Experimental And Clinical Studies On Roles Of Epidermis In Regulation Of Scar Formation

The etiology of hypertrophic scarring, a pathological end point of wound healing, is still not fully elucidated. Scars is the end result of any form of wounding process , but it has been most frequently studied in burn patients for because the scars may constitute the most troublesome life-long sequelae. The incidence of scar hypertrophy is high in pediatric burn patients under the age of five. The scars are often red, raised, and hard, leading to disfigurements and disabling contractures at joint sites. Hypertrophic scars commonly occur when re-epithelialization has been delayed, and are conventionally described as a dermal pathology in which the epidermis has been thought to play a passive role. Notwithstanding, wound healing is a complex cascade of events involving the epidermis, dermis, endothelial cells, and inflammatory response, and in its process it might be considered as the final result of abnormalities in the epidermal-mesenchymal interaction, rather than isolated defects in the dermis.PART ONE Punch biopsies were taken both of hypertrophic scars from partial-thickness burn and of match unbumed skin adjacent to scars. The biopsies were analyzed using histoimmunochemical staining for markers of keratinocyte proliferation, differentiation and activation (keratin 14, 10 and 16). We observed a higher expression of keratin 16 and keratin 14, but a weaker expression of keratin 10 in the epidermis of scars compared with normal control skins. Meanwhile, the total RNAs from epidermis of hypertrophic scar and normal skin in 4 patients were isolated and purified to mRNAs, which were reversely transcribed to cDNAs with the incorporations of fluorescent dCTP, for preparing the hybridization probes. The mixed probes were hybridized to the cDNA microarray containing PCR products of about 14000 human genes. The fluorescent signals of cDNA microarray were recorded by scanner and analyzed by computers. Among 14000 target genes, the expression levels of 138 genes differed between hypertrophic scar and normal epidermis in all the 4 patients, including TGF- β , IL-1, and ICAM-1, etc. Our results suggest that the persistence of activated keratinocytes in epidermis may instigate the formation ofhypertrophic scar.PART TWO Purified normal skin-derived keratinocytes and normal skin-/scar-derived fibroblasts cell strains were developed from normal human skin and hypertrophic scar tissue. Conditioned media in different concentrations (0%, 5%, 10%, 20%) were created from serum-free medium which had been used to incubate keratinocytes for 12 hours. Nearly confluent fibroblast cultures in 96-well plate, 104 cells in each well, were exposed to graded concentrations of conditioned medium. Replication was quantified by the incorporation of 3H-thymidine. Collagen synthesis was quantified by the incorporation of 3H-proline into collagen-sensitive protein. The result showed that keratinocyte conditioned medium induced a significant increase in replication and a decrease in collagen synthesis in normal skin-derived fibroblasts cell. These suggest that ideal strategy to decrease hypertrophic scar is early wound closure with skin grafting or cultured epithelial autograft.PART THREE 11 patients admitted to our plastic unit undergoing split-thickness skin transplantation were randomly selected for the study. Each wound in donor site was divided into two areas, one half receiving microskin autograft (M group) and another half covered with vaseline gauze (V group). The length of total epithelialization and wound conditions were followed. Although epithelialization in M group was delayed for about 3.8 days compared with V group, the healing was significantly better in term of color, texture and thickness. The results suggests that microskin autograft, significantly decreasing scar hypertrophy, could be applied not only to the wound on split-thickness skin donor site, but also to deep partial-thickness burn wound in order to reduce scar formation. The thickness and density of skin particle for the grafting are key points for achieving satisfactory results.