Effect of passage number and matrix characteristics on differentiation of endothelial cells cultured for tissue engineering

Cells can sense the physical and chemical properties of artificial materials used as scaffolds for tissue engineering and regulate their behavior. Therefore, biomimetic and biospecific molecules are coated on materials to regulate function of cells on the tissue-engineered product. These bioactive molecules can be attached in a defined spectrum, concentration and spatial distribution in order to control adhesion, growth, viability, differentiation, and function of the cells. When autologous cells are used for tissue engineering, initially limited cells obtained may often need an amplification of cell number by passage in tissue culture before they are seeded on a biomaterial or scaffold. We have conducted this study to understand how the characteristics of bioactive molecule coating might affect proliferation, apoptosis and differentiation when endothelial cell (EC) is serially passaged. Proliferation was assessed by proliferating cell nuclear antigen (PCNA) staining along with counting of cells harvested from confluent monolayer. Apoptosis was assessed by Annexin V staining and differentiation by semi quantitative reverse transcriptase polymerase chain reaction (RT-PCR) for von Willebrand factor (vWF) expression and quantification of its release using enzyme linked immunosorbant assay (ELISA), and thrombogenicity by comparing platelet adhesion to EC monolayer Dacron grafts (DG) with specific protein coating. The results indicate that ECs easily lose its proliferation potential when they are cultured repeatedly on gelatin, turn apoptotic and over express the prothrombotic protein- vWF. Whereas, when it is grown on a matrix composed of fibrin, fibronectin, gelatin and vascular EC growth factor (VEGF), the cells retained their ability to proliferate, remained viable and were relatively less thrombogenic, even when passage number progressed. It is concluded that if ECs are grown on the composite matrix that mimics natural vessel scaffold, the cell number can be amplified without affecting its normal physiological function and may be used to generate effective tissue-engineered cardiovascular constructs.