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Regulation of the Spatial Organization of Mesenchymal Connective Tissue: Effects of Cell-Associated versus Released Isoforms of Platelet-Derived Growth Factor

https://doi.org/10.1016/S0002-9440(10)65274-1Get rights and content

Platelet-derived growth factor (PDGF), a mitogen and chemoattractant for mesenchymal cells, occurs as cell-associated or released isoforms. To investigate their in vivo role, human keratinocytes, which normally synthesize both types of PDGF, were genetically modified to overexpress either wild-type PDGF-B (cell-associated) or the truncation mutant PDGF-B211 (released). Cells expressing the mutant isoform released 20 times more PDGF (145 ng/hour/107 cells) than cells expressing the wild-type isoform (6 ng/hour/107 cells). When grafted as epithelial sheets onto athymic mice, modified cells formed a stratified epithelium and induced a connective tissue response that differed depending on the PDGF isoform expressed. Expression of PDGF-B211 induced a thick connective tissue with increased numbers of fibroblasts, mononuclear cells, and blood vessels evenly distributed throughout the connective tissue layer, whereas expression of PDGF-B induced a zone of fibroblasts and mononuclear cells localized to the interface of the epidermis and connective tissue, which often disrupted the continuity of the basement membrane. Immunostaining revealed that wild-type PDGF protein was deposited in the basement membrane region. These data suggest that the different binding properties of PDGF isoforms control the spatial organization of cellular events in regenerating mesenchymal tissue in vivo.

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Supported by grants from the Shriners Hospitals for Children, the National Institutes of Health, and the Fritz Thyssen and German Research Foundation.

S.A. Eming's present address: Department of Dermatology, University of Cologne, Cologne, Germany.

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