Elucidation of molecular mechanism of exocytosis in adipocytes

脂肪细胞通过胞吐作用释放脂联素，增加葡萄糖转运体-4 （GLUT4）分子的表面表达。我们开发了评估GLUT4在3T3脂肪细胞和心肌细胞中的易位的实验，发现氧化应激H_2O_2通过amp依赖性蛋白激酶（AMPK）途径诱导心肌细胞中GLUT4易位。小GTPase Ral已被证明在调节脂肪细胞中GLUT4易位中起重要作用。我们已经证明，在我们建立的颗粒分泌试验中，Ral通过其效应物，囊栓因子复合物，通过增强钙离子对胞吐的敏感性来调节颗粒分泌。然后，我们首次确定了Ral GAPs，即Ral的抑制调节因子。我们培育出了缺乏Ral GAPs的小鼠。我们正在研究他们的脂肪组织结构和血清葡萄糖水平对胰岛素的反应。另一方面，我们建立了一种利用逆转录病毒插入介导的随机突变来鉴定脂肪细胞分化因子的基因陷阱方法。通过这种方法，我们鉴定出了包括tg相互作用因子和脑啡肽在内的几个分子。低脂联素血症是动脉粥样硬化性疾病的危险因素。我们发现血清脂联素水平与慢性心力衰竭患者较高的死亡率相关。

By exocytosis, adipocytes release adiponectin and increase of surface expression of glucose transporter-4 (GLUT4) molecules. We have developed assays for evaluating GLUT4 translocation in 3T3 adipocytes and cardiac muscle cells and found that H_2O_2, an oxidative stress, induced GLUT4 translocation via AMP-dependent protein kinase (AMPK) pathway in cardiac muscle cells. The small GTPase Ral have been demonstrated to play an important role in the regulation of GLUT4 translocation in adipocytes. We have demonstarated that Ral regulates the granule secretion via its effector, the exocyst tethering factor complex, by enhancing the calcium-ion sensitivity of the exocytosis in our established granule secretion assay using permeabilized platelets. We then identified Ral GAPs, the inhibitory regulators for Ral, for the first time. We have generated mice lacking Ral GAPs. We are investigating their adipose tissue structures and their serum glucose levels in response to insulin. On the other hand, we have established a gene trap method for identification of adipocyte differentiation factors using retrovirus insertion-mediated random mutagenesis. With the method, we have identified several molecules including TG-interacting factor and enkepharin. Hypoadiponectinemia is a risk of atherosclerotic diseases. We have found that serum adiponectin levels are associated with higher motality in chronic heart failure patients.