PROJECT SUMMARY/ABSTRACT Alzheimer's disease (AD) is the most common cause of dementia with progressive loss of memory and cognitive functions. In several AD model mice, the deficits in memory and cognitive functions are highly correlated with an impairment in basal synaptic transmission and synaptic plasticity. Intriguingly, many of the AD model mice show significant deficits in synaptic transmission and plasticity before the development of b-amyloid deposits, which is a typical hallmark of AD pathology. Thus, synaptic dysfunction is a potentially important component of AD pathogenesis. However, to understand the synaptic dysfunction in AD at molecular levels, we face a significant obstacle, which is heterogeneity at multiple levels, due to neuronal heterogeneity and synaptic history (synaptic plasticity). There is, therefore, a critical need to develop a biochemical method that can analyze synaptic molecular constituents in a spatiotemporal manner to understand in substance the synaptic molecular alterations involved in AD. Here, the overall objective in this application is the development of systems-type biochemical methods that enable cell-type-specific and high-resolution profiling of postsynaptic proteomes. The rationale for this project is that these method developments are likely to advance the isolation of molecularly homogeneous postsynaptic proteomes, which will ultimately provide more substantive maps of synaptic protein changes that contribute to the synaptic dysfunction seen in AD. To attain the overall objectives, the following two specific aims will be pursued: 1) Develop cell-type-specific profiling methods of postsynaptic proteomes using Cre recombinase-dependent strategies; and 2) Develop high- resolution profiling methods to identify sub-synaptic proteomes. This innovation in postsynaptic proteomics is expected to allow us to isolate postsynaptic proteomes from the defined population of synapses and sub-synaptic domains in AD model mice. More substantive profiles of synaptic molecular alterations in AD model mice will provide a significant advance in the understanding of synaptic dysfunction in AD at molecular levels and new opportunities for discovering therapeutic targets of AD.