Centre for Muscle Research, Department of Anatomy and Physiology, The University of Melbourne, Melbourne, Victoria, Australia.
Am J Physiol Cell Physiol. 2021 Jun 1;320(6):C956-C965. doi: 10.1152/ajpcell.00513.2020. Epub 2021 Mar 17.
The dystrophin-glycoprotein complex (DGC) is a multiprotein structure required to maintain muscle fiber membrane integrity, transmit force by linking the actin cytoskeleton with the extracellular matrix, and maintain muscle homeostasis. Membrane localization of dystrophin is perturbed in muscles wasting as a consequence of cancer cachexia, tenotomy, and advanced aging, which are all associated with low level, chronic inflammation. Strategies to preserve dystrophin expression at the sarcolemma might therefore combat muscle wasting. Phosphorylation of dystrophin serine 3059 (S3059) enhances the interaction between dystrophin and β-dystroglycan. To test the contribution of amino acid phosphorylation to muscle fiber size changes, dystrophin constructs with phospho-null and phosphomimetic mutations were transfected into C2C12 muscle cells or AAV-293 cells in the presence or absence of kinase inhibitors/activators to assess effects on myotube diameter and protein function. Overexpression of a dystrophin construct with a phospho-null mutation at S3059 in vitro reduced myotube size in healthy C2C12 cells. Conversely overexpression of a phosphomimetic mutation at S3059 attenuated inflammation-induced myotube atrophy. Increased ERK activation by addition of phorbol myristate acetate (PMA) also reduced inflammation-associated myotube atrophy and increased the interaction between dystrophin and β-dystroglycan. These findings demonstrate a link between increased ERK activation, dystrophin S3059 phosphorylation, stabilization of the DGC, and the regulation of muscle fiber size. Interventions that increase dystrophin S3059 phosphorylation to promote stronger binding of dystrophin to β-dystroglycan may have therapeutic potential for attenuation of inflammation-associated muscle wasting.
肌营养不良蛋白聚糖复合物（DGC）是一种多蛋白结构，对于维持肌肉纤维膜的完整性、通过将肌动蛋白细胞骨架与细胞外基质连接来传递力以及维持肌肉内稳态至关重要。在癌症恶病质、肌腱切开术和衰老等导致的肌肉消耗中，肌营养不良蛋白的细胞膜定位受到干扰，这些情况都与低水平、慢性炎症有关。因此，保留肌膜上的肌营养不良蛋白表达的策略可能有助于对抗肌肉消耗。肌营养不良蛋白丝氨酸 3059 位的磷酸化（S3059）增强了肌营养不良蛋白与β-肌聚糖之间的相互作用。为了测试氨基酸磷酸化对肌纤维大小变化的贡献，将带有磷酸化缺失和磷酸化模拟突变的肌营养不良蛋白构建体转染到 C2C12 肌肉细胞或 AAV-293 细胞中，在存在或不存在激酶抑制剂/激活剂的情况下评估对肌管直径和蛋白功能的影响。体外过表达 S3059 位磷酸化缺失突变的肌营养不良蛋白构建体可减少健康 C2C12 细胞中的肌管大小。相反，过表达 S3059 位磷酸化模拟突变可减轻炎症诱导的肌管萎缩。添加佛波醇肉豆蔻酸酯（PMA）增加 ERK 激活也可减少与炎症相关的肌管萎缩并增加肌营养不良蛋白和β-肌聚糖之间的相互作用。这些发现表明 ERK 激活增加、肌营养不良蛋白 S3059 磷酸化、DGC 稳定以及肌纤维大小调节之间存在联系。增加肌营养不良蛋白 S3059 磷酸化以促进肌营养不良蛋白与β-肌聚糖更强结合的干预措施可能具有减轻与炎症相关的肌肉消耗的治疗潜力。
