Mechanisms underlying Paxillin-mediated amelioration of muscle degeneration

描述(申请人提供)：肌肉疾病和营养不良会导致儿童的衰弱疾病，并与几乎所有受影响的患者的过早死亡有关。许多肌肉疾病，如Duchenne、Becker和Merosin缺乏性肌营养不良，是由将肌肉细胞固定在周围基底膜(BM)上的黏附复合体突变引起的。尽管在确定许多肌病的遗传基础方面取得了很大进展，但调节骨髓组装和黏附的机制还不是很清楚。特别是，需要小分子疗法和发现药物开发的新靶点。我们已经证明NAD+的生物合成是肌肉发育所必需的，并且足以纠正斑马鱼营养不良的表型。烟酰胺核苷激酶2b(Nrk2b)介导的NAD+生物合成通过增加BM组织化和促进细胞内整合素结合蛋白paxlin的亚细胞定位来改善肌肉退化。巴西林是调节细胞黏附、形态和迁移的重要信号网络。初步数据表明，过表达paxlin显著改善了营养不良斑马鱼的肌肉结构，减少了退化，但其机制尚不清楚。这项研究的基本原理是，由于肌肉纤维与其周围的BM之间细胞黏附的机械故障是许多肌病的病因，Nrk2b通路可能对多发性先天性肌营养不良(CMD)具有治疗作用。本应用的目的是阐明在该途径中的帕西林功能的分子基础。我们的中心假设是，Nrk2b介导的NAD+生物合成调节巴西林的亚细胞定位，导致下游信号事件增加BM微环境的组织和结构。预计这项拟议研究的贡献将是阐明营养不良斑马鱼恢复肌肉结构/功能的新途径背后的分子机制。这一贡献意义重大，因为这是根除肌病努力的一个新范例。这种方法是创新的，因为它代表了思维的转变。而不是集中在“规范的”肌肉黏附蛋白，重点是黏附蛋白的代偿反应，传统上在肌肉中的研究不足。因此，这种独特的方法侧重于通过加强现有的机械来改善肌肉结构。这项工作的长期目标是利用阐明一种改善营养不良的新途径来确定治疗肌肉退行性疾病的新药物靶点。

DESCRIPTION (provided by applicant): Muscle myopathies and dystrophies cause debilitating disease in children and are associated with premature death in nearly all patients affected. Many muscle disorders, such as Duchenne, Becker, and Merosin-deficient muscular dystrophies, are caused by mutations in adhesion complexes that anchor muscle cells to their surrounding basement membrane (BM). Despite great strides in identifying the genetic basis of many myopathies, mechanisms that mediate BM assembly and adhesion are not well understood. In particular, there is a need for small molecule therapeutics and discovery of new targets for drug development. We have shown that NAD+ biosynthesis is necessary for muscle development and sufficient to correct dystrophic phenotypes in zebrafish. Nicotinamide Riboside Kinase 2b (Nrk2b)-mediated NAD+ biosynthesis ameliorates muscle degeneration by increasing BM organization and promoting the subcellular localization of an intracellular Integrin-binding protein, Paxillin. Paxillin is an essential signaling nexus that regulates cell adhesion, morphology, and migration. Preliminary data indicate that Paxillin overexpression dramatically improves muscle structure and decreases degeneration in dystrophic zebrafish, but the mechanisms are not known. The rationale of the proposed research is that because mechanical failure in cell adhesion between muscle fibers and their surrounding BM underlies the etiology of many myopathies, the Nrk2b pathway may have therapeutic utility for multiple congenital muscular dystrophies (CMDs). The objectives of this application are to elucidate the molecular underpinnings of Paxillin function in this pathway. Our central hypothesis is that Nrk2b-mediated NAD+ biosynthesis regulates subcellular localization of Paxillin; resulting in downstream signaling events that increase organization and structure of the BM microenvironment. The contribution of the proposed research is expected to be the elucidation of molecular mechanisms underlying a novel pathway that restores muscle structure/function in dystrophic zebrafish. This contribution is significant because this is a new paradigm in the effort to eradicate myopathies. The approach is innovative because it represents a shift in thinking. Instead of focusing on "canonical" muscle adhesion proteins, the focus is on the compensatory response of adhesion proteins that are traditionally understudied in muscle. Thus, this unique approach focuses on improving muscle structure by strengthening existing machinery. The long-term goal of this work is to capitalize on elucidation of a novel pathway that ameliorates dystrophy to identify new drug targets for the treatment of muscle degenerative disorders.