脑内糖原存在于星形胶质细胞，被认为是脑的能量储存库，在无糖时提供能量。但人们对此一直存在疑问。根据糖原分解具有瞬间启动和敏感的特点，我们提出了糖原分解是星形胶质细胞信号传导重要能量来源的论点。在随后的实验中我们证实了这一点, 并发现ERK1/2参与糖原分解。近年来基于大量研究结果，星形胶质细胞在情感障碍中的作用逐渐得到关注。我们发现氟西汀在原代培养的星形胶质细胞引起多种基因表达的改变。继之，用荧光标记星形胶质细胞的转基因动物证实了脑内星形胶质细胞具有同样的改变。氟西汀所引起的与糖原相关的变化有：1)增强AKT的磷酸化可降低GSK3活性,进而增加糖原含量; 2)通过下调TRPC1和上调Cav1.2，影响细胞内Ca2+浓度，进而选择性改变细胞的糖原分解和信号传导。在本项目中，我们将确认ERK1/2在糖原磷酸化酶激酶的作用靶点，并系统性研究抑郁和氟西汀对糖原合成，分解和细胞信号传导的作用。

Glycogen in brain is located in astrocytes. It was thought as an energy substrate only functioning during glucose deficiency. Since the content of brain glycogen is very low, it is only enough to maintain brain energy metabolism for a few minutes. During the last 20 years, evidence has accumulated that a series of important astrocytic functions is critically dependent on glycogenolytic activity. Because glycogenolysis can be induced without initial phosphorylation and sensitive to many neurotransmitters and a small increase of extracellular K+, we suggests that glycogenolysis is essential for many signaling processes in astrocytes. Experiments with inhibitor of glycogenolysis have shown that it is the case for a number of transmitters, such as 5-HT, noradrenalin, ATP and glutamate. Interestingly, in astrocytes Ca2+ plays a critical role in of glycogenolysis and ERK1/2 is also involved in the process. Recently, we have found that fluoxetine, a SSRI used in clinic regulates gene expression in both cultured astrocytes and astrocytes isolated by FACS from brain in vivo. Two findings in astrocytes chronic treated with fluoxetine that are related to glycogenolysis are: 1) increase of AKT phosphorylation that in turn decreases GSK3 activity but increases glycogen synthesis; 2) downregulation of TRPC1 and upregulation of Cav1.2 that would selectively decrease IP3R-induced Ca2+ release but increase Ca2+ influx by high K+. In this project, we will study the target of ERK1/2 on glycogen phosphorylase kinase, the effects of depression and fluoxetine on glycogen synthesis, glycogenolysis and signal transduction using cultured astrocytes and depression animal model.

在本课题的研究过程中,我们共完成论文3篇，均为SCI收录，影响因子总和10.286。培养博士研究生6名,硕士研究生4名。我们的主要发现：1)氟西汀增加星形胶质细胞糖原合成的信号传导通路为0.5-1 microM抑制Calveolin-1 mRNA 和蛋白的表达，进而降低细胞膜PTEN的含量。而PTEN的降低增强AKT的活性，升高了GSK-3的磷酸化使其活性降低，导致GS活性升高。2）抑郁症小鼠脑内糖原含量降低，氟西汀处理增加糖原含量。3）此信号传导通路也适用于其它中枢神经系统疾病。如肝性脑病引起的高血氨降低星形胶质细胞糖元含量。信号传导通路为NH4Cl增加 Calveolin-1 mRNA 和蛋白的表达，进而增加细胞膜PTEN的含量。而PTEN的增加抑制AKT的活性，降低了GSK3的磷酸化使其活性升高，导致GS活性的降低。我们的发现为了解病理条件下星形胶质细胞糖原含量的变化提供了一个新的思路。