Hypoxic cellular injury and axonal degeneration are two of the most devastating causes of morbidity and mortality in the US. Despite a tremendous longstanding scientific effort, no treatment has proven to be effective at ameliorating either hypoxic injury or axonal degeneration in humans. The NAD biosynthetic enzyme nicotinamide mononucleotide adenylyl transferase 1 (Nmnat1) has been shown to block both axonal degeneration and hypoxic injury in mouse. Despite the profound medically relevant phenotype, the mechanism whereby Nmnat1 protects from either hypoxic injury or axonal degeneration is obscure. This application proposes to utilize the powerful genetic model organism C. elegans to develop a new model to study the cytoprotective mechanisms of Nmnat1. Preliminary experiments from my lab have shown that expression in C. elegans of a mutant form of mouse Nmnat1 protects the nematode from hypoxic injury. In addition, we have discovered that Nmnat1 more than doubles lifespan in C. elegans, demonstrating a strong cytoprotective function of Nmnat1 against aging. This project will develop additional tools in C. elegans to study the function of mouse Nmnat1 and answer fundamental questions about the protective mechanisms of Nmnat1 against hypoxic injury and aging. Completion of aim 1 will determine in what cell types Nmnat1 expression provides protection from hypoxic cellular injury and organismal aging. Additionally, we will determine whether Nmnat1 acts to protect only the cells in which it is expressed (cell autonomous activity) or whether Nmnat1 acts to protect cells in which it is not expressed (cell non-autonomous function).
Aim 1 will also define when Nmnat1 functions to protect from hypoxia and extend lifespan, in particular, before or after the hypoxic insult and early or late in life, respectively.
Aim 2 will use transgenic strains generated in aim to test a specific Nmnat1 mechanistic hypothesis suggested by our preliminary results. We will ask if the mitochondrial unfolded protein response is required for the protective action of Nmnat1 and whether Nmnat1 regulates the activity of the mitochondrial unfolded protein response. Completion of these aims will develop a powerful new model to study this important enzyme and may define a mechanism whereby Nmnat1 protects from hypoxia and lengthens lifespan.
Hypoxic cell death in the form of stroke and myocardial infarction is the number one cause of mortality in the US. Development of a novel genetically tractable model system for the study of the hypoxia protective Nmnat1 gene will provide distinct new avenues and sets of methods to define the mechanism of hypoxic protection. These discoveries could lead to the development of therapies for this devastating group of diseases.