Secretory Pathway Protein Degradation Maintains Insulin Biogenesis + Secretion

胰腺β细胞合成大量胰岛素。越来越多的证据表明，胰岛素生物合成（遗传性或获得性）中的任何一种缺陷都可能导致糖尿病。我们知道胰岛素的生物合成始于前胰岛素原的翻译。这种短寿命的前体必须易位到内质网（ER）中，切除信号肽，并正确折叠胰岛素原，以便从ER成功输出，输送到远端分泌途径，在该途径中最终发生胰岛素原到胰岛素的加工和胰岛素在分泌颗粒中的储存。相反，不成功的分子可能在它们甚至易位到ER中之前就被降解，或者可能被抑制从ER的顺行输出-事实上，强有力的证据表明错误折叠的胰岛素原分子是降解的靶向。分泌途径蛋白质降解还涉及有助于分化的胰腺辟田胞表型的其他内源性底物。这种多PI的竞争延续。R 01将有助于阐明分泌途径蛋白质处置的三种主要机制-易位前降解; ER相关降解（ERAD）;和自噬-对于适当的β细胞功能都是至关重要的。该提案延续了三位密切合作的研究者（Qi，Tsai，Arvan）的长期合作，他们正是这些过程的专家：前胰岛素原易位到ER腔中，随后胰岛素原折叠/错误折叠，通过ERAD的分泌途径蛋白质降解，以及我们认为主要是ER-自噬（ER-吞噬）的ER-溶酶体降解途径。我们有充分的理由相信，这些质量控制机制的缺陷与胰岛素不足导致的2型糖尿病（T2 D）有关，这一信念得到了初步数据的支持。在这个提议中，我们试图研究与胰腺β细胞早期分泌途径相关的三个相互关联的领域。首先，我们将继续研究前胰岛素原跨内质网膜易位的不忠实性与胰岛素原和胰岛素生物合成缺陷直接相关，直接导致糖尿病。其次，我们将跟踪一些显著的初步数据，这些数据表明胰腺β细胞的去分化是由有效ERAD功能的丧失引发的，也直接导致胰岛素缺乏型糖尿病。最后，我们不仅深入研究了触发错误折叠的胰岛素原的ER吞噬降解的ER因素，而且我们还提出了对无效或不适当的ER吞噬如何触发β细胞衰竭的更深入理解，这也直接导致胰岛素缺乏型糖尿病。这些新的研究方向使我们寻求一种新的β细胞分泌途径功能障碍的治疗方法，重点是刺激细胞内蛋白质清除机制，以预防糖尿病发作和/或限制其进展。

Pancreatic beta-cells synthesize large quantities of insulin. Growing evidence indicates that any of a number of deficiencies in insulin biosynthesis (genetic, or acquired) can lead to diabetes. We know that insulin biosynthesis begins with translation of preproinsulin. This short-lived precursor must be translocated into the endoplasmic reticulum (ER), signal peptide excised, and proinsulin properly folded in order to undergo successful export from the ER for delivery to the distal secretory pathway in which proinsulin-to-insulin processing and insulin storage in secretory granules finally occurs. In contrast, unsuccessful molecules may be degraded before they are even translocated into the ER, or may be restrained from anterograde export from the ER — indeed, strong evidence indicates that misfolded proinsulin molecules are targeted for degradation. Secretory pathway protein degradation also involves other endogenous substrates that contribute to the differentiated pancreatic beta cell phenotype. The competing continuation of this multi-P.I. R01 will help clarify how three major mechanisms of secretory pathway protein disposal – pre-translocation degradation; ER-Associated Degradation (ERAD); and Autophagy – are all critical for proper beta-cell function. This proposal continues the longstanding association of three tightly collaborative investigators (Qi, Tsai, Arvan) that are experts in exactly these processes: preproinsulin translocation into the ER lumen with the subsequent folding/misfolding of proinsulin, secretory pathway protein degradation via ERAD, and an ER-to-lysosome degradative pathway that we believe is primarily ER-autophagy (ER-phagy). We have strong reason to believe that defects in these quality control mechanisms are linked to type 2 diabetes (T2D) as a result of insulin insufficiency, and this belief is supported by preliminary data. In this proposal, we seek to examine three interlinked areas related to the early secretory pathway of pancreatic beta-cells. For one, we will pursue studies in which infidelity of preproinsulin translocation across the ER membrane is directly linked to deficient proinsulin and insulin biosynthesis, leading directly to diabetes. Second, we will follow-up on some remarkable preliminary data demonstrating that de-differentiation of pancreatic beta-cells is triggered by a loss of efficient ERAD function, also leading directly to insulin-deficient diabetes. Finally, we not only delve deeply into the ER factors that trigger ER-phagic degradation of misfolded proinsulin, but we also propose a deeper understanding of how ineffective or improper ER-phagy can trigger beta cell failure, which also leads directly to insulin-deficient diabetes. These new research directions lead us to pursue a novel therapeutic approach to beta-cell secretory pathway dysfunction focused on stimulating intracellular protein clearance mechanisms, in order to prevent diabetes onset and/or limit its progression.