Cholesterol efflux from bovine sperm. I. Induction of the acrosome reaction with lysophosphatidylcholine after reducing sperm cholesterol

Small and Large Extracellular Vesicles of Porcine Seminal Plasma Differ in Lipid Profile

Seminal plasma contains a heterogeneous population of extracellular vesicles (sEVs) that remains poorly characterized. This study aimed to characterize the lipidomic profile of two subsets of differently sized sEVs, small (S-) and large (L-), isolated from porcine seminal plasma by size-exclusion chromatography and characterized by an orthogonal approach. High-performance liquid chromatography-high-resolution mass spectrometry was used for lipidomic analysis. A total of 157 lipid species from 14 lipid classes of 4 major categories (sphingolipids, glycerophospholipids, glycerolipids, and sterols) were identified. Qualitative differences were limited to two cholesteryl ester species present only in S-sEVs. L-sEVs had higher levels of all quantified lipid classes due to their larger membrane surface area. The distribution pattern was different, especially for sphingomyelins (more in S-sEVs) and ceramides (more in L-sEVs). In conclusion, this study reveals differences in the lipidomic profile of two subsets of porcine sEVs, suggesting that they differ in biogenesis and functionality.

Treatment with cholesterol just after thawing maintains the fertility of bull sperm

Freezing and thawing diminish sperm motility and fertility by disrupting the cholesterol balance in sperm plasma and organelle membranes. The aim of this study was to elucidate the mechanisms through which exogeneous cholesterol treatment enhances the quality of frozen-thawed bull sperm. The incorporation of cholesterol was investigated using boron-dipyrromethene (BODIPY)-cholesterol, and BODIPY signals were detected not only in the plasma membrane but also in the midpiece region immediately after thawing. The positive signal of cholesterol in the midpiece region was inhibited by a scavenger receptor class B Type I (SR-BI) inhibitor, block lipid transport 1 (BLT-1). To comprehend the role of exogenous cholesterol in the functions of the plasma membrane, propidium iodide (PI)/Annexin V and peanut agglutinin lectin (PNA) staining were performed. The results showed that treatment with exogenous cholesterol increased the number of acrosome-intact sperm and decreased the number of sperm with damage to the plasma membrane. Moreover, since BODIPY signals were also observed in the midpiece region, mitochondrial function was evaluated using a flux analyzer and a flow cytometer with 5,5',6,6'-tetrachloro-1,1',3,3'-tetraethylbenzimidazolyl carbocyanine iodide (JC-1) staining, revealing an increase in the number of sperm with high-mitochondrial activity and oxygen consumption. Finally, to assess sperm fertility, computer-assisted sperm analysis (CASA) and IVF were carried out. Sperm velocities and fertilization rates in IVF were significantly enhanced by the addition of cholesterol just after thawing. Thus, the treatment with cholesterol after thawing protected the plasma membrane from the stress of thawing and maintained mitochondrial function, thereby preserving the fertilization ability of frozen-thawed bull sperm for conventional IVF and artificial insemination (AI). Therefore, the application of cholesterol just after thawing is a promising option for improving the fertility of frozen-thawed sperm.

The stallion sperm acrosome: Considerations from a research and clinical perspective

During the fertilization process, the interaction between the sperm and the oocyte is mediated by a process known as acrosomal exocytosis (AE). Although the role of the sperm acrosome on fertilization has been studied extensively over the last 70 years, little is known about the molecular mechanisms that govern acrosomal function, particularly in species other than mice or humans. Even though subfertility due to acrosomal dysfunction is less common in large animals than in humans, the evaluation of sperm acrosomal function should be considered not only as a complementary but a routine test when individuals are selected for breeding potential. This certainly holds true for stallions, which might display lower levels of fertility in the face of "acceptable" sperm quality parameters determined by conventional sperm assays. Nowadays, the use of high throughput technologies such as flow cytometry or mass spectrometry-based proteomic analysis is commonplace in the research arena. Such techniques can also be implemented in clinical scenarios of males with "idiopathic" subfertility. The current review focuses on the sperm acrosome, with particular emphasis on the stallion. We aim to describe the physiological events that lead to the acrosome formation within the testis, the role of very specific acrosomal proteins during AE, the methods to study the occurrence of AE under in vitro conditions, and the potential use of molecular biology techniques to discover new markers of acrosomal function and subfertility associated with acrosomal dysfunction in stallions.

Phospholipases and Reactive Oxygen Species Derived Lipid Biomarkers in Healthy and Diseased Humans and Animals - A Focus on Lysophosphatidylcholine

Phospholipids (PL) are converted into lipid biomarkers by the action of phospholipases and reactive oxygen species (ROS), which are activated or released under certain physiological and pathophysiological conditions. Therefore, the in vivo concentration of such lipid biomarkers [e.g., lysophospholipids (LPLs)] is altered in humans and animals under different conditions such as inflammation, stress, medication, and nutrition. LPLs are particularly interesting because they are known to possess pro- and anti-inflammatory properties and may be generated by two different pathways: either by the influence of phospholipase A₂ or by different reactive oxygen species that are generated in significant amounts under inflammatory conditions. Both lead to the cleavage of unsaturated acyl residues. This review provides a short summary of the mechanisms by which lipid biomarkers are generated under in vitro and in vivo conditions. The focus will be on lysophosphatidylcholine (LPC) because usually, this is the LPL species which occurs in the highest concentration and is, thus, easily detectable by chromatographic and spectroscopic methods. Finally, the effects of lipid biomarkers as signaling molecules and their roles in different human and animal pathologies such as infertility, cancer, atherosclerosis, and aging will be shortly discussed.

Sperm Lipid Markers of Male Fertility in Mammals

Sperm plasma membrane lipids are essential for the function and integrity of mammalian spermatozoa. Various lipid types are involved in each key step within the fertilization process in their own yet coordinated way. The balance between lipid metabolism is tightly regulated to ensure physiological cellular processes, especially referring to crucial steps such as sperm motility, capacitation, acrosome reaction or fusion. At the same time, it has been shown that male reproductive function depends on the homeostasis of sperm lipids. Here, we review the effects of phospholipid, neutral lipid and glycolipid homeostasis on sperm fertilization function and male fertility in mammals.

Silk protein sericin pretreatment enhances osmotic tolerance and post-thaw sperm quality but reduces the ability of sperm cells to undergo in vitro induced acrosome reaction in rabbit

Effect of sericin pretreatment of sperm cells on the osmotic tolerance, ability to undergo acrosome reaction induced by calcium ionophore (CI), heparin (H) or lysophosphatidylcholine (LPC), post-thaw sperm quality and in vivo fertility was evaluated in four successive experiments in rabbit. In experiment 1, fresh semen was pretreated with sericin (0, 0.1% or 0.5% w/v) before exposing to fructose solutions adjusted to either 50, 100, 290, 500 or 1000 mOsm/L. Sericin pretreatment increased sperm livability in addition to live-membrane intact and total membrane intact sperm rates (P < 0.05) in 50 and 290 mOsm/L groups. In experiment 2, sperm samples were pretreated by either 0.1 or 0.5% sericin after removal of the semen plasma. CI, H or LPC were used to induce acrosome reaction in pretreated sperm samples. Sericin pretreatment, reduced the ability of sperm cells to undergo acrosome reaction (P < 0.05) in vitro. In experiment 3, ejaculates were frozen with or without sericin pretreatment in DMSO-sucrose extender. In post-thaw samples sericin pretreatment improved total and progressive motility, livability, membrane and acrosome integrity in a dose dependent manner (P < 0.05). In vivo fertility trials by artificial inseminations revealed contradictory results in experiment 4. Although 0.5% sericin pretreatment totally inhibited fertility, 0.1% sericin provided high pregnancy rates. In conclusion; sericin pretreatment enhances osmotic tolerance and post-thaw sperm quality, but reduces the ability of rabbit sperm cells to undergo in vitro induced acrosome reaction, but this effect is restored in vivo by dose dependent manner.

Stage-dependent changes in oviductal phospholipid profiles throughout the estrous cycle in cattle

Sperm capacitation, fertilization and embryo development take place in the oviduct during the periovulatory period of the estrous cycle. Phospholipids are crucial metabolites for sperm capacitation and early embryo development. The aim of this study was to monitor the abundance of phospholipids in the bovine oviductal fluid (OF) according to the stage of the estrous cycle and the side relative to ovulation. Pairs of bovine oviducts were collected in a slaughterhouse and classified into four stages of the estrous cycle: post-ovulatory (Post-ov), mid-luteal (Mid-lut), late-luteal (Late-lut) and pre-ovulatory (Pre-ov) phases (n = 17 cows/stage). Cell-free OF from oviducts ipsilateral and contralateral to the site of ovulation were analyzed using MALDI-TOF mass spectrometry. Lipid identification was achieved by high resolution mass spectrometry. A total of 274 lipid masses were detected in the mass range of 400-1000 Da, corresponding mostly to phosphatidylcholines (PC), lysoPC, phosphatidylethanolamine (PE), lysoPE and sphingomyelins (SM). Ipsilateral and contralateral OF did not differ in their lipid profiles at any stage of the cycle. However, 127 and 96 masses were differentially abundant between stages in ipsilateral and contralateral OF, respectively. Highest differences in lipid profiles were observed in the Pre-ov vs. Mid-lut and Pre-ov vs. Late-lut comparisons in both sides relative to ovulation. Differential abundance of specific molecules of PC, PE, SM and l-carnitine were observed at Pre-ov and Post-ov compared with the luteal phase. This work proposes new candidates potentially able to regulate sperm capacitation and early embryo development.

Cholesterol-Loaded Cyclodextrin Increases the Cholesterol Content of Goat Sperm to Improve Cold and Osmotic Resistance and Maintain Sperm Function after Cryopreservation

The success of semen cryopreservation depends on sperm membrane integrity and function after thawing. Cholesterol-loaded cyclodextrin (CLC) is used for in vitro incorporation of cholesterol to protect cells against cold temperatures. We hypothesized that CLC treatment also enhances sperm cholesterol content to increase tolerance to osmotic shock and cryoresistance, thereby improving fertility. We confirmed the fact that treatment of goat semen with 3 mg/ml CLC increases sperm cholesterol content using both the Liebermann-Burchard approach and filipin III labeling of membrane cholesterol. Sperm were then treated with or without CLC and cryopreserved. After thawing, sperm cholesterol dramatically fell, even in the presence of CLC, which explains the mechanism of cryocapacitation. CLC treatment, however, maintained a normal prefreeze cholesterol level in sperm after cryopreservation. Furthermore, fresh sperm treated with CLC and subjected to either cold shock or incubated in hypo-, iso-, and hyperosmotic media, designed to mimic stresses associated with freezing/thawing, displayed increased temperature and osmotic tolerance. CLC treatment also improved sperm viability, motility, and acrosome integrity after thawing. Furthermore, CLC treatment did not affect the sperm's ability to undergo in vitro capacitation according to chlortetracycline fluorescence and protein tyrosine phosphorylation. A pilot field trial demonstrated that artificial insemination with sperm that underwent increased cholesterol levels following CLC treatment yielded higher fertility ( ITALIC! P< 0.1) and proliferation ( ITALIC! P< 0.05) rates in vivo than untreated semen from the same ejaculate samples. These observations suggest that CLC treatment could be used to improve cryoprotection during the freezing and thawing of goat sperm.

Sperm volumetric dynamics during in vitro capacitation process in bovine spermatozoa

Previous studies have demonstrated that sperm head morphometry can be used as a potential diagnostic tool for detecting biophysical changes associated with sperm viability in bovine spermatozoa. In this study, sperm head morphometry was used to investigate its value as a biophysical marker for detecting volumetric changes in bovine spermatozoa under in vitro capacitating and non-capacitating incubation conditions. To further test this hypotesis, aliquots of pooled, washed bovine sperm were incubated in either Tyrode's complete medium with heparin (TCMH; a capacitating medium containing Ca2+, NaHCO3 and heparin), Tyrode's complete medium heparin-free (TCM; a medium containing just Ca2+ and NaHCO3) or Tyrode's basal medium (TBM; a non-capacitating medium free of Ca2+, NaHCO3 and heparin, used as control). Aliquots of sperm were processed for morphometric analysis at different incubation-time intervals (0, 3 and 6 h at 38°C), and the chlortetracycline assay was used simultaneously to confirm the ability of the sperm to undergo capacitation (B pattern) and the acrosome reaction (AR pattern) status in each medium. After 3 h of incubation under TCMH conditions, a significant increase was observed in the percentage of B and AR patterns and a significant decrease was found in all sperm morphometric parameters (P<0.01). Interestingly, after 6 h of incubation in TCMH, the percentage of B and AR patterns increased drastically over time and marked differences were found in the dimensional and shape parameters, which were significantly smaller compared with TBM or TCM media (P<0.001). Significant correlations were observed between sperm size and AR pattern (r=-0.875, P<0.01). In conclusion, sperm head morphometry can be used as a potential biophysical marker for detecting volumetric changes during capacitation process in bovine spermatozoa.

Epididymosomes, prostasomes, and liposomes: their roles in mammalian male reproductive physiology

Mammalian spermatozoa are unique cells in many ways, and the acquisition of their main function, i.e. fertilization capacity, is a multistep process starting in the male gonad and ending near the female egg for the few cells reaching this point. Owing to the unique character of this cell, the molecular pathways necessary to achieve its maturation also show some specific characteristics. One of the most striking specificities of the spermatozoon is that its DNA is highly compacted after the replacement of histones by protamines, making the classical processes of transcription and translation impossible. The sperm cells are thus totally dependent on their extracellular environment for their protection against oxidative stress, for example, or for the molecular changes occurring during the transit of the epididymis; the first organ in which post-testicular maturation takes place. The molecular mechanisms underlying sperm maturation are still largely unknown, but it has been shown in the past three decades that extracellular vesicles secreted by the male reproductive tract are involved in this process. This review will examine the roles played by two types of naturally occurring extracellular vesicles, epididymosomes and prostasomes, secreted by the epididymis and the prostate respectively. We will also describe how the use of artificial vesicles, liposomes, contributed to the study of male reproductive physiology.

Boar seminal plasma exosomes: effect on sperm function and protein identification by sequencing

Mammalian seminal plasma contains membranous vesicles (exosomes), with a high content of cholesterol and sphingomyelin and a complex protein composition. Their physiological role is uncertain because sperm stabilization and activation effects have been reported. To analyze a putative modulatory role for semen exosomes on sperm activity in the boar, the effects of these vesicles on several sperm functional parameters were examined. Additionally, boar exosome proteins were sequenced and their incorporation into sperm was explored. Boar sperm were incubated under conditions that induce capacitation, manifested as increased tyrosine phosphorylation, cholesterol loss and greater fluidity in apical membranes, and the ability to undergo the lysophosphatidylcholine-induced acrosome reaction. After establishing this cluster of capacitation-dependent functional parameters, the effect produced by exosomes when present during or after sperm capacitation was analyzed. Exosomes inhibited the capacitation-dependent cholesterol efflux and fluidity increase in apical membranes, and the disappearance of a 14-kD phosphorylated polypeptide. In contrast, the acrosome reaction (spontaneous and lysophosphatidylcholine-induced) was not affected, and sperm binding to the oocyte zona pellucida was reduced only when vesicles were present during gamete coincubation. Liposomes with a lipid composition similar to that present in exosomes mimicked these effects, except the one on zona pellucida binding. Interaction between exosomes and sperm was confirmed by transfer of aminopeptidase activity. In addition, the major exosome protein, identified as actin, appeared to associate with sperm after coincubation. Exosome composition had a predominance for structural proteins (actin, plastin, ezrin, and condensin), enzymes, and several porcine seminal plasma-specific polypeptides (e.g., spermadhesins). Transfer of proteins from exosome to sperm and their ability to block cholesterol efflux supports a direct interaction between these vesicles and sperm, whereas inhibition of some capacitation-dependent features suggests a stabilizing function for exosomes in boar semen.

Involvement of ABCB1 and ABCC1 transporters in sea urchin Echinometra lucunter fertilization

Fertilization is an ordered sequence of cellular interactions that promotes gamete fusion to form a new individual. Since the pioneering work of Oskar Hertwig conducted on sea urchins, echinoderms have contributed to the understanding of cellular and molecular aspects of the fertilization processes. Studies on sea urchin spermatozoa reported the involvement of a plasma membrane protein that belongs to the ABC proteins superfamily in the acrosome reaction. ABC transporters are expressed in membranes of eukaryotic and prokaryotic cells, and are associated with the transport of several compounds or ions across biomembranes. We aimed to investigate ABCB1 and ABCC1 transporter activity in sea urchin spermatozoa and their involvement in fertilization. Our results indicate that Echinometra lucunter spermatozoa exhibit a low intracellular calcein accumulation (18.5% stained cells); however, the ABC blockers reversin205, verapamil, and MK571 increased dye accumulation (93.0-96.6% stained cells). We also demonstrated that pharmacologically blocking ABCB1 and ABCC1 decreased spermatozoa fertilizing capacity (70% inhibition), and this phenotype was independent of extracellular calcium. These data suggest that functional spermatozoa ABCB1 and ABCC1 transporters are crucial for a successful fertilization. Additional studies must be performed to investigate the involvement of membrane lipid homeostasis in the fertilization process.

Toxicity of titanium oxide nanoparticles causes functionality and DNA damage in buffalo (Bubalus bubalis) sperm in vitro

The present study has examined the effect of different concentrations (1 μg/ml, 10 μg/ml and 100 μg/ml) of titanium oxide (TiO2) nanoparticles (NPs) (<100 nm) on viability, membrane integrity, capacitation status and DNA integrity of buffalo spermatozoa. Characterization of NPs was done by the transmission electron microscopy (TEM) and dynamic light scattering (DLS). Sperm chromatin dispersion (SCD) test and acridine orange test (AOT) were employed to detect DNA fragmentation in sperm treated with NPs. There was significant (p < 0.05) decrease in cell viability and membrane integrity (assessed by enzyme leakage) at 6 h of incubation with NPs. However, significant (p < 0.05) increase in sperm capacitation was observed for TiO2 NP albeit at lower concentrations. In DNA fragmentation assay, there was dose-dependent increase in the DNA fragmentation (r = 0.96). Ultrathin cross-sections revealed TiO2 NPs inside head and plasma membrane of the buffalo spermatozoa as assessed by TEM. These studies suggest that TiO2 NPs may have cytotoxic effect on buffalo spermatozoa by affecting sperm functionality and causing high amount of DNA fragmentations.

Human serum albumin as a new interacting partner of prolactin inducible protein in human seminal plasma

Prolactin inducible protein (PIP) is a 17 kDa glycoprotein. It binds to many proteins including fibrinogen, actin, keratin, myosin, immunoglobulin G, CD4, and human zinc-alpha-2 glycoprotein. Its ability to bind a large array of proteins indicates its multifaceted role in various biological processes, such as fertility, immunoregulation, antimicrobial activity, apoptosis, and tumor progression. Here, we present the first report of native human serum albumin (HSA)-PIP complex formation in seminal plasma. The complex was purified by chromatographic separation techniques, analyzed by gel electrophoresis, identified by MALDI-TOF mass spectrometry and validated by co-immunoprecipitation coupled with western blotting experiments. Moreover, the behavior of complex in solution was analyzed by dynamic light scattering and interacting residues were identified by in silico protein-protein docking. The purified protein complex shows two bands (67 kDa and 17 kDa) on SDS-PAGE gel and a single band (~85 kDa) on native PAGE gel. The predicted complex structure has 13 intermolecular hydrogen bonds, which may contribute to the overall stability of the complex. As HSA has been known to preserve the motility of sperm, native HSA-PIP complex formation may point towards an important role of PIP, which can directly be correlated with male fertility/infertility.

The effects of methyl-β-cyclodextrin on in vitro fertilization and the subsequent development of bovine oocytes

In this study, we investigated the effects of methyl-β-cyclodextrin (MBCD) on in vitro fertilization and the subsequent development of bovine oocytes. Bovine oocytes matured in serum-free medium were inseminated with frozen-thawed sperm pre-incubated in protein-free modified Brackett and Oliphant medium (BO) containing various concentrations of MBCD for various periods. MBCD decreased the frequency of live sperm, however enhanced the capacitation and acrosome reaction of the live sperm. Pre-incubation of sperm with 0.5, 1.0 and 1.5 mM MBCD for 2 and 4 h increased the frequency of normal fertilization. Embryos derived from oocytes fertilized with spermatozoa pre-incubated with MBCD developed normally to the blastocyst stage and term. There were individual differences and similar tendencies in four different sires in terms of the effects of MBCD upon fertilization. These results indicate that the pre-incubation of bovine sperm with MBCD affects viability and capacitation status of the sperm and promotes fertilization in vitro. Embryos derived from oocytes fertilized with sperm pre-incubated with MBCD developed normally to the blastocyst stage and term.

Clusterin facilitates exchange of glycosyl phosphatidylinositol-linked SPAM1 between reproductive luminal fluids and mouse and human sperm membranes

Glycosyl phosphatidylinositol (GPI)-linked proteins, which are involved in post-testicular maturation of sperm and have a role in fertilization, are acquired on the sperm surface from both vesicular and membrane-free soluble fractions of epididymal luminal fluid (LF) and uterine LF. Herein, we investigate the mechanism of uptake of these proteins from the soluble fraction of LFs using sperm adhesion molecule 1 (SPAM1) as a model. Ultracentrifugation and native Western blot analysis of the soluble fraction revealed that SPAM1 is present in low-molecular-weight (monomeric) and high-molecular-weight (oligomeric) complexes. The latter are incapable of transferring SPAM1 and may serve to produce monomers. Monomers are stabilized by hydrophobic interactions with clusterin (CLU), a lipid carrier that is abundantly expressed in LFs. We show that CLU is involved in the transfer of SPAM1 monomers, whose delivery was decreased by anti-CLU antibody under normal and apolipoprotein-enhanced conditions. Coimmunoprecipitation revealed an intimate association of CLU with SPAM1. Both plasma and recombinant CLU had a dose-related effect on transfer efficiency: high concentrations reduced and low concentrations enhanced delivery of SPAM1 to human and mouse sperm membranes, reflecting physiological states in the epididymal tract. We propose a lipid exchange model (akin to the lipid-poor model for cholesterol efflux) for the delivery of GPI-linked proteins to sperm membranes via CLU. Our investigation defines specific conditions for membrane-free GPI-linked protein transfer in vitro and could lead to technology for improving fertility or treating sperm pathology by the addition of relevant GPI-linked proteins critical for successful fertilization in humans and domestic animals.

Effects of methyl-beta-cyclodextrin and cholesterol on cryosurvival of spermatozoa from C57BL/6 mouse

MBCD and Cholesterol-Loaded-Cyclodextrin (CLC) were examined for their abilities to increase the cryosurvival of C57BL/6 mouse sperm, the main strain of genetically engineered mice. The intactness of acrosome and motility of frozen/thawed spermatozoa were used to monitor cryosurvival. In this experimental study, male mice were randomly divided in 6 groups: control 1, experimental 1, experimental 2, control 2, experimental 3 and experimental 4. In experimental groups 1 and 2 spermatozoa were exposed to 0.75 and 1 mM MBCD and in experimental groups 3 and 4 were exposed to two different concentrations of CLC (1 and 2 mg mL(-1)) over a period of 1 h and were subsequently cryopreserved. Spermatozoa in control 1 group were frozen without any exposure to CLC or MBCD and in control 2 (vehicle), sperms were incubated with 4 mM MBCD. The post-thaw sperms were evaluated for their motility and acrosomal status. The values of the intact acrosome and motility increased significantly with concentration of CLC compared to controls and MBCD experimental groups (p<0.05). These results indicate that cryosurvival of C57BL/6 mouse spermatozoa is enhanced by exposure to MBCD which loaded with cholesterol (CLC) before freezing and MBCD alone can not protect sperm from freeze-thaw damage efficiently compare to CLC.

ATP-binding cassette transporters ABCA1, ABCA7, and ABCG1 in mouse spermatozoa

Mammalian spermatozoa lose plasma membrane cholesterol during their maturation in the epididymis and during their capacitation in the female reproductive tract. While acceptors such as high-density lipoproteins (HDL) and apolipoproteins A-I (apoA-I) and J have been found in male and female reproductive tracts, transporters that mediate cholesterol efflux from plasma membranes of spermatozoa to such acceptors have not yet been defined. Candidate transporters are members of the ATP-binding cassette (ABC) transporter superfamily including ABCA1, ABCA7, ABCG1 and ABCG4, which have all been implicated in the transport of sterols and phospholipids to apolipoproteins and HDL. Here we show that mouse spermatozoa in the seminiferous tubules and epididymis express ABCA1, ABCA7 and ABCG1, but not ABCG4. Moreover, we show that ABCA1, ABCA7, and ABCG1 antibodies decrease cholesterol efflux from spermatozoa to lipid acceptors apoA-I and albumin and inhibit in vitro fertilization.

Membrane fluidity changes in goat sperm induced by cholesterol depletion using beta-cyclodextrin

Cholesterol efflux from membranes promotes acrosome reaction in goat spermatozoa. In 1 h of incubation of sperm in the presence of beta-cyclodextrin (beta CD), all the interchangeable cholesterol is desorbed from sperm membranes, although acrosome reaction is fully accomplished only after 3-4 h of incubation, as previously published. In the present paper we investigate the effect of cholesterol removal from mature goat spermatozoa on the overall membrane "fluidity" of live cell membranes and of liposomes from sperm lipid extracts. Using steady state fluorescence anisotropy of 1,6-diphenyl-1,3,5-hexatriene (DPH), we studied the average thermotropic behaviour of membrane lipids, after incubation of live sperm for 1 h in BSA-free medium with the presence/absence of 8 mM beta-cyclodextrin, as a cholesterol acceptor. Unimodal and bimodal theoretical sigmoids fitted best to the experimental thermotropic profiles of liposomes and whole cells, respectively. In the case of whole sperm, two phase transitions, attributable to different lipid domains, were clearly separated by using the fitting parameters. After cholesterol removal, important changes in the relative anisotropy range of the two transitions were found, indicating an increase in the "fluidity" of some of the lipid microdomains of sperm membranes. These changes in sperm lipid dynamics are produced before the onset of sperm acrosome reaction.

Cholesterol-to-phospholipid ratio in whole sperm and seminal plasma from fertile stallions and stallions with unexplained subfertility

Semen samples were collected from six fertile stallions and seven stallions with unexplained infertility. Percentages of motile sperm (77.5 +/- 11.3 versus 67.5 +/- 12.2, P = 0.2), and progressively motile sperm (70.8 +/- 13.6 versus 60.7 +/- 14.0, P = 0.2) were similar between fertile and subfertile stallions, respectively. Morphologic characteristics in ejaculates of control and affected stallions (% normal: 60.2 +/- 18.2 versus 52.9 +/- 11.3, P = 0.4; % abnormal heads 7.3 +/- 4.8 versus 12.1 +/- 5.0, P = 0.11; and % abnormal acrosomes 1.6 +/- 2.1 versus 3.0 +/- 3.4, P = 0.4) did not differ. After incubation with the calcium ionophore A23187, acrosome reaction rate of sperm from fertile stallions was 96 +/- 2.8% whereas only 2.9 +/- 2.5% of sperm from stallions with unexplained subfertility had acrosome reacted (P < 0.001). Molar amounts of cholesterol and phospholipid in whole sperm and seminal plasma did not differ (P > 0.1) between fertile and subfertile stallions. However, the molar ratio of cholesterol-to-phospholipid was 2.5 times greater in the seminal plasma (P = 0.09) and 1.9 times greater (P = 0.009) in whole sperm of subfertile stallions compared to fertile stallions.

Effect of methyl-β-cyclodextrin treatment of pig spermatozoa on in vitro fertilization and embryo development in the absence or presence of caffeine

A series of experiments were carried out to develop a new method to reduce pig polyspermic fertilization and produce more normal embryos, in vitro. Experiment 1 determined the effect of methyl-beta-cyclodextrin (MCD) treatment during cryopreservation on sperm acrosome reaction and sperm fertilization. Compared to the non-MCD-treated control, MCD treatment increased the percentage of acrosome-reacted spermatozoa at thawing and 2h after incubation in fertilization medium (P<0.01). Treatment with MCD also increased (P<0.05) sperm-penetration rate, number of spermatozoa in oocytes, and fertilization efficiency in the caffeine-free fertilization medium. Experiment 2 was designed to examine the effect of withdrawal of caffeine (caffeine-free) from fertilization medium on fertilization parameters and early embryo development. Using MCD-treated spermatozoa, there was no difference in sperm-penetration rate, oocyte cleavage rate, and blastocyst formation rate between the caffeine-free and caffeine-supplemented groups. However, polyspermic fertilization rate was lower, and fertilization efficiency and blastocyst cell number were higher in the caffeine-free group compared to the caffeine-supplemented group (P<0.05). Experiment 3 studied the effect of caffeine and different concentrations of spermatozoa on fertilization parameters. Sperm-penetration rate did not differ between the caffeine-free and the caffeine-supplemented groups at different sperm concentrations. Caffeine and sperm concentration had an effect on the number of spermatozoa in oocytes and on the polyspermic fertilization rate (P<0.002). Caffeine also affected fertilization efficiency (P<0.05). In conclusion, treating spermatozoa with MCD and withdrawing caffeine from fertilization medium may provide a new method to produce a large number of normal embryos, in vitro.

Fertility evaluation of frozen/thawed semen

In vitro semen analyses have been used for more than half a century to estimate the fertilizing potential of a semen sample. Unfortunately, none of the assays developed provide results that consistently correlate well with fertility. The reasons for this lack of consistency, due in part to the complexity of the spermatozoon itself, the collection of fertility data, and factors beyond control of the semen analyses themselves, are discussed. Different spermatozoal attributes that are necessary for a spermatozoon to fertilize an oocyte are presented and assays used to evaluate each attribute described. Although laboratory assay results do not correlate well with semen fertility, the importance of conducting laboratory assays on every semen sample used for artificial insemination or to attempt to determine causes for infertility, is discussed.

Immunolocalization of cubilin, megalin, apolipoprotein J, and apolipoprotein A-I in the uterus and oviduct

Spermatozoa maturation and capacitation occurring in the male and female reproductive tracts, respectively, involves the remodeling of the spermatozoa plasma membrane. Apolipoprotein J (apoJ) and apolipoprotein A-I (apoA-I) have been implicated in the process of lipid exchange from the spermatozoa plasma membrane to epithelial cells lining the male reproductive tract. Evidence suggests that this process is mediated by the cooperative action of the endocytic lipoprotein receptors megalin and cubilin, which are expressed at the apical surface of absorptive epithelia in various tissues, including the efferent ducts and epididymis. Here, we investigated the possibility that these receptors and their lipid-binding ligands, apoJ and apoA-I, might function similarly in the female reproductive tract. We show that megalin and cubilin are expressed in the uterine epithelium at all stages of the estrous cycle, maximally during estrous and metestrous stages. In the oviduct, there is pronounced expression of both megalin and cubilin in the nonciliated cells of the proximal oviduct and epithelial cells of the distal oviduct, particularly during estrous and metestrous stages. In both uterine and oviduct epithelial cells, megalin and cubilin were located on the apical regions of the cells, consistent with a distribution at the cell surface and in endosomes. ApoJ and apoA-I were both detected in apical regions of uterine and oviduct epithelial cells. Secretory cells of the uterine glands were found to express apoJ and apoA-I suggesting that the glands are a site of synthesis for both proteins. In summary, our findings indicate that megalin and cubilin function within the female reproductive tract, possibly mediating uterine and oviduct epithelial cell endocytosis of apoJ/apoA-I-lipid complexes and thus playing a role in lipid efflux from the sperm plasma membrane, a major initiator of capacitation.

Effect of time of ovulation on fertilization after intrabursal transfer of spermatozoa (ITS): improvement of a new method for artificial insemination in mice

The timing of AI in relation to ovulation was examined to improve intrabursal transfer of spermatozoa (ITS) in mice, a new method of AI that involves transfer of spermatozoa into a space near the infundibulum. Two microliters of fresh epididymal B6C3F1 spermatozoa (containing 2 x 10(5) spermatozoa) were inseminated 1, 7, 12, or 17 h after hCG administration. At 1.7 days after ITS, normal cleaving embryos were recovered at rates ranging from 6 to 50% (21.5 +/- 15.8%; mean +/- S.D.), 40-100% (75.2 +/- 20.2%), 33-100% (60.1 +/- 19.3%), and 6-47% (22.7 +/- 13.3%), respectively. The rate obtained by ITS 7h after hCG administration was comparable (P > 0.05) to that (90.5 +/- 6.3%) for embryos obtained after natural mating (control), but rates at all other times were significantly less than control. To examine whether in vivo fertilization rate differs when spermatozoa from various mouse strains are used, B6C3F1 females were inseminated with spermatozoa from ICR, C57BL/6N and C3H/HeN mice 7 h after hCG administration. There were strain differences (P < 0.01 for ICR and B6C3F1 versus C57BL/6N and C3H/HeN) for in vivo fertilization rates (83.9 +/- 10.3%, 75.2 +/- 20.2%, 33.6 +/- 24.5% and 25.6 +/- 16.1% for ICR, B6C3F1, C57BL/6N and C3H/HeN, respectively). Similar rates (72.9 +/- 7.3% and 27.5 +/- 46.2% for ICR and C57BL/6N, respectively) were also obtained when oocytes were inseminated with spermatozoa of the same strain. In addition, females (B6C3F1) inseminated by ITS of fresh B6C3F1 spermatozoa 7 h after hCG administration yielded normal mid-gestational fetuses with an average litter size of 7.0 +/- 4.9, which seemed much higher than the previously reported litter size of 3.2. In conclusion, the timing of AI was considered a key factor affecting in vivo fertilization efficiency.

Current status of sperm cryopreservation: why isn't it better?

Cryopreservation extends the availability of sperm for fertilization; however, the fertilizing potential of the frozen-thawed sperm is compromised because of alterations in the structure and physiology of the sperm cell. These alterations, characteristics of sperm capacitation, are present in the motile population and decrease sperm life-span, ability to interact with female tract, and fertilizing ability. The etiology of such alterations may represent a combination of factors, such as inherited fragility of the sperm cell to withstand the cryopreservation process and the semen dilution. Although the former is difficult to address, approaches that make-up for the dilution of seminal fluid may be sought. The aim of this work is to review aspects of sperm cryopreservation paralleled by events of capacitation and evaluate the possible roles of sperm membrane cholesterol, reactive oxygen species, and seminal plasma as mediators of cryopreservation effects on sperm function.

Radioimmunoassays for bull seminal plasma proteins (BSP-A1/-A2, BSP-A3, and BSP-30-Kilodaltons), and their quantification in seminal plasma and sperm

Three proteins, BSP-A1/-A2, BSP-A3, and BSP-30 kilodaltons (collectively called BSP proteins), represent the major proteins of bovine seminal plasma (BSP). At ejaculation, these proteins bind to the sperm surface and induce molecular changes in the plasma membrane that are deemed to be essential for sperm capacitation. The present study was carried out to develop specific radioimmunoassays (RIAs) for the quantification of each of the BSP proteins in BSP and sperm. RIAs were developed using polyclonal antibodies raised in rabbits against each BSP protein. The purified and iodinated BSP proteins were used as standard and tracer, respectively. The RIAs that were developed were shown to be specific for each protein and the cross-reactivity toward various antigens was negligible (<2%). The average sensitivity limit was 5 ng/ml of sample for BSP-A1/-A2 and BSP-A3, and 40 ng/ml of sample for BSP-30-kDa. The concentration of BSP proteins was determined by analyzing the RIA data with spline function. BSP proteins represented 40% to 57% of seminal plasma total protein (25% to 47% of BSP-A1/-A2, 3% to 5% of BSP-A3, and 3% to 7% of BSP-30 kDa) and 4% to 6% of sperm total protein (2.5% to 4% of BSP-A1/-A2, 0.4% to 0.9% of BSP-A3, and 0.5% to 1% of BSP-30-kDa). We also determined the concentration of BSP proteins that were sperm-bound after semen cryopreservation in Tris-egg yolk-glycerol extender. A significant decrease (70%-80%) in sperm-bound BSP proteins was noted after cryopreservation. The availability of reliable RIA procedures should aid in the further understanding of the role of BSP proteins in sperm function as well as their effect on sperm cryopreservation.

Cholesterol efflux promotes acrosome reaction in goat spermatozoa

Cholesterol efflux and membrane destabilization play an important role in sperm capacitation and membrane fusion in the acrosome reaction (AR). In this study we establish the effect of cholesterol removal from spermatozoa on acrosomal responsiveness. Mature goat spermatozoa were incubated in BSA-free medium in the presence of beta-cyclodextrin (betaCD) as cholesterol acceptor. After incubation with 8 mM betaCD, 50-60% of cholesterol was released from sperm membranes with no loss in the phospholipid content, and 35% of AR was induced. However, when 30% of cholesterol was lost, this moderate cholesterol decrease was unable to initiate AR. Cholesterol desorption was very rapid, following an exponential kinetics with a half-time of around 10 min, which is in contrast with the slow sigmoidal kinetics of acrosomal responsiveness: around 2 h was required for maximal AR. Our results suggest that cholesterol efflux has a direct influence on the onset of the AR, that is, merely removing cholesterol would trigger the AR.

Effect of methyl-beta-cyclodextrin on the acrosomal responsiveness of human sperm

Human sperm incubated in vitro gradually become capable of acrosome-reacting in response to the agonist, progesterone (P4). Loss of unesterified cholesterol is an obligatory step in the development of acrosomal responsiveness. These experiments tested the ability of methyl-beta-cyclodextrin (MbetaCD) to accelerate sperm cholesterol loss and the development of acrosomal responsiveness. Incubating sperm 30 min in MbetaCD (2.5-10 mM) decreased sperm cholesterol by as much as 89% in a dose-dependent fashion. MbetaCD caused some sperm (maximum of 16% following treatment with 5 mM MbetaCD) to become responsive to P4, and it caused a dose-dependent increase in spontaneous acrosome reactions. The number of responsive sperm increased in the first 3 hr following their removal from MbetaCD. Continuing incubation to 24 hr increased the numbers of spontaneously reacted sperm and dead sperm, but not P4-responsive sperm. It appears, therefore, that up to 3 hr are required for the full expression of P4-responsiveness in cholesterol-depleted sperm. The observed effects of MbetaCD are due to its cholesterol-depleting properties, because including sufficient cholesterol with MbetaCD to reduce the loss of sperm cholesterol inhibited the effects of MbetaCD on cell viability, spontaneous acrosome reactions, and responsiveness to P4. MbetaCD accelerates the appearance of the functional stages that sperm normally pass through during incubation in vitro, reinforcing the view that cholesterol loss is an important determinant of the rate at which sperm become acrosomally responsive.

Identification of ampullary and isthmic oviductal fluid proteins that associate with the bovine sperm membrane

The objective of this study was to define the complement of ampullary and isthmic oviductal fluid proteins that associate with the sperm membrane during the non-luteal and luteal stages of the oestrous cycle. Oviductal fluid was obtained from three dairy cows via indwelling cannulae in the ampulla and isthmus of the same oviduct. Daily samples of oviductal fluid were combined by region and stage of the cycle to create pools consisting of non-luteal isthmic, luteal isthmic, non-luteal ampullary, and luteal ampullary oviductal fluid. An aliquot from each oviductal fluid pool was biotinylated by incubation in biotin reagent. Spermatozoa from three fertile bulls were pooled, washed and incubated for 4 h in each of the four pools of biotinylated oviductal fluid. After incubation, sperm membrane proteins were solubilized, and proteins subjected to one-dimensional sodium dodecyl sulfate polyacrylamide gel electrophoresis and western blotting. The biotinylated oviductal fluid proteins that associated with the sperm membranes were detected by avidin-horseradish peroxidase and diaminobenzidine substrate. Eight oviductal fluid proteins with apparent molecular weights of 97, 75, 66, 55, 48, 34, 28 and 24 kDa were consistently detected to associate with the sperm membrane. Differences in ampullar and isthmic fluid proteins that associated with sperm during the luteal and non-luteal stage of the oestrous cycle were not detected.

Cyclodextrin removes cholesterol from mouse sperm and induces capacitation in a protein-free medium

Cyclodextrin, which stimulates cholesterol efflux from cells, was examined for its ability to induce capacitation of mouse spermatozoa. A chemically defined, protein-free medium was used for in vitro fertilization of cumulus-free mouse eggs. Fertilization did not occur in modified Krebs-Ringer bicarbonate medium (TYH) supplemented with 1 mg/ml polyvinylalcohol instead of BSA. However, fertilization was observed when spermatozoa were preincubated with methyl-beta-cyclodextrin (MBCD); fertilization rates increased dose-dependently from 0.25 to 0.75 mM MBCD. The fertilization rate decreased when 0.75 mM MBCD was added to both preincubation and fertilization media versus only the preincubation medium (21% vs. 53%); in sharp contrast, fertilization increased when 4 mg/ml BSA was present in both of the media versus the preincubation medium only (66% vs. 25%). At 0.75 mM, 2-hydroxy-beta-cyclodextrin had a lower ability to capacitate spermatozoa in vitro than MBCD (14% vs. 41%). Eggs fertilized by spermatozoa treated with MBCD (0.75 mM) developed to blastocysts (45%, 36 of 80) when cultured in KSOM. When 160 fertilized eggs were transferred to ICR recipients, 62 live offspring were born. After incubation of mouse spermatozoa for 90 min in 0.75 mM MBCD in TYH medium, the cholesterol content of the spermatozoa was significantly (p < 0.01) lower than that of the control (2.27 +/- 0.09 vs. 4.13 +/- 0.09 nmol unesterified cholesterol/10(7) sperm; mean +/- SEM, n = 5). The proportion of capacitated (B pattern) spermatozoa determined by chlortetracycline fluorescence was higher with MBCD treatment for 90 min than for the control (45% vs. 15%; p < 0.01). The proportion of acrosome-reacted (AR pattern) spermatozoa was not different between MBCD treatment and the control. Therefore, MBCD increased capacitation rather than the acrosome reaction of spermatozoa.

Major proteins of bovine seminal plasma and high-density lipoprotein induce cholesterol efflux from epididymal sperm

One of the hypotheses to explain the mechanism of capacitation involves the loss of sperm membrane cholesterol. Here, we studied whether or not the major proteins of bovine seminal plasma designated as BSP-A1, -A2, -A3, and -30-kDa (collectively called BSP proteins), which are implicated in sperm capacitation, induce cholesterol efflux. When epididymal sperm were labeled with [3H]cholesterol and incubated with bovine seminal plasma (0.05-2%) or BSP proteins (20-120 microg/ml) for 8 h, the sperm lost [3H]cholesterol (3.6-fold and 3-fold, respectively). The same results in the presence of BSP-A1/-A2 were obtained (3.5-fold) by direct determination of cholesterol on unlabeled epididymal sperm. Analysis of efflux particles by ultracentrifugation on a sucrose gradient revealed a single symmetrical peak of radioactivity at 1.14 g/ml. Immunoblotting of the fractions obtained from size-exclusion chromatography of the efflux particles showed that a portion of the BSP proteins were associated with [3H]cholesterol. Heparin (12 microg/ml) alone did not stimulate cholesterol efflux. In contrast, high-density lipoprotein (HDL, 100 microg/ml) alone stimulated cholesterol efflux up to 3.1-fold after 8 h. When labeled epididymal sperm were preincubated for 20 min with BSP-A1/-A2 (120 microg/ml), washed, and incubated with HDL (100 microg/ml) for 8 h, the total cholesterol efflux of the sperm suspension was 51.8 +/- 5.0% compared to 39.3 +/- 1.2% when HDL alone was used. These results indicate that BSP proteins and HDL play an important role in the sperm sterol efflux that occurs during capacitation. Furthermore, the heparin-induced sperm capacitation did not involve the efflux of sperm membrane cholesterol.

Experimental hypercholesterolaemia in rabbits. Effect on lipid domains in homologous spermatozoa

The distribution of membrane filipin sterol complexes (FSC) in the plasma membrane of the acrosomal region (PMAR) of rabbit sperm from epididymis and testis, in normal and hypercholesterolaemic rabbits, was examined at ultrastructural level. Membrane FSG were quantitatively analysed on freeze fracture replicas of filipin-treated cells. Cauda epididymal sperm shows a significant increase in filipin sterol complexes concentration in PMAR of hypercholesterolaemic animals compared to normal rabbits. Hypercholesterolaemic animals had 0.53 +/- 0.08 FSC micron-2 in the marginal segment of PMAR and 0.26 +/- 0.03 FSC micron-2 for normal animals. In the principal piece we found 0.70 +/- 0.07 FSC micron-2 for hypercholesterolaemic and 0.43 +/- 0.03 FSC micron-2 for control animals. We also counted 0.58 +/- 0.04 FSC micron-2 in the equatorial segment of PMAR for hypercholesterolaemic and 0.38 +/- 0.03 FSC micron-2 for normal animals respectively. The FSC concentration of testicular sperm, like sperm from corpus and caput of epididymis in hypercholesterolaemic animals, did not differ from the controls. Cholesterol, phospholipids and cholesterol:phospholipid ratio in caudal epididymal sperm from treated males did not differ from controls. Only the sphingomyelin concentration decreases in cauda epididymal sperm from hypercholesterolaemic males compared to controls. The results presented in this paper suggest that the lipidic domains in PMAR of hypercholesterolaemic rabbits changes when the gametes go through the epididymis.

Seminal plasma affects membrane integrity and motility of equine spermatozoa after cryopreservation

Effects of seminal plasma on post-thaw motility and membrane integrity of cryopreserved horse spermatozoa were investigated. Carboxyfluorescein diacetate staining was used for the assessment of sperm membrane integrity. Adding 30% of seminal plasma from stallions with high post-thaw sperm motility to ejaculates from stallions with low post-thaw sperm motility increased progressive motility from 24.0 +/- 1.6 to 34.5 +/- 1.9% (P < 0.05) and membrane integrity from 27.0 +/- 2.1 to 34.3 +/- 2.3% membrane-intact spermatozoa (P < 0.05). Conversely, the addition of seminal plasma from stallions with low post-thaw sperm motility to ejaculates from stallions with high post-thaw motility decreased progressive motility from 36.0 +/- 1.6 to 30.0 +/- 2.7% (P < 0.05) but did not induce changes in membrane integrity. Seminal plasma from stallions with opposite post-thaw motility therefore clearly influenced the resistance of spermatozoa to the freezing and thawing process. We conclude that the individual composition of seminal plasma affects the suitability of stallions for semen cryopreservation.

Functions of proteins secreted by oviduct epithelial cells

Studies on embryonic development in vitro as well as observations in vivo, suggested that two aspects of oviduct physiology are important for early development. On one side has to be considered the oviduct "environment": temperature, pH, osmotic pressure, nutrients, oxygen tension, free radical scavengers, etc. On the other, the oviduct "active components": stimulatory and/or regulatory molecules, supposed to finely regulate the fertilisation process and the first differentiative steps. While the physical environment of the oviduct has been under investigation for some decades, studies on oviduct-specific molecules and their functions have only been developed much more recently. The amount of information on this topic, however, has rapidly reached the size that demands a summary. In this review the descriptive literature on oviduct specific proteins will be examined as a basis for illustrating the possible functions of these molecules. In particular their role in fertilisation and early embryonic cleavages will be analysed in some details. Finally a section is devoted to the presence and physiological significance of growth factors in oviduct fluid.

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.

Estrous sheep serum as a potent agent for ovine IVF: Effect on cholesterol efflux from spermatozoa and the acrosome reaction

The aim of the present study was to evaluate the effect of heat-inactivated estrous sheep serum (ESS) on sheep IVF. When the capacitation and the fertilization media contained 20% ESS, a fertilization rate of 85% was achieved. The beneficial effect of ESS on sheep IVF was further demonstrated since the fertilization rate was null when ESS was omitted during sperm capacitation and fertilization. Estrous sheep serum supported both sperm capacitation and fertilization as shown by the results of experiments in which it was omitted during one of these steps: sperm capacitation in serum-free medium resulted in delayed sperm-oocyte penetration, while fertilization in serum-free medium significantly decreased the percentage of fertilized oocytes. To investigate the influence of serum on sperm ability to undergo the acrosome reaction, salt-stored follicular sheep oocytes were inseminated, and the acrosomal status of spermatozoa attached to zonae was examined by electron microscopy after a 4-h period of coincubation. Quantitative analysis on thin sections demonstrated that fewer acrosome-reacted spermatozoa were observed when the capacitation and insemination steps were carried out in DM-H medium without serum than in DM-H-SS supplemented with 20% ESS (0.08, [0; 0.34], (median, range)/100 microm zona vs 1.32, [0.90; 2.28]/100 microm zona; P<0.01). Since a higher number of spermatozoa attached to the zona surface in DM-H medium, the proportion of acrosome-reacted spermatozoa was much lower (0.7%, [0%; 2.2%], (median, range) vs 54%, [25%; 100%]; P<0.01) in the absence of serum. These results indicate that in our IVF system the development of the acrosome reaction depended on serum. Sperm cholesterol efflux during in vitro capacitation was measured on [3H] cholesterol labeled spermatozoa resuspended in DM-H or DM-H-SS medium. A time-dependent cholesterol removal was observed in the presence of serum (60+/-5%, mean+/-SD, after 5 h), whereas it was limited to 14+/-3% in DM-H medium; hence addition of serum to the capacitation medium efficiently supports cholesterol efflux, which is thought to be a key-event in the capacitation process.

Composition and morphology of lipid droplets from oviduct epithelial cells

This study was undertaken to determine the composition and morphology of lipid droplets in situ and isolated from oviductal epithelial cells and oviductal fluid. Oviductal epithelial cells were harvested enzymatically from oviducts of cows in either the luteal or the follicular stages of the ovarian cycle. Lipid droplets were isolated from cellular homogenates and characterized biochemically using thin layer chromatography. The morphology of lipid droplets in oviductal epithelial cells and in fractions isolated by ultracentrifugation from cellular homogenates was examined by electron microscopy. Lipid droplets isolated from oviduct epithelial cells varied in composition with the ovarian cycle and the oviductal region. There was more total lipid in droplets isolated from cows in the luteal than follicular phase of the ovarian cycle. Most of this difference was due to large amounts of esterified cholesterol present in the samples from luteal-stage animals. The most esterified cholesterol was found in droplets isolated from the oviductal isthmus of luteal cows. Droplets similar in lipid composition to those isolated from epithelial cells were found in oviductal fluid. Four distinct types of lipid inclusions were evident in electron micrographs of oviductal epithelia and characterized as osmiophilic droplets, lipofuscin-like clusters, lamellar structures, and composite bodies. All of the lipid inclusions were found in droplet isolates except for the extracted lipid portion of the composite body. The presence and diversity of oviduct epithelial lipid inclusions suggest that the oviductal epithelium may be very active in lipid metabolism, particularly cholesterol dynamics.

Inverse relationship between the induction of human sperm capacitation and spontaneous acrosome reaction by various biological fluids and the superoxide scavenging capacity of these fluids

Capacitation of spermatozoa is essential for fertilization, and can be induced by various agents or biological fluids. Previous reports have shown that foetal cord serum (FCS) and the superoxide anion trigger human sperm hyperactivation and capacitation, and that superoxide dismutase (SOD) prevents these processes. We investigated: (1) the capacity of seminal plasma (SP) and follicular fluid (FF) (whole, or fractionated into high and low molecular weight components), in the presence or absence of SOD, to induce the spontaneous acrosome reaction (no stimulant needed, AR) and capacitation (as measured by the lysophosphatidyl-choline-induced AR, LPC-AR); (2) a possible relationship between the levels of AR and capacitation obtained with these biological fluids and the superoxide scavenging capacity of the same fluids. The highest levels of LPC-AR were obtained with FF ultrafiltrate (48 +/- 6%), followed by SP ultrafiltrate (31.9 +/- 0.8%), FF (30 +/- 5%), dialysed FF (27 +/- 4%), and finally, by FCS ultrafiltrate (23 +/- 1%), SP (21 +/- 1%) and dialysed SP (18.9 +/- 0.8%). A similar order of potency for the fluids existed when sperm AR was studied, the levels of AR observed ranging from 16 +/- 2% to 5.3 +/- 0.8% after incubation with FF ultrafiltrate and SP respectively. None of these treatments had detrimental effects on sperm motility. In the presence of SOD, there was always an important reduction (52-86%) of the AR and LPC-AR observed.(ABSTRACT TRUNCATED AT 250 WORDS)

Lysophosphatidylcholine disrupts the acrosome of tammar wallaby (Macropus eugenii) spermatozoa

The acrosomal status of wallaby spermatozoa was evaluated by light and electron microscopy after incubation in 1-100 microM lysophosphatidylcholine (LPC) for up to 120 min. Treatment with 1 and 10 microM LPC for 120 min did not lead to acrosomal loss, or detectable alteration to the acrosome, as detected by Bryan's staining and light microscopy. Incubation with 25 microM LPC had little effect on acrosomal loss, however statistically significant changes (P < 0.05) in the acrosomal matrix (altered) were detected after 10-min incubation by light microscopy. Around 50% of acrosomes were altered after 20-min incubation in 50 microM LPC (P < 0.001), and 40% of spermatozoa had lost their acrosome after 60-min incubation (P < 0.001). Treatment with 75 and 100 microM LPC led to rapid acrosomal loss from around 50% of spermatozoa within 10 min (P < 0.001), and by 60 min acrosomal loss was 70-80%. LPC, like the diacylglycerol DiC8 (1,2-dioctanoyl-sn-glycerol), is thus an effective agent to induce loss of the relatively stable wallaby sperm acrosome, and it also induces changes within the acrosomal matrix. Ultrastructure of the LPC-treated spermatozoa revealed that the plasma membrane and the acrosomal membranes were disrupted in a manner similar to that seen after detergent treatment (Triton X-100). There was no evidence of point fusion between the plasma membrane overlying the acrosome and the outer acrosomal membrane. The plasma membrane was the first structure to disappear from the spermatozoa. The acrosomal membranes and matrix showed increasing disruption with time and LPC concentration.(ABSTRACT TRUNCATED AT 250 WORDS)

Cholesterol and polyunsaturated acid enriched diet: effect on kinetics of the acrosome reaction in rabbit spermatozoa

In this study we examined the effect of cholesterol (Diet 2), cholesterol and fish oil (FO) polyunsaturated acid (Diet 3), and polyunsaturated acid (Diet 4) enriched diets upon the acrosome reaction (AR) of New Zealand White rabbit spermatozoa. Male rabbits fed with cholesterol alone or with FO increased their cholesterol and LDL-cholesterol serum levels after 15 days of diet. Ten semen samples were obtained after 2 months of diet. Our results suggest that hypercholesterolemia and hypertriglyceridemia in male rabbits could produce a decreased capacity of sperm AR after 4 h (0%, 0%, and 60% lower than the control), 6 h (0%, 68%, and 44%), or 8 h (58%, 52% and 32%) of incubation in capacitating medium. Another set of experiments were made with lysophosphatidylcholine (LPC), 80 micrograms/ml, and the same pattern of AR was seen. Nevertheless, the high cholesterol and total lipids (TL) levels in serum did not affect the cholesterol levels in seminal plasma (SP) but affect the SP total lipids. The diminished capacity of rabbit sperm to undergo the AR was not reverted by in vitro incubation with the Shinitsky medium for cholesterol depletion (MDC). These results indirectly suggest that the cholesterol/phospholipid ratio in hypercholesterolemic sperm is similar to that of controls and are in agreement with preliminary studies made in our laboratory that evidenced the same cholesterol/phospholipid ratio in rabbit sperm from hypercholesterolemic animals than from controls.(ABSTRACT TRUNCATED AT 250 WORDS)

Neutral lipid droplets in bovine oviductal epithelium and lipid composition of epithelial cell homogenates

This study was undertaken to locate and to quantify lipids within the oviduct epithelial cells that might serve as a source of luminal lipids. Oviduct epithelial cells were analyzed from 12 cows in either the follicular or luteal stage of the ovarian cycle. Histochemical differences in neutral lipid droplets and phospholipids containing choline were detected among the oviductal regions. Neutral lipid staining was greatest in the preampulla and the ampulla and least in the isthmus. Staining of phospholipids containing choline was similar in preampullary and ampullary epithelia but was concentrated in isthmic crypts. Neutral lipid droplets, detected fluorescently with Nile Red, were present in a greater percentage of preampullary epithelial cells (76.8 +/- 1.8) than ampullary (42.1 +/- 2.1) or isthmic cells (12.2 +/- 1.3). Neither ovarian cycle stage nor side of ovulation affected the concentration of epithelial lipid droplets. Colorimetric lipid assays determined that concentrations of free cholesterol and glycerides in the preampulla were higher than in other regions. Most esterified cholesterol was detected in the isthmus. These findings indicate that the bovine oviduct epithelium exhibits regional differences in phospholipid and neutral lipid distribution. Because many of the lipids studied affect gamete and early embryo membranes, localization differences may affect the functional variability of the oviductal regions.

Distribution of filipin-sterol complexes in sperm membranes from hypercholesterolaemic rabbits

The distribution of membrane filipin-sterol complexes (FSC) was examined ultrastructurally in cauda epididymal sperm from normal and hypercholesterolaemic rabbits. Membrane FSC were quantitatively analysed on replicas of filipin-treated cells. We determined a significant difference in FSC concentration in the plasma membrane of the acrosome region (PMAR) of hypercholesterolaemic animals compared to normal rabbits. Hypercholesterolaemic animals had 0.56 +/- 0.05 FSC complex per micron 2 (enriched Cholesterol diet: Diet 2) in the marginal segment of PMAR; 0.62 +/- 0.05 FSC complex per micron 2 (enriched Cholesterol and fish oil diet: Diet 3) and only 0.28 +/- 0.01 FSC complex per micron 2 for normal animals (Control Diet 1). In the principal (anterior) segment we found 0.54 +/- 0.10 FSC complex per micron 2 (Diet 2), 0.56 +/- 0.03 FSC complex per micron 2 (Diet 3) and 0.30 +/- 0.04 FSC complex per micron 2 (Control Diet 1). We also counted 0.47 +/- 0.1 FSC complex per micron 2 in the equatorial segment of PMAR for Diet 2, 0.27 +/- 0.05 and 0.28 +/- 0.04 FSC complex per micron 2 in Diet 1 and Diet 3 respectively. Diet 4 (fish oil) did not differ from the control. An increase in the Cholesterol (Chol) level in biological membranes or a difference in the Chol membrane domains could cause a variation in the membrane rigidity that could modify the sperm membrane fusion capacity and functionality. The results presented in this paper are in agreement and could explain the decrease in the kinetic of the sperm acrosome reaction that we have observed in experimentally hypercholesterolaemic rabbits (Díaz-Fontdevila & Bustos-Obregón, 1992).