Insulin granule dynamics in pancreatic beta cells

2型糖尿病（TTDM）胰岛素分泌受损的机制尚不清楚。在健康情况下，大约75%的胰岛素分泌以离散脉冲释放，周期约为6分钟，调节这些脉冲的幅度有助于调节胰岛素分泌速率。在TTDM患者中，胰岛素的分泌率受到脉冲质量（脉冲期间胰岛素释放量）选择性减少的影响，而不是脉冲频率。此外，在TTDM的第一阶段，胰岛素分泌对葡萄糖丸的反应受到损害。即使TTDM患者的胰岛中似乎有大量储存的胰岛素，这些缺陷仍然存在。胰高血糖素样肽-1恢复搏动和第一期分泌。综上所述，这些观察结果表明，在离散胰岛素脉冲或第一阶段分泌中，可用于快速排出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胰岛素颗粒易释放池的减少。三个具体目标验证了这一总体假设：目标1：验证TTDM中胰岛素分泌受损是由于胰岛素颗粒易于释放池大小减少的假设。目的2：检验导致这种赤字的机制是储备池中颗粒对接不足的假设。目的3：验证易释放池和胰岛素分泌可以通过增强颗粒对接和/或抑制颗粒分离的药物来恢复的假设。我们将使用全内反射荧光显微镜（TIRFM）的方法，这种方法可以在活的分泌细胞内的质膜附近显示单个颗粒。我们完全有能力利用以下资源来解决这些假设：(1)一个完全建立的TIRFM设备。(2)获得多种TTDM啮齿动物模型，包括GK和ZDF大鼠以及表达人类IAPP的转基因大鼠模型。(3)获取人体胰岛。(4)南加州大学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.