INTEGRIN EXPRESSION BY HUMAN ARTICULAR CHONDROCYTES

Objective. To perform a comprehensive analysis of the integrin forms e xpressed by normal human articular chondrocytes. Methods. Cartilage se ctions and collagenase- released chondrocytes were probed with a compr ehensive panel of integrin isoform-specific monoclonal antibodies (MAb ), using in situ immunohistochemistry techniques, indirect immunofluor escence and flow cytometry, and immunoprecipitation/sodium dodecyl sul fate-polyacrylamide gel electrophoresis (SDS-PAGE). Results. Chondrocy tes 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 a lpha(v) beta(5) heterodimers. They also reacted with a polyclonal anti body specific for the intracytoplasmic portion of the alpha(1) subunit . MAb specific for the alpha(v) subunit reacted more strongly with cho ndrocytes near the articular surface than with those in deeper layers of cartilage, and the alpha(v) beta(3)-specific MAb reacted exclusivel y with chondrocytes within the most superficial 30 mu m of cartilage. Flow cytometric analysis and SDS-PAGE analysis of immunoprecipitates p repared from extracts of cell-surface radioiodinated chon-drocytes con firmed the above observations, and additionally revealed the presence of the alpha(3) beta(1) integrin. Conclusion. Normal human articular c hondrocytes prominently display substantial quantities of the alpha(1) alpha(1), alpha(5) beta(1), and alpha(v) beta(5) integrin heterodimer s, as well as lesser quantities of the alpha(3) beta(1) and alpha(v) b eta(3) heterodimers. The alpha(v) subunit-containing integrins are det ected more readily on the more superficial chondrocytes than on chondr ocytes deep within cartilage. These observations provide the basis for analysis of the role of chondrocyte integrins in cartilage homeostasi s and in the pathogenesis of joint diseases.