Static equibiaxial stretch -mediated mechanotransduction in adult cardiac fibroblast

Mechanical stresses and strains act on many individual and cooperative cellular components in a variety of tissues and have emerged as a major determinant of functional responses of cells. In the heart, mechanical factors have been implicated in a variety of responses of cardiac myocytes and nonmyocytes to mechanical load. How cells "sense," " integrate," and "respond" to distinct applications of mechanical stimuli, and in turn transduce these stimuli into biochemical signals, remains poorly understood. We determined whether cardiac fibroblasts could respond to differences in well-defined applications of mechanical stimuli and subsequently alter their functional characteristics in a precise manner.;We examined effects of varying modes of equibiaxial strain on mitogen-activated protein kinase (MAPK) cascades in adult cardiac fibroblasts. Applications of mechanical stretch and compression to adult cardiac fibroblasts resulted in distinct responses. These experiments demonstrated that cardiac fibroblasts can effectively differentiate between states of tension and compression, and generate specific patterns of MAPK activity. Examination of the MAPK, extracellular signal-regulated kinase (ERK), responses to mechanical stimulation in adult cardiac fibroblasts revealed distinct activation patterns that are transient, time-dependent, magnitude-dependent and appear biphasic at higher magnitudes of strain.;To measure effects of mechanical stimulation on transcriptional activity of fibronectin (FN), we transfected 3T3 fibroblasts with a FN promoter construct. 3T3 fibroblasts initially served as a model for poorly transfectable adult cardiac fibroblasts. These studies indicate that the FN promoter is regulated by a range of mechanical stimuli.;To determine whether mechanical stimulation regulates FN gene expression, we examined FN mRNA levels. These experiments showed that exposure of 3T3 fibroblasts to mechanical strain causes an increase in the expression of FN mRNA's.;We also identified AP-1 sites on the rat FN promoter as possible regulators of mechanically induced expression of FN in fibroblasts. Our experiments suggest that stretch enhances AP-1 binding and ERK kinase (MEK) inhibition attenuates this response.;In summary, quantitative studies of effects of differing magnitudes and patterns of stretch and compression on cardiac fibroblast and 3T3 fibroblast function suggest that mechanical stimuli play important roles in specific cellular processes, which are dependent on the type of mechanical stimuli applied.