Growth Factors Regulate Expression of Osteoblast-associated Genes

Background: The goal of periodontal regenerative therapies is to reconstruct periodontal tissues such as bone, cementum, and periodontal ligament cells (PDL). The need to establish predictable treatment modalities is important for reconstruction of these tissues. The aim of this study was to determine the effects of a low molecular extract of bovine bone protein (BP) containing bone morphogenetic proteins (BMPs) 2, 3, 4, 6, 7, 12, and 13, alone or in combination with platelet-derived growth factor (PDGF) and/or insulin-like growth factor (IGF) on osteoblast differentiation in vitro.

Methods: BP, mixed with a collagen matrix, was added to a poly (DL-lactide-co-glycolide) polymer (PLG) and placed at orthotopic sites in the skullcaps of Sprague-Dawleys rats. At day 28, rats were sacrificed for histological analysis. All sites treated with the polymer/BP produced bone while control sites (without BP) showed no bone formation. Having established the biological activity of BP, in vitro studies were initiated using MC3T3-E1 cells, a mouse osteoprogenitor cell line. The ability of BP and other growth factors to alter cell proliferation was determined by Coulter counter, and differentiation was determined by Northern analysis for specific genes.

Results: When compared with cells treated with 2% serum alone, PDGF enhanced cell numbers at 10 and 20 ng/ml; IGF produced no significant effect at these doses; and BP at 10 and 20 microg/ml decreased cell proliferation. Northern analysis revealed that PDGF blocked gene expression of osteopontin (OPN) and osteocalcin (OCN), while BP and IGF promoted gene expression of bone sialoprotein (BSP) and OPN. The combination of BP and IGF enhanced expression of OPN beyond that of either BP or IGF alone. PDGF was able to block the effects of IGF on gene expression, but not those of BP.

Conclusions: These results indicate that BP, PDGF, and IGF influence cell activity differently, and thus raise the possibility that combining factors may enhance the biological activity of cells.