Antihyaluronidase Action of Ellagic Acid Effectively Prevents Polyspermy As a Result of Suppression of the Acrosome Reaction Induced by Sperm-Zona Interaction During In Vitro Fertilization of Porcine Oocytes

The present study was conducted to examine the effects of three tannin relatives (tannic acid, TA; gallic acid, GA; and ellagic acid, EA) on antihyaluronidase and reactive oxygen species (ROS) scavenging activity, in vitro fertilization (IVF) parameters, and the acrosome reaction (AR) induced by sperm-zona interaction. Among the three tannin relatives, TA and EA showed the strongest potency for blocking the hyaluronidase activity of boar sperm, with concentration-dependent inhibition over the range of 2-10 microg/ml. In contrast, ROSs were effectively scavenged by TA and GA, but not EA. When cumulus-free oocytes were inseminated in IVF medium containing 5 microg/ml of the tannin relatives, polyspermy was significantly reduced by TA and EA (32 and 29%, respectively) compared with oocytes treated with or without GA (51 and 69%, respectively) under conditions that maintained a high sperm penetration rate (P<0.05). Interestingly, induction of the AR by treatment of preincubated sperm with progesterone was blocked by TA and GA as a result of their higher levels of ROS scavenging activity, while EA, which possessed weak ROS scavenging activity, did not disturb induction of the AR with progesterone. However, the incidence of AR induced by sperm-zona interaction was significantly decreased by the strong antihyaluronidase actions of TA and EA compared with that in the absence of these compounds. Treatment with the compounds caused neither a protective proteolytic modification of the zona pellucida matrix before fertilization nor a reduction in acrosomal proteolytic activity or the number of zona-bound sperm. These findings suggest that the antihyaluronidase action of EA effectively prevents polyspermy by suppression of AR functionality induced by sperm-zona interaction and that hyaluronidase intervention is therefore required during porcine IVF.

Binding of recombinant human proacrosin/acrosin to zona pellucida (ZP) glycoproteins. I. Studies with recombinant human ZPA, ZPB, and ZPC

OBJECTIVE

To characterize proacrosin/acrosin interaction with isolated zona pellucida (ZP) components.

DESIGN

Prospective study.

SETTING

Basic research laboratory.

PATIENT(S)

Recombinant proteins derived from human proacrosin (Rec-40, Rec-30, Rec-20, Rec-10, and Rec-6) and from human ZP glycoproteins (rec-hZPA, ZPB, and ZPC).

INTERVENTION(S)

In vitro binding assay developed to assess proacrosin/acrosin-ZP interaction.

MAIN OUTCOME MEASURE(S)

Zona pellucida glycoprotein binding to proacrosin/acrosin; estimation of binding affinity.

RESULT(S)

Of all ZP proteins, rec-hZPA demonstrated the highest binding activity toward acrosin (Rec-30) (rec-hZPB: 42% of rec-hZPA; rec-hZPC: 39% of rec-hZPA; P<.0005). Rec-hZPA interaction was disturbed by dextran sulphate (75% inhibition with 10 microM), fucose (67% inhibition with 1.5 microM), and mannose (69% inhibition with 333 mM). Comparing binding activity of proacrosin with other N-terminal acrosin fragments, Rec-40 showed 2.6-3 times higher levels. Moreover, saturable high affinity binding of Rec-40 to ZP components was observed (Kd: 34 nM for rec-hZPA, 38 nM for rec-hZPB, 63 nM for rec-hZPC).

CONCLUSION(S)

The rec-hZPA is the major ZP ligand for human proacrosin/acrosin. The interaction involves mannosyl, fucosyl, and sulfated glycans. Binding sites for rec-hZP would be located both at the N- and C-terminus of proacrosin, revealing a key role of the proenzyme in the interaction.

Sperm-zona pellucida interaction involves a carbonyl reductase activity in the hamster

For successful fertilization to occur, the spermatozoa must transit through an egg-specific extracellular matrix or zona pellucida (zp) to reach and ultimately fuse with the oocyte plasma membrane. This process involves ligand-receptor recognition between the zp and the acrosomal cap of the sperm. The hamster sperm protein P26h, a receptor which is acquired during epididymal transit, has been suggested to act in sperm-zp binding. The cloning and characterization of the full-length cDNA-encoding hamster P26h revealed 85% identity with a porcine lung carbonyl reductase. To better understand the mechanism by which P26h interacts with zp proteins, we investigated carbonyl reductase activity during gamete interactions. In the present study, we show that specific inhibitors of carbonyl reductase such as diclofenac and phenylbutazone decreases sperm-zp binding without affecting the motility, progressivity or acrosome integrity of sperm. We also detected, and partly purified, carbonyl reductase activities from cauda epididymal sperm protein extract and this activity was associated with an enriched fraction of P26h. Removing P26h from the partly purified protein fractions by immunoaffinity chromatography led to the loss of carbonyl reductase activity. The findings that sperm-zp binding is blocked by carbonyl reductase inhibitors and that P26h is active in mature sperm suggest that P26h could play an important role in the fertilization process.

Regulation of the strypsin-related proteinase ISP2 by progesterone in endometrial gland epithelium during implantation in mice

Hormones prepare the uterus for the arrival and subsequent invasion of the embryo during pregnancy. Extracellular matrix-degrading proteinases and their inhibitors are involved in this integration process. Recent genetic evidence indicates that there is redundancy within the implantation proteinase cascade, indicating that additional proteinases may be involved. Recently, we described a novel implantation serine proteinase (ISP1) gene that encodes the embryo-derived enzyme strypsin, which is necessary for blastocyst hatching in vitro and the initiation of invasion. The evidence presented in the present study indicates that a second proteinase secreted from the uterus also participates in lysis of the zona pellucida. A second implantation serine proteinase gene (ISP2) was isolated, which encodes a related secreted tryptase expressed specifically within uterine endometrial glands. In pseudopregnancy, ISP2 gene expression is dependent on progesterone priming and is inhibited by the antiprogestin RU486. On the basis of similarities between ISP2 gene expression and that of a progesterone-regulated luminal proteinase associated with lysis of the zona pellucida, it is possible that the strypsin-related protein, ISP2, may encode a zona lysin proteinase.

Morphological dynamics of cumulus-oocyte complex during oocyte maturation

The recent advances on the cytoplasmic regulators of the induction of germinal vesicle break down, maturation and degeneration of oocytes, and glycosaminoglycan composition during cumulus expansion of cumulus-oocyte complexes are discussed. A) Inactive mitogen-activated protein kinases (MAPKs) are present in the oocytes at germinal vesicle (GV) stage, and are activated with germinal vesicle breakdown (GVBD), and remain highly active throughout maturation in porcine oocytes. Inactive MAPKs are localized in the cytoplasm of GV-arrested oocytes and active MAPKs were detected in the GV just before GVBD. B) Cumulus expansion of porcine cumulus-oocyte complexes (COCs) was reduced by oocy tectomy. The profile of total glycosaminoglycan synthesis was attributed to hyaluronic acid rather than chondroitin sulfate in intact COCs and oocytectomy reduced hyaluronic acid synthesis. C) The abnormalities of chromosomes and alpha-tubulin morphology were observed in the oocytes of c-mos deficient mice. MAPK activity of c-mos deficient oocytes did not significantly fluctuate throughout maturation and was clearly lower than that of wild-type oocytes. One of the most drastic abnormalities in c-mos knockout mouse oocytes was their entrance into the interphase instead of second meiosis after first polar body emission. D) Reverse transcriptase/polymerase chain reaction-Southern blot hybridization demonstrated positive expression of Fas in intraovarian mouse oocytes. In contrast, expression of Fas ligand was detected in granulosa cells. These findings were histologically confirmed by in situ hybridization with Fas- and FasL-specific probes. Co-culture of intact and zona-free eggs and granulosa cells demonstrated positive TUNEL staining only zona-free eggs.

Galactosyltransferase function during mammalian fertilization

Gamete recognition has been studied extensively in the mouse. In this system, it is generally believed that sperm bind to a class of O-linked oligosaccharides on the zona pellucida glycoprotein, ZP3. The best characterized sperm receptor for ZP3 is beta1, 4-galactosyltransferase (GalT), which functions in a lectin-like capacity by binding to N-terminal N-acetylglucosamine residues on ZP3 oligosaccharides. Multivalent oligosaccharides on ZP3, as well as synthetic polymers terminating in N-acetylglucosamine aggregate GalT, leading to activation of a heterotrimeric G protein cascade and culminating in the acrosome reaction. Following fertilization, cortical granules release N-acetylglucosaminidase, which removes the binding site for sperm GalT and facilitates the zona block to polyspermic binding. Genetic manipulation of GalT expression has confirmed its function as a ZP3 receptor. Overexpressing GalT on sperm leads to increased binding of ZP3, increased G protein activation, and precocious acrosome reactions. In contrast, sperm from mice made null for GalT by homologous recombination are refractory to ZP3, in that they are unable to bind soluble ZP3 and fail to undergo the acrosome reaction in response to zona glycoproteins. Surprisingly, GalT null sperm still bind to the zona and achieve low rates of fertilization in vitro. This then suggests that sperm-egg binding involves receptor-ligand interactions independent of GalT and ZP3. The current model suggests that GalT functions as the ZP3 receptor that is responsible for inducing the acrosome reaction, whereas initial sperm-zona binding is dictated by other sperm surface receptors. Consistent with this, at least three other zona pellucida monosaccharides have been implicated in sperm binding, and novel sperm surface glycoproteins have been suggested to function in gamete binding. A large scaffolding protein has been identified that associates with the GalT cytoplasmic domain and may be responsible for orchestrating its signal transduction capacities that lead to the acrosome reaction.

Evidence for the involvement of a species-specific embryonic protease in zona escape of hamster blastocysts

The source and nature of zona lytic factors during zona escape of hamster blastocyts were investigated. When cultured in hamster embryo culture medium (HECM)-2h, all 8-cell embryos (n = 135) developed to zona escaped-blastocysts with complete zona lysis. In addition, 2-cell embryos, when co-cultured with zona escaping-blastocysts (at a ratio of 1:10), exhibited zona lysis. Various other embryos at the 1-8-cell stages also showed zona lysis when cultured with zona-escaping blastocysts. However, zonae from mice, rats, sheep and humans were resistant to lysis under these conditions. Pronase treatment resulted in rapid zona lysis in hamsters (7 +/- 1 s), whereas in other species zona lysis was much slower: mouse (662 +/- 27 s), rat (532 +/- 16 s), sheep (120 +/- 12 s) and human (104 +/- 8 s). When cysteine protease inhibitors (antipain, leupeptin, E-64 and p-hydromercuricbenzoate) were tested, they completely inhibited zona escape, while trypsin inhibitors (TLCK and SBTI) did not. Uterine zona lysin contribution in zona escape was discounted since: (i) uterine luminal flushing and endometrial extract from day 4 (the time of zona escape in vivo) pregnant females failed to lyse zonae and (ii) endogenous oocytes and transferred 2-cell embryos (to day 3 pseudopregnant recipients) were all zona-intact, while 71% of transferred blastocysts exhibited zona escape, following their recovery after 24 h. These observations suggest that a species-specific, embryonic proteolytic factor, with a cysteine protease-like activity, is involved in the zona escape of blastocysts in hamsters.

Lectin histochemical detection of sulfoglycans in the zona pellucida of mammalian antral oocytes

Sulphated esters are important to increase effectiveness of specific biological activities of carbohydrates. Biochemical studies revealed the presence of distinct sulphated glycoproteins in mammal zona pellucida (ZP) that bind proacrosin and thus participate in the sperm-egg fusion processes. In the present study, 6 lectin-horseradish peroxidase conjugates (SBA, PNA, RCA-I, GSA-IB4, GSA-II and DBA) were used in combination with desulphation and sialidase digestion to identify sulphocarbohydrates in the terminal and/or subterminal position of oligosaccharide side chains of glycoproteins in the ZP of bovine, ovine, caprine and porcine antral oocytes. In particular, we identified the following terminal sulphoglycans located in the outer layer of the ZP only: SO4-GalNAc in bovine ZP; SO4-Galbeta1,3GalNAc in bovine and ovine ZP; SO4-Galbeta1,4GlcNAc in bovine, ovine and caprine ZP; SO4-alpha-Gal in bovine, caprine and porcine ZP. Subterminal sulphoglycans linked to sialic acid residues were evenly distributed throughout the entire thickness of the ZP: Neu5Ac-SO4-Galbeta1,3GalNAc in bovine and porcine ZP; Neu5Ac-SO4-Galbeta1,4GlcNAc in caprine ZP; Neu5Ac-SO4-alpha-Gal in porcine ZP; Neu5AcSO4-GlcNAc in bovine ZP. The results demonstrate that the chemical composition of the ZP differs among species determining the species-specificity of gamete interactions.

Porcine sperm surface beta1,4galactosyltransferase binds to the zona pellucida but is not necessary or sufficient to mediate sperm-zona pellucida binding

The binding of sperm to the zona pellucida is an integral part of the mammalian fertilization process, investigated most extensively in the mouse. Several sperm receptors for the murine zona pellucida have been studied (Snell WJ, White JM. 1996. Cell 85:629-637; Wassarman PM. 1999. Cell 96:175-183), but the most compelling evidence exists for beta-1,4-galactosyltransferase (GalTase). Considering that GalTase is present on the surface of porcine sperm (Larson JL, Miller DJ. 1997. Biol Reprod 57:442-453), we investigated the role of GalTase in porcine sperm-zona binding. Sperm surface GalTase catalyzed the addition of uridine diphosphate-[(3)H]galactose to the 55 kDa group of the porcine zona pellucida proteins implicated in sperm binding, demonstrating that GalTase binds the porcine zona. The functional importance of GalTase-zona pellucida binding was tested. Addition of uridine diphosphate galactose, a substrate that completes the GalTase enzymatic reaction and disrupts GalTase mediated adhesion, had no effect on binding of sperm to porcine oocytes. Furthermore, removal of the GalTase zona ligand by incubation of oocytes with N-acetylglucosaminidase had no effect on binding of sperm to oocytes. These results suggest that GalTase is not necessary for sperm to bind to the zona pellucida. Digestion of isolated porcine zona proteins with N-acetylglucosaminidase did not affect the biological activity of soluble porcine zona proteins in competitive sperm-zona binding assays, suggesting that GalTase alone is not sufficient to mediate sperm-zona attachment. From these results, it appears that, although GalTase is able to bind porcine zona proteins, its function in porcine sperm-zona binding is not necessary or sufficient for sperm-zona binding. This supports the contention that porcine sperm-zona binding requires redundant gamete receptors.

Protein kinase C plays an important role in the human zona pellucida-induced acrosome reaction

To investigate the involvement of protein kinases in signal transduction in the human zona pellucida (ZP)-induced acrosome reaction (AR), the effects of protein kinase (PK) activators, dibutyryl cAMP (PKA) and cGMP (PKG), phorbol 12-myristate 13-acetate (PMA, PKC), and the PKC inhibitor, staurosporine were studied. Sperm samples were obtained from normozoospermic men with normal sperm-ZP binding. Oocytes were obtained from other patients with failure of fertilization in vitro. Motile spermatozoa selected by a swim-up technique were pre-incubated with 2.5-20 microM PMA, 1 mM dibutyryl cAMP or cGMP, 3 mM pentoxifylline or 0.125-2.0 microM staurosporine for 30 min and then incubated with four oocytes for 2 h in human tubal fluid supplemented with bovine serum albumin. The spermatozoa bound to the ZP were dislodged by repeatedly aspirating the oocytes with a small bore pipette and the state of the AR was determined by fluorescein-labelled Pisum sativum agglutinin. Motility and movement characteristics were assessed by computer-assisted sperm analysis (CASA) after incubation of spermatozoa with PMA for 30 min and 2 h. The dibutyryl cAMP and cGMP analogues had a small positive effect (P < 0.05) but pentoxifylline had no effect on stimulating the ZP-induced AR (P > 0.05). In contrast, PMA stimulated ZP-induced AR in a marked dose-dependent manner. Only the highest concentrations (15-20 microM) of PMA significantly decreased percentage motility (P < 0.001). Doses of 2.5-15 microM of PMA significantly stimulated ZP-induced AR without decreasing motility (P < 0.001). The PKC inhibitor, staurosporine (0.125-0.25 microM) significantly inhibited ZP-induced AR without affecting motility (P < 0.001). Sperm samples from 33 normozoospermic men were used for studies of the ZP-induced AR augmented with 15 microM PMA. One sample did not show a response to PMA stimulation. Among the 14 men with low ZP-induced AR, half had normal responses to PMA and other half had low responses to PMA. In conclusion, activation or inhibition of PKC significantly increases or decreases human ZP-induced AR suggesting that PKC plays a important role in the signal transduction pathway for the physiological AR.

Hardening of zona pellucida of mouse oocytes and embryos in vivo and in vitro

OBJECTIVE

To evaluate the effect of in vitro culture on zona pellucida resistance in mouse oocytes and embryos.

METHOD

Zona pellucida resistance was assessed by comparing duration of zona lysis in the presence of alpha-chymotrypsin. The effects of artificial or physiological conditions of development were evaluated by comparing embryos in vitro with those left to reach the same stage of development in vivo.

RESULTS

The time required for zona lysis of oocytes increased after 2, 24, and 48 hours in vitro (P < .001). The same observation holds true for oocytes left in vivo during 24 hours. Fertilization both in vivo and in vitro induced a major increase in zona resistance. At the two-cell stage, in vitro culture did not harden the zona pellucida. At the morula stage and beyond, enzymatic lysis was slightly longer in vitro as compared to that of similar stages recovered from the genital tract.

CONCLUSIONS

Our data indicate that in vitro culture conditions do not modify zona hardening in oocytes and only slightly increased zona resistance from the morula stage on.

Roles of heterotrimeric and monomeric G proteins in sperm-induced activation of mouse eggs

Results of several lines of experimentation suggest that sperm-induced egg activation has several features in common with G protein-coupled receptor signal transduction mechanisms. We report that microinjection of GDP beta S into metaphase II-arrested mouse eggs blocks sperm-induced egg activation. Since GDP beta S inactivates both heterotrimeric and monomeric classes of G proteins, the involvement of members of each of these families in sperm-induced egg activation was evaluated. Neither pertussis toxin treatment of eggs nor microinjection of eggs with inhibitory antibodies toward G alpha q blocked sperm-induced egg activation. Nevertheless, microinjection of phosducin, a protein that binds tightly to free G protein beta gamma subunits, specifically inhibited second polar body emission, the fertilization evoked decrease of H1 kinase activity and pronucleus formation. Microinjection of phosducin, however, did not inhibit the fertilization-induced modifications of the zona pellucida and microinjection of beta gamma t did not result in egg activation in the absence of sperm. Inactivation of the monomeric Rho family of G proteins with C3 transferase from Clostridium botulinum inhibited emission of the second polar body and cleavage to the 2-cell stage, but did not affect the modifications of the zona pellucida or pronucleus formation. Microinjection of Rasval12, which is a constitutively active form of Ras, did not result in egg activation in the absence of sperm. Moreover, microinjection of either an anti-Ras neutralizing antibody (Y13-259) or a dominant negative form of Ras (RasT) did not affect events of sperm-induced egg activation. In contrast, microinjection of RasT inhibited embryo cleavage to the 2-cell stage. These results suggest that both heterotrimeric and monomeric G proteins are involved in various aspects of sperm-induced egg activation.

Acrosin inhibitor in extract of the zonae pellucidae of porcine oocytes

Zonae pellucidae isolated from porcine oocytes were solubilized in 0.15 M NaCl at pH 2.5. The zonal extract contained a protein with relatively low molecular weight, which inhibited the amidase activity of boar acrosin and bovine trypsin. This protein was immunologically related to the BUSI II proteinase inhibitor isolated from bull seminal plasma.