Modulation of the purinergic P2X7 receptor attenuates lipopolysaccharide-mediated microglial activation and neuronal damage in inflamed brain.
We investigated the involvement and roles of the ionotropic purinergic receptor P2X(7)R 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 P2X(7)R 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 P2X(7)R 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 kappaB. Most importantly, in vivo, oxATP blockade of P2X(7)R 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-1beta (IL-1beta), IL-6, IL-12, and tumor necrosis factor-alpha; all factors were inhibited by oxATP. A novel finding was that LPS potentiated intracellular [Ca(2+)](i) mobilization induced by the P2X(7)R ligand 2',3'-O-(4-benzoyl-benzoyl) ATP, which could serve as a mechanistic link for P2X(7)R amplification of inflammatory responses. Our results suggest critical roles for P2X(7)R 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.
Choi
Hyun B
HB
Department of Anesthesiology, Pharmacology, and Therapeutics, University of British Columbia, Vancouver, British Columbia, Canada.
Ryu
Jae K
JK
Kim
Seung U
SU
McLarnon
James G
JG
D000818:Animals; D001921:Brain / Q000187:drug effects / Q000378:metabolism* / Q000473:pathology*; D002478:Cells, Cultured; D006801:Humans; D007249:Inflammation / Q000139:chemically induced / Q000378:metabolism / Q000473:pathology; D008070:Lipopolysaccharides / Q000633:toxicity*; D008297:Male; D017628:Microglia / Q000187:drug effects / Q000378:metabolism* / Q000473:pathology; D009474:Neurons / Q000187:drug effects / Q000378:metabolism* / Q000473:pathology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D018048:Receptors, Purinergic P2 / Q000502:physiology*; D058486:Receptors, Purinergic P2X7
D008070:Lipopolysaccharides; C546468:P2RX7 protein, human; C546470:P2rx7 protein, rat; D018048:Receptors, Purinergic P2; D058486:Receptors, Purinergic P2X7