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|10||AMP-activated protein kinase regulates nicotinamide phosphoribosyl transferase expression in skeletal muscle.|
Brandauer J; Vienberg SG; Andersen MA; Ringholm S; Risis S; Larsen PS; Kristensen JM; Frosig C; Leick L; Fentz J; Jorgensen S; Kiens B; Wojtaszewski JF; Richter EA; Zierath JR; Goodyear LJ; Pilegaard H; Treebak JT
J Physiol 2013; 591(Pt 2): 5207-20
PubMed ID: 23918774
Deacetylases such as sirtuins (SIRTs) convert NAD to nicotinamide (NAM). Nicotinamide phosphoribosyl transferase (Nampt) is the rate-limiting enzyme in the NAD salvage pathway responsible for converting NAM to NAD to maintain cellular redox state. Activation of AMP-activated protein kinase (AMPK) increases SIRT activity by elevating NAD levels. As NAM directly inhibits SIRTs, increased Nampt activation or expression could be a metabolic stress response. Evidence suggests that AMPK regulates Nampt mRNA content, but whether repeated AMPK activation is necessary for increasing Nampt protein levels is unknown. To this end, we assessed whether exercise training- or 5-amino-1-beta-D-ribofuranosyl-imidazole-4-carboxamide (AICAR)-mediated increases in skeletal muscle Nampt abundance are AMPK dependent. One-legged knee-extensor exercise training in humans increased Nampt protein by 16% (P < 0.05) in the trained, but not the untrained leg. Moreover, increases in Nampt mRNA following acute exercise or AICAR treatment (P < 0.05 for both) were maintained in mouse skeletal muscle lacking a functional AMPK alpha2 subunit. Nampt protein was reduced in skeletal muscle of sedentary AMPK alpha2 kinase dead (KD), but 6.5 weeks of endurance exercise training increased skeletal muscle Nampt protein to a similar extent in both wild-type (WT) (24%) and AMPK alpha2 KD (18%) mice. In contrast, 4 weeks of daily AICAR treatment increased Nampt protein in skeletal muscle in WT mice (27%), but this effect did not occur in AMPK alpha2 KD mice. In conclusion, functional alpha2-containing AMPK heterotrimers are required for elevation of skeletal muscle Nampt protein, but not mRNA induction. These findings suggest AMPK plays a post-translational role in the regulation of skeletal muscle Nampt protein abundance, and further indicate that the regulation of cellular energy charge and nutrient sensing is mechanistically related. Brandauer, Josef