Identification of hydrolase binding activities of the acrosomal matrix of hamster spermatozoa

Identification of bovine sperm acrosomal proteins that interact with a 32-kDa acrosomal matrix protein

Mammalian fertilization is accomplished by the interaction between sperm and egg. Previous studies from this laboratory have identified a stable acrosomal matrix assembly from the bovine sperm acrosome termed the outer acrosomal membrane-matrix complex (OMC). This stable matrix assembly exhibits precise binding activity for acrosin and N-acetylglucosaminidase. A highly purified OMC fraction comprises three major (54, 50, and 45 kDa) and several minor (38-19 kDa) polypeptides. The set of minor polypeptides (38-19 kDa) termed "OMCrpf polypeptides" is selectively solubilized by high-pH extraction (pH 10.5), while the three major polypeptides (55, 50, and 45 kDa) remain insoluble. Proteomic identification of the OMC32 polypeptide (32 kDa polypeptide isolated from high-pH soluble fraction of OMC) yielded two peptides that matched the NCBI database sequence of acrosin-binding protein. Anti-OMC32 recognized an antigenically related family of polypeptides (OMCrpf polypeptides) in the 38-19-kDa range with isoelectric points ranging between 4.0 and 5.1. Other than glycohydrolases, OMC32 may also be complexed to other acrosomal proteins. The present study was undertaken to identify and localize the OMC32 binding polypeptides and to elucidate the potential role of the acrosomal protein complex in sperm function. OMC32 affinity chromatography of a detergent-soluble fraction of bovine cauda sperm acrosome followed by mass spectrometry-based identification of bound proteins identified acrosin, lactadherin, SPACA3, and IZUMO1. Co-immunoprecipitation analysis also demonstrated the interaction of OMC32 with acrosin, lactadherin, SPACA3, and IZUMO1. Our immunofluorescence studies revealed the presence of SPACA3 and lactadherin over the apical segment, whereas IZUMO1 is localized over the equatorial segment of Triton X-100 permeabilized cauda sperm. Immunoblot analysis showed that a significant portion of SPACA3 was released after the lysophosphatidylcholine (LPC)-induced acrosome reaction, whereas the IZUMO1 and lactadherin polypeptides remain associated to the particulate fraction. Almost entire population of bovine sperm IZUMO1 relocates to the equatorial segment during the LPC-induced acrosome reaction. We propose that the interaction of OMC32 matrix polypeptide with detergent-soluble acrosomal proteins regulates the release of hydrolases/other acrosomal protein(s) during the acrosome reaction.

Identification and characterization of a bovine sperm acrosomal matrix protein and its mechanism of interaction with acrosomal hydrolases

Fertilization, the union of male and female gametes to create offspring, is an intricate biological process dependent upon several biochemical and physiological events. Our understanding of the functions of protein constituents of the outer acrosomal membrane-associated matrix complex (OMC) is limited. A highly purified OMC fraction isolated from bovine cauda sperm heads comprised 54, 50, 45, and 38-19 kDa polypeptides. The objective of this study is to identify and characterize the 45 kDa (OMC45) polypeptide, to define its role in binding acrosomal hydrolases, and to examine the fate of OMC45 polypeptide during the acrosome reaction. We isolated OMC45 polypeptide from the high-pH insoluble fraction of OMC. Proteomic analysis of OMC45 by MALDI-TOF-TOF yielded eight peptides that matched the NCBI database sequence of Tektin 3 (TEKT3). Triton X-100-permeabilized cauda sperm exhibited intense staining of the acrosomal segment with anti-OMC45 and anti-TEKT3. The OMC45 polypeptide was solubilized by radio-immunoprecipitation assay buffer extraction. The solubilized fraction was subjected to immunoprecipitation analysis. The OMC45 polypeptide was recovered in the anti-OMC45 immunoprecipitation pellet. An identical blot stained with anti-TEKT3 exhibited the presence of TEKT3 polypeptide in the anti-OMC45 pellet. Our immunofluorescence and biochemical studies confirm the proteomics identification of OMC45 polypeptide and that it exhibits a sequence similarity to TEKT3. OMC45 glycoprotein possesses both N-linked and O-linked oligosaccharides. Deglycosylated OMC45 revealed a significant reduction in both acrosin and N-acetylglucosaminidase (NAGA) binding in comparison with acrosin and NAGA binding to a native OMC45 polypeptide, demonstrating the important role of oligosaccharides in hydrolase binding. OMC45 polypeptide is not released during the acrosome reaction but remains in the particulate cell subfraction, associated with the hybrid membrane complex.

Identification of peroxiredoxin-5 in bovine cauda epididymal sperm

Developing spermatozoa require a series of posttesticular modifications within the luminal environment of the epididymis to achieve maturation; this involves several surface modifications including changes in plasma membrane lipids, proteins, carbohydrates, and alterations in the outer acrosomal membrane. Epididymal maturation can therefore allow sperm to gain forward motility and fertilization capabilities. The objective of this study was to identify maturation-dependent protein(s) and to investigate their role with the production of functionally competent spermatozoa. Lectin blot analyses of caput and cauda sperm plasma membrane fractions identified a 17.5 kDa wheat germ agglutinin (WGA)-binding polypeptide present in the cauda sperm plasma membrane not in the caput sperm plasma membrane. Among the several WGA-stained bands, the presence of a 17.5 kDa WGA-binding polypeptide band was detected only in cauda epididymal fluid not in caput epididymal fluid suggesting that the 17.5 kDa WGA-binding polypeptide is secreted from the cauda epididymis and binds to the cauda sperm plasma membrane during epididymal transit. Proteomic identification of the 17.5 kDa polypeptide yielded 13 peptides that matched the sequence of peroxiredoxin-5 (PRDX5) protein (Bos Taurus). We propose that bovine cauda sperm PRDX5 acts as an antioxidant enzyme in the epididymal environment, which is crucial in protecting the viable sperm population against the damage caused by endogeneous or exogeneous peroxide.

Surfing the wave, cycle, life history, and genes/proteins expressed by testicular germ cells. Part 2: changes in spermatid organelles associated with development of spermatozoa

Spermiogenesis is a long process whereby haploid spermatids derived from the meiotic divisions of spermatocytes undergo metamorphosis into spermatozoa. It is subdivided into distinct steps with 19 being identified in rats, 16 in mouse and 8 in humans. Spermiogenesis extends over 22.7 days in rats and 21.6 days in humans. In this part, we review several key events that take place during the development of spermatids from a structural and functional point of view. During early spermiogenesis, the Golgi apparatus forms the acrosome, a lysosome-like membrane bound organelle involved in fertilization. The endoplasmic reticulum undergoes several topographical and structural modifications including the formation of the radial body and annulate lamellae. The chromatoid body is fully developed and undergoes structural and functional modifications at this time. It is suspected to be involved in RNA storing and processing. The shape of the spermatid head undergoes extensive structural changes that are species-specific, and the nuclear chromatin becomes compacted to accommodate the stream-lined appearance of the sperm head. Microtubules become organized to form a curtain or manchette that associates with spermatids at specific steps of their development. It is involved in maintenance of the sperm head shape and trafficking of proteins in the spermatid cytoplasm. During spermiogenesis, many genes/proteins have been implicated in the diverse dynamic events occurring at this time of development of germ cells and the absence of some of these have been shown to result in subfertility or infertility.

Impairment of adult male reproductive function in rats exposed to ethanol since puberty

The objective of this work was to evaluate reproductive function in adult male rats exposed to ethanol since puberty. Male Wistar rats, 50 days old, received a liquid diet with 36% of the daily calories derived from ethanol or an isocaloric control diet for 55 days. The ethanol treatment impaired sexual behavior and only 22% of these rats reached ejaculation. The fertility of ethanol-treated animals was significantly reduced, mainly after natural mating. Serum testosterone levels, daily sperm production and sperm count in the epididymis were also significantly diminished after ethanol treatment, associated with an acceleration of the sperm transit time in the cauda epididymidis, decrease in sperm motility and increased percentage of abnormal shaped sperm cells. The results showed that chronic consumption of ethanol beginning at puberty impairs the reproductive function of adult male rats.

Sperm-zona pellucida interaction and immunological infertility

Immune reactions against gametes appear to be physiologically important for the maintenance of homeostasis in reproduction. In contrast, aberration of the immune homeostasis might give rise to 'immunological infertility'. Antisperm antibodies cause infertility by blocking fertilization. The mechanism can be explained as inhibiting the acrosome reaction of sperm by their blocking effect on capacitation through inhibiting an increase of fluidity of the sperm membrane. Autoantibodies against zona pellucida also cause infertility by blocking sperm-zona pellucida interaction, though the definitive mechanism has not been elucidated. Pretreatment of spermatozoa with D-mannnose completely inhibited sperm penetration through, but not binding to, the zona pellucida. Furthermore, very rapid kinetics between sperm extracts and D-mannnose by a BIAcore apparatus suggest that a D-mannose ligand of the sperm surface is easy to bind to and dissociate from a D-mannose residue in the sperm receptor site on the zona pellucida. Thus, D-mannnose on the human zona pellucida might be an essential molecule acting as a second sperm receptor, through which sperm penetrate into the zona pellucida. Because these antibodies appear to not cause any deleterious clinical symptoms, sperm and zona pellucida antigens are promising candidates in the development of an immunocontraceptive. (Reprod Med Biol 2006; 5: 95-104).

Sperm-zona pellucida interaction and immunological infertility

Immune reactions against gametes appear to be physiologically important for the maintenance of homeostasis in reproduction. In contrast, aberration of the immune homeostasis might give rise to 'immunological infertility'. Antisperm antibodies cause infertility by blocking fertilization. The mechanism can be explained as inhibiting the acrosome reaction of sperm by their blocking effect on capacitation through inhibiting an increase of fluidity of the sperm membrane. Autoantibodies against zona pellucida also cause infertility by blocking sperm-zona pellucida interaction, though the definitive mechanism has not been elucidated. Pretreatment of spermatozoa with D-mannnose completely inhibited sperm penetration through, but not binding to, the zona pellucida. Furthermore, very rapid kinetics between sperm extracts and D-mannnose by a BIAcore apparatus suggest that a D-mannose ligand of the sperm surface is easy to bind to and dissociate from a D-mannose residue in the sperm receptor site on the zona pellucida. Thus, D-mannnose on the human zona pellucida might be an essential molecule acting as a second sperm receptor, through which sperm penetrate into the zona pellucida. Because these antibodies appear to not cause any deleterious clinical symptoms, sperm and zona pellucida antigens are promising candidates in the development of an immunocontraceptive. (Reprod Med Biol 2006; 5: 95-104).

Zonadhesin assembly into the hamster sperm acrosomal matrix occurs by distinct targeting strategies during spermiogenesis and maturation in the epididymis

Zonadhesin is the only sperm protein known to bind in a species-specific manner to the zona pellucida. The zonadhesin precursor is a mosaic protein with a predicted transmembrane segment and large extracellular region composed of cell adhesion, mucin, and tandem von Willebrand D domains. Because the precursor possesses a predicted transmembrane segment and localizes to the anterior head, the mature protein was presumed to be a sperm surface zona pellucida-binding protein. In this study of hamster spermatozoa, we demonstrate that zonadhesin does not localize to the sperm surface but is instead a constituent of the acrosomal matrix. Immunoelectron microscopy revealed that distinct targeting pathways during spermiogenesis and sperm maturation in the epididymis result in trafficking of zonadhesin to the acrosomal matrix. In round spermatids, zonadhesin localized specifically to the acrosomal membrane, where it appeared to be evenly distributed between the outer and inner membrane domains. Subsequent redistribution of zonadhesin resulted in its elimination from the inner acrosomal membrane and restriction to the outer acrosomal membrane of the apical and principal segments and the contents of the posterior acrosome. During sperm maturation in the epididymis, zonadhesin dissociated from the outer acrosomal membrane and became incorporated into the forming acrosomal matrix. These data suggest an important structural role for zonadhesin in assembly of the acrosomal matrix and further support the view that the species specificity of zona pellucida adhesion is mediated by egg-binding proteins contained within the acrosome rather than on the periacrosomal plasma membrane.

Involvement of carbohydrate molecules on zona pellucida in human fertilization

Although the involvement of several receptors and ligand molecules in sperm-zona interaction in many species have been proposed, there has been a little analysis of the kinetics between these molecules during the interaction. In the present study, we applied the detection method using surface plasmon resonance (SPR) by a BIAcore apparatus for the analysis of the putative receptor-ligand interaction of sperm-egg binding. Mannose-BSA or [man](5)-[GlcNAc](2)-Asp was immobilized on the surface of a sensor chip. When concanavalin A (Con A) was delivered to each of two different sensor chips to evaluate their usefulness, the resonance signal after sample injection onto a [man](5)-[GlcNAc](2)-Asp-fixed chip decreased rapidly than the mannose-BSA-fixed chip. However, the amount of binding for Con A during the injection onto the [man](5)-[GlcNAc](2)-Asp-fixed chip was high. When acid sperm extracts (acid extracts) and fractions through a CM column, containing protease activity (protease fractions), were delivered to the mannose-BSA-fixed chip, the SPR signal during the injection was not obviously changed compared with that of the control. However, when sperm samples were delivered to the [man](5)-[GlcNAc](2)-Asp-fixed chip, the SPR response during the injection was enormous. These results suggest that the [man](5)-[GlcNAc](2)-Asp-fixed chip is more useful than the mannose-BSA-fixed chip for investigating the interactions with sperm extracts and that the sensitive method using SPR by a BIAcore apparatus is applicable for the analysis of the putative receptor-ligand interaction of sperm-egg binding.

A mouse acrosomal cortical matrix protein, MC41, has ZP2-binding activity and forms a complex with a 75-kDa serine protease

Sperm with a large acrosome such as that of guinea pigs and hamsters have a subdomain structure in the anterior acrosome, but the mouse acrosome looks homogeneous and its matrix has not been precisely analyzed. The intra-acrosomal protein MC41 is localized in the cortical region of the mouse anterior acrosome, suggesting a subdomain structure in the mouse acrosome. Thus, the present study was undertaken to analyze the mouse acrosomal matrix using an anti-MC41 antibody. When mouse sperm were treated with 2% Triton X-100, Triton-insoluble matrix components remained in the acrosomal cortical region. Immunogold for MC41 labeled the Triton X-100 and high-salt-insoluble matrix components, demonstrating that MC41 is a subdomain-specific acrosomal matrix protein. We further examined interactions of MC41 with acrosomal proteases and zona proteins. A serine protease of 75 kDa was associated with MC41 under low-salt conditions, presumably forming a complex. Far Western blotting technique indicated that MC41 bound to both ZP2 and ZP2(f) in the presence of high-salt-soluble sperm proteins. In acrosome-reacting sperm, MC41 was present on the hybrid vesicles formed by the fusion of the plasma and outer acrosomal membranes. Presumably, MC41 has a significant role in secondary sperm-zona binding during the acrosomal reaction.

Alkalinization of acrosome measured by GFP as a pH indicator and its relation to sperm capacitation

We previously targeted EGFP (a mutant of green fluorescent protein) to the lumen of the mouse sperm acrosome and reported the time course of EGFP release during the acrosome reaction. In the study reported here, we estimated the pH within the mouse sperm acrosome utilizing the pH-dependent nature of EGFP fluorescence. The average intra-acrosomal pH was estimated to be 5.3 +/- 0.1 immediately after sperm preparation, gradually increasing to 6.2 +/- 0.3 during 120 min of incubation in TYH media suitable for capacitation. Spontaneous acrosome reactions were noted to increase concomitantly with acrosomal alkalinization during incubation. We also demonstrated that acrosomal antigens detected by monoclonal antibodies MN7 and MC41 did not dissolve following the acrosome reaction in pH 5.3 media, but dissolved at pH 6.2. These data suggest that acrosomal alkalinization during incubation conducive for sperm capacitation may function to alter acrosomal contents and prepare them for release during the acrosome reaction.

Differential release of guinea pig sperm acrosomal components during exocytosis

The contents of the sperm acrosome are compartmentalized at the biochemical and morphological levels. Biochemically, the acrosome can be considered to be comprised of two compartments: one consisting of readily soluble proteins and one containing a particulate acrosomal matrix. To test the hypothesis that compartmentalization affects the release of acrosomal components during the course of secretion in guinea pig sperm, we examined the relationship between the presence of specific proteins and acrosomal status and monitored the recovery of acrosomal constituents in the medium surrounding sperm induced to undergo exocytosis with the ionophore A23187. Cysteine-rich secretory protein 2 (CRISP-2), a soluble component of the acrosome, was rapidly lost from the acrosome soon after ionophore treatment. However, acrosomal matrix components remained associated with the sperm for longer periods. AM67, a matrix component and the guinea pig orthologue of the mouse sperm zona pellucida-binding protein sp56, was released at a slower rate than was CRISP-2 but at a faster rate than were two other matrix proteins, AM50 and proacrosin. Coincident with their release from the sperm, AM50 and proacrosin were posttranslationally modified, probably by proteolysis. The release of proacrosin from the matrix appears associated with the conversion of this protein to the enzymatically active acrosin protease. These results provide strong support for the hypothesis that compartmentalization plays a significant role in regulating the release of proteins during the course of acrosomal exocytosis. Acrosomal matrix proteins remain associated with the sperm for prolonged periods of time following the induction of acrosomal exocytosis, suggesting that transitional acrosomal intermediates may have significant functions in the fertilization process.

Identification of a hamster epididymal region-specific secretory glycoprotein that binds nonviable spermatozoa

Even though the epididymis produces an environment promoting sperm maturation and viability, some sperm do not survive transit through the epididymal tubule. Mechanisms that segregate the epididymal epithelium and/or the viable sperm population from degenerating spermatozoa are poorly understood. We report here the identification and characterization of HEP64, a 64-kDa glycoprotein secreted by principal cells of the corpus and proximal cauda epididymidis of the hamster that specifically binds to and coats dead/dying spermatozoa. The HEP64 monomer contains approximately 12 kDa carbohydrate and, following chemical deglycosylation, migrates as a approximately 52-kDa polypeptide. Both soluble (luminal fluid) and sperm-associated HEP64 are assembled into disulfide-linked high molecular weight oligomers that migrate as a doublet band of 260/280 kDa by nonreducing SDS-PAGE. In the epididymal lumen, HEP64 is concentrated into focal accumulations containing aggregates of structurally abnormal or degenerating spermatozoa, and examination of sperm suspensions reveals that HEP64 forms a shroudlike coating surrounding abnormal spermatozoa. The HEP64 glycoprotein firmly binds degenerating spermatozoa and is not released by either nonionic detergent or high salt extraction. Electron microscopic immunocytochemistry demonstrates that HEP64 localized to an amorphous coating surrounding the abnormal spermatozoa. The potential mechanisms by which this epididymal secretory protein binds dead spermatozoa as well as its possible functions in the sperm storage function of the cauda epididymidis are discussed.

Abnormalities in sperm acid glycosidases from infertile men with idiopathic oligoasthenoteratozoospermia

OBJECTIVE

To analyze and compare acid beta-glucuronidase, alpha-mannosidase, alpha-glycosidase, alpha-galactosidase, beta-galactosidase, and beta-N-acetylglucosaminidase activities in fertile and infertile patients.

DESIGN

An observational, controlled, clinical study.

SETTING

A university tertiary hospital.

PATIENT(S)

Thirty-six fertile controls, 24 infertile oligoasthenoteratozoospermic (OAT) patients, and 10 azoospermic patients, who served as negative controls.

INTERVENTION(S)

None.

MAIN OUTCOME MEASURE(S)

Analysis of the six glycosidase activities in seminal plasma and in solubilized spermatozoa.

RESULT(S)

alpha-galactosidase and beta-galactosidase activities in spermatozoa were significantly correlated with the serum levels of gonadotropins both in fertile controls and in OAT patients. The relative contribution of alpha-galactosidase and beta-galactosidase from the soluble fraction of spermatozoa to the total activity measured in the ejaculate of OAT patients was significantly lower than in fertile controls. The activities of beta-galactosidase and beta-N-acetylglucosaminidase in the soluble fraction of spermatozoa from OAT patients were significantly lower than in fertile controls. In seminal plasma, the activity of alpha-mannosidase from OAT patients was significantly higher than in fertile controls. The activity of beta-N-acetylglucosaminidase in the nonsoluble fraction of spermatozoa from OAT patients was three times higher than in fertile controls.

CONCLUSION(S)

The abnormalities in the distributions and contents of alpha-galactosidase, beta-galactosidase, and beta-N-acetylglucosaminidase in sperm suggest possible functional defects in spermatozoa from OAT infertile patients.

Difference of acrosomal serine protease system between mouse and other rodent sperm

A fraction of acrosomal proteins dispersed during calcium ionophore A23187-induced acrosome reaction was prepared from cauda epididymal sperm of wild-type and acrosin-deficient mice, rat, and hamster. The acrosome-reacted sperm were further extracted by Nonidet P-40 to obtain the detergent-soluble protein fraction. Activities of serine proteases in the two protein fractions were examined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis in the presence of gelatin. A mixture of 42- and 41-kDa gelatin-hydrolyzing proteases was found in both fractions of the wild-type mouse sperm, whereas the acrosin-deficient mouse sperm contained the active 42-kDa protease and apparently lacked the activity of the 41-kDa protease. However, exogenous bovine pancreatic trypsin compensated for the absence of acrosin in the protein fractions of the mutant mouse sperm; the gelatin-hydrolyzing activity of the 41-kDa protease appeared when the sperm proteins of the mutant mice were treated with pancreatic trypsin. Two-dimensional polyacrylamide gel electrophoresis revealed that the 42- and 41-kDa proteases were distinguished from acrosin by the isoelectric point and immunoreactivity with affinity-purified antibody against an oligopeptide corresponding to the N-terminal amino acid sequence of mouse proacrosin. Moreover, the gelatin-hydrolyzing proteins corresponding to these two proteases were not detected in rat and hamster sperm, in spite of the treatment of the sperm extracts with pancreatic trypsin, and the total amount of gelatin-hydrolyzing activities in mouse was much smaller than those in rat and hamster. These results may reflect the difference of the serine protease system for the sperm penetration through the egg zona pellucida between mouse and other rodent animals, possibly explaining why the acrosin-deficient mouse sperm are capable of penetrating the zona pellucida.

Use of lectins to characterize plasma membrane preparations from boar spermatozoa: a novel technique for monitoring membrane purity and quantity

The object of this study was to develop a method to quantify the amount of outer acrosomal membrane material in isolated plasma membranes from boar sperm cells. The cells were fractionated by nitrogen cavitation, and plasma membranes were isolated by subsequent differential centrifugation steps. Marker enzyme measurement showed that the plasma membrane isolates were enriched in plasma membrane markers and did not contain nuclei, inner acrosomal membranes, or mitochondria. Since there is no marker enzyme known for the outer acrosomal membrane, lectins were used for the detection of this membrane. The membrane specificity of a number of lectin conjugates was tested with fluorescence microscopy and transmission electron microscopy. Membrane binding of these lectin conjugates was quantified with flow-cytometry and an enzyme-linked lectin binding assay. Wheat germ agglutinin was specific for the plasma membrane while peanut agglutinin was specific for the outer acrosomal membrane. The use of these lectins made it possible for the first time to discriminate between these two membranes. The isolated plasma membrane fraction was enriched more than 10-fold (17-fold after further purification by a sucrose gradient) in plasma membrane material compared to outer acrosomal membrane material. Highly purified sperm plasma membranes should prove to be useful for research on primary sperm-zona interactions.

Effects of ethanol ingestion on epididymal glycosidases and fertility in the rat

Epididymal glycosidases play a role in sperm maturation by modifying sperm surface glycoproteins. To study the effects of ethanol on epididymal sperm maturation, ethanol (3 g/kg body weight as 25%, v/v) was administered to a group of rats by gastric-intubation twice daily for 30 days. In another group, rats were also treated with alcohol for 30 days but were then withdrawn from treatment for 30 days to assess the reversibility of ethanol-induced effects. Ethanol-induced changes in epididymal tissue and sperm glycosidases, cauda epididymal sperm motility and the fertility of rats were assessed. Ethanol treatment caused a marked decrease in the specific activities of glycosidases in both tissues and spermatozoa from epididymal segments. Cauda epididymal sperm motility and the fertility of ethanol-treated rats were significantly impaired compared to control rats fed an isocaloric diet. These changes are likely to be the consequence of direct and indirect effects of ethanol mediated through subnormal testosterone and dihydrotestosterone. Most of these changes were found to be reversible. The present study suggests that impaired activity of sperm glycosidases may be one of the factors responsible for defective sperm motility and fertilizing potential in ethanol-treated rats.