Spatial organization of extracellular matrix and fibroblast activity: effects of serum, transforming growth factor beta, and fibronectin

The goal of our research is to understand reciprocal relationships between cell function and tissue organization. We studied the regulation of fibroblast activity in an in vitro culture model that recapitulates in continuous fashion the cycle of events occurring during connective tissue repair. We present evidence that concomitant with spatial reorganization of the extracellular matrix, there was a dramatic decline in extracellular matrix synthesis and cell proliferation. Therefore, spatial reorganization was a crucial turning point for fibroblast activity. Factors that regulated the timing of spatial reorganization included serum, transforming growth factor beta, and fibronectin. By accelerating spatial reorganization of the cultures, transforming growth factor beta led to a relative decrease in cell proliferation and extracellular matrix synthesis. By retarding spatial reorganization of the cultures, fibronectin led to a relative increase in cell proliferation and extracellular matrix synthesis. The results indicate that spatial information in the three-dimensional cell-matrix interaction permits higher order, tissue-level regulation of fibroblast function.