Glycogen Metabolism and Lafora Disease

描述（由申请方提供）：本研究的目的是了解Lafora肌阵挛性癫痫（癫痫，进行性肌阵挛，2型，EPM 2）的分子基础以及糖原代谢异常在疾病中的作用。Lafora病的一个一致特征是在神经元、肌肉和其他组织中积累含有异常分支的糖原样聚合物（聚葡聚糖）的Lafora体。糖原是葡萄糖的分支储存聚合物，通常被认为是作为能量储备。约90%的Lafora病病例可归因于编码laforin（一种磷酸酶）的EPM 2A基因或编码malin（一种E3泛素连接酶）的EPM 2B/NHLRC 1基因的突变。然后，目标部分地减少到了解laforin和malin的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laforin是一种糖原磷酸酶，laforin缺陷的小鼠具有磷酸化程度增加的糖原，在老年小鼠中，导致糖原具有严重异常的特性。该提案有四个目标：（1）更好地理解糖原磷酸化的化学性质及其引入糖原的机制。这些知识对糖原代谢具有基本的重要性，并且还将为疾病的治疗设计提供信息，迄今为止还不存在这种治疗。(2)Epm 2A和EPM 2B突变在患者和小鼠中导致通常相似的表型。更好地理解拉福林和马林之间的遗传、物理和机械相互作用是很重要的。(3)几项研究表明，laforin和malin突变导致自噬受损，这可能影响异常糖原的溶酶体处置。因此，重要的是要探讨自噬或相关过程在Lafora病中的作用，特别是要问malin是否是通过运输到溶酶体的糖原处置的正调节剂。(4)Malin在生物化学上是E3泛素连接酶。已经提出了几种潜在的底物，但并非所有的都通过malin-/-小鼠的研究得到证实。因此，无偏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，这可能会提供重要的新信息的malin的作用机制。

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.