Transcriptome analysis of trigeminal ganglia following masseter muscle inflammation in rats

Chronic pain in masticatory muscles is a major medical problem. Although mechanisms underlying persistent pain in masticatory muscles are not fully understood, sensitization of nociceptive primary afferents following muscle inflammation or injury contributes to muscle hyperalgesia. It is well known that craniofacial muscle injury or inflammation induces regulation of multiple genes in trigeminal ganglia, which is associated with muscle hyperalgesia. However, overall transcriptional profiles within trigeminal ganglia following masseter inflammation have not yet been determined. In the present study, we performed RNA sequencing assay in rat trigeminal ganglia to identify transcriptome profiles of genes relevant to hyperalgesia following inflammation of the rat masseter muscle.

Masseter inflammation differentially regulated >3500 genes in trigeminal ganglia. Predominant biological pathways were predicted to be related with activation of resident non-neuronal cells within trigeminal ganglia or recruitment of immune cells. To focus our analysis on the genes more relevant to nociceptors, we selected genes implicated in pain mechanisms, genes enriched in small- to medium-sized sensory neurons, and genes enriched in TRPV1-lineage nociceptors. Among the 2320 candidate genes, 622 genes showed differential expression following masseter inflammation. When the analysis was limited to these candidate genes, pathways related with G protein-coupled signaling and synaptic plasticity were predicted to be enriched. Inspection of individual gene expression changes confirmed the transcriptional changes of multiple nociceptor genes associated with masseter hyperalgesia (e.g., Trpv1, Trpa1, P2rx3, Tac1, and Bdnf) and also suggested a number of novel probable contributors (e.g., Piezo2, Tmem100, and Hdac9).

These findings should further advance our understanding of peripheral mechanisms involved in persistent craniofacial muscle pain conditions and provide a rational basis for identifying novel genes or sets of genes that can be potentially targeted for treating such conditions.