CHARACTERIZATION OF CROSS-LINKED COLLAGENS SYNTHESIZED BY MATURE ARTICULAR CHONDROCYTES CULTURED IN ALGINATE BEADS - COMPARISON OF 2 DISTINCT MATRIX COMPARTMENTS

We have characterized immunohistochemically and biochemically the coll agens accumulating in two compartments of the matrix formed by mature bovine articular chondrocytes in alginate beads. At all times of the 2 8-day culture period, more than 90% of the collagen molecules were rec overed from the rim of cell-associated matrix (CM) which encapsulates individual chondrocytes and chondrocyte clusters. Both the total amoun t and concentration of collagens in this matrix compartment rose progr essively with time, The ratio of collagen/proteoglycan remained relati vely constant with time and was always five to seven times higher in t he CM than in the interterritorial matrix compartment further removed from the cells. In the CM, collagen types II, IX, and XI were present on Day 28 in relative proportions (95/1/3) similar to those in adult c artilage. A higher proportion of newly synthesized collagen type XI th an types II or IX molecules did not become incorporated into the peric ellular rim of matrix but accumulated in the further removed matrix, A lthough collagen type I was synthesized in small amounts by flattened cells at the surface of the beads, it did not become incorporated as h eterotrimers or homotrimers in the matrix. Mature pyridinium crosslink s, principally pyridinoline, were detected as early as Day 7 of cultur e but became much more abundant between Days 15 and 28, especially in the CM which contained at all times more than 90% of the crosslinks fo rmed. The codistribution of collagen types II, IX, and XI and mature c ollagen-specific crosslinks support the contention that mature chondro cytes cultured in alginate matrix surround themselves with a protectiv e shell whose composition is very similar to that which encapsulated t he cells in vivo. (C) 1996 Academic Press, Inc.