School of Human Sciences, University of Western Australia, Perth, Western Australia, Australia.
School of Molecular Sciences, University of Western Australia, Perth, Western Australia, Australia.
J Physiol. 2023 Dec;601(23):5257-5275. doi: 10.1113/JP285263. Epub 2023 Oct 21.
Duchenne muscular dystrophy (DMD) is a fatal X-linked disease characterised by severe muscle wasting. The mechanisms underlying the DMD pathology likely involve the interaction between inflammation, oxidative stress and impaired Ca signalling. Hypochlorous acid (HOCl) is a highly reactive oxidant produced endogenously via myeloperoxidase; an enzyme secreted by neutrophils that is significantly elevated in dystrophic muscle. Oxidation of Ca -handling proteins by HOCl may impair Ca signalling. This study aimed to determine the effects of HOCl on skeletal muscle function and its potential contribution to the dystrophic pathology. Extensor digitorum longus (EDL), soleus and interosseous muscles were surgically isolated from anaesthetised C57 (wild-type) and mdx (dystrophic) mice for measurement of ex vivo force production and intracellular Ca concentration. In whole EDL muscle, HOCl (200 μM) significantly decreased maximal force and increased resting muscle tension which was only partially reversible by dithiothreitol. The effects of HOCl (200 μM) on maximal force in slow-twitch soleus were lower than found in the fast-twitch EDL muscle. In single interosseous myofibres, HOCl (10 μM) significantly increased resting intracellular Ca concentration and decreased Ca transient amplitude. These effects of HOCl were reduced by the application of tetracaine, Gd or streptomycin, implicating involvement of ryanodine receptors and transient receptor potential channels. These results demonstrate the potent effects of HOCl on skeletal muscle function potentially mediated by HOCl-induced oxidation to Ca signalling proteins. Hence, HOCl may provide a link between chronic inflammation, oxidative stress and impaired Ca handling that is characteristic of DMD and presents a potential therapeutic target for DMD. KEY POINTS: Duchenne muscular dystrophy is a fatal genetic disease with pathological mechanisms which involve the complex interaction of chronic inflammation, increased reactive oxygen species production and increased cytosolic Ca concentrations. Hypochlorous acid can be endogenously produced by neutrophils via the enzyme myeloperoxidase. Both neutrophil and myeloperoxidase activity are increased in dystrophic mice. This study found that hypochlorous acid decreased muscle force production and increased cytosolic Ca concentrations in isolated muscles from wild-type and dystrophic mice at relatively low concentrations of hypochlorous acid. These results indicate that hypochlorous acid may be key in the Duchenne muscular dystrophy disease pathology and may provide a unifying link between the chronic inflammation, increased reactive oxygen species production and increased cytosolic Ca concentrations observed in Duchenne muscular dystrophy. Hypochlorous acid production may be a potential target for therapeutic treatments of Duchenne muscular dystrophy.
杜氏肌营养不良症（DMD）是一种致命的 X 连锁疾病，其特征是严重的肌肉萎缩。DMD 病理学的机制可能涉及炎症、氧化应激和钙信号受损之间的相互作用。次氯酸（HOCl）是一种内源性产生的高反应性氧化剂，通过髓过氧化物酶产生；髓过氧化物酶是一种由中性粒细胞分泌的酶，在营养不良的肌肉中显著升高。HOCl 对钙处理蛋白的氧化可能会损害钙信号。本研究旨在确定 HOCl 对骨骼肌功能的影响及其对营养不良病理的潜在贡献。在麻醉的 C57（野生型）和 mdx（营养不良型）小鼠中，通过手术分离伸趾长肌（EDL）、比目鱼肌和骨间肌，用于测量离体力产生和细胞内 Ca 浓度。在整个 EDL 肌肉中，HOCl（200 μM）显著降低了最大力，并增加了静息肌肉张力，而二硫苏糖醇只能部分逆转这种作用。HOCl（200 μM）对慢肌比目鱼肌最大力的作用低于对快肌 EDL 肌肉的作用。在单个骨间肌纤维中，HOCl（10 μM）显著增加了静息细胞内 Ca 浓度并降低了 Ca 瞬变幅度。HOCl 的这些作用通过应用三甲卡因、Gd 或链霉素而降低，表明涉及ryanodine 受体和瞬时受体电位通道。这些结果表明，HOCl 对骨骼肌功能具有强大的作用，可能是由 HOCl 诱导的钙信号蛋白氧化介导的。因此，HOCl 可能在 DMD 中提供了一个慢性炎症、氧化应激和钙处理受损之间的联系，并为 DMD 提供了一个潜在的治疗靶点。关键点：杜氏肌营养不良症是一种致命的遗传性疾病，其病理机制涉及慢性炎症、活性氧物质产生增加和细胞内 Ca 浓度增加等复杂的相互作用。次氯酸可以通过中性粒细胞中的酶髓过氧化物酶内源性产生。中性粒细胞和髓过氧化物酶的活性在营养不良的小鼠中均增加。本研究发现，在相对较低浓度的次氯酸作用下，次氯酸降低了野生型和营养不良型小鼠离体肌肉的肌肉力产生并增加了细胞内 Ca 浓度。这些结果表明，次氯酸可能是杜氏肌营养不良症疾病病理学的关键因素，并可能为杜氏肌营养不良症中观察到的慢性炎症、活性氧物质产生增加和细胞内 Ca 浓度增加之间提供一个统一的联系。次氯酸的产生可能是杜氏肌营养不良症治疗的一个潜在靶点。
