Transplant of Bone Marrow and Muscle-Derived Connective Tissue Cultures in Diffusion Chambers for Bioassay of Bone Morphogenetic Protein

Abstract

To promote a high concentration gradient, syngeneic bone marrow and muscle connective tissue cell cultures and subcultures were exposed to bone morphogenetic protein and associated noncollagenous bone matrix proteins (BMP/NCP) in vitro, transferred to diffusion chambers, and then transplanted into the anterior abdominal wall of isogeneic rats. Both muscle- and marrow-derived cells differentiated into cartilage and chondroosteoid on the inside of diffusion chambers. New bone developed on the vascularized outside surfaces in juxtaposition to avascular tissue on the inside. Levels of glycosaminoglycans (GAGs) and DNA synthesis in tissues inside the chambers were sharply elevated. These data, correlated with histologic observations, demonstrate that the BMP/NCP recruits mesenchymal-type cells for a skeletal tissue pathway of development. Muscle-derived cells, as distinguished from marrow-derived cells, originate in a nonosseous environment but differentiate into osteoprogenitor (osteogenic stem) cells and display levels of DNA synthesis almost as high as marrow stroma-derived cells. The rise in DNA synthesis was maximal in the interval from two to three weeks after transplantation. Whether the bone marrow stroma mesenchymal cell target for BMP is only the osteogenic stem cell population or also includes colony-forming units fibroblasts (CFU-F) remains to be investigated by experiments on established cell lines.