Modulation of the purinergic P2X7 receptor attenuates lipopolysaccharide-mediated microglial activation and neuronal damage in inflamed brain

Abstract

We investigated the involvement and roles of the ionotropic purinergic receptor P2X7R in microglia in mediating lipopolysaccharide (LPS)-induced inflammatory responses and neuronal damage in rat striatum. A detailed in vivo study showed that LPS injection into striatum markedly increased the expression of P2X7R in microglia compared with control (saline)-injected animals. Additionally, LPS injection upregulated a broad spectrum of proinflammatory mediators, including inducible nitric oxide synthase (nitric oxide production marker), 3-nitrotyrosine (peroxynitrite-mediated nitration marker), 4-hydroxynonenal (lipid peroxidation marker), and 8-hydroxy-2′-deoxyguanosine (oxidative DNA damage marker), and reduced neuronal viability. The P2X7R antagonist oxidized ATP (oxATP) was effective in attenuating expressions of all inflammatory mediators and in addition inhibited LPS-induced activation of the cellular signaling factors p38 mitogen-activated protein kinase and transcriptional factor nuclear factor κB. Most importantly, in vivo, oxATP blockade of P2X7R also reduced numbers of caspase-3-positive neurons and increased neuronal survival in LPS-injected brain. In vitro, LPS stimulation of cultured human microglia enhanced cellular expressions of a host of proinflammatory factors, including cyclooxygenase-2, interleukin-1β(IL-1β), IL-6, IL-12, and tumor necrosis factor-α; all factors were inhibited by oxATP. A novel finding was that LPS potentiated intracellular [Ca2+]i mobilization induced by the P2X7R ligand 2′,3′-O-(4- benzoyl-benzoyl) ATP, which could serve as a mechanistic link for P2X 7R amplification of inflammatory responses. Our results suggest critical roles for P2X7R in mediating inflammation and inhibition of this subtype purinergic receptor as a novel therapeutic approach to reduce microglial activation and confer neuroprotection in inflamed and diseased brain. Copyright © 2007 Society for Neuroscience.