Broad-spectrum effects of 4-aminopyridine to modulate amyloid beta1-42-induced cell signaling and functional responses in human microglia.
We investigated the modulating actions of the nonselective K(+) channel blocker 4-aminopyridine (4-AP) on amyloid beta (Abeta(1-42))-induced human microglial signaling pathways and functional processes. Whole-cell patch-clamp studies showed acute application of Abeta(1-42) (5 mum) to human microglia led to rapid expression of a 4-AP-sensitive, non-inactivating outwardly rectifying K(+) current (I(K)). Intracellular application of the nonhydrolyzable analog of GTP, GTPgammaS, induced an outward K(+) current with similar properties to the Abeta(1-42)-induced I(K) including sensitivity to 4-AP (IC(50) = 5 mm). Reverse transcriptase-PCR showed a rapid expression of a delayed rectifier Kv3.1 channel in Abeta(1-42)-treated microglia. Abeta(1-42) peptide also caused a slow, progressive increase in levels of [Ca(2+)](i) (intracellular calcium) that was partially blocked by 4-AP. Chronic exposure of human microglia to Abeta(1-42) led to enhanced p38 mitogen-activated protein kinase and nuclear factor kappaB expression with factors inhibited by 4-AP. Abeta(1-42) also induced the expression and production of the pro-inflammatory cytokines interleukin (IL)-1beta, IL-6, and tumor necrosis factor-alpha, the chemokine IL-8, and the enzyme cyclooxygenase-2; 4-AP was effective in reducing all of these pro-inflammatory mediators. Additionally, toxicity of supernatant from Abeta(1-42)-treated microglia on cultured rat hippocampal neurons was reduced if 4-AP was included with peptide. In vivo, injection of Abeta(1-42) into rat hippocampus induced neuronal damage and increased microglial activation. Daily administration of 1 mg/kg 4-AP was found to suppress microglial activation and exhibited neuroprotection. The overall results suggest that 4-AP modulation of an Abeta(1-42)-induced I(K) (candidate channel Kv3.1) and intracellular signaling pathways in human microglia could serve as a therapeutic strategy for neuroprotection in Alzheimer's disease pathology.
Franciosi
Sonia
S
Departments of Anesthesiology, University of British Columbia, Vancouver, British Columbia, Canada.
Ryu
Jae K
JK
Choi
Hyun B
HB
Radov
Lesley
L
Kim
Seung U
SU
McLarnon
James G
JG
D015761:4-Aminopyridine / Q000494:pharmacology*; D016229:Amyloid beta-Peptides / Q000494:pharmacology*; D000818:Animals; D001921:Brain / Q000166:cytology; D002118:Calcium / Q000378:metabolism; D002478:Cells, Cultured; D051546:Cyclooxygenase 2 / Q000378:metabolism; D016207:Cytokines / Q000235:genetics / Q000378:metabolism; D004347:Drug Interactions; D005333:Fetus; D015870:Gene Expression / Q000187:drug effects; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000494:pharmacology; D006801:Humans; D007150:Immunohistochemistry / Q000379:methods; D008564:Membrane Potentials / Q000187:drug effects / Q000528:radiation effects; D008565:Membrane Proteins / Q000378:metabolism; D017628:Microglia / Q000187:drug effects*; D016328:NF-kappa B / Q000378:metabolism; D009474:Neurons / Q000737:chemistry / Q000502:physiology; D018408:Patch-Clamp Techniques / Q000379:methods; D010446:Peptide Fragments / Q000494:pharmacology*; D026902:Potassium Channel Blockers / Q000494:pharmacology*; D051381:Rats; D020133:Reverse Transcriptase Polymerase Chain Reaction / Q000379:methods; D051670:Shaw Potassium Channels / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects*; D048051:p38 Mitogen-Activated Protein Kinases / Q000378:metabolism
D016229:Amyloid beta-Peptides; D016207:Cytokines; D008565:Membrane Proteins; D016328:NF-kappa B; D010446:Peptide Fragments; D026902:Potassium Channel Blockers; D051670:Shaw Potassium Channels; C075222:amyloid beta-protein (1-42); D016244:Guanosine 5'-O-(3-Thiotriphosphate); D015761:4-Aminopyridine; D051546:Cyclooxygenase 2; C496540:PTGS2 protein, human; D048051:p38 Mitogen-Activated Protein Kinases; D002118:Calcium