Effects of heparan-like polymers associated with growth factors on osteoblast proliferation and phenotype expression

Heparan-like polymers derived from dextran, named RGTA, were shown to stimulate bone repair in different bone defect models. Like heparin and heparan sulfates, RGTA potentiate in vitro the biological activities of heparin-binding growth factors (HBGFs), such as fibroblast growth factor (FGF), by stabilizing them against denaturations and by enhancing their binding with cellular receptors. RGTA were postulated to stimulate bone healing by interacting with HBGFs released in the wound site and, subsequently, by promoting the proliferation and/or differentiation of cells implicated in this process. We examined the effects of RGTA alone and associated with HBGFs on MC3T3-E1 osteoblastic cell proliferation and differentiation. RGTA inhibited cell proliferation, as measured by [3H]-thymidine incorporation into DNA. They enhanced the inhibition of DNA synthesis caused by transforming growth factor-beta (TGF-beta1) and bone morphogenetic protein-2 (BMP-2). RGTA alone increased the alkaline phosphatase and parathyroid hormone-responsive adenylate cyclase activities in MC3T3. RGTA enhanced the stimulation of the alkaline phosphatase activity induced by BMP-2 and decreased or suppressed the inhibition caused by TGF-beta1 and FGF-2. Furthermore, RGTA increased the response to parathyroid hormone stimulated by BMP-2. In conclusion, RGTA stimulate the expression of osteoblast phenotype features alone or in association with HBGFs. The ability to promote the differentiation of bone-forming cells is a potential explanation of the stimulating effect of RGTA on bone repair.