No abstract

The messenger RNAs and core proteins of the two small chondroitin/dermatan sulfate proteoglycans, biglycan and decorin, were localized in developing human bone and other tissues by both 35S-labeled RNA probes and antibodies directed against synthetic peptides corresponding to nonhomologous regions of the two core proteins. Biglycan and decorin expression and localization were substantially divergent and sometimes mutually exclusive. In developing bones, spatially restricted patterns of gene expression and/or matrix localization of the two proteoglycans were identified in articular regions, epiphyseal cartilage, vascular canals, subperichondral regions, and periosteum, and indicated the association of each molecule with specific developmental events at specific sites. Study of non-skeletal tissues revealed that decorin was associated with all major type I (and type II) collagen-rich connective tissues. Conversely, biglycan was expressed and localized in a range of specialized cell types, including connective tissue (skeletal myofibers, endothelial cells) and epithelial cells (differentiating keratinocytes, renal tubular epithelia). Biglycan core protein was localized at the cell surface of certain cell types (e.g., keratinocytes). Whereas the distribution of decorin was consistent with matrix-centered functions, possibly related to regulation of growth of collagen fibers, the distribution of biglycan pointed to other function(s), perhaps related to cell regulation.

Human bone cell cultures were established by maintaining collagenase-treated bone fragments in low Ca++ medium. The resulting cell cultures exhibited a high level of alkaline phosphatase activity and produced a significant increase in intracellular cAMP when exposed to the 1-34 fragment of human parathyroid hormone. With continued culture, the cells formed a thick, extracellular matrix that mineralized when cultures were provided daily with normal levels of calcium, fresh ascorbic acid (50 micrograms/ml) and 10 mM beta-glycerol phosphate. Biosynthetically, these cells produced type I collagen (without any type III collagen), and the bone-specific protein, osteonectin. In addition, the cells produced sulfated macromolecules electrophoretically identical to those positively identified as the bone proteoglycan in parallel cultures of fetal bovine bone cells. This technique provides a useful system for the study of osteoblast metabolism in vitro.