Hypothalamic glucokinase in obesity and diabetes

下丘脑神经元可以感知并对葡萄糖浓度的变化做出反应，但功能性的 这种葡萄糖敏感特性的意义仍有待确定。就像在胰腺β细胞中一样， 葡萄糖激酶(GK)是下丘脑葡萄糖敏感机制的重要组成部分。纯合子 全身切除GK基因会导致致命的新生儿糖尿病，以及杂合性全身切除 GK基因的缺失会导致葡萄糖稳态受损和肥胖表型，包括POMC和 下丘脑神经元AgRP基因表达增加。有趣的是，纯合子全身消融 胰岛素受体也会导致致命的新生儿糖尿病，以及胰岛素的神经元特异性表达 受体部分挽救了这一表型。我们现在已经证明了杂合子和纯合子 在神经元中特异性地去除GK基因可重现相应的全身GK基因敲除 表型。另一方面，其他研究表明下丘脑张力细胞中的GK(一种 神经胶质细胞)也在代谢动态平衡中发挥作用。因此，我们提出新陈代谢的不同方面 动态平衡依赖于POMC神经元、AgRP神经元或张力细胞中GK的表达。致信地址 这一假说，在特定的目标1中，我们建议通过杂交来特异性地消融POMC神经元中的GK POMC启动子控制下表达cre重组酶的转基因小鼠(POMC-cre) 它的GK基因两侧是lox位点。作为对这些研究的补充，我们建议恢复GK 特别是在(纯合或杂合)全身GK基因敲除小鼠的POMC神经元中，使用 冈本等人提出的“敲入”策略。通过恢复胰岛素受体挽救致命的新生儿糖尿病 特别是对全身胰岛素受体基因敲除小鼠的神经元。小鼠将维持在低脂肪或 高脂肪饮食。代谢表型，包括瘦素敏感性、葡萄糖和胰岛素耐量试验、食物摄入量、 将评估体重、肥胖、代谢率和体温。小鼠将被牺牲，基因 将确定其在下丘脑和其他组织中的表达。我们建议在特定目标上进行类似的研究。 2和3，使用AgRP或GFAP cre重组酶(在松弛细胞中表达)来消融或恢复GK 在AgRP神经元中，或在Tanyctes中消融GK。我们预计，在特定的下丘脑细胞中消融GK TYPE将部分概括全身消融GK所产生的特定代谢损伤，并且 将GK恢复到POMC或AgRP神经元将逆转全脑缺血所致的特异性代谢损伤。 身体GK缺乏症

Hypothalamic neurons can sense and respond to changes in glucose concentration, but the functional significance of this glucose-sensing property remains to be determined. As in pancreatic beta cells, glucokinase (GK) constitutes a key component of the hypothalamic glucose-sensing mechanism. Homozygous whole-body ablation of the GK gene produces lethal neonatal diabetes, and heterozygous whole-body ablation of the GK gene causes impaired glucose homeostasis and obese phenotypes, including reduced POMC and increased AgRP gene expression in hypothalamic neurons. Interestingly, homozygous whole-body ablation of the insulin receptor also produces lethal neonatal diabetes, and neuron-specific expression of the insulin receptor partially rescues this phenotype. We have now demonstrated that heterozygous and homozygous ablation of the GK gene specifically in neurons recapitulates the respective whole-body GK knockout phenotypes. On the other hand, other studies have suggested that GK in hypothalamic tanycytes (a type of glial cell) also plays a role in metabolic homeostasis. We therefore propose that different aspects of metabolic homeostasis are dependent on GK expression in POMC neurons, AgRP neurons, or tanycytes. To address this hypothesis, in Specific Aim 1 we propose to ablate GK specifically from POMC neurons by crossing transgenic mice expressing cre-recombinase under control of the POMC promoter (POMC-cre) with mice in which the GK gene is flanked by lox sites. Complementing these studies, we propose to restore GK specifically in POMC neurons in (homozygous or heterozygous) whole-body GK knockout mice, using the "knock-in" strategy by which Okamoto et al. rescued lethal neonatal diabetes by restoring insulin receptors specifically to neurons in whole-body insulin receptor knockout mice. Mice will be maintained on a low-fat or a high-fat diet. Metabolic phenotypes, including leptin sensitivity, glucose and insulin tolerance tests, food intake, body weight, adiposity, metabolic rate, and temperature will be assessed. Mice will be sacrificed, and gene expression will be determined in hypothalamus and other tissues. We propose similar studies in Specific Aims 2 and 3, using AgRP, or GFAP cre-recombinase (expressed in tanycytes) to ablate or restore GK specifically in in AgRP neurons, or to ablate GK in tanyctes. We anticipate that ablation of GK in specific hypothalamic cell types will partially recapitulate specific metabolic impairments produced by whole-body ablation of GK, and that restoration of GK to POMC or AgRP neurons will reverse specific metabolic impairments caused by whole- body GK deficiency