HD6277 Suppresses Muscle Atrophy by Promoting Myogenic Factors and Inhibiting Proteolysis in Aged Mice

Background: G protein–coupled receptor 40 (GPR40) acts as a modulator of various physiological functions, including glycaemic lowering, anti-inflammation and antioxidative stress, in several tissues. However, the role of GPR40 in skeletal muscles remains unclear. Methods: To investigate the roles of muscle GPR40, C2C12 myoblasts and myotubes were stimulated with palmitate and HD6277, a GPR40 agonist. Muscle strength and myofiber thickness were measured in obese and aged mice fed HD6277. Results: In C2C12 myoblasts, the addition of HD6277 induced phosphorylated Akt levels and expression of the myogenic factors, myogenin (MyoG), myocyte enhancer factor 2C (Mef2c) and myosin heavy chain (MyHC, p < 0.05). These changes resulted in accelerated muscle differentiation from myoblasts to myotubes (MyHC-positive area +56.52%; myotube width +34.08% vs. Veh, p < 0.05). In C2C12 myotubes, a palmitate-mediated decrease in the phosphorylation of forkhead box protein O1A (FOXO1A) and increase in the expression of E3 ubiquitin ligases, atrogin-1 and muscle RING-finger protein 1 (MuRF1) were reversed by HD6277 (p < 0.05). Additionally, HD6277 inhibited palmitate-induced apoptotic events such as the Bcl-2 (Bcl2)-associated X protein (Bax)/Bcl-2 ratio, caspase 3 cleavage and nuclear fragmentation in C2C12 myoblasts and myotubes (p < 0.05). These beneficial HD6277-mediated actions disappeared after the addition of an Akt inhibitor (p < 0.05). Similar to in vitro studies, HD6277 administration in obese and aged mice increased myogenic factors and decreased E3 ubiquitin ligase expression and apoptotic events (p < 0.05). HD6277 increased muscle strength (+9.88% vs. Aged, p < 0.05) and myofiber thickness (+29.01% vs. Aged, p < 0.05) in aging mice but only improved myofiber thickness (+11.84% vs. HFD, p < 0.05) in obese mice. Conclusion: HD6277 can increase myogenic factors and reduce E3 ligase-mediated proteolysis to inhibit muscle atrophy in aged mice. Our results suggest that GPR40 agonists may have potential as therapeutic agents for sarcopenia.