Effect of BMP on the differentiation of bone marrow stromal cells into osteoblasts in a collagen-gel culture.

Abstract

In-gel administration of recombinant BMP 2 (rBMP 2) to cultured bone marrow cells induces differentiation into osteoblasts much more efficiently than the conventional addition of rBMP 2 to the culture medium. We recently found that bone marrow cells cultured on collagen-gel could form bone-like calcified nodules withintwo weeks after confluence without the addition of the strong differentiationinducer dexamethasone. Using these cells on collagen-gel culture, the present studysought to evaluate the effects of rBMP 2 on cell differentiation. rBMP 2 was added to cultured rat bone marrow cells under three different conditions:(1) cellswere cultured in α-MEM with 15% fetal calf serum (standard medium) which contained various concentrations rBMP 2, (2) cells were cultured in standard medium which contained 10-8M dexamethasone (Dex), 10 mM β-glycerophosphate (β-GP), and rBMP 2 at different concentrations, and (3) cells were cultured on collagen-gel which contained rBMP 2 at different concentrations. In the standard medium (condition 1), the addition of rBMP 2 did not induce the cells to differentiate to form calcified nodules within a week, although both alkaline phosphatase activity and DNA content increased in a dose-dependent manner. In contrast, the addition of rBMP 2 as a component of collagen-gel (condition 3) markedly accelerated the phenotype expression of alkaline phosphatase and osteocalcin, as well as calcified nodule formation. This is the first report to demonstrate that collagen-gel enhances the effect of BMP in vitro. A similar effect wasobserved with rBMP 2 inthe presence of Dex and β-GP (condition 2).