Abstract: 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.

Key words: Grifola frondosa polysaccharide, muscle atrophy, dexamethasone, AMPK/FOXO3a signaling pathway