A Review of Temporomandibular Joint (TMJ) Synovitis and the Important Role of the Nuclear Protein, High Mobility Group Box 1 (HMGB1)

Studies identifying TMJ synovitis biomarkers are few and far between. During the late 1990s, Chuck Milam's oxidative stress and re-perfusion models elucidated the molecular mechanisms of TMJ synovitis which centrally involves the cytokines TNF-alpha, IL-1 beta, and IL-6. However, a new understanding of TMJ synovitis has been developed given the fields current knowledge on pattern recognition receptors (PRRs), damage-associated molecular patterns (DAMPs), pathogen-associated molecular patterns (PAMPs) and most notably, high mobility group box 1 (HMGB1). Among these molecular markers, the oxidation of HMGB1 plays a key role in promoting pathological inflammation. In this perspective, we explore the role of HMGB1 during TMJ synovitis and how a traumatized TMJ responds to different HMGB1 post translational modifications (PTMs). Specifically, synovial inflammation will be explored in the context of how different PTMs of HMGB1 directs leukocytes to produce chemokines or cytokines. We will also look at the different modifications of HMGB1 molecule via Reduction Oxygenation Reactions. These recently identified mechanisms provide a suitable addition to the currently understood molecular actions of TMJ synovitis noted by Milam and others in the late 1990s and early 2000s. We will then conclude with a discussion on the use of antibodies to the HMGB1 molecule for a variety of conditions: cancers, sepsis, liver disease, traumatic brain injuries and early intervention for joint synovitis along with the use of different delivery modalities.