Long-term soluble Aβ_1–40 activates CaM kinase II in organotypic hippocampal cultures

Abstract 

Recent findings suggested a role for soluble amyloid-β (Aβ) peptides in Alzheimer's disease associated cognitive decline. We investigated the action of soluble, monomeric Aβ_1–40 on CaM kinase II, a kinase involved in neuroplasticity and cognition. We treated organotypic hippocampal cultures short-term (up to 4h) and long-term (5 days) with Aβ_1–40 (1nM–5μM). Aβ did not induce cell damage, apoptosis or synaptic loss. Short-term treatment down-regulated enzymatic activity of the kinase, by reducing its Thr²⁸⁶ phosphorylation. In contrast, long-term treatment (1nM–5μM) markedly and significantly up-regulated enzymatic activity, with peak stimulation at 10nM (three-fold). Up-regulation of activity was associated with increased expression of the α-isoform of CaM kinase II, increased phosphorylation at Thr²⁸⁶ (activator residue) and decreased phosphorylation at Thr^305–306 (inhibitory residues). We investigated the effect of glutamate on CaM kinase II following exposure to 1 or 10nM Aβ_1–40. As previously reported, glutamate increased CaM kinase II activity. However, the glutamate effect was not altered by pretreatment of slices with Aβ.

Short- and long-term Aβ treatment showed opposite effects on CaM kinase II, suggesting that long-term changes are an adaptation to the kinase early down-regulation. The marked effect of Aβ_1–40 on the kinase suggests that semi-physiological and slowly raising peptide concentrations may have a significant impact on synaptic plasticity in the absence of synaptic loss or neuronal cell death.

Keywords: Alzheimer, Amyloid, CaM kinase II, Synaptic plasticity, Protein phosphorylation, Glutamate