Mechanism of pancreatic β cell dysfunction in obese diabetes model db/db mice

众所周知，胰腺b细胞功能紊乱是2型糖尿病的重要生理机制。为了阐明β细胞功能障碍的机制，我们对C57BL/KSJ db/db小鼠的胰岛进行了结构和功能分析，并观察了吡格列酮对胰岛形态和功能的影响。此外，采用激光捕获显微切割技术和实时荧光定量RT-PCR方法分析了胰岛基因表达谱。吡格列酮已被证明不仅对周围组织有效，而且对胰腺β细胞也有效。为了评价吡格列酮对肥胖糖尿病动物模型db/db小鼠胰腺β细胞损伤的预防作用，并探讨其作用机制，我们对db/db小鼠给予吡格列酮，对胰腺进行组织学观察，并与未治疗组和db/+非糖尿病组小鼠的胰岛进行生化和生理学比较。十二周的…给db/db小鼠(6-18周龄)增加吡格列酮(100 mg/kg或30 mg/kg，每日灌胃)治疗。能显著降低18周龄空腹血糖水平(未处理对照组260±12vs554±62 mg/dl，p&lt；0.05)。经吡格列酮治疗的db/db小鼠的胰岛面积百分比显著大于未治疗的对照组db/db小鼠(2.54±0.28vs1.16±0.06%，p&lt；0.001)。免疫组织化学检测显示，吡格列酮治疗组小鼠胰岛β细胞占细胞总数的比例也较高(80.6±12.0vs73.4±2.2%，p&lt；0.01)。经吡格列酮治疗6周后，血糖、甘油三酯、游离脂肪酸水平显著降低，脂联素水平显著升高(65.2±18.0vs18.3±1.3μg/ml，P<0.05)。胰岛素耐量试验显示，吡格列酮增加了胰岛素敏感性。吡格列酮可显著降低胰岛甘油三酯含量(43.3±3.6vs65.6±7.6 ng/胰岛，P<0.05)。用吡格列酮治疗后，对照组小鼠胰岛分泌受损的葡萄糖刺激的胰岛素得到恢复。在db/db小鼠中，在胰岛核心区观察到胰腺激素如胰高血糖素和生长抑素的基因表达，表明胰岛结构紊乱。此外，在db/db小鼠中，凋亡基因的表达加速。在db/+小鼠中，胰岛素基因的表达出现了代偿性上调。这些结果证实了db/db小鼠β细胞功能紊乱的分子机制，并提示吡格列酮通过增加胰岛素敏感性和减少db/db小鼠胰岛脂肪蓄积来改善血糖毒性。较少

It is well known that deranged pancreatic b cell function is an important phathophysiology in type 2 diabetes. In order to clarify the mechanism of β cell dysfunction, structural and functional analyses of the pancreatic islet of C57BL/KsJ db/db mice were carried out, and effects of pioglitazone on islet morphology and function were also examined. In addition, gene expression profiles of pancreatic islet was analyzed by using Laser Capture microdissection method and real time RT-PCR method. Pioglitazone has been demonstrated to have potency not only on peripheral tissues but also pancreatic β cells. To evaluate preventive effects of pioglitazone on pancreatic β-cell damage in db/db mice, an obese diabetic animal model, and to elucidate their mechanisms, we administered pioglitazone on db/db mice, and investigated the pancreas histologically, and compared pancreatic islets biochemically and physiologically with those obtained from untreated mice and db/+ non-diabetic mice. Twelve weeks' … More treatment (6-18 weeks of age) in db/db mice with pioglitazone (100 mg/kg or 30 mg/kg daily p.o.) induced a significant reduction in the fasting blood glucose level (260±12 vs 554±62 mg/dl in untreated control at 18 weeks of age, p<0.05). The % islet area in the pancreas was significantly larger in pioglitazone-treated mice than in the untreated control db/db mice (2.54±0.28 vs 1.16±0.06%, p<0.001). The ratio of β-cells determined by immunohistochemistry to total cells in a pancreatic islet was also greater in the pioglitazone-treated mice (80.6±12.0 vs 73.4±2.2 % in untreated control, p<0.01). After six weeks' treatment with pioglitazone (100 mg/kg daily p.o.), the plasma levels of glucose, triglyceride, and free fatty acid were significantly decreased, while the plasma adiponectin level increased significantly (65.2±18.0 vs 18.3±1.3 μg/ml in untreated control, p<0.05). Insulin tolerance tests revealed that pioglitazone increased insulin sensitivity. The triglyceride content in pancreatic islets was significantly reduced by pioglitazone (43.3±3.6 vs 65.6±7.6 ng/islet in untreated control, p<0.05). Impaired glucose-stimulated insulin secretion from pancreatic islets in the control mice was restored by the treatment with pioglitazone. In the db/db mice, gene expression for pancreatic hormones such as glucagons and somatostatin was observed in the core area of islet, indicating deranged islet architecture. In addition, apoptotic gene expression was accerelated in db/db mice. A compensatory up-regulation of insulin gene expression was suggested in the db/+ mice. The present results demonstrate a molecular mechanism of deranged β cell function in db/db mice, and suggest that pioglitazone improves glucolipotoxicity by increasing insulin sensitivity and reducing fat accumulation in the islets in db/db mice. Less