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

这个项目的灵感来自于一个前提，即β细胞外部的信号和底物触发细胞周期的进入，并且β细胞细胞周期的重新激活将为恢复糖尿病中β细胞的质量和功能提供潜力。我们发表的和初步的数据表明，翻译因子eIF5A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，eIF5A是唯一含有独特的多胺衍生氨基酸hypusine的蛋白质，这是其功能所必需的。Hypusine的形成发生在翻译后，由两种限速酶，鸟氨酸脱羧酶（ODC）和脱氧Hypusine合成酶（DHPS）控制。ODC从精氨酸（间接从谷氨酰胺、脯氨酸、蛋氨酸、苯丙氨酸、亮氨酸）产生细胞内多胺，DHPS利用多胺亚精胺在eIF5A上形成hypusine。总的来说，我们将ODC/DHPS/eIF5A蛋白称为“多胺/hypusine通路”。因为多胺和hypusine的产生可以被饮食和/或小分子控制，它们代表了现实世界中干预β细胞生长和复制的目标。我们假设，产生多胺和hypusine的途径将营养信号（氨基酸、葡萄糖）与mRNA翻译联系起来，从而实现适应性β细胞复制。这个多pi R01应用程序的优势是博士之间的合作努力。R. Mirmira （β-细胞多胺/hypusine通路专家）和L. Alonso （β-细胞复制专家）；我们的团队在相关专业知识、新型条件敲除小鼠和mRNA翻译评估工具方面具有独特的优势，可以验证这一假设。我们提出以下3个目标：目的1：阐明多胺/hypusine通路在肥胖和高血糖模型中调控适应性β细胞增殖的机制。目的2：描述多胺生物合成如何作为营养素激活的看门人，在β细胞中由UPR诱导的增殖信号中发挥作用。目的3：揭示eIF5A作为氨基酸和多胺供应的生物传感器的不寻常功能。我们将使用最先进的成像和细胞生物学技术以及新型试剂的综合工具箱，包括唯一收集的ODC/DHPS/eIF5A敲除小鼠，以揭示在β细胞增殖中的作用，否则是一个神秘的途径。因此，该建议的主要影响是多胺/hypusine途径在啮齿动物和人类β细胞复制中的鉴定和机制。

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.