P2X7/P2Z purinoreceptor-mediated activation of transcription factor NFAT in microglial cells.
ABSTRACT ATP is released from neurons and other cell types during several physiological and stress conditions under which it exerts various biological effects upon binding to purinoreceptors. A rather peculiar purinoreceptor called P2X7/P2Z is expressed on microglial and other myeloic cells. Although increasing evidence implicates an important role for P2Z in inflammatory processes, little information exists about underlying signaling pathways. Here, we report that in N9 microglial cells, extracellular ATP potently activates nuclear factor of activated T cells (NFAT), a central transcription factor involved in cytokine gene expression. ATP activated NFAT rapidly (within 1 min), whereas activation of nuclear factor kappaB was much delayed, with strikingly distinct kinetics. During ATP stimulation, both NFAT-1 and NFAT-2 were activated by a calcineurin-dependent pathway that required the influx of extracellular calcium ions. Based on the pharmacological profile, NFAT activation was specifically mediated by P2Z and not by other purinoreceptors. N9 cells that lacked P2Z but still expressed P2Y purinoreceptors failed to respond to NFAT activation. We conclude that P2Z-mediated NFAT activation may represent a novel mechanism by which extracellular ATP can modulate early inflammatory gene expression within the nervous and immune system.
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ABSTRACT: Similar to peripheral immune/inflammatory cells, neuroglial cells appear to rely on calcineurin (CN) signaling pathways to regulate cytokine production and cellular activation. Several studies suggest that harmful immune/inflammatory responses may be the most impactful consequence of aberrant CN activity in glial cells. However, newly identified roles for CN in glutamate uptake, gap junction regulation, Ca2+ dyshomeostasis, and amyloid production suggest that CN¿s influence in glia may extend well beyond neuroinflammation. The following review will discuss the various actions of CN in glial cells, with particular emphasis on astrocytes, and consider the implications for neurologic dysfunction arising with aging, injury, and/or neurodegenerative disease.Journal of Neuroinflammation 09/2014; 11(1):158. · 4.35 Impact Factor
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ABSTRACT: Runt-related transcription factor-2 (Runx2) is the master regulator of osteoblastogenesis with an ability to promote differentiation of mesenchymal stem cells into the osteoblastic lineage. We have previously shown constitutive and functional expression of Runx2 by astroglial cells. In this study, we investigated the possible expression of Runx2 by both murine microglia and microglial cell line BV-2 cells. Runx2 expression was seen in cultured microglia and BV-2 cells, while sustained exposure to 1 mM ATP led to a significant but transient increase in mRNA and corresponding protein expression of Runx2 within 24 h. The increase in Runx2 expression was invariably prevented by several chemicals with antagonistic properties for P2X7 purinergic receptor, calmodulin and calcineurin in BV-2 cells, with a P2X7 receptor agonist more than quadrupling Runx2 expression. A significant increase in Runx2 expression was seen in osteoclastic cells, but not in osteoblastic or chondrocytic cells, when exposed to a high concentration of ATP. In BV2-cells with control siRNA, a significant decrease was found in the number of cells with at least one process within 3 h after the exposure to 1 mM ATP, followed by an increase up to 24 h. However, Runx2 siRNA significantly deteriorated the property to induce delayed process extension during 6 to 24 h after exposure to ATP along with drastically decreased Runx2 protein levels. These results suggest that Runx2 is constitutively and functionally expressed by microglial cells with responsiveness to ATP for upregulation in the murine brain.Neurochemistry International 04/2014; · 2.66 Impact Factor
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ABSTRACT: Microglial cells, the immunocompetent cells of the central nervous system (CNS), exhibit a resting phenotype under healthy conditions. In response to injury, however, they transform into an activated state, which is a hallmark feature of many CNS diseases. Factors or agents released from the neurons, blood vessels, and/or astrocytes could activate these cells, leading to their functional and structural modifications. Microglial cells are well equipped to sense environmental changes within the brain under both physiological and pathological conditions. Entry of calcium ions (Ca(2+) ) plays a critical role in the process of microglial transformation; several channels and receptors have been identified on the surface of microglial cells. These include store-operated channel, Orai1, and its sensor protein, stromal interaction molecule 1 (STIM1), in microglial cells, and their functions are modulated under pathological stimulations. Transient receptor potential (TRP) channels and voltage- and ligand-gated channels (ionotropic and metabotropic receptors) are also responsible for Ca(2+) influx into the microglial cells. An elevation of intracellular Ca(2+) concentration subsequently regulates microglial cell functions by activating a diverse array of Ca(2+) -sensitive signaling cascades. Perturbed Ca(2+) homeostasis contributes to the progression of a number of CNS disorders. Thus, regulation of Ca(2+) entry into microglial cells could be a pharmacological target for several CNS-related pathological conditions. This Review addresses the recent insights into microglial cell Ca(2+) influx mechanisms, their roles in the regulation of functions, and alterations of Ca(2+) entry in specific CNS disorders. © 2014 Wiley Periodicals, Inc.Journal of Neuroscience Research 01/2014; · 2.97 Impact Factor