Extracellular adenine nucleotides inhibit the activation of human CD4+ T lymphocytes

Glycolysis: A multifaceted metabolic pathway and signaling hub

Glycolysis is a highly conserved metabolic pathway responsible for the anaerobic production of adenosine triphosphate (ATP) from the breakdown of glucose molecules. While serving as a primary metabolic pathway in prokaryotes, glycolysis is also utilized by respiring eukaryotic cells, providing pyruvate to fuel oxidative metabolism. Furthermore, glycolysis is the primary source of ATP production in multiple cellular states (e.g., hypoxia) and is particularly important in maintaining bioenergetic homeostasis in the most abundant cell type in the human body, the erythrocyte. Beyond its role in ATP production, glycolysis also functions as a signaling hub, producing several metabolic intermediates which serve roles in both signaling and metabolic processes. These signals emanating from the glycolytic pathway can profoundly impact cell function, phenotype, and fate and have previously been overlooked. In this review, we will discuss the role of the glycolytic pathway as a source of signaling molecules in eukaryotic cells, emphasizing the newfound recognition of glycolysis' multifaceted nature and its importance in maintaining cellular homeostasis, beyond its traditional role in ATP synthesis.

P2Y4, P2Y6 and P2Y11 receptors: From the early days of cloning to their function

The family of P2Y nucleotide receptors is composed of eight members differentiated by their pharmacology and their coupling to specific G-proteins and transduction mechanisms. The laboratory studying these nucleotide receptors at IRIBHM institute (Free University of Brussels) has participated actively in their cloning. We used classical cloning by homology strategies relying on polymerase chain reactions with degenerate primers or on DNA libraries screening with P2Y receptors-related primers or probes, respectively. We identified and characterised four of the eight human P2Y receptors cloned so far: P2Y₄, P2Y₆, P2Y₁₁ and P2Y₁₃ receptors. These human receptors displayed specific features in terms of pharmacology such as affinity for pyrimidine nucleotides for P2Y₄ and P2Y₆ receptors and differential G-protein coupling. Their specific and restricted tissue distribution compared to ubiquitous P2Y₁ and P2Y₂ receptors led us to study their physiological role in chosen cell systems or using mice deficient for these P2Y subtypes. These studies revealed over the years that the P2Y₁₁ receptor was able to confer tolerogenic and tumorigenic properties to human dendritic cells and that P2Y₄ and P2Y₆ receptors were involved in mouse heart post-natal development and cardioprotection. P2Y receptors and their identified target genes could constitute therapeutic targets to regulate cardiac hypertrophy and regeneration. The multiple roles of P2Y receptors identified in the ischemic heart and cardiac adipose tissue could have multiple innovative clinical applications and present a major interest in the field of cardiovascular diseases. P2Y receptors can induce cardioprotection by the regulation of cardiac inflammation and the modulation of the volume and composition of cardiac adipose tissue. These findings might lead to the pre-clinical validation of P2Y receptors as new targets for the treatment of myocardial ischemia.

Triple‑negative breast cancer therapy: Current and future perspectives (Review)

Triple-negative breast cancer (TNBC) accounts for 10-15% of all breast cancer cases. TNBCs lack estrogen and progesterone receptors and express low levels of HER2, and therefore do not respond to hormonal or anti-HER2 therapies. TNBC is a particularly aggressive form of breast cancer that generally displays poorer prognosis compared to other breast cancer subtypes. TNBC is chemotherapy sensitive, and this treatment remains the standard of care despite its limited benefit. Recent advances with novel agents have been made for specific subgroups with PD-L1⁺ tumors or germline Brca-mutated tumors. However, only a fraction of these patients responds to immune checkpoint or PARP inhibitors and even those who do respond often develop resistance and relapse. Various new agents and combination strategies have been explored to further understand molecular and immunological aspects of TNBC. In this review, we discuss clinical trials in the management of TNBC as well as perspectives for potential future treatments.

The purinergic receptor P2Y11 choreographs the polarization, mitochondrial metabolism, and migration of T lymphocytes

T cells must migrate to encounter antigen-presenting cells and perform their roles in host defense. Here, we found that autocrine stimulation of the purinergic receptor P2Y11 regulates the migration of human CD4 T cells. P2Y11 receptors redistributed from the front to the back of polarized cells where they triggered intracellular cAMP/PKA signals that attenuated mitochondrial metabolism at the back. The absence of P2Y11 receptors at the front of cells resulted in hotspots of mitochondrial metabolism and localized ATP production that stimulated P2X4 receptors, Ca²⁺ influx, and pseudopod protrusion at the front. This regulatory function of P2Y11 receptors depended on their subcellular redistribution and autocrine stimulation by cellular ATP release and was perturbed by indiscriminate global stimulation. We conclude that excessive extracellular ATP-such as in response to inflammation, sepsis, and cancer-disrupts this autocrine feedback mechanism, which results in defective T cell migration, impaired T cell function, and loss of host immune defense.

Targeting Adenosine in Cancer Immunotherapy to Enhance T-Cell Function

T cells play a critical role in cancer control, but a range of potent immunosuppressive mechanisms can be upregulated in the tumor microenvironment (TME) to abrogate their activity. While various immunotherapies (IMTs) aiming at re-invigorating the T-cell-mediated anti-tumor response, such as immune checkpoint blockade (ICB), and the adoptive cell transfer (ACT) of natural or gene-engineered ex vivo expanded tumor-specific T cells, have led to unprecedented clinical responses, only a small proportion of cancer patients benefit from these treatments. Important research efforts are thus underway to identify biomarkers of response, as well as to develop personalized combinatorial approaches that can target other inhibitory mechanisms at play in the TME. In recent years, adenosinergic signaling has emerged as a powerful immuno-metabolic checkpoint in tumors. Like several other barriers in the TME, such as the PD-1/PDL-1 axis, CTLA-4, and indoleamine 2,3-dioxygenase (IDO-1), adenosine plays important physiologic roles, but has been co-opted by tumors to promote their growth and impair immunity. Several agents counteracting the adenosine axis have been developed, and pre-clinical studies have demonstrated important anti-tumor activity, alone and in combination with other IMTs including ICB and ACT. Here we review the regulation of adenosine levels and mechanisms by which it promotes tumor growth and broadly suppresses protective immunity, with extra focus on the attenuation of T cell function. Finally, we present an overview of promising pre-clinical and clinical approaches being explored for blocking the adenosine axis for enhanced control of solid tumors.

Lipopolysaccharide suppresses T cells by generating extracellular ATP that impairs their mitochondrial function via P2Y11 receptors

T cell suppression contributes to immune dysfunction in sepsis. However, the underlying mechanisms are not well-defined. Here, we show that exposure of human peripheral blood mononuclear cells to bacterial lipopolysaccharide (LPS) can rapidly and dose-dependently suppress interleukin-2 (IL-2) production and T cell proliferation. We also report that these effects depend on monocytes. LPS did not prevent the interaction of monocytes with T cells, nor did it induce programmed cell death protein 1 (PD-1) signaling that causes T cell suppression. Instead, we found that LPS stimulation of monocytes led to the accumulation of extracellular ATP that impaired mitochondrial function, cell migration, IL-2 production, and T cell proliferation. Mechanistically, LPS-induced ATP accumulation exerted these suppressive effects on T cells by activating the purinergic receptor P2Y11 on the cell surface of T cells. T cell functions could be partially restored by enzymatic removal of extracellular ATP or pharmacological blocking of P2Y11 receptors. Plasma samples obtained from sepsis patients had similar suppressive effects on T cells from healthy subjects. Our findings suggest that LPS and ATP accumulation in the circulation of sepsis patients suppresses T cells by promoting inappropriate P2Y11 receptor stimulation that impairs T cell metabolism and functions. We conclude that inhibition of LPS-induced ATP release, removal of excessive extracellular ATP, or P2Y11 receptor antagonists may be potential therapeutic strategies to prevent T cell suppression and restore host immune function in sepsis.

Purinergic regulation of the immune system

Cellular stress or apoptosis triggers the release of ATP, ADP and other nucleotides into the extracellular space. Extracellular nucleotides function as autocrine and paracrine signalling molecules by activating cell-surface P2 purinergic receptors that elicit pro-inflammatory immune responses. Over time, extracellular nucleotides are metabolized to adenosine, leading to reduced P2 signalling and increased signalling through anti-inflammatory adenosine (P1 purinergic) receptors. Here, we review how local purinergic signalling changes over time during tissue responses to injury or disease, and we discuss the potential of targeting purinergic signalling pathways for the immunotherapeutic treatment of ischaemia, organ transplantation, autoimmunity or cancer.

A critical look at the function of the P2Y11 receptor

The P2Y11 receptor is a member of the purinergic receptor family. It has been overlooked, somewhat due to the lack of a P2ry11 gene orthologue in the murine genome, which prevents the generation of knockout mice, which have been so helpful for defining the roles of other P2Y receptors. Furthermore, some of the studies reported to date have methodological shortcomings, making it difficult to determine the function of P2Y11 with certainty. In this review, we discuss the lack of a murine "P2Y11-like receptor" and highlight the limitations of the currently available methods used to investigate the P2Y11 receptor. These methods include protein recognition with antibodies that show very little specificity, gene expression studies that completely overlook the existence of a fusion transcript between the adjacent PPAN gene and P2RY11, and agonists/antagonists reported to be specific for the P2Y11 receptor but which have not been tested for activity on numerous other adenosine 5'-triphosphate (ATP)-binding receptors. We suggest a set of criteria for evaluating whether a dataset describes effects mediated by the P2Y11 receptor. Following these criteria, we conclude that the current evidence suggests a role for P2Y11 in immune activation with cell type-specific effects.

CD39 expression on Treg and Th17 cells is associated with metabolic factors in patients with type 2 diabetes

Th17 cells are involved in the pathogenesis of multiple inflammatory diseases such as type two diabetes (T2D). CD39(+) Treg cells have been implicated as responsible for suppressing Th17 cells. The aim of this study was to evaluate the number and function of CD4(+)CD25(high)CD39(+) Treg and Th17 cells in peripheral blood mononuclear cells (PBMC) from T2D patients and healthy control subjects. The Th17 cells were detected in PBMC under culture with human anti-CD3/CD28 and PMA/ionomycin and the levels of IL-17 were assessed by ELISA and qPCR. The T2D patients with obesity showed significantly lower percentages of CD39(+) Treg cells. A negative correlation between CD39(+) Treg cells and weight, and body mass index was detected. In contrast, the low levels of CD4(+)IL-17(+) cells in overweight and obese T2D patients showed a positive correlation with glucose and HbA1c. Additionally, we found a subpopulation of Th17 cells that express CD39 and were correlated with glucose and HbA1c. Our findings suggest that the expression of CD39 on Treg cells and also in CD4(+)IL-17(+) cells from T2D patients is related to hyperglycemia as well as to overweight and obesity and therefore may participate as a modulator of the effector capacity of Th17 cells.

Purinergic signalling and immune cells

This review article provides a historical perspective on the role of purinergic signalling in the regulation of various subsets of immune cells from early discoveries to current understanding. It is now recognised that adenosine 5'-triphosphate (ATP) and other nucleotides are released from cells following stress or injury. They can act on virtually all subsets of immune cells through a spectrum of P2X ligand-gated ion channels and G protein-coupled P2Y receptors. Furthermore, ATP is rapidly degraded into adenosine by ectonucleotidases such as CD39 and CD73, and adenosine exerts additional regulatory effects through its own receptors. The resulting effect ranges from stimulation to tolerance depending on the amount and time courses of nucleotides released, and the balance between ATP and adenosine. This review identifies the various receptors involved in the different subsets of immune cells and their effects on the function of these cells.

Purinergic signaling in inflammatory cells: P2 receptor expression, functional effects, and modulation of inflammatory responses

Extracellular ATP and related nucleotides promote a wide range of pathophysiological responses via activation of cell surface purinergic P2 receptors. Almost every cell type expresses P2 receptors and/or exhibit regulated release of ATP. In this review, we focus on the purinergic receptor distribution in inflammatory cells and their implication in diverse immune responses by providing an overview of the current knowledge in the literature related to purinergic signaling in neutrophils, macrophages, dendritic cells, lymphocytes, eosinophils, and mast cells. The pathophysiological role of purinergic signaling in these cells include among others calcium mobilization, actin polymerization, chemotaxis, release of mediators, cell maturation, cytotoxicity, and cell death. We finally discuss the therapeutic potential of P2 receptor subtype selective drugs in inflammatory conditions.

Extracellular ATP exerts opposite effects on activated and regulatory CD4+ T cells via purinergic P2 receptor activation

It has been reported that ATP inhibits or stimulates lymphoid cell proliferation depending on the cellular subset analyzed. In this study, we show that ATP exerts strikingly opposite effects on anti-CD3/CD28-activated and regulatory CD4(+) T cells (T(regs)), based on nucleotide concentration. We demonstrate that physiological concentrations of extracellular ATP (1-50 nM) do not affect activated CD4(+) T cells and T(regs). Conversely, higher ATP concentrations have a bimodal effect on activated CD4(+) T cells. Whereas 250 nM ATP stimulates proliferation, cytokine release, expression of adhesion molecules, and adhesion, 1 mM ATP induces apoptosis and inhibits activated CD4(+) T cell functions. The expression analysis and pharmacological profile of purinergic P2 receptors for extracellular nucleotides suggest that activated CD4(+) T cells are induced to apoptosis via the upregulation and engagement of P2X7R and P2X4R. On the contrary, 1 mM ATP enhances proliferation, adhesion, migration, via P2Y2R activation, and immunosuppressive ability of T(regs). Similar results were obtained when activated CD4(+) T cells and T(regs) were exposed to ATP released by necrotized leukemic cells. Taken together, our results show that different concentrations of extracellular ATP modulate CD4(+) T cells according to their activated/regulatory status. Because extracellular ATP concentration highly increases in fast-growing tumors or hyperinflamed tissues, the manipulation of purinergic signaling might represent a new therapeutic target to shift the balance between activated CD4(+) T cells and T(regs).

Immunoregulation through extracellular nucleotides

Extracellular ATP (eATP), the most abundant among nucleotides, can act as a mediator during inflammatory responses by binding to plasmamembrane P2 purinergic receptors, which are widely expressed on cells of the immune system. eATP is generally considered as a classical danger signal, which stimulates immune responses in the presence of tissue damage. Converging evidence from several studies using murine models of chronic inflammation have supported this hypothesis; however, the role of eATP in the regulation of human immune function appears to be more complex. Chronic stimulation with micromolar eATP concentrations inhibits the proliferation of T and NK lymphocytes and enhances the capacity of dendritic cells to promote tolerance. The effect of eATP depends on multiple factors, such as the extent of stimulation, eATP concentration, presence/absence of other mediators in the microenvironment, and pattern of P2 receptor engagement. Small but significant differences in the pattern of P2 receptor expression in mice and humans confer the diverse capacities of ATP in regulating the immune response. Such diversity, which is often overlooked, should therefore be carefully considered when evaluating the role of eATP in human inflammatory and autoimmune diseases.

Nicotine alters the ectonucleotidases activities in lymphocytes: In vitro and in vivo studies

The aim of the present study was to investigate the effects in vivo and in vitro of nicotine, an important immunosuppressive agent, on NTPDase and ADA activities in lymphocytes of adult rats. The following nicotine doses in vivo study were evaluated: 0.0, 0.25 and 1.0mg/kg/day injected subcutaneously in rats for 10days. The activity of the enzymes were significantly decreased with nicotine 0.25 and 1mg/kg which inhibited ATP (22%, 54%), ADP (44%, 30%) hydrolysis and adenosine (43%, 34%) deamination, respectively. The expression of the protein NTPDase in rat lymphocytes was decreased to nicotine 1mg/kg and the lymphocytes count was decreased in both nicotine doses studied. The purine levels measured in serum of the rats treated with nicotine 0.25mg/kg significantly increased to ATP (39%), ADP (39%) and adenosine (303%). The nicotine exposure marker was determinate by level of cotinine level which significantly increased in rats treated with nicotine 0.25 (39%) and 1mg/kg (131%) when compared to rats that received only saline. The second set of study was in vitro assay which the ATP-ADP-adenosine hydrolysis were decreased by nicotine concentrations 1mM (0% - 0% - 16%, respectively), 5mM (42% - 32% - 74%, respectively), 10mM (80% - 27% - 80%, respectively) and 50mM (96% - 49% - 98%, respectively) when compared with the control group. We suggest that alterations in the activities of these enzymes may contribute to the understanding of the mechanisms involved in the suppression of immune response caused by nicotine.

Stat3 and Gfi-1 transcription factors control Th17 cell immunosuppressive activity via the regulation of ectonucleotidase expression

Although Th17 cells are known to promote tissue inflammation and autoimmunity, their role during cancer progression remains elusive. Here, we showed that in vitro Th17 cells generated with the cytokines IL-6 and TGF-β expressed CD39 and CD73 ectonucleotidases, leading to adenosine release and the subsequent suppression of CD4(+) and CD8(+) T cell effector functions. The IL-6-mediated activation of the transcription factor Stat3 and the TGF-β-driven downregulation of Gfi-1 transcription factor were both essential for the expression of ectonucleotidases during Th17 cell differentiation. Stat3 supported whereas Gfi-1 repressed CD39 and CD73 expression by binding to their promoters. Accordingly, Th17 cells differentiated with IL-1β, IL-6, and IL-23 but without TGF-β did not express ectonucleotidases and were not immunosuppressive. Finally, adoptive transfer of Th17 cells induced by TGF-β and IL-6 promoted tumor growth in a CD39-dependent manner. Thus, ectonucleotidase expression supports the immunosuppressive fate of Th17 cells in cancer.

The therapeutic potential of adenosine triphosphate as an immune modulator in the treatment of HIV/AIDS: a combination approach with HAART

Extracellular adenosine triphosphate (eATP) is a potent molecule that has the capacity to modulate various aspects of cell functions including gene expression. This element of modulation is essential to the role of ATP as a therapeutic agent. The hypothesis presented is that ATP can have an important impact on the treatment of HIV infection. This is supported in part by published research, although a much greater role for ATP is suggested than prior authors ever thought possible. ATP has the ability to enhance the immune system and could thus improve the host's own defense mechanisms to eradicate the virus-infected cells and restore normal immune function. This could provide effective therapy when used in conjunction with highly active antiretroviral therapies (HAART) to eliminate the latently infected cells. The key lies in applying ATP through the methodology described. This article presents a strategy for using ATP therapeutically along with background evidence to substantiate the importance of using ATP in the treatment of HIV infection.

Immune cell regulation by autocrine purinergic signalling

Stimulation of almost all mammalian cell types leads to the release of cellular ATP and autocrine feedback through a diverse array of purinergic receptors. Depending on the types of purinergic receptors that are involved, autocrine signalling can promote or inhibit cell activation and fine-tune functional responses. Recent work has shown that autocrine signalling is an important checkpoint in immune cell activation and allows immune cells to adjust their functional responses based on the extracellular cues provided by their environment. This Review focuses on the roles of autocrine purinergic signalling in the regulation of both innate and adaptive immune responses and discusses the potential of targeting purinergic receptors for treating immune-mediated disease.

Common variants in P2RY11 are associated with narcolepsy

Growing evidence supports the hypothesis that narcolepsy with cataplexy is an autoimmune disease. We here report genome-wide association analyses for narcolepsy with replication and fine mapping across three ethnic groups (3,406 individuals of European ancestry, 2,414 Asians and 302 African Americans). We identify a SNP in the 3' untranslated region of P2RY11, the purinergic receptor subtype P2Y₁₁ gene, which is associated with narcolepsy (rs2305795, combined P = 6.1 × 10⁻¹⁰, odds ratio = 1.28, 95% CI 1.19-1.39, n = 5689). The disease-associated allele is correlated with reduced expression of P2RY11 in CD8(+) T lymphocytes (339% reduced, P = 0.003) and natural killer (NK) cells (P = 0.031), but not in other peripheral blood mononuclear cell types. The low expression variant is also associated with reduced P2RY11-mediated resistance to ATP-induced cell death in T lymphocytes (P = 0.0007) and natural killer cells (P = 0.001). These results identify P2RY11 as an important regulator of immune-cell survival, with possible implications in narcolepsy and other autoimmune diseases.

P2Y receptors in health and disease

The purine- and pyrimidine-sensitive P2Y receptors belong to the large group of G-protein-coupled receptors that are the target of approximately one-third of the pharmaceutical drugs used in the clinic today. It is therefore not unexpected that the P2Y receptors could be useful targets for drug development. This chapter will discuss P2Y receptor-based therapies currently used, in development and possible future developments. The platelet inhibitors blocking the ADP-receptor P2Y(12) reduce myocardial infarction, stroke, and mortality in patients with cardiovascular disease. Clopidogrel (Plavix) was for many years the second most selling drug in the world. The improved P2Y(12) inhibitors prasugrel, ticagrelor, and elinogrel are now entering the clinic with even more pronounced protective effects. The UTP-activated P2Y(2) receptor stimulates ciliary movement and secretion from epithelial cells. Cystic fibrosis is a monogenetic disease where reduced chloride ion secretion results in a severe lung disease and early death. No specific treatment has been available, but the P2Y(2) agonist Denufosol has been shown to improve lung function and is expected to be introduced as treatment for cystic fibrosis soon. In preclinical studies, there are indications that P2Y receptors can be important for diabetes, osteoporosis, cardiovascular, and atherosclerotic disease. In conclusion, P2Y receptors are important for the health of humans for many diseases, and we can expect even more beneficial drugs targeting P2Y receptors in the future.

Real-time monitoring of suspension cell-cell communication using an integrated microfluidics

For the first time, we have developed a microfluidic device for on-chip monitoring of suspension cell-cell communication from stimulated to recipient HL-60 cells. A deformable PDMS membrane was developed as a compressive component to perform cell entrapment and exert different modes of mechanical stimulation. The number of cells trapped by this component could be modulated by flushing excessive cells towards the device outlet. The trapped cells could be triggered to release mediators by mechanical stimulation. Sandbag microstructures were used to immobilize recipient cells at well-defined positions. These recipient cells were evoked by mediators released from mechanically stimulated cells trapped in the compressive component. Normally closed microvalves were integrated to provide continuous-flow and static environment. We studied cell-cell communication between stimulated (in compressive component) and recipient (in sandbag structures) cells. Calcium oscillations were observed in some recipient cells only when a low number of cells were stimulated. Different mechanical stimulation and flow environment were also employed to study their impact on the behavior of cell-cell communication. We observed that both the duration and intensity of intracellular calcium responses increased in persistent stimulation and decreased in flowing environment. This microdevice may open up new avenues for real-time monitoring of suspension cell-cell communication, which propagates via gap-junction independent mechanism, with multiple variables under control.

The role of purinergic signaling in the liver and in transplantation: effects of extracellular nucleotides on hepatic graft vascular injury, rejection and metabolism

Extracellular nucleotides (e.g. ATP, UTP, ADP) are released by activated endothelium, leukocytes and platelets within the injured vasculature and bind specific cell-surface type-2 purinergic (P2) receptors. This process drives vascular inflammation and thrombosis within grafted organs. Importantly, there are also vascular ectonucleotidases i.e. ectoenzymes that hydrolyze extracellular nucleotides in the blood to generate nucleosides (viz. adenosine). Endothelial cell NTPDase1/CD39 has been shown to critically modulate levels of circulating nucleotides. This process tends to limit the activation of platelet and leukocyte expressed P2 receptors and also generates adenosine to reverse inflammatory events. This vascular protective CD39 activity is rapidly inhibited by oxidative reactions, such as is observed with liver ischemia reperfusion injury. In this review, we chiefly address the impact of these signaling cascades following liver transplantation. Interestingly, the hepatic vasculature, hepatocytes and all non-parenchymal cell types express several components co-ordinating the purinergic signaling response. With hepatic and vascular dysfunction, we note heightened P2- expression and alterations in ectonucleotidase expression and function that may predispose to progression of disease. In addition to documented impacts upon the vasculature during engraftment, extracellular nucleotides also have direct influences upon liver function and bile flow (both under physiological and pathological states). We have recently shown that alterations in purinergic signaling mediated by altered CD39 expression have major impacts upon hepatic metabolism, repair mechanisms, regeneration and associated immune responses. Future clinical applications in transplantation might involve new therapeutic modalities using soluble recombinant forms of CD39, altering expression of this ectonucleotidase by drugs and/or using small molecules to inhibit deleterious P2-mediated signaling while augmenting beneficial adenosine-mediated effects within the transplanted liver.

Gene expression profiling defines ATP as a key regulator of human dendritic cell functions

Extracellular ATP and PGE2 are two cAMP-elevating agents inducing semimaturation of human monocyte-derived dendritic cells (MoDCs). We have extensively compared the gene expression profiles induced by adenosine 5'-O-(3-thiotriphosphate) (ATPgammaS) and PGE2 in human MoDCs using microarray technology. At 6 h of stimulation, ATPgammaS initiated an impressive expression profile compared with that of PGE2 (1125 genes compared with 133 genes, respectively) but after 24 h the number of genes regulated by ATPgammaS or PGE2 was more comparable. Many target genes involved in inflammation have been identified and validated by quantitative RT-PCR experiments. We have then focused on novel ATPgammaS and PGE2 target genes in MoDCs including CSF-1, MCP-4/CCL13 chemokine, vascular endothelial growth factor-A, and neuropilin-1. ATPgammaS strongly down-regulated CSF-1 receptor mRNA and CSF-1 secretion, which are involved in monocyte and dendritic cell (DC) differentiation. Additionally, ATPgammaS down-regulated several chemokines involved in monocyte and DC migration including CCL2/MCP-1, CCL3/MIP-1alpha, CCL4/MIP-1beta, CCL8/MCP-2, and CCL13/MCP-4. Interestingly, vascular endothelial growth factor A, a major angiogenic factor displaying immunosuppressive properties, was secreted by MoDCs in response to ATPgammaS, ATP, or PGE2, alone or in synergy with LPS. Finally, flow cytometry experiments have demonstrated that ATPgammaS, ATP, and PGE2 down-regulate neuropilin-1, a receptor playing inter alia an important role in the activation of T lymphocytes by DCs. Our data give an extensive overview of the genes regulated by ATPgammaS and PGE2 in MoDCs and an important insight into the therapeutic potential of ATP- and PGE2-treated human DCs.

P2 receptors in cardiovascular regulation and disease

The role of ATP as an extracellular signalling molecule is now well established and evidence is accumulating that ATP and other nucleotides (ADP, UTP and UDP) play important roles in cardiovascular physiology and pathophysiology, acting via P2X (ion channel) and P2Y (G protein-coupled) receptors. In this article we consider the dual role of ATP in regulation of vascular tone, released as a cotransmitter from sympathetic nerves or released in the vascular lumen in response to changes in blood flow and hypoxia. Further, purinergic long-term trophic and inflammatory signalling is described in cell proliferation, differentiation, migration and death in angiogenesis, vascular remodelling, restenosis and atherosclerosis. The effects on haemostasis and cardiac regulation is reviewed. The involvement of ATP in vascular diseases such as thrombosis, hypertension and diabetes will also be discussed, as well as various heart conditions. The purinergic system may be of similar importance as the sympathetic and renin-angiotensin-aldosterone systems in cardiovascular regulation and pathophysiology. The extracellular nucleotides and their cardiovascular P2 receptors are now entering the phase of clinical development.

Purinergic receptors involved in the immunomodulatory effects of ATP in human blood

We recently showed that the physiological compound ATP simultaneously inhibited TNF-alpha and stimulated IL-10 release in LPS-PHA stimulated blood. The purpose of the present study was to determine the mechanism involved in the concerted modulatory effect of ATP on TNF-alpha and IL-10. Incubation of blood with ATP in the presence of selective P2 receptor antagonists showed that the stimulatory effect of ATP on IL-10 release was completely annihilated by both 2-MeSAMP (a P2Y12/13 receptor antagonist) and PSB-0413 (a P2Y12 receptor antagonist). On the other hand, the inhibitory effect of ATP on TNF-alpha release was completely reversed by 5'-AMPS (a P2Y11 receptor antagonist) as well as by H-89, an inhibitor of cAMP-activated PKA. The concerted inhibition by ATP of TNF-alpha release via P2Y11 activation and stimulation of IL-10 release via P2Y12 activation implicates a novel approach towards immunomodulation by altering the balance among pro- and anti-inflammatory cytokines.

Relationships between cystic fibrosis transmembrane conductance regulator, extracellular nucleotides and cystic fibrosis

Cystic fibrosis (CF) is one of the most common lethal autosomal recessive genetic diseases in the Caucasian population, with a frequency of about 1 in 3000 livebirths. CF is due to a mutation in the cystic fibrosis transmembrane conductance regulator (CFTR) gene encoding the CFTR protein, a cyclic adenosine 5'-monophosphate (cAMP)-regulated chloride channel localized in the apical membrane of epithelial cells. CFTR is a multifunctional protein which, in addition to be a Cl-channel, is also a regulator of multiple ion channels and other proteins. In particular CFTR has been reported to play a role in the outflow of adenosine 5'-triphosphate (ATP) from cells, but this remains controversial. Extracellular nucleotides are signaling molecules that regulate ion transport and mucociliary clearance by acting on P2 nucleotide receptors, in particular the P2Y(2) receptor. Nucleotides activating the P2Y(2) receptor represent thus one pharmacotherapeutic strategy to treat CF disease, via improvement of mucus hydration and mucociliary clearance in airways. Phase II clinical trials have recently shown that aerosolized denufosol (INS37217, Inspire(R)) improves pulmonary function in CF patients: denufosol was granted orphan drug status and phase III trials are planned. Here, we review what is known about the relationship between extracellular nucleotides and CFTR, the role of extracellular nucleotides in epithelial pathophysiology and their putative role as therapeutic agents.

Adenosine 5'-triphosphate and adenosine as endogenous signaling molecules in immunity and inflammation

Human health is under constant threat of a wide variety of dangers, both self and nonself. The immune system is occupied with protecting the host against such dangers in order to preserve human health. For that purpose, the immune system is equipped with a diverse array of both cellular and non-cellular effectors that are in continuous communication with each other. The naturally occurring nucleotide adenosine 5'-triphosphate (ATP) and its metabolite adenosine (Ado) probably constitute an intrinsic part of this extensive immunological network through purinergic signaling by their cognate receptors, which are widely expressed throughout the body. This review provides a thorough overview of the effects of ATP and Ado on major immune cell types. The overwhelming evidence indicates that ATP and Ado are important endogenous signaling molecules in immunity and inflammation. Although the role of ATP and Ado during the course of inflammatory and immune responses in vivo appears to be extremely complex, we propose that their immunological role is both interdependent and multifaceted, meaning that the nature of their effects may shift from immunostimulatory to immunoregulatory or vice versa depending on extracellular concentrations as well as on expression patterns of purinergic receptors and ecto-enzymes. Purinergic signaling thus contributes to the fine-tuning of inflammatory and immune responses in such a way that the danger to the host is eliminated efficiently with minimal damage to healthy tissues.

Modulation of inflammation by extracellular nucleotides

In this issue, Seiffert et al. show that adenosine triphosphate enhances the production of inflammatory mediators by human dermal endothelial cells. However, a growing literature shows that adenosine triphosphate exerts anti-inflammatory effects, partly by inducing a semi-maturation of dendritic cells associated with immune tolerance. These discrepancies can be reconciled knowing that extracellular nucleotides constitute danger signals that are released in response to both external aggression (chemical, microbial) and excess inflammation.

Pathophysiology and therapeutic potential of purinergic signaling

The concept of a purinergic signaling system, using purine nucleotides and nucleosides as extracellular messengers, was first proposed over 30 years ago. After a brief introduction and update of purinoceptor subtypes, this article focuses on the diverse pathophysiological roles of purines and pyrimidines as signaling molecules. These molecules mediate short-term (acute) signaling functions in neurotransmission, mechanosensory transduction, secretion and vasodilatation, and long-term (chronic) signaling functions in cell proliferation, differentiation, and death involved in development and regeneration. Plasticity of purinoceptor expression in pathological conditions is frequently observed, including an increase in the purinergic component of autonomic cotransmission. Recent advances in therapies using purinergic-related drugs in a wide range of pathological conditions will be addressed with speculation on future developments in the field.

Molecular mechanisms of extracellular adenine nucleotides-mediated inhibition of human Cd4(+) T lymphocytes activation

We have previously reported that ATPgammaS, a slowly hydrolyzed analog of ATP, inhibits the activation of human CD4(+) T lymphocytes by anti-CD3 and anti-CD28 mAb. In this report we have partially characterized the signaling mechanisms involved in this immunosuppressive effect. ATPgammaS had no inhibitory effect on CD4(+) T-cell activation induced by PMA and anti-CD28, indicating that it acts proximally to the TCR. It had no effect on the calcium rise induced by CD3/CD28 stimulation, but inhibited the phosphorylation of three kinases, ERK2, p38 MAPK and PKB, that play a key role in the activation of T cells. The receptor involved in these actions remains unidentified.

Thrombospondin-1 and indoleamine 2,3-dioxygenase are major targets of extracellular ATP in human dendritic cells

Extracellular adenosine triphosphate affects the maturation of human monocyte-derived dendritic cells (DCs), mainly by inhibiting T-helper 1 (Th1) cytokines, promoting Th2 cytokines, and modulating the expression of costimulatory molecules. In this study, we report that adenosine triphosphate (ATP) can induce immunosuppression through its action on DCs, defining a new role for extracellular nucleotides. Microarray analysis of ATP-stimulated human DCs revealed inter alia a drastic up-regulation of 2 genes encoding mediators involved in immunosuppression: thrombospondin-1 (TSP-1) and indoleamine 2,3-dioxygenase (IDO). The release of TSP-1 by DCs in response to ATP was confirmed at the protein level by enzyme-linked immunosorbent assay (ELISA), immunodetection, and mass spectrometry analysis, and has an antiproliferative effect on T CD4+ lymphocytes through TSP-1/CD47 interaction. Our pharmacologic data support the involvement of purinergic receptor P2Y11 in this ATP-mediated TSP-1 secretion. We demonstrate also that ATP significantly potentiates the up-regulation of IDO--a negative regulator of T lymphocyte proliferation--and kynurenine production initiated by interferon-gamma (IFN-gamma) in human DCs. Thus, extracellular ATP released from damaged cells and previously considered as a danger signal is also a potent regulator of mediators playing key roles in immune tolerance. Consequently, nucleotides' derivatives may be considered as useful tools for DC-based immunotherapies.

Immunoregulatory effects of adenosine 5'-triphosphate on cytokine release from stimulated whole blood

In vitro studies suggest that extracellular nucleotides and nucleosides may be important regulators of inflammatory and immune responses. Most studies with adenosine 5'-triphosphate (ATP) have been performed in cell lines, which are remote from the human situation. The purpose of the present study was to determine the effects of ATP on TNF-alpha, IL-6 and IL-10 release in stimulated whole blood. Blood samples were drawn from healthy volunteers and incubated with ATP and lipopolysaccharide (LPS) + phytohemagglutinin (PHA) for 24 h. Contrary to expectations, ATP at 100 microM and 300 microM induced a reduction in TNF-alpha secretion by 32+/-8% (mean +/- SEM) and 65+/-4%, respectively. Furthermore, these ATP concentrations induced an increase in IL-10 secretion by 48+/-5% and 62+/-7% in whole blood. The ATP analogue adenosine 5'-O-(3-thiotriphosphate) (ATP-gamma-S) and adenosine 5'-diphosphate (ADP) also inhibited TNF-alpha release, but only ADP showed a stimulatory effect on IL-10. Co-treatment with adenosine deaminase did not reverse the ATP effect on TNF-alpha and IL-10. These results show, for the first time, that ATP inhibits the inflammatory response in stimulated whole blood as indicated by inhibition of TNF-alpha and stimulation of IL-10 release and that this effect is predominantly mediated by ATP and not by adenosine.

Adenine nucleotides inhibit cytokine generation by human mast cells through a Gs-coupled receptor

ATP and ADP activate functionally distinct G protein-coupled purinergic (P2Y) receptors. We determined the expression and function of adenine nucleotide-specific P2Y receptors on cord blood-derived human mast cells (hMCs). Human MCs expressed mRNA encoding the ADP-specific P2Y1, P2Y12, and P2Y13 receptors; the ATP/UTP-specific P2Y2 receptor; and the ATP-selective P2Y11 receptor. ADP (0.05-50 muM) induced calcium flux that was completely blocked by a P2Y1 receptor-selective antagonist and was not cross-desensitized by ATP. Low doses of ADP induced strong phosphorylation of ERK and p38 MAPKs; higher doses stimulated eicosanoid production and exocytosis. Although MAPK phosphorylation was blocked by a combination of P2Y1- and P2Y12-selective antagonists, neither interfered with secretion responses. Unexpectedly, both ADP and ATP inhibited the generation of TNF-alpha in response to the TLR2 ligand, peptidoglycan, and blocked the production of TNF-alpha, IL-8, and MIP-1beta in response to leukotriene D(4). These effects were mimicked by two ATP analogues, adenosine 5'-O-(3-thiotriphosphate) and 2',3'-O-(4-benzoyl-benzoyl) adenosine 5'-triphosphate (BzATP), but not by adenosine. ADP, ATP, adenosine 5'-O-(3-thiotriphosphate), and 2',3'-O-(4-benzoyl-benzoyl) adenosine 5'-triphosphate each induced cAMP accumulation, stimulated the phosphorylation of CREB, and up-regulated the expression of inducible cAMP early repressor, a CREB-dependent inhibitor of cytokine transcription. Human MCs thus express several ADP-selective P2Y receptors and at least one G(s)-coupled ADP/ATP receptor. Nucleotides could therefore contribute to MC-dependent microvascular leakage in atherosclerosis, tissue injury, and innate immunity while simultaneously limiting the extent of subsequent inflammation by attenuating the generation of inducible cytokines by MCs.

Adenosine 5'-(gamma-thio) triphosphate (ATPgammaS) stimulates both P2Y receptors linked to inositol phosphates production and cAMP accumulation in bovine adrenocortical fasciculata cells

The study was aimed to investigate the existence of at least two kinds of P2Y receptors linked to steroidogenesis in bovine adrenocortical fasciculata cells (BAFCs). Extracellular nucleotides facilitated steroidogenesis in BAFCs. The potency order was UTP > adenosine 5'-(gamma-thio) triphosphate (ATPgammaS) > ATP > 2-methylthio ATP (2MeSATP) > adenosine 5'-(beta-thio) diphosphate (ADPbetaS) > alpha,beta-methylene ATP (alpha,beta-me-ATP), beta,gamma-methylene ATP (beta,gamma -me-ATP). ATPgammaS (10-100 microM) remarkably stimulated both total inositol phosphates (IPs) production and cyclic AMP (cAMP) accumulation. Competitive displacement experiments by using [35S]ATPgammaS as a radioactive ligand in BAFCs showed that the potency under these unlabelled ligands was ATPgammaS > ATP > ADPbetaS > 2MeSATP > UTP > alpha,beta-me-ATP, beta,gamma-me-ATP. These suggest that two different binding sites of [35S]ATPgammaS, namely P2Y receptors, exist in BAFCs, and that these receptors are linked to steroidogenesis via distinct second messenger systems in the cells.

Impaired germinal center maturation in adenosine deaminase deficiency

Mice deficient in the enzyme adenosine deaminase (ADA) have small lymphoid organs that contain reduced numbers of peripheral lymphocytes, and they are immunodeficient. We investigated B cell deficiency in ADA-deficient mice and found that B cell development in the bone marrow was normal. However, spleens were markedly smaller, their architecture was dramatically altered, and splenic B lymphocytes showed defects in proliferation and activation. ADA-deficient B cells exhibited a higher propensity to undergo B cell receptor-mediated apoptosis than their wild-type counterparts, suggesting that ADA plays a role in the survival of cells during Ag-dependent responses. In keeping with this finding, IgM production by extrafollicular plasmablast cells was higher in ADA-deficient than in wild-type mice, thus indicating that activated B cells accumulate extrafollicularly as a result of a poor or nonexistent germinal center formation. This hypothesis was subsequently confirmed by the profound loss of germinal center architecture. A comparison of levels of the ADA substrates, adenosine and 2'-deoxyadenosine, as well resulting dATP levels and S-adenosylhomocysteine hydrolase inhibition in bone marrow and spleen suggested that dATP accumulation in ADA-deficient spleens may be responsible for impaired B cell development. The altered splenic environment and signaling abnormalities may concurrently contribute to a block in B cell Ag-dependent maturation in ADA-deficient mouse spleens.

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.

Involvement of P2Y receptors in the differentiation of haematopoietic cells

The effects of extracellular nucleotides are mediated by multiple P2X ionotropic receptors and G protein-coupled P2Y receptors. These receptors are ubiquitous, but few physiological roles have been firmly identified. In this review article, we present a survey of the functional expression of P2Y receptors in the different haematopoietic lineages by analyzing the selectivity of these cells for the various adenine and uracil nucleotides as well as the second messenger signaling pathways involved. The pharmacological profiles of metabotropic nucleotide receptors are different among myeloid, megakaryoid, erythroid, and lymphoid cells and change during differentiation. A role of P2Y receptors in the differentiation and maturation of blood cells has been proposed: In particular the P2Y(11)receptor seems to be involved in the granulocytic differentiation of promyelocytes and in the maturation of monocyte-derived dendritic cells. It is suggested that the role of P2Y receptors in the maturation of blood cells may be more important than believed so far.

Secretion of IL-2 and IFN-gamma, but not IL-4, by antigen-specific T cells requires extracellular ATP

Extracellular ATP and other nucleotides transmit signals to cells via surface-associated molecules whose binding sites face the extracellular milieu. Ecto-nucleoside triphosphate diphosphohydrolase is such an ATP-binding enzyme that is expressed by activated lymphocytes. We have previously shown that nonhydrolyzable ATP analogs block the lytic activity of NK cells and CD8(+) T cells as well as their E-NTPDase activity. These results suggest that the hydrolysis of ATP may play a role in lymphocyte function. Here we report that E-NTPDase activity is up-regulated within 15 min of T cell stimulation and that reversible and irreversible enzyme inhibitors profoundly reduce secretion of IL-2 and IFN-gamma, but not IL-4. TNF-alpha, IL-10, and IL-5 production showed intermediate sensitivity to these ATP analogs. Depletion of extracellular ATP also inhibited secretion of IFN-gamma, but not IL-4, supporting the interpretation that extracellular ATP is required for secretion of some, but not all, cytokines. E-NTPDase antagonists reduced transcription of IL-2 mRNA and inhibited TCR-mediated intracellular calcium flux. These results suggest that extracellular ATP plays an essential role in the TCR-mediated signal transduction cascade for expression of certain cytokine genes.