Sperm proteins that serve as receptors for the zona pellucida and their post-testicular modification

Elucidation of the involvement of p14, a sperm protein during maturation, capacitation and acrosome reaction of caprine spermatozoa

Mammalian sperm capacitation is an essential prerequisite to fertilization. Although progress is being made in understanding the physiology and biochemistry of capacitation, little has been yet explored about the potential role(s) of individual sperm cell protein during this process. Therefore elucidation of the role of different sperm proteins in the process of capacitation might be of great importance to understand the process of fertilization. The present work describes the partial characterization of a 14-kDa protein (p14) detected in goat spermatozoa using an antibody directed against the purified protein. Confocal microscopic analysis reveals that the protein is present in both the intracellular and extracellular regions of the acrosomal and postacrosomal portion of caudal sperm head. Though subcellular localization shows that p14 is mainly cytosolic, however it is also seen to be present in peripheral plasma membrane and soluble part of acrosome. Immuno-localization experiment shows change in the distribution pattern of this protein upon induction of capacitation in sperm cells. Increased immunolabeling in the anterior head region of live spermatozoa is also observed when these cells are incubated under capacitating conditions, whereas most sperm cells challenged with the calcium ionophore A23187 to acrosome react, lose their labeling almost completely. Intracellular distribution of p14 also changes significantly during acrosome reaction. Interestingly, on the other hand the antibody raised against this 14-kDa sperm protein enhances the forward motility of caprine sperm cells. Rose-Bengal staining method shows that this anti-p14 antibody also decreases the number of acrosome reacted cells if incubated with capacitated sperm cells before induction of acrosome reaction. All these results taken together clearly indicate that p14 is intimately involved and plays a critical role in the acrosomal membrane fusion event.

Diagnosis and treatment of immunologically infertile males with antisperm antibodies

The presence of antisperm antibodies (ASA) can reduce fecundity in both males and females. The present review describes a strategy, established by investigations of the diverse inhibitory effects of ASA on fertility, for the appropriate diagnosis and treatment of infertile males with ASA. For infertile males with ASA, diagnosis using the direct-immunobead test (D-IBT), the postcoital test (PCT) and the hemizona assay (HZA) should be carried out as the basis for decision-making. If the patient with ASA has an abnormal hemizona index, it seems reasonable to advise selecting intracytoplasmic sperm injection-embryo transfer (ICSI-ET) as a primary treatment. However, it has been shown that some immunologically infertile males with normal fertilizing ability established pregnancy by timed intercourse (TI) or intrauterine insemination (IUI). In such patients with ASA having normal hemizona index, TI or IUI can be selected based on the PCT result. Therefore, the treatment strategy for males with ASA is similar to that for infertile males with oligozoospermia or asthenozoospermia. In conclusion, it should be emphasized that a diversity of ASA exists and their effects on fertility in infertile males. Although there is an argument that routine testing for ASA in males is not always necessary, one should be aware that in some cases of failed IUI or IVF, ICSI is selected afterward because of the diagnosis of ASA. (Reprod Med Biol 2005; 4: 133-141).

Isolation, partial characterization and biological activity of mannosyl glycopeptides from seminal plasma

Affinity chromatography on Concanavalin-A Sepharose, followed by gel filtration and hydrophobic interaction chromatography, permits the isolation of low molecular weight N-glycosidically linked oligomannosidic glycopeptides (MGp) from the autoproteolysis products of human seminal plasma. The monosaccharide composition of MGp showed only mannose, N-acetylglucosamine and a small amount of galactose. Structural studies were carried out by methylation analysis and chromium trioxide oxidation, and results were consistent with the structures accepted for high-mannose N-glycans. MGp was capable of inhibiting the sperm acrosomal exocytosis mediated by sperm-surface receptors. These data suggest that MGp act as a "decapacitation" factor preventing premature sperm exocytosis.

Sperm antigens and their use in the development of an immunocontraceptive

PROBLEM

Overpopulation is a global problem of significant magnitude, with grave implications for the future. World population is predicted to reach 10 billion people by the year 2050, an increase of more than 75% over the current population. Development of new contraceptives is necessary, since current forms of birth control are unavailable to many individuals due to sociological, financial, or educational limitations.

METHODS

In an effort to identify new contraceptive alternatives, sperm-specific antigens are under the investigation as the basis for immunological regulation of fertility through contraceptive immunization. Anti-sperm antibodies (ASA) inhibit sperm function in vitro, induce infertility in experimental models, and have been implicated in some cases of clinical infertility. Furthermore, the development of ASA in vasectomized men does not lead to physiological complications despite the persistence of these antibodies for years; thus, ASA induced by immunization of men and women may be similarly harmless. Immunization has several conceptual advantages as a method of fertility regulation. Employment of non-pharmacologically active agents, convenience of administration, low cost, and the potential for relatively long-lasting yet reversible effects.

RESULTS

Various approaches have been taken to identify candidate sperm antigens for immunocontraceptive development. Studies that utilized monoclonal antibodies and polyclonal antisera generated against sperm preparations have identified such promising candidates as PH-20, fertilin, SP-17, and SP-10. In animal model, 100% contraceptive effects were induced following PH-20 immunization and the effects were reversible. More recently, ASA from the sera of infertile patients were employed to identify several candidates as expressed by testis cDNA libraries. Perhaps the most extensively characterized and effective immunogen candidate identified thus far is lactate dehydrogenase-C4 (LDH-C4). Active immunization with LDH-C4 suppressed fertility in a variety of mammalian species, including primates, and the reversibility of these effects was demonstrated.

CONCLUSION

The successful results obtained thus far support the feasibility of an effective immunocontraceptive and indicate the importance for continued investigation of additional sperm antigens as contraceptive immunogen candidates.

Wheat germ agglutinin receptors on human sperm membranes and sperm morphology

Sperm membrane components play an important role in the determination of sperm fertilizing ability. During spermatogenesis, epididymal transit, and capacitation, the sperm membrane undergoes various subtle changes which are important maturational events for the production of viable spermatozoa and hence partly determine fertility. Localization and intensity of wheat germ agglutinin (WGA) receptors are reported to be directly associated with male fertility. We examined the correlations and differences between the distribution patterns and intensities of WGA receptors of 75 semen samples, classified according to the strict criteria described for sperm morphology, namely P-pattern (0-4% normal forms, n = 19), G-pattern (5-14% normal forms, n = 41) and normal samples (> 15% normal forms, n = 15). Results indicate distinct differences in WGA receptor intensity in all of the three groups as well as significantly (P < 0.05) lower per-cent staining of the equatorial segment amongst the P-pattern group when compared to the other two groups. It would appear that there is a close relationship between WGA receptors on human sperm membranes and sperm morphology.