Keratins and the skin

Evaluation of anionic surfactants effects on the skin barrier function based on skin permeability

Anionic surfactants are often used for cleaning and pharmaceutical purposes because of their strong surfactancy and foaming property. However, they are rarely ingested orally, the skin is a part of the human body most affected by surfactants. Barrier function of the skin is very strong, but the anionic surfactants can cause serious damages to it. Recently, amino acid-based surfactants have attracted attention as a safer option owing to their biocompatibility. Cytotoxicity examinations revealed that the amino acid-based surfactants are superior to sulfate-based surfactants. However, a systematical and comprehensive study related to the effect of these surfactants on skin barrier function has not yet been reported. In this work, skin permeation test using the skin of hairless mice and HPLC method is carried out. The material transmission speed through skin in a steady state was different between each surfactant treatment. We performed a comprehensive analysis of the effect of surfactants on skin barrier function and defined Transmission Index as an index for the degree of effect of surfactants. Glutamate series amino acid-based surfactant were effective to Transmission Index and we guessed the cause was due to adsorption. Based on the finding this study, we suggest using adsorptive property as a measure to the effect on the skin barrier function.

Keratinocytes mediate innocuous and noxious touch via ATP-P2X4 signaling

The first point of our body’s contact with tactile stimuli (innocuous and noxious) is the epidermis, the outermost layer of skin that is largely composed of keratinocytes. Here, we sought to define the role that keratinocytes play in touch sensation in vivo and ex vivo. We show that optogenetic inhibition of keratinocytes decreases behavioral and cellular mechanosensitivity. These processes are inherently mediated by ATP signaling, as demonstrated by complementary cutaneous ATP release and degradation experiments. Specific deletion of P2X4 receptors in sensory neurons markedly decreases behavioral and primary afferent mechanical sensitivity, thus positioning keratinocyte-released ATP to sensory neuron P2X4 signaling as a critical component of baseline mammalian tactile sensation. These experiments lay a vital foundation for subsequent studies into the dysfunctional signaling that occurs in cutaneous pain and itch disorders, and ultimately, the development of novel topical therapeutics for these conditions.

The skin is the largest sensory organ of the body, and the first point of contact with the outside world. Whether it is being pinched or caressed, the skin’s sense of touch informs organisms about their surroundings and allows them to react appropriately.

Nerve cells present in the skin capture information about touch and transmit it to the brain where it is decoded. However, there are many other types of cells in the skin besides nerve cells. The role that these other skin cells play in perceiving non-painful and painful touch is still unclear.

Moehring et al. now report how the skin cells that form 95% of the most outer layer of the skin are involved in detecting touch. In mutant mice whose cells can be ‘switched off’ by a certain light, artificially deactivating these cells makes the animals less able to respond to tactile stimuli. Further experiments show that when pressure is applied onto the skin, the surface skin cells release a chemical messenger, which then binds specifically to the nerve cells. When the messaging molecule is experimentally destroyed or prevented from attaching to the nerve cell, the mice react less to non-painful and painful touch. This means the cells at the surface of the skin detect tactile signals from the environment and then communicate this information to the nerve cells, where it is taken to the brain.

Disrupted communication between the cells in the outer layer of the skin and the nerve cells is found in painful and itchy skin conditions such as eczema and psoriasis. Knowing how these two types of cells normally work together may help with finding new pain and itch treatments for these skin disorders.

Microscopic and immunohistochemical analyses of the claw of the nesting dinosaur, Citipati osmolskae

One of the most well-recognized Cretaceous fossils is Citipati osmolskae (MPC-D 100/979), an oviraptorid dinosaur discovered in brooding position on a nest of unhatched eggs. The original description refers to a thin lens of white material extending from a manus ungual, which was proposed to represent original keratinous claw sheath that, in life, would have covered it. Here, we test the hypothesis that this exceptional morphological preservation extends to the molecular level. The fossil sheath was compared with that of extant birds, revealing similar morphology and microstructural organization. In living birds, the claw sheath consists primarily of two structural proteins; alpha-keratin, expressed in all vertebrates, and beta-keratin, found only in reptiles and birds (sauropsids). We employed antibodies raised against avian feathers, which comprise almost entirely of beta-keratin, to demonstrate that fossil tissues respond with the same specificity, though less intensity, as those from living birds. Furthermore, we show that calcium chelation greatly increased antibody reactivity, suggesting a role for calcium in the preservation of this fossil material.

Deciphering psoriasis. A bioinformatic approach

BACKGROUND

Psoriasis is an immune-mediated, inflammatory and hyperproliferative disease of the skin and joints. The cause of psoriasis is still unknown. The fundamental feature of the disease is the hyperproliferation of keratinocytes and the recruitment of cells from the immune system in the region of the affected skin, which leads to deregulation of many well-known gene expressions.

OBJECTIVE

Based on data mining and bioinformatic scripting, here we show a new dimension of the effect of psoriasis at the genomic level.

METHODS

Using our own pipeline of scripts in Perl and MySql and based on the freely available NCBI Gene Expression Omnibus (GEO) database: DataSet Record GDS4602 (Series GSE13355), we explore the extent of the effect of psoriasis on gene expression in the affected tissue.

RESULTS

We give greater insight into the effects of psoriasis on the up-regulation of some genes in the cell cycle (CCNB1, CCNA2, CCNE2, CDK1) or the dynamin system (GBPs, MXs, MFN1), as well as the down-regulation of typical antioxidant genes (catalase, CAT; superoxide dismutases, SOD1-3; and glutathione reductase, GSR). We also provide a complete list of the human genes and how they respond in a state of psoriasis.

CONCLUSION

Our results show that psoriasis affects all chromosomes and many biological functions. If we further consider the stable and mitotically inheritable character of the psoriasis phenotype, and the influence of environmental factors, then it seems that psoriasis has an epigenetic origin. This fit well with the strong hereditary character of the disease as well as its complex genetic background.

Human papillomavirus type 18 E5 oncogene supports cell cycle progression and impairs epithelial differentiation by modulating growth factor receptor signalling during the virus life cycle

Deregulation of proliferation and differentiation-dependent signalling pathways is a hallmark of human papillomavirus (HPV) infection. Although the manipulation of these pathways by E6 and E7 has been extensively studied, controversies surround the role of the E5 oncoprotein during a productive virus life cycle. By integrating primary keratinocytes harbouring wild type or E5 knockout HPV18 genomes with pharmacological and gain/loss of function models, this study aimed to provide molecular information about the role of E5 in epithelial proliferation and differentiation. We show that E5 contributes to cell cycle progression and unscheduled host DNA synthesis in differentiating keratinocytes. E5 function correlates with increased EGFR activation in differentiating cells and blockade of this pathway impairs differentiation-dependent cell cycle progression of HPV18 containing cells. Our findings provide a functional requirement of enhanced EGFR signalling for suprabasal cellular DNA synthesis during the virus life cycle. They also reveal an unrecognised contribution of E5 towards the impaired keratinocyte differentiation observed during a productive HPV infection. E5 suppresses a signalling axis consisting of the keratinocyte growth factor receptor (KGFR) pathway. Inhibition of this pathway compensates for the loss of E5 in knockout cells and re-instates the delay in differentiation. The negative regulation of KGFR involves suppression by the EGFR pathway. Thus our data reveal an unappreciated role for E5-mediated EGFR signalling in orchestrating the balance between proliferation and differentiation in suprabasal cells.

Traceless Targeting and Isolation of Gene-Edited Immortalized Keratinocytes from Epidermolysis Bullosa Simplex Patients

Epidermolysis bullosa simplex (EBS) is a blistering skin disease caused by dominant-negative mutations in either KRT5 or KRT14, resulting in impairment of keratin filament structure and epidermal fragility. Currently, nearly 200 mutations distributed across the entire length of these genes are known to cause EBS. Genome editing using programmable nucleases enables the development of ex vivo gene therapies for dominant-negative genetic diseases. A clinically feasible strategy involves the disruption of the mutant allele while leaving the wild-type allele unaffected. Our aim was to develop a traceless approach to efficiently disrupt KRT5 alleles using TALENs displaying unbiased monoallelic disruption events and devise a strategy that allows for subsequent screening and isolation of correctly modified keratinocyte clones without the need for selection markers. Here we report on TALENs that efficiently disrupt the KRT5 locus in immortalized patient-derived EBS keratinocytes. Inactivation of the mutant allele using a TALEN working at sub-optimal levels resulted in restoration of intermediate filament architecture. This approach can be used for the functional inactivation of any mutant keratin allele regardless of the position of the mutation within the gene and is furthermore applicable to the treatment of other inherited skin disorders.

The Surface Protein SdrF Mediates Staphylococcus epidermidis Adherence to Keratin

Background

Staphylococcus epidermidis, a major component of skin flora, is an opportunist, often causing prosthetic device infections. A family of structurally related proteins mediates staphylococcal attachment to host tissues, contributing to the success of S. epidermidis as a pathogen. We examined the ability of the surface protein SdrF to adhere to keratin, a major molecule expressed on the skin surface.

Methods

A heterologous Lactococcus lactis expression system was used to express SdrF and its ligand-binding domains. Adherence to keratin types 1 and 10, human foreskin keratinocytes, and nasal epithelial cells was examined.

Results

SdrF bound human keratins 1 and 10 and adhered to keratinocytes and epithelial cells. Binding involved both the A and B domains. Anti-SdrF antibodies reduced adherence of S. epidermidis to keratin and keratinocytes. RNA interference reduced keratin synthesis in keratinocytes and, as a result, SdrF adherence. Direct force measurements using atomic force microscopy showed that SdrF mediates bacterial adhesion to keratin 10 through strong and weak bonds involving the A and B regions; strong adhesion was primarily mediated by the A region.

Conclusions

These studies demonstrate that SdrF mediates adherence to human keratin and suggest that SdrF may facilitate S. epidermidis colonization of the skin.

The Molecular Revolution in Cutaneous Biology: Keratin Genes and their Associated Disease: Diversity, Opportunities, and Challenges

The abundance of keratin proteins and the filaments they form in surface epithelia has long been appreciated. This said, the remarkable diversity of keratin proteins and the notion that they are encoded by one of the largest gene families in the human genome has come to the fore relatively recently, coinciding with the sequencing of whole genomes. This complexity has generated some practical challenges, notably in terms of nomenclature and tractability. More importantly, however, studies of keratin have seeded the discovery of the genetic basis for a large number of genodermatoses and continue to provide a unique perspective on and insight into epithelial cells and tissues, whether normal or diseased.

Molecular and histological characterization of age spots

Age spots, also called solar lentigines and lentigo senilis, are light brown to black pigmented lesions of various sizes that typically develop in chronically sun-exposed skin. It is well known that age spots are strongly related to chronic sun exposure and are associated with photodamage and an increased risk for skin cancer; however, the mechanisms underlying their development remain poorly understood. We used immunohistochemical analysis and microarray analysis to investigate the processes involved in their formation, focusing on specific markers associated with the functions and proliferation of melanocytes and keratinocytes. A total of 193 genes were differentially expressed in age spots, but melanocyte pigment genes were not among them. The increased expression of keratins 5 and 10, markers of basal and suprabasal keratinocytes, respectively, in age spots suggests that the increased proliferation of basal keratinocytes combined with the decreased turnover of suprabasal keratinocytes leads to the exaggerated formation of rete ridges in lesional epidermis which in turn disrupts the normal processing of melanin upwards from the basal layer. Based on our results, we propose a model for the development of age spots that explains the accumulation of melanin and the development of extensive rete ridges in those hyperpigmented lesions.

Keratin mediates the recognition of apoptotic and necrotic cells through dendritic cell receptor DEC205/CD205

Clearance of dead cells is critical for maintaining homeostasis and prevents autoimmunity and inflammation. When cells undergo apoptosis and necrosis, specific markers are exposed and recognized by the receptors on phagocytes. DEC205 (CD205) is an endocytotic receptor on dendritic cells with antigen presentation function and has been widely used in immune therapies for vaccine generation. It has been shown that human DEC205 recognizes apoptotic and necrotic cells in a pH-dependent fashion. However, the natural ligand(s) of DEC205 remains unknown. Here we find that keratins are the cellular ligands of human DEC205. DEC205 binds to keratins specifically at acidic, but not basic, pH through its N-terminal domains. Keratins form intermediate filaments and are important for maintaining the strength of cells and tissues. Our results suggest that keratins also function as cell markers of apoptotic and necrotic cells and mediate a pH-dependent pathway for the immune recognition of dead cells.

Keratin 17 Is Induced in Oral Cancer and Facilitates Tumor Growth

Keratin subtypes are selectively expressed depending on the cell type. They not only provide structural support, but regulate the metabolic processes and signaling pathways that control the growth of the epithelium. KRT17 (keratin 17) is induced in the regenerative epithelium and acts on diverse signaling pathways. Here, we demonstrate that KRT17 is invariably and permanently induced in oral squamous cell carcinoma (OSCC), as revealed by immunohistochemistry and cDNA microarray analysis. Two representative OSCC cell lines; KRT17-weakly expressing Ca9-22 and KRT17-highly expressing HSC3 were used to establish KRT17-overexpressing Ca9-22 and KRT17-knockdown HSC3 cells. Analysis of these cells revealed that KRT17 promoted cell proliferation and migration by stimulating the Akt/mTOR pathway. KRT17 also upregulated the expression of SLC2A1 (solute carrier family 2 member 1/Glut1) and glucose uptake. To further investigate the effect of KRT17 on tumorigenesis, KRT17-knockout HSC3 cells were established and were transplanted to the cephalic skin of nude mice. The tumors that developed from KRT17-knockout HSC3 cells had a lower Ki-67 labeling index and were significantly smaller compared to the controls. These results indicate that KRT17 stimulates the Akt/mTOR pathway and glucose uptake, thereby facilitating tumor growth. We could not confirm the relationship between KRT17 and SFN (stratifin) in the cells examined in this study. However, our study reinforces the concept that the cellular properties of cancer are regulated by a series of molecules similar to those found in wound healing. In OSCC, KRT17 acts as a pathogenic keratin that facilitates tumor growth through the stimulation of multiple signaling pathways, highlighting the importance of KRT17 as a multifunctional promoter of tumorigenesis.

Genetic Predictors of Susceptibility to Dermatophytoses

Countless observational studies conducted over the last century reveal that dermatophytes infect humans of every age, race, gender, and socioeconomic status with strikingly high rates. The curious disparity in dermatophyte infection patterns observed within and between populations has led countless investigators to explore whether genetics underlie a susceptibility to, or confer protection against, dermatophyte infections. This paper examines the data that offer a link between genetics and dermatophytoses and discusses the underlying mechanisms that support these observations.

Evaluation of fibrin-based dermal-epidermal organotypic cultures for in vitro skin corrosion and irritation testing of chemicals according to OECD TG 431 and 439

Reconstructed human epidermis (RhE) models have been used for in vitro testing of the potential harmful effects of exposure to chemical compounds on health. In the past, skin irritation and corrosion were evaluated in animal models; however, in recent years, due to the bioethics implications of the method and, to minimize the use of experimental animals, alternative procedures have been proposed. The Organisation for Economic Co-operation and Development (OECD) in its test guidelines (TG) 431 and 439 indicates the requirements for validating new methods for the evaluation of skin corrosion and irritation, respectively. Here, we present an in-house human dermal-epidermal model, useful for the performance of these tests. Using the methods described in this work, it was possible to obtain human fibrin-based dermal-epidermal organotypic skin cultures (ORGs) displaying similar histological characteristics to native skin and expressing specific differentiation epithelial proteins. The end points to classify a substance as irritant or corrosive were cell viability evaluated by MTT assay, and cytokine release measured by BD CBA for human inflammatory cytokines. According to the MTT test, the ORGs correctly classified irritating and corrosive substances. Moreover, the cytokine release assay was difficult to interpret in the context of testing chemical hazard classification. Further experiments are needed to validate this new model for the evaluation of surfactants because the fibrin matrix was affected in the presence of these substances.

Gene Expression Architecture of Mouse Dorsal and Tail Skin Reveals Functional Differences in Inflammation and Cancer

Inherited germline polymorphisms can cause gene expression levels in normal tissues to differ substantially between individuals. We present an analysis of the genetic architecture of normal adult skin from 470 genetically unique mice, demonstrating the effect of germline variants, skin tissue location, and perturbation by exogenous inflammation or tumorigenesis on gene signaling pathways. Gene networks related to specific cell types and signaling pathways, including sonic hedgehog (Shh), Wnt, Lgr family stem cell markers, and keratins, differed at these tissue sites, suggesting mechanisms for the differential susceptibility of dorsal and tail skin to development of skin diseases and tumorigenesis. The Pten tumor suppressor gene network is rewired in premalignant tumors compared to normal tissue, but this response to perturbation is lost during malignant progression. We present a software package for expression quantitative trait loci (eQTL) network analysis and demonstrate how network analysis of whole tissues provides insights into interactions between cell compartments and signaling molecules.

Laminin α5 in the keratinocyte basement membrane is required for epidermal-dermal intercommunication

Laminin α5 is broadly expressed in the epidermal basement membrane (BM) of mature mice and its elimination at this site (Lama5^Ker5 mouse) results in hyperproliferation of basal keratinocytes and a delay in hair follicle development, which correlated with upregulation of the dermally-derived laminin α2 and laminin α4 chains in the epidermal BM and of tenascin-C subjacent to the BM. In vitro studies revealed laminin 511 to be strongly adhesive for primary keratinocytes and that loss of laminin α5 does not result in cell autonomous defects in proliferation. Flow cytometry reveals that the loss of laminin α5 resulted in increased numbers of CD45⁺, CD4⁺ and CD11b⁺ immune cells in the skin, which temporo-spatial analyses revealed were detectable only subsequent to the loss of laminin α5 and the appearance of the hyperproliferative keratinocyte phenotype. These findings indicate that immune cell changes are the consequence and not the cause of keratinocyte hyperproliferation. Loss of laminin α5 in the epidermal BM was also associated with changes in the expression of several dermally-derived growth factors involved in keratinocyte proliferation and hair follicle development in adult but not new born Lama5^Ker5 skin, including KGF, EGF and KGF-2. In situ binding of FGF-receptor-2α (IIIb)-Fc chimera (FGFR2IIIb) to mouse skin sections revealed decoration of several BMs, including the epidermal BM, which was absent in Lama5^Ker5 skin. This indicates reduced levels of FGFR2IIIb ligands, which include KGF and KGF-2, in the epidermal BM of adult Lama5^Ker5 skin. Our data suggest an initial inhibitory effect of laminin α5 on basal keratinocyte proliferation and migration, which is exacerbated by subsequent changes in growth factor expression by epidermal and dermal cells, implicating laminin α5 in epidermal-dermal intercommunication.

Microbial decomposition of keratin in nature-a new hypothesis of industrial relevance

Discovery of keratin-degrading enzymes from fungi and bacteria has primarily focused on finding one protease with efficient keratinase activity. Recently, an investigation was conducted of all keratinases secreted from a fungus known to grow on keratinaceous materials, such as feather, horn, and hooves. The study demonstrated that a minimum of three keratinases is needed to break down keratin, an endo-acting, an exo-acting, and an oligopeptide-acting keratinase. Further, several studies have documented that disruption of sulfur bridges of the keratin structure acts synergistically with the keratinases to loosen the molecular structure, thus giving the enzymes access to their substrate, the protein structure. With such complexity, it is relevant to compare microbial keratin decomposition with the microbial decomposition of well-studied polymers such as cellulose and chitin. Interestingly, it was recently shown that the specialized enzymes, lytic polysaccharide monoxygenases (LPMOs), shown to be important for breaking the recalcitrance of cellulose and chitin, are also found in keratin-degrading fungi. A holistic view of the complex molecular self-assembling structure of keratin and knowledge about enzymatic and boosting factors needed for keratin breakdown have been used to formulate a hypothesis for mode of action of the LPMOs in keratin decomposition and for a model for degradation of keratin in nature. Testing such hypotheses and models still needs to be done. Even now, the hypothesis can serve as an inspiration for designing industrial processes for keratin decomposition for conversion of unexploited waste streams, chicken feather, and pig bristles into bioaccessible animal feed.

Comparative transcriptomic profiling of hydrogen peroxide signaling networks in zebrafish and human keratinocytes: Implications toward conservation, migration and wound healing

Skin wounds need to be repaired rapidly after injury to restore proper skin barrier function. Hydrogen peroxide (H₂O₂) is a conserved signaling factor that has been shown to promote a variety of skin wound repair processes, including immune cell migration, angiogenesis and sensory axon repair. Despite growing research on H₂O₂ functions in wound repair, the downstream signaling pathways activated by this reactive oxygen species in the context of injury remain largely unknown. The goal of this study was to provide a comprehensive analysis of gene expression changes in the epidermis upon exposure to H₂O₂ concentrations known to promote wound repair. Comparative transcriptome analysis using RNA-seq data from larval zebrafish and previously reported microarray data from a human epidermal keratinocyte line shows that H₂O₂ activates conserved cell migration, adhesion, cytoprotective and anti-apoptotic programs in both zebrafish and human keratinocytes. Further assessment of expression characteristics and signaling pathways revealed the activation of three major H₂O₂–dependent pathways, EGF, FOXO1, and IKKα. This study expands on our current understanding of the clinical potential of low-level H₂O₂ for the promotion of epidermal wound repair and provides potential candidates in the treatment of wound healing deficits.

Management of Epidermolytic Ichthyosis in the Newborn

Epidermolytic ichthyosis (EI) is a rare autosomal dominant genodermatosis that presents at birth as a bullous disease, followed by a lifelong ichthyotic skin disorder. Essentially, it is a defective keratinization caused by mutations of keratin 1 (KRT1) or keratin 10 (KRT10) genes, which lead to skin fragility, blistering, and eventually hyperkeratosis. Successful management of EI in the newborn period can be achieved through a thoughtful, directed, and interdisciplinary or multidisciplinary approach that encompasses family support. This condition requires meticulous care to avoid associated morbidities such as infection and dehydration. A better understanding of the disrupted barrier protection of the skin in these patients provides a basis for management with daily bathing, liberal emollients, pain control, and proper nutrition as the mainstays of treatment. In addition, this case presentation will include discussions on the pathophysiology, complications, differential diagnosis, and psychosocial and ethical issues.

Skin Keratins

Keratins comprise the type I and type II intermediate filament-forming proteins and occur primarily in epithelial cells. They are encoded by 54 evolutionarily conserved genes (28 type I, 26 type II) and regulated in a pairwise and tissue type-, differentiation-, and context-dependent manner. Keratins serve multiple homeostatic and stress-enhanced mechanical and nonmechanical functions in epithelia, including the maintenance of cellular integrity, regulation of cell growth and migration, and protection from apoptosis. These functions are tightly regulated by posttranslational modifications as well as keratin-associated proteins. Genetically determined alterations in keratin-coding sequences underlie highly penetrant and rare disorders whose pathophysiology reflects cell fragility and/or altered tissue homeostasis. Moreover, keratin mutation or misregulation represents risk factors or genetic modifiers for several acute and chronic diseases. This chapter focuses on keratins that are expressed in skin epithelia, and details a number of basic protocols and assays that have proven useful for analyses being carried out in skin.

The dynamic anatomy and patterning of skin

The skin is often viewed as a static barrier that protects the body from the outside world. Emphasis on studying the skin's architecture and biomechanics in the context of restoring skin movement and function is often ignored. It is fundamentally important that if skin is to be modelled or developed, we do not only focus on the biology of skin but also aim to understand its mechanical properties and structure in living dynamic tissue. In this review, we describe the architecture of skin and patterning seen in skin as viewed from a surgical perspective and highlight aspects of the microanatomy that have never fully been realized and provide evidence or concepts that support the importance of studying living skin's dynamic behaviour. We highlight how the structure of the skin has evolved to allow the body dynamic form and function, and how injury, disease or ageing results in a dramatic changes to the microarchitecture and changes physical characteristics of skin. Therefore, appreciating the dynamic microanatomy of skin from the deep fascia through to the skin surface is vitally important from a dermatological and surgical perspective. This focus provides an alternative perspective and approach to addressing skin pathologies and skin ageing.

Bedding Material Affects Mechanical Thresholds, Heat Thresholds, and Texture Preference

It has long been known that the bedding type on which animals are housed can affect breeding behavior and cage environment, yet little is known about its effects on evoked behavior responses or nonreflexive behaviors. C57BL/6 mice were housed for 2 weeks on 1 of 5 bedding types: aspen Sani-Chips (standard bedding for our institute), ALPHA-Dri, Cellu-Dri, Pure-o'Cel, or TEK-Fresh. Mice housed on aspen exhibited the lowest (most sensitive) mechanical thresholds and those on TEK-Fresh exhibited 3-fold higher thresholds. Although bedding type had no effect on responses to punctate or dynamic light touch stimuli, TEK-Fresh-housed animals exhibited greater responsiveness in a noxious needle assay than did those housed on the other bedding types. Heat sensitivity was also affected by bedding because animals housed on aspen exhibited the shortest (most sensitive) latencies to withdrawal, whereas those housed on TEK-Fresh had the longest (least sensitive) latencies to response. Slight differences between bedding types were also seen in a moderate cold temperature preference assay. A modified tactile conditioned place preference chamber assay revealed that animals preferred TEK-Fresh to aspen bedding. Bedding type had no effect in a nonreflexive wheel running assay. In both acute (2 day) and chronic (5 week) inflammation induced by injection of complete Freund's adjuvant in the hindpaw, mechanical thresholds were reduced in all groups regardless of bedding type, but TEK-Fresh and Pure-o'Cel groups exhibited a greater dynamic range between controls and inflamed cohorts than aspen-housed mice.

PERSPECTIVE

These findings indicate that the bedding type routinely used to house animals can markedly affect the dynamic range of mechanical and heat behavior assays under normal and tissue injury conditions. Among beddings tested, TEK-Fresh bedding resulted in the least sensitive baseline thresholds for mechanical and thermal stimuli and the greatest dynamic range after tissue injury. Therefore, selection of routine cage bedding material should be carefully considered for animals that will be tested in behavioral somatosensory assays.

Low-level laser irradiation promotes the proliferation and maturation of keratinocytes during epithelial wound repair

Low-level laser therapy (LLLT) has been extensively employed to improve epithelial wound healing, though the exact response of epithelium maturation and stratification after LLLT is unknown. Thus, this study aimed to assess the in vitro growth and differentiation of keratinocytes (KCs) and in vivo wound healing response when treated with LLLT. Human KCs (HaCaT cells) showed an enhanced proliferation with all the employed laser energy densities (3, 6 and 12 J/cm(2) , 660 nm, 100 mW), together with an increased expression of Cyclin D1. Moreover, the immunoexpression of proteins related to epithelial proliferation and maturation (p63, CK10, CK14) all indicated a faster maturation of the migrating KCs in the LLLT-treated wounds. In that way, an improved epithelial healing was promoted by LLLT with the employed parameters; this improvement was confirmed by changes in the expression of several proteins related to epithelial proliferation and maturation. Immunofluorescent expression of cytokeratin 10 (red) and Cyclin D1 (green) in (A) Control keratinocytes and (B) Low-level laser irradiated cells. Blue color illustrates the nuclei of the cells (DAPI staining).

Assessing the sensitivity of human skin hyperspectral responses to increasing anemia severity levels

Anemia is a prevalent medical condition that seriously affects millions of people all over the world. In many regions, not only its initial detection but also its monitoring are hindered by limited access to laboratory facilities. This situation has motivated the development of a wide range of optical devices and procedures to assist physicians in these tasks. Although noticeable progress has been achieved in this area, the search for reliable, low-cost, and risk-free solutions still continues, and the strengthening of the knowledge base about this disorder and its effects is essential for the success of these initiatives. We contribute to these efforts by closely examining the sensitivity of human skin hyperspectral responses (within and outside the visible region of the light spectrum) to reduced hemoglobin concentrations associated with increasing anemia severity levels. This investigation, which involves skin specimens with distinct biophysical and morphological characteristics, is supported by controlled in silico experiments performed using a predictive light transport model and measured data reported in the biomedical literature. We also propose a noninvasive procedure to be employed in the monitoring of this condition at the point-of-care.

A mechanism for nano-titanium dioxide-induced cytotoxicity in HaCaT cells under UVA irradiation

Nano-TiO2 has been reported to be an efficient photocatalyst, which is able to produce reactive oxygen species (ROS) under UVA irradiation. In this study, we investigated the effects of nano-TiO2 on the cytotoxicity, induction of apoptosis, and the putative pathways of its actions in HaCaT cells. We show that nano-TiO2 is a potent inducer of apoptosis and that it transduces the apoptotic signal via ROS generation, thereby inducing mitochondrial permeability transition (MPT) and activating Caspase-3 from HaCaT cells. ROS production, mitochondrial alteration, and subsequent apoptotic cell death in nano-TiO2-treated cells were blocked by the MPT pore-blocker cyclosporin A. Taken together, our data indicate that nano-TiO2 induces the ROS-mediated MPT and resultant Caspase-3 activation.

Emerging roles of sumoylation in the regulation of actin, microtubules, intermediate filaments, and septins

Sumoylation is a powerful regulatory system that controls many of the critical processes in the cell, including DNA repair, transcriptional regulation, nuclear transport, and DNA replication. Recently, new functions for SUMO have begun to emerge. SUMO is covalently attached to components of each of the four major cytoskeletal networks, including microtubule-associated proteins, septins, and intermediate filaments, in addition to nuclear actin and actin-regulatory proteins. However, knowledge of the mechanisms by which this signal transduction system controls the cytoskeleton is still in its infancy. One story that is beginning to unfold is that SUMO may regulate the microtubule motor protein dynein by modification of its adaptor Lis1. In other instances, cytoskeletal elements can both bind to SUMO non-covalently and also be conjugated by it. The molecular mechanisms for many of these new functions are not yet clear, but are under active investigation. One emerging model links the function of MAP sumoylation to protein degradation through SUMO-targeted ubiquitin ligases, also known as STUbL enzymes. Other possible functions for cytoskeletal sumoylation are also discussed.

Gene expression analysis of skin grafts and cultured keratinocytes using synthetic RNA normalization reveals insights into differentiation and growth control

Background

Keratinocytes (KCs) are the most frequent cells in the epidermis, and they are often isolated and cultured in vitro to study the molecular biology of the skin. Cultured primary cells and various immortalized cells have been frequently used as skin models but their comparability to intact skin has been questioned. Moreover, when analyzing KC transcriptomes, fluctuation of polyA+ RNA content during the KCs’ lifecycle has been omitted.

Results

We performed STRT RNA sequencing on 10 ng samples of total RNA from three different sample types: i) epidermal tissue (split-thickness skin grafts), ii) cultured primary KCs, and iii) HaCaT cell line. We observed significant variation in cellular polyA+ RNA content between tissue and cell culture samples of KCs. The use of synthetic RNAs and SAMstrt in normalization enabled comparison of gene expression levels in the highly heterogenous samples and facilitated discovery of differences between the tissue samples and cultured cells. The transcriptome analysis sensitively revealed genes involved in KC differentiation in skin grafts and cell cycle regulation related genes in cultured KCs and emphasized the fluctuation of transcription factors and non-coding RNAs associated to sample types.

Conclusions

The epidermal keratinocytes derived from tissue and cell culture samples showed highly different polyA+ RNA contents. The use of SAMstrt and synthetic RNA based normalization allowed the comparison between tissue and cell culture samples and thus proved to be valuable tools for RNA-seq analysis with translational approach. Transciptomics revealed clear difference both between tissue and cell culture samples and between primary KCs and immortalized HaCaT cells.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-015-1671-5) contains supplementary material, which is available to authorized users.

Loricrin - an overview

Loricrin is a terminally differentiating structural protein comprising more than 70% of the cornified envelope. It contributes to the protective barrier function of the stratum corneum. In vivo, loricrin is expressed inall mammalian stratified epithelia with the highest levels of expression in humid tissues such as newborn epidermis, the epithelia of oral and anal mucosa, esophagus, foreskin, vagina and the epidermal parts of sweat ducts. Loricrin is not expressed in non keratinizing epithelia and its expression at these sites actually represents a defensive or protective mechanismof the body. An insight into this protein- “Loricrin” can shed light to its potential as a marker in the early stages of potentially malignant disorders like oral sub mucous fibrosis and leukoplakia. This compilation has been done by taking into account the existing literature, reviews and original studies on loricrin, a major component of the cornifiedcell envelope, its structure and the alterations that result due to its absence or presence of both the epidermis and the oral mucosa.

Anaerobic digestibility of beef hooves with swine manure or slaughterhouse sludge

Anaerobic digestion is an effective method for treating animal by-products, generating at the same time green energy as methane (CH4). However, the methods and mechanisms involved in anaerobic digestion of α-keratin wastes like hair, nails, horns and hooves are still not clear. In this study we investigated the feasibility of anaerobically co-digesting ground beef hooves in the presence of swine manure or slaughterhouse sludge at 25 °C using eight 42-L Plexiglas lab-scale digesters. Our results showed addition of beef hooves statistically significantly increased the rate of CH4 production with swine manure, but only increased it slightly with slaughterhouse sludge. After 90-day digestion, 73% of beef hoof material added to the swine manure-inoculated digesters had been converted into CH4, which was significantly higher than the 45% level achieved in the slaughterhouse sludge inoculated digesters. BODIPY-Fluorescent casein staining detected proteolytic bacteria in all digesters with and without added beef hooves, and their relative abundances corresponded to the rate of methanogenesis of the digesters with the different inocula. Fluorescence in situ hybridization in combination with BODIPY-Fluorescent casein staining identified most proteolytic bacteria as members of genus Alkaliphilus in the subfamily Clostridiaceae 2 of family Clostridiaceae. They thus appear to be the bacteria mainly responsible for digestion of beef hooves.

Overexpression of galectin-7 in mouse epidermis leads to loss of cell junctions and defective skin repair

BACKGROUND

The proteins of the galectin family are implicated in many cellular processes, including cell interactions, polarity, intracellular trafficking, and signal transduction. In human and mouse, galectin-7 is almost exclusively expressed in stratified epithelia, notably in the epidermis. Galectin-7 expression is also altered in several human tumors of epithelial origin. This study aimed at dissecting the consequences of galectin-7 overexpression on epidermis structure and functions in vivo.

METHODS

We established transgenic mice specifically overexpressing galectin-7 in the basal epidermal keratinocytes and analyzed the consequences on untreated skin and after UVB irradiation or mechanical injury.

RESULTS

The intercellular cohesion of the epidermis is impaired in transgenic animals, with gaps developing between adjacent keratinocytes, associated with loss of adherens junctions. The epidermal architecture is aberrant with perturbations in the multilayered cellular organisation of the tissue, and structural defects in the basement membrane. These transgenic animals displayed a reduced re-epithelialisation potential following superficial wound, due to a defective collective migration of keratinocytes. Finally, a single mild dose of UVB induced an abnormal apoptotic response in the transgenic epidermis.

CONCLUSION

These results indicate that an excess of galectin-7 leads to a destabilisation of adherens junctions associated with defects in epidermal repair. As this phenotype shares similarities with that of galectin-7 null mutant mice, we conclude that a critical level of this protein is required for maintaining proper epidermal homeostasis. This study brings new insight into the mode of action of galectins in normal and pathological situations.

Therapeutic potential of a non-steroidal bifunctional anti-inflammatory and anti-cholinergic agent against skin injury induced by sulfur mustard

Sulfur mustard (bis(2-chloroethyl) sulfide, SM) is a highly reactive bifunctional alkylating agent inducing edema, inflammation, and the formation of fluid-filled blisters in the skin. Medical countermeasures against SM-induced cutaneous injury have yet to be established. In the present studies, we tested a novel, bifunctional anti-inflammatory prodrug (NDH 4338) designed to target cyclooxygenase 2 (COX2), an enzyme that generates inflammatory eicosanoids, and acetylcholinesterase, an enzyme mediating activation of cholinergic inflammatory pathways in a model of SM-induced skin injury. Adult SKH-1 hairless male mice were exposed to SM using a dorsal skin vapor cup model. NDH 4338 was applied topically to the skin 24, 48, and 72 h post-SM exposure. After 96 h, SM was found to induce skin injury characterized by edema, epidermal hyperplasia, loss of the differentiation marker, keratin 10 (K10), upregulation of the skin wound marker keratin 6 (K6), disruption of the basement membrane anchoring protein laminin 322, and increased expression of epidermal COX2. NDH 4338 post-treatment reduced SM-induced dermal edema and enhanced skin re-epithelialization. This was associated with a reduction in COX2 expression, increased K10 expression in the suprabasal epidermis, and reduced expression of K6. NDH 4338 also restored basement membrane integrity, as evidenced by continuous expression of laminin 332 at the dermal-epidermal junction. Taken together, these data indicate that a bifunctional anti-inflammatory prodrug stimulates repair of SM induced skin injury and may be useful as a medical countermeasure.

Derivation and osmotolerance characterization of three immortalized tilapia (Oreochromis mossambicus) cell lines

Fish cell cultures are becoming more widely used models for investigating molecular mechanisms of physiological response to environmental challenge. In this study, we derived two immortalized Mozambique tilapia (Oreochromis mossambicus) cell lines from brain (OmB) and lip epithelium (OmL), and compared them to a previously immortalized bulbus arteriosus (TmB) cell line. The OmB and OmL cell lines were generated without or with Rho-associated kinase (ROCK) inhibitor/3T3 feeder layer supplementation. Although both approaches were successful, ROCK inhibitor/feeder layer supplementation was found to offer the advantages of selecting for epithelial-like cell type and decreasing time to immortalization. After immortalization (≥ passage 5), we characterized the proteomes of the newly derived cell lines (OmB and OmL) using LCMS and identified several unique cell markers for each line. Subsequently, osmotolerance for each of the three cell lines following acute exposure to elevated sodium chloride was evaluated. The acute maximum osmotolerance of these tilapia cell lines (>700 mOsm/kg) was markedly higher than that of any other known vertebrate cell line, but was significantly higher in the epithelial-like OmL cell line. To validate the physiological relevance of these tilapia cell lines, we quantified the effects of acute hyperosmotic challenge (450 mOsm/kg and 700 mOsm/kg) on the transcriptional regulation of two enzymes involved in biosynthesis of the compatible organic osmolyte, myo-inositol. Both enzymes were found to be robustly upregulated in all three tilapia cell lines. Therefore, the newly established tilapia cells lines represent valuable tools for studying molecular mechanisms involved in the osmotic stress response of euryhaline fish.

Spray-assisted layer-by-layer assembly on hyaluronic acid scaffolds for skin tissue engineering

Tissue engineering approaches for the development of a single epidermal-dermal scaffold to treat full-thickness skin defects have been limited by difficulties in the fabrication of a bilayer scaffold combining the specific properties of the epidermis and the dermis. Here we present an innovative approach to developing a scaffold that holds promise for skin tissue engineering. We utilize the spray-assisted layer-by-layer assembly technique to deposit a polyelectrolyte multilayer film composed of hyaluronic acid and poly-L-lysine (the epidermal component) on a porous hyaluronic acid scaffold (the dermal component), in a rapid and controlled manner. The multilayer film promotes cell adhesion, contributing to regeneration of the epidermal barrier functions of skin. While human keratinocytes attached and proliferated on the coated porous scaffolds, they did not invade the porous dermal component, thus leaving room for seeding of relevant fibroblast cell types in this scaffold. This scaffold therefore holds promise for co-culture of different cells, which may be useful for treatment of full-thickness skin defects as well as other tissue engineering applications.

Keratinization of the esophageal epithelium of domesticated mammals

We studied the esophageal epithelium for keratinization characteristics from samples of domesticated mammals of three nutrition groups (herbivores: horse, cattle, sheep; omnivores: pig, dog, rat; carnivores: cat) using histochemistry (keratins, disulfides), sulfur measurements, and cryo-SEM. Keratins were found in all esophageal layers of all species, except for the equine Stratum corneum. The positive reaction staining of Pan-keratin was remarkable, but decreased in intensity toward the outer layers, whereas in the pig and cat, staining was confined to the corneal layer. The herbivores revealed positive staining reactions in the upper Stratum spinosum, particularly in the sheep. Regarding single keratins, CK6 immunostating was found in most esophageal layers, but only weakly or negatively in the porcine and equine Stratum corneum. CK13 staining was restricted to the sheep and here was found in all layers. CK14 could be detected in the equine and feline Stratum basale, and upper vital layers of the dog and rat. CK17 appeared only in the Stratum spinosum and Stratum granulosum, but in all layers of the dog and cat. Disulfides reacted strongest in the Stratum corneum of the herbivores, as corroborated by the sulfur concentrations in the esophagus. Our study emphasized that keratins are very important for the mechanical stability of the epithelial cells and cell layers of the mammalian esophagus. The role of these keratins in the esophageal epithelia is of specific interest owing to the varying feed qualities and mechanical loads of different nutrition groups, which have to be countered.

Effect of reduced EPHB4 expression in thymic epithelial cells on thymocyte development and peripheral T cell function

The Eph kinase (EPH) and ephrin (EFN) families are involved in a broad range of developmental processes. Increasing evidence is demonstrating the important roles of EPHBs and EphrinBs in the immune system. In this study on epithelial cell-specific Ephb4 knockout (KO) mice, we investigated T-cell development and function after EPHB4 deletion. KO mice presented normal thymic weight and cellularity. Their thymocyte subpopulation percentages were in the normal range. KO mice had normal T-cell numbers and percentages in the spleen, and T cells were activated and proliferated normally upon TCR ligation. Furthermore, naïve spleen CD4 cells from KO and wild type mice were capable of differentiating, in a comparable manner, into Th1, Th17 and Treg cells. In vivo, KO mice mounted effective delayed type hypersensitivity responses, indicating that thymocytes develop normally in the absence of TEC EPHB4, and T cells derived from EPHB4-deleted thymic epithelian cells (TEC) have normal function. Our data suggest that heavy redundancy and promiscuous interaction between EPHs and EFNs compensate for the missing EPHB4 in TECs, and TEC EPHB4's role in T cell development might only be revealed if multiple EPHs are ablated simultaneously. We cannot exclude the possibility that (1) some immunological parameters not examined in this study are affected by the deletion; (2) the deletion is not complete due to the leaky Cre-LoxP system, and the remaining EPHB4 in TEC is sufficient for thymocyte development; or (3) EPHB4 expression in TEC is not required for T cell development and function.

Keratins as the main component for the mechanical integrity of keratinocytes

Keratins are major components of the epithelial cytoskeleton and are believed to play a vital role for mechanical integrity at the cellular and tissue level. Keratinocytes as the main cell type of the epidermis express a differentiation-specific set of type I and type II keratins forming a stable network and are major contributors of keratinocyte mechanical properties. However, owing to compensatory keratin expression, the overall contribution of keratins to cell mechanics was difficult to examine in vivo on deletion of single keratin genes. To overcome this problem, we used keratinocytes lacking all keratins. The mechanical properties of these cells were analyzed by atomic force microscopy (AFM) and magnetic tweezers experiments. We found a strong and highly significant softening of keratin-deficient keratinocytes when analyzed by AFM on the cell body and above the nucleus. Magnetic tweezers experiments fully confirmed these results showing, in addition, high viscous contributions to magnetic bead displacement in keratin-lacking cells. Keratin loss neither affected actin or microtubule networks nor their overall protein concentration. Furthermore, depolymerization of actin preserves cell softening in the absence of keratin. On reexpression of the sole basal epidermal keratin pair K5/14, the keratin filament network was reestablished, and mechanical properties were restored almost to WT levels in both experimental setups. The data presented here demonstrate the importance of keratin filaments for mechanical resilience of keratinocytes and indicate that expression of a single keratin pair is sufficient for almost complete reconstitution of their mechanical properties.

Forward genetics identifies Kdf1/1810019J16Rik as an essential regulator of the proliferation-differentiation decision in epidermal progenitor cells

Cell fate decisions during embryogenesis and adult life govern tissue formation, homeostasis and repair. Two key decisions that must be tightly coordinated are proliferation and differentiation. Overproliferation can lead to hyperplasia or tumor formation while premature differentiation can result in a depletion of proliferating cells and organ failure. Maintaining this balance is especially important in tissues that undergo rapid turnover like skin however, despite recent advances, the genetic mechanisms that balance cell differentiation and proliferation are still unclear. In an unbiased genetic screen to identify genes affecting early development, we identified an essential regulator of the proliferation-differentiation balance in epidermal progenitor cells, the Keratinocyte differentiation factor 1 (Kdf1; 1810019J16Rik) gene. Kdf1 is expressed in epidermal cells from early stages of epidermis formation through adulthood. Specifically, Kdf1 is expressed both in epidermal progenitor cells where it acts to curb the rate of proliferation as well as in their progeny where it is required to block proliferation and promote differentiation. Consequently, Kdf1 mutants display both uncontrolled cell proliferation in the epidermis and failure to develop terminal fates. Our findings reveal a dual role for the novel gene Kdf1 both as a repressive signal for progenitor cell proliferation through its inhibition of p63 and a strong inductive signal for terminal differentiation through its interaction with the cell cycle regulator Stratifin.

Immunohistochemical demonstration of keratins in the epidermal layers of the Malayan pangolin (Manis javanica), with remarks on the evolution of the integumental scale armour

Using immunohistochemistry, the study demonstrates the distribution of keratins (pankeratin with CK1-8, 10, 14-16, 19; keratins CK1, 5, 6, 9, 10; hair keratins AE13, AE14) in the epidermis of the Malayan pangolin (Manis javanica). A varying reaction spectrum was observed for pan-keratin, with body region-dependent negative to very strong reaction intensities. The dorsolateral epidermis exhibited positive reactions only in its vital layers, whereas the abdominal epidermis showed strong positive reactions in the soft two outer strata. The single acidic and basic-to-neutral (cyto)keratins produced clear variations compared to the pan-keratin tinging. For example, CK1 appeared in all epidermal layers of both body regions, except for the ventral stratum corneum, whereas CK5, 6, 9, 10 were restricted to the soft ventral epidermis. Here, distinctly positive reactions were confined to the stratum granulosum, except for CK6 that appeared in the soft stratum corneum. A different staining pattern was obvious for the hair keratins, i.e., positive reactions of AE13 concentrated only in the granular layer of the dorsal epidermis. In the abdominal epidermis, remarkable tinging for AE14 was visible in the stratum basale, decreasing toward the corneal layer, but was also found in the outer root sheath cells of the hair follicles in the ventral body part. Our findings are discussed related to the evolution of the horny dorsal scales of the pangolin, which may have started from the tail root, projecting forward to the head.

Oral epithelial stem cells in tissue maintenance and disease: the first steps in a long journey

The identification and characterization of stem cells is a major focus of developmental biology and regenerative medicine. The advent of genetic inducible fate mapping techniques has made it possible to precisely label specific cell populations and to follow their progeny over time. When combined with advanced mathematical and statistical methods, stem cell division dynamics can be studied in new and exciting ways. Despite advances in a number of tissues, relatively little attention has been paid to stem cells in the oral epithelium. This review will focus on current knowledge about adult oral epithelial stem cells, paradigms in other epithelial stem cell systems that could facilitate new discoveries in this area and the potential roles of epithelial stem cells in oral disease.

Mathematical modeling of the impact of actin and keratin filaments on keratinocyte cell spreading

Keratin intermediate filaments (IFs) form cross-linked arrays to fulfill their structural support function in epithelial cells and tissues subjected to external stress. How the cross-linking of keratin IFs impacts the morphology and differentiation of keratinocytes in the epidermis and related surface epithelia remains an open question. Experimental measurements have established that keratinocyte spreading area is inversely correlated to the extent of keratin IF bundling in two-dimensional culture. In an effort to quantitatively explain this relationship, we developed a mathematical model in which isotropic cell spreading is considered as a first approximation. Relevant physical properties such as actin protrusion, adhesion events, and the corresponding response of lamellum formation at the cell periphery are included in this model. Through optimization with experimental data that relate time-dependent changes in keratinocyte surface area during spreading, our simulation results confirm the notion that the organization and mechanical properties of cross-linked keratin filaments affect cell spreading; in addition, our results provide details of the kinetics of this effect. These in silico findings provide further support for the notion that differentiation-related changes in the density and intracellular organization of keratin IFs affect tissue architecture in epidermis and related stratified epithelia.

Analysis of the KRT9 gene in a Mexican family with epidermolytic palmoplantar keratoderma

Epidermolytic palmoplantar keratoderma (EPPK), an autosomal-dominant genodermatosis, is the most frequently occurring hereditary palmoplantar keratoderma. EPPK is characterized by hyperkeratosis of the palms and soles. Approximately 90% of patients present with mutations in the KRT9 gene, which encodes for keratin 9. Many of these mutations are located within the highly conserved coil 1A region of the alpha-helical rod domain of keratin 9, an important domain for keratin heterodimerization. The objective was to assess the clinical and molecular characteristics of a Mexican family with EPPK. The clinical characteristics of members of this family were analyzed. The KRT9 gene of affected members was polymerase chain reaction amplified from genomic DNA and sequenced. All affected members of the family had hyperkeratosis of the palms and soles with knuckle pads. The R163W mutation in the KRT9 gene was present in all affected individuals who were tested. Although R163W is the most frequent KRT9 mutation in patients with EPPK, only two families have been reported with knuckle pads associated with this mutation. Our findings indicate that knuckle pads can be associated with EPPK and the R163W mutation in a family with a genetic background different from that described here.

The expanding significance of keratin intermediate filaments in normal and diseased epithelia

Intermediate filaments are assembled from a diverse group of evolutionary conserved proteins and are specified in a tissue-dependent, cell type-dependent, and context-dependent fashion in the body. Genetic mutations in intermediate filament proteins account for a large number of diseases, ranging from skin fragility conditions to cardiomyopathies and premature aging. Keratins, the epithelial-specific intermediate filaments, are now recognized as multi-faceted effectors in their native context. In this review, we emphasize the recent progress made in defining the role of keratins towards the regulation of cytoarchitecture, cell growth and proliferation, apoptosis, and cell motility during embryonic development, in normal adult tissues, and in select diseases such as cancer.

STAT3 signal transduction through interleukin-22 in oral squamous cell carcinoma

Interleukin (IL)-22 is a member of the IL-10 family. Its main targets are epithelial cells, not immune cells. We examined IL-22 signal transduction in oral squamous cell carcinoma (OSCC) cells. Immunohistochemical staining revealed that IL-22R was expressed more highly in OSCC compared to normal regions. An IL-22R signal was also observed in metastatic OSCC cells in the lymph node. RT-PCR showed that the human OSCC cell lines MISK81-5, HSC-3, HSC-4, SAS and SQUU-B expressed IL-22 receptor chains. Immunoblotting showed that IL-22 induced a transient tyrosine phosphorylation of STAT3 (pY705-STAT3) in MISK81-5 cells. The change in the serine phosphorylation of STAT3 was subtle during the examination periods. Simultaneously, pY705-STAT3 activation in HSC-3 cells was undetectable after IL-22 stimulation. Immunocytochemistry demonstrated that IL-22 induced the translocation of phosphorylated STAT3 into the nucleus of MISK81-5 cells. IL-22 temporarily upregulated the expression of anti-apoptotic and mitogenic genes such as Bcl-x, survivin and c-Myc, as well as SOCS3. IL-22 transiently activated ERK1/2 and induced a delayed phosphorylation of p38 MAP kinase, but negligibly involved the activation of NF-κB in MISK81-5 cells. MISK81-5 and SQUU-B cells treated with IL-22 showed mild cellular proliferation. MISK81-5, HSC-4 and SAS cells treated with IL-22 downregulated the keratinocyte differentiation-related genes compared with unstimulated cells. Conversely, STAT3 suppression by STAT3 siRNA strongly disrupted the downregulation of these genes by IL-22, but it did not significantly affect the activation of ERK1/2 by IL-22. The OSCC cells used in this study upregulated the expression of SERPINB3/4 (SCCA1/2), well-known SCC markers, following treatment with IL-22. These results indicate that IL-22 differentially activates the STAT3 signaling system depending on the type of OSCC. IL-22 may therefore play a role in tumor growth, cell differentiation and progression through STAT3-dependent and -independent pathways.