Skeletal muscle NAMPT is induced by exercise in humans.
Level 4 - case-series / case-control
Cross-sectional human comparison combined with an uncontrolled pre-post exercise intervention and in vitro cell culture.
PubMed 19887595 · doi:10.1152/ajpendo.00318.2009
What was done
Researchers conducted a cross-sectional study comparing skeletal muscle NAMPT protein expression among athletes, sedentary nonobese individuals, sedentary obese individuals, and individuals with type 2 diabetes. They also ran an exercise intervention assessing muscle NAMPT protein in sedentary nonobese subjects before and after 3 weeks of exercise training. Correlations between NAMPT levels and mitochondrial markers (complex III, maximal ATP synthesis via magnetic resonance spectroscopy, and VO2max) were analyzed. Primary human myotubes were treated in vitro with forskolin (cAMP pathway activator), ionomycin, or AICAR (AMPK activator) to examine regulatory mechanisms.
What was found
Athletes showed roughly twofold higher muscle NAMPT protein expression compared to sedentary obese, nonobese, and type 2 diabetic subjects (P < 0.05). NAMPT protein correlated with complex III protein content (R2 = 0.28, P < 0.01), maximal ATP synthesis (R2 = 0.37, P = 0.002), and VO2max (R2 = 0.63, P < 0.0001). In sedentary nonobese subjects, 3 weeks of exercise training increased NAMPT protein by 127% (P < 0.01). In primary myotubes, forskolin stimulated an approximately 2.5-fold increase in NAMPT protein, ionomycin had no effect, and AICAR increased NAMPT mRNA ~3.4-fold (P < 0.05) with modest increases in NAMPT protein (P < 0.05) and mitochondrial content (P < 0.05).
Why it matters
This study provides direct human evidence that exercise induces skeletal muscle NAMPT, identifying a key pathway linking physical activity and cellular energy sensing to NAD+ synthesis and mitochondrial capacity.
Limits
The abstract does not report participant sample sizes, participant demographics (such as age or sex), or the exact exercise training protocol (type, frequency, intensity). The exercise intervention lacked a non-exercising control group, and direct measurements of NAD+ levels or long-term clinical metabolic endpoints were not reported.
Cited by
- supports Marathon runners have resting NAD levels roughly 50% higher than untrained individuals.