Regulation of Exercise-induced Increase in GLUT4 Expression

已知在高脂饮食和db/db小鼠中，通过使肌肉组织中的GLUT 4的量加倍，可以完全预防糖尿病的发生。事实上，有规律的运动训练增加了骨骼肌中GLUT 4的含量，并防止了糖尿病的发展。因此，我们正在研究运动介导的糖尿病预防与GLUT 4调节相关的分子机制。先前的研究表明，小鼠GLUT 4基因的脂肪组织特异性元件（ASE）位于5 '侧翼序列的-551和-506之间，并且用于下调GLUT 4基因的高脂反应元件（HFRE）位于碱基-701和-552。核因子1（NF 1）的结合位点位于碱基-700和-688之间，NF 1介导3 T3-L1脂肪细胞中胰岛素和cAMP诱导的GLUT 4抑制。为了研究NF 1在体内调节白色脂肪组织（WAT）中GLUT 4基因表达中的作用，我们建立了两种类型的转基因小鼠，其在GLUT 4小基因构建体中具有突变的NF 1结合位点的5'或3'半位点。在这两种情况下，GLUT 4小基因在WAT中不表达，而在棕色脂肪组织、骨骼肌和心脏中保持表达。这是一个出乎意料的发现，因为在WAT中表达了不具有NF 1结合位点的-551 GLUT 4小基因。我们提出了一个模型，解释了在WAT中表达GLUT 4需要ASE和NF 1结合位点。此外，我们建立了在GLUT 4小基因构建体中携带MEF 2结合位点的转基因小鼠。在这些转基因小鼠中，GLUT 4小基因在心脏中不表达，而在棕色脂肪组织、骨骼肌和WAT中表达较低但维持。MEF 2结合位点是心脏GLUT 4表达所必需的。

It is known that the occurrence of diabetes mellitus can be completely prevented in high-fat diet and db/db mice by doubling the amount of GLUT4 in muscle tissues. Indeed, regular exercise training increased GLUT4 amount in skeletal muscles and prevented development of diabetes mellitus. We are therefore studying molecular mechanisms for exercise-mediated prevention of diabetes mellitus in relation to GLUT4 regulation.Previous studies demonstrated that an adipose tissue specific element(s) (ASE) of the murine GLUT4 gene is located between -551 and -506 in the 5'-flanking sequence and that a high-fat responsive element(s) (HFRE) for down-regulation of the GLUT4 gene is located between bases -701 and -552. A binding site for nuclear factor 1 (NF1), that mediates insulin and cAMP-induced repression of GLUT4 in 3T3-L1 adipocytes is located between bases -700 and -688. To examine the role of NF1 in the regulation of GLUT4 gene expression in white adipose tissues (WAT) in vivo, we created two types of transgenic mice harboring mutated either 5' or 3' half-site of NF1 binding sites in GLUT4 minigene constructs. In both cases, the GLUT4 minigene was not expressed in WAT, while expression was maintained in brown adipose tissue, skeletal muscle, and heart. This was an unexpected finding, since a -551 GLUT4 minigene that did not have the NF1 binding site, was expressed in WAT. We propose a model that explains the requirement for both the ASE and the NF1 binding site for expression of GLUT4 in WAT.In addition, we created of transgenic mice harboring MEF2 binding sites in GLUT4 minigene constructs. In these transgenic mice, the GLUT4 minigene was not expressed in heart, while expression was lower but maintained in brown adipose tissue, skeletal muscle, and WAT. MEF 2 binding site is necessary for GLUT4 expression in heart.