Insulinotropin: A Modulator Of B-Cell Glucose Signaling

胰高血糖素样肽-1 （Glucagon-like peptide-1, GLP-1; Insulinotropin）是一种肠源性降血糖激素，可刺激胰腺胰岛素分泌，目前正在研究将其作为治疗2型糖尿病的药物。本文提出的中心假设是，GLP-1对朗格汉斯胰岛有益的促胰岛素作用部分源于GLP-1刺激胰腺β细胞代谢d -葡萄糖的能力。研究表明，GLP-1增加了β细胞中葡萄糖依赖性ATP的产生，如线粒体靶向荧光素酶报告者的单光子计数所示。GLP-1的作用发生在[Ca2+]i的增加之前，这反映了内质网Ca2+储存中Ca2+的动员，并被认为是为了促进线粒体脱氢酶的酶活性，从而增加[ATP]i。随后抑制atp敏感的K+通道（K- atp）产生去极化，振荡Ca2+内流和胰岛素的搏动性胞外分泌。为了验证我们的假设，并验证人类β细胞中GLP-1信号转导的模型，基于发光的[ATP]i测量将与[Ca2+]i的fura-2测定相结合，同时使用膜片钳技术监测K-ATP。它将被确定：1)如果GLP-1增加葡萄糖的效力和功效来刺激ATP的产生，2)如果GLP-1对[Ca2+]i和[ATP]的刺激作用解释了这种激素是如何抑制K-ATP的，以及3)哪些第二信使和蛋白激酶介导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的复杂细胞信号转导特性，解释其在治疗糖尿病中的有效性。

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.