Proinsulin Trafficking for Insulin Biosynthesis

胰腺β细胞储存胰岛素并在血糖升高时释放胰岛素.再加上 每顿饭，健康的胰岛细胞合成新的胰岛素来补充失去的胰岛素。合成途径开始于 平均每秒向内质网（ER）引入约6，000个新的胰岛素原分子， 每单位电池。在正常条件下，这些分子必须将其胰岛素部分折叠至天然状态，包括 形成3个进化上保守的二硫键。不过，我们现在已经确定 胰岛素原错误折叠状态发生在人类胰岛、啮齿类动物胰岛或胰岛细胞系的ER中，并变得更糟（更多 丰富）与ER折叠环境的扰动。我们认为，这是一个重要因素， 异常增加的胰岛细胞内质网应激-在突变INS基因诱导的糖尿病疾病中甚至更糟 青春期（MIDY）-由任何一个>30杂合（显性阴性）INS基因编码序列引起 突变。当前提案中的一部分工作将集中在MIDY模型上，但我们也提出了重要的 新的数据强调了含有胰岛素原的错误折叠蛋白质复合物的形成， 在2型糖尿病（T2 D）发病之前，在胰岛β细胞中丰富而没有INS突变。在我们的第一 目的，我们将进一步分析ER环境和糖尿病的条件，促进形成 胰岛素原的错误折叠复合物，使用分子，细胞和生理工具。在第二个目标中，我们 建议通过使用各种MIDY模型来了解更多关于错误折叠的分子机制， 特别是，我们提出的实验将使我们能够确定有多少错误折叠的胰岛素原必须 积累起来才能引发糖尿病。最后，在我们的第三个目标中，我们提出了一种限制胰岛素原的策略， 为了改善、延缓或预防糖尿病而错误折叠。

Pancreatic ß-cells store insulin and release it in response to an elevation of blood glucose. Additionally, with each meal, healthy ß-cells synthesize new insulin to replace what they have lost. The synthesis pathway begins with introducing into the endoplasmic reticulum (ER) on average ~6,000 new proinsulin molecules every second per ß-cell. Under normal conditions, these molecules must fold their insulin moiety to the native state, including the formation of 3 evolutionarily conserved disulfide bonds. However, we have now definitively identified proinsulin misfolded states that occur in the ER of human islets, rodent islets, or ß-cell lines, and get worse (more abundant) with perturbations of the ER folding environment. We believe that this is an important contributor to abnormally increased ß-cell ER stress – and it is even worse in the disease of Mutant INS-gene induced Diabetes of Youth (MIDY) – caused by any one of >30 heterozygous (dominant-negative) INS gene coding sequence mutations. A portion of the work in the current proposal will focus on MIDY models, but we also present important new data highlighting the formation of misfolded protein complexes containing proinsulin that are especially abundant in islet ß-cells without INS mutation, preceding the onset of type 2 diabetes (T2D). In our first Aim, we will further analyze the ER environment and diabetogenic conditions promoting the formation of misfolded complexes of proinsulin, using molecular, cellular, and physiological tools. In our second Aim, we propose to understand more about the molecular mechanism of misfolding by using various MIDY models, and particularly, we propose experiments that will allow us to determine how much misfolded proinsulin must accumulate in order to trigger diabetes. Finally, in our third Aim, we propose a strategy to limit proinsulin misfolding with the intent to ameliorate, delay, or prevent diabetes.