Engineering of bone tissue could help to overcome the need for extensive reconstruction and associated donor site morbidity, and it has been proposed that osteogenic biomaterials, which are scaffolds that contain osteocompetent cells, could be used to fill large bone defects. This study investigated the potential of osteogenically-induced human dermal fibroblasts cultured on gelatin microcarriers combined with platelet-rich plasma in a model of a femoral defect in athymic rats. Defects were transplanted with one of the following six combinations: 1 = sodium chloride, 2 = platelet-rich plasma, 3 = microcarriers + platelet-rich plasma, 4 = human dermal fibroblasts on microcarriers + platelet-rich plasma, 5 = human osteoblasts on microcarriers + platelet-rich plasma, and 6 = osteogenically induced human dermal fibroblasts on microcarriers + platelet-rich plasma. The femoral defects were assessed 4 weeks postoperatively with computed tomography (CT), routine histological staining, fluorescence in situ hybridisation, and polyclonal antibodies directed towards osteocalcin and osteonectin. Radiographs of all groups taken 4 weeks postoperatively showed unhealed defects. Femoral defects transplanted with osteogenically-induced human dermal fibroblasts on microcarriers (group 6) contained dense clusters of cells with large quantities of extracellular matrix. These clusters were exclusive to this group and stained strongly for osteocalcin and osteonectin. Fluorescence in situ hybridisation showed viable human cells in femoral defects that had been transplanted with microcarriers seeded with cells, which confirmed the survival of implanted cells. In conclusion, osteogenically-induced human dermal fibroblasts survived in this new niche, and bone-like structures were apparent in the defects.

Autologous cell-based therapies promise important developments for reconstructive surgery. In vitro expansion as well as differentiation strategies could provide a substantial benefit to cellular therapies. Human dermal fibroblasts, considered ubiquitous connective tissue cells, can be coaxed towards different cellular fates, are readily available and may altogether be a suitable cell source for tissue engineering strategies. Global gene expression analysis was performed to investigate the changes of the fibroblast phenotype after four-week inductions toward adipocytic, osteoblastic and chondrocytic lineages. Differential gene regulation, interpreted through Gene Set Enrichment Analysis, highlight important similarities and differences of induced fibroblasts compared to control cultures of human fibroblasts, adipocytes, osteoblasts and articular chondrocytes. Fibroblasts show an inherent degree of phenotype plasticity that can be controlled to obtain cells supportive of multiple tissue types.

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.