Sensory neuronal P2RX4 receptors controls BDNF signaling in inflammatory pain

Sarah Lalisse,Nathalie Linck,Lauriane Ulmann,Jennifer Hua,François Rassendren,Manon Lenoir

doi:10.1038/s41598-018-19301-5

Abstract

Chronic inflammatory and neuropathic pains are major public health concerns. Potential therapeutic targets include the ATP-gated purinergic receptors (P2RX) that contribute to these pathological types of pain in several different cell types. The purinergic receptors P2RX2 and P2RX3 are expressed by a specific subset of dorsal root ganglion neurons and directly shape pain processing by primary afferents. In contrast the P2RX4 and P2RX7 are mostly expressed in myeloid cells, where activation of these receptors triggers the release of various pro-inflammatory molecules. Here, we demonstrate that P2RX4 also controls calcium influx in mouse dorsal root ganglion neurons. P2RX4 is up-regulated in pain-processing neurons during long lasting peripheral inflammation and it co-localizes with Brain-Derived Neurotrophic Factor (BDNF). In the dorsal horn of the spinal cord, BDNF-dependent signaling pathways, phosphorylation of Erk1/2 and of the GluN1 subunit as well as the down regulation of the co-transporter KCC2, which are triggered by peripheral inflammation are impaired in P2RX4-deficient mice. Our results suggest that P2RX4, expressed by sensory neurons, controls neuronal BDNF release that contributes to hyper-excitability during chronic inflammatory pain and establish P2RX4 in sensory neurons as a new potential therapeutic target to treat hyperexcitability during chronic inflammatory pain.

Highlights

Pain is a sensory modality that is encoded by specialized nociceptive neurons in the dorsal root ganglion (DRG)
The expression of P2RX2 and P2RX3 in sensory neurons is well established and they are clearly involved in the transmission of inflammatory pain
Staining of DRG from P2RX4−/− mice with anti-βgalactosidase antibody can give an indication of the likely intended whereabouts of and report on normal p2rx[4] transcriptional activity19. ßgal immunostaining of P2RX4−/− DRG slices revealed a neuronal expression which was totally absent in wild-type as expected (Fig. 1B). ßgal immunostaining was observed in non-neuronal cells surrounding neuronal cell bodies

Summary

Introduction

Pain is a sensory modality that is encoded by specialized nociceptive neurons in the dorsal root ganglion (DRG). All the P2RX subunit mRNAs are expressed in DRG neurons[2], but evidence for their functional expression and potential involvement in pain processing remains limited to a few of them[3,4]. P2RX3 and P2RX2/3 receptors are mainly expressed in small-to-medium diameter C- and Aδ-nociceptive neurons, and are localized on both peripheral and central termini of the fibers[5]. Gene inactivation of p2rx[4] and p2rx[78–10] as well as highly potent specific P2RX7 antagonists[11] clearly implicated P2RX4 and P2RX7 in inflammatory and neuropathic pain the mechanisms underlying their respective contributions are not fully understood. Direct evidence for a function for P2RX4 in sensory neurons is still lacking

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Conclusion