Fletcher RS Ratajczak J Doig CL Oakey LA Callingham R Da Silva Xavier G Garten A Elhassan YS Redpath P Migaud ME Philp A Brenner C Canto C Lavery GG 2017 OBJECTIVE Augmenting nicotinamide adenine dinucleotide (NAD+) availability may protect skeletal muscle from age-related metabolic decline. Dietary supplementation of NAD+ precursors nicotinamide mononucleotide (NMN) and nicotinamide riboside (NR) appear efficacious in elevating muscle NAD+. Here we sought to identify the pathways skeletal muscle cells utilize to synthesize NAD+ from NMN and NR and provide insight into mechanisms of muscle metabolic homeostasis. METHODS We exploited expression profiling of muscle NAD+ biosynthetic pathways, single and double nicotinamide riboside kinase 1/2 (NRK1/2) loss-of-function mice, and pharmacological inhibition of muscle NAD+ recycling to evaluate NMN and NR utilization. RESULTS Skeletal muscle cells primarily rely on nicotinamide phosphoribosyltransferase (NAMPT), NRK1, and NRK2 for salvage biosynthesis of NAD+. NAMPT inhibition depletes muscle NAD+ availability and can be rescued by NR and NMN as the preferred precursors for elevating muscle cell NAD+ in a pathway that depends on NRK1 and NRK2. Nrk2 knockout mice develop normally and show subtle alterations to their NAD+ metabolome and expression of related genes. NRK1, NRK2, and double KO myotubes revealed redundancy in the NRK dependent metabolism of NR to NAD+. Significantly, these models revealed that NMN supplementation is also dependent upon NRK activity to enhance NAD+ availability. CONCLUSIONS These results identify skeletal muscle cells as requiring NAMPT to maintain NAD+ availability and reveal that NRK1 and 2 display overlapping function in salvage of exogenous NR and NMN to augment intracellular NAD+ availability. https://sonar.ch/global/documents/180573 eng info:eu-repo/semantics/altIdentifier/doi/10.1016/j.molmet.2017.05.011 info:eu-repo/semantics/altIdentifier/pmid/28752046 Molecular metabolism. - 2017 Energy metabolism NAD+ Nicotinamide riboside Skeletal muscle Animals Cell Line Cells, Cultured Cytokines Female Male Mice Mice, Inbred C57BL Muscle Fibers, Skeletal Niacinamide Nicotinamide Mononucleotide Nicotinamide Phosphoribosyltransferase Phosphotransferases (Alcohol Group Acceptor) Nicotinamide riboside kinases display redundancy in mediating nicotinamide mononucleotide and nicotinamide riboside metabolism in skeletal muscle cells. http://purl.org/coar/resource_type/c_6501