Nucleotide Supplements Reverse Age-Related Muscle Loss in Accelerated-Aging Mice
Long-term nucleotide supplementation boosted muscle mass, strength, and fiber size in aging mice by suppressing key protein-degradation genes.
Summary
Researchers fed senescence-accelerated SAMP8 mice a nucleotide (NT) mixture for 9–15 months and found significant improvements in lean mass, grip strength, gait speed, and muscle fiber cross-sectional area—particularly type IIb fibers. RNA sequencing revealed downregulation of sarcopenia-linked genes (Trim63, Fbxo32, Dkk3, Mt1, p53), while metabolomic analysis identified branched-chain amino acid metabolites that further inhibit protein degradation and promote synthesis. Cell studies in H₂O₂-stressed C2C12 myotubes confirmed these findings. The results suggest dietary nucleotides may act as a conditionally essential nutrient in older adults, offering a practical nutritional strategy against sarcopenia.
Detailed Summary
Sarcopenia—the age-related loss of skeletal muscle mass and strength—affects up to 60% of adults over 80 and currently lacks approved pharmacological treatments. Because nucleotide (NT) levels decline in aging muscle and prior cell-culture work showed cytoprotective effects, this study asked whether long-term dietary NT supplementation could attenuate sarcopenia in a validated animal model.
The team used Senescence-Accelerated Mouse Prone-8 (SAMP8) mice, a well-established accelerated-aging model, divided into cohorts sacrificed at 12 or 18 months. Animals received diets supplemented with an NT mixture (AMP:CMP:GMP:UMP = 32.6:90.3:33.4:46.8 g/kg, mirroring breast milk ratios) at low (0.3 g/kg), medium (0.6 g/kg), or high (1.2 g/kg) doses from 3 months of age. Outcomes included body composition (EchoMRI), physical performance (grip strength, wire hang, horizontal bar, gait analysis), immunofluorescence of muscle fiber cross-sectional area (CSA) and fiber typing, RNA sequencing of quadriceps, RT-qPCR and western blotting in tibialis anterior and gastrocnemius, and targeted LC-MS/MS metabolomics of extensor digitorum longus tissue.
NT supplementation significantly increased lean mass as a proportion of body weight (p<0.01, η²=0.434) and improved grip strength at 7, 9, and 11 months of age (η² ranging 0.293–0.507) as well as gait speed (p<0.0001, η²=0.386). Immunofluorescence showed larger muscle fiber CSA (p<0.0001, η²=0.108), predominantly in fast-twitch type IIb fibers. RNA-seq identified robust downregulation of ubiquitin-ligase genes Trim63 (MuRF1) and Fbxo32 (Atrogin-1), the Wnt-inhibitor Dkk3, metallothionein Mt1, and tumor suppressor p53—all confirmed by RT-qPCR and/or western blot (p<0.05). These genes are central to the FoxO-driven ubiquitin–proteasome protein degradation axis. Western blot additionally showed reduced FoxO1/FoxO3 protein and enhanced phospho-Akt and phospho-S6K, consistent with a shift toward anabolic signaling.
Integrated RNA-seq and metabolomic analyses pinpointed changes in branched-chain amino acid (BCAA) catabolism metabolites—specifically ketoleucine, 3-hydroxyisovalerylcarnitine, and 3-methyl-2-oxovaleric acid—as likely intermediaries linking NT intake to altered gene expression. Bayesian mediation/SEM modeling supported indirect mechanistic pathways. In vitro, NT monomers and mixtures increased C2C12 myotube diameter and suppressed atrogene expression under H₂O₂-induced oxidative stress, corroborating the in vivo data.
The study concludes that exogenous NTs may qualify as a conditionally essential nutrient for older individuals, improving the protein synthesis/degradation balance via FoxO-Atrogin-1/MuRF1 suppression and favorable BCAA metabolism. Human trials are needed to confirm efficacy and safety.
Key Findings
- NT supplementation increased lean mass/body weight ratio significantly (p<0.01, η²=0.434) in aging SAMP8 mice.
- Grip strength improved at 7, 9, and 11 months; gait speed increased (p<0.0001, η²=0.386) with NT treatment.
- Muscle fiber CSA—especially type IIb fast-twitch fibers—was significantly larger in NT-supplemented mice.
- Sarcopenia genes Trim63, Fbxo32, Dkk3, Mt1, and p53 were downregulated; Akt/S6K anabolic signaling was enhanced.
- BCAA-related metabolites (ketoleucine, 3-hydroxyisovalerylcarnitine) mediated NT effects on muscle protein balance.
Methodology
SAMP8 accelerated-aging mice received NT-enriched diets (0.3–1.2 g/kg) for 9 or 15 months; outcomes included EchoMRI body composition, functional performance tests, immunofluorescence fiber typing, RNA-seq, RT-qPCR, western blot, and targeted LC-MS/MS metabolomics. C2C12 myotube experiments under H₂O₂-induced atrophy validated in vivo findings in vitro.
Study Limitations
The study used only male SAMP8 mice, an accelerated-aging model that may not fully reflect normal human aging; no human trials were conducted. Mechanistic pathways were partly inferred from correlational integrated omics without complete causal validation. Long-term safety and optimal dosing in humans remain unknown.
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