Mechanistic studies of synaptopathies associated with Alzheimer's risk factors

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PROJECT SUMMARY/ABSTRACT One of the earliest changes in Alzheimer’s Disease (AD) is dysfunction of synaptic transmission, thus interfering with information processing by neuronal networks. However, despite intensive study, the factors contributing to synaptic dysfunction, and thus cognitive decline, are not understood. Thus, it is of fundamental importance to understand how candidate genes implicated in AD such as amyloid precursor protein (APP) and superoxide dismutase (SOD) disrupt synaptic signaling. The scientific premise of the current proposal is to generate animal models of AD and undertake a genetics-based, systems biology approach to gain a fundamental understanding of how AD changes neuronal function(s). In contrast to complementary efforts in other systems, what distinguishes the current proposal is single neuron resolution, a focus on real-time in vivo intracellular transport of synaptic receptors and APP, and a systematic effort to discover regulatory, homeostatic and gene expression pathways that control or modify synaptic receptors and neurotransmission. We have modeled the overexpression of SOD and APP in transgenic C. elegans to gain new insights into the pathophysiology of AD. In preliminary experiments, we observed striking disruption of synaptic function in transgenic worms that overexpressed either SOD-1 or APL-1 (C. elegans homologs of SOD and APP, respectively). In particular, we found that motor-mediated transport of AMPA-type ionotropic glutamate receptors and glutamate-gated currents were severely disrupted, leading to altered behavior of the animals. These results provide a new conceptual framework for investigating the pathophysiology of synaptic dysfunction in AD. In this proposal, we test mechanistic models of SOD-1 and APL-1 mediated disruption of synaptic function, and we outline a strategy to identify novel genetic modifiers that restore synaptic transmission in our transgenic models of AD. Because of evolutionary conservation of APP, SOD, synaptic proteins, microtubule-dependent motors and most intracellular signaling pathways, our studies will have immediate relevance to the pathophysiology of AD in humans. Additionally, we expect our studies will provide new therapeutic strategies, and entry points for the treatment of AD and other neurodegenerative disorders associated with APP and SOD.