3D scaffolds co-seeded with human endothelial progenitor and mesenchymal stem cells: evidence of prevascularisation within 7 days.

Blood supply is a critical issue in most tissue engineering approaches for large defect healing. As vessel ingrowth from surrounding tissues is proven to be insufficient, current strategies are focusing on the neo-vascularisation process. In the present study, we developed an in vitro pre-vascularised construct using 3D polyurethane (PU) scaffolds, based on the association of human Endothelial Progenitor Cells (EPC, CD34+ and CD133+) with human Mesenchymal Stem Cells (MSC). We showed the formation of luminal tubular structures in the co-seeded scaffolds as early as day 7 in culture. These tubular structures were proven positive for endothelial markers von Willebrand Factor and PECAM-1. Of special significance in our constructs is the presence of CD146-positive cells, as a part of the neovasculature scaffolding. These cells, coming from the mesenchymal stem cells population (MSC or EPC-depleted MSC), also expressed other markers of pericyte cells (NG2 and αSMA) that are known to play a pivotal function in the stabilisation of newly formed pre-vascular networks. In parallel, in co-cultures, osteogenic differentiation of MSCs occurred earlier when compared to MSCs monocultures, suggesting the close cooperation between the two cell populations. The presence of angiogenic factors (from autologous platelet lysates) in association with osteogenic factors seems to be crucial for both cell populations' cooperation. These results are promising for future clinical applications, as all components (cells, growth factors) can be prepared in an autologous way.

Platelet-released supernatant induces osteoblastic differentiation of human mesenchymal stem cells: potential role of BMP-2.

Platelet-rich preparations have recently gained popularity in maxillofacial and dental surgery, but their beneficial effect is still under debate. Furthermore, very little is known about the effect of platelet preparations at the cellular level, and the underlying mechanisms. In this study, we tested the effect of platelet-released supernatant (PRS) on human mesenchymal stem cell (MSC) differentiation towards an osteoblastic phenotype in vitro. Cultures of MSC were supplemented with PRS and typical osteoblastic markers were assessed at up to 28 days post-confluence. PRS showed an osteoinductive effect on MSC, as shown by an increased expression of typical osteoblastic marker genes such as collagen Ialpha1, bone sialoprotein II, BMP-2 and MMP-13, as well as by increased 45Ca²+ incorporation. Our results suggest that the effect of PRS on human MSC could be at least partially mediated by BMP-2. Activated autologous PRS could therefore provide an alternative to agents like recombinant bone growth factors by increasing osteoblastic differentiation of bone precursor cells at bone repair sites, although further studies are needed to fully support our observations.