GPR160 de-orphanization reveals critical roles in neuropathic pain in rodents

Treating neuropathic pain is challenging and novel non-opioid based medicines are needed. Using unbiased receptomics, transcriptomic analyses, immunofluorescence and in situ hybridization, expression of the orphan GPCR (oGPCR) GPR160 increased in the rodent dorsal horn of the spinal cord (DH-SC) following traumatic nerve injury. Genetic and immunopharmacological approaches demonstrated that GPR160 inhibition in the spinal cord prevented and reversed neuropathic pain in male and female rodents without altering normal pain response. GPR160 inhibition in the spinal cord attenuated sensory processing in the thalamus, a key relay in the sensory discriminative pathways of pain. We also identified cocaine- and amphetamine-regulated transcript peptide (CARTp) as a GPR160 ligand. Inhibiting endogenous CARTp signaling in spinal cord attenuated neuropathic pain, whereas exogenous intrathecal (i.th.) CARTp evoked painful hypersensitivity through GPR160-dependent ERK and cAMP response element-binding protein (CREB). Our findings de-orphanize GPR160, identify it as a determinant of neuropathic pain and potential therapeutic target, and provide insights to its signaling pathways. CARTp is involved in many diseases including depression, reward and addiction, de-orphanization of GPR160 is a major step forward understanding the role of CARTp signaling in health and disease. Methods: The dorsal horn of the spinal cord (lumbar L4-L6) was harvested on d9 post CCI or SHAM surgery. Tissues were immediately preserved in RNALater® overnight at 4°C. Total RNA was isolated the next day using RNeasy® Plus Universal Mini Kit (Qiagen, Germantown, MD USA) and quantitated by NanoDropTM (ThermoFisher Scientific). Total RNA samples were assessed for RNA quality and sequenced by the Genome Technology Access Center (GTAC) at Washington University in Saint Louis using Illumina HiSeq. Gene expression was normalized using Kallisto followed by Trimmed Mean of M-values methods and differential gene expression between CCI and SHAM groups were tested using negative binomial and generalized linear regression models by edgeR. Differentially expressed genes were defined as those with a fold change >=1.5-fold and a false discovery rate (FDR) <=0.05.