Female-specific role of trigeminal dynorphin in temporomandibular disorder and its comorbidity - Project Summary: Epidemiological studies have shown that temporomandibular disorders (TMDs) pain and migraine headache are closely associated. Specifically, migraine headache appears to be more prevalent in women with myogenic TMD. However, the molecular mechanisms for TMD pain and its comorbidity with migraine as well as their sex differences remain poorly understood. Our long-term goal is to identify potential targets for developing a novel therapy for TMD and migraine overlapping pain. In our preliminary studies, we have developed an animal model to study TMD pain and its comorbidity with migraine by combining masseter muscle tendon ligation (MMTL)- produced myogenic TMD with systemic injection of nitroglycerin (NTG)-induced migraine-like pain, and this work has been published recently. Using RNA sequencing followed by qPCR confirmation, we identified trigeminal dynorphin as a potential female-specific therapeutic target for this overlapping pain condition. We observed for the first time that blockade of dynorphin in the spinal trigeminal nucleus caudalis (Sp5C) of female mice significantly inhibits myogenic TMD pain and diminishes TMD-enhanced migraine-like pain, and that Sp5C injection of dynorphin enables a non-sensitizing dose of NTG to produce persistent migraine-like pain in female mice, but not male mice. We further found that Sp5C antagonism of bradykinin receptor, but not kappa opioid receptor, inhibits such overlapping pain in female mice. Moreover, bradykinin receptor B2 (BKRB2), but not BKRB1, is expressed in the Sp5C, and MMTL plus NTG treatment decreases the binding of BKRB2 with neuronal nitric oxide synthase (nNOS) and increases NOS activity in the Sp5C, which will increase nitric oxide production and then promote migraine pain development. These results suggest that Sp5C dynorphin could play a female- specific role in TMD pain and its comorbidity with migraine through a non-opioid receptor mechanism. In this project, we will determine the central mechanisms by which trigeminal dynorphin contributes to TMD and migraine overlapping pain condition. Our hypothesis is that trigeminal dynorphin enhances TMD and migraine comorbidity in female mice by activating bradykinin receptor BKRB2 and then inhibiting its binding with nNOS to increase nitric oxide production in the Sp5C, thereby promoting TMD and migraine overlapping pain. To test this central hypothesis, we will use multidisciplinary approaches to characterize female-specific role of trigeminal dynorphin in TMD and migraine overlapping pain (Aim 1), determine the receptor mechanism for dynorphin in trigeminal pain regulation (Aim 2), and define the downstream pathway of dynorphin signaling in trigeminal nociceptive system (Aim 3). Collectively, we expect to reveal the central mechanisms by which trigeminal dynorphin specifically contributes to TMD and migraine comorbidity in females. The proposed research is significant since it will advance our understanding of TMD pain and its comorbidity. The proposed studies are innovative since these studies will identify a previously unrecognized female-specific role for dynorphin in trigeminal overlapping pain condition.
