Toward a tissue engineered blood vessel. Cell cultivation, hemodynamic influences and matrix production

Abstract: Cardiovascular diseases are the leading causes of mortality in the western world. Thereplacement or repair of diseased blood vessels with human autografts (vein or arteries) orsynthetic vascular grafts (ePTFE or Dacron) has become a routine treatment. Autologous graftsare not always available in all patients. Synthetic substitutes are not able to grow or remodel andare prone to complications like stenosis, thrombosis, calcification and infection. Tissueengineered blood vessels (TEBVs) could offer a promising approach to reduce the limitations insmall vessel grafting by creating viable constructs with repair and remodelling capabilities.The aim of this thesis is to form biologically active TEBVs in vitro. In particular, the importanceof a cell-cell contact in expression of angiogenic factors in the vascular wall was studied in a coculturesystem of endothelial cells (ECs) and smooth muscle cells (SMCs). Also, the effects ofthe physiological level of laminar shear stress on vascular cells in the co-culture wereinvestigated. Furthermore, the production of extracellular matrix (ECM) components in TEBVswas evaluated. Finally, mesenchymal stem cells were compared to vascular SMCs when appliedto cyclic strains in order to investigate if these cells can be an alternative cell source for vasculartissue engineering.Direct cell-cell interactions of vascular ECs and SMCs were found to affect the gene and proteinexpression of angiogenic factors. Shear stress modulated the expression profiles of genes relatedto cytoskeleton/ECM modelling, cell proliferation, signal transduction, and immuneresponses/inflammation in co-cultured ECs and SMCs. The gene expression and proteinproduction of different SMCs' specific markers and ECM components in tissue engineeredconstruct were lower in the constructs compared to native veins and arteries after a period of 6weeks. Human MSCs were demonstrated to be capable of responding to mechanical stress, andthey hold great potential as a cell source of autologous vascular cells.To increase the success of engineered vascular grafts, the blood vessel constructs should bedesigned to mimic the properties of native blood vessels. Therefore, understanding theimportance of ECM and regulation of cellular behaviour is particularly necessary.