TMJ-on-a-chip for delineating multi-tissue crosstalk in inflammation and pathophysiological mechanical loadings - Project summary Over 80% of symptomatic temporomandibular joint disorders (TMJD) patients have a TMJ disc displacement, linked with osteoarthritis (OA). The abnormal jaw mechanics involved with TMJ disc displacement can lead to disc thinning and perforation, frequently progressing into OA. In the last decade, we and others have actively explored regenerative approaches for severely damaged TMJ discs with some promising pre-clinical outcomes. However, the regenerative strategies for TMJ disc should be evaluated considering the abnormal joint mechanics and inflammation caused by joint trauma or disc displacement. In addition, TMJ is a multi-tissue organ where multiple tissues, including cartilage, bone, TMJ discs, synovium, ligaments, and surrounding fat, are believed to interact with each other for joint function, homeostasis, disease initiation, and progress. Unfortunately, we have an extremely limited understanding of multi-tissue crosstalk in TMJ, linked with a paucity of reliable experimental models. The objective of this proposal is to develop and validate a patient-specific TMJ-on-a-chip (TMJoC) model for investigating multi-tissue crosstalk regulating TMJ disc injury and healing under inflammation and pathophysiological mechanical stimulation. Our team has extensive experience in joint-on-a-chip (JoC) for multi- tissue interactions in the knee joint during meniscus injury and healing. Based on the expertise, we have developed a TMJoC integrated into a novel TMJ disc-specific bioreactor, consisting of i) a joint cavity where discs are cultured and physio/chemically stimulated, ii) bioprinted synovial membrane layered with lining macrophages and synovial mesenchymal stem/progenitor cells (MSCs), iii) tissue-engineered ligaments, iv) engineered osteochondral tissues and v) MSCs-derived adipose tissues. Gene expression profiles of the engineered tissues were validated using RNA-seq data from human tissues. Tissue compartments were separated by semi-permeable membranes, and under-layered microfluidic channels supply tissue-specific media. Mechanical loading units replicating patient-specific condyle and fossa anatomy are integrated to apply physiological loading to TMJ discs in the TMJoC via 3-axis micro-precise motion controllers. Our preliminary data suggest that the healing of TMJ disc perforation by our well-established bioactive glue was interfered with IL-1β, and physiological loading attenuates the harmful effect of IL-1β. Interactions with synovium further hampered disc healing with elevated pro-inflammatory cytokines, mitigated by an existence of adipose tissue. scRNA-seq with CellChat analysis suggested robust communications between adipocytes, MSCs, and macrophages in discs healing, highlighting fat's notable metabolic and anti-inflammatory functions. As supported by solid preliminary data, we aim to 1) determine the roles of multi-tissue crosstalk in TMJ under inflammation and pathophysiological mechanical loadings and 2) establish a patient-specific TMJoC from human iPSCs. The proposed TMJoC, as a patient-specific platform, has a wide range of research applications, including TMJ homeostasis, metabolism, biology of disease initiation and progress.
