NAD(+) and ATP Released from Injured Cells Induce P2X(7)-Dependent Shedding of CD62L and Externalization of Phosphatidylserine by Murine T Cells
ABSTRACT 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.
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ABSTRACT: A paradigm shift in immunology has been the recent discovery of regulatory T cells (T reg cells), of which CD4(+)Foxp3(+) cells are proven as essential to self-tolerance. Using transgenic B6.Foxp3(hCD2) mice to isolate and ablate Foxp3(+) T reg cells with an anti-hCD2 antibody, we show for the first time that CD4(+)Foxp3(+) cells are crucial for infectious tolerance induced by nonablative anti-T cell antibodies. In tolerant animals, Foxp3(+) T reg cells are constantly required to suppress effector T cells still capable of causing tissue damage. Tolerated tissue contains T cells that are capable of rejecting it, but are prevented from doing so by therapeutically induced Foxp3(+) T reg cells. Finally, Foxp3(+) cells have been confirmed as the critical missing link through which infectious tolerance operates in vivo. Peripherally induced Foxp3(+) cells sustain tolerance by converting naive T cells into the next generation of Foxp3(+) cells. Empowering Foxp3(+) regulatory T cells in vivo offers a tractable route to avoid and correct tissue immunopathology.Journal of Experimental Medicine 08/2011; 208(10):2043-53. DOI:10.1084/jem.20110767 · 13.91 Impact Factor
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ABSTRACT: Nicotinamide adenine dinucleotide (NAD(+)) is an essential co-enzyme that can be released in the extracellular milieu. Here, it may elicit signals through binding purinergic receptors. Alternatively, NAD(+) may be dismantled to adenosine, up-taken by cells and transformed to reconstitute the intracellular nucleotide pool. An articulated ecto-enzyme network is responsible for the nucleotide-nucleoside conversion. CD38 is the main mammalian enzyme that hydrolyzes NAD(+), generating Ca(2+)-active metabolites. Evidence suggests that this extracellular network may be altered or used by tumor cells to (i) nestle in protected areas, and (ii) evade the immune response. We have exploited chronic lymphocytic leukemia as a model to test the role of the ecto-enzyme network, starting by analyzing the individual elements that make up the whole picture.FEBS letters 06/2011; 585(11):1514-20. DOI:10.1016/j.febslet.2011.04.036 · 3.34 Impact Factor
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ABSTRACT: NAD(+) plays central roles in energy metabolism as redox carrier. Recent research has identified important signalling functions of NAD(+) that involve its consumption. Although NAD(+) is synthesized mainly in the cytosol, nucleus and mitochondria, it has been detected also in vesicular and extracellular compartments. Three protein families that consume NAD(+) in signalling reactions have been characterized on a molecular level: ADP-ribosyltransferases (ARTs), Sirtuins (SIRTs), and NAD(+) glycohydrolases (NADases). Members of these families serve important regulatory functions in various cellular compartments, e.g., by linking the cellular energy state to gene expression in the nucleus, by regulating nitrogen metabolism in mitochondria, and by sensing tissue damage in the extracellular compartment. Distinct NAD(+) pools may be crucial for these processes. Here, we review the current knowledge about the compartmentation and biochemistry of NAD(+)-converting enzymes that control NAD(+) signalling.FEBS letters 03/2011; 585(11):1651-6. DOI:10.1016/j.febslet.2011.03.045 · 3.34 Impact Factor