ABSTRACT Current pharmacologic therapies for TMD pain are largely ineffective and plagued with side effects because their mechanisms of action to TMD pain have not been validated. Validation of potential pain targets for TMD pain can facilitate the development of mechanism-based approaches. Emerging evidence suggests that lysophosphatidic acid (LPA)/LPA receptor (LPAR) signaling is a promising target for spinally-mediated neuropathic pain. However, whether it contributes to trigeminally-mediated TMD pain, which involves anatomically and functionally unique target tissues and distinct etiology, is not known. In addition, there are several roadblocks which hamper the translatability of LPA/LPAR to pain therapeutics: 1) this potential pain target has been rarely validated in human tissues; 2) its mechanisms in pain, particularly where and how it drives pain, remain poorly understood; and 3) its addiction liability has not been evaluated. The objective of this project is to identify and validate LPA/LPAR in trigeminal ganglion (TG) sensory neurons as a novel mechanistic target for the treatment of TMD pain. Our preliminary results revealed that LPA levels in the plasma and TGs are elevated in mouse models of chronic TMD. In line with results from mice, we also found that LPA in plasma is increased in TMD patients and, importantly, positively correlated with pain intensity ratings. In addition, immunostaining analysis showed that LPAR are localized in both mouse and human TG sensory neurons. Systemic inhibition of LPA/LPAR or local inhibition of LPA/LPAR in TG neurons-innervating TMJ tissues attenuated mechanical pain and masticatory pain in mouse models of TMD, while they did not show addictive effects. Moreover, electrophysiological recording revealed LPA/LPAR can sensitize PIEZO2, a mechanical transducer, in response to mechanical stimuli. Therefore, we hypothesize that LPA/LPAR in TG neurons drive TMD pain via PIEZO2 ion channel. This central hypothesis will be tested in experiments that seek to: 1) determine the contribution of elevated LPA to TMD pain; 2) dissect the contribution of LPAR in TG sensory neurons to LPA-driven TMD pain; and 3) examine whether LPA/LPAR in TG neurons drive TMD pain via PIEZO2 ion channel. The proposed experiments will include rigorous validation using complementary clinically-relevant animal models, pain measures, human tissues and replication of key experiments across laboratories. We will also perform extensive experiments evaluating the addiction liability of LPA/LPAR. Success completion of this project will substantively advance our understanding of TMD pain mechanisms. Importantly, the proposal is clinically significant because it validates LPA/LPAR as a mechanistic target with exciting potential to prevent chronic TMD pain.

PROJECT NARRATIVE Temporomandibular disorder (TMD), characterized by mechanical pain and masticatory allodynia, is the most common form of orofacial pain and negatively impact patients’ quality of life. In this project, we aim to identify and validate if and how LPA/LPAR signaling contributes to TMD pain. Success of this project may open new doors for development of safe and effective methods to prevent and treat TMD pain.