Synovium Immunoprivilege and the Modulation of Resident Synovial Macrophage Functions in Lyme Arthritis - Lyme Arthritis is indicative of disseminated B. burgdorferi that has invaded the joint space to cause both acute infection and/or relapsing/remitting disease. Even if appropriately treated, Lyme Arthritis (LA) may transition to Antibiotic-Refractory Lyme Arthritis (ARLA), a condition with significant morbidity and long-term disability. The transition from LA to ARLA is not well understood, but understanding how an infectious arthritis becomes an inflammatory arthritis is essential to both treating and preventing this disease of growing prevalence. This is in line with NIAMS’ mission of supporting research into the causes, treatment, and prevention of arthritis. The central hypothesis of this proposal is that the joint space is immune-privileged and typically protected by anti-inflammatory/M2 resident synovial macrophages. In ARLA, however, these intimal-lining macrophages transition to an inflammatory M1 phenotype. Our rationale is that a similar mechanism has been observed in Rheumatoid Arthritis (RA), where these intimal lining RSMs dissociate tight junctions to allow circulating cells and/or pathogens to gain entry to the typically acellular synovial fluid (SF). The objective of this proposal is to determine the role of intimal and sub-intimal RSMs during B. burgdorferi infection and development of ARLA. We intend to evaluate this using 3 aims: 1) quantify the integrity of the RSM intimal lining during ex vivo infection using confocal microscopy and histomorphometry; 2) evaluate phagocytic and ROS capabilities of in situ RSMs exposed to B. burgdorferi using RNAscope and compare this to alterations in the immune transcriptome using spatial transcriptomics; 3) relate loss of barrier integrity to bone/cartilage damage based on SF and media transfer experiments. Our long-term goal is to prevent the transition of LA to ARLA and use the same principles to prevent the transition of any infectious arthritis to inflammatory arthritis. The significance of this proposal is in its focus on mechanisms of tick-borne disease, a growing public health concern; but also, in the likely universal mechanism of joint space inflammation, and how lessons learned through these experiments can be applied to other forms of infections and inflammatory arthritis. The innovation of this proposal is in the pioneering use of primary human synovial explants to truly evaluate human-relevant disease processes, in addition to the novel methodologies of RNAscope and spatial transcriptomics. The former will provide direct visualization of B. burgdorferi in relation to RSM tight junction integrity, ROS generation, and phagocytosis; the latter will provide functional immune information directly comparing differing layers of the synovium simultaneously. We expect these experiments to provide not only great insight into the initiation and propagation of the joint-specific immune response, but also provide new therapeutic targets for LA and ARLA treatment. This work will have a cross- specialty impact on mechanisms of infection, autoimmunity, synovial pathology, all of which will be applicable to patients suffering from a multitude of arthridities. This proposal is essential to the PI’s career goal of reaching independence, and has essential training provided by a panel of successful, multi-specialty mentors.
