Metabolic tracing reveals novel adaptations to skeletal muscle cell energy production pathways in response to NAD+ depletion [version 1; peer review: 2 approved]

Oakey, L.A., Fletcher, R.S., Elhassan, Y.S., Cartwright, D.M., Doig, C.L. ORCID: 0000-0001-9694-4230, Garten, A., Thakker, A., Maddocks, O.D.K., Zhang, T., Tennant, D.A., Ludwig, C. and Lavery, G.G., 2019. Metabolic tracing reveals novel adaptations to skeletal muscle cell energy production pathways in response to NAD+ depletion [version 1; peer review: 2 approved]. Wellcome Open Research, 3: 147. ISSN 2398-502X

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Abstract

Background: Skeletal muscle is central to whole body metabolic homeostasis, with age and disease impairing its ability to function appropriately to maintain health. Inadequate NAD+ availability is proposed to contribute to pathophysiology by impairing metabolic energy pathway use. Despite the importance of NAD+ as a vital redox cofactor in energy production pathways being well-established, the wider impact of disrupted NAD+ homeostasis on these pathways is unknown.

Methods: We utilised skeletal muscle myotube models to induce NAD+ depletion, repletion and excess and conducted metabolic tracing to provide comprehensive and detailed analysis of the consequences of altered NAD+ metabolism on central carbon metabolic pathways. We used stable isotope tracers, [1,2-13C] D-glucose and [U-13C] glutamine, and conducted combined 2D-1H,13C-heteronuclear single quantum coherence (HSQC) NMR spectroscopy and GC-MS analysis.

Results: NAD+ excess driven by nicotinamide riboside (NR) supplementation within skeletal muscle cells resulted in enhanced nicotinamide clearance, but had no effect on energy homeostasis or central carbon metabolism. Nicotinamide phosphoribosyltransferase (NAMPT) inhibition induced NAD+ depletion and resulted in equilibration of metabolites upstream of glyceraldehyde phosphate dehydrogenase (GAPDH). Aspartate production through glycolysis and TCA cycle activity was increased in response to low NAD+, which was rapidly reversed with repletion of the NAD+ pool using NR. NAD+ depletion reversibly inhibits cytosolic GAPDH activity, but retains mitochondrial oxidative metabolism, suggesting differential effects of this treatment on sub-cellular pyridine pools. When supplemented, NR efficiently reversed these metabolic consequences. However, the functional relevance of increased aspartate levels after NAD+ depletion remains unclear, and requires further investigation.

Conclusions: These data highlight the need to consider carbon metabolism and clearance pathways when investigating NAD+ precursor usage in models of skeletal muscle physiology.

Item Type: Journal article
Publication Title: Wellcome Open Research
Creators: Oakey, L.A., Fletcher, R.S., Elhassan, Y.S., Cartwright, D.M., Doig, C.L., Garten, A., Thakker, A., Maddocks, O.D.K., Zhang, T., Tennant, D.A., Ludwig, C. and Lavery, G.G.
Publisher: Wellcome Trust
Date: 8 September 2019
Volume: 3
ISSN: 2398-502X
Identifiers:
NumberType
10.12688/wellcomeopenres.14898.2DOI
1215195Other
Divisions: Schools > School of Science and Technology
Depositing User: Jonathan Gallacher
Date Added: 11 Nov 2019 09:31
Last Modified: 11 Nov 2019 09:31
URI: http://irep.ntu.ac.uk/id/eprint/38193

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