Lz. Sailor et al., RECOMBINANT HUMAN BONE MORPHOGENETIC PROTEIN-2 MAINTAINS THE ARTICULAR CHONDROCYTE PHENOTYPE IN LONG-TERM CULTURE, Journal of orthopaedic research, 14(6), 1996, pp. 937-945
Bone morphogenetic proteins have been shown to increase matrix synthes
is by articular ghondrocytes in short-term cultures. Members of this f
amily of proteins have also been shown to induce endochondral ossifica
tion in vivo. The present study was performed to determine if the addi
tion of human recombinant bone morphogenetic protein-2 to a long-term
monolayer articular chondrocyte cell culture system affected the abili
ty of the chondrocytes to divide in vitro, whether the cytokine altere
d expression of the articular chondrocyte phenotype and synthesis of m
atrix proteoglycans, and whether the cytokine was capable of inducing
differentiation to a hypertrophic chondrocyte. Human recombinant bone
morphogenetic protein-2 did not alter cell proliferation. It caused 3.
5-6.2 times more proteoglycan synthesis by articular chondrocytes duri
ng each of the time points tested after 4 days in culture. Total prote
oglycan accumulation in the extracellular matrix after 28 days in cult
ure was 6.7 times as great in the treated cultures as in the control.
Treatment with human recombinant bone morphogenetic protein-2 maintain
ed the articular chondrocyte phenotype of cells in culture as demonstr
ated by Northern blot analysis: the expression of type-I collagen gene
s was increased and that of type-II collagen and aggrecan mRNA was los
t in untreated chondrocyte cultures after 14-21 days in culture. In co
ntrast, exposure to 100 ng/ml human recombinant bone morphogenetic pro
tein-2 maintained expression of type-II collagen and increased express
ion of aggrecan compared with controls during the 28-day culture perio
d. Northern blot analysis of the expression of type-X collagen and ost
eocalcin by chondrocytes treated with human recombinant bone morphogen
etic protein-2 showed a lack of expression of these genes, indicating
no alteration in phenotype. These experiments demonstrated the ability
of human recombinant bone morphogenetic protein-2 to promote the arti
cular chondrocyte phenotype and matrix synthesis in long-term culture.
Characteristics of cell growth were not affected, and the cytokine di
d not induce differentiation to a hypertrophic chondrocyte.