Biglycan and decorin induce morphological and cytoskeletal changes involving signalling by the small GTPases RhoA and Rac1 resulting in lung fibroblast migration

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Abstract
Biglycan and decorin are small chondroitin/dermatan sulphate proteoglycans in the extracellular matrix of connective tissue that belong to the family of structurally related proteoglycans called small leucine-rich repeat proteins. We show for the first time that biglycan and decorin induce morphological and cytoskeletal changes in fibroblasts, resulting in an increase in migration. Biglycan changed the cell shape of fibroblasts with formation of long protruding filamentous processes. This was also seen for decorin but to a lesser extent. Using fluorescence staining of F-actin fibres it was possible to show that these long filamentous processes were supported by long thick bundles of actin, together with an induced formation of stress fibres after stimulation with biglycan and decorin. Moreover, a reorganisation of α-smooth muscle actin was clearly seen in these cultures. Decorin also stimulated α-smooth muscle actin expression in the cells. Using cDNA Atlas Arrays we were also able to show that the mRNA level of a number of the intracellular regulators and effectors involved in cell migration were increased. For example, the focal adhesion proteins paxillin and zyxin, and some of the small Rho GTPases such as RhoA, Rac1 and Cdc42 were upregulated. After treatment with biglycan or decorin, additional results showed an increased activation of RhoA (1.8- and 1.5-fold, respectively) and Rac1 (1.8- and 1.5-fold, respectively) after 15 minutes. These factors are known to be involved in fibroblast migration, and as expected a 1.3- to 1.6-fold increase in migration could be observed after stimulation with biglycan or decorin. This induced migration was caused by the core protein, as treatment with glycosaminoglycan chains alone did not have any effect. In summary, these data indicate that biglycan- and decorin-induced fibroblast cytoskeletal and signalling changes result in an increased cell migration, and demonstrate their potential role in the remodelling process.

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