Hauck J Spencer, Howard Zachary M, Lowe Jeovanna, Rastogi Neha, Pico Madison G, Swager Sarah A, Petrosino Jennifer M, Gomez-Sanchez Celso E, Gomez-Sanchez Elise P, Accornero Federica, Rafael-Fortney Jill A
Department of Physiology and Cell Biology, College of Medicine, The Ohio State University, Columbus, OH, United States.
Dorothy M. Davis Heart and Lung Research Institute, College of Medicine, The Ohio State University, Columbus, OH, United States.
Front Physiol. 2019 Oct 25;10:1324. doi: 10.3389/fphys.2019.01324. eCollection 2019.
Acute skeletal muscle injury is followed by a temporal response of immune cells, fibroblasts, and muscle progenitor cells within the muscle microenvironment to restore function. These same cell types are repeatedly activated in muscular dystrophy from chronic muscle injury, but eventually, the regenerative portion of the cycle is disrupted and fibrosis replaces degenerated muscle fibers. Mineralocorticoid receptor (MR) antagonist drugs have been demonstrated to increase skeletal muscle function, decrease fibrosis, and directly improve membrane integrity in muscular dystrophy mice, and therefore are being tested clinically. Conditional knockout of MR from muscle fibers in muscular dystrophy mice also improves skeletal muscle function and decreases fibrosis. The mechanism of efficacy likely results from blocking MR signaling by its endogenous agonist aldosterone, being produced at high local levels in regions of muscle damage by infiltrating myeloid cells. Since chronic and acute injuries share the same cellular processes to regenerate muscle, and MR antagonists are clinically used for a wide variety of conditions, it is crucial to define the role of MR signaling in normal muscle repair after injury. In this study, we performed acute injuries using barium chloride injections into muscles both in myofiber MR conditional knockout mice on a wild-type background (MRcko) and in MR antagonist-treated wild-type mice. Steps of the muscle regeneration response were analyzed at 1, 4, 7, or 14 days after injury. Presence of the aldosterone synthase enzyme was also assessed during the injury repair process. We show for the first time aldosterone synthase localization in infiltrating immune cells of normal skeletal muscle after acute injury. MRcko mice had an increased muscle area infiltrated by aldosterone synthase positive myeloid cells compared to control injured animals. Both MRcko and MR antagonist treatment stabilized damaged myofibers and increased collagen infiltration or compaction at 4 days post-injury. MR antagonist treatment also led to reduced myofiber size at 7 and 14 days post-injury. These data support that MR signaling contributes to the normal muscle repair process following acute injury. MR antagonist treatment delays muscle fiber growth, so temporary discontinuation of these drugs after a severe muscle injury could be considered.
急性骨骼肌损伤后，肌肉微环境中的免疫细胞、成纤维细胞和肌肉祖细胞会发生阶段性反应以恢复功能。在慢性肌肉损伤导致的肌肉营养不良中，这些相同的细胞类型会反复被激活，但最终，循环中的再生部分会被破坏，纤维化取代退化的肌纤维。盐皮质激素受体（MR）拮抗剂药物已被证明可增强骨骼肌功能、减少纤维化，并直接改善肌肉营养不良小鼠的膜完整性，因此正在进行临床试验。在肌肉营养不良小鼠中，从肌纤维中条件性敲除MR也可改善骨骼肌功能并减少纤维化。其疗效机制可能是通过阻断MR信号通路的内源性激动剂醛固酮来实现的，醛固酮由浸润的髓样细胞在肌肉损伤区域高水平产生。由于慢性和急性损伤在肌肉再生过程中具有相同的细胞过程，且MR拮抗剂在临床上被广泛用于多种病症，因此明确MR信号通路在损伤后正常肌肉修复中的作用至关重要。在本研究中，我们通过向野生型背景的肌纤维MR条件性敲除小鼠（MRcko）和接受MR拮抗剂治疗的野生型小鼠肌肉内注射氯化钡来造成急性损伤。在损伤后1、4、7或14天分析肌肉再生反应的步骤。在损伤修复过程中还评估了醛固酮合酶的存在情况。我们首次展示了急性损伤后醛固酮合酶在正常骨骼肌浸润免疫细胞中的定位。与对照损伤动物相比，MRcko小鼠中醛固酮合酶阳性髓样细胞浸润的肌肉面积增加。在损伤后4天，MRcko和MR拮抗剂治疗均使受损肌纤维稳定，并增加了胶原蛋白浸润或压实。MR拮抗剂治疗还导致损伤后7天和14天肌纤维尺寸减小。这些数据支持MR信号通路有助于急性损伤后的正常肌肉修复过程。MR拮抗剂治疗会延迟肌纤维生长，因此在严重肌肉损伤后可考虑暂时停用这些药物。
