One of the major challenges for the U.S. Department of Veterans Affairs is to extend the health-span of the veterans and their families as their physical and/or cognitive performance capabilities decline with age. Human neurodegenerative protein misfolding disorders or proteinopathies, are associated with abnormal protein depositions in brain neurons. They include polyglutamine (polyQ) disorders such as Huntington's disease and α-synucleinopathies such as Parkinson's disease. Disclosing the basic molecular and metabolic alterations that occur during aging of post-mitotic cells such as neurons, under proteotoxic stress is crucial for understanding the etiology of neuro-proteinopathies. Metabolic and mitochondrial alterations are hallmarks of aging and neurodegeneration. Over the last decade, we and others have shown that enhancement of mitogenesis or overexpression of NMNAT/NMA1, an enzyme in the NAD+ biosynthetic salvage pathway, act as powerful suppressors of proteotoxicities in yeast, fly and mouse models. Although the mechanisms involved remain to be fully understood, our preliminary data suggest that the two mechanisms are independent and that NMNAT could act as a chaperone to promote clearance of misfolded proteins. Recent screens in yeast models in our lab allowed us to identify three additional enzymes of the NAD+ biosynthetic salvage pathway that perform similar functions in protection against proteotoxic stress: NADS/QNS1, NaPTRase/NPT1 and NDase/PNC1. These observations suggest the existence of an evolutionarily conserved strategy of `repurposing' (or `moonlighting') housekeeping enzymes under stress conditions, and further reveal the intricate balance of metabolic activity and stress response in neurons. The main objective of this proposal is to investigate the cytoprotective roles of NAD+ biosynthetic enzymes and mitochondria in normal and proteotoxic environments. We will test the hypothesis that NAD+ biosynthetic enzymes are a new class of chaperones that perform this function independently of their catalytic activities and without requiring mitochondrial functions. Furthermore, we will test whether neuroprotection offered by enhanced mitochondrial biogenesis is additive or synergistic to protection exerted by the chaperone function of NAD+ biosynthetic enzymes. These hypotheses will be investigated in yeast models of polyQ toxicity during yeast chronological lifespan (CLS), a model of neuronal aging. Furthermore, the results obtained will be validated in human striatal cells differentiated from induced pluripotent stem cells (iPSCs) derived from human fibroblasts. Three aims will be pursued: First, we will establish the effectiveness of NAD+ biosynthetic proteins in cellular aging and protection against proteotoxicity. Second, we will perform structure-function correlation studies to define the domains in NAD+ biosynthetic proteins required for chaperone or enzymatic activity and their requirement for protection against proteoto...