The cellular basis of protease-activated receptor 2-evoked mechanical and affective pain.

Shayne N Hassler,Moeno Kume,Juliet Mwirigi,Theodore J Price,Pradipta Ray,Dhananjay K Naik,Sergei N Belugin,Gregory Dussor,Ayesha Ahmad,Armen N Akopian,Josef Vagner,Stephanie Shiers,Michael D Burton,Scott Boitano,Andi Wangzhou

doi:10.1172/jci.insight.137393

Shayne N Hassler, Moeno Kume + Show 13 more

Open Access

https://doi.org/10.1172/jci.insight.137393

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Abstract

Protease-activated receptor 2 (PAR2) has long been implicated in inflammatory and visceral pain, but the cellular basis of PAR2-evoked pain has not been delineated. Although PAR2-evoked pain has been attributed to sensory neuron expression, RNA-sequencing experiments show ambiguous F2rl1 mRNA detection. Moreover, many pharmacological tools for PAR2 are nonspecific, acting also on the Mas-related GPCR family (Mrg) that are highly enriched in sensory neurons. We sought to clarify the cellular basis of PAR2-evoked pain. We developed a PAR2-conditional knockout mouse and specifically deleted PAR2 in all sensory neurons using the PirtCre mouse line. Our behavioral findings show that PAR2 agonist-evoked mechanical hyperalgesia and facial grimacing, but not thermal hyperalgesia, are dependent on PAR2 expression in sensory neurons that project to the hind paw in male and female mice. F2rl1 mRNA is expressed in a discrete population (~4%) of mostly small-diameter sensory neurons that coexpress the Nppb and IL31ra genes. This cell population has been implicated in itch, but our work shows that PAR2 activation in these cells causes clear pain-related behaviors from the skin. Our findings show that a discrete population of DRG sensory neurons mediate PAR2-evoked pain.

Highlights

Protease-activated receptors (PARs) are G protein–coupled receptors (GPCRs) that are targeted by endogenous proteases
Recent RNA-sequencing studies find very low expression levels for F2rl1 mRNA in dorsal root ganglion (DRG) neurons [14,15,16], a surprising finding given the large literature on Protease-activated receptor 2 (PAR2) signaling in DRG neurons [1]
Single-cell expression for F2rl1 was identified in a subpopulation of neurons with gene markers Il31ra and Nppb that coexpress Hrh1 and Mrgprx1, all genes thought to mark a set of sensory neurons that are important for itch sensation [13, 23, 24]

Summary

Introduction

Protease-activated receptors (PARs) are G protein–coupled receptors (GPCRs) that are targeted by endogenous proteases These proteases cleave the extracellular N-terminus of the receptor to reveal a tethered peptide ligand that induces cellular signaling [1]. Given that the Mrg family of receptors is highly enriched in dorsal root ganglion (DRG) neurons [12, 13], this complicates interpretation of some of the pharmacological literature on the topic Another emerging issue in the field is that coagulation factor II (thrombin) receptor-like 1 (F2rl1) gene expression in many bulk and single-cell DRG-sequencing data sets is either undetectable or on the threshold of detection limits [14, 15]. These findings are surprising given that PAR2 is widely considered an important therapeutic target for visceral pain with the model that PAR2 in visceral afferents is activated by endogenous proteases released during visceral inflammation [2, 17,18,19,20]

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