Investigating the Activation Mechanism of SARM1 during Axon Degeneration

项目总结

PROJECT SUMMARY After injury, axons begin to die via a process that is characterized by axonal fragmentation and disintegration of myelin sheath. This process is often termed Wallerian degeneration after Augustus Waller. Wallerian-like degeneration, which is morphologically similar to Wallerian degeneration, is associated with the early stages of many neurodegenerative diseases, including as Alzheimer’s, Huntington’s, and Parkinson’s Diseases. Wallerian degeneration was long thought to occur passively, but the discovery of proteins that actively prevent or promote degeneration negated this idea. One such protein is SARM1. SARM1 is a NAD+ hydrolase that cleaves NAD+ to nicotinamide, ADPR, and cyclic ADPR; generation of these products ultimately leads to axonal degeneration. Moreover, SARM1 knockout delays degeneration in animal models of Wallerian-like diseases, including traumatic brain injury and peripheral neuropathy. Given the critical role of SARM1 in Wallerian-like diseases, the central hypothesis of this proposal is that SARM1 inhibition would prevent the pathophysiology of axon degeneration associated with neurodegenerative diseases. However, development of SARM1 inhibitors is limited by the lack of knowledge surrounding the regulation, structure, and mechanism of this enzyme. As such, the goal of this proposal is to understand SARM1 regulation in the context of Wallerian degeneration, and this goal will be achieved by pursing the following Specific Aims. Aim 1 focuses on identifying proteins that regulate SARM1 activity. Proximity dependent labeling will also be used to identify proteins that interact with SARM1. The impact of SARM1 interacting proteins on NAD+ hydrolase activity and SARM1-mediated axon degeneration will also be assessed. These experiments will identify intermolecular events that regulate SARM1 during axon degeneration. Aim 2 will focus on understanding the structure and function of TIR-1, the C. elegans ortholog of SARM1. Here, we will solve the TIR-1 structure and characterize the enzymatic mechanism of this enzyme. These studies will complement recent structural and kinetic studies of SARM1 and will yield insights into the intramolecular characteristics of SARM1/TIR-1 that contribute to its degenerative capacity. Investigation into the regulation of SARM1, both inter- and intramolecularly, is a rapidly growing field in the context of neurodegenerative diseases. As such, completion of this work will significantly enhance our understanding of the fundamental molecular mechanisms that control axonal degeneration. These studies will yield insights into the role of SARM1 in axon degeneration, which will have broad implications in the development of therapeutics for neurodegenerative diseases.