Intraneuronal Aß accumulation induces hippocampal neuron hyperexcitability through A-type K(+) current inhibition mediated by activation of caspases and GSK-3.

Amyloid ß-protein (Aß) pathologies have been linked to dysfunction of excitability in neurons of the hippocampal circuit, but the molecular mechanisms underlying this process are still poorly understood. Here, we applied whole-cell patch-clamp electrophysiology to primary hippocampal neurons and show that intracellular Aß42 delivery leads to increased spike discharge and action potential broadening through downregulation of A-type K(+) currents. Pharmacologic studies showed that caspases and glycogen synthase kinase 3 (GSK-3) activation are required for these Aß42-induced effects. Extracellular perfusion and subsequent internalization of Aß42 increase spike discharge and promote GSK-3-dependent phosphorylation of the Kv4.2 α-subunit, a molecular determinant of A-type K(+) currents, at Ser-616. In acute hippocampal slices derived from an adult triple-transgenic Alzheimer's mouse model, characterized by endogenous intracellular accumulation of Aß42, CA1 pyramidal neurons exhibit hyperexcitability accompanied by increased phosphorylation of Kv4.2 at Ser-616. Collectively, these data suggest that intraneuronal Aß42 accumulation leads to an intracellular cascade culminating into caspases activation and GSK-3-dependent phosphorylation of Kv4.2 channels. These findings provide new insights into the toxic mechanisms triggered by intracellular Aß42 and offer potentially new therapeutic targets for Alzheimer's disease treatment.