Time Resolved Assay of Synaptic Enzyme Activity by Mass Spectrometry

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DESCRIPTION (provided by applicant): We will develop a new method to measure the time courses of activation of biochemical regulatory networks that control changes in synaptic strength which underlie processing and storage of information in neural networks. The proposed method will permit unprecedented time resolution and will enable measurement of the time courses of activation of at least 20, and eventually as many as 50 to 100 enzymes in brain tissue that has been rapidly frozen at intervals as small as one second following an electrical or pharmacological stimulus. The method will be immediately applicable to basic research on, and target development for, mental illnesses and Alzheimer's disease. Upon scale-up, it will be applicable to screening for drugs to treat these diseases. The method will involve substantial adaptation of two existing technologies: "plunge-freezing" and "Selected/ Multiple Reaction Monitoring" (S/MRM) by mass spectrometry. Once developed, both technologies can be scaled up for medium or high throughput screening. The project has three aims. First, we will develop a plunge freeze apparatus to rapidly freeze slices of hippocampal tissue at accurate time intervals following application of a stimulus to the perfused slice. We will accomplish this by making modifications and additions to a plunge-freeze apparatus now commercially available from Leica (Leica EM GP). We will devise an optimal design for a sample chamber to maintain the health of slices during perfusion, and to deliver electrical stimuli to the Schaffer collateral pathway, a major hippocampal axon tract, prior to rapidly freezing the slice by plunging it into a -1900 C liquid propane/ethane bath. We estimate that freezing time to the center of the slice upon plunge will be ~ 200 msecs or less. This freezing time is compatible with a resolution of one second for time intervals following application of a discrete stimulus. Second, we will develop methods to measure the activation of a panel of 20-25 protein kinases or their key substrate proteins located at positions in the regulatory networks that are believed to control synaptic plasticity in excitatory synapses in the hippocampus. Each enzyme or substrate that we will measure is regulated by addition of a phosphate group to key residues in the protein structure. Mass spectrometry will be used to measure changes in the levels of these phosphorylated sites in the frozen slice tissue. Third, once the assays are developed, we will carry out "proof of principle" experiments by combining the technologies developed in Aims 1 and 2 to acquire time courses of activation of each the enzymes in hippocampal slices after delivery of stimuli that alter synaptic plasticity. PUBLIC HEALTH RELEVANCE: This project will develop a new method for measuring activity in biochemical pathways that do not function properly in individuals with mental illnesses or Alzheimer's disease. The method will be used to support research on the causes of mental illnesses and Alzheimer's disease and for efficient screening for new drugs to treat these diseases.