Abstract: Objective To observe the alterations of Sirt1 and mTOR activity in gastrocnemius muscles of mice with sarcopenia. Methods aged (26 months old) and young (6 months old) male C57BL/6J mice (n=16,respectively) were randomly arranged into 2 groups respectively，n=8 in each group: middle-aged control(MC), middle-aged suspension(MS), aged control(AC) and aged suspension(AS). Aged mice were hindlimb suspended for two weeks to establish a sarcopenic model. Kits and Western blot were used to determine related factors and protein expression of Sirt1 and mTOR pathway. Results 1.the content of NAD+ and the ratio of NAD+/NADH: AC group was significantly lower than MC group (P＜0.01 or P＜0.05), HLS group was significantly less than the control group (P<0.01 or P<0.05). 2. Sirt1 expression: AC group were significantly higher than MC group (P<0.05), and HLS group was significantly higher than that of the control group (P<0.05).3. Sirt1 downstream substrates (PGC-1α, FOXO1 and P53), NAMPT protein expression and Sirt1 activity: AC group was significantly lower than MC group (P＜0.05 or P＜0.05 or P＜0.01), HLS group was significantly less than the control group (P<0.05 or P<0.05 or P<0.05). 4. phosphorylation of mTOR, p70S6K and 4E-BP1: AC group was significantly higher than MC group (P<0.05), HLS group was significantly less than the control group (P<0.05). Conclusions Sirt1 and mTOR are involved in the pathogenesis of mice with sarcopenia.

Key words: Sarcopenia, Sirt1, mTOR