Development of anti-diabetic agents based on investigating the mechanism of the onset of type 2 diabetes due to protein glycosilation

在丝氨酸或苏氨酸残基上，有许多O-连接的N-乙酰氨基葡萄糖(O-GlcNAc)部分修饰的非核蛋白和细胞质蛋白。我们认为这种O-GlcNAc修饰(丹宁O-GlcN酰化)是一种调节性修饰，类似于磷酸化，即封顶潜在的磷酸化位点。O-GlcNAc转移酶(OGT)是一种负责蛋白质O-GlcN酰化的酶。己糖胺生物合成途径在胰岛素抵抗的诱导过程中起着重要作用。在这一途径中，谷氨酰胺：果糖-6-磷酸氨基转移酶(GFAT)在胰岛素抵抗的发生发展中起着不可或缺的作用。OGT酶利用胞质尿苷二磷酸-N-乙酰氨基葡萄糖(UDP-GlcNAc)，它是在氨基己糖生物合成途径中合成的。患有糖尿病和高血糖的动物表现出包括UDP-GlcNAc在内的氨基己糖代谢物浓度显著增加。这种氨基己糖生物合成的增加可以刺激OGT的活性，包括对参与葡萄糖运输系统或颗粒分泌的蛋白质进行O-GlcNAc修饰。因此，高血糖的影响可能是由于O-GlcN酰化异常所致。本研究以链脲佐菌素(STZ)诱导的糖尿病小鼠和3T3-L1细胞为模型，研究了钒、锌、锰等金属络合物对OGT活性的抑制作用和对O-GlcN酰化的影响。结果表明，钒麦芽糖酸相关络合物能够抑制STZ-小鼠器官中蛋白质的O-GlcN酰化。此外，锌化合物能刺激培养的3T3-L1细胞蛋白质去谷氨酰化，但不抑制OGT活性，提示锌化合物可增强O-GlcN酰化蛋白的降解酶O-GlcNAcase活性。

There are many nonle.ar and cytoplasmic proteins that are modified by a single O-linked N-acetylglucosamine (O-GlcNAc) moiety at serine or threonine residues. We proposed that this O-GlcNAc modification (tanned O-GlcNAcylation) is a regulatory modification, analogous to phosphorylation, that is, capping of the potential phosphorylation sites. O-GlcNAc transferase (OGT) is an enzyme responsible for O-GlcNAcylation of proteins. The hexosmine biosynthesis pathway plays an important part in the induction of insulin resistance. In this pathway, glutamine: fructose-6-phosphate amidotransferase (GFAT) has an integral role in the development of insulin resistance. The OGT enzyme uses cytoplasmic uridine diphospho-N-acetylglucosamine (UDP-GlcNAc), which is synthesized in the hexosamine biosynthetic pathway. Animals with diabetes and hyperglycaemia show greatly increased concentrations of hexosamine metabolites including UDP-GlcNAc. This increase in hexosamine biosynthesis could stimulate OGT activity, including O-GlcNAc modification of proteins that are involved in the glucose transport system or in granule secretion. Therefore, it is likely that the effects of hyperglycaemia result from abnormal O-GlcNAcylation. In this study, the effects of metal complexes such as vanadium, zinc, and manganese on the inhibition of OGT activity and on O-GlcNAcylation were investigated in the streptozotocin (STZ)-induced diabetic mice and 3T3-L1 cell lines. As a result, vanadyl-maltolate related complexes were exhibited to suppress the O-GlcNAcylation of proteins in organs of STZ-mice. In addition, zinc compounds were hind to stimulate the de-GlcNAcylation of proteins in the cultured 3T3-L1 cells, without inhibiting the OGT activity, indicating that zinc compounds may enhance the activity of O-GlcNAcase, an degradating enzyme of O-GlcNAcylated proteins.