Direct High Affinity Interaction between Aβ42 and GSK3α Stimulates Hyperphosphorylation of Tau. A New Molecular Link in Alzheimer's Disease?

Amyloid beta peptide (A beta 42) assemblies are considered central to the development of Alzheimer's disease, but the mechanism of this toxicity remains unresolved. We screened protein microarrays with on-pathway oligomeric A beta 42 to identify candidate proteins interacting with toxic A beta 42 species. Samples prepared from Alexa546-A beta 42 and A beta 42 monomers at 1:5 molar ratio were incubated with the array during a time window of the amyloid fibril formation reaction during which the maximum number of transient oligomers exist in the reaction flux. A specific interaction was detected between A beta 42 and glycogen synthase kinase 3 alpha (GSK3 alpha), a kinase previously implicated in the disease pathology. This interaction was validated with anti-GSK3 alpha immunoprecipitation assays in neuronal cell lysates. Confocal microscopy studies further identified colocalization of A beta 42 and GSK3 alpha in neurites of mature primary mouse neurons. A high binding affinity (K-D = 1 nM) was measured between Alexa488-A beta 42 and GSK3 alpha in solution using thermophoresis. An even lower apparent K-D was estimated between GSK3 alpha and dextranimmobilized A beta 42 in surface plasmon resonance experiments. Parallel experiments with GSIC3 beta also identified colocalization and high affinity binding to this isoform. GSK3 alpha-mediated hyperphosphorylation of the protein tau was found to be stimulated by A beta 42 in in vitro phosphorylation assays and identified a functional relationship between the proteins. We uncover a direct and functional molecular link between A beta 42 and GSK3 alpha, which opens an important avenue toward understanding the mechanism of A beta 42-mediated neuronal toxicity in Alzheimer's disease.