APP as a mediator of amyloid beta effects on CaMKII synaptic functions

项目总结

Project Summary The proper functioning of learning, memory, and cognition requires the activity-dependent strengthening of excitatory synapses in the hippocampus via a process known as long-term potentiation (LTP). LTP can be impaired in ex vivo hippocampal slices by incubation with the peptide amyloid-β (Aβ); increased concentrations of this peptide are highly associated with early synaptic deficits in Alzheimer’s disease (AD), a progressive neurodegenerative disease. LTP is known to require the Ca2+/calmodulin-dependent protein kinase II (CaMKII), and specifically its localization to excitatory synapses, driven by direct binding of CaMKII to the NMDA-type glutamate receptor GluN2B. This localization of CaMKII to excitatory synapses is impaired by incubation with Aβ, revealing a potential mechanism underlying Aβ-induced synaptic deficits. Interestingly, the impairments of LTP and CaMKII movement caused by exogenous Aβ incubation are alleviated by loss of the amyloid precursor protein (APP). While the proteolytic cleavage that APP undergoes to form Aβ is well-characterized, this apparent downstream role as a mediator of Aβ-induced impairment remains largely unexplored. Importantly, individuals with Down syndrome (DS), a genetic developmental disorder, express increased levels of APP due to triplication of the APP gene. As loss of endogenous APP “desensitizes” neurons to the synaptic deficits caused by Aβ, it may conversely be true that these increased APP levels “sensitize” neurons to the effects of Aβ. Initial results indicate that APP is not only necessary to mediate CaMKII impairments caused by exogenous Aβ, but also sufficient to impair CaMKII-GluN2B binding in heterologous cells, further implicating APP as a direct mediator of downstream Aβ-induced CaMKII impairments. Thus, this proposal will investigate various aspects of APP’s role as a mediator of Aβ, including whether neurons expressing higher levels of APP are more sensitive to Aβ-induced synaptic impairments, which domain(s) of the APP protein are necessary to mediate these impairments, and which specific mechanism(s) downstream of APP and Aβ are driving impairments in LTP-related CaMKII movement. To answer these questions, we will be utilizing several different genetic mouse lines, including a model of DS, various mutant constructs of APP, and a recently developed photoactivatable CaMKII. The results of the experiments outlined in this proposal will provide valuable insight into the role of APP in driving synaptic impairment (underlying hippocampal memory deficits) caused by Aβ in both AD and DS.