The role of plasma membrane type sialidase gene Neu3 on the pathogenesis of type 2 diabetes mellitusin Japanese.

神经节苷脂是一类含唾液酸的神经节苷脂家族，存在于细胞表面膜上。一些证据表明，它们在调节包括细胞生长、细胞分化和跨膜信号在内的广泛的生物过程中发挥着重要的功能作用。质膜相关唾液酸酶(Neu3)是神经节苷脂水解酶的关键酶，在细胞表面功能的调节中起着关键作用。我们证明了过度表达人类NEU3的小鼠会出现糖尿病表型，并伴有高胰岛素血症、胰岛增生和胰岛β细胞质量增加。与野生型相比，转基因肌肉中胰岛素刺激的胰岛素受体(IR)和胰岛素受体底物I的磷酸化水平显著降低，磷脂酰肌醇3-激酶和糖原合成酶的活性也较低。IR磷酸化Wa…更多的S在出现贫血之前已在较年轻的小鼠中减重。瞬时将NEU3基因导入3T3-L1脂肪细胞和L6心肌细胞后，IR信号明显减少。作为对胰岛素的反应，NEU3被发现经历了酪氨酸磷酸化，随后与Grb2蛋白结合，从而被激活，导致胰岛素信号的负调控。事实上，转基因组织中可能的唾液酸酶产物GM1和GM2的积累导致了体外IR磷酸化的抑制，并且阻断了与Grb2的关联导致了L6细胞中受损的胰岛素信号的逆转。这些数据表明，NEU3确实参与了胰岛素信号的调控，可能是通过调节神经节苷脂和与Grb2的相互作用，小鼠可以作为人类胰岛素抵抗糖尿病的有价值的模型。我们还研究了NEU3的单核苷酸多态(SNPs)在2型糖尿病发病中的可能作用。我们调查了298名日本2型糖尿病患者和两名对照日本人的NEU3基因SNPs，其中一人包括148名符合严格标准的非糖尿病患者，包括年龄超过60岁且没有糖尿病证据(HbA1c&lt；5.6%)，以及另外308名正常糖耐量(NGT)的人。我们发现了8个编码区有氨基酸替换的SNPs和5个没有氨基酸替换的SNPs。其中一个SNPs的等位基因频率在2型糖尿病患者中显著高于老年正常人和NGT患者，而其他SNPs的等位基因频率在这三组中基本相同。此外，在NGT受试者中，SNP与口服葡萄糖耐量试验中显著较低的胰岛素敏感指数相关。这些结果有力地表明，在日本，NEU32基因中的SNP通过减少胰岛素信号与2型糖尿病的发生有关。较少

Gangliosides are a family of sialic acid-containing glycosphingolipids present in the cell surface membranes. Several lines of evidence suggest their important functional roles in regulating a wide range of biological processes including cell growth, cell differentiation, and transmembrane signaling. Plasma membrane-associated sialidase (Neu3) is a key enzyme for ganglioside hydrolysis, thereby playing crucial roles in regulation of cell surface functions.We have investigated effects of overexpression in transgenic mice by using the human NEU3 cDNA. We demonstrated that mice overexpressing the human NEU3 develop diabetic phenotype associated with hyperinsulinemia, islet hyperplasia, and increased beta-cell mass. As compared with the wild type, insulin-stimulated phosphorylation of the insulin receptor (IR) and insulin receptor substrate I was significantly reduced, and activities of phosphatidylinositol 3-kinase and glycogen synthase were low in transgenic muscle. IR phosphorylation wa … More s already attenuated in the younger mice before manifestation of cemia. Transient transfection of NEU3 into 3T3-L1 adipocytes and L6 myocytes caused a significant decrease in IR signaling. In response to insulin, NEU3 was found to undergo tyrosine phosphorylation and subsequent association with the Grb2 protein, thus being activated and causing negative regulation of insulin signaling. In fact, accumulation of GM1 and GM2, the possible sialidase products in transgenic tissues, caused inhibition of IR phosphorylation in vitro, and blocking of association with Grb2 resulted in reversion of impaired insulin signaling in L6 cells. The data indicate that NEU3 indeed participates in the control of insulin signaling, probably via modulation of gangliosides and interaction with Grb2, and that the mice can serve as a valuable model for human insulin-resistant diabetes.We also investigate the possible contribution of single nucleotide polymorphisms (SNPs) in NEU3 to the development of type 2 diabetes. We surveyed SNPs in the NEU3 gene in 298 Japanese subjects with type 2 diabetes mellitus and two control Japanese populations : one consisting of 148 elderly subjects who met stringent criteria for being non-diabetic including age above 60 years and no evidence of diabetes (HbA1c<5.6%), and another 308 subjects with normal glucose tolerance (NGT). We identified eight SNPs with and five SNPs without amino acid substitutions in their coding regions. The allele frequency of one of SNPs was significantly higher in type 2 diabetic patients than in both elderly normal and NGT subjects, whereas the allele frequency of other SNPs was essentially identical in these three groups. Furthermore, in the NGT subjects, the SNP was associated with a significantly lower insulin sensitivity index on oral glucose tolerance test. These results strongly suggest that, in Japanese, the SNP in the NEU32 gene is associated with the development of type 2 diabetes, via reduced insulin signaling. Less