β-羟基-β-甲基丁酸对衰老小鼠腓肠肌蛋白质合成的影响研究

Effects of Beta-hydroxy-beta-methylbutyrate Supplementation on Protein Synthesis in Skeletal Muscle of Aged Mice

探索膳食添加β-羟基-β-甲基丁酸(HMβ)对衰老小鼠骨骼肌蛋白质合成的调节作用及其作用机理。方法:16月龄雄性C57BL/6J小鼠24只随机纳入3个处理组:膳食添加HMβ组、添加等氮剂量丙氨酸组及空白对照组,其中HMβ组小鼠和丙氨酸组小鼠饲料中分别添加4.5%HMβ和3.4%丙氨酸,空白对照组则饲以国家标准维持饲料,共计干预8周。期间记录各组小鼠体质量与采食量,测量小鼠后肢的最大抓握力。各组小鼠于末次饲食后禁食12 h,麻醉后摘眼球采血处死,移除腓肠肌外侧头浅层白肌并称重。测定骨骼肌蛋白质总量、肌原纤维与肌浆蛋白含量且免疫印迹检测MHCⅡ、mTOR^(Ser2448)、p70s6k^(Thr389)和4EBP1^(Thr37/46)磷酸化表达的组间差异。结果:膳食添加4.5%剂量的HMβ未显著影响衰老小鼠体重与采食量,但可见腓肠白肌湿重、湿重/体重校正比值增加,且增幅具有统计学意义;腓肠白肌蛋白质总量、肌原纤维与肌浆蛋白质含量及MHCⅡ总量表达均显著增长;mTOR^(Ser2448)、p70s6k^(Thr389)与4EBP1^(Thr37/46)磷酸化水平亦有明显上调。结论:膳食添加4.5%比例HMβ具有促进骨骼肌蛋白质合成,削弱衰老性骨骼肌萎缩与功能衰退的重要潜力,其作用机理可能涉及mTOR/p70s6k/4EBP1信号转导通路的活化。

Objective:To investigate the effects of beta-hydroxy-beta-methylbutyrate(HMβ)supplementation on protein synthesis in aged mice and preliminarily explore the possible mechanism of action.Method:Twenty four C57BL/6J male mouse,16-month old,were randomly allocated to three groups:HMβsupplementation,isonitrogenous alanine supplementation and blank control group.Mice in HMβand alanine group were treated with standard chow diet supplemented with 4.5%HMβand 3.4%alanine respectively for 8 weeks,while blank control group were fed with normal diet.Both body weight and food intake were recorded during research,the maximal grip strength of lateral limb was also determined.Twelve hours of fasting after the last feeding,mice exposed to anesthesia and then sacrificed via drawing blood.The white gastrocnemius muscle was removed and weighed.The total protein,myofibrillar and sarcoplasmic protein content in white gastrocnemius were determined,and the phosphorylation of mTORSer2448,p70s6kThr389and 4EBP1Thr37/46 was also measured using western blotting.Results:Both body weight and food intake of aged mice were not significantly influenced by dietary HMβsupplementation.The wet weight of white gastrocnemius,and re-adjusted ratio of white gastrocnemius to body weight were significantly improved.The total protein,myofibrillar and sarcoplasmic protein content,and expression of MHCⅡwere greatly increased.Furthermore,the phosphorylation rate of mTORSer2448,p70s6kThr389 and 4EBP1Thr37/46 were also found to be elevated significantly.Conclusion:Dietary HMβsupplementation with 4.5%dosage was capable of promoting muscular protein synthesis,and thus it has the potential to attenuate age-related skeletal muscle atrophy and functional decline.In terms of the possible mechanism,the mTOR/p70s6k/4EBP1 signaling pathway may be directly or at least to some extent involved in this process.