Calcium-sensing receptor and voltage-gated potassium channel type 7 crosstalk : a potential therapeutic target for persistent neuropathic orofacial pain /

Abstract

Neuropathic orofacial pain’s mechanisms remain uncertain with most current literature suggesting they entail alterations of the neuronal proteins controlling excitability. The calcium (Ca2+)-sensing receptor (CaSR) is a G protein coupled receptor (GPCR) that transduces changes of extracellular Ca2+ into intracellular signals, subsequently altering the activity of neuronal ion channels and thus excitability. The voltage-gated potassium (K+ ) channel type 7 (Kv7) is one of the principal regulators of neuronal excitability, and its dysfunction is associated with neuropathic pain. It has been reported that neuronal Kv7 channels are regulated by GPCR signalling, but any role the CaSR might play in regulation of Kv7 channel function is still unknown. This thesis explores the potential crosstalk between the CaSR and neuronal Kv7 channels and CaSR’s potential as a novel therapeutic target for neuropathic (orofacial) pain. Experiments were conducted in vitro using patch-clamp electrophysiology and molecular biology techniques. Stimulation of the CaSR induces depolarisation via Kv7.2/7.3 channel inhibition in recombinant cell models, human induced pluripotent stem cell (hiPSC)-derived nociceptive neuron-like cells and mouse dorsal root ganglion neurons. Investigation of the CaSR-Kv7.2/7.3 channel crosstalk pathway indicates the involvement of Gi/o proteinadenylate cyclase-cyclic adenosine monophosphate-protein kinase A signalling cascade. Based upon these findings, CaSR’s role in neuropathic pain (hyperexcitability) development and management was explored. A calcilytic (CaSR negative allosteric modulator) was shown to rescue hiPSC-derived nociceptive neuron-like cells from hyperexcitability induced by chronic administration of algogenic mediators. The systematic review performed also demonstrates that trigeminal nerve injury-induced neuropathic pain is associated with upregulation of calcitonin gene-related peptide (CGRP), a neuropeptide whose release can be controlled by neuronal Kv7 channels. The CaSR may, therefore, also play an indirect role in CGRP regulation. To conclude, this thesis demonstrates that the CaSR-Kv7.2/7.3 channel crosstalk regulates neuronal excitability and the hyperexcitability-suppressing effect of the calcilytic in vitro.