Oligomers of Amyloid Prevent Physiological Activation of the Cellular Prion Protein-Metabotropic Glutamate Receptor 5 Complex by Glutamate in Alzheimer Disease

The dysfunction and loss of synapses in Alzheimer disease are central to dementia symptoms. We have recently demonstrated that pathological Amyloid oligomer (Ao) regulates the association between intracellular protein mediators and the synaptic receptor complex composed of cellular prion protein (PrPC) and metabotropic glutamate receptor 5 (mGluR5). Here we sought to determine whether Ao alters the physiological signaling of the PrPC-mGluR5 complex upon glutamate activation. We provide evidence that acute exposure to Ao as well as chronic expression of familial Alzheimer disease mutant transgenes in model mice prevents protein-protein interaction changes of the complex induced by the glutamate analog 3,5-dihydroxyphenylglycine. We further show that 3,5-dihydroxyphenylglycine triggers the phosphorylation and activation of protein-tyrosine kinase 2- (PTK2B, also referred to as Pyk2) and of calcium/calmodulin-dependent protein kinase II in wild-type brain slices but not in Alzheimer disease transgenic brain slices or wild-type slices incubated with Ao. This study further distinguishes two separate Ao-dependent signaling cascades, one dependent on extracellular Ca2+ and Fyn kinase activation and the other dependent on the release of Ca2+ from intracellular stores. Thus, Ao triggers multiple distinct PrPC-mGluR5-dependent events implicated in neurodegeneration and dementia. We propose that targeting the PrPC-mGluR5 complex will reverse aberrant Ao-triggered states of the complex to allow physiological fluctuations of glutamate signaling.