Concomitant proliferation and formation of a stratified epithelial sheet by explant outgrowth of epidermal keratinocytes from adult mice

Isolation and long-term expansion of murine epidermal stem-like cells

Epidermis is the most outer layer of the skin and a physical barrier protecting the internal tissues from mechanical and environmental insults. The basal keratinocytes, which, through proliferation and differentiation, supply diverse cell types for epidermal homeostasis and injury repair. Sustainable culture of murine keratinocyte, however, is a major obstacle. Here we developed murine keratinocyte lines using low-Ca²⁺ (0.06 mM) keratinocyte serum-free medium (KSFM-Ca²⁺) without feeder cells. Cells derived in this condition could be subcultured for >70 passages. They displayed basal epithelial cell morphology and expressed keratin (Krt) 14, but lacked the epithelial-characteristic intercellular junctions. Moreover, these cells could be adapted to grow in the Defined-KSFM (DKSFM) media containing 0.15 mM Ca²⁺, and the adapted cells established tight- and adherens-junctions and exhibited increased Krt1/10 expression while retained subculture capacity. Global gene expression studies showed cells derived in KSFM-Ca²⁺ media had enriched stem/proliferation markers and cells adapted in DKSFM media had epithelial progenitor signatures. Correspondingly, KSFM-Ca²⁺-derived cells exhibited a remarkable capacity of clonal expansion, whereas DKSFM-adapted cells could differentiate to suprabasal epithelial cell types in 3-dimentional (3D) organoids. The generation of stem-like murine keratinocyte lines and the conversion of these cells to epithelial progenitors capable of terminal differentiation provide the critically needed resources for skin research.

Keratinocyte stem cells and the targets for nonmelanoma skin cancer

The mammalian skin is a complex dynamic organ composed of thin multilayered epidermis and a thick underlying connective tissue layer dermis. The epidermis undergoes continuous renewal throughout life. The stems cells uniquely express particular surface markers utilized for their identification, isolation and localization in specific niches in epidermis as well as hair follicles (HFs). The two stage skin carcinogenesis model involves stepwise accumulation of genetic alterations and ultimately leading to malignancy. Whereas early research on skin carcinogenesis focused on the molecular nature of carcinogens and tumor promoters, more recent studies have focused on the identification of the target cells and tumor promoting cells for both chemical and physical carcinogens and promoters. Recent studies support the hypothesis that keratinocyte stem cells are the targets in skin carcinogenesis. In this review, we discuss briefly the localization of stem cells in the epidermis and HFs, and review the possibility that skin papillomas and carcinomas are derived from stem cells, as well as from other cells in the cutaneous epithelium whose stem cell properties are not well known.

Isolation and short-term culture of primary keratinocytes, hair follicle populations and dermal cells from newborn mice and keratinocytes from adult mice for in vitro analysis and for grafting to immunodeficient mice

Protocols for preparing and culturing primary keratinocytes from newborn and adult mouse epidermis have evolved over the past 35 years. This protocol is now routinely applied to mice of various genetic backgrounds for in vitro studies of signaling pathways in differentiation and cell transformation, and for assessing the in vivo phenotype of altered keratinocytes in grafts of cells on immunodeficient mice. Crucial in the development and application of the procedure was the observation that keratinocytes proliferate in media of low calcium concentration, but rapidly commit to differentiation at calcium concentrations >0.07 mM after the initial attachment period. Preparing primary keratinocytes from ten newborn mice requires 2-3 h of hands-on time. Related procedures are also provided: preparing immature hair follicle buds, developing dermal hair follicles and fibroblasts from newborn mice, preparing primary keratinocytes from adult mice and grafting cell mixtures on athymic nude mice.

Differentiation status of cultured murine keratinocytes modulates induction of genes responsive to 2,3,7,8-tetrachlorodibenzo-p-dioxin

Primary murine keratinocytes were cultured in a chemically defined, serum-free medium which facilitated manipulation of their differentiation status. Exposure of basal cell and differentiating cultures to >/= 0.1 nM 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) preferentially elevated 7-ethoxyresorufin O-deethylase specific activities in differentiating cultures (28-fold versus 4-fold increases after 36 h of exposure). Semiquantitative reverse-transcription polymerase chain reaction (RT-PCR) analyses demonstrated the presence of constitutive mRNA transcripts corresponding to four known TCDD-inducible genes (e.g., Cyp1a1, Cyp1b1, Ahd4, and Nmo1) in both differentiating and proliferating cultures of murine keratinocytes. All four genes were induced in differentiating cultures following exposure to TCDD. No induction occurred in comparably treated basal cell cultures. Indirect immunofluorescence analyses demonstrated the presence of aryl hydrocarbon receptor (AHR) and aryl hydrocarbon receptor nuclear translocator (ARNT) proteins in both basal and differentiating keratinocytes. Both proteins appeared to be associated with the nucleus and their nuclear association was independent of prior exposure to TCDD. These studies suggest that AHR activation in murine skin is regulated as a function of the keratinocyte differentiation program.

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.

Cultured human keratinocytes as a model for studying the dopamine metabolism in schizophrenia

The dopamine hypothesis is the major etiological hypothesis of schizophrenia which proposes that enhanced central nervous system dopaminergic activity is the causative factor for this disease. The hypothesis remains unproven despite decades of research. The major difficulty in studying the disease is due to the unavailability of a suitable animal model. Studies with human blood, cerebrospinal fluid or post-mortem brains lead only to inconclusive results, due to the effects of medication and other environmental factors. No extra-neuronal cells, with the exception of adrenal medulla, have been reported to contain a dopamine metabolic pathway. Literature evidence and our own study suggest that human keratinocytes express the enzymes to synthesize and degrade dopamine. We have compared the properties of tyrosine hydroxylase, the rate-limiting enzyme, from mouse striatum and from human skin keratinocytes cultured in vitro. Moreover we could also detect dopamine beta hydroxylase and catechol-o-methyl transferase in keratinocytes. We propose that human keratinocytes cultured in vitro can be used to study the relevance of dopamine metabolism to schizophrenia under controlled conditions avoiding the effects of medication and other environmental factors.