Characterization of an eppin protein complex from human semen and spermatozoa

Understanding seminal plasma in male infertility: emerging markers and their implications

Infertility affects a significant proportion of the reproductive-aged population, with male-associated factors contributing to over half of the cases. However, current diagnostic tools have limitations, leading to an underestimation of the true prevalence of male infertility. While traditional semen parameters provide some insights, they fail to determine the true fertility potential in a substantial number of instances. Therefore, it is crucial to investigate additional molecular targets responsible for male infertility to improve understanding and identification of such cases. Seminal plasma, the main carrier of molecules derived from male reproductive glands, plays a crucial role in reproduction. Amongst its multifarious functions, it regulates processes such as sperm capacitation, sperm protection and maturation, and even interaction with the egg's zona pellucida. Seminal plasma offers a non-invasive sample for urogenital diagnostics and has shown promise in identifying biomarkers associated with male reproductive disorders. This review aims to provide an updated and comprehensive overview of seminal plasma in the diagnosis of male infertility, exploring its composition, function, methods used for analysis, and the application of emerging markers. Apart from the application, the potential challenges of seminal plasma analysis such as standardisation, marker interpretation and confounding factors have also been addressed. Moreover, we have also explored future avenues for enhancing its utility and its role in improving diagnostic strategies. Through comprehensive exploration of seminal plasma's diagnostic potential, the present analysis seeks to advance the understanding of male infertility and its effective management.

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.

Interactions of the male contraceptive target EPPIN with semenogelin-1 and small organic ligands

Novel male contraceptives will promote gender equality in sharing contraceptive responsibility. The sperm-associated protein epididymal protease inhibitor (EPPIN) is a promising target for non-hormonal male contraception. EPPIN interacts with the semen coagulum protein semenogelin-1 (SEMG1) on the sperm surface, leading to transient inhibition of sperm motility after ejaculation. Small organic molecules targeting EPPIN's SEMG1-binding are under development as male contraceptives. Here, we combined computational approaches to uncover key aspects underlying EPPIN binding to SEMG1 and small organic ligands. We generated a human EPPIN model showing a typical arrangement of the WFDC (Whey-acid four disulfide core)-type and Kunitz-type domains, connected by a hinge region. Determining the EPPIN model's intrinsic motion by molecular dynamics simulations and normal mode analysis revealed a conformation, presenting a binding pocket that accommodates SEMG1Glu229-Gln247, EP055, and EP012. EPPIN's residues Phe63 and Lys68 (WFDC domain), Asp71 (hinge region), and Asn113, Asn114, and Asn115 (Kunitz domain) were identified as hot spots for SEMG1, EP055, and EP012 binding. Moreover, hydrophobic and hydrophilic residues in the WFDC and Kunitz domains allow plasma membrane anchoring, orienting the EPPIN binding pocket to the solvent. Targeting EPPIN's essential residues for its biomolecular interactions may improve the rational design of EPPIN ligands as spermiostatic compounds.

The Association between Clusterin Sialylation Degree and Levels of Oxidative–Antioxidant Balance Markers in Seminal Plasmas and Blood Sera of Male Partners with Abnormal Sperm Parameters

Nearly 30% of infertility cases are caused by male factor. This study aimed at checking the associations between the sialylation degree of glycoprotein clusterin (CLU) and levels of oxidative–antioxidant balance markers in infertile men. Using lectin-ELISA with biotinylated lectins specific to α2,6-linked (Sambucus nigra agglutinin, SNA) and α2,3-linked (Maackia amurensis agglutinin, MAA) sialic acid (SA), the CLU sialylation in 132 seminal plasmas (SP) and 91 blood sera (BS) were analyzed. Oxidative–antioxidant status was measured by determining Sirtuin-3 (SIRT3), Sirtuin-5 (SIRT5), total antioxidant status (TAS), and ferric reducing antioxidant power (FRAP) levels. We indicate that multiple sperm disorders are associated with decreased expression of MAA-reactive SA in SP. Decreased SP SIRT3 concentrations may be associated with teratozoospermia and oligoasthenoteratozoospermia. ROC curve and cluster analysis revealed that SP relative reactivity of CLU glycans with MAA, the value of MAA/SNA ratio, and SIRT3 and SIRT5 concentrations may constitute an additional set of markers differentiating infertile oligoasthenoteratozoospermic patients (OAT) from normozoospermic (N), asthenoteratozoospermic (AT) and teratozoospermic (T). The multinomial logistic regression analysis confirmed the potential utility of SIRT3 determinations for differentiation between N and OAT groups as well as between N and T groups for SIRT3 and SIRT5. For BS, based on ROC curve and cluster analysis, relative reactivities of CLU glycans with SNA, MAA, SIRT3 and FRAP concentrations may be useful in the differentiation of normozoospermic patients from those with sperm disorders. The multinomial logistic regression analysis showed that the SNA relative reactivity with CLU glycans significantly differentiated the N group from AT, OAT and T groups, and FRAP concentrations significantly differed between N and AT groups, which additionally confirms the potential utility of these biomarkers in the differentiation of infertile patients with abnormal sperm parameters. The knowledge about associations between examined parameters may also influence future research aimed at seeking new male infertility therapies.

Ureaplasma urealyticum induces polymorphonuclear elastase to change semen properties and reduce sperm motility: a prospective observational study

Objective

To elucidate the mechanism underlying how Ureaplasma urealyticum (UU) affects sperm quality and identify a therapeutic target.

Methods

In this prospective observational study, the differences in and relationships among semen volume, pH, viscosity, liquefaction time, sperm concentration, sperm motility [progressive motility (PR)], and seminal polymorphonuclear (PMN) elastase were analyzed in 198 normal semen samples (control group) and 198 UU-infected semen samples (observation group). The UU-infected samples were treated and the above parameters were compared between the two groups.

Results

The semen volume, viscosity, liquefaction time, and seminal PMN elastase were significantly higher in the observation than control group, but the pH and PR were significantly lower. In the observation group, the pH and PR were significantly higher after than before treatment, whereas the semen volume, PMN elastase, viscosity, and liquefaction time were lower. UU was closely related to semen volume, pH, viscosity, liquefaction time, sperm motility (PR), and PMN elastase. PMN elastase had significant negative effects on semen pH and sperm motility (PR) but positive effects on viscosity and liquefaction time.

Conclusion

UU might induce PMN elastase to increase the liquefaction time and viscosity of semen, eventually decreasing PR. PMN elastase might be a therapeutic target of UU.

Semenogelin, a coagulum macromolecule monitoring factor involved in the first step of fertilization: A prospective review

Human male infertility affects approximately 1/10 couples worldwide, and its prevalence is found more in developed countries. Along with sperm cells, the secretions of the prostate, seminal vesicle and epididymis plays a major role in proper fertilization. Many studies have proven the functions of seminal vesicle secretions, especially semenogelin protein, as an optimiser for fertilization. Semenogelin provides the structural components for coagulum formation after ejaculation. It binds with eppin and is found to have major functions like motility of sperm, transporting the sperm safely in the immune rich female reproductive tract until the sperm cells reach the egg intact. The capacitation process is essential for proper fertilization and semenogelin involved in mediating capacitation in time. Also, it has control of events towards the first step in the fertilization process. It is a Zn ions binding protein, and Zn ions act as a cofactor that helps in the proper motility of sperm cells. Therefore, any imbalance in protein that automatically affect sperm physiology and fertility status. This review sheds a comprehensive and critical view on the significant functions of semenogelin in fertilization. This review can open up advanced proteomics research on semenogelin towards unravelling molecular mechanisms in fertilization.

Influence of Risk Factors for Male Infertility on Sperm Protein Composition

Male infertility is a common health problem that can be influenced by a host of lifestyle risk factors such as environment, nutrition, smoking, stress, and endocrine disruptors. These effects have been largely demonstrated on sperm parameters (e.g., motility, numeration, vitality, DNA integrity). In addition, several studies showed the deregulation of sperm proteins in relation to some of these factors. This review inventories the literature related to the identification of sperm proteins showing abundance variations in response to the four risk factors for male infertility that are the most investigated in this context: obesity, diabetes, tobacco smoking, and exposure to bisphenol-A (BPA). First, we provide an overview of the techniques used to identify deregulated proteins. Then, we summarise the main results obtained in the different studies and provide a compiled list of deregulated proteins in relation to each risk factor. Gene ontology analysis of these deregulated proteins shows that oxidative stress and immune and inflammatory responses are common mechanisms involved in sperm alterations encountered in relation to the risk factors.

Dissecting EPPIN protease inhibitor domains in sperm motility and fertilizing ability: repercussions for male contraceptive development

EPPIN (epididymal protease inhibitor) is a mammalian conserved sperm-binding protein displaying an N-terminal WFDC (whey-acidic protein four-disulfide core) and a C-terminal Kunitz protease inhibitor domains. EPPIN plays a key role in regulating sperm motility after ejaculation via interaction with the seminal plasma protein SEMG1 (semenogelin-1). EPPIN ligands targeting the SEMG1 binding site in the Kunitz domain are under development as male contraceptive drugs. Nevertheless, the relative contributions of EPPIN WFDC and Kunitz domains to sperm function remain obscure. Here, we evaluated the effects of antibodies targeting specific epitopes in EPPIN's WFDC (Q20E antibody, Gln20-Glu39 epitope) and Kunitz (S21C and F21C antibodies, Ser103-Cys123 and Phe90-C110 epitopes, respectively) domains on mouse sperm motility and fertilizing ability. Computer-assisted sperm analysis showed that sperm co-incubation with S21C antibody (but not F21C antibody) lowered progressive and hyperactivated motilities and impaired kinematic parameters describing progressive (straight-line velocity; VSL, average path velocity; VAP and straightness; STR) and vigorous sperm movements (curvilinear velocity; VCL, amplitude of lateral head movement; ALH, and linearity; LIN) compared with control. Conversely, Q20E antibody-induced milder inhibition of progressive motility and kinematic parameters (VAP, VCL and ALH). Sperm co-incubation with S21C or Q20E antibodies affected in vitro fertilization as revealed by reduced cleavage rates, albeit without changes in capacitation-induced tyrosine phosphorylation. In conclusion, we show that targeting specific epitopes in EPPIN Kunitz and WFDC domains inhibits sperm motility and capacitation-associated events, which decrease their fertilizing ability; nevertheless, similar observations in vivo remain to be demonstrated. Simultaneously targeting residues in S21C and Q20E epitopes is a promising approach for the rational design of EPPIN-based ligands with spermostatic activity.

The possible association of clusterin fucosylation changes with male fertility disorders

In the seminal plasma (n = 118) and serum (n = 90) clusterin (CLU) the fucosylation and the expression of selected fucosyltransferases (FUTs) were analyzed. Samples from infertile men were divided into groups based on the results of the standard semen analysis: normozoospermic (N), teratozoospermic (T), asthenoteratozoospermic (AT) and oligoasthenoteratozoospermic (OAT). The CLU fucosylation was analyzed using lectin-ELISAs with biotinylated lectins specific to α1,3-, α1,2-linked antennary fucose, and α1,6-linked core fucose (LTA, UEA, and LCA, respectively). The concentrations of FUT3 and FUT4, reflecting the expression of Le oligosaccharide structures, were measured using ELISA tests. The differences in serum CLU and FUT4 concentrations, and in the expression of core fucose and antennary fucose α1,2-linked in CLU glycans between the N group and other groups examined suggest that the disturbances in sperm count, motility, and morphology are not the only cause of male infertility. Lack of similarities between levels of examined parameters in blood serum and seminal plasma may suggest the differences in mechanisms leading to glycoproteins glycosylation. It confirmed the observed differences in concentrations of seminal plasma CLU, FUT3, and FUT4 between the OAT group and N, T, AT groups, indicating that decreased sperm count may be related to these parameters expression. The serum CLU concentrations and expression of core fucose and fucose α1,2-linked in CLU, seem to be good markers differentiating normozoospermic men from those with abnormal sperm parameters, which was not observed for seminal plasma.

siRNA-mediated Eppin testicular silencing causes changes in sperm motility and calcium currents in mice

Epididymal protease inhibitor (EPPIN) is differentially expressed in the reproductive tissues (such as testicles, outlet tubes, epididymis, vas deferens, and seminal vesicles). Its critical role in sperm function and male reproduction has shed light on EPPIN as a candidate target for male contraceptive vaccines. In this study, we endeavored to further reveal the mechanism through which EPPIN exerts its function. We created a mouse model of reduced Eppin expression by microinjecting small interfering RNA targeting Eppin expression into seminiferous tubules of mice. This mouse model was then used to explore the effects of low Eppin expression on sperm function, which was assessed by Computer Assisted Semen Analysis and patch clamp recording of T-type Ca²⁺ current in spermatogenic cells. We found that the sperm motility significantly declined when Eppin was downregulated. Further investigation demonstrated that Eppin downregulation significantly affected T-type Ca²⁺ currents and messenger RNA expression of three subtypes of T-type Ca²⁺ channels in spermatogenic cells. These findings indicate that low Eppin gene expression induces decreased T-type Ca²⁺ currents and mRNA expression, which in turn results in the reduced sperm motility.

Large-scale discovery of male reproductive tract-specific genes through analysis of RNA-seq datasets

Background

The development of a safe, effective, reversible, non-hormonal contraceptive method for men has been an ongoing effort for the past few decades. However, despite significant progress on elucidating the function of key proteins involved in reproduction, understanding male reproductive physiology is limited by incomplete information on the genes expressed in reproductive tissues, and no contraceptive targets have so far reached clinical trials. To advance product development, further identification of novel reproductive tract-specific genes leading to potentially druggable protein targets is imperative.

Results

In this study, we expand on previous single tissue, single species studies by integrating analysis of publicly available human and mouse RNA-seq datasets whose initial published purpose was not focused on identifying male reproductive tract-specific targets. We also incorporate analysis of additional newly acquired human and mouse testis and epididymis samples to increase the number of targets identified. We detected a combined total of 1178 genes for which no previous evidence of male reproductive tract-specific expression was annotated, many of which are potentially druggable targets. Through RT-PCR, we confirmed the reproductive tract-specific expression of 51 novel orthologous human and mouse genes without a reported mouse model. Of these, we ablated four epididymis-specific genes (Spint3, Spint4, Spint5, and Ces5a) and two testis-specific genes (Pp2d1 and Saxo1) in individual or double knockout mice generated through the CRISPR/Cas9 system. Our results validate a functional requirement for Spint4/5 and Ces5a in male mouse fertility, while demonstrating that Spint3, Pp2d1, and Saxo1 are each individually dispensable for male mouse fertility.

Conclusions

Our work provides a plethora of novel testis- and epididymis-specific genes and elucidates the functional requirement of several of these genes, which is essential towards understanding the etiology of male infertility and the development of male contraceptives.

Mechanism of semen liquefaction and its potential for a novel non-hormonal contraception†

Semen liquefaction is a proteolytic process where a gel-like ejaculated semen becomes watery due to the enzymatic activity of prostate-derived serine proteases in the female reproductive tract. The liquefaction process is crucial for the sperm to gain their motility and successful transport to the fertilization site in Fallopian tubes (or oviducts in animals). Hyperviscous semen or failure in liquefaction is one of the causes of male infertility. Therefore, the biochemical inhibition of serine proteases in the female reproductive tract after ejaculation is a prime target for novel contraceptive development. Herein, we will discuss protein components in the ejaculates responsible for semen liquefaction and any developments of contraceptive methods in the past that involve the liquefaction process.

Epididymal protease inhibitor (EPPIN) is a protein hub for seminal vesicle-secreted protein SVS2 binding in mouse spermatozoa

EPPIN is a sperm-surface drug target for male contraception. Here we investigated EPPIN-interacting proteins in mouse spermatozoa. We showed that EPPIN is an androgen-dependent gene, expressed in the testis and epididymis, but also present in the vas deferens, seminal vesicle and adrenal gland. Mature spermatozoa presented EPPIN staining on the head and flagellum. Immunoprecipitation of EPPIN from spermatozoa pre-incubated with seminal vesicle fluid (SVF) followed by LC-MS/MS or Western blot revealed the co-immunoprecipitation of SVS2, SVS3A, SVS5 and SVS6. In silico and Far-Western blot approaches demonstrated that EPPIN binds SVS2 in a protein network with other SVS proteins. Immunofluorescence using spermatozoa pre-incubated with SVF or recombinant SVS2 demonstrated the co-localization of EPPIN and SVS2 both on sperm head and flagellum. Our data show that EPPIN's roles in sperm function are conserved between mouse and human, demonstrating that the mouse is a suitable experimental model for translational studies on EPPIN.

Role of Seminal Plasma Proteins in Effective Zygote Formation- A Success Road to Pregnancy

Seminal plasma proteins contributed by secretions of accessory glands plays a copious role in fertilization. Their role is overlooked for decades and even now, as Artificial Reproduction Techniques (ART) excludes the plasma components in the procedures. Recent evidences suggest the importance of these proteins starting from imparting fertility status to men, fertilization and till successful implantation of the conceptus in the female uterus. Seminal plasma is rich in diverse proteins, but a major part of the seminal plasma is constituted by very lesser number of proteins. This makes isolation and further research on non abundant protein a tough task. With the advent of much advanced proteomic techniques and bio informatics tools, studying the protein component of seminal plasma has become easy and promising. This review is focused on the role of seminal plasma proteins on various walks of fertilization process and thus, the possible exploitation of seminal plasma proteins for understanding the etiology of male related infertility issues. In addition, a compilation of seminal plasma proteins and their functions has been done.

Proteomic characterization of human sperm plasma membrane-associated proteins and their role in capacitation

BACKGROUND

Plasma membranes of ejaculated sperm are covered by epididymal and accessory glands secreted proteins that must be released from sperm surface during the female reproductive tract passage in order to capacitate and fertilize the oocyte.

OBJECTIVES

As human sperm plasma membrane-associated proteins (SMAP) have not yet been investigated, the aim of this study was to characterize the SMAP released during in vitro human capacitation and to study their possible role as decapacitation factors.

MATERIALS AND METHODS

SMAP were characterized by 2-dimensional electrophoresis and mass spectrometry analysis. Besides, we explored SMAP effects on motility, protein tyrosine phosphorylation, and calcium ionophore-induced acrosome reaction of spermatozoa either incubated for 6 h in capacitating medium ± SMAP or for 5 h in capacitating medium alone followed by incubation for 1 h ± SMAP.

RESULTS

Mass spectrometry analysis allowed the identification of 29 proteins, all of which have previously been identified in the human seminal fluid. Spermatozoa incubated for 6 h under capacitating conditions in the presence of the SMAP showed a significant decrease in the incidence of non-progressive motility, hyperactivation, protein tyrosine phosphorylation, and calcium ionophore-induced acrosome reaction. However, spermatozoa incubated for 5 h in capacitating medium and further incubated for 1 h with the SMAP showed a lower percentage of spermatozoa with non-progressive motility and hyperactivated cells but no effects on protein tyrosine phosphorylation were detected.

DISCUSSION AND CONCLUSIONS

Our results indicate that SMAP inhibit the progress of human sperm capacitation, but only motility changes related to capacitation may be reversed by these proteins. The study of the identified proteins on sperm function and their mechanisms of action on this cell may contribute to the understanding of their role during capacitation.

Presence of Round Cells Proteins do not Interfere with Identification of Human Sperm Proteins from Frozen Semen Samples by LC-MS/MS

In sperm proteomic experiments round cells and leukocyte proteins are profiled along with sperm proteome. The influence of round cell and leukocyte proteins on the sperm proteome has not been investigated. The objective of this study was to identify if the proteins from round cells, including leukocytes, interfere with the proteomic analysis of spermatozoa in frozen semen samples. Proteomic profiling of sperm was performed using liquid chromatography-tandem mass spectrometry in four groups: Group 1 contained neat semen with round cells and leukocytes ≥ 1 × 10⁶/mL, group 2 contained neat semen with round cells ≥ 1 × 10⁶/mL that was processed by 65% density gradient to remove the round cells and leukocytes, group 3 contained neat semen with round cells < 1 × 10⁶/mL, and group 4 contained neat semen with round cells < 1 × 10⁶/mL that was processed by 65% density gradient to remove the round cells. Pure leukocyte culture was used as control group. A total of 1638, 1393, 1755, and 1404 proteins were identified in groups 1, 2, 3, and 4, respectively. Comparative analysis of group 1 vs. 3 revealed 26 (1.18%) differentially expressed proteins (DEPs). On the other hand, only 6 (0.31%) DEPs were observed with group 2 vs. 4. Expression of these DEPs were either absent or very low in the control group. The results of our proteomics analysis failed to show any influence of non-spermatogenic round cell proteins on sperm proteome identification. These results validate the use of neat semen samples for sperm proteomic studies.

Proteins from male and female reproductive tracts involved in sperm function regulation

Spermatogenesis is a dynamic process that culminates in the production of mature spermatozoa in the seminiferous tubules of sexually mature animals. Although sperm leaving the testis are fully differentiated, they must further undergo two additional maturation steps before acquiring the capability to fertilize the egg. Such processes take place during the epididymal residency and transport in the seminal fluid during ejaculation and, after delivery into the female reproductive tract, during the journey aiming the encountering the egg in the oviduct. Throughout this trip, spermatozoa are exposed to different reproductive fluids whose molecular compositions regulate the progress towards obtaining a fertilized competent cell. This review summarizes the evidence obtained so far supporting the participation of male and female reproductive tract-derived proteins in the modulation of sperm fertilizing ability and discusses the mechanisms by which such regulation may be accomplished.

Epididymal approaches to male contraception

Today, a vast arsenal of contraceptive methods interfering at different levels of the female reproductive axis is available. This is not the case for men for whom, until now, there is no reliable male reversible method and for whom vasectomy, condom and withdrawal are the only options available. Despite this limited supply, more than one third of all contraceptive methods used worldwide rely on the cooperation of the male partner. Besides developing hormonal approaches to stop sperm production, there may be attractive approaches that will interfere with sperm functions rather than production. Sperm functions are primarily established during post-testicular maturation, with the epididymis accounting for the majority. The purpose of this review is to present some of the promising and/or already abandoned leads that emerge from research efforts targeting the epididymis and its activities as potential means to achieve male post-meiotic contraception.

Clusterin in the mouse epididymis: possible roles in sperm maturation and capacitation

Clusterin (CLU) is known as an extracellular chaperone for proteins under stress, thus preventing them from aggregation and precipitation. We showed herein that CLU, expressed by principal cells of the mouse caput epididymis, was present in high amounts in the lumen. In the cauda epididymis, CLU bound tightly to the sperm head surface and its amount on total sperm was similar to that in the bathing luminal fluid. In both immotile and motile caudal epididymal sperm, CLU was localized over the entire sperm head except at the convex ridge, although in the motile sperm population, the CLU immunofluorescence pattern was distinctively mottled with a lower intensity. However, when motile sperm became capacitated, CLU was relocalized to the head hook region, with immunofluorescence intensity being higher than that on the non-capacitated counterparts. Under a slightly acidic pH of the epididymal lumen, CLU may chaperone some luminal proteins and deliver them onto the sperm surface. Immunoprecipitation of epididymal fluid proteins indicated that CLU interacted with SED1, an important egg-binding protein present in a high amount in the epididymal lumen. In a number of non-capacitated sperm, fractions of SED1 and CLU co-localized, but after capacitation, SED1 and CLU dissociated from one another. While CLU moved to the sperm head hook, SED1 translocated to the head convex ridge, the egg-binding site. Overall, CLU localization patterns can serve as biomarkers of immotile sperm, and non-capacitated and capacitated sperm in mice. The chaperone role of CLU may also be important for sperm maturation and capacitation.

Mutations in the prostate specific antigen (PSA/KLK3) correlate with male infertility

Prostate specific antigen (PSA/KLK3) is known to be the chief executor of the fragmentation of semenogelins, dissolution of semen coagulum, thereby releasing sperm for active motility. Recent research has found that semenogelins also play significant roles in sperm fertility by affecting hyaluronidase activity, capacitation and motility, thereby making PSA important for sperm fertility beyond simple semen liquefaction. PSA level in semen has been shown to correlate with sperm motility, suggesting that PSA level/activity can affect fertility. However, no study investigating the genetic variations in the KLK3/PSA gene in male fertility has been undertaken. We analyzed the complete coding region of the KLK3 gene in ethnically matched 875 infertile and 290 fertile men to find if genetic variations in KLK3 correlate with infertility. Interestingly, this study identified 28 substitutions, of which 8 were novel (not available in public databases). Statistical comparison of the genotype frequencies showed that five SNPs, rs266881 (OR = 2.92, P < 0.0001), rs174776 (OR = 1.91, P < 0.0001), rs266875 (OR = 1.44, P = 0.016), rs35192866 (OR = 4.48, P = 0.025) and rs1810020 (OR = 2.08, P = 0.034) correlated with an increased risk of infertility. On the other hand, c.206 + 235 T > C, was more freuqent in the control group, showing protective association. Our findings suggest that polymorphisms in the KLK3 gene correlate with infertility risk.

Characterisation of eppin function: expression and activity in the lung

Eppin is a serine protease inhibitor expressed in male reproductive tissues.

The aim of this study was to investigate the localisation and regulation of eppin expression in myeloid and epithelial cell lines, and explore its potential role as a multifunctional host defence protein.

Using immunohistochemistry and Western blotting, eppin was detected in the lungs of patients with acute respiratory distress syndrome and cystic fibrosis lung disease. Expression of eppin in monocytic cells was unaffected by stimulation with Toll-like receptor agonists, cytokines and hormone receptor agonists. However, upregulated expression and secretion of eppin was observed following treatment of monocytes with epidermal growth factor. Incubation of recombinant eppin with monocytic cells resulted in significant inhibition of lipopolysaccharide-induced chemokine production. Furthermore, eppin inhibited lipopolysaccharide-induced NF-κB activation by a mechanism which involved accumulation of phosphorylated IκBα. In anin vivomodel of lung inflammation induced by lipopolysaccharide, eppin administration resulted in decreased recruitment of neutrophils to the lung with a concomitant reduction in the levels of the neutrophil chemokine macrophage inflammatory protein-2.

Overall, these results suggest a role for eppin outside of the reproductive tract and that eppin may have a role in the innate immune response in the lung.

Non-hormonal male contraception: A review and development of an Eppin based contraceptive

Developing a non-hormonal male contraceptive requires identifying and characterizing an appropriate target and demonstrating its essential role in reproduction. Here we review the development of male contraceptive targets and the current therapeutic agents under consideration. In addition, the development of EPPIN as a target for contraception is reviewed. EPPIN is a well characterized surface protein on human spermatozoa that has an essential function in primate reproduction. EPPIN is discussed as an example of target development, testing in non-human primates, and the search for small organic compounds that mimic contraceptive antibodies; binding EPPIN and blocking sperm motility. Although many hurdles remain before the success of a non-hormonal male contraceptive, continued persistence should yield a marketable product.

Applying emerging science to contraception research: implications for the clinic

Emerging science will make an important contribution towards the development of improved contraceptives. While long-acting reversible contraceptives remain the most effective method, new user-controlled, mid-acting methods will avoid the need for procedures requiring trained providers. Contraceptives combined with other agents may bring additional health benefits, such as dual protection against both pregnancy and sexually transmitted infections. Emerging research areas in proteomics allowed the discovery of new reproductive targets that may lead to non-hormonal contraceptives for both men and women. Current research objectives include the improvement of existing contraceptive methods, as well as discovery of new materials able to deliver new molecules more specifically to their target without systemic actions.

Heparin binding carboxypeptidase E protein exhibits antibacterial activity in human semen

Carboxypeptidase E (CPE) cleaves basic amino acid residues at the C-terminal end and involves in the biosynthesis of numerous peptide hormones and neurotransmitters. It was purified from human seminal plasma by ion exchange, heparin affinity and gel filtration chromatography followed by identification through SDS-PAGE and MALDI-TOF/MS analysis, which was further confirmed by western blotting. CPE was characterized as glycoprotein by Periodic Acid Schiff (PAS) staining and treating with deglycosylating enzyme N-glycosidase F. The interaction of CPE with heparin was illustrated by surface plasmon resonance (SPR) and in silico interaction analysis. The association constant (KA) and dissociation constant (KD) of CPE with heparin was determined by SPR and found to be 1.06 × 10(5)M and 9.46 × 10(-6)M, respectively. It was detected in human spermatozoa also by western blotting using mouse anti-CPE primary antibody. 20-100 μg/ml concentration of CPE was observed as highly effective in killing Escherichia coli by colony forming unit (CFU) assay. We suggest that CPE might act not only in the innate immunity of male reproductive tract but also regulate sperm fertilization process by interacting heparin.

Correlation of epididymal protease inhibitor and fibronectin in human semen

Objective

Epididymal protease inhibitor (Eppin) was located on the surface of spermatozoa and modulates the liquefaction of human semen. Here, we identify the correlative protein partner of Eppin to explore the molecular mechanism of liquefaction of human semen.

Methods

(1) Human seminal vesicle proteins were transferred on the membrane by Western blotting and separated by 2-D electrophoresis and incubated in recombinant Eppin. The correlative protein was identified by Mass Spectrometry (MS) (2). Western blotting was used to determine the relation of rEppin and rFibronectin(Fn); (3) Co-localization in spermatozoa were detected using immunofluorescence; (4) Correalation of Eppin and Fn was proved by co-immunoprecipitation.

Results

Fn was identified as the binding partner of recombinant Eppin by MS. Recombinant of Eppin was made and demonstrated that the Eppin fragment binds the fn 607-1265 fragment. The Eppin-Fn complex presents on the sperm tail and particularly in the midpiece region of human ejaculated spermatozoa. Immunoprecipitation indicated that Eppin in the spermatozoa lysates was complexed with Fn.

Conclusions

Our study demonstrates that Eppin and Fn bind to each other in human semen and on human ejaculated spermatozoa. Eppin-Fn complex may involve in semen coagulation, liquefaction and the survival and preparation of spermatozoa for fertility in the female reproductive tract.

Prostate Secretory Protein of 94 amino acids (PSP94) binds to prostatic acid phosphatase (PAP) in human seminal plasma

Prostate Secretory Protein of 94 amino acids (PSP94) is one of the major proteins present in the human seminal plasma. Though several functions have been predicted for this protein, its exact role either in sperm function or in prostate pathophysiology has not been clearly defined. Attempts to understand the mechanism of action of PSP94 has led to the search for its probable binding partners. This has resulted in the identification of PSP94 binding proteins in plasma and seminal plasma from human. During the chromatographic separation step of proteins from human seminal plasma by reversed phase HPLC, we had observed that in addition to the main fraction of PSP94, other fractions containing higher molecular weight proteins also showed the presence of detectable amounts of PSP94. This prompted us to hypothesize that PSP94 could be present in the seminal plasma complexed with other protein/s of higher molecular weight. One such fraction containing a major protein of ~47 kDa, on characterization by mass spectrometric analysis, was identified to be Prostatic Acid Phosphatase (PAP). The ability of PAP present in this fraction to bind to PSP94 was demonstrated by affinity chromatography. Co-immunoprecipitation experiments confirmed the presence of PSP94-PAP complex both in the fraction studied and in the fresh seminal plasma. In silico molecular modeling of the PSP94-PAP complex suggests that β-strands 1 and 6 of PSP94 appear to interact with domain 2 of PAP, while β-strands 7 and 10 with domain 1 of PAP. This is the first report which suggests that PSP94 can bind to PAP and the PAP-bound PSP94 is present in human seminal plasma.

Preparation, characterization, and determination of immunological activities of transfer factor specific to human sperm antigen

OBJECTIVE. The objective of this study was to prepare, characterize, and determine immunological activities of specific transfer factor (STF) specific to human sperm antigen (HSA) for the preparation of antisperm contraceptive vaccine that can be used as an immunocontraceptive. METHODS. HSA-STF was prepared using the spleens of rabbits vaccinated with HSA. The specific immunological activities were examined by lymphocyte proliferation test (LPT), leukocyte adhesion inhibition test (LAIT), and by determining the concentrations of IL-4, γ -IFN, and IL-21. HSA-STF was a helveolous substance, having a pH value of 7.0 ± 0.4 and UV absorption maxima at 258 ± 6 nm. It contained seventeen amino acids; glycine and glutamic acids were the highest in terms of concentrations (38.8 μ g/mL and 36.3 μ g/mL, resp.). RESULTS. The concentration of polypeptide was 2.34 ± 0.31 mg/mL, and ribose was 0.717 ± 0.043 mg/mL. The stimulation index for lymphocyte proliferation test was 1.84, and the leukocyte adhesion inhibition rate was 37.7%. There was a statistically significant difference between the cultural lymphocytes with HSA-STF and non-HSA-STF for γ -IFN and IL-21 (P < 0.05), but there was no statistical significance for IL-4 (P > 0.05). CONCLUSION. HSA-STF was prepared and characterized successfully. It had immunological activity which could transfer the immune response specific to HSA and prove to be a potential candidate for the development of male immunocontraceptive agents.

Epididymal protease inhibitor (EPPIN) is differentially expressed in the male rat reproductive tract and immunolocalized in maturing spermatozoa

EPPIN (epididymal protease inhibitor; SPINLW1), an antimicrobial cysteine-rich protein containing both Kunitz and whey acidic protein (WAP)-type four disulfide core protease inhibitor consensus sequences, is a target for male contraception because of its critical role in sperm motility. Here, we characterized EPPIN's expression and cellular distribution in rat tissues and its in vivo regulation by androgens in the epididymis. EPPIN (mRNA and protein) was abundantly expressed in the rat testis and epididymis; we also found that the vas deferens, seminal vesicles, and brain were novel sites of EPPIN expression. PCR studies demonstrated that in addition to Sertoli cells, spermatogenic cells expressed Eppin mRNA. EPPIN was immunolocalized in Sertoli cells and spermatogenic cells (pachytene spermatocytes and round and elongated spermatids) and in epithelial cells and spermatozoa from efferent ductules and epididymis. EPPIN staining was observed on the middle and principal pieces of the flagellum of testicular spermatozoa. Epididymal spermatozoa had more intense EPPIN staining on the flagellum, and the EPPIN staining became apparent on the head and neck regions. This suggested that the EPPIN found on maturing spermatozoa was secreted primarily by the epithelial cells of the epididymis. Surgical castration down-regulated EPPIN expression levels (mRNA and protein) in the caput and cauda epididymis, an effect reversed by testosterone replacement. Altogether, our data suggested that EPPIN expression in rats is more widespread than in humans and mice, and is androgen-dependent in the epididymis. This species could be used as an experimental model to further study EPPIN's role in male fertility.

Characterization of EPPIN's semenogelin I binding site: a contraceptive drug target

Epididymal protease inhibitor (EPPIN) is found on the surface of spermatozoa and works as a central hub for a sperm surface protein complex (EPPIN protein complex [EPC]) that inhibits sperm motility on the binding of semenogelin I (SEMG1) during ejaculation. Here, we identify EPPIN's amino acids involved in the interactions within the EPC and demonstrate that EPPIN's sequence C102-P133 contains the major binding site for SEMG1. Within the same region, the sequence F117-P133 binds the EPC-associated protein lactotransferrin (LTF). We show that residues Cys102, Tyr107, and Phe117 in the EPPIN C-terminus are required for SEMG1 binding. Additionally, residues Tyr107 and Phe117 are critically involved in the interaction between EPPIN and LTF. Our findings demonstrate that EPPIN is a key player in the protein-protein interactions within the EPC. Target identification is an important step toward the development of a novel male contraceptive, and the functionality of EPPIN's residues Cys102, Tyr107, and Phe117 offers novel opportunities for contraceptive compounds that inhibit sperm motility by targeting this region of the molecule.

Les approches épididymaires de la contraception masculine

L’offre en matière de moyens contraceptifs masculins est limitée et, en particulier, à ce jour il n’existe pas de contraception hormonale masculine sur le marché. L’épididyme, dans lequel les spermatozoïdes acquièrent leurs capacités fécondantes et où ils sont stockés, s’avère être un site intéressant à cibler. Cette revue vise à présenter de façon synthétique les quelques pistes prometteuses qui ont émergé ces dernières années.

Lactoferrin: an alternative view of its role in human biological fluids

Lactoferrin is a major component of biologically important mucosal fluids and of the specific granules of neutrophils. Understanding its biological function is essential for understanding neutrophil- and mucosal-mediated immunity. In this review, we reevaluate the in vivo functions of human lactoferrin (hLF) emphasizing in vivo studies and in vitro studies performed in biologically relevant fluids. We discuss the evidence in the literature that supports (or does not support) proposed roles for hLF in mucosal immunity and in neutrophil function. We argue that the current literature supports a microbiostatic role, but not a microbicidal role, for hLF in vivo. The literature also supports a role for hLF in inhibiting colonization and infection of epithelial surfaces by microorganisms and in protecting tissues from neutrophil-mediated damage. Using this information, we briefly discuss hLF in the context of the complex biological fluids in which it is found.

Presence, localization, and origin of clusterin in normal human spermatozoa

PURPOSE

Clusterin in mammalian semen is a secretory form of clusterin (sCLU) with the heterodimeric structure. It is secreted by the epididymis and seminal vesicle. It is generally agreed that clusterin mainly exists on the surface of abnormal spermatozoa and is implicated in decreased sperm motility, sperm aggregation and infertility. However, few studies observe clusterin in normal spermatozoa, which is presumed to be a novel form. Up to now, the systematical information about the presence, localization, origin and function of clusterin in normal human spermatozoa has yet not been established. The aim of our current study is to systematically research clusterin in normal human spermatozoa.

METHODS

We detected the presence of clusterin via western blot, explored the localization of clusterin using immunofluorescence, and investigated the origin and distribution of clusterin in human testis by western blot and immunohistochemistry.

RESULTS

We found native clusterin in the inner plasma membrane of normal human spermatozoa. It was derived from the testis and showed similar molecular weight and heterodimeric structure compared with sCLU in semen and on the surface of abnormal spermatozoa.

CONCLUSION

Clusterin in normal spermatozoa should be self-synthesized during the later stage of spermatogenesis. The different localization and origin suggested that the clusterin observed by us may be a novel form compared with conventional sCLU on the surface of abnormal spermatozoa.

Loss of calcium in human spermatozoa via EPPIN, the semenogelin receptor

The development of a new male contraceptive requires a transition from animal model to human and an understanding of the mechanisms involved in the target's inhibition of human spermatozoan fertility. We now report that semenogelin (SEMG1) and anti-EPPIN antibodies to a defined target site of 21 amino acids on the C terminal of EPPIN cause the loss of intracellular calcium, as measured by Fluo-4. The loss of intracellular calcium explains our previous observations of an initial loss of progressive motility and eventually the complete loss of motility when spermatozoa are treated with SEMG1 or anti-EPPIN antibodies. Thimerosal can rescue the effects of SEMG1 on motility, implying that internal stores of calcium are not depleted. Additionally, SEMG1 treatment of spermatozoa decreases the intracellular pH, and motility can be rescued by ammonium chloride. The results of this study demonstrate that EPPIN controls sperm motility in the ejaculate by binding SEMG1, resulting in the loss of calcium, most likely through a disturbance of internal pH and an inhibition of uptake mechanisms. However, the exact steps through which the EPPIN-SEMG1 complex exerts its effect on internal calcium levels are unknown. Anti-EPPIN antibodies can substitute for SEMG1, and, therefore, small-molecular weight compounds that mimic anti-EPPIN binding should be able to substitute for SEMG1, providing the basis for a nonantibody, nonhormonal male contraceptive.

Functional studies of eppin

Our laboratory has characterized EPPIN [epididymal protease inhibitor; SPINLW1] as a novel gene on human chromosome 20q12-13.2, which encodes a cysteine-rich protein of 133 amino acids with a calculated molecular mass of 15.283 kDa, containing both Kunitz-type and WAP (whey acidic protein)-type four-disulfide core consensus sequences. Eppin is secreted by Sertoli cells in the testis and epididymal epithelial cells; it is predominantly a dimer, although multimers often exist, and in its native form eppin is found on the human sperm surface complexed with LTF (lactotransferrin) and clusterin. During ejaculation SEMG (semenogelin) from the seminal vesicles binds to the eppin protein complex, initiating a series of events that define eppin's function. Eppin's functions include (i) modulating PSA (prostate-specific antigen) enzyme activity, (ii) providing antimicrobial protection and (iii) binding SEMG thereby inhibiting sperm motility. As PSA hydrolyses SEMG in the ejaculate coagulum, spermatozoa gain progressive motility. We have demonstrated that eppin is essential for fertility because immunization of male monkeys with recombinant eppin results in complete, but reversible, contraception. To exploit our understanding of eppin's function, we are developing compounds that inhibit eppin–SEMG interaction and mimic anti-eppin, inhibiting sperm motility. These compounds should have potential as a male contraceptive.

Differing evolutionary histories of WFDC8 (short-term balancing) in Europeans and SPINT4 (incomplete selective sweep) in Africans

The whey acidic protein four-disulfide core (WFDC) gene cluster on human chromosome 20q13, harbors 15 small serine protease inhibitor genes with roles in innate immunity, reproduction, and regulation of endogenous proteases kallikreins. The WFDC cluster has emerged as a prime example of rapid diversification and adaptive evolution in primates. This study sought a better understanding of the evolutionary history of WFDC genes in humans and focused on exploring the adaptive selection signatures found in populations of European (Utah residents with ancestry from northern and western Europe [CEU]) and African (Yoruba from Ibadan, in Nigeria [YRI]) ancestry in a genome-wide scan for putative targets of recent adaptive selection. Our approach included resequencing coding and noncoding regions of WFDC6, EPPIN, and WFDC8 in 20 CEU and of SPINT4 in 20 YRI individuals. We generated 302 kb and 60 kb of high-quality sequence data from CEU and of YRI populations, respectively, enabling the identification of 72 single nucleotide polymorphisms. Using classic neutrality tests, empirical and haplotype-based analysis, we pinpointed WFDC8 and SPINT4 as the likely targets of short-term balancing selection in the CEU population, and recent positive selection (incomplete selective sweep) in the YRI population. Putative candidate variants targeted by selection include 44A (rs7273669A) for WFDC8, which may downregulate gene expression by abolishing the binding site of two transcription factors; and a haplotype configuration [Ser73+98A] (rs6017667A-rs6032474A) for SPINT4, which may simultaneously affect protein function and gene regulation. We propose that the evolution of WFDC8 and SPINT4 has been shaped by complex selective scenarios due to the interdependence of variant fitness and ecological variables.

Identification of increased amounts of eppin protein complex components in sperm cells of diabetic and obese individuals by difference gel electrophoresis

Metabolic disorders like diabetes mellitus and obesity may compromise the fertility of men and women. To unveil disease-associated proteomic changes potentially affecting male fertility, the proteomes of sperm cells from type-1 diabetic, type-2 diabetic, non-diabetic obese and clinically healthy individuals were comparatively analyzed by difference gel electrophoresis. The adaptation of a general protein extraction procedure to the solubilization of proteins from sperm cells allowed for the resolution of 3187 fluorescent spots in the difference gel electrophoresis image of the master gel, which contained the entirety of solubilized sperm proteins. Comparison of the pathological and reference proteomes by applying an average abundance ratio setting of 1.6 and a p ≤ 0.05 criterion resulted in the identification of 79 fluorescent spots containing proteins that were present at significantly changed levels in the sperm cells. Biometric evaluation of the fluorescence data followed by mass spectrometric protein identification revealed altered levels of 12, 71, and 13 protein species in the proteomes of the type-1 diabetic, type-2 diabetic, and non-diabetic obese patients, respectively, with considerably enhanced amounts of the same set of one molecular form of semenogelin-1, one form of clusterin, and two forms of lactotransferrin in each group of pathologic samples. Remarkably, β-galactosidase-1-like protein was the only protein that was detected at decreased levels in all three pathologic situations. The former three proteins are part of the eppin (epididymal proteinase inhibitor) protein complex, which is thought to fulfill fertilization-related functions, such as ejaculate sperm protection, motility regulation and gain of competence for acrosome reaction, whereas the putative role of the latter protein to function as a glycosyl hydrolase during sperm maturation remains to be explored at the protein/enzyme level. The strikingly similar differences detected in the three groups of pathological sperm proteomes reflect a disease-associated enhanced formation of predominantly proteolytically modified forms of three eppin protein complex components, possibly as a response to enduring hyperglycemia and enhanced oxidative stress.

Is there a role for immunocontraception?

The world's population is continuing to grow at an alarming rate and yet no novel methods of contraception have been introduced since 1960s. The paucity of our current contraceptive armoury is indicated by the 46 million abortions that are performed each year, largely in developing countries where population growth is greatest. Thus, whatever new forms of fertility control we develop for the next millennium, the particular needs of developing countries should be borne in mind. Contraceptive vaccines have the potential to provide safe, effective, prolonged, reversible protection against pregnancy in a form that can be easily administered in the Third World. In this review we consider the contraceptive targets that might be pursued, how vaccines might be engineered and the problems generated by inter-individual variations in antibody titre. We conclude that the specifications for a safe, effective, reversible vaccine are more likely to be met in animals than man.

The use of anti-VDAC2 antibody for the combined assessment of human sperm acrosome integrity and ionophore A23187-induced acrosome reaction

Voltage-dependent anion channel (VDAC) is mainly located in the mitochondrial outer membrane and participates in many biological processes. In mammals, three VDAC subtypes (VDAC1, 2 and 3) have been identified. Although VDAC has been extensively studied in various tissues and cells, there is little knowledge about the distribution and function of VDAC in male mammalian reproductive system. Several studies have demonstrated that VDAC exists in mammalian spermatozoa and is implicated in spermatogenesis, sperm maturation, motility and fertilization. However, there is no knowledge about the respective localization and function of three VDAC subtypes in human spermatozoa. In this study, we focused on the presence of VDAC2 in human spermatozoa and its possible role in the acrosomal integrity and acrosome reaction using specific anti-VDAC2 monoclonal antibody for the first time. The results exhibited that native VDAC2 existed in the membrane components of human spermatozoa. The co-incubation of spermatozoa with anti-VDAC2 antibody did not affect the acrosomal integrity and acrosome reaction, but inhibited ionophore A23187-induced intracellular Ca²⁺ increase. Our study suggested that VDAC2 was located in the acrosomal membrane or plasma membrane of human spermatozoa, and played putative roles in sperm functions through mediating Ca²⁺ transmembrane transport.

Characterization of lactoferrin receptor on human spermatozoa

Lactoferrin (LF) is abundant in human seminal plasma and on sperm surfaces. However, lactoferrin receptor (LFR) on human spermatozoa has not yet been reported. To study the expression, localization and characteristics of LFR on human spermatozoa, different experimental approaches were applied: LFR gene was amplified from a human testis cDNA library and recombinant LFR (rLFR) protein was produced in the expression vector Escherichia coli BL21 (DE3); human sperm membrane proteins were extracted and analysed via Western blot; the binding of LF to LFR was investigated by Far-Western blot, immunoprecipitation and autoradiography analysis and the localization of LFR on sperm surfaces was detected using immunofluorescence. LFR gene was amplified from a human testis cDNA library and the molecular weight of rLFR was 34kDa. The native LFR on human spermatozoa was a 136-kDa tetramer which was anchored to the sperm head and mid-piece through glycophosphatidylinositol. LF could bind to LFR competitively in vitro. As far as is known, this study has elucidated for the first time that LFR was expressed at the testis level, was anchored to the sperm membrane by glycophosphatidylinositol during spermatogenesis. LFR may play important roles through binding to and mediating LF.