Immunolocalization of multiple Galpha subunits in mammalian spermatozoa and additional evidence for Galphas

The SLC9C2 Gene Product (Na+/H+ Exchanger Isoform 11; NHE11) Is a Testis-Specific Protein Localized to the Head of Mature Mammalian Sperm

Na+/H+ exchangers (NHEs) are a family of ion transporters that regulate the pH of various cell compartments across an array of cell types. In eukaryotes, NHEs are encoded by the SLC9 gene family comprising 13 genes. SLC9C2, which encodes the NHE11 protein, is the only one of the SLC9 genes that is essentially uncharacterized. Here, we show that SLC9C2 exhibits testis/sperm-restricted expression in rats and humans, akin to its paralog SLC9C1 (NHE10). Similar to NHE10, NHE11 is predicted to contain an NHE domain, a voltage sensing domain, and finally an intracellular cyclic nucleotide binding domain. An immunofluorescence analysis of testis sections reveals that NHE11 localizes with developing acrosomal granules in spermiogenic cells in both rat and human testes. Most interestingly, NHE11 localizes to the sperm head, likely the plasma membrane overlaying the acrosome, in mature sperm from rats and humans. Therefore, NHE11 is the only known NHE to localize to the acrosomal region of the head in mature sperm cells. The physiological role of NHE11 has yet to be demonstrated but its predicted functional domains and unique localization suggests that it could modulate intracellular pH of the sperm head in response to changes in membrane potential and cyclic nucleotide concentrations that are a result of sperm capacitation events. If NHE11 is shown to be important for male fertility, it will be an attractive target for male contraceptive drugs due to its exclusive testis/sperm-specific expression.

Everything you ever wanted to know about PKA regulation and its involvement in mammalian sperm capacitation

The 3', 5'-cyclic adenosine monophosphate (cAMP) dependent protein kinase (PKA) is a tetrameric holoenzyme comprising a set of two regulatory subunits (PKA-R) and two catalytic (PKA-C) subunits. The PKA-R subunits act as sensors of cAMP and allow PKA-C activity. One of the first signaling events observed during mammalian sperm capacitation is PKA activation. Thus, understanding how PKA activity is restricted in space and time is crucial to decipher the critical steps of sperm capacitation. It is widely accepted that PKA specificity depends on several levels of regulation. Anchoring proteins play a pivotal role in achieving proper localization signaling, subcellular targeting and cAMP microdomains. These multi-factorial regulation steps are necessary for a precise spatio-temporal activation of PKA. Here we discuss recent understanding of regulatory mechanisms of PKA in mammalian sperm, such as post-translational modifications, in the context of its role as the master orchestrator of molecular events conducive to capacitation.

System analysis of teratozoospermia mRNA profile based on integrated bioinformatics tools

mRNA has an important role in spermatogenesis and the maintenance of fertility, and may act as a potential biomarker for the clinical diagnosis of infertility. In the present study, potential biomarkers associated with teratozoospermia were screened through systemic bioinformatics analysis. Initially, genome-wide expression profiles were downloaded from the Gene Expression Omnibus and primary analysis was conducted using R software, which included preprocessing of raw microarray data, transformation between probe ID and gene symbol and identification of differentially expressed genes. Subsequently, a functional enrichment analysis was conducted using the Database for Annotation, Visualization and Integrated Discovery to investigate the biological processes involved in the development of teratozoospermia. Finally, a protein-protein interaction network of notable differentially expressed genes was constructed and cross-analysis performed for multiple datasets, to obtain a potential biomarker for teratozoospermia. It was observed that G protein subunit β 3, G protein subunit α o1 and G protein subunit g transducin 1 were upregulated and enriched using Kyoto Encyclopedia of Genes and Genomes (KEGG) in the network and in cross analysis. Furthermore, ribosomal protein S3 (RPS3), RPS5, RPS6, RPS16 and RPS23 were downregulated and enriched using KEGG in teratozoospermia. In conclusion, the results of the present study identified several mRNAs involved in sperm morphological development, which may aid in the understanding and treatment of infertility.

Impact of glycosylation on the unimpaired functions of the sperm

One of the key factors of early development is the specification of competence between the oocyte and the sperm, which occurs during gametogenesis. However, the starting point, growth, and maturation for acquiring competence during spermatogenesis and oogenesis in mammals are very different. Spermatogenesis includes spermiogenesis, but such a metamorphosis is not observed during oogenesis. Glycosylation, a ubiquitous modification, is a preliminary requisite for distribution of the structural and functional components of spermatids for metamorphosis. In addition, glycosylation using epididymal or female genital secretory glycans is an important process for the sperm maturation, the acquisition of the potential for fertilization, and the acceleration of early embryo development. However, nonemzymatic unexpected covalent bonding of a carbohydrate and malglycosylation can result in falling fertility rates as shown in the diabetic male. So far, glycosylation during spermatogenesis and the dynamics of the plasma membrane in the process of capacitation and fertilization have been evaluated, and a powerful role of glycosylation in spermatogenesis and early development is also suggested by structural bioinformatics, functional genomics, and functional proteomics. Further understanding of glycosylation is needed to provide a better understanding of fertilization and embryo development and for the development of new diagnostic and therapeutic tools for infertility.

Distinct roles of soluble and transmembrane adenylyl cyclases in the regulation of flagellar motility in Ciona sperm

Adenylyl cyclase (AC) is a key enzyme that synthesizes cyclic AMP (cAMP) at the onset of the signaling pathway to activate sperm motility. Here, we showed that both transmembrane AC (tmAC) and soluble AC (sAC) are distinctly involved in the regulation of sperm motility in the ascidian Ciona intestinalis. A tmAC inhibitor blocked both cAMP synthesis and the activation of sperm motility induced by the egg factor sperm activating and attracting factor (SAAF), as well as those induced by theophylline, an inhibitor of phoshodiesterase. It also significantly inhibited cAMP-dependent phosphorylation of a set of proteins at motility activation. On the other hand, a sAC inhibitor does not affect on SAAF-induced transient increase of cAMP, motility activation or protein phosphorylation, but it reduced swimming velocity to half in theophylline-induced sperm. A sAC inhibitor KH-7 induced circular swimming trajectory with smaller diameter and significantly suppressed chemotaxis of sperm to SAAF. These results suggest that tmAC is involved in the basic mechanism for motility activation through cAMP-dependent protein phosphorylation, whereas sAC plays distinct roles in increase of flagellar beat frequency and in the Ca2+-dependent chemotactic movement of sperm.

Central role of soluble adenylyl cyclase and cAMP in sperm physiology

Cyclic adenosine 3',5'-monophosphate (cAMP), the first second messenger to be described, plays a central role in cell signaling in a wide variety of cell types. Over the last decades, a wide body of literature addressed the different roles of cAMP in cell physiology, mainly in response to neurotransmitters and hormones. cAMP is synthesized by a wide variety of adenylyl cyclases that can generally be grouped in two types: transmembrane adenylyl cyclase and soluble adenylyl cyclases. In particular, several aspects of sperm physiology are regulated by cAMP produced by a single atypical adenylyl cyclase (Adcy10, aka sAC, SACY). The signature that identifies sAC among other ACs, is their direct stimulation by bicarbonate. The essential nature of cAMP in sperm function has been demonstrated using gain of function as well as loss of function approaches. This review unifies state of the art knowledge of the role of cAMP and those enzymes involved in cAMP signaling pathways required for the acquisition of fertilizing capacity of mammalian sperm. This article is part of a Special Issue entitled: The role of soluble adenylyl cyclase in health and disease.

Compartmentalization of distinct cAMP signaling pathways in mammalian sperm

Fertilization competence is acquired in the female tract in a process known as capacitation. Capacitation is needed for the activation of motility (e.g. hyperactivation) and to prepare the sperm for an exocytotic process known as acrosome reaction. Although the HCO3(-)-dependent soluble adenylyl cyclase Adcy10 plays a role in motility, less is known about the source of cAMP in the sperm head. Transmembrane adenylyl cyclases (tmACs) are another possible source of cAMP. These enzymes are regulated by stimulatory heterotrimeric Gs proteins; however, the presence of Gs or tmACs in mammalian sperm has been controversial. In this study, we used Western blotting and cholera toxin-dependent ADP-ribosylation to show the Gs presence in the sperm head. Also, we showed that forskolin, a tmAC-specific activator, induces cAMP accumulation in sperm from both WT and Adcy10-null mice. This increase is blocked by the tmAC inhibitor SQ22536 but not by the Adcy10 inhibitor KH7. Although Gs immunoreactivity and tmAC activity are detected in the sperm head, PKA is only found in the tail, where Adcy10 was previously shown to reside. Consistent with an acrosomal localization, Gs reactivity is lost in acrosome-reacted sperm, and forskolin is able to increase intracellular Ca(2+) and induce the acrosome reaction. Altogether, these data suggest that cAMP pathways are compartmentalized in sperm, with Gs and tmAC in the head and Adcy10 and PKA in the flagellum.

New mutations at the imprinted Gnas cluster show gene dosage effects of Gsα in postnatal growth and implicate XLαs in bone and fat metabolism but not in suckling

The imprinted Gnas cluster is involved in obesity, energy metabolism, feeding behavior, and viability. Relative contribution of paternally expressed proteins XLαs, XLN1, and ALEX or a double dose of maternally expressed Gsα to phenotype has not been established. In this study, we have generated two new mutants (Ex1A-T-CON and Ex1A-T) at the Gnas cluster. Paternal inheritance of Ex1A-T-CON leads to loss of imprinting of Gsα, resulting in preweaning growth retardation followed by catch-up growth. Paternal inheritance of Ex1A-T leads to loss of imprinting of Gsα and loss of expression of XLαs and XLN1. These mice have severe preweaning growth retardation and incomplete catch-up growth. They are fully viable probably because suckling is unimpaired, unlike mutants in which the expression of all the known paternally expressed Gnasxl proteins (XLαs, XLN1 and ALEX) is compromised. We suggest that loss of ALEX is most likely responsible for the suckling defects previously observed. In adults, paternal inheritance of Ex1A-T results in an increased metabolic rate and reductions in fat mass, leptin, and bone mineral density attributable to loss of XLαs. This is, to our knowledge, the first report describing a role for XLαs in bone metabolism. We propose that XLαs is involved in the regulation of bone and adipocyte metabolism.

Calcium Channels in the Development, Maturation, and Function of Spermatozoa

A proper dialogue between spermatozoa and the egg is essential for conception of a new individual in sexually reproducing animals. Ca2+ is crucial in orchestrating this unique event leading to a new life. No wonder that nature has devised different Ca2+-permeable channels and located them at distinct sites in spermatozoa so that they can help fertilize the egg. New tools to study sperm ionic currents, and image intracellular Ca2+ with better spatial and temporal resolution even in swimming spermatozoa, are revealing how sperm ion channels participate in fertilization. This review critically examines the involvement of Ca2+ channels in multiple signaling processes needed for spermatozoa to mature, travel towards the egg, and fertilize it. Remarkably, these tiny specialized cells can express exclusive channels like CatSper for Ca2+ and SLO3 for K+, which are attractive targets for contraception and for the discovery of novel signaling complexes. Learning more about fertilization is a matter of capital importance; societies face growing pressure to counteract rising male infertility rates, provide safe male gamete-based contraceptives, and preserve biodiversity through improved captive breeding and assisted conception initiatives.

The opening of maitotoxin-sensitive calcium channels induces the acrosome reaction in human spermatozoa: differences from the zona pellucida

The acrosome reaction (AR), an absolute requirement for spermatozoa and egg fusion, requires the influx of Ca²(+) into the spermatozoa through voltage-dependent Ca²(+) channels and store-operated channels. Maitotoxin (MTx), a Ca²(+)-mobilizing agent, has been shown to be a potent inducer of the mouse sperm AR, with a pharmacology similar to that of the zona pellucida (ZP), possibly suggesting a common pathway for both inducers. Using recombinant human ZP3 (rhZP3), mouse ZP and two MTx channel blockers (U73122 and U73343), we investigated and compared the MTx- and ZP-induced ARs in human and mouse spermatozoa. Herein, we report that MTx induced AR and elevated intracellular Ca²(+) ([Ca²(+)](i)) in human spermatozoa, both of which were blocked by U73122 and U73343. These two compounds also inhibited the MTx-induced AR in mouse spermatozoa. In disagreement with our previous proposal, the AR triggered by rhZP3 or mouse ZP was not blocked by U73343, indicating that in human and mouse spermatozoa, the AR induction by the physiological ligands or by MTx occurred through distinct pathways. U73122, but not U73343 (inactive analogue), can block phospholipase C (PLC). Another PLC inhibitor, edelfosine, also blocked the rhZP3- and ZP-induced ARs. These findings confirmed the participation of a PLC-dependent signalling pathway in human and mouse zona protein-induced AR. Notably, edelfosine also inhibited the MTx-induced mouse sperm AR but not that of the human, suggesting that toxin-induced AR is PLC-dependent in mice and PLC-independent in humans.

Surfing the wave, cycle, life history, and genes/proteins expressed by testicular germ cells. Part 3: developmental changes in spermatid flagellum and cytoplasmic droplet and interaction of sperm with the zona pellucida and egg plasma membrane

Spermiogenesis constitutes the steps involved in the metamorphosis of spermatids into spermatozoa. It involves modification of several organelles in addition to the formation of several structures including the flagellum and cytoplasmic droplet. The flagellum is composed of a neck region and middle, principal, and end pieces. The axoneme composed of nine outer microtubular doublets circularly arranged to form a cylinder around a central pair of microtubules is present throughout the flagellum. The middle and principal pieces each contain specific components such as the mitochondrial sheath and fibrous sheath, respectively, while outer dense fibers are common to both. A plethora of proteins are constituents of each of these structures, with each playing key roles in functions related to the fertility of spermatozoa. At the end of spermiogenesis, a portion of spermatid cytoplasm remains associated with the released spermatozoa, referred to as the cytoplasmic droplet. The latter has as its main feature Golgi saccules, which appear to modify the plasma membrane of spermatozoa as they move down the epididymal duct and hence may be partly involved in male gamete maturation. The end product of spermatogenesis is highly streamlined and motile spermatozoa having a condensed nucleus equipped with an acrosome. Spermatozoa move through the female reproductive tract and eventually penetrate the zona pellucida and bind to the egg plasma membrane. Many proteins have been implicated in the process of fertilization as well as a plethora of proteins involved in the development of spermatids and sperm, and these are high lighted in this review.

The "switching on" of mammalian spermatozoa: molecular events involved in promotion and regulation of capacitation

Following the discovery of mammalian sperm capacitation and its fundamental importance for the acquisition of fertilizing potential, it has gradually become possible to identify some specific molecules and molecular events that play pivotal roles in the "switching on" of spermatozoa. These are discussed in the context of the promotion and regulation of capacitation, emphasizing differences between commonly used conditions in vitro and the environment in vivo where spermatozoa normally undergo capacitation. Although typical culture media used in vitro do support capacitation, they do not prevent capacitated cells from undergoing spontaneous acrosome reactions and so losing fertilizing potential. This is not a problem in vitro, but could be in vivo where few spermatozoa reach the site of fertilization. Several small molecules, known to be present in vivo, have been shown in vitro to bind to spermatozoa and to regulate capacitation, first accelerating capacitation and then inhibiting spontaneous acrosome reactions, by regulating cAMP production. Since spermatozoa would contact these molecules during and after ejaculation, it is plausible that they serve a similar function in vivo. The mechanisms whereby the presence or absence of decapacitation factors might alter plasma membrane architecture and so alter functionality of a number of membrane-associated enzymes involved in capacitation are also considered. Finally, several unresolved issues relating to events during capacitation are discussed.

Progestin signaling through an olfactory G protein and membrane progestin receptor-alpha in Atlantic croaker sperm: potential role in induction of sperm hypermotility

Progestin stimulation of sperm hypermotility remains poorly understood despite having been described in numerous vertebrate species. We show here that progestin stimulation of sperm hypermotility in a teleost, the Atlantic croaker (Micropogonias undulatus) is associated with activation of an olfactory G protein (Golf). Furthermore, we provide evidence that this progestin action is mediated by membrane progestin receptor-alpha (mPRalpha). Golf was identified in croaker sperm membranes and was specifically activated after treatment with the progestin 17,20beta,21-trihydroxy-4-pregnen-3-one (20beta-S). Treatment of sperm membranes with 20beta-S caused an increase in cAMP production, which was blocked by pretreatment with cholera toxin and two membrane adenylyl cyclase inhibitors: 2',5'-dideoxyadenosine and SQ22536. Moreover, preincubation of croaker sperm with 2',5'-dideoxyadenosine and SQ22536 resulted in a significant inhibition of 20beta-S-stimulated hypermotility. Binding of [3H]20beta-S to sperm membranes was decreased after pretreatment with GTPgammaS but not pertussis toxin, suggesting the receptor is coupled to a pertussis toxin-insensitive G protein. Golf and mPRalpha were coexpressed on the sperm midpiece and flagella and were coimmunoprecipitated from sperm membranes. Finally, expression of mPRalpha protein on sperm increased after in vivo treatment with LHRH and was associated with increased induction of sperm motility by 20beta-S. These results suggest that 20beta-S activates mPRalpha in croaker sperm, which in turn activates Golf and membrane adenylyl cyclase to stimulate sperm hypermotility. Taken together these findings provide a plausible mechanism by which progestins stimulate sperm hypermotility in croaker and provide the first evidence of hormonal activation of Golf in any species.

Activation of the progesterone-signaling pathway by methyl-beta-cyclodextrin or steroid in Xenopus laevis oocytes involves release of 45-kDa Galphas

Treatment of Xenopus laevis oocytes with cholesterol-depleting methyl-beta-cyclodextrin (MebetaCD) stimulates phosphorylation of mitogen-activated protein kinase (MAPK) and oocyte maturation, as reported previously [Sadler, S.E., Jacobs, N.D., 2004. Stimulation of Xenopus laevis oocyte maturation by methyl-beta-cyclodextrin. Biol. Reprod. 70, 1685-1692.]. Here we report that treatment of oocytes with MebetaCD increased levels of immunodetectable 39-kDa mos protein. The protein synthesis inhibitor, cycloheximide, blocked the appearance of Mos, blocked MebetaCD-stimulated phosphorylation of MAPK, and inhibited MebetaCD-induced oocyte maturation. These observations suggest that MebetaCD activates the progesterone-signaling pathway. Chemical inhibition of steroid synthesis and mechanical removal of follicle cells were used to verify that MebetaCD acts at the level of the oocyte and does not require production of steroid by surrounding follicle cells. Cortical Galpha(s) is contained in low-density membrane; and treatment of oocytes with progesterone or MebetaCD reduced immunodetectable levels of Galpha(s) protein in cortices and increased internal levels of 45-kDa Galpha(s) in cortical-free extracts. Dose-dependent increases in internal Galpha(s) after treatment of oocytes with progesterone correlated with the steroid-induced maturation response, and the increase in internal Galpha(s) after hormone treatment was comparable to the decrease in cortical Galpha(s). These results are consistent with a model in which release of Galpha(s) from the plasma membrane is involved in activation of the progesterone-signaling pathway that leads to amphibian oocyte maturation.

Expression of the G-protein α-subunit gustducin in mammalian spermatozoa

Although chemotaxis has been proposed to guide sperm to egg throughout the animal kingdom, sperm attractants released from mammalian eggs have not been identified. Since the G protein subunit alpha-gustducin is accepted as a marker of chemosensitive cells, attempts were made to explore whether alpha-gustducin is also expressed in spermatozoa of mammals. Immunohistochemical approaches using an anti-alpha-gustducin-specific antibody revealed the most intense immunoreactivity in differentiating spermatids. Further evidence for the alpha-gustducin expression was obtained analyzing testicular and sperm-derived tissue preparations in western blot analyses. To elucidate whether alpha-gustducin is retained in mature spermatozoa, epididymal mouse and rat sperm were subjected to immunocytochemistry as well as immunogold electron microscopy. A specific staining was obtained within the circumference of the midpiece-localized mitochondria, on the axoneme and the outer dense fibers surrounding the microtubules of this region, whereas no labeling was detectable in the end piece regions. The analysis of ejaculated bovine and human sperm revealed a comparable segmental distribution pattern for alpha-gustducin. Although a possible function for alpha-gustducin has yet to be determined, the axonemal-associated localization within the midpiece and principal piece of different mammalian spermatozoa raises the possibility that this G protein alpha-subunit may process intracellular signals controlling sperm motility.

Soluble adenylyl cyclase (sAC) is indispensable for sperm function and fertilization

We previously demonstrated that male mice deficient in the soluble adenylyl cyclase (sAC) are sterile and produce spermatozoa with deficits in progressive motility and are unable to fertilize zona-intact eggs. Here, analyses of sAC(-/-) spermatozoa provide additional insights into the functions linked to cAMP signaling. Adenylyl cyclase activity and cAMP content are greatly diminished in crude preparations of sAC(-/-) spermatozoa and are undetectable after sperm purification. HCO(3)(-) is unable to rapidly accelerate the flagellar beat or facilitate evoked Ca(2+) entry into sAC(-/-) spermatozoa. Moreover, the delayed HCO(3)(-)-dependent increases in protein tyrosine phosphorylation and hyperactivated motility, which occur late in capacitation of wild-type spermatozoa, do not develop in sAC(-/-) spermatozoa. However, sAC(-/-) sperm fertilize zona-free oocytes, indicating that gamete fusion does not require sAC. Although ATP levels are significantly reduced in sAC(-/-) sperm, cAMP-AM ester increases flagellar beat frequency, progressive motility, and alters the pattern of tyrosine phosphorylated proteins. These results indicate that sAC and cAMP coordinate cellular energy balance in wild-type sperm and that the ATP generating machinery is not operating normally in sAC(-/-) spermatozoa. These findings demonstrate that sAC plays a critical role in cAMP signaling in spermatozoa and that defective cAMP production prevents engagement of multiple components of capacitation resulting in male infertility.

Mammalian sperm phosphodiesterases and their involvement in receptor-mediated cell signaling important for capacitation

This study investigated the presence and function of intracellular cyclic nucleotide phosphodiesterases (PDEs) in mature mouse spermatozoa. PCR analysis detected gene transcripts for most of the 11 known PDE families in whole testis, but mainly for PDEs 1, 3, 6, and 8 in spermatozoa. Using specific antibodies, the strongest evidence was obtained for PDE proteins 1, 4, 6, 8, 10, and 11 in both sperm lysates and intact cells. These showed a range of subcellular localizations, with PDE 1A being primarily in the flagellum but PDEs 4D and 10A being in both the acrosomal region and the flagellum, similar to specific G proteins and adenylyl cyclases implicated in cAMP regulation during capacitation. In live spermatozoa, inhibitors selective for PDE 1 (MMPX) and 4 (rolipram) significantly increased cAMP over control levels but only rolipram significantly stimulated capacitation and in-vitro fertilizing ability; this suggests that compartmentalization has functional implications since only PDE 4 was abundant in both head and flagellum. Treatment of spermatozoa with CGS 21680, a stimulatory adenosine receptor agonist, significantly reduced cAMP-PDE activity at the same time-point when it causes increased cAMP. Thus, certain receptor-regulated cAMP processes in spermatozoa may be controlled by changes in both PDE and cyclase activities. In addition to demonstrating for the first time that some of the more recently discovered PDE isoforms, including PDE 6 (usually associated with the retina), are present in mature spermatozoa, this study provides clear evidence that the intracellular location of specific PDEs has important functional significance during capacitation and fertilization.

Odorant receptors and olfactory-like signaling mechanisms in mammalian sperm

Since their discovery in 1991, members of the odorant receptor (OR) family have been found in various ectopic tissues, including testis and sperm. It took, however, more than a decade for the first mammalian testicular ORs to be functionally characterized and implicated in a reproductively relevant scenario. Activation of hOR17-4 and mOR23 in human and mouse sperm, respectively, mediates distinct flagellar motion patterns and chemotactic behavior in various bioassays. For hOR17-4, receptor function and downstream signal transduction events are shown to be subject to pharmacological manipulation. Further insight into the basic principles that govern sperm OR operation as well as into the molecular logic that underlies OR-mediated signaling could set the stage for pioneering future applications in procreation and/or contraception.

Identification of functional alpha2- and beta-adrenergic receptors in mammalian spermatozoa

BACKGROUND

A recent study of several compounds, structurally related to amphetamine, provided evidence that mammalian spermatozoa might have adrenergic receptors able to regulate cAMP production. The present study investigated this possibility using physiological and immunochemical analyses of mouse and human spermatozoa.

METHODS

Antibodies specific for different receptor subtypes were used for Western blotting of mouse and human sperm lysates and for immunocytochemical evaluation of whole mouse and human spermatozoa. Uncapacitated and capacitated mouse spermatozoa were incubated with specific agonists and antagonists for alpha2-, beta1-, beta2- and beta3-adrenergic receptors for approximately 35 min and then assessed using chlortetracycline (CTC) fluorescence.

RESULTS

Western blotting revealed proteins of the correct size for all these receptors; immunolocalization indicated their presence on the head, especially acrosomal and neck regions, and flagellum of both mouse and human spermatozoa. CTC results indicated significant responses to agonists for all of the beta-receptors in uncapacitated cells, with agonist effectiveness being beta1 > beta2 > beta3; relevant antagonists blocked responses. In contrast, an agonist and antagonist for alpha2-receptors acted only on capacitated spermatozoa.

CONCLUSION

These experiments provide the first good evidence that mammalian spermatozoa have both beta-adrenergic receptors, known to stimulate cAMP production by membrane-associated adenylyl cyclases (mACs), and alpha2-adrenergic receptors, known to inhibit cAMP production by mACs. Responses are capacitation state dependent and provide a mechanism for inhibiting spontaneous acrosome reactions and helping to maintain fertilizing ability. These results suggest that the use of amphetamine-related compounds, either for medical or for social reasons, might have an unexpected positive impact on fertility.

Effects of estrogenic xenobiotics on human and mouse spermatozoa

OBJECTIVE

To investigate human sperm responsiveness to the estrogenic xenobiotic genistein and seek further information regarding the mechanism of action of estrogenic xenobiotics using mouse spermatozoa.

METHODS

Uncapacitated human spermatozoa were incubated with genistein and assessed using chlortetracycline (CTC) fluorescence. CTC was also used to evaluate mouse sperm responses to daidzein and combinations of genistein, 8-prenylnaringenin and nonylphenol. Several steroids were tested to determine structure-function relationships, and possible involvement of cAMP and G proteins in responses was also investigated.

RESULTS

Genistein significantly accelerated capacitation and acrosome loss in human spermatozoa, with 1, 10 and 100 nmol/l being equally effective. In mouse spermatozoa, daidzein produced significant responses, and combinations of xenobiotics at low concentrations were more effective than used singly. The compounds appear to act at the cell surface, and responses to three different steroids were nonidentical. A protein kinase-A inhibitor blocked responses to xenobiotics, while genistein and nonylphenol significantly stimulated cAMP production. Pertussis toxin and dideoxyadenosine blocked responses, suggesting involvement of inhibitory G proteins and membrane-associated adenylyl cyclases.

CONCLUSION

Human and mouse sperm responses to genistein are very similar, but human gametes appear to be even more sensitive. The mechanism of action may involve unregulated stimulation of cAMP production, leading to significant acrosome loss, undesirable because already acrosome-reacted cells are nonfertilizing. Xenobiotics were even more effective in combination. Since simultaneous exposure to low concentrations of multiple xenobiotics is likely to occur in animals and humans, further investigation is needed to determine whether this could impair fertility.

Phosphodiesterase 11 (PDE11) regulation of spermatozoa physiology

Fertilization is well correlated with sperm concentration, rate of forward motility, and percentage of live, uncapacitated ejaculated spermatozoa, which is regulated in part by cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP). Phosphodiesterases (PDEs) hydrolyze cyclic nucleotides to their corresponding monophosphates, thereby counterbalancing the activities of cAMP and cGMP, and PDE11 is highly expressed in the testis, prostate, and developing spermatozoa. However, a physiological role of PDE11 is not known. We generated PDE11 knockout (PDE11-/-) mice to investigate the role of PDE11 in spermatozoa physiology. Ejaculated sperm from PDE11-/- mice displayed reduced sperm concentration, rate of forward progression, and percentage of live spermatozoa. Pre-ejaculated sperm from PDE11-/- mice displayed increased premature/spontaneous capacitance. These data are consistent with human data and suggest a role for PDE11 in spermatogenesis and fertilization potential. This is the first phenotype described for the PDE11-/- mouse and the first report of a physiological role for PDE11.

First messenger regulation of mammalian sperm function via adenylyl cyclase/cAMP

When released into an appropriate environment, mammalian spermatozoa begin to capacitate and then continue until fully capacitated and able to fertilize. During capacitation in vitro, some cells 'over-capacitate' and undergo spontaneous acrosome reactions; this would be highly undesirable in vivo since already acrosome-reacted spermatozoa are non-fertilizing. Recent studies have revealed that seminal plasma contains several small molecules that bind to specific receptors on the sperm plasma membrane and act as 'first messengers', causing biologically important changes in availability of the 'second messenger' cAMP. Fertilization promoting peptide (FPP), calcitonin and adenosine all regulate cAMP production, stimulating it in uncapacitated spermatozoa and then inhibiting it in capacitated cells; in contrast, angiotensin II stimulates cAMP throughout capacitation. The molecules that regulate cAMP appear to do so via G protein-modulated changes in membrane associated adenylyl cyclases (mACs). Both mouse and human spermatozoa have been shown to have Galphas and Galphai2, as well as several isoforms of mAC, located in the same regions as the specific receptors. Thus spermatozoa possess the required elements for several separate signal transduction pathways, many of which regulate mAC/cAMP and so maintain sperm fertilizing ability. In vivo, such responses could increase the chances of successful fertilization.

Mechanisms of action of angiotensin II on mammalian sperm function

Angiotensin II (AII) stimulates capacitation and fertilizing ability in mammalian spermatozoa, with the binding of AII to its receptors resulting in stimulation of cAMP production in both uncapacitated and capacitated cells. This study investigated possible mechanisms whereby AII affects cAMP availability. The first question was whether extracellular Ca2+ is required for responses in mouse spermatozoa and, using chlortetracycline fluorescence analysis, it was clear that cells responded to AII only when the medium contained CaCl2, with both 90 microM and 1.80 mM supporting a significant acceleration of capacitation. Consistent with those results, AII significantly stimulated cAMP production in both CaCl2-containing media tested, the response being greater in that containing 1.80 mM. Several different agents that might affect the signalling pathway stimulated by AII were then evaluated in uncapacitated suspensions. Chlortetracycline analysis revealed that pertussis toxin abolished responses to AII, suggesting the involvement of an inhibitory Galpha subunit; dideoxyadenosine, a specific membrane-associated adenylyl cyclase (mAC) P-site inhibitor, also blocked responses, suggesting involvement of an mAC. cAMP determinations confirmed that both reagents also abolished AII's stimulation of cAMP. In contrast, nifedipine, a Ca2+ channel blocker, did not inhibit AII's effects on spermatozoa. Finally, in capacitated suspensions, both pertussis toxin and dideoxyadenosine were again shown to block AII's stimulation of cAMP. These results suggest that responses to AII involve an inhibitory G protein and an mAC, but it is likely that AII-receptor coupling does not stimulate directly mAC but rather does so in an indirect manner, perhaps by altering the intracellular Ca2+ concentration.

Cathine and norephedrine, both phenylpropanolamines, accelerate capacitation and then inhibit spontaneous acrosome loss

BACKGROUND

Cathinone, released when Catha edulis leaves (khat) are chewed, has euphoric, stimulatory properties. It is metabolized to the phenylpropanolamines (PPAs) cathine and norephedrine. This study investigated whether PPAs affect mammalian sperm function, using primarily mouse, but also human, spermatozoa.

METHODS

Uncapacitated sperm suspensions were treated with cathine, norephedrine, adrenaline and noradrenaline, then assessed using chlortetracycline (CTC) fluorescence. Cathine and adrenaline were also evaluated using in vitro fertilization. Capacitated suspensions were treated with PPAs+/-progesterone and+/-pertussis toxin. Finally, cAMP production was evaluated in uncapacitated and capacitated suspensions.

RESULTS

In uncapacitated mouse spermatozoa, cathine, norephedrine, adrenaline and noradrenaline all significantly accelerated capacitation; uncapacitated human spermatozoa responded similarly to cathine. Consistent with these results, cathine- and adrenaline-treated suspensions were significantly more fertile than controls. In capacitated spermatozoa, both PPAs inhibited spontaneous acrosome reactions (ARs) but progesterone could over-ride this inhibition. Pertussis toxin abolished cathine's inhibition of ARs, suggesting G protein involvement. Finally, cathine and adrenaline significantly stimulated cAMP production in uncapacitated suspensions, but significantly inhibited it in capacitated suspensions.

CONCLUSIONS

This is the first demonstration that PPAs can directly affect mammalian sperm function, accelerating capacitation and inhibiting spontaneous ARs. These responses correlated with initial stimulation and subsequent inhibition of cAMP production. Adrenaline/noradrenaline elicited similar responses, suggesting the presence of adrenergic receptors. Therefore, regulation of adenylyl cyclase/cAMP in a G protein-mediated fashion by PPAs may possibly involve adrenergic receptors. These results suggest that PPAs, at appropriate doses, might provide a novel approach to enhance natural fertility.

Angiotensin II stimulates cAMP production and protein tyrosine phosphorylation in mouse spermatozoa

Angiotensin II (AII), found in seminal plasma, has been shown to stimulate capacitation in uncapacitated mammalian spermatozoa. The present study investigated the location of AII receptors on spermatozoa and AII's mechanism of action. AT1 type receptors for AII are present on the acrosomal cap region and along the whole of the flagellum of both mouse and human spermatozoa. Because combinations of low concentrations of AII and either calcitonin or fertilization-promoting peptide (FPP), both known to regulate the adenylyl cyclase (AC)/cAMP signal transduction pathway, elicited a significant response, this study investigated the hypothesis that these peptides act on the same pathway. AII was shown to significantly stimulate cAMP production in both uncapacitated and capacitated mouse spermatozoa and this was associated with increases in protein tyrosine phosphorylation. Using an anti-phosphotyrosine antibody to visualize the location of tyrosine phosphoproteins within individual cells, AII significantly stimulated phosphorylation within 20 min in both the head, especially in the acrosomal cap region, and the flagellum, especially in the principal piece, of uncapacitated mouse spermatozoa; combined AII + FPP was stimulatory within 5 min. In addition, Western blotting revealed that AII stimulation increased phosphorylation in a number of tyrosine phosphoproteins in both uncapacitated and capacitated mouse spermatozoa, with some being altered only in the latter category of cells. These results support the hypothesis that AII stimulates AC/cAMP in mammalian spermatozoa.

Sperm from beta1,4-galactosyltransferase I-null mice exhibit precocious capacitation

Mammalian sperm must undergo a physiological maturation, termed capacitation, before they are able to fertilize eggs. Despite its importance, the molecular mechanisms underlying capacitation are poorly understood. In this paper, we describe the capacitation phenotype of sperm lacking the long isoform of beta1,4-galactosyltransferase I (GalT I), a sperm surface protein that functions as a receptor for the zona pellucida glycoprotein, ZP3, and as an inducer of the acrosome reaction following ZP3-dependent aggregation. As expected, wild-type sperm must undergo capacitation in order to bind the zona pellucida and undergo a Ca(2+) ionophore-induced acrosome reaction. By contrast, GalT I-null sperm behave as though they are precociously capacitated, in that they demonstrate maximal binding to the zona pellucida and greatly increased sensitivity to ionophore-induced acrosome reactions without undergoing capacitation in vitro. The loss of GalT I from sperm results in an inability to bind epididymal glycoconjugates that normally maintain sperm in an 'uncapacitated' state; removing these decapacitating factors from wild-type sperm phenocopies the capacitation behavior of GalT I-null sperm. Interestingly, capacitation of GalT I-null sperm is independent of the presence of albumin, Ca(2+) and HCO(3)(-); three co-factors normally required by wild-type sperm to achieve capacitation. This implies that intracellular targets of albumin, Ca(2+) and/or HCO(3)(-) may be constitutively active in GalT I-null sperm. Consistent with this, GalT I-null sperm have increased levels of cAMP that correlate closely with both the accelerated kinetics and co-factor-independence of GalT I-null sperm capacitation. By contrast, the kinetics of protein tyrosine phosphorylation and sperm motility are unaltered in mutant sperm relative to wild-type. These data suggest that GalT I may function as a negative regulator of capacitation in the sperm head by suppressing intracellular signaling pathways that promote this process.

Evidence for multiple distinctly localized adenylyl cyclase isoforms in mammalian spermatozoa

In addition to a bicarbonate-regulated soluble adenylyl cyclase (sAC), mammalian spermatozoa, like somatic cells, appear to contain receptor/G protein-regulated AC activity that contributes to the modulation of specialized cell processes. This study provides evidence that agents, known to influence somatic membrane-associated AC (mAC) but apparently not germ cell sAC, can modulate cAMP production and functional state in mouse spermatozoa. Specifically, forskolin significantly enhanced cAMP production and capacitation, while inclusion of 2',5'-dideoxyadenosine significantly blocked these responses. Furthermore, GTPgammaS and NaF stimulated cAMP, but GDPbetaS and mastoparan had no apparent effect, consistent with recent evidence that G(s), but not G(i), contributes to AC/cAMP regulation in uncapacitated cells. In addition, intact mouse spermatozoa were screened for all known mAC isoforms by immunolocalization, using commercially available specific antibodies. The most abundant isoforms appeared to be AC2, AC3, and AC8, each with distinct distributions in the acrosomal and flagellar regions; AC1 and AC4 also appeared to be present, although less abundantly, in the midpiece and acrosomal cap regions, respectively. Intriguingly, however, Western blotting revealed that the major immunoreactive proteins in mouse sperm lysates were considerably smaller (approximately 50-60 kDa) than their somatic cell counterparts, suggesting that mature spermatozoa contain multiple mACs which may function in a shortened form. Of particular interest were AC3 and AC8, located in the same regions as, and hence possibly directly associated with, specific cell surface receptors and G proteins that are able to regulate the spermatozoon's acquisition and maintenance of fertilizing ability via changes in AC/cAMP.

Calcitonin acts as a first messenger to regulate adenylyl cyclase/cAMP and mammalian sperm function

Calcitonin stimulates capacitation in uncapacitated mouse spermatozoa and then inhibits spontaneous acrosome loss in capacitated cells, responses similar to those elicited by fertilization promoting peptide (FPP), a peptide known to regulate the adenylyl cyclase/cAMP pathway. This study investigated the hypothesis that calcitonin also modulates this pathway. Calcitonin significantly stimulated cAMP production in uncapacitated spermatozoa and then inhibited it in capacitated cells; the magnitude of both stimulatory and inhibitory changes was similar to that obtained with FPP but the inhibitory responses to FPP preceded those of calcitonin. This possibly reflects the involvement of two different adenosine receptors in response to FPP compared with one calcitonin receptor. Calcitonin receptors were located on the acrosomal cap and the flagellum, the midpiece having a greater abundance than the principal piece. Although both calcitonin and adenosine receptors are found in the head and flagellum, there was no evidence for cross-talk between them. Chlortetracycline investigations to determine the minimum extracellular Ca(2+) requirement for responses to calcitonin revealed that calcitonin significantly stimulated capacitation in Ca(2+)-deficient medium but FPP did not. Calcitonin also significantly stimulated cAMP production under these conditions, and similarly preincubated suspensions, when diluted into +Ca(2+) medium, were significantly more fertile in vitro than untreated controls. These results indicate that calcitonin, like FPP, acts as a first messenger to regulate the production of cAMP and mammalian sperm function, but the differences in Ca(2+) requirements suggest that calcitonin and FPP may regulate different isoforms of adenylyl cyclase.