Caspase-independent exposure of aminophospholipids and tyrosine phosphorylation in bicarbonate responsive human sperm cells

Analysis of selected sperm by density gradient centrifugation might aid in the estimation of in vivo fertility of thawed ram spermatozoa

The aim of the present study was to evaluate the effect of selecting a sperm subpopulation by means of a discontinuous density gradient centrifugation (DGC) on the quality of ram thawed semen, and the relationships between sperm parameters assessed in unselected and in selected sperm samples with in vivo fertility after intrauterine artificial insemination (IUI) using unselected sperm samples. Semen samples from twenty males were collected by artificial vagina and cryopreserved following a standard protocol. After thawing, unselected sperm samples were used in an in vivo fertility trial and sperm motility (subjective and objective, assessed by means of CASA) and membrane and acrosomal integrities (microscopy) were evaluated on unselected and selected sperm samples. In addition, plasmalemma integrity (YO-PRO-1/PI), membrane fluidity (Merocyanine 540/YO-PRO-1), mitochondrial activity (Mitotracker Deep Red/YO-PRO-1), and DNA fragmentation index (%DFI) assessed by Sperm Chromatin Structure Assay (SCSA) were evaluated by flow cytometry before and after sperm processing using DGC. Results showed that DGC improved all sperm parameters significantly, except the %DFI, which increased after the selection procedure. No relationships were found between sperm parameters evaluated in unselected sperm samples and in vivo fertility. However, we found a positive correlation between spermatozoa with high membrane fluidity within the viable sperm population (VIABMerocyanine+) evaluated in selected sperm samples and in vivo fertility (r = 0.370, P = 0.019). In conclusion, our results suggest that selected spermatozoa represent a sperm subpopulation different to the unselected one that could be related with the in vivo fertility.

Whole-body heat exposure induces membrane changes in spermatozoa from the cauda epididymidis of laboratory mice

This study was carried out to determine if exposure to hot environmental temperatures had a direct, detrimental effect on sperm quality. For this the effect of whole-body heat exposure on epididymal spermatozoa of laboratory mice was investigated. C57BL/6 mice (n = 7) were housed in a microclimate chamber at 37 degrees C-38 degrees C for 8 h per day for three consecutive days, while control mice (n = 7) were kept at 23 degrees C-24 degrees C. Cauda epididymal spermatozoa were obtained 16 h after the last heat treatment. The results showed that sperm numbers were similar in the two groups (P = 0.23), but after heat treatment, a significant reduction in the percentage of motile sperm was present (P < 0.0001). Membrane changes of the spermatozoa were investigated by staining with phycoerythrin (PE)-conjugated Annexin V, which detects exteriorization of phosphotidylserine from the inner to the outer leaflet of the sperm plasma membrane, and 7-aminoactinomycin D (7-AAD), which binds to the sperm nucleus when the plasma membrane is damaged. The percentage of spermatozoa showing positive staining with Annexin V-PE or 7-AAD or both, was significantly higher (P < 0.05) in heat-exposed mice compared with controls. These results show that whole-body heat exposure to 37 degrees C-38 degrees C induces membrane changes in the epididymal spermatozoa of mice, which may lead to apoptosis.

Impact of caspase activation in human spermatozoa

Caspases are central components in the apoptosis signaling cascade. The family of cysteine proteases transduces and enhances the apoptosis signal, and activation of effector caspases results in controlled cellular degradation. Although initially the presence of caspases in spermatozoa was controversially discussed in recent years, many studies demonstrated their activation in male germ cells. Activated apoptosis signaling results in decreased fertilizing capacity of the sperm. This review presents the current knowledge on the role of caspases in human sperm. Techniques of caspase monitoring are highlighted. With regard to the high impact of caspases on the sperm fertilizing potential, physiological and pathological settings of caspase activation and inactivation are discussed. Finally, the effects of depletion of caspase-positive sperm are shown with various standard and molecular sperm preparation methods.

Relationship between caspase activity and apoptotic markers in human sperm in response to hydrogen peroxide and progesterone

Apoptosis plays an essential role in normal spermatogenesis, but deregulations of this biological process, which is closely associated with male infertility, have been found. Whereas calcium homeostasis is a key regulator of cell survival, sustained elevation of intracellular calcium plays a role in apoptosis. The aim of this research was to determine the role of two different calcium mobilizing agents, hydrogen peroxide (H(2)O(2)) and the physiological agonist progesterone, on the apoptosis process of human ejaculated spermatozoa. Translocation of membrane phosphatidylserine was examined with an annexin V binding assay, DNA damage was detected by terminal deoxynucleotidyl transferase-mediated dUTP nick-end labelling (TUNEL assay) and caspase-3 activity was assessed using a fluorometric assay. After incubation of spermatozoa for 1 h with either 10 microM H(2)O(2) or 20 microM of progesterone, there was a significant increase in both caspase-3 activity and the percentage of annexin V-positive cells. Similarly, the TUNEL results were significantly higher 1 h after incubation with either 10 microM H(2)O(2) or 20 microM of progesterone. In fact, progesterone-treated cells showed a three-fold increase (from 17.6 to 52.9%) of TUNEL-positive cells compared to untreated cells, while H(2)O(2)-treated cells exhibited a two-fold increase (from 17.6 to 37.9%). In sum, our results suggest that spermatozoa treated with calcium mobilizing agents, such as H(2)O(2) and progesterone, seem to undergo an apoptosis process that is dependent on caspase-3 activation.

FLUOROMETRIC STUDY OF RABBIT SPERM HEAD MEMBRANE PHOSPHOLIPID ASYMMETRY DURING CAPACITATION AND ACROSOME REACTION USING ANNEXIN-V FITC

This study was conducted to evaluate phosphatidylserine translocation in head plasma membrane of Percoll-gradient purified of rabbit cauda epididymal sperm during capacitation and acrosome reaction (AR) using Annexin-V. Propidium iodide was used as control to reject dead or dying cells. The presence and distribution of Annexin-V binding sites were analyzed using flow fluorocytometry and confocal microscopy. After 6 h of incubation of sperm in capacitation medium, the number of cells positively stained with Annexin-V showed a small but significant increment. The Annexin-V binding sites produced during capacitation were found mainly in the post-acrosomal region of the sperm head plasma membrane. After AR induction with progesterone, the localization of phosphatidylserine was changed and the Annexin-V binding sites were found almost only in the acrosomal region, but with higher number of binding sites in the equatorial area. On the contrary, after AR induction with A23187, phosphatidylserine translocation, although predominant over the acrosomal region, was also observed in the post-acrosomal region. Plasma membrane destabilization during capacitation and AR may be important for sperm-oocyte fusion.

Syntaxin and VAMP association with lipid rafts depends on cholesterol depletion in capacitating sperm cells

Sperm cells represent a special exocytotic system since mature sperm cells contain only one large secretory vesicle, the acrosome, which fuses with the overlying plasma membrane during the fertilization process. Acrosomal exocytosis is believed to be regulated by activation of SNARE proteins. In this paper, we identified specific members of the SNARE protein family, i.e., the t-SNAREs syntaxin1 and 2, and the v-SNARE VAMP, present in boar sperm cells. Both syntaxins were predominantly found in the plasma membrane whereas v-SNAREs are mainly located in the outer acrosomal membrane of these cells. Under non-capacitating conditions both syntaxins and VAMP are scattered in well-defined punctate structures over the entire sperm head. Bicarbonate-induced in vitro activation in the presence of BSA causes a relocalization of these SNAREs to a more homogeneous distribution restricted to the apical ridge area of the sperm head, exactly matching the site of sperm zona binding and subsequent induced acrosomal exocytosis. This redistribution of syntaxin and VAMP depends on cholesterol depletion and closely resembles the previously reported redistribution of lipid raft marker proteins. Detergent-resistant membrane isolation and subsequent analysis shows that a significant proportion of syntaxin emerges in the detergent-resistant membrane (raft) fraction under such conditions, which is not the case under those conditions where cholesterol depletion is blocked. The v-SNARE VAMP displays a similar cholesterol depletion-dependent lateral and raft redistribution. Taken together, our results indicate that redistribution of syntaxin and VAMP during capacitation depends on association of these SNAREs with lipid rafts and that such a SNARE-raft association may be essential for spatial control of exocytosis and/or regulation of SNARE functioning.

[Sperm apoptosis: myth or reality?]

Apoptosis has become a popular biologic concept, for many reasons. From embryonic development to adult tissues, apoptosis is necessary to maintain tissues homeostasis in most organ systems during organogenesis and in the adult. Human spermatogenetic epithelium is also concerned. Dysregulations of this process are involved in many pathologies (leukaemia, auto-immune diseases, etc...), and some forms of male infertility also. Apoptotic features have been found in human semen from infertile patients, and could become useful in order to appreciate semen quality, especially in Assisted Reproductive Technology (ART). Despite numerous studies, some questions remain, especially about meaning of apoptotic damages of spermatozoa.

P2X7 receptors regulate multiple types of membrane trafficking responses and non-classical secretion pathways

Activation of the P2X7 receptor (P2X7R) triggers a remarkably diverse array of membrane trafficking responses in leukocytes and epithelial cells. These responses result in altered profiles of cell surface lipid and protein composition that can modulate the direct interactions of P2X7R-expressing cells with other cell types in the circulation, in blood vessels, at epithelial barriers, or within sites of immune and inflammatory activation. Additionally, these responses can result in the release of bioactive proteins, lipids, and large membrane complexes into extracellular compartments for remote communication between P2X7R-expressing cells and other cells that amplify or modulate inflammation, immunity, and responses to tissue damages. This review will discuss P2X7R-mediated effects on membrane composition and trafficking in the plasma membrane (PM) and intracellular organelles, as well as actions of P2X7R in controlling various modes of non-classical secretion. It will review P2X7R regulation of: (1) phosphatidylserine distribution in the PM outer leaflet; (2) shedding of PM surface proteins; (3) release of PM-derived microvesicles or microparticles; (4) PM blebbing; (5) cell-cell fusion resulting in formation of multinucleate cells; (6) phagosome maturation and fusion with lysosomes; (7) permeability of endosomes with internalized pathogen-associated molecular patterns; (8) permeability/integrity of mitochondria; (9) exocytosis of secretory lysosomes; and (10) release of exosomes from multivesicular bodies.

Removal of spermatozoa with externalized phosphatidylserine from sperm preparation in human assisted medical procreation: effects on viability, motility and mitochondrial membrane potential

BACKGROUND

Externalization of phosphatidylserine (EPS) occurs in apoptotic-like spermatozoa and could be used to remove them from sperm preparations to enhance sperm quality for assisted medical procreation. We first characterized EPS in sperms from infertile patients in terms of frequency of EPS spermatozoa as well as localization of phosphatidylserine (PS) on spermatozoa. Subsequently, we determined the impact of depleting EPS spermatozoa on sperm quality.

METHODS

EPS were visualized by fluorescently-labeled annexin V binding assay. Double staining with annexin V and Hoechst differentiates apoptotic from necrotic spermatozoa. We used magnetic-activated cell sorting using annexin V-conjugated microbeads (MACS-ANMB) technique to remove EPS spermatozoa from sperm prepared by density gradient centrifugation (DGC). The impact of this technique on sperm quality was evaluated by measuring progressive motility, viability, and the integrity of the mitochondrial membrane potential (MMP) by Rhodamine 123.

RESULTS

Mean percentages of EPS spermatozoa were 14% in DGC sperm. Four subpopulations of spermatozoa were identified: 70% alive, 3% early apoptotic, 16% necrotic and 11% late apoptotic or necrotic. PS were localized on head and/or midpiece or on the whole spermatozoa. MACS efficiently eliminates EPS spermatozoa. MACS combined with DGC allows a mean reduction of 70% in EPS and of 60% in MMP-disrupted spermatozoa with a mean increase of 50% in sperm survival at 24 h.

CONCLUSION

Human ejaculates contain EPS spermatozoa which can mostly be eliminated by DGC plus MACS resulting in improved sperm long term viability, motility and MMP integrity. EPS may be used as an indicator of sperm quality and removal of EPS spermatozoa may enhance fertility potential in assisted medical procreation.

Sperm DNA fragmentation in infertile men with genitourinary infection by Chlamydia trachomatis and Mycoplasma

OBJECTIVE

To determine the frequency of sperm cells with fragmented DNA in semen samples from men with genitourinary infection by Chlamydia trachomatis and Mycoplasma and the influence of antibiotic therapy, using the sperm chromatin dispersion test with the Halosperm kit.

DESIGN

Prospective study.

SETTING

University-affiliated reproductive medicine center, medical genetics laboratory, and academic biology center.

PATIENT(S)

One hundred forty-three male member of couples attending the andrology infertility center and a group of 50 fertile subjects. The effect of antibiotic treatment was evaluated in 95 male patients.

INTERVENTION(S)

None.

MAIN OUTCOME MEASURE(S)

Classical semen analysis (concentration, motility, morphology, and vitality), sperm DNA fragmentation, and clinical outcome.

RESULT(S)

The mean percentage of sperm cells with fragmented DNA was 35.2% +/- 13.5%, 3.2 times higher than in the control fertile group (10.8% +/- 5.6%). Concentration, morphology, and motility were also significantly affected but to a much lower degree. Sperm vitality was not significantly affected. After 3.8 +/- 2.2 months of antibiotic treatment, the mean frequency of spermatozoa with fragmented DNA decreased from 37.7% +/- 13.6% to 24.2% +/- 11.2%. Sperm concentration and motility were not significantly improved. In a group of 16 couples who attempted pregnancy during antibiotic treatment course, only 12.5% achieved pregnancy. However, in a group of 14 couples who attempted pregnancy after finishing the antibiotic treatment, 85.7% achieved it. The only significant differences found between groups was the rate of sperm DNA fragmentation and morphology.

CONCLUSION(S)

Patients with genitourinary infection by Chlamydia trachomatis and Mycoplasma have increased sperm DNA fragmentation in comparison with fertile controls. This increase is proportionally greater than the influence on classical semen parameters and could result in a decreased fertility potential. Antibiotic therapy appears to be important in providing a remedy for infection-induced high DNA fragmentation levels.

Study of apoptosis-related markers in ram spermatozoa

Certain features of capacitated or frozen-thawed spermatozoa have been considered to be an apoptosis-like phenomenon, and, it has been suggested that the presence of apoptotic sperm in seminal doses could be one of the reasons for poor fertility. The objective of this study was to determine whether phosphatidylserine (PS) translocation, caspase activity and DNA fragmentation, which are considered to be apoptotic markers in somatic cells, occur in ram sperm. Fresh ejaculates and sperm samples in different physiological state (cold-shocked, in vitro capacitated and acrosome-reacted (AR)) were compared. Simultaneous staining with 6-carboxifluorescein diacetate (6-CFDA) and Annexin V-Cy3.18 (AnnV) revealed four different sperm subpopulations in ejaculates. The main subpopulation was composed of viable cells without PS exposure (CFDA+/AnnV-). A total of 40.8% of sperm showed inverted PS, with two levels of alteration: CFDA+/AnnV+ in midpiece ("type I AnnV+"), and in acrosome and midpiece ("type II AnnV+"). The fewest subpopulation contained non-viable cells showing Annexin labelling in the entire cell (CFDA-/AnnV+). Labeling of caspases-3 and -7 by immunocytochemistry revealing different sperm subtypes depending on their localization in apical, equatorial, post-acrosomal regions and tail. The results obtained by western-blot showed, for the first time to our knowledge, that caspase-like proteins are present in fresh ram semen as both inactive and active forms. The proportion of sperm with fragmented DNA [terminal transferase-mediated dUDP nick end-labeling (TUNEL)-positive] were found rarely (2.7+/-0.5%) in all fresh ejaculates involved in this study. The analysis of total activity of both caspases by a fluorometric method showed a decrease in vitro capacitated and acrosome-reacted samples as well as in cryoinjured samples. However, the percentage of TUNEL-positive sperm demonstrating DNA fragmentation was significantly increased after in vitro induced capacitation and acrosome reaction, as well as after cold-shock although this augment was not significant. PS exposure is not totally dependent on caspases in ram spermatozoa as the addition of a caspase inhibitor prevented the increase in PS inversion due to incubation in capacitating conditions but not to the ionophore-induced acrosome reaction or cold-shock.

Detecting subtle changes in sperm membranes in veterinary andrology

Thanks to the increasing use of flow cytometry in research in veterinary spermatology, many new membrane integrity assays have been developed over the past decade. These assays are important because of their superior ability to forecast fertility when compared with other tests, such as sperm motility. This major component of the sperm quality assessment has generated new investigations with the aim of developing tests that can detect membrane damage in a very early state. Using phospholipid transposition tests, early changes in membrane permeability and fluidity can be assessed in a large number of spermatozoa using fluorescent probes in combination with flow cytometry.

Mitochondrial activity and forward scatter vary in necrotic, apoptotic and membrane-intact spermatozoan subpopulations

In the present study, we have related mitochondrial membrane potential (DeltaPsim) and forward scatter (FSC) to apoptotic-related changes in spermatozoa. Thawed red deer spermatozoa were incubated in synthetic oviductal fluid medium (37 degrees C, 5% CO2), with or without antioxidant (100 microm Trolox). At 0, 3, 6 and 9 h, aliquots were assessed for motility and were stained with a combination of Hoechst 33342, propidium ioide (PI), YO-PRO-1 and Mitotracker Deep Red for flow cytometry. The proportion of spermatozoa YO-PRO-1+ and PI+ (indicating a damaged plasmalemma; DEAD) increased, whereas that of YO-PRO-1- and PI- (INTACT) spermatozoa decreased. The proportion of YO-PRO-1+ and PI- spermatozoa (altered plasmalemma; APOPTOTIC) did not change. Both DEAD and APOPTOTIC spermatozoa had low DeltaPsim. Most high-DeltaPsim spermatozoa were INTACT, and their proportion decreased with time. The FSC signal also differed between different groups of spermatozoa, in the order APOPTOTIC > DEAD > INTACT/low DeltaPsim > INTACT/high DeltaPsim; however, the actual meaning of this difference is not clear. APOPTOTIC spermatozoa seemed motile at 0 h, but lost motility with time. Trolox only slightly improved the percentage of INTACT spermatozoa (P < 0.05). The population of APOPTOTIC spermatozoa in the present study may be dying cells, possibly with activated cell death pathways (loss of DeltaPsim). We propose that the sequence of spermatozoon death here would be: (1) loss of DeltaPsim; (2) membrane changes (YO-PRO-1+ and PI-); and (3) membrane damage (PI+). INTACT spermatozoa with low DeltaPsim or altered FSC may be compromised cells. The present study is the first that directly relates membrane integrity, apoptotic markers and mitochondrial status in spermatozoa. The results of the present study may help us understand the mechanisms leading to loss of spermatozoon viability after thawing.

A glance at the structural and functional diversity of membrane lipids

In the postgenomic era, spatially and temporally regulated molecular interactions as signals are beginning to take center stage in the understanding of fundamental biological events. For years, reductionism derived from the "fluid mosaic" model of the cell membrane has portrayed membrane lipids as rather passive molecules that, whereas separating biologically relevant aqueous phases, provided an environment so that membrane proteins could fulfill the specificity and selectivity required for proper cell signaling. Whereas these roles for membrane lipids still stand, the structural diversity of lipids and their complex arrangement in supramolecular assemblies have expanded such limited, although fundamental roles. Growing developments in the field of membrane lipids help to understand biological phenomena at the nanoscale domain, and reveal this heterogeneous group of organic compounds as a long underestimated group of key regulatory molecules. In this introductory chapter, brief overviews of the structural diversity of membrane lipids, the impact of different lipids on membrane properties, the vertical organization of lipids into rafts and caveolae, and the functional role of lipids as mediators of inter- and intracellular signals are provided. Any comprehensive review on membrane lipids, whether emphasizing structural or functional aspects, will require several volumes. The purpose of this chapter is to provide both introduction and rationale for the selection of topics that lie ahead in this book. For this reason, the list of references primarily includes reviews on particular issues dealing with membrane lipids wherein the reader can find further references.

Utility of magnetic cell separation as a molecular sperm preparation technique

Assisted reproductive techniques (ARTs) have become the treatment of choice in many cases of infertility; however, the current success rates of these procedures remain suboptimal. Programmed cell death (apoptosis) most likely contributes to failed ART and to the decrease in sperm quality after cryopreservation. There is a likelihood that some sperm selected for ART will display features of apoptosis despite their normal appearance, which may be partially responsible for the low fertilization and implantation rates seen with ART. One of the features of apoptosis is the externalization of phosphatidylserine (PS) residues, which are normally present on the inner leaflet of the sperm plasma membrane. Colloidal superparamagnetic microbeads ( approximately 50 nm in diameter) conjugated with annexin V bind to PS and are used to separate dead and apoptotic spermatozoa by magnetic-activated cell sorting (MACS). Cells with externalized PS will bind to these microbeads, whereas nonapoptotic cells with intact membranes do not bind and could be used during ARTs. We have conducted a series of experiments to investigate whether the MACS technology could be used to improve ART outcomes. Our results clearly indicate that integrating MACS as a part of sperm preparation techniques will improve semen quality and cryosurvival rates by eliminating apoptotic sperm. Nonapoptotic spermatozoa prepared by MACS display higher quality in terms of routine sperm parameters and apoptosis markers. The higher sperm quality is represented by an increased oocyte penetration potential and cryosurvival rates. Thus, the selection of nonapoptotic spermatozoa by MACS should be considered to enhance ART success rates.

Infertility in a dog due to proximal cytoplasmic droplets in the ejaculate: investigation of the significance for sperm functionality in vitro

A 4-year-old Basque Shepherd male dog was presented for breeding soundness evaluation after the dog failed to impregnate the three bitches he had mated. Clinical examination showed no anomaly of the reproductive system. Semen evaluation showed normal sperm count (640 x 10(6)), 80% had progressively motile spermatozoa, and 96% had morphologically abnormal sperm of which 84% had proximal cytoplasmic droplet and 12% had proximal droplet plus other anomaly. A zona pellucida-binding assay, using canine oocytes derived from frozen-thawed ovaries, was performed in order to investigate the zona-binding ability of dog spermatozoa with proximal cytoplasmic droplets. For the zona pellucida-binding assay, ovaries were thawed and minced in phosphate-buffered saline + 0.4% bovine serum albumin, the oocytes recovered were divided into two groups of 35-40 oocytes to be, respectively, used with the infertile dog and with a control fertile dog. Spermatozoa were capacitated in Canine Capacitating Medium (CCM) at 38.5 degrees C and 5% CO(2) in air for 2 h before oocyte insemination. Groups of five to six oocytes placed in 45 microl droplets of CCM were incubated for 1 h. Afterwards, 5 microl of CCM containing 25,000 spermatozoa were added to each droplet and co-incubated for 2 h before fixation and evaluation of the complexes. After oocyte insemination, sperm motility and viability were evaluated: the sample from the infertile dog had 85% sperm motility with fast and linear progressive movement, and sperm viability of 92%. The sample from the control dog showed 40% sperm motility with fast and highly curvilinear and erratic movement, high degree of sperm agglutination and sperm viability of 32%. For the infertile dog the mean number of bound spermatozoa/oocyte was 0.33 whereas for the control dog it was 1.80. It was concluded that dog sperm with proximal cytoplasmic droplets seem to lack normal capacitating ability in vitro, and consequently, they may have reduced capacity to bind to the zona pellucida of canine oocytes.

Apical phosphatidylserine externalization in auditory hair cells

In hair cells of the inner ear, phosphatidylserine (PS), detected with fluorescent annexin V labeling, was rapidly exposed on the external leaflet of apical plasma membranes upon dissection of the organ of Corti. PS externalization was unchanged by caspase inhibition, suggesting that externalization did not portend apoptosis or necrosis. Consistent with that conclusion, mitochondrial membrane potential and hair-cell nuclear structure remained normal during externalization. PS externalization was triggered by forskolin, which raises cAMP, and blocked by inhibitors of adenylyl cyclase. Blocking Na(+) influx by inhibiting the mechanoelectrical transduction channels and P2X ATP channels also inhibited external PS externalization. Diminished PS externalization was also seen in cells exposed to LY 294002, which blocks membrane recycling in hair cells by inhibiting phosphatidylinositol 3-kinase. These results indicate that PS exposure on the external leaflet, presumably requiring vesicular transport, results from elevation of intracellular cAMP, which can be triggered by Na(+) entry into hair cells.

Capacitation and Acrosome Reaction in Nonapoptotic Human Spermatozoa

Capacitation and acrosome reaction (AR) of human spermatozoa are prerequisites for fertilization. Annexin-V-MACS is able to separate apoptotic from nonapoptotic sperm on the basis of their externalization of phosphatidylserine (EPS). The nonapoptotic (EPS-) fraction is characterized by the lowest amounts of membrane alterations, caspase activation, disrupted mitochondrial potential, and DNA fragmentation. The aim of our study was to investigate the separation effect of Annexin-V-MACS on capacitation and AR in nonapoptotic sperm. Semen specimens from 10 healthy donors were separated into 2 samples each, one was left untreated (control) and the second was subjected to Annexin-V-MACS. Two aliquots of both, the control as well as the EPS- fraction after Annexin-V-MACS, were incubated in HTF at 37 degrees C, 5% CO2 for 3 h either with 3% BSA (capacitation) or without additives. Capacitation was monitored by tyrosine phosphorylation (TyrP) using Western blot technique. AR was determined by labeling with CD46-FITC before and after stimulation with calcium-ionophore A23187, followed by flow cytometric evaluation of the percentage of CD46+ sperm. Densitometric analyses of the 105-kDa and 80-kDa bands of the TyrP Western blots demonstrated highest TyrP in the capacitated EPS- aliquots. There was no difference in spontaneous AR in all groups. AR was best inducible in EPS-negative sperm after capacitation. Nonapoptotic human spermatozoa with intact plasma membranes are characterized by superior ability to capacitate and consequently by maximum potential to perform AR after stimulation. Selection of EPS-negative sperm may be of advantage for assisted reproduction in order to prepare the sperm subpopulation with the highest fertilizing potential.

Phosphatidylserine induces functional and structural alterations of the membrane-associated pleckstrin homology domain of phospholipase C-δ1

The membrane binding affinity of the pleckstrin homology (PH) domain of phospholipase C (PLC)-delta1 was investigated using a vesicle coprecipitation assay and the structure of the membrane-associated PH domain was probed using solid-state (13)C NMR spectroscopy. Twenty per cent phosphatidylserine (PS) in the membrane caused a moderate but significant reduction of the membrane binding affinity of the PH domain despite the predicted electrostatic attraction between the PH domain and the head groups of PS. Solid-state NMR spectra of the PH domain bound to the phosphatidylcholine (PC)/PS/phosphatidylinositol 4,5-bisphosphate (PIP(2)) (75 : 20 : 5) vesicle indicated loss of the interaction between the amphipathic alpha2-helix of the PH domain and the interface region of the membrane which was previously reported for the PH domain bound to PC/PIP(2) (95 : 5) vesicles. Characteristic local conformations in the vicinity of Ala88 and Ala112 induced by the hydrophobic interaction between the alpha2-helix and the membrane interface were lost in the structure of the PH domain at the surface of the PC/PS/PIP(2) vesicle, and consequently the structure becomes identical to the solution structure of the PH domain bound to d-myo-inositol 1,4,5-trisphosphate. These local structural changes reduce the membrane binding affinity of the PH domain. The effects of PS on the PH domain were reversed by NaCl and MgCl(2), suggesting that the effects are caused by electrostatic interaction between the protein and PS. These results generally suggest that the structure and function relationships among PLCs and other peripheral membrane proteins that have similar PH domains would be affected by the local lipid composition of membranes.

Fertilization induced changes in sea urchin sperm: mitochondrial deformation and phosphatidylserine exposure

This study demonstrates that the single mitochondrion of the sea urchin sperm undergoes a shape change at fertilization that is linked to respiration. The mitochondrion swells and shifts to the lateral side of the sperm head on contact with the homologous egg jelly or egg surface; Mg(2+)- or Na(+)-free seawater or respiratory inhibitors also induce this change. During the mitochondrial deformation, the sperm decreases the rate of oxygen consumption and their redox-state of cytochromes is disrupted b-c(1)/c. Simultaneously, the adenine nucleotides content changes precipitously. This suggests that mitochondrial morphology is strongly associated with respiratory activities in the sea urchin sperm. These changes in mitochondrial morphology and function are similar to the mitochondrial changes in apoptotic cells such as swelling, decrease in its membrane potential, and release of cytochrome c. In apoptotic cells, the exposure of phosphatidylserine from the inner to outer leaflet of the plasma membrane is one of prominence phenomena. This change was visualized by staining the sea urchin sperm with Annexin V-Fluorescein. It is possible that mitochondrial deformation is an initial sign of sperm destruction, which like as apoptotic cells.

Comparative analysis of apoptotic pathways in rat, mouse, and hamster spermatozoa

Apoptosis is a type of cell death characterized by the activation of a family of cysteine-proteases called caspases. We made a comparative study to determine the presence of several caspases and other regulators of apoptosis in rat, mouse, and hamster spermatozoa. Our results showed that the three species have both active and inactive caspases-8 and -3, the proapoptotic protein BID, p53, and the endogenous caspase inhibitor cIAP-1. However, we did not find evidence for the presence of active caspase-9. The acrosome reaction (i.e., the exocytic process of sperm acrosome) and sperm viability were not affected by the presence of a general caspase inhibitor. On the other hand, valinomycin, which promotes caspase-dependent cell death in somatic cells, induced caspase-independent cell death in spermatozoa. TRAIL, a ligand whose receptor induces apoptosis in malignant cells, did not have any effect in the viability of mouse spermatozoa, despise the presence of its receptor in rat and mouse, but not in hamster spermatozoa. Therefore, our results strongly suggest that rodent spermatozoa have some components of the apoptotic pathway. However, the role of caspases in mammalian spermatozoa appears to be unrelated to sperm survival or to the acrosome reaction under physiological conditions.

Capacitation-like changes in equine spermatozoa following cryopreservation

The primary objective of this study was to assess plasma membrane characteristics and activation of signal transduction pathways in equine spermatozoa during both in vitro capacitation and cryopreservation. Significant plasma membrane restructuring, as assessed by measurement of plasma membrane lipid disorder and phospholipid scrambling, was not observed until after cryopreservation and subsequent thawing (P < 0.05). Although in vitro capacitated cells also displayed increased plasma membrane lipid disorder and phospholipid scrambling (P < 0.05), it appeared that regulation of these events in in vitro capacitated versus cryopreserved equine spermatozoa was not identical. Addition of 5 microM staurosporine to the capacitation media reduced plasma membrane phospholipid scrambling (P < 0.05), but supplementation to the freezing extender prior to cryopreservation did not. Furthermore, progesterone was able to induce a greater degree of acrosomal exocytosis in in vitro capacitated versus frozen/thawed spermatozoa. Expression of phospholipid scramblase, a protein thought to be important in plasma membrane phospholipid scrambling, did not differ between treatments. Comparison of protein tyrosine phosphorylation patterns between in vitro capacitated and cryopreserved cells demonstrated a divergence in signal transduction. Cellular signaling in in vitro capacitated equine spermatozoa appeared to be in part dependent on activation of the cAMP/PKA pathway, whereas signaling in cryopreserved cells seemed to proceed predominantly through alternative pathways. Taken together, these data support the idea that capacitation and "cryocapacitation" are not equivalent processes.

Selection of Nonapoptotic Spermatozoa As a New Tool for Enhancing Assisted Reproduction Outcomes: An In Vitro Model1

Magnetic cell sorting (MACS) using annexin V-conjugated microbeads eliminates apoptotic spermatozoa based on the externalization of phosphatidylserine residues. The procedure delivers two sperm fractions: annexin V-negative (nonapoptotic) and annexin V-positive (apoptotic). Our aim was to determine whether the sperm fertilizing potential can be improved by selecting a nonapoptotic fraction using MACS. Semen samples (n = 35) were subjected to separation on a density gradient followed by MACS. Extent of apoptosis was assessed by measuring levels of activated caspase 3 using fluorescein-labeled inhibitors of caspase, alterations in mitochondrial membrane potential (MMP) using a lipophilic cationic dye, and DNA fragmentation using terminal deoxynucleotidyl transferase-mediated fluorescein-dUTP nick end labeling assay. The sperm fertilization potential was assessed using hamster oocyte penetration assay and hamster oocyte-intracytoplasmic sperm injection (ICSI). Annexin V-negative sperm displayed superior quality in terms of high motility, low caspase 3 activation, MMP integrity, and small extent of DNA fragmentation. Annexin V-negative sperm demonstrated higher oocyte penetration capacity but comparable sperm chromatin decondensation (SCD) following ICSI. Conversely, the annexin V-positive sperm presented with poor quality and fertilization potential. The oocyte penetration rate was negatively correlated with apoptotic marker expression, whereas SCD following ICSI was only associated with apoptosis on sperm-damaged membranes. We conclude that apoptosis appears to impact sperm-oocyte penetration rate; however, it does not seem to affect early stages of fertilization such as SCD in spermatozoa of healthy donors. The selection of nonapoptotic sperm by MACS may be used to enhance results of in vitro fertilization by increasing sperm-oocyte penetration.

A unique mechanism for cyclic adenosine 3',5'-monophosphate-induced increase of 32-kDa tyrosine-phosphorylated protein in boar spermatozoa

A cAMP-induced increase of tyrosine-phosphorylated proteins is involved in the expression of fertilizing ability in mammalian spermatozoa. We (Harayama, 2003: J Androl 24:831-842) reported that incubation of boar spermatozoa with a cell-permeable cAMP analog (cBiMPS) increased a 32-kDa tyrosine-phosphorylated protein (TyrP32). The purpose of this study is to characterize the signaling cascades that regulate the cAMP-induced increase of TyrP32. We examined effects of tyrosine kinase inhibitor (lavendustin A), tyrosine phosphatase inhibitor (Na3VO4), cell-permeable calcium chelator (BAPTA-AM), and cholesterol acceptor (methyl-beta-cyclodextrin: MBC) on the increase of TyrP32 and the change and loss of acrosomes in boar spermatozoa. The spermatozoa were used for detection of tyrosine-phosphorylated proteins by Western blotting and indirect immunofluorescence and for examination of acrosomal integrity by Giemsa staining. At least eight tyrosine-phosphorylated proteins including TyrP32 exhibited the cAMP-dependent increase during incubation with cBiMPS. In many proteins of them, this increase was reduced by lavendustin A but was enhanced by Na3VO4. In contrast, the cAMP-induced increase of TyrP32 was abolished by Na3VO4 but was hardly affected by lavendustin A. Giemsa staining showed that the increase of spermatozoa with weakly Giemsa-stained acrosomes (severely damaged acrosomes) or without acrosomes was correlative to the cAMP-induced increase of TyrP32. Moreover, the lack of calcium chloride in the incubation medium or pretreatment of spermatozoa with BAPTA-AM blocked the change and loss of acrosomes and the increase of TyrP32, suggesting these events are dependent on the extracellular and intracellular calcium. On the other hand, incubation of spermatozoa with MBC in the absence of cBiMPS could mimic the change and loss of acrosomes and increase of TyrP32 without increase of other tyrosine-phosphorylated proteins. Based on these results, we conclude that the cAMP-induced increase of TyrP32 is regulated by a unique mechanism that may be linked to the calcium-dependent change and loss of acrosomes.

Detection of damage in mammalian sperm cells

Ejaculated semen is washed for in vitro fertilization or diluted and processed to allow optimal and long-term low temperature liquid- and cryo-preservation. However, sperm are vulnerable to the washing, dilution, temperature and osmotic changes involved in sperm storage. In this review, a number of techniques are considered for detecting damaged spermatozoa. Staining protocols have been developed to detect the membrane and organelle integrity of mammalian sperm cells. Plasma membrane integrity is usually assessed after staining cells with membrane-impermeable dyes or alternatively with acetylated membrane (AM) permeable probes that are selectively de-esterified and become membrane impermeable and thus entrapped into viable cells only (AM ester loading). Organelle-specific dyes are commonly used to detect functionality of mitochondria or the acrosome. A distortion in the lateral and bilayer organization of lipids as well as the peroxidation of fatty acid moieties can be quantified and localized in living sperm. The relation of a disordering in the sperm membrane's lipid architecture and sperm deterioration versus capacitation is discussed. Finally, the integrity of sperm DNA can be measured at three different levels by assessing the degree of DNA-protamine condensation, the incidence of breaks and nicks in the DNA and the frequency of fragmentation of the nuclei into sub-haploid apoptotic bodies. The relevance of detecting DNA aberrations and especially the putative link to the incidence of apoptosis is critically considered.

L'apoptose : bases fondamentales et applications médicales

Apoptosis has become a most popular concept of cell death. What makes apoptosis particularly exciting for medicine is that its dysfunctions play a central role in the pathogenesis of several human diseases. This review summarizes the considerable knowledge about the cell death pathways. The purpose of this article is to provide a background of relevance to clinicians on apoptosis, and the rationale for future therapeutic interventions directed toward the apoptotic machinery.

Place des marqueurs de l'apoptose dans l'exploration de l'infertilité masculine

Ejaculated spermatozoa, particularly in infertile men, have been shown to display numerous features that are typical of apoptosis in somatic cells including Fas expression, ROS production, activation of caspases, DNA fragmentation, reduction in mitochondrial membrane potential, plasma membrane translocation of phosphatidylserine and permeability. In this review we summarize the biological significance and the potential role of these markers in the exploration of men infertility.

Phosphatidylserine externalization in human sperm induced by calcium ionophore A23187: relationship with apoptosis, membrane scrambling and the acrosome reaction

BACKGROUND

Translocation of phosphatidylserine (PS) from the inner to the outer leaflet of the plasma membrane is a modification of the lipid architecture occurring in sperm. This is one of the earliest signs of apoptosis that can be monitored by the calcium-dependent binding of annexin V.

METHODS AND RESULTS

Flow cytometric analysis of annexin V binding was performed. Calcium ionophore A23187 led to a significant increase in the proportion of living sperm with PS exposure: 7.3 3.2% of cells in the untreated ejaculate versus 47.5 5.6% of cells after 1 h of incubation with A23187. Conversely, diminution of mitochondrial membrane potential [DiOC6(3)/propidium iodide (PI) assay], caspase activation [fluorescein isothiocyanate (FITC)-Val-Ala-Asp-fluoromethylketone (VAD-FMK)/PI assay], increased plasma membrane permeability (Yo-Pro-1/PI assay) and increased DNA fragmentation [TdT (terminal deoxynucleotidyl transferase)-mediated dUDP nick-end labelling assay], which are among the main signs of apoptosis, were not observed in sperm, even after 4 h of incubation with A23187. However, A23187 significantly increased the proportion of sperm with plasma membrane scrambling and with a reacted acrosome, as detected with the merocyanine 540 probe (M540) and the monoclonal anti-human CD46-PE antibody respectively.

CONCLUSIONS

Our results suggest that PS exposure in human sperm, as induced by A23187, is mainly related to the acrosome reaction rather than to apoptosis.

Apoptosis of ejaculated human sperm is induced by co-incubation with Chlamydia trachomatis lipopolysaccharide

BACKGROUND

Previous work has shown that co-incubation of human sperm with Chlamydia trachomatis serovars E and LGV leads to premature sperm death and that this is due primarily to chlamydial lipopolysaccharide (LPS). Here, we investigated the possible involvement of apoptosis in this premature sperm death.

METHODS

Highly motile preparations of sperm from normozoospermic patients were co-incubated for 6 h with extracted LPS from C. trachomatis serovars E and LGV. Three different methods were used to determine if LPS-treated sperm underwent apoptosis, including: (i) flow cytometry; (ii) measurement of ADP:ATP ratios; and (iii) measurement of mono- and oligonucleosomal DNA fragments. Caspase activity was also investigated by fluorimetry and by use of a pan-caspase inhibitor and caspase-3 inhibitor.

RESULTS

All three methods used for detection indicated that C. trachomatis LPS induced some apoptosis in sperm after 6 h when compared with a staurosporine (apoptosis-positive) control. Moreover, a greater degree of apoptosis was seen with C. trachomatis serovar E than with serovar LGV. It was also shown that C. trachomatis LPS-induced apoptosis of sperm could be blocked with a pan-caspase inhibitor and a caspase-3 inhibitor. Moreover, by using a fluorogenic substrate, apoptosis was shown to be caspase-mediated.

CONCLUSIONS

In general it is believed that apoptosis does not occur in C. trachomatis-infected host cells. However, using three different methods, our findings clearly indicate that co-incubation of sperm with C. trachomatis LPS results in cellular death which is in part due to apoptosis and is caspase-mediated. These findings provide an explanation as to how C. trachomatis can mediate premature death in human sperm.

Adhesion activity of fetal gonadal cells to EGF and discoidin domains of milk fat globule-EGF factor 8 (MFG-E8), a secreted integrin-binding protein which is transiently expressed in mouse early gonadogenesis

MFG-E8, a secreted integrin-binding protein, consists of two EGF domains containing a RGD motif and two discoidin domains. In mouse embryogenesis, MFG-E8 is highly expressed in gonadal stromal cells near mesonephros at 11.5-12.5 dpc, but its function in gonadogenesis has not been characterized. To clarify a possible role of MFG-E8 in developing gonads, we analyzed the adhesion activity of 10.5-15.5 dpc gonadal cells to recombinant proteins of EGF or discoidin domains of MFG-E8. In EGF-coated wells, the gonadal cells at 11.5-12.5 dpc revealed a significantly higher adhesion activity as compared to those at 10.5 and 15.5 dpc, while discoidin domains showed a constant number of the adhered cells throughout these stages. To identify the adhesive cells of 11.5-dpc gonads, immunohistochemistry with anti-SF1/Ad4Bp antibody (a specific marker for supporting, steroidogenic, and coelomic epithelial cells) and staining for alkaline phosphatase (a germ cell marker) were carried out. As a result, EGF domains, as well as discoidin domains, were capable of binding to all three groups of SF1/Ad4Bp-positive and negative somatic cells, and germ cells of 11.5-dpc gonads. These findings therefore suggest that MFG-E8 mediates the cell-to-cell interaction among several somatic cell types and germ cells in mouse early gonadogenesis.

A new and simple method to evaluate early membrane changes in frozen-thawed boar spermatozoa

Detection of early changes in the sperm plasma membrane during cryopreservation is of utmost importance when designing freezing protocols and has previously been studied in the pig species using annexin-V detection of phosphatidylserine translocation. In the present study we designed a new assay to detect these changes in boar spermatozoa, based on the slight increase of sperm membrane permeability occurring during the early stages of cryoinjury, using the combination of three fluorescent probes, SNARF-1, YO-PRO-1 and ethidium homodimer. Four ejaculates from five different boars were frozen-thawed and flow cytometrically (FC) evaluated as paired samples. One of the samples was assayed using the annexin-V/propidium iodide staining and the other sample was evaluated using the new triple staining. Using this combination of probes, four sperm subpopulations were easily detected: viable, with stable membranes (SNARF-1 positive cells), and three with compromised membranes, one of YO-PRO-1+/Eth- cells, one ethidium homodimer+ spermatozoa and, finally spermatozoa stained both with YO-PRO-1 and ethidium homodimer (YO-PRO-1+/Eth+). The latter three categories corresponded to dead spermatozoa, but with different degree of membrane damage, being YO-PRO+/Eth- an earlier stage of membrane destabilization, (manifested by an increase in membrane permeability, while still maintaining membrane integrity) than YO-PRO+/Eth+. A method agreement analysis between both methods was performed revealing good agreement, although the percentage of live cells was 9.44% larger for the triple stain than the annexin-V assay. The new assay stained all sperm sub-populations present in the sample, making it especially suitable for both fluorescence microscopy and flow cytometry, facilitating the exclusion of debris and egg-yolk particles when using FC.

Caspase activation in human spermatozoa in response to physiological and pathological stimuli

OBJECTIVE

To investigate caspase activation in response to a variety of pathological and physiological stimuli in light of the fact that current research offers no clear consensus about caspase activation pathways in spermatozoa.

DESIGN

A prospective, controlled study.

SETTING

Male infertility clinic, Glickman Urological Institute, Cleveland Clinic Foundation, Cleveland, Ohio.

PATIENT(S)

Fifteen healthy volunteers.

INTERVENTION(S)

Spermatozoa were exposed to [1] Fibroblast-associated (Fas) death receptor activation, [2] mitochondrial apoptosis induction using betulinic acid, [3] oxidative stress, and [4] prolonged incubation up to 3 hours without any external stimuli.

MAIN OUTCOME MEASURE(S)

Active caspases-1, -3, -8, and -9 were examined in human spermatozoa by flow cytometry using carboxyfluorescein derivatives.

RESULT(S)

Inducing Fas antibody did not result in any caspase activation. Conversely, betulinic acid significantly triggered caspase-9 and -3 activation. The application of oxidative stress and prolonged incubation (3 hours) failed to result in caspase activation.

CONCLUSION(S)

These results suggest that Fas has no functional relevance in mediating caspase activation in human ejaculated spermatozoa. Although spermatozoal mitochondria are highly susceptible to specific agonists of apoptosis such as betulinic acid via caspase activation, oxidative stress-induced apoptosis appears to be caspase independent.

Dynamics of Carbohydrate Affinities at the Cell Surface of Capacitating Bovine Sperm Cells

In vivo capacitation of eutherian sperm cells coincides with changes in carbohydrate-dependent interaction with the oviduct epithelia (fucose-dependent for bovine). Heparin-like glycosaminoglycans (GAG) secreted by the oviduct compete for sperm-oviduct binding and are believed to release capacitated sperm cells from oviduct epithelia. A biochemical assay to quantify the specificity and dynamics of carbohydrate-mediated bovine sperm-oviduct binding is developed. Sperm apical plasma membranes (SPM) were purified by a factor eight and biotinylated carbohydrate probes were used for quantitative evaluation of carbohydrate binding. SPM of fresh sperm showed >12 times higher binding capacity for biotinylated fucose than for LewisA. SPM from fresh sperm also efficiently bound biotinylated fucoidan and mannan. Binding of biotinylated fucose could be inhibited by various mono- and oligosaccharides such as fucoidan, mannan, heparin, maltose, and, to a lesser extent, glucose (50% binding at 0.2 mM, 2 mM, 0.3 microg/ml, 15 mM, 50 mM, respectively). SPM from sperm cells that were in vitro capacitated for 4 h in bicarbonate-enriched media (either with or without 10 microg/ml heparin) showed a 70-85% reduction in fucose binding. This was also achieved by follicular fluid or by GAG, both obtained from dominant follicles. Total follicular fluid was much more potent in competing with fucose for sperm binding than the isolated GAG moieties (50% competition at 0.02 microg/ml, 20 microg/ml based on number of GAG moieties, respectively). These results support the hypothesis that in vivo capacitation of sperm cells is regulated by carbohydrate moieties similar to those regulating sperm-oviduct adhesion.

Regulatory and necrotic volume increase in boar spermatozoa

Spermatozoa of many species initially respond to hypotonicity as perfect osmometers. Thereafter they undergo a regulatory process resulting in a decrease in cell volume, similar to that reported for somatic cells. Regulatory volume increase (RVI), a complementary process which is assumed to occur following initial shrinkage of sperm volume after exposure to a hypertonic medium, has not yet been described in detail for spermatozoa. In this study, we investigated whether spermatozoa are able to regulate their volume after hypertonic stress and whether this ability is maintained in preserved sperm. Cell volume changes were recorded using electronic cell sizing. Sperm response to the ion channels blockers quinidine, tamoxifen, and dydeoxyforskolin, and to protein kinase/phosphatase inhibitors lavendustin, staurosporine, and vanadate was studied to investigate possible mechanisms of RVI. Annexin V staining was used in combination with propidium iodide to determine whether hypertonic stress may induce apoptosis. Overall protein tyrosine phosphorylation under hypertonic conditions was measured via flow cytometry using antiphosphotyrosine antibody. Spermatozoa exposed to hypertonic stress initially responded with an abundant subpopulation according to the perfect osmometer model and recovered their volume from this shrinkage after 20 min. RVI was inhibited by quinidine and tamoxifen, which indicates the involvement of the important cellular ions sodium and chloride in this process. Volume regulatory ability was essentially maintained during storage of liquid semen. However, the response of the sperm population was heterogeneous. A second population raised, containing spermatozoa with larger volumes, which demonstrated irregularities in the volume response with respect to osmotic challenge, ion channel blockers, and storage. Under hypertonic conditions, both protein kinase inhibitors (PKI) led to increased isotonic volumes and to elevated initial relative volumes and subsequent volume decrease. RVI was inhibited by the vanadate. Hypertonic stress did not result in an increase in early apoptotic cells, but produced a shift toward late necrotic cells. Substitution of sodium and chloride by choline and sulfate resulted in decreased isotonic volume of sperm treated with lavendustin. Tyrosine phosphorylation levels were reduced after 20 min under hypertonic conditions. It was concluded that RVI is regulated via a protein tyrosine kinase-dependent pathway, and that dephosphorylation occurs when volume regulation is required. The necrotic volume increase (NVI) is associated with the accumulation of sodium and chloride following uncontrolled opening of the channels. The ability to regulate volume after exposure to hypertonic conditions is important for sperm functionality and can have practical applications in spermatological diagnostics and cryopreservation.

Bicarbonate-induced membrane processing in sperm capacitation

During capacitation, major changes take place in the sperm plasma membrane so as to render it fusogenic and responsive to zona pellucida glycoproteins. However, the mechanisms involved have not been defined. As bicarbonate is known to be the key component that induces capacitation, we have investigated the bicarbonate-dependent changes in the boar sperm's plasma membrane architecture. We have discovered that bicarbonate induces a rapid collapse of phospholipid transverse asymmetry, exposing phosphatidylethanolamine and phosphatidylserine at the outer surface of the lipid bilayer. The collapse, which is reversible, is brought about as a result of activation of the phospholipid scramblase that exchanges phospholipids in a non-specific fashion between the two leaflets of the lipid bilayer. The activation takes place via a cyclic AMP-protein kinase A-dependent pathway and is initiated via stimulation of the so-called 'soluble' adenylyl cyclase in the sperm cell by bicarbonate. As a result of the collapse and the concurrent increase in phospholipid exchange, removal of cholesterol by albumin is facilitated (perhaps due to increased lipid packing disorder). This finding is in conflict with earlier surmises that cholesterol loss precedes activation of the cyclic AMP-protein kinase A axis. We have noted that not all cells in a given sperm population show rapid changes in response to bicarbonate stimulation; samples from individual boars also differ in their response. Maturation differences between cells have been found to play an important role in such functional heterogeneity.

Impact of storage prior to cryopreservation on plasma membrane function and fertility of boar sperm

Occasionally, boar semen must be shipped to another location for cryopreservation. We increased the initial holding time for the cooling of extended semen at 15 degrees C from 3 to 24 h to determine the effects on sperm characteristics and fertility. Thirty-one gilts and sows were inseminated once with subsequently cryopreserved and thawed semen. Increasing the holding time from 3 to 24 h had no significant effect on pregnancy rate 23 days after AI with frozen-thawed semen (64.5%) but decreased (P<0.05) embryo number from 15 to 9 and recovered embryos as fraction of CL from 73 to 47%. While the longer holding time at 15 degrees C did decrease potential litter size, the loss incurred was not too great to preclude the incorporation of a longer holding time into the cryopreservation protocol. An experiment was conducted to test the hypothesis that processing and freeze-thawing of boar semen would induce phospholipid scrambling in the plasma membrane similar to that evoked by incubation in bicarbonate-containing media. Merocyanine staining after incubation in the presence and absence of bicarbonate indicated that changes in plasma membrane phospholipid scrambling of processed and cryopreserved sperm differed from those in fresh semen undergoing bicarbonate-induced capacitation. The level of Annexin-V binding in boar spermatozoa increased from 1.6% in live spermatozoa in fresh semen to 18.7% in cryopreserved sperm. Apoptosis is unlikely to operate in mature spermatozoa. Apoptotic morphology in ejaculated spermatozoa is probably a result of incomplete deletion of apoptotic spermatocytes during spermatogenesis. Increased Annexin-V binding in thawed spermatozoa probably results from plasma membrane damage incurred during freezing and thawing.

Correlation between tyrosine phosphorylation intensity of a 107 kDa protein band and A23187-induced acrosome reaction in human spermatozoa

This study, performed using semen samples from 10 men, investigated the relationship between sperm protein tyrosine phosphorylation and acrosomal status in conditions supporting in vitro capacitation. Percoll-selected spermatozoa (cells from the 95% fraction) were incubated for 3 h at 37 degrees C under an atmosphere of 5% CO2 in air, in a polyvinyl alcohol (1 mg ml(-1)) containing Biggers-Whitten-Whittingham's medium, nonsupplemented or supplemented with either bovine serum albumin (BSA; fatty acid free, 3 mg ml(-1)) or 2-hydroxy-propyl-beta-cyclodextrin (2-OH-p-beta-CD; 0.5, 1, 2 mmol l(-1)). Sperm suspension in each medium was split into two aliquots. The first was used to evaluate the acrosomal status by staining with the fluorescein isothiocyanate Pisum sativum agglutinin after induction of the acrosome reaction (AR) for 45 min with 10 micromol l(-1) of A23187 calcium ionophore. The second aliquot was used for sodium dodecyl sulphate polyacrylamide gel electrophoresis and immunoblotting, followed by a densitometric analysis. Compared with the nonsupplemented medium, BSA- or 2-OH-p-beta-CD-supplementation induced an increase in both the percentage of live acrosome-reacted sperm and the tyrosine phosphorylation intensity of the main phosphorylated 107 kDa protein. A correlation between the percentage of live acrosome-reacted sperm and the 107-kDa protein phosphotyrosine intensity was observed. Therefore, the 107 kDa protein-phosphotyrosine level measurement would bring additional information to conventional semen parameters in the assessment of the human sperm functionality.

Somatic cell apoptosis markers and pathways in human ejaculated sperm: potential utility as indicators of sperm quality

In this study we extended earlier work to determine whether sperm respond to somatic cell apoptotic stimuli and whether apoptotic phenotypes are significant indicators of human sperm quality. We evaluated ejaculated sperm from fertile donors and subfertile patients following purification of fractions of high and low motility. In unstimulated conditions, caspase enzymatic activity was higher in motile fractions from subfertile patients than in donors, and was higher in low motility fractions from both groups. Staurosporine, but not a Fas ligand or H2O2, significantly increased caspase activity, but only in high motility fractions. Procaspase-3, -7 and -9 and low levels of active caspase-3, -7 and -9 were identified by immunoblot analysis. Apoptosis-inducing factor (AIF) was present in all samples but poly ADP-ribose polymerase-1 (PARP-1) was not detected. Phosphatidylserine translocation was significantly increased only with H2O2 treatment. In ejaculates of both subfertile and fertile men, we demonstrated the presence and activation of several proteins that are key constituents of apoptosis-related pathways in somatic cells, which may serve as markers for sperm quality.