The role of the cytoskeleton in the viscoelastic properties of human articular chondrocytes

Biomechanical factors are believed to play an important role in regulating the metabolic activity of chondrocytes in articular cartilage. Previous studies suggest that cytoskeletal proteins such as actin, vimentin, and tubulin influence cellular mechanical properties, and may therefore influence the mechanical interactions between the chondrocyte and the surrounding tissue matrix. In this study, we investigated the role of specific cytoskeletal components on the mechanical properties of individual chondrocytes isolated from normal or osteoarthritic hip articular cartilage. Chondrocytes were exposed to a range of concentrations of chemical agents that disrupt the primary cytoskeletal elements (cytochalasin D for F-actin microfilaments, acrylamide for vimentin intermediate filaments, and colchicine for microtubules). Chondrocyte mechanical properties were determined using the micropipette aspiration technique coupled with a viscoelastic solid model of the cell. Chondrocyte stiffness (elastic modulus) was significantly increased with osteoarthritis. With increasing cytochalasin D treatment, chondrocyte stiffness decreased by up to 90% and apparent viscosity decreased by up to 80%. The effect of cytochalasin D was greater on normal chondrocytes than those isolated from osteoarthritic cartilage. Treatment with acrylamide also decreased the moduli and viscosity, but only at the highest concentration tested. No consistent changes in cell mechanical properties were observed with colchicine treatment. These findings suggest that microfilaments and possibly intermediate filaments provide the viscoelastic properties of the chondrocyte, and changes in the structure and properties of these cytoskeletal elements may reflect changes in the chondrocyte with osteoarthritis.