Src family kinases as a molecular switch in migraine pathogenesis

Background: Migraine has complicated pathological processes, including cortical spreading depression (CSD), trigeminovascular sensitisation, neuroinflammation, and abnormal brain perfusion. However, the underlying molecular mechanism is still elusive. Src family kinases (SFKs), the non-receptor tyrosine kinases, have shown an emerging role in migraine pathogenesis. Direct brain delivery of a SFKs inhibitor PP2 reduces CSD susceptibility, mechanical allodynia, and cerebral arterial contraction in animal models of migraine. However, whether and how systemic modulation of SFKs activity mediates these pathological events are unclear. Aims: This project aims to understand the effects of (1) systemic deactivation of SFKs on CSD and CSD-induced cortical neuroinflammation reflected by inflammatory cytokine gene expression in rats and (2) modulating SFKs activity on trigeminal ganglion (TG) activation and sensitisation reflected by the known target for migraine therapy calcitonin gene-related peptide (CGRP) release and inflammatory cytokine release and gene expression in mouse TG. Furthermore, (3) how SFKs mediate the above phenomena is investigated by examining the hypotheses that SFKs transmit P2X7 receptor pathway to facilitate CSD and CSD-induced neuroinflammation and that SFKs transmit a stress-sensing channel transient receptor potential ankyrin 1 (TRPA1) pathway to facilitate TG activation and sensitisation. Methods: Multi-disciplinary methods were used in this project - high potassium-induced CSD induction and recording in rats via electrophysiology and in mouse brain slices via intrinsic optical imaging; mouse TG culture; quantitative polymerase chain reaction for gene expression analysis; glutamate assay, enzyme-linked immunosorbent assay, multiplex immunoassay, western blot for protein level analysis, and immunohistochemistry. Results: Systemic deactivation of SFKs by their inhibitor PP2 reduced CSD susceptibility and CSD-induced interleukin 1 beta (IL-1β) and tumour necrosis factor alpha gene expression in rat cerebral cortices ipsilateral to CSD. Disrupting the interaction between SFKs and P2X7 receptor by an inhibitory peptide TAT-P2X7 reduced CSD susceptibility and CSD-induced IL-1β gene expression and glutamate release in mouse brain slices. The reduced CSD susceptibility was restored by activation of N-methyl-Daspartate (NMDA) receptor using its agonist NMDA. Besides, deactivation of SFKs by another SFKs inhibitor saracatinib dose-dependently reduced CGRP release and the inflammatory cytokines IL-1β, C-X-C motif ligand 1, C-C motif ligand 2 (CCL2) release and IL-1β, CCL2 gene expression in mouse TG, which alleviated TG activation and sensitisation. Furthermore, SFKs activity was increased by activation of TRPA1 using its agonist umbellulone via protein kinase A to facilitate TRPA1-dependent CGRP release and IL-1β gene expression in mouse TG. Conclusion: These findings, for the first time, reveal that: 1. SFKs contribute to CSD susceptibility and CSD-induced cortical neuroinflammation by transmitting P2X7 receptor signalling involving glutamatergic pathway activation; 2. SFKs contribute to TG activation and sensitisation by transmitting TRPA1 signalling. It is concluded that SFKs facilitate central sensitisation and trigeminovascular sensitisation in migraine pathogenesis by being a molecular switch for different pathways, which highlights the therapeutic potential of SFKs-targeted migraine therapy.