School of Sport, Exercise and Rehabilitation Sciences, University of Birmingham, Birmingham, United Kingdom.
National Institute for Health Research, Birmingham Biomedical Research Centre, University Hospitals Birmingham NHS Foundation Trust and University of Birmingham, Birmingham, United Kingdom.
Am J Physiol Cell Physiol. 2021 Jul 1;321(1):C26-C37. doi: 10.1152/ajpcell.00093.2021. Epub 2021 Apr 28.
In vitro models of muscle aging are useful for understanding mechanisms of age-related muscle loss and aiding the development of targeted therapies. To investigate mechanisms of age-related muscle loss in vitro utilizing ex vivo human serum, fasted blood samples were obtained from four old (72 ± 1 yr) and four young (26 ± 3 yr) men. Older individuals had elevated levels of plasma CRP, IL-6, HOMA-IR, and lower concentric peak torque and work-per-repetition compared with young participants ( < 0.05). C2C12 myotubes were serum and amino acid starved for 1 h and conditioned with human serum (10%) for 4 h or 24 h. After 4 h, C2C12 cells were treated with 5 mM leucine for 30 min. Muscle protein synthesis (MPS) was determined through the surface sensing of translation (SUnSET) technique and regulatory signaling pathways were measured via Western blot. Myotube diameter was significantly reduced in myotubes treated with serum from old, in comparison to young donors (84%, < 0.001). MPS was reduced in myotubes treated with old donor serum, compared with young serum before leucine treatment (32%, < 0.01). MPS and the phosphorylation of Akt, p70S6K, and eEF2 were increased in myotubes treated with young serum in response to leucine treatment, with a blunted response identified in cells treated with old serum ( < 0.05). Muscle protein breakdown signaling pathways did not differ between groups. In summary, we show that myotubes conditioned with serum from older individuals had decreased myotube diameter and MPS compared with younger individuals, potentially driven by low-grade systemic inflammation.
体外肌肉衰老模型有助于理解与年龄相关的肌肉丧失的机制，并有助于开发有针对性的治疗方法。为了利用体外的人类血清研究与年龄相关的肌肉丧失的机制，从 4 名老年人（72 ± 1 岁）和 4 名年轻人（26 ± 3 岁）中采集禁食后的血液样本。与年轻参与者相比，老年人的血浆 CRP、IL-6、HOMA-IR 水平升高，向心峰扭矩和重复工作的功降低（<0.05）。C2C12 肌管在血清和氨基酸饥饿 1 小时后，用 10%的人血清培养 4 小时或 24 小时。4 小时后，用 5 mM 亮氨酸处理 C2C12 细胞 30 分钟。通过翻译表面感应（SUnSET）技术测定肌肉蛋白合成（MPS），通过 Western blot 测定调节信号通路。与年轻供体血清相比，用老年供体血清处理的肌管的肌管直径明显减小（84%，<0.001）。在亮氨酸处理之前，用老年供体血清处理的肌管的 MPS 低于用年轻血清处理的肌管（32%，<0.01）。与用老年血清处理的细胞相比，用年轻血清处理的肌管中亮氨酸处理后 MPS 和 Akt、p70S6K 和 eEF2 的磷酸化增加，反应减弱（<0.05）。肌肉蛋白分解信号通路在各组之间没有差异。总之，我们表明，用来自老年人的血清处理的肌管与年轻人相比，肌管直径和 MPS 降低，这可能是由低度系统性炎症引起的。
