Insulinotropin: A Modulator Of B-Cell Glucose Signaling

胰升糖素样肽-1(GLP-1；Insulinotroin)是一种肠道来源的降血糖激素，可刺激胰腺胰岛素的分泌，目前正在研究作为治疗2型糖尿病的药物。这里提出的中心假设是，GLP-1在朗格汉斯胰岛的有益的胰岛素调节作用，部分是由于GLP-1通过胰岛β细胞刺激D-葡萄糖代谢的能力。研究表明，GLP-1增加了β细胞中依赖葡萄糖的ATP的产生，这是通过线粒体靶标荧光素酶报告的单光子计数成像的。在GLP-1的作用之前，[Ca~(2+)]i的升高反映了内质网Ca~(2+)库中的Ca~(2+)的动员，这被认为是为了促进线粒体脱氢酶的活性，从而提高[ATP]i。随后抑制ATP敏感的K+通道(K-ATP)会产生去极化、振荡的Ca~(2+)内流和搏动性的胰岛素胞吐。为了验证我们的假设，并验证GLP-1在人类β细胞中的信号转导模型，基于发光的[ATP]i的测量将与Fura-2的[Ca+]i测定相结合，同时使用膜片钳技术监测K-ATP。将确定：1)GLP-1是否增加葡萄糖刺激ATP产生的效力和效力；2)GLP-1对[Ca2+]i和[ATP]i的刺激作用是否解释了该激素如何抑制K-ATP；3)哪些第二信使和蛋白激酶介导了GLP-1对β细胞葡萄糖代谢的刺激作用。我们的目标是阐明GLP-1复杂的细胞信号转导特性，解释其在糖尿病治疗中的有效性。

Glucagon-like peptide-1 (GLP-1; Insulinotropin) is an intestinally-derived blood glucose-lowering hormone that stimulates pancreatic insulin secretion and which is now under investigation for use as a therapeutic agent in treatment of type-2 diabetes mellitus. The Central Hypothesis presented here is that the beneficial insulinotropic action of GLP-1 at the islets of Langerhans results, in part, from an ability of GLP-1 to stimulate metabolism of D-glucose by the pancreatic beta- cells. Studies are presented demonstrating that GLP-1 augments the glucose-dependent production of ATP in beta-cells, as imaged by single photon counting of mitochondrially-targeted luciferase reporters. The action of GLP-1 is preceded by an increase of [Ca2+]i that reflects mobilization of Ca2+ from endoplasmic reticulum Ca2+ stores, and which is proposed to facilitate the enzymatic activity of mitochondrial dehydrogenases, thereby increasing [ATP]i. Subsequent inhibition of ATP-sensitive K+ channels (K-ATP) produces depolarization, oscillatory Ca2+ influx, and pulsatile exocytosis of insulin. To test our hypothesis, and to validate this model of GLP-1 signal transduction in human beta-cells, luminescence-based measurements of [ATP]i will be combined with fura-2 determinations of [Ca2+]i while monitoring K-ATP using the patch clamp technique. It will be determined: 1) if GLP-1 increases the potency and efficacy of glucose to stimulate production of ATP, 2) if stimulatory effects of GLP-1 on [Ca2+]i and [ATP]i explain how this hormone inhibits K-ATP, and 3) which second messengers and protein kinases mediate stimulatory effects of GLP-1 on beta-cell glucose metabolism. Our goal is to elucidate the complex cellular signal transduction properties of GLP-1 that explain its effectiveness for use in treatment of diabetes mellitus.