Cultivation, serial transfer, and differentiation of epidermal keratinocytes in serum-free medium

Decorin gene expression and its regulation in human keratinocytes

In various cell types, including cancer cells, decorin is involved in regulation of cell attachment, migration and proliferation. In skin, decorin is seen in dermis, but not in keratinocytes. We show that decorin gene (DCN) is expressed in the cultured keratinocytes, and the protein is found in the cytoplasm of differentiating keratinocytes and in suprabasal layers of human epidermis. RT-PCR experiments showed that DCN expression is regulated by pro-inflammatory and proliferative cytokines. Our data suggest that decorin should play a significant role in keratinocyte terminal differentiation, cutaneous homeostasis and dermatological diseases.

Serum-free primary human fibroblast and keratinocyte coculture

Research has shown that the inclusion of a fibroblast cell support layer is required for the isolation and expansion of primary keratinocytes. Recent advances have provided keratinocyte culture with fibroblast-free alternatives. However, these technologies are often undefined and rely on the incorporation of purified proteins/components. To address this problem we developed a medium that used recombinant proteins to support the serum-free isolation and expansion of human dermal fibroblasts and keratinocytes. The human dermal fibroblasts were able to be isolated serum free by adding recombinant human albumin to a collagenase solution. These fibroblasts were then expanded using a serum-free medium containing recombinant proteins: epidermal growth factor, basic fibroblast growth factor, chimeric vitronectin:insulin-like growth factor-I protein, and recombinant human albumin. These fibroblasts maintained a typical morphology and expressed fibroblast markers during their serum-free isolation, expansion, and freezing. Moreover, these fibroblasts were able to support the serum-free isolation and expansion of primary keratinocytes using these recombinant proteins. Real-time polymerase chain reaction and immunofluorescence analysis confirmed that there were no differences in expression levels of p63 or keratins 1, 6, and 10 when keratinocytes were grown in either serum-supplemented or serum-free medium. Using a three-dimensional human skin equivalent model we demonstrated that these keratinocytes also maintained their ability to reform an epidermal layer. In summary, the techniques described provide a valuable alternative for culturing fibroblasts and keratinocytes using recombinant proteins.

Cleft Palate Cells Can Regenerate a Palatal Mucosa in vitro

Cleft palate repair leaves full-thickness mucosal defects on the palate. Healing might be improved by implantation of a mucosal substitute. However, the genetic and phenotypic deviations of cleft palate cells may hamper tissue engineering. The aim of this study was to construct mucosal substitutes from cleft palate cells, and to compare these with substitutes from normal palatal cells, and with native palatal mucosa. Biopsies from the palatal mucosa of eight children with cleft palate and eight age-matched control individuals were taken. Three biopsies of both groups were processed for (immuno)histochemistry; 5 were used to culture mucosal substitutes. Histology showed that the substitutes from cleft-palate and non-cleft-palate cells were comparable, but the number of cell layers was less than in native palatal mucosa. All epithelial layers in native palatal mucosa and mucosal substitutes expressed the cytokeratins 5, 10, and 16, and the proliferation marker Ki67. Heparan sulphate and decorin were present in the basal membrane and the underlying connective tissue, respectively. We conclude that mucosal cells from children with cleft palate can regenerate an oral mucosa in vitro.

Fibromodulin gene is expressed in human epidermal keratinocytes in culture and in human epidermis in vivo

Fibromodulin is a small leucine-rich proteoglycan that has a central role in the maintenance of collagen fibrils structure, and in regulation of TGF-beta biological activity. Although, it is mainly found in cartilage and tendon, little is known regarding the expression of the fibromodulin gene in other cell types. By RT-PCR, real time PCR and immunohistochemistry, we describe the expression of the fibromodulin gene and the presence of the protein in human epidermal keratinocytes (HEK), both in culture and in normal human epidermis. Our results show, for the first time, that fibromodulin gene is constantly expressed in HEK during culture time. Immunostaining showed that fibromodulin is located intracytoplasmically in basal and stratified keratinocytes of the growing colonies, confluent cultures, and epidermis in vivo. The expression and intracellular localization of fibromodulin in HEK is a new finding and opens new possible biological roles for the SLRP family.

Medium (DMEM/F12)-containing chitosan hydrogel as adhesive and dressing in autologous skin grafts and accelerator in the healing process

Autologous skin grafts are considered necessary for the treatment of extensive skin defects. However, skin graft by suturing is a time-consuming medical handling and rather stressful event for recipients. To that end, tissue adhesives have been suggested in skin grafts. Chitosan hydrogel is well known as a wound dressing and tissue adhesive material showing biocompatibility, anti-infective activity, and the ability to accelerate wound healing. In this report, we evaluated the application of the chitosan hydrogel as a tissue adhesive in skin grafts. Although chitosan hydrogel shortened the operation time and resulted in a high graft absorption rate in comparison with suturing, wound epithelization was rather retarded. On the other hand, chitosan hydrogel was found more biocompatible than the commonly used tissue adhesive octyl-2-cyanoacrylate. When the chitosan hydrogel was premixed with a serum-free tissue culture medium DMEM/F12, it was found to easily degrade and promote wound epithelization. Histological examination revealed that the medium (DMEM/F12)-containing chitosan hydrogel was associated with the accumulation of polymorphonuclear leukocytes and neovascularization. In addition, immunohistochemical staining showed that the vascular endothelial growth factor (VEGF) was localized in the chitosan hydrogel degraded matrices. And infiltration of leukocytes determined the degradation activity with the D-glucose in the medium (DMEM/F12) suggested to play a central role in chitosan hydrogel degradation. Therefore, the medium (DMEM/F12)-containing chitosan hydrogel may become commonly accepted as a beneficial wound dressing and tissue adhesive in extensive wound management and skin grafts.

The impact of skin viability on drug metabolism and permeation—BSA toxicity on primary keratinocytes

For testing cutaneous absorption of drugs, ingredients of cosmetics and also for risk assessment of industrial compounds predictable in vitro test protocols are under investigation using excised skin or reconstructed human epidermis. Since the metabolizing enzymes expressed by viable skin can influence the absorption behaviour of substances by changing their structure and thereby their physicochemical characteristics, the metabolic capacity should be considered in the design of the test protocols of compounds susceptible to metabolism. Then data, generated using viable reconstructed epidermis may reflect the in vivo situation. Interestingly, bovine serum albumin (BSA) commonly used in receptor media in permeation studies to facilitate solubility of highly lipophilic substances strongly inhibited the metabolism of topically applied prednicarbate in reconstructed epidermis. Here, we show that 5% BSA is toxic to reconstructed epidermis and keratinocytes which was consistent with the earlier findings. While media toxicity (deficiency media) was at least partly the cause of both apoptotic and necrotic processes in keratinocytes, BSA only slightly increased the rate of necrotic cells. Moreover, caspase inhibitors did not reduce BSA toxicity. Yet, the results show that BSA toxicity on keratinocytes has to be carefully considered if this protein is used in permeation studies with reconstructed epidermis.

Interleukin-6 promotes human epidermal keratinocyte proliferation and keratin cytoskeleton reorganization in culture

We have studied the effects of interleukin-6 (IL-6) on human epidermal keratinocytes by using serum-free culture conditions that allow the serial transfer, differentiation, and formation of well-organized multilayered epithelia. IL-6 at 2.5 ng/ml or higher concentrations promoted keratinocyte proliferation, with an ED(50) of about 15 ng/ml and a maximum effect at 50 ng/ml. IL-6 was 10-fold less potent than epidermal growth factor (EGF) or transforming growth factor-alpha (TGF-alpha) and supported keratinocyte growth for up to eight cumulative cell generations. IL-6-treated keratinocytes formed highly stratified colonies with a narrower proliferative/migratory rim than those keratinocytes stimulated with EGF or TGF-alpha; confluent epithelial sheets treated with IL-6 also underwent an increase in the number of cell layers. We also examined the effect of IL-6 on the keratin cytoskeleton. Immunostaining with anti-K16 monoclonal antibodies showed that the keratin network was aggregated and reorganized around cell nucleus and that this was not attributable to changes in keratin levels. This is the first report concerning the induction of the reorganization of keratin intermediate filaments by IL-6 in human epidermal keratinocytes.

Directing stem cells into the keratinocyte lineage in vitro

A major area of research in regenerative medicine is the potential application of stem cells in skin grafting and tissue engineering. This would require well defined and efficient protocols for directing the commitment and differentiation of stem cells into the keratinocyte lineage, together with their selective purification and proliferation in vitro. The development of such protocols would reduce the likelihood of spontaneous differentiation of stem cells into divergent lineages upon transplantation, as well as reduce the risk of teratoma formation in the case of embryonic stem cells. Additionally, such protocols could provide useful in vitro models for studying skin tissue biology, as well as facilitate the genetic manipulation of stem cells for therapeutic applications. The development of pharmacokinetic and cytotoxicity/genotoxicity screening tests for skin-related biomaterials and drugs could also utilize protocols developed for the commitment and differentiation of stem cells into the keratinocyte lineage. Hence, this review critically examines the various strategies that could be employed to direct the commitment and differentiation of stem cells into the keratinocyte lineage in vitro.

Investigation of initial pellicle formation on modified titanium dioxide (TiO2) surfaces by reflectometric interference spectroscopy (RIfS) in a model system

OBJECTIVES

Plaque accumulation, leading to inflammatory processes and bone loss, is one of the main reasons for failure of dental implants. Pellicle formation plays a key role in bacterial adhesion and plaque accumulation. The influence of experimental bioactive implant surface coatings on the initial process of pellicle formation was investigated in a model system.

METHODS

TiO2-films were modified by covalent binding of laminin and human epidermal growth factor (EGF) to promote adhesion of epithelial cells. Adsorption and dissociation behavior of bovine serum albumin (BSA) and salivary proteins on these surfaces were monitored by time-resolved reflectometric interference spectroscopy (RIfS).

RESULTS

The thickness of the irreversibly adsorbed salivary protein layer was reduced from 2.78 +/- 0.71 nm on unmodified TiO2 to 0.78 +/- 0.22 nm on laminin-coated surfaces and to 1.18 +/- 0.29 nm on EGF-coated surfaces. The percentage of initially adsorbed proteins remaining irreversibly bound was reduced from 51 +/- 8% on titanium to 23 +/- 5% by laminin coating and to 44 +/- 11% on EGF-coated surfaces. The highest reduction of protein adsorption (layer thickness lower than 0.05 nm) was achieved on DC-PEG-layers used as spacer for protein coupling.

SIGNIFICANCE

Laminin and EGF were shown to be promising candidates for use as biological coatings on the transmucosal part of titanium dental implants where the objective is to enhance epithelial adhesion and inhibit adsorption of salivary proteins and bacteria.