Project Summary Fabry disease is the most common lysosomal storage disorder, arising from mutations in the X-linked gene Gla and subsequent accumulation of intracellular globotriaosylceramide (Gb3) and lyso-Gb3. Patients with Fabry disease frequently develop a painful small fiber neuropathy, which is exacerbated following heat-induced pain crises. Little is known, however, about the mechanisms contributing to pain in Fabry disease, and even less is known about the mechanisms of pain exacerbation during pain crises in these patients. This is in part due to the evidence that mouse Fabry models poorly recapitulate the pain in patients with Fabry disease. In rodent models of painful neuropathy, sensory neurons in the dorsal root ganglion often exhibit spontaneous activity and increased excitability. Our rat model of Fabry disease exhibits sensitization of mechanical pain behaviors, spontaneous activity, and both mechanical- and current-evoked excitability of dorsal root ganglion neurons. We have recently demonstrated a p11-dependent glial-neuron signaling axis in Fabry disease that results in increased current-evoked excitability and voltage-gated sodium (NaV) channel current density. This suggests NaV channels may contribute to sensory neuronal hyperexcitability and pain behaviors in Fabry disease; however, it is not clear which NaV channels are hyper functional in Fabry disease, nor is it clear whether neuronal-intrinsic mechanisms also contribute to their dysregulation. Moreover, it is unknown whether heat contributes to increased neuronal excitability in Fabry disease. In the aims outlined in this proposal, I will use voltage-clamp patch electrophysiology, mechanical- and current-evoked patch electrophysiology, and a battery of reflexive and non-reflexive behavioral measures of pain to identify molecular mechanisms contributing to neuronal and behavioral sensitization in Fabry disease at steady state (Aim 1) and following heat-induced pain crises (Aim 2). In Aim 1, I will identify which NaV channels exhibit altered biophysics in Fabry disease sensory neurons at steady-state (Aim 1A) and determine whether these channels are similarly dysregulated by Gb3 and lyso-Gb3 (Aim 1B). In Aim 2, I will determine whether Fabry rats are sensitized to reflexive and non- reflexive behavioral measures of pain following heat treatment (Aim 2A). Further studies will determine whether heat-treatment potentiates mechanically evoked (Aim 2B) and current-evoked (Aim 2C) excitability in dorsal root ganglia neurons from Fabry rats. These studies will ultimately identify which voltage-gated sodium channels underpin increased neuronal excitability at steady state and whether further increased neuronal excitability contributes to heat-evoked pain crises in Fabry disease. Overall, the proposed aims will definitively determine mechanisms contributing to excitability and pain in Fabry disease, potentially revealing therapeutic targets to reduce pain and improve quality of lif...