Mechanisms of Skeletal Muscle Pathogenesis in Myotonic Dystrophy Type 1

项目概要 强直性肌营养不良是肌营养不良的第二常见原因，也是最常见的原因 成人发病的肌营养不良症。疾病死亡的主要原因是进行性骨骼肌 虚弱和消瘦。该项目的长期目标是确定导致骨骼损伤的机制 强直性肌营养不良 1 型 (DM1) 的肌肉发病机制。 DM1 是一种常染色体显性遗传病，由 DMPK 基因 3' 非翻译区的 CTG 重复扩增。该疾病的分子基础 是包含已转录的扩展 CUG 重复序列 (CUGexp RNA) 的 RNA 的毒性功能增益 来自突变等位基因。 CUGexp RNA 在核 RNA 灶中积累并导致功能丧失 肌盲样 (MBNL) RNA 结合蛋白被隔离在核灶内的 CUGexp RNA 上。 CUGexp RNA 还会诱导 CELF1 蛋白上调，该蛋白已被证明对骨骼有毒害作用 肌肉。 MBNL 和 CELF1 蛋白调节大量基因的选择性剪接转变 骨骼肌产后发育。它们在 DM1 骨骼肌中的功能改变导致失调 成人骨骼肌中胎儿蛋白亚型的选择性剪接和不适当表达导致 疾病特征。虽然MBNL功能丧失的基础已经建立，但导致MBNL功能丧失的机制 骨骼肌中 CELF1 的上调尚不清楚。我们发现成人中 Mbnl1/Mbnl2 双敲除 小鼠骨骼肌导致 CELF1 蛋白上调，表明 MBNL 之间存在机制联系 功能丧失和 CELF1 活性增加。我们还建立了 DM1 转基因小鼠模型 含有扩展 CUG 重复序列的人 DMPK mRNA 的骨骼肌特异性表达 再现 DM1 功能，包括 CELF1 上调。该提案的目标是确定 Mbnl1/Mbnl2 双敲除和表达导致 CELF1 上调的分子机制 有毒的 CUGexp RNA 并确定 CELF1 上调对骨骼肌的贡献 发病机制由MBNL功能丧失和CUGexp RNA引起。

Project Summary Myotonic dystrophy is the second most common cause of muscular dystrophy and the most common cause of adult onset muscular dystrophy. The primary cause of disease mortality is progressive skeletal muscle weakness and wasting. The long term goal of this project is to determine the mechanisms that cause skeletal muscle pathogenesis in myotonic dystrophy type 1 (DM1). DM1 is an autosomal dominant disease caused by a CTG repeat expansion in the 3’ untranslated region of the DMPK gene. The molecular basis for the disease is a toxic gain of function of the RNA containing expanded CUG repeats (CUGexp RNA) that is transcribed from the mutant allele. CUGexp RNA accumulates in nuclear RNA foci and causes loss of function of Muscleblind like (MBNL) RNA binding proteins that are sequestered on CUGexp RNA within the nuclear foci. CUGexp RNA also induces upregulation of CELF1 protein that has been shown to be toxic to skeletal muscle. MBNL and CELF1 proteins regulate alternative splicing transitions of a large number of genes during skeletal muscle postnatal development. Their altered functions in DM1 skeletal muscle causes misregulated alternative splicing and inappropriate expression of fetal protein isoforms in adult skeletal muscle that leads to disease features. While the basis for MBNL loss of function has been established, the mechanisms causing CELF1 upregulation in skeletal muscle are unknown. We find that Mbnl1/Mbnl2 double knockout in adult mouse skeletal muscle results in CELF1 protein upregulation, indicating a mechanistic link between MBNL loss of function and increased CELF1 activity. We also established a transgenic mouse model for DM1 in which skeletal muscle specific expression of a human DMPK mRNA containing expanded CUG repeats reproduces DM1 features including CELF1 upregulation. The goals of this proposal are to determine the molecular mechanisms of CELF1 upregulation in response to Mbnl1/Mbnl2 double knockout and expression of the toxic CUGexp RNA and to determine the contributions of CELF1 upregulation to skeletal muscle pathogenesis caused by MBNL loss of function and CUGexp RNA.