PROCEEDINGS |
Cardiac fibroblasts synthesize myocardial extracellular matrix (ECM) proteins, including fibronectin (FN) and collagen types I and III. We have previously implicated mechanical load as an important regulator of cardiac fibroblast function. To examine transcriptional activity of the FN gene, 3T3 fibroblasts were used as an easily transfectable cell culture model. Cells were transfected with a chimeric construct containing the chloramphenicol acetyltransferase (CAT) gene linked to the promoter region of the FN gene. Our equibiaxial stretch apparatus was used to apply tensile and compressive strains to cultured adult cardiac fibroblasts. Mechanical stretch of cardiac fibroblasts led to a 1.5 to 2-fold enhancement of CAT activity in cells stimulated by either 3% stretch or compression of -3% and -6%. 6% stretch led to a 3-fold induction of CAT activity. We also examined regulation of the upstream kinase, extracellular signal-regulated kinase (ERK), in cardiac fibroblasts responding to equibiaxial tensile and compressive strains. ERK activity was measured in cardiac fibroblasts stimulated by (1%, 4%, 6% and 10%) stretch and (-1% and -10%) compression. Mechanical stretch of cardiac fibroblasts induced a time-dependent increase in ERK activation levels, whereas compression led to an inhibition of this observed activity, compared to unstimulated controls. In summary, stretch and compression appear to be effective, differential regulators of FN transcriptional activity in 3T3 fibroblasts. Also, ERK signaling pathways, which may couple with FN regulation, appear to respond to mechanostimulation by varying their level of activation, which may be coupled to the magnitude of applied mechanical stimuli.