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Am J Physiol Endocrinol Metab. 2018 Apr 1;314(4):E377-E395. doi: 10.1152/ajpendo.00213.2017. Epub 2017 Dec 5.

Perturbations of NAD+ salvage systems impact mitochondrial function and energy homeostasis in mouse myoblasts and intact skeletal muscle.

Author information

1
Section of Integrative Physiology, Novo Nordisk Foundation Center for Basic Metabolic Research, University of Copenhagen , Copenhagen , Denmark.
2
Laboratory of Genomics and Molecular Biomedicine, Department of Biology, University of Copenhagen , Copenhagen , Denmark.
3
Xlab, Center for Healthy Aging, Department of Biomedical Sciences, University of Copenhagen , Copenhagen , Denmark.
4
Section for Translational Metabolic Physiology, Novo Nordisk Foundation Center for Basic Metabolic Research, and Department of Biomedical Sciences, University of Copenhagen , Copenhagen , Denmark.

Abstract

Nicotinamide adenine dinucleotide (NAD+) can be synthesized by nicotinamide phosphoribosyltransferase (NAMPT). We aimed to determine the role of NAMPT in maintaining NAD+ levels, mitochondrial function, and metabolic homeostasis in skeletal muscle cells. We generated stable Nampt knockdown (sh Nampt KD) C2C12 cells using a shRNA lentiviral approach. Moreover, we applied gene electrotransfer to express Cre recombinase in tibialis anterior muscle of floxed Nampt mice. In sh Nampt KD C2C12 myoblasts, Nampt and NAD+ levels were reduced by 70% and 50%, respectively, and maximal respiratory capacity was reduced by 25%. Moreover, anaerobic glycolytic flux increased by 55%, and 2-deoxyglucose uptake increased by 25% in sh Nampt KD cells. Treatment with the NAD+ precursor nicotinamide riboside restored NAD+ levels in sh Nampt cells and increased maximal respiratory capacity by 18% and 32% in control and sh Nampt KD cells, respectively. Expression of Cre recombinase in muscle of floxed Nampt mice reduced NAMPT and NAD+ levels by 38% and 43%, respectively. Glucose uptake increased by 40%, and mitochondrial complex IV respiration was compromised by 20%. Hypoxia-inducible factor (HIF)-1α-regulated genes and histone H3 lysine 9 (H3K9) acetylation, a known sirtuin 6 (SIRT6) target, were increased in shNampt KD cells. Thus, we propose that the shift toward glycolytic metabolism observed, at least in part, is mediated by the SIRT6/HIF1α axis. Our findings suggest that NAMPT plays a key role for maintaining NAD+ levels in skeletal muscle and that NAMPT deficiency compromises oxidative phosphorylation capacity and alters energy homeostasis in this tissue.

KEYWORDS:

HIF-1α; NAMPT; SIRT6; glycolysis; nicotinamide riboside

PMID:
29208611
DOI:
10.1152/ajpendo.00213.2017
[Indexed for MEDLINE]

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