570. Ectopic Expression of Adenoviral Smad7 Significantly Reduces Hypertrophic Scarring in Rabbit Ears by Abrogating TGFβ1 Signalling

Top of pageAbstract Introduction. Hypertrophic scarring is a fibroproliferative disorder unique in humans resulting in excessive deposition of extracellular matrix and / or establishment of contractions. Affected individuals often suffer from severe disfigurement, functional impairment and social isolation. Previous in vitro studies have identified TGF|[beta]|1 as one of the main pathogenic factors during initialization and ongoing development of cutaneous fibrogenic processes. Binding of TGF|[beta]|1 to its specific receptor complex results in activation of a cytokine specific signalling pathway mediated by Smad proteins. In undisturbed cellular systems this pathway is subjected to a self regulatory mechanism by expression of Smad7, thereby providing a steady state of matrix deposition and catabolism by blocking phosphorylation of Smad2 and 3 as crucial initial step of downstream signalling. However, in hypertrophic scarring this regulatory mechanism is impaired, resulting in excessiveoverexpression of cytokine depending functional proteins. This study addressed the question whether ectopic overexpression of adenoviral Smad7 may result in abrogation off TGF|[beta]|1 signalling, thereby reducing hypertrophic scar formation in an animal model. Materials and methods. In order to achieve hypertrophic scar formation, 12 white female New Zealand rabbits (2.5 |[ndash]| 3 kg) were anaesthezised and full-thickness skin defects were created on the inner side of each ear measuring 5 by 1.5 cm without injuring the perichondrium. The resulting defects were covered with hydrocolloid dressings exchanged every other day. 28 days following defect creation one ear was infected with an adenovirus encoding for Smad7 by using a dermojet. Contralateral ears were infected with adenoviral LacZ and served as controls. On post boost days 2, 4, 6, 8, 10 and 42 2 rabbits each were sacrificed and scar areas were completely excised including a small surrounding area of healthy soft tissue. One part of the biopsies was subjected to immunohistochemical investigations; the other part was used for western blotting and LightCycler analysis. Additionally, planimetry of scar areas was performed to detect the amount of wound contraction. Results. In all ears hypertrophic scar formation was observed. Application of adenoviral Smad7 resulted in reduced scar contraction as well as decreased deposition off extracellular matrix confirmed by planimetry and immunohistochemical investigations. Western blotting and LightCycler analysis revealed distinctive downregulation of TGF|[beta]|1 and depending expression of fibrosis related proteins on mRNA and protein levels compaired to controls. Further, expression of SMAD proteins 2 and 3 was clearly downregulated by ectopically overexpressed Smad7. Conclusions. Our results demonstrate that abrogation of TGF|[beta]|1 specific signalling by ectopically overexpressing Smad7 in vivo can positively influence fibroproliferative processes. However, since the potential role of Smad7 in tumourigenesis remains controversial our results proof, that targeting TGF|[beta]| signalling may be a possible basis for new therapeutic approaches tackling the clinical problem of hypertrophic scarring.