Abstract. Extracellular matrix (ECM) and growth factors are potent regulators of cell phenotype. These biological mediators of cellular responses are potentially interactive and as such could drive cells through progressive phenotypes to create new tissue as in morphogenesis and wound repair. In fact, ECM composition changes during tissue formation accompanied by alterations in cell growth and migration. How alterations in the ECM regulate cell activities is poorly defined. To address this question in wound repair, we cultured normal human dermal skin fibroblasts in relaxed collagen gels, fibronectin-rich cultures or stressed fibrin gels, and stressed collagen gels to model normal dermis, early wound provisional matrix, and late granulation tissue, respectively. Integrin subunits, ~2, ~3, and ors, that define receptor specificity for collagen and provisional matrix, respectively, were measured at mRNA steady-state level before and after stimulation with platelet-derived growth factor-BB (PDGF-BB), a potent mitogen and chemoattractant for fibroblasts. Fibronectin-rich cultures and fibrin gels supported PDGF-BB induction of et 3 and et5 mRNA. In contrast, both stressed and relaxed collagen attenuated these responses while promoting maximal a2 mRNA expression. Posttranscriptional regulation was an important mechanism in this differential response. Together PDGF-BB and collagen gels promoted et2, but not et 3 and et 5, mRNA stability. Conversely, when fibroblasts were in fibronectin-rich cultures, PDGF-BB promoted et 3 and o~5, but not a2, mRNA stability. We suggest that ECM alterations during wound healing or any new tissue formation cause cells to respond differently to repeated growth factor stimuli. An ordered progression of cell phenotypes results, ultimately consummating tissue repair or morphogenesis.URING cutaneous wound repair, cells must attach to new matrix molecules and migrate (Welch et al., 1990). Soon after wounding, a provisional matrix of fibronectin, fibrinogen, fibrin, and vitronectin forms in the wound area (Gailit and Clark, 1994a). In the fibrin network, platelets release growth factors such as PDGF that stimulate proliferation and chemoattraction of fibroblasts (Deuel et al., 1991). Activated fibroblasts must move from surrounding collagenous connective tissues into a fibrin/fibronectin-filled wound and subsequently synthesize new collagenous matrix. Clearly, fibroblast responses to these extracellular matrix (ECM) 1 molecules and growth factors are essential for the healing process to progress.To address the mechanisms by which ECM molecules regulate cell activities, three-dimensional ECM-based culture systems are increasingly used. Since type I collagen is a ubiquitous component of dermal ECM much attention has been devoted to cells cultured in stressed and/or relaxed collagen gels. The relaxed collagen gel is considered

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The ability to fabricate tissue engineering scaffolds containing systematic gradients in the distributions of stimulators provides additional means for the mimicking of the important gradients observed in native tissues. Here the concentration distributions of two bioactive agents were varied concomitantly for the first time (one increasing, whereas the other decreasing monotonically) in between the two sides of a nanofibrous scaffold. This was achieved via the application of a new processing method, that is, the twin-screw extrusion and electrospinning method, to generate gradients of insulin, a stimulator of chondrogenic differentiation, and β-glycerophosphate (β-GP), for mineralization. The graded poly(ɛ-caprolactone) mesh was seeded with human adipose-derived stromal cells and cultured over 8 weeks. The resulting tissue constructs were analyzed for and revealed indications of selective differentiation of human adipose-derived stromal cells toward chondrogenic lineage and mineralization as functions of position as a result of the corresponding concentrations of insulin and β-GP. Chondrogenic differentiation of the stem cells increased at insulin-rich locations and mineralization increased at β-GP-rich locations.

A three-dimensional collagen lattice can provide skin fibroblasts with a cell culture environment that simulates normal dermis. Such a collagen matrix environment regulates interstitial collagenase (type I metalloproteinase [MMP-1], collagenase-1) and collagen receptor α2 subunit mRNA expression in both unstimulated or platelet-derived growth factor–stimulated dermal fibroblasts (Xu, J., and R.A.F. Clark. 1996. J. Cell Biol. 132:239–249). Here we report that the collagen gel can signal protein kinase C (PKC)-ζ activation in human dermal fibroblasts. An in vitro kinase assay demonstrated that autophosphorylation of PKC-ζ immunoprecipitates was markedly increased by a collagen matrix. In contrast, no alteration in PKC-ζ protein levels or intracellular location was observed. DNA binding activity of nuclear factor κB (NF-κB), a downstream regulatory target of PKC-ζ, was also increased by fibroblasts grown in collagen gel. The composition of the NF-κB/Rel complexes that contained p50, was not changed. The potential role of PKC-ζ in collagen gel–induced mRNA expression of collagen receptor α2 subunit and human fibroblast MMP-1 was assessed by the following evidence. Increased levels of α2 and MMP-1 mRNA in collagen gel–stimulated fibroblasts were abrogated by bisindolylmaleimide GF 109203X and calphostin C, chemical inhibitors for PKC, but retained when cells were depleted of 12-myristate 13-acetate (PMA)–inducible PKC isoforms by 24 h of pretreatment with phorbol PMA. Antisense oligonucleotides complementary to the 5′ end of PKC-ζ mRNA sequences significantly reduced the collagen lattice–stimulated α2 and MMP-1 mRNA levels. Taken together, these data indicate that PKC-ζ, a PKC isoform not inducible by PMA or diacylglycerol, is a component of collagen matrix stimulatory pathway for α2 and MMP-1 mRNA expression. Thus, a three-dimensional collagen lattice maintains the dermal fibroblast phenotype, in part, through the activation of PKC-ζ.