The biology and regulation of corneodesmosomes

PRSS3/mesotrypsin as a putative regulator of the biophysical characteristics of epidermal keratinocytes in superficial layers

Mesotrypsin, encoded by the PRSS3 gene, is a distinctive trypsin isoform renowned for its exceptional resistance to traditional trypsin inhibitors and unique substrate specificity. Within the skin epidermis, this protein primarily expresses in the upper layers of the stratified epidermis and plays a crucial role in processing pro-filaggrin (Pro-FLG). Although prior studies have partially elucidated its functions using primary cultured keratinocytes, challenges persist due to these cells' differentiation-activated cell death program. In the present study, HaCaT keratinocytes, characterized by minimal endogenous mesotrypsin expression and sustained proliferation in differentiated states, were utilized to further scrutinize the function of mesotrypsin. Despite the ready degradation of the intact form of active mesotrypsin in these cells, fusion with Venus, flanked by a peptide linker, enables evasion from the protein elimination machinery, thus facilitating activation of the Pro-FLG processing system. Inducing Venus-mesotrypsin expression in the cells resulted in a flattened phenotype and reduced proliferative capacity. Moreover, these cells displayed altered F-actin assembly, enhanced E-cadherin adhesive activity, and facilitated tight junction formation without overtly influencing epidermal differentiation. These findings underscore mesotrypsin's potentially pivotal role in shaping the characteristic cellular morphology of upper epidermal layers.

Epidermal barrier function in dry, flaky and sensitive skin: A narrative review

The stratum corneum (SC)-the outermost layer of the epidermis-is the principal permeability and protective barrier of the skin. Different components of the SC, including corneocytes, natural moisturizing factor, a variety of enzymes and their inhibitors, antimicrobial peptides and lipids, work interactively to maintain barrier function. The main barrier properties of the SC are the limitation of water loss and the prevention of infection and contact with potentially harmful exogenous factors. Although the SC functions consistently as a protective barrier throughout the body, variations in functions and morphology occur across body sites with age and skin type. Healthy SC function also depends on the interplay between the chemosensory barrier, the skin's microbiome and the innate immune system. Dysregulation of SC barrier function can lead to the development of skin disorders, such as dry, flaky or sensitive skin, but the complete underlying pathophysiology of these are not fully understood. This review provides insight into the current literature and emerging themes related to epidermal barrier changes that occur in the context of dry, flaky and sensitive skin. Additional studies are needed to further elucidate the underlying aetiology of dry, flaky and sensitive skin and to provide tailored treatment.

Proteolytic and Antiproteolytic Activity in the Skin: Gluing the Pieces Together

Epidermal differentiation is ultimately aimed at the formation of a functional barrier capable of protecting the organism from the environment while preventing loss of biologically vital elements. Epidermal differentiation entails a delicately regulated process of cell-cell junction formation and dissolution to enable upward cell migration and desquamation. Over the past two decades, the deciphering of the genetic basis of a number of inherited conditions has delineated the pivotal role played in this process by a series of proteases and protease inhibitors, including serpins, cathepsins, and cystatins, suggesting novel avenues for therapeutic intervention in both rare and common disorders of cornification.

Key Factors in the Complex and Coordinated Network of Skin Keratinization: Their Significance and Involvement in Common Skin Conditions

The epidermis serves many vital roles, including protecting the body from external influences and healing eventual injuries. It is maintained by an incredibly complex and perfectly coordinated keratinization process. In this process, desquamation is essential for the differentiation of epidermal basal progenitor cells into enucleated corneocytes, which subsequently desquamate through programmed death. Numerous factors control keratinocyte differentiation: epidermal growth factor, transforming growth factor-α, keratinocyte growth factor, interleukins IL-1-β and IL-6, elevated vitamin A levels, and changes in Ca2+ concentration. The backbone of the keratinocyte transformation process from mitotically active basal cells into fully differentiated, enucleated corneocytes is the expression of specific proteins and the creation of a Ca2+ and pH gradient at precise locations within the epidermis. Skin keratinization disorders (histologically characterized predominantly by dyskeratosis, parakeratosis, and hyperkeratosis) may be categorized into three groups: defects in the α-helical rod pattern, defects outside the α-helical rod domain, and disorders of keratin-associated proteins. Understanding the process of keratinization is essential for the pathogenesis of many dermatological diseases because improper desquamation and epidermopoiesis/keratinization (due to genetic mutations of factors or due to immune pathological processes) can lead to various conditions (ichthyoses, palmoplantar keratodermas, psoriasis, pityriasis rubra pilaris, epidermolytic hyperkeratosis, and others).

Are the Cutaneous Microbiota a Guardian of the Skin's Physical Barrier? The Intricate Relationship between Skin Microbes and Barrier Integrity

The skin is a tightly regulated, balanced interface that maintains our integrity through a complex barrier comprising physical or mechanical, chemical, microbiological, and immunological components. The skin's microbiota affect various properties, one of which is the establishment and maintenance of the physical barrier. This is achieved by influencing multiple processes, including keratinocyte differentiation, stratum corneum formation, and regulation of intercellular contacts. In this review, we summarize the potential contribution of Cutibacterium acnes to these events and outline the contribution of bacterially induced barrier defects to the pathogenesis of acne vulgaris. With the combined effects of a Westernized lifestyle, microbial dysbiosis, epithelial barrier defects, and inflammation, the development of acne is very similar to that of several other multifactorial diseases of barrier organs (e.g., inflammatory bowel disease, celiac disease, asthma, atopic dermatitis, and chronic rhinosinusitis). Therefore, the management of acne requires a complex approach, which should be taken into account when designing novel treatments that address not only the inflammatory and microbial components but also the maintenance and strengthening of the cutaneous physical barrier.

Applications and recent advances in transdermal drug delivery systems for the treatment of rheumatoid arthritis

Rheumatoid arthritis is a chronic, systemic autoimmune disease predominantly based on joint lesions with an extremely high disability and deformity rate. Several drugs have been used for the treatment of rheumatoid arthritis, but their use is limited by suboptimal bioavailability, serious adverse effects, and nonnegligible first-pass effects. In contrast, transdermal drug delivery systems (TDDSs) can avoid these drawbacks and improve patient compliance, making them a promising option for the treatment of rheumatoid arthritis (RA). Of course, TDDSs also face unique challenges, as the physiological barrier of the skin makes drug delivery somewhat limited. To overcome this barrier and maximize drug delivery efficiency, TDDSs have evolved in terms of the principle of transdermal facilitation and transdermal facilitation technology, and different generations of TDDSs have been derived, which have significantly improved transdermal efficiency and even achieved individualized controlled drug delivery. In this review, we summarize the different generations of transdermal drug delivery systems, the corresponding transdermal strategies, and their applications in the treatment of RA.

The Skin Barrier and Moisturization: Function, Disruption, and Mechanisms of Repair

BACKGROUND

The anatomic layers of the skin are well-defined, and a functional model of the skin barrier has recently been described. Barrier disruption plays a key role in several skin conditions, and moisturization is recommended as an initial treatment in conditions such as atopic dermatitis. This review aimed to analyze the skin barrier in the context of the function model, with a focus on the mechanisms by which moisturizers support each of the functional layers of the skin barrier to promote homeostasis and repair.

SUMMARY

The skin barrier is comprised of four interdependent layers - physical, chemical, microbiologic, and immunologic - which maintain barrier structure and function. Moisturizers target disruption affecting each of these four layers through several mechanisms and were shown to improve transepidermal water loss in several studies. Occlusives, humectants, and emollients occlude the surface of the stratum corneum (SC), draw water from the dermis into the epidermis, and assimilate into the SC, respectively, in order to strengthen the physical skin barrier. Acidic moisturizers bolster the chemical skin barrier by supporting optimal enzymatic function, increasing ceramide production, and facilitating ideal conditions for commensal microorganisms. Regular moisturization may strengthen the immunologic skin barrier by reducing permeability and subsequent allergen penetration and sensitization.

KEY MESSAGES

The physical, chemical, microbiologic, and immunologic layers of the skin barrier are each uniquely impacted in states of skin barrier disruption. Moisturizers target each of the layers of the skin barrier to maintain homeostasis and facilitate repair.

Permeable Cornified Envelope Layer Regulates the Solute Transport in Human Stratum Corneum

To unravel the diffusion mechanisms of percutaneous drug delivery, suitable numerical analysis of stratum corneum structure is essential. In this research paper, we accounted for the permeable envelope layer in the brick-and-mortar finite element models of human stratum corneum. Both penetration and desorption experiments for tritiated water were simulated by transient finite element analysis. Rivet-shaped corneodesmosomes were included in the brick and mortar model. Results showed that cornified lipid permeability (Penv) is a determinant in desorption of the solute, while lipid transverse diffusion coefficient (Dlip-trans) is prominent during penetration. These two major unknowns (Penv and Dlip-trans) were obtained by extensive fitting of the finite element model to the experimental water data. Penv and Dlip-trans were determined to be 1×10-2 cm/s and 5.7×10-10 cm2/s, respectively.

Regulation of Physiological Barrier Function by the Commensal Microbiota

A fundamental characteristic of living organisms is their ability to separate the internal and external environments, a function achieved in large part through the different physiological barrier systems and their component junctional molecules. Barrier integrity is subject to multiple influences, but one that has received comparatively little attention to date is the role of the commensal microbiota. These microbes, which represent approximately 50% of the cells in the human body, are increasingly recognized as powerful physiological modulators in other systems, but their role in regulating barrier function is only beginning to be addressed. Through comparison of the impact commensal microbes have on cell-cell junctions in three exemplar physiological barriers-the gut epithelium, the epidermis and the blood-brain barrier-this review will emphasize the important contribution microbes and microbe-derived mediators play in governing barrier function. By extension, this will highlight the critical homeostatic role of commensal microbes, as well as identifying the puzzles and opportunities arising from our steadily increasing knowledge of this aspect of physiology.

Polarity in skin development and cancer

The epidermis is a stratified squamous epithelium that forms the outermost layer of the skin. Its primary function is to act as a barrier, keeping pathogens and toxins out and moisture in. This physiological role has necessitated major differences in the organization and polarity of the tissue as compared to simple epithelia. We discuss four aspects of polarity in the epidermis - the distinctive polarities of basal progenitor cells as well as differentiated granular cells, the polarity of adhesions and the cytoskeleton across the tissue as keratinocytes differentiate, and the planar cell polarity of the tissue. These distinctive polarities are essential for the morphogenesis and the function of the epidermis and have also been implicated in regulating tumor formation.

Altered epidermal proliferation, differentiation, and lipid composition: Novel key elements in the vitiligo puzzle

Vitiligo is an acquired skin depigmentation disease involving multiple pathogenetic mechanisms, which ultimately direct cytotoxic CD8+ cells to destroy melanocytes. Abnormalities have been described in several cells even in pigmented skin as an expression of a functional inherited defect. Keratinocytes regulate skin homeostasis by the assembly of a proper skin barrier and releasing and responding to cytokines and growth factors. Alterations in epidermal proliferation, differentiation, and lipid composition as triggers for immune response activation in vitiligo have not yet been investigated. By applying cellular and lipidomic approaches, we revealed a deregulated keratinocyte differentiation with altered lipid composition, associated with impaired energy metabolism and increased glycolytic enzyme expression. Vitiligo keratinocytes secreted inflammatory mediators, which further increased following mild mechanical stress, thus evidencing immune activation. These findings identify intrinsic alterations of the nonlesional epidermis, which can be the prime instigator of the local inflammatory milieu that stimulates immune responses targeting melanocytes.

Multiscale modelling of desquamation in the interfollicular epidermis

Maintenance of epidermal thickness is critical to the barrier function of the skin. Decreased tissue thickness, specifically in the stratum corneum (the outermost layer of the tissue), causes discomfort and inflammation, and is related to several severe diseases of the tissue. In order to maintain both stratum corneum thickness and overall tissue thickness it is necessary for the system to balance cell proliferation and cell loss. Cell proliferation in the epidermis occurs in the basal layer and causes constant upwards movement in the tissue. Cell loss occurs when dead cells at the top of the tissue are lost to the environment through a process called desquamation. Desquamation is thought to occur through a gradual reduction in adhesion between cells, due to the cleaving of adhesion proteins by enzymes, in the stratum corneum.

In this paper we will investigate combining a (mass action) subcellular model of desquamation with a three dimensional (cell centre based) multicellular model of the interfollicular epidermis to better understand maintenance of epidermal thickness. Specifically, our aim is to determine if a hypothesised biological model for the degradation of cell-cell adhesion, from the literature, is sufficient to maintain a steady state tissue thickness. These investigations show the model is able to provide a consistent rate of cell loss in the multicellular model. This loss balances proliferation, and hence maintains a homeostatic tissue thickness. Moreover, we find that multiple proliferative cell populations in the basal layer can be represented by a single proliferative cell population, simplifying investigations with this model.

The model is used to investigate a disorder (Netherton Syndrome) which disrupts desquamation. The model shows how biochemical changes can cause disruptions to the tissue, resulting in a reduced tissue thickness and consequently diminishing the protective role of the tissue. A hypothetical treatment result is also investigated: we compare the cases of a partially effective homogeneous treatment (where all cells partially recover) and a totally effective heterogeneous treatment (in which a proportion of the cells totally recover) with the aim to determine the difference in the response of the tissue to these different scenarios. Results show an increased benefit to corneum thickness from the heterogeneous treatment over the homogeneous treatment.

Characterization of silver diamine fluoride cytotoxicity using microfluidic tooth-on-a-chip and gingival equivalents

OBJECTIVE

This study aims to characterize the cytotoxicity potential of silver diamine fluoride (SDF) on dental pulp stem cells (DPSC) and gingival equivalents.

METHODS

DPSC cultured on 96-well plates was exposed directly to SDF (0.0001-0.01%) and cell viability (IC₅₀) quantified. Effect of SDF on DPSC viability under flow (with dentin barrier) conditions was evaluated using a custom-designed microfluidic "tooth-on-a-chip". Permeability of dentin discs (0.5-1.5 mm thickness) was evaluated using lucifer yellow permeation assay. Dentin discs were treated with 38% SDF (up to 3 h), and cell viability (live/dead assay) of the DPSC cultured in the inlet (unexposed) and outlet (exposed) regions of the pulp channel was evaluated. To assess the mucosal corrosion potential, gingival equivalents were treated with 38% SDF for 3 or 60 min (OECD test guideline 431) and characterized by MTT assay and histomorphometric analysis.

RESULTS

DPSC exposed directly to SDF showed a dose-dependent reduction in cell viability (IC₅₀: 0.001%). Inlet channels (internal control) of the tooth-on-a-chip exposed to PBS and SDF-exposed dentin discs showed> 85% DPSC viability. In contrast, the outlet channels of SDF-exposed dentin discs showed a decreased viability of< 31% and 0% (1.5 and ≤1.0 mm thick dentin disc, respectively) (p < 0.01). The gingiva equivalents treated with SDF for 3 and 60 min demonstrated decreased epithelial integrity, loss of intercellular cohesion and corneal layer detachment with significant reduction in intact epithelial thickness (p < 0.05).

SIGNIFICANCE

SDF penetrated the dentin (≤1 mm thick) inducing significant death of the pulp cells. SDF also disrupted gingival epithelial integrity resulting in mucosal corrosion.

Dsg1 and Dsg3 Composition of Desmosomes Across Human Epidermis and Alterations in Pemphigus Vulgaris Patient Skin

Desmosomes are important epidermal adhesion units and signalling hubs, which play an important role in pemphigus pathogenesis. Different expression patterns of the pemphigus autoantigens desmoglein (Dsg)1 and Dsg3 across different epidermal layers have been demonstrated. However, little is known about changes in desmosome composition in different epidermal layers or in patient skin. The aim of this study was thus to characterize desmosome composition in healthy and pemphigus skin using super-resolution microscopy. An increasing Dsg1/Dsg3 ratio from lower basal (BL) to uppermost granular layer (GL) was observed. Within BL desmosomes, Dsg1 and Dsg3 were more homogeneously distributed whereas superficial desmosomes mostly comprised one of the two molecules or domains containing either one but not both. Extradesmosomal, desmoplakin (Dp)-independent, co-localization of Dsg3 with plakoglobin (Pg) was found mostly in BL and extradesmosomal Dsg1 co-localization with Pg in all layers. In contrast, in the spinous layer (SL) most Dsg1 and Dsg3 staining was confined to desmosomes, as revealed by the co-localization with Dp. In pemphigus patient skin, Dsg1 and Dsg3 immunostaining was altered especially along blister edges. The number of desmosomes in patient skin was reduced significantly in basal and spinous layer keratinocytes with only few split desmosomes found. In addition, Dsg1-Pg co-localization at the apical BL and Dsg3-Pg co-localization in SL were significantly reduced in patients, suggesting that that extradesmosomal Dsg molecules were affected. These results support the hypothesis that pemphigus is a desmosome assembly disease and may help to explain histopathologic differences between pemphigus phenotypes.

Stratum corneum as polymer sheet: concept and cornification processes

The skin barrier protects our body from external insults and water loss through a specialized layer, the stratum corneum. The stratum corneum, an accumulation of dead keratinocytes (corneocytes), comprises lipids and supporting cell bodies. We propose a framework of lipid-filled polymer sheet of corneocytes, a unique structure that achieves flexibility and robustness, updating the rigid image of the historical bricks-and-mortar model. The polymerization of polymer sheet (cornification) by cell death of keratinocytes (corneoptosis) is delicately and dynamically controlled by cytoplasmic calcium ion and pH. Understanding the structure and formation of the stratum corneum can lead to better treatments for skin diseases and a better understanding of the evolution of the stratum corneum.

Topical Ectoine Application in Children and Adults to Treat Inflammatory Diseases Associated with an Impaired Skin Barrier: A Systematic Review

Introduction

Inflammatory skin diseases are a significant burden on affected patients. Inflammation is caused by various stress factors to the epidermis resulting in, e.g., dryness, redness, and pruritus. Emollients are used in basic therapy to restore the natural skin barrier and relieve symptoms. A systematic review was performed to evaluate the efficacy and safety of ectoine-containing topical formulations in inflammatory skin diseases characterized by an impaired skin barrier.

Methods

A systematic review was carried out in PubMed, the Cochrane Library, and Microsoft Academic up to October 2021. Inclusion criteria were ectoine-containing topical formulations (creams, emollients) used for (adjuvant) therapy of inflammatory skin diseases. Clinical studies of any design published in any language were included.

Results

A total of 230 references were screened for eligibility, of which six were selected for inclusion in the review (five studies on atopic dermatitis and one study on prevention and management of retinoid dermatitis). The application of topical formulations containing 5.5–7.0% ectoine positively influenced skin dryness and, consequently, pruritus and dermatitis-specific scores in patients with atopic dermatitis. Especially in infants and children, who belong to the most frequently affected group, the formulations were well-tolerated when applied for up to 4 weeks. In studies where ectoine was used as an adjuvant therapy, application was associated with a decreased need for pharmacological therapy and also improved the effectiveness of, e.g., topical corticosteroids. In patients undergoing isotretinoin therapy, ectoine was as effective as dexpanthenol in reducing retinoid dermatitis or improving symptoms.

Conclusion

Ectoine is an effective natural substance with an excellent tolerability and safety profile, representing a beneficial alternative as basic therapy or to increase the efficacy of the pharmacological treatment regimen for patients with inflammatory skin diseases, including infants and children.

Nanodelivery Strategies for Skin Diseases with Barrier Impairment: Focusing on Ceramides and Glucocorticoids

The human epidermis has a characteristic lipidic composition in the stratum corneum, where ceramides play a crucial role in the skin barrier homeostasis and in water-holding capacity. Several skin diseases, such as atopic dermatitis and psoriasis, exhibit a dysfunction in the lipid barrier with altered ceramide levels and increased loss of transepidermal water. Glucocorticoids are normally employed in the therapeutical management of these pathologies. However, they have shown a poor safety profile and reduced treatment efficiency. The main objective of this review is to, within the framework of the limitations of the currently available therapeutical approaches, establish the relevance of nanocarriers as a safe and efficient delivery strategy for glucocorticoids and ceramides in the topical treatment of skin disorders with barrier impairment.

NFAT5 Controls the Integrity of Epidermis

The skin protects the human body against dehydration and harmful challenges. Keratinocytes (KCs) are the most abundant epidermal cells, and it is anticipated that KC-mediated transport of Na⁺ ions creates a physiological barrier of high osmolality against the external environment. Here, we studied the role of NFAT5, a transcription factor whose activity is controlled by osmotic stress in KCs. Cultured KCs from adult mice were found to secrete more than 300 proteins, and upon NFAT5 ablation, the secretion of several matrix proteinases, including metalloproteinase-3 (Mmp3) and kallikrein-related peptidase 7 (Klk7), was markedly enhanced. An increase in Mmp3 and Klk7 RNA levels was also detected in transcriptomes of Nfat5^-/- KCs, along with increases of numerous members of the 'Epidermal Differentiation Complex' (EDC), such as small proline-rich (Sprr) and S100 proteins. NFAT5 and Mmp3 as well as NFAT5 and Klk7 are co-expressed in the basal KCs of fetal and adult epidermis but not in basal KCs of newborn (NB) mice. The poor NFAT5 expression in NB KCs is correlated with a strong increase in Mmp3 and Klk7 expression in KCs of NB mice. These data suggests that, along with the fragile epidermis of adult Nfat5^-/- mice, NFAT5 keeps in check the expression of matrix proteases in epidermis. The NFAT5-mediated control of matrix proteases in epidermis contributes to the manifold changes in skin development in embryos before and during birth, and to the integrity of epidermis in adults.

Sphingosine 1-Phosphate Receptor 2 Is Central to Maintaining Epidermal Barrier Homeostasis

The outer layer of the epidermis composes the skin barrier, a sophisticated filter constituted by layers of corneocytes in a lipid matrix. The matrix lipids, especially the ceramide-generated sphingosine 1-phosphate, are the messengers that the skin barrier uses to communicate with the basal layer of the epidermis where replicating keratinocytes are located. Sphingosine 1-phosphate is a bioactive sphingolipid mediator involved in various cellular functions through S1PR1‒5, expressed by keratinocytes. We discovered that the S1pr2 absence is linked to an impairment in the skin barrier function. Although S1pr2^-/- mouse skin has no difference in its phenotype and barrier function compared with that of wild-type mouse, after tape stripping, S1pr2^-/- mouse showed significantly higher transepidermal water loss and required another 24 hours to normalize their transepidermal water loss levels. Moreover, after epicutaneous Staphylococcus aureus application, impaired S1pr2^-/- mouse epidermal barrier function allowed deeper bacterial penetration and denser neutrophil infiltration in the dermis. Microarray and RNA sequence of S1pr2^-/- mouse epidermis linked the barrier dysfunction with a decrease in FLG2 and tight junction components. In conclusion, S1pr2^-/- mice have compromised skin barrier function and increased bacteria permeability, making them a suitable model for diseases that present similar characteristics, such as atopic dermatitis.

Corneocytes: Relationship between Structural and Biomechanical Properties

BACKGROUND

Skin is the interface between an organism and the external environment, and hence the stratum corneum (SC) is the first to withstand mechanical insults that, in certain conditions, may lead to integrity loss and the development of pressure ulcers. The SC comprises corneocytes, which are vital elements to its barrier function. These cells are differentiated dead keratinocytes, without organelles, composed of a cornified envelope and a keratin-filled interior, and connected by corneodesmosomes (CDs).

SUMMARY

The current review focusses on the relationship between the morphological, structural, and topographical features of corneocytes and their mechanical properties, to understand how they assist the SC in maintaining skin integrity and in responding to mechanical insults. Key Messages: Corneocytes create distinct regions in the SC: the inner SC is characterized by immature cells with a fragile cornified envelope and a uniform distribution of CDs; the upper SC has resilient cornified envelopes and a honeycomb distribution of CDs, with a greater surface area and a smaller thickness than cells from the inner layer. The literature indicates that this upward maturation process is one of the most important steps in the mechanical resistance and barrier function of the SC. The morphology of these cells is dependent on the body site: the surface area in non-exposed skin is about 1,000-1,200 μm2, while for exposed skin, for example, the cheek and forehead, is about 700-800 μm2. Corneocytes are stiff cells compared to other cellular types, for example, the Young's modulus of muscle and fibroblast cells is typically a few kPa, while that of corneocytes is reported to be about hundreds of MPa. Moreover, these skin cells have 2 distinct mechanical regions: the cornified envelope (100-250 MPa) and the keratin matrix (250-500 MPa).

Capsaicin: Plants of the Genus Capsicum and Positive Effect of Oriental Spice on Skin Health

BACKGROUND

Capsaicin, the main pungent ingredient in hot chili peppers, causes excitation of small sensory neurons. It also provides the basic pungent flavor in Capsicum fruits.

SUMMARY

Capsaicin plays a vital role as an agonist for the TRPV1 (transient receptor potential cation channel, subfamily V, member 1) receptor. TRPV1 is essential for the reduction of oxidative stress, pain sensations, and inflammation. Therefore, it has many pros related to health issue. Activation and positive impact of TRPV1 via capsaicin has been studied in various dermatological conditions and in other skin-related issues. Past studies documented that capsaicin plays a vital role in the prevention of atopic dermatitis as well as psoriasis. Moreover, TRPV1 is also very important for skin health because it acts as a capsaicin receptor. It is found in nociceptive nerve fibers and nonneural structures. It prompts the release of a compound that is involved in communicating pain between the spinal cord nerves and other parts of the body. Key Messages: Here, we summarize the growing evidence for the beneficial role of capsaicin and TRPV1 and how they help in the relief of skin diseases such as inflammation, permeation, dysfunction, atopic dermatitis, and psoriasis and in pain amplification syndrome.

Foray into Concepts of Design and Evaluation of Microemulsions as a Modern Approach for Topical Applications in Acne Pathology

With a fascinating complexity, governed by multiple physiological processes, the skin is considered a mantle with protective functions which during lifetime are frequently impaired, triggering dermatologic disorders. As one of the most prevalent dermatologic conditions worldwide, characterized by a complex pathogenesis and a high recurrence, acne can affect the patient's quality of life. Smart topical vehicles represent a good option in the treatment of a versatile skin condition. By surpassing the stratum corneum known for diffusional resistance, a superior topical bioavailability can be obtained at the affected place. In this direction, the literature study presents microemulsions as a part of a condensed group of modern formulations. Microemulsions are appreciated for their superior profile in matters of drug delivery, especially for challenging substances with hydrophilic or lipophilic structures. Formulated as transparent and thermodynamically stable systems, using simplified methods of preparation, microemulsions have a simple and clear appearance. Their unique structures can be explained as a function of the formulation parameters which were found to be the mainstay of a targeted therapy.

Generation of recombinant antibodies against human tissue kallikrein 7 to treat skin diseases

Human tissue kallikreins (KLKs) constitute a family of 15 serine proteases that are distributed in various tissues and implicated in several pathological disorders. KLK7 is an unusual serine protease that presents both trypsin-like and chymotrypsin-like specificity and appears to be upregulated in pathologies that are related to skin desquamation processes, such as atopic dermatitis, psoriasis and Netherton syndrome. In recent years, various groups have worked to develop specific inhibitors for this enzyme, as KLK7 represents a potential target for new therapeutic procedures for diseases related to skin desquamation processes. In this work, we selected nine different single-chain variable fragment antibodies (scFv) from a human naïve phage display library and characterized their inhibitory activities against KLK7. The scFv with the lowest IC₅₀ against KLK7 was affinity maturated, which resulted in the generation of four new scFv-specific antibodies for the target protease. These new antibodies were expressed in the scFv-Fc format in HEK293-6E cells, and the characterization of their inhibitory activities against KLK7 showed that three of them presented IC₅₀ values lower than that of the original antibody. The cytotoxicity analysis of these recombinant antibodies demonstrated that they can be safely used in a cellular model. In conclusion, our research showed that in our case, a phage-display methodology in combination with enzymology assays can be a very suitable tool for the development of inhibitors for KLKs, suggesting a new strategy to identify therapeutic protease inhibitors for diseases related to uncontrolled kallikrein activity.

Recent trends, challenges and future outlook of transdermal drug delivery systems for rheumatoid arthritis therapy

At present, several drug molecules have been used for the treatment of rheumatoid arthritis (RA). However, the utilization of these compounds through the oral and parenteral route is limited due to low bioavailability, rapid metabolism, poor absorption, first-pass effect, and serious adverse effects. A transdermal delivery system is an appealing option in this scenario, as it possesses the proficiency to overcome drawbacks associated with the oral and parenteral route. With the innovation of several enhancement strategies, many therapeutic agents have been administered transdermally, proposing an exceptional approach to treat RA. The present article provides an insight into the etiology and pathophysiology of RA. The challenges of the transdermal route and the strategies to improve those problems are described. The current advances in increasing the transdermal efficiency of the therapeutics against RA are discussed. Limitations and advantages regarding the state of the art transdermal delivery system and future outlook are also summarized.

Phenotypic suppression of acral peeling skin syndrome in a patient with autosomal recessive congenital ichthyosis

Autosomal recessive congenital ichthyosis (ARCI) manifests with generalized scaling often associated with generalized erythema. Mutations in at least 13 different genes have been reported to cause ARCI. Acral peeling skin syndrome (APSS) is a rare autosomal recessive disorder manifesting with peeling over the distal limbs and dorsal surfaces of hands and feet. APSS is mostly due to mutations in TGM5, encoding transglutaminase 5. Both ARCI and APSS are fully penetrant genetic traits. Here, we describe a consanguineous family in which one patient with mild ARCI was found to carry a homozygous mutation in ALOXE3 (c.1238G > A; p.Gly413Asp). The patient was also found to carry a known pathogenic homozygous mutation in TGM5 (c.1335G > C; p.Lys445Asn) but did not display acral peeling skin. Her uncle carried the same homozygous mutation in TGM5 but carried the ALOXE3 mutation in a heterozygous state and showed clinical features typical of APSS. Taken collectively, these observations suggested that the ALOXE3 mutation suppresses the clinical expression of the TGM5 variant. We hypothesized that ALOXE3 deficiency may affect the expression of a protein capable of compensating for the lack of TGM5 expression. Downregulation of ALOXE3 in primary human keratinocytes resulted in increased levels of corneodesmosin, which plays a critical role in the maintenance of cell-cell adhesion in the upper epidermal layers. Accordingly, ectopic corneodesmosin expression rescued the cell-cell adhesion defect caused by TGM5 deficiency in keratinocytes as ascertained by the dispase dissociation assay. The present data thus provide evidence for phenotypic suppression in a human hereditary skin disorder.

Surface Proteins of Staphylococcus aureus

The surface of Staphylococcus aureus is decorated with over 20 proteins that are covalently anchored to peptidoglycan by the action of sortase A. These cell wall-anchored (CWA) proteins can be classified into several structural and functional groups. The largest is the MSCRAMM family, which is characterized by tandemly repeated IgG-like folded domains that bind peptide ligands by the dock lock latch mechanism or the collagen triple helix by the collagen hug. Several CWA proteins comprise modules that have different functions, and some individual domains can bind different ligands, sometimes by different mechanisms. For example, the N-terminus of the fibronectin binding proteins comprises an MSCRAMM domain which binds several ligands, while the C-terminus is composed of tandem fibronectin binding repeats. Surface proteins promote adhesion to host cells and tissue, including components of the extracellular matrix, contribute to biofilm formation by stimulating attachment to the host or indwelling medical devices followed by cell-cell accumulation via homophilic interactions between proteins on neighboring cells, help bacteria evade host innate immune responses, participate in iron acquisition from host hemoglobin, and trigger invasion of bacteria into cells that are not normally phagocytic. The study of genetically manipulated strains using animal infection models has shown that many CWA proteins contribute to pathogenesis. Fragments of CWA proteins have the potential to be used in multicomponent vaccines to prevent S. aureus infections.

Calcium-sensing receptor deletion in the mouse esophagus alters barrier function

Calcium-sensing receptor (CaSR) is the molecular sensor by which cells respond to small changes in extracellular Ca²⁺ concentrations. CaSR has been reported to play a role in glandular and fluid secretion in the gastrointestinal tract and to regulate differentiation and proliferation of skin keratinocytes. CaSR is present in the esophageal epithelium, but its role in this tissue has not been defined. We deleted CaSR in the mouse esophagus by generating keratin 5 CreER;CaSR^Flox+/+compound mutants, in which loxP sites flank exon 7 of CaSR gene. Recombination was initiated with multiple tamoxifen injections, and we demonstrated exon 7 deletion by PCR analysis of genomic DNA. Quantitative real-time PCR and Western blot analyses showed a significant reduction in CaSR mRNA and protein expression in the knockout mice (^EsoCaSR^-/-) as compared with control mice. Microscopic examination of ^EsoCaSR^-/- esophageal tissues showed morphological changes including elongation of the rete pegs, abnormal keratinization and stratification, and bacterial buildup on the luminal epithelial surface. Western analysis revealed a significant reduction in levels of adherens junction proteins E-cadherin and β catenin and tight junction protein claudin-1, 4, and 5. Levels of small GTPase proteins Rac/Cdc42, involved in actin remodeling, were also reduced. Ussing chamber experiments showed a significantly lower transepithelial resistance in knockout (KO) tissues. In addition, luminal-to-serosal-fluorescein dextran (4 kDa) flux was higher in KO tissues. Our data indicate that CaSR plays a role in regulating keratinization and cell-cell junctional complexes and is therefore important for the maintenance of the barrier function of the esophagus.NEW & NOTEWORTHY The esophageal stratified squamous epithelium maintains its integrity by continuous proliferation and differentiation of the basal cells. Here, we demonstrate that deletion of the calcium-sensing receptor, a G protein-coupled receptor, from the basal cells disrupts the structure and barrier properties of the epithelium.

The Differentiation-Associated Keratinocyte Protein Cornifelin Contributes to Cell-Cell Adhesion of Epidermal and Mucosal Keratinocytes

Cornifelin (CNFN) has been identified as a protein component of epidermal corneocytes. Here, we investigated the tissue distribution of CNFN and potential consequences of CNFN deficiency on epithelial function in in vitro models of human skin and oral mucosa. Our detailed bioinformatics and immunostaining analysis revealed that CNFN is not only expressed in human epidermis but also in noncornifying oral mucosa. In normal epidermis, CNFN was confined to the upper granular layer and the stratum corneum. By contrast, in both partly cornifying and noncornifying oral mucosa, CNFN was expressed in a cell membrane-associated pattern over several suprabasal layers. Small interfering RNA-mediated knockdown of CNFN in epidermal keratinocytes (KCs) was associated with only subtle alterations of the overall epidermal architecture in skin models in vitro but led to altered morphology of corneodesmosomes, as detected by electron microscopy. Using dispase treatment followed by mechanical stress, epithelial sheets of CNFN-deficient epidermal KCs were easily disrupted, whereas their CNFN-competent counterparts remained intact. In contrast to the epidermal KCs, CNFN knockdown in oral KCs had a more severe effect and caused pronounced acantholysis in organotypic models of oral mucosa. Together, these findings indicate that CNFN is a structural component of the cell adhesion system of differentiated KCs in both epidermis and oral mucosa.

Capsaicin induces atopic dermatitis-like manifestations through dysregulation of proteolytic system and alteration of filaggrin processing in rats

Atopic dermatitis (AD) is a complex disease featuring pruritic skin inflammation. Many animal models have been developed. In a rat model, subcutaneous capsaicin injection within 48 hours after birth induces AD-like skin manifestations of dermatitis and scratching behaviour 3 weeks after the injection. When 2- to 4-week-old rats were injected with capsaicin, the lag period was shortened, and the severity of skin manifestations was significantly reduced, suggesting influences of postnatal development. Lgr6 is an epidermal stem cell marker that is normally restricted to the isthmus area of hair follicles at postnatal 2 weeks. Lgr6 persisted in the interfollicular epidermis of capsaicin-injected rats beyond 3 weeks after birth, indicating that capsaicin-induced skin manifestations were influenced by postnatal epidermal development. Capsaicin injection induced alteration of proteolytic processing of filaggrin and corneodesmosin, suggesting epidermal barrier dysfunction. Inappropriate degradation of matriptase was observed. Degrees of proteolysis of these proteins were corelated with the severity of manifestations, suggesting that inappropriate proteolysis might be a possible cause of the skin manifestations. These results strongly suggest that capsaicin may dysregulate the protease system, resulting in alteration of profilaggrin and corneodesmosin proteolysis and skin manifestations. These events may be influenced by postnatal epidermal development.

Use of contraceptive depot medroxyprogesterone acetate is associated with impaired cervicovaginal mucosal integrity

BACKGROUND

Injectable depot medroxyprogesterone acetate (DMPA) is one of the most popular contraception methods in areas of high HIV seroprevalence. Evidence is accumulating that use of DMPA might be associated with an increased risk of HIV-1 acquisition by women; however, mechanisms of this association are not completely understood. The goal of this study was to gain insight into mechanisms underlying the possible link between use of DMPA and risk of HIV-1 acquisition, exploring transcription profiling of ectocervical tissues.

METHODS

Healthy women received either DMPA (n = 31) or combined oral contraceptive (COC), which has not been linked to an increased risk of HIV acquisition (n = 32). We conducted a comparative microarray-based whole-genome transcriptome profiling of human ectocervical tissues before and after 6 weeks of hormonal contraception use.

RESULTS

The analysis identified that expression of 235 and 76 genes was significantly altered after DMPA and COC use, respectively. The most striking effect of DMPA, but not COC, was significantly altered expression (mostly downregulation) of many genes strategically involved in the maintenance of mucosal barrier function; the alterations, as indicated by Ingenuity Pathway Analysis (IPA), were most likely due to the DMPA-induced estrogen deficiency. Furthermore, IPA predicted that transcriptome alterations related to ectocervical immune responses were in general compatible with an immunosuppressive effect of DMPA, but, in some women, also with an inflammatory-like response.

CONCLUSION

Our results suggest that impairment of cervicovaginal mucosal integrity in response to DMPA administration is an important mechanism contributing to the potential increased risk of HIV-1 acquisition in DMPA users.

TRIAL REGISTRATION

ClinicalTrials.gov NCT01421368.

FUNDING

This study was supported by the United States Agency for International Development (USAID) under Cooperative Agreement GPO-A-00-08-00005-00.

Shadow Cell Differentiation: A Comparative Analysis of Modes of Cell Death with Apoptosis and Epidermal/Trichilemmal Keratinization

Shadow cells are characterized by an eosinophilic cytoplasm and a ghost-like nuclear contour; the cell shape is preserved, in spite of nuclear disappearance. Shadow cell nests (SCNs) are frequently observed in pilomatricoma (PMX), where the transitional cells immediately adjacent to SCNs often have a crescent-shaped nucleus showing fragmentation similar to that of apoptotic bodies. They show nuclear accumulation of beta-catenin and DNA double strand breaks (as revealed by in situ 3′-tailing reaction or immunohistochemistry for single-stranded DNA [ssDNA]), while they are negative for cleaved caspase-3 or cleaved lamin A, suggesting that shadow cell differentiation (SCD) is a caspase-independent programmed cell death. SCD can be differentiated from epidermal keratinization (EK) and trichilemmal keratinization (TK) based on the expression pattern of beta-catenin, ssDNA, and caspase-14/CD138. SCD is observed not only in PMX, but also sometimes in basal cell carcinomas, gonadal teratomas, and various extra-cutaneous carcinomas. In particular, SCNs are found in 24$ of endometrial adenoacanthoma and are derived from squamoid morules. This establishes a link between basaloid cells in PMX and squamoid morules in endometrial adenoacanthomas as common precursors of shadow cells. Overall, it is suggested that SCD is different from, but partly similar to, apoptosis and that SCD and EK/TK should be differentiated from the standpoint of cell death/differentiation.

Filaggrin 2 Deficiency Results in Abnormal Cell-Cell Adhesion in the Cornified Cell Layers and Causes Peeling Skin Syndrome Type A

Peeling skin syndromes form a large and heterogeneous group of inherited disorders characterized by superficial detachment of the epidermal cornified cell layers, often associated with inflammatory features. Here we report on a consanguineous family featuring noninflammatory peeling of the skin exacerbated by exposure to heat and mechanical stress. Whole exome sequencing revealed a homozygous nonsense mutation in FLG2, encoding filaggrin 2, which cosegregated with the disease phenotype in the family. The mutation was found to result in decreased FLG2 RNA levels as well as almost total absence of filaggrin 2 in the patient epidermis. Filaggrin 2 was found to be expressed throughout the cornified cell layers and to colocalize with corneodesmosin that plays a crucial role in maintaining cell-cell adhesion in this region of the epidermis. The absence of filaggrin 2 in the patient skin was associated with markedly decreased corneodesmosin expression, which may contribute to the peeling phenotype displayed by the patients. Accordingly, using the dispase dissociation assay, we showed that FLG2 downregulation interferes with keratinocyte cell-cell adhesion. Of particular interest, this effect was aggravated by temperature elevation, consistent with the clinical phenotype. Restoration of corneodesmosin levels by ectopic expression rescued cell-cell adhesion. Taken together, the present data suggest that filaggrin 2 is essential for normal cell-cell adhesion in the cornified cell layers.

Inherited Nonsyndromic Ichthyoses: An Update on Pathophysiology, Diagnosis and Treatment

Hereditary ichthyoses are due to mutations on one or both alleles of more than 30 different genes, mainly expressed in the upper epidermis. Syndromic as well as nonsyndromic forms of ichthyosis exist. Irrespective of etiology, virtually all types of ichthyosis exhibit a defective epidermal barrier that constitutes the driving force for hyperkeratosis, skin scaling, and inflammation. In nonsyndromic forms, these features are most evident in severe autosomal recessive congenital ichthyosis (ARCI) and epidermolytic ichthyosis, but to some extent also occur in the common type of non-congenital ichthyosis. A correct diagnosis of ichthyosis-essential not only for genetic counseling but also for adequate patient information about prognosis and therapeutic options-is becoming increasingly feasible thanks to recent progress in genetic knowledge and DNA sequencing methods. This paper reviews the most important aspects of nonsyndromic ichthyoses, focusing on new knowledge about the pathophysiology of the disorders, which will hopefully lead to novel ideas about therapy.

Commensal microbiota modulate gene expression in the skin

BACKGROUND

The skin harbors complex communities of resident microorganisms, yet little is known of their physiological roles and the molecular mechanisms that mediate cutaneous host-microbe interactions. Here, we profiled skin transcriptomes of mice reared in the presence and absence of microbiota to elucidate the range of pathways and functions modulated in the skin by the microbiota.

RESULTS

A total of 2820 genes were differentially regulated in response to microbial colonization and were enriched in gene ontology (GO) terms related to the host-immune response and epidermal differentiation. Innate immune response genes and genes involved in cytokine activity were generally upregulated in response to microbiota and included genes encoding toll-like receptors, antimicrobial peptides, the complement cascade, and genes involved in IL-1 family cytokine signaling and homing of T cells. Our results also reveal a role for the microbiota in modulating epidermal differentiation and development, with differential expression of genes in the epidermal differentiation complex (EDC). Genes with correlated co-expression patterns were enriched in binding sites for the transcription factors Klf4, AP-1, and SP-1, all implicated as regulators of epidermal differentiation. Finally, we identified transcriptional signatures of microbial regulation common to both the skin and the gastrointestinal tract.

CONCLUSIONS

With this foundational approach, we establish a critical resource for understanding the genome-wide implications of microbially mediated gene expression in the skin and emphasize prospective ways in which the microbiome contributes to skin health and disease.

Severe pre-eclampsia is associated with alterations in cytotrophoblasts of the smooth chorion

Pre-eclampsia (PE), which affects ∼8% of first pregnancies, is associated with faulty placentation. Extravillous cytotrophoblasts (CTBs) fail to differentiate properly, contributing to shallow uterine invasion and deficient spiral artery remodeling. We studied the effects of severe PE (sPE) on the smooth chorion portion of the fetal membranes. The results showed a significant expansion of the CTB layer. The cells displayed enhanced expression of stage-specific antigens that extravillous CTBs normally upregulate as they exit the placenta. Transcriptomics revealed the dysregulated expression of many genes (e.g. placental proteins, markers of oxidative stress). We confirmed an sPE-related increase in production of PAPPA1, which releases IGF1 from its binding protein. IGF1 enhanced proliferation of smooth chorion CTBs, a possible explanation for expansion of this layer, which may partially compensate for the placental deficits.

Highlighted article: Cytotrophoblasts (CTBs) within the smooth chorion of the human placenta are implicated in severe pre-eclampsia, undergoing significant expansion and changes in gene expression.

Novel concepts of prevention and treatment of atopic dermatitis through barrier and immune manipulations with implications for the atopic march

Skin barrier abnormalities have been suggested to play an essential role in initiation of early atopic dermatitis (AD). Antigen penetration through a compromised barrier likely leads to increased innate immune responses, antigen-presenting cell stimulation, and priming of overt cutaneous disease. In a T_H2-promoting environment, T-cell/B-cell interactions occurring in regional lymph nodes lead to excessive IgE switch. Concurrent redistribution of memory T cells into the circulation not only leads to exacerbation of AD through T-cell skin infiltration but also spreads beyond the skin to initiate the atopic march, which includes food allergy, asthma, and allergic rhinitis. Possible primary interventions to prevent AD are focusing on improving skin barrier integrity, including supplementing barrier function with moisturizers. As for secondary prophylaxis in children with established AD, this can be stratified into prevention of disease exacerbations by using proactive approaches (with either topical corticosteroids or topical calcineurin inhibitors) in mild AD cases or the prevention of other atopic disorders that will probably mandate systemic immunosuppression in severe AD cases.

Skin Barrier Development Depends on CGI-58 Protein Expression during Late-Stage Keratinocyte Differentiation

Adipose triglyceride lipase (ATGL) and its coactivator comparative gene identification-58 (CGI-58) are limiting in cellular triglyceride catabolism. Although ATGL deficiency is compatible with normal skin development, mice globally lacking CGI-58 die postnatally and exhibit a severe epidermal permeability barrier defect, which may originate from epidermal and/or peripheral changes in lipid and energy metabolism. Here, we show that epidermis-specific disruption of CGI-58 is sufficient to provoke a defect in the formation of a functional corneocyte lipid envelope linked to impaired ω-O-acylceramide synthesis. As a result, epidermis-specific CGI-58-deficient mice show severe skin dysfunction, arguing for a tissue autonomous cause of disease development. Defective skin permeability barrier formation in global CGI-58-deficient mice could be reversed via transgenic restoration of CGI-58 expression in differentiated but not basal keratinocytes suggesting that CGI-58 is essential for lipid metabolism in suprabasal epidermal layers. The compatibility of ATGL deficiency with normal epidermal function indicated that CGI-58 may stimulate an epidermal triglyceride lipase beyond ATGL required for the adequate provision of fatty acids as a substrate for ω-O-acylceramide synthesis. Pharmacological inhibition of ATGL enzyme activity similarly reduced triglyceride-hydrolytic activities in wild-type and CGI-58 overexpressing epidermis implicating that CGI-58 participates in ω-O-acylceramide biogenesis independent of its role as a coactivator of epidermal triglyceride catabolism.

Putative functions of tissue kallikrein-related peptidases in vaginal fluid

Cervical-vaginal fluid (CVF) is a complex biological fluid that hydrates the mucosa of the lower female reproductive system. In-depth proteomic and biochemical studies on CVF have revealed that it contains large amounts of endogenous proteases and protease inhibitors, including an abundance of several members of the tissue kallikrein-related peptidase (KLK) family. Despite their ubiquitous presence in human tissues and fluids, KLK expression levels vary considerably, with maximum expression observed in reproduction-related tissues and fluids. The roles of KLKs in the lower female reproductive system are not fully understood. The activation of KLKs in CVF is dependent on pH and various modes of KLK regulation in the vagina exist. KLKs have been postulated to have roles in physiological functions related to antimicrobial processes, vaginal and cervical epithelial desquamation, sperm transport, and the processing of fetal membranes as observed in preterm premature rupture of membranes. Increased understanding of the functional roles of KLKs in the lower female reproductive system could lead to new diagnostic and therapeutic modalities for conditions such as vaginal infections and vaginal atrophy.

Expressions of isopeptide bonds and corneodesmosin in middle ear cholesteatoma

OBJECTIVE

Isopeptide bonds form cross-links between constituent proteins in the horny layer of the epidermis. Corneodesmosin (CDSN) is a major component of corneodesmosomes, which bind corneocytes together. Both play important roles in maintaining epidermal barrier functions. In the present study, we investigated the expressions of isopeptide bonds, CDSN, and related enzymes in middle ear cholesteatoma in comparison with the skin.

DESIGN

Prospective case series of patients with middle ear cholesteatoma.

SETTING

Tertiary medical institute.

PARTICIPANTS

Cholesteatoma and normal postauricular skin were collected from patients with acquired middle ear cholesteatoma during tympanomastoidectomy.

MAIN OUTCOME MEASURES

Expression of e-(g-glutamyl)lysine isopeptide bonds was examined by immunohistochemistry; Expressions of transglutaminase (TGase)1, TGase2, TGase3, and TGase5 by immunohistochemistry and quantitative RT-PCR (qRT-PCR); expression of CDSN by immunohistochemistry, qRT-PCR, and Western blot; and expressions of tissue kallikrein-related peptidase (KLK)5, KLK7, KLK14, and serine peptidase inhibitor Kazal type 5 (SPINK5) by qRT-PCR.

RESULTS

TGase2 was higher (P=0.0046) and TGase5 was lower (P=0.0008) in cholesteatoma than in the postauricular skin. Immunoreactivity for isopeptide bonds was localized in the granular and horny layers, and was not different between the two tissues. Immunoreactivity for CDSN was localized in the granular layer, and was lower in cholesteatoma than in the skin (P=0.0090). Western blot and qRT-PCR confirmed that the expression of CDSN was lower in cholesteatoma than in the skin. Expressions of KLK5, KLK7, KLK14, or SPINK5 were not different between the two tissues.

CONCLUSIONS

These results indicate that the production of CDSN is likely to be suppressed in cholesteatoma, which would account, at least in part, for the mechanical fragility and increased permeability of the cholesteatoma epithelium.

Epidermal barrier disorders and corneodesmosome defects

Corneodesmosomes are modified desmosomes present in the stratum corneum (SC). They are crucial for SC cohesion and, thus, constitute one of the pivotal elements of the functional protective barrier of human skin. Expression of corneodesmosomes and, notably, the process of their degradation are probably altered during several dermatoses leading to the disruption of the permeability barrier or to abnormal, often compensative, SC accumulation. These different situations are reviewed in the present paper.