Expression Profiles for Ret-Positive Drg Neurons

Jain, Sanjay

Abstract

This is a Research Project to generate expression profiles of a specific population of nociceptors in the dorsal root sensory ganglia (DRG) during development and postnatal period in mice as a part of the nGUDMAP project. There is extensive heterogeneity in DRG at several levels including neurochemistry, pharmacology, morphology, and molecular profiles. There is also cross- sensitization of visceral and somatic sensory nervous systems. The molecular basis for this heterogeneity and diversity, its implication in normal and abnormal genitourinary sensory function is lacking and is an obstacle to understanding mechanisms of nociception and devising rational approaches to treat conditions such as painful bladder syndrome/interstitial cystitis. Delineating gene expression patterns and molecular networks in distinct types of DRG neurons during ontogeny is an essential first step to overcome this obstacle. We study a subtype of nociceptor that depends on glial cell line-derive neurotrophic factor (GDNF) family ligands (GFLs) for postnatal survival. GFLs activate receptor tyrosine kinase Ret in nociceptors and a subset of low threshold mechanoreceptors. Activation of GFL-RET downstream signaling is important for axon maintenance, survival, nociception, and pain sensitivity. Ret-positive sensory neurons in the DRG show molecular, neurochemical and structural changes in bladder injury models in mice and in humans in conditions such as painful bladder syndrome or interstitial cystitis (IC/PBS), they participate in both somatic and visceral sensation, express key ion channels that are implicated in somatic and visceral pain (TrpV1, TrpA1), and GFLs can produce analgesia and hyperalgesia. We will delineate genes expressed in Ret-positive DRG sensory neurons. We have made innovative Ret-reporter mice that constitutively or conditionally label Ret-expressing cells with green fluorescence protein for the first time. We will use these in conjunction with FACS and RNA-Seq to accomplish three miniobjectives: 1) To generate expression profiles of Ret+ DRG sensory neurons in early midgestation through postnatal period, 2) To generate expression profiles of Ret+ Nav1.8+ nociceptors at the same time points as above, and 3) Generate expression profiles of Ret+ L6-S1 DRG sensory neurons to enrich isolation of bladder visceral afferents using Ret- reporter male and female postnatal mice. Our preliminary data provide evidence for Ret+ sensory neurons in the DRG and in bladder afferents, their normal activation of TrpV1 and TrpA1 ion channels, their successful isolation using FACS and access to genomic technology in collaboration with bioinformaticists to generate RNA-Seq data and depositing it in the GUDMAP database. Interactions with members of other GUDMAP projects and the community will provide synergies that will accelerate discovery and mechanism based projects related to pelvic visceral sensory system.

Public Health Relevance

The biological basis of normal and noxious sensory responses from the pelvic viscera is not clearly understood. Delineating genes expressed during development and maturation of pelvic visceral sensory system is necessary to understand mechanisms of pelvic pain disorders such as painful bladder syndrome/interstitial cystitis. The proposed research will catalogue the expression of genes in a specific population of sensory neurons, Ret-positive nociceptors that mediate sensory responses to normal and noxious stimuli to lower urinary tract including the bladder. We leverage the expertise in genomic technologies at our institution and our innovative genetically engineered mice that label sensory neurons that express the receptor tyrosine kinase Ret. The long term hope is that the data generated will lead to devising mechanism-based studies to better understand pelvic visceral sensory system.