in mouse sperm, VCP plays a pivotal role in regulating cAMP production, probably by the modulation of soluble adenylyl cyclase activity.

The role of nitric oxide in the development of diseases of the male reproductive system and its potential applications in clinical practice

Nitric oxide (NO), a reactive nitrogen species, is a molecule of high physiological and pathological importance. Physiological mechanisms mediated by NO mainly include angiogenesis, growth, puberty, and senescence. NO has vital roles in normal reproduction, including steroidogenesis, gametogenesis, and the regulation of germ-cell apoptosis. In males, NO is a key player in steroidogenesis, erectile functions, sperm capacitation, and acrosome reaction. Moreover, NO is also a regulator of Sertoli cell-germ cell interaction and maintenance of the blood-testis barrier. In pathological conditions such as infections, increased nitric oxide synthase activities stimulate the excessive synthesis of NO which acts as a proinflammatory mediator inducing oxidative stress, detrimental to reproductive functions in males. Excessive NO synthesis disrupts gonadal functions and induces germ cell apoptosis and oxidative damage to the germ cells. This review elucidates how the differences in NO expression levels account for its beneficial and adverse impacts on male fertility.

A side-by-side comparison of different capacitation media in developing mouse sperm fertilizing ability

To acquire the ability to fertilize the egg, mammalian spermatozoa must undergo a series of changes occurring within the highly synchronized and specialized environment of the female reproductive tract, collectively known as capacitation. In an attempt to replicate this process in vitro, various culture media for mouse sperm were formulated over the past decades, sharing a similar overall composition but differing mainly in ion concentrations and metabolic substrates. The widespread use of the different media to study the mechanisms of capacitation might hinder a comprehensive understanding of this process, as the medium could become a confounding variable in the analysis. In this context, the present side-by-side study compares the influence of four commonly used culture media (FD, HTF and two TYH versions) on mouse sperm capacitation. We evaluated the induction of protein kinase A phosphorylation pathway, motility, hyperactivation and acrosome reaction. Additionally, in vitro fertilization and embryo development were also assessed. By analyzing these outcomes in two mouse colonies with different reproductive performance, our study provides critical insights to improve the global understanding of sperm function. The results obtained highlight the importance of considering variations in medium composition, and their potential implications for the future interpretation of results.

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

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

Variation of sperm quality and circular RNA content in men exposed to environmental contamination with heavy metals in 'Land of Fires', Italy.

Can illegal discharge of toxic waste into the environment induce a new condition of morpho-epigenetic pathozoospermia in normozoospermic young men? Toxic environmental contaminants promote the onset of a new pathozoospermic condition in young normozoospermic men, consisting of morpho-functional defects and a sperm increase of low-quality circular RNA (circRNA) cargo, tightly linked to contaminant bioaccumulation in seminal plasma. Epidemiological findings have reported several reproductive anomalies depending on exposure to contaminants discharged into the environment, such as germ cell apoptosis, steroidogenesis defects, oxidative stress induction, blood-testis barrier dysfunctions, and poor sperm quality onset. In this scenario, a vast geographical area located in Campania, Italy, called the 'Land of Fires', has been associated with an excessive illegal discharge of toxic waste into the environment, negatively impacting human health, including male reproductive functions. Semen samples were obtained from healthy normozoospermic men divided into two experimental groups, consisting of men living in the 'Land of Fires' (LF; n = 80) or not (CTRL; n = 80), with age ranging from 25 to 40 years. The study was carried out following World Health Organization guidelines. Quality parameters of semen from CTRL- and LF-normozoospermic men were evaluated by computer-assisted semen analysis; high-quality spermatozoa from CTRL and LF groups (n = 80 for each experimental group) were obtained using a 80-40% discontinuous centrifugation gradient. Seminal plasma was collected following centrifugation and used for the dosage of chemical elements, dioxins and steroid hormones by liquid chromatography with tandem mass spectrometry. Sperm morpho-functional investigations (cellular morphology, acrosome maturation, IZUMO1 fertility marker analysis, plasma membrane lipid state, oxidative stress) were assessed on the purified high-quality spermatozoa fraction by immunochemistry/immunofluorescence and western blot analyses. Sperm circRNA cargo was evaluated by quantitative RT-PCR, and the physical interaction among circRNAs and fused in sarcoma (FUS) protein was detected using an RNA-binding protein immunoprecipitation assay. Protein immunoprecipitation experiments were carried out to demonstrate FUS/p-300 protein interaction in sperm cells. Lastly, in vitro lead (Pb) treatment of high-quality spermatozoa collected from normozoospermic controls was used to investigate a correlation between Pb accumulation and onset of the morpho-epigenetic pathozoospermic phenotype. Several morphological defects were identified in LF-spermatozoa, including: a significant increase (P < 0.05 versus CTRL) in the percentage of spermatozoa characterized by structural defects in sperm head and tail; and a high percentage (P < 0.01) of peanut agglutinin and IZUMO1 null signal cells. In agreement with these data, abnormal steroid hormone levels in LF seminal plasma suggest a premature acrosome reaction onset in LF-spermatozoa. The abnormal immunofluorescence signals of plasma membrane cholesterol complexes/lipid rafts organization (Filipin III and Flotillin-1) and of oxidative stress markers [3-nitrotyrosine and 3-nitrotyrosine and 4-hydroxy-2-nonenal] observed in LF-spermatozoa and associated with a sperm motility reduction (P < 0.01), demonstrated an affected membrane fluidity, potentially impacting sperm motility. Bioaccumulation of heavy metals and dioxins occurring in LF seminal plasma and a direct correlation between Pb and deregulated circRNAs related to high- and low-sperm quality was also revealed. In molecular terms, we demonstrated that Pb bioaccumulation promoted FUS hyperacetylation via physical interaction with p-300 and, in turn, its shuttling from sperm head to tail, significantly enhancing (P < 0.01 versus CTRL) the endogenous backsplicing of sperm low-quality circRNAs in LF-spermatozoa. Participants were interviewed to better understand their area of origin, their eating habits as well as their lifestyles, however any information incorrectly communicated or voluntarily omitted that could potentially compromise experimental group determination cannot be excluded. A possible association between seminal Pb content and other heavy metals in modulating sperm quality should be explored further. Future investigations will be performed in order to identify potential synergistic or anti-synergistic effects of heavy metals on male reproduction. Our study provides new findings regarding the effects of environmental contaminants on male reproduction, highlighting how a sperm phenotype classified as normozoospermic may potentially not match with a healthy morpho-functional and epigenetic one. Overall, our results improve the knowledge to allow a proper assessment of sperm quality through circRNAs as biomarkers to select spermatozoa with high morpho-epigenetic quality to use for ART. This study was supported by 'Convenzione Azienda Sanitaria Locale (ASL) Caserta, Regione Campania' (ASL CE Prot. N. 1217885/DIR. GE). The authors have no conflict of interest to declare. N/A.

Loss of DIS3L in the initial segment is dispensable for sperm maturation in the epididymis and male fertility

DIS3L, a catalytic exoribonuclease associated with the cytoplasmic exosome complex, degrades cytoplasmic RNAs and is implicated in cancers and certain other diseases in humans. Epididymis plays a pivotal role in the transport, maturation, and storage of sperm required for male fertility. However, it remains unclear whether DIS3L-mediated cytoplasmic RNA degradation plays a role in epididymis biology and functioning. Herein, we fabricated a Dis3l conditional knockout (Dis3l cKO) mouse line in which DIS3L was ablated from the principal cells of the initial segment (IS). Morphological analyses showed that spermatogenesis and IS differentiation occurred normally in Dis3l cKO mice. Additionally, the absence of DIS3L had no dramatic influence on the transcriptome of IS. Moreover, the sperm count, morphology, motility, and acrosome reaction frequency in Dis3l cKO mice were comparable to that of the control, indicating that the Dis3l cKO males had normal fertility. Collectively, our genetic model demonstrates that DIS3L inactivation in the IS is nonessential for sperm maturation and male fertility.

PH Homeodynamics and Male Fertility: A Coordinated Regulation of Acid-Based Balance during Sperm Journey to Fertilization.

pH homeostasis is crucial for spermatogenesis, sperm maturation, sperm physiological function, and fertilization in mammals. HCO3- and H+ are the most significant factors involved in regulating pH homeostasis in the male reproductive system. Multiple pH-regulating transporters and ion channels localize in the testis, epididymis, and spermatozoa, such as HCO3- transporters (solute carrier family 4 and solute carrier family 26 transporters), carbonic anhydrases, and H+-transport channels and enzymes (e.g., Na+-H+ exchangers, monocarboxylate transporters, H+-ATPases, and voltage-gated proton channels). Hormone-mediated signals impose an influence on the production of some HCO3- or H+ transporters, such as NBCe1, SLC4A2, MCT4, etc. Additionally, ion channels including sperm-specific cationic channels for Ca2+ (CatSper) and K+ (SLO3) are directly or indirectly regulated by pH, exerting specific actions on spermatozoa. The slightly alkaline testicular pH is conducive to spermatogenesis, whereas the epididymis's low HCO3- concentration and acidic lumen are favorable for sperm maturation and storage. Spermatozoa pH increases substantially after being fused with seminal fluid to enhance motility. In the female reproductive tract, sperm are subjected to increasing concentrations of HCO3- in the uterine and fallopian tube, causing a rise in the intracellular pH (pHi) of spermatozoa, leading to hyperpolarization of sperm plasma membranes, capacitation, hyperactivation, acrosome reaction, and ultimately fertilization. The physiological regulation initiated by SLC26A3, SLC26A8, NHA1, sNHE, and CFTR localized in sperm is proven for certain to be involved in male fertility. This review intends to present the key factors and characteristics of pHi regulation in the testes, efferent duct, epididymis, seminal fluid, and female reproductive tract, as well as the associated mechanisms during the sperm journey to fertilization, proposing insights into outstanding subjects and future research trends.

Male infertility and perfluoroalkyl and poly-fluoroalkyl substances: evidence for alterations in phosphorylation of proteins and fertility-related functional attributes in bull spermatozoa†.

Perfluoroalkyl and poly-fluoroalkyl substances (PFAS) are pervasive environmental pollutants and potential threats to reproductive health. Epidemiological studies have established an association between PFAS and male infertility, but the underlying mechanisms are unclear. Investigate the effect of perfluorooctane sulfonic acid (PFOS), the most prevalent and representative PFAS, on bull sperm protein phosphorylation and function. We exposed bull sperm to PFOS at 10 (average population exposure) and 100μM (high-exposure scenario), and analyzed global proteomic and phosphoproteomic analysis by TMT labeling and Nano LC-MS/MS. We also measured sperm fertility functions by flow cytometry. PFOS at 10-μM altered sperm proteins linked to spermatogenesis and chromatin condensation, while at 100μM, PFOS affected proteins associated with motility and fertility. We detected 299 phosphopeptides from 116 proteins, with 45 exhibiting differential expression between control and PFOS groups. PFOS dysregulated phosphorylation of key proteins (ACRBP, PRKAR2A, RAB2B, SPAG8, TUBB4B, ZPBP, and C2CD6) involved in sperm capacitation, acrosome reaction, sperm-egg interaction, and fertilization. PFOS also affected phosphorylation of other proteins (AQP7, HSBP9, IL4I1, PRKAR1A, and CCT8L2) related to sperm stress resistance and cryotolerance. Notably, four proteins (PRM1, ACRBP, TSSK1B, and CFAP45) exhibited differential regulation at both proteomic and phosphoproteomic levels. Flow cytometric analysis confirmed that PFOS increased protein phosphorylation in sperm and also decreased sperm motility, viability, calcium, and mitochondrial membrane potential and increased mitochondrial ROS in a dose-dependent manner. This study demonstrates that PFOS exposure negatively affects phosphorylation of proteins vital for bull sperm function and fertilization.

Influence of extracellular ATP on mammalian sperm physiology.

In addition to its central role in cellular metabolism, adenosine 5'-triphosphate (ATP) is an important extracellular signalling molecule involved in various physiological processes. In reproduction, extracellular ATP participates in both autocrine and paracrine paths regulating gametogenesis, gamete maturation and fertilisation. This review focusses on how extracellular ATP modulates sperm physiology with emphasis on the mammalian acrosome reaction. The presence of extracellular ATP in the reproductive tract is primarily determined by the ion channels and transporters that influence its movement within the cells comprising the tract. The main targets of extracellular ATP in spermatozoa are its own transporters, particularly species-specific sperm purinergic receptors. We also discuss notable phenotypes from knock-out mouse models and human Mendelian inheritance related to ATP release mechanisms, along with immunological, proteomic, and functional observations regarding sperm purinergic receptors and their involvement in sperm signalling.

Proteomic analysis of sperm from fertile stallions and subfertile stallions due to impaired acrosomal exocytosis

Thoroughbred stallions that carry a double-homozygous genotype A/A-A/A for SNPs rs397316122 and rs69101140 in exon 5 of the FKBP6 gene (chr13; EquCab3.0) are uniquely subfertile due to impaired acrosomal exocytosis (IAE). In this study, the sperm proteome in frozen/thawed semen from subfertile Thoroughbred stallions was studied and compared to that of frozen/thawed sperm from fertile Thoroughbred stallions. A total of 2,220 proteins was identified, of which 140 proteins were found to be differentially abundant in sperm from the subfertile stallions compared to that of fertile stallions (83 less and 57 more abundant). Proteins of differential abundance in sperm from the subfertile stallions were mainly overrepresented in the “metabolism” and the “metabolism of lipids” pathways. One of these proteins, arylsulfatase F (ARSF), was studied by immunofluorescence. A lower proportion of sperm displaying ARSF signal at the acrosome region was observed in sperm from subfertile Thoroughbred stallions. In addition, heterologous zona pellucida binding assays revealed that sperm from subfertile Thoroughbred stallions bound at a lower proportion to zonae pellucidae than sperm from fertile Thoroughbred stallions. In conclusion, a group of differential abundance proteins, including some of acrosome origin, were identified in sperm from subfertile stallions with acrosome dysfunction.

Effect of exogenous sperm capacitation inducers on stallion sperm

Although under appropriate laboratory conditions, sperm from different mammalian species can be capacitated in vitro, the optimal conditions for sperm capacitation in the stallion have been elusive. This study evaluated the effect of different capacitating inducers in Whitten and Tyrode media and assessed their impact on capacitation-related factors. Stallion sperm were incubated with different combinations of capacitating inducers at 38.5 °C in an air atmosphere. Sperm quality variables such as motility, mitochondrial membrane potential, and lipid peroxidation were assessed. Membrane fluidity and intracellular calcium levels were evaluated as early markers of capacitation, while tyrosine phosphorylation events and the sperm's ability to perform acrosomal exocytosis were used as late capacitation markers. Finally, these sperm were evaluated using a heterologous zona pellucida binding assay. The findings confirm that capacitating conditions evaluated increase intracellular calcium levels and membrane fluidity in both media. Similarly, including 2 or 3 inducers in both media increased tyrosine phosphorylation levels and acrosomal exocytosis after exposure to progesterone, confirming that stallion sperm incubated in these conditions shows cellular and molecular changes consistent with sperm capacitation. Furthermore, the zona pellucida binding assay confirmed the binding capacity of sperm incubated in capacitation conditions, a key step for stallion in vitro fertilization success. Further studies are needed to evaluate the effect of these conditions on in vitro fertilization in the horse.

Effect of bicarbonate and polyvinyl alcohol on in vitro capacitation and fertilization ability of cryopreserved equine spermatozoa.

Factors contributing to the limited success of in vitro fertilization in horses remain to be studied. In this work, we elucidated the effect of different essential capacitation media components, bicarbonate, and bovine serum albumin or polyvinyl-alcohol, and the incubation microenvironment on sperm parameters associated with capacitation, acrosome reaction, and their ability to activate oocytes via heterologous intracytoplasmic spermatozoa injection in equine cryopreserved spermatozoa. Frozen-thawed spermatozoa underwent incubation at different time intervals in either Tyrode's albumin lactate pyruvate medium (non-capacitating; NC) or Tyrode's albumin lactate pyruvate supplemented with bicarbonate, bicarbonate and polyvinyl-alcohol, bicarbonate and bovine serum albumin, polyvinyl-alcohol and bovine serum albumin alone. Protein kinase A-phosphorylated substrates and tyrosine phosphorylation levels, sperm motility, and acrosome reaction percentages were evaluated. After determining the best condition media (capacitating; CAP), heterologous intracytoplasmic spermatozoa injection on pig oocytes was performed and the phospholipase C zeta sperm localization pattern was evaluated. Incubation of frozen-thawed equine spermatozoa with bicarbonate and polyvinyl-alcohol in atmospheric air for 45min induced an increase in protein kinase A-phosphorylated substrates and tyrosine phosphorylation levels compared to NC condition. Sperm incubation in bicarbonate and polyvinyl-alcohol medium showed an increase in total motility and progressive motility with respect to NC (p ≤ 0.05). Interestingly, three parameters associated with sperm hyperactivation were modulated under bicarbonate and polyvinyl-alcohol conditions. The kinematic parameters curvilinear velocity and amplitude of lateral head displacement significantly increased, while straightness significantly diminished (curvilinear velocity: bicarbonate and polyvinyl-alcohol=120.9±2.9 vs. NC=76.91±6.9µm/s) (amplitude of lateral head displacement: bicarbonate and polyvinyl-alcohol=1.15±0.02 vs. NC=0.77±0.03µm) (straightness: bicarbonate and polyvinyl-alcohol=0.76±0.01 vs. NC=0.87±0.02) (p ≤ 0.05). Moreover, the spontaneous acrosome reaction significantly increased in spermatozoa incubated in this condition. Finally, bicarbonate and polyvinyl-alcohol medium was established as CAP medium. Although no differences were found in phospholipase C zeta localization pattern in spermatozoa incubated under CAP, equine spermatozoa pre-incubated in CAP condition for 45min showed higher fertilization rates when injected into matured pig oocytes (NC: 47.6% vs. CAP 76.5%; p ≤ 0.05). These findings underscore the importance of bicarbonate and polyvinyl-alcohol in supporting critical events associated with in vitro sperm capacitation in the horse, resulting in higher oocyte activation percentages following heterologous intracytoplasmic spermatozoa injection. This protocol could have an impact on reproductive efficiency in the equine breeding industry.