AKG Reverses Age-Related Muscle Loss by Restoring Protein Balance and Mitochondrial Health

Sarcopenia—the progressive age-related loss of muscle mass, strength, and function—affects a growing proportion of the global elderly population, with muscle mass declining roughly 1–2% per year after age 50 and strength falling even faster. Current interventions including protein supplementation, resistance training, and hormone therapy each carry significant limitations in elderly patients with comorbidities. This study investigated whether AKG, a naturally occurring metabolite and key TCA cycle intermediate that declines with age, could counteract sarcopenia through dietary supplementation.

The researchers established a sarcopenia model in 8-week-old male C57BL/6J mice using daily subcutaneous injections of D-galactose (500 mg/kg) for 8 weeks to induce oxidative stress and accelerated aging phenotypes. A treatment group received concurrent AKG injections (1 mg/kg/day). Animals were assessed for body composition using an awake body composition analyzer, and functional performance was evaluated via treadmill endurance tests, maximal running speed, and grip strength measurements. Cold tolerance was assessed by thermal imaging after acute 4°C exposure. Tibialis anterior muscle tissue was collected for histology (H&E staining), transmission electron microscopy, gene expression (qRT-PCR), and protein analysis (Western blot).

AKG-treated mice showed significant improvements across all measured outcomes. Lean muscle mass increased, grip strength was restored toward control levels, and exercise endurance and maximal running speed improved compared to D-gal-only animals. Cold tolerance, a proxy for metabolic muscle activity, was also enhanced. Histologically, muscle fiber cross-sectional area was significantly larger in AKG-treated mice, indicating preservation of myofiber size. Electron microscopy revealed improved mitochondrial morphology and integrity in skeletal muscle of AKG-treated animals.

At the molecular level, AKG restored protein homeostasis by upregulating the Akt/mTOR anabolic signaling pathway and simultaneously downregulating the ubiquitin-proteasome atrogenes MuRF1 and Atrogin-1 (Fbx32), which are key mediators of muscle protein degradation during atrophy. AKG also activated the SIRT1/PGC-1α/Nrf2 antioxidant axis, increasing SOD (superoxide dismutase) activity and reducing ROS accumulation in skeletal muscle. Inflammatory cytokines IL-6 and TNF-α were also reduced, consistent with AKG's known anti-inflammatory properties. Together, these molecular actions converged to preserve both the quantity and quality of skeletal muscle tissue.

These findings are notable because AKG is endogenously produced, recognized as safe by regulatory agencies, and is readily available as a dietary supplement. The dual mechanism—simultaneously addressing protein degradation and mitochondrial/oxidative dysfunction—makes it a particularly attractive candidate for sarcopenia intervention. However, translational caution is warranted given the preclinical model and subcutaneous rather than oral delivery route used here.