Insulin granule dynamics in pancreatic beta cells

2型糖尿病（TTDM）胰岛素分泌受损的机制知之甚少。 在健康状况下，大约75%的分泌胰岛素以大约6分钟的周期性离散脉冲释放，并且这些脉冲的幅度的调制用于调节胰岛素分泌速率。 在TTDM患者中，胰岛素分泌速率受到脉冲质量（脉冲期间释放的胰岛素量）而不是脉冲频率的选择性减少的影响。此外，在TTDM中，响应于葡萄糖推注的第一时相胰岛素分泌受损。 尽管TTDM患者的胰岛中似乎储存了大量胰岛素，但仍存在这些缺陷。 肠促胰岛素激素胰高血糖素样肽-1恢复搏动和第一相分泌。 总之，这些观察结果表明，在离散胰岛素脉冲或第一时相分泌中可用于快速放电的胰岛素颗粒数量在TTDM中不足。 我们对目前研究的总体假设是，TTDM中胰岛素分泌受损的机制是易于释放的胰岛素颗粒池减少。三个具体的目的测试这个整体假设：目的1：测试的假设，受损的胰岛素分泌TTDM是由于减少的大小容易释放池的胰岛素颗粒。目的2：检验导致该缺陷的机制是来自储备池的颗粒对接不足的假设。目标3：检验易释放池和胰岛素分泌可以通过增强颗粒对接和/或抑制脱离的药物恢复的假设。我们将使用全内反射荧光显微镜（TIRFM）的方法，这种方法可以使活分泌细胞内质膜附近的单个颗粒可视化。 我们很好地定位，以解决这些假设与以下资源：（1）一个完整的建立仪器TIRFM。 (2)获得了一些TTDM的啮齿动物模型，包括GK和ZDF大鼠以及表达人IAPP的转基因大鼠模型。(3)进入人类胰岛。(4)USC糖尿病研究中心的支持。

The mechanism of impaired insulin secretion in type 2 diabetes (TTDM) is poorly understood. In health, approximately 75 percent of secreted insulin is released in discrete pulses with a periodicity of approximately 6 minutes, and modulation of the magnitude of these pulses serves to regulate the insulin secretion rate. In patients with TTDM, the rate of insulin secretion is impaired by a selective reduction of the pulse mass (amount of insulin released during a pulse), not pulse frequency. In addition, in TTDM first phase insulin secretion in response to a glucose bolus is impaired. These deficits are present even though there appears to be abundant stored insulin in the islets of patients with TTDM. The incretin hormone glucagon-like peptide-1 restores pulsatility and first phase secretion. Taken together these observations suggest that the number of insulin granules available for rapid discharge in a discrete insulin pulse or first phase secretion is deficient in TTDM. Our overall hypothesis for the present studies is that the mechanisms of impaired insulin secretion in TTDM is a decrease in the readily releasable pool of insulin granules. Three specific aims test this overall hypothesis: Aim 1: Test the hypothesis that impaired insulin secretion in TTDM is due to a reduction in the size of the readily releasable pool of insulin granules. Aim 2: Test the hypothesis that the mechanism leading to this deficit is insufficient docking of granules from the reserve pool. Aim 3: Test the hypothesis that the readily releasable pool and insulin secretion can be restored by agents that enhance granules docking and/or inhibit undocking. We will use the method of total internal reflection fluorescence microscopy (TIRFM), a method that enables the visualization of individual granules near the plasma membrane within living secretory cells. We are well positioned to address these hypotheses with the following resources: (1) A fully established apparatus for TIRFM. (2) Access to a number of rodent models of TTDM, including GK and ZDF rats and a transgenic rat model in which human IAPP is expressed. (3) Access to human islets. (4) The support of the USC Diabetes Research Center.