Interleukin-1β and tumor necrosis factor-a increase stiffness and impair contractile function of articular chondrocytes

Interleukin-1β （IL-1β） and tumor necrosis factor-α （TNF-α） are major proinflammatory cytokines involved in osteoarthritis （OA）. These cytokines disturb chondrocyte metabolism by suppressing the synthesis of extracellular matrix proteins and stimulating the release of catabolic proteases, but little is known about their role in chondrocyte mechanics. Thus, the aim of this study was to measure the effects of IL-1β and TNF-α on the mechanical properties of the chondrocytes. Chondro- cytes from goat knee joints were cultured in 96-well plates. The cellular stiffness and contractile func- tion were probed using optical magnetic twisting cytometry, the cytoskeleton and the expression of extracellular matrix proteins were visualized using immunofluorescent staining, and chondrocyte phenotypical expression was measured by western blot analysis. Results showed that chondrocyte stiffness was dramatically decreased by disruption of F-actin but was unaffected by disruption of the intermediate filament vimentin. Treatment with 10 ng/ml IL-1β or 40 ng/ml TNF-α for 24 h sub- stantially increased the expression level of F-actin and cellular stiffness, and impaired cell stiffening in response to the contractile agonist histamine, but these effects were blocked by the Rho-associated protein kinase inhibitor Y27632. In conclusion, IL-1β and TNF-α substantially change the mechanical properties of the chondrocytes in vitro. While changes of chondrocyte mechanics in vivo during OA progression remain unclear, this finding reveals a prominent role of these cyto- kines in cellular mechanics and provides insight for anti-cytokine therapies of OA.