Controlling matrix formation and cross-linking by hypoxia in cardiovascular tissue engineering

van Vlimmeren MA, Driessen-Mol A, van den Broek M, Bouten CV, Baaijens FP. Controlling matrix formation and cross-linking by hypoxia in cardiovascular tissue engineering. J Appl Physiol 109: 1483-1491, 2010. First published September 16, 2010; doi: 10.1152/japplphysiol.00571.2010.-In vivo functionality of cardiovascular tissue engineered constructs requires in vitro control of tissue development to obtain a well developed extracellular matrix (ECM). We hypothesize that ECM formation and maturation is stimulated by culturing at low oxygen concentrations. Gene expression levels of monolayers of human vascular-derived myofibroblasts, exposed to 7, 4, 2, 1, and 0.5% O-2 (n = 9 per group) for 24 h, were measured for vascular endothelial growth factor (VEGF), procollagen alpha 1(I) and alpha 1(III), elastin, and cross-link enzymes lysyl oxidase (LOX) and lysyl hydroxylase 2 (LH2). After 4 days of exposure to 7, 2, and 0.5% O-2 (n = 3 per group), protein synthesis was evaluated. All analyses were compared with control cultures at 21% O-2. Human myofibroblasts turned to hypoxia-driven gene expression, indicated by VEGF expression, at oxygen concentrations of 4% and lower. Gene expression levels of procollagen alpha 1(I) and alpha 1(III) increased to 138 +/- 26 and 143 +/- 19%, respectively, for all oxygen concentrations below 4%. At 2% O-2, LH2 and LOX gene expression levels were higher than control cultures (340 +/- 53 and 136 +/- 29%, respectively), and these levels increased even further with decreasing oxygen concentrations (611 +/- 176 and 228 +/- 45%, respectively, at 0.5% O-2). Elastin gene expression levels remained unaffected. Collagen synthesis and LH2 protein levels increased at oxygen concentrations of 2% and lower. Oxygen concentrations below 4% induce enhanced ECM production by human myofibroblasts. Implementation of these results in cardiovascular tissue engineering approaches enables in vitro control of tissue development.