Microglial alpha7 nicotinic acetylcholine receptors drive a phospholipase C/IP3 pathway and modulate the cell activation toward a neuroprotective role.
Microglia perform both neuroprotective and neurotoxic functions in the brain, with this depending on their state of activation and their release of mediators. Upon P2X(7) receptor stimulation, for example, microglia release small amounts of TNF, which protect neurons, whereas LPS causes massive TNF release leading to neuroinflammation. Here we report that, in rat primary cultured microglia, nicotine enhances P2X(7) receptor-mediated TNF release, whilst suppressing LPS-induced TNF release but without affecting TNF mRNA expression via activation of alpha7 nicotinic acetylcholine receptors (alpha7 nAChRs). In microglia, nicotine elicited a transient increase in intracellular Ca(2+) levels, which was abolished by specific blockers of alpha7 nAChRs. However, this response was independent of extracellular Ca(2+) and blocked by U73122, an inhibitor of phospholipase C (PLC), and xestospongin C, a blocker of the IP(3) receptor. Repeated experiments showed that currents were not detected in nicotine-stimulated microglia. Moreover, nicotine modulation of LPS-induced TNF release was also blocked by xestospongin C. Upon LPS stimulation, inhibition of TNF release by nicotine was associated with the suppression of JNK and p38 MAP kinase activation, which regulate the post-transcriptional steps of TNF synthesis. In contrast, nicotine did not alter any MAP kinase activation, but enhanced Ca(2+) response in P2X(7) receptor-activated microglia. In conclusion, microglial alpha7 nAChRs might drive a signaling process involving the activation of PLC and Ca(2+) release from intracellular Ca(2+) stores, rather than function as conventional ion channels. This novel alpha7 nAChR signal may be involved in the nicotine modification of microglia activation towards a neuroprotective role by suppressing the inflammatory state and strengthening the protective function.
Suzuki
Tomohisa
T
Department of Pharmacology, Graduate School of Biomedical Sciences, Hiroshima University, Hiroshima, Japan.
Hide
Izumi
I
Matsubara
Akiyo
A
Hama
Chihiro
C
Harada
Kana
K
Miyano
Kanako
K
Andrä
Matthias
M
Matsubayashi
Hiroaki
H
Sakai
Norio
N
Kohsaka
Shinichi
S
Inoue
Kazuhide
K
Nakata
Yoshihiro
Y
D000818:Animals; D000831:Animals, Newborn; D015220:Calcium Channels / Q000378:metabolism; D020013:Calcium Signaling / Q000187:drug effects / Q000502:physiology; D018929:Cell Culture Techniques; D002465:Cell Movement / Q000187:drug effects / Q000502:physiology; D049109:Cell Proliferation / Q000187:drug effects; D002470:Cell Survival / Q000187:drug effects / Q000502:physiology; D019610:Cytoprotection / Q000187:drug effects / Q000502:physiology; D004660:Encephalitis / Q000378:metabolism* / Q000503:physiopathology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005911:Gliosis / Q000378:metabolism* / Q000503:physiopathology; D015544:Inositol 1,4,5-Trisphosphate / Q000378:metabolism*; D053496:Inositol 1,4,5-Trisphosphate Receptors; D008070:Lipopolysaccharides / Q000494:pharmacology; D020935:MAP Kinase Signaling System / Q000187:drug effects / Q000502:physiology; D017628:Microglia / Q000187:drug effects / Q000378:metabolism*; D009538:Nicotine / Q000494:pharmacology; D051381:Rats; D018160:Receptors, Cytoplasmic and Nuclear / Q000037:antagonists & inhibitors / Q000378:metabolism; D011978:Receptors, Nicotinic / Q000187:drug effects / Q000378:metabolism*; D018048:Receptors, Purinergic P2 / Q000187:drug effects / Q000378:metabolism; D058486:Receptors, Purinergic P2X7; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology; D014409:Tumor Necrosis Factor-alpha / Q000378:metabolism; D010738:Type C Phospholipases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D064569:alpha7 Nicotinic Acetylcholine Receptor
D015220:Calcium Channels; C579165:Chrna7 protein, rat; D004791:Enzyme Inhibitors; D053496:Inositol 1,4,5-Trisphosphate Receptors; D008070:Lipopolysaccharides; C546470:P2rx7 protein, rat; D018160:Receptors, Cytoplasmic and Nuclear; D011978:Receptors, Nicotinic; D018048:Receptors, Purinergic P2; D058486:Receptors, Purinergic P2X7; D014409:Tumor Necrosis Factor-alpha; D064569:alpha7 Nicotinic Acetylcholine Receptor; D009538:Nicotine; D015544:Inositol 1,4,5-Trisphosphate; D010738:Type C Phospholipases