Role of Polyamines and Hypusine in Nutrient-Induced Beta-Cell Growth and Replication
This project is inspired by the premise that signals and substrates extrinsic to the ?-cell trigger cell cycle entry, and that reactivation of the cell cycle in ?-cells would provide the potential for restoring ?-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 ?-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 ?-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 ?-cells) and L. Alonso (an expert in ?-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 ?-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 ?-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 ?-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 ?-cell replication.