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Expression of interleukin‐6 in osteoarthritic chondrocytes and effects of fluid‐induced shear on this expression in normal human chondrocytes in vitro

This study tested the effect of fluid‐induced shear on interleukin‐6 expression in normal human articular chondrocytes in vitro. As determined by Northern blot analysis, interleukin‐6 mRNA expression occurs in chondrocytes from osteoarthritic cartilage but not in normal chondrocytes. Applying fluid‐induced shear stress to primary high density cultures of chondrocytes increased interleukin‐6 mRNA signal 4‐fold at 1 hour and 10 to 15‐fold at 48 hours compared with unsheared control cultures. At 48 hours, fluid‐induced shear stress increased interleukin‐6 protein levels in the culture medium 9 to 10‐fold compared with unsheared controls, mRNA signals for interleukin‐1α, interleukin‐1β, and tumor necrosis factor‐α in RNA from sheared or control chondrocytes were not detected by Northern blotting. Transforming growth factor‐β mRNA signal was detectable but was not affected by shear. In contrast, human lung fibroblasts (WI‐38) responded to fluid‐induced shear with increased signal for transforming growth factor‐β but not interleukin‐6, mRNA. Both cell types did respond to interleukin‐1α with increased interleukin‐6 mRNA signal. These data demonstrate that distortional forces, such as fluid‐induced shear stress, alter interleukin‐6 levels in normal chondrocytes in vitro and suggest that increased interleukin‐6 expression in osteoarthritic cartilage may result, in part, from alterations in the mechanical loading of the tissue.