A therapeutic approach to muscle wasting by limiting protein breakdown

描述（由申请人提供）：当蛋白质降解的总速率超过蛋白质合成时，废用、肌营养不良、糖皮质激素治疗（如库欣综合征）和许多全身性疾病（如癌症恶病质、糖尿病、禁食）都会发生肌肉萎缩。大多数类型的萎缩具有主要通过泛素（Ub）-蛋白酶体途径的细胞内蛋白质降解的普遍增加，并且共享一组共同的转录变化。目前，没有有效的药物治疗萎缩。对蛋白酶体抑制剂和Ub-蛋白酶体途径的转录调节的研究表明蛋白酶体是一个很好的靶点。然而，我最近对细胞培养的研究表明，溶酶体（自噬）过程也有助于蛋白质丢失。研究不同原因导致的肌肉萎缩的小鼠模型（去神经支配、糖皮质激素给药和mdx小鼠--一种肌肉萎缩症），我有三个目标。1)为了确定溶酶体和蛋白酶体途径在多大程度上有助于去神经支配和糖皮质激素诱导的萎缩，我将使用这些途径的特异性抑制剂，同时测量孵育肌肉的总体蛋白质降解率。2)为了了解Velcade，一种被批准用于癌症治疗的特异性蛋白酶体抑制剂，如何影响成年小鼠去神经萎缩期间的蛋白质分解，我将量化肌肉蛋白质组分，孵育肌肉的等长收缩能力，并通过使用已知转录因子或泛素连接酶的实时PCR和蛋白质印迹法确定激活这些途径的分子。（去神经萎缩预期通过FOXO转录因子或可能通过NF κ B激活。3)为了探索万珂给药对mdx小鼠的有效性，我将测试可以增加肌营养不良蛋白含量的万珂是否可以改善离体肌肉中的肌萎缩性肌肉收缩功能，以及突变型肌营养不良蛋白含量的增加是否是由于对这种短寿命蛋白的特定影响或对整体蛋白降解的影响（通过蛋白质印迹和特定蛋白降解测定）。总之，这些研究应该推进我们开发可行的肌肉萎缩疗法的长期目标。本案无关肌肉萎缩是肌肉废用、禁食和许多全身性疾病（如癌症、艾滋病或肌肉萎缩症）的常见并发症。由于这些肌肉萎缩有许多共同的特征，我们对减缓蛋白质分解的疗法和机制的研究可能会为这些人带来可行的治疗方法。

DESCRIPTION (provided by applicant): Muscle atrophy occurs with disuse, muscular dystrophy, glucocorticoid treatment (as in Cushing's syndrome), and with many systemic diseases (e.g. cancer cachexia, diabetes, fasting), when overall rates of protein degradation exceed protein synthesis. Most types of atrophy have a general increase in degradation of intracellular proteins mainly through the ubiquitin(Ub)-proteasome pathway and share a common set of transcriptional changes. Currently, no effective pharmaceutical treatments for atrophy are available. Work on proteasome inhibitors and the transcriptional regulation of the Ub- proteasome pathway has suggested that the proteasome is an excellent target. However, my recent studies with cell culture suggest that the lysosomal (autophagic) process also contributes to protein loss. Studying mouse models of muscle wasting with very different causes (denervation, glucocorticoid administration, and mdx mice - a muscular dystrophy), I have three aims. 1) To determine to what extent the lysosmal and proteasomal pathways contribute to denervation and glucocorticoid-induced atrophy, I will use specific inhibitors of these pathways while measuring overall protein degradation rates in incubated muscles. 2) To learn how Velcade, a specific proteasome inhibitor approved for cancer therapy, can influence protein breakdown during denervation atrophy in adult mice, I will quantify muscle protein fractions, isometric contractile ability in incubated muscle and determine the molecules that activate these pathways by using real-time PCR and Western blotting for known transcription factors or ubiquitin ligases. (Denervation atrophy would be expected to be activated via the FOXO transcription factors or possibly through NFkB.) 3) To explore the efficacy of Velcade administraction to mdx mice, I will test whether Velcade, which can increase dystrophin content, can improve dytrophic muscle contractile function in isolated muscles and whether the increased content of mutant dystrophin it due to specific effects on this short-lived protein or a result of effects on overall protein degradation (by Western blotting and specific protein degradation assays). Taken together, these studies should advance our long-term goal of developing viable therapies for muscle wasting. RELEVANCE. Muscle wasting is an often debilitating complication of muscle disuse, fasting and many systemic diseases such as cancer, AIDS, or muscular dystrophy. Since these muscle atrophies share many common features, our research on therapies and mechanisms of slowing protein breakdown may lead to a viable treatment for these individuals.