Chronic stretch of engineered heart tissue induces hypertrophy and functional improvement

To examine the influence of chronic mechanical stretch on functional behavi or of cardiac myocytes, we reconstituted embryonic chick or neonatal rat ca rdiac myocytes to a 3-dimensional engineered heart tissue (EHT) by mixing f reshly isolated cells with neutralized collagen I and culturing them betwee n two Velcro-coated silicone tubes, held at a fixed distance with a metal s pacer. After 4 days, EHTs were subjected to a phasic unidirectional stretch for 6 days in serum-containing medium. Compared to unstretched controls, R NA/DNA and protein/cell ratios increased by 100% and 50%, respectively. ANF mRNA and a-sarcomeric actin increased by 98% and 40%, respectively. Morpho logically, stretched EHTs exhibited improved organization of cardiac myocyt es into parallel arrays of rod-shaped cells, increased cell length and widt h, longer myofilaments, and increased mitochondrial density. Thus, stretch induced phenotypic changes, generally referred to as hypertrophy. Concomita ntly, force of contraction was two- to fourfold higher both under basal con ditions and after stimulation with calcium or the beta-adrenergic agonist i soprenaline. Contraction kinetics were accelerated with a 14-44% decrease i n twitch duration under all those conditions. In summary, we have developed a new in vitro model that allows morphological, molecular, and functional consequences of stretch to be studied under defined conditions. The main fi nding was that stretch of EHTs induced cardiac myocyte hypertrophy, which w as accompanied by marked improvement of contractile function.-Fink, C., Erg un, S., Kralisch, D., Remmers, U., Weil, J., Eschenhagen, T. Chronic stretc h of engineered heart tissue induces hypertrophy and functional improvement .