Enhanced osteoblastic differentiation and bone formation in co-culture of human bone marrow mesenchymal stromal cells and peripheral blood mononuclear cells with exogenous VEGF.

BACKGROUND: Despite recent advances in bone tissue engineering, efficient bone formation and vascularization remains a challenge for clinical applications.

HYPOTHESIS: The aim of this study was to investigate if the osteoblastic differentiation of human mesenchymal stromal cells (MSCs) can be enhanced by co-culturing them with peripheral blood (PB) mononuclear cells (MNCs), with and without vascular endothelial growth factor (VEGF), a coupling factor of bone formation and angiogenesis.

MATERIALS AND METHODS: Human bone marrow (BM) derived MSCs were co-cultured with PB-MNCs in osteogenic medium with or without VEGF. Osteoblastic differentiation and mineral deposition were studied by staining for alkaline phosphatase (ALP), and von Kossa, respectively, and measurements for ALP activity and calcium concentration (Ca). Cell proliferation was assayed with Alamar blue. The mechanism(s) were further studied by Transwell(®) cell culture experiments.

RESULTS: Both ALP and mineralization (von Kossa and Ca) were significantly higher in the MSC-MNC co-cultures compared to plain MSC cultures. VEGF alone had no effect on osteoblastic differentiation of MSCs, but further enhanced differentiation in co-culture settings. The mechanism was shown to require cell-cell contact between MSCs and MNCs and the factors contributing to further differentiation appear to be soluble. No differences were observed in cell proliferation.

CONCLUSION: Our study demonstrates that the in vitro ALP activity and mineralization of human BM-MSCs is more efficient in the presence of PB-MNCs, and exogenously added VEGF further enhances the stimulatory effect. This indicates that PB-MNCs could be a potential cell source in development of co-culture systems for novel tissue engineering applications for enhanced bone healing.