Spinal PAR2 Activation Contributes to Hypersensitivity Induced by Peripheral Inflammation in Rats.

Petra Mrozkova,Jiri Palecek,Diana Spicarova

doi:10.3390/ijms22030991

Abstract

The mechanisms of inflammatory pain need to be identified in order to find new superior treatments. Protease-activated receptors 2 (PAR2) and transient receptor potential vanilloid 1 (TRPV1) are highly co-expressed in dorsal root ganglion neurons and implicated in pain development. Here, we examined the role of spinal PAR2 in hyperalgesia and the modulation of synaptic transmission in carrageenan-induced peripheral inflammation, using intrathecal (i.t.) treatment in the behavioral experiments and recordings of spontaneous, miniature and dorsal root stimulation-evoked excitatory postsynaptic currents (sEPSCs, mEPSCs and eEPSCs) in spinal cord slices. Intrathecal PAR2-activating peptide (AP) administration aggravated the carrageenan-induced thermal hyperalgesia, and this was prevented by a TRPV1 antagonist (SB 366791) and staurosporine i.t. pretreatment. Additionally, the frequency of the mEPSC and sEPSC and the amplitude of the eEPSC recorded from the superficial dorsal horn neurons were enhanced after acute PAR2 AP application, while prevented with SB 366791 or staurosporine pretreatment. PAR2 antagonist application reduced the thermal hyperalgesia and decreased the frequency of mEPSC and sEPSC and the amplitude of eEPSC. Our findings highlight the contribution of spinal PAR2 activation to carrageenan-induced hyperalgesia and the importance of dorsal horn PAR2 and TRPV1 receptor interactions in the modulation of nociceptive synaptic transmission.

Highlights

IntroductionNumerous endogenous proteases target proteaseactivated receptor 2 (PAR2) to cleave the extracellular amino terminus at canonical cleavage sites (trypsin and mast cell tryptase) [8] to activate canonical pathways of G protein-coupled receptor (GPCR) signaling or at distinct sites (neutrophil elastase or macrophage cathepsin S) to activate the biased mechanisms [7,9,10]
366791: 22.8 ± 2.7 pA and SB 366791/proteaseactivated receptor 2 (PAR2) activating peptide (AP): 20.4 ± 2.3 pA). These results indicate that, under the inflammatory conditions, PAR2 activation increased the Miniature Excitatory Postsynaptic Currents (mEPSCs) frequency in the superficial dorsal horn neurons, and this was mediated by the transient receptor potential vanilloid 1 (TRPV1) receptor activation
We show for the first time that the intrathecal application of the PAR2 antagonist FSLLRY-NH2 had a substantial antinociceptive effect on carrageenan-induced inflammation and reduced the enhanced activation of dorsal horn neurons demonstrated by recordings of mEPSC, sEPSC and evoked EPSC (eEPSC)

Summary

Introduction

Numerous endogenous proteases target PAR2 to cleave the extracellular amino terminus at canonical cleavage sites (trypsin and mast cell tryptase) [8] to activate canonical pathways of GPCR signaling or at distinct sites (neutrophil elastase or macrophage cathepsin S) to activate the biased mechanisms [7,9,10]. Several synthetic PAR2-activating peptides (PAR2 AP) were developed, and in our experiments, we used SLIGKV-NH2, which corresponds to the tethered ligand domain and mimics the canonical mechanism of activation by the endogenous activators [11,12]. Proteolytic cleavage at the canonical sites of PAR2 induces both signaling at the cell membrane and, endosomal signaling pathways [7,13,14]. Signaling from the plasma membrane involves the phospholipase C (PLC)-dependent production of inositol trisphosphate (IP3 ) and diacylglycerol (DAG), followed by an IP3 -stimulated release of

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