Background: The role of bone tissue engineering is to regenerate tissue using biomaterials and stem cell based approaches. Combination of two or more cell types is one of the strategies to promote bone formation. Endothelial progenitor cells (EPCs) may enhance the osteogenic properties of mesenchymal stem cells (MSCs) and promote bone healing, this study aimed to investigate the possible mechanisms of EPCs on promoting osteogenic differentiation of MSCs.
Methods: MSCs and EPCs were isolated and co-cultured in Transwell chambers, the effects of EPCs on the regulation of MSC biological properties was investigated. Real-time PCR array, qRT-PCR and western blotting were performed to explore possible signaling pathways involved in osteogenesis. The expression of osteogenesis markers and calcium nodule formation was quantified by qRT-PCR, western blotting and Alizarin Red staining.
Results: Results showed that when co-cultured with EPCs, MSCs exhibited greater alkaline phosphatase (ALP) activity and increased calcium mineral deposition significantly. The mitogen-activated protein kinase (MAPK) signaling pathway was involved in this process. p38 gene expression and p38 protein phosphorylation levels showed significant up-regulation in co-cultured MSCs. Silence expression of p38 in co-cultured MSCs reduced osteogenic gene expression, protein synthesis, ALP activity and calcium nodule formation.
Conclusions: These data suggest paracrine signaling from EPCs influence the biological function and promote MSCs osteogenic differentiation. Activation of the p38MAPK pathway may be the key to enhancing MSCs osteogenic differentiation via indirect interactions with EPCs.