Contribution of microRNA-27b-3p to synovial fibrotic responses in knee osteoarthritis

OBJECTIVES: Synovial fibrosis contributes to osteoarthritis (OA) pathology but the underlying mechanisms remain unknown. We have observed increased microRNA (miR)-27b-3p levels in synovial fluid of late-stage radiographic knee OA patients. Here, we determined the contribution of miR-27b-3p to synovial fibrosis. METHODS: Synovium sections obtained from Kellgren-Lawrence-graded knee OA patients and a mouse model of knee OA (destabilization of medial meniscus; DMM) were stained for miR-27b-3p using in situ hybridization. Effects of intra-articular injections of miR-27b-3p mimic into naïve mouse knee joints, and miR-27b-3p inhibitor in the DMM model were also examined. MiR-27b-3p mimic or inhibitor transfection experiments were performed on human OA fibroblast-like synoviocytes (FLS) using RT-qPCR array, RNA sequencing, RT-qPCR, Western blotting, immunofluorescence and migration assays. RESULTS: MiR-27b-3p expression increased in the synovium of knee OA patients and after DMM surgery in mice. Intra-articular injections of miR-27b-3p mimic injected in mouse knee joints induced a synovial fibrosis-like phenotype with increased synovitis scores and increased COL1A1 and α-SMA expression. In the DMM model, miR-27b-3p inhibitor decreased α-SMA with unchanged COL1A1 expression and synovitis scores. MiR-27b-3p mimic treatment of human OA FLS induced pro-fibrotic responses including increased migration and expression of key extracellular matrix (ECM) genes, while inhibitor transfection had opposite effects. RNA-sequencing identified a PPARG/ADAMTS8 signaling axis regulated by miR-27b-3p in OA FLS. MiR-27b-3p mimic-transfected OA FLS treated with the PPARG agonist rosiglitazone or ADAMTS8-siRNA exhibited altered expression of select ECM genes. CONCLUSIONS: This study demonstrates a key role of miR-27b-3p in ECM regulation associated with synovial fibrosis during OA

Macrophage migration inhibitory factor drives pathology in a mouse model of spondyloarthritis and is associated with human disease

Spondyloarthritis (SpA), a type 3 immunity-mediated inflammatory arthritis, is a systemic rheumatic disease that primarily affects the joints, spine, gut, skin, and eyes. Macrophage migration inhibitory factor (MIF) is a proinflammatory cytokine, yet MIF's pathological role in SpA is unknown. Here, we observed that the expression of MIF and its receptor CD74 is increased in blood and tissues of curdlan ((beta-glucan)-treated SKG mice, a mouse model of SpA. We found that neutrophils substantially expanded and produced MIF in curdlan-treated SKG mice and that human neutrophils from SpA patients secreted higher concentrations of MIF compared to healthy individuals. Although genetic deletion of Mif (Mif(-/-)) substantially suppressed the severity of SpA features, adoptive transfer of inflammatory neutrophils induced SpA pathology in curdlan-treated Mif(-/-)SKG mice; in contrast, blocking the function of neutrophils with anti-Gr-1 antibody suppressed the curdlan-induced SpA-like phenotype. We also determined that systemic MIF overexpression was sufficient to induce SpA-like clinical features in SKG mice with enhanced type 3 immunity, whereas SKG mice treated with a MIF antagonist prevented or attenuated curdlan-induced SpA manifestations. Mechanistically, we identified that MIF intensifies type 3 immunity by boosting human and mouse T regulatory cell (T-reg) acquisition of a T(H)17 cell-like phenotype, including the up-regulation of interleukin-17 (IL-17) and IL-22 in vitro. T-regs in blood and synovial fluids from SpA patients have a pathologic T(H)17 phenotype. These results indicate that MIF is a crucial regulator and a potential therapeutic target in type 3 immunity-mediated arthritis