Human Mas-Related G Protein-Coupled Receptors-X1 Induce Chemokine Receptor 2 Expression in Rat Dorsal Root Ganglia Neurons and Release of Chemokine Ligand 2 from the Human LAD-2 Mast Cell Line

Abstract

Primate-specific Mas-related G protein-coupled receptors-X1 (MRGPR-X1) are highly enriched in dorsal root ganglia (DRG) neurons and induce acute pain. Herein, we analyzed effects of MRGPR-X1 on serum response factors (SRF) or nuclear factors of activated T cells (NFAT), which control expression of various markers of chronic pain. Using HEK293, DRG neuron-derived F11 cells and cultured rat DRG neurons recombinantly expressing human MRGPR-X1, we found activation of a SRF reporter gene construct and induction of the early growth response protein-1 via extracellular signal-regulated kinases-1/2 known to play a significant role in the development of inflammatory pain. Furthermore, we observed MRGPR-X1-induced up-regulation of the chemokine receptor 2 (CCR2) via NFAT, which is considered as a key event in the onset of neuropathic pain and, so far, has not yet been described for any endogenous neuropeptide. Up-regulation of CCR2 is often associated with increased release of its endogenous agonist chemokine ligand 2 (CCL2). We also found MRGPR-X1-promoted release of CCL2 in a human connective tissue mast cell line endogenously expressing MRGPR-X1. Thus, we provide first evidence to suggest that MRGPR-X1 induce expression of chronic pain markers in DRG neurons and propose a so far unidentified signaling circuit that enhances chemokine signaling by acting on two distinct yet functionally co-operating cell types. Given the important role of chemokine signaling in pain chronification, we propose that interruption of this signaling circuit might be a promising new strategy to alleviate chemokine-promoted pain.

Pharmacology and Signaling of MAS-Related G Protein–Coupled Receptors

“…However, their similarities notwithstanding, several pharmacological differences between murine and rat MRGPRC have also been observed (see Fig. 4B): NPFF peptides displayed lower potency to activate the rat MRGPRC compared with the murine counterpart, and dynorphin-14 did not activate rat MRGPRC at all (Han et al, 2002;Grazzini et al, 2004;Solinski et al, 2013). Regarding efficacy, g 2 -MSH and BAM peptides are the most efficacious activators of both MRGPRC, with g 2 -MSH clearly surmounting BAM peptides (Solinski et al, 2013).…”

“…However, high amounts of MRGPRB3 and -8 transcripts, as well as lower copy numbers of the remaining three rat MRGPRB members, were measured in rat peritoneal mast cells, whereas transcripts of MRGPRA or -C were not present in these cells (Tatemoto et al, 2006). Recently, MRGPRX1 and -2 expression was also shown in human mast cells (Tatemoto et al, 2006;Subramanian et al, 2011b;Solinski et al, 2013). Thus, human MRGPRX mirror the expression pattern of rodent MRGPRB and -A/C, lending support to the current theory of MRGPR evolution, implying that MRGPRX1 and -2 genes inherited promoter elements from ancestral MRGPRB and -A/C genes (for details see section II.D).…”

“…MAS-Related G Protein-Coupled Receptors Heo et al, 2007a;Solinski et al, 2010Solinski et al, , 2013. Among these peptides are g 2 -melanocyte stimulating hormone (g 2 -MSH), BAM peptides, dynorphin-14, and proneuropeptide-FF-A peptides.…”

“…4B): NPFF peptides displayed lower potency to activate the rat MRGPRC compared with the murine counterpart, and dynorphin-14 did not activate rat MRGPRC at all (Han et al, 2002;Grazzini et al, 2004;Solinski et al, 2013). Regarding efficacy, g 2 -MSH and BAM peptides are the most efficacious activators of both MRGPRC, with g 2 -MSH clearly surmounting BAM peptides (Solinski et al, 2013). Using in silico modeling and site-directed mutagenesis, Heo and coworkers (2007a) Several peptides that are now recognized as MRGPRC agonists were previously shown to activate distinct receptors from other GPCR families, e.g., g 2 -MSH also binds to melanocortin 3 receptors and some BAM peptides to opioid receptors (OR).…”

“…MRGPRC may also be responsible for inflammatory pain, because complete Freund's adjuvant (CFA)-induced thermal hyperalgesia was alleviated by RNAi-mediated MRGPRC knockdown in rats (Ndong et al, 2009). (Han et al, 2002;Lembo et al, 2002;Grazzini et al, 2004;Liu et al, 2009Liu et al, , 2011Solinski et al, 2013). For simplicity, ligands that exhibit potencies more than 10 times lower than g 2 -MSH (in the case of MRGPRC) or BAM8-22 (in the case of MRGPRX1) are not shown.…”