BMP7 promotes adipogenic but not osteo-/chondrogenic differentiation of adult human bone marrow-derived stem cells in high-density micro-mass culture

The objective of our study was to elucidate the potential of bone morphogenetic protein-7 (BMP7) to initiate distinct mesenchymal lineage development of human adult mesenchymal stem cells (MSC) in three-dimensional micro-mass culture. Expanded MSC were cultured in high-density micro-masses under serum-free conditions that favor chondrogenic differentiation and were stimulated with 50-200 ng/ml BMP7 or 10 ng/ml transforming growth factor-β3 (TGFβ3) as control. Histological staining of proteoglycan with alcian blue, mineralized matrix according to von Kossa, and lipids with Oil Red O, immunostaining of type II collagen as well as real-time gene expression analysis of typical chondrogenic, adipogenic, and osteogenic marker genes showed that BMP7 promoted adipogenic differentiation of MSC. Micro-masses stimulated with BMP7 developed adipocytic cells filled with lipid droplets and showed an enhanced expression of the adipocyte marker genes fatty acid binding protein 4 (FABP4) and the adipose most abundant transcript 1 (apM1). Development along the chondrogenic lineage or stimulation of osteogenic differentiation were not evident upon stimulation with BMP7 in different concentrations. In contrast, TGFβ3 directed MSC to form a cartilaginous matrix that is rich in proteoglycan and type II collagen. Gene expression analysis of typical chondrocyte marker genes like cartilage oligomeric matrix protein (COMP), link protein, aggrecan, and types IIα1 and IXα3 collagen confirmed chondrogenic differentiation of MSC treated with TGFβ3. These results suggest that BMP7 promotes the adipogenic and not the osteogenic or chondrogenic lineage development of human stem cells when assembled three-dimensionally in micro-masses.