Glycogen Metabolism and Lafora Disease

描述（由申请人提供）：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，EPM2）中分支不良的糖原积累的分子基础以及磷酸化在糖原正常代谢中的作用。拉福拉病的一个一贯特征是拉福拉体在神经元、肌肉和其他组织中积聚，其中含有异常支化的糖原样聚合物（聚葡萄糖）。糖原是葡萄糖的支链储存聚合物，通常被认为是一种能量储备。90%左右的拉福拉病是由编码拉福拉素的EPM2A基因和编码E3泛素连接酶malin的EPM2B基因突变引起的。目的在一定程度上是为了理解去甲素和malin的缺陷如何影响糖原代谢，并导致糖原结构和形成的异常。我们实验室最近的研究表明，劳力素是一种糖原磷酸酶，能够从多糖中释放磷酸盐。此外，我们发现去甲糖苷缺陷小鼠的糖原磷酸化程度增加，在老年小鼠中，导致糖原具有严重异常的特性。因此，这一建议的部分目的是为了更好地理解糖原磷酸化的化学作用及其从糖原中引入和去除的机制。在该疾病的小鼠模型中，异常糖原沉积的形成与与糖原相关的代谢酶水平的变化相关，我们计划调查这种观察与聚合物的缺陷积累在多大程度上相关。无论致病突变是在EPM2A还是EPM2B/NHLRC1基因，Lafora患者的临床症状大致相似。它们都具有拉弗拉体的特征。如果像我们认为的那样，去甲素的主要功能是从糖原中去除磷酸盐，那么分析EPM2B基因和malin的功能可以为理解去甲素体形成的机制提供另一种重要途径。近年来，人们越来越关注malin的潜在靶点的识别和对malin功能的了解，这将为了解Lafora体形成和Lafora病的机制提供新的视角。公共卫生相关性：糖原是糖的一种储存形式，作为能量储备在许多细胞中积累，其正常使用模式的破坏与许多疾病有关。神经细胞中糖原的异常使用会导致几种疾病，包括拉福拉病，这是一种罕见但致命的癫痫。本申请中提出的研究旨在了解拉福拉病中糖原储存的问题，这可能有助于为新的治疗方案提供线索。

DESCRIPTION (provided by applicant): The goal of this study is to understand the molecular basis for the accumulation of poorly branched glycogen in the myoclonic epilepsy of Lafora (epilepsy, progressive myoclonus, type 2, EPM2) and the role of phosphorylation in the normal metabolism of glycogen. 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 that places in the dual specificity protein phosphatase family based on sequence, or the EPM2B 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. Recent work from our laboratory has indicated that laforin is a glycogen phosphatase, able to release phosphate from the polysaccharide. Furthermore, we found that mice defective in laforin have glycogen with an increased degree of phosphorylation that, in older mice, leads to glycogen with grossly aberrant properties. Part of this proposal therefore is aimed at understanding better the chemistry of glycogen phosphorylation and the mechanism(s) for its introduction into and removal from glycogen. In the mouse model of the disease, the formation of the abnormal glycogen deposits correlates with changes in the level of metabolic enzymes that associate with glycogen and we plan to investigate to what degree this observation relates to the defective accumulation of the polymer. Lafora patients have generally similar clinical symptoms whether the causative mutation is in the EPM2A or EPM2B/NHLRC1 gene. All have the characteristic formation of Lafora bodies. If, as we believe, a primary function of laforin is to remove phosphate from glycogen, then analysis of the EPM2B gene and malin function can provide another important approach to understanding the mechanism of Lafora body formation. Much attention has been directed recently at identifying potential targets of malin and understanding malin function should provide new insight into the mechanism of Lafora body formation and Lafora disease. PUBLIC HEALTH RELEVANCE: Glycogen is a storage form of sugar accumulated as an energy reserve in many cells, and disruption of its normal pattern of usage is associated with a number of diseases. Abnormal glycogen use in nerve cells causes several illnesses, including Lafora disease which is a rare but deadly form of epilepsy. The research proposed in this application seeks to understand what is wrong with glycogen storage in Lafora disease, which could help provide clues to new treatment regimens.