ABNORMALITIES OF CARDIAC GLYCOGEN METABOLISM

描述（由申请人提供）：最近在实验室的研究使我们研究了糖原的溶酶体处理。我们的工作表明，糖原结合蛋白Stbd1可能参与介导糖原向溶酶体转移的自噬样机制，并且可能允许优先运输，从而去除积累异常结构的糖原，其特征是共价磷酸化增加和分支减少。某些心脏糖原，如在Pompe病、Danon病和Wolff-Parkinson-White综合征中观察到的，在心肌细胞内的囊泡室中有糖原的过度积累。目前的建议旨在了解Stbd1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，并测试对细胞进行干扰糖原结构的操作是否会影响糖原运输。Aim （ii）的目的是测试对囊泡糖原运输的遗传操作是否会影响两种已建立的小鼠心脏糖原模型的表型。第一种是Gaa-/-小鼠，它复制了庞贝病的大部分特征。在第二项研究中，在突变体Prkag2的心脏中进行转基因过表达，提供了一种啮齿类动物版本的沃尔夫-帕金森-怀特综合征。这两种小鼠系都与糖原在溶酶体或晚期内体囊泡中的大量心脏过度积累有关，这被认为对相应的人类疾病的病理很重要。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。第一种是条件敲除Stbd1基因；根据我们对Stbd1功能的推测，我们预计Stbd1的缺失将严重限制糖原向溶酶体的转运。第二种小鼠系是malin-/-小鼠，主要是作为另一种疾病拉福拉病的模型而产生的。malin在体内的功能仍在积极研究中，但其功能的一种假设是它促进溶酶体处理结构异常的糖原。因此，这两种小鼠模型都能抑制水疱糖原运输。通过将这些小鼠与Gaa-/-或Prkag2突变小鼠杂交，我们假设限制糖原运输到溶酶体可能减轻Pompe或WPW的症状。相反，人们会期望胞质糖原的积累，更类似于在麦卡德尔病中发现的情况，后者的表型要轻得多。简单地说，我们希望将一种糖原病转化为一种不那么严重的糖原病。然而，最重要的结果将是表明特异性靶向糖原运输的疗法是否可能是治疗庞培病或沃尔夫-帕金森-怀特综合征的有效方法。

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.