Role of Polyamines and Hypusine in Nutrient-Induced Beta-Cell Growth and Replication

该项目的灵感来自于β细胞外部的信号和底物触发细胞周期进入的前提，并且β细胞中细胞周期的重新激活将提供恢复糖尿病中β细胞质量和功能的潜力。我们发表的和初步的数据表明，翻译因子eIF 5A作为一种急性反应因子，催化特定mRNA的翻译，使细胞复制。引人注目的是，eIF 5A是唯一含有独特的多胺衍生氨基酸羟腐胺赖氨酸的蛋白质，这是其功能所必需的。羟腐胺赖氨酸的形成发生在产后，并由两种限速酶，鸟氨酸脱羧酶（ODC）和脱氧羟腐胺赖氨酸合酶（DHPS）。ODC从精氨酸（以及间接从谷氨酰胺、脯氨酸、甲硫氨酸、苯丙氨酸、亮氨酸）产生细胞内多胺，DHPS利用多胺亚精胺在eIF 5A上形成羟腐胺赖氨酸。总的来说，我们将ODC/DHPS/eIF 5A蛋白称为属于“多胺/羟腐胺赖氨酸途径”。由于多胺和羟腐胺赖氨酸的产生可以通过饮食和/或小分子来操纵，因此它们代表了干预β细胞生长和复制的现实目标。我们假设产生多胺和羟腐胺赖氨酸的途径将营养信号（氨基酸、葡萄糖）与mRNA翻译联系起来，以实现适应性β细胞复制。该Multi-PI R 01应用程序的优势在于R. Mirmira（β细胞中多胺/羟腐胺赖氨酸途径的专家）和L. Alonso（β细胞复制专家）;我们的团队拥有独特的相关专业知识，新型条件性敲除小鼠和mRNA翻译评估工具来验证这一假设。我们提出了以下3个目标：目标1：阐明多胺/羟腐胺赖氨酸途径在肥胖和高血糖模型中调控适应性β细胞增殖的机制。目标二：描述多胺生物合成如何作为β细胞中UPR诱导的增殖信号的营养激活看门人发挥作用。目的3：揭示eIF 5A作为氨基酸和多胺供应生物传感器的独特功能。我们将使用最先进的成像和细胞生物学技术和新型试剂的综合工具箱，包括ODC/DHPS/eIF 5A敲除小鼠的唯一集合，以揭示β细胞增殖中的作用，否则神秘的途径。因此，该提案的主要影响是啮齿动物和人类β细胞复制中多胺/羟腐胺赖氨酸途径的鉴定和机制。

This project is inspired by the premise that signals and substrates extrinsic to the β-cell trigger cell cycle entry, and that reactivation of the cell cycle in β-cells would provide the potential for restoring β-cell mass and function in diabetes. Our published and preliminary data suggest that the translation factor eIF5A functions as an acute response factor that catalyzes translation of specific mRNAs, enabling cellular replication. Strikingly, eIF5A is the only protein containing the unique, polyamine-derived amino acid hypusine, which is required for its function. Hypusine formation occurs posttranslationally and is governed by two rate-limiting enzymes, ornithine decarboxylase (ODC) and deoxyhypusine synthase (DHPS). ODC generates intracellular polyamines from arginine (and indirectly from glutamine, proline, methionine, phenylalanine, leucine), and DHPS utilizes the polyamine spermidine to form hypusine on eIF5A. Collectively, we refer to the ODC/DHPS/eIF5A proteins as belonging to the “polyamine/hypusine pathway.” Because polyamine and hypusine productions can be manipulated by diet and/or small molecules, they represent real-world targets to intervene in β-cell growth and replication. We hypothesize that the pathway that generates polyamines and hypusine links nutritional signals (amino acids, glucose) to mRNA translation to enable adaptive β-cell replication. The strength of this Multi-PI R01 application is the collaborative effort between Drs. R. Mirmira (an expert in the polyamine/hypusine pathway in β-cells) and L. Alonso (an expert in β-cell replication); our Team is uniquely positioned with the relevant expertise, novel conditional knockout mice, and mRNA translation assessment tools to test this hypothesis. We propose the following 3 aims: Aim 1: Elucidate the mechanisms by which the polyamine/hypusine pathway governs adaptive β-cell proliferation in models of obesity and hyperglycemia. Aim 2: Characterize how polyamine biosynthesis functions as a nutrient-activated gatekeeper for the proliferative signal induced by the UPR in β-cells. Aim 3: Reveal an unusual function of eIF5A as a biosensor for amino acid and polyamine supply. We will use a comprehensive toolbox of state-of-the-art imaging and cell biology techniques and novel reagents, including the only collection of ODC/DHPS/eIF5A knockout mice, to reveal a role in β-cell proliferation for an otherwise enigmatic pathway. Therefore, the primary impact of this proposal is the identification and mechanisms of the polyamine/hypusine pathway in rodent and human β-cell replication.