(212) Gene Expression Profile of Nociceptor Hyper-Excitability in Painful Diabetic Neuropathy

Abstract

Painful diabetic neuropathy (PDN) is an intractable complication of diabetes that affects 25% of patients. PDN is characterized by neuropathic pain and small-fiber degeneration, accompanied by dorsal root ganglion (DRG) nociceptor hyperexcitability and loss of their axons within the skin. The molecular mechanisms underlying DRG nociceptor hyperexcitability and small-fiber degeneration in PDN are unknown. To delineate the molecular mechanisms behind nociceptor hyperexcitability and small-fiber degeneration, it becomes important to uniquely identify changes in the nociceptor population from within the heterogeneous population of neurons in the DRG. To identify genes that are differentially expressed in PDN, we compared the RNA profile of mice fed a regular-diet (RD) or a high-fat diet (HFD), a commonly used model of PDN. To capture the translational state of these nociceptive neurons, we used transgenic mice expressing tagged ribosomal subunits (RiboTag) in the nociceptor population expressing the sodium channel-Nav1.8. Analysis of the RiboTagged mRNA between HFD and RD mice at 10 weeks revealed 84 upregulated genes and 70 downregulated genes. We identified candidate genes like ApoD, known to increase excitatory signaling through CXCR4/CXCL12. Previously our work demonstrated that CXCR4/CXCR12 signaling is critical for the development of mechanical allodynia and small-fiber degeneration in PDN. Further analysis implicated changes in pathways relating to extracellular matrix organization, gliogenesis and, complex 1 biogenesis. In addition to the translational profiling, we plan to perform single-cell RNA sequencing of the Nav1.8-positive DRG neuron population using Nav1.8-Cre;Ai9 mice fed an RD or an HFD. Single-cell RNA sequencing will give us a better understanding of the transcriptional status of subpopulations within the Nav1.8-positive DRG neurons and generate candidate genes at a higher resolution. This study will provide insight into the genes that are involved in the pathogenesis of neuropathic pain and small-fiber degeneration and yield potential translational targets for disease-modifying treatments for PDN.