Type XI Collagen is Associated with the Chondrocyte Surface in Suspension Culture

Abstract

Chondrocytes from bovine articular cartilage were stripped of matrix, then allowed to reconstitute their pericellular matrix in suspension culture. After incubation, the cells were centrifuged through a Percoll (TM) cushion and separated into a cell fraction, a medium fraction, and an interface fraction. The collagen in each fraction was analyzed by SDS-polyacrylamide gel electrophoresis and immunolocation with antisera against type XI and type II. Under these conditions, type XI collagen was recovered in the cell fraction, but was not detectable by immunolocation in the medium fraction or the interface fraction. In contrast, type II collagen was found in all three of these fractions. Insoluble type XI fibers subjected to the same fractionation scheme in the absence of cells were recovered in the medium and interface fractions, but not in the cell fraction. Incubation of intact cells with collagenase digested the cell-associated collagen, indicating that it was outside of the cells. The type XI collagen was removed from the cells by extraction with 4M guanidinium chloride. These results indicate that type XI collagen is preferentially retained at the chondrocyte surface, and are consistent with our proposal that it is involved in organization of the pericellular matrix.