Epidermal differentiation and basement membrane formation by HaCaT cells in surface transplants

Highly scalable and standardized organ-on-chip platform with TEER for biological barrier modeling

The development of new therapies is hampered by the lack of predictive, and patient-relevant in vitro models. Organ-on-chip (OOC) technologies can potentially recreate physiological features and hold great promise for tissue and disease modeling. However, the non-standardized design of these chips and perfusion control systems has been a barrier to quantitative high-throughput screening (HTS). Here we present a scalable OOC microfluidic platform for applied kinetic in vitro assays (AKITA) that is applicable for high, medium, and low throughput. Its standard 96-well plate and 384-well plate layouts ensure compatibility with existing laboratory workflows and high-throughput data collection and analysis tools. The AKITA plate is optimized for the modeling of vascularized biological barriers, primarily the blood-brain barrier, skin, and lung, with precise flow control on a custom rocker. The integration of trans-epithelial electrical resistance (TEER) sensors allows rapid and repeated monitoring of barrier integrity over long time periods. Together with automated liquid handling and compound permeability testing analyses, we demonstrate the flexibility of the AKITA platform for establishing human-relevant models for preclinical drug and precision medicine's efficacy, toxicity, and permeability under near-physiological conditions.

Macrocystis pyrifera Lipids Reduce Cytokine-Induced Pro-Inflammatory Signalling and Barrier Dysfunction in Human Keratinocyte Models

Atopic dermatitis is a chronic condition where epidermal barrier dysfunction and cytokine production by infiltrating immune cells exacerbate skin inflammation and damage. A total lipid extract from Macrocystis pyrifera, a brown seaweed, was previously reported to suppress inflammatory responses in monocytes. Here, treatment of human HaCaT keratinocytes with M. pyrifera lipids inhibited tumour necrosis factor (TNF)-α induced TNF receptor-associated factor 2 and monocyte chemoattractant protein (MCP)-1 protein production. HaCaT cells stimulated with TNF-α, interleukin (IL)-4, and IL-13 showed loss of claudin-1 tight junctions, but little improvement was observed following lipid pre-treatment. Three-dimensional cultures of HaCaT cells differentiated at the air-liquid interface showed increased MCP-1 production, loss of claudin-1 tight junctions, and trans-epidermal leakage with TNF-α, IL-4, and IL-13 stimulation, with all parameters reduced by lipid pre-treatment. These findings suggest that M. pyrifera lipids have anti-inflammatory and barrier-protective effects on keratinocytes, which may be beneficial for the treatment of atopic dermatitis or other skin conditions.

Immortalization of Human Keratinocytes Using the Catalytic Subunit of Telomerase

A new stable line of human keratinocytes was obtained. The cells have altered morphology, both abnormal chromosomal composition and expression of keratinocyte markers, do not show contact inhibition, could be cultured in various media and have limited stratification ability in vitro. Upon transplantation into nude mice the cells have tumorigenic properties.

Tissue Stem Cells: Architects of Their Niches

Stem cells (SCs) maintain tissue homeostasis and repair wounds. Despite marked variation in tissue architecture and regenerative demands, SCs often follow similar paradigms in communicating with their microenvironmental "niche" to transition between quiescent and regenerative states. Here we use skin epithelium and skeletal muscle-among the most highly-stressed tissues in our body-to highlight similarities and differences in niche constituents and how SCs mediate natural tissue rejuvenation and perform regenerative acts prompted by injuries. We discuss how these communication networks break down during aging and how understanding tissue SCs has led to major advances in regenerative medicine.

A comparative study of materials assembled from recombinant K31 and K81 and extracted human hair keratins

Natural biopolymers have found success in tissue engineering and regenerative medicine applications. Their intrinsic biocompatibility and biological activity make them well suited for biomaterials development. Specifically, keratin-based biomaterials have demonstrated utility in regenerative medicine applications including bone regeneration, wound healing, and nerve regeneration. However, studies of structure-function relationships in keratin biomaterials have been hindered by the lack of homogeneous preparations of materials extracted and isolated from natural sources such as wool and hair fibers. Here we present a side-by-side comparison of natural and recombinant human hair keratin proteins K31 and K81. When combined, the recombinant proteins (i.e. rhK31 and rhK81) assemble into characteristic intermediate filament-like fibers. Coatings made from natural and recombinant dimers were compared side-by-side and investigated for coating characteristics and cell adhesion. In comparison to control substrates, the recombinant keratin materials show a higher propensity for inducing involucrin and hence, maturation in terms of potential skin cell differentiation.

Basement membranes in the cornea and other organs that commonly develop fibrosis

Basement membranes are thin connective tissue structures composed of organ-specific assemblages of collagens, laminins, proteoglycan-like perlecan, nidogens, and other components. Traditionally, basement membranes are thought of as structures which primarily function to anchor epithelial, endothelial, or parenchymal cells to underlying connective tissues. While this role is important, other functions such as the modulation of growth factors and cytokines that regulate cell proliferation, migration, differentiation, and fibrosis are equally important. An example of this is the critical role of both the epithelial basement membrane and Descemet's basement membrane in the cornea in modulating myofibroblast development and fibrosis, as well as myofibroblast apoptosis and the resolution of fibrosis. This article compares the ultrastructure and functions of key basement membranes in several organs to illustrate the variability and importance of these structures in organs that commonly develop fibrosis.

Rational Surface Design of Upconversion Nanoparticles with Polyethylenimine Coating for Biomedical Applications: Better Safe than Brighter?

Upconversion nanoparticles (UCNPs) coated with polyethylenimine (PEI) are popular background-free optical contrast probes and efficient drug and gene delivery agents attracting attention in science, industry, and medicine. Their unique optical properties are especially useful for subsurface nanotheranostics applications, in particular, in skin. However, high cytotoxicity of PEI limits safe use of UCNP@PEI, and this represents a major barrier for clinical translation of UCNP@PEI-based technologies. Our study aims to address this problem by exploring additional surface modifications to UCNP@PEI to create less toxic and functional nanotheranostic materials. We designed and synthesized six types of layered polymer coatings that envelop the original UCNP@PEI surface, five of which reduced the cytotoxicity to human skin keratinocytes under acute (24 h) and subacute (120 h) exposure. In parallel, we examined the photoluminescence spectra and lifetime of the surface-modified UCNP@PEI. To quantify their brightness, we developed original methodology to precisely measure the colloidal concentration to normalize the photoluminescence signal using a nondigesting mass spectrometry protocol. Our results, specified for the individual coatings, show that, despite decreasing the cytotoxicity, the external polymer coatings of UCNP@PEI quench the upconversion photoluminescence in biologically relevant aqueous environments. This trade-off between cytotoxicity and brightness for surface-coated UCNPs emphasizes the need for the combined assessment of the viability of normal cells exposed to the nanoparticles and the photophysical properties of postmodification UCNPs. We present an optimized methodology for rational surface design of UCNP@PEI in biologically relevant conditions, which is essential to facilitate the translation of such nanoparticles to the clinical applications.

Annurca Apple Nutraceutical Formulation Enhances Keratin Expression in a Human Model of Skin and Promotes Hair Growth and Tropism in a Randomized Clinical Trial

Several pharmaceutical products have been formulated over the past decades for the treatment of male and female alopecia, and pattern baldness, but relatively few metadata on their efficacy have been published. For these reasons, the pharmaceutical and medical attention has recently focused on the discovery of new and safer remedies. Particularly, great interest has been attracted by oligomeric procyanidin bioactivity, able to promote hair epithelial cell growth as well as to induce the anagen phase. Specifically, the procyanidin B2, a dimeric derivative extracted from apples, has demonstrated to be one of the most effective and safest natural compounds in promoting hair growth, both in vitro and in humans by topical applications. By evaluating the polyphenolic content of different apple varieties, we have recently found in the apple fruits of cv Annurca (AFA), native to Southern Italy, one of the highest contents of oligomeric procyanidins, and, specifically, of procyanidin B2. Thus, in the present work we explored the in vitro bioactivity of AFA polyphenolic extract as a nutraceutical formulation, named AppleMets (AMS), highlighting its effects on the cellular keratin expression in a human experimental model of adult skin. Successively, testing the effects of AMS on hair growth and tropism in healthy subjects, we observed significant results in terms of increased hair growth, density, and keratin content, already after 2 months. This study proves for the first time the impact of apple procyanidin B2 on keratin biosynthesis in vitro, and highlights its effect as a nutraceutical on human hair growth and tropism.

MicroRNA-520a suppresses the proliferation and mitosis of HaCaT cells by inactivating protein kinase B

Psoriasis is a chronic inflammatory disease of the skin for which an effective treatment strategy remains to be developed. Characteristics of psoriasis include an altered differentiation of keratinocytes and hyperplasia of the skin. The present study aimed to investigate the role served by miR-520a in psoriasis. The results demonstrated that miR-520a inhibited the proliferation of HaCaT cells. miR-520a directly regulated the mRNA and protein expression of its target gene, protein kinase B (AKT). The siRNA silencing of AKT expression in these cells was also evaluated. miRNA-520a repressed the proliferation and mitotic entry of HaCaT cells, and promoted cell apoptosis. AKT silencing suppressed the proliferation of HaCaT cells. These results suggest that miRNA-520a regulates the survival of HaCaT cells by inhibiting AKT expression. miRNA-520a and AKT may therefore be novel targets for the treatment of patients with psoriasis.

Differential regulation of surface receptor expression, proliferation, and apoptosis in HaCaT cells stimulated with interferon-γ, interleukin-4, tumor necrosis factor-α, or muramyl dipeptide

Keratinocytes are routinely subjected to both internal and external stimulation. This study investigates the effects of interferon gamma, interleukin-4, tumor necrosis factor alpha, and the synthetic immunomodulator muramyl dipeptide on the human keratinocyte cell line, HaCaT. Following HaCaT stimulation with cytokines or muramyl dipeptide for different time periods, changes in the expression of different cell surface receptors, cell proliferation, and cell apoptosis were evaluated by flow cytometry, tritiated thymidine uptake, and annexin-V staining, respectively. A significant decrease in the expression of CD49d was found upon treatment with interleukin-4. Interferon gamma and tumor necrosis factor alpha increased the expression of intercellular adhesion molecule 1 and major histocompatibility complex class I, whereas major histocompatibility complex class II and CD1b were only upregulated by interferon gamma. Interferon gamma and tumor necrosis factor alpha had opposite effects regarding CD119 expression, with the former downregulating, while the latter upregulating its expression. Of the stimuli tested, only interferon gamma and tumor necrosis factor alpha significantly inhibited proliferation of HaCaT cells, yet only interferon gamma played a significant role in inducing HaCaT cell apoptosis. Our data demonstrate differential effects of the three tested cytokines on keratinocytes and reveal that the absence of HaCaT cell responses to muramyl dipeptide is associated with undetectable levels of its cytoplasmic receptor, nucleotide-binding oligomerization domain-containing protein 2.

Cysteine Prevents the Reduction in Keratin Synthesis Induced by Iron Deficiency in Human Keratinocytes

L-cysteine is currently recognized as a conditionally essential sulphur amino acid. Besides contributing to many biological pathways, cysteine is a key component of the keratin protein by its ability to form disulfide bridges that confer strength and rigidity to the protein. In addition to cysteine, iron represents another critical factor in regulating keratins expression in epidermal tissues, as well as in hair follicle growth and maturation. By focusing on human keratinocytes, the aim of this study was to evaluate the effect of cysteine supplementation as nutraceutical on keratin biosynthesis, as well as to get an insight on the interplay of cysteine availability and cellular iron status in regulating keratins expression in vitro. Herein we demonstrate that cysteine promotes a significant up-regulation of keratins expression as a result of de novo protein synthesis, while the lack of iron impairs keratin expression. Interestingly, cysteine supplementation counteracts the adverse effect of iron deficiency on cellular keratin expression. This effect was likely mediated by the up-regulation of transferrin receptor and ferritin, the main cellular proteins involved in iron homeostasis, at last affecting the labile iron pool. In this manner, cysteine may also enhance the metabolic iron availability for DNA synthesis without creating a detrimental condition of iron overload. To the best of our knowledge, this is one of the first study in an in vitro keratinocyte model providing evidence that cysteine and iron cooperate for keratins expression, indicative of their central role in maintaining healthy epithelia.

Photocrosslinkable Gelatin Hydrogel for Epidermal Tissue Engineering

Natural hydrogels are promising scaffolds to engineer epidermis. Currently, natural hydrogels used to support epidermal regeneration are mainly collagen- or gelatin-based, which mimic the natural dermal extracellular matrix but often suffer from insufficient and uncontrollable mechanical and degradation properties. In this study, a photocrosslinkable gelatin (i.e., gelatin methacrylamide (GelMA)) with tunable mechanical, degradation, and biological properties is used to engineer the epidermis for skin tissue engineering applications. The results reveal that the mechanical and degradation properties of the developed hydrogels can be readily modified by varying the hydrogel concentration, with elastic and compressive moduli tuned from a few kPa to a few hundred kPa, and the degradation times varied from a few days to several months. Additionally, hydrogels of all concentrations displayed excellent cell viability (>90%) with increasing cell adhesion and proliferation corresponding to increases in hydrogel concentrations. Furthermore, the hydrogels are found to support keratinocyte growth, differentiation, and stratification into a reconstructed multilayered epidermis with adequate barrier functions. The robust and tunable properties of GelMA hydrogels suggest that the keratinocyte laden hydrogels can be used as epidermal substitutes, wound dressings, or substrates to construct various in vitro skin models.

Individual and Complementary Effects of Human Papillomavirus Oncogenes on Epithelial Cell Proliferation and Differentiation

Previous studies on human papillomavirus (HPV) type 16 protein functions have established the oncogenic nature of three viral proteins: E5, E6 and E7. Here we have studied the functions of these proteins by functional deletion of the individual E5, E6 or E7, or both E6 and E7 oncogenes in the context of the whole viral genome. These mutants, or the intact wild-type genome, were expressed from the natural viral promoters along with differentiation of epithelial HaCaT cells in three-dimensional collagen raft cultures. High episomal viral copy numbers were obtained using a transfection-based loxp-HPV16-eGFP-N1 vector system. All epithelial equivalents carrying the different HPV type 16 genomes showed pronounced hyperplastic and dysplastic morphology. Particularly the E7 oncogene, with contribution of E6, was shown to enhance cell proliferation. Specifically, the crucial role of E7 in HPV-associated hyperproliferation was clearly manifested. Based on morphological characteristics, immunohistochemical staining for differentiation and proliferation markers, and low expression of E1^E4, we propose that our raft culture models produce cervical intraepithelial neoplasia (CIN)1 and CIN2-like tissue. Our experimental setting provides an alternative tool to study concerted functions of HPV proteins in the development of epithelial dysplasia.

Interleukin-1β-induced Reduction of CD44 Ser-325 Phosphorylation in Human Epidermal Keratinocytes Promotes CD44 Homomeric Complexes, Binding to Ezrin, and Extended, Monocyte-adhesive Hyaluronan Coats

The proinflammatory cytokine interleukin-1β (IL-1β) attracts leukocytes to sites of inflammation. One of the recruitment mechanisms involves the formation of extended, hyaluronan-rich pericellular coats on local fibroblasts, endothelial cells, and epithelial cells. In the present work, we studied how IL-1β turns on the monocyte adhesion of the hyaluronan coat on human keratinocytes. IL-1β did not influence hyaluronan synthesis or increase the amount of pericellular hyaluronan in these cells. Instead, we found that the increase in the hyaluronan-dependent monocyte binding was associated with the CD44 of the keratinocytes. Although IL-1β caused a small increase in the total amount of CD44, a more marked impact was the decrease of CD44 phosphorylation at serine 325. At the same time, IL-1β increased the association of CD44 with ezrin and complex formation of CD44 with itself. Treatment of keratinocyte cultures with KN93, an inhibitor of calmodulin kinase 2, known to phosphorylate Ser-325 in CD44, caused similar effects as IL-1β (i.e. homomerization of CD44 and its association with ezrin) and resulted in increased monocyte binding to keratinocytes in a hyaluronan-dependent way. Overexpression of wild type CD44 standard form, but not a corresponding CD44 mutant mimicking the Ser-325-phosphorylated form, was able to induce monocyte binding to keratinocytes. In conclusion, treatment of human keratinocytes with IL-1β changes the structure of their hyaluronan coat by influencing the amount, post-translational modification, and cytoskeletal association of CD44, thus enhancing monocyte retention on keratinocytes.

S100A6 expression in keratinocytes and its impact on epidermal differentiation

S100A6 is a calcium binding protein expressed in many types of epithelia including epidermis. S100A6 is a binding partner of a number of proteins engaged in cytoskeletal organization, cell cycle control, stress response or apoptosis. So far the effect of its overexpression or knock-down on cell physiology has been studied only at the cellular level. Here, we used an in vitro model of differentiating epidermis to study the role of S100A6 at the tissue level and in the context of tissue differentiation. First of all we have shown that S100A6 mRNA level diminished several fold during primary keratinocyte differentiation and investigated the epigenetic and transcriptional mechanisms involved in this tight expression control. Using bisulfite treatment, luciferase assay and chromatin immunoprecipitation we found that changes in S100A6 expression were DNA methylation independent but could be orchestrated by epidermal specific factors: the ΔNp63 transcription factor and retinoic acid. To investigate if the drop-down in S100A6 expression is indeed critical for keratinocyte differentiation we developed HaCaT cells with stable S100A6 knock-down or overexpression and tested them in 2- and 3-dimensional (organotypic) culture conditions. S100A6 overexpressing cells exhibited accelerated proliferation, enhanced adhesion properties and suppressed loricrin expression - features typical for undifferentiated keratinocytes. In organotypic culture these cells formed thicker epidermis with more Ki67 positive cells, keratin 10 expression spatially limited to the uppermost cell layers and non-detectable loricrin expression. Together, results obtained in both culture models proved that increased S100A6 content in keratinocytes dramatically changed the pace and extent of epidermal differentiation.

Immature truncated O-glycophenotype of cancer directly induces oncogenic features

Aberrant expression of immature truncated O-glycans is a characteristic feature observed on virtually all epithelial cancer cells, and a very high frequency is observed in early epithelial premalignant lesions that precede the development of adenocarcinomas. Expression of the truncated O-glycan structures Tn and sialyl-Tn is strongly associated with poor prognosis and overall low survival. The genetic and biosynthetic mechanisms leading to accumulation of truncated O-glycans are not fully understood and include mutation or dysregulation of glycosyltransferases involved in elongation of O-glycans, as well as relocation of glycosyltransferases controlling initiation of O-glycosylation from Golgi to endoplasmic reticulum. Truncated O-glycans have been proposed to play functional roles for cancer-cell invasiveness, but our understanding of the biological functions of aberrant glycosylation in cancer is still highly limited. Here, we used exome sequencing of most glycosyltransferases in a large series of primary and metastatic pancreatic cancers to rule out somatic mutations as a cause of expression of truncated O-glycans. Instead, we found hypermethylation of core 1 β3-Gal-T-specific molecular chaperone, a key chaperone for O-glycan elongation, as the most prevalent cause. We next used gene editing to produce isogenic cell systems with and without homogenous truncated O-glycans that enabled, to our knowledge, the first polyomic and side-by-side evaluation of the cancer O-glycophenotype in an organotypic tissue model and in xenografts. The results strongly suggest that truncation of O-glycans directly induces oncogenic features of cell growth and invasion. The study provides support for targeting cancer-specific truncated O-glycans with immunotherapeutic measures.

Role for heat shock protein 90α in the proliferation and migration of HaCaT cells and in the deep second-degree burn wound healing in mice

Inflammation, proliferation, and tissue remodeling are essential steps for wound healing. The hypoxic wound microenvironment promotes cell migration through a hypoxia—heat shock protein 90 alpha (Hsp90α)—low density lipoprotein receptor-related protein-1 (LRP-1) autocrine loop. To elucidate the role of this autocrine loop on burn wound healing, we investigated the expression profile of Hsp90α at the edge of burn wounds and found a transient increase in both mRNA and protein levels. Experiments performed with a human keratinocyte cell line—HaCaT also confirmed above results. 17-dimethylaminoethylamino-17demethoxygeldanamycin hydrochloride (17-DMAG), an Hsp90α inhibitor, was used to further evaluate the function of Hsp90α in wound healing. Consistently, topical application of Hsp90α in the early stage of deep second-degree burn wounds led to reduced inflammation and increased tissue granulation, with a concomitant reduction in the size of the wound at each time point tested (p<0.05). Consequently, epidermal cells at the wound margin progressed more rapidly causing an expedited healing process. In conclusion, these results provided a rationale for the therapeutic effect of Hsp90α on the burn wound management.

Effects of fiber density and plasma modification of nanofibrous membranes on the adhesion and growth of HaCaT keratinocytes

It may be possible to regulate the cell colonization of biodegradable polymer nanofibrous membranes by plasma treatment and by the density of the fibers. To test this hypothesis, nanofibrous membranes of different fiber densities were treated by oxygen plasma with a range of plasma power and exposure times. Scanning electron microscopy and mechanical tests showed significant modification of nanofibers after plasma treatment. The intensity of the fiber modification increased with plasma power and exposure time. The exposure time seemed to have a stronger effect on modifying the fiber. The mechanical behavior of the membranes was influenced by the plasma treatment, the fiber density, and their dry or wet state. Plasma treatment increased the membrane stiffness; however, the membranes became more brittle. Wet membranes displayed significantly lower stiffness than dry membranes. X-ray photoelectron spectroscopy (XPS) analysis showed a slight increase in oxygen-containing groups on the membrane surface after plasma treatment. Plasma treatment enhanced the adhesion and growth of HaCaT keratinocytes on nanofibrous membranes. The cells adhered and grew preferentially on membranes of lower fiber densities, probably due to the larger area of void spaces between the fibers.

Phosphoproteome analysis reveals differences in phosphosite profiles between tumorigenic and non-tumorigenic epithelial cells

Oral cancer disease represents a significant fraction of all human cancer types and its poor early diagnosis contributes to reduced individual survival rate. The identification of proteins modulated in tumorigenic cells and its post-translational modifications may improve our understanding of tumor development in epithelial cells. We have analyzed the phosphoproteome of tumorigenic (SCC-9) and non-tumorigenic (HaCaT) cell lines using MS-based approach in order to identify phosphopeptides with differing patterns of modifications and/or abundance. Our results revealed the identity of 4,206 protein phosphorylation sites with sixty-two sites showing to be significantly modulated between the two cell lines. The phosphoproteome data showed an overrepresentation of proteins with a possible role in nuclear regulatory functions. Pathway analysis was further performed on the phosphoproteome dataset and differences and commonalities of the functional pathways present in tumorigenic and non-tumorigenic cells were identified. Phosphopeptides that belong to the proteins lamina-associated polypeptide 2 isoform alpha and serine-arginine repetitive matrix protein 2 were identified with differential abundance and they appear as promising tumor-related phosphopeptides. These two proteins may be related to the structural alterations generally found in the nucleus of tumorigenic cells. The identification of phosphorylation sites in tumorigenic cells may contribute to disclose novel signaling mechanisms associated with OSCC.

SIGNIFICANCE

Oral Squamous Cell Carcinoma (OSCC) is an important cancer disease affecting thousands of people worldwide. Many cellular processes related to the development of oral cancer remain unknown; however, the studies performed in vitro with cancer cells have contributed to guide more specific research which may be further performed by using in vivo approaches or clinical samples. To our knowledge, only few studies have been published showing the results of phosphoproteome profiling of squamous cell carcinoma models, and many signaling proteins must be identified and functionally characterized in order to increase the knowledge available about the complexity of the signaling networks responsible for oral cancer development and its progression. Furthermore, our knowledge regarding proteins exclusive or very low abundant in cancer cells remains limited. A better understanding of the differences between signaling pathways present in epithelial cell lines may contribute to reveal the processes underlying the OSCC.

HaCaT Keratinocytes and Primary Epidermal Keratinocytes Have Different Transcriptional Profiles of Cornified Envelope-Associated Genes to T Helper Cell Cytokines

HaCaT cells are the immortalized human keratinocytes and have been extensively used to study the epidermal homeostasis and its pathophysiology. T helper cells play a role in various chronic dermatological conditions and they can affect skin barrier homeostasis. To evaluate whether HaCaT cells can be used as a model cell system to study abnormal skin barrier development in various dermatologic diseases, we analyzed the gene expression profile of epidermal differentiation markers of HaCaT cells in response to major T helper (Th) cell cytokines, such as IFNγ, IL-4, IL-17A and IL-22. The gene transcriptional profile of cornified envelope-associated proteins, such as filaggrin, loricrin, involucrin and keratin 10 (KRT10), in HaCaT cells was generally different from that in normal human keratinocytes (NHKs). This suggests that HaCaT cells have a limitation as a model system to study the pathophysiological mechanism associated with the Th cell cytokine-dependent changes in cornified envelope-associated proteins which are essential for normal skin barrier development. In contrast, the gene transcription profile change of human β2-defensin (HBD2) in response to IFNγ, IL-4 or IL-17A in HaCaT cells was consistent with the expression pattern of NHKs. IFNγ also up-regulated transglutaminase 2 (TGM2) gene transcription in both HaCaT cells and NHKs. As an alternative cell culture system for NHKs, HaCaT cells can be used to study molecular mechanisms associated with abnormal HBD2 and TGM2 expression in response to IFNγ, IL-4 or IL-17A.

Consistency of the proteome in primary human keratinocytes with respect to gender, age, and skin localization

Keratinocytes account for 95% of all cells of the epidermis, the stratified squamous epithelium forming the outer layer of the skin, in which a significant number of skin diseases takes root. Immortalized keratinocyte cell lines are often used as research model systems providing standardized, reproducible, and homogenous biological material. Apart from that, primary human keratinocytes are frequently used for medical studies because the skin provides an important route for drug administration and is readily accessible for biopsies. However, comparability of these cell systems is not known. Cell lines may undergo phenotypic shifts and may differ from the in vivo situation in important aspects. Primary cells, on the other hand, may vary in biological functions depending on gender and age of the donor and localization of the biopsy specimen. Here we employed metabolic labeling in combination with quantitative mass spectrometry-based proteomics to assess A431 and HaCaT cell lines for their suitability as model systems. Compared with cell lines, comprehensive profiling of the primary human keratinocyte proteome with respect to gender, age, and skin localization identified an unexpected high proteomic consistency. The data were analyzed by an improved ontology enrichment analysis workflow designed for the study of global proteomics experiments. It enables a quick, comprehensive and unbiased overview of altered biological phenomena and links experimental data to literature. We guide through our workflow, point out its advantages compared with other methods and apply it to visualize differences of cell lines compared with primary human keratinocytes.

Skin basement membrane: the foundation of epidermal integrity--BM functions and diverse roles of bridging molecules nidogen and perlecan

The epidermis functions in skin as first defense line or barrier against environmental impacts, resting on extracellular matrix (ECM) of the dermis underneath. Both compartments are connected by the basement membrane (BM), composed of a set of distinct glycoproteins and proteoglycans. Herein we are reviewing molecular aspects of BM structure, composition, and function regarding not only (i) the dermoepidermal interface but also (ii) the resident microvasculature, primarily focusing on the per se nonscaffold forming components perlecan and nidogen-1 and nidogen-2. Depletion or functional deficiencies of any BM component are lethal at some stage of development or around birth, though BM defects vary between organs and tissues. Lethality problems were overcome by developmental stage- and skin-specific gene targeting or by cell grafting and organotypic (3D) cocultures of normal or defective cells, which allows recapitulating BM formation de novo. Thus, evidence is accumulating that BM assembly and turnover rely on mechanical properties and composition of the adjacent ECM and the dynamics of molecular assembly, including further "minor" local components, nidogens largely functioning as catalysts or molecular adaptors and perlecan as bridging stabilizer. Collectively, orchestration of BM assembly, remodeling, and the role of individual players herein are determined by the developmental, tissue-specific, or functional context.

Vitamin D: metabolism, molecular mechanisms, and mutations to malignancies

The potential protective effects of vitamin D against cutaneous carcinogenesis are still poorly understood. The inhibition, by vitamin D, of various cancers in in vitro and in vivo models has triggered detailed investigation of vitamin D effects on neoplastic behavior. Recent studies highlight that such neoplastic features as the tumor microenvironment, angiogenesis, DNA mutagenesis, and apoptosis are all connected to vitamin D metabolic pathways. This review discusses these connections. Vitamin D modulation of the cell cycle, DNA repair and apoptosis via its receptors (VDRs) may have a suppressive effect on skin cancer as some studies suggest. The regulation of multiple tumor signaling pathways by vitamin D may have an implication in cutaneous carcinogenesis and tumor progression to malignancy.

Growth and differentiation of HaCaT keratinocytes

HaCaT cells are a spontaneously immortalized, human keratinocyte line that has been widely used for studies of skin biology and differentiation. Under typical culture conditions HaCaT cells have a partially to fully differentiated phenotype due to the high calcium content of both standard media and fetal bovine serum. This chapter describes low-calcium culture conditions for reverting HaCaT cells to the fully basal state followed by subsequent controlled differentiation using calcium induction.

A novel three-dimensional cell culture method to analyze epidermal cell differentiation in vitro

Studies of the epidermis have been carried out in various models, such as the monolayer culture in vitro model and three-dimensional (3D) skin models, that are spatially organized to display the architectural features seen in human skin. These models have furthered our understanding of epidermal cell biology and provided quite a few lines of evidence on proliferation, cellular metabolism, morphological status, and state of differentiation. In this chapter, we describe a novel method using epithelial cell aggregates embedded in a collagen gel, instead of individual cells, for building cell-cell and cell-matrix interactions. Analyzing cell behaviors during epidermal differentiation would be helpful. Our method would help to analyze a possible regulatory mechanism underlying epidermal differentiation.

Ethyl acetate fraction of Radix rubiae inhibits cell growth and promotes terminal differentiation in cultured human keratinocytes

ETHNOPHARMACOLOGICAL RELEVANCE

In Chinese medicine practice, Radix rubiae, the dry root of Rubia cordifolia L. is commonly used for the treatment of psoriasis.

AIM OF THE STUDY

Psoriasis is a chronic inflammatory skin disorder characterized by hyperproliferation and aberrant differentiation of epidermal keratinocytes. Our previous studies identified Radix rubiae to have potent antiproliferative action on cultured HaCaT keratinocytes and to induce keratinocyte differentiation in mouse tail model. The present study aimed to investigate whether Radix rubiae could also induce terminal differentiation in cultured human keratinocytes.

METHODS AND RESULTS

The cornified envelope (CE) formation assay showed that ethyl acetate (EA) fraction of Radix rubiae significantly accentuated the CE formation, a well-recognized marker of terminal differentiation, in cultured HEK and HaCaT cells in a dose and time dependent manner. Western blot analyses demonstrated that EA fraction of Radix rubiae at a concentration of 3.2μg/ml significantly increased transglutaminase type I and involucrin expression in both HEK and HaCaT keratinocytes after 96 h treatment, a response similar to that of Ca²⁺ positive control. Moreover, the expression level of cytokeratin 5/14, which is specifically related to cell proliferation, was significantly downregulated while terminal differentiation markers cytokeratin 1/10 were markedly increased by Radix rubiae treatment in both HEK and HaCaT cells.

CONCLUSION

The present experimental findings unequivocally confirmed the keratinocyte terminal differentiation promoting capacity of Radix rubiae, and strongly suggest that Radix rubiae is a promising antipsoriatic agent warranting further clinical development for psoriasis treatment.

Different domains in nidogen-1 and nidogen-2 drive basement membrane formation in skin organotypic cocultures

Nidogen-1 and nidogen-2 are homologous proteins found in all basement membranes (BMs). They show comparable binding activities in vitro and partially redundant functions in vivo. Previously, we showed that in skin organotypic cocultures, BM formation was prevented in the absence of nidogens and that either nidogen was able to rescue this failure. We now dissected the two nidogens to identify the domains required for BM deposition. For that purpose, HaCaT cells were grown on collagen matrices containing nidogen-deficient, murine fibroblasts. After addition of nidogen-1 or nidogen-2 protein fragments comprising different binding domains, BM deposition was analyzed by immunofluorescence and electron microscopy. We could demonstrate that the rod-G3 domain of nidogen-2 was sufficient to achieve deposition of BM components at the epidermal-collagen interface. In contrast, for nidogen-1, both the G2 and G3 domains were required. Immunoblot analysis confirmed that all BM components were present in comparable amounts under all culture conditions. This finding demonstrates that nidogens, although homologous proteins, exert their effect on BM assembly through different binding domains, which may in turn result in alterations of BM structure and functions, thus providing an explanation for the phenotypical differences observed between nidogen-1 and -2 deficient mice.

Evaluation of signal transduction pathways after transient cutaneous adenoviral gene delivery

Background

Adenoviral vectors have provided effective methods for in vivo gene delivery in therapeutic applications. However, these vectors can induce immune responses that may severely affect the ability of vector re-application. There is limited information about the mechanisms and signal transduction pathways involved in adenoviral recognition. For optimization of cutaneous gene therapy it is necessary to investigate molecular mechanisms of virus recognition in epidermal cells. The aim of this study was to investigate the signal transduction of the innate immunity after adenoviral DNA internalization in keratinocytes.

Methods

In vitro, keratinocytes were transfected with DNA, in the presence and absence of inhibitors for signalling molecules. In vivo, immunocompetent and athymic mice (n = 3 per group) were twice transduced with an Ad-vector.

Results

The results show an acute induction of type-I-interferon after in vitro transfection. Inhibition of PI3K, p38 MAPK, JNK and NFkappaB resulted in a decreased expression of type-I-interferon. In contrast to immunocompetent mice, athymic mice demonstrated a constant transgene expression and reduced inflammatory response in vivo.

Conclusion

The results suggest an induction of the innate immunity triggered by cytoplasm localised DNA which is mediated by PI3K-, p38 MAPK-, JNK-, NFkappaB-, JAK/STAT- and ERK1/2-dependent pathways. A stable transgene expression and a reduced inflammatory response in immunodeficient mice have been observed. These results provide potential for an effective adenoviral gene delivery into immunosupressed skin.

Basement membrane deposition of nidogen 1 but not nidogen 2 requires the nidogen binding module of the laminin gamma1 chain

The nidogen-laminin interaction is proposed to play a key role in basement membrane (BM) assembly. However, though there are similarities, the phenotypes in mice lacking nidogen 1 and 2 (nidogen double null) differ to those of mice lacking the nidogen binding module (γ1III4) of the laminin γ1 chain. This indicates different cell- and tissue-specific functions for nidogens and their interaction with laminin and poses the question of whether the phenotypes in nidogen double null mice are caused by the loss of the laminin-nidogen interaction or rather by other unknown nidogen functions. To investigate this, we analyzed BMs, in particular those in the skin of mice lacking the nidogen binding module. In contrast to nidogen double null mice, all skin BMs in γ1III4-deficient mice appeared normal. Furthermore, although nidogen 1 deposition was strongly reduced, nidogen 2 appeared unchanged. Mice with additional deletion of the laminin γ3 chain, which contains a γ1-like nidogen binding module, showed a further reduction of nidogen 1 in the dermoepidermal BM; however, this again did not affect nidogen 2. This demonstrates that in vivo only nidogen 1 deposition is critically dependent on the nidogen binding modules of the laminin γ1 and γ3 chains, whereas nidogen 2 is independently recruited either by binding to an alternative site on laminin or to other BM proteins.

Usage of heparan sulfate, integrins, and FAK in HPV16 infection

Human papillomavirus type 16 (HPV16) is the major causative agent of cervical cancer. Studies regarding the early binding and signaling molecules that play a significant role in infection are still lacking. The current study analyzes the role of heparan sulfate, integrins, and the signaling molecule FAK in HPV16 infection of human adult keratinocytes cell line (HaCaTs). Our data demonstrate that infection requires the binding of viral particles to heparan sulfate followed by activation of focal adhesion kinase through an integrin. Infections were reduced in the presence of the FAK inhibitor, TAE226. TAE226 was observed to inhibit viral entry to the early endosome a known infectious route. These findings suggest that FAK can serve as a novel target for antiviral therapy.

Integrin alpha3 subunit regulates events linked to epithelial repair, including keratinocyte migration and protein expression

Two integrins, alpha3beta1 and alpha6beta4, are high-affinity receptors for laminin 332, the major laminin isoform of the dermal-epidermal junction, although they are thought to have different functions. Biological and genetic studies have firmly established that the alpha6beta4 integrin is indispensable for the stable anchorage of the epidermis to the underlying dermis. In contrast, the alpha3beta1 integrin is thought to be important for cell migration, although the issue is controversial, and both positive and negative effects have been reported. To address the function of alpha3beta1 integrin, we used small interfering RNA to down-regulate the alpha3 subunit in human keratinocytes. The resulting phenotype indicates that lack of alpha3beta1 integrin compromises intercellular adhesion and collective migration, while it enhances single cell migration with a concomitant increase of both focal adhesion kinase and extracellular signal-regulated kinase. In addition, down-regulation of integrin alpha3 subunit results in an increased expression of fibronectin and precursor laminin 332, two extracellular matrix proteins known to be up-regulated during wound healing. Thus, down-regulation of alpha3beta1 integrin recapitulates crucial events governing keratinocyte migration associated with wound healing and tissue repair.

Simplified purification procedure of laminin-332 and laminin-511 from human cell lines

Laminins are glycoproteins expressed in the basement membrane of multiple epithelial tissues. Previously described purification procedures for the human laminin variants laminin-5 (LN-332) and laminin-10 (LN-511) use tissue as starting material and have multiple steps. We demonstrate a two-step laminin immunoaffinity purification method to produce consistent quantities of intact and biologically active LN-332 and LN-511 from human keratinocyte (HaCaT) and human lung carcinoma (A549) cell lines, respectively. The purification of LN-332 and LN-551 was demonstrated by PAGE analysis, silver staining and Western blot analysis. The purification procedure includes instruction on removing a cell adhesion contaminant known as galectin-3 binding protein from purified LN-511. The biological activity of purified laminin was tested in a standard cell adhesion assay and compared to commercially available LN-111. This rapid and reproducible purification method will contribute to understanding the role of LN-332 and LN-511 in cell behavior, signaling, and gene expression.

Basement membranes in skin are differently affected by lack of nidogen 1 and 2

Nidogens have been proposed to play a key role in basement membrane (BM) formation. However, recent findings using genetic approaches and organotypic coculture models demonstrated distinct tissue requirements thus changing the classical view of BM assembly. Toward this end, we have analyzed the dermo-epidermal junction and the microvasculature in skin of nidogen-deficient mice for their BM composition and structural assembly. Histology of nidogen double-null embryos at embryonic day (E)18.5 revealed overall normal skin morphology with a regularly differentiated epidermis. However, in the dermis, numerous erythrocytes had extravasated out of the microvasculature. Residual composition and ultrastructure of the dermo-epidermal BM are not altered in the absence of nidogens, demonstrating that the deposition of laminin, collagen IV, and perlecan occurs and allows cutaneous BM formation. In contrast, in capillaries, BM formation is severely impaired in the absence of nidogens, showing an irregular, patchy distribution and a dramatically reduced deposition of collagen IV, perlecan, and particularly laminin-411. Ultrastructure revealed thin fragile walls in the small blood vessels next to the epidermis, completely lacking a distinct endothelial BM. In summary, our results indicate that in skin the laminin composition of the various BMs determines whether nidogens are required for their assembly and stabilization.

Vitronectin: growth factor complexes hold potential as a wound therapy approach

Topical administration of growth factors has displayed some potential in wound healing, but variable efficacy, high doses, and costs have hampered their implementation. Moreover, this approach ignores the fact that wound repair is driven by interactions between multiple growth factors and extracellular matrix (ECM) proteins. We report herein that complexes comprising IGF and IGF-binding proteins bound to the ECM protein vitronectin (VN) significantly enhance cellular functions relevant to wound repair in human skin keratinocytes in two- and three-dimensional in vitro cell models and are active, even in the presence of wound fluid. Moreover, these responses require activation of both the IGF receptor and the VN-binding alpha(v) integrins. Further, we assessed the complexes as a topical agent in the treatment of deep dermal partial thickness burns in a porcine model. This pilot study revealed that the complexes may hold promise as a wound healing therapy. Critically, the significant responses observed in vitro and the encouraging preliminary data in vivo were obtained with nanogram doses of growth factors. This suggests that coupling delivery of growth factors to ECM proteins such as VN may ultimately prove to be a more effective strategy for developing a wound healing therapy.

Reference gene selection for real-time rtPCR in human epidermal keratinocytes

BACKGROUND

RNA interference represents a powerful tool with which to achieve suppression of specific target mRNA. Real-time rtPCR is a useful technique for assessing levels of mRNA expression. Critically, for real-time rtPCR to yield meaningful results, it is necessary to normalise expression of the gene of interest to stably expressed endogenous control genes.

OBJECTIVES

The study involved establishing expression profiles for 11 housekeeping genes in human epidermal keratinocyte cell lines determining their relative stability. Furthermore, the effect of the presence of shRNA on these expression profiles has been established.

METHODS

Keratinocytes were transfected using lipid-based transfection or AMAXA nucleofection. Real-time rtPCR was used to establish RNA expression levels. Data analysis was carried out using geNORM.

RESULTS

When using HaCaT or adult NHEK cells any combination of 8 of the housekeeping genes would be appropriate for normalisation. In contrast, with juvenile NHEK cells only 4 of the housekeeping genes were found to be sufficiently stable to be deemed appropriate for normalisation of expression data. Furthermore data demonstrated that the expression of housekeeping genes may sometimes be affected by the induction of the RNAi pathway.

CONCLUSIONS

The data obtained highlight the importance of characterising housekeeping gene expression profiles in each specific cell type prior to choosing a set of housekeeping genes for expression studies. The results from this study are applicable to researchers working with human epidermal keratinocytes and the experimental approach is more broadly applicable to any researcher carrying out real-time rtPCR.