Abstract
Joint injuries often result in inflammation and cartilage defects. When inflamed, the synovium secretes factors that prevent successful cartilage repair by inhibiting chondrogenic differentiation of progenitor cells. In particular the pro-inflammatory macrophages in the synovium are indicated to contribute to this anti-chondrogenic effect. Thus, we aimed to counteract the anti-chondrogenic effect of inflamed synovium by modulating synovial inflammation and its macrophages. Synovium tissue obtained from osteoarthritic patients undergoing a total knee replacement was cut into explants and cultured for 72 hours +/− 1 µM of the anti-inflammatory drug triamcinolone acetonide (TAA) (Sigma Aldrich). TAA significantly decreased gene expression of TNFA, IL1β and IL6, and increased expression of CCL18, IL1RA in synovial explants (all with p < 0.001). On the other hand, TAA significantly decreased the percentages of pro-inflammatory CD14+/CD80+ and CD14+/CD86+ macrophages in the synovium (both p < 0.001) as assessed by flow cytometry analyses. The percentages of anti-inflammatory CD14+/CD163+ macrophages, is significantly increased (p < 0.001) in TAA treated synovium. Conditioned medium (CM) from synovium explants downregulated the gene expression of cartilage matrix components collagen type-2 and aggrecan expression in chondrogenic MSCs. This chondrogenesis inhibiting effect was reduced by treating synovium with TAA during the production of the CM. Our findings indicate that reducing synovial inflammation might improve the joint environment for better cartilage repair, possibly by modulation of macrophage phenotypes.
