Dissection of the Mechanism of Insulin Resistance by Transgenic and knockout Mice Technology

2型糖尿病是由两种生理缺陷引起的：对胰岛素作用的抵抗和胰岛素分泌缺陷。用于创建2型糖尿病动物模型的转基因和基因敲除技术对新鉴定的参与体内葡萄糖稳态调节的分子的调节产生了重大影响。(i)IRS-1和IRS-2基因敲除小鼠胰岛素抵抗和糖尿病的发生为了理解2型糖尿病发展的分子基础，我们已经产生了IRS- 1和IRS-2敲除小鼠（Tamemoto H，et al. Nature 372：182-186，1994 ; Kubota，N.，例如，Diabetes，49：1880-1889，2000）。我们证明了这两种小鼠都表现出胰岛素抵抗。然而，虽然IRS-1敲除小鼠保持正常的葡萄糖耐量，其中β细胞能够增殖（Terauchi Y，et al. J Clin Invest 99：861-866，1997），IRS-2敲除小鼠发展糖尿病，其中β细胞不能增殖。有可能β细胞的能力， 关于我们 2型糖尿病的发病机制可能与胰岛素抵抗有关。我们还证明了缺乏PI 3-激酶85 kDa亚基的小鼠显示出增加的胰岛素敏感性（Terauchi，Y.et al.，Nature Genetics 21：230-235，1999）。(ii)肥胖引起的胰岛素抵抗的机制肥胖被定义为脂肪组织的过度积累。我们研究了肥胖诱导胰岛素抵抗的分子基础。首先，我们研究了噻唑烷二酮（thiazolidinedione），一种PPAR γ激动剂，改善胰岛素抵抗的分子机制。TZD对Zucker fa/fa大鼠的给药导致胰岛素抵抗的显著改善。脂肪组织的组织学检查显示较小脂肪细胞的数量显著增加，而较大脂肪细胞的数量减少（Okuno，A.，例如，J.Clin. Invest. 101：1354-1361，1998）。我们进一步产生了PPAR γ敲除小鼠（Kubota N，et al.，Mol Cell 4：597-609，1999），并证明杂合子在高脂肪饮食下被保护免于肥胖和胰岛素抗性。杂合子胰岛素抵抗的改善，至少部分地解释了血清瘦素浓度的增加。我们还证明，在人中，较低活性的PPARg多态性（密码子12处的丙氨酸）与较高活性的PPARg多态性（密码子12处的脯氨酸）相比，被保护免于胰岛素抗性和糖尿病的发展（Hara，K.，等人：Biochem.Biophys.Res. Commun. 271：212-216，2000减

Type 2 diabetes is caused by two physiological defects : resistance to insulin action and defects in insulin secretion. Transgenic and knockout technology used to create animal models of type 2 diabetes have had a major impact in the regulation of newly identified molecules implicated in the regulation of glucose homeostasis in vivo.(i) Development of insulin resistance and diabetes in IRS-1 and IRS-2 knockout mice. To understand the molecular basis of type 2 diabetes development, we have generated IRS- 1 and IRS-2 knockout mice (Tamemoto H, et al. Nature 372 : 182-186, 1994 ; Kubota, N., et al., Diabetes, 49 : 1880-1889, 2000). We demonstrated that both of these mice showed insulin resistance. However, while IRS-1 knockout mice remained normal glucose tolerance in which β cells are able to proliferate (Terauchi Y, et al., J Clin Invest 99 : 861-866, 1997), IRS-2 knockout mice developed diabetes in which β cells are not able to proliferate. It is possible that the ability of β cells to … More proliferate in response to insulin resistance may determine the process for human type 2 diabetes development. We also demonstrated that mice lacking PI3-kinase 85kDa subunit showed increased insulin sensitivity (Terauchi, Y.et al., Nature Genetics 21 : 230-235, 1999).(ii) Mechanisms of obesity-induced insulin resistanceObesity is defined as an excessive accumulation of adipose tissue. We investigated the molecular basis of obesityinduced insulin resistance. First, we studied the molecular mechanism of how thiazolidinedione, a PPAR γ agonist, improves insulin resistance. Administration of TZD into Zucker fa/fa rats resulted in a marked improvement of insulin resistance. Histological examination of adipose tissue revealed a marked increase in the number of smaller adipocytes with a decreased number of larger adipocytes (Okuno, A., et al., J.Clin. Invest. 101 : 1354-1361, 1998). We further generated PPAR γ knockout mice (Kubota N, et al., Mol Cell 4 : 597-609, 1999) and demonstrated that heterozygotes were protected from obesity and insulin resistance under a high-fat diet. Amelioration of insulin resistance in heterozygotes were explained, at least in part, by increased serum leptin concentration. We also demonstrated that, in human, the lower activity PPARg polymorphism, alanine at codn 12, are protected from the development of insulin resistance and diabetes compared the higher one, proline at codon 12 (Hara, K., et al : Biochem.Biophys.Res. Commun. 271 : 212-216, 2000 Less