Abstract: BACKGROUND: Dexamethasone and hindlimb suspension are commonly used methods for modeling sarcopenia in animal experiments due to their short modeling time, ease of operation, and low cost. 
OBJECTIVE: To compare the differences in muscle mass, strength and functional phenotypes and molecular mechanisms between two mouse sarcopenia models induced by dexamethasone and hindlimb suspension.
METHODS: Thirty male C57BL/6 mice were randomly divided into three groups (n=10 per group). The normal control group received no intervention. The dexamethasone group received daily intraperitoneal injections of 1 mg/kg/d dexamethasone sodium phosphate solution for 6 continuous days to establish sarcopenia models in mice, while mice in the hindlimb suspension group were suspended by tail harness for 16 hours, once per day, to establish sarcopenia models. Within 6 weeks after modeling, changes in body mass were monitored. After 6 weeks of modeling, mice were tested for limb grip strength, mobility (swimming test), skeletal muscle wet mass, and skeletal muscle pathological morphology. Expressions of skeletal muscle protein synthesis and catabolism indexes as well as the AMPK/FoXO3α signaling pathway were detected by RT-PCR and western blot.
RESULTS AND CONCLUSION: (1) Two weeks after modeling, both dexamethasone and hindlimb suspension groups showed a significant decrease in body mass compared with the normal control group (P < 0.001). After 6 weeks of modeling, grip strength of mice in both dexamethasone and hindlimb suspension groups was lower than that in the normal control group (P < 0.001). The wet mass of gastrocnemius and extensor digitorum longus muscles and the cross-sectional area of gastrocnemius and soleus muscles in the dexamethasone group were lower than those in the normal control group (P < 0.05). Compared with the hindlimb suspension group, the cross-sectional area of gastrocnemius muscle was significantly smaller in the dexamethasone group (P < 0.05), while the cross-sectional area of soleus muscle was larger in the dexamethasone group (P < 0.05). Mice in the dexamethasone group had reduced mobility when compared with those in the normal control group and the hindlimb suspension group (P < 0.05). (3) Compared with the normal control group, PI3K, mTOR, AMPK, and PGC-1α mRNA expression and P-AMPK/AMPK protein were decreased in the two modeling groups (P < 0.05), and FoXO3α mRNA expression and PGC-1α and FoXO3 protein expression were elevated (P < 0.05); in the dexamethasone group, Akt1 mRNA expression was decreased (P < 0.05), while Atrogin-1 and MuRF-1 mRNA expression was elevated (P < 0.05); in the hindlimb suspension group, Akt1 mRNA expression was elevated (P < 0.05). (4) Compared with the dexamethasone group, mTOR, Akt1, and FoXO3α mRNA expression was elevated in the hindlimb suspension group (P < 0.05), while Atrogin-1 and MuRF-1 mRNA expression was decreased (P < 0.05). To conclude, both modeling methods could decrease the levels of mitochondrial energy metabolism in skeletal muscle, with the dexamethasone group mediating atrophy of skeletal muscle through the dual action of ubiquitin proteasome and energy metabolism pathways, and the hindlimb suspension group inducing atrophy of skeletal muscle by mediating the energy metabolism pathway through the AMPK/FoXO3α signaling pathway, subsequently causing a reduction in mass, strength, and function of skeletal muscle. 

中国组织工程研究杂志出版内容重点：组织构建；骨细胞；软骨细胞；细胞培养；成纤维细胞；血管内皮细胞；骨质疏松；组织工程

Key words: sarcopenia, mouse model, muscle protein synthesis gene, autophagy lysosome gene, ubiquitin proteasome gene