Grifola frondosa polysaccharide improves dexamethasone induced atrophy of myotube models from mouse skeletal muscle cell line C2C12

Objective To investigate the mechanism by which Grifola frondosa polysaccharide (GFP) mitigates dexamethasone (DEX)-induced atrophy of myotubes in mouse skeletal muscle cell line C2C12(C2C12 myotube). Methods C2C12 cells were divided into normal group (NOR), dexamethasone group (DEX), low-dose GFP (GFP-L), medium-dose GFP (GFP-M) and high-dose GFP-H intervention DEX groups (concentrations of 20, 50, and 100 μg/mL, respectively).Immunofluorescence microscopy and Western blot were employed to assess myosin heavy chain (MyHC) expression. Western blot and RT-qPCR were utilized to evaluate the protein and mRNA levels of muscle-specific ring finger protein 1 (MuRF1), muscle atrophy F-box protein (Atrogin1) as well as phosphorylation of AMPK and forkhead box protein O3 (FOXO3a).The expression of SIRT1.ATP and mitochon- drial protein content were measured with commercially available kits. Results GFP-M and GFP-H groups significantly increased myotube length, fusion index and MyHC expression in DEX-treated cells(P＜0.05). Additionally, GFP treatment markedly down-regulated the protein and mRNA expression level of Atrogin1, MuRF1 and Myostatin(P＜0.05). The phosphorylation level of AMPK and FOXO3a and the expression of SIRT1 were also significantly reduced(P＜0.05).The SIRT1 inhibitor-induced aberrant expression of FOXO3a, Atrogin1, and MuRF1 was effectively reversed by GFP. Conclusions Grifola frondosa polysaccharide may alleviate DEX-induced atrophy of C2C12 myotubes through a SIRT1-mediated AMPK/FOXO3a signaling pathway.