Broad-spectrum effects of 4-aminopyridine to modulate amyloid β1-42-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( A beta(1-42))-induced human microglial signaling pathways and functional processes. Whole-cell patch-clamp studies showed acute application of A beta(1-42) ( 5 mu M) 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, GTP gamma S, induced an outward K+ current with similar properties to the A beta(1-42)-induced IK including sensitivity to 4-AP ( IC50 = 5 mM). Reverse transcriptase-PCR showed a rapid expression of a delayed rectifier Kv3.1 channel in A beta(1-42)-treated microglia. A beta(1-42) peptide also caused a slow, progressive increase in levels of [ Ca2+] (i) ( intracellular calcium) that was partially blocked by 4-AP. Chronic exposure of human microglia to A beta(1-42) led to enhanced p38 mitogen-activated protein kinase and nuclear factor kappa B expression with factors inhibited by 4-AP. A beta(1-42) also induced the expression and production of the pro-inflammatory cytokines interleukin ( IL)-1 beta, 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 A beta(1-42)-treated microglia on cultured rat hippocampal neurons was reduced if 4-AP was included with peptide. In vivo, injection of A beta(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 A beta(1-42)-induced IK ( candidate channel Kv3.1) and intracellular signaling pathways in human microglia could serve as a therapeutic strategy for neuroprotection in Alzheimer's disease pathology.