Transforming growth factor-beta, a potent modulator of cell function, induces fibroblasts cultured on plastic to increase collagen synthesis. In 5- and 7-day porcine skin wounds, which have minimal to moderate collagen matrix, respectively, transforming growth factor-beta and type I procollagen were coordinately expressed throughout the granulation tissue. However, in 10-day collagen-rich granulation tissue type I procollagen expression diminished despite persistence of transforming growth factor-beta. To investigate whether collagen matrix attenuates the collagen-synthetic response of fibroblasts to transforming growth factor-beta, we cultured human dermal fibroblasts in conditions that simulate collagen-rich granulation tissue. Therefore, human dermal fibroblasts were suspended in attached collagen gels and collagen and noncollagen production was assayed in the absence and presence of transforming growth factor-beta. Although transforming growth factor-beta stimulated collagen synthesis by fibroblasts cultured in the collagen gels, these fibroblasts consistently produced less collagen than similarly treated fibroblasts cultured on plastic. This phenomenon was not secondary to nonspecific binding of transforming growth factor-beta to the collagen matrix. Fibroblasts cultured in a fibrin gel responded to transforming growth factor-beta similarly to fibroblasts cultured on plastic. Using immunofluorescence probes to type I procollagen, we observed that transforming growth factor-beta increased type I procollagen expression in most fibroblasts cultured on plastic, but only in occasional fibroblasts cultured in collagen gels. From these data we conclude that collagen matrices attenuate the collagen synthetic response of fibroblast to transforming growth factor-beta in vitro and possibly in vivo.
Cell-specific Delivery of a Transforming Growth Factor-beta Type I Receptor Kinase Inhibitor to Proximal Tubular Cells for the Treatment of Renal Fibrosis