A common and powerful non-genetic method used to extend an organism''s lifespan is caloric restriction, yet the underlying molecular mechanisms of this increased longevity remain unclear. In yeast, Pnc1 (nicotinamidase), an enzyme in the NAD+ salvage pathway that converts nicotinamide to nicotinic acid to assist in regenerating NAD+, can mediate lifespan extension under caloric restriction and mild stresses. We have previously shown that Pnc1 is nuclear, cytoplasmic, and peroxisomal in yeast and that caloric restriction and stress, like salt, causes a significant up-regulation in expression (Anderson, 2003). To understand the impact of this nicotinamidase on longevity and stress resistance in multi-cellular organisms, we are using C. elegans as a model. We show that the worm ortholog PNC-1 also has robust nicotinamidase activity in vitro and that increased gene dosage in C. elegans protects against salt stress and extends lifespan. Interestingly, this longevity effect is sirtuin dependent. In addition, lifespan extension mediated by PNC-1 over-expression is not additive with caloric restriction-induced longevity, suggesting that PNC-1 is an important component of this pathway. Accordingly, inactivation of the
pnc-1 gene leads to a defect in caloric restriction-induced longevity in C. elegans. Using a GFP reporter, we found that
pnc-1 is expressed in the pharynx and nervous system, including the chemosensory ASK neurons. We are currently using cell-specific promoters to dissect the biological relevance of these sites of expression. Interestingly, invertebrate PNC-1 and the mammalian PBEF/Visfatin catalyze analogous biochemical steps; we are expressing the human PBEF/Visfatin in
pnc-1 loss-of-function animals to test the functional conservation of these enzymes across species. Collectively, this study elucidates a functional role for PNC-1 in metazoans and expands our understanding of conserved pathways involved in longevity and stress resistance across organisms.