Screening and identification of dominant functional fragments of human epididymal protease inhibitor

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

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

ZNF185-derived peptide induces fertility suppression in mice

Zinc finger protein 185 (ZNF185) belongs to the ZNF family and is involved in male reproduction. However, it is unclear whether ZNF185 may be a target candidate for contraceptive vaccines. In this study, antigenic peptides derived from ZNF185 were prepared, and their immune contraceptive effects were investigated using mice. Results from enzyme-linked immunosorbent assay (ELISAs) showed that peptide immunization induced an antibody titre increase that reached a peak in week 12. Peptide-3 and peptide-4 were then chosen for subsequent experiments. The results of the fertility assays showed that peptide immunization inhibited the mating and fertility rates of the mice, whereas there were no obvious changes in the number of pups per litter. Subsequently, epididymal sperm was analysed. The results demonstrated that the sperm count and sperm motility were significantly decreased in the peptide group, while the amount of abnormal sperm was significantly increased in the peptide-3 group. The male reproductive organs were also evaluated. There were no obvious differences in testis or epididymal weights, in the diameters of the seminiferous tubules, or in the thicknesses of the seminiferous epithelium between the peptide group and the phosphate buffer saline (PBS) group. In addition, histological analysis indicated that there were no obvious pathologic changes in testis and epididymal histology in the peptide group; however, the number of spermatozoa present in the epididymal lumen of the peptide group was significantly decreased when compared with the PBS group. Our study demonstrates for the first time that peptides derived from ZNF185 may induce fertility suppression in mice without damaging reproductive organs. These peptides have the potential to be used as a male contraceptive vaccine.

Immunocontraceptives: new approaches to fertility control

The rapidly increasing global population has bowed the attention of family planning and associated reproductive health programmes in the direction of providing a safe and reliable method which can be used to limit family size. The world population is estimated to exceed a phenomenal 10 billion by the year 2050 A.D., thus presenting a real jeopardy of overpopulation with severe implications for the future. Despite the availability of contraceptive methods, there are over one million elective abortions globally each year due to unintended pregnancies, having devastating impact on reproductive health of women worldwide. This highlights the need for the development of newer and improved contraceptive methods. A novel contraceptive approach that is gaining substantial attention is "immunocontraception" targeting gamete production, gamete outcome, or gamete function. Amongst these, use of sperm antigens (gamete function) seems to be an exciting and feasible approach. However, the variability of immune response and time lag to attain titer among vaccinated individuals after active immunization has highlighted the potential relevance of preformed antibodies in this league. This review is an attempt to analyze the current status and progress of immunocontraceptive approaches with respect to their establishment as a future fertility control agent.