BackgroundSarcopenia is a prevalent muscle disorder in old people leading to higher fracture rate, mortality, and other adverse clinical outcomes. Evidence indicates that short‐chain fatty acids (SCFAs), which are beneficial gut microbial metabolites, were reduced in old people with sarcopenia. This study aimed to determine whether the use of SCFAs as a supplement can be a therapeutic strategy of sarcopenia in a pre‐clinical model.MethodsSeven‐month‐old pre‐sarcopenic senescent accelerated mouse prone 8 (SAMP8) mice received daily SCFAs cocktail (acetate, butyrate, and propionate) for 3 months. Age‐matched senescence accelerated mouse resistant 1 (SAMR1) and SAMP8 mice receiving sodium‐matched drinking water were control groups. The gut microbiota composition analysis of aged mice with or without sarcopenia was conducted by 16S rDNA sequencing. Gut barrier‐related proteins and lipopolysaccharide (LPS) concentration were biomarkers of gut permeability. Colon inflammation levels, circulatory SCFAs concentration, muscle quality, function, and underlying pathways were detected by cell number counting, RT‐qPCR, gas chromatography–mass spectrometry, measurements of muscle wet weight and grip strength, ex vivo functional test, treadmill endurance test, transcriptomic sequencing, morphological and immunofluorescent staining, as well as western blot. To investigate the role of mTOR signalling pathways in SCFAs treatment, C2C12 myotubes were treated with rapamycin.ResultsAged SAMP8 mice had different microbiota composition, and lower serum butyric acid compared with SAMR1 mice (P < 0.05). SCFAs treatment reversed the increment of colon inflammation (2.8‐fold lower of il‐1β) and gut barrier permeability (1.7‐fold lower of LPS) in SAMP8 mice. Increased muscle mass, myofibre cross‐sectional area, grip strength, twitch and tetanic force were found in SCFAs‐treated mice compared with control SAMP8 mice (P < 0.05). Anti‐fatigue capacity (1.6‐fold) and muscle glycogen (2‐fold) also improved after SCFAs treatment (P < 0.05). Transcriptomic analysis showed that AMPK, insulin, and mTOR pathways were involved in SCFAs treatment (P < 0.05). Regulation of AKT/mTOR/S6K1 and AMPK/PGC1α pathways were found. SCFAs attenuated fat infiltration and improved mitochondria biogenesis of atrophic muscle. In vitro studies indicated that SCFAs inhibited FoxO3a/Atrogin1 and activated mTOR pathways to improve myotube growth (P < 0.05), and rapamycin attenuated the effect of SCFAs through the inhibition of mTOR pathways.ConclusionsThis study demonstrated that bacterial metabolites SCFAs could attenuate age‐related muscle loss and dysfunction, and protein synthesis‐related mTOR signalling pathways were involved both in vivo and in vitro.

中文翻译：

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短链脂肪酸通过激活肌肉减少性小鼠的 mTOR 信号通路来增强肌肉质量和功能


背景肌肉减少症是老年人中普遍存在的肌肉疾病，导致较高的骨折率、死亡率和其他不良临床结果。有证据表明，短链脂肪酸 （SCFA） 是有益的肠道微生物代谢物，在患有肌肉减少症的老年人中减少。本研究旨在确定使用 SCFA 作为补充剂是否可以作为临床前模型中肌肉减少症的治疗策略。方法7 个月大的肌肉减少前衰老加速小鼠易感 8 （SAMP8） 小鼠每天接受 SCFA 鸡尾酒（乙酸盐、丁酸盐和丙酸盐），持续 3 个月。年龄匹配的衰老加速小鼠耐药 1 （SAMR1） 和接受钠匹配的饮用水的 SAMP8 小鼠是对照组。通过 16S rDNA 测序对伴有或不伴有肌肉减少症的老年小鼠进行肠道菌群组成分析。肠道屏障相关蛋白和脂多糖 （LPS） 浓度是肠道通透性的生物标志物。通过细胞数计数、RT-qPCR、气相色谱-质谱法、肌肉湿重和握力测量、离体功能试验、跑步机耐力试验、转录组测序、形态学和免疫荧光染色以及蛋白质印迹法检测结肠炎症水平、循环 SCFAs 浓度、肌肉质量、功能和潜在途径。为了研究 mTOR 信号通路在 SCFA 治疗中的作用，用雷帕霉素处理 C2C12 肌管。结果与 SAMR1 小鼠相比，老年 SAMP8 小鼠的菌群组成不同，血清丁酸水平较低 （P < 0.05）。SCFAs 治疗逆转了 SAMP8 小鼠结肠炎症的增加 （il-1β 的低 2.8 倍） 和肠道屏障通透性 （LPS 的低 1.7 倍）。 与对照 SAMP8 小鼠相比，在 SCFA 治疗的小鼠中发现肌肉质量、肌纤维横截面积、握力、抽搐和手足风捣乱力增加 （P < 0.05）。SCFAs 治疗后抗疲劳能力 （1.6 倍） 和肌糖原 （2 倍） 也有所改善 （P < 0.05）。转录组学分析显示 AMPK 、 胰岛素和 mTOR 通路参与 SCFAs 治疗 （P < 0.05）。发现 AKT/mTOR/S6K1 和 AMPK/PGC1α 通路的调节。SCFAs 减弱脂肪浸润并改善萎缩肌的线粒体生物发生。体外研究表明，SCFAs 抑制 FoxO3a/Atrogin1 并激活 mTOR 通路以改善肌管生长 （P < 0.05），雷帕霉素通过抑制 mTOR 通路减弱 SCFA 的作用。结论本研究证明，细菌代谢物 SCFAs 可以减轻与年龄相关的肌肉损失和功能障碍，蛋白质合成相关的 mTOR 信号通路在体内和体外均参与。