A central goal of research in Alzheimer's disease (AD) is the identification and reversal of the earliest pathological changes in affected brain systems and neural circuits. Although numerous structural and biochemical changes have been documented in late-stage AD brains, the early microscopic events that initiate neuronal dysfunction provide potentially more attractive therapeutic targets. Among the initial targets of AD pathogenesis are neuronal synapses. In its earliest phases, AD is characterized by a remarkably pure impairment of memory that has been attributed to 'subpathological' alterations in excitatory synaptic transmission in the hippocampus. Recent studies strongly support the involvement of misprocessed amyloid precursor protein (APP) and A-beta deposition in the early synaptic and cognitive changes of AD. However, little is known about the molecular mechanisms by which exposure to A-beta affects synaptic plasticity, or potential compensatory mechanisms that could be used to counteract aberrant plasticity. In the proposed research, we will define the molecular targets for A-beta-induced synaptic dysfunction. A newly recognized mechanism for changing synaptic strength is the rapid removal of postsynaptic receptors via endocytosis. We have recently found that dendritic spines contain a zone of clathrin assembly and endocytosis adjacent to, but spatially segregated from, the postsynaptic density. Moreover, we have found that the protein machinery for postsynaptic endocytosis is functionally altered by aging and may be upregulated by exposure to A-beta. These findings present an opportunity to clarify in molecular detail the mechanisms by which A-beta influences excitatory transmission and synaptic plasticity. These studies will provide much-needed insight into the cell biological mechanisms that underlie AD-related changes in synaptic plasticity, and will identify molecular signaling pathways that may correct A-beta-induced changes in synaptic function. As such, the proposed research holds promise for the development of new therapeutic approaches for AD-associated memory loss and cognitive deficit.
