Effects of cartilage-derived morphogenetic proteins and osteogenic protein-1 on osteochondrogenic differentiation of periosteum-derived cells

Localization studies and genetic evidence have implicated cartilage-derived morphogenetic proteins-1, -2 (CDMP-1 and CDMP-8), and osteogenic protein-1 (OP-1) in the osteochondrogenic differentiation of mesenchymal progenitor cells during embryonic development and in postnatal life. Based on their ex pression pattern and the evidence that periosteum contains mesenchymal cell s in the cambium layer that can undergo bone and cartilage formation, we hy pothesized that CDMPs and OP-1 may be involved in long bone development and fracture healing. To test this hypothesis, periosteum-derived cells from y oung calves were cultured as monolayers under serum-free conditions with an d without the addition of recombinant CDMP-1, CDMP-8 and OP-1. Phenotypic a nalysis indicate that periosteum-derived cell populations prepared, expande d, and cultured under the conditions described below, constitutively expres s messenger RNAs for the bone markers osteocalcin, osteopontin and collagen type I, and the chondrogenic markers collagen type II and aggrecan as dete rmined by RT-PCR. Moreover, histologic examinations showed positive stainin g for alcian blue and alkaline phosphatase (AP). Treatment of periosteum-de rived cells with CDMPs and OP-1 resulted in a dose-dependent increase of ce ll proliferation; CDMP-2 was less active in this regard. Furthermore, all g rowth factors enhanced osteogenic differentiation as assessed by a time- an d dose-dependent stimulation of AP activity and OP-1 increased messenger RN A expression for osteocalcin and collagen type I. We further examined the e ffects of CDMPs and OP-1 on chondrogenic differentiation of periosteum-deri ved cells. Both CDMPs and OR-1 stimulated S-35-sulfate incorporation into n ewly synthesized macromolecules with OF-1 having a more pronounced stimulat ory effect when compared with CDMP-1 and CDMP-8. Our results indicate that distinct members of the BMP-family increase the mitotic and metabolic activ ity of periosteum-derived cells. The enhancement of both the chondrogenic a nd osteogenic differentiation suggests that these growth factors might cont ribute to the local regulation of bone formation and fracture repair.