Increased in vitro binding and fertilizing ability of mouse sperm exposed to a synthetic peptide

We report use of an in vitro assay (Barbato et al., 1998: Biol Reprod 58:686-699) to assess binding ability of cauda epididymal mouse sperm to a surrogate zona pellucida and effect of a synthetic peptide (Amann et al., 1999: J Androl 20: 42-46) on fertilization ability in in vitro fertilization (IVF) tests. Sperm from C57Bl/6, CD1, and CF1 mice (4 replicates each) were evaluated for binding ability after exposure to 0 (control) and 80-1280 pM peptide. For control sperm, endogenous binding was C57Bl/6 < CD1 = CF1 (P < 0.05, 1-way ANOVA). Across all three strains, exposure to > 320 pM peptide increased relative binding of sperm (P < 0.05; 2-way general linear model; GLM). Strains differed both in basal binding ability and in response to synthetic peptide. To determine if IVF rate increased after exposure of sperm to peptide, ova from B6C3 mice (four replicate pools) were collected after eCG and hCG stimulation. Cumulus-oocyte complexes (COC; 8-15 ova in each of 3-6 drops/treatment) were incubated with hyperactivated C57Bl/6 sperm at approximately 1500 sperm per ovum. Data for incubations were corrected for false-positive classification to yield a better estimate of true cleavage rate, and then related to results observed with a tenfold greater sperm concentration. Relative cleavage rates were 0 peptide (0.48); 420 pM (0.78, P < 0.05); and 840 pM (0.90, P < 0.01; GLM and Tukey tests). IVF rate was increased by exposure of mouse sperm to peptide at concentrations effective in the in vitro assay, and use of peptide allowed use of 1/10 as many sperm.

Changes in epididymal protein anti-agglutinin on ejaculated boar spermatozoa during capacitation in vitro

This study is a detailed investigation of changes in epididymal protein anti-agglutinin on ejaculated boar spermatozoa during an incubation designed to promote capacitation in vitro. Ejaculated spermatozoa were collected from six mature boars, washed, and incubated to promote capacitation. Sperm samples were subjected to Western blotting-densitometric analyses, flow cytometry after immunostaining and immunocytochemical observation by indirect immunofluorescence. An antiserum to anti-agglutinin was raised in a rabbit by subcutaneous injection of a purified antigen, as described previously (Harayama et al. 1999). Western blotting-densitometric analyses revealed an approximate halving of the amount of sperm-bound anti-agglutinin during the first 45-min incubation, followed by a gradual decrease thereafter. Comparison between immunostained sperm samples by flow cytometry before and after incubation confirmed this decrease in sperm-bound anti-agglutinin during the incubation. Microscopic characterization established that this decrease occurred mainly on the acrosome. Supplementation with seminal plasma (5% or 10%, v/v) attenuated the decrease. These findings are consistent with the conclusion that a large portion of the anti-agglutinin bound to sperm acrosomes is released at an early stage of the capacitation process in vitro.

Flow cytometric analysis of transmembrane phospholipid movement in bull sperm

Fluorescent phospholipids are useful to investigate phospholipid dynamics in biological membranes. We used flow cytometry to investigate transbilayer phospholipid movement in live sperm cells. Acyl-labeled N-4-nitrobenzo-2-oxa-1,3-diazole (NBD) -phosphatidylcholine (-PC), -phosphatidylethanolamine (-PE), or -phosphatidylserine (-PS) were incorporated into sperm cells, and the transbilayer location was determined by extraction of probe from cell with excess bovine serum albumin (BSA) or by chemical destruction of probe by sodium dithionite. Using these methods, we have measured the head group specific outer leaflet to inner leaflet movement (flip) of the aminophospholipids NBD-PS and NBD-PE. The fluorescent phospholipids moved inward across the plasma membrane with half-times of 1.8, 2.5, and 11.2 min, for NBD-PS, NBD-PE, and NBD-PC and reached apparent equilibrium levels of 88%, 94%, and 32% inside, respectively. The inward movement of NBD-PE was inhibited by sulfhydryl reagents, elevated intracellular Ca2+, and depletion of cellular ATP. Analysis of the kinetics of NBD-PE and -PS extraction by BSA allows determination of the rates for outward movement (flop) across the plasma membrane. Half-times for flop were 4.7 and 4.5 min for NBD-PS and -PE, respectively. Based on these measurements, a simple model of NBD-phospholipid equilibria was developed and fit to the kinetic data. Computer-generated fits reflected major features of the experimental data and provide a potential tool for predicting the dynamics of endogenous lipids.

Lectins and heparin-binding features of human spermatozoa as analyzed by flow cytometry

Sperm cell surface characteristics may serve as a useful diagnostic feature for the evaluation of seminal samples, but to date no useful analytical method(s) is available for their routine quantitative analysis. Fluorescein isothiocyanate-conjugated lectins, proteins with unique and specific saccharide-binding characteristics, and heparin are potentially useful markers for such an analytical procedure. A protocol is outlined whereby frozen semen is thawed and treated with either fluorescein isothiocyanate-conjugated soybean agglutinin SBA (Glycine max), peanut agglutinin PNA (Arachis hypogaea), and garden pea agglutinin PSA (Pisum sativum) lectins or fluorescein isothiocyanate-heparin to assess differences in spermatozoa-bound fluorochrome by flow cytometry. Use of propidium iodide to identify nuclei containing sperm cells within the ejaculate is essential to the method because of the large amount of debris associated with the samples. The precision of the assay is high, with the coefficient of variation for the individual probes being less than 20%. Analysis of a patient pool of 22 revealed that a range in binding properties is observed and a mode of grouping these samples into classes for later analysis is outlined. Semen parameters and fluorescein isothiocyanate-ligand binding values were different in a population of unproven fertility as compared with a comparable population of known fertility. A positive correlation (p less than 0.001) for garden pea agglutinin PSA binding and concentration of motile cells, percentage of motility, and number of motile cells was found. These data suggest the possible utility of flow cytometry for the assessment of human seminal samples.

Isolation and characterization of the plasma membrane of rat cauda epididymal spermatozoa

Cauda epididymal rat spermatozoa were isolated by flushing the excised epididymis and the plasma membrane was detached by a nitrogen cavitation treatment (500 psi, 10 minutes equilibration at 4 C). Membrane vesicles were recovered after sucrose gradient centrifugation. Portions of the sperm surface releasing the plasma membrane were assessed by light microscopy of fluoroscein isothiocyanate-succinylated concanavalin A-treated spermatozoa and by transmission electron microscopy. Plasma membrane was detached from the region overlying the acrosome from most spermatozoa and from the middle-piece overlying the mitochondria from some cells. Thus, the fraction analyzed was derived from at least two portions of the sperm surface. The fractions from the sucrose density gradient were analyzed for gross chemical composition (phospholipid, protein and sterol) and the protein components were detected after electrophoresis under denaturing conditions; the peak fractions (at density approximately 1.13 g/ml) were judged homogeneous. Replicate analyses of such preparations established mass ratios of protein to phospholipid of 0.63, total sterol to phospholipid of 0.18, and demosterol to cholesterol of 0.32. The molecular composition of the phospholipid fraction was determined to be 10% phosphatidylserine (mole percent), 3% phosphatidylinosital, 3% sphingomyelin, 31% phosphatidylethanolamine, 27% phosphatidylcholine, 10% diphosphatidylglycerol and 5% of an unknown component. Fatty acyl analyses of the phospholipid fraction revealed that approximately 70% of the residues consisted of palmitoyl (16:0) and stearoyl (18:0) acyl groups, with the balance distributed among various unsaturated acyl groups (18:1, 22:3, 22:4 and 22:5); about 40% of the recovered phospholipids represented ether acyl phosphatides. Differences in the lipid composition of rat vesicles described here and similar vesicles isolated from ram and boar spermatozoa (described previously) are discussed. The partitioning of the nitroxyl spin label 3-doxylheptane into vesicles isolated from rat and ram spermatozoa was assessed by electron paramagnetic resonance spectroscopy at temperatures between 4 C and 26 C; no difference in the response of the spin label in the two vesicle preparations was detected.

Changes in lectin-binding features of ram sperm surfaces associated with epididymal maturation and ejaculation

Ram sperm, isolated from the caput, corpus, and cauda epididymidis, plus ejaculated cells were washed free of loosely bound components and tested for their ability to bind fluorescein-conjugated lectins (Con A, SBA, RCA, PNA, ECA and WGA) as assessed by epiluminescent-fluorescence light microscopy and flow cytometry. Detailed preliminary studies established an appropriate lectin-to-sperm ratio and incubation conditions for quantitative comparisons of sperm cell types and permitted a detailed analysis of both the amount of lectin bound as well as its distribution on the various aspects of the cell surface. Con A (mannose positive) bound weakly over the entire surface, with little change associated with maturation in the male tract. SBA (N-acetylgalactosamine positive) bound moderately strongly to caput sperm, with an emphasis on the apical ridge portion of the cell; during epididymal transit this binding was greatly diminished and was regained upon ejaculation. RCA, PNA, and ECA (galactose positive) gave generally equivalent results, where initially strong binding to the entire sperm surface decreased (over all parts of the surface except the anterior head) during epididymal maturation, with no change associated with ejaculation. WGA (sialic acid positive) binding initially was weak, but increased with epididymal transit and ejaculation. In vitro incubations with beta-galactosidase and neuraminidase confirmed the assignments given above. These data, when coupled with previous reports describing the heterogeneous distribution of proteins and lipids and changes in their distribution associated with epididymal maturation, serve to quantitatively describe changes in those aspects of the cell surface that are probably responsible for the acquisition of the capacity of the sperm to bind successfully to the oocyte.

Alterations in motility and metabolism associated with sperm interaction with accessory sex gland fluids

Sperm passing through the male tract interact with accessory sex gland fluids during ejaculation. Cellular metabolism is stimulated by this interaction for unknown reasons. These experiments involved calorimetric measurements [P.B. Inskeep and R.H. Hammerstedt (1983) J. Biochem. Biophys. Methods 7, 199-210] on ejaculated sperm (EJS) and cauda epididymal sperm (CES) from bulls to establish the contribution of individual pathways to total cellular ATP synthesis. Parallel incubations outside the calorimeter yielded samples for oxygen consumption measurements and for motility analysis, the major ATP-consuming reaction of sperm. Energy charge values were identical for incubations of EJS and CES with glucose, thereby establishing that the ratios of rates of ATP synthesis and degradation were equivalent for these cells under this incubation condition. The total rate of ATP synthesis was greater for EJS than for CES (5 vs 13 mumol ATP h-1/10(8) cells) with less than 2 mumol ATP h-1 for each cell type coming from degradation of endogenous reserves. Thus, ejaculation is associated with a large increase in catabolic rate that is satisfied by degradation of extracellular glucose. No difference in percentage of motile sperm was noted, but mean velocity was lower for CES (58 micron s-1) than for EJS (85 micron s-1). A difference in forward motility pattern was observed (wig-wag to flipping). We conclude from these data that interaction with accessory sex gland fluids alters ATP requiring activities of sperm, with one obvious alteration being their motility pattern. The increase in ATP requirement is satisfied by increased degradation of extracellular substrates, but not intracellular reserves, to provide sufficient ATP to satisfy cellular needs.