Electrophysiological and transcriptomic correlates of neuropathic pain in human dorsal root ganglion neurons

Abstract

Neuropathic pain encompasses a diverse array of clinical entities affecting 7–10% of the population, which is challenging to adequately treat. Several promising therapeutics derived from molecular discoveries in animal models of neuropathic pain have failed to translate following unsuccessful clinical trials suggesting the possibility of important cellular-level and molecular differences between animals and humans. Establishing the extent of potential differences between laboratory animals and humans, through direct study of human tissues and/or cells, is likely important in facilitating translation of preclinical discoveries to meaningful treatments. Patch-clamp electrophysiology and RNA-sequencing was performed on dorsal root ganglia taken from patients with variable presence of radicular/neuropathic pain. Findings establish that spontaneous action potential generation in dorsal root ganglion neurons is associated with radicular/neuropathic pain and radiographic nerve root compression. Transcriptome analysis suggests presence of sex-specific differences and reveals gene modules and signalling pathways in immune response and neuronal plasticity related to radicular/neuropathic pain that may suggest therapeutic avenues and that has the potential to predict neuropathic pain in future cohorts.

A pharmacological interactome platform for discovery of pain mechanisms and targets

“…This suggests that recruitment of these immune cells to the peripheral nerve may be a key factor in driving persistent pain rather than plasticity in the transcriptomes of these cell types. This notion is supported by recent studies in rodent models (Krukowski et al, 2016;Davies et al, 2019;Yu et al, 2020) and patient transcriptional profiling (North et al, 2019). This cell-type and gene module bi-clustering approach reveals specific ligand-receptor interactions for peripheral cell types with sensory neurons that can be further mined for identification of new pain targets.…”

“…Macrophage recruitment by TNFa induces Mmp9 signaling which then promotes neuropathic pain after peripheral nerve injury (Shubayev et al, 2006). Il1b and Osm have also been identified as important pain signaling molecules in previous studies in rodent pain models (Sweitzer et al, 1999) and in DRG samples from neuropathic pain patients (North et al, 2019). The T-cell and natural killer cell cluster showed many genes associated with the TNFa super-family including Lta, Tnfsf14 and Tnfsf11 but also highlights the Ltbr gene which is paired with several of these T-cell and natural killer cell expressed ligands ( Figure 2C).…”

“…First, we used single cell RNA-seq (scRNA-seq) data from colon-innervating nociceptors in the mouse (Hockley et al, 2018) to illustrate how these neurons interact with normal and inflamed enteric glial cells (Delvalle et al, 2018). Second, we examined how human DRG (hDRG) neurons (Ray et al, 2018;North et al, 2019) interact with macrophages taken from the joints of people with rheumatoid arthritis (RA) (Kuo et al, 2019). Finally, we assessed how pancreatic cancer (Tomczak et al, 2015) drives pharmacological interactions with hDRG neurons that could reveal new targets to provide relief for this notoriously painful disease.…”

“…Genome-wide (GWAS) and transcriptome-wide (TWAS) association studies for identifying painrelated genes have been performed in multiple studies on mice (LaCroix-Fralish et al, 2011) and humans (Meloto et al, 2018;North et al, 2019) and including scRNA-seq studies (Hu et al, 2016). However, to the best of our knowledge, only one GWAS study has linked associated genes to protein signaling (Parisien et al, 2019).…”

Intra-articular AAV-PHP.S mediated chemogenetic targeting of knee-innervating dorsal root ganglion neurons alleviates inflammatory pain in mice

“…Peripheral sensitization, manifested by an increase in excitability of dorsal root ganglion (DRG) neurons, underlies many chronic pain pathologies, such as inflammatory arthritis (1). There is great heterogeneity of DRG neurons based upon gene expression (2,3) and functional attributes (4), and this heterogeneity is further compounded by target innervation (5,6). This variation in DRG neurons offers a unique opportunity to selectively tune the excitability of a distinct subset of DRG neuron in order to provide pain relief with reduced side-effects.…”