MRGX1-TRPAI in inflammatory pain signalling

Abstract

Painful stimuli are detected at the peripheral terminals of specialised primary sensory neurons known as nociceptors. Nociceptors detect noxious (painful) stimuli to evoke pain sensation via the activation of Transient Receptor Potential Ankyrin 1 (TRPA1). TRPA1 activity can be modulated by G-Protein Coupled Receptors (GPCR), leading to sensitisation and hyperalgesia (enhanced pain sensation), typically seen in inflammatory pain conditions. Human Mas-related G-protein-coupled receptor X1 (MRGX1) is a promising target for pain relief, mainly because of its restricted expression in nociceptors. To date however, the role MRGX1 plays in inflammatory pain regulation in humans remains unclear as functional nociceptors from humans are not available and rodents do not harbour MRGX1-encoding genes. Here, we generated in vitro models of human nociceptors from 1) neural crest stem cells using a previously validated method and 2) human neural progenitors using magnetic-activating cell sorting (MACs) technology, both derived from human dental pulp as well as an ex-vivo model of trigeminal nerves. Immunofluorescent staining revealed MRGX1 expression ex-vivo in dental afferents, which was more intense in inflamed versus healthy dental pulps. Endogenous MRGX1 protein expression was confirmed in both in-vitro models of human nociceptors. The functionality of MRGX1 and its interaction with TRPA1, as well as the mechanisms involved was confirmed by calcium imaging. Results showed that MRGX1 indirectly activates TRPA1 via IP3- mediated store release of calcium ions and sensitises TRPA1 to agonist stimulation via PKC. MRGX1 modulates TRPA1 activity via two distinct xxi mechanisms suggesting an important nociceptive role. MRGX1 therefore is a potential pain relief target with minimal side effects due to restricted neuronal expression.

Date of Award	Jul 2020
Original language	English
Awarding Institution	Queen's University Belfast
Sponsors	Animal Free Research UK
Supervisor	Ikhlas El Karim (Supervisor), Fionnuala Lundy (Supervisor) & Tim Curtis (Supervisor)