Genetic Control of Phospholipid Biosynthesis and Muscular Dystrophy

描述(申请人提供)：这个项目的长期目标是确定细胞器膜脂生物合成和维持的失调如何导致先天性肌营养不良症(CMD)，我们如何成功地设计治疗这种疾病的策略，以及这种疾病机制如何影响其他类型的肌营养不良症。我们首先在轮尾型肌营养不良(RMD)突变小鼠中发现PC稳态对骨骼肌维持至关重要，后来在胆碱激酶β(CHKB)基因功能突变丧失的人类CMD患者中也发现PC稳态对骨骼肌维持至关重要。CHKB是肯尼迪途径中催化胆碱磷酸化为磷胆碱的两种哺乳动物酶之一。CHKB活性的丧失导致骨骼肌PC水平显著降低和进行性肌营养不良表型，并伴有核膜变形和明显增大的线粒体(巨线粒体)，呼吸功能降低。我们假设，膜PC含量的改变直接影响骨骼肌细胞器(核和线粒体)的功能特性，恢复膜PC水平的策略将在治疗上受益。在目标1中，我们将定义线粒体和核功能障碍的调控机制。我们建议a)确定PC缺乏是否破坏了内质网/线粒体接触点的线粒体分裂，b)使用高分辨率FPALM显微镜定义调控线粒体分裂/融合的机制，以测试线粒体膜曲率变化的实时动态，以及c)确定核膜变化是否在功能上与LMNA Emery-Dreifuss MD中看到的变化有关。在目标2中，我们将通过a)使用转基因方法确定CHK-α(CHKA)是否可以替代CHKB缺乏，b)测试线粒体裂变蛋白的过度表达或线粒体融合蛋白的敲除是否可以缓解巨线粒体疾病的表型，以及c)测试PC或中间代谢物是否可以用于治疗以恢复磷脂稳态，来测试治疗策略。 公共卫生相关性：细胞和细胞器膜形态和功能的改变已被证明是多种人类疾病的关键，包括肌肉、神经和代谢紊乱。我们在RMD小鼠和最近发现CHKB基因零突变的人类先天性肌营养不良症中发现了胆碱激酶β(Chkb)突变，这是磷脂合成改变可导致肌肉疾病中线粒体和核膜缺陷的第一个迹象。我们建议的线粒体光激活成肌细胞系的发展，以及我们使用高分辨率FPALM显微镜来研究膜的组成和结构以及肌肉疾病的影响，将是进一步了解膜磷脂在广泛的人类疾病中的作用的重要组成部分。

DESCRIPTION (provided by applicant): The long-term goals of this project are to determine how the dysregulation of organelle membrane lipid biosynthesis and maintenance leads to a congenital muscular dystrophy (CMD), how we can successfully design strategies to treat this disorder, and how this disease mechanism can inform upon other types of muscular dystrophy. We first identified PC homeostasis as critical for skeletal muscle maintenance in the rostrocaudal muscular dystrophy (rmd) mutant mouse, and later in human CMD patients with loss of function mutations in the choline kinase beta (CHKB) gene. CHKB is one of two mammalian enzymes catalyzing the phosphorylation of choline to phosphocholine in the Kennedy pathway. Loss of CHKB activity results in significantly reduced skeletal muscle PC levels and a progressive muscular dystrophy phenotype with nuclear membrane dysmorphology and distinctly enlarged mitochondria (megamitochondria) with reduced respiratory function. We hypothesize that alterations in membrane PC content directly affect the functional properties of skeletal muscle organelles (nuclei and mitochondria) and that a strategy to restore membrane PC levels will be therapeutically beneficial. In aim 1, we will define the mechanisms regulating mitochondrial and nuclear dysfunction. We propose to a) determine if PC deficiency disrupts mitochondrial fission at points of ER/mitochondrial contact, b) define mechanisms regulating mitochondrial fission/fusion using high-resolution FPALM microscopy to test the real-time dynamics of mitochondrial membrane curvature changes, and c) determine if nuclear membrane changes are functionally related to those seen in LMNA Emery-Dreifuss MD. In aim 2, we will test therapeutic strategies by a) determining if CHK-alpha (CHKA) can substitute for CHKB deficiency using a transgenic approach, b) testing if overexpression of mitochondrial fission proteins, or knockout of mitochondrial fusion proteins can alleviate the megamitochondrial disease phenotype, and c) testing if PC or an intermediate metabolite can be administered therapeutically to restore phospholipid homeostasis. PUBLIC HEALTH RELEVANCE: Alterations in cell and organelle membrane morphology and function have been shown to be key to a variety of human diseases, including muscular, neurological, and metabolic disorders. Our discovery of choline kinase beta (Chkb) mutations in the rmd mouse, and in a recently identified human congenital muscular dystrophy with null mutations in the CHKB gene, are the first indications that altered phospholipid synthesis can result in mitochondrial and nuclear membrane defects in muscle disease. The development of our proposed mitochondrial photoactivatable myoblast cell line, and our use of high-resolution FPALM microscopy to study the impact of membrane composition and architecture and muscular disease, will be a vital component for further understanding of the role of membrane phospholipids in a wide range of human illnesses.