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.