Protease Activated Receptor 2 (PAR2) Activation Causes Migraine-Like Pain Behaviors in Mice

Background Pain is the most debilitating symptom of migraine. The cause of migraine pain likely requires activation of meningeal nociceptors. Mast cell degranulation, with subsequent meningeal nociceptor activation, has been implicated in migraine pathophysiology. Degranulating mast cells release serine proteases that can cleave and activate protease activated receptors. The purpose of these studies was to investigate whether protease activated receptor 2 is a potential generator of nociceptive input from the meninges by using selective pharmacological agents and knockout mice. Methods Ratiometric Ca⁺⁺ imaging was performed on primary trigeminal and dural cell cultures after application of 2at-LIGRL-NH₂, a specific protease activated receptor 2 agonist. Cutaneous hypersensitivity and facial grimace was measured in wild-type and protease activated receptor 2⁻ᐟ⁻ mice after dural application of 2at-LIGRL-NH₂ or compound 48-80, a mast cell degranulator. Behavioral experiments were also conducted in mice after dural application of 2at-LIGRL-NH₂ (2AT) in the presence of either C391, a selective protease activated receptor 2 antagonist, or sumatriptan. Results 2at-LIGRL-NH₂ evoked Ca²⁺ signaling in mouse trigeminal neurons, dural fibroblasts and in meningeal afferents. Dural application of 2at-LIGRL-NH₂ or 48-80 caused dose-dependent grimace behavior and mechanical allodynia that were attenuated by either local or systemic application of C391 as well as in protease activated receptor 2⁻ᐟ⁻ mice. Nociceptive behavior after dural injection of 2at-LIGRL-NH₂ was also attenuated by sumatriptan. Conclusions Functional protease activated receptor 2 receptors are expressed on both dural afferents and fibroblasts and activation of dural protease activated receptor 2 produces migraine-like behavioral responses. Protease activated receptor 2 may link resident immune cells to meningeal nociceptor activation, driving migraine-like pain and implicating protease activated receptor 2 as a therapeutic target for migraine in humans.