The role of Nav1.9 in the modulation of inflammatory pain: is GPR35 involved?

G protein-coupled receptor (GPCR) 35 (GPR35) is an orphan receptor thought to play a role in inflammatory pain. Although some interaction partners have been proposed, the major functional pathways in which GPR35 is involved remain undiscovered. However, GPR35 agonists can induce pain relieve in mouse inflammatory pain models and inhibit adenylate cyclase activation upon application of prostaglandin E2 (PGE2), a pro-inflammatory mediator. The voltage-gated sodium channel Nav1.9 also plays a role in inflammatory pain. Motivated by 1) preliminary RNAseq data revealing the abundant expression of GPR35 in a subset of Nav1.9+ dorsal root ganglia (DRG); 2) previous reports suggesting functional links between Nav1.9 and GPCRs; and 3) similar biological roles in sensory perception, we now want to investigate a possible interaction of this channel with GPR35. To investigate this hypothesis, we defined three major goals. First, we plan to create a stable human Nav1.9 cell line for electrophysiological recordings. Second, we will determine the effect of GPR35 on Nav1.9 gating properties using patch-clamp experiments in the absence/presence and before/after application of GPR35 (ant)agonists. Third, we aim to examine GPR35-linked Nav1.9 function in inflammatory pain by comparison of PGE2-elicited inflammatory hyperalgesia in wild-type, Nav1.9-/-, and GPR35-/- mouse lines using the Von Frey assay as well as the hot/cold plate test.