Integrin expression by human articular chondrocytes

Abstract

Objective. To perform a comprehensive analysis of the integrin forms expressed by normal human articular chondrocytes. Methods. Cartilage sections and collagenase‐released chondrocytes were probed with a comprehensive panel of integrin isoform–specific monoclonal antibodies (MAb), using in situ immunohistochemistry techniques, indirect immunofluorescence and flow cytometry, and immunoprecipitation/sodium dodecyl sulfate–polyacrylamide gel electrophoresis (SDS‐PAGE). Results. Chondrocytes in cartilage sections reacted with MAb specific for the α₅, α_v, and β₁ integrin subunits and the α_vβ₃ and α_vβ₅ heterodimers. They also reacted with a polyclonal antibody specific for the intracytoplasmic portion of the α₁ subunit. MAb specific for the α_v subunit reacted more strongly with chondrocytes near the articular surface than with those in deeper layers of cartilage, and the α_vβ₃‐specific MAb reacted exclusively with chondrocytes within the most superficial 30 μm of cartilage. Flow cytometric analysis and SDS‐PAGE analysis of immunoprecipitates prepared from extracts of cell‐surface radioiodinated chondrocytes confirmed the above observations, and additionally revealed the presence of the α₃β₁ integrin. Conclusion. Normal human articular chondrocytes prominently display substantial quantities of the α₁β₁, α₅β₁, and α_vβ₅ integrin heterodimers, as well as lesser quantities of the α₃β₁ and α_vβ₃ heterodimers, The α_v subunit–containing integrins are detected more readily on the more superficial chondrocytes than on chondrocytes deep within cartilage. These observations provide the basis for analysis of the role of chondrocyte integrins in cartilage homeostasis and in the pathogenesis of joint diseases.