The objective of this study was to detail the topographical and zonal distribution of alpha and beta subunits of the integrin superfamily in normal and osteoarthritic cartilage.
Immunohistochemistry utilising antibodies towards alpha and beta subunits was performed on cryostat sections of human articular cartilage from macroscopically normal (n = 6) and osteoarthritic (n = 6) femoral heads. Samples of articular cartilage were obtained from 12 topographically distinct sites from each femoral head. Each section was divided into zones (superficial, middle, deep) and staining scores were recorded.
Normal cartilage stained for integrin subunits alpha 1, alpha 5, alpha V, beta 1, beta 4, and beta 5, but not for alpha 2, alpha 3, alpha 4, alpha 6, beta 2, beta 3, and beta 6. Intact and non-intact residual cartilage from osteoarthritic femoral heads stained for alpha 1, alpha 2, alpha 5, alpha V, beta 1, beta 4, and beta 5. Staining was occasionally seen for alpha 4 and beta 2, but not for alpha 3, alpha 6, beta 3, and beta 6. There was no topographical variation in the staining for any of the subunits in either normal or osteoarthritic cartilage. The only subunit that displayed a zonal variation was alpha V; staining for this subunit was most pronounced in the superficial zone compared with the middle and deep zones.
Chondrocytes in normal and osteoarthritic cartilage express the integrin subunits alpha 1, alpha 5, alpha V, beta 1, beta 4, and beta 5. Chondrocytes in osteoarthritic cartilage, in addition, express the alpha 2, alpha 4, and beta 2 subunits. The alpha v subunit is expressed by more chondrocytes in the superficial zone in comparison with cells in the deeper zones. None of the subunits display topographical variation in expression.