Angiogenesis is essential in bone fracture healing for restoring blood flow to the fracture site. Vascular endothelial growth factor (VEGF) and its receptor have been implicated in this process. Despite the importance of angiogenesis for the healing processes of damaged bones, the role of VEGF signaling in modulation of osteogenic differentiation in human mesenchymal stem cells has not been investigated in great detail. We examined the expression of VEGF-A and VEGFR-1 in human adult mesenchymal stem cells derived from trabecular bone (hTBCs). VEGF-A was found to be secreted in a differentiation dependent manner during osteogenesis. Transcripts for VEGF-A were also seen to be elevated during osteogenesis. In addition, transcripts for VEGF-A and the corresponding receptor VEGFR-1 were upregulated under hypoxic conditions in undifferentiated hTBCs. To investigate the signaling of VEGF-A on osteogenesis recombinant hTBCs were generated. High expression of VEGF-A stimulated mineralization, whereas high expression of sFLT-1, an antagonist to VEGF-A, reduced mineralization suggesting that VEGF-A acts as autocrine factor for osteoblast differentiation. In addition, VEGF-A secreted by hTBCs promotes sprouting of endothelial cells (HUVE) demonstrating a paracrine role in blood vessel formation. In summary, an in vitro analysis of transgene effects on cellular behavior can be used to predict an effective ex vivo gene therapy.

Healing of fractures is dependent on vascularization of bone, which is in turn promoted by VEGF. It was shown that 0.1 and 1 mg of pVEGF 165 -GAM led to a significant increase in vascularization and bone regeneration in defects that would otherwise have led to atrophic nonunions.

The potential of adult mesenchymal stem cells (MSCs) to differentiate towards cartilage, bone, adipose tissue, or muscle is well established. However, the capacity of MSCs to differentiate towards intervertebral disc (IVD)-like cells is unknown. The aim of this study was to compare the molecular phenotype of human IVD cells and articular chondrocytes and to analyze whether mesenchymal stem cells can differentiate towards both cell types after transforming growth factor β (TGFβ)-mediated induction in vitro.Bone marrow-derived MSCs were differentiated in spheroid culture towards the chondrogenic lineage in the presence of TGFβ 3 , dexamethasone, and ascorbate. A customized cDNA-array comprising 45 cartilage-, bone-, and stem cell-relevant genes was used to quantify gene expression profiles.After TGFβ-mediated differentiation, MSC spheroids turned positive for collagen type II protein and expressed a large panel of genes characteristic for chondrocytes, including aggrecan, decorin, fibromodulin, and cartilage oligomeric matrix protein, although at levels closer to IVD tissue than to hyaline articular cartilage. Like IVD tissue, the spheroids were strongly positive for collagen type I and osteopontin. MSC spheroids expressed more differentiation markers at higher levels than culture-expanded IVD cells and chondrocytes, which both dedifferentiated in monolayer culture.In conclusion, mesenchymal stem cells adopted a gene expression profile that resembled native IVD tissue more closely than native joint cartilage. Thus, these cells may represent an attractive source from which to obtain IVD-like cells, whereas modification of culture conditions is required to approach the molecular phenotype of chondrocytes in hyaline cartilage. 2005;23:403-411 Stem Cells

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