P2X7 receptor-dependent and -independent T cell death is induced by nicotinamide adenine dinucleotide

Tumour immune escape via P2X7 receptor signalling

While P2X7 receptor expression on tumour cells has been characterized as a promotor of cancer growth and metastasis, its expression by the host immune system is central for orchestration of both innate and adaptive immune responses against cancer. The role of P2X7R in anti-tumour immunity is complex and preclinical studies have described opposing roles of the P2X7R in regulating immune responses against tumours. Therefore, few P2X7R modulators have reached clinical testing in cancer patients. Here, we review the prognostic value of P2X7R in cancer, how P2X7R have been targeted to date in tumour models, and we discuss four aspects of how tumours skew immune responses to promote immune escape via the P2X7R; non-pore functional P2X7Rs, mono-ADP-ribosyltransferases, ectonucleotidases, and immunoregulatory cells. Lastly, we discuss alternative approaches to offset tumour immune escape via P2X7R to enhance immunotherapeutic strategies in cancer patients.

The new insight into extracellular NAD+ degradation-the contribution of CD38 and CD73 in calcific aortic valve disease

Nicotinamide adenine dinucleotide (NAD+ ) is crucial for cell energy metabolism and many signalling processes. Recently, we proved the role of ecto-enzymes in controlling adenine nucleotide-dependent pathways during calcific aortic valve disease (CAVD). This study aimed to investigate extracellular hydrolysis of NAD+ and mononucleotide nicotinamide (NMN) in aortic valves and aorta fragments of CAVD patients and on the inner aortic surface of ecto-5'-nucleotidase knockout mice (CD73-/-). Human non-stenotic valves (n = 10) actively converted NAD+ and NMN via both CD73 and NAD+ -glycohydrolase (CD38) according to our analysis with RP-HPLC and immunofluorescence. In stenotic valves (n = 50), due to reduced CD73 activity, NAD+ was degraded predominantly by CD38 and additionally by ALP and eNPP1. CAVD patients had significantly higher hydrolytic rates of NAD+ (0.81 ± 0.07 vs 0.56 ± 0.10) and NMN (1.12 ± 0.10 vs 0.71 ± 0.08 nmol/min/cm2 ) compared with controls. CD38 was also primarily engaged in human vascular NAD+ metabolism. Studies using specific ecto-enzyme inhibitors and CD73-/- mice confirmed that CD73 is not the only enzyme involved in NAD+ and NMN hydrolysis and that CD38 had a significant contribution to these pathways. Modifications of extracellular NAD+ and NMN metabolism in aortic valve cells may be particularly important in valve pathology and could be a potential therapeutic target.

P2X7 Receptor at the Crossroads of T Cell Fate

The P2X7 receptor is a ligand-gated, cation-selective channel whose main physiological ligand is ATP. P2X7 receptor activation may also be triggered by ARTC2.2-dependent ADP ribosylation in the presence of extracellular NAD. Upon activation, this receptor induces several responses, including the influx of calcium and sodium ions, phosphatidylserine externalization, the formation of a non-selective membrane pore, and ultimately cell death. P2X7 receptor activation depends on the availability of extracellular nucleotides, whose concentrations are regulated by the action of extracellular nucleotidases such as CD39 and CD38. The P2X7 receptor has been extensively studied in the context of the immune response, and it has been reported to be involved in inflammasome activation, cytokine production, and the migration of different innate immune cells in response to ATP. In adaptive immune responses, the P2X7 receptor has been linked to T cell activation, differentiation, and apoptosis induction. In this review, we will discuss the evidence of the role of the P2X7 receptor on T cell differentiation and in the control of T cell responses in inflammatory conditions.

NAD metabolism in aging and cancer

IMPACT STATEMENT

NAD is a central metabolite connecting energy balance and organismal growth with genomic integrity and function. It is involved in the development of malignancy and has a regulatory role in the aging process. These processes are mediated by a diverse series of enzymes whose common focus is either NAD's biosynthesis or its utilization as a redox cofactor or enzyme substrate. These enzymes include dehydrogenases, cyclic ADP-ribose hydrolases, mono(ADP-ribosyl)transferases, poly(ADP-ribose) polymerases, and sirtuin deacetylases. This article describes the manifold pathways that comprise NAD metabolism and promotes an increased awareness of how perturbations in these systems may be important in disease prevention and/or progression.

Synthesis and sensing integration: A novel enzymatic reaction modulated Nanoclusters Beacon (NCB) "Illumination" strategy for label-free biosensing and logic gate operation

A novel fluorescent label-free "turn-on" NAD(+) and adenosine triphosphate (ATP) biosensing strategy is proposed by fully exploiting ligation triggered Nanocluster Beacon (NCB). In the presence of the target, the split NCB was brought to intact, which brought the C-rich sequence and enhancer sequence in close proximity resulting in the lightening of dark DNA/AgNCs ("On" mode). Further application was presented for logic gate operation and aptasensor construction. The feasibility was investigated by Ultraviolet-visible spectroscopy (UV-vis), Fluorescence, lifetime and High Resolution Transmission Electron Microscopy (HRTEM) etc. The strategy displayed good performance in the detection of NAD(+) and ATP, with the detection limit of 0.002nM and 0.001mM, the linear range of 10-1000nM and 0.003-0.01mM, respectively. Due to the DNA/AgNCs as fluorescence reporter, the completely label-free fluorescent strategy boasts the features of simplicity and low cost, and showing little reliance on the sensing environment. Meanwhile, the regulation by overhang G-rich sequence not relying on Förster energy transfer quenching manifests the high signal-to-background ratios (S/B ratios). This method not only provided a simple, economical and reliable fluorescent NAD(+) assay but also explored a flexible G-rich sequence regulated NCB probe for the fluorescent biosensors. Furthermore, this sensing mode was expanded to the application of a logic gate design, which exhibited a high performance for not only versatile biosensors construction but also for molecular computing application.

Label-free biosensor based on dsDNA-templated copper nanoparticles for highly sensitive and selective detection of NAD+

A novel label-free biosensor for high sensing of NAD⁺ based on dsDNA-templated CuNPs and DNA ligation reaction.

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.

Pannexin1 channels act downstream of P2X 7 receptors in ATP-induced murine T-cell death

Death of murine T cells induced by extracellular ATP is mainly triggered by activation of purinergic P2X 7 receptors (P2X 7Rs). However, a link between P2X 7Rs and pannexin1 (Panx1) channels, which are non-selective, has been recently demonstrated in other cell types. In this work, we characterized the expression and cellular distribution of pannexin family members (Panxs 1, 2 and 3) in isolated T cells. Panx1 was the main pannexin family member clearly detected in both helper (CD4+) and cytotoxic (CD8+) T cells, whereas low levels of Panx2 were found in both T-cell subsets. Using pharmacological and genetic approaches, Panx1 channels were found to mediate most ATP-induced ethidium uptake since this was drastically reduced by Panx1 channel blockers (10Panx1, Probenecid and low carbenoxolone concentration) and absent in T cells derived from Panx1-/- mice. Moreover, electrophysiological measurements in wild-type CD4+ cells treated with ATP unitary current events and pharmacological sensitivity compatible with Panx1 channels were found. In addition, ATP release from T cells treated with 4Br-A23187, a calcium ionophore, was completely blocked with inhibitors of both connexin hemichannels and Panx1 channels. Panx1 channel blockers drastically reduced the ATP-induced T-cell mortality, indicating that Panx1 channels mediate the ATP-induced T-cell death. However, mortality was not reduced in T cells of Panx1-/- mice, in which levels of P2X 7Rs and ATP-induced intracellular free Ca2+ responses were enhanced suggesting that P2X 7Rs take over Panx1 channels lose-function in mediating the onset of cell death induced by extracellular ATP.

Technical Advance: a new cell preparation strategy that greatly improves the yield of vital and functional Tregs and NKT cells

Release of NAD(+) during preparation of murine lymphocytes causes enzymatic ADP-ribosylation of cell-surface proteins on T cells, catalyzed by toxin-related ecto-ADP-ribosyltransferase, ARTC2. ADP-riboslyation activates the cytolytic P2X7 ion channel and affects, in particular, the vitality and function of Tregs and NKT cells. Here, we describe a simple method-injection of an ARTC2-blocking nanobody-to greatly improve Treg and NKT cell vitality and to preserve their function during in vitro assays and in adoptive-transfer experiments. Moreover, we present a method for the sorting of functional, primary NKT cells, based on coexpression of ARTC2 and NK1.1. Our results pave the way for the efficient ex vivo proliferation of Tregs and NKT cells and for new experimental and therapeutic uses of these important regulatory cells.

Mechanisms of cytolysin-induced cell damage -- a role for auto- and paracrine signalling

Cytolysins inflict cell damage by forming pores in the plasma membrane. The Na(+) conductivity of these pores results in an ion influx that exceeds the capacity of the Na(+) /K(+) -pump to extrude Na(+) . This net load of intracellular osmolytes results in swelling and eventual lysis of the attacked cell. Many nucleated cells have the capacity to reduce the potential damage of pore-forming proteins, whereas erythrocytes have been regarded as essentially defenceless against cytolysin-induced cell damage. This review addresses how autocrine/paracrine signalling and the cells intrinsic volume regulation markedly influence the fate of the cell after membrane insertion of cytolysins. Moreover, it regards the various steps that may explain the relative large degree of diversity between cell types and species as well as highlights some of the current gaps in the mechanistic understanding of cytolysin-induced cell injury.

Diversification of NAD biological role: the importance of location

Over 100 years after its first discovery, several new aspects of the biology of the redox co-factor NAD are rapidly emerging. NAD, as well as its precursors, its derivatives, and its metabolic enzymes, have been recently shown to play a determinant role in a variety of biological functions, from the classical role in oxidative phosphorylation and redox reactions to a role in regulation of gene transcription, lifespan and cell death, from a role in neurotransmission to a role in axon degeneration, and from a function in regulation of glucose homeostasis to that of control of circadian rhythm. It is also becoming clear that this variety of specialized functions is regulated by the fine subcellular localization of NAD, its related nucleotides and its metabolic enzymatic machinery. Here we describe the known NAD biosynthetic and catabolic pathways, and review evidence supporting a specialized role for NAD metabolism in a subcellular compartment-dependent manner.

Pulmonary natural killer T cells play an essential role in mediating hyperoxic acute lung injury

Critically ill patients are routinely exposed to high concentrations of supplemental oxygen for prolonged periods of time, which can be life-saving in the short term, but such exposure also causes severe lung injury and increases mortality. To address this therapeutic dilemma, we studied the mechanisms of the tissue-damaging effects of oxygen in mice. We show that pulmonary invariant natural killer T (iNKT) cells are unexpectedly crucial in the development of acute oxygen-induced lung injury. iNKT cells express high concentrations of the ectonucleotidase CD39, which regulates their state of activation. Both iNKT cell-deficient (Jα18(-/-)) and CD39-null mice tolerate hyperoxia, compared with wild-type control mice that exhibit severe lung injury. An adoptive transfer of wild-type iNKT cells into Jα18(-/-) mice results in hyperoxic lung injury, whereas the transfer of CD39-null iNKT cells does not. Pulmonary iNKT cell activation and proliferation are modulated by ATP-dependent purinergic signaling responses. Hyperoxic lung injury can be induced by selective P2X7-receptor blockade in CD39-null mice. Our data indicate that iNKT cells are involved in the pathogenesis of hyperoxic lung injury, and that tissue protection can be mediated through ATP-induced P2X7 receptor signaling, resulting in iNKT cell death. In conclusion, our data suggest that iNKT cells and purinergic signaling should be evaluated as potential novel therapeutic targets to prevent hyperoxic lung injury.

CD8-β ADP-ribosylation affects CD8(+) T-cell function

The CD8αβ coreceptor is crucial for effective peptide: MHC-I recognition by the TCR of CD8(+) T cells. Adenosine diphosphate ribosyl transferase 2.2 (ART2.2) utilizes extracellular NAD(+) to transfer ADP-ribose to arginine residues of extracellular domains of surface proteins. Here, we show that in the presence of extracellular NAD(+) , ART2.2 caused ADP-ribosylation of CD8-β on murine CD8(+) T cells in vitro and in vivo. Treatment with NAD(+) prevented binding of anti-CD8-β mAb YTS156.7.7 but not of mAb H35-17.2, indicating that NAD(+) caused modification of certain epitopes and not a general loss of CD8-β. Loss of antibody binding was strictly dependent on ART2.2, because it was not observed on ART2-deficient T cells or in the presence of inhibitory anti-ART2.2 single-domain antibodies. ADP-ribosylation of CD8-β occurred during cell isolation, particularly when cells were isolated from CD38-deficient mice. Incubation of ART2-expressing, but not of ART2-deficient, OVA-specific CD8(+) T cells with NAD(+) interfered with binding of OVA257-264 :MHC-I tetramers. In line with this result, treatment of WT mice with NAD(+) resulted in reduced CD8(+) T-cell mediated cytotoxicity in vivo. We propose that ADP-ribosylation of CD8-β can regulate the coreceptor function of CD8 in the presence of elevated levels of extracellular NAD(+) .

Extracellular ATP-stimulated macrophages produce macrophage inflammatory protein-2 which is important for neutrophil migration

Macrophages are the major source of the chemokines macrophage inflammatory protein-2 (MIP-2) and keratinocyte-derived chemokine (KC), which play a major role in neutrophil migration to sites of inflammation. Although extracellular ATP from inflammatory tissues induces several immune responses in macrophages, it is unclear whether ATP-stimulated macrophages affect neutrophil migration. Therefore, the aim of the present study was to investigate the role of ATP-induced MIP-2 production by macrophages. When ATP was injected intraperitoneally into mice, the number of neutrophils within the peritoneal cavity markedly increased, along with the levels of MIP-2 and KC in the peritoneal lavage fluid. Consistent with this, ATP induced MIP-2 production, but not that of KC, by peritoneal exudate macrophages (PEMs) in vitro. This occurred via interactions with the P2X(7) receptor and P2Y(2) receptor. Furthermore, treatment of PEMs with ATP led to the production of reactive oxygen species. The ATP-induced MIP-2 production was inhibited by treatment with the antioxidant N-acetyl-l-cysteine. Also, MIP-2 production was inhibited by pre-incubating PEMs with inhibitors of extracellular signal-regulated kinase 1/2 or p38 mitogen-activated protein kinase. The MIP-2 neutralization reduced the increase in neutrophil numbers observed in ATP-treated mice. Taken together, these results suggest that increased production of reactive oxygen species by ATP-stimulated macrophages activates the signalling pathways that promote MIP-2 production which, in turn, induces neutrophil migration.

NAD induces astrocyte calcium flux and cell death by ART2 and P2X7 pathway

Mono-ADP-ribosyltransferase 2 (ART2) is found in mouse T cells and has mediated NAD-induced cell death (NICD) alongside the P2X7 pathway. We determined whether ART2 was expressed in mouse brain astrocytes and the possible function of the NAD-ART2-P2X7 pathway in astrocytes. Our results demonstrate that ART2 existed both in cultured mouse astrocytes and mouse brain slices. Exposure of astrocytes to the ART2 substrate, NAD, induced calcium elevation, which was blocked by ART2 and P2X7 inhibitors. ATP and NAD had an additive effect on calcium elevation. NICD in low-calcium conditions was blocked by ART2 and P2X7 inhibitors. The harmful effect of ATP on astrocytes was inhibited by P2X7 and ART2 inhibitors, meaning that endogenous NAD release may occur. Both NICD function and oxygen-glucose deprivation injury in mouse brain slices were also involved in the ART2-P2X7 pathway. Collectively, to our knowledge, our study provides the first evidence that ART2 exists in mouse brain astrocytes and NAD induces calcium elevation and astrocyte death by an ART2 and P2X7-mediated mechanism. The results suggest a novel approach for manipulating astrocyte death.

A common missense variant in the ATP receptor P2X7 is associated with reduced risk of cardiovascular events

Background and Purpose

Extracellular adenosine triphosphate (ATP) regulates inflammatory cells by activation of the P2X₇ receptor. We hypothesized that polymorphisms in P2RX7 influence the risk of ischemic heart disease (IHD), ischemic stroke (IS) and cardiovascular risk factors and tested this hypothesis using genetic association studies.

Methods

Two loss-of-function SNPs in P2RX7 were genotyped in 1244 IHD cases and 2488 controls as well as 5969 individuals with cardiovascular risk factors. Eleven SNPs in a 250 kb region on chromosome 12 spanning P2RX7 as well as neighboring genes OASL, P2RX4 and CAMKK2 were genotyped in 4138 individuals with IS and 2528 controls. Association was examined using linear and logistic regression models with an additive genetic model.

Results

The common loss-of-function variant rs3751143 was significantly associated with a decreased risk of IHD in smokers (P = 0.03) as well as decreased risk of IS (OR 0.89; 95% CI = 0.81–0.97; P = 0.012). In addition, an intronic SNP in CAMKK2, rs2686342, were associated with a decreased risk of IS (OR 0.89; 95% CI = 0.82–0.97; P = 0.011). In subgroup analyses, both SNPs were associated with decreased risk of IS in individuals with hypertension (P = 0.045 and 0.015, respectively).

Conclusions

A common loss-of-function missense variant in the gene encoding the P2X₇ receptor is associated with reduced risk of IS and with IHD in smokers. These findings might implicate a role of purinergic signaling in atherogenesis or atherothrombosis.

A label-free fluorescence DNA probe based on ligation reaction with quadruplex formation for highly sensitive and selective detection of nicotinamide adenine dinucleotide

A simple label-free fluorescent sensing scheme for sensitive and selective detection of nicotinamide adenine dinucleotide (NAD(+)) has been developed based on DNA ligation reaction with ligand-responsive quadruplex formation. This approach can detect 0.5 nM NAD(+) with high selectivity against other NAD(+) analogs.

Transgenic overexpression of toxin-related ecto-ADP-ribosyltransferase ART2.2 sensitizes T cells but not B cells to NAD-induced cell death

T cells constitutively express low amounts of a toxin-related ADP-ribosylating ecto-enzyme, ART2.2. In inflammatory settings, cells release NAD, the substrate for ART2.2. The ART2.2 catalyzed ADP-ribosylation of cell surface proteins induces cell death. However, the low expression levels of ART2.2 have hampered analysis of ART2.2 in physiological settings. Here we report the generation of transgenic mice over-expressing ART2.2 under the control of the H2K promoter and Igμ enhancer. ART2.2 transgenic mice were healthy and fertile and exhibited normal development of the major lymphocyte subsets. Most T cells and a small subpopulation of B cells from transgenic mice showed more than 10-fold higher levels of ART2.2 expression than their wild-type counterparts. Exposure of ART2.2-transgenic T cells to low, submicromolar concentrations of NAD caused cell membrane alterations including uptake of propidium iodide, externalization of phosphatidylserine, and shedding of CD62L, while ART2.2-transgenic B cells were resistant to NAD. The ART2.2-overexpressing animals described here confirm that ART2.2 is an essential component for the regulation of T-cell functions by extracellular NAD and provide a useful tool to further elucidate the function of ART2.2 in vivo.

Polymyxin B increases the depletion of T regulatory cell induced by purinergic agonist

Regulatory T cells (Treg) are important in the development of immune tolerance under normal physiological conditions. However, in pathological situations such as cancer, Treg increases have been correlated with bad prognoses. Treg depletion can be achieved in vitro under several stimuli, including the activation of the purinergic P2X7 receptor. Our aim was to determine whether polymyxin B (PMB), which is a positive modulator of this receptor, could affect mice Treg depletion by ATP and related compounds. For that purpose, we evaluated by flow cytometry changes in Treg populations under several treatments with PMB and/or purinergic agonists and antagonists. We found that both ATP and NAD induce a dose-dependent decrease on the Treg CD4+ CD25+ population. PMB not only potentiated the effect of exogenous ATP and NAD, but also decreased the CD4+ CD25+ population when it was applied alone. While ATP mediated effects are related to the P2X7 receptor, PMB effects appear to be related to another mechanism. We conclude that PMB positively modulates the depletion of the CD4+ CD25+ population of Treg. Therefore PMB could constitute a non-canonical drug with potential use on Treg depletion and cancer treatment.

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.

Graft-versus-host disease is enhanced by extracellular ATP activating P2X7R

Danger signals released upon cell damage can cause excessive immune-mediated tissue destruction such as that found in acute graft-versus-host disease (GVHD), allograft rejection and systemic inflammatory response syndrome. Given that ATP is found in small concentrations in the extracellular space under physiological conditions, and its receptor P2X(7)R is expressed on several immune cell types, ATP could function as a danger signal when released from dying cells. We observed increased ATP concentrations in the peritoneal fluid after total body irradiation, and during the development of GVHD in mice and in humans. Stimulation of antigen-presenting cells (APCs) with ATP led to increased expression of CD80 and CD86 in vitro and in vivo and actuated a cascade of proinflammatory events, including signal transducer and activator of transcription-1 (STAT1) phosphorylation, interferon-γ (IFN-γ) production and donor T cell expansion, whereas regulatory T cell numbers were reduced. P2X(7)R expression increased when GVHD evolved, rendering APCs more responsive to the detrimental effects of ATP, thereby providing positive feedback signals. ATP neutralization, early P2X(7)R blockade or genetic deficiency of P2X(7)R during GVHD development improved survival without immune paralysis. These data have major implications for transplantation medicine, as pharmacological interference with danger signals that act via P2X(7)R could lead to the development of tolerance without the need for intensive immunosuppression.

Side chain specificity of ADP-ribosylation by a sirtuin

Endogenous mono-ADP-ribosylation in eukaryotes is involved in regulating protein synthesis, signal transduction, cytoskeletal integrity, and cell proliferation, although few cellular ADP-ribosyltransferases have been identified. The sirtuins constitute a highly conserved family of protein deacetylases, and several family members have also been reported to perform protein ADP-ribosylation. We characterized the ADP-ribosylation reaction of the nuclear sirtuin homolog Trypanosoma brucei SIR2-related protein 1 (TbSIR2RP1) on both acetylated and unacetylated substrates. We demonstrated that an acetylated substrate is not required for ADP-ribosylation to occur, indicating that the reaction performed by TbSIR2RP1 is a genuine enzymatic reaction and not a side reaction of deacetylation. Biochemical and MS data showed that arginine is the major ADP-ribose acceptor for unacetylated substrates, whereas arginine does not appear to be the major ADP-ribose acceptor in reactions with acetylated histone H1.1. We performed combined ab initio quantum mechanical/molecular mechanical molecular dynamics simulations, which indicated that sirtuin ADP-ribosylation at arginine is energetically feasible, and involves a concerted mechanism with a highly dissociative transition state. In comparison with the corresponding nicotinamide cleavage in the deacetylation reaction, the simulations suggest that sirtuin ADP-ribosylation would be several orders slower but less sensitive to nicotinamide inhibition, which is consistent with experimental results. These results suggest that TbSIR2RP1 can perform ADP-ribosylation using two distinct mechanisms, depending on whether or not the substrate is acetylated.

Basal and inducible expression of the thiol-sensitive ART2.1 ecto-ADP-ribosyltransferase in myeloid and lymphoid leukocytes

ADP-ribosylation of cell surface proteins in mammalian cells is a post-translational modification by which ecto-ADP-ribosyltransferases (ARTs) transfer ADP-ribose from extracellular NAD to protein targets. The ART2 locus at murine chromosome 7 encompasses the tandem Art2a and Art2b genes that encode the distinct ART2.1 and ART2.2 proteins. Although both ecto-enzymes share 80% sequence identity, ART2.1 activity is uniquely regulated by an allosteric disulfide bond that is reducible in the presence of extracellular thiols, such as cysteine and glutathione, that accumulate in hypoxic and ischemic tissues. Previous studies have characterized the expression of ART2.1 and ART2.2 in murine T lymphocytes but not in other major classes of lymphoid and myeloid leukocytes. Here, we describe the expression of ART2.1 activity in a wide range of freshly isolated or tissue-cultured murine myeloid and lymphoid leukocytes. Spleen-derived macrophages, dendritic cells (DC), and B cells constitutively express ART2.1 as their predominant ART while spleen T cells express both ART2.1 and the thiol-independent ART2.2 isoform. Although bone-marrow-derived macrophages (BMDM) and dendritic cells (BMDC) constitutively express ART2.1 at low levels, it is markedly up-regulated when these cells are stimulated in vitro with IFNbeta or IFNgamma. ART2.1 expression and activity in splenic B cells is modestly up-regulated during incubation in vitro for 24 h, a condition that promotes B cell apoptosis. This increase in ART2.1 is attenuated by IL-4 (a B cell survival factor), but is not affected by IFNbeta/gamma, suggesting a possible induction of ART2.1 as an ancillary response to B cell apoptosis. In contrast, ART2.1 and ART2.2, which are highly expressed in freshly isolated splenic T cells, are markedly down-regulated when purified T cells are incubated in vitro for 12-24 h. Studies with the BW5147 mouse thymocyte line verified basal expression of ART2.1 and ART2.2, as in primary spleen T cells, and demonstrated that both isoforms can be up-regulated when T cells are maintained in the presence of IFNs. Comparison of the surface proteins which are ADP-ribosylated by ART2.1 in the different leukocyte subtypes indicated both shared and cell-specific proteins as ART2.1 substrates. The LFA-1 integrin, a major target for ART2.2 in T cells, is also ADP-ribosylated by the ART2.1 expressed in macrophages. Thus, ART2.1, in contrast to ART2.2, is expressed in a broad range of myeloid and lymphoid leukocytes. The thiol redox-sensitive nature of this ecto-enzyme suggests an involvement in purinergic signaling that occurs in the combined context of inflammation and hypoxia/ischemia.

NAD+ and ATP released from injured cells induce P2X7-dependent shedding of CD62L and externalization of phosphatidylserine by murine T cells

Extracellular NAD(+) and ATP trigger the shedding of CD62L and the externalization of phosphatidylserine on murine T cells. These events depend on the P2X(7) ion channel. Although ATP acts as a soluble ligand to activate P2X(7), gating of P2X(7) by NAD(+) requires ecto-ADP-ribosyltransferase ART2.2-catalyzed transfer of the ADP-ribose moiety from NAD(+) onto Arg125 of P2X(7). Steady-state concentrations of NAD(+) and ATP in extracellular compartments are highly regulated and usually are well below the threshold required for activating P2X(7). The goal of this study was to identify possible endogenous sources of these nucleotides. We show that lysis of erythrocytes releases sufficient levels of NAD(+) and ATP to induce activation of P2X(7). Dilution of erythrocyte lysates or incubation of lysates at 37 degrees C revealed that signaling by ATP fades more rapidly than that by NAD(+). We further show that the routine preparation of primary lymph node and spleen cells induces the release of NAD(+) in sufficient concentrations for ART2.2 to ADP-ribosylate P2X(7), even at 4 degrees C. Gating of P2X(7) occurs when T cells are returned to 37 degrees C, rapidly inducing CD62L-shedding and PS-externalization by a substantial fraction of the cells. The "spontaneous" activation of P2X(7) during preparation of primary T cells could be prevented by i.v. injection of either the surrogate ART substrate etheno-NAD or ART2.2-inhibitory single domain Abs 10 min before sacrificing mice.

Activation of the P2X7 ion channel by soluble and covalently bound ligands

The homotrimeric P2X7 purinergic receptor has sparked interest because of its capacity to sense adenosine triphosphate (ATP) and nicotinamide adenine dinucleotide (NAD) released from cells and to induce calcium signaling and cell death. Here, we examine the response of arginine mutants of P2X7 to soluble and covalently bound ligands. High concentrations of ecto-ATP gate P2X7 by acting as a soluble ligand and low concentrations of ecto-NAD gate P2X7 following ADP-ribosylation at R125 catalyzed by toxin-related ecto-ADP-ribosyltransferase ART2.2. R125 lies on a prominent cysteine-rich finger at the interface of adjacent receptor subunits, and ADP-ribosylation at this site likely places the common adenine nucleotide moiety into the ligand-binding pocket of P2X7.

The importance of NAD in multiple sclerosis

The etiology of multiple sclerosis (MS) is unknown but it manifests as a chronic inflammatory demyelinating disease in the central nervous system (CNS). During chronic CNS inflammation, nicotinamide adenine dinucleotide (NAD) concentrations are altered by (T helper) Th1-derived cytokines through the coordinated induction of both indoleamine 2,3-dioxygenase (IDO) and the ADP cyclase CD38 in pathogenic microglia and lymphocytes. While IDO activation may keep auto-reactive T cells in check, hyper-activation of IDO can leave neuronal CNS cells starving for extracellular sources of NAD. Existing data indicate that glia may serve critical functions as an essential supplier of NAD to neurons during times of stress. Administration of pharmacological doses of non-tryptophan NAD precursors ameliorates pathogenesis in animal models of MS. Animal models of MS involve artificially stimulated autoimmune attack of myelin by experimental autoimmune encephalomyelitis (EAE) or by viral-mediated demyelination using Thieler's murine encephalomyelitis virus (TMEV). The Wld(S) mouse dramatically resists razor axotomy mediated axonal degeneration. This resistance is due to increased efficiency of NAD biosynthesis that delays stress-induced depletion of axonal NAD and ATP. Although the Wld(S) genotype protects against EAE pathogenesis, TMEV-mediated pathogenesis is exacerbated. In this review, we contrast the role of NAD in EAE versus TMEV demyelinating pathogenesis to increase our understanding of the pharmacotherapeutic potential of NAD signal transduction pathways. We speculate on the importance of increased SIRT1 activity in both PARP-1 inhibition and the potentially integral role of neuronal CD200 interactions through glial CD200R with induction of IDO in MS pathogenesis. A comprehensive review of immunomodulatory control of NAD biosynthesis and degradation in MS pathogenesis is presented. Distinctive pharmacological approaches designed for NAD-complementation or targeting NAD-centric proteins (SIRT1, SIRT2, PARP-1, GPR109a, and CD38) are outlined towards determining which approach may work best in the context of clinical application.

The Poly(ADP-ribose) polymerase PARP-1 is required for oxidative stress-induced TRPM2 activation in lymphocytes

TRPM2 cation channels are widely expressed in the immune system and are thought to play a role in immune cell responses to oxidative stress. Patch clamp analyses suggest that TRPM2 channel activation can occur through a direct action of oxidants on TRPM2 channels or indirectly through the actions of a related group of adenine nucleotide 2nd messengers. However, the contribution of each gating mechanism to oxidative stress-induced TRPM2 activation in lymphocytes remains undefined. To better understand the molecular events leading to TRPM2 activation in lymphocytes, we analyzed oxidative stress-induced turnover of intracellular NAD, the metabolic precursor of adenine nucleotide 2nd messengers implicated in TRPM2 gating, and oxidative stress-induced TRPM2-mediated currents and Ca2+ transients in DT40 B cells. TRPM2-dependent Ca2+ entry did not influence the extent or time course of oxidative stress-induced turnover of NAD. Furthermore, expression of oxidative stress-activated poly(ADP-ribose) polymerases (PARPs) was required for oxidative stress-induced NAD turnover, TRPM2 currents, and TRPM2-dependent Ca2+ transients; no oxidant-induced activation of TRPM2 channels could be detected in PARP-deficient cells. Together, our results suggest that during conditions of oxidative stress in lymphocytes, TRPM2 acts as a downstream effector of the PARP/poly(ADP-ribose) glycohydrolase pathway through PARP-dependent formation of ADP-ribose.

P2x7 deficiency suppresses development of experimental autoimmune encephalomyelitis

Background

The purinergic receptor P2x7 is expressed on myeloid cells as well as on CNS glial cells, and P2x7 activation has been shown to increase both glial and T-cell activation. These properties suggest a role in the development of autoimmune disease including multiple sclerosis.

Methods

The animal model of MS, experimental autoimmune encephalomyelitis (EAE) using myelin oligodendrocyte glycoprotein (MOG) peptide residues 35–55 was induced in wildtype C57BL6 mice and in P2x7 deficient mice ('P2x7 mice') that were backcrossed to C57BL6 mice. Disease progression was monitored by appearance of clinical signs, immunocytochemical staining to assess brain inflammation and neuronal damage, and by measurement of Tcell cytokine production.

Results

The incidence of EAE disease in P2x7 mice was reduced 4-fold compared to the wildtype mice; however the P2x7 mice that became ill had similar days of onset and clinical scores as the wildtype mice. Splenic T-cells isolated from P2x7 null mice produced greater IFNγ and IL-17 (from 3 to 12 fold greater levels) than wildtype cells, however cytokine production from P2x7 derived cells was not increased by a selective P2x7 agonist as was cytokine production from wildtype cells. Although infiltrating cells were detected in brains of both the P2x7 and wildtype mice, astroglial activation and axonal damage was reduced versus wildtype mice, and the distribution of astroglial activation was markedly distinct in the two strains. In contrast, microglial activation was similar in the two strains.

Conclusion

P2x7 deficiency resulted in compensatory changes leading to increased T-cell cytokine production, and activated T-cells were detected in the brains of P2x7 null mice with no clinical signs. However, the greatly reduced incidence of disease suggests that an initiating event is absent in these mice, and points to a role for astroglial P2x7 in development of EAE disease.

ADP-ribosylation at R125 gates the P2X7 ion channel by presenting a covalent ligand to its nucleotide binding site

ADP-ribosylation is a post-translational modification regulating protein function in which amino acid-specific ADP-ribosyltransferases (ARTs) transfer ADP-ribose from NAD onto specific target proteins. Attachment of the bulky ADP-ribose usually inactivates the target by sterically blocking its interaction with other proteins. P2X7, an ATP-gated ion channel with important roles in inflammation and cell death, in contrast, is activated by ADP-ribosylation. Here, we report the structural basis for this gating and present the first molecular model for the activation of a target protein by ADP-ribosylation. We demonstrate that the ecto-enzyme ART2.2 ADP-ribosylates P2X7 at arginine 125 in a prominent, cysteine-rich region at the interface of 2 receptor subunits. ADP-ribose shares an adenine-ribonucleotide moiety with ATP. Our results indicate that ADP-ribosylation of R125 positions this common chemical framework to fit into the nucleotide-binding site of P2X7 and thereby gates the channel.

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.

Single domain antibodies from llama effectively and specifically block T cell ecto-ADP-ribosyltransferase ART2.2 in vivo

The purpose of our study was to develop a tool for blocking the function of a specific leukocyte ecto-enzyme in vivo. ART2.2 is a toxin-related ecto-enzyme that transfers the ADP-ribose moiety from NAD onto other cell surface proteins. ART2.2 induces T cell death by activating the cytolytic P2x7 purinoceptor via ADP-ribosylation. Here, we report the generation of ART2.2-blocking single domain antibodies from an immunized llama. The variable domain of heavy-chain antibodies (VHH domain) represents the smallest known antigen-binding unit generated by adaptive immune responses. Their long CDR3 endows VHH domains with the extraordinary capacity to extend into and block molecular clefts. Following intravenous injection, the ART2.2-specific VHH domains effectively shut off the enzymatic and cytotoxic activities of ART2.2 in lymphatic organs. This blockade was highly specific (blocking ART2.2 but not the related enzymes ART1 or ART2.1), rapid (within 15 min after injection), and reversible (24 h after injection). Our findings constitute a proof of principle that opens up a new avenue for targeting leukocyte ecto-enzymes in vivo and that can serve as a model also for developing new antidotes against ADP-ribosylating toxins.

P2X7 receptor expression levels determine lethal effects of a purine based danger signal in T lymphocytes

Contact of T lymphocytes with nicotinamide adenine dinucleotide (NAD) or ATP causes cell death that requires expression of purinergic receptor P2X(7) (P2X(7)R). T cell subsets differ in their responses to NAD and ATP, which awaits a mechanistic explanation. Here, we show that sensitivity to ATP correlates with P2X(7)R expression levels in CD4 cells, CD8 cells and CD4(+)CD25(+) cells from both C57BL/6 and BALB/c mice. But P2X(7)R ligands do not only induce cell death but also shedding of CD62L. It is shown here that in CD62L(high) T cells, CD62L shedding correlates with low expression of P2X(7)Rs and lower cell death, whereas in CD62L(low) cells P2X(7)R expression and death are higher. The possibility is therefore investigated that P2X(7)Rs induce T cell activation. Experiments show that spontaneous T cell proliferation is somewhat higher in cells expressing P2X(7)Rs, but this effect we suggest is caused by P2X(7)R expression on accessory cells.

HCV core expression in hepatocytes protects against autoimmune liver injury and promotes liver regeneration in mice

Hepatitis C virus (HCV) infection causes acute and chronic liver disease often leading to liver cirrhosis and hepatocellular carcinoma. Numerous studies have shown that despite induction of virus specific immunity, a curative response is often not attained; this has led to the hypothesis that HCV genes modulate immunity, thereby enabling chronic infections. This study examined the effects on immune-mediated liver injury in transgenic mice expressing core protein throughout the body and bone marrow chimeras expressing core protein in either the lymphoid compartment or liver parenchyma. Presence of core protein in the liver parenchyma but not in lymphoid cells protects from autoimmune hepatitis induced by mitogen concanavalin A (ConA). Consistent with this observation, core transgenic hepatocytes are relatively resistant to death induced by anti-Fas antibody and tumor necrosis factor alpha (TNFalpha). This protective effect is associated with preferential activation of signal transducer and activation of transcription factor 3 (STAT3) versus STAT1 in livers of ConA-injected animals. In agreement with this effect of core protein on the Janus kinase (JAK)-STAT signaling pathway, transgenic mice accelerate liver regeneration after partial hepatectomy but are not protected from hepatocyte death. In conclusion, HCV core inhibits STAT1 and stimulates STAT3 activation, which protects infected hepatocytes from attack by the cell-mediated immune system and promotes their proliferation.

Immunostimulatory combinations: designing the next generation of vaccine adjuvants

Agents that activate dendritic cells are essential components for vaccines and can be conceptualized as molecular adjuvants. Other molecular adjuvants affect downstream factors that shape the resulting immune response. This review provides a compendium of recently studied molecular adjuvants, focusing on CD8+ T cell responses, which have important roles in HIV vaccines. Reference is also made to CD8+ T cell antitumor responses, where parallel studies of molecular adjuvants are being pursued. Molecular adjuvants can be considered in the following groups: TNF superfamily molecules such as CD40 ligand; agonists for TLRs; agonists for NAIP, CIITA, HET-E, TP-1-leucine-rich repeat pathway receptors, such as nucleotide-binding and oligomerization domain (NOD)1, NOD2, and cryopyrin; chemokines; ILs; CSFs; IFNs; alarmins; and purinergic P2X7 receptor agonists. Complementing these positively acting agents are strategies to reduce the immunosuppressive effects of CD4+CD25+ regulatory T cells and negatively acting factors such as TGF-beta, IL-10, suppressor of cytokine signaling 1, and programmed cell death-1 using neutralizing antibodies, antisense, and small interfering RNA. Especially effective are combinations of molecular adjuvants, which can elicit a massive expansion of antigen-specific CD8+ T cells and show unprecedented efficacy in vaccine and tumor models. Taken together, these new approaches provide significant incremental progress in the development of vaccines to elicit cell-mediated immunity against HIV and other pathogens.

Extracellular NAD+ is an agonist of the human P2Y11 purinergic receptor in human granulocytes

Micromolar concentrations of extracellular beta-NAD+ (NAD(e)+) activate human granulocytes (superoxide and NO generation and chemotaxis) by triggering: (i) overproduction of cAMP, (ii) activation of protein kinase A, (iii) stimulation of ADP-ribosyl cyclase and overproduction of cyclic ADP-ribose (cADPR), a universal Ca2+ mobilizer, and (iv) influx of extracellular Ca2+. Here we demonstrate that exposure of granulocytes to millimolar rather than to micromolar NAD(e)+ generates both inositol 1,4,5-trisphosphate (IP3) and cAMP, with a two-step elevation of intracellular calcium levels ([Ca2+]i): a rapid, IP3-mediated Ca2+ release, followed by a sustained influx of extracellular Ca2+ mediated by cADPR. Suramin, an inhibitor of P2Y receptors, abrogated NAD(e)+-induced intracellular increases of IP3, cAMP, cADPR, and [Ca2+]i, suggesting a role for a P2Y receptor coupled to both phospholipase C and adenylyl cyclase. The P2Y(11) receptor is the only known member of the P2Y receptor subfamily coupled to both phospholipase C and adenylyl cyclase. Therefore, we performed experiments on hP2Y(11)-transfected 1321N1 astrocytoma cells: micromolar NAD(e)+ promoted a two-step elevation of the [Ca2+]i due to the enhanced intracellular production of IP3, cAMP, and cADPR in 1321N1-hP2Y(11) but not in untransfected 1321N1 cells. In human granulocytes NF157, a selective and potent inhibitor of P2Y(11), and the down-regulation of P2Y(11) expression by short interference RNA prevented NAD(e)+-induced intracellular increases of [Ca2+]i and chemotaxis. These results demonstrate that beta-NAD(e)+ is an agonist of the P2Y(11) purinoceptor and that P2Y(11) is the endogenous receptor in granulocytes mediating the sustained [Ca2+]i increase responsible for their functional activation.

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.

Targeted disruption of CD38 accelerates autoimmune diabetes in NOD/Lt mice by enhancing autoimmunity in an ADP-ribosyltransferase 2-dependent fashion

Ubiquitously expressed CD38 and T cell-expressed ADP-ribosyltransferase 2 (ART2) are ectoenzymes competing for NAD substrate. CD38 exerts pleiotropic actions in hemopoietic and nonhemopoietic compartments via effects on calcium mobilization. ART2 is an ADP-ribosyltransferase on naive CD4+ and CD8+ T cells. ART2-catalyzed ADP-ribosylation of the P2X7 purinoreceptor elicits apoptosis. Transfer of a genetically disrupted CD38 allele into the autoimmune diabetes-prone NOD/Lt background accelerated diabetes onset in both sexes, whereas transfer of a disrupted ART2 complex had no effect. However, the fact that the accelerated pathogenesis mediated by CD38 deficiency required ART2 activity was demonstrated by combining both ART2 and CD38 deficiencies. Reciprocal bone marrow reconstitution studies demonstrated accelerated diabetes only when CD38-deficient bone marrow was transferred into CD38-deficient recipients. Neither decreases in beta cell function nor viability were indicated. Rather, the balance between T-effectors and T-regulatory cells was disturbed in CD38-deficient but ART2-intact NOD mice. In these mice, significant reductions in total viable CD8+ T cells were observed. This was accompanied by an age-dependent increase in a diabetogenic CD8 clonotype. This in turn correlated with impaired T-regulatory development (10-fold reduction in Foxp3 mRNA expression). These changes were corrected when CD38 deficiency was combined with ART2 deficiency. Both ART2-deficient and CD38/ART2 combined deficient T cells were resistant to NAD-induced killing in vitro, whereas CD38-deficient but ART2-intact T cells showed increased sensitivity, particularly the CD4+ CD25+ subset. Unexpectedly, diabetes development in the combined CD38/ART2 stock was strongly suppressed, possibly through epistatic interactions between genes linked to the targeted CD38 on Chromosome 5 and the ART2 complex on Chromosome 7.

Extracellular NAD+ regulates intracellular calcium levels and induces activation of human granulocytes

Beta-NAD+e (extracellular beta-NAD+), present at nanomolar levels in human plasma, has been implicated in the regulation of [Ca2+]i (the intracellular calcium concentration) in various cell types, including blood cells, by means of different mechanisms. Here, we demonstrate that micromolar NAD+e (both the alpha and the beta extracellular NAD+ forms) induces a sustained [Ca2+]i increase in human granulocytes by triggering the following cascade of causally related events: (i) activation of adenylate cyclase and overproduction of cAMP; (ii) activation of protein kinase A; (iii) stimulation of ADP-ribosyl cyclase activity and consequent overproduction of cADP-ribose, a universal Ca2+ mobilizer; and (iv) influx of extracellular Ca2+. The NAD+e-triggered [Ca2+]i elevation translates into granulocyte activation, i.e. superoxide and nitric oxide generation, and enhanced chemotaxis in response to 0.1-10 microM NAD+e. Thus extracellular beta-NAD+e behaves as a novel pro-inflammatory cytokine, stimulating human granulocytes and potentially recruiting them at sites of inflammation.

P2X7 receptors regulate NKT cells in autoimmune hepatitis

Adenine nucleotides induce danger signals in T cells via purinergic receptors, raising the question whether they exert similar effects on innate immunity. Here we show that micromolar concentrations of nicotinamide adenine dinucleotide (NAD) induce a rapid increase of annexin V staining in NKT cells in vitro, a response that requires expression of P2X(7)Rs. Consistent with this result, treatment of mice with NAD causes a temporary decrease of NKT cells in the liver and protects from Con A- and alpha-galactosylceramide-induced hepatitis, both of which require functional NKT cells. Resistance to liver injury is associated with decreased cytokine production by NKT cells in NAD-treated mice. In contrast, when NAD is injected into Con A- or alpha-galactosylceramide-primed mice, liver injury is exacerbated and cytokine production by NKT cells is increased. This effect is caused by P2X(7)R-mediated stimulation of activated NKT cells. In agreement, mice lacking P2X(7)Rs on lymphocytes suffer reduced liver injury, and animals lacking ADP-ribosyltransferase, the enzyme that uses NAD to attach ADP-ribosyl groups to cell surfaces, are also resistant to Con A-induced hepatitis. These results prompt the conclusion that engagement of P2X(7)Rs on NKT cells inhibits naive, while stimulating activated cells, resulting in suppression or stimulation of autoimmune hepatitis.

Exacerbation of Experimental Autoimmune Encephalomyelitis in P2X7R−/−Mice: Evidence for Loss of Apoptotic Activity in Lymphocytes

The purinergic receptor P2X7R is a nucleotide-gated ion channel that has been proposed to function as a major regulator of inflammation. In this study we examined the role of this receptor in regulating inflammation in the CNS by determining the effects of the loss of this receptor (P2X7R-/-) on experimental autoimmune encephalomyelitis (EAE), an animal model for multiple sclerosis. We show here that P2X7R-/- mice developed more severe clinical and pathological expression of EAE than wild type (WT) controls and that spleen and lymph node cells from P2X7R-/- mice proliferated more vigorously to Ag in vitro. Bone marrow (BM) radiation chimeras revealed that enhanced susceptibility to EAE was detected in chimeric mice of WT host engrafted with P2X7R-/- BM cells, indicating that the genotype of the BM cells regulated disease susceptibility. Coculture of P2X7R-/- macrophages with WT lymphocytes and vice versa showed that enhanced proliferative activity resided within the P2X7R-/- lymphocyte population and correlated with reduced levels of IFN-gamma and NO and apoptosis of lymphocytes. mRNA and protein for IFN-gamma were also significantly reduced in the CNS of P2X7R-/- mice with EAE. FACS analysis of cells isolated from the CNS showed significantly fewer annexin V/propidium iodide-positive lymphocytes in the CNS of P2X7R-/- mice early in the disease, and TUNEL staining of inflamed CNS tissues supported this result. From these data we conclude that enhanced susceptibility of P2X7R-/- mice to EAE reflects a loss of apoptotic activity in lymphocytes, supporting an important role for this receptor in lymphocyte homeostasis.

The Anti–Human Leukocyte Antigen-DR Monoclonal Antibody 1D09C3 Activates the Mitochondrial Cell Death Pathway and Exerts a Potent Antitumor Activity in Lymphoma-Bearing Nonobese Diabetic/Severe Combined Immunodeficient Mice

The fully human anti-HLA-DR antibody 1D09C3 has been shown to delay lymphoma cell growth in severe combined immunodeficient (SCID) mice. The present study was aimed at (a) investigating the mechanism(s) of 1D09C3-induced cell death and (b) further exploring the therapeutic efficacy of 1D09C3 in nonobese diabetic (NOD)/SCID mice. The chronic lymphocytic leukemia cell line JVM-2 and the mantle cell lymphoma cell line GRANTA-519 were used. Generation of reactive oxygen species (ROS) and mitochondrial membrane depolarization were measured by flow cytometry following cell incubation with dihydroethidium and TMRE, respectively. Western blot analysis was used to detect c-Jun-NH(2)-kinase (JNK) phosphorylation and apoptosis-inducing factor (AIF). NOD/SCID mice were used to investigate the activity of 1D09C3 in early- or advanced-stage tumor xenografts. In vitro, 1D09C3-induced cell death involves a cascade of events, including ROS increase, JNK activation, mitochondrial membrane depolarization, and AIF release from mitochondria. Inhibition of JNK activity significantly reduced 1D09C3-induced apoptosis, indicating that 1D09C3 activity involves activation of the kinase. In vivo, 1D09C3 induces long-term disease-free survival in a significant proportion of tumor-bearing mice treated at an early stage of disease. Treatment of mice bearing advanced-stage lymphoma results in a highly significant prolongation of survival. These data show that 1D09C3 (a) exerts a potent antitumor effect by activating ROS-dependent, JNK-driven cell death, (b) cures the great majority of mice treated at an early-stage of disease, and (c) significantly prolongs survival of mice with advanced-stage disease.

Ecto-ADP-ribose transferases: cell-surface response to local tissue injury

Ecto-ADP-ribose transferases (ecto-ARTs) catalyze the transfer of ADP-ribose from NAD(+) to arginine residues in cell-surface proteins. Since the concentration of extracellular NAD(+) is very low under normal physiological conditions but rises significantly upon tissue injury or membrane stress, it is postulated that the main role of ecto-ARTs is to ADP-ribosylate and regulate the function of certain membrane receptors in response to elevated levels of NAD(+).

"Agouti NOD": identification of a CBA-derived Idd locus on Chromosome 7 and its use for chimera production with NOD embryonic stem cells

Penetrance of the complex of genes predisposing the nonobese diabetic (NOD) mouse to autoimmune diabetes is affected by the maternal environment. NOD.CBALs-Tyr(+)/Lt is an agouti-pigmented Chromosome 7 congenic stock of NOD/Lt mice produced as a resource for embryo transfer experiments to provide the necessary maternal factors and allow the easy identification of NOD (albino) embryo donor phenotype. CBcNO6/Lt, a recombinant congenic agouti stock already containing approximately 50% NOD genome, was used as the donor source of a wild-type CBA tyrosinase allele. When the incidence of diabetes was assessed after nine generations of backcrossing and one generation of sib-sib mating, significant reduction in diabetes development was observed. No difference in diabetes development was observed in Tyr/Tyr(c) heterozygotes, showing that protection was recessive. Analysis of diabetes progression in another NOD stock congenic for C57BL/6 alleles on Chromosome 7 linked to the glucose phosphate isomerase (Gpi1(b)) locus provided no protection, indicating that the diabetes resistance (Idd) gene was distal to 34 cM (D7Mit346). Approximately 5 cM of the distal congenic region overlaps a region from C57L previously associated with protection when homozygous. The delayed onset and reduced frequency of diabetes in the NOD.CBALs-Tyr(+)/Lt stock is an advantage when females of this stock are used as surrogate mothers in studies involving hysterectomy or embryo transfers. Indeed, a newly developed NOD embryonic stem (ES) cell line injected into NOD.CBALs- Tyr(+)/Lt blastocysts produced approximately 50% live-born mice, of which approximately 11% were chimeric. Presumably because of high genomic instability, no germline transmission was observed.

High sensitivity of CD4+CD25+ regulatory T cells to extracellular metabolites nicotinamide adenine dinucleotide and ATP: a role for P2X7 receptors

Although regulatory lymphocytes play an important role in the immune system, the regulation of their functions is poorly understood and remains to be elucidated. In this study we demonstrate that micromolar concentrations of the common cell metabolite NAD induce death in murine forkhead/winged helix transcription factor gene-expressing CD4+CD25+ regulatory T cells with high efficiency and within minutes. Similar, but less dramatic, effects are demonstrable with ATP and its nonhydrolysable derivative, benzoylbenzoyl-ATP. Other T cell subsets are more resistant, with CD8 cells being the least sensitive and CD4 cells expressing intermediate sensitivity. The higher sensitivity of CD4+CD25+ cells is demonstrable in vivo. Injection of NAD or benzoylbenzoyl-ATP causes preferential induction of a cell death signal in CD4+CD25+ cells. Transmission of the death signal requires functional P2X7 receptors, pointing to a role for these receptors in regulation and homeostasis of CD4+CD25+ regulatory T cells. Consistent with this, P2X7R gene-deleted mice possess increased levels of forkhead/winged helix transcription factor gene-expressing CD4+CD25+ cells.