A Model Multi-systems Approach for Understanding the Role of the PIX Pathway in Cardiac Muscle and Cardiomyopathy

理解 PIX 通路在心肌和心肌病中作用的模型多系统方法

• 批准号: 10340546
• 负责人: GUY Martin BENIAN
• 金额: $ 59.2万
• 依托单位: EMORY UNIVERSITY
• 依托单位国家: 美国
• 财政年份: 2022
• 资助国家: 美国
• 起止时间: 2022-01-01 至 2025-12-31
• 项目状态: 未结题
• 来源: https://reporter.nih.gov/project-details/10340546
• 关键词: Adhesions; Age-Months; Animals; Automobile Driving; Biological Models; Caenorhabditis elegans; Cardiomyopathies; Cell membrane; Cell-Matrix Junction; Cells; Complex; DH Domain; Defect; Dilated Cardiomyopathy; Drosophila genus; Dystrophin; Extracellular Matrix; Focal Adhesions; GTP Binding; GTPase-Activating Proteins; Genes; Genetic; Genetic Screening; Glycoproteins; Heart; Hereditary Disease; Human; Inherited; Integral Membrane Protein; Integrins; Knockout Mice; Learning; Location; Locomotion; Mammals; Mitochondria; Modeling; Molecular; Mus; Muscle; Muscle Cells; Muscle Contraction; Muscular dystrophy cardiomyopathy; Mutation; Myocardium; Myofibrils; Nature; Nematoda; Organism; Orthologous Gene; PAK-1 kinase; PIX protein; Pathway interactions; Phenotype; Phosphotransferases; Population; Prevalence; Protein Kinase; Proteins; Publishing; Reporting; Role; Sarcolemma; Sarcomeres; Skeletal Muscle; Striated Muscles; System; Testing; Ventricular; analog; cell type; congenital myopathy; fly; human disease; insight; knock-down; loss of function; member; mortality; muscular structure; mutant; overexpression; protein complex; scaffold

Myofibrils located at the periphery of the muscle cell are attached to the sarcolemma via costameres, muscle- specific integrin adhesion complexes (IACs), that transmit the force of muscle contraction to the outside of the cell. IACs consist of the transmembrane protein integrin and hundreds of proteins in a complex both in the ECM and especially intracellularly. Although much is known about the composition of IACs and mechanisms that initiate their assembly, we do not know how the composition of an IAC is determined, and what determines where an IAC will form. We exploit the conservation of muscle structure/function and the power of genetics in C. elegans. From a genetic screen, we identified a gene, pix-1, which is required for the formation of IACs at muscle cell boundaries (MCBs), but not the other IACs (M-lines and dense bodies). PIX-1 is the nematode ortholog of human b-PIX, which contains a RhoGEF domain known to be an activator of Rac1 and Cdc42. pix- 1 mutants show decreased whole animal locomotion. As compared to wild type, a pix-1 null mutant, shows 50% reduction in the level of activated (GTP bound) Rac in muscle. In addition to deficiency of PIX-1, overexpression of wild type PIX-1 protein results in decreased locomotion and disrupted MCBs. PIX-1 localizes to all 3 IACs in muscle—M-lines, dense bodies and MCBs. Loss of function mutants in each of the known PIX pathway proteins (PIX, Rac, GIT) result in disrupted MCBs. The protein kinase activity of PAK-1 is essential for its MCB function: a kinase-dead PAK-1 mutant has disrupted MCBs. Although PIX proteins are known to be important in several cell types in mammals and nematodes, our results are the first to demonstrate that a PIX protein is required for assembly of an IAC, and is required in striated muscle. A GAP protein (inactivates Rac) for this pathway has not been reported for any cell type or organism, but we now have two candidate GAPs. Remarkably, we found that heart specific knockout of the mouse ortholog b-PIX results in dilated cardiomyopathy at 8 months of age. Similarly, heart-specific knockdown of the Drosophila ortholog, dPix, also results in cardiomyopathy. We hypothesize that PIX proteins, through their RacGEF activity, direct assembly of IACs by activating PAK kinases to phosphorylate key substrate(s) in muscle. We will leverage the unique advantages of 3 model systems to learn new conserved functions of the PIX pathway in striated and cardiac muscle. Aim 1: Exploiting the power of studying muscle in C. elegans we will: (a) identify the GAP protein(s); (b) determine the localization, function and substrates of PAK kinases, and (c) test the hypothesis that PIX-1 is only required at MCBs because there are additional RacGEF proteins at the other IAC locations. Aim 2: We will determine how b-PIX functions in the mouse heart and how its absence leads to cardiomyopathy. Aim 3: We will take advantage of the power of genetic modifier screens in Drosophila to identify new members of the PIX pathway in muscle, and more specifically, cardiac muscle. There is a need to identify additional cardiomyopathy genes in humans and genes encoding members of the PIX pathway may be new candidates.

位于肌肉细胞外围的肌原纤维通过胞囊附着在肌膜上，肌肉-- 特殊的整合素黏附复合体(IAC)，将肌肉收缩的力量传递到肌肉的外部 手机。IACS由跨膜蛋白整合素和数百种蛋白质组成的复合体，两者都在 细胞外基质，尤其是细胞内。尽管关于IAC的组成和机制已知很多 我们不知道IAC的组成是如何决定的，以及是什么决定了 在那里将成立一个IAC。我们利用肌肉结构/功能的保守性和遗传学的力量 线虫。从基因筛查中，我们确定了一个基因pix-1，它是形成iac所必需的。 肌细胞边界(MCB)，而不是其他IAC(M线和致密小体)。PIX-1是线虫 人b-PIX的同源序列，它包含一个已知是rac1和cdc42激活剂的Rhogef结构域。PIX- 1个突变体表现出整体动物运动能力下降。与野生型相比，pix-1缺失突变体显示 肌肉中激活的(GTP结合的)RAC水平降低50%。除了PIX-1缺乏外， 野生型PIX-1蛋白的过度表达导致运动减少和MCBs中断。PIX-1本地化 肌间肌线、致密小体和单核细胞中的3个IAC。每个已知PIX中的功能突变体丢失 途径蛋白(PIX、RAC、GIT)导致MCBs的破坏。PAK-1的蛋白激酶活性是 其MCB功能：一个激酶死亡的PAK-1突变体扰乱了MCB。尽管已知PIX蛋白是 在哺乳动物和线虫的几种细胞类型中很重要，我们的结果首次证明了PIX 蛋白质是组装IAC所必需的，也是横纹肌所必需的。GAP蛋白(使RAC失活) 因为这条途径还没有关于任何细胞类型或生物体的报道，但我们现在有两个候选缺口。 值得注意的是，我们发现心脏特异的敲除小鼠的b-pix基因会导致扩张。 8个月龄的心肌病。同样，对果蝇直系同源基因dPix的心脏特异性敲除也 会导致心肌病。我们假设PIX蛋白，通过它们的racgef活性，直接组装 通过激活PAK激酶来磷酸化肌肉中的关键底物(S)，从而对IACs产生影响。我们将利用独一无二的 3种模型系统在学习新的纹状体和心脏PIX通路保守功能方面的优势 肌肉。目的1：利用线虫肌肉研究的力量，我们将：(A)鉴定GAP蛋白(S)； (B)确定PAK激酶的定位、功能和底物，以及(C)检验PIX-1是 仅在MCB中需要，因为在其他IAC位置还有额外的racgef蛋白。目标2：我们 将确定b-PIX在小鼠心脏中如何发挥作用，以及它的缺失如何导致心肌病。目标3： 我们将利用果蝇中遗传修饰物筛选的力量来识别 肌肉中的PIX途径，更具体地说，是在心肌中。有必要确定其他 人类的心肌病基因和编码PIX途径成员的基因可能是新的候选基因。