Integrin‐mediated adhesion of human articular chondrocytes to cartilage

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Abstract
Objective To determine 1) the kinetics and strength of adhesion of human articular chondrocytes to a cut cartilage surface, and 2) the role of specific integrins in mediating such adhesion, using an in vitro model. Methods Human articular chondrocytes isolated from cadaveric donors (mean ± SD age 38 ± 13 years) were cultured in high-density or low-density monolayer. Following release from culture with trypsin and a 2–2.5-hour recovery period, chondrocytes were analyzed either for adhesion to cartilage or for integrin expression by flow cytometry. Results Following culture in monolayer, adhesion of chondrocytes to cartilage increased with time, from 6–16% at 10 minutes to a maximum of 59–82% at 80–320 minutes. After 80 minutes of adhesion, the resistance of cells to flow-induced shear stress (50% detachment) was ∼21 Pa. Chondrocyte adhesion to cartilage decreased with pretreatment of cells with monoclonal antibodies that bound to and blocked certain integrins. After an 80-minute incubation time, adhesion of chondrocytes cultured in high-density monolayer decreased from the value of IgG1-treated controls (55%) with blocking of the β1 integrin subunit (to 23%) or with blocking of α5β1 (to 36%). Following expansion of chondrocytes in low-density monolayer, the mechanisms of adhesion to cartilage were generally similar. After an 80-minute incubation time, adhesion of chondrocytes cultured in low-density monolayer decreased from the value of IgG1-treated controls (62%) with blocking of the β1 integrin subunit (to 30%) or with blocking of α5β1 (to 44%). Additionally, adhesion of these cells decreased to 46% by blocking of αvβ5, with a similar trend in effect for chondrocytes cultured in high-density monolayer. Blocking of the α1 or α3 integrin subunits or αvβ3 had no detectable effect on adhesion, even though these receptors were detected by flow cytometry. Conclusion Under the culture and seeding conditions studied, β1, α5β1, and αvβ5 integrins mediate human chondrocyte adhesion to cartilage. These chondrocyte integrins have a potential role in the initial adhesion and retention of chondrocytes at a cartilage defect site following clinical procedures of chondrocyte transplantation.

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