Glycogen metabolism and its regulation

描述（由申请人提供）：糖原是葡萄糖的支链储存聚合物，在许多细胞类型中作为能量储备。从绝对意义上讲，哺乳动物的肝脏和骨骼肌储存了最多的糖原，对全身葡萄糖代谢至关重要。本提案的总体目标是提高对糖原合成的机制和控制的理解，其与全身葡萄糖代谢的相关性以及其在代谢性疾病如糖尿病和某些糖原储存疾病中的损害。糖原合成酶是一个重要的调节位点，它是一种关键的糖原生物合成酶，受胰岛素和肾上腺素等几种激素以及运动的控制。目的(1)运动过程中糖原合成酶的控制。运动对糖原合成酶活性的影响复杂且尚不清楚。小鼠的穷尽性运动导致肌糖原合成酶的稳定失活，其机制无法通过磷酸化对酶的共价控制来解释。这一目标将试图确定这种潜在的新型控制机制的性质。目的（ii）糖原合成酶活性的新型潜在调节因子。在最近的资助期间，出现了两种新的糖原合成酶的潜在调节因子。首先，发现一种双特异性磷酸酶BEDP在培养细胞中共表达时激活糖原合成酶。将寻求这种激活的机制和负责的BEDP底物的身份。其次，一种蛋白激酶，PAS激酶，其酵母同源物使酵母糖原合成酶磷酸化，被发现也是一种有效的哺乳动物酶失活剂。目的是试图确定这种激酶在体内是否有作用。目的（iii）糖原在小鼠葡萄糖稳态模型中的作用。在葡萄糖耐量试验中，肌糖原合成酶基因（GYS1）被破坏的小鼠葡萄糖耐量改善，血清胰岛素升高比野生型小鼠更持久。这些动物的胰岛功能是否发生改变将是研究的重点之一。它还将通过其他小鼠模型，包括缺乏肝糖原的小鼠（也是0型糖原储存病的模型）或GYS1基因组织特异性消融的小鼠，解决肝脏和肌肉糖原储存对全身糖代谢的相对重要性。目标（三）糖原分支、劳力素和劳力素病。劳力素是一种含有糖原结合域的双特异性蛋白磷酸酶。编码劳力素的EPM2A基因的突变会导致劳力素病，这是一种癫痫的形式，其中缺乏分支的糖原沉积，劳力素体，积聚在神经元和其他组织中。目的是了解这种糖原相关磷酸酶的缺陷如何导致支链不良的糖原积累。目的（iv） udp -葡萄糖焦磷酸酶（UGPPase）。这种最近发现的酶能将糖原合成酶的底物udp -葡萄糖水解为葡萄糖-1- p和UMP。因此，它的作用可以深刻地影响糖原代谢。本目的目的是确定UGPPase是否影响体内udp -葡萄糖和糖原水平。

DESCRIPTION (provided by applicant): Glycogen is a branched storage polymer of glucose that serves as an energy reserve in many cell types. In absolute terms, liver and skeletal muscle house the largest glycogen deposits in mammals and are critical to whole body glucose metabolism. The overall goal of this proposal is to improve understanding of the mechanism and control of glycogen synthesis, its relevance to whole body glucose metabolism and its impairment in metabolic diseases like diabetes and certain glycogen storage diseases. An important site of regulation is glycogen synthase, a key glycogen biosynthetic enzyme, which is controlled by several hormones, including insulin and epinephrine as well as by exercise. Aim (i) Control of glycogen synthase during exercise. Exercise has complex and poorly understood effects on the activity of glycogen synthase. Exhaustive exercise of mice led to a stable inactivation of muscle glycogen synthase by a mechanism not explained by known covalent control of the enzyme by phosphorylation. This aim would attempt to determine the nature of this potentially novel control mechanism. Aim (ii) Novel potential regulators of glycogen synthase activity. During the last funding period, two novel potential regulators of glycogen synthase emerged. First, a dual specificity phosphatase, BEDP, was discovered that activates glycogen synthase when co-expressed in cultured cells. The mechanism for this activation and the identity of responsible BEDP substrate(s) will be sought. Second, a protein kinase, PAS kinase, whose yeast orthologs phosphorylate yeast glycogen synthase, was found to be also a potent inactivator of the mammalian enzyme. The aim will attempt to establish whether the kinase has a role in vivo. Aim (iii) Glycogen in mouse models of glucose homeostasis. Mice with the muscle glycogen synthase gene (GYS1) disrupted have improved glucose tolerance and elevated serum insulin is more sustained than in wild type mice during a glucose tolerance test. Whether there is altered islet function in these animals will be one focus of the aim. It will also address the relative importance of the liver and muscle glycogen stores for whole body glucose metabolism through other mouse models, including mice lacking liver glycogen (also a model for glycogen storage disease type 0) or with tissue-specific ablation of the GYS1 gene. Aim (iii) Glycogen branching, laforin and Lafora disease. Laforin is a dual specificity protein phosphatase that contains a glycogen binding domain. Mutations in the EPM2A gene, encoding laforin, cause Lafora disease, a form of epilepsy in which poorly branched glycogen deposits, Lafora bodies, accumulate in neurons and other tissues. The goal is to understand how defects in this glycogen associated phosphatase cause the accumulation of poorly branched glycogen. Aim (iv) UDP-glucose pyrophosphatase (UGPPase). This recently discovered enzyme hydrolyzes the substrate for glycogen synthase, UDP-glucose, to glucose-1-P and UMP. Its action could therefore profoundly affect glycogen metabolism. The goal of this aim is to establish whether UGPPase influences UDP-glucose and glycogen levels in vivo.