Establishment of a tri-culture system mimicking the structural organization of a blood vessel

Cardiovascular diseases, including coronary artery diseases, are a major cause of mortality worldwide. Consequently, there is a pressing need to develop small-diameter vascular vessels for bypass surgery and other vascular reconstructive procedures. Tissue engineering offers the prospect of being able to meet this medical demand, as it allows the development of structurally complex blood vessels substitutes¹. Accordingly, the ultimate aim of this work is to develop small diameter vascular substitutes based on layering multiple cell types (i.e. endothelial, smooth muscle and fibroblastic cells)². Electrospun nanofibrous meshes (NFM), which restrict cell migration although enabling biochemical communication³, were used as culturing substrate. Co-culture systems of human endothelial-smooth muscle cells and fibroblastic-smooth muscle cells were established. These co-cultures were then assembled to develop a tri-culture system, which mimics the structural organization of a blood vessel.

In both co-culture systems was possible to observe a viable and proliferative cell populations through the 7 days of culture. Concerning the tri-culture system, cell viability presents a similar trend to the co-cultures. Interestingly, the tri-culture system presents values of protein synthesis much higher than the co-cultures. The HE staining of cross-sections of the co- and tri-culture systems showed that the different cell types remain on their original side of the NFM, confirming the desirable cellular layering. Additionally, on immunofluorescence micrographs of the co-culture systems was possible to observe that the endothelial, smooth muscle and fibroblastic cells maintain their phenotype, even in the presence of another cell type. Quantification of lineage-specific growth factors, namely vascular endothelial growth factor (VEGF), platelet-derived growth factor (PDGF) and basic fibroblast growth factor (bFGF), on the conditioned media of co- and tri-culture systems demonstrated a synergistic interplay between VEGF and bFGF. VEGF is mainly expressed by smooth muscle cells, which leads to increase levels in the co- and tri-culture systems. A similar trend is observed with the levels of bFGF, expectedly produced by the fibroblast cells. By its side, PDGF levels remain unaltered among conditions. These results demonstrate the potential inter-cellular communication mediated by lineage-specific soluble proteins.

This study demonstrated the fundamental importance of the intercellular crosstalk between endothelial, smooth muscle and fibroblastic cells. It reinforces the potential of a tri-culture system in the development of tissue engineered blood vessel substitutes.