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

ABSTRACT: 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.

ORGANISM(S): Mus musculus

PROVIDER: GSE195817 | GEO | 2022/05/04

REPOSITORIES: GEO

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Project description:Rheumatoid arthritis is an inflammatory disease of the synovial joints that affects ~1% of the human population, with severe distress due to progressive joint inflammation and deformation. When addressing the links between specific components of the apoptotic cell clearance machinery and human disease, we noted a correlation between single nucleotide polymorphisms (SNPs) in ELMO1, DOCK2, and RAC1 genes and rheumatoid arthritis. ELMO1 is a cytoplasmic adapter protein that associates with DOCK2 and RAC1 to promote cytoskeletal reorganization needed for apoptotic cell uptake by phagocytes. We initially hypothesized that, since ELMO1 is linked to apoptotic cell clearance, loss of ELMO1 would lead to increased inflammation in arthritis. Contrary to the accumulation of apoptotic cells and greater disease severity that we predicted, we observed significantly reduced joint inflammation in two models of arthritis in mice lacking ELMO1. Using genetic and cell biological approaches in vivo and ex vivo, we determined that ELMO1 deficiency significantly reduces neutrophil recruitment to inflamed joints, but does not result in general inhibition of inflammatory responses. Through proteomic analyses, we find that ELMO1 protein associates with cellular receptors that contribute to neutrophil function in arthritis, and regulates C5a and LTB4 receptor-mediated activation and early neutrophil recruitment to the joints. Neutrophil-specific transcriptomics show that ELMO1 modulates neutrophil-specific gene expression that includes genes with known linkages to human arthritis. Finally, neutrophils from the peripheral blood of human donors that carry the SNP in ELMO1 associated with arthritis display increased migratory capacity, whereas ELMO1 knockdown reduces human neutrophil migration to LTB4. These data identify key ‘non-canonical’ roles for engulfment machinery components in arthritis, and ELMO1 as an important regulator of specific neutrophil receptors and signaling linked to arthritis.

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

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