SYNERGISTIC ACTION OF TRANSFORMING-GROWTH-FACTOR-BETA AND INSULIN-LIKE GROWTH-FACTOR-I INDUCES EXPRESSION OF TYPE-II COLLAGEN AND AGGRECAN GENES IN ADULT HUMAN ARTICULAR CHONDROCYTES

Reexpression of aggrecan and type II collagen genes in dedifferentiate d adult human articular chondro cytes (AHAC) in suspension culture var ied widely depending on the specific lot of bovine serum used to suppl ement the culture medium. Some lots of serum provided strong induction of aggrecan and type II collagen expression by AHAC while others did not stimulate significant production of these hyaline cartilage extrac ellular matrix molecules even following several weeks in culture. Addi tion of 50 ng/ml insulin-like growth factor-I (IGF-I) to a deficient s erum lot significantly enhanced its ability to induce aggrecan and typ e II collagen mRNA. Given this observation, IGF-I and other growth fac tors were tested in defined serum-free media for their effects on the expression of these genes. Neither IGF-I nor insulin nor transforming growth factor beta (TGF-beta) alone stimulated induction of aggrecan o r type II collagen production by dedifferentiated AHAC. However, TGF-b eta 1 or TGF-beta 2 combined with IGE-I or insulin provided a strong i nduction as demonstrated by RNase protection and immunohistochemical a ssays. Interestingly, type I collagen, previously shown to be downregu lated in serum supplemented suspension cultures of articular chondrocy tes, persisted for up to 12 weeks in AHAC cultured in defined medium s upplemented with TGF-beta and IGF-I. (C) 1997 Academic Press.