Pathophysiology and Treatment of Recessive RYR1 Related Myopathy

编码骨骼肌I型兰尼碱受体（RYR 1）的基因突变导致广泛的 肌肉疾病共同构成非营养不良性肌病的最常见原因。最 RYR 1相关肌病（RYR 1-RM）的严重病例表现出隐性遗传模式， 婴儿期肌肉萎缩，虚弱，呼吸功能不全，身材矮小， RYR 1蛋白在肌肉中的表达。尽管其严重性，高患病率和与显著 残疾和早期死亡，没有治疗或RYR 1-RM的疾病修饰疗法。一个主要 治疗发展的障碍是缺乏反映早期发病和临床症状的动物模型。 隐性RYR 1-RM的严重程度。为了克服这一障碍，我们开发了两种小鼠模型， RYR 1-RM是人类疾病的表型复制关键特征，包括肌纤维萎缩，减少 肌肉/身体质量、肌肉无力、RYR 1表达显著降低和过早死亡。 这项提议的科学前提是，这些新的RYR 1-RM小鼠模型提供了一个独特的 有机会探索RYR 1-RM的潜在病理机制，并测试RYR 1-RM的治疗效果。 基于机制的干预。该项目的总体目标是阐明病理机制 负责隐性RYR 1-RM中的肌肉功能障碍，并开发和验证有效的治疗方法。 我们假设突变的RYR 1同源四聚体的折叠/稳定性降低导致RYR 1 蛋白质降解显著降低RYR 1表达，即使RYR 1 表达或功能将改善肌病并延长存活。此外，我们还假设 RYR 1-RM中肌纤维尺寸的减小是疾病发病机制的一个关键方面， 表观遗传异常，靶向表观基因组或促进肌肉生长的药物可以改善 疾病表型。这些假设的有效性将严格评估在三个具体目标。 目的1将描述RYR 1在两种严重隐性遗传性肌病小鼠模型中的表达、功能和肌病。 RYR 1-RM，并评估FDA批准的药物依布硒啉全身治疗的治疗潜力 和已知的RYR 1激活剂。目的2将阐明我们的小鼠中RYR 1表达减少的机制 RYR 1-RM小鼠模型，并评估用化学品全身治疗的治疗功效 伴侣蛋白和ER应激抑制剂（4PBA）。目的3将确定导致肌肉萎缩的机制 并测试用HDAC抑制剂或肌纤维调节剂治疗的潜力 尺寸这些研究的结果将提供新的见解的病理机制负责 在隐性RYR 1-RM中减少RYR 1表达和肌纤维萎缩，并确定治疗 几种基于机制的干预措施的潜力，旨在增强RYR 1功能，减少RYR 1 降解，并限制隐性RYR 1-RM的临床前模型中的肌肉萎缩。

Mutations in the gene that encodes the skeletal muscle type I ryanodine receptor (RYR1) result in a wide range of muscle disorders that collectively comprise the most common cause of non-dystrophic myopathy. The most severe cases of RYR1-related myopathy (RYR1-RM) exhibit a recessive pattern of inheritance and present in infancy with muscle hypotrophy, weakness, respiratory insufficiency, short stature, and a marked reduction in RYR1 protein expression in muscle. Despite their severity, high prevalence and association with significant disability and early mortality, there are no treatments or disease-modifying therapies for RYR1-RM. A major barrier to therapy development has been the lack of an animal model that mirrors the early onset and clinical severity of recessive RYR1-RM. To overcome this barrier, we developed two mouse models of recessive RYR1-RM that pheno-copy key characteristics of the human disorder including myofiber hypotrophy, reduced muscle/body mass, muscle weakness, markedly reduced RYR1 expression, and premature death. The scientific premise of this proposal is that these new mouse models of RYR1-RM provide a unique opportunity to explore the underlying patho-mechanisms of RYR1-RM and test the therapeutic efficacy of mechanism-based interventions. The overall goal of the project is to elucidate the patho-mechanisms responsible for muscle dysfunction in recessive RYR1-RM and to develop and validate effective treatments. We hypothesize that reduced folding/stability of mutated RYR1 homotetramers results in increased RYR1 protein degradation that markedly reduces RYR1 expression, and that even a modest increase in either RYR1 expression or function will ameliorate the myopathy and prolong survival. Furthermore, we also hypothesize that reduced myofiber size in RYR1-RM is a key aspect of disease pathogenesis, that hypotrophy is due to epigenetic abnormalities, and that drugs that target the epigenome or promote muscle growth can ameliorate the disease phenotype. The validity of these hypotheses will rigorously evaluated in three specific aims. Aim 1 will characterize RYR1 expression, function and myopathy in two mouse models of severe, recessive RYR1-RM and assess the therapeutic potential of systemic treatment with ebselen, an FDA-approved drug and known RYR1 activator. Aim 2 will elucidate the mechanism(s) for reduced RYR1 expression in our mouse models of RYR1-RM mice and evaluate the therapeutic efficacy of systemic treatment with a chemical chaperone and ER stress inhibitor (4PBA). Aim 3 will determine the mechanisms leading to muscle hypotrophy in RYR1-RM mice and test the potential of treatment with either HDAC inhibitors or modulators of myofiber size. The results of these studies will provide novel insights into the patho-mechanisms responsible for reduced RYR1 expression and muscle fiber hypotrophy in recessive RYR1-RM and determine the therapeutic potential of several mechanism-based interventions designed to enhance RYR1 function, reduce RYR1 degradation, and limit muscle hypotrophy in pre-clinical models of recessive RYR1-RM.