Extracellular Matrix Modulation of rhGDF-5-Induced Cellular Differentiation

Growth and differentiation factor-5 (GDF-5) is a divergent member of the TGF-β/bone morphogenetic protein (BMP) superfamily that is required for proper skeletal patterning and joint development in the vertebrate limb. Based on the homology of GDF-5 to other bone-inducing BMP family members, the inductive activity of a recombinant form of human GDF5 (rhGDF-5), and the influence of the extracellular matrix (ECM) on this inductive activity was evaluated in a series of well-defined in vitro assays. Fetal rat calvarial (FRC) cells were plated on various purified extracellular matrix proteins in the presence of rhGDF-5 (100 ng/mL) for 3 weeks and scored for differentiation at the level of morphology, overall proteoglycan synthesis and deposition, aggrecan and Type II collagen mRNA and protein expressions. Results show that GDF-5 stimulated chondrogenic nodule formation by FRC cells plated on Type I collagen but to a lesser extent on tissue culture plastic or fibronectin. These chondrogenic nodules stained heavi...