Protease-activated receptor 2 enhances innate and inflammatory mechanisms induced by lipopolysaccharide in macrophages from C57BL/6 mice

New insight into the agonism of protease-activated receptors as an immunotherapeutic strategy

The activation and mobilization of immune cells play a crucial role in immunotherapy. Existing therapeutic interventions, such as cytokines administration, aim to enhance immune cell activity. However, these approaches usually result in modest effectiveness and toxic side effects, thereby restricting their clinical application. Protease-activated receptors (PARs), a subfamily of G protein-coupled receptors, actively participate in the immune system by directly activating immune cells. The activation of PARs by proteases or synthetic ligands can modulate immune cell behavior, signaling, and responses to treat immune-related diseases, suggesting the significance of PARs agonism in immunotherapy. However, the agonism of PARs in therapeutical applications remains rarely discussed, since it has been traditionally considered that PARs activation facilitates disease progressions. This review aims to comprehensively summarize the activation, rather than inhibition, of PARs in immune-related physiological responses and diseases. Additionally, we will discuss the emerging immunotherapeutic potential of PARs agonism, providing a new strategic direction for PARs-mediated immunotherapy.

PAR2 activation in the dura causes acute behavioral responses and priming to glyceryl trinitrate in a mouse migraine model

BACKGROUND

Migraine is a severely debilitating disorder that affects millions of people worldwide. Studies have indicated that activation of protease-activated receptor-2 (PAR2) in the dura mater causes headache responses in preclinical models. It is also well known that vasodilators such as nitric oxide (NO) donors can trigger migraine attacks in migraine patients but not controls. In the current study we examined whether activation of PAR2 in the dura causes priming to the NO donor glyceryl trinitrate (GTN).

METHODS

A preclinical behavioral model of migraine was used where stimuli (PAR2 agonists: 2at-LIGRL-NH₂ (2AT) or neutrophil elastase (NE); and IL-6) were applied to the mouse dura through an injection made at the intersection of the lamdoidal and sagittal sutures on the skull. Following dural injection, periorbital von Frey thresholds and facial grimace responses were measured until their return to baseline. GTN was then given by intraperitoneal injection and periorbital hypersensitivity and facial grimace responses observed until they returned to baseline.

RESULTS

We found that application of the selective PAR2 agonist 2at-LIGRL-NH₂ (2AT) onto the dura causes headache-related behavioral responses in WT but not PAR2^-/- mice with no differences between sexes. Additionally, dural PAR2 activation with 2AT caused priming to GTN (1 mg/kg) at 14 days after primary dural stimulation. PAR2^-/- mice showed no priming to GTN. We also tested behavioral responses to the endogenous protease neutrophil elastase, which can cleave and activate PAR2. Dural neutrophil elastase caused both acute responses and priming to GTN in WT but not PAR2^-/- mice. Finally, we show that dural IL-6 causes acute responses and priming to GTN that is identical in WT and PAR2^-/- mice, indicating that IL-6 does not act through PAR2 in this model.

CONCLUSIONS

These results indicate that PAR2 activation in the meninges can cause acute headache behavioral responses and priming to an NO donor, and support further exploration of PAR2 as a novel therapeutic target for migraine.