Abstract. Platelet-derived growth factor (PDGF) and transforming growth factor-~ (TGF-/~) markedly potentiate tissue repair in vivo. In the present experiments, both in vitro and in vivo responses to PDGF and TGF-B were tested to identify mechanisms whereby these growth factors might each enhance the woundhealing response. Recombinant human PDGF B-chain homodimers (PDGF-BB) and TGF-B1 had identical dose-response curves in chemotactic assays with monocytes and fibroblasts as the natural proteins from platelets. Single applications of PDGF-BB (2 #g, 80 pmol) and TGF-B1 (20 #g, 600 pmol) were next applied to linear incisions in rats and each enhanced the strength required to disrupt the wounds at 5 d up to 212% of paired control wounds. Histological analysis of treated wounds demonstrated an in vivo chemotactic response of macrophages and fibroblasts to both PDGF-BB and to TGF-/~ 1 but the response to TGF-B1 was significantly less than that observed with PDGF-

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Recent studies have demonstrated that tropoelastin and elastin-derived peptides are chemotactic for fibroblasts and monocytes. To identify the chemotactic sites on elastin, we examined the chemotactic activity of VaI-Gly-VaI-Ala-Pro-Gly (VGVAPG), a repeating peptide in tropoelastin. We observed that VGVAPG was chemotactic for fibroblasts and monocytes, with optimal activity at ~10 -8 M, and that the chemotactic activity of VGVAPG was substantial (half or greater) relative to the maximum responses to other chemotactic factors such as platelet-derived growth factor for fibroblasts and formyl-methionyl-leucylphenylalanine for monocytes. The possibility that at least part of the chemotactic activity in tropoelastin and elastin peptides is contained in VGVAPG sequences was supported by the following: (a) polyclonal antibody to bovine elastin selectively blocked the fibroblast and monocyte chemotactic activity of both elastin-derived peptides and VGVAPG; (b) monocyte chemotaxis to VGVAPG was selectively blocked by preexposing the cells to elastin peptides; and (c) undifferentiated (nonelastin producing) bovine ligament fibroblasts, capable of chemotaxis to platelet-derived growth factor, did not show chemotactic responsiveness to either VGVAPG or elastin peptides until after matrix-induced differentiation and the onset of elastin synthesis. These studies suggest that small synthetic peptides may be able to reproduce the chemotactic activity associated with elastin-derived peptides and tropoelastin.Chemotactic activity has been associated with several components of the extracellular matrix including collagen (18), fibronectin (1, 5, 17), laminin (27), peptides of insoluble elastin (6, 22,23), and tropoelastin (23). The sites of chemotactic activity on collagen (16) and fibronectin (1, 25) have been partially localized, however the chemotactically active regions of laminin and elastin have not yet been established. The present study was undertaken to identify the site(s) of chemotactic activity on elastin.In approaching the molecular basis of the chemotactic activity of elastin peptides two points seemed important: first, the presence of fibroblast chemotactic activity in tropoelastin (23), the soluble precursor of insoluble elastin (20), suggested that the lysine-derived cross-links characteristic of insoluble elastin are not essential for the chemotactic activity of elastin peptides; and second, the presence of repeating peptide sequences in tropoelastin (4, 19) directed us to look at these peptide repeats as the possible source of the chemotactic activity. In this report, we present evidence that some of the chemotactic activity of elastin is associated with Val-Gly-ValAla-Pro-Gly (VGVAPG),~ a hexamer that repeats six times in one tryptic fragment of porcine tropoelastin (20). MATERIALS AND METHODS Preparation of Elastin-derived Peptides:Bovine ligament elastin, obtained from Elastin Products (St. Louis, MO), was solubilized with porcine pancreatic elastase (Sigma Chemical Co., St. Louis, MO) by incubation a...

The platelet-derived growth factor (PDGF) is shown to be chemotactic for monocytes and neutrophils. Maximum monocyte chemotaxis to PDGF is fully equal to that achieved with C5a and occurs at congruent to 20 ng/ml (congruent to 0.7 nM). Maximum neutrophil chemotaxis is congruent to 60% that achieved with C5A but occurs at congruent to 1 ng/ml (congruent to 32 pM). The chemotactic activity of PDGF is blocked by specific antisera to PDGF and by protamine sulfate, a competitive inhibitor of PDGF binding to cell surfaces. In contrast to PDGF, epidermal growth factor shows no chemotactic activity for inflammatory cells at 0.5-100 ng/ml. The high level of chemotactic activity of PDGF suggests that in addition to its role as a mitogen for smooth muscle cells and fibroblasts, PDGF may be involved in attracting inflammatory cells to sites of platelet release.