ATP-P2X7 receptor signaling controls basal and TNFa-stimulated glial cell proliferation

Activation and proliferation of glial cells and their progenitors is a key process of neuroinflammation associated with many neurodegenerative disorders. Under neuropathological conditions where glial cell activation and proliferation is evident, controlling the population of glia might be of therapeutic importance. The proliferative action of the cytokine tumor necrosis factor alpha (TNFa) on microglia has been reported, but the molecular mechanism of TNFa regulation of glial cell proliferation is largely unknown. Using a model of organotypic hippocampalentorhinal cortex (HEC) slice culture, we investigated the role of ATP-P2X7 receptor signaling in glial proliferation by TNFa. Populations of proliferating cells in HEC culture were labeled with 5-bromo-2'-deoxyuridine (BrdU). Treatment with TNFa induced strong expression of P2X7 receptor mRNA and immunoreactivity in BrdU+ cells while markedly increasing proliferation of BrdU+ cells. In addition, TNFa increased aquaporin 4 (AQP4) expression, an ion channel involved in glial proliferation. The proliferative action of TNFa was attenuated by blocking the P2X7 receptors with the specific antagonists oxATP, BBG, and KN62, or by lowering extracellular ATP with ATP hydrolysis apyrase. Basal proliferation of BrdU+ cells was also sensitive to blockade of ATP-P2X7 signaling. Furthermore, TNFa activation of P2X7 receptors appear to regulate AQP4 expression through protein kinase C cascade and down regulation of AQP4 expression can reduce TNFa-stimulated BrdU+ cell proliferation. Taken together, these novel findings demonstrate the importance of ATP-P2X7 signaling in controlling proliferation of glial progenitors under the pathological conditions associated with increased TNFa. (c) 2012 Wiley Periodicals, Inc.