Proper growth and development require the orderly synthesis and deposition of individual components of the extracellular matrix (ECM) into well ordered networks. Once formed, the ECM maintains tissue structure and houses resident cells. One ECM component, ␤ig-h3, is a highly conserved transforming growth factor-␤-inducible protein that has been hypothesized to function as a bifunctional linker between individual matrix components and resident cells. To gain insights into its physiological function, full-length ␤ig-h3 protein was produced using a baculovirus expression system and purified under native conditions. Human fibroblasts attached and spread on ␤ig-h3-coated plates and developed actin stress fibers. Purified ␤ig-h3 binds fibronectin (FN) and type I collagen (Col I) but does not bind gelatin. Using defined fragments of FN, we localized the ␤ig-h3 recognition region to the gelatin/collagen binding domain present in the N-terminal region of the FN molecule. Our results identify FN and Col I as two ligands of ␤ig-h3 in the ECM.

Periodontal ligament fibroblasts (PDLFs) are a heterogeneous population of cells that are involved in the normal maintenance, repair and regeneration of both the ligament and adjacent hard tissues. Additionally, the ability of these cells to respond to mechanical stimulation suggests that they have a central role in mediating the osseous remodeling that underlies physiological and orthodontic tooth movement. To characterize their role further in this process, the current study evaluated the effect of tensional stress on the biosynthesis of extracellular matrix (ECM) proteins by human PDLFs. Cell strains were established from extracted human premolars and third molars. Cells exposed to 5% biaxial deformation (strain) at a frequency of 30 times/min for 24 hr exhibited statistically significant increases in type I collagen and fibronectin synthesis, and a statistically signficant decrease in tropoelastin production relative to unstretched controls. Cells exposed to 10% strain exhibited similar responses for fibronectin and tropoelastin while the amount of type I collagen synthesized by stretched cells did not differ from control levels. These results indicate that mechanical stimulation of PDLFs alters type I collagen, tropoelastin and fibronectin production and that these cells are differentially responsive to varying levels of mechanical stress. The ability of these cells to alter ECM protein synthesis in response to specific magnitudes of tensional stress may in part explain how PDLFs regulate ligament and hard tissue remodeling.

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