Immunolocalization of A1 adenosine receptors in mammalian spermatozoa

Sperm DNA Integrity in Leukocytospermia and Its Association with Seminal Adenosine Deaminase

Background:

The study aimed to examine the effect of leukocytospermia on sperm quality and the levels of seminal adenosine deaminase (ADA) enzyme in males attending an infertility clinic in a tertiary hospital and to detect the association, if any, between seminal ADA and sperm quality.

Methodology:

Consenting male subjects, between 21 and 45 years, attending the infertility clinic and qualifying the eligibility criteria were recruited following informed consent. The collected semen samples were analyzed for the routine parameters based on the WHO protocols and for sperm DNA fragmentation. The seminal leukocyte count was detected using the peroxidase method, and the seminal ADA was assessed using spectrophotometry.

Results:

Samples from 110 participants were included in the study; leukocytospermia was detected in 33% of the samples. A significant reduction in the sperm quality with respect to conventional semen parameters (sperm motility and sperm vitality) and sperm DNA fragmentation index (SDFI) was noted in the presence of leukocytospermia. Furthermore, a significant positive correlation between the levels of seminal ADA and SDFI was noted (P = 0.000, r = 0.412).

Conclusion:

The sperm motility and DNA integrity are significantly compromised in the presence of leukocytospermia when the leukocyte count is > 1 million/mL of semen as well as 0.5–1 million/mL of semen. The positive correlation noted between seminal ADA levels and increased sperm DNA damage paves way for the possibility of seminal ADA to be an indicator of silent male genital tract inflammation as well as low-quality semen.

Cyclic nucleotide phosphodiesterases in human spermatozoa and seminal fluid: Presence of an active PDE10A in human spermatozoa

BACKGROUND

Cyclic adenosine monophosphate (cAMP) plays a crucial role as a signaling molecule for sperm functions such as capacitation, motility and acrosome reaction. It is well known that cAMP degradation by phosphodiesterase (PDE) enzyme has a major impact on sperm functions. The present study was undertaken to characterize cAMP-PDE activity in human semen.

METHODS

cAMP-PDE activity was measured in human sperm and seminal plasma using family specific PDE inhibitors. Three sperm fractionation methods were applied to assess cAMP-PDE activity in spermatozoa. Western blots were used to validate the presence of specific family in sperm and seminal plasma.

RESULTS

Using three sperm fractionation methods, we demonstrated that in human sperm, the major cAMP-PDE activity is papaverine-sensitive and thus ascribed to PDE10. In seminal plasma, total cAMP-PDE activity was 1.14±0.39fmol of cAMP hydrolyzed per minute per μg of protein. Using specific inhibitors, we showed that the major cAMP-PDE activity found in human seminal plasma is ascribed to PDE4 and PDE11. Western blot analysis, immunoprecipitation with a specific monoclonal antibody, and mass spectrometry confirmed the presence of PDE10 in human spermatozoa.

CONCLUSION

This study provides the first demonstration of the presence of functional PDE10 in human spermatozoa and functional PDE4 and PDE11 in human seminal plasma.

GENERAL SIGNIFICANCE

Since the contribution of cyclic nucleotides in several sperm functions is well known, the finding that PDE10 is an active enzyme in human spermatozoa is novel and may lead to new insight into fertility.

Characterization of cAMP-phosphodiesterase activity in bovine seminal plasma

The second messenger cyclic adenosine monophosphate (cAMP) has a central role in sperm physiology. Extracellular cAMP can be sequentially degraded into 5'AMP and adenosine by ecto-phosphodiesterases (ecto-PDE) and ecto-nucleotidases, a phenomenon called extracellular cAMP-adenosine pathway. As cAMP-adenosine pathway is involved in sperm capacitation, we hypothesize that extracellular PDEs are functionally present in seminal plasma. Exclusively measuring cAMP-PDE activity, total activity in bovine seminal plasma was 10.1 ± 1.5 fmoles/min/μg. Using different family-specific PDE inhibitors, we showed that in seminal plasma, the major cAMP-PDE activity was papaverine sensitive (47.5%). These data support the presence of PDE10 in bovine seminal plasma and was further confirmed by western blot. In epididymal fluid, total cAMP-PDE activity was 48.2 ± 14.8 fmoles/min/μg and we showed that the major cAMP-PDE activity was 3-isobutyl-methylxanthine insensitive and thus ascribed to PDE8 family. PDE10A mRNAs were found in the testis, epididymis, and seminal vesicles. cAMP-PDE activity is present in bovine seminal plasma and epididymal fluid. The results suggest a role for ecto-PDEs present in those fluids in the signaling pathways involved in sperm functions.

The Role of G22 A Adenosine Deaminase 1 Gene Polymorphism and the Activities of ADA Isoenzymes in Fertile and Infertile Men

OBJECTIVE

To evaluate frequency distribution of adenosine deaminase 1 (ADA1) G22 A alleles and genotypes in fertile and infertile men.

METHODS

In this study we evaluate frequency distribution of ADA1 G22 A alleles and genotypes in 200 fertile and 200 infertile men. The polymerase chain reaction-restriction fragment length polymorphism technique was used for determining ADA1 G22 A variants. In addition, ADA isoenzymes activities (ADA1 and ADA2) were measured using colorimetric method.

RESULTS

The frequency of GG genotype was significantly higher and GA genotype was lower in infertile males compared with fertile men (P = .048 and P = .045, respectively). However, there was not any noticeable difference in allele distribution between groups (P >.05). Based on logistic regression analysis, the GA genotype has a protective role and can decrease the risk of male infertility 1.7 times (P = .046). There were significantly higher activities of ADAT and its isoenzymes in infertile males compared with fertile men (P <.05). Also, the ADA1 activity with GG genotype was higher than GA carriers in all population (P = .001).

CONCLUSION

Our results revealed that the activity of ADA isoenzymes and distribution of ADA1 G22 A genotypes were different among fertile and infertile men and more likely the GA genotype, which had lower ADA1 activity and was higher in fertile men is a protective factor against infertility.

Purinergic signalling in the reproductive system in health and disease

There are multiple roles for purinergic signalling in both male and female reproductive organs. ATP, released as a cotransmitter with noradrenaline from sympathetic nerves, contracts smooth muscle via P2X1 receptors in vas deferens, seminal vesicles, prostate and uterus, as well as in blood vessels. Male infertility occurs in P2X1 receptor knockout mice. Both short- and long-term trophic purinergic signalling occurs in reproductive organs. Purinergic signalling is involved in hormone secretion, penile erection, sperm motility and capacitation, and mucous production. Changes in purinoceptor expression occur in pathophysiological conditions, including pre-eclampsia, cancer and pain.

Cyclic AMP efflux, via MRPs and A1 adenosine receptors, is critical for bovine sperm capacitation

Sperm capacitation has been largely associated with an increase in cAMP, although its relevance in the underlying mechanisms of this maturation process remains elusive. Increasing evidence shows that the extrusion of cAMP through multidrug resistance associated protein 4 (MRP4) regulates cell homeostasis not only in physiological but also in pathophysiological situations and studies from our laboratory strongly support this assumption. In the present work we sought to establish the role of cAMP efflux in the regulation of sperm capacitation. Sperm capacitation was performed in vitro by exposing bovine spermatozoa to bicarbonate 40 and 70 mM; cAMP; probenecid (a MRPs general inhibitor) and an adenosine type 1 receptor (A1 adenosine receptor) selective antagonist (DPCPX). Capacitation was assessed by chlortetracycline assay and lysophosphatidylcholine-induced acrosome reaction assessed by PSA-FITC staining. Intracellular and extracellular cAMP was measured by radiobinding the regulatory subunit of PKA under the same experimental conditions. MRP4 was detected by western blot and immunohistochemistry assays. Results showed that the inhibition of soluble adenylyl cyclase significantly inhibited bicarbonate-induced sperm capacitation. Furthermore, in the presence of 40 and 70 mM bicarbonate bovine spermatozoa synthesized and extruded cAMP. Interestingly, in the absence of IBMX (a PDEs inhibitor) cAMP efflux still operated in sperm cells, suggesting that cAMP extrusion would be a physiological process in the spermatozoa complementary to the action of PDE. Blockade of MRPs by probenecid abolished the efflux of the cyclic nucleotide resulting not only in the accumulation of intracellular cAMP but also in the inhibition of bicarbonate-induced sperm capacitation. The effect of probenecid was abolished by exposing sperm cells to cAMP. The high-affinity efflux pump for cAMP, MRP4 was expressed in bovine spermatozoa and localized to the midpiece of the tail as previously reported for soluble adenylyl cyclase and A1 adenosine receptor. Additionally, blockade of A1 adenosine receptor abolished not only bicarbonate-induced sperm capacitation but also that stimulated by cAMP. Present findings strongly support that cAMP efflux, presumably through MRP4, and the activation of A1 adenosine receptor regulate some events associated with bicarbonate-induced sperm capacitation, and further suggest a paracrine and/or autocrine role for cAMP.

Involvement of A1Adenosine Receptors in the Acquisition of Fertilizing Capacity

Ejaculated mammalian spermatozoa acquire competence to fertilize oocytes by a two-step process: capacitation followed by acrosome reaction. The biochemical and biophysical modifications occurring in vivo in the female reproductive tract can be reproduced in vitro, and previous studies have suggested a capacitative role for adenosine A(1) receptor (A(1)R). Mice with a targeted disruption of the Adora 1 gene (A(1)R-/- mice) provide a useful model for better understanding the role of the A(1)R in fertility. Murine spermatozoa express A(1)R in the head, neck, midpiece region, and tail. The number of capacitated spermatozoa incubated in human tubal fluid was significantly reduced in A(1)R-/- compared with A(1)R+/+ and A(1)R+/- spermatozoa. The difference between A(1) R+/+ and A(1)R-/- mouse spermatozoa was mainly in the time necessary to reach the maximum percentage of capacitation. A(1)R+/+ murine sperm obtained the full state of capacitation within 90 minutes whereas A(1)R-/- sperm required 240 minutes. Caffeine, a known antagonist of A(1) and A(2A) adenosine receptors, lowered the number of capacitated sperm and affected the time of capacitation in a dose-dependent manner, mimicking the effects of the lack of A(1) receptors. Although number, motility, and viability of A(1)R-/- murine sperm was not significantly different from A(1)R+/+ mouse spermatozoa, a significant reduction of the number of pups produced by A(1)R-/- male mice suggests that A(1) receptors must be fully operative to accomplish the optimal degree of capacitation and thereby fertilization.

Adenosine deaminase activity in fertile and infertile men

Adenosine deaminase (ADA; E.C.3.5.4.4) catalyses the deamination of adenosine to inosine. In the human reproductive system, the importance of enzymes that affect metabolism of adenosine, particularly adenosine deaminase, has been noticed. The purpose of this study was to determine the plasma activities of total adenosine deaminase (ADAT), and its isoenzymes, ADA1 and ADA2, in fertile and infertile men. Plasma activities of ADA and its isoenzymes were measured in 55 fertile men and 70 infertile men. There was a significant difference in the ADA1 and ADA2 activities between fertile and infertile individuals (P < 0.01). The activity of ADAT, ADA2 and ADA1 in infertile men was higher than that in fertile individuals. This alteration in ADA activity can lead to reduced adenosine levels, which may be involved in disturbing the fertility process.

Testicular expression of Adora3i2 in Adora3 knockout mice reveals a role of mouse A3Ri2 and human A3Ri3 adenosine receptors in sperm

Adenosine is a candidate modulator of sperm motility in the female reproductive tract that increases sperm flagellar beat frequency in vitro. Past work suggested that this acceleration may involve equilibrative (ENT) and concentrative (CNT) nucleoside transporters. Here we show that Slc29a1 (ENT-1) is the predominant nucleoside transporter expressed in the mouse testis. Unexpectedly, the beat of Slc29a1-null sperm still accelerates in response to 2-chloro-2'-deoxyadenosine (Cl-dAdo). Moreover, in wild-type sperm neither blockade of CNTs by removal of external Na(+), nor inhibition of ENTs with nitrobenzylthioionosine, prevents acceleration of the sperm beat by Cl-dAdo. In contrast, pertussis toxin produces strong blockade, indicating involvement of a Gα(i/o)-coupled adenosine receptor. Although agonists selective for adenosine receptors A1R, A2aR, and A2bR are ineffective, A3R-selective agonists Cl-IB-MECA and IB-MECA do accelerate the beat. Consistent with this pharmacological profile, the predominant Adora transcripts in the testis are products of the nested Adora3i1 and Adora3i2 genes. Surprisingly, Cl-IB-MECA and Cl-dAdo still accelerate the beat of Adora3i1-null sperm indicating that the remaining Adora3i2 transcript produces an A3R that functions in sperm. When cloned Adora3i2 is heterologously expressed in tsA-201 cells, Cl-dAdo decreases forskolin-evoked accumulation of cAMP, indicating that Adora3i2 specifies a functional A3Ri2 adenosine receptor that couples through Gα(i). Database mining reveals that mouse Adora3i2 is expressed primarily in testis, almost exclusively in spermatids. Expression of the orthologous ADORA3i3 transcript also is most prominent in human testis; presumably producing an A3Ri3 receptor that is functional in sperm and that may be a target for development of male-directed contraceptives.

Changes in expression and activity levels of ecto-5'-nucleotidase/CD73 along the mouse female estrous cycle

AIM

Extracellular ATP and its hydrolysis product adenosine modulate various reproductive functions such as those requiring contraction, hormone synthesis and maintenance of fluid composition. Moreover, adenosine is a key molecule for sperm capacitation. Extracellular nucleotide and nucleoside levels are affected by cell surface ectonucleotidases, amongst which the ectonucleoside triphosphate diphosphohydrolase (E-NTPDase) family is the most abundant and effective to hydrolyse ATP and ADP to AMP. In the female reproductive tract three members of this family have been recently identified: NTPDase1, NTPDase2 and NTPDase3 (Histochem. Cell Biol.131, 2009, 615). The purpose of the present study was to characterize in this system the expression profile of ecto-5'-nucleotidase (CD73), the enzyme generating adenosine from AMP.

METHODS

Immunological techniques and in situ enzymatic assays were used to characterize the ecto-5'-nucleotidase expression in the mouse female reproductive tract along the four stages of the estrous cycle, that were determined by vaginal smear examination.

RESULTS

Ecto-5'-nucleotidase was abundantly detected in the corpora lutea of the ovaries, as well as in several epithelia, such as that of oviducts, uterus and endometrial glands. Marked changes in endometrial ecto-5'-nucleotidase expression and activity along the estrous cycle are described, these being maximum at estrus phase, coinciding with optimal female sexual receptivity.

CONCLUSION

The adenosine generated thereby, besides other functions, might contribute to sperm capacitation, thus significantly influencing fertility.

Adenosine and Catecholamine Agonists Speed the Flagellar Beat of Mammalian Sperm by a Non-Receptor-Mediated Mechanism1

Activation of rapid motility apparently is one of the first steps of sperm capacitation and can be studied in vitro. Previously we found that 2-chloro-2'-deoxyadenosine or the catecholamine isoproterenol activates mouse sperm motility in vitro via a pathway mediated by cAMP that requires extracellular Ca2+, the atypical sperm adenylyl cyclase, and sperm-specific protein kinase A. We now show that several other adenosine analogs and catecholamines accelerate the flagellar beat of mouse and human sperm. Unexpectedly, the potent adenosine receptor agonist CGS21680 does not accelerate the beat, and the adenosine receptor antagonist DPCPX does not diminish the accelerating action of 2-chloro-2'-deoxyadenosine. The pharmacological profile for activation by catecholamines is also unusual. Both agonists and antagonists of beta-adrenergic receptors elevate the beat frequency. Moreover, both l-(-) and d-+ isomers of epinephrine, norepinephrine, and isoproterenol produce similar acceleration of the beat. In contrast, inhibitors of equilibrative nucleoside transporters effectively slow the onset of the accelerating action of adenosine analogs. Replacement of external Na+ with Li+ also diminishes the accumulation of cAMP and slows the resultant accelerating action of 2-chloro-2'-deoxyadenosine, suggesting the involvement of a Na+-dependent concentrative nucleoside transporter. Our results show that adenosine and catecholamine agonists act in a novel signaling pathway that does not involve G protein-coupled cell-surface receptors that link to conventional adenylyl cyclases. Instead, adenosine and analogs may be transported into sperm via equilibrative and concentrative nucleoside transporters to act on unknown intracellular targets.

Functionalized polymer colloids bearing primary amino groups

Polymer colloids are prepared via radicalic emulsion polymerisation of butylacrylate. Functionalization with amino groups is achieved by copolymerisation of 2-amino-ethylmethacrylates. In order to over-compensate the positive surface charges resulting from the amino groups additionally vinylbenzenesulfonic acid is copolymerized. The size of the resulting particles is controlled by the molar ratio of amino to sulfonic acid groups. The suitability of amino groups for coupling reactions is demonstrated by electrophilic addition of fluorescein-5-isothiocyanate. The resulting particles are characterized by dynamic light scattering and zeta potential measurements as well as by optical spectroscopy. The suitability of labelled particles for optical tracer experiments is demonstrated by fluorescence correlation spectroscopy.

The sperm, a neuron with a tail: 'neuronal' receptors in mammalian sperm

A number of plasma membrane receptor types originally thought to be specific to neurons have been found in other somatic cells. More surprisingly, the mammalian sperm and neuron appear to share many of these 'neuronal' receptors. The morphology, chromosome number, genomic activity, and functions of those two cell types are as unlike as any two cells in the body, but they both achieve their highly disparate goals with the aid of a number of the same receptors. Exocytosis in neurons and sperm is essential to the functions of these cells and is strongly influenced by similar receptors. 'Neuronal' receptor types in sperm may also play a role in the control of sperm motility (a function of course not shared by neurons). This review will consider the evidence for the presence of sperm plasma membrane 'neuronal' receptors and for their significance to mammalian sperm function. The persuasiveness of the evidence varies depending on the receptor being considered, but there is strong experimental support for the presence and importance of a number of 'neuronal' receptors in sperm.

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

Like somatic cells, mammalian spermatozoa appear to contain several different heterotrimeric G protein alpha-subunits that could mediate specialized cell responses. However, the precise Galpha subunits present, their subcellular location and their possible roles are still incompletely defined. In this study, using commercially available specific antibodies, we have shown by immunoblotting that Galpha(s) is present in human and mouse sperm lysates. Immunolocalization using intact spermatozoa from both species revealed this protein to be in the acrosomal cap region and the flagellum, particularly the principal piece. Treatment of permeabilized mouse spermatozoa with cholera toxin led to enhanced ADP-ribosylation of a protein the same size as Galpha(s), as well as an increase in cAMP, providing further proof for Galpha(s). Evidence for the presence and distinct localizations of Galpha(i2), Galpha(i3), Galpha(o), Galpha(q/11), and Galpha(olf) was also obtained. Of particular interest was Galpha(i2) which, like Galpha(s), was present in the acrosomal cap region and flagellum, the same regions where stimulatory and inhibitory adenosine receptors are localized. These observations are consistent with our hypothesis that G proteins mediate adenosine receptor modulation of adenylyl cyclase, with consequent alterations in cAMP production, apparently crucial for the spermatozoon's acquisition and maintenance of fertilizing ability.

Extracellular purines from cells of seminiferous tubules

It has been long postulated that extracellular purines can modulate the function of the male reproductive system by interacting with different purinergic receptors of Sertoli and germinative cells. Many authors have described the biological changes induced by extracellular ATP and/or adenosine in these cells, and some hypothetical models for paracrine communication mediated by purines were proposed; however, the cellular source(s) of these molecules in seminiferous tubules remains unknown. In this study, we demonstrated for the first time that Sertoli cells are able to release ATP (0.3 nmol/mg protein) and adenosine (0.1 nmol/mg protein) in the extracellular medium, while germinative and myoid peritubular cells are able to secrete adenosine (0.02 and 0.37 nmol/mg protein, respectively). Indeed, all the three types of cells were able to release inosine at significant concentrations (about 0.4 nmol/mg protein). This differential secretion depending on the cellular type suggests that these molecules may be involved in the paracrine regulation and/or control of the maturation processes of these cells.

Type II gonadotropin-releasing hormone receptor transcripts in human sperm

GnRH regulates reproduction via the well-characterized mammalian pituitary GnRH receptor (type I). In addition, two homologous genes for a second form of the GnRH receptor (type II) are present in the human genome, one on chromosome 14 and the second on chromosome 1. The chromosome 14 gene is ubiquitously transcribed at high levels in the antisense orientation but lacks exon 1, required to encode a full-length receptor. In comparison, the chromosome 1 gene contains all three exons. The issue of whether this gene is transcribed in any human tissue(s), and whether these transcripts encode a functional receptor protein, remains unresolved. We have directly addressed this by screening a panel of human RNAs by hybridization and RT-PCR. These analyses showed that, unlike the chromosome 14 gene, chromosome 1 gene expression is limited and of low abundance. Exon 1-containing transcripts were detected by in situ hybridization in mature sperm and in human postmeiotic testicular cells. Further sequence analysis revealed that although all the potential coding segments were present, the human transcripts, like the gene, contain a stop codon within the coding region and a frame-shift relative to other mammalian GnRH receptors. Although this suggests that the human gene may be a transcribed pseudogene, a functional type II GnRH receptor cDNA has recently been cloned from monkeys. Given the well-established role of GnRH in spermatogenesis and reported evidence of type II GnRH receptor immunoreactivity in human tissues, it is possible that the chromosome 1 gene is functional.

Capacitation state-dependent changes in adenosine receptors and their regulation of adenylyl cyclase/cAMP

This study was designed to localize adenosine receptors and to provide evidence that specific receptors are active only in either uncapacitated or capacitated mouse spermatozoa, where they play a role in regulating cAMP production. Using specific antibodies, stimulatory A(2A) receptors were localized primarily on the acrosomal cap region and the flagellar principal piece. Interestingly, the staining was much more pronounced in uncapacitated than in capacitated spermatozoa, suggesting capacitation-dependent changes in epitope accessibility. A(1) receptors showed a very similar distribution, but the staining was markedly greater in capacitated than in uncapacitated cells. After addition of purified decapacitation factor (DF) to capacitated cells, strong staining for A(2A) was regained, suggesting reversibility in epitope accessibility. Chlortetracycline analysis revealed that an agonist specific for A(2A) receptors had no detectable effect on capacitated cells, but after DF-induced decapacitation, the agonist then stimulated capacitation. That agonist also significantly stimulated cAMP production in uncapacitated cells, had no effect on capacitated cells, but regained the ability to stimulate cAMP in the latter following DF treatment. In contrast, an A(1) agonist inhibited cAMP in capacitated cells. These results indicate that specific adenosine receptors function in a reversible manner in one or other capacitation state, resulting in regulation of cAMP.

Stimulation by N6-Cyclopentyladenosine of A1 Adenosine Receptors, Coupled to Gαi2 Protein Subunit, Has a Capacitative Effect on Human Spermatozoa1

The effects of selective A(1) receptor agonist on human spermatozoa were examined to verify physiological responses and to investigate the signal transduction pathway. N6-Cyclopentyladenosine on uncapacitated spermatozoa did not induce spontaneous acrosome reaction after 5 h capacitation, whereas the number of capacitated spermatozoa, assessed by lysophosphatidylcholine-induced acrosome reaction with Pisum sativum agglutinin staining, was significantly increased. N6-Cyclopentyladenosine was also added to capacitated human spermatozoa to find out whether the agonist could induce the acrosome reaction. Results, although statistically significant, could not be considered biologically significant. A1-Mediated capacitation was followed by the increase of tyrosine phosphorylation of a protein subset ranging between M(r) = 200 000 and 30 000. Stimulation of A1 receptor with the selective agonist elicited an agonist-induced inositol phospholipid hydrolysis leading to a transient rise of inositol triphosphate (IP3). This increase was not induced by A(1) receptor antagonist and was blocked by phospholipase C inhibitor. Coimmunoprecipitation experiments showed that the A(1) receptor is coupled to Galphai2 subunit suggesting that the activation of phospholipase C is mediated by betagamma subunits. In conclusion, the A(1) adenosine receptor in human spermatozoa is coupled to Galphai2, signals via IP3, and affects the capacitative status of ejaculated spermatozoa.