Serum-free culture of rat keratinocytes

Immortalization and Characterization of Rat Lingual Keratinocytes in a High-Calcium and Feeder-Free Culture System Using ROCK Inhibitor Y-27632

Cultured keratinocytes are desirable models for biological and medical studies. However, primary keratinocytes are difficult to maintain, and there has been little research on lingual keratinocyte culture. Here, we investigated the effect of Y-27632, a Rho kinase (ROCK) inhibitor, on the immortalization and characterization of cultured rat lingual keratinocyte (RLKs). Three Y-27632-supplemented media were screened for the cultivation of RLKs isolated from Sprague-Dawley rats. Phalloidin staining and TUNEL assay were applied to visualize cytoskeleton dynamics and cell apoptosis following Y-27632 removal. Label-free proteomics, RT-PCR, calcium imaging, and cytogenetic studies were conducted to characterize the cultured cells. Results showed that RLKs could be conditionally immortalized in a high-calcium medium in the absence of feeder cells, although they did not exhibit normal karyotypes. The removal of Y-27632 from the culture medium led to reversible cytoskeletal reorganization and nuclear enlargement without triggering apoptosis, and a total of 239 differentially expressed proteins were identified by proteomic analysis. Notably, RLKs derived from the non-taste epithelium expressed some molecular markers characteristic of taste bud cells, yet calcium imaging revealed that they rarely responded to tastants. Collectively, we established a high-calcium and feeder-free culture method for the long-term maintenance of RLKs. Our results shed some new light on the immortalization and differentiation of lingual keratinocytes.

Establishment of an in vitro model of cultured viable human, porcine and canine skin and comparison of different media supplements

Transdermal drug delivery provides several advantages over conventional drug administration, such as the avoidance of first-pass metabolism and better patient compliance. In vitro research can abbreviate and facilitate the pharmaceutical development considerably compared to in vivo research as drug screening and clinical studies can be reduced. These advantages led to the development of corresponding skin models. Viable skin models are more useful than non-viable ones, due to the influence of skin metabolism on the results. While most in vitro studies concentrate on evaluating human-based models, the current study is designed for the investigation of both human and animal diseases. So far, there is little information available in the literature about viable animal skin cultures which are in fact intended for application in the veterinary and not the human field. Hence, the current study aims to fill the gap. For the in vitro viable skin model, specimens of human, porcine and canine skin were cultured over two weeks under serum-free conditions. To evaluate the influence of medium supplementation on skin viability, two different supplement mixtures were compared with basic medium. The skin specimens were maintained at a viability-level >50% until the end of the study. From the tested supplements, the addition of bovine pituitary extract and epidermal growth factor increased skin viability whereas hydrocortisone and insulin induced a decrease. This in vitro viable skin model may be a useful tool for the investigation of skin diseases, especially for the veterinary field.

Harvesting epithelial keratinocyte sheets from temperature-responsive dishes preserves basement membrane proteins and improves cell survival in a skin defect model

Cultured epithelial autograft (CEA) therapy has been used in clinical applications since the 1980s. However, there are some issues related to this treatment that still remain unsolved. Enzymatic treatment is typically used in the collection of epithelial keratinocyte sheets, but it tends to break the adhesion and basement membrane proteins. It is thought that the loss of proteins after enzymatic treatment is responsible for the poor survival of transplanted cell sheets. Our laboratory has developed a temperature-responsive culture dish that does not require enzymatic treatment to harvest the cells. In this study, we compare morphological and survival results from rat epithelial keratinocyte cell sheets harvested by temperature-reducing treatment (TT sheets) against cell sheets harvested by enzymatic (dispase) treatment (DT sheets). TT sheets preserve keratin structure in better conditions and express higher levels of collagen IV and laminin 5 than DT sheets. In order to evaluate cell sheet survival after transplantation, we created an in vivo transplant model. Keratinocyte sheets obtained from GFP-positive animals were transplanted into athymic rats. The survival rate 7 days after transplantation of TT sheet was higher than that of DT sheets. Collagen IV and Laminin 5 expression was observed in the TT sheet transplantation group. These results indicate that the remaining basement membrane proteins are important for initial attachment and cell survival. We believe that the cell sheet harvesting method using temperature-responsive culture dishes provides superior cell survival and can solve one of the roadblocks in CEA therapy. Copyright © 2016 John Wiley & Sons, Ltd.

Isolation and propagation of keratinocytes derived from Cashmere goat fetus

The study was conducted to isolate epidermal keratinocytes from Cashmere goat fetus with the aim to develop suitable conditions for keratinocyte cultivation and propagation. The methods developed for keratinocyte culture include (i) use of a feeder-layer of mitotically inactivated fibroblasts obtained from goat and mouse fetal skin, (ii) use of a substrate such as collagen IV, or (iii) without use of any substrate. Epidermal cell removal was established by enzymatically separating keratinocytes from 12 to 16 weeks aged fetal skin tissues treated with 0.125% trypsin solution overnight at 4 degrees C. The cells were maintained in all culture conditions with serum containing medium. Keratinocyte multiplication and proliferation were comparable in different culture conditions and the improved cellular attachment and growth have been obtained in cultures on feeder layers. Colony forming keratinocytes on feeder layer were heterogeneous in their growth potential. In feeder free conditions, high cellular density was required at plating for sub-cultivation as their poor attachment in culture dishes. This study reports the comparative efficacy of different culture conditions for keratinocyte isolation and in vitro propagation originating from Cashmere goat fetus.

Trophic effects of keratinocytes on the axonal development of sensory neurons in a coculture model

The epidermis, the outermost structure of the skin, fulfils important roles as a physical barrier between the organism and its environment and as a neuroendocrine, immune and sensory organ. It is innervated by unmyelinated sensory fibres conveying nociceptive and thermoceptive information. Little is known concerning the functional interactions between these sensory fibres and the keratinocytes, which constitute 95% of the epidermal cells. We have developed a coculture model of primary rat sensory neurons and keratinocytes, as well as of equivalent cell-lines: ND7-23 neurons and A431 keratinocytes. We show that primary dorsal root ganglion neurons survive well in a standard keratinocyte reference medium containing a low concentration of calcium, but fail to extend axons. However, when neurons are cocultured with keratinocytes, axonal outgrowth is strongly stimulated. The use of a Transwell culture system indicated that the stimulation of axonal growth depends on a soluble factor secreted by keratinocytes. Axon outgrowth was also induced by nerve growth factor or brain-derived neurotrophic factor, but not by neurotrophin 3 or glial cell-derived neurotrophic factor. Neurons cocultured with keratinocytes did not change their responses to ATP, capsaicin or high potassium solution, as measured by calcium imaging. The trophic effect of keratinocytes concerned essentially a population of medium-sized (17-25 microm) neurons, some of which expressed substance P-like immunoreactivity and responded to capsaicin. Our preparation, in which cells are maintained at low external calcium concentration, could represent a useful in vitro model for characterizing the effect of skin-derived guidance and trophic factors.

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.

Predictive value of in vitro model systems in toxicology

The application of in vitro model systems to evaluate the toxicity of xenobiotics has significantly enhanced our understanding of drug- and chemical-induced target toxicity. From a scientific perspective, there are several reasons for the popularity of in vitro model systems. From the public perspective, in vitro model systems enjoy increasing popularity because their application may allow a reduction in the number of live animals employed in toxicity testing. In this review, we present an overview of the use of in vitro model systems to investigate target organ toxicity of drugs and chemicals, and provide selective examples of these model systems to better understand cutaneous and ocular toxicity and the role of drug metabolism in the hepatotoxicity of selected agents. We conclude by examining the value and use of in vitro model systems in industrial development of new pharmaceutical agents.

Further optimization of culture method for rat keratinocytes: titration of glucose and sodium chloride

The present study further improved the serum-free method of culturing rat keratinocytes. To obtain the best growth of rat keratinocytes, we modified our previous serum-free medium (MCDB153 based medium), particularly the amounts of glucose and sodium chloride (NaCl). Titration experiments showed the optimal concentration to be 0.8 mM for glucose and 100 mM for NaCl. This modification eliminated the requirement for albumin, which had been essential for colony formation when our previous medium was used. Titration of glucose and NaCl, followed by adjustment of essential amino acids and growth factors, produced a new formulation. More satisfactory and better growth was achieved with the new medium than with the previous medium. Accumulation of monoalkyldiacylglycerol (MADAG) was consistently noted in this study, representing the unusual lipid profile. A tendency toward normalization was, however, noted with the neutral lipid profile of keratinocytes cultivated in the new medium: lower production of MADAG was obtained with the new formulation, rather than the previous one.

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

We describe serum-free culture conditions for human epidermal keratinocytes using lethally treated 3T3 cells as feeder layers and normal Ca++ concentrations (1.2 mM), in a DMEM/F12-Ham nutrient mixture supplemented with several additives, and 10 mg/ml bovine serum albumin instead of animal serum. Keratinocytes were serially grown to 15-18 cell generations (4 subcultivations) and formed a stratified squamous epithelium that could be detached as a graftable epithelial sheet. EGF and TGF alpha significantly increased keratinocyte proliferation under these conditions; EGF reduced the expression of keratin K1, which is specific for stratified and terminally differentiated epidermal keratinocytes. In contrast with previous reports, the serum-free medium we describe here supports serial growth and normal differentiation of human epidermal keratinocytes, and the formation of graftable stratified epithelia; it also supports the assay of a variety of cytokines or compounds that modulate epidermal keratinocyte proliferation and differentiation.

Serum-free conditions for the long term growth and differentiation of neoplastic canine keratinocytes

Long term cultures of canine keratinocytes have been established but culture conditions currently used require supplementation with fetal bovine serum (FBS). Unfortunately, FBS contains many non-defined components which may interfere with in vitro studies. This study describes the development of defined serum-free culture conditions for neoplastic canine keratinocytes grown submerged and at the air-liquid interface. Two commercially available serum-free media established for human epidermal cells failed to support canine keratinocyte growth. In contrast, a defined serum-free medium developed in our laboratory successfully supported proliferation of neoplastic canine keratinocytes for at least 40 passages. Cells showed a slower growth rate, but reached similar final densities and were morphologically identical to those cultured in FBS. Grown at the air-liquid interface, the cells reached the same degree of differentiation as in vivo stratified squamous epithelium and cultures grown in FBS. These results demonstrate that canine keratinocytes require different serum-free growth conditions than human cells. Neoplastic canine keratinocyte cultures, grown under serum-free culture conditions, provide an ideal in vitro system for comparative studies of keratinocyte biology and pathogenesis of various dermatoses.

Accumulation of 1-o-alkyl-2,3-diacylglycerols in cultured rat keratinocytes

The present study was undertaken to identify the chemical structure of neutral lipid accumulated in cultured rat keratinocytes and to address their metabolism. Neutral lipid of similar mobility with alkyldiacylglycerol was isolated from cultured rat keratinocytes by thin layer chromatography. The long-chain diols derived from the neutral lipids were identified as 1-alkylglycerol based on the mass spectra of their nicotinylidene derivatives. Thus these neutral lipids were identified as 1-o-alkyl-2,3-diacylglycerols (ADAG). Addition of rat serum elevated the level of ADAG with increasing trend of linoleic acid concentration in this fraction. [14C]Acetate added to the confluent plates was incorporated into alkyl- and acyl-chains of ADAG with incubation in 24 h, and remained un-metabolized up to 72 h. This, however, is not the case for the label incorporation into phospholipid and triacylglycerol. Radioactivities of these two lipid fractions appeared to reach the maximum in 24 h, and thereafter decreased to 72 h with a similar decay curve. Incorporation of [14C]acetate into phospholipid and ADAG was significantly depressed, and that into triacylglycerol and free cholesterol was increased by the supplementation of the medium with rat serum. In concomitance with the accumulation of ADAG, the concentration of ethanolamine-plasmalogen increased in the cultured keratinocytes. The results of the present study first showed the elevated level of ether lipid synthesis in the proliferating primary culture of rat keratinocytes.