Adenosine triphosphate induces Ca2+ signal in epithelial cells of the mouse caput epididymis through activation of P2X and P2Y purinergic receptors

Insights on Platelet-Derived Growth Factor Receptor α-Positive Interstitial Cells in the Male Reproductive Tract

Male infertility is a significant factor in approximately half of all infertility cases and is marked by a decreased sperm count and motility. A decreased sperm count is caused by not only a decreased production of sperm but also decreased numbers successfully passing through the male reproductive tract. Smooth muscle movement may play an important role in sperm transport in the male reproductive tract; thus, understanding the mechanism of this movement is necessary to elucidate the cause of sperm transport disorder. Recent studies have highlighted the presence of platelet-derived growth factor receptor α (PDGFRα)-positive interstitial cells (PICs) in various smooth muscle organs. Although research is ongoing, PICs in the male reproductive tract may be involved in the regulation of smooth muscle movement, as they are in other smooth muscle organs. This review summarizes the findings to date on PICs in male reproductive organs. Further exploration of the structural, functional, and molecular characteristics of PICs could provide valuable insights into the pathogenesis of male infertility and potentially lead to new therapeutic approaches.

Extracellular nucleotides in smooth muscle contraction

Extracellular nucleotides and nucleosides are crucial signalling molecules, eliciting diverse biological responses in almost all organs and tissues. These molecules exert their effects by activating specific nucleotide receptors, which are finely regulated by ectonucleotidases that break down their ligands. In this comprehensive review, we aim to elucidate the relevance of extracellular nucleotides as signalling molecules in the context of smooth muscle contraction, considering the modulatory influence of ectonucleotidases on this intricate process. Specifically, we provide a detailed examination of the involvement of extracellular nucleotides in the contraction of non-vascular smooth muscles, including those found in the urinary bladder, the airways, the reproductive system, and the gastrointestinal tract. Furthermore, we present a broader overview of the role of extracellular nucleotides in vascular smooth muscle contraction.

Released ATP Mediates Spermatozoa Chemotaxis Promoted by Uterus-Derived Factor (UDF) in Ascaris suum

Fertilization requires sperm migration toward oocytes and subsequent fusion. Sperm chemotaxis, a process in which motile sperm are attracted by factors released from oocytes or associated structures, plays a key role in sperm migration to oocytes. Here, we studied sperm chemotaxis in the nematode Ascaris suum. Our data show that uterus-derived factor (UDF), the protein fraction of uterine extracts, can attract spermatozoa. UDF is heat resistant, but its activity is attenuated by certain proteinases. UDF binds to the surface of spermatozoa but not spermatids, and this process is mediated by membranous organelles that fuse with the plasma membrane. UDF induces spermatozoa to release ATP from intracellular storage sites to the extracellular milieu, and extracellular ATP modulates sperm chemotaxis. Moreover, UDF increases protein serine phosphorylation (pS) levels in sperm, which facilitates sperm chemotaxis. Taken together, we revealed that both extracellular ATP and intracellular pS signaling are involved in Ascaris sperm chemotaxis. Our data provide insights into the mechanism of sperm chemotaxis in Ascaris suum.

Purinergic signaling in the male reproductive tract

Purinergic receptors are ubiquitously expressed throughout the body and they participate in the autocrine and paracrine regulation of cell function during normal physiological and pathophysiological conditions. Extracellular nucleotides activate several types of plasma membrane purinergic receptors that form three distinct families: P1 receptors are activated by adenosine, P2X receptors are activated by ATP, and P2Y receptors are activated by nucleotides including ATP, ADP, UTP, UDP, and UDP-glucose. These specific pharmacological fingerprints and the distinct intracellular signaling pathways they trigger govern a large variety of cellular responses in an organ-specific manner. As such, purinergic signaling regulates several physiological cell functions, including cell proliferation, differentiation and death, smooth muscle contraction, vasodilatation, and transepithelial transport of water, solute, and protons, as well as pathological pathways such as inflammation. While purinergic signaling was first discovered more than 90 years ago, we are just starting to understand how deleterious signals mediated through purinergic receptors may be involved in male infertility. A large fraction of male infertility remains unexplained illustrating our poor understanding of male reproductive health. Purinergic signaling plays a variety of physiological and pathophysiological roles in the male reproductive system, but our knowledge in this context remains limited. This review focuses on the distribution of purinergic receptors in the testis, epididymis, and vas deferens, and their role in the establishment and maintenance of male fertility.

Novel and differentially abundant microRNAs in sperm cells, seminal plasma, and serum of boars due to porcine reproduction and respiratory syndrome virus infection

The objectives of this study were to identify and determine relative abundance of miRNAs in boar sperm, seminal plasma (SP), and serum pre- and post-viral infection. Functional enrichment analyses on predicted targets of miRNAs of interest were performed. Boars (n = 6) were inoculated with porcine reproductive and respiratory syndrome virus (PRRSv) strain 1-8-4 (Day 0). Semen and serum were collected on Day -2 and 6. Sperm and SP were separated and aliquots were flash frozen and stored at -80 °C. Serum was frozen and stored at -80 °C. Total RNA was isolated from sperm and SP samples and subjected to RNA sequencing. Microarray analysis was performed using the Day -2 and 6 RNA samples from serum, sperm and SP. Potential miRNA targets were predicted using miRanda 3.3a and targets were then analyzed for enrichment of Gene Ontology) and InterPro terms and were considered to be enriched if P <  0.01 using the Bonferroni correction. Microarray analyses resulted in 83, 13, and 10 miRNAs with differences in abundances in sperm, serum, and SP, respectively, when comparing Day -2 and 6. Results from enrichment analyses indicated that the predicted targets of 35, nine, and five miRNAs with differences in abundances for sperm, SP, and serum, respectively, that have functions and/or conserved protein domains that are enriched when compared to the pig genome. Enriched terms for P2X purinoceptors were identified for sperm, SP and serum. Enriched terms for cell adhesion were identified for sperm and serum transcripts. Enriched terms for cell signaling were identified for sperm and SP transcripts.

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.

Establishment of cell-cell cross talk in the epididymis: control of luminal acidification

Male infertility is often caused by sperm that have low motility and interact poorly with the oocyte. Spermatozoa acquire these crucial functions in the epididymis. A low luminal bicarbonate (HCO(3)(-)) concentration and low pH keep sperm quiescent during their maturation and storage in this organ. This review describes how epididymal epithelial cells work in a concerted manner, together with spermatozoa, to establish and maintain this acidic luminal environment. Clear cells express the proton-pumping ATPase (V-ATPase) in their apical membrane and actively secrete protons. HCO(3)(-) induces V-ATPase accumulation in apical microvilli in clear cells via HCO(3)(-)-sensitive adenylyl cyclase-dependent cAMP production. HCO(3)(-) is secreted from principal cells following basolateral stimulation, to transiently "prime" spermatozoa before ejaculation. Luminal ATP and adenosine also induce V-ATPase apical accumulation in clear cells via activation of P2 and P1 receptors, respectively. ATP is released into the lumen from sperm and principal cells and is then metabolized into adenosine by local nucleotidases. In addition, the V-ATPase is regulated by luminal angiotensin II via activation of basal cells, which can extend narrow body projections that cross the tight junction barrier. Basal cells then secrete nitric oxide, which diffuses out to stimulate proton secretion in clear cells via activation of the cGMP pathway. Thus, an elaborate communication network is present between principal cells and clear cells, and between basal cells and clear cells, to control luminal acidification. Monitoring and decoding these "intercellular conversations" will help define pathophysiologic mechanisms underlying male infertility.

Role of purinergic signaling pathways in V-ATPase recruitment to apical membrane of acidifying epididymal clear cells

Extracellular purinergic agonists regulate a broad range of physiological functions via P1 and P2 receptors. Using the epididymis as a model system in which luminal acidification is essential for sperm maturation and storage, we show here that extracellular ATP and its hydrolysis product adenosine trigger the apical accumulation of vacuolar H(+)-ATPase (V-ATPase) in acidifying clear cells. We demonstrate that the epididymis can hydrolyze luminal ATP into other purinergic agonists such as ADP via the activity of nucleotidases located in the epididymal fluid and in the apical membrane of epithelial cells. Alkaline phosphatase activity and abundant ecto-5'-nucleotidase protein were detected in the apical pole of principal cells. In addition, we show that nine nucleotidase genes (Nt5e, Alpl, Alpp, Enpp1, 2, and 3, and Entpd 2, 4, and 5), seven ATP P2 receptor genes (P2X1, P2X2, P2X3, P2X4, P2X6, P2Y2, P2Y5), and three adenosine P1 receptor genes (A1, A2B, and A3) are expressed in epithelial cells isolated by laser cut microdissection (LCM). The calcium chelator BAPTA-AM abolished the apical V-ATPase accumulation induced by ATP, supporting the contribution of P2X or P2Y in this response. The PKA inhibitor myristoylated protein kinase inhibitor (mPKI) inhibited adenosine-dependent V-ATPase apical accumulation, indicating the participation of the P1 A2B receptor. Altogether, these results suggest that the activation of P1 and P2 purinergic receptors by ATP and adenosine might play a significant role in luminal acidification in the epididymis, a process that is crucial for the establishment of male fertility.

Localization of plasma membrane bound NTPDases in the murine reproductive tract

Extracellular nucleotides might influence aspects of the biology of reproduction in that ATP affects smooth muscle contraction, participates in steroidogenesis and spermatogenesis, and also regulates transepithelial transport, as in oviducts. Activation of cellular nucleotide purinergic receptors is influenced by four plasma membrane-bound members of the ectonucleoside triphosphate diphosphohydrolase (E-NTPDase) family, namely NTPDase1, NTPDase2, NTPDase3, and NTPDase8 that differ in their ecto-enzymatic properties. The purpose of this study was to characterize the expression profile of the membrane-bound NTPDases in the murine female and male reproductive tracts by immunological techniques (immunolabelling, Western blotting) and by enzymatic assays, in situ and on tissue homogenates. Other than the expected expression on vascular endothelial and smooth muscle cells, NTPDase1 was also detected in Sertoli cells and interstitial macrophages in testes, in ovarian granulosa cells, and in apical cells from epididymal epithelium. NTPDase2 was largely expressed by cells in the connective tissue; NTPDase3 in secretory epithelia, and finally, NTPDase8 was not detected in any of the tissues studied here. In addition, NTPDase6 was putatively detected in Golgi-phase acrosome vesicles of round spermatids. This descriptive study suggests close regulation of extracellular nucleotide levels in the genital tract by NTPDases that may impact specific biological functions.

Extracellular adenosine 5'-triphosphate alters motility and improves the fertilizing capability of mouse sperm

Extracellular adenosine 5'-triphosphate (ATPe) treatment of human sperm has been implicated in improving in vitro fertilization (IVF) results. We used the mouse model to investigate mechanisms of action of ATPe on sperm. ATPe treatment significantly enhanced IVF success as indicated by both rate of pronuclear formation and percentage cleavage to the 2-cell stage. However, ATPe did not increase the percentage of sperm undergoing spontaneous acrosomal exocytosis nor change the pattern of protein tyrosine phosphorylation normally observed in capacitated sperm. ATPe altered sperm motility parameters; in particular, both noncapacitated and capacitated sperm swam faster and straighter. The percentage of hyperactivated sperm did not increase in capacitated ATPe-treated sperm compared to control sperm. ATPe induced a rapid increase in the level of intracellular calcium that was inhibited by two distinct P2 purinergic receptor inhibitors, confirming that these receptors have an ionotropic role in sperm function. The observed motility changes likely explain, in part, the improved fertilizing capability when ATPe-treated sperm were used in IVF procedures and suggest a mechanism by which ATPe treatment may be beneficial for artificial reproductive techniques.

Functional expression of ionotropic purinergic receptors on mouse taste bud cells

Neurotransmitter receptors on taste bud cells (TBCs) and taste nerve fibres are likely to contribute to taste transduction by mediating the interaction among TBCs and that between TBCs and taste nerve fibres. We investigated the functional expression of P2 receptor subtypes on TBCs of mouse fungiform papillae. Electrophysiological studies showed that 100 microm ATP applied to their basolateral membranes either depolarized or hyperpolarized a few cells per taste bud. Ca(2+) imaging showed that similarly applied 1 mum ATP, 30 microm BzATP (a P2X(7) agonist), or 1 microm 2MeSATP (a P2Y(1) and P2Y(11) agonist) increased intracellular Ca(2+) concentration, but 100 microm UTP (a P2Y(2) and P2Y(4) agonist) and alpha,beta-meATP (a P2X agonist except for P2X(2), P2X(4) and P2X(7)) did not. RT-PCR suggested the expression of P2X(2), P2X(4), P2X(7), P2Y(1), P2Y(13) and P2Y(14) among the seven P2X subtypes and seven P2Y subtypes examined. Immunohistostaining confirmed the expression of P2X(2). The exposure of the basolateral membranes to 3 mm ATP for 30 min caused the uptake of Lucifer Yellow CH in a few TBCs per taste bud. This was antagonized by 100 microm PPADS (a non-selective P2 blocker) and 1 microm KN-62 (a P2X(7) blocker). These results showed for the first time the functional expression of P2X(2) and P2X(7) on TBCs. The roles of P2 receptor subtypes in the taste transduction, and the renewal of TBCs, are discussed.

Physiology and pathophysiology of purinergic neurotransmission

This review is focused on purinergic neurotransmission, i.e., ATP released from nerves as a transmitter or cotransmitter to act as an extracellular signaling molecule on both pre- and postjunctional membranes at neuroeffector junctions and synapses, as well as acting as a trophic factor during development and regeneration. Emphasis is placed on the physiology and pathophysiology of ATP, but extracellular roles of its breakdown product, adenosine, are also considered because of their intimate interactions. The early history of the involvement of ATP in autonomic and skeletal neuromuscular transmission and in activities in the central nervous system and ganglia is reviewed. Brief background information is given about the identification of receptor subtypes for purines and pyrimidines and about ATP storage, release, and ectoenzymatic breakdown. Evidence that ATP is a cotransmitter in most, if not all, peripheral and central neurons is presented, as well as full accounts of neurotransmission and neuromodulation in autonomic and sensory ganglia and in the brain and spinal cord. There is coverage of neuron-glia interactions and of purinergic neuroeffector transmission to nonmuscular cells. To establish the primitive and widespread nature of purinergic neurotransmission, both the ontogeny and phylogeny of purinergic signaling are considered. Finally, the pathophysiology of purinergic neurotransmission in both peripheral and central nervous systems is reviewed, and speculations are made about future developments.

Estradiol inhibits the effects of extracellular ATP in human sperm by a non genomic mechanism of action

Steroid hormones, beside their classical genomic mechanism of action, exert rapid, non genomic effects in different cell types. These effects are mediated by still poorly characterized plasma membrane receptors that appear to be distinct from the classic intracellular receptors. In the present study we evaluated the non genomic effects of estradiol (17βE₂) in human sperm and its effects on sperm stimulation by extracellular ATP, a potent activator of sperm acrosome reaction. In human sperm 17βE₂ induced a rapid increase of intracellular calcium (Ca²⁺) concentrations dependent on an influx of Ca²⁺ from the extracellular medium. The monitoring of the plasma membrane potential variations induced by 17βE₂ showed that this steroid induces a rapid plasma membrane hyperpolarization that was dependent on the presence of Ca²⁺ in the extracellular medium since it was absent in Ca²⁺ free-medium. When sperm were pre-incubated in the presence of the K⁺ channel inhibitor tetra-ethylammonium, the 17βE₂ induced plasma membrane hyperpolarization was blunted suggesting the involvement of K⁺ channels in the hyperpolarizing effects of 17βE₂. Extracellular ATP induced a rapid plasma membrane depolarization followed by acrosome reaction. Sperm pre-incubation with 17βE₂ inhibited the effects of extracellular ATP on sperm plasma membrane potential variations and acrosome reaction. The effects of 17βE₂ were specific since its inactive steroisomer 17αE₂ was inactive. Furthermore the effects of 17βE₂ were not inhibited by tamoxifen, an antagonist of the classic 17βE₂ intracellular receptor.

Smooth muscle and purinergic contraction of the human, rabbit, rat, and mouse testicular capsule

The smooth-muscle cells of the testicular capsule (tunica albuginea) of man, rat, and mouse were examined by electron microscopy. They were characteristically flattened, elongated, branching cells and diffusely incorporated into the collagenous matrix and did not form a compact muscle layer. Contractile and synthetic smooth-muscle cell phenotypes were identified. Nerve varicosities in close apposition to smooth muscle were seen in human tissue. Contractions induced by adenosine 5'-triphosphate (ATP), alpha, beta-methylene ATP, noradrenaline (NA), acetylcholine (ACh), and electrical field stimulation (EFS) of autonomic nerves were investigated. Nerve-mediated responses of the rabbit and human tunica albuginea were recorded. The EFS-induced human responses were completely abolished by prazosin. In the rabbit, EFS-induced contractile responses were reduced by pyridoxalphosphate-6-azophenyl-2',4'-disulphonic acid by 36% and by prazosin by 77%. Both antagonists together almost completely abolished all EFS-induced contractions. The human tunica albuginea was contracted by NA, ATP, and alpha, beta-methylene ATP, but not by ACh. The rabbit and rat tunica albuginea were contracted by NA, ATP, alpha, beta-methylene ATP, and ACh. The mouse tunica albuginea was contracted by ACh, ATP, and alpha, beta-methylene ATP, but relaxed to NA. Immunohistochemical studies showed that P2X1 (also known as P2RX1) and P2X2 (also known as P2RX2) receptors were expressed on the smooth muscle of the rodent testicular capsule, expression being less pronounced in man. The testicular capsule of the rat, mouse, rabbit, and man all contain contractile smooth muscle. ATP, released as a cotransmitter from sympathetic nerves, can stimulate the contraction of rabbit smooth muscle. Human, rat, and mouse testicular smooth muscle demonstrated purinergic responsiveness, probably mediated through the P2X1 and/or P2X2 receptors.

P2Y receptors play a critical role in epithelial cell communication and migration

Cellular injury induces a complex series of events that involves Ca2+ signaling, cell communication, and migration. One of the first responses following mechanical injury is the propagation of a Ca2+ wave (Klepeis et al. [2001] J Cell Sci 114(Pt 23):4185-4195). The wave is generated by the extracellular release of ATP, which also induces phosphorylation of ERK (Yang et al. [2004] J Cell Biochem 91(5):938-950). ATP and other nucleotides, which bind to and activate specific purinergic receptors were used to mimic injury. Our goal was to determine which of the P2Y purinergic receptors are expressed and stimulated in corneal epithelial cells and which signaling pathways are activated leading to changes in cell migration, an event critical for wound closure. In this study, we demonstrated that the P2Y1, P2Y2, P2Y4, P2Y6, and P2Y11 receptors were present in corneal epithelial cells. A potency profile was determined by Ca2+ imaging for nucleotide agonists as follows: ATP > or = UTP > ADP > or = UDP. In contrast, negligible responses were seen for beta,gamma-meATP, a general P2X receptor agonist and adenosine, a P1 receptor agonist. Homologous desensitization of the Ca2+ response was observed for the four nucleotides. However, P2Y receptor internalization and degradation was not detected following stimulation with ATP, which is in contrast to EGFR internalization observed in response to EGF. ATP induced cell migration was comparable to that of EGF and was maximal at 1 microM. Cells exposed to ATP, UTP, ADP, and UDP demonstrated a rapid twofold increase in phosphorylation of paxillin at Y31 and Y118, however, there was no activation elicited by beta,gamma-meATP or adenosine. Additional studies demonstrated that wound closure was inhibited by reactive blue 2. These results indicate that P2Y receptors play a critical role in the injury repair process.

Cellular Distribution and Functions of P2 Receptor Subtypes in Different Systems

This review is aimed at providing readers with a comprehensive reference article about the distribution and function of P2 receptors in all the organs, tissues, and cells in the body. Each section provides an account of the early history of purinergic signaling in the organ?cell up to 1994, then summarizes subsequent evidence for the presence of P2X and P2Y receptor subtype mRNA and proteins as well as functional data, all fully referenced. A section is included describing the plasticity of expression of P2 receptors during development and aging as well as in various pathophysiological conditions. Finally, there is some discussion of possible future developments in the purinergic signaling field.