Gene Expression Profiles in Engineered Cardiac Tissues Respond to Mechanical Loading and Inhibition of Tyrosine Kinase

We tested the hypothesis that global ECT gene expression patterns are sensitive to mechanical loading conditions and tyrosine kinase inhibitors, similar to the maturing myocardium. We generated 3D ECTs from day 14.5 rat embryo ventricular cells, as previously published, and then treated constructs after 5 days in culture for 48 hours with mechanical stretch (5%, 0.5 Hz) and/or the p38MAPK (p38 mitogen-activated protein kinase) selective inhibitor BIRB796. RNA was isolated from 3 sets of experiments and assayed using a standard Agilent rat 4x44k V3 microarray and Pathway Analysis software for transcript expression fold changes and changes in regulatory molecules and networks. At the threshold of a 1.5 fold change in expression, mechanical stretch altered 1,559 transcripts, versus 1,411 for BIRB796, and 1,846 for stretch plus BIRB796. As anticipated, top pathways altered in response to these stimuli include Cellular Development, Cellular Growth and Proliferation; Tissue Development; Cell Death, Cell Signaling, and Small Molecule Biochemistry as well as numerous other pathways. Changes in transcript expression were confirmed by quantitative-PCR for selected regulatory molecules. Thus, ECTs display a broad spectrum of altered gene expression in response to mechanical load and/or tyrosine kinase inhibition, reflecting the complex regulation of proliferation, differentiation, and architectural alignment that occurs during ECT maturation and adaptation. This approach can now be used to test the role of individual molecules and pathways on the regulation of ECT maturation and remodeling.