Diabetes affects over 10% of the US population and another 35% are at imminent risk of developing diabetes. As many as half of the diabetic population will develop chronic pain that is poorly treated with current medications. Chronic pain is a major contributor to a poor quality of life in diabetic individuals. While we do not know the exact cause of diabetic neuropathic pain, increases plasma levels of methylglyoxal (MGO), a chemical by-product of energy production, have been correlated with pain in diabetes. We have recently shown that MGO induces the integrated stress response (ISR) in nociceptors, causing them to become hyperexcitable. The ISR controls protein synthesis by repressing eukaryotic initiation factor 2α (eIF2α) and recruiting eIF2A to the mRNA translation machinery. This leads to a global suppression of translation while promoting the translation of select mRNA transcripts, particularly those with an upstream open reading frame. We predict that eIF2A-mediated translation following the induction of ISR regulates the excitability of these cells. Our initial work shows that the ISR is engaged in mouse and rat models of diabetes as well as human sensory neurons treated with MGO. Our overarching hypothesis is that the ISR causes pain in diabetes and that the ISR pathway can be targeted for treating pain in diabetes. As such, initial experiments in mice lacking eIF2A show that the loss of eIF2A protects these mice against evoked and spontaneous pain caused by a single or repeated MGO injections. Aim 1 will harness the power of mouse genetics to generate Nav1.8+ nociceptor-specific knockout of eIF2A. We aim to show that the ISR in mouse nociceptors is required for MGO- evoked and diabetic neuropathic pain. We will further use this model to examine the translatome and identify which mRNAs are translated under the influence of eIF2A, especially after MGO treatment. For Aim 2, we will use cultured neurons and nervous tissues from organ donors to find out how MGO changes gene expression and excitability of human neurons and whether treatment with an ISR inhibitor (ISRIB) can reverse these aberrant changes. Our access to donor tissue presents a unique opportunity to test these hypotheses in a model system that is representative of the people that this research will benefit. Finally, Aim 3 will take advantage of a rat model of type II diabetes, the Zucker Diabetic Fatty (ZDF) rats, to understand how targeting the ISR can be used to treat diabetic pain. We plan to use non-opioid therapies that are currently in development, such as ISRIB, in the ZDF rats. We aim to show that targeting the ISR is an effective strategy for preventing and reversing diabetic neuropathic pain and its electrophysiology correlates. We will also perform RNA sequencing on ZDF rats treated with ISRIB to examine pathways influenced by ISR in a whole animal model of diabetes. By using rodent and human models we will create a unique opportunity to clinically model therapies with a specific biomarker that can be used to select patients and monitor drug efficacy. The ultimate goal of this project is to promote the development of non-opioid therapies targeting the ISR, such as ISRIB

Our work is aimed at gaining a better understanding of molecular events that drive diabetic neuropathic pain and then using this knowledge to identify new molecular targets for diabetic neuropathic pain treatment. We have found a key stress signaling pathway surrounding mRNA translation that regulates nociceptor excitability that occur in diabetic neuropathy. The combined use of pharmacology, genetics, and next generation sequencing technologies across mouse, rat, and human model systems in our project will give unprecedented insight into mechanisms of diabetic neuropathic pain and will identify novel therapeutic opportunities to treat this highly prevalent and exceedingly difficult to manage disorder.