Targeting Nociceptors and Transient Receptor Potential Channels for the Treatment of Migraine

Migraine is a highly prevalent neurovascular disorder that is a leading cause of disability and consequent economic losses. The underlying mechanisms giving rise to this complex disorder remain elusive. Identification of CGRP as a key neuropeptide implicated in migraine has led to the development of several pharmacotherapies that target CGRP signaling. While these treatments represent a significant advance in this often-intractable disorder, there is still an unmet need for efficacious and safe therapies. Activation and sensitization of afferent nociceptive neurons innervating the meninges and its associated vasculature is postulated to play a central role in migraine. These nociceptors are rich in TRP channels, some of which have been implicated in migraine, thus making them promising migraine therapeutic targets. Recent studies in our lab identified a novel role for the TRPC4 channel in psoriasiform itch via regulation of CGRP release. In a separate study we found that a lipid mediator, RvD3, attenuated itch and pain as well as CGRP release via a TRPV1 mediated mechanism. Results of this research prompted the studies undertaken and described in this thesis including: 1) Elucidating the role of TRPC4 in migraine related pain, and 2) Investigation of resolvins as a potential novel class of migraine therapeutics. To probe these questions, we utilized a common, validated mouse model of migraine involving administration of nitroglycerin (NTG), a potent vasodilator and known migraine trigger. We characterized two experimental paradigms of this model: single injection of NTG to model acute episodic migraine, and repeated intermittent NTG injections to mimic development of chronic migraine. Next, we performed various behavioral assays to assess the effects of NTG in both experimental paradigms and concluded that mechanical hypersensitivity was the most robust behavioral endpoint. Both the TRPC4 and resolvin studies sought to uncover alternate targets for migraine therapy. In our TRPC4 study we showed that ML-204, a TRPC4 selective antagonist, prevented NTG-evoked mechanical hypersensitivity in our NTG model, and notably these effects were observed in male and female mice. To probe the mechanisms behind the analgesic effect of TRPC4 inhibition, we analyzed expression of migraine associated genes in DRG and found decreased CGRP transcripts in ML-204 treated male and female mice. We further revealed that TRPC4 is highly expressed in trigeminal ganglia (TG), specifically in CGRP-positive neurons, suggesting a functional role in TG related pain. Using cultured primary sensory neurons, we showed that ML-204 inhibited CGRP release in neurons treated with Englerin A, a TRPC4/5 agonist, thus demonstrating that TRPC4 inhibition has direct effects on sensory neurons. We next sought to determine if resolvins, which act as TRP channel modulators, would prevent migraine associated pain. The analgesic effects of several resolvins were tested in our acute NTG migraine model. Our results indicate that resolvin D3 (RvD3) prevented NTG evoked mechanical hypersensitivity in female mice. Altogether, our studies provide evidence for two novel approaches for treating migraine related pain: 1) Targeting TRPC4, a TRP channel not associated with thermoregulation, and 2) Using resolvins to indirectly target TRP channels.