Lymphatic dysfunction drives inflammatory temporomandibular joint osteoarthritis (TMJOA) and pain

Temporomandibular joint (TMJ) arthritis is a craniofacial disorder characterized by joint dysfunction and orofacial pain. Despite of its established roles in fluid and immune regulation, lymphatic regulation, and function in TMJ remain unknown. Using genetic report mouse, uDISCO tissue clearing, and 3D volume imaging, we defined lymphatic vessel morphology, structure, anatomic location in adult mouse TMJ. We demonstrate in a mouse model of TMJ osteoarthritis (TMJOA) that arthritis induces inflammatory lymphangiogenesis and leads to impaired synovial lymphatic functions, including decreases in synovial influx and lymph node fluid drainage. To establish the causative link between lymphatic remodeling and TMJOA, we performed lymphatic loss- and gain-of-function studies. Lymphatic deficiency exacerbated cartilage defects, bone loss, synovitis, synovial fibrosis, and pain behaviors in TMJOA mice. Conversely, lymphatic activation via a hydrogel-mediated VEGF-C delivery to TMJ reduced TMJ pain, inflammation, and arthritis-like pathogenesis. Therefore, we defined lymphatic structure in TMJ and found that lymphatic dysfunction drives TMJOA pathogenesis and pain, suggesting its potential as a therapeutic target. Overall design: To elucidate the role of lymphatic vessels in TMJ arthritis, we employed a lymphatic loss-of-function approach using Prox1 mutant mice. TMJ arthritis was induced by intra-articular injection of complete Freund's adjuvant (CFA). Subsequently, TMJs from both wild-type and Prox1 mutant mice were harvested. Single-cell suspensions were prepared from dissected TMJ tissues and subjected to scRNA-seq for transcriptomic profiling and comparative analysis.