Mc. Stewart et al., Phenotypic stability of articular chondrocytes in vitro: The effects of culture models, bone morphogenetic protein 2, and serum supplementation, J BONE MIN, 15(1), 2000, pp. 166-174
Numerous in vitro culture models have been developed for the investigation
of chondrocyte and cartilage biology. In this study, we investigated the st
ability of the chondrocytic phenotype in monolayer, aggregate, pellet, and
explant culture models and assessed the effects of recombinant human bone m
orphogenetic protein 2 (rhBMP-2) and serum supplementation on the phenotype
in each model. Phenotypic effects were assessed by analyses of procollagen
type TT, aggrecan, (V+C)(-) fibronectin, and procollagen type I messenger
RNA expression. In monolayer cultures, we noted a characteristic loss of pr
ocollagen type IT and induction of procollagen type I expression. The aggre
gate and pellet culture models supported matrix protein gene expression pro
files more reflective of in vivo levels. In explant cultures, expression of
matrix protein genes was consistently depressed. Treatment with rhBMP-2 si
gnificantly increased the expression of procollagen type IZ and aggrecan in
monolayer cultures; however, other models showed comparatively little resp
onse. Similarly, serum supplementation significantly down-regulated procoll
agen type ZI and aggrecan expression in monolayer cultures but had less eff
ect on gene expression in the other models. Serum supplementation increased
procollagen type I expression in monolayer and aggregate cultures. These r
esults suggest that the influence of exogenous BMP-2 and serum on expressio
n of chondrocyte-specific matrix protein genes is influenced by aspects of
substrate attachments, cellular morphology, and/or cytoskeletal organizatio
n. Finally, the analyses of fibronectin expression suggest that V and C reg
ion alternative splicing in chondrocytes is linked to the establishment of
a three-dimensional multicellular complex.