The P2X7 Receptor in Infection and Inflammation.

Adenosine triphosphate (ATP) accumulates at sites of tissue injury and inflammation. Effects of extracellular ATP are mediated by plasma membrane receptors named P2 receptors (P2Rs). The P2R most involved in inflammation and immunity is the P2X7 receptor (P2X7R), expressed by virtually all cells of innate and adaptive immunity. P2X7R mediates NLRP3 inflammasome activation, cytokine and chemokine release, T lymphocyte survival and differentiation, transcription factor activation, and cell death. Ten human P2RX7 gene splice variants and several SNPs that produce complex haplotypes are known. The P2X7R is a potent stimulant of inflammation and immunity and a promoter of cancer cell growth. This makes P2X7R an appealing target for anti-inflammatory and anti-cancer therapy. However, an in-depth knowledge of its structure and of the associated signal transduction mechanisms is needed for an effective therapeutic development.

Fetal bovine serum contains biologically available ATP.

ATP is a ubiquitous extracellular messenger released in a wide number of pathophysiological conditions. ATP is known to be present in minute amounts in the extracellular space in healthy tissues and in the blood, and to modulate a multiplicity of cell responses. Cell culture systems are widely used to explore purinergic signaling. We show here that currently used fetal bovine sera contain ATP in the 300-1300 pmol/L range. Serum ATP is associated with albumin as well as with microparticle/microvesicle fraction. Serum microparticles/microvesicles affect in vitro cell responses due to their content of miRNAs, growth factors, and other bioactive molecules. ATP is likely to be one of these bioactive factors found in a variable amount in sera of different commercial sources. ATP in serum supports ATP-dependent biochemical reactions such as the hexokinase-dependent phosphorylation of glucose to glucose 6-phosphate, and affects purinergic signaling. These findings show that cells growing in vitro in serum-supplemented media are exposed to varying levels of extracellular ATP, and thus to varying degrees of purinergic stimulation.

Immunological evidence of an early seroconversion to oncogenic Merkel cell polyomavirus in healthy children and young adults.

Oncogenic Merkel cell polyomavirus (MCPyV) provokes a widespread and asymptomatic infection in humans. Herein, sera from healthy children and young adults (HC, n = 344) aged 0-20 years old were evaluated for anti-MCPyV immunoglobulin G (IgG) and IgM antibodies employing a recently developed immunoassay. Serum MCPyV IgG data from healthy subjects (HS, n = 510) and elderlies (ES, n = 226), aged 21-65/66-100 years old, from our previous studies, were included. The anti-MCPyV IgG and IgM rates in HC sera were 40.7% and 29.7%, respectively. A lower prevalence of anti-MCPyV IgGs was found in HC aged 0-5 years old (13%) compared to 6-10 (52.3%), 11-15 (60.5%) and 16-20 years old (61.6%) cohorts. Age-stratified HCs exhibited similar anti-MCPyV IgM rates (27.9%-32.9%). Serological profiles indicated that anti-MCPyV IgGs and IgMs had low optical densities (ODs) during the first years of life, while IgM ODs appeared to decrease throughout young adulthood. A lower anti-MCPyV IgGs rate was found in HC (40.7%) than HS (61.8%) and ES (63.7%). Upon the 5-years range age-stratification, a lower anti-MCPyV IgGs rate was found in the younger HC cohort aged 0-5 years old compared to the remaining older HC/HS/ES cohorts (52.3%-72%). The younger HC cohort exhibited the lowest anti-MCPyV IgG ODs than the older cohorts. Low anti-MCPyV IgMs rates and ODs were found in the 21-25 (17.5%) and 26-30 (7.7%) years old cohorts. Our data indicate that, upon an early-in-life seroconversion, the seropositivity for oncogenic MCPyV peaks in late childhood/young adulthood and remains at high prevalence and relatively stable throughout life.

The Coming of Age of the P2X7 Receptor in Diagnostic Medicine.

The discovery of the P2X7 receptor (P2X7R, originally named P2Z) in immune cells, its cloning, and the identification of its role in a multiplicity of immune-mediated diseases raised great hopes for the development of novel and more potent anti-inflammatory medicaments. Unfortunately, such hopes were partially deluded by the unsatisfactory results of most early clinical trials. This failure substantially reduced the interest of the pharmaceutical and biotech industries in the clinical development of P2X7R-targeted therapies. However, recent findings ushered in a second life for the P2X7R in diagnostic medicine. New P2X7R radioligands proved to be very reliable tools for the diagnosis of neuroinflammation in preclinical and clinical studies, and detection and measurement of free P2X7 receptor (or P2X7 subunit) in human blood suggested its potential use as a circulating marker of inflammation. Here we provide a brief review of these novel developments.

Blocking P2X7 by intracerebroventricular injection of P2X7-specific nanobodies reduces stroke lesions.

BACKGROUND: Previous studies have demonstrated that purinergic receptors could be therapeutic targets to modulate the inflammatory response in multiple models of brain diseases. However, tools for the selective and efficient targeting of these receptors are lacking. The development of new P2X7-specific nanobodies (nbs) has enabled us to effectively block the P2X7 channel. METHODS: Temporary middle cerebral artery occlusion (tMCAO) in wild-type (wt) and P2X7 transgenic (tg) mice was used to model ischemic stroke. Adenosine triphosphate (ATP) release was assessed in transgenic ATP sensor mice. Stroke size was measured after P2X7-specific nbs were injected intravenously (iv) and intracerebroventricularly (icv) directly before tMCAO surgery. In vitro cultured microglia were used to investigate calcium influx, pore formation via 4,6-diamidino-2-phenylindole (DAPI) uptake, caspase 1 activation and interleukin (IL)-1ß release after incubation with the P2X7-specific nbs. RESULTS: Transgenic ATP sensor mice showed an increase in ATP release in the ischemic hemisphere compared to the contralateral hemisphere or the sham-treated mice up to 24 h after stroke. P2X7-overexpressing mice had a significantly greater stroke size 24 h after tMCAO surgery. In vitro experiments with primary microglial cells demonstrated that P2X7-specific nbs could inhibit ATP-triggered calcium influx and the formation of membrane pores, as measured by Fluo4 fluorescence or DAPI uptake. In microglia, we found lower caspase 1 activity and subsequently lower IL-1ß release after P2X7-specific nb treatment. The intravenous injection of P2X7-specific nbs compared to isotype controls before tMCAO surgery did not result in a smaller stroke size. As demonstrated by fluorescence-activated cell sorting (FACS), after stroke, iv injected nbs bound to brain-infiltrated macrophages but not to brain resident microglia, indicating insufficient crossing of the blood-brain barrier of the nbs. Therefore, we directly icv injected the P2X7-specific nbs or the isotype nbs. After icv injection of 30 µg of P2X7 specific nbs, P2X7 specific nbs bound sufficiently to microglia and reduced stroke size. CONCLUSION: Mechanistically, we can show that there is a substantial increase of ATP locally after stroke and that blockage of the ATP receptor P2X7 by icv injected P2X7-specific nbs can reduce ischemic tissue damage.

Expression and function of the P2X7 receptor in human osteoblasts: The role of NFATc1 transcription factor.

Bone mineralization is an orchestrated process by which mineral crystals are deposited by osteoblasts; however, the detailed mechanisms remain to be elucidated. The presence of P2X7 receptor (P2X7R) in immature and mature bone cells is well established, but contrasting evidence on its role in osteogenic differentiation and deposition of calcified bone matrix remains. To clarify these controversies in the present study, we investigated P2X7R participation in bone maturation. We demonstrated that the P2X7R is expressed and functional in human primary osteoblasts, and identified in the P2RX7 promoter several binding sites for transcription factors involved in bone mineralization. Of particular interest was the finding that P2X7R expression is enhanced by nuclear factor of activated T cells cytoplasmic 1 (NFATc1) overexpression, and accordingly, NFATc1 is recruited at the P2RX7 gene promoter in SaOS2 osteoblastic-like cells. In conclusion, our data provide further insights into the regulation of P2X7R expression and support the development of drugs targeting this receptor for the therapy of bone diseases.

The P2X7 receptor directly interacts with the NLRP3 inflammasome scaffold protein.

The P2X7 receptor (P2X7R) is a known and powerful activator of the NOD-like receptor (NLR)P3 inflammasome; however, the underlying pathways are poorly understood. Thus, we investigated the molecular mechanisms involved. The effect of P2X7R expression and activation on NLRP3 expression and recruitment was investigated by Western blot, RT-PCR, coimmunoprecipitation, and confocal microscopy in microglial mouse cell lines selected for reduced P2X7R expression and in primary cells from P2X7R(-/-) C57BL/6 mice. We show here that P2X7R activation by ATP (EC50 = 1 mM) or benzoyl-ATP (EC50 = 300 µM) and P2X7R down-modulation caused a 2- to 8-fold up-regulation of NLRP3 mRNA in mouse N13 microglial cells. Moreover, NLRP3 mRNA was also up-regulated in primary microglial and macrophage cells from P2X7R(-/-) mice. Confocal microscopy and immunoprecipitation assays showed that P2X7R and NLRP3 closely interacted at discrete subplasmalemmal sites. Finally, P2X7R stimulation caused a transient (3-4 min) cytoplasmic Ca(2+) increase localized to small (2-3 µm wide) discrete subplasmalemmal regions. The Ca(2+) increase drove P2X7R recruitment and a 4-fold increase in P2X7R/NLRP3 association within 1-2 min. These data show a close P2X7R and NLRP3 interaction and highlight the role of P2X7R in the localized cytoplasmic ion changes responsible for both NLRP3 recruitment and activation.

The adjuvant MF59 induces ATP release from muscle that potentiates response to vaccination.

Vaccines are the most effective agents to control infections. In addition to the pathogen antigens, vaccines contain adjuvants that are used to enhance protective immune responses. However, the molecular mechanism of action of most adjuvants is ill-known, and a better understanding of adjuvanticity is needed to develop improved adjuvants based on molecular targets that further enhance vaccine efficacy. This is particularly important for tuberculosis, malaria, AIDS, and other diseases for which protective vaccines do not exist. Release of endogenous danger signals has been linked to adjuvanticity; however, the role of extracellular ATP during vaccination has never been explored. Here, we tested whether ATP release is involved in the immune boosting effect of four common adjuvants: aluminum hydroxide, calcium phosphate, incomplete Freund's adjuvant, and the oil-in-water emulsion MF59. We found that intramuscular injection is always associated with a weak transient release of ATP, which was greatly enhanced by the presence of MF59 but not by all other adjuvants tested. Local injection of apyrase, an ATP-hydrolyzing enzyme, inhibited cell recruitment in the muscle induced by MF59 but not by alum or incomplete Freund's adjuvant. In addition, apyrase strongly inhibited influenza-specific T-cell responses and hemagglutination inhibition titers in response to an MF59-adjuvanted trivalent influenza vaccine. These data demonstrate that a transient ATP release is required for innate and adaptive immune responses induced by MF59 and link extracellular ATP with an enhanced response to vaccination.

The NFATc1/P2X7 receptor relationship in human intervertebral disc cells.

A comprehensive understanding of the molecules that play key roles in the physiological and pathological homeostasis of the human intervertebral disc (IVD) remains challenging, as does the development of new therapeutic treatments. We recently found a positive correlation between IVD degeneration (IDD) and P2X7 receptor (P2X7R) expression increases both in the cytoplasm and in the nucleus. Using immunocytochemistry, reverse transcription PCR (RT-PCR), overexpression, and chromatin immunoprecipitation, we found that NFATc1 and hypoxia-inducible factor-1α (HIF-1α) are critical regulators of P2X7R. Both transcription factors are recruited at the promoter of the P2RX7 gene and involved in its positive and negative regulation, respectively. Furthermore, using the proximity ligation assay, we revealed that P2X7R and NFATc1 form a molecular complex and that P2X7R is closely associated with lamin A/C, a major component of the nuclear lamina. Collectively, our study identifies, for the first time, P2X7R and NFATc1 as markers of IVD degeneration and demonstrates that both NFATc1 and lamin A/C are interaction partners of P2X7R.

The P2X7 Receptor is a Master Regulator of Microparticle and Mitochondria Exchange in Mouse Microglia.

Microparticles (MPs) are secreted by all cells, where they play a key role in intercellular communication, differentiation, inflammation, and cell energy transfer. P2X7 receptor (P2X7R) activation by extracellular ATP (eATP) causes a large MP release and affects their contents in a cell-specific fashion. We investigated MP release and functional impact in microglial cells from P2X7R-WT or P2X7R-KO mice, as well as mouse microglial cell lines characterized for high (N13-P2X7RHigh) or low (N13-P2X7RLow) P2X7R expression. P2X7R stimulation promoted release of a mixed MP population enriched with naked mitochondria. Released mitochondria were taken up and incorporated into the mitochondrial network of the recipient cells in a P2X7R-dependent fashion. NLRP3 and the P2X7R itself were also delivered to the recipient cells. Microparticle transfer increased the energy level of the recipient cells and conferred a pro-inflammatory phenotype. These data show that the P2X7R is a master regulator of intercellular organelle and MP trafficking in immune cells.

The P2X7 receptor and Pannexin-1 are both required for the promotion of multinucleated macrophages by the inflammatory cytokine GM-CSF.

The P2X(7) receptor (P2X(7)R), an ATP-gated ion channel, has been implicated in the process of cell-to-cell fusion into multinucleated macrophages (MA), but its contribution to MA fusion driven by physiological/pathological stimuli is not clearly established. Based on several lines of evidence, we demonstrate that P2X(7)R is critical for the induction of multinucleated MA by the inflammatory cytokine GM-CSF: 1) pharmacological inhibition of P2X(7)R with oxidized ATP (oATP), KN-62, and the selective antagonist A740003 abrogated GM-CSF action on rat alveolar MA and murine peritoneal MA; 2) a murine J774 P2X(7) low MA clone, selected for defective P2X(7)R function, was unresponsive; 3) MA from mice lacking P2X(7)R failed to respond to GM-CSF, in contrast to wild-type. GM-CSF also stimulated ATP-induced membrane permeabilization in J774 P2X(7) high MA and rat alveolar MA, an effect absent in the P2X(7) low MA clone and inhibited by the P2X(7) blockers oATP and KN-62. Notably, the stimulatory effects of GM-CSF on pore formation and MA fusion were both inhibited by blocking functional Pannexin-1 (Panx-1), and GM-CSF failed to stimulate MA fusion in cells from Panx-1 knockout mice. We provide further evidence that extracellular ATP release from peritoneal MA is dependent on P2X(7) but not on Panx-1 expression and that its metabolism to adenosine mediates P2X(7)-dependent MA fusion. These data demonstrate that both P2X(7) and Panx-1 are required for GM-CSF promotion of MA fusion but likely act independently through different signaling pathway(s).

Extracellular ATP: A powerful inflammatory mediator in the central nervous system.

Nucleotides play a crucial role in extracellular signaling across species boundaries. All the three kingdoms of life (Bacteria, Archea and Eukariota) are responsive to extracellular ATP (eATP) and many release this and other nucleotides. Thus, eATP fulfills different functions, many related to danger-sensing or avoidance reactions. Basically all living organisms have evolved sensors for eATP and other nucleotides with very different affinity and selectivity, thus conferring a remarkable plasticity to this signaling system. Likewise, different intracellular transduction systems were associated during evolution to different receptors for eATP. In mammalian evolution, control of intracellular ATP (iATP) and eATP homeostasis has been closely intertwined with that of Ca2+, whether in the extracellular milieu or in the cytoplasm, establishing an inverse reciprocal relationship, i.e. high extracellular Ca2+ levels are associated to negligible eATP, while low intracellular Ca2+ levels are associated to high eATP concentrations. This inverse relationship is crucial for the messenger functions of both molecules. Extracellular ATP is sensed by specific plasma membrane receptors of widely different affinity named P2 receptors (P2Rs) of which 17 subtypes are known. This confers a remarkable plasticity to P2R signaling. The central nervous system (CNS) is a privileged site for purinergic signaling as all brain cell types express P2Rs. Accruing evidence suggests that eATP, in addition to participating in synaptic transmission, also plays a crucial homeostatic role by fine tuning microglia, astroglia and oligodendroglia responses. Drugs modulating the eATP concentration in the CNS are likely to be the new frontier in the therapy of neuroinflammation. This article is part of the Special Issue on 'Purinergic Signaling: 50 years'.

The Concise Guide to PHARMACOLOGY 2023/24: Ion channels.

The Concise Guide to PHARMACOLOGY 2023/24 is the sixth in this series of biennial publications. The Concise Guide provides concise overviews, mostly in tabular format, of the key properties of approximately 1800 drug targets, and over 6000 interactions with about 3900 ligands. There is an emphasis on selective pharmacology (where available), plus links to the open access knowledgebase source of drug targets and their ligands (https://www.guidetopharmacology.org/), which provides more detailed views of target and ligand properties. Although the Concise Guide constitutes almost 500 pages, the material presented is substantially reduced compared to information and links presented on the website. It provides a permanent, citable, point-in-time record that will survive database updates. The full contents of this section can be found at http://onlinelibrary.wiley.com/doi/10.1111/bph.16178. Ion channels are one of the six major pharmacological targets into which the Guide is divided, with the others being: G protein-coupled receptors, nuclear hormone receptors, catalytic receptors, enzymes and transporters. These are presented with nomenclature guidance and summary information on the best available pharmacological tools, alongside key references and suggestions for further reading. The landscape format of the Concise Guide is designed to facilitate comparison of related targets from material contemporary to mid-2023, and supersedes data presented in the 2021/22, 2019/20, 2017/18, 2015/16 and 2013/14 Concise Guides and previous Guides to Receptors and Channels. It is produced in close conjunction with the Nomenclature and Standards Committee of the International Union of Basic and Clinical Pharmacology (NC-IUPHAR), therefore, providing official IUPHAR classification and nomenclature for human drug targets, where appropriate.

ATP secreted by endothelial cells blocks CX3CL 1-elicited natural killer cell chemotaxis and cytotoxicity via P2Y11 receptor activation.

Endothelial cells (ECs) represent a major source of actively secreted adenosine triphosphate (ATP). Natural killer (NK) cells can mediate vascular injury in several pathologic conditions, including cytomegalovirus infection and vascular leak syndrome. We studied NK-cell expression of P2 receptors and the role of these nucleotide receptors in the regulation of endothelial-NK cell cross-talk. NK cells from healthy subjects expressed P2Y(1,2,4,6,11,12,13,14) and P2X(1,4,5,6,7) receptors. NK cells stimulated with ATP, but not uridine triphosphate, increased intracellular Ca²(+) and chemokinesis. Moreover, ATP, but not uridine triphosphate, inhibited NK chemotaxis in response to CX3CL1, whereas chemotaxis to CXCL12 was increased. CX3CL1 elicited killing of human umbilical vein ECs and human coronary artery ECs by NK cells. However, in the presence of ATP, CX3CL1 failed to stimulate killing of ECs. Such inhibitory effect was lost on exogenous addition of the ATP-hydrolyzing enzyme apyrase or by pharmacologic inhibition of the P2Y11R, and correlated with increased intracellular cyclic adenosine monophosphate concentrations induced by ATP or other P2Y11R agonists, including NAD(+). Extracellular ATP regulates NK-cell cytotoxicity via P2Y11R activation, protecting ECs from CX3CL1-elicited NK cell-mediated killing. These findings point out the P2Y11R as a potential target for pharmacologic intervention aimed at reducing NK-mediated vascular injury.

P2X7 receptor drives osteoclast fusion by increasing the extracellular adenosine concentration.

Defects in bone homeostasis are a major health problem. Osteoclast differentiation and activation have a crucial role in bone remodeling in health and disease. Osteoclasts are bone-resorbing cells derived from mononuclear phagocyte progenitors. The key event in osteoclast formation is fusion of mononucleate precursors to form mature multinucleated osteclasts. Here we provide evidence of an absolute requirement for the P2X7 receptor, ATP release, and adenosine signaling in human osteoclast formation, as shown by the following findings: macrophage-colony stimulating factor/receptor activator for nuclear factor-κB ligand (M-CSF/RANKL)-stimulated fusion of human monocytes is fully prevented by an anti-P2X7 mAb, by specific P2X7 pharmacological antagonists, or by inhibition of CD39/NTPDase; fusion-competent monocytes release ATP via the P2X7 receptor; accelerated degradation of released ATP by addition of either apyrase or hexokinase strongly increases fusion; removal of extracellular adenosine by adenosine deaminase blocks, while addition of exogenous adenosine strongly potentiates, fusion; and pharmacologic stimulation of the adenosine A2A receptor increases, while selective A2A blockade inhibits, fusion. These results show that the purinergic axis plays a crucial and as yet undescribed role in osteoclast formation and reconcile previous evidence advocating a key role for either ATP or adenosine receptors in multinucleated giant cell formation.

Modulation of Cell Energy Metabolism by the P2X7 Receptor.

For many years the P2X7 receptor (P2X7R) was considered the prototypic cytolytic receptor due to its ability to cause dramatic changes in plasma membrane permeability, eventually leading to cell death. However, later studies revealed that controlled P2X7R activation has beneficial effects on cell metabolism and nowadays our perception of the physiological role of this receptor has radically changed. Some of the biochemical pathways underlying the trophic effect of the P2X7R are being unveiled, thus disclosing an unanticipated role of P2X7Rs in mitochondrial and glycolytic metabolism. We provide here an update of the effects of the P2X7R on cell energy metabolism.

Signalling by extracellular nucleotides in health and disease.

Nucleotides are released from all cells through regulated pathways or as a result of plasma membrane damage or cell death. Outside the cell, nucleotides act as signalling molecules triggering multiple responses via specific plasma membrane receptors of the P2 family. In the nervous system, purinergic signalling has a key function in neurotransmission. Outside the nervous system, purinergic signalling is one of the major modulators of basal tissue homeostasis, while its dysregulation contributes to the pathogenesis of various disease, including inflammation and cancer. Pre-clinical and clinical evidence shows that selective P2 agonists or antagonists are effective treatments for many pathologies, thus highlighting the relevance of extracellular nucleotides and P2 receptors as therapeutic targets.

Extracellular ATP is increased by release of ATP-loaded microparticles triggered by nutrient deprivation.

Rationale: Caloric restriction improves the efficacy of anti-cancer therapy. This effect is largely dependent on the increase of the extracellular ATP concentration in the tumor microenvironment (TME). Pathways for ATP release triggered by nutrient deprivation are largely unknown. Methods: The extracellular ATP (eATP) concentration was in vivo measured in the tumor microenvironment of B16F10-inoculated C57Bl/6 mice with the pmeLuc probe. Alternatively, the pmeLuc-TG-mouse was used. Caloric restriction was in vivo induced with hydroxycitrate (HC). B16F10 melanoma cells or CT26 colon carcinoma cells were in vitro exposed to serum starvation to mimic nutrient deprivation. Energy metabolism was monitored by Seahorse. Microparticle release was measured by ultracentrifugation and by Nanosight. Results: Nutrient deprivation increases eATP release despite the dramatic inhibition of intracellular energy synthesis. Under these conditions oxidative phosphorylation was dramatically impaired, mitochondria fragmented and glycolysis and lactic acid release were enhanced. Nutrient deprivation stimulated a P2X7-dependent release of ATP-loaded, mitochondria-containing, microparticles as well as of naked mitochondria. Conclusions: Nutrient deprivation promotes a striking accumulation of eATP paralleled by a large release of ATP-laden microparticles and of naked mitochondria. This is likely to be a main mechanism driving the accumulation of eATP into the TME.

Trophic activity of a naturally occurring truncated isoform of the P2X7 receptor.

P2X7 is the largest member of the P2X subfamily of purinergic receptors. A typical feature is the carboxyl tail, which allows formation of a large pore. Recently a naturally occurring truncated P2X7 splice variant, isoform B (P2X7B), has been identified. Here we show that P2X7B expression in HEK293 cells, a cell type lacking endogenous P2X receptors, mediated ATP-stimulated channel activity but not plasma membrane permeabilization, raised endoplasmic reticulum Ca(2+) content, activated the transcription factor NFATc1, increased the cellular ATP content, and stimulated growth. In addition, P2X7B-transfected HEK293 cells (HEK293-P2X7B), like most tumor cells, showed strong soft agar-infiltrating ability. When coexpressed with full-length P2X7 (P2X7A), P2X7B coassembled with P2X7A into a heterotrimer and potentiated all known responses mediated by this latter receptor. P2X7B mRNA was found to be widely distributed in human tissues, especially in the immune and nervous systems, and to a much higher level than P2X7A. Finally, P2X7B expression was increased on mitogenic stimulation of peripheral blood lymphocyte. Altogether, these data show that P2X7B is widely expressed in several human tissues, modulates P2X7A functions, participates in the control of cell growth, and may help understand the role of the P2X7 receptor in the control of normal and cancer cell proliferation.

Activation of microglia by amyloid {beta} requires P2X7 receptor expression.

Extracellular ATP is a mediator of intercellular communication and a danger signal. Release of this and other nucleotides modulates microglia responses via P2Y and P2X receptors, among which the P2X(7) subtype stands out for its proinflammatory activity and for up-regulation in a transgenic model of Alzheimer disease and in brains from Alzheimer disease patients. Here we show that amyloid beta (Abeta) triggered increases in intracellular Ca(2+) ([Ca(2+)](i)), ATP release, IL-1beta secretion, and plasma membrane permeabilization in microglia from wild-type but not from P2X(7)-deleted mice. Likewise, intra-hippocampal injection of Abeta caused a large accumulation of IL-1beta in wild-type but not in P2X(7)(-/-) mice. These observations suggest that Abeta activates a purinergic autocrine/paracrine stimulatory loop of which the P2X(7) receptor is an obligate component. Identification of the P2X(7) receptor as a non-dispensable factor of Abeta-mediated microglia stimulation may open new avenues for the treatment of Alzheimer disease.