ABNORMALITIES OF CARDIAC GLYCOGEN METABOLISM

描述（由申请人提供）：最近的实验室研究使我们研究了糖原的溶酶体处置。我们的工作表明，糖原结合蛋白Stbd 1可能参与介导将糖原转移到溶酶体的自噬样机制，并且还可能允许优先运输，因此去除积累异常结构的糖原，其特征在于增加的共价磷酸化和减少的分支。某些心脏糖原累积症，如在庞贝氏症、达农氏症和沃尔夫-帕金森-白色综合征中观察到的，共同点是心肌细胞内囊泡隔室中糖原过度累积。目前的建议旨在了解Stbd 1如何参与这一过程。目的（i）将利用基于细胞的实验来检查糖原运输的机制，并测试是否操纵细胞干扰糖原结构影响糖原运输。目的（ii）是测试囊泡糖原运输的遗传操作是否会影响两种已建立的心脏糖原合成小鼠模型的表型。第一种是Gaa-/-小鼠，复制了庞贝氏症的大多数特征。在第二种情况下，突变体Prkag 2在心脏中的转基因过表达提供了Wolff-Parkinson-白色综合征的啮齿动物版本。两种小鼠系均与糖原在溶酶体或晚期胞内体囊泡中的大量心脏过度积累相关，这被认为对相应人类疾病的病理学很重要。我们正在研究另外两种可能影响细胞内糖原运输的遗传小鼠模型。第一种是有条件地敲除Stbd 1基因;根据我们对Stbd 1功能的提议，我们预计Stbd 1的缺失将严重限制糖原向溶酶体的转运。第二个小鼠系是malin-/-小鼠，主要作为另一种疾病Lafora病的模型产生。malin在体内的功能仍在积极的研究中，但其功能的一个假设是，它促进溶酶体处置结构异常的糖原。因此，这两种小鼠模型都可以抑制囊泡糖原运输。通过将这些小鼠与Gaa-/-或Prkag 2突变小鼠杂交，我们假设限制糖原运输到溶酶体可能会减轻庞贝氏症或WPW的症状。相反，人们会期望细胞溶质糖原的积聚，更类似于在McArdle病中发现的情况，其具有严重得多的表型。简单地说，我们希望将一种糖原增多症转变为不太严重的糖原增多症。然而，最重要的结果是表明特异性靶向糖原转运的疗法是否可能是治疗庞贝氏症或沃尔夫-帕金森-白色综合征的有效方法。 公共卫生相关性：糖原是糖的一种储存形式，通常在细胞中积累。然而，在某些疾病状态下，异常糖原积累并损害细胞功能。这项建议探讨是否操纵一个特殊的机制，糖原处置（溶酶体途径），可以减轻损害所造成的异常糖原在某些心脏疾病。

DESCRIPTION (provided by applicant): Recent research in the laboratory has led us to study the lysosomal disposal of glycogen. Our work has suggested that the glycogen-binding protein Stbd1 may participate in mediating an autophagy- like mechanism for the transfer of glycogen to lysosomes and furthermore may allow for the preferential trafficking, hence removal, of glycogen that accumulates abnormal structure, as characterized by increased covalent phosphorylation and decreased branching. Certain cardiac glycogenoses, as observed in Pompe disease, Danon disease, and Wolff-Parkinson-White syndrome, have in common the hyper-accumulation of glycogen in vesicular compartments within cardiomyocytes.. The current proposal is aimed at understanding how Stbd1 is involved in this process. Aim (i) will utilize cell-based experiments to examine the mechanism of glycogen trafficking and to test whether manipulations of cells to disturb glycogen structure influences glycogen trafficking. The goal of Aim (ii) is to test whether genetic manipulation of vesicular glycogen trafficking can affect the phenotypes of two established mouse models of cardiac glycogenoses. The first, the Gaa-/- mouse, duplicates most features of Pompe disease. In the second, transgenic over- expression in heart of mutant Prkag2, provides a rodent version of Wolff-Parkinson-White syndrome. Both mouse lines are associated with massive cardiac overaccumulation of glycogen, in lysosomes or late endosomic vesicles, which is believed to be important to the pathology of the corresponding human disease. We are working on two other genetic mouse models that could impact intracellular glycogen trafficking. The first is a conditional knockout of the Stbd1 gene; based on our proposal for the function of Stbd1, we would anticipate that the absence of Stbd1 would severely limit the transport of glycogen to the lysosome. The second mouse line is malin-/- mice, generated primarily as a model of another disorder, Lafora disease. The function of malin in vivo is still under active investigation but one hypothesis for its function is that it promotes lysosomal disposal of abnormally structured glycogen. Thus, both of these mouse models could suppress vesicular glycogen trafficking. By crossing these mice with either Gaa-/- or Prkag2 mutant mice, we hypothesize that limitation of glycogen trafficking to the lysosome may alleviate symptoms of Pompe or WPW. Instead, one would expect a build-up of cytosolic glycogen, more similar to what is found in McArdle disease, which has a much less severe phenotype. In crude terms, we would hope to convert one glycogenosis to a less serious one. The most important outcome though would be to indicate whether therapies that specifically target glycogen trafficking might be a fruitful approach for the treatment of Pompe disease or Wolff-Parkinson-White syndrome. PUBLIC HEALTH RELEVANCE: Glycogen is a storage form of sugar that normally accumulates in cells. However, in certain disease states abnormal glycogen accumulates and impairs cell function. This proposal examines whether manipulation of a particular mechanism for glycogen disposal (the lysosomal pathway) can alleviate the damage caused by abnormal glycogen in certain heart diseases.