Glycogen Metabolism and Lafora Disease

描述(申请人提供)：这项研究的目标是了解Lafora肌阵挛癫痫(癫痫，进行性肌阵挛，2型，EPM2)的分子基础以及糖原代谢异常在疾病中的作用。Lafora病的一个一贯特征是在神经元、肌肉和其他组织中积聚含有异常分支的糖原样聚合物(聚葡聚糖)的Lafora小体。糖原是葡萄糖的一种分支储存聚合物，通常被认为是一种能量储备。约90%的拉福拉病病例可归因于编码拉福林的EPM2A基因或编码E3泛素连接酶马林的EPM2B/NHLRC1基因的突变。然后，目标部分归结为了解Laforin和Malin缺陷如何影响糖原代谢，并导致糖原结构异常和Lafora小体的形成。我们发现拉福林是一种糖原磷酸酶，而拉福林缺陷小鼠的糖原具有磷酸化程度增加的糖原，在老年小鼠中，这会导致糖原具有严重的异常性质。这一建议有四个目的：(1)更好地理解糖原磷酸化的化学及其引入糖原的机制(S)。这些知识对糖原代谢具有基本的重要性，也将为设计治疗这种疾病的方法提供信息，目前还没有任何治疗方法。(2)EPm2A和EPM2B突变导致患者和小鼠的表型基本相似。更好地了解拉福林和马林之间的遗传、物理和机制相互作用是很重要的。(3)一些研究表明，Laforin和Malin突变会导致自噬功能受损，这可能会影响溶酶体对异常糖原的处理。因此，重要的是探索自噬或相关过程在拉福拉病中的作用，特别是询问Malin是否是通过运输到溶酶体来处理糖原的积极调节因子。(4)Malin是一种E3泛素连接酶。已经提出了几种潜在的底物，但并不是所有的底物都被对Malin-/-小鼠的研究证实。因此，无偏倚的蛋白质组学分析将被应用于鉴定候选的Malin底物和相互作用的蛋白质，这将为Malin的作用机制提供重要的新信息。

DESCRIPTION (provided by applicant): The goal of this study is to understand the molecular basis for the myoclonic epilepsy of Lafora (epilepsy, progressive myoclonus, type 2, EPM2) and the role of abnormal glycogen metabolism in the disease. A consistent feature of Lafora disease is the accumulation, in neurons, muscle and other tissues, of Lafora bodies which contain an abnormally branched glycogen-like polymer (polyglucosan). Glycogen is a branched storage polymer of glucose that is thought normally to serve as an energy reserve. Some 90% of cases of Lafora disease can be attributed to mutations in the EPM2A gene which encodes laforin, a phosphatase, or the EPM2B/NHLRC1 gene which encodes malin, an E3 ubiquitin ligase. The objective then reduces in part to understanding how defects in laforin and malin affect glycogen metabolism and lead to abnormalities in glycogen structure and formation of Lafora bodies. We showed that laforin is a glycogen phosphatase and mice defective in laforin have glycogen with an increased degree of phosphorylation that, in older mice, leads to glycogen with grossly aberrant properties. This proposal has four aims: (1) Understanding better the chemistry of glycogen phosphorylation and the mechanism(s) for its introduction into glycogen. Such knowledge is of basic importance to glycogen metabolism and will also inform the design of therapies for the disease, of which none exist to date. (2) Epm2A and EPM2B mutations lead to generally similar phenotypes in patients and mice. It is important to understand better the genetic, physical and mechanistic interactions between laforin and malin. (3) Several studies suggest that laforin and malin mutations cause impaired autophagy which could impact the lysosomal disposal of abnormal glycogen. It is thus important to explore the role of autophagy or related processes in Lafora disease and specifically to ask whether malin is a positive regulator of glycogen disposal by trafficking to the lysosome. (4) Malin biochemically is an E3 ubiquitin ligase. Several potential substrates have been proposed but not all are confirmed by study of malin-/- mice. Therefore, unbiased proteomic analyses will be applied to identification of candidate malin substrates and interacting proteins, which could provide significant new information about the mechanism of malin action.