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PubMed1994

Potential assays for sperm capacitation in mammals.

Sperm capacitation is an essential process in fertilization. It apparently involves a large number of processes, the common denominator of which is that they donate to sperm the potential to undergo the acrosome reaction, i.e., to release proteolytic enzymes enabling sperm penetration through the egg coat. Although the phenomenon of capacitation has been known for more than 40 years, it is far from understood, and, consequently, there is, as yet, no operational definition of it. The lack of an assay to identify capacitated spermatozoa is both the cause and the effect of this situation. Here we critically review the major changes that are thought to occur during sperm capacitation, and assess their potential use as markers for the identification of capacitated spermatozoa.

Animals↗
PubMed1992

A comparison of the frequency and type of chromosomal abnormalities in human sperm after different sperm capacitation conditions.

Human sperm karyotypes can be prepared after fusion of human sperm with Golden hamster oocytes. Most laboratories use one of two methods of sperm capacitation: incubation of freshly-ejaculated sperm in Biggers, Whitten, and Whittingham (BWW) medium for 5-7 h at 37 degrees C or sperm storage in (N-tris [hydroxymethyl]methyl-2-aminoethanesulfonic acid; 2-([2-hydroxy-1,1-bis(hydroxymethyl)ethyl]amino)ethanesulfonic acid) (TES)-Tris yolk buffer (TYB) for 1-3 days at 4 degrees C. Since there have been conflicting reports as to whether there is a difference in the frequency of structural chromosomal abnormalities between BWW capacitation and storage in TYB for 2 days, we analyzed a larger number of karyotypes (8974) from 136 donors to determine if there was any difference in the frequency or type of chromosomal abnormalities in sperm treated by fresh BWW capacitation, storage in TYB for 1 day (TYB-1), or storage in TYB for 2 days (TYB-2). There was no difference in the frequency of numerical chromosomal abnormalities or sex ratio in any of the three treatment groups. However, there was a significantly increased frequency of structural chromosomal abnormalities after storage in TYB-1 and TYB-2. There was no difference in the frequency or type of structural chromosomal abnormalities after sperm storage in TYB-1 compared to TYB-2.

Adult↗
PubMed2000

Evidence for the involvement of calmodulin in mouse sperm capacitation.

Although Ca(2+) is of fundamental importance in mammalian sperm capacitation, its downstream targets have not been definitively demonstrated. The purpose of this study was to use the calmodulin (CaM) antagonists W7 and calmidazolium (CZ) to investigate the possible role of CaM, a Ca(2+)-specific binding protein, in capacitation. Sperm membrane changes associated with capacitation were assessed by the B pattern after chlortetracycline staining and by the ability to undergo the acrosome reaction (AR) in response to lysophosphatidylcholine (LPC). The percentage of B pattern sperm was significantly inhibited by W7 or CZ in a concentration-dependent manner. At 100 microM W7 or 10 microM CZ, these inhibitors also significantly reduced the sperm's ability to undergo the LPC-induced AR. Inhibition of the B pattern and the LPC-induced AR was overcome by exogenous cAMP analogues. Treatment of the sperm with 100 microM W7 also resulted in a significant decrease in their ability to fertilize eggs in vitro. At 100 microM, W5, a less potent dechlorinated W7 analogue, had no effect on the B pattern, LPC-induced AR, or fertilization competence. Sperm viability and protein tyrosine phosphorylation were not substantially affected by 100 microM W7 (relative to 100 microM W5) or 10 microM CZ; however, the percentages of motile and hyperactivated sperm were significantly reduced. The antagonist-inhibited sperm motility was restored by dilution in control medium, but not by cAMP analogues. These results suggest that CaM participates in the regulation of membrane changes important for mouse sperm capacitation, at a point upstream from cAMP, and that this pathway is at least partially separable from pathways controlling tyrosine phosphorylation and hyperactivation.

1-Methyl-3-isobutylxanthine↗
PubMed1993

Effect of bovine serum albumin concentration and source on sperm capacitation in the golden hamster.

Since virtually all experiments on sperm capacitation routinely include serum albumin in the culture media, the relative effect of BSA concentration on sperm capacitation was investigated. The fertile life of hamster sperm, as measured by the ability to penetrate the zona pellucida, decreased from 5 to 3 h as the concentration of BSA was increased from 3 to 18 mg/ml. To determine the extent of sperm capacitation in sperm populations that resulted in 100% penetration, the rate and timing of sperm penetration through the zona pellucida was determined. For each insemination, the rate of sperm penetration (%/min), the time when 50% of the eggs were zona-penetrated (T50), and the sperm capacitation index (T50/rate) were calculated. The extent of sperm capacitation as measured by all three parameters increased as the duration of preincubation or the BSA concentration was increased. The data on the duration of preincubation and the BSA concentration matrix indicated two properties of the effect of BSA on sperm capacitation: 1) the extent of sperm capacitation after the first hour of preincubation was independent of BSA concentration; and 2) when sperm were preincubated for two or more hours, the capacitating effectiveness of BSA was saturable; the saturating concentration of BSA decreased as the duration of preincubation increased. To determine whether the first hour of preincubation is independent of BSA, sperm were preincubated for 1 h without BSA and then 2 h with BSA. The extent of sperm capacitation of these sperm was equal to that of the 3-h control sperm; thus the first hour of capacitation is independent of BSA.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed2003

Tyrosine phosphorylation of HSP-90 during mammalian sperm capacitation.

The process of sperm capacitation is correlated with activation of a signal transduction pathway leading to protein tyrosine phosphorylation. Whereas phosphotyrosine expression is an essential prerequisite for fertilization, the proteins that are phosphorylated during capacitation have not yet been identified. In the present study, we observed that a major target of this signaling pathway is the molecular chaperone protein, heat shock protein (HSP)-86, a member of the HSP-90 family of HSPs. We used cross-immunoprecipitation experiments to confirm the tyrosine phosphorylation of HSP-86, a process that is not inhibited by the ansamycin antibiotic, geldanamycin. The general significance of these findings was confirmed by studies in which HSP-90 was also found to be tyrosine phosphorylated in human and rat spermatozoa when incubated under conditions that support capacitation. To our knowledge, these results represent the first report of a protein that undergoes tyrosine phosphorylation during mouse sperm capacitation and the first study implicating molecular chaperones in the processes by which mammalian spermatozoa gain the ability to fertilize the oocyte.

Amino Acid Sequence↗
PubMed2004

Bovine sperm capacitation: assessment of phosphodiesterase activity and intracellular alkalinization on capacitation-associated protein tyrosine phosphorylation.

Mammalian sperm capacitation is the obligatory maturational process leading to the development of the fertilization-competent state. Heparin is known to be a unique species-specific inducer of bovine sperm capacitation in vitro and glucose a unique inhibitor of this induction. Heparin-induced capacitation of bovine sperm has been shown to correlate with protein kinase A (PKA)-dependent protein tyrosine phosphorylation driven by an increase in intracellular cAMP. This study examines the possible roles of cyclic nucleotide phosphodiesterase (PDE) activity and intracellular alkalinization on bovine sperm capacitation and the protein tyrosine phosphorylation associated with it. Measurement of whole cell PDE kinetics during capacitation reveals neither a substantial change with heparin nor one with glucose: PDE activity is effectively constitutive in maintaining intracellular cAMP levels during capacitation. In contrast to a transient increase in intracellular pH, a sustained increase in medium pH by switching from 5% CO(2)/95% air incubation to 1% CO(2)/99% air incubation over 4 hr in the absence of heparin resulted in an increase in protein tyrosine phosphorylation and in the extent of induced acrosome reaction comparable to that observed following heparin-induced capacitation in 5% CO(2). These results suggest that increased bicarbonate-dependent adenylyl cyclase activity, driven by alkalinization, increases intracellular cAMP and so increases PKA activity mediating protein tyrosine phosphorylation. Quantitative analysis of the lactic acid production rate by bovine sperm glycolysis accounts fully for intracellular acidification sufficient to offset heparin-induced alkalinization, thus inhibiting capacitation. The mechanism by which heparin uniquely induces intracellular alkalinization in bovine sperm leading to capacitation remains obscure, inviting future investigation.

3',5'-Cyclic-AMP Phosphodiesterases↗
PubMed1996

Cyclic adenosine 3',5'monophosphate-dependent regulation of protein tyrosine phosphorylation in relation to human sperm capacitation and motility.

The involvement of cAMP in the process of sperm capacitation has been the subject of several studies. In addition, the importance of protein-tyrosine phosphorylation in this process has been investigated, although only a few studies have been reported in the human. Since agents regulating the intracellular concentrations of cAMP affect sperm capacitation rates, the role of cAMP on the expression of phosphotyrosine-containing proteins was investigated during human sperm capacitation. Fetal cord serum ultrafiltrate, a known capacitation inducer in human spermatozoa, caused an increase in the phosphotyrosine content of 105- and 81-kDa proteins (p105 and p81), the two major phosphotyrosine-containing proteins of human spermatozoa. Similar effects were observed when spermatozoa were incubated with phosphodiesterase inhibitors or cell-permeant cAMP analogs, suggesting that cAMP is involved in these two processes. Forskolin, an adenylyl cyclase activator, also caused an increase in both sperm capacitation rates and tyrosine phosphorylation of p105 and p81, while 12-O-tetradecanoyl phorbol 13-acetate stimulated both capacitation and tyrosine phosphorylation of p105 and p81 only when spermatozoa were incubated in the presence of bicarbonate, in agreement with its reported effects on cAMP production and hamster sperm capacitation. The inhibition of these phenomena by cAMP-dependent protein kinase inhibitors, and the stimulation by protein phosphatase inhibitors, suggest that Ser/Thr protein phosphorylation plays an important role in the regulation of both sperm capacitation and protein-tyrosine phosphorylation pathways. However, observations that both calyculin A and okadaic acid stimulated sperm capacitation, whereas only calyculin A increased p105 and p81 phosphotyrosine content and sperm velocity, suggest that protein phosphatase PP1 is involved in the two latter phenomena while PP2A mediates sperm capacitation. These results suggest that divergent pathways might regulate tyrosine phosphorylation of p105 and p81 and sperm capacitation after cAMP-dependent phosphorylation of an intermediate protein.

Adenylyl Cyclases↗
PubMed1993

[Effect of epidermal growth factor (EGF) on mouse sperm capacitation].

The effect of epidermal growth factor (EGF) on the kinetics of mouse sperm capacitation was examined. The chlortetracycline (CTC) fluorescence assay was used to monitor capacitated sperm, featuring a B pattern. One hundred ng/ml EGF significantly stimulated capacitation at 15 minutes after the addition. However, 0.1 pg/ml EGF did not stimulate capacitation. EGF affected neither the motility nor the appearance of the S or AR pattern. The EGF-induced stimulation of capacitation was attenuated by 20 micrograms/ml genistein, an inhibitor of protein tyrosine kinase, or by 100 ng/ml thapsigargin, a non-phorbol tumor promoter, which inhibits EGF action by enhancing phosphorylation of the threonine 669 residue of the EGF-receptor. However, 3 ng/ml 12-O-tetradecanoly phorbol 13-acetate (TPA), a stimulator of protein kinase C, did not attenuate the appearance of the B pattern enhanced by 100 ng/ml EGF. These data suggest that EGF stimulates mouse sperm capacitation by activating the tyrosine kinase of the EGF-receptor which is regulated by multisite phosphorylation.

Animals↗
PubMed1986

Inconsistent reactivity of an anti-sperm monoclonal antibody and its relationship to sperm capacitation.

An anti-sperm monoclonal antibody was developed from female C57BL/6 mice immunized with epididymal sperm from a syngeneic male mouse. Immunofluorescence staining revealed that the antibody did not react to fresh epididymal sperm but attached to the capacitated sperm found in the peri-vitelline spaces of the ova. When the antibody was applied to sperm incubated in vitro, variously stained sperm were observed. It was presumed that the antigenic site detected by the antibody was hidden in the fresh epididymal sperm and was spread from the acrosomal cap region to the entire head during the capacitation process.

Animals↗
PubMed1989

Study on in vitro sperm capacitation and egg-penetration of giant panda.

A preliminary report on in vitro sperm capacitation and egg-penetration of giant panda is briefly presented. The panda spermatozoon consists of head, neck and tail, just like the spermatozoa of other animals. Before capacitation sperm heads clustered together and dispersed after capacitation. They were then able to swim straight forward. During the time of in vitro capacitation the plasma membrane of the sperm head was first expanded to various degrees, then disintegrated, and finally became detached. The electro-dense material in the acrosome appeared in small clumps with high density. Extensive vesiculation occurred between the bi-layered acrosome membranes and thus led to disintegration. Vesiculation in panda sperm differs from that reported in hamsters. When the capacitated panda spermatozoa came into contact with the hamster eggs, the region between the acrosome collar and postacrosome cap first fused with the egg membrane followed by the penetration of the nucleus into the cortex of the egg. Some of the penetrating sperm nuclei became decondensed and some did not. The success of in vitro sperm capacitation and egg-penetration of giant panda is of great significance, suggesting that it is possible to carry out in vitro fertilization and embryo transplantation in this endangered species.

Acrosome↗
PubMed2002

Structural features of sterols required to inhibit human sperm capacitation.

Ejaculated mammalian sperm must undergo a final maturation (capacitation) before they can acrosome-react and fertilize eggs. Loss of cholesterol is an essential step in the capacitation of human sperm. Experimentally maintaining a high level of cholesterol inhibits capacitation, but the mechanism is unknown. The present study investigated the structural features that are required for cholesterol's inhibitory activity. Human sperm also contain much desmosterol, which is lost from sperm during capacitation. Preventing the loss of desmosterol inhibited capacitation (as assessed by acrosomal responsiveness), with an effectiveness approximately equal to cholesterol's inhibitory activity. Other structural analogs were added to the incubation medium to replace sperm cholesterol and desmosterol. Most inhibited capacitation, including those that lacked cholesterol's 3beta-OH group (cholesteryl methyl ether and epicholesterol) and those with modified C17 groups (ergosterol and diosgenin). Two steroids did not inhibit capacitation well. Coprostanol, which has a nonplanar steroid nucleus, had low inhibitory activity that could be explained by an elevated endogenous cholesterol concentration. Epicoprostanol, which has a nonplanar ring structure and a 3alpha-OH group, promoted rather than inhibited capacitation. The inhibitory activity of the analogs was correlated with their ability to promote order of egg phosphatidylcholine as measured by fluorescence anisotropy. In summary, a planar ring structure is required for sterol inhibitory activity, but a 3beta-OH group and a saturated cholesterol-like aliphatic tail on C17 are not required. The present results support the hypothesis that sperm sterols block capacitation by increasing order of phospholipids.

Cholestanol↗
PubMed1993

Effect of epidermal growth factor on human sperm capacitation.

OBJECTIVE: To examine the effect of epidermal growth factor (EGF) on human sperm capacitation and the involvement of protein phosphorylation in the regulation of the EGF action. DESIGN: Human sperm were capacitated in modified Krebs-Ringer's bicarbonate medium of Biggers, Whitten, and Whittingham in the presence of EGF and various agents known to phosphorylate the EGF receptor. The chlortetracycline fluorescence assay was used to monitor capacitated sperm. Capacitation was confirmed by the ability of sperm to undergo the acrosome reaction in response to solubilized mouse zonae pellucidae (ZP). RESULTS: In 15 minutes, the appearance of the clear perimeter pattern increased significantly in the sperm treated with 100 ng/mL EGF compared with the controls. In EGF-treated sperm, the percent clear perimeter pattern remained stable for 3 hours without affecting the acrosome reaction pattern and the motility. Epidermal growth factor stimulated the appearance of the clear perimeter pattern at concentrations > 100 pg/mL. The stimulation by EGF was attenuated by the treatment with genistein, 12-O-tetradecanoylphorbol-13-acetate, or thapsigargin. In sperm that were incubated in the presence of 100 ng/mL EGF for 30 minutes and further induced the acrosome reaction by mouse ZP, the percent acrosome reaction pattern increased significantly compared with the controls. CONCLUSION: Epidermal growth factor stimulates human sperm capacitation by activating the tyrosine kinase of the EGF receptor which is regulated by multisite phosphorylation.

Acrosome↗
PubMed1992

Purification and characterization of a human follicular fluid lipid transfer protein that stimulates human sperm capacitation.

Identification of the mechanisms responsible for sperm capacitation has been an active area of research for nearly four decades. Changes in the lipid composition of the sperm membrane is one of the biochemical events that occurs during sperm capacitation. We have been studying physiological effectors of some of these changes and have identified lipid transfer activity in fractions of human follicular fluid that stimulates sperm penetration of zona-free hamster oocytes. We report here the purification of a lipid transfer protein by sequential chromatography from human follicular fluid. This protein was purified greater than 20,000-fold for lipid transfer activity and greater than 28,000-fold for sperm penetration-inducing activity. This 64,000 molecular weight protein has a pI of approximately 5.0 and shares physicochemical characteristics with the plasma lipid transfer protein, LTP-I. Antibodies to LTP-I also recognize this protein and depletion of LTP-I from human follicular fluid by immunoaffinity chromatography renders the follicular fluid incapable of stimulating sperm penetration. We conclude that purified LTP-I is able to stimulate human sperm capacitation and that LTP-I is a molecule responsible for this stimulation in follicular fluid.

Antibodies, Monoclonal↗
PubMed1999

Reactive oxygen species requirements for bovine sperm capacitation and acrosome reaction.

Sperm capacitation is necessary for the fertilization of oocytes. During capacitation intracellular and membrane changes occur, that culminate with an exocytotic event called the acrosome reaction. The aim of this work was to study the participation of the superoxide anion (O2-.) and of hydrogen peroxide (H2O2) in the capacitation process and acrosome reaction in spermatozoa from cryopreserved bovine semen. Samples were capacitated with heparin or treated with the xanthine-xanthine oxidase-catalase system (X-XO-C) for the production of O2-. The percentage of capacitated spermatozoa was determined using the chlortetracycline (CTC) technique, by means of epifluorescence microscopy. Addition of X-XO-C to the incubation medium significantly induced capacitation (P < 0.05), but there were no differences with samples incubated with heparin. When the medium contained heparin or the X-XO-C, addition of superoxide dismutase (SOD, 0.5 mg/mL) significantly inhibited capacitation (P < 0.05). In samples treated with heparin and with diverse concentrations of H2O2 (10, 25, 50 and 250 microM) in the incubation medium, the percentage of capacitated spermatozoa was significantly reduced (P < 0.05); however, acrosome reaction was produced at concentrations of 10 and 25 microM H2O2. At concentrations greater than 25 microM H2O2 a deleterious effect was observed on sperm motility. From these results it may be inferred that O2-. is required in the capacitation process and that H2O2 may participate as an inductor of the acrosome reaction in spermatozoa from cryopreserved bovine semen.

Acrosome Reaction↗
PubMed2000

Anti-mouse sperm monoclonal antibody, A-1, inhibits sperm capacitation, acrosome reaction and calcium influx into spermatocytes.

An anti mouse sperm monoclonal antibody (A-1) inhibited sperm penetration into the egg zona pellucida and bound to an acrosomal area of sperm. In this study, we examined whether or not the antibody affects the sperm capacitation and the acrosome reaction. Sperm were incubated in modified Krebs-Ringer bicarbonate medium in the presence or absence of the antibody. The capacitation of sperm was assessed by chlortetracycline fluorescence pattern assay. The percentage of capacitated sperm did not increase in the presence of antibody, but increased time-dependently in its absence. The acrosome reaction of the capacitated sperm was induced by the addition of ionophore. The ionophore, however, failed to induce the reaction in the presence of the A-1 antibody. Next, the calcium influx into spermatocytes was examined. The capacitated sperm, preloaded with Fura-2, were treated with ionomycin in the presence or absence of the A-1 antibody. The influx of calcium ions into capacitated spermatozoa was also inhibited by the antibody. Thus a monoclonal antibody, A-1, inhibited the sperm capacitation, acrosome reaction and calcium influx into spermatocytes.

Acrosome Reaction↗
PubMed1993

Effects of modulators of protein kinase C on human sperm capacitation.

OBJECTIVE: To examine the effects of stimulators or inhibitors of protein kinase C on capacitation and protein phosphorylation in human sperm. DESIGN: Capacitated sperm treated with or without modulators of protein kinase C were monitored by the chlortetracycline fluorescence assay. Capacitation was confirmed by the ability of sperm to undergo the acrosomal reaction in response to mouse zonae pellucidae. 32P-labeled sperm phosphoproteins were analyzed by one-dimensional gel electrophoresis to detect the effect of protein kinase C stimulator, 12-O-tetradecanoyl-phorbol-13-acetate, on protein phosphorylation. RESULTS: The treatment of sperm with protein kinase C stimulators resulted in the following: [1] the rapid appearance of the clear perimeter pattern, featuring distribution of fluorescence over the entire head exhibiting a bright perimeter and bright midpiece; [2] an accelerated ability to undergo the acrosomal reaction; and [3] an enhanced phosphorylation of 57.5-kd sperm phosphoprotein. Furthermore, these stimulatory effects were inhibited by protein kinase C inhibitors. CONCLUSION: Protein phosphorylation mediated by protein kinase C may be involved in the regulation of human sperm capacitation.

Acrosome↗
PubMed2004

Effect of adding cholesterol to bull sperm membranes on sperm capacitation, the acrosome reaction, and fertility.

When cholesterol is added to sperm membranes before cryopreservation, higher percentages of motile and viable cells are recovered after thawing. However, because one of the first steps in sperm capacitation is cholesterol efflux from the sperm plasma membrane, adding cholesterol to enhance cryosurvival may retard sperm capacitation. These studies evaluated the ability of sperm treated with cholesterol-loaded cyclodextrins (CLC) to capacitate, acrosome react, and fertilize oocytes. Control (non-CLC-treated) and CLC-treated sperm were treated with heparin, dilauroylphosphatidylcholine (PC12), or calcium ionophore A23187 (A23187) to capacitate and induce the acrosome reaction. Sperm capacitation, assessed by an increase in intracellular calcium level, and acrosome-reacted sperm were measured using flow cytometry. Fresh CLC-treated sperm cells underwent capacitation and/or the acrosome reaction at rates different from control samples, and the differences detected were dependent on the method used to induce sperm capacitation and the acrosome reaction. After cryopreservation, however, CLC-treated and control sperm underwent capacitation and the acrosome reaction at similar rates regardless of the method used to induce capacitation and the acrosome reaction. The primary concern for CLC-treated sperm, however, is whether this treatment would affect in vitro or in vivo fertility. Adding either control or CLC-treated cryopreserved sperm to bovine oocytes in vitro resulted in similar oocyte cleavage rates and blastocyst formation rates. In addition, when inseminated into heifers, pregnancy rates for control and CLC-treated sperm were also similar. Therefore, treating bull sperm with CLC permits greater numbers of sperm to survive cryopreservation while preserving the fertilizing potential of each individual sperm.

Acrosome Reaction↗
PubMed2007

Ginsenoside Re promotes human sperm capacitation through nitric oxide-dependent pathway.

The regulation of sperm capacitation is important for successful fertilization. Ginsenosides, the biologically effective components of ginseng, have been found to enhance intracellular nitric oxide (NO) production and the latter has recently been indicated to play a significant role in modulation of sperm functions. We investigated the effect of Ginsenoside Re on human sperm capacitation in vitro and the mechanism by which the Ginsenosides play their roles. Spermatozoa were separated by Percoll and incubated with 0, 1, 10, or 100 microM of Ginsenoside Re. The percentages of spontaneous and lysophosphatidylcholine (LPC)-induced acrosome reaction (AR), as a measure of sperm capacitation, were assayed with fluorescein isothiocyanate-conjugated Pisum sativum agglutinin (FITC-PSA). The intracellular cGMP level was measured by [(3)H] cGMP radioimmunoassay system. The results showed that the percentages of both spontaneous and LPC-induced AR and intracellular cGMP level were significantly enhanced by Ginsenoside Re with a concentration-dependent manner. Sodium nitroprusside (SNP, 100 nM), a NO donor, mimicked the effects of Ginsenoside Re. And pretreatment with a NOS inhibitor N(omega)-nitro-l-arginine methyl ester (L-NAME, 100 microM) or a NO scavenger N-acetyl-l-cysteine (LNAC, 1 mM) completely blocked the effects of Ginsenoside Re. Furthermore, the AR-inducing effect of Ginsenoside Re was significantly reduced in the presence of the soluble guanylate cyclase inhibitor LY83583 or cGMP-dependent protein kinase (PCK) inhibitor KT5823, whereas addition of the cGMP analogue 8-Br-cGMP significantly increased the AR of human spermatozoa. Data suggested that Ginsenoside Re is beneficial to sperm capacitation and AR, and that the effect is accomplished through NO/cGMP/PKG pathway.

Acrosome Reaction↗