Chondrogenic/osteogenic differentiation of a mesenchymal progenitor stimulated by BMP-13 (CDMP-2) was studied. C3H10T1/2 cells were transduced by an adenoviral construct containing BMP-13 or BMP-2. BMP-13 supported chondrogenesis but not terminal differentiation, whereas BMP-2 stimulated endochondral ossification. The studies show that BMP-13 may fail to support terminal chondrocyte differentiation.Introduction: Bone morphogenetic protein (BMP)-13 is a member of the transforming growth factor ␤ (TGF-␤) superfamily of growth factors. Although the biological functions of BMP-13 remain poorly understood, continued postnatal expression of BMP-13 in articular cartilage suggests that this protein may function in an autocrine/paracrine fashion to regulate growth and maintenance of articular cartilage. The purpose of this study was to elucidate the role of BMP-13 in chondrogenic differentiation. Materials and Methods: Replication-deficient adenoviruses carrying human BMP-13 (Adv-hBMP13), bacterial ␤-galactosidase (Adv-␤gal), and human BMP-2 (Adv-hBMP2) were constructed. Murine mesenchymal progenitor cells (C3H10T1/2) were transduced with these vectors, and differentiation to the chondrogenic lineage was assessed by reverse transcriptase-polymerase chain reaction (RT-PCR), biochemical, and histological analyses. Results and Conclusions: Our findings revealed that hBMP-13 transduced cells differentiated into round cells that stained with Alcian blue. Analysis of gene expression in hBMP-13-transduced cells demonstrated presence of cartilage-specific markers, absence of hypertrophic chondrocyte specific markers, and upregulation of proteoglycan biosynthesis. In particular, hBMP-13-transduced cells had significantly less and delayed expression of alkaline phosphatase activity and calcium mineral accumulation than hBMP-2-transduced cells. Except for BMPR-IB/ ALK-6, expression of BMP receptors was identified constitutively in C3H10T1/2 cells and was not affected by the presence of either of the BMPs. In summary, hBMP-13, while stimulating chondrogenesis, failed to support differentiation to hypertrophic chondrocytes and endochondral ossification similar to hBMP-2. Thus, this may prove to be a useful strategy for cell-based regeneration of articular cartilage.

DAP12 (also known as KARAP) is a novel ITAM-bearing transmembrane adapter molecule that is ex-2-5 Although the expression of KARs is restricted to natural killer and T-cell subsets, 6 DAP12 is expressed in a wide variety of cell types, including peripheral blood granulocytes, monocytes, macrophages, and dendritic cells.2,4,7 Several myeloid cell-specific DAP12-associating receptors have been identified. 8 -10

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Chondrocytes from osteoarthritic knees in older patients exhibited similar immunomodulatory properties in vitro to those in juveniles or adults.