Transcriptional profiling of murine macrophages stimulated with cartilage fragments revealed a strategy for treatment of progressive osteoarthritis

Accumulating evidence suggests that synovitis is associated with osteoarthritic process. Macrophages play principal role in development of synovitis. Our earlier study suggests that interaction between cartilage fragments and macrophages exacerbates osteoarthritic process. However, molecular mechanisms by which cartilage fragments trigger cellular responses remain to be investigated. Therefore, the current study aims at analyzing molecular response of macrophages to cartilage fragments. To this end, we analyzed the transcriptional profiling of murine macrophages exposed to cartilage fragments by RNA sequencing. A total 153 genes were differentially upregulated, and 105 genes were down-regulated in response to cartilage fragments. Bioinformatic analysis revealed that the most significantly enriched terms of the upregulated genes included scavenger receptor activity, integrin binding activity, TNF signaling, and toll-like receptor signaling. To further confirm our results, immunohistochemical staining was performed to detected regulated molecules in synovial tissues of OA patients. In consistence with RNA-seq results, MARCO, TLR2 and ITG alpha 5 were mainly detected in the intima lining layer of synovial tissues. Moreover, blockade of TLR2 or ITG alpha 5 but not Marco using specific antibody significantly reduced production of TNF-alpha in stimulated macrophages by cartilage fragments. Our data suggested that blocking TLR2 or ITG alpha 5 might be promising therapeutic strategy for treating progressive osteoarthritis

Flightless I is a catabolic factor of chondrocytes that promotes hypertrophy and cartilage degeneration in osteoarthritis

Synovial macrophages that are activated by cartilage fragments initiate synovitis, a condition that promotes hypertrophic changes in chondrocytes leading to cartilage degeneration in OA. In this study, we analyzed the molecular response of chondrocytes under condition of this type of stimulation to identify a molecular therapeutic target. Stimulated macrophages promoted hypertrophic changes in chondrocytes resulting in production of matrix-degrading enzymes of cartilage. Among the top-upregulated genes, FliI was found to be released from activated chondrocytes and exerted autocrine/paracrine effects on chondrocytes leading to an increase in expression of catabolic and hypertrophic factors. Silencing FliI in stimulated cells significantly reduced expression of catabolic and hypertrophic factors in cocultured chondrocytes. Our further results demonstrated that the FliI-TLR4-ERK1/2 axis is involved in the hypertrophic signaling of chondrocytes and catabolism of cartilage. Our findings provide a new insight into the pathogenesis of OA and identify a potentially new molecular target for diagnostics and therapeutics