Pathogenic Mechanisms in Limb Girdle Muscular Dystrophies

描述（由申请人提供）：肢带型肌营养不良症（LGMD）是累及骨盆和肩带肌肉的肌肉消耗性疾病。十三个基因定义的肢带型肌营养不良症突变已被确定与大多数突变的基因编码的结构蛋白。然而，两个LGMD突变不编码结构蛋白，而是具有酶活性。钙蛋白酶3（calpain 3，CAPN 3）和Trim 32均参与蛋白质降解途径。到目前为止，还不清楚这些降解酶的突变如何导致肌肉疾病。以前，我们表明，CAPN 3是肌肉重塑的重要，它的作用上游的泛素-蛋白酶体途径。这些先前的观察使我们将注意力转向LGMD 2 H，它涉及Trim 32的突变。三种等位基因常染色体隐性遗传疾病导致Trim 32突变，包括LGMD 2 H、肌管性肌病（SM）和Bardet Biedl（BB）综合征。LGMD 2 H被认为是比SM更温和的肌肉萎缩症形式。Bardet Biedl是一种复杂的遗传异质性疾病，涉及视网膜营养不良、肥胖、肾脏异常和多指（趾）畸形。目前尚不清楚为什么一个基因的不同突变会导致临床上如此多样的表型。为了更好地了解Trim 32的生物学功能，我们已经产生了独特的试剂，如抗体，重组蛋白和缺乏Trim 32的转基因小鼠。为了解决有关Trim 32的生物学功能以及为什么突变会导致疾病的问题，我们将执行以下目标：目标1：我们将表征缺乏Trim 32（T32 KO）的小鼠的表型，以更好地了解其生物学功能。目的2：我们将产生LGMD 2 H的动物模型（携带LGMD 2 H突变的敲入小鼠），并将该小鼠与Trim 32敲除小鼠进行比较。目的3：我们将探索Trim 32在肌肉中的生物学作用，并开始探索LGMD 2 H的致病机制。目的4：我们将鉴定Trim 32的底物，并确定LGMD 2 H突变体是否具有降低的泛素化这些底物的能力。

DESCRIPTION (provided by applicant): The limb girdle muscular dystrophies (LGMD) are muscle-wasting disorders involving muscles of the pelvis and shoulder girdle. Thirteen genetically defined limb girdle muscular dystrophy mutations have been identified with most of the mutated genes encoding structural proteins. However, two LGMD mutations do not encode for structural proteins rather, they possess enzymatic activity. These proteins named calpain 3 (CAPN3) and Trim32 both function in protein degradative pathways. Until now, it has been unclear how mutations in these degradative enzymes might lead to muscle disease. Previously we showed that CAPN3 is important for muscle remodeling and that it acts upstream of the ubiquitin-proteasome pathway. These prior observations have led us to turn our attention to LGMD2H, which involves a mutation in Trim32. Three allelic, autosomal recessive diseases result in mutations in Trim32 including LGMD2H, Sarcotubular myopathy (SM) and Bardet Biedl (BB) syndrome. LGMD2H is believed to be a milder form of muscular dystrophy than SM. Bardet Biedl is a complex and genetically heterogeneous disorder involving retinal dystrophy, obesity, kidney abnormalities and polydactyly. It is currently not understood why different mutations in one gene can result in such clinically diverse phenotypes. In an effort to better understand the biological function of Trim32, we have generated unique reagents such as antibodies, recombinant proteins and a genetically modified mouse lacking Trim32. To address questions about Trim32's biological function and why mutations result in disease, we will perform the following aims: Aim 1: We will characterize the phenotype of mice lacking Trim32 (T32KO) to better understand its biological function. Aim 2: We will generate an animal model for LGMD2H (knock in mouse carrying the LGMD2H mutation) and compare this mouse to the Trim32 knock out mouse. Aim 3: We will explore the biological role of Trim32 in muscle and begin to explore pathogenic mechanisms in LGMD2H. Aim 4: We will identify substrates of Trim32 and determine if the LGMD2H mutant has a reduced ability to ubiquitinate these substrates.