Stimulus secretion coupling in pancreatic beta-cells

胰腺β细胞的刺激分泌耦合

• 批准号: 10697712
• 负责人: Arthur Sherman
• 金额: $ 12.74万
• 依托单位: NATIONAL INSTITUTE OF DIABETES AND DIGESTIVE AND KIDNEY DISEASES
• 依托单位国家: 美国
• 资助国家: 美国
• 起止时间: 至
• 项目状态: 未结题
• 来源: https://reporter.nih.gov/project-details/10697712
• 关键词: Action Potentials; Adenosine Monophosphate; Adult; Alpha Cell; Area; Back; Behavior; Beta Cell; Biology; Biophysical Process; Blood Circulation; Ca(2+)-Transporting ATPase; Calcium; Calcium Oscillations; Cells; Chemicals; Child; Consumption; Coupled; Coupling; D Cells; Defect; Diabetes Mellitus; Differential Equation; Endocrine; Enzymes; Exocytosis; Feedback; Fructose; Gases; Gasoline; Generations; Glucagon; Glucokinase; Glucose; Glyburide; Glycolysis; Hand; Hereditary Disease; Hormone secretion; Human; Hybrids; Hyperinsulinism; Hypoglycemia; Impairment; In Vitro; Individual; Insulin; Ion Channel; Islets of Langerhans; Journals; Laboratories; Life; Link; Liver; Metabolic; Modeling; Motor; Non-Insulin-Dependent Diabetes Mellitus; Oral; Organ; PFKM gene; Pacemakers; Pancreas; Paper; Pathogenesis; Periodicity; Pharmaceutical Preparations; Physiologic pulse; Physiological; Plasma; Play; Potassium; Production; Protein Isoforms; Protein Kinase C; Pump; Reporting; Rest; Rodent; Role; Running; Signal Pathway; Somatostatin; Speed; Stimulus; Structure of beta Cell of islet; Study models; Suggestion; Sulfonylurea Compounds; System; Testing; Time; Tissues; Tolbutamide; Work; basal insulin; base; calcium metabolism; cell type; clinically significant; design; enzyme activity; expectation; experimental study; gain of function mutation; genome wide association study; glucose metabolism; insulin granule; insulin secretion; interest; ion dynamics; islet; loss of function mutation; mathematical model; millisecond; model building; model development; neglect; neonatal diabetes mellitus; novel; predictive modeling; response; tool

Impaired insulin secretion is a key step in the pathogenesis of type 2 diabetes, along with inefficient use of insulin by target tissues. The two main components of secretion are calcium entry into pancreatic beta cells and triggering of insulin granule exocytosis by that calcium. We have modeled both components and their contributions to diabetes. We have focused mainly on the mechanisms of calcium oscillations over a range of periods, from seconds to minutes. The slower class of oscillations (5 - 10 minute period) is the main driver of pulsatile insulin concentration in the circulation, which has been shown to be optimal for the response of insulin-sensitive tissues, especially the liver. Details of the historical development of the model can be found in our reports from previous years and in a current review article (ref. #1). We call the resulting model the integrated oscillator model (IOM) to indicate that the oscillations result from the partnership of an electrical oscillator (EO) and a metabolic oscillator (MO). The electrical oscillator (EO) is based on negative feedback of calcium onto ion channels, directly onto calcium-activated potassium (K(Ca)) channels and indirectly onto ATP-dependent potassium (K(ATP)) channels because calcium reduces the ATP/ADP ratio. The metabolic oscillator (MO) is governed by positive feedback of fructose 1,6 bisphosphate (FBP) on the enzyme in glycolysis that produces it, phosphofructokinase (PFK). The MO communicates with the EO via the K(ATP) channels, which transduce the metabolic state of the cell (ATP/ADP ratio) into electrical depolarization. K(ATP) channels are of clinical significance as they are a target of insulin-stimulating drugs, such as the sulfonylureas tolbutamide and glyburide, the first class of oral medications developed for the treatment of Type 2 Diabetes. Severe gain-of-function mutations of K(ATP) are a major cause of neo-natal diabetes mellitus, whereas moderate gain-of-function mutations have been linked in genome-wide association studies (GWAS) to the milder but more common adult-onset form of diabetes, type 2 diabetes. Conversely, loss-of-function mutations of K(ATP) are a major cause of familial hyperinsulinism, a hereditary disease found in children in which beta cells are persistently electrically active and secrete insulin in the face of normal or low glucose, causing life-threatening hypoglycemia. Another major cause of hyperinsulinism is excessive activity of the enzyme glucokinase (GK), which also plays a key role in the DOM. Notwithstanding the central role of PFK, the model predicted that oscillations in calcium and ATP could occur in the absence of the most important isoform of PFK, PFKm, because other isoforms could substitute for it. This was described in last year's report, and a paper has now appeared (ref. #2). Because increases in cytosolic calcium activate pumps that consume ATP to bring calcium back down, any oscillation in calcium will be reflected in a oscillations in ATP/ADP. However, our model shows that when ATP/ADP is the cause, not just a consequence, of calcium oscillations, then the ATP/ADP ratio remains constant as glucose is increased within the range that supports oscillations. This theoretical result runs counter to the natural expectation that increases in glucose increase ATP production. However, this neglects the fact that, when ATP, acting through KATP channels, is the driver of the calcium oscillations, then consumption of ATP by calcium pumps increases in tandem. This novel theoretical prediction is straightforward to test, and experiments in the Satin laboratory have confirmed that the ATP/ADP ratio is nearly invariant within the oscillatory regime, as detailed in ref. #3. This supports our hypothesis that ATP/ADP is the primary active driver of the calcium oscillations. We are therefore confident that metabolic oscillations are central in the generation of calcium oscillations and of pulsatile insulin secretion. However, we have come to appreciate that metabolic oscillations come in two flavors. They can arise through the autonomous activity of a glycolytic oscillator, which we call Active Metabolic Oscillations (AMOs), or by passively responding to consumption of ATP due to the need to pump calcium out of the cells, which we call Passive Metabolic Oscillations (PMOs). At the higher glucose concentrations (ca. 200 mg/dl) usually studied in vitro, PMOs predominate, but physiologically glucose mainly fluctuates in a lower range from a basal level of less than 100 mg/dl to post-prandial level of about 120 mg/dl. Large amplitude calcium oscillations, which are obligatory in PMO mode do not occur in basal glucose, yet pulsatile insulin secretion, albeit of small amplitude, still occurs. This led us to propose a hypothesis that the basal insulin pulses are driven by AMOs. Not only is this hypothesis novel, but the need to explain the basal oscillations had not been previously recognized in the field. Furthermore, as glucose increases after meals, AMOs smoothly give way to PMOs. In ref. #4 we made the analogy to a hybrid gas-electric car, in which an electric motor active at low speeds smoothly hands over control to a gasoline engine at higher speeds. This concept was featured on the cover of that issue of the journal. Another area of contention in islet biology is how the hundreds of beta cells in each pancreatic islet coordinate their activity to produce coherent oscillation. For many years, islets were viewed as democratic, with all the cells contributing and no central pacemaker needed to conduct the orchestra. Recently, however, an alternative hypothesis has been proposed that a small subset of beta cells, called "hub cells" because they are highly coupled to the rest of the beta cells, are required to coherent activity. The existence of such hub cells is well established, but we and others have questioned the suggestion that coordinated oscillations cannot occur in their absence. For one thing, this would render islets very vulnerable to loss of a handful of cells, which seems like a poor design principle. The intriguing and challenging hub hypothesis has led to a number of modeling studies by others to investigate whether islets could or do work in this oligarchical manner. We have summarized the results of those studies in a review paper(ref. #5) and concluded that most of the experimental observations can be accommodated but that the existence of obligatory pacemakers is unlikely.

胰岛素分泌受损以及靶组织无法有效利用胰岛素是 2 型糖尿病发病机制的关键步骤。 分泌的两个主要成分是钙进入胰腺β细胞并通过钙触发胰岛素颗粒胞吐作用。 我们对这两种成分及其对糖尿病的影响进行了建模。 我们主要关注从几秒到几分钟的一系列时间段内钙振荡的机制。 较慢的振荡类型（5 - 10 分钟周期）是循环中脉动胰岛素浓度的主要驱动因素，这已被证明对于胰岛素敏感组织（尤其是肝脏）的反应是最佳的。 该模型历史发展的详细信息可以在我们前几年的报告和当前的评论文章（参考文献#1）中找到。 我们将所得模型称为集成振荡器模型 (IOM)，以表明振荡是由电振荡器 (EO) 和代谢振荡器 (MO) 合作产生的。 电振荡器 (EO) 基于钙离子通道上的负反馈，直接反馈到钙激活钾 (K(Ca)) 通道上，并间接反馈到 ATP 依赖性钾 (K(ATP)) 通道上，因为钙会降低 ATP/ADP 比率。 代谢振荡器 (MO) 受果糖 1,6 二磷酸 (FBP) 对糖酵解中产生果糖的酶磷酸果糖激酶 (PFK) 的正反馈的控制。 MO 通过 K(ATP) 通道与 EO 通信，将细胞的代谢状态（ATP/ADP 比率）转换为电去极化。 K(ATP) 通道具有临床意义，因为它们是胰岛素刺激药物的靶标，例如磺酰脲类甲苯磺丁脲和格列本脲，这是为治疗 2 型糖尿病而开发的第一类口服药物。 K(ATP) 的重度功能获得性突变是新生儿糖尿病的主要原因，而全基因组关联研究 (GWAS) 中已将中度功能获得性突变与较轻但更常见的成人发病型糖尿病（2 型糖尿病）联系起来。 相反，K(ATP) 功能丧失突变是家族性高胰岛素血症的主要原因，这是一种在儿童中发现的遗传性疾病，其中β细胞在正常或低血糖的情况下持续电活动并分泌胰岛素，导致危及生命的低血糖。高胰岛素血症的另一个主要原因是葡萄糖激酶 (GK) 的过度活性，该酶在 DOM 中也起着关键作用。 尽管 PFK 发挥着核心作用，但该模型预测，在缺乏最重要的 PFK 同工型 PFKm 的情况下，钙和 ATP 的振荡可能会发生，因为其他同工型可以替代它。 去年的报告对此进行了描述，现在已经发表了一篇论文（参考文献#2）。 由于细胞质钙的增加会激活泵，消耗 ATP 使钙下降，因此钙的任何波动都会反映在 ATP/ADP 的波动中。 然而，我们的模型表明，当 ATP/ADP 是钙振荡的原因而不仅仅是结果时，随着葡萄糖在支持振荡的范围内增加，ATP/ADP 比率保持恒定。 这一理论结果与葡萄糖增加会增加 ATP 产生的自然预期背道而驰。 然而，这忽略了这样一个事实：当 ATP 通过 KATP 通道发挥作用时，是钙振荡的驱动因素，那么钙泵对 ATP 的消耗也会随之增加。这种新颖的理论预测很容易测试，并且 Satin 实验室的实验已经证实 ATP/ADP 比率在振荡范围内几乎不变，如参考文献中详述。 ＃3。 这支持了我们的假设，即 ATP/ADP 是钙振荡的主要主动驱动因素。 因此，我们相信代谢振荡是钙振荡和脉动胰岛素分泌产生的核心。 然而，我们逐渐认识到代谢振荡有两种形式。 它们可以通过糖酵解振荡器的自主活动产生，我们称之为主动代谢振荡 (AMO)，或者由于需要将钙泵出细胞而被动响应 ATP 的消耗，我们称之为被动代谢振荡 (PMO)。 通常在体外研究的较高葡萄糖浓度（约 200 mg/dl）下，PMO 占主导地位，但生理上葡萄糖主要在较低范围内波动，从低于 100 mg/dl 的基础水平到约 120 mg/dl 的餐后水平。 PMO 模式中必需的大幅度钙振荡不会在基础葡萄糖中发生，但脉动胰岛素分泌（尽管幅度较小）仍然会发生。 这导致我们提出一个假设，即基础胰岛素脉冲是由 AMO 驱动的。 这一假设不仅新颖，而且该领域之前并未认识到解释基础振荡的必要性。 此外，随着餐后血糖升高，AMO 会顺利让位于 PMO。 在参考文献中。 #4 我们将其类比为混合动力油电汽车，其中低速运行的电动机平稳地将控制权移交给高速运行的汽油发动机。 这一概念出现在该期刊的封面上。 胰岛生物学的另一个争论领域是每个胰岛中的数百个β细胞如何协调其活动以产生相干振荡。 多年来，胰岛被认为是民主的，所有细胞都做出贡献，并且不需要中央起搏器来指挥管弦乐队。 然而，最近提出了另一种假设，即一小部分 β 细胞（称为“中枢细胞”）因为它们与其余 β 细胞高度耦合，需要保持一致的活动。 这种枢纽细胞的存在是众所周知的，但我们和其他人对“在它们不存在的情况下协调振荡不会发生”的建议提出了质疑。 一方面，这将使胰岛非常容易丢失少量细胞，这似乎是一个糟糕的设计原则。 有趣且具有挑战性的枢纽假说引发了其他人的许多模型研究，以调查胰岛是否可以或确实以这种寡头方式工作。 我们在一篇综述论文（参考文献#5）中总结了这些研究的结果，并得出结论，大多数实验观察结果是可以接受的，但强制性起搏器的存在不太可能。