The apparent need of an autologous cell source for tissueengineering applications has led researchers to explore thepresence of cells with stem cell plasticity in several humantissues. Dermal fibroblasts (FBs) are easy to harvest, expandin vitro and store, rendering them plausible candidates forcell-based therapies. The aim of the present study was toobserve the effects of adipogenic, chondrogenic and osteogenicinduction media on the phenotype of human FBs.Human preadipocytes obtained from fat tissue have beenproposed as an adult stem cell source with suitable characteristics,and were used as control cells in regard to their differentiationpotential. Routine staining, immunohistochemicalanalysis and alkaline phosphatase assay were employed,in order to study the phenotypic shift. FBs were shown topossess multilineage potential, giving rise to fat-, cartilageandbone-like cells. To exclude contaminant progenitor cellsor cell fusion giving rise to tissue with adipocyte-, chondrocyte-and osteoblast-like cells, single-cell cloning was performed.Single-cell-cloned FBs (sccFBs) displayed a similardifferentiation potential as primary-culture FBs. The pres-ence of ‘stem-cell-specific’ surface antigens was analyzedusing flow cytometry. The results reveal that sccFBs haveseveral of the markers associated with cells exhibiting stemcell plasticity. The findings presented here are corroboratedby the findings of other groups, and suggest the use of humandermal FBs in cell-based therapies for the reconstructionof fat, cartilage and bone.

Scar formation as a result of burn wounds leads to contraction of the formed granulation tissue, which causes both aesthetic and functional impairment for the patient. Currently, the main treatment methods focus on stretching to prevent tissue contraction. The myofibroblasts play a key role in the contraction of granulation tissue during scar formation, but their presence should normally decrease after wound re-epithelialization. In hypertrophic scars the myofibroblasts persist and is believed to cause further hypertrophy. Previous studies have shown that mechanical tension leads to increased myofibroblast numbers in granulation tissue. In order to evaluate the effect mechanical tension as a result of stretching has on the number of myofibroblasts in burn wound scars, an in vitro model was used. This model used human burn scar biopsies which were stretched and examined after 1 and 6 days to evaluate the effect on the number of myofibroblasts. The stretching caused an increase in the number of myofibroblasts after mechanical stimulation. This indicates that mechanical stimulation using stretching induces fibroblast to myofibroblast transdifferentiation, thus underlining the importance of further investigations of optimal methods of this regime for treating burn scars.

We investigated the capacity of normal human dermal fibroblasts to alter their phenotype into an endothelialcell-like phenotype. By utilising in vitro cell culture models, the part played by different types of serum andmedium constituents in inducing a phenotypic change of fibroblasts was investigated. The experiments usedprimary cultures of human endothelial cells, human dermal fibroblasts and single-cell clone fibroblasts. Thelatter cell type was obtained by clonal expansion using a micromanipulator technique. The results showed thatthe presence of human serum in the cell culture medium caused both types of fibroblasts to express vonWillebrand factor, to incorporate fluorochrome-labelled LDL, and to start forming capillary-like networks in asimilar way to endothelial cells. The phenotypic shift was detectable after 4 days of cell culture and reached amaximum after 7-10 days. To our knowledge this is the first report to describe differentiation of humanfibroblasts towards an endothelial cell-like phenotype. The results also show that the underlying mechanism ofthe phenotypic shift is a change in gene expression in the dermal fibroblasts and not fusion between different celltypes. Collectively, the present results indicate that human dermal fibroblasts may be a novel cell source forcreating vascular endothelium.

BACKGROUND: Recently, there has been an intense ongoing search for suitable cell sources for vascular tissue engineering. Previous studies report that cells with multilineage potential have been found within the connective stroma of the skin. In line with this, preliminary data from our group suggest that human dermal fibroblasts have the capacity to alter their phenotype into an endothelial cell-like phenotype in vitro. As a first step in using these cells in vascular tissue engineering, we investigated their ability to form an endothelial cell-like layer on a scaffold in vitro. Furthermore, we studied the possibility of seeding dermal fibroblasts on a scaffold and later commencing with induction toward an endothelial cell-like phenotype. METHODS: Cells cultured in either normal fibroblast medium or endothelial induction medium were seeded on a gelatin-based scaffold. To study the organization of cells, routine staining was performed. Differentiation was confirmed by Western blotting and immunohistochemistry with antibodies directed toward molecules commonly used to identify endothelial cells. RESULTS AND CONCLUSION: Our data support that human dermal fibroblasts differentiated toward endothelial cell-like cells prior to seeding showed histological resemblance to mature endothelial cells, while fibroblasts seeded and later induced into endothelial differentiation grew in multilayer. However, expression of various surface molecules indicative of an endothelial phenotype was seen using both techniques. In conclusion, the results presented in this study indicate that human dermal fibroblasts differentiated toward an endothelial cell-like phenotype may be a novel cell source for endothelialization of vascular grafts.

The use of adult stem cells in tissue engineering applications is a promising alternativewhen the possibility of acquiring autologous cells for transplantation is limited. Even so, theadult stem cell populations identified up to this point are far from optimal in aspects ofharvest and culture expansion. With the recent suggestion of stem cell plasticity inherent inhuman dermal fibroblasts, a new plausible candidate for use as cell source in tissuereconstruction has emerged. Fibroblast cultures can be induced to differentiate towardsadipocyte, chondrocyte and osteoblast-like cells in vitro, by the use of induction media. Thepresent works utilizes Affymetrix full expression micro array to identify if genes commonlyexpressed in stem cells differentiating towards the above-mentioned lineages also areexpressed in induced fibroblasts. Several genes important for differentiation andmaintenance of an adipose, cartilage or bone phenotype were found up-regulated in theinduced cultures. The results presented here provide further evidence for the plasticity ofhuman dermal fibroblasts, and their possible use in tissue engineering and reconstructivesurgery.