Project Summary: Temporomandibular disorders (TMDs) are the most common temporomandibular joint (TMJ) pain condition; however, the underlying mechanisms remain poorly understood. As such, TMJ pain has long confounded medical and dental health care providers, and current treatment of chronic TMJ pain are often unsatisfactory. Our recent work suggests that gut microbiome perturbation and reduction of short-chain fatty acids (SCFAs) in the gut may be involved in the pathogenesis of TMJ pain and recovering SCFAs to normal levels could be developed into a new complementary non-opioid therapy for such pain. Our preliminary results further suggest that SCFAs may contribute to TMJ pain via an epigenetic mechanism. In this project, we will reveal specific epigenetic mechanisms by which SCFAs regulate chronic TMJ pain. Our hypothesis is that gut microbiome perturbation-produced SCFA reduction enhances chronic TMJ pain by epigenetically suppressing Gad2 transcription, and that SCFA supplementation inhibits such pain via normalizing the epigenetic regulation. To address this central hypothesis, we will conduct the studies proposed in three specific aims. In Aim 1, we will determine the therapeutic effect of SCFA supplementation on chronic TMJ pain. In Aim 2, we will identify the epigenetic mechanism that underlies the role of SCFAs in chronic TMJ pain. In Aim 3, we will define the role of vagus nerve in SCFA-mediated epigenetic regulation of chronic TMJ pain. Together, we expect to reveal a critical epigenetic mechanism that underlies the role of SCFAs in TMJ pain. The proposed research is significant since it will demonstrate whether and how SCFAs regulate TMJ pain. The proposed studies are innovative since these studies will identify a previously unrecognized role for SCFAs in the epigenetic regulation of TMJ pain.