Levels of sulfogalactosylglycerolipid in capacitated motile and immotile mouse spermatozoa

17BIPHE2, an engineered cathelicidin antimicrobial peptide with low susceptibility to proteases, is an effective spermicide and microbicide against Neisseria gonorrhoeae

STUDY QUESTION

Is 17BIPHE2, an engineered cathelicidin antimicrobial peptide with low susceptibility to proteases, a better spermicide in cervicovaginal fluid (CVF) than its parental peptides, LL-37 and GF-17?

SUMMARY ANSWER

At the same mass concentration, 17BIPHE2 exhibited the highest spermicidal activity on human sperm resuspended in CVF-containing medium.

WHAT IS KNOWN ALREADY

LL-37 and its truncated peptide GF-17 exert both spermicidal and microbicidal activities, although they are prone to proteolytic degradation in body fluids.

STUDY DESIGN, SIZE, DURATION

Spermicidal activities of 17BIPHE2 were evaluated in vitro in mouse and human sperm, both resuspended in medium, and then on human sperm incubated in CVF-containing medium; in the latter condition, the spermicidal activity and peptide stability in CVF of 17BIPHE2 were compared with that of LL-37 and GF-17. The in vivo contraceptive effects of 17BIPHE2 and the reversibility thereof were then assessed in mice. Finally, in vitro microbicidal effects of 17BIPHE2 on Neisseria gonorrhoeae were determined.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Sperm motility and plasma membrane integrity were assessed by videomicroscopy and exclusion of Sytox Green, a membrane-impermeable fluorescent dye, respectively. Successful in vitro fertilization (IVF) was determined by the presence of two pronuclei in oocytes following their coincubation with capacitated untreated or 17BIPHE2-treated sperm. Sperm alone or with 17BIPHE2 were transcervically injected into female mice and successful in vivo fertilization was indicated by the formation of two-cell embryos 42-h postinjection, and by pregnancy through pup delivery 21-25 days afterwards. Peptide intactness was assessed by immunoblotting and HPLC. Reversibility of the contraceptive effects of 17BIPHE2 was evaluated by resumption of pregnancy of the female mice, pretranscervically injected with 17BIPHE2, following natural mating with fertile males. Minimum inhibitory/bactericidal concentrations of 17BIPHE2 on N. gonorrhoeae were obtained through microdilution broth assay.

MAIN RESULTS AND THE ROLE OF CHANCE

At the same mass concentration, 17BIPHE2 was a more effective spermicide than LL-37 or GF-17 on human sperm resuspended in CVF-containing medium, with the spermicidal concentration of 32.4 µM. This was mainly due to lower susceptibility of 17BIPHE2 to CVF proteases. Importantly, the reproductive tract of mouse females treated three times with 32.4 µM 17BIPHE2 remained normal and their fecundity resumed after stopping 17BIPHE2 treatment.

LIMITATIONS, REASONS FOR CAUTION

For ethical reasons, the inhibitory effects of 17BIPHE2 on fertilization and pregnancy cannot presently be performed in women. Also, while our study has proven the effectiveness of 17BIPHE2 as a spermicide for mouse and human sperm in vitro, dosage formulation (e.g. in hydrogel) of 17BIPHE2 still needs to be developed to allow 17BIPHE2 to remain in the vagina/uterine cavity with controlled release for its spermicidal action.

WIDER IMPLICATIONS OF THE FINDINGS

Since 17BIPHE2 also exerted bactericidal activity against N. gonorrhoeae at its spermicidal concentration, it is a promising candidate to be developed into a vaginal multipurpose prevention technology agent, thus empowering women against unplanned pregnancies and sexually transmitted infections.

STUDY FUNDING/COMPETING INTEREST(S)

This work was supported by the Canadian Institutes of Health Research (PJT 173268 to N.T.). There are no competing interests to declare.

TRIAL REGISTRATION NUMBER

N/A.

Accumulation of Seminolipid in Sertoli Cells Is Associated with Increased Levels of Reactive Oxygen Species and Male Subfertility: Studies in Aging Arsa Null Male Mice

Seminolipid (also known as sulfogalactosylglycerolipid-SGG), present selectively in male germ cells, plays important roles in spermatogenesis and sperm–egg interaction. The proper degradation of SGG in apoptotic germ cells is also as important. Sertoli cells first phagocytose apoptotic germ cells, then Sertoli lysosomal arylsulfatase A (ARSA) desulfates SGG, the first step of SGG degradation. We have reported that aging male Arsa^−/− mice become subfertile with SGG accumulation in Sertoli cell lysosomes, typical of a lysosomal storage disorder (LSD). Since reactive oxygen species (ROS) levels are increased in other glycolipid-accumulated LSDs, we quantified ROS in Arsa^−/− Sertoli cells. Our analyses indicated increases in superoxide and H₂O₂ in Arsa^−/− Sertoli cells with elevated apoptosis rates, relative to WT counterparts. Excess H₂O₂ from Arsa^−/− Sertoli cells could travel into testicular germ cells (TGCs) to induce ROS production. Our results indeed indicated higher superoxide levels in Arsa^−/− TGCs, compared with WT TGCs. Increased ROS levels in Arsa^−/− Sertoli cells and TGCs likely caused the decrease in spermatogenesis and increased the abnormal sperm population in aging Arsa^−/− mice, including the 50% decrease in sperm SGG with egg binding ability. In summary, our study indicated that increased ROS production was the mechanism through which subfertility manifested following SGG accumulation in Sertoli cells.

Castration causes an increase in lysosomal size and upregulation of cathepsin D expression in principal cells along with increased secretion of procathepsin D and prosaposin oligomers in adult rat epididymis

In the epididymis, lysosomal proteins of the epithelial cells are normally targeted from the Golgi apparatus to lysosomes for degradation, although their secretion into the epididymal lumen has been documented and associated with sperm maturation. In this study, cathepsin D (CatD) and prosaposin (PSAP) were examined in adult epididymis of control, and 2-day castrated rats without (Ct) and with testosterone replacement (Ct+T) to evaluate their expression and regulation within epididymal epithelial cells. By light microscope-immunocytochemistry, a quantitative increase in size of lysosomes in principal cells of Ct animals was noted from the distal initial segment to the proximal cauda. Androgen replacement did not restore the size of lysosomes to control levels. Western blot analysis revealed a significant increase in CatD expression in the epididymis of Ct animals, which suggested an upregulation of its expression in principal cells; androgens restored levels of CatD to that of controls. In contrast, PSAP expression in Ct animals was not altered from controls. Additionally, an increase in procathepsin D levels was noted from samples of the epididymal fluid of Ct compared to control animals, accompanied by an increased complex formation with PSAP. Moreover, an increased oligomerization of prosaposin was observed in the epididymal lumen of Ct rats, with changes reverted to controls in Ct+T animals. Taken together these data suggest castration causes an increased uptake of substrates that are acted upon by CatD in lysosomes of principal cells and in the lumen by procathepsin D. These substrates may be derived from apoptotic cells noted in the lumen of proximal regions and possibly by degenerating sperm in distal regions of the epididymis of Ct animals. Exploring the mechanisms by which lysosomal enzymes are synthesized and secreted by the epididymis may help resolve some of the issues originating from epididymal dysfunctions with relevance to sperm maturation.

Discovery of the First Human Arylsulfatase A Reversible Inhibitor Impairing Mouse Oocyte Fertilization

Arylsulfatase A (ARSA) plays a crucial role in the reproduction of mammals due to its involvement in the specific gamete interaction preceding sperm and egg fusion leading to fertilization. Recently, it has been shown that zona pellucida (ZP) sperm binding and in vivo fertilization in mice are markedly hampered by using a specific anti-ARSA antibody. Herein, the design and discovery of the first ARSA small molecule inhibitor based on a coumarin-containing polycycle are presented. Through a structure-based approach applied on our in-house library, compound 1r was identified as an ARSA reversible inhibitor (ARSAi); then its activity was validated through both surface plasmon resonance and biochemical inhibition experiments, the first providing a K_D value of 21 μM and the latter an IC₅₀ value of 13.2 μM. Further investigations highlighted that compound 1r induced 20% sperm death at 25 μM and also impaired sperm motility; nevertheless both the effects were mediated by ROS production, since they were rescued by the cotreatment of 1r and N-acetyl cysteine (NAC). Interestingly, while 1r was not able to hamper the ZP/sperm binding, it markedly decreased the in vitro oocyte fertilization by mouse sperm up to 60%. Notably, this effect was not hampered by 1r/NAC coadministration, hence allowing the ruling out of an ROS-dependent mechanism. In conclusion, herein is reported the first ever hit of ARSAi as a chemical tool that will enable better exploration of ARSA's biological role in fertilization as well as provide a starting point for developing 1r structure optimization aimed at increasing enzyme inhibition potency but also providing a deeper understanding of the involvement of ARSA in the fertilization pathway mechanism.

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.

5-aza-2'-deoxycytidine impairs mouse spermatogenesis at multiple stages through different usage of DNA methyltransferases

Mammalian spermatogenesis is a progressive process comprising spermatogonial proliferation, spermatocytic meiosis, and later spermiogenesis, which is considered to be under the regulation of epigenetic parameters. To gain insights into the significance of DNA methylation in early spermatogenesis, 5-azadC was used as a molecular biological tool to mimic the level of DNA methylation in vivo. Since the drug is incorporated into DNA during the S-phase, spermatogonia and spermatocytes would be affected primarily in mouse spermatogenesis. Adult male ICR mice were intraperitoneally injected with 5-azadC at a dose of 0.25mg/kg/day for 10 consecutive days, allowing us to examine its maximum effect on the kinetics of spermatogonia and spermatocytes. In this short-term protocol, 5-azadC induced significant histological abnormalities, such as a marked increase in apoptosis of spermatogonia and spermatocytes, followed by severe loss of spermatids, while after termination of 5-azadC treatment, normal histology was restored in the testis within 35days. Quantification of the methylation level of CCGG sites as well as whole DNA showed spermatogonial hypomethylation, which correlated with increased apoptosis of spermatogonia. Interestingly, the hypomethylated cells were simultaneously positive for tri-methylated histone H3 at K4. On the other hand, no changes in methylation level were found in spermatocytes, but PCNA staining clearly showed disordered accumulation of S-phase spermatocytes, which increased their apoptosis in stage XII. In addition, different immunohistochemical staining pattern was found for DNA methyltransferases (DNMTs); DNMT1was expressed in the majority of all germ cells, but DNMT3a and b were only expressed in spermatogonia. Our results indicate that 5-azadC caused DNA hypomethylation in spermatogonia, but induced prolongation of S-phase in spermatocytes, resulting in the induction of apoptosis in both cases. Thus, 5-azadC affects spermatogenesis at more than one differentiation stage with different mechanisms, probably due to the specific usage of DNMTs.

Effects of mechanical stresses on sperm function and fertilization rate in mice

In this study, we investigated whether any of the observed changes in mouse sperm function tests secondary to mechanical stresses (centrifugation and pipetting) correlate with sperm fertilization ability. Chinese Kunming mice were used as sperm and oocyte donors. Sperm samples were allocated evenly into centrifugation, pipette, and control groups. Sperm plasma membrane integrity (PMI), mitochondrial membrane permeability (MMP), baseline and stimulated intracellular ROS, and sperm fertilization ability were measured by hypo-osmotic swelling, flow cytometry, and fertilization tests. Parallel studies were conducted and all tests were repeated six times. Our results showed that after centrifugation, the progressive motility, average path velocity, and overall sperm motility and PMI decreased significantly (p < 0.05). In addition, the MMP level decreased significantly in viable sperm when the centrifugation condition reached 1,400 g × 15 minutes (p < 0.05). When pipetting was performed two or more times, progressive motility, average path velocity, and overall sperm motility decreased significantly (p < 0.05); when it was performed four or more times, sperm membrane integrity and intracellular basal ROS level of viable sperm was also significantly decreased (p < 0.05). In conclusion, various mechanical stresses seem to affect sperm function, however this does not appear to alter fertilization rate. Laboratory handling steps should be minimized to avoid unnecessary mechanical stresses being applied to sperm samples.

Investigation of the mechanisms by which the molecular chaperone HSPA2 regulates the expression of sperm surface receptors involved in human sperm-oocyte recognition

A unique characteristic of mammalian spermatozoa is that, upon ejaculation, they are unable to recognize and bind to an ovulated oocyte. These functional attributes are only realized following the cells' ascent of the female reproductive tract whereupon they undergo a myriad of biochemical and biophysical changes collectively referred to as 'capacitation'. We have previously shown that this functional transformation is, in part, engineered by the modification of the sperm surface architecture leading to the assembly and/or presentation of multimeric sperm-oocyte receptor complexes. In this study, we have extended our findings through the characterization of one such complex containing arylsulfatase A (ARSA), sperm adhesion molecule 1 (SPAM1) and the molecular chaperone, heat shock 70kDa protein 2 (HSPA2). Through the application of flow cytometry we revealed that this complex undergoes a capacitation-associated translocation to facilitate the repositioning of ARSA to the apical region of the human sperm head, a location compatible with a role in the mediation of sperm-zona pellucida (ZP) interactions. Conversely, SPAM1 appears to reorient away from the sperm surface, possibly reflecting its primary role in cumulus matrix dispersal preceding sperm-ZP recognition. The dramatic relocation of the complex was completely abolished by incubation of capacitating spermatozoa in exogenous cholesterol or broad spectrum protein kinase A (PKA) and tyrosine kinase inhibitors suggesting that it may be driven by alterations in membrane fluidity characteristics and concurrently by the activation of a capacitation-associated signal transduction pathway. Collectively these data afford novel insights into the sub-cellular localization and potential functions of multimeric protein complexes in human spermatozoa.

Quantification of seminolipid by LC-ESI-MS/MS-multiple reaction monitoring: compensatory levels in Cgt(+/⁻) mice

Seminolipid, also known as sulfogalactosylglycerolipid (SGG), plays important roles in male reproduction. Therefore, an accurate and sensitive method for SGG quantification in testes and sperm is needed. Here we compare SGG quantitation by the traditional colorimetric Azure A assay with LC-ESI-MS/MS using multiple reaction monitoring (MRM). Inclusion of deuterated SGG as the internal standard endowed accuracy to the MRM method. The results showed reasonable agreement between the two procedures for purified samples, but for crude lipid extracts, the colorimetric assay significantly overestimated the SGG content. Using ESI-MS/MS MRM, C16:0-alkyl/C16:0-acyl SGG of Cgt(+/⁻) mice was quantified to be 406.06 ± 23.63 μg/g testis and 0.13 ± 0.02 μg/million sperm, corresponding to 78% and 87% of the wild-type values, respectively. CGT (ceramide galactosyltransferase) is a critical enzyme in the SGG biosynthesis pathway. Cgt⁻/⁻ males depleted of SGG are infertile due to spermatogenesis arrest. However, Cgt(+/⁻) males sire offspring. The higher than 50% expression level of SGG in Cgt(+/⁻) animals, compared with the wild-type expression, might be partly due to compensatory translation of the active CGT enzyme. The results also indicated that 78% of SGG levels in Cgt(+/⁻) mice were sufficient for normal spermatogenesis.

Surfing the wave, cycle, life history, and genes/proteins expressed by testicular germ cells. Part 3: developmental changes in spermatid flagellum and cytoplasmic droplet and interaction of sperm with the zona pellucida and egg plasma membrane

Spermiogenesis constitutes the steps involved in the metamorphosis of spermatids into spermatozoa. It involves modification of several organelles in addition to the formation of several structures including the flagellum and cytoplasmic droplet. The flagellum is composed of a neck region and middle, principal, and end pieces. The axoneme composed of nine outer microtubular doublets circularly arranged to form a cylinder around a central pair of microtubules is present throughout the flagellum. The middle and principal pieces each contain specific components such as the mitochondrial sheath and fibrous sheath, respectively, while outer dense fibers are common to both. A plethora of proteins are constituents of each of these structures, with each playing key roles in functions related to the fertility of spermatozoa. At the end of spermiogenesis, a portion of spermatid cytoplasm remains associated with the released spermatozoa, referred to as the cytoplasmic droplet. The latter has as its main feature Golgi saccules, which appear to modify the plasma membrane of spermatozoa as they move down the epididymal duct and hence may be partly involved in male gamete maturation. The end product of spermatogenesis is highly streamlined and motile spermatozoa having a condensed nucleus equipped with an acrosome. Spermatozoa move through the female reproductive tract and eventually penetrate the zona pellucida and bind to the egg plasma membrane. Many proteins have been implicated in the process of fertilization as well as a plethora of proteins involved in the development of spermatids and sperm, and these are high lighted in this review.

Sperm-zona pellucida interaction: molecular mechanisms and the potential for contraceptive intervention

At the moment of insemination, millions of mammalian sperm cells are released into the female reproductive tract with the single goal of finding the oocyte. The spermatozoa subsequently ignore the thousands of cells they make contact with during their journey to the site of fertilization, until they reach the surface of the oocyte. At this point, they bind tenaciously to the acellular coat, known as the zona pellucida, which surrounds the oocyte and orchestrate a cascade of cellular interactions that culminate in fertilization. These exquisitely cell- and species- specific recognition events are among the most strategically important cellular interactions in biology. Understanding the cellular and molecular mechanisms that underpin them has implications for the etiology of human infertility and the development of novel targets for fertility regulation. Herein we describe our current understanding of the molecular basis of successful sperm-zona pellucida binding.

Presence of arylsulfatase A and sulfogalactosylglycerolipid in mouse ovaries: localization to the corpus luteum

Arylsulfatase A (AS-A) is a lysosomal enzyme, which catalyzes the desulfation of certain sulfogalactolipids, including sulfogalactosylglycerolipid (SGG), a molecule implicated in cell adhesion. In this report, immunocytochemistry revealed the selective presence of AS-A in the corpus luteum of mouse ovaries. Immunoblotting indicated that mouse corpus luteum AS-A had a molecular mass of 66 kDa, similar to AS-A of other tissues. Corpus luteum AS-A was active, capable of desulfating the artificial substrate, p-nitrocatechol sulfate, at the optimum pH of five. To understand further the role of AS-A in female reproduction, levels of AS-A were determined during corpus luteum development in pseudopregnant mice and during luteolysis after cessation of pseudopregnancy. Immunocytochemistry, immunoblotting and desulfation activity showed that AS-A expression was evident at the onset of pseudopregnancy in the newly formed corpora lutea, and its level increased steadily during gland development. The increase in the expression and activity of AS-A continued throughout luteolysis after the decrease in serum progesterone levels. We also observed the selective presence of SGG on the luteal cell surface in developed corpora lutea, as shown by immunofluorescence of mouse ovary sections as well as high-performance thin-layer chromatography of lipids isolated from mouse and pig corpora lutea. The identity of the "SGG" band on the thin layer silica plate was further validated by electrospray ionization mass spectrometry. Significantly, SGG disappeared in regressing corpora lutea. Therefore, lysosomal AS-A may be involved in cell-surface remodeling during luteolysis by desulfating SGG after its endocytosis and targeting to the lysosome.

Sperm surface arylsulfatase A can disperse the cumulus matrix of cumulus oocyte complexes

Cumulus cell layers of expanded cumulus oocyte complexes (COCs) are interlinked with networks of hyaluronic acid, chondroitin sulfate B proteoglycans and link proteins, and they can be dispersed by sperm surface hyaluronidases. In this report, we showed that arylsulfatase A (AS-A), existing on the sperm head surface, also had this dispersion action. Purified AS-A free of protease, hyaluronidase and chondroitinase activities could disperse the cumulus matrix of expanded COCs. However, this COC dispersion action was not associated with AS-A desulfation activity, assayed by using p-nitrocatecholsulfate (artificial substrate). COCs incubated for 1 h with sperm pretreated with anti-AS-A IgG in the presence of apigenin (a hyaluronidase inhibitor) did not exhibit matrix dispersion, whereas several cumulus layers were already dispersed in COCs incubated with sperm pretreated with preimmune IgG. Furthermore, sperm from AS-A null mice showed a significant delay in COC dispersion, compared with wild-type sperm. Within 1 h of sperm-COC co-incubation, the size of COCs incubated with AS-A null sperm was 65% of the original dimension, whereas that of COCs inseminated with wild-type sperm was only 17%. A further delay in COC dispersion by AS-A(-/-) mouse sperm was observed when apigenin was present in the co-incubation. We also showed for the first time that AS-A had a specific affinity for chondroitin sulfate B, a component of cumulus matrix proteoglycan networks; this might provide a mechanism of cumulus matrix destabilization induced by sperm surface AS-A.

The ether lipid-deficient mouse: Tracking down plasmalogen functions

Chemical and physico-chemical properties as well as physiological functions of major mammalian ether-linked glycerolipids, including plasmalogens were reviewed. Their chemical structures were described and their effect on membrane fluidity and membrane fusion discussed. The recent generation of mouse models with ether lipid deficiency offered the possibility to study ether lipid and particularly plasmalogen functions in vivo. Ether lipid-deficient mice revealed severe phenotypic alterations, including arrest of spermatogenesis, development of cataract and defects in central nervous system myelination. In several cell culture systems lack of plasmalogens impaired intracellular cholesterol distribution affecting plasma membrane functions and structural changes of ER and Golgi cisternae. Based on these phenotypic anomalies that were accurately described conclusions were drawn on putative functions of plasmalogens. These functions were related to cell-cell or cell-extracellular matrix interactions, formation of lipid raft microdomains and intracellular cholesterol homeostasis. There are several human disorders, such as Zellweger syndrome, rhizomelic chondrodysplasia punctata, Alzheimer's disease, Down syndrome, and Niemann-Pick type C disease that are distinguished by altered tissue plasmalogen concentrations. The role plasmalogens might play in the pathology of these disorders is discussed.

Percoll Gradient-Centrifuged Capacitated Mouse Sperm Have Increased Fertilizing Ability and Higher Contents of Sulfogalactosylglycerolipid and Docosahexaenoic Acid-Containing Phosphatidylcholine Compared to Washed Capacitated Mouse Sperm1

Although Percoll gradient centrifugation has been used routinely to prepare motile human sperm, its use in preparing motile mouse sperm has been limited. Here, we showed that Percoll gradient-centrifuged (PGC) capacitated mouse sperm had markedly higher fertilizing ability (sperm-zona pellucida [ZP] binding and in vitro fertilization) than washed capacitated mouse sperm. We also showed that the lipid profiles of PGC capacitated sperm and washed capacitated sperm differed significantly. The PGC sperm had much lower contents of cholesterol and phospholipids. This resulted in relative enrichment of male germ cell-specific sulfogalactosylglycerolipid (SGG), a ZP-binding ligand, in PGC capacitated sperm, and this would explain, in part, their increased ZP-binding ability compared with that of washed capacitated sperm. Analyses of phospholipid fatty acyl chains revealed that PGC capacitated sperm were enriched in phosphatidylcholine (PC) molecular species containing highly unsaturated fatty acids (HUFAs), with docosahexaenoic acid (DHA; C22: 6n-3) being the predominant HUFA (42% of total hydrocarbon chains of PC). In contrast, the level of PC-HUFAs comprising arachidonic acid (20:4n-6), docosapentaenoic acid (C22:5n-6), and DHA in washed capacitated sperm was only 27%. Having the highest unsaturation degree among all HUFAs in PC, DHA would enhance membrane fluidity to the uppermost. Therefore, membranes of PGC capacitated sperm would undergo fertilization-related fusion events at higher rates than washed capacitated sperm. These results suggested that PGC mouse sperm should be used in fertilization experiments and that SGG and DHA should be considered to be important biomarkers for sperm fertilizing ability.

Acquisition of arylsulfatase A onto the mouse sperm surface during epididymal transit

Arylsulfatase A (AS-A) is localized to the sperm surface and participates in sperm-zona pellucida binding. We investigated how AS-A, usually known as an acrosomal enzyme, trafficked to the sperm surface. Immunocytochemistry of the mouse testis confirmed the existence of AS-A in the acrosomal region of round and elongating spermatids. However, immunofluorescence and flow cytometry indicated the absence of AS-A on the surface of live testicular sperm. In contrast, positive AS-A staining was observed in the heads of live caudal epididymal and vas deferens sperm. The results suggested that acquisition of AS-A on the sperm surface occurred during epididymal transit. Immunocytochemistry of the epididymis revealed AS-A in narrow and apical cells in the initial segment and in clear cells in all epididymal regions. However, these epithelial cells are in the minority and are not involved in secretory activity. In the caudal epididymis and vas deferens, AS-A was also localized to principal cells, the major epithelial cells. Because principal cells have secretory activity, they may secrete AS-A into the epididymal fluid. This hypothesis was supported by our results revealing the presence of AS-A in the epididymal and vas deferens fluid (determined by immunoblotting and ELISA) and an AS-A transcript in the epididymis (by reverse transcription polymerase chain reaction). Alexa-430 AS-A bound to epididymal sperm with high affinity (Kd = 46 nM). This binding was inhibited by treatment of sperm with an antibody against sperm surface sulfogalactosylglycerolipid. This finding suggests that AS-A in the epididymal fluid may deposit onto sperm via its affinity to sulfogalactosylglycerolipid.

Role of sperm surface arylsulfatase A in mouse sperm-zona pellucida binding

We have previously described the zonae pellucidae (ZP) binding ability of a pig sperm surface protein, P68. Our recent results on peptide sequencing of 3 P68 tryptic peptides and molecular cloning of pig testis arylsulfatase A (AS-A) revealed the identity of P68 as AS-A. In this report, we demonstrate the presence of AS-A on the mouse sperm surface and its role in ZP binding. Using anti-AS-A antibody, we have shown by immunoblotting that AS-A was present in a Triton X-100 extract of mouse sperm. The presence of AS-A on the sperm plasma membrane was conclusively demonstrated by indirect immunofluorescence, immunogold electron microscopy, and AS-A's desulfation activity on live mouse sperm. The AS-A remained on the head surface of in vivo capacitated sperm, as revealed by positive immunofluorescent staining of oviductal/uterine sperm. Significantly, the role of mouse sperm surface AS-A on ZP binding was demonstrated by dose-dependent decreases of sperm-ZP binding on sperm pretreatment with anti-AS-A IgG/Fab. Furthermore, Alexa-430 conjugated AS-A bound to mouse ZP of unfertilized eggs but not to fertilized ones, and this level of binding increased and approached saturation with increasing Alexa-430 AS-A concentrations. Moreover, in vivo fertilization was markedly decreased when mouse sperm pretreated with anti-AS-A IgG were artificially inseminated into females. All of these results designated a new function for AS-A in mouse gamete interaction.

Binding of arylsulfatase A to mouse sperm inhibits gamete interaction and induces the acrosome reaction

We have shown previously that male germ cell-specific sulfoglycolipid, sulfogalactosylglycerolipid (SGG), is involved in sperm-zona pellucida binding, and that SGG and its desulfating enzyme, arylsulfatase A (AS-A), coexist in the same sperm head area. However, AS-A exists at a markedly low level in sperm as compared to SGG (i.e., 1/400 of SGG molar concentration). In the present study, we investigated whether perturbation of this molar ratio would interfere with sperm-egg interaction. We demonstrated that purified AS-A bound to the mouse sperm surface through its high affinity with SGG. When capacitated, Percoll gradient-centrifuged mouse sperm were treated for 1 h with various concentrations of AS-A, their binding to zona-intact eggs was inhibited in a dose-dependent manner and reached the background level with 63 nM AS-A. This inhibition could be partially explained by an increase in premature acrosome reaction. The acrosome-reacted sperm population of the 63 nM AS-A-treated sperm sample was twice that of the control sample (treated with 63 nM ovalbumin) at 1 h (i.e., 32% vs. 15%) and rose to 53% at 2 h. This induction was presumably due to SGG aggregation attributed to AS-A, existing as a dimer at neutral pH, and could be mimicked by anti-SGG immunoglobulin (Ig) G/IgM + secondary IgG antibody. Drastic inhibition (75%) of in vivo fertilization was also observed in females inseminated with sperm suspension containing 630 nM AS-A as compared to the rate in females inseminated with sperm suspension included with 630 nM ovalbumin. Our results demonstrate a promising potential for AS-A as a nonhormonal, vaginal contraceptive.

Role of sperm sulfogalactosylglycerolipid in mouse sperm-zona pellucida binding

Sulfogalactosylglycerolipid (SGG) is the major sulfoglycolipid of mammalian male germ cells. Like other sulfoglycolipids, SGG is believed to be involved in cell-cell/extracellular matrix adhesion. Specifically, we investigated whether sperm SGG played a role in sperm-egg interaction. Initially, we produced an affinity-purified, rabbit polyclonal immunoglobulin (Ig) G antibody that specifically recognized SGG (anti-SGG). Indirect immunofluorescence using anti-SGG IgG localized SGG to the convex and concave ridges and the postacrosome of the mouse sperm head. Pretreatment of sperm with anti-SGG IgG/Fab inhibited sperm-zona pellucida (ZP) binding in vitro in a concentration-dependent manner (to a maximum of 62%). This inhibition was observed at the level of primary binding. Sperm treated with anti-SGG IgG underwent the spontaneous and ZP-induced acrosome reaction at the same rate as control sperm treated with preimmune rabbit serum IgG. Fluorescently labeled SGG liposomes were shown to associate specifically with the egg ZP, whereas fluorescently labeled liposomes of galactosylglycerolipid (SGG's parental lipid) and phosphatidylserine (negatively charged like SGG) did not. Furthermore, coincubation of SGG liposomes with sperm and isolated ZP inhibited sperm-ZP binding in a concentration-dependent manner. These results strongly suggest an involvement of sperm SGG in direct binding to the ZP.

Role of egg sulfolipidimmobilizing protein 1 on mouse sperm-egg plasma membrane binding

We have shown that sperm sulfolipidimmobilizing protein 1 (SLIP1, molecular mass of 68 kDa), a sulfogalactosylglycerolipid (SGG)-binding protein, is significant in sperm-zona pellucida (ZP) interaction. The objective of this study was to localize SLIP1 on the egg and determine its role in gamete interaction. Immunofluorescence and immunoprotein A gold electron microscopy localized SLIP1 to the egg plasma membrane. In vitro gamete binding, using zona-free eggs preincubated with antiSLIP1 Fab before coincubation with sperm, showed a significant, dose-dependent decrease in sperm-egg plasma membrane binding. Similar results were obtained when affinity-purified antiSLIP1 IgG was used for egg pretreatment. The significance of egg SLIP1 in sperm-egg plasma membrane binding was further demonstrated by a decrease (36-52%) in in vitro fertilization when zona-intact eggs were pretreated with antiSLIP1 IgG. Since SLIP1 has been shown to bind SGG in vitro, we investigated the possibility that sperm SGG may participate in sperm-egg plasma membrane binding through egg SLIP1. Pretreatment of sperm with antiSGG Fab prior to coincubation with zona-free eggs resulted in a dose-dependent decrease in sperm-egg plasma membrane binding. Collectively, these findings strongly suggest a role for egg SLIP1 in sperm-egg plasma membrane interaction, which may be through its binding to sperm SGG.

Localization and role of sulfoglycolipid immobilizing protein 1 on the mouse sperm head

Sulfoglycolipid immobilizing protein 1 (SLIP 1) is an evolutionally conserved sperm head plasma membrane protein (M(r) = 68 kDa) that binds to sulfogalactosylglycerolipid (SGG), the major sulfoglycolipid present in mammalian sperm. The purpose of this study was to characterize the initial localization and the immunoaggregated relocalization of SLIP1 on the mouse sperm head. Direct immunofluorescence (DF) of live sperm using FITC-antiSLIP1 Fab fragments and FITC-antiSLIP1 IgG indicated that SLIP1 was present in the postacrosomal region of the sperm head, although the intensity of immunostaining by FITC-antiSLIP1 IgG was greatest at the border between the postacrosomal region and the acrosome. Unlike that observed with FITC-antiSLIP1 Fab, DF using FITC-antiSLIP1 IgG indicated that SLIP1 was also present in the anterior tip of the sperm head convex ridge. Results from electron microscopic studies, using antiSLIP1 IgG followed by protein A-gold on live mouse sperm, were similar to the DF findings. In contrast, indirect immunofluorescence (IIF) of live mouse sperm using antiSLIP1 IgG and FITC-secondary antibody IgG detected SLIP1 in the sperm head convex ridge only. The IIF and DF results strongly suggest that these bivalent antibodies could induce the sperm antigen relocalization on live sperm heads. SLIP1 redistribution may be dependent on availability of excess SGG, the SLIP1 binding ligand, based on the observation that purified exogenous biotinylated SLIP1 bound to live mouse sperm at both the postacrosomal and convex ridge regions of the mouse sperm head. Immunoaggregation induced by the primary antiSLIP1 IgG or antiSLIP1 Fab with secondary antibody IgG did not cause the acrosome reaction, suggesting that SLIP1 is not involved in sperm signal transduction. Furthermore, postacrosomal SLIP1 was shown to be involved in zona binding, since sperm pretreated with antiSLIP1 Fab fragments (100 micrograms/ml) bound to the egg zona pellucida in vitro at approximately 35% of control levels.

Centrifugation on Percoll gradient enhances fluorescent lectin binding on human sperm: a flow cytometric analysis

Centrifugation on a Percoll gradient is commonly used to enrich sperm preparations in mobile forms prior to in vitro fertilization attempts. It has been suggested that this method also induces the capacitation of sperm, a step preceding the acrosomal reaction allowing egg fertilization. The modifications of the acrosomal membrane involved in these physiological events likely include alterations of glycosylation patterns. This hypothesis was investigated by comparing the membrane binding of 15 fluorescein-conjugated lectins on 60 samples of sperm, before and after Percoll centrifugation. The numbers of labeled sperm and their mean fluorescence intensity, recorded in flow cytometry, significantly increased for 10 and 14 of the 15 lectins tested. Microscopic examination of the labeled sperm showed that the acrosome and equatorial plates were more often labeled after Percoll centrifugation, confirming the hypothesis that this method modifies the glycosylation pattern of structures important for egg fertilization.

Cholesterol and phospholipid levels of washed and percoll gradient centrifuged mouse sperm: presence of lipids possessing inhibitory effects on sperm motility

Levels of DNA, cholesterol, and phospholipids of mouse caudal epididymal and vas deferens sperm that were processed through simple washing and Percoll gradient centrifugation were measured. The DNA and cholesterol contents of washed sperm and Percoll gradient centrifuged (PGC) sperm (DNA = 3.6 +/- 0.3 pg/sperm and 3.4 +/- 0.3 pg/sperm, respectively; cholesterol = 0.219 +/- 0.057 nmole/microgram DNA and 0.224 +/- 0.030 nmole/microgram DNA, respectively, for washed and PGC sperm) were not significantly different from each other; however, the phospholipid level of PGC sperm was only one half of that of washed sperm (0.315 +/- 0.071 nmole/microgram DNA versus 0.720 +/- 0.075 nmole/microgram DNA, respectively). The presence of 0.3% bovine serum albumin (BSA) in the culture medium used in sperm washing did not change the cholesterol and phospholipid contents of washed sperm. Similarly, the cholesterol and phospholipid levels of washed sperm and PGC sperm that were further incubated in BSA-containing medium for 30 min remained the same. Interestingly, substantial amounts of lipids, as determined by the cholesterol and phospholipid levels, were released into the supernatants of the sperm washes, and sperm needed to be washed at least twice to ensure their stable levels of cholesterol and phospholipids. The lipid mixture in the first sperm wash supernatant was shown to have inhibitory effects on PGC sperm motility.

Interaction of divalent cations with germ cell specific sulfogalactosylglycerolipid and the effects on lipid chain dynamics

Sulfogalactosylglycerolipid (SGG) is a sulfoglycolipid found ubiquitously in the plasma membrane of mammalian male germ cells. Although its exact cellular function(s) is unknown, it is speculated that SGG may play a role in cation transport, which may be important in sperm-egg interaction. Given the significant role of Ca2+ in many fertilization-related events, the purpose of this study was to determine whether Ca2+ interaction with the negatively charged sulfate group of SGG results in changes to the SGG lipid chain molecular dynamics and to compare these lipid dynamics with those resulting from Na+, Mg2+, or Sr2+ interaction with SGG. Pressure-tuning Fourier transform infrared spectroscopy was used in this study. The results obtained showed that all three divalent cations interacted electrostatically with the sulfate moiety of hydrated SGG, although with varying degrees of strength. It was found that the hydrocarbon chains of hydrated SGG-Na+ multilamellar bilayers were interdigitated, thus increasing disorderedness of the terminal CH3 group of the hydrocarbon chains. The presence of each of the three divalent cations abolished this interdigitation state. Presumably, this is through the cross-linking interaction of each divalent cation with the sulfate groups of neighboring lipid molecules. Moreover, divalent cation interaction was found to increase the lipid chain dynamics of SGG, with Mg2+ inducing the greatest chain disorder followed by Ca2+ and then Sr2+. An increase in chain disorder would increase the bilayer fluidity. Such a phenomenon may prove relevant to the changes observed in the sperm plasma membrane during fertilization-related events.

Characterization of three arylsulfatases in semen: seminolipid sulfohydrolase activity is present in seminal plasma

Sperm cells and seminal plasma of various mammals contain high levels of arylsulfatase. In the present study, we investigated the composition of soluble AS in these compartments of boar semen by analysing sperm cells and seminal plasma using anion-exchange chromatography. Seminal plasma contained both arylsulfatase B (2.4 units per ml), an enzyme which desulfates sulfoglycosaminoglycans and probably sulfoglycoproteins, and arylsulfatase A (10.2 units per ml), an enzyme which desulfates sulfogalactolipids. Sperm cells contained only arylsulfatase A, which differed biochemically from the extracellular arylsulfatase A of seminal plasma (2.6 units per ml). Both types of arylsulfatase A desulfate seminolipid, the natural sulfolipid substrate in sperm, as well as two brain sulfatides. The possible physiological consequences of the presence of extracellular arylsulfatases in seminal plasma for spermatozoa are discussed.

Role of a germ cell-specific sulfolipid-immobilizing protein (SLIP1) in mouse in vivo fertilization

Sulfolipid-immobilizing protein 1 (SLIP1) is a germ cell plasma membrane protein that binds specifically to sulfogalactosylglycerolipid, a sulfoglycolipid found preferentially in mammalian male germ cells (Lingwood, Can. J. Biochem. Cell. Biol. 63:1077-1085, 1985b). SLIP1 in mouse and rat sperm exists on the periacrosomal membrane, where sperm initially bind to eggs. Using the in vitro mouse sperm-egg binding assay with in vitro-capacitated sperm, we obtained results previously suggesting that sperm SLIP1 is involved in mouse sperm-zona pellucida interaction. In this study, using the in vitro sperm-egg binding assay, we showed that SLIP1 in uterine sperm was similarly engaged in this process. Involvement of mouse sperm SLIP1 was also shown to be important in the in vivo fertilization process. Superovulated females inseminated with caudal epidididymal and vas deferens sperm preexposed to anti-SLIP1 IgG yielded only 20% fertilized zygotes, while 80% fertilization was observed in females inseminated with sperm preincubated with preimmune serum IgG. The lower fertilization rate was not due to changes in the sperm capacitation rate as assessed by chlortetracycline staining.