Induced chondroblastic differentiation of human fibroblasts by three-dimensional culture with demineralized bone matrix

Demineralized bone powder (DBP) implanted in vivo induces endochondral bone formation (osteoinduction). Connective tissue cells migrate to the powders and they begin to produce cartilage matrix. Subsequently, vascularization is stimulated and the cartilage is replaced by bone and marrow. Demineralized bone implants have been used clinically for a variety of osseous reconstructive applications. We designed a novel three-dimensional (3-D) device to examine the mechanism of chondroinduction in vitro. Normal human dermal fibroblasts (hDFs) were cultured in 3-D collagen sponges with and without DBP. The cells migrated through the collagen lattice and they attached to and spread onto particles of demineralized bone. Cells vicinal to the DBP produced cartilage matrix proteoglycans. Induced cells expressed cartilage-specific gene products, type II collagen and aggrecan. Control hDFs did not produce cartilage matrix when cultured in plain collagen sponges. This experimental system has the potential to reveal mechanisms of gene activation and other early steps in postnatal chondro/osteoinduction. Further, these results suggest that it may be possible to engineer human cartilage for transplantation by culturing autogenous dermal fibroblasts with a chondroinductive agent.