Loss of NAD Homeostasis Leads to Progressive and Reversible Degeneration of Skeletal Muscle.
Level 5 - mechanism / opinion, no new human data
Mechanistic animal research (murine knockout and overexpression models)
PubMed 27508874 · doi:10.1016/j.cmet.2016.07.005
What was done
Investigators generated muscle-specific Nampt knockout mice to deplete intramuscular NAD and evaluated muscle fiber histology, strength, and treadmill endurance. They tested whether administration of the NAD precursor nicotinamide riboside could rescue these deficits, and assessed the effects of lifelong Nampt overexpression in aged mice.
What was found
Knockout mice exhibited an 85% decline in intramuscular NAD content along with muscle fiber degeneration and progressive loss of muscle strength and treadmill endurance. Administration of nicotinamide riboside rapidly ameliorated functional deficits and restored muscle mass with only a modest increase in intramuscular NAD. Lifelong Nampt overexpression preserved muscle NAD levels and exercise capacity in aged mice. Specific numerical values for muscle mass, strength, and endurance changes were not reported in the abstract.
Why it matters
The findings demonstrate that tissue-autonomous NAD salvage via Nampt is essential for skeletal muscle structure and function, and that muscle degeneration driven by NAD loss is reversible with nicotinamide riboside supplementation in mice.
Limits
The study was conducted entirely in mice, so translational relevance to human muscle aging and sarcopenia remains unproven. Genetic ablation of Nampt creates an extreme 85% NAD depletion that may not reflect standard physiological aging. Sample sizes, treatment dosages, and numerical outcome data for functional tests were not reported in the abstract.
Cited by
- supports Administering nicotinamide riboside, a precursor to NAD, causes mice to gain or maintain muscle mass.