Integrin expression by human articular chondrocytes

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 alpha 5, alpha v, and beta 1 integrin subunits and the alpha v beta 3 and alpha v beta 5 heterodimers. They also reacted with a polyclonal antibody specific for the intracytoplasmic portion of the alpha 1 subunit. MAb specific for the alpha v subunit reacted more strongly with chondrocytes near the articular surface than with those in deeper layers of cartilage, and the alpha v beta 3-specific MAb reacted exclusively with chondrocytes within the most superficial 30 microns 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 alpha 3 beta 1 integrin. CONCLUSION: Normal human articular chondrocytes prominently display substantial quantities of the alpha 1 beta 1, alpha 5 beta 1, and alpha v beta 5 integrin heterodimers, as well as lesser quantities of the alpha 3 beta 1 and alpha v beta 3 heterodimers. The alpha 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.