Pathophysiology and Treatment of Recessive RYR1 Related Myopathy

编码骨骼肌I型兰诺定受体(RYR1)的基因突变导致广泛的 这些肌肉疾病共同构成了非营养不良肌病最常见的原因。最多的 重症RYR1相关性肌病(RYR1-RM)表现为隐性遗传和遗传 婴儿期，伴有肌肉萎缩、虚弱、呼吸功能不全、身材矮小和 RyR1蛋白在肌肉中的表达。尽管其严重性、高患病率以及与显著的 在残疾和早期死亡率方面，目前还没有针对RYR1-RM的治疗或疾病修正疗法。一位少校 治疗发展的障碍是缺乏反映早期发病和临床的动物模型 隐性RYR1-Rm的严重程度。为了克服这一障碍，我们开发了两种隐性遗传的小鼠模型。 RyR1-Rm是人类疾病的主要特征，包括肌纤维减少 肌肉/身体质量、肌肉无力、RYR1表达显著减少，以及过早死亡。 这项提议的科学前提是，这些新的RYR1-RM小鼠模型提供了一种独特的 有机会探索RYR1-RM的潜在致病机制并测试其治疗效果 以机制为基础的干预。该项目的总体目标是阐明致病机制。 负责隐性RYR1-RM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RYR1同源异构体的折叠/稳定性降低会导致RYR1增加 蛋白质降解显著降低RYR1的表达，即使RYR1或RYR1的表达略有增加 表达或功能可改善肌病，延长生存期。此外，我们还假设 RYR1-RM中的肌纤维尺寸减小是疾病发病机制的一个关键方面，营养不良是由于 表观遗传学异常，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从三个具体目标进行严格评估。 目的1将表征RYR1在两种严重隐性遗传性小鼠模型中的表达、功能和肌病 并评估FDA批准的药物Ebselen全身治疗的潜力 和已知的RYR1激活剂。目的2将阐明我们的小鼠RYR1表达降低的机制(S) RYR1-RM小鼠模型的建立及全身化学治疗的疗效评价 伴侣和内质网应激抑制物(4PBA)。目标3将确定导致肌肉萎缩的机制 并测试HDAC抑制剂或肌纤维调节剂的治疗潜力 尺码。这些研究的结果将提供对致病机制的新见解。 隐性RYR1-RM的RYR1表达降低和肌纤维萎缩及其治疗 旨在增强RYR1功能、降低RYR1的几种基于机制的干预措施的潜力 隐性RYR1-RM临床前模型中的降解和限制肌肉萎缩。

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.