AMP‐activated protein kinase regulates nicotinamide phosphoribosyl transferase expression in skeletal muscle

Abstract

Key points• NAD is a substrate for sirtuins (SIRTs), which regulate gene transcription in response to specific metabolic stresses.• Nicotinamide phosphoribosyl transferase (Nampt) is the rate-limiting enzyme in the NAD salvage pathway.• Using transgenic mouse models, we tested the hypothesis that skeletal muscle Nampt protein abundance would increase in response to metabolic stress in a manner dependent on the cellular nucleotide sensor, AMP-activated protein kinase (AMPK).• Exercise training, as well as repeated pharmacological activation of AMPK by 5-amino-1-β-D-ribofuranosyl-imidazole-4-carboxamide (AICAR), increased Nampt protein abundance. However, only the AICAR-mediated increase in Nampt protein abundance was dependent on AMPK.• Our results suggest that cellular energy charge and nutrient sensing by SIRTs may be mechanistically related, and that Nampt may play a key role for cellular adaptation to metabolic stress. Abstract 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-β-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 α2 subunit. Nampt protein was reduced in skeletal muscle of sedentary AMPK α2 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 α2 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 α2 KD mice. In conclusion, functional α2-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.

Expression and effect of NAMPT (visfatin) on progesterone secretion in hen granulosa cells

“…It is well known that NAMPT treatment activates various signalling pathways, including PRKA, AKT1, MAPK3/1 and MAPK14, in different cell types (Cheng et al 2011, Brandauer et al 2013, Reverchon et al 2013a, Song et al 2014. We showed that in hen granulosa cells from F1 hierarchical follicles, NAMPT treatment decreased MAPK3/1 phosphorylation after 30 or 60 min of stimulation (Fig.…”

AMPK activation protects cells from oxidative stress‐induced senescence via autophagic flux restoration and intracellular NAD + elevation

“…Reduced cellular NAD + level is a feature of aging (Gomes et al ., 2013), and a link between NAD + synthesis and AMPK has been suggested (Brandauer et al ., 2013). For these reasons, we next examined the relationships among AMPK, NAD + synthesis and senescence.…”

“…On the other hand, we displayed the direct association of the downregulated NAD + synthesis, particularly involving its salvage pathway, with senescence, and also the regulatory effect of AMPK on NAD + synthesis. In the fact, consistent results have been reported by others (Yoshino et al ., 2011; Brandauer et al ., 2013;). In addition to the salvage pathway of NAD + synthesis, we also preliminarily addressed the impact on the de novo pathway of NAD + synthesis.…”

“…However, the reasons why the NAD + decreases with age are not fully understood. Interestingly, AMPK activation raises the intracellular NAD + concentrations and activates SIRT1 (Cantó et al ., 2009), which is mediated via an increase in the protein activity and abundance of NAMPT, a key enzyme in the salvage pathway of NAD + synthesis (Brandauer et al ., 2013). It is currently unclear whether another pathway of NAD + synthesis, the de novo pathway, is related to the aging‐associated NAD + decline or whether AMPK plays a role.…”

Epigenetics and Metabolism

“…Second, AMPK activation leads to an increase in cellular NAD + levels, possibly by increasing Nampt expression. 109,110 Pharmacological or physiological activation of AMPK increased NAD + levels to coordinately enhance SIRT1 activity, leading to the deacetylation and altered transactivity of downstream SIRT1 targets: peroxisome proliferator-activated receptor-γ coactivator 1α (PGC-1α) and forkhead transcription factors FOXO1 and FOXO3a. 94 These changes in transcription factor deacetylation and consequent activity elevate the expression of mitochondrial and lipid oxidation genes in low glucose 111 and may represent a mechanism by which gene programs are poised for response to energy demands.…”