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The role of small leucine-rich proteoglycans in non-scarring human oral mucosal wound healing Honardoust, Dariush

Abstract

Small leucine-rich proteoglycans (SLRPs) decorin, biglycan, fibromodulin and lumican are extracellular matrix (ECM) molecules that regulate collagen fibrilogenesis, cell functions and activity of transforming growth factor-P (TGF-ß). Thus, SLRPs may play critical roles in wound healing. In contrast to dermal wounds, gingival wounds regenerate with minimal scaring. However, the cellular and molecular mechanisms involved in this processes are not known. The aim of this study was to analyze the abundance of SLRPs, TGF-ß and Endo180, the major collagen endocytosis receptor in fibroblasts, in normal unwounded gingiva and during wound healing. The association of Endo180 with decorin was also investigated during wound healing. We hypothesized that compared to normal unwounded tissue, gingiva shows distinct localization and altered accumulation of SLRPs, TGF-ß and Endo180 during wound healing. To further analyze functions of SLRPs, we studied interaction of decorin with cultured gingival fibroblasts. Double immunostaining was used to study the localization of SLRPs, Endo180 or TGF-ß in tissue sections from normal human gingiva and up to 60 days after experimental wounding. The expression of Endo180 in cultured fibroblasts and keratinocytes was studied by immunoblotting and reverse transcriptase-polymerase chain reaction. To study interaction of cultured fibroblasts with decorin and decorin-induced signaling we used immunoblotting, function-blocking antibodies, pharmacological inhibitors, quantitative immunocytochemistry and RNA interference. In normal gingiva and during wound healing, SLRPs localized to collagen in a sitespecific manner. The immunoreactivity of SLRPs, TGF-ß1, TGF-ß3 and Endo180 was spatially and temporally regulated in myofibroblasts, pericytes, macrophages, endothelial and epithelial cells during wound healing. During wound healing, decorin colocalized with Endo180 in myofibroblasts. In cultured fibroblasts, decorin induced phosphorylation of distinct receptor tyrosine kinases leading to formation of reactive oxygen species (ROS) via the PI3K/mTOR signaling pathway. This was necessary for decorin endocytosis mainly via the clathrin-pathway. SLRPs may play a role in gingival wound re-epithelialization, collagen fibrilogenesis, ECM remodeling and cell signaling. Specifically, increased abundance of fibromodulin, decorin and TTGF-ß3 relative toTGF-ß1 may contribute to the reduced scaring during gingival wound healing. Decorin may interact with Endo180 to modulate its function and regulates cell signaling by inducing ROS formation.

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