Lipid changes of goat sperm plasma membrane during epididymal maturation

Fatty acid composition and biophysical characteristics of the cell membrane of feline spermatozoa

Sperm membrane composition and biophysical characteristics play a pivotal role in many physiological processes (i.e. sperm motility, capacitation, acrosome reaction and fusion with the oocyte) as well as in semen processing (e.g. cryopreservation). The aim of this study was to characterize the fatty acid content and biophysical characteristics (anisotropy, generalized polarization) of the cell membrane of domestic cat spermatozoa. Semen was collected from 34 adult male cats by urethral catheterization. After a basic semen evaluation, the fatty acid content of some of the samples (n = 11) was evaluated by gas chromatography. Samples from other individuals (n = 23) were subjected to biophysical analysis: membrane anisotropy (which is inversely proportional to membrane fluidity) and generalized polarization (describing lipid order); both measured by fluorimetry at three temperature points: 38 °C, 25 °C and 5 °C. Spermatozoa from some samples (n = 10) were cryopreserved in TRIS egg yolk-glycerol extender and underwent the same biophysical analysis after thawing. Most fatty acids in feline spermatozoa were saturated (69.76 ± 24.45%), whereas the polyunsaturated fatty acid (PUFA) content was relatively low (6.12 ± 5.80%). Lowering the temperature caused a significant decrease in membrane fluidity and an increase in generalized polarization in fresh spermatozoa, and these effects were even more pronounced following cryopreservation. Anisotropy at 38 °C in fresh samples showed strong positive correlations with viability and motility parameters after thawing. In summary, feline spermatozoa are characterized by a very low PUFA content and a low ratio of unsaturated:saturated fatty acids, which may contribute to low oxidative stress. Cryopreservation alters the structure of the sperm membrane, increasing the fluidity of the hydrophobic portion of the bilayer and the lipid order in the hydrophilic portion. Because lower membrane fluidity in fresh semen was linked with better viability and motility after cryopreservation, this parameter may be considered an important factor in determination of sperm cryoresistance.

Understanding sperm motility mechanisms and the implication of sperm surface molecules in promoting motility

Background

It is estimated that approximately 8–12% of couples globally face problems associated with infertility. A large number of men exhibit suboptimal sperm parameters. Sperm motility is one of the factors that is measured when analysing sperm parameters. The indication of several crucial sperm surface molecules, having the ability to modulate motility, has opened new avenues in understanding the complex processes involved in motility.

Main body of the abstract

There are various mechanisms that regulate and enhance sperm motility. Several surface molecules on sperm cells can also regulate motility, thus showing their possible application as a treatment for infertility caused by impaired motility. Sperm motility is regulated by intracellular and extracellular pH, along with calcium ions (Ca2+) and carbonate ion (HCO3−) concentrations. Moreover, sperm cells have an array of surface proteins which play a critical role in their function and motility. The indication of surface molecules presented new opportunities for understanding sperm motility and the possibility of treating infertility caused by impaired sperm function. Infertility and problems associated with conception can cause underlying stress and mental trauma. Although there are several methods for treating infertility, most are complex, invasive, and expensive.

Conclusion

It is important to understand how surface molecules and proteins on the sperm cell regulate motility. This will enable us to treat anomalies associated with proper sperm function. This review highlights the general mechanisms that regulate sperm motility, and it stresses the importance and relevance of sperm surface molecules in regulating sperm motility.

An Update on Semen Physiology, Technologies, and Selection Techniques for the Advancement of In Vitro Equine Embryo Production: Section I

Simple Summary

Male fertility is often estimated by simple sperm assessment, and therefore, it is crucial to establish species-specific baselines for normal sperm parameters. In this paper, sperm physiology, function, and common abnormalities in stallions will be reviewed.

Abstract

As the use of assisted reproductive technologies (ART) and in vitro embryo production (IVP) expand in the equine industry, it has become necessary to further our understanding of semen physiology as it applies to overall fertility. This segment of our two-section review will focus on normal sperm parameters, beginning with development and extending through the basic morphology of mature spermatozoa, as well as common issues with male factor infertility in IVP. Ultimately, the relevance of sperm parameters to overall male factor fertility in equine IVP will be assessed.

Uncovering sperm metabolome to discover biomarkers for bull fertility

Background

Subfertility decreases the efficiency of the cattle industry because artificial insemination employs spermatozoa from a single bull to inseminate thousands of cows. Variation in bull fertility has been demonstrated even among those animals exhibiting normal sperm numbers, motility, and morphology. Despite advances in research, molecular and cellular mechanisms underlying the causes of low fertility in some bulls have not been fully elucidated. In this study, we investigated the metabolic profile of bull spermatozoa using non-targeted metabolomics. Statistical analysis and bioinformatic tools were employed to evaluate the metabolic profiles high and low fertility groups. Metabolic pathways associated with the sperm metabolome were also reported.

Results

A total of 22 distinct metabolites were detected in spermatozoa from bulls with high fertility (HF) or low fertility (LF) phenotype. The major metabolite classes of bovine sperm were organic acids/derivatives and fatty acids/conjugates. We demonstrated that the abundance ratios of five sperm metabolites were statistically different between HF and LF groups including gamma-aminobutyric acid (GABA), carbamate, benzoic acid, lactic acid, and palmitic acid. Metabolites with different abundances in HF and LF bulls had also VIP scores of greater than 1.5 and AUC- ROC curves of more than 80%. In addition, four metabolic pathways associated with differential metabolites namely alanine, aspartate and glutamate metabolism, β-alanine metabolism, glycolysis or gluconeogenesis, and pyruvate metabolism were also explored.

Conclusions

This is the first study aimed at ascertaining the metabolome of spermatozoa from bulls with different fertility phenotype using gas chromatography-mass spectrometry. We identified five metabolites in the two groups of sires and such molecules can be used, in the future, as key indicators of bull fertility.

Effects of adding egg yolks of different avian species to Tris glycerol extender on the post-thawing quality of buck semen

The effects of adding egg yolks (EY) of different avian species to the Tris glycerol extender was evaluated for post-thawing quality of buck semen. The semen samples collected from seven Aardi bucks were pooled and diluted 1:4 with the Tris glycerol diluents containing the egg yolks of chicken (C), pigeon (P), goose (G), Japanese quail (Q), duck (D), or turkey (T). The diluted semen samples were gradually cooled to 5 °C within 2 h, equilibrated at 5 °C for 2 h, and then frozen in liquid nitrogen vapor for 8 min before storing them at -196 °C. The frozen straws were thawed at 37 °C for 30 s and evaluated for sperm motility, vitality, abnormality, plasma-membrane integrity, and DNA fragmentation. The malondialdehyde (MDA) and reduced glutathione (GSH) activities were measured. The egg yolk samples of the above-mentioned avian species (n = 7/species) were analyzed for moisture, ash, protein, fatty acid (FA), and trace element contents. The use of the chicken EY (C) diluent resulted in better post-thawing buck semen quality, including the total progressive sperm motility parameters, sperm vitality, plasma membrane intactness, DNA integrity, and sperm abnormalities percentages, in comparison with the EY diluents of the other avian species. The lowest MDA and the highest GSH activities were observed in the C diluent. The chicken EY had the highest percentages of margaric and linolenic FAs and the lowest percentages of palmitoleic and myristic FAs. Moreover, the percentage of oleic FA was lower in the chicken EY than in the EYs of other species, except turkey. Additionally, the chicken EY had the significantly lowest concentration of Cu, Zn, Fe, and Mn. In conclusion, the use of chicken egg yolk extender is recommended for buck semen cryopreservation. The egg yolks of the other avian species studied cannot substitute the chicken EY as they gave poorer post-thawing semen quality. The EY composition, especially FA profile and trace elements concentration, significantly affected the post-thawing quality of buck semen.

Possible mechanisms of cholesterol-loaded cyclodextrin action on sperm during cryopreservation

Artificial insemination (AI) with cryopreserved semen has a pivotal role in wider dissemination of germplasm of elite livestock and also for conservation of various endangered species. Cryopreservation allows storage of semen for a prolonged period of time and facilitates greater exchange of genetic material among distant populations. Cryopreservation, however, leads to certain deleterious effects on sperm including premature induction of the acrosome reaction, reduced sperm motility and viability, and impaired sperm DNA integrity and fertility. During cooling procedures, membrane phase transitions take place, which result in micro-domain formation from aggregation of lipids, leading to impaired functions of the sperm membrane, and gap formation between gel and fluid domains. Cyclodextrins are produced by enzymatic degradation of starch and possess a unique feature, that when added alone to sperm cyclodextrins facilitate the removal of cholesterol from the membrane. When preloaded with cholesterol, however, cyclodextrins stimulate the insertion of cholesterol into the sperm membrane due to presence of a hydrophobic core in addition to an outer hydrophilic face. Treating sperm of various species with cholesterol-loaded cyclodextrin improves the quality of sperm during cryopreservation. It is still not clearly known how cholesterol-loaded cyclodextrin functions at sperm cells to enhance the survival during cryopreservation. The present review, therefore, highlights possible mechanisms of cholesterol-loaded cyclodextrin action on sperm during cryopreservation.

Molecular changes and signaling events occurring in spermatozoa during epididymal maturation

After leaving the testis, spermatozoa have not yet acquired the ability to move progressively and are unable to fertilize oocytes. To become fertilization competent, they must go through an epididymal maturation process in the male, and capacitation in the female tract. Epididymal maturation can be defined as those changes occurring to spermatozoa in the epididymis that render the spermatozoa the ability to capacitate in the female tract. As part of this process, sperm cells undergo a series of biochemical and physiological changes that require incorporation of new molecules derived from the epididymal epithelium, as well as post-translational modifications of endogenous proteins synthesized during spermiogenesis in the testis. This review will focus on epididymal maturation events, with emphasis in recent advances in the understanding of the molecular basis of this process.

Polyunsaturated Fatty Acids in Male Ruminant Reproduction - A Review

Fatty acids such as n-3 and n-6 polyunsaturated fatty acids (PUFA) are critical nutrients, used to improve male reproductive performance through modification of fatty acid profile and maintenance of sperm membrane integrity, especially under cold shock or cryopreservation condition. Also, PUFA provide the precursors for prostaglandin synthesis and can modulate the expression patterns of many key enzymes involved in both prostaglandin and steroid metabolism. Many studies carried out on diets supplemented with PUFA have demonstrated their capability to sustain sperm motility, viability and fertility during chilling and freezing as well as improving testis development and spermatogenesis in a variety of livestock species. In addition to the type and quantity of dietary fatty acids, ways of addition of PUFA to diet or semen extender is very crucial as it has different effects on semen quality in male ruminants. Limitation of PUFA added to ruminant ration is due to biohydrogenation by rumen microorganisms, which causes conversion of unsaturated fatty acids to saturated fatty acids, leading to loss of PUFA quantity. Thus, many strategies for protecting PUFA from biohydrogenation in rumen have been developed over the years. This paper reviews four aspects of PUFA in light of previous research including rumen metabolism, biological roles, influence on reproduction, and strategies to use in male ruminants.

Cholesterol-loaded cyclodextrin improves ram sperm cryoresistance in skim milk-extender

Cholesterol-loaded cyclodextrin (CLC) is known to improve ram sperm cryosurvival. This study expands on previous research to: (1) determine the mechanism by which CLC improves ram sperm cryosurvival and (2) compare the efficiency of a novel, skim milk-based extender containing CLC to a traditional egg yolk-based extender. Hypothesis #1 was that CLC enhances membrane cholesterol content to increase the resistance of ram sperm to cold and osmotic stress, thereby improving cryosurvival. We first assessed the ability of fresh sperm treated with CLC to withstand cold shock. Second, fresh sperm were treated with CLC to evaluate their tolerance to osmotic stress. Third, to confirm that cholesterol is incorporated into the sperm using CLC, we quantified sperm cholesterol. To test Hypothesis #2 that CLC is most effective in a medium without competing cholesterol, we compared sperm cryosurvival and fertility in skim milk-based extender containing CLC versus in a traditional egg yolk-based freezing extender without CLC. Our data confirmed that CLC treatment improves ram sperm cold shock and osmotic stress resistance, and augments sperm cholesterol content. Semen in skim milk-based extender containing CLC prior to freezing, had more motile sperm with intact acrosomes after thawing compared to semen in egg yolk-based extender. In contrast, sperm plasma membrane integrity and in vivo fertility of the semen cryopreserved in the skim milk-based extender with CLC did not differ from semen that was cryopreserved in egg yolk-based extender. Further research is warranted to combine CLC with other cryoprotection strategies or to modify the insemination protocol.

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.

Organization of Membrane Rafts in Chicken Sperm

Being transcriptionally and translationally inactive, sperm must utilize preassembled pathways into specific compartments in which they function to fertilize ovum. Membrane rafts are specific membrane regions enriched in sterols and glycosphingolipids such as ganglioside G_M1 (G_M1) and play an important role in a variety of cellular functions. Recent findings have demonstrated that membrane rafts are present in mammalian sperm and are involved in regulating the induction of acrosome exocytosis. However, no information is available on whether avian sperm possess membrane rafts. Thus, we investigated the organization of membrane rafts in chicken sperm. Our localization experiments for G_M1 and sterols showed that the plasma membrane overlaying the sperm head possesses specific membrane domains enriched in both aforementioned lipids. Caveolin-1, which localizes into membrane rafts in other systems, was localized only to the sperm tail. Based on the biochemical definition that membrane rafts are insoluble membranes when subjected to a Triton X-100 treatment, we isolated detergent-insoluble membranes from chicken sperm and quantified the G_M1 content, which showed an enrichment of G_M1 in the membrane fraction relative to the detergent-soluble fraction. Together with the results of localization and biochemical experiments, we demonstrate for the first time that membrane rafts exist in chicken sperm. Thus, our results provide a foundation for investigating a novel cellular pathway inherent in avian sperm membranes that might be involved in functions necessary to achieve fertilization.

Role of Membrane Lipid Fatty Acids in Sperm Cryopreservation

Lipid is an important constituent of cell membrane. Membrane lipid composition of spermatozoa has been correlated to different function. Many researchers have related membrane lipid with survival success after cryopreservation or cold shock. Sperm maturation and acrosome reactions are natural phenomenon, but cryopreservation or cold shock is not. Therefore, sperm cells are not programmed for such change and undergo stress. So the change in membrane lipid composition due to cold shock or cryopreservation may be looked upon as response of spermatozoa to a certain stressed condition. A significant body of research worked on the relationship between membrane lipid and fatty acid composition and ability of cell to tolerate adverse change in temperature. However, as the approach of different research groups was different, it is very difficult to compare the changes. Studies have been done with different species, ejaculated/seminal or epididymal sperm. Lipid analyses have been done with whole cell membrane isolated by different methods. Fatty acids estimated were from whole cell, plasma membrane, head membrane, or phospholipids. The cryopreservation condition, media composition, and diluents/cryoprotectants were also different. At this onset a comprehensive review is needed to cover changes of sperm membrane lipid composition of different species under different cryopreservation conditions.

Seminal vesicle secretion 2 acts as a protectant of sperm sterols and prevents ectopic sperm capacitation in mice

Seminal vesicle secretion 2 (SVS2) is a protein secreted by the mouse seminal vesicle. We previously demonstrated that SVS2 regulates fertilization in mice; SVS2 is attached to a ganglioside GM1 on the plasma membrane of the sperm head and inhibits sperm capacitation in in vitro fertilization as a decapacitation factor. Furthermore, male mice lacking SVS2 display prominently reduced fertility in vivo, which indicates that SVS2 protects spermatozoa from some spermicidal attack in the uterus. In this study, we tried to investigate the mechanisms by which SVS2 controls in vivo sperm capacitation. SVS2-deficient males that mated with wild-type partners resulted in decreased cholesterol levels on ejaculated sperm in the uterine cavity. SVS2 prevented cholesterol efflux from the sperm plasma membrane and incorporated liberated cholesterol in the sperm plasma membrane, thereby reversibly preventing the induction of sperm capacitation by bovine serum albumin and methyl-beta-cyclodextrin in vitro. SVS2 enters the uterus and the uterotubal junction, arresting sperm capacitation in this area. Therefore, our results show that SVS2 keeps sterols on the sperm plasma membrane and plays a key role in unlocking sperm capacitation in vivo.

Antioxidant effect of lemon balm (Melissa officinalis) and mate tea (Ilex paraguensys) on quality, lipid peroxidation and DNA oxidation of cryopreserved boar epididymal spermatozoa

In this study, we investigated the protective ability of the addition of two antioxidant herb extracts, mate tea and lemon balm, on boar epididymal frozen-thawed spermatozoa quality. Testes from mature boars were collected at local slaughterhouse, and sperm samples from epididymis were recovered by flushing. Spermatozoa were cryopreserved in lactose-egg yolk buffer supplemented with various concentrations of lemon balm and mate tea (0, 2.5, 5 and 10 g l(-1) ) using the straw-freezing procedure. Motion parameters, acrosome and plasma membrane integrity, lipoperoxidation levels and DNA oxidative damage (8-hydroxy-2'-deoxyguanosine base lesion) were evaluated. There were no differences among experimental groups with regard to motility characteristics, viability, acrosome and plasma membrane integrity; however, the highest concentration of lemon balm produced significant (P < 0.05) improvement in curvilinear trajectory, straightness and amplitude of lateral head displacement after thawing. The supplementation of freezing extender with mate tea and lemon balm reduced sperm lipid membrane peroxidation, and only mate tea protected DNA against oxidative damage during cryopreservation at 120 min post-thawing (P < 0.05). Mate tea experimental extender at concentration of 10 g l(-1) showed the lowest percentage of sperm oxidised DNA and malondialdehyde generation; thus, mate tea is a potential candidate such as antioxidant compound on boar sperm cryopreservation medium.

Trans fatty acid intake is inversely related to total sperm count in young healthy men

STUDY QUESTION

Is intake of fatty acids related to semen quality among young men?

SUMMARY ANSWER

The intake of trans fatty acids is inversely related to total sperm count in healthy young men.

WHAT IS KNOWN ALREADY

Spain has seen an increase in the proportion of calories consumed as fat over the same period that a downward trend in semen quality has been observed. In addition, rodent models suggest that trans fat intake may severely affect testicular function.

STUDY DESIGN, SIZE, DURATION

Cross-sectional study of 209 men recruited between October 2010 and November 2011.

PARTICIPANTS/MATERIALS, SETTING, METHODS

A group of 209 healthy young university students 18-23 years of age provided a semen sample and completed a previously validated food frequency questionnaire. The association between intake of fatty acids with semen quality parameters (sperm concentration, motility, morphology and total count) was assessed using multivariate linear regression.

MAIN RESULTS AND THE ROLE OF THE CHANCE

Trans fatty acid intake was inversely related to total sperm count after adjusting for potential confounders (P, trend = 0.03). The multivariate adjusted mean (95% confidence interval) total sperm count in increasing quartiles of trans fat intake was 144 (110-190), 113 (87-148), 100 (18-130) and 89 (69-117). There also was an inverse association between cholesterol intake and ejaculate volume (P, trend = 0.04). No other statistically significant relations were observed.

LIMITATIONS, REASONS FOR CAUTION

The cross-sectional design of the study limits causal inference, we cannot exclude the possibility of unmeasured confounding and there was insufficient statistical power to identify modest associations.

WIDER IMPLICATIONS OF THE FINDINGS

The results of this study, together with previous experimental work in rodents and biomarker studies among infertility patients, suggest that intake of trans fatty acids may be related to lower semen quality. Although the data provide further evidence that diet is a modifiable factor that could impact male fertility, it is not known whether the observed differences in sperm count translate into differences in fertility.

STUDY FUNDING/COMPETING INTEREST(S)

This work was supported by The Seneca Foundation, Regional Agency of Science and Technology, grant no 00694/PI/04, Ministerio de Ciencia e Innovación, Instituto de Salud Carlos III (FIS), grant no PI10/00985, and grant P30 DK46200 from the National Institutes of Health. The authors have no competing interests to declare.

Sterols in spermatogenesis and sperm maturation

Mammalian spermatogenesis is a complex developmental program in which a diploid progenitor germ cell transforms into highly specialized spermatozoa. One intriguing aspect of sperm production is the dynamic change in membrane lipid composition that occurs throughout spermatogenesis. Cholesterol content, as well as its intermediates, differs vastly between the male reproductive system and nongonadal tissues. Accumulation of cholesterol precursors such as testis meiosis-activating sterol and desmosterol is observed in testes and spermatozoa from several mammalian species. Moreover, cholesterogenic genes, especially meiosis-activating sterol-producing enzyme cytochrome P450 lanosterol 14α-demethylase, display stage-specific expression patterns during spermatogenesis. Discrepancies in gene expression patterns suggest a complex temporal and cell-type specific regulation of sterol compounds during spermatogenesis, which also involves dynamic interactions between germ and Sertoli cells. The functional importance of sterol compounds in sperm production is further supported by the modulation of sterol composition in spermatozoal membranes during epididymal transit and in the female reproductive tract, which is a prerequisite for successful fertilization. However, the exact role of sterols in male reproduction is unknown. This review discusses sterol dynamics in sperm maturation and describes recent methodological advances that will help to illuminate the complexity of sperm formation and function.

Epididymis cholesterol homeostasis and sperm fertilizing ability

Cholesterol, being the starting point of steroid hormone synthesis, is a long known modulator of both female and male reproductive physiology especially at the level of the gonads and the impact cholesterol has on gametogenesis. Less is known about the effects cholesterol homeostasis may have on postgonadic reproductive functions. Lately, several data have been reported showing how imbalanced cholesterol levels may particularly affect the post-testicular events of sperm maturation that lead to fully fertile male gametes. This review will focus on that aspect and essentially centers on how cholesterol is important for the physiology of the mammalian epididymis and spermatozoa.

Baculo-expression and enzymatic characterization of CES7 esterase

The male reproductive tracts in different species are characterized by similar patterns of male-dependent overexpression of carboxylesterases. This phenomenon indicates male sex-associated functions of these enzymes for spermatogenesis, sperm maturation, and sperm use. Recently, a novel epididymis-specific gene named Ces7 was cloned and characterized, which belongs to the carboxylesterase family. To study the functions of CES7 in sperm maturation and storage, CES7 recombinant protein was expressed in baculovirus system. The recombinant protein had carboxylesterase activity hydrolyzing cholesterol ester and choline ester. CES7 as carboxylesterase might be involved in ester hydrolysis, sperm maturation, and storage in male reproductive tract.

Hypotonic resistance of boar spermatozoa: sperm subpopulations and relationship with epididymal maturation and fertility

Hypotonic resistance of boar spermatozoa was investigated by measuring the ratio of live/dead spermatozoa (SYBR-14/propidium iodide) by flow cytometry after hypotonic stress. The survival rate of ejaculated spermatozoa incubated in hypotonic solutions ranging from 3 to 330 mmol/kg followed a sigmoid curve that fitted a simple logistic model. The critical osmolality value (Osmcrit) at which 50% of spermatozoa died was determined with this model. Hypotonic resistance of spermatozoa increased with temperature between 15 and 39 °C and decreased after hydrogen superoxide treatment, but was not modified during 8 days of preservation in Beltsville thawing solution. Hypotonic resistance markedly decreased during epididymal maturation and after ejaculation as Osmcritat 15 °C was 54.7±3.2, 68.5±10.6, 116.7±2.1 and 194.3±3.7 mmol/kg for the caput, corpus, cauda and ejaculated spermatozoa respectively. Hypo-osmotic stress of 100 mmol/kg revealed a sperm subpopulation exhibiting increased hypotonic resistance compared with the whole ejaculate (Osmcrit=67.8±2.1 mmol/kg). Consistent differences were observed between lean and standard breeds (Pietrain versus Large White) and between boars within the same breed. According to data collected by artificial insemination centers during a large-scale field trial, hypotonic resistance of ejaculates was found to be positively correlated within vivofertility.

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.

Current concepts of molecular events during bovine and porcine spermatozoa capacitation

Spermatozoa are required to undergo the processes of capacitation before they obtain fertilizing ability. The molecular changes of capacitation are still not fully understood. However, it is accepted that capacitation is a sequential process involving numerous physiological changes including destabilization of the plasma membrane, alterations of intracellular ion concentrations and membrane potential, and protein phosphorylation. There are no known morphological changes that occur to the spermatozoon during capacitation. The purpose of this review is to summarize current evidence on the molecular aspects of capacitation both in vivo and in vitro in bovine and porcine spermatozoa. For the purpose of this review, the process of sperm capacitation will encompass maturational events that occur following ejaculation up to binding to the zona pellucida, that triggers acrosomal exocytosis and initiates fertilization.

Role of the epididymis in sperm competition

Although it is generally understood that the testes recruited kidney ducts for reproductive function during the evolution of vertebrates, little is understood of the biological significance of the adaptation. In the context of the evolution of the mammalian epididymis, this report provides evidence that a major role of the epididymis is to enhance a male's chance of achieving paternity in a competitive mating system. A unique example of sperm cooperation in monotremes is used as evidence that the epididymis produces sperm competition proteins to form groups of 100 sperm into bundles that have a forward motility nearly thrice that of individual spermatozoa. As it required 3-h incubation in vitro under capacitation conditions to release motile sperm from the bundles, it is suggested that the monotremes provide an example of capacitation that is quite different from capacitation in higher mammals. It is suggested that variation between species in the intensity of sperm competition could explain the variation that occurs between species in the amount of post-testicular sperm maturation and storage in the epididymis, an explanation of why the human epididymis does not play as important a role in reproduction as the epididymis of most mammals.

Lipid Remodeling of Murine Epididymosomes and Spermatozoa During Epididymal Maturation1

We have isolated vesicular structures from mouse epididymal fluid, referred to as epididymosomes. Epididymosomes have a roughly spherical aspect and a bilayer membrane, and they are heterogeneous in size and content. They originate from the epididymal epithelium, notably from the caput region, and are emitted in the epididymal lumen by way of apocrine secretion. We characterized their membranous lipid profiles in caput and cauda epididymidal fluid samples and found that epididymosomes were particularly rich in sphingomyelin (SM) and arachidonic acid. The proportion of SM increased markedly during epididymal transit and represented half the total phospholipids in cauda epididymidal epididymosomes. The cholesterol:phospholipid ratio increased from 0.26 in the caput to 0.48 in the cauda epididymidis. Measures of epididymosomal membrane anisotropy revealed that epididymosomes became more rigid during epididymal transit, in agreement with their lipid composition. In addition, we have characterized the membrane lipid pattern of murine epididymal spermatozoa during their maturation. Here, we have shown that mouse epididymal spermatozoa were distinguished by high percentages of SM and polyunsaturated membranous fatty acids (PUFAs), principally represented by arachidonic, docosapentanoic, and docosahexanoic acids. Both SM and PUFA increased throughout the epididymal tract. In particular, we observed a threefold rise in the ratio of docosapentanoic acid. Epididymal spermatozoa had a constant cholesterol:phospholipid ratio (average, 0.30) during epididymal transit. These data suggest that in contrast with epididymosomes, spermatozoal membranes seem to become more fluid during epididymal maturation.

ILA 147 immunoreactivity of the bull spermatozoa membrane during epididymal maturation

A cytochemical quantitative study was carried out to detect immunostaining of bull spermatozoa during epididymal maturation using an ILA 147 monoclonal antibody and a standard immunoperoxidase method. This antibody recognizes a bovine panleukocyte determinant. Microdensitometric measurements were made on spermatozoa collected from different sites of the male genital tract (caput, corpus and cauda epididymidis and ductus deferens). On the basis of ILA 147 staining, at least 5 subpopulations of sperm cells from each site of the genital tract were found. These subpopulations showed: 1) immunostaining in the acrosome domain and in the cytoplasmic droplet in a proximal position; 2) immunostaining in the acrosome domain and in the distal cytoplasmic droplet; 3) immunostaining in the acrosomal region and lack of a cytoplasmic droplet; 4) immunostaining only in the cytoplasmic droplet; 5) lack of a cytoplasmic droplet and absence of staining of the head. The possible relationship between the presence of ILA 147 on the sperm head and the maturation process was evaluated, and we suggest that the most significant changes in ILA 147 expression occur in the corpus epididymidis. The absence of immunocytochemical staining in some spermatozoa may be related to plasma membrane damage due to spontaneous peroxidative damage of lipids.

Optimizing and quantifying fusion of liposomes to mammalian sperm using resonance energy transfer and flow cytometric methods

BACKGROUND

Liposomes are used to carry pharmaceutical agents and to alter the lipid composition of cell membranes. This study compared resonance energy transfer (RET), fluorescence dequenching, and flow cytometry as monitors and quantifiers of fusion between liposomes and mammalian spermatozoa.

METHODS

Preliminary experiments used RET to determine the optimum sperm concentration for fusion of DL-alpha-phosphatidylcholine dipalmitoyl (PC)/DL-alpha-phosphatidylethanolamine dipalmitoyl (PE) liposomes at 35 degrees C +/- 5 mM Ca2+. Microscopy confirmed the fusion of liposomes, not just adhesion (n = 3). Dequenching tested the time-dependent fusion of liposomes of two different lipid compositions to sperm, both, (n = 3) +/- 1 mM Ca2+ and (n = 3) without Ca2+ at two sperm concentrations. Finally, flow cytometry absolutely quantified the percentage of sperm fusing to liposomes at different liposome-to-sperm ratios (n = 4) and with sperm from different donors (n = 3).

RESULTS

RET detected fusion of liposomes with sperm and microscopy confirmed the interaction to be true fusion. Dequenching detected more fusion of liposomes with sperm at 100 x 10(6) sperm per milliliter than at lower concentrations (P < 0.05). Fusion dynamics differed with lipid composition but Ca2+ had no effect. Flow cytometry reliably quantified the percentage of sperm fusing with liposomes, which varied from bull to bull (P < 0.05).

CONCLUSION

Liposome fusion with mammalian sperm membranes can be quantified cytometrically and varies with lipid composition, sperm-to-liposome ratio, and individual animals.

Bicarbonate stimulated phospholipid scrambling induces cholesterol redistribution and enables cholesterol depletion in the sperm plasma membrane

Mammalian sperm cells are activated prior to fertilization by high bicarbonate levels, which facilitate lipoprotein-mediated cholesterol efflux. The role of bicarbonate and cholesterol acceptors on the cholesterol organization in the sperm plasma membrane was tested. Bicarbonate induced an albumin-independent change in lipid architecture that was detectable by an increase in merocyanine staining (due to protein kinase A-mediated phospholipid scrambling). The response was limited to a subpopulation of viable sperm cells that were sorted from the non-responding subpopulation by flow cytometry. The responding cells had reduced cholesterol levels (30% reduction) compared with non-responding cells. The subpopulation differences were caused by variable efficiencies in epididymal maturation as judged by cell morphology. Membrane cholesterol organization was observed with filipin, which labeled the entire sperm surface of non-stimulated and non-responding cells, but labeled only the apical surface area of bicarbonate-responding cells. Addition of albumin caused cholesterol efflux, but only in bicarbonate-responding cells that exhibited virtually no filipin labeling in the sperm head area. Albumin had no effect on other lipid components, and no affinity for cholesterol in the absence of bicarbonate. Therefore, bicarbonate induces first a lateral redistribution in the low cholesterol containing spermatozoa, which in turn facilitates cholesterol extraction by albumin. A model is proposed in which phospholipid scrambling induces the formation of an apical membrane raft in the sperm head surface that enables albumin mediated efflux of cholesterol.

Laurdan fluorescence: a simple method to evaluate sperm plasma membrane alterations

OBJECTIVE

To determine, by a simple fluorescence method, sperm plasma membrane alterations related with changes of lipid bilayer that, together with routine semen analysis, could help to elucidate the causes of the unexplained male infertility problems.

DESIGN

Pilot study.

SETTING

Andrology laboratory and biochemistry institute, medical school.

PATIENT(S)

Men whose semen was studied for infertility problems.

INTERVENTIONS(S)

No therapeutic intervention was performed on patients.

MAIN OUTCOME MEASURE(S)

Presence of spermatozoa plasma membrane alterations evidenced by evaluation of Laurdan fluorescence Generalized Polarization (GP) and reported as a function of increasing cell concentration, spermatozoa total motility, linear speed, and vitality.

RESULT(S)

Reporting GP values as a function of increasing sperm cell concentration, it is evident that the samples are distributed in two distinct areas: at >32 x 10(6) cells per milliliter, mean GP value was 0.303 +/- 0.015, whereas for lower sperm cell concentrations, the mean GP was 0.365 +/- 0.026 (P<.001). These data indicate that the spermatozoa plasma membranes are characterized by liquid-crystalline phases with different ordering degree and polarity and that about 50% of samples with normal semen characteristics (> or =20 x 10(6) cells per milliliter) show high GP values.

CONCLUSION(S)

Laurdan fluorescence can be used as a simple method to evaluate spermatozoa plasma membrane alterations, particularly in a group of infertile men presenting normal semen parameters. In these samples, Laurdan could be used as a simple tool for infertility assessment. In fact, it is known that compositional and physicochemical alterations of bilayer features can be important for the fertilizing ability of spermatozoa because they are necessary for a proper physiological membrane activity.

Expression, activity, and subcellular localization of testicular hormone-sensitive lipase during postnatal development in the guinea pig

The present work reports on testicular hormone-sensitive lipase (HSL), the biological significance of which has been documented in male fertility. The HSL protein levels and enzymatic activity were measured, respectively, by densitometry of immunoreactive bands in Western blots, performed with antibodies against recombinant rat HSL, and by spectrophotometry in seminiferous tubules (STf) and interstitial tissue (ITf) enriched fractions generated from neonatal, pubertal, and adult guinea pig testes. In addition, HSL was studied in subcellular fractions obtained from STf isolated from adult testes and in epididymal spermatozoa (Spz). A 104-kDa HSL protein was detected in STf and ITf, the expression and activity of which increased with testicular development. Three immunoreactive bands of 104, 110, and 120 kDa were detected in the lysosomal subfraction, and two bands of 104 and 120 kDa were detected in Spz. The HSL activity was positively correlated with free (FC) and esterified (EC) cholesterol ratios in STf and ITf, but not with triglyceride (TG) levels, during testicular development. Immunolabeling localized HSL to elongated spermatids and Sertoli cells, where its distribution was stage-dependent, and within the cells lining the excurrent ducts of the testis. The findings of the 104- and 120-kDa HSL immunoreactive bands and of HSL activity in Spz as well, as the detection of the 104-, 110-, and 120-kDa immunoreactive bands in lysosomes, suggest that part of HSL may originate from germ cells and be imported in Sertoli cells. The HSL protein levels and enzymatic activity in ITf and STf were positively correlated with serum testosterone levels during development. To the best of our knowledge, this study is the first to contribute insights regarding the impact of HSL on FC:EC cholesterol ratios and TG levels in the interstitial tissue and tubules in relation to serum testosterone levels during postnatal development, and regarding the immunolocalization of the enzyme in regions of the male gamete consistent with spermatozoa-oocyte interaction.

Phospholipid composition of human sperm and seminal plasma in relation to sperm fertility

The phospholipid and fatty acid composition of sperm was studied in 8 healthy and 16 infertile men. Infertile men randomly formed from the patients with normal semen parameters according to WHO criterion. Therefore, all semen parameters of infertile patients were similar to the same characteristics of the semen of healthy men, except the abnormal forms. The amount of abnormal forms in infertile men was significantly higher than in healthy men. Sperm from infertile men show a drastic loss of phosphatidyl ethanolamine. At the same time, the significant increase of phosphatidyl serine in the sperm and seminal plasma of sterile patients was found. Lysophosphatidyl serine in the sperm of the infertile men was detected. Fatty acid composition of the semen of infertile men was altered. The levels of stearic and n-3 polyunsaturated fatty acids (eicosopentaenoic and docosahexaenoic acids) was dramatically lowered, but the values of some n-6 polyunsaturated fatty acids (linolenic and docosatetraenoic) acids increased. There was significant positive correlation between docosahexaenoic acid and sperm motility (r = .82, p < .001) and negative correlation between linolenic acid and spermatozoa motility (r = -0.58. p < .05). Infertility of men with normal semen quality can originate from the disorder of sperm lipid metabolism. The drastic loss of phosphatidyl ethanolamine and n-3 polyunsaturated fatty acids with simultaneous enhancement of phosphatidyl serine and some n-6 polyunsaturated fatty acids in sperm could be an important cause of male infertility.

Incorporating lipids into boar sperm decreases chilling sensitivity but not capacitation potential

Fresh boar sperm were incubated with small unilamellar liposomes composed of either the total lipids extracted from head plasma membranes (HPM) of fresh boar sperm or selected lipids (SL) of five defined phospholipids with specific acyl chains. To optimize fusion, liposomes with 2 mol% octadecyl rhodamine fluorophore in Beltsville Thawing Solution +/- 1 mM CaCl(2) were incubated at 35 degrees C with 1;ts 10(7) or 10(8) spermatozoa/ml and monitored over 60 min, using flow cytometry and fluorescence microscopy. The HPM fused to both sperm concentrations faster than SL but was equivalent by 30 min (10(8) sperm/ml) or 60 min (10(7) sperm/ml; 57.5 +/- 3% and 67.1 +/- 8% sperm fused to HPM and SL, respectively) +/- Ca(2+). Neither HPM nor SL affected onset of capacitation or spontaneous or ionophore-induced acrosome reactions at 0 or 3 h (chlortetracycline and fluorescein isothiocyanate-Pisum sativum agglutinin; n = 3). During cooling and after cryopreservation (n = 4 ejaculates), SL but not HPM significantly improved sperm motility and viability (Sybr14/propidium iodide staining) +/- 20% egg yolk, but egg yolk alone was more effective than SL alone. Liposomes of complex composition can fuse to boar sperm without harming in vitro capacitation or acrosome reaction and reduce sperm chilling sensitivity.

Variation of docosahexaenoic acid content in subsets of human spermatozoa at different stages of maturation: implications for sperm lipoperoxidative damage

The oxidation of phospholipid-bound docosahexaenoic acid (DHA) has been shown to be one of the major factors that limit the motile life span of sperm in vitro. Sperm samples show high cell-to-cell variability in life span and, consequently, in susceptibility toward lipid peroxidation. Therefore, we postulated that there is also cell-to-cell variability in DHA concentration in human spermatozoa. In this study, the concentration of DHA in subsets of human spermatozoa isolated by a discontinuous Percoll density gradient was determined by gas chromatography. Four subsets of human spermatozoa were isolated using a discontinuous Percoll gradient: fraction 1 was enriched in immature germ cells and immature sperm, fractions 2 and 3 contained, mostly, immature sperm with cytoplasmic droplets, and fraction 4 contained, for the most part, morphologically normal sperm, as determined by histochemical analysis. The results indicated that there were significant differences in DHA content in sperm from all 4 fractions. DHA content in sperm from fraction 1 was 2.5-fold higher than that found in fraction 4. DHA content in mouse sperm obtained from the seminiferous tubules was 3-fold higher than that found in mouse sperm obtained from the epididymis, consistent with the findings observed in ejaculated human sperm. The results of this study indicate (i) there is cell-to-cell variability in the concentration of DHA in human sperm and (ii) that there is a net decrease in DHA content in sperm during the process of sperm maturation.

Targeted disruption of hormone-sensitive lipase results in male sterility and adipocyte hypertrophy, but not in obesity

Hormone-sensitive lipase (HSL) is known to mediate the hydrolysis not only of triacylglycerol stored in adipose tissue but also of cholesterol esters in the adrenals, ovaries, testes, and macrophages. To elucidate its precise role in the development of obesity and steroidogenesis, we generated HSL knockout mice by homologous recombination in embryonic stem cells. Mice homozygous for the mutant HSL allele (HSL-/-) were superficially normal except that the males were sterile because of oligospermia. HSL-/- mice did not have hypogonadism or adrenal insufficiency. Instead, the testes completely lacked neutral cholesterol ester hydrolase (NCEH) activities and contained increased amounts of cholesterol ester. Many epithelial cells in the seminiferous tubules were vacuolated. NCEH activities were completely absent from both brown adipose tissue (BAT) and white adipose tissue (WAT) in HSL-/- mice. Consistently, adipocytes were significantly enlarged in the BAT (5-fold) and, to a lesser extent in the WAT (2-fold), supporting the concept that the hydrolysis of triacylglycerol was, at least in part, impaired in HSL-/- mice. The BAT mass was increased by 1.65-fold, but the WAT mass remained unchanged. Discrepancy of the size differences between cell and tissue suggests the heterogeneity of adipocytes. Despite these morphological changes, HSL-/- mice were neither obese nor cold sensitive. Furthermore, WAT from HSL-/- mice retained 40% of triacylglycerol lipase activities compared with the wild-type WAT. In conclusion, HSL is required for spermatogenesis but is not the only enzyme that mediates the hydrolysis of triacylglycerol stored in adipocytes.

A porcine homolog of the major secretory protein of human epididymis, HE1, specifically binds cholesterol

A porcine homolog of the major secretory protein of human epididymis, HE1, was for the first time purified from the porcine cauda epididymal fluid. The HE1 homolog was secreted into the epididymal fluid as a 19-kDa glycoprotein, whose sugar moiety was gradually processed to form a 16-kDa protein during transit through the epididymis. The HE1 homolog mRNA was detected only in the caput and corpus epididymis among the porcine tissues examined. The purified HE1 homolog specifically bound cholesterol with high affinity (Kd=2. 3 microM). The binding stoichiometry was determined to be 0.94 mol/mol, suggesting that 1 mol of cholesterol binds to 1 mol of the protein. It was also found that the HE1 homolog is a major cholesterol-binding protein in the porcine epididymal fluid. The possibility that the HE1 homolog is involved in the regulation of the lipid composition of the sperm membranes during the maturation in epididymis is discussed.

Lipid diffusion in the plasma membrane of ram and boar spermatozoa during maturation in the epididymis measured by fluorescence recovery after photobleaching

Maturation of spermatozoa in the epididymis involves remodelling of many protein and lipid components of the plasma membrane. In this investigation we have examined whether (a) diffusion of lipid molecules in the surface membrane changes during epididymal maturation; (b) diffusion is spatially restricted; and (c) differences in lipid diffusion can be related to known changes in membrane composition. For this purpose we have used the technique of fluorescence recovery after photobleaching (FRAP) to measure diffusion of the lipid reporter probe ODAF (5-(octa-decanoyl)aminofluorescein) in spermatozoa from two species: ram, where substantial changes in membrane lipids occur during passage through the epididymis, and boar, where there are relatively few changes. Results on ram spermatozoa show that between the testis and cauda epididymidis, diffusion coefficients values (D) for ODAF increase significantly in all the surface domains. Percentage recovery values (%R) remain constant irrespective of maturational status. In boar spermatozoa, however, D and %R values do not change significantly between epididymal regions. Cholesterol, which has widespread effects on the behaviour of lipid molecules in cell membranes, was visualized by binding of filipin. In both species filipin was concentrated over the acrosomal domain and cytoplasmic droplet of testicular spermatozoa, but in the epididymis it had a heterogenous distribution over the whole head and tail. These results are discussed in relation to the establishment and maintenance of lipid domains in spermatozoa and their influence on development of fertilizing capacity.

Molecular speciation of fish sperm phospholipids: large amounts of dipolyunsaturated phosphatidylserine

The molecular species compositions of the main diacyl phosphoglyceride classes and ether-linked subclasses from sperm of three species of fish, sea bass Dicentrarchus labrax, Atlantic salmon Salmo salar and Chinook salmon Onchorhynchus tsawytscha, were determined. The phospholipids from sperm were highly unsaturated, dipolyunsaturated fatty acid (diPUFA) molecular species comprised 64.6 to 71.8% of phosphatidylserine (PS), 10.1 to 17.4% of phosphatidylethanolamine (PE), and 3.3 to 10.1% of phosphatidylcholine (PC). In sea bass sperm, di22:6n-3 phospholipid was the predominant diPUFA molecular species, but in both salmon species 22:5n-3/22:6n-3 was also a major constituent of PS. Phospholipids containing 22:6n-3 dominated in sea bass sperm with 16:0/22:6n-3 as a major component of PC and PE, and 18:0/22:6n-3 of PE and PS in addition to di22:6n-3 in the latter two classes. In contrast, both salmon species contained much more 20:5n-3 and less 22:6n-3 so that saturated/20:5n-3 and monounsaturated/20:5n-3 molecular species were more abundant than the corresponding molecules containing 22:6n-3. Ether-linked lipids comprised 11.3-36.3% of choline and ethanolamine phosphoglycerides in each fish species. Molecular species containing 22:6n-3 were the major components of 1-O-alkyl-2-acyl-glycerophosphocholine, especially 16:0a/22:6n-3 in sea bass and 18:1a/22:6n-3 in the two salmon species, while in 1-O-alk-1'-enyl-2-acyl-glycerophosphoethanolamine, 16:0a/22:6n-3 was the major component in both salmon and 18:0a/22:6n-3 in sea bass with 18:1a/22:6n-3 abundant in all three species. In Atlantic salmon 1-O-alkyl-2-acyl-glycerophosphoethanolamine comprised 24.6% of ethanolamine glycerophospholipids which were predominantly 16:0a/22:6n-3 and 18:1a/22:6n-3. Phosphatidylinositol from sperm was dominated by stearoyl/C20 PUFA molecular species, in sea bass overwhelmingly 18:0/20:4n-6, while in both salmon species 18:0/20:4n-6 and 18:0/20:5n-3 were equally abundant.

Laurdan fluorescence spectroscopy reveals a single liquid-crystalline lipid phase and lack of thermotropic phase transitions in the plasma membrane of living human sperm

Membrane lipid phase(s), phase coexistence, and thermotropic phase transitions have been investigated in viable human spermatozoa using Laurdan fluorescence spectroscopy. Generalized polarization (GP) values derived from Laurdan excitation and emission spectra confirm that the sperm plasma membrane is a low polar, highly rigid (liquid-ordered) structure, and give evidence that, in the range from 10 degrees C to 42 degrees C, membrane lipids are in a single liquid-crystalline phase. The absence of phase transitions in the same thermal range argues against the hypothesis that the lipid domains previously detected on the sperm surface are produced by lipid lateral phase separation. The above findings are likely accounted for by the high cholesterol to phospholipid molar ratio found in the human sperm membrane. This is the first time that membrane lipid phase and polarity have been detected and quantified in living mammalian spermatozoa.

Cholesterol and phospholipid levels of washed and percoll gradient centrifuged mouse sperm: presence of lipids possessing inhibitory effects on sperm motility

Levels of DNA, cholesterol, and phospholipids of mouse caudal epididymal and vas deferens sperm that were processed through simple washing and Percoll gradient centrifugation were measured. The DNA and cholesterol contents of washed sperm and Percoll gradient centrifuged (PGC) sperm (DNA = 3.6 +/- 0.3 pg/sperm and 3.4 +/- 0.3 pg/sperm, respectively; cholesterol = 0.219 +/- 0.057 nmole/microgram DNA and 0.224 +/- 0.030 nmole/microgram DNA, respectively, for washed and PGC sperm) were not significantly different from each other; however, the phospholipid level of PGC sperm was only one half of that of washed sperm (0.315 +/- 0.071 nmole/microgram DNA versus 0.720 +/- 0.075 nmole/microgram DNA, respectively). The presence of 0.3% bovine serum albumin (BSA) in the culture medium used in sperm washing did not change the cholesterol and phospholipid contents of washed sperm. Similarly, the cholesterol and phospholipid levels of washed sperm and PGC sperm that were further incubated in BSA-containing medium for 30 min remained the same. Interestingly, substantial amounts of lipids, as determined by the cholesterol and phospholipid levels, were released into the supernatants of the sperm washes, and sperm needed to be washed at least twice to ensure their stable levels of cholesterol and phospholipids. The lipid mixture in the first sperm wash supernatant was shown to have inhibitory effects on PGC sperm motility.

Thermal acclimation and dietary lipids alter the composition, but not fluidity, of trout sperm plasma membrane

The effect of a long-term adaptation of rainbow trout to 8 and 18 degrees C combined with a corn oil- or a fish oil-supplemented diet on the characteristics of the spermatozoan plasma membrane was investigated. The experiment lasted up to 22 mon during which spermatozoa were collected from the mature males. Spermatozoan plasma membranes were isolated by nitrogen cavitation, and the cholesterol content, phospholipid composition and fatty acid pattern were investigated. Membrane viscosity was assessed on whole cells by electron spin resonance using spin-labeled phospholipids. Neither diet nor rearing temperature influenced the cholesterol content of the plasma membrane nor the phospholipid class distribution. The rearing temperature of the broodstock only slightly affected the phospholipid fatty acids. A minor decrease in 18:0 and increase in monounsaturated fatty acids was observed for the cold-adapted fish. These modifications were not sufficient to affect membrane fluidity, and we conclude that trout spermatozoa do not display any homeoviscous adaptations in these conditions. On the contrary, the dietary fatty acid intake greatly modified the fatty acid profile of plasma membrane phospholipids. The fish oil-fed trout displayed a much higher n-3/n-6 fatty acid ratio than did the corn oil-fed ones, but the 22:6n-3 levels remained unchanged. Modifications in plasma membrane composition by the diet were obtained although neither of the two diets was deficient in essential fatty acids. The enrichment in n-3 fatty acids, however, did not affect plasma membrane fluidity which was unchanged by the diets.

Naturally occurring ether-linked phosphatidylcholine activates phosphatidylinositol 3-kinase and stimulates cell growth

Phosphatidylcholine (PC) from marine invertebrates is enriched in ether-linked forms. PCs from ray fish, Dasyatis sp., and bivalve, Macoma birmanica, used in the present study, contain 65% and 75% (w/w of total PC) of ether-linked forms, respectively. Ether-linked PCs also occur in mammalian membranes. Agonist-mediated hydrolysis of PC generates second messengers which participate in cellular responses. In this study, we tested whether PCs from marine invertebrates directly affect mammalian cell growth and activity of phosphatidylinositol (Pl-3-kinase). Pl-3-kinase participates in mitogenesis initiated by a variety of growth factors. Pl-3-kinase converts polyphosphoinositides to 3' phosphorylated isomers and these products accumulate in response to mitogenic stimuli. Whether cell membrane lipids regulate Pl-3-kinase activity is not known. The marine animal-derived PCs and dioleoyl DAG (dioleoylglycerol) stimulated growth of murine pre-B lymphocytes, whereas chicken PC (egg lecithin) inhibited growth of these cells. Egg lecithin is also a potent inhibitor of Pl-3-kinase activity in vitro. We studied the effect of PCs and DAG on Pl-3-kinase activity. Unlike egg lecithin, marine animal PCs enhanced Pl-3-kinase activity. We investigated the effect of lipids on Pl-3-kinase substrate utilization. PCs enriched in ether-linked species increased utilization of substrates by Pl-3-kinase. PCs purified from marine organisms also contain a substantially higher percentage of the cis-unsaturated fatty acids, especially of the -omega 3 series (25% and 30% of total fatty acids for Dasyatis sp. and Macoma birmanica, respectively), as compared to vertebrate sources. In spite of differences in fatty acid composition, marine PCs and dioleoyl DAG showed similar effects on cell growth and Pl-3-kinase activity. These findings indicate that ether-linked phospholipids activate Pl-3-kinase and may participate in mitogenic responses.