The Effect of Suppressing Discoidin Domain Receptor Expression on Keloid Formation and Proliferation
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Abstract: Background. Discoidin domain receptors (DDR) with tyrosine kinase activity have been identified as novel receptors for modulating collagen production and organization in scar tissue. The purpose of this study was to explore the effect of blocking discoidin domain receptor 1 (DDR1), signaling of keloid fibroblast cells on the inhibition of keloid formation, and proliferation, by means of gene therapy. Methods. The expression of DDR1 in keloid tissues was investigated by immunohistology and the expression of DDR1 protein in keloid fibroblasts was examined by Western blot analysis. Keloid dermal fibroblasts were infected in vitro with modified phosphorothioate and liposome-encapsulation DDR1-antisense oligodeoxynucleotide (ASODN). Northern blot was used to analyze gene expression of DDR1 in infected keloid dermal fibroblasts and the effect on type I and type III collagen gene expression. Extracellular matrix production in infected fibroblasts was analyzed by [3H] proline incorporation. Results. In keloid tissues, the expression of DDR1 was observed to be widely and strongly distributed. The expression of DDR1 protein was also highly increased in keloid fibroblasts compared to normal skin fibroblasts. This was markedly downregulated in lipid-encoding DDR1-ASODN infected fibroblasts compared to lipid encoding DDR1-NSODN infected fibroblasts and lipid-infected fibroblasts. Type I and type III collagen gene expression and extracellular matrix production also were downregulated markedly in DDR1 ASODN infected fibroblasts. Moreover, the ratio of type I and type III collagen was significantly improved. Conclusion. An intrinsic functional difference exists between normal human dermal and keloid fibroblasts in terms of higher DDR1 gene expression in keloid fibroblasts. The quality and quantity of collagen can be improved by downregulating the expression of DDR1 using ASODN. This intervention is potentially useful in controlling fibrosis and keloid formation in clinical settings.
Address correspondence to:
Yuzhi Jiang, MD, PhD and
Xin Xing, MD, PhD
Shanghai Burn Institute, Ruijin Hospital
Shanghai Jiaotong University
197 Ruijin No.2 Road
Shanghai 200025, P. R. China
Successful wound healing involves a complete orchestration of cytokines, growth factors, and extracellular matrix (ECM) components. The regulation of ECM components, especially collagen, is key in tissue remodeling and represents a vital step in the wound healing process, with or without scarring. Keloids are abnormal scars that grow beyond the boundary of the original site of skin injury and are characterized by excess accumulation of ECM components. The underlying mechanisms of pathogenesis remain unknown. Clinically, the keloid is a significant cosmetic problem, yet present treatment methods remain largely ineffective.1
Many hypotheses have attempted to explain the etiology of keloid formation,2 and many studies have been devoted to the comparison of normal dermal and keloid fibroblasts.3,14–16 Recently, researchers have focused on transforming growth factor-beta (TGF-β),3 which has a probable role in scar formation.
Additionally, cellular signaling mechanisms may indicate inherent differences in response to injury between keloid fibroblasts and normal dermal fibroblasts Specifically, the major difference in gene regulation that leads to abnormal excess production of ECM in keloid fibroblasts is due to the interaction of cell surface receptors and the ECM.
Wound healing is a dynamic biological process involving many cell-cell and cell-matrix interactions in a complex milieu. Keloids are a result of an “overhealed” wound. The interaction of ECM and the cell result in abnormal cell behavior.
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