Article

A2A Adenosine Receptor Signaling in Lymphocytes and the Central Nervous System Regulates Inflammation during Experimental Autoimmune Encephalomyelitis

Department of Microbiology and Immunology, College of Veterinary Medicine, Cornell University, Ithaca, NY 14853, USA.
The Journal of Immunology (Impact Factor: 4.92). 04/2012; 188(11):5713-22. DOI: 10.4049/jimmunol.1200545
Source: PubMed

ABSTRACT

Extracellular adenosine has an important role in regulating the severity of inflammation during an immune response. Although there are four adenosine receptor (AR) subtypes, the A2AAR is both highly expressed on lymphocytes and known as a prime mediator of adenosine's anti-inflammatory effects. To define the importance of A2AAR signaling during neuroinflammatory disease progression, we used the experimental autoimmune encephalomyelitis (EAE) animal model for multiple sclerosis. In EAE induction experiments, A2AAR antagonist treatment protected mice from disease development and its associated CNS lymphocyte infiltration. However, A2AAR(-/-) mice developed a more severe acute EAE phenotype characterized by more proinflammatory lymphocytes and activated microglia/macrophages. Interestingly, very high levels of A2AAR were expressed on the choroid plexus, a well-established CNS lymphocyte entry point. To determine the contribution of A2AAR signaling in lymphocytes and the CNS during EAE, we used bone marrow chimeric mice. Remarkably, A2AAR(-/-) donor hematopoietic cells potentiated severe EAE, whereas lack of A2AAR expression on nonhematopoietic cells protected against disease development. Although no defect in the suppressive ability of A2AAR(-/-) regulatory T cells was observed, A2AAR(-/-) lymphocytes were shown to proliferate more and produced more IFN-γ following stimulation. Despite this more proinflammatory phenotype, A2AAR antagonist treatment still protected against EAE when A2AAR(-/-) lymphocytes were adoptively transferred to T cell-deficient A2AAR(+/+) mice. These results indicate that A2AAR expression on nonimmune cells (likely in the CNS) is required for efficient EAE development, while A2AAR lymphocyte expression is essential for limiting the severity of the inflammatory response.

    • "In the middle cerebral artery occlusion (MCAo), a rodent model of brain ischemia, the selective A 2A antagonist SCH58261 prevented myelin disorganization in basal nuclei, and reduced brain damage, microglial activation, and neurological deficits (Melani et al., 2009). In vivo blockade of the A 2A receptor also prevented the onset of experimental autoimmune encephalomyelitis (EAE), a rodent model of MS (Mills et al., 2012). Upregulation of the A 2A receptor was observed in the white matter of patients with secondary progressive MS, and the density of this receptor positively correlated with worsening of disability in patients (Rissanen et al., 2013), suggesting that aberrant A 2A receptor regulation may participate to the onset of demyelination and/or to impaired myelin repair. "
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    ABSTRACT: Oligodendrocytes are the myelin-forming cells in the CNS. They enwrap axons, thus permitting fast impulse transmission and exerting trophic actions on neurons. Demyelination accompanied by neurological deficit is a rather frequent condition that is not only associated with multiple sclerosis but has been also recognized in several other neurodegenerative diseases, including brain trauma and stroke, Alzheimer's disease and amyotrophic lateral sclerosis. Recently, alterations of myelin function have been also reported in neuropsychiatric diseases, like depression and autism. Highly relevant for therapeutic purposes, oligodendrocyte precursor cells (OPCs) still persist in the adult brain and spinal cord. These cells are normally rather quiescent, but under specific circumstances, they can be stimulated to undergo differentiation and generate mature myelinating oligodendrocytes. Thus, approaches aimed at restoring myelin integrity and at fostering a correct oligodendrocyte function are now viewed as novel therapeutic opportunities for both neurodegenerative and neuropsychiatric diseases. Both OPCs and mature oligodendrocytes express purinergic receptors. For some of these receptors, expression is restricted at specific differentiation stages, suggesting key roles in OPCs maturation and myelination. Some of these receptors are altered under demyelinating conditions, suggesting that their disregulation may contribute to disease development and could represent adequate new targets for remyelinating therapies. Here, we shall describe the current literature available on all these receptors, with special emphasis on the P2Y-like GPR17 receptor, that represents one of the most studied receptor subtypes in these cells.
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    • "In the A 2A RÀ/À mice, the acute presentation of EAE was less severe than WT controls. However, after 10 d the disease presentation was comparable (Mills et al., 2012). The same reduction in macrophage activation markers is seen in the spinal cord of EAE rats subsequent to IL-10 gene therapy administered intrathecally in EAE rats (Sloane et al., 2009). "
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    ABSTRACT: A single intrathecal dose of adenosine 2A receptor (A2AR) agonist was previously reported to produce a multi-week reversal of allodynia in two different models of neuropathic pain in addition to downregulating glial activation markers in the spinal cord. We aimed to determine whether a single intrathecal administration of an A2AR agonist was able to attenuate motor symptoms induced by experimental autoimmune encephalopathy. Two A2AR agonists (CGS21680 and ATL313) significantly attenuated progression of motor symptoms following a single intrathecal administration at the onset of motor symptoms. OX-42, a marker of microglial activation, was significantly attenuated in the lumbar spinal cord following A2AR administration compared to vehicle. Therefore, A2AR agonists attenuate motor symptoms of EAE by acting on A2AR in the spinal cord. Copyright © 2015. Published by Elsevier Inc.
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    • "Adenosine resistance in supTh17 cells is likely to be conferred by low levels of A2A adenosine receptor and by higher levels of adenosine catalysis. The A2A adenosine receptor is primarily known to mediate anti-inflammatory effects: lymphocytes from A2A receptor (−/−) mice show higher rates of cell proliferation and produce high IFNγ levels upon stimulation [50]. A2A receptor stimulation has established inhibitory effects on Th1 and Th17 effector cell generation and, in contrast, favors generation of FOXP3+ and LAG-3+ regulatory T-cells [51]. "
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    ABSTRACT: Induced regulatory T-cells (iT-reg) and T helper type 17 (Th17) in the mouse share common CD4 progenitor cells and exhibit overlapping phenotypic and functional features. Here, we show that human Th17 cells endowed with suppressor activity (supTh17) can be derived following exposure of iT-reg populations to Th17 polarizing conditions. In contrast to "pathogenic" Th17, supTh17 display immune suppressive function and express high levels of CD39, an ectonucleotidase that catalyzes the conversion of pro-inflammatory extracellular nucleotides ultimately generating nucleosides. Accordingly, supTh17 exhibit nucleoside triphosphate diphosphohydrolase activity, as demonstrated by the efficient generation of extracellular AMP, adenosine and other purine derivatives. In addition supTh17 cells are resistant to the effects of adenosine as result of the low expression of the A2A receptor and accelerated adenosine catalysis by adenosine deaminase (ADA). These supTh17 can be detected in the blood and in the lamina propria of healthy subjects. However, these supTh17 cells are diminished in patients with Crohn's disease. In summary, we describe a human Th17 subpopulation with suppressor activity, which expresses high levels of CD39 and consequently produces extracellular adenosine. As these uniquely suppressive CD39(+) Th17 cells are decreased in patients with inflammatory bowel disease, our findings might have implications for the development of novel anti-inflammatory therapeutic approaches in these and potentially other immune disorders.
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