Genetic Control of Phospholipid Biosynthesis and Muscular Dystrophy

描述（由申请人提供）：肌肉萎缩症包括一组不同的遗传异质性疾病，影响全球1:2000的出生率。这些疾病的特点是进行性肌肉无力和消瘦，导致严重残疾，往往过早死亡。rostroaudal muscular dystrophy （rmd）是一种新的小鼠隐性突变，可导致从喙侧到尾侧严重程度梯度的进行性肌肉营养不良。我们已经确定rmd突变是胆碱激酶β (Chkb)基因中1.6 kb的缺失，导致Chkb蛋白和酶活性的丧失。CHKB是两种哺乳动物胆碱激酶（CHK）酶之一，在生物合成主要膜磷脂磷脂酰胆碱（PC）过程中催化胆碱磷酸化为磷酸胆碱。PC是真核细胞中最丰富的磷脂，它不仅是膜双层的结构基础，而且是几种脂质信使的前体。虽然突变型rmd小鼠在所有检查组织中显示CHK活性显著降低，但该疾病仅在骨骼肌组织中表现明显，显示总PC含量减少30%。在肌膜或核膜上起作用的膜相关蛋白中发现了几种肌营养不良突变。然而，rmd突变小鼠是第一个证明膜磷脂组成改变可导致进行性肌营养不良表型的小鼠。我们的建议的目的是：1)验证rmd肌营养不良是由于骨骼肌中CHKB细胞自主丧失的假设。2)验证线粒体功能障碍导致小鼠成肌细胞培养和成人骨骼肌进行性退化的假说。3)筛选巴西大量先天性肌营养不良症（CMD）和肢带性肌营养不良症（LGMD）患者的同源人类CHKB基因突变。在与Mayana Zatz博士的合作下，我们将在患者的DNA样本中检测人类CHKB突变，这些患者之前已经因已知的肌肉萎缩症分子原因而被筛选和消除。本研究的主要目标是利用新的小鼠rmd突变来探索骨骼肌中这种缺陷的细胞自主性质，剖析肌肉变性的分子和遗传机制，并确定CHKB缺陷的范围，这些缺陷是以前未发现的人类肌肉萎缩症的基础。rmd小鼠首次证明了导致肌肉萎缩症的磷脂生物合成酶缺陷，并可能揭示干预疾病过程的独特切入点。

DESCRIPTION (provided by applicant): Muscular dystrophies include a diverse group of genetically heterogeneous disorders that affect 1:2000 births worldwide. The diseases are characterized by progressive muscle weakness and wasting that lead to severe disability and often premature death. Rostrocaudal muscular dystrophy (rmd) is a new recessive mouse mutation causing a progressive muscular dystrophy with a rostral-to-caudal gradient of severity. We have identified the rmd mutation as a 1.6 kb deletion within the choline kinase beta (Chkb) gene, resulting in loss of CHKB protein and enzymatic activity. CHKB is one of two mammalian choline kinase (CHK) enzymes catalyzing the phosphorylation of choline to phosphocholine in the biosynthesis of the major membrane phospholipid phosphatidylcholine (PC). PC is the most abundant phospholipid in eukaryotic cells and it serves not only as a structural foundation for membrane bilayers, but also as a precursor for several lipid messengers. While mutant rmd mice show dramatically decreased CHK activity in all tissues examined, the disease is only evident in skeletal muscle tissues which display a 30% reduction in total PC content. Several muscular dystrophy mutations have been identified in membrane-associated proteins that function at the sarcolemma or nuclear envelope. However, the rmd mutant mouse is the first to demonstrate that alterations in membrane phospholipid composition can result in a progressive muscular dystrophy phenotype. The aims of our proposal are: 1) To test the hypothesis that rmd muscular dystrophy is due to a cell autonomous loss of CHKB in skeletal muscles. 2) To test the hypothesis that mitochondrial dysfunction underlies the progressive skeletal muscle degeneration in primary mouse myoblast cultures and adult skeletal muscles. 3) To screen a large Brazilian population of congenital muscular dystrophy (CMD) and limb-girdle muscular dystrophy (LGMD) patients for mutations in the orthologous human CHKB gene. In collaboration with Dr. Mayana Zatz, we will test for human CHKB mutations in DNA samples from patients that have previously been screened and eliminated for known molecular causes of muscular dystrophy. The primary goals of this proposal are to use the novel mouse rmd mutation to explore the cell-autonomous nature of this defect in skeletal muscles, to dissect the molecular and genetic mechanisms of muscular degeneration and to determine the range of defects in CHKB that underlie previously unidentified human muscular dystrophies. The rmd mouse offers the first demonstration of a defect in a phospholipid biosynthetic enzyme causing muscular dystrophy and may reveal unique entry points in which to intervene in the disease process.