The study for molecular mechanisms of obesity, insulin resistance and atherosclerosis in the PPAR gamma deficient mice

1. 针对杂合子PPARgamma缺陷小鼠在高脂肪饮食下可避免肥胖和胰岛素抵抗的发生，我们采用DNA芯片比较了高脂肪饮食下PPARgamma缺陷小鼠与野生型小鼠白色脂肪组织中基因表达的差异。脂联素和瘦素在PPARgamma缺陷小鼠中的表达高于野生型小鼠。这些数据提示脂联素可能是一种由脂肪组织分泌的胰岛素增敏激素。事实上，脂联素可以增加肌肉中的脂肪酸燃烧，从而改善肥胖小鼠的胰岛素抵抗。这些观察结果表明，补充脂联素可能为胰岛素抵抗和2型糖尿病提供一种新的治疗方式。PPARgamma是一种配体激活的转录因子，作为异源二聚体与类视黄醇X受体（RXR）一起发挥作用。我们鉴定了一种合成的RXR拮抗剂HX531…More，并研究了PPARgamma/RXR的功能性拮抗剂是否可用于治疗肥胖和2型糖尿病。RXR拮抗剂HX531通过增加瘦素作用，增加脂肪酸燃烧和能量耗散，降低白色脂肪组织、骨骼肌和肝脏中的TG含量，从而改善肥胖和胰岛素抵抗。我们的数据表明，适当的PPARgamma/RXR功能拮抗剂可能是预防肥胖和相关疾病（如2型糖尿病）的一种合乎逻辑的方法。在人PPARgamma2基因中检测到Pro12Ala多态性。由于这种氨基酸取代导致PPARgamma转录活性降低，这种多态性可能与胰岛素敏感性增加和2型糖尿病风险降低有关。为了验证这一假设，我们对日本糖尿病和非糖尿病受试者进行了Pro12Ala PPARgamma2多态性的病例对照研究。糖尿病组Ala12的表达频率明显低于对照组。在超重或肥胖组中，携带Ala12的受试者比不携带Ala12的受试者对胰岛素更敏感。这些结果表明PPARgamma2是一个节俭基因，而Pro12Ala PPARgamma2多态性在日本人群中对2型糖尿病具有保护作用。我们利用杂合子PPARγ缺失（PPARγ+/-）小鼠研究了PPARγ在动脉粥样硬化发展中的作用。当我们在股动脉周围放置一个袖带以诱导外膜炎症和随后的新内膜形成时，在袖带放置2周后，PPARgamma+/-小鼠的新内膜形成比野生型小鼠多2倍。此外，与野生型小鼠相比，内皮依赖性血管舒张在PPARγ+/-小鼠中明显受损，内皮型一氧化氮合酶（eNOS）的表达在PPARγ+/-小鼠中显著低于野生型小鼠。这些数据表明，PPAR在调节血管内皮功能和防止炎症诱导的新内膜形成中起着至关重要的作用。少

1. Focusing on the fact that heterozygous PPARgamma deficient mice were protected from the development of obesity and insulin resistance under a high-fat diet, we compared the differences of the gene expression in white adipose tissues between PPARgamma deficient mice and wild-type mice under a high-fat diet by using DNA chip. Adiponectin as well as leptin expression was higher in the PPARgamma deficient mice than in the wild-type mice. These data suggested that adiponectin may be an insulin-sensitizing hormone secreted by adipose tissue. In fact, administration of adiponectin increases fatty acid combustion in muscle, thereby ameliorating insulin resistance in obese mice. These observations indicate that the replenishment of adiponectin might provide a novel treatment modality for insulin resistance and type 2 diabetes.2. PPARgamma is a ligand-activated transcription factor and functions as a heterodimer with a retinoid X receptor (RXR). We identified a synthetic RXR antagonist, HX531 … More and investigated whether functional, antagonism toward PPARgamma/RXR could be used to treat obesity and type 2 diabetes. Administration of the RXR antagonist HX531 decreases TG content in white adipose tissue, skeletal muscle, and the liver due to increased leptin effects and increased fatty acid combustion and energy dissipation, thereby ameliorating obesity and insulin resistance. Our data suggest that appropriate functional antagonism of PPARgamma/RXR may be a logical approach to protect against obesity and related diseases such as type 2 diabetes.3. A Pro12Ala polymorphism has been detected in the human PPARgamma2 gene. Since this amino acid substitution causes a reduction in the transcriptional activity of PPARgamma, this polymorphism may be associated with increased insulin sensitivity and decreased risk of type 2 diabetes. To investigate this hypothesis, we performed a case-control study of the Pro12Ala PPARgamma2 polymorphism in Japanese diabetic and non-diabetic subjects. The frequency of Ala12 was significantly lower in the diabetic group than in the control group. In an overweight or obese group, subjects with Ala12 were more insulin sensitive than those without Ala12. These results suggest that the PPARgamma is a thrifty gene and that the Pro12Ala PPARgamma2 polymorphism protects against type 2 diabetes in the Japanese population.4. We investigated the role of PPARgamma in the development of atherosclerosis using heterozygous PPARgamma deficient (PPARγ+/-) mice. When we placed a cuff around the femoral artery to induce inflammation of the adventitia and subsequent neointimal formation, the PPARgamma+/- mice showed 2 fold more neointimal formation than the wild-type mice 2 weeks after cuff placement. Moreover, endothelium-dependent vascular relaxation was significantly impaired in the PPARγ+/- mice compared with the wild-type mice and the expression of endothelial nitric oxide synthase (eNOS) was significantly lower in the PPARgamma+/- mice than in the wild-type mice. These data suggested that PPAR amma plays a crucial role in the regulation of vascular endothelial function and the protection from inflammation induced neointimal formation. Less