The Key Laboratory of Cardiovascular Remodeling and Function Research, Chinese Ministry of Education, Chinese National Health Commission and Chinese Academy of Medical Sciences, The State and Shandong Province Joint Key Laboratory of Translational Cardiovascular Medicine, Department of Cardiology, Qilu Hospital of Shandong University, Jinan, Shandong, China.
Department of General Practice, Qilu Hospital of Shandong University, Jinan, China.
J Cachexia Sarcopenia Muscle. 2020 Aug;11(4):1104-1120. doi: 10.1002/jcsm.12560. Epub 2020 Feb 25.
Sarcopenia causes several adverse events in elderly people. Muscle fibre atrophy and interstitial fibrosis are the main histopathological changes in sarcopenia and account for decreased muscle function. Tribbles homologue 3 (TRB3) was previously reported to exhibit age-related expression and play a vital role in cell proliferation, differentiation, and fibrosis. We aimed to investigate how TRB3 affects sarcopenia.
Wild-type and TRB3 knockout C57/BL6J mice were randomly divided into young and old groups. Exercise capacity was evaluated, and single-muscle function was detected by electrophysiological techniques, after which the mice were sacrificed to collect their gastrocnemius muscles for assessment of atrophy and fibrosis by histopathological and molecular biological methods. TRB3 expression, autophagy level, and MAPK signalling pathway activity were evaluated through western blotting. The interaction of TRB3 with P62 and the association between TRB3 and the MAPK signalling pathway were detected by co-immunoprecipitation.
In aged mice, exercise capacity and cross-sectional area of skeletal muscle fibres were decreased significantly, whereas TRB3, atrophy-related markers atrogin 1 and MuRF 1, and interstitial fibrosis, including collagen volume fraction, contents of collagens I and III, and ratio of collagens I to III, were increased significantly (P < 0.05 for all). Following TRB3 knockout, the cross-sectional area of muscle fibres, mainly fast fibres, was elevated (P < 0.05 for both), the atrogin 1 expression was decreased (P = 0.0163), and the corresponding tetanic force of fast muscles was increased (P = 0.0398). Conversely, interstitial fibrosis was substantially decreased and exercise capacity was significantly increased in the knockout mice. In terms of the underlying mechanisms, the autophagy receptor p62 was markedly increased and the MAPK signalling pathway was activated in aged skeletal muscles, which might be attributed to the interaction of TRB3 with p62 and MAPKKs, including MEK1/MEK2, MEK3/MEK6, and MEK4/MKK4. Notably, TRB3 knockout reduced the accumulation of p62 and LC3 (P < 0.05 for both), decreased the phosphorylation of JNK (P = 0.0015), and increased p38 phosphorylation (P = 0.0021).
TRB3 knockout in mice attenuated muscle fibre atrophy and reduced skeletal muscle fibrosis by increasing autophagy and inhibiting the MAPK signalling pathway. Correspondingly, in aged knockout mice, exercise capacity was improved. Interfering with TRB3 expression in aged skeletal muscles may serve as a target for the prevention and treatment of age-related sarcopenia.
肌肉减少症会导致老年人发生多种不良事件。肌肉纤维萎缩和间质纤维化是肌肉减少症的主要组织病理学变化，导致肌肉功能下降。此前有报道称，TRB3（Tribbles 同源物 3）具有与年龄相关的表达，并在细胞增殖、分化和纤维化中发挥重要作用。本研究旨在探讨 TRB3 如何影响肌肉减少症。
将野生型和 TRB3 敲除 C57/BL6J 小鼠随机分为年轻组和老年组。通过电生理技术检测运动能力，检测单肌功能，然后处死小鼠，收集比目鱼肌，通过组织病理学和分子生物学方法评估萎缩和纤维化。通过 Western blot 评估 TRB3 表达、自噬水平和 MAPK 信号通路活性。通过免疫共沉淀检测 TRB3 与 P62 的相互作用以及 TRB3 与 MAPK 信号通路的关联。
在老年小鼠中，运动能力和骨骼肌纤维横截面积显著下降，而 TRB3、萎缩相关标志物 Atrogin-1 和 MuRF1 以及间质纤维化，包括胶原容积分数、I 型和 III 型胶原含量以及 I 型和 III 型胶原比值，均显著增加（均 P < 0.05）。TRB3 敲除后，肌肉纤维横截面积（主要为快肌纤维）增加（均 P < 0.05），Atrogin-1 表达减少（P = 0.0163），快肌的相应强直力增加（P = 0.0398）。相反，间质纤维化显著减少，运动能力明显提高。在潜在机制方面，衰老骨骼肌中自噬受体 p62 明显增加，MAPK 信号通路被激活，这可能归因于 TRB3 与 p62 和 MAPKKs（包括 MEK1/MEK2、MEK3/MEK6 和 MEK4/MKK4）的相互作用。值得注意的是，TRB3 敲除减少了 p62 和 LC3 的积累（均 P < 0.05），降低了 JNK 的磷酸化（P = 0.0015），并增加了 p38 的磷酸化（P = 0.0021）。
在小鼠中敲除 TRB3 通过增加自噬和抑制 MAPK 信号通路减轻肌肉纤维萎缩和减少骨骼肌纤维化。相应地，在老年敲除小鼠中，运动能力得到改善。干扰衰老骨骼肌中的 TRB3 表达可能成为预防和治疗与年龄相关的肌肉减少症的靶点。
