Bovine articular chondrocytes do not undergo hypertrophy when cultured in the presence of serum and osteogenic protein-1

Osteogenic protein-1 (hOP-1, BMP-7) is a member of the transforming growth factor-β superfamily. We have recently shown that hOP-1 induces and promotes maturation and hypertrophy of chick sternal chondrocytes, cultured in monolayer or suspension in the presence or absence of serum. In the present study we demonstrate that bovine articular chondrocytes, grown for up to 5 weeks in the presence of 0.5% or 10% serum in combination with 30 ng/ml hOP-1, do not undergo hypertrophy, as determined by cell size, the absence of type X collagen expression and synthesis, and of alkaline phosphatase activity. Treatment with hOP-1 (30 ng/ml) resulted in increased matrix synthesis as measured by [³⁵S]sulfate incorporation and by collagen type II synthesis and expression, without influencing cell proliferation. These data suggest that primary mammalian articular chondrocytes are not able to undergo hypertrophy in conditions previously shown to be permissive for hypertrophy of both chick sternal and chick articular chondrocytes.