TRANSFORMING GROWTH-FACTOR-BETA-1 - INDUCTION OF BONE MORPHOGENETIC PROTEIN GENES EXPRESSION DURING ENDOCHONDRAL BONE-FORMATION IN THE BABOON, AND SYNERGISTIC INTERACTION WITH OSTEOGENIC PROTEIN-1 (BMP-7)

Certain members of the bone morphogenetic protein (BMP) and transformi ng growth factor-beta (TGF-beta) families are inducers of endochondral bone formation in vivo. TGF-beta s, however, do not initiate bone for mation when implanted in heterotopic (extraskeletal) sites of rodents. Here we show that platelet-derived porcine TGF-beta 1 (pTGF-beta 1) i nduces endochondral bone in heterotopic sites of the baboon (Papio urs inus) at doses of 5 mu g per 100 mg of guanidinium-inactivated collage nous bone matrix as carrier, with an inductive efficiency comparable t o 5 and 25 mu g of recombinant osteogenic protein-1 (hOP-1, BMP-7), a well characterized inducer of bone formation. We further demonstrate t hat pTGF-beta 1 and hOP-1 interact synergistically to induce large oss icles in the rectus abdominis of the primate as evaluated by key param eters of bone formation on day 14 and 30. Tissue generated on day 30 b y 5 mu g pTGF-beta 1 or 25 mu g hOP-1 induced comparable expression le vels of OP-1, BMP-3 and type IV collagen mRNA transcripts, whereas TGF -beta 1 and type II collagen expression was 2 to 3 fold higher in pTGF -beta 1-treated implants, as determined by Northern analysis. In ossic les generated by 25 mu g hOP-1 in combination with relatively low dose s of pTGF-beta 1 (0.5, 1.5 and 5 mu g), type II collagen expression in creased in a pTGF-beta 1 dose-dependent manner, whilst type IV collage n was synergistically upregulated with a 3 to 4 fold increase compared to ossicles generated by a single application of 5 mu g pTGF-beta 1 o r 25 mu g hOP-1. Morphogen combinations (5 mu g pTGF-beta 1 with 20 mu g hOP-1, and 5 and 15 mu g pTGF-beta 1 with 100 mu g hOP-1 per g of c ollagenous matrix as carrier) induced exuberant tissue formation and g reater amounts of osteoid than hOP-1 alone when implanted in calvarial defects of the baboon as evaluated on day 30 and 90, with displacemen t of the temporalis muscle above the defects. Since a single applicati on of TGF-beta 1 in the primate did not induce bone formation in calva rial defects, whilst it induces endochondral bone differentiation in h eterotopic sites, our data indicate that the bone inductive activity o f TGF-beta 1 is site and tissue specific. mRNA expression of multiple members of the TGF-beta superfamily suggests complex autocrine and par acrine activities of the ligands and different signalling pathways on responding cells during the cascade of endochondral bone formation in the primate. The present findings may provide the basis for synergisti c molecular therapeutics for cartilage and bone regeneration in clinic al contexts.