Cardiac fibroblasts support endothelial cell proliferation and sprout formation but not the development of multicellular sprouts in a fibrin gel co-culture model.

A primary impediment to cardiac tissue engineering lies in the inability to adequately vascularize the constructs to optimize survival upon implantation. During normal angiogenesis, endothelial cells (ECs) require a support cell to form mature patent lumens and it has been demonstrated that pericytes, vascular smooth muscle cells and mesenchymal stem cells (MSCs) are all able to support the formation of mature vessels. In the heart, cardiac fibroblasts (CFs) provide important electrical and mechanical functions, but to date have not been sufficiently studied for their role in angiogenesis. To study CFs role in angiogenesis, we co-cultured different concentrations of various cell types in fibrin hemispheres with appropriate combinations of their specific media, to determine the optimal conditions for EC growth and sprout formation through DNA analysis, flow cytometry and immunohistology. ECs proliferated best when co-cultured with CFs and analysis of immunohistological images demonstrated that ECs formed the longest and most numerous sprouts with CFs as compared to MSCs. However, ECs were able to produce more multicellular sprouts when in culture with the MSCs. Moreover, these effects were dependent on the ratio of support cell to EC in co-culture. Overall, CFs provide a good support system for EC proliferation and sprout formation; however, MSCs allow for more multicellular sprouts, which is more indicative of the in vivo process.