Discovery of two eukaryotic nicotinamide riboside salvage pathways: New nutritional approaches to promote Sir2 function.

We recently discovered that nicotinamide riboside, previously thought to be a bacterial NAD precursor, is a vitamin precursor of NAD in yeast and humans, which is converted to NAD in a pathway initiated by specific nicotinamide riboside kinases. Nicotinamide riboside has been shown to allow dorsal ganglion root neurons to resist axonopathy and the nicotinamide riboside kinase 2 gene has been shown to be induced by damage. In this study, we describe a second biosynthetic pathway for nicotinamide riboside salvage in yeast and human cells. We establish the conditions in which yeast cells take up the compound and convert it to NAD and we show that both of the newly identified nicotinamide riboside salvage pathways increase Sir2 activity in gene silencing and promote yeast cell longevity in the absence of calorie restriction. [ABSTRACT FROM AUTHOR]