Macrophages in human autoimmune tissue pathology

About This Grant

PROJECT SUMMARY Rheumatoid arthritis (RA) compromises the health of ~1% of the population, and identifying a medication that works well for a given individual is challenging. It remains unclear why RA patients respond differently to the same medications, and some remain refractory to all treatments. It is believed that RA may encompass several endotypes driven by distinct pathogenic mechanisms that would be responsive to distinct therapies. To this end, large-scale studies have recently identified putative endotypes defined by synovial tissues molecular patterns. This includes efforts in the UK (led by Pitzalis) and in the U.S. (by the Accelerating Medicines Partnership (AMP) consortium), where both studies concluded that up to one-third of RA patients have myeloid-rich synovial tissue, notably distinct from the widely described lymphocyte-rich tissues. Data from the AMP report (Zhang et al. Nature 2023), identified that the predominant myeloid population in myeloid-rich tissues is a non-inflammatory monocyte-derived macrophage state. Our preliminary data cross referencing transcriptomic datasets show that the signature of “non-inflammatory” macrophages in RA joints resembles that of Pro-Fibrotic monocyte-derived macrophages from tissues affected by fibrosis. Further, we have defined their functional pathways to include wound-healing/fibrosis, coagulation, lipid metabolism, and proliferation (markers including: SPP1, SERPINE1, FABP5, and CSF1, respectively). Using spatial transcriptomics, we now find these RA synovial Pro-Fibrotic macrophages at high densities in fibrin-rich deposits at the synovial lining. In healing wounds, fibrin deposits serve as a template for the generation of new connective tissue. Notably, the synovium lacks an epithelial layer that, in other tissues, limits where the new tissue can form. Thus, we hypothesize in RA synovium, Pro-Fibrotic macrophages together with fibroblasts and fibrin matrices drive pathologic tissue outgrowth and that targeting this process will reduce pannus formation. We therefore aim to define how Pro-Fibrotic macrophages differentiate in RA synovium and modify fibrin deposits using paired single-nuclei transcriptomics-epigenomics analyses and assays testing fibrin coagulation, degradation and ingestion (Aim 1). To determine how Pro-Fibrotic macrophages impact RA synovial tissue outgrowth, we will use spatial transcriptomics of RA patient synovium to quantify the extent of Pro-Fibrotic macrophage localization to fibrin deposits, and test how Pro-Fibrotic macrophages embedded in fibrin impact synovial fibroblast entry and collagen production using a microfluidic chamber system (Aim 2). Lastly, we will test how “anti-inflammatory” RA medications (e.g. methotrexate, TNFi, IL6Ri) affect Pro- Fibrotic and Inflammatory macrophages in RA patient synovial ex vivo drug assays and in fibrin coagulation and clearance assays. Using data from the new AMP-AIM consortium, we will test how patient drug response rates relate to Pro-Fibrotic macrophage (v. lymphocyte) levels in synovial biopsies via spatial transcriptomics (Aim 3). Completion of these aims will extend our understanding of mechanisms underlying treatment discrepancies and advance development of precision treatment strategies in RA patients based on molecular patterns of disease.