Tight Junction Proteins in the Skin

Microvesicles derived from dermal myofibroblasts modify the integrity of the blood and lymphatic barriers using distinct endocytosis pathways

Microvesicles (MVs) are a subtype of extracellular vesicles that can transfer biological information from their producer cells to target cells. This communication can in turn affect both normal and pathological processes. Mounting evidence has revealed that dermal wound myofibroblasts (Wmyo) produce MVs, which can transfer biomolecules impacting receptor cells such as human dermal microvascular endothelial cells (HDMECs). While the effects of MVs on HDMECs are generally well described in the literature, little is known about the transport of MVs across the HDMEC barrier, and their potential effect on the barrier integrity remains unknown. Here, we investigated these roles of Wmyo-derived MVs on two sub-populations of HDMECs, blood endothelial cells (BECs) and lymphatic endothelial cells (LECs). Using an in vitro model to mimic the endothelial barrier, we showed that MVs crossed the LEC barrier but not the BEC barrier. In addition, we demonstrated that MVs were able to influence the cell-cell junctions of HDMECs. Specifically, we observed that after internalization via the predominantly caveolin-dependent pathway, MVs induced the opening of junctions in BECs. Conversely, in LECs, MVs mainly use the macropinocytosis pathway and induce closure of these junctions. Moreover, proteins in the MV membrane were responsible for this effect, but not specifically those belonging to the VEGF family. Finally, we found that once the LEC barrier permeability was reduced by MV stimuli, MVs ceased to cross the barrier. Conversely, when the BEC barrier was rendered permeable following stimulation with MVs, they were subsequently able to cross the barrier via the paracellular pathway. Taken together, these results suggest that the study of Wmyo-derived MVs offers valuable insights into their interaction with the HDMEC barrier in the context of wound healing. They highlight the potential significance of these MVs in the overall process.

Engineering of Uniform Epidermal Layers via Sacrificial Gelatin Bioink-Assisted 3D Extrusion Bioprinting of Skin

To reconstruct an ideal full-thickness skin model, basal keratinocytes must be distributed as a confluent monolayer on the dermis. However, the currently available extrusion bioprinting method for the skin is limited when producing an air-exposed cellular monolayer because the cells are encapsulated within a bioink. This is the first study to use sacrificial gelatin-assisted extrusion bioprinting to reproduce a uniform and stratified epidermal layer. Experimental analyses of the rheological properties, printability, cell viability, and initial keratinocyte adhesion shows that the optimal gelatin bioink concentration is 4 wt.%. The appropriate thickness of the bioprinted gelatin structure for achieving a confluent keratinocyte layer is determined to be 400 µm. The suggested strategy generates a uniform keratinocyte monolayer with tight junctions throughout the central and peripheral regions, whereas manual seeding generates non-uniform cellular aggregates and vacancies. These results influence gene expression, exhibiting a propensity for epidermal differentiation. Finally, the gelatin-assisted keratinocytes are bioprinted onto a dermis composed of gelatin methacryloyl and dermis-derived decellularized extracellular matrix to establish a full-thickness skin model. Thus, this strategy leads to significant improvements in epidermal differentiation/stratification. The findings demonstrate that the gelatin-assisted approach is advantageous for recreating reliable full-thickness skin models with significant consistency for mass production.

Optical Methods for Non-Invasive Determination of Skin Penetration: Current Trends, Advances, Possibilities, Prospects, and Translation into In Vivo Human Studies

Information on the penetration depth, pathways, metabolization, storage of vehicles, active pharmaceutical ingredients (APIs), and functional cosmetic ingredients (FCIs) of topically applied formulations or contaminants (substances) in skin is of great importance for understanding their interaction with skin targets, treatment efficacy, and risk assessment-a challenging task in dermatology, cosmetology, and pharmacy. Non-invasive methods for the qualitative and quantitative visualization of substances in skin in vivo are favored and limited to optical imaging and spectroscopic methods such as fluorescence/reflectance confocal laser scanning microscopy (CLSM); two-photon tomography (2PT) combined with autofluorescence (2PT-AF), fluorescence lifetime imaging (2PT-FLIM), second-harmonic generation (SHG), coherent anti-Stokes Raman scattering (CARS), and reflectance confocal microscopy (2PT-RCM); three-photon tomography (3PT); confocal Raman micro-spectroscopy (CRM); surface-enhanced Raman scattering (SERS) micro-spectroscopy; stimulated Raman scattering (SRS) microscopy; and optical coherence tomography (OCT). This review summarizes the state of the art in the use of the CLSM, 2PT, 3PT, CRM, SERS, SRS, and OCT optical methods to study skin penetration in vivo non-invasively (302 references). The advantages, limitations, possibilities, and prospects of the reviewed optical methods are comprehensively discussed. The ex vivo studies discussed are potentially translatable into in vivo measurements. The requirements for the optical properties of substances to determine their penetration into skin by certain methods are highlighted.

Limonene protects human skin keratinocytes against UVB-induced photodamage and photoaging by activating the Nrf2-dependent antioxidant defense system

Long term exposure to solar ultraviolet B (UVB) radiation is one of the primary factors of premature skin aging and is referred to as photoaging. Also, mammalian skin exposed to UVB triggers an increase in production of α-melanocyte-stimulating hormone (α-MSH), which is critically involved in the pathogenesis of hyperpigmentary skin diseases. This study investigated the protective effect of limonene on UVB-induced photodamage and photoaging in immortalized human skin keratinocytes (HaCaT) in vitro. Initially, we determined cell viability and levels of reactive oxygen species (ROS) in UVB-irradiated HaCaT cells. Pretreatment with limonene increased cell viability followed by inhibition of intracellular ROS generation in UVB-irradiated HaCaT cells. Interestingly, the antioxidative activity of limonene was directly correlated with an increase in expression of endogenous antioxidants, including heme oxygenase 1 (HO-1), NAD(P)H:quinone oxidoreductase 1 (NQO-1), and γ-glutamylcysteine synthetase (γ-GCLC), which was associated with enhanced nuclear translocation and activation of NF-E2-related factor-2 (Nrf2). Indeed, Nrf2 knockdown reduced limonene's protective effects. Additionally, we observed that limonene treatment inhibited UVB-induced α-MSH secretion followed by inhibition of proopiomelanocortin (POMC) via suppression of p53 transcriptional activation. Moreover, limonene prevented UVB-mediated depletion of tight junction regulatory proteins, including occludin and zonula occludens-1. On the other hand, limonene treatment significantly decreased matrix metalloproteinase-2 levels in UVB-irradiated HaCaT cells. Based on these results, limonene may have a dermato-protective effect in skin cells by activating the Nrf2-dependent cellular antioxidant defense system.

Natural products in cosmetics

The global cosmetics market reached US$500 billion in 2017 and is expected to exceed US$800 billion by 2023, at around a 7% annual growth rate. The cosmetics industry is emerging as one of the fastest-growing industries of the past decade. Data shows that the Chinese cosmetics market was US$60 billion in 2021. It is expected to be the world's number one consumer cosmetics market by 2050, with a size of approximately US$450 billion. The influence of social media and the internet has raised awareness of the risks associated with the usage of many chemicals in cosmetics and the health benefits of natural products derived from plants and other natural resources. As a result, the cosmetic industry is now paying more attention to natural products. The present review focus on the possible applications of natural products from various biological sources in skin care cosmetics, including topical care products, fragrances, moisturizers, UV protective, and anti-wrinkle products. In addition, the mechanisms of targets for evaluation of active ingredients in cosmetics and the possible benefits of these bioactive compounds in rejuvenation and health, and their potential role in cosmetics are also discussed.

Claudin targeting as an effective tool for directed barrier modulation of the viable epidermis

Tight junction (TJ) formation is vital for epidermal barrier function. We aimed to specifically manipulate TJ barriers in the reconstructed human epidermis (RHE) by claudin-1 and -4 knockdown (KD) and by claudin-binding fusion proteins of glutathione S-transferase and modified C-terminal fragments of Clostridium perfringens enterotoxin (GST-cCPE). Impedance spectroscopy and tracer permeability imaging were employed for functional barrier assessment and investigation of claudin contribution. KD of claudin-1, but not claudin-4, impaired the paracellular barrier in vitro. Similarly, claudin-binding GST-cCPE variants weakened the paracellular but not the stratum corneum barrier. Combining both TJ targeting methods, we found that claudin-1 targeting by GST-cCPE after claudin-4 KD led to a marked decrease in paracellular barrier properties. Conversely, after claudin-1 KD, GST-cCPE did not further impair the barrier. Comparison of GST-cCPE variants with different claudin-1/claudin-4 affinities, NHS-fluorescein tracer detection, and immunostaining of RHE paraffin sections showed that GST-cCPE variants bind to extrajunctional claudin-1 and -4, which are differentially distributed along the stratum basale-stratum granulosum axis. GST-cCPE binding blocks these claudins, thereby specifically opening the paracellular barrier of RHE. The data indicate a critical role for claudin-1 in regulating paracellular permeability for ions and small molecules in the viable epidermis. Claudin targeting is presented as a proof-of-concept for precise barrier modulation.

Nephrin expression in human epidermal keratinocytes and its implication in poor wound closure

Nephrin is a type-1 transmembrane protein and a component of the slit diaphragm renal-filtration barrier. It has several functions in actin remodeling and cell-cell adhesion. Nephrin is principally located in the kidney glomerulus, but several studies have reported that nephrin is found in the pancreas, brain, and placenta. However, nephrin expression and its role in human skin have not yet been reported. First, using single-cell RNA sequencing, immunohistochemistry, and immuno-electron microscopy, nephrin expression was confirmed in human-skin epidermal keratinocytes. Nephrin expression colocalized with the expression of zonula occludens-1 in keratinocytes and was closely related to keratinocyte cell density, proliferation, and migration. High glucose treatment decreased nephrin expression and compromised keratinocyte cell migration without yes-associated protein nuclear entry. This reduced cell migration under high glucose conditions was improved in nephrin-overexpressing keratinocytes. Nephrin was highly expressed on the margins of re-epithelized epidermis based on in vivo mice and ex vivo human skin wound models. The results demonstrate that nephrin is expressed in human-skin keratinocytes and functions in cell adhesion, proliferation, and migration. In conclusion, this study suggests that nephrin may have a variety of physiological roles in human skin.

Atopic dermatitis: molecular, cellular, and clinical aspects

Atopic dermatitis (AD) is a complicated, inflammatory skin disease, which numerous genetic and environmental factors play roles in its development. AD is categorized into different phenotypes and stages, although they are mostly similar in their pathophysiological aspects. Immune response alterations and structural distortions of the skin-barrier layer are evident in AD patients. Genetic makeup, lifestyle, and environment are also significantly involved in contextual factors. Genes involved in AD-susceptibility, including filaggrin and natural moisturizing, cause considerable structural modifications in the skin's lipid bilayer and cornified envelope. Additionally, the skin's decreased integrity and altered structure are accompanied by biochemical changes in the normal skin microflora's dysbiosis. The dynamic immunological responses, genetic susceptibilities, and structural modifications associated with AD's pathophysiology will be extensively discussed in this review, each according to the latest achievements and findings.

Claudin-7 in keratinocytes is downregulated by the inhibition of HMG-CoA reductase and is highly expressed in the stratum granulosum of the psoriatic epidermis

BACKGROUND

Cholesterol is de novo synthesized in the upper epidermis and plays an important role in maintaining the normality of skin. Studying the impact of the inhibition of cholesterol de novo synthesis in the epidermis may help understand how skin homeostasis is regulated.

OBJECTIVE

In this study, we created a gene expression profile to investigate the effect of hydroxymethylglutaryl-coenzyme A (HMG-CoA) reductase inhibitors on epidermal homeostasis.

METHODS

A microarray analysis was performed using normal keratinocytes with or without HMG-CoA reductase inhibitor (pitavastatin) treatment. Real-time PCR confirmed the reproducibility of genes with altered expression in keratinocytes treated with HMG-CoA reductase inhibitors. Among these genes, we focused on reduced expression of claudin 7 histologically confirmed by immunohistochemical staining, in situ hybridization, and immunoelectron microscopy.

RESULTS

Claudin-7 was highly expressed in the stratum granulosum of psoriatic lesions but was not expressed in the normal epidermis. Immunoelectron microscopy revealed that claudin-7 was localized in the keratohyalin granules of psoriatic lesions.

CONCLUSION

These results indicate that claudin-7 expression was regulated by HMG-CoA reductase in the epidermis and might play a pathogenic role in the keratohyalin granules found in the epidermal granular layer of psoriasis.

Maternal supplementation with a combination of wheat bran and sugar beet pulp during late gestation and lactation improves growth and intestinal functions in piglets

Maternal diet has a profound impact on growth and immune development of offspring. This study aimed to evaluate the effects of maternal supplementation with a combination of wheat bran (WB, a source of insoluble dietary fiber) and sugar beet pulp (SBP, a source of soluble dietary fiber) on growth and intestinal morphology, immunity, barrier function and microbiota in piglets. Thirty sows (Landrace × Yorkshire; 3-6 parity) were randomly allocated to 2 dietary treatments from d 85 of gestation to weaning (d 21 of lactation). The 2 dietary treatments were: a control diet (CON, a corn-soybean meal diet) and a dietary fiber diet (DF, 15% WB and 10% SBP during gestation and 7.5% WB and 5% SBP during lactation). Maternal DF supplementation improved growth, serum growth hormones and ileal morphology in piglets. Piglets fed DF showed enhanced intestinal barrier function as indicated by reduced serum concentrations of diamine oxidase and endotoxin, and increased ileal mRNA level of occludin. Maternal DF supplementation reduced pro-inflammatory cytokines in the colostrum, milk and serum of piglets. Furthermore, maternal DF supplementation decreased the colonic abundance of Subdoligranulum and Mogibacterium, and increased the colonic abundance of Lactobacillus and norank_f__Bacteroidales_S24-7_group and the colonic concentration of acetate and butyrate in piglets. In summary, maternal supplementation with a combination of SBP and WB during late gestation and lactation improved cytokines in colostrum and milk, growth, immune responses, intestinal morphology, barrier function and microbiota in piglets, which may be a potential strategy to improve offspring growth and intestinal functions.

Effect of 3D-Fibroblast Dermis Constructed by Layer-by-Layer Cell Coating Technique on Tight Junction Formation and Function in Full-Thickness Skin Equivalent

Human skin equivalents (HSEs) consisting of an epidermis and dermis have been used as promising tools for drug evaluation and for clinical applications in regenerative medicine. Normal human dermal fibroblasts (NHDFs) are essential for the fabrication of HSEs because they play an important role in the maturation of the epidermis. Recently, epidermal tight junctions (TJs), which are complex cell-cell junctions, have attracted much attention as a second barrier and regulator for other barrier functions. In a previous study, we revealed the expression of TJ-related proteins and the time course of formation of TJ structure in the HSE (layer-by-layer (LbL)-three-dimensional (3D) Skin) constructed by layer-by-layer (LbL) cell coating technique that have a unique dermis consisting of NHDFs only (3D-fibroblast dermis). However, the effect of the 3D-fibroblast dermis on the formation of functional epidermal TJs is unknown. In this study, we investigated the effect of the 3D-fibroblast dermis on the expression of TJ-related proteins and TJ function in LbL-3D Skin. We demonstrated that the 3D-fibroblast dermis affects the long-term expression of TJ-related proteins and the formation of TJ with barrier function in the epidermis. These results show that the 3D-fibroblast dermis in LbL-3D Skin contributes to the formation and maintenance of functional TJs as in native human skin by direct contact with KCs.

Computer Simulation of Skin Permeability of Hydrophobic and Hydrophilic Chemicals - Influence of Follicular Pathway

A recently published mechanistic skin permeability model (Kasting et al., 2019. J Pharm Sci 108:337-349) that included a follicular diffusion pathway has been extended to describe transient diffusion and finite dose applications. The model follows the disposition of two components, solute and solvent, so that solvent deposition processes can be explicitly represented. Experimentally-calibrated permeability characteristics of the follicular pathway leading to the permeation of highly hydrophilic permeants are further refined. Details of the refinements and a comparison with the earlier model using two large experimental datasets are presented. An example calculation shows the marked difference between the time scales for achievement of near steady-state diffusion for large hydrophilic and lipophilic compounds, with the former being more than 100-fold faster than the latter. However, the true steady state for the hydrophilic compound is not reached until much later due to the very slow filling of the corneocyte phase.

Weak Ultraviolet B Enhances the Mislocalization of Claudin-1 Mediated by Nitric Oxide and Peroxynitrite Production in Human Keratinocyte-Derived HaCaT Cells

A tight junction (TJ) makes a physical barrier in the epidermal cells of skin. Ultraviolet (UV) light may disrupt the TJ barrier, but the mechanism has not been well clarified. Weak UVB (5 mJ/cm²) caused mislocalization of claudin-1 (CLDN1), a component of the TJ strand, and disruption of TJ barrier in human keratinocyte-derived HaCaT cells. The UVB-induced mislocalization of CLDN1 was inhibited by monodansylcadaverine (MDC), a clathrin-dependent endocytosis inhibitor, suggesting that UVB enhances the internalization of CLDN1. Transepidermal electrical resistance and paracellular flux of lucifer yellow, a fluorescent hydrophilic marker, were rescued by MDC. UVB changed neither the total nor phosphorylation levels of CLDN1, but it increased both mono-ubiquitination and tyrosine nitration levels of CLDN1. Fluorescence measurements revealed that UVB increased intracellular free Ca²⁺, nitric oxide (NO), and peroxynitrite contents, which were inhibited by Opsin2 (OPN2) siRNA, suggesting that OPN2 functions as a UVB sensor. The effects of UVB were inhibited by an antagonist of transient receptor potential type vanilloid 1 (TRPV1) and Ca²⁺ chelator. Both NO donor and peroxynitrite donor induced the mislocalization of CLDN1 and disruption of TJ barrier, which were rescued by a NO synthase (NOS) inhibitor and a peroxynitrite scavenger. Weak UVB irradiation induced the disruption of TJ barrier mediated by mislocalization of CLDN1 in HaCaT cells. The OPN2/TRPV1/NOS signaling pathway may be a novel target for preventing destruction of the TJ barrier by UVB irradiation.

Fully Three-Dimensional Bioprinted Skin Equivalent Constructs with Validated Morphology and Barrier Function

Development of high-throughput, reproducible, three-dimensional (3D) bioprinted skin equivalents (BPSEs) that are morphologically and functionally comparable to native skin tissue is advancing research in skin diseases, and providing a physiologically relevant platform for the development of therapeutics, transplants for regenerative medicine, and testing of skin products like cosmetics. Current protocols for the production of engineered skin grafts are limited in their ability to control 3D geometry of the structure and contraction leading to variability of skin function between constructs. In this study, we describe a method for the biofabrication of skin equivalents (SEs) that are fully bioprinted using an open-market bioprinter, made with commercially available primary cells and natural hydrogels. The unique hydrogel formulation allows for the production of a human-like SE with minimal lateral tissue contraction in a multiwell plate format, thus making them suitable for high-throughput bioprinting in a single print with fast print and relatively short incubation times. The morphology and barrier function of the fully 3D BPSEs are validated by immunohistochemistry staining, optical coherence tomography, and permeation assays.

Bicellular Tight Junctions and Wound Healing

Bicellular tight junctions (TJs) are intercellular junctions comprised of a variety of transmembrane proteins including occludin, claudins, and junctional adhesion molecules (JAMs) as well as intracellular scaffold proteins such as zonula occludens (ZOs). TJs are functional, intercellular structures that form a barrier between adjacent cells, which constantly seals and unseals to control the paracellular passage of molecules. They are primarily present in the epithelial and endothelial cells of all tissues and organs. In addition to their well-recognized roles in maintaining cell polarity and barrier functions, TJs are important regulators of signal transduction, which modulates cell proliferation, migration, and differentiation, as well as some components of the immune response and homeostasis. A vast breadth of research data is available on TJs, but little has been done to decipher their specific roles in wound healing, despite their primary distribution in epithelial and endothelial cells, which are essential contributors to the wound healing process. Some data exists to indicate that a better understanding of the functions and significance of TJs in healing wounds may prove crucial for future improvements in wound healing research and therapy. Specifically, recent studies demonstrate that occludin and claudin-1, which are two TJ component proteins, are present in migrating epithelial cells at the wound edge but are absent in chronic wounds. This indicates that functional TJs may be critical for effective wound healing. A tremendous amount of work is needed to investigate their roles in barrier function, re-epithelialization, angiogenesis, scar formation, and in the interactions between epithelial cells, endothelial cells, and immune cells both in the acute wound healing process and in non-healing wounds. A more thorough understanding of TJs in wound healing may shed new light on potential research targets and reveal novel strategies to enhance tissue regeneration and improve wound repair.

Anisomycin, a JNK and p38 activator, suppresses cell-cell junction formation in 2D cultures of K38 mouse keratinocyte cells and reduces claudin-7 expression, with an increase of paracellular permeability in 3D cultures

Keratinocytes in the oral mucosal epithelium, which is a non-keratinized stratified epithelium, are exposed to various stimuli from the oral cavity. JNK and p38 are stress-activated mitogen-activated protein kinases (MAPKs) that are phosphorylated by various stimuli and are involved in the assembly and disassembly of tight junctions (TJs) in keratinocytes. Therefore, we investigated the effects of stress-activated MAPKs on TJs in a mouse keratinocyte cell line during cell-cell junction formation in two-dimensional (2D) cultures or stratification to form non-keratinized epithelium in 3D cultures. In 2D cultures, calcium induced zipper-like staining for ZO-1 at 2 h and string-like staining for ZO-1 at 12 h, which indicated immature and mature cell-cell junctions, respectively. Anisomycin (AM), a JNK and p38 activator, inhibited formation of string-like staining for ZO-1, whereas inhibition of JNK, but not p38, after AM treatment restored string-like staining for ZO-1, although claudins (CLDNs) 4, 6, and 7 did not completely colocalize to ZO-1-positive sites. In 3D cultures, AM treatment for 2 weeks activated only p38, suppressed flattening of the superficial cells, removed CLDN7 from ZO-1-positive spots on the surface of 3D cultures, which represent TJs, and decreased transepithelial electrical resistance. Thus, short-term AM treatment inhibited maturation of cell-cell junctions by JNK, but not p38, activation. p38 activation by long-term AM treatment affected morphology of stratified structures and paracellular permeability, which was increased by CLDN7 removal from TJs. Various chronic stimuli that activate stress-activated MAPKs may weaken the keratinocyte barrier and be involved in TJ-related diseases.

Scaffolding proteins in the development and maintenance of the epidermal permeability barrier

The skin of mammals and other terrestrial vertebrates protects the organism against the external environment, preventing heat, water and electrolyte loss, as well as entry of chemicals and pathogens. Impairments in the epidermal permeability barrier function are associated with the genesis and/or progression of a variety of pathological conditions, including genetic inflammatory diseases, microbial and viral infections, and photodamage induced by UV radiation. In mammals, the outside-in epidermal permeability barrier is provided by the joint action of the outermost cornified layer, together with assembled tight junctions in granular keratinocytes found in the layers underneath. Tight junctions serve as both outside-in and inside-out barriers, and impede paracellular movements of ions, water, macromolecules and microorganisms. At the molecular level, tight junctions consist of integral membrane proteins that form an extracellular seal between adjacent cells, and associate with cytoplasmic scaffold proteins that serve as links with the actin cytoskeleton. In this review, we address the roles that scaffold proteins play specifically in the establishment and maintenance of the epidermal permeability barrier, and how various pathologies alter or impair their functions.

Increased permeability of the epithelium of middle ear cholesteatoma

OBJECTIVE

We investigated the electrical impedance of and the expressions of tight junction molecules in the cholesteatoma epithelium to provide supporting evidence for the acid lysis theory of bone resorption in middle ear cholesteatoma.

METHODS

Study subjects were patients with primary acquired middle ear cholesteatoma and those with non-cholesteatomatous chronic otitis media who underwent tympanomastoidectomy. The electrical impedance of the cholesteatoma epithelium was measured during tympanomastoidectomy by loading alternating currents of 320 Hz and 30.7 kHz. The expressions of tricellulin (MARVELD2), claudin-1 (CLDN1) and claudin-3 (CLDN3) were examined by fluorescence immunohistochemistry and quantitative reverse transcription-polymerase chain reaction.

RESULTS

The electrical impedance of the cholesteatoma epithelium was significantly lower than that of the post-auricular skin and external auditory canal skin at both 320 Hz and 30.7 kHz. Immunoreactivity for MARVELD2, CLDN1 and CLDN3 was localised mainly in the granular layer, and to lesser degree, in the horny and spinous layers in both the cholesteatoma tissue and post-auricular skin. Fluorescence intensity was moderate for MARVELD2, weak for CLDN1 and strong for CLDN3. The expressions of MARVELD2, CLDN1 and CLDN3 mRNA were significantly lower in the cholesteatoma tissue than in the post-auricular skin.

CONCLUSIONS

These results indicate the increased permeability of the cholesteatoma epithelium and suggest that this change is, at least partially, dependent on the decrease in the expressions of the tight junction molecules. This evidence supports the acid lysis hypothesis of bone resorption in cholesteatoma.

Electrical Impedance and Expression of Tight Junction Components of the Nasal Turbinate and Polyp

PURPOSE

We investigated the electrical impedance and expression of tight junction components of the turbinate mucosa, nasal polyp, and normal skin.

PROCEDURES

The inferior turbinate and nasal polyp of patients with chronic rhinosinusitis and the postauricular skin of patients with otitis media were examined. Electrical impedance was measured in vivo using a tissue conductance meter. Expressions of claudin-1 and tricellulin were examined by fluorescence immunohistochemistry and quantitative RT-PCR.

RESULTS

Electrical impedance was higher in the skin than in the turbinate and polyp, but did not differ between the turbinate and polyp. Immunoreactivities for claudin-1 and tricellulin were seen in the epithelial/epidermal layer. Expression of claudin-1 was higher in the skin than in the turbinate and polyp. The polyp tended to show higher expression of claudin-1 but showed lower expression of tricellulin than the turbinate. The ratio of claudin-1 to tricellulin was highest in the skin and lowest in the turbinate. The correlation between expressions of the two tight junction components was strongly positive in the skin (r = 0.964) and negative (r = -0.527) in the turbinate and polyp.

CONCLUSIONS

These results suggest that the roles of claudin-1 and tricellulin in barrier function may be complementary, and may thereby maintain a constant level of permeability of the mucosal tissues.

Epidermal tight junctions in health and disease

The skin, the largest organ of the body, is an essential barrier that under homeostatic conditions efficiently protects and/or minimizes damage from both environmental (e.g. microorganisms, physical trauma, ultraviolet radiation) and endogenous (e.g., cancers, inflammation) factors. This formidable barrier function resides mainly in the epidermis, a dynamic, highly-stratified epithelium. The epidermis has 2 major barrier structures: stratum corneum, the outmost layer and tight junctions, intercellular junctions that seal adjacent keratinocytes in the stratum granulosum, found below the stratum corneum. In recent years there have been significant advances in our understanding of tight junction function, composition and regulation. Herein we review what is known about tight junctions in healthy skin and keratinocyte culture systems and highlight the dynamic crosstalk observed between tight junctions and the cutaneous immune system. Finally we discuss the preliminary observations suggesting that tight junction function or protein expression may be relevant for the pathogenesis of a number of common cutaneous inflammatory and neoplastic conditions.

Selective hair therapy: bringing science to the fiction

Investigations on carrier-based drug delivery systems for higher selectivity in hair therapy have clearly evolved from dye release and model studies to highly sophisticated approaches, many of which specifically tackle hair indications and the delivery of hair-relevant molecules. Here, we group recent hair disease-oriented work into efforts towards (i) improved delivery of conventional drugs, (ii) delivery of novel drug classes, for example biomolecules and (iii) targeted delivery on the cellular/molecular level. Considering the solid foundation of experimental work, it does not take a large step outside the current box of thinking to follow the idea of using large carriers (>500 nm, unlikely to penetrate as a whole) for follicular penetration, retention and protection of sensitive compounds. Yet, reports on particles <200 nm being internalized by keratinocytes and dendritic cells at sites of barrier disruption (e.g., hair follicles) combined with recent advances in nanodermatology add interesting new facets to the possibilities carrier technologies could offer, for example, unprecedented levels of selectivity. The authors provide thought-provoking ideas on how smart delivery technologies and advances in our molecular understanding of hair pathophysiology could result in a whole new era of hair therapeutics. As the field still largely remains in preclinical investigation, determined efforts towards production of medical grade material and truly translational work are needed to demonstrate surplus value of carrier systems for clinical applications.

Immunohistochemical expression of VDR is associated with reduced integrity of tight junction complex in psoriatic skin

BACKGROUND

Cell junctions are crucial for the formation and maintenance of the paracellular barrier and for cell polarity in simple epithelia and endothelia. Altered localization and formation of tissue junction proteins in the epidermis have been described in plaque-type psoriasis. Vitamin D receptor (VDR) is a nuclear hormone involved in anti-proliferative and pro-differentiation pathways in keratinocytes. However, still to date, vitamin D/VDR signalling involved in tissue barrier related to psoriasis remains largely unknown.

OBJECTIVE

To study the expression of VDR and tight junctions (TJ) proteins (claudin 1, ZO-1 and occludin) in psoriatic skin, and to correlate the expression of VDR with that of the junctional proteins claudin- 1, occludin and ZO- 1.

METHODS

A total of 20 psoriatic tissue samples were included in the analysis. Immunohistochemical studies for VDR, claudin-1, occludin and ZO-1 were performed.

RESULTS

We observed a reduction of VDR, claudin-1 and ZO-1 expression in psoriatic skin if compared to normal skin, and the statistical analysis showed a significant correlation between a downgrading of VDR expression and that of claudin-1 (P < 0.005) and ZO-1(P < 0.005).

CONCLUSIONS

Our results suggest a new role of VDR in the maintenance of the homeostasis skin barrier. Although the exiguity of our cohort, VDR status appears to be associated with the expression level and functions of TJ proteins, suggesting multiple and different cellular functions of the VDR.

Trends in drug delivery through tissue barriers containing tight junctions

A limitation in the uptake of many drugs is the restricted permeation through tissue barriers. There are two general ways to cross barriers formed by cell layers: by transcytosis or by diffusion through the intercellular space. In the latter, tight junctions (TJs) play the decisive role in the regulation of the barrier permeability. Thus, transient modulation of TJs is a potent strategy to improve drug delivery. There have been extensive studies on surfactant-like absorption enhancers. One of the most effective enhancers found is sodium caprate. However, this modulates TJs in an unspecific fashion. A novel approach would be the specific modulation of TJ-associated marvel proteins and claudins, which are the main structural components of the TJs. Recent studies have identified synthetic peptidomimetics and RNA interference techniques to downregulate the expression of targeted TJ proteins. This review summarizes current progress and discusses the impact on TJs' barrier function.

Flightless I over-expression impairs skin barrier development, function and recovery following skin blistering

Development of an intact epidermis is critical for maintaining the integrity of the skin. Patients with epidermolysis bullosa (EB) experience multiple erosions, which breach the epidermal barrier and lead to increased microbial colocalization of wounds, infections and sepsis. The cytoskeletal protein Flightless I (Flii) is a known regulator of both development and wound healing. Using Flii(+/-), WT and Flii(Tg/Tg) mice, we investigated the effect of altering Flii levels in embryos and adult mice on the development of the epidermal barrier and, consequently, how this affects the integrity of the skin in EB. Flii over-expression resulted in delayed formation of the epidermal barrier in embryos and decreased expression of tight junction (TJ) proteins Claudin-1 and ZO-2. Increased intercellular space and transepidermal water loss was observed in Flii(Tg)(/Tg) adult mouse skin, while Flii(Tg/Tg) keratinocytes showed altered TJ protein localization and reduced transepithelial resistance. Flii is increased in the blistered skin of patients with EB, and over-expression of Flii in experimental EBA showed impaired Claudin-1 and -4 TJ protein expression and delayed recovery of functional barrier post-blistering. Immunoprecipitation confirmed Flii associated with TJ proteins and in vivo actin assays showed that the effect of Flii on actin polymerization underpinned the impaired barrier function observed in Flii(Tg/Tg) mice. These results therefore demonstrate an important role for Flii in the development and regulation of the epidermal barrier, which may contribute to the impaired healing and skin fragility of EB patients.

A microscopic multiphase diffusion model of viable epidermis permeability

A microscopic model of passive transverse mass transport of small solutes in the viable epidermal layer of human skin is formulated on the basis of a hexagonal array of cells (i.e., keratinocytes) bounded by 4-nm-thick, anisotropic lipid bilayers and separated by 1-μm layers of extracellular fluid. Gap junctions and tight junctions with adjustable permeabilities are included to modulate the transport of solutes with low membrane permeabilities. Two keratinocyte aspect ratios are considered to represent basal and spinous cells (longer) and granular cells (more flattened). The diffusion problem is solved in a unit cell using a coordinate system conforming to the hexagonal cross section, and an efficient two-dimensional treatment is applied to describe transport in both the cell membranes and intercellular spaces, given their thinness. Results are presented in terms of an effective diffusion coefficient, D¯(epi), and partition coefficient, K¯(epi/w), for a homogenized representation of the microtransport problem. Representative calculations are carried out for three small solutes-water, L-glucose, and hydrocortisone-covering a wide range of membrane permeability. The effective transport parameters and their microscopic interpretation can be employed within the context of existing three-layer models of skin transport to provide more realistic estimates of the epidermal concentrations of topically applied solutes.

Immunolocalization of junctional proteins in human hairs indicates that the membrane complex stabilizes the inner root sheath while desmosomes contact the companion layer through specific keratins

The inner root sheath (IRS) sustains and addresses the hair shaft outside the follicle. Ultrastructural analysis of immunolabeling for beta-catenin, plakophilin-1, desmoglein-4 and keratin-17 in human hairs has indicated that adherens junctions and desmosomes initially connect cells in mature IRS and the companion layer. Beta-catenin immunolabeling for adherens junctions is only seen in sparse regions of differentiating Huxley cells, Flugelzellen cells and Henle cells, but disappears in cornified cells of the IRS. Desmoglein-4 and plakophilin-1 immunolabeling are observed in differentiating and cornified desmosomes of the Huxley and Henle layers and in the membrane complex joining these cells. Desmoglein-4 and plakophilin-1 are more frequently immunolocalized in the intracellular side of the junctions, but some labeling is also present in the delta-layer of the membrane complex. The labeling indicates a prevalent intracellular redistribution of desmoglein-4 and plakophilin-1 when the final cornification of the IRS occurs. Intense keratin-17 immunolabeling is observed in tonofilaments of the companion layer joining the plakophilin-1 rich desmosomes of the Henle layer. This suggests that this elastic type of keratin is present at desmosome junctions during the movements of the companion layer along the slippage plane of the hair shaft.

Disruption of precise regulation of αPKC expression and cellular localization is associated with cervical cancer progression

PURPOSE

To understand the pathogenesis of cervical cancer (CC) associated with polarity protein αPKC and the potential roles of αPKC in clinical management of CC.

METHODS

Tissue samples were collected from women who received colposcopy biopsy or hysterectomy surgery, including 9 CIN1, 8 CIN2, 15 CIN3, and 12 invasive cervical squamous cancer (ICC). 16 normal controls were from the normal region of tumor samples, HE and immunofluorescence staining of αPKC were performed on these samples. ANOVA and Kruslal-wallis test were used to quantitate the abnormal distribution and expression level of αPKC among different cervical lesions.

RESULTS

Disruption of polarized apical localization and increased cytoplasmic accumulation of αPKC were identified in cervical lesions. In normal cervical epithelium, αPKC was detected on the apical membrane of endocervical columnar epithelial cells and of exocervical epithelial cells located at basal layer of squamous epithelium. While in squamous metaplasia, a precancerous lesion of cervical neoplasia, the polarized apical membrane localization of αPKC was disrupted, and intensed cytoplasmic accumulation was identified in the immature squamous metaplastic cells. Compared with normal cervix, number of epithelial cells with abnormal αPKC distribution was progressively increased in CINs and ICC (P < 0.05), and cytoplasmic accumulation of αPKC was increased in CIN2, CIN3, and ICC compared with CIN1 (P < 0.05).

CONCLUSIONS

Disruption of polarized apical localization and increased cytoplasmic accumulation of αPKC were associated with CC progression, indicating that precise regulation of αPKC may play important roles in CC progression, and αPKC may be a potential molecular target for clinical diagnoses and treatment of CC.

Contribution of tight junction proteins to ion, macromolecule, and water barrier in keratinocytes

Tight junctions (TJs) form a selective barrier for ions, water, and macromolecules in simple epithelia. In keratinocytes and epidermis, TJs were shown to be involved in individual barrier functions. The absence of the TJ protein claudin-1 (Cldn1) in mice results in a skin-barrier defect characterized by lethal water loss. However, detailed molecular analyses of the various TJ barriers in keratinocytes and the contribution of distinct TJ proteins are missing. Herein, we discriminate TJ-dependent paracellular resistance from transcellular resistance in cultured keratinocytes using the two-path impedance spectroscopy. We demonstrate that keratinocyte TJs form a barrier for Na(+), Cl(-), and Ca(2+), and contribute to barrier function for water and larger molecules of different size. In addition, knockdown of Cldn1, Cldn4, occludin, and zonula occludens-1 increased paracellular permeabilities for ions and larger molecules, demonstrating that all of these TJ proteins contribute to barrier formation. Remarkably, Cldn1 and Cldn4 are not critical for TJ barrier function for water in submerged keratinocyte cultures. However, Cldn1 influences stratum corneum (SC) proteins important for SC water barrier function, and is crucial for TJ barrier formation for allergen-sized macromolecules.

Indigo naturalis upregulates claudin-1 expression in human keratinocytes and psoriatic lesions

ETHNOPHARMACOLOGICAL RELEVANCE

Indigo naturalis is used in traditional Chinese medicine to treat various dermatoses. Our previous clinical studies showed that indigo naturalis is an effective treatment for psoriasis. Herein, the capabilities of indigo naturalis extract and its derivatives to increase claudin-1 expression and tight junction (TJ) function in human keratinocytes and psoriatic lesions were further studied.

MATERIALS AND METHODS

Claudin-1 expression in psoriatic plaques with or without indigo naturalis treatment was analyzed by immunohistochemical methods. In primary human keratinocytes, the expression of claudin-1 was analyzed by fluorescent immunostaining, a real-time RT-PCR, and Western blot analysis. The effect of indigo naturalis on TJs was evaluated by measuring the transepithelial electrical resistance (TEER) and paracellular tracer flux.

RESULTS

The indigo naturalis extract upregulated mRNA and protein expressions of claudin-1 and function of TJs in primary human keratinocytes in concentration-dependent manners. Its main components, indirubin, indigo, and tryptanthrin, exerted synergistic effects on upregulating TJ functions in primary human keratinocytes. In addition, indigo naturalis increased the activity of protein kinase C (PKC), and a known potent PKC inhibitor, Ro318220, attenuated the indigo naturalis-induced claudin-1 expression. Significantly, restoration of claudin-1 was observed in healed psoriatic lesions after indigo naturalis treatment.

CONCLUSIONS

Indigo naturalis upregulates claudin-1 expression and restores TJ function in keratinocytes. Our data also suggest that indirubin, indigo, and tryptanthrin have a synergistic effect on TJ function.

Barriers and more: functions of tight junction proteins in the skin

Although the existence of tight junction (TJ) structures (or a secondary epidermal barrier) was postulated for a long time, the first description of TJ proteins in the epidermis (occludin, ZO-1, and ZO-2) was only fairly recent. Since then, a wealth of new insights concerning TJs and TJ proteins, including their functional role in the skin, have been gathered. Of special interest is that the epidermis as a multilayered epithelium exhibits a very complex localization pattern of TJ proteins, which results in different compositions of TJ protein complexes in different layers. In this review, we summarize our current knowledge about the role of TJ proteins in the epidermis in barrier function, cell polarity, vesicle trafficking, differentiation, and proliferation. We hypothesize that TJ proteins fulfill TJ structure-dependent and structure-independent functions and that the specific function of a TJ protein may depend on the epidermal layer where it is expressed.

Tight junctions in skin: new perspectives

Tight junctions (TJs) are intercellular contacts that seal the space between the individual cells of an epithelial sheet or stratifying epithelia, such as the epidermis, so that they can collectively separate tissue compartments. Intercellular junctions, such as adherens and TJs, play a crucial role in the formation and maintenance of epithelial and endothelial barriers. A variety of components including claudins, occludin, tricellulin, zonula occluden proteins and junctional adhesion molecules have been identified in complex localization patterns in mammalian epidermis. In several skin diseases that are characterized by impaired skin barrier function, altered proliferation/differentiation of the epidermis and/or infiltration of inflammatory cells, altered expression patterns of TJ proteins have been observed. This review is aimed at providing an insight into the molecular composition, tools for identification and understanding the role of TJs in skin diseases and barrier function regulation.

Batrachochytrium dendrobatidis zoospore secretions rapidly disturb intercellular junctions in frog skin

Global amphibian declines are in part driven by the chytrid fungus Batrachochytrium dendrobatidis, causing superficial dermatomycosis with epidermal hyperplasia and hyperkeratosis in infected amphibians. The susceptibility to chytridiomycosis and the severity of epidermal lesions in amphibians with chytridiomycosis are not consistent across species or even among individuals. Severe infections cause death of the animal most likely through disturbance of ion homeostasis. The mechanism by which this superficial skin infection results in epidermal lesions has so far eluded precise definition. It was the aim of this study to unravel how B. dendrobatidis causes alterations that affect skin integrity. Exposure of Xenopus laevis skin to B. dendrobatidis zoospore supernatant using skin explants and Ussing chambers caused rapid disruption of intercellular junctions, demonstrated using histology and transmission electron microscopy. The loss of intercellular junctions led to detachment-induced cell apoptosis, or anoikis. The zoospore supernatant induced neither apoptosis nor necrosis in isolated primary keratinocytes of X. laevis. This supports the idea that the loss of cell contacts triggered apoptosis in the skin explants. Mass spectrometric analysis of the protein composition of the supernatant revealed a complex mixture, including several new virulence associated proteins, such as proteases, biofilm-associated proteins and a carotenoid ester lipase. Protease and lipase activity of the supernatant was confirmed with a protease and lipase assay. In conclusion, B. dendrobatidis zoospores produce a complex mixture of proteins that quickly disturbs epidermal intercellular junctions leading to anoikis in the anuran skin. The role of the identified proteins in this process remains to be determined.

Tight junctions and differentiation--a chicken or the egg question?

Skin barrier function is indispensable to prevent the uncontrolled loss of water and solutes and to protect the body from external assaults. To fulfil this function, keratinocytes undergo a complex pathway of differentiation that terminates in the formation of the stratum corneum. Additionally, tight junctions (TJs), which are cell-cell junctions localized in the stratum granulosum, are involved in the barrier function of the skin. Important biological and clinical roles of TJs are strongly suggested by altered TJ protein levels and distribution in skin diseases like psoriasis, ichthyosis and atopic dermatitis. Because these skin diseases show alterations in differentiation and TJs, it was suggested that changes in TJs might simply be a consequence of altered differentiation. However, in this viewpoint, we like to argue that the situation is not as simple and depends on the specific microenvironment. We discuss three hypotheses regarding the interplay between TJs/TJ proteins and differentiation: (1) TJs/TJ proteins are influenced by differentiation, (2) differentiation is influenced by TJs/TJ proteins, and (3) TJs/TJ proteins and differentiation are independent of each other. In addition, the concept is introduced that both processes are going on at the same time, which means that while one specific TJ protein/barrier component might be influenced by differentiation, the other may influence differentiation.

Polyploidization of glia in neural development links tissue growth to blood-brain barrier integrity

Proper development requires coordination in growth of the cell types composing an organ. Many plant and animal cells are polyploid, but how these polyploid tissues contribute to organ growth is not well understood. We found the Drosophila melanogaster subperineurial glia (SPG) to be polyploid, and ploidy is coordinated with brain mass. Inhibition of SPG polyploidy caused rupture of the septate junctions necessary for the blood-brain barrier. Thus, the increased SPG cell size resulting from polyploidization is required to maintain the SPG envelope surrounding the growing brain. Polyploidization likely is a conserved strategy to coordinate tissue growth during organogenesis, with potential vertebrate examples.

Tight junction proteins and the epidermis

Epithelia are found at the interfaces between body compartments where they act as selective permeability barriers that maintain the unique composition of the compartments on either side. Epithelial barrier function is dependent on tight junctions (TJs), which seal the intercellular or paracellular spaces but may permit selective permeability. In simple epithelia (one cell thick), the function of TJs is relatively well understood. By contrast, our understanding of TJ structure and function in stratified epithelia (e.g. the epidermis) is limited. This article briefly discusses what is known about TJs and their components in simple epithelia and speculates about their roles in the epidermis.

Skin moisturization mechanisms: new data

The main function of the skin is to protect the body against exogenous substances and excessive water loss. The skin barrier is located in the outermost layer of the skin, called the stratum corneum, which is composed of corneocytes, originating from the keratinocytes differentiation process, embedded in organized complex lipid domains. Moisturizing of the skin is recognized as the first anti-aging skin care. Skin moisturization is essential for its appearance, protection, complexion, softness and the reinforcement of its barrier properties against deleterious and exogenous environmental factors. The intrinsic water binding capacity of skin is not only due to the complex natural moisturizing factor present in corneocytes, but also to hyaluronic acid and a regulated water transport within the skin. Recent data shows that the water movements between the cells at the different levels of the epidermis are due to dedicated water and glycerol transport proteins named aquaporins. Their role in the skin moisturization is completed by corneodesmosomes and tight junctions. Water and pH are now shown to be of prime importance in the regulation of the epidermal enzymes linked to corneocytes desquamation and lipid synthesis. Furthermore, the level of moisturization of the skin is important in its protection against repeated exposure to various irritant agents or phenomena such as very frequent washing with strong tensioactive materials.

Characterization of tight junctions and their disruption by UVB in human epidermis and cultured keratinocytes

It has not been confirmed whether tight junctions (TJs) function as a paracellular permeability barrier in adult human skin. To clarify this issue, we performed a TJ permeability assay using human skin obtained from abdominal plastic surgery. Occludin, a marker protein of TJs, was expressed in the granular layer, in which a subcutaneously injected paracellular tracer, Sulfo-NHS-LC-Biotin (556.59 Da), was halted. Incubation with ochratoxin A decreased the expression of claudin-4, an integral membrane protein of TJs, and the diffusion of paracellular tracer was no longer prevented at the TJs. These results demonstrate that human epidermis possesses TJs that function as an intercellular permeability barrier at least against small molecules (∼550 Da). UVB irradiation of human skin xenografts and human skin equivalents (HSEs) resulted in functional deterioration of TJs. Immunocytochemical staining of cultured keratinocytes showed that occludin was localized into dot-like shapes and formed a discontinuous network when exposed to UVB irradiation. Furthermore, UVB irradiation downregulated the active forms of Rac1 and atypical protein kinase C, suggesting that their inactivation caused functional deterioration of TJs. In conclusion, TJs function as a paracellular barrier against small molecules (∼550 Da) in human epidermis and are functionally deteriorated by UVB irradiation.

Tight junctions: is there a role in dermatology?

A variety of tight junction (TJ) proteins including claudins, occludin, tricellulin, zonula occludens-proteins and junctional adhesion molecules have been identified in complex localization patterns in mammalian epidermis. Their expression and/or localization is frequently altered in skin diseases including skin tumors. However, our understanding of the function(s) of TJ and TJ proteins in the skin is, even though rapidly increasing, still limited. This review summarizes our current knowledge of the involvement of TJ and TJ proteins in mammalian skin in functions ascribed to TJ in simple epithelia, such as barrier function, polarity, gene expression, proliferation, differentiation, and vesicle transport.

Alteration of tight junction proteins is an early event in psoriasis: putative involvement of proinflammatory cytokines

Psoriasis is an inflammatory skin disease characterized by hyperproliferation of keratinocytes, impaired barrier function, and pronounced infiltration of inflammatory cells. Tight junctions (TJs) are cell-cell junctions that form paracellular barriers for solutes and inflammatory cells. Altered localization of TJ proteins in the epidermis was described in plaque-type psoriasis. Here we show that localization of TJ proteins is already altered in early-stage psoriasis. Occludin, ZO-1, and claudin-4 are found in more layers than in normal epidermis, and claudin-1 and -7 are down-regulated in the basal and in the uppermost layers. In plaque-type psoriasis, the staining patterns of occludin and ZO-1 do not change, whereas the claudins are further down-regulated. Near transmigrating granulocytes, all TJ proteins except for junctional adhesion molecule-A are down-regulated. Treatment of cultured keratinocytes with interleukin-1beta and tumor necrosis factor-alpha, which are present at elevated levels in psoriatic skin, results in an increase of transepithelial resistance at early time points and a decrease at later time points. Injection of interleukin-1beta into an ex vivo skin model leads to an up-regulation of occludin and ZO-1, resembling TJ protein alteration in early psoriasis. Our results show for the first time that alteration of TJ proteins is an early event in psoriasis and is not the consequence of the more profound changes found in plaque-type psoriasis. Our data indicate that cytokines are involved in alterations of TJ proteins observed in psoriasis.

Characterization of the ubinuclein protein as a new member of the nuclear and adhesion complex components (NACos)

BACKGROUND INFORMATION

We characterized previously a cellular protein through its interaction with cellular and viral transcription factors from the bZip family. The corresponding mRNA was detected in a wide range of cell types and the protein was highly expressed in the nucleus of human keratinocytes. On the basis of these observations, we named this protein ubinuclein.

RESULTS

Using a specific monoclonal antibody, we have shown in the present study that, although endogenous ubinuclein was mainly nuclear in sparse MDCK (Madin-Darby canine kidney) cells, it was exclusively present in the cell-cell junctions in confluent MDCK cultures or in polarized HT29 cells, where it co-localized with the tight junction marker ZO-1 (zonula occludens 1). In accordance with this, we have shown that ubinuclein interacted with ZO-1 in vitro and in vivo. In cultures of undifferentiated human keratinocytes, ubinuclein was essentially nuclear, but in differentiated cells, in which involucrin and periplakin reside at the apical cell membrane and at the cell-cell junctions, ubinuclein staining was observed at the lateral cell-cell borders. In human skin, ubinuclein appeared as a thread-like pattern between the upper granular cell layer and the cornified cell layer. In mouse epithelia, including bile canaliculi, bronchioli, salivary gland ducts, and oral and olfactory epithelium, ubinuclein co-localized with tight junction markers. Ubinuclein was, however, not present in endothelial cell-cell junctions. In addition, when overexpressed, ubinuclein localized to the nucleus and prevented MDCK cells from entering cytokinesis, resulting in multinucleated giant cells after several cycles of endoreplication.

CONCLUSIONS

Ubinuclein mRNA and its corresponding protein are expressed in almost all cell types. Analyses have revealed that in most cells ubinuclein occurred in the nucleoplasm, but in cells forming tight junctions it is recruited to the plaque structure of the zonula occludens. This recruitment appeared to be dependent on cell density. Therefore ubinuclein is a new NACos (nuclear and adhesion complex component) protein.

The skin: an indispensable barrier

The skin forms an effective barrier between the organism and the environment preventing invasion of pathogens and fending off chemical and physical assaults, as well as the unregulated loss of water and solutes. In this review we provide an overview of several components of the physical barrier, explaining how barrier function is regulated and altered in dermatoses. The physical barrier is mainly localized in the stratum corneum (SC) and consists of protein-enriched cells (corneocytes with cornified envelope and cytoskeletal elements, as well as corneodesmosomes) and lipid-enriched intercellular domains. The nucleated epidermis also contributes to the barrier through tight, gap and adherens junctions, as well as through desmosomes and cytoskeletal elements. During epidermal differentiation lipids are synthesized in the keratinocytes and extruded into the extracellular domains, where they form extracellular lipid-enriched layers. The cornified cell envelope, a tough protein/lipid polymer structure, resides below the cytoplasmic membrane on the exterior of the corneocytes. Ceramides A and B are covalently bound to cornified envelope proteins and form the backbone for the subsequent addition of free ceramides, free fatty acids and cholesterol in the SC. Filaggrin is cross-linked to the cornified envelope and aggregates keratin filaments into macrofibrils. Formation and maintenance of barrier function is influenced by cytokines, 3',5'-cyclic adenosine monophosphate and calcium. Changes in epidermal differentiation and lipid composition lead to a disturbed skin barrier, which allows the entry of environmental allergens, immunological reaction and inflammation in atopic dermatitis. A disturbed skin barrier is important for the pathogenesis of contact dermatitis, ichthyosis, psoriasis and atopic dermatitis.