Dissecting the molecular control of immune cell accumulation in the inflamed joint

Mechanisms governing entry and exit of immune cells into, and out of, inflamed joints, remain poorly understood. We sought herein to identify the key molecular pathways regulating such migration. Using murine models of inflammation in conjunction with mice expressing a photoconvertible fluorescent protein we characterized the migration of cells from joints to draining lymph nodes (LN) and performed RNA-seq analysis on isolated cells, identifying genes associated with migration and retention. We further refined the gene list to those specific for joint inflammation. RNA-seq data revealed pathways and genes previously highlighted as characteristic of Rheumatoid arthritis (RA) in patient studies, validating the methodology. Focusing on pathways associated with cell migration, adhesion and movement, we identified genes involved in the retention of immune cells in the inflamed joint, namely JAM-A, and identified a role for such molecules in T cell differentiation in vivo. Thus, using a combination of novel cell tracking approaches and murine models of inflammatory arthritis we have identified genes, pathways and anatomically specific tissue signatures regulating cell migration in a variety of inflamed sites. This unique skin and joint specific dataset will be an invaluable resource for the identification of novel therapeutic targets for arthritis and other inflammatory disorders. Overall design: Bulk RNA-seq of non-migrated and migrated CD45+ leukocytes from inflammed ear and joint.