Type I collagen synthesis in cultured human fibroblasts: regulation by cell spreading, platelet-derived growth factor and interactions with collagen fibers

Abstract
Type I collagen protein and pro-alpha 1(I) collagen mRNA levels were investigated in human dermal fibroblasts cultured on substrates which induced distinct morphologies. Induction of type I collagen protein synthesis required cell spreading in monolayer cultures; mere attachment to dishes coated with 2-hydroxyethyl methacrylate (poly(HEMA)) did not suffice. Spread cells or round cells cultured on poly(HEMA) differed in collagen type I production, but pro-alpha 1(I) collagen mRNA levels were similar. Recombinant human platelet-derived growth factor (PDGF)-BB could replace cell spreading as a stimulus for collagen synthesis in cells cultured on poly(HEMA). At later time points, pro-alpha 1(I) collagen mRNA levels were down-regulated, although relatively less than type I collagen synthesis. Type I collagen synthesis by fibroblasts cultured in three-dimensional collagen gels was strongly down-regulated at both the protein and RNA levels. In addition to its capacity to stimulate collagen synthesis, PDGF-BB induced elongation and the formation of long processes by fibroblasts cultured in collagen gels. The stimulatory effect by cell spreading and PDGF-BB on collagen synthesis was inhibited by the phosphatidylinositol 3-kinase (PI3K) inhibitor LY294002. However, inhibition of PI3K only inhibited induction of collagen synthesis by actively spreading cells or by PDGF-BB and did not induce a down-regulation of collagen synthesis in cells which had already spread. These data demonstrate that type I collagen protein synthesis is partly independent of pro-alpha 1(I) collagen mRNA levels but highly regulated by cell shape, although this could be decoupled by PDGF-BB. Both cell shape- and PDGF-BB-induced stimulation of collagen type I synthesis depends on a signalling pathway involving PI3K. Furthermore, levels of pro-alpha 1(I) collagen mRNA in fibroblasts are partly cell shape independent but are down-regulated by fibroblast interactions with native collagen fibers.