Sparks 2014 Abstract MiP2014

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NAMPT remodels substrate metabolism in skeletal muscle.
Link:
Sparks LM
Mitochondr Physiol Network 19.13 - MiP2014

Sparks LM, Stephens NA, Gabriel M, Gardell SJ, Smith SR (2014)

Event: MiP2014

In mammals, nicotinamide phosphoribosyltransferase (NAMPT) is responsible for the first and rate-limiting step in the “salvage pathway” that converts nicotinamide to nicotinamide adenine dinucleotide (NAD+). We previously showed that exercise increased skeletal muscle NAMPT expression, which correlates with mitochondrial content in humans [1]. Caloric restriction-induced beneficial effects in oxidative stress, mitochondrial biogenesis and metabolic adaptation in mice require NAMPT [2]. The mechanisms responsible for metabolic adaption are unclear. We hypothesized that muscle-specific overexpression of NAMPT in mice (NamptTg) would improve muscle respiratory capacity and control and would be additive with endurance exercise training in these mice.

Based on western blotting studies, NamptTg mice express 10-fold more skeletal muscle NAMPT protein compared to wild type (WT) mice. A concomitant elevation of NMN (5-fold) and NAD+ (3-fold) in NamptTg skeletal muscle revealed increased NAMPT enzymatic activity. WT and NamptTg mice were housed with ('trained') or without ('sedentary') running wheels to elicit voluntary exercise for a period of 7 weeks (WT Sedentary; WT Trained; NamptTg Sedentary; NamptTg Trained). No differences were observed in the proclivity of NamptTg mice to engage in voluntary exercise. Mice were fasted for 5 h prior to sacrifice. Quadriceps muscles were used for the respiration measurements. SUIT protocols were performed in permeabilized fiber bundles using either Complex I-linked substrates (CI, pyruvate+glutamate+malate) or a fatty acid oxidation (FAO, palmitoyl-carnitine+malate) plus CI–linked (glutamate) substrate combination (CI&FAO; Fig. 1)

NamptTg mice had an increased CI&FAO capacity after training (P<0.05; Fig. 1A). Notably, this training-induced improvement in the NamptTg mice tended to be higher than the trivial increase in CI&FAO flux with training in WT mice (P=0.0595; Fig. 1A). Increased NAMPT levels were sufficient to dramatically improve mitochondrial coupling efficiency, as reflected by the significant reduction in the ratio of proton leak-linked respiration (L) to OXPHOS capacity (P) in the NamptTg mice compared with WT mice at baseline (P<0.05; Figure 1B). While training improved coupling efficiency in the WT mice (P<0.05, Figure 1B), it tended to further improve coupling efficiency in the NamptTg mice as well (P=0.107; Fig. 1B).

Taken together, decreased LEAK/OXPHOS ratios (i.e. improved biochemical coupling efficiency) and an increased capacity to burn CI&FAO-linked substrates indicate a synergistic improvement in muscle mitochondrial function via NAMPT and endurance exercise, whereby an increased amount of NAMPT is sufficient to enhance the exercise-induced improvements in substrate metabolism.


O2k-Network Lab: US FL Orlando Sparks LM


Labels: MiParea: Respiration, mt-Biogenesis;mt-density, Exercise physiology;nutrition;life style 


Organism: Mouse  Tissue;cell: Skeletal muscle  Preparation: Permeabilized tissue 

Regulation: Coupling efficiency;uncoupling  Coupling state: LEAK, OXPHOS  Pathway: N, S  HRR: Oxygraph-2k  Event: B1, Oral  MiP2014 

Affiliation

1-Translational Research Inst Metabolism Diabetes, Florida Hospital; 2-Sanford Burnham Medical Research Inst; Orlando, FL, USA. - lauren.sparks@flhosp.org

Figure 1

MiP2014 Sparks Figure.jpg
Figure 1. Overexpression of NAMPT improves mitochondrial function after training in skeletal muscle. Respiration was measured in permeabilized muscle fiber bundles using a SUIT protocol with combined CI&FAO-linked substrates, adding a fatty acid substrate (palmitoyl-carnitine) and Complex I (CI)-linked substrates glutamate+malate simultaneously. A: OXPHOS (P) capacities in the presence of adenylates (ADP) are presented as respiration per mtDNA copy number. B: LEAK (L) respiration was measured in the absence of adenylates (ADP) and coupling control ratios are presented as LEAK divided by OXPHOS capacity. Bars represent mean±SEM for wild type (WT) sedentary and trained mice and for NAMPT Transgenic (TG) sedentary and trained mice. Letters different from each other indicate statistically significant differences (P<0.05; Tukey’s HSD). N=6 (WT sedentary); N=7 (WT Trained); N=6 (TG sedentary); N=5 (TG trained).


References

  1. Costford SR, Bajpeyi S, Pasarica M, Albarado DC, Thomas SC, Xie H, Church TS, Jubrias SA, Conley KE, Smith SR (2010) Skeletal muscle NAMPT is induced by exercise in humans. Am J Physiol Endocrinol Metab 298: 117-26.
  2. Song J, Ke SF, Zhou CC, Zhang SL, Guan YF, Xu TY, Sheng CQ, Wang P, Miao CY (2014) Nicotinamide phosphoribosyltransferase is required for the calorie restriction-mediated improvements in oxidative stress, mitochondrial biogenesis, and metabolic adaptation. J Gerontol A Biol Sci Med Sci 69: 44-57.