Bone morphogenetic protein 9: a potent modulator of cartilage development in vitro.

Few publications describe the activity of bone morphogenetic protein-9 (BMP-9), but the consensus of these largely in vivo studies is that while BMP-9 can induce ectopic bone formation at relatively large concentrations, it is primarily active in non-skeletal locations--including the liver, nervous system and marrow. To study the effects of BMP-9 on chondrogenesis in a well-defined environment, calf articular chondrocytes were seeded onto biodegradable PGA scaffolds. The resulting cell-polymer constructs were cultured in either control medium or medium supplemented with 1, 10, 50 or 100 ng/ml of BMP-9. After 4 weeks of in vitro culture, all concentrations of BMP-9 increased the total mass of the constructs, and the amounts of collagen, glycosaminoglycans (GAG) and cells per construct. On a mass percentage basis, BMP-9 tended to increase GAG, to decrease the relative amount of collagen and had little effect on the relative amount of cells. BMP-9 elicited qualitatively similar responses as BMP-2, -12 and -13. However, in contrast to BMP-12 and -13, BMP-9 (at concentrations > or = 10 ng/ml) induced hypertrophic chondrocyte formation and was the only BMP tested to induce mineralization. Taken together, these data suggest that BMP-9 is a potent modulator of cartilage development in vitro.

Bone morphogenetic proteins-2, -12, and -13 modulate in vitro development of engineered cartilage.

Bovine calf articular chondrocytes were seeded onto biodegradable polyglycolic acid (PGA) scaffolds and cultured in either control medium or medium supplemented with 1, 10, or 100 ng/mL of bone morphogenetic proteins (BMPs) BMP-2, BMP-12, or BMP-13. Under all conditions investigated, cell-polymer constructs cultivated for 4 weeks in vitro macroscopically and histologically resembled native cartilage. Addition of 100 ng/mL of BMP-2, BMP-12, or BMP-13 increased the total mass of the constructs relative to the controls by 121%, 80%, and 62%, respectively, which was accompanied by increases in the absolute amounts of collagen, glycosaminoglycans (GAG), and cells. The addition of 100 ng/mL of BMP-2, BMP-12, or BMP-13 increased the weight percentage of GAG in the constructs by 27%, 18%, and 15%, and decreased the weight percent of total collagen to 63%, 89%, and 83% of controls, respectively. BMP-2, but not BMP-12 or BMP-13 promoted chondrocyte hypertrophy. Taken together, these data suggest that BMP-2, BMP-12, and BMP-13 increase growth rate and modulate the composition of engineered cartilage and that 100 ng/mL of BMP-2 has the greatest effect. In addition, in vitro engineered cartilage provides a system for studying the effects of BMPs on chondrogenesis in a well-defined environment.

IGF-I and mechanical environment interact to modulate engineered cartilage development.

Bovine calf articular chondrocytes were seeded onto biodegradable polyglycolic acid scaffolds and cultured for four weeks using in vitro systems providing different mechanical environments (static and mixed Petri dishes, static and mixed flasks, and rotating vessels) and different biochemical environments (medium with and without supplemental insulin-like growth factor I, IGF-I). Under all conditions, the resulting engineered tissue histologically resembled cartilage and contained its major constituents: glycosaminoglycans, collagen, and cells. The mechanical environment and supplemental IGF-I (a) independently modulated tissue morphology, growth, biochemical composition, and mechanical properties (equilibrium modulus) of engineered cartilage as previously reported; (b) interacted additively or in some cases nonadditively producing results not suggested by the independent responses, and (c) in combination produced tissue superior to that obtained by modifying these factors individually.