Cell attachment, collagen binding, and receptor analysis on bovine articular chondrocytes

The purpose of this study was to investigate collagen receptors on primary bovine articular chondrocytes from full-thickness and different layers of b ovine articular cartilage. Cytometric studies with antibodies showed that a pproximately 56% of the chondrocytes from the superficial layer and 29% of the chondrocytes from the deep layer bound anti-annexin V. A similar tenden cy was found for alpha 5 and beta 1 integrin antibodies. Flow cytometric an alysis initially detected annexin V on chondrocytes following isolation; th e level of detection subsequently decreased by 24 hours, whereas that of al pha 5 and beta 1 integrins increased. Treatment of chondrocytes with collag enase at 24 hours restored the initially high epitope recognition of annexi n V, indicating masking of annexin V by newly formed collagen matrix. There was little effect on detection levels for beta 1 integrin. Contrary to the specific matrix receptor expression, chondrocytes from superficial and dee p layers differed little in attachment to immobilized types I and II collag ens. However, the attachment was more effectively inhibited with anti-annex in V than with integrin antibodies. Competition studies with preparations o f soluble collagens revealed a preferential binding of bovine type-II colla gen compared with bovine type-I collagen. Anti-annexin V antibodies inhibit ed binding of type-II collagen more effectively than anti-alpha 5 or anti-b eta 1 integrin antibodies. Evidently, under the in vitro conditions of this study, annexin V is the quantitatively predominant type-II collagen recept or on bovine articular chondrocytes. This opens a discussion of the possibl y dualistic metabolic/mechanical annexin V-integrin receptor elements.