Conclusion
These findings support a role for NR in improving cellular energetics and functional capacity in mice, which support the translation of this work into clinical settings as a strategy for improving and/or maintaining health span during aging.
Methods
We treated 15-mo-old male C57BL/6J mice with NR at 300 mg·kg·d-1 (NR3), 600 mg·kg·d-1 (NR6), or placebo (PLB), n = 8 per group, and assessed changes in physical performance, muscle histology, and NAD+ content after 4 wk of treatment.
Results
NR increased total NAD+ in muscle tissue (NR3 P = 0.01; NR6 P = 0.004, both versus PLB), enhanced treadmill endurance and open-field activity, and prevented decline in grip strength. Histologic analysis revealed NR-treated mice exhibited enlarged slow-twitch fibers (NR6 versus PLB P = 0.014; NR3 P = 0.16) and a trend toward more slow fibers (NR3 P = 0.14; NR6 P = 0.22). We next carried out experiments to characterize NR effects on mitochondrial activity and cellular energetics in vitro. We observed that NR boosted basal and maximal cellular aerobic and anaerobic respiration in both mouse and human myoblasts and human myotubes. Additionally, NR treatment improved the differentiating capacity of myoblasts and increased myotube size and fusion index upon stimulation of these progenitors to form multinucleated myotubes.