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。在健康中，大约75%的分泌胰岛素以大约6分钟的周期以离散的脉冲形式释放，这些脉冲的大小的调制有助于调节胰岛素的分泌速率。在TTDM患者中，胰岛素分泌速率是通过选择性地降低脉搏质量(脉搏期间释放的胰岛素量)而不是脉搏频率而受损的。此外，在TTDM患者中，对葡萄糖推注作出反应的第一阶段胰岛素分泌受损。尽管TTDM患者的胰岛中似乎储存了大量的胰岛素，但这些缺陷仍然存在。胰升糖素样肽-1可恢复搏动性和第一时相分泌。综上所述，这些观察结果表明，TTDM患者在离散的胰岛素脉冲或第一阶段分泌中可用于快速释放的胰岛素颗粒数量不足。我们目前研究的总体假设是，TTDM患者胰岛素分泌受损的机制是易释放的胰岛素颗粒减少。三个特定的目标测试这一总体假设：目标1：测试TTDM患者胰岛素分泌受损是由于容易释放的胰岛素颗粒的大小减少这一假设。目标2：检验导致这一赤字的机制是储备库中颗粒对接不足的假设。目的3：验证一种假说，即可通过促进颗粒对接和/或抑制脱离对接的药物来恢复容易释放的池和胰岛素分泌。我们将使用全内反射荧光显微镜(TIRFM)的方法，这是一种能够显示活的分泌细胞内质膜附近的单个颗粒的方法。我们有能力用以下资源解决这些假设：(1)一个完全建立起来的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IAPP的转基因大鼠模型。(3)人的胰岛通道。(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.