Aberrant distribution patterns of corneodesmosomal components of tape-stripped corneocytes in atopic dermatitis and related skin conditions (ichthyosis vulgaris, Netherton syndrome and peeling skin syndrome type B)

Effects of eczema calming lotion on the stratum corneum in atopic dermatitis: Corneodesmosin and intercellular lipid lamellae

OBJECTIVE

Atopic dermatitis (AD) is characterized by compositional and structural changes to the skin at lesional sites. Alteration to the levels and organization of both protein and lipid components are associated with disease status and lead to impaired barrier and hydration. Corneodesmosin (CDSN) and the arrangement and length of the intercellular lipid lamellae (ICLL) are altered in disrupted skin states. The aim of this research was to profile the distribution of CDSN and the ICLL in the stratum corneum (SC) at lesional and non-lesional sites in AD-prone skin and to investigate the impact of an eczema calming lotion containing petroleum jelly, fatty acids, and colloidal oatmeal.

METHODS

An IRB-approved study was conducted with participants with active AD. From a small subset of participants, tape strips were collected from lesional and non-lesional sites on the arm, prior to and after twice daily application, over 4 weeks of an eczema calming lotion containing petroleum jelly, fatty acids, and colloidal oatmeal. Fluorescent antibody staining was used to investigate the distribution of CDSN. Transmission electron microscopy (TEM) was used to characterize the ICLL.

RESULTS

The distribution/coverage of CDSN was similar between lesional and non-lesional sites at baseline; application of the lotion resulted in a more defined honeycomb/peripheral distribution. Normalized ICLL (nICLL) was lower in baseline samples from lesional sites relative to non-lesional sites. Application of the lotion increased this parameter by the end of the study at all sites.

CONCLUSION

The eczema calming lotion containing petroleum jelly, fatty acids and colloidal oatmeal provided changes in corneodesmosomal proteins distribution and ICLL, consistent with improvements in corneocyte maturation and improved barrier function in the skin of individuals with atopic dermatitis.

Desmosomes at a glance

Desmosomes are relatives of ancient cadherin-based junctions, which emerged late in evolution to ensure the structural integrity of vertebrate tissues by coupling the intermediate filament cytoskeleton to cell-cell junctions. Their ability to dynamically counter the contractile forces generated by actin-associated adherens junctions is particularly important in tissues under high mechanical stress, such as the skin and heart. Much more than the simple cellular 'spot welds' depicted in textbooks, desmosomes are in fact dynamic structures that can sense and respond to changes in their mechanical environment and external stressors like ultraviolet light and pathogens. These environmental signals are transmitted intracellularly via desmosome-dependent mechanochemical pathways that drive the physiological processes of morphogenesis and differentiation. This Cell Science at a Glance article and the accompanying poster review desmosome structure and assembly, highlight recent insights into how desmosomes integrate chemical and mechanical signaling in the epidermis, and discuss desmosomes as targets in human disease.

Characterisation of topographical, biomechanical and maturation properties of corneocytes with respect to anatomical location

BACKGROUND

The Stratum Corneum (SC) is the first barrier of the skin. The properties of individual cells are crucial in understanding how the SC at different anatomical regions maintains a healthy mechanical barrier. The aim of the current study is to present a comprehensive description of the maturation and mechanical properties of superficial corneocytes at different anatomical sites in the nominal dry state.

MATERIALS AND METHODS

Corneocytes were collected from five anatomical sites: forearm, cheek, neck, sacrum and medial heel of 10 healthy young participants. The surface topography was analysed using Atomic Force Microscopy (AFM) and Scanning Electron Microscopy (SEM). The level of positive-involucrin cornified envelopes (CEs) and desmoglein-1 (Dsg1) were used as indirect measures of immature CEs and corneodesmosomes, respectively. In addition, AFM nanoindentation and stress-relaxation experiments were performed to characterise the mechanical properties.

RESULTS

Volar forearm, neck and sacrum corneocytes presented similar topographies (ridges and valleys) and levels of Dsg1 (13-37%). In contrast, cheek cells exhibited circular nano-objects, while medial heel cells were characterized by villi-like structures. Additionally, medial heel samples also showed the greatest level of immature CEs (32-56%, p < 0.001) and Dsg1 (59-78%, p < 0.001). A large degree of inter-subject variability was found for the Young's moduli of the cells (0.19-2.03 GPa), which was correlated with the level of immature CEs at the cheek, neck and sacrum (p < 0.05).

CONCLUSION

It is concluded that a comprehensive study of the mechanical and maturation properties of corneocytes may be used to understand the barrier functions of the SC at different anatomical sites.

The Discovery and Function of Filaggrin

Keratohyalin granules were discovered in the mid-19th century in cells that terminally differentiate to form the outer, cornified layer of the epidermis. The first indications of the composition of these structures emerged in the 1960s from a histochemical stain for histidine, followed by radioautographic evidence of a high incidence of histidine incorporation into newly synthesized proteins in cells containing the granules. Research during the next three decades revealed the structure and function of a major protein in these granules, which was initially called the ‘histidine-rich protein’. Steinert and Dale named the protein ‘filaggrin’ in 1981 because of its ability to aggregate keratin intermediate filaments. The human gene for the precursor, ‘profilaggrin,’ was reported in 1991 to encode 10, 11 or 12 nearly identical repeats. Remarkably, the mouse and rat genes encode up to 20 repeats. The lifetime of filaggrin is the time required for keratinocytes in the granular layer to move into the inner cornified layer. During this transition, filaggrin facilitates the collapse of corneocytes into ‘building blocks’ that become an impermeable surface barrier. The subsequent degradation of filaggrin is as remarkable as its synthesis, and the end-products aid in maintaining moisture in the cornified layer. It was apparent that ichthyosis vulgaris and atopic dermatitis were associated with the absence of this protein. McLean’s team in 2006 identified the cause of these diseases by discovering loss-of-function mutations in the profilaggrin gene, which led to dysfunction of the surface barrier. This story illustrates the complexity in maintaining a healthy, functional epidermis.

Improving and evaluating the adhesion and stability of make-up by enhancing the affinity between skin/make-up layer

PURPOSE

upMake-up clumps, bumps and collapses are the three factors that determine how well make-up has been performed. The purpose of this study is to reduce the three factors mentioned above by using amphiphilic substances to increase the affinity between the skin and the make-up layer. In addition, it aims to evaluate the improvement of the make-up layer by developing an objective make-up layer evaluation method.

METHODS

Experiments were performed in an attempt to increase the affinity between the skin and the make-up layer by minimizing the difference in surface energy between the two. Multiple types of artificial skin (leather and bio-skin) were used and treated to form the liquid foundation layer. Qualitative evaluation of the make-up layer was conducted by analyzing the surface, cross-section, and fracture area of the make-up layer, using the evaluation method proposed in this study.

RESULTS

After applying this method and taking measurements by 3D surface analysis, the surface roughness of the make-up layer reduced by 46%, and the maximum thickness of the make-up layer reduced by about 50% in comparison with the control group (method not applied). In the case of the make-up layer to which this method was applied, two-dimensional cross-sectional Scanning Electron Microscope (SEM) image analysis confirmed that agglomeration was reduced, and the thickness of the make-up layer was also reduced by an average of 54%. According to this result, the technique of increasing the affinity between the skin and the make-up layer reduces the level of aggregation of make-up and encourages the formation of a uniform and thin make-up layer. Also, the fracture area after motion simulation was reduced by 33%. These results indicate that the method of increasing the affinity between skin/make-up membranes positively affects the formation of a uniform make-up layer.

CONCLUSION

Increasing the affinity by reducing the surface energy between the skin and the make-up layer plays an important role in forming a thin and uniform make-up layer by improving the problems of lifting, agglomeration, and collapse of the make-up. In addition, it has been confirmed that through this method, the quality of consumer experience related to make-up satisfaction can be improved. The results show that objective analyses of make-up help the understanding of the quality of consumer experience on make-up.

Atopic dermatitis: Role of the skin barrier, environment, microbiome, and therapeutic agents

Atopic dermatitis (AD) is a chronic, inflammatory skin disorder characterized by eczematous and pruritic skin lesions. In recent decades, the prevalence of AD has increased worldwide, most notably in developing countries. The enormous progress in our understanding of the complex composition and functions of the epidermal barrier allows for a deeper appreciation of the active role that the skin barrier plays in the initiation and maintenance of skin inflammation. The epidermis forms a physical, chemical, immunological, neuro-sensory, and microbial barrier between the internal and external environment. Not only lesional, but also non-lesional areas of AD skin display many morphological, biochemical and functional differences compared with healthy skin. Supporting this notion, genetic defects affecting structural proteins of the skin barrier, including filaggrin, contribute to an increased risk of AD. There is evidence to suggest that natural environmental allergens and man-made pollutants are associated with an increased likelihood of developing AD. A compromised epidermal barrier predisposes the skin to increased permeability of these compounds. Numerous topical and systemic therapies for AD are currently available or in development; while anti-inflammatory therapy is central to the treatment of AD, some existing and novel therapies also appear to exert beneficial effects on skin barrier function. Further research on the skin barrier, particularly addressing epidermal differentiation and inflammation, lipid metabolism, and the role of bacterial communities for skin barrier function, will likely expand our understanding of the complex etiology of AD and lead to identification of novel targets and the development of new therapies.

Staphylococcus aureus binds to the N-terminal region of corneodesmosin to adhere to the stratum corneum in atopic dermatitis

Staphylococcus aureus colonizes the skin of the majority of patients with atopic dermatitis (AD), and its presence increases disease severity. Adhesion of S. aureus to corneocytes in the stratum corneum is a key initial event in colonization, but the bacterial and host factors contributing to this process have not been defined. Here, we show that S. aureus interacts with the host protein corneodesmosin. Corneodesmosin is aberrantly displayed on the tips of villus-like projections that occur on the surface of AD corneocytes as a result of low levels of skin humectants known as natural moisturizing factor (NMF). An S. aureus mutant deficient in fibronectin binding protein B (FnBPB) and clumping factor B (ClfB) did not bind to corneodesmosin in vitro. Using surface plasmon resonance, we found that FnBPB and ClfB proteins bound with similar affinities. The S. aureus binding site was localized to the N-terminal glycine-serine-rich region of corneodesmosin. Atomic force microscopy showed that the N-terminal region was present on corneocytes containing low levels of NMF and that blocking it with an antibody inhibited binding of individual S. aureus cells to corneocytes. Finally, we found that S. aureus mutants deficient in FnBPB or ClfB have a reduced ability to adhere to low-NMF corneocytes from patients. In summary, we show that FnBPB and ClfB interact with the accessible N-terminal region of corneodesmosin on AD corneocytes, allowing S. aureus to take advantage of the aberrant display of corneodesmosin that accompanies low NMF in AD. This interaction facilitates the characteristic strong binding of S. aureus to AD corneocytes.

Patients with Atopic Dermatitis Colonized with Staphylococcus aureus Have a Distinct Phenotype and Endotype

Patients with atopic dermatitis (AD) are commonly colonized with Staphylococcus aureus (AD S. aureus⁺), but what differentiates this group from noncolonized AD patients (AD S. aureus^-) has not been well studied. To evaluate whether these two groups have unique phenotypic or endotypic features, we performed a multicenter, cross-sectional study enrolling AD S. aureus⁺ (n = 51) and AD S. aureus^- (n = 45) participants defined by the presence or absence of S. aureus by routine culture techniques and nonatopic, noncolonized control individuals (NA S. aureus^-) (n = 46). Filaggrin (FLG) genotypes were determined, and disease severity (Eczema Area and Severity Index, Rajka-Langeland Severity Score, Investigator's Global Assessment score, Numerical Rating Scale, and Dermatology Life Quality Index) was captured. Skin physiology was assessed (transepidermal water loss [TEWL], stratum corneum integrity, hydration, and pH), and serum biomarkers were also measured. We found that AD S. aureus⁺ patients had more severe disease based on all scoring systems except itch (Numerical Rating Scale), and they had higher levels of type 2 biomarkers (eosinophil count, tIgE, CCL17, and periostin). Additionally, AD S. aureus⁺ patients had significantly greater allergen sensitization (Phadiatop and tIgE), barrier dysfunction (TEWL and stratum corneum integrity), and serum lactate dehydrogenase (LDH) than both the AD S. aureus^- and NA S. aureus^- groups. FLG mutations did not associate with S. aureus⁺ colonization. In conclusion, adult patients with AD who are colonized on their skin with S. aureus have more severe disease, greater type 2 immune deviation, allergen sensitization, barrier disruption, and LDH level elevation than noncolonized patients with AD.

In a three-dimensional reconstructed human epidermis filaggrin-2 is essential for proper cornification

Atopic dermatitis is a chronic inflammatory skin disease with defects in the epidermal barrier. In a cohort of African-American children, a FLG2 nonsense mutation has been associated with the disease. In the epidermis of European patients, the expression of filaggrin-2, the filaggrin-related protein encoded by FLG2, is decreased. To describe the function of filaggrin-2 and evaluate the impact of its deficiency, its expression was downregulated using lentivirus-mediated shRNA interference in a three-dimensional reconstructed human epidermis (RHE) model. This resulted in parakeratosis and a compact stratum corneum, presence of abnormal vesicles inside the corneocytes, increased pH and reduced amounts of free amino acids at the RHE surface, leading to increased sensitivity to UVB radiations. The expression of differentiation markers was slightly modified. However, we observed reduced proteolytic processing of corneodesmosin, hornerin and filaggrin in parallel with reduced amounts of caspase-14 and bleomycin hydrolase. Our data demonstrated that filaggrin-2 is important for a proper cornification and a functional stratum corneum. Its downregulation in atopic patients may be involved in the disease-associated epidermis impairment.

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.

Retention of corneodesmosomes and increased expression of protease inhibitors in dandruff

BACKGROUND

Dandruff is a common, relapsing and uncomfortable scalp condition affecting a large proportion of the global population. The appearance of flakes on the scalp and in the hair line, and associated itch are thought to be consequences of a damaged skin barrier, altered corneocyte cohesion and abnormal desquamation in dandruff. The balance between skin proteases and protease inhibitors is essential for driving the key events, including corneodesmosome degradation, in the desquamation process and to maintain stratum corneum (SC) barrier integrity.

OBJECTIVES

To investigate the distribution of corneodesmosomes, the key component of the SC cohesivity and barrier function, and the protease inhibitors lympho-epithelial Kazal-type-related inhibitor (LEKTI-1) and squamous cell carcinoma antigen (SCCA1) in the scalp of dandruff-affected participants.

METHODS

The methods utilized were immunohistochemistry, scanning immunoelectron microscopy, phase-contrast microscopy, Western blotting and serine protease activity assay on tape-stripped SC or scalp skin biopsies.

RESULTS

In SC samples from healthy subjects, corneodesmosomes were peripherally located in the corneocytes. In samples of dandruff lesions, corneodesmosomes were located both peripherally and on the entire surface area of the corneocytes. LEKTI-1 and SCCA1 protein levels and parakeratosis were found to be highly elevated in the lesional samples.

CONCLUSIONS

The persistence of nonperipheral corneodesmosomes is a characteristic feature of the perturbed desquamation seen in dandruff. The increased expression levels of LEKTI-1 and SCCA1 are consistent with the view that the dandruff condition is characterized by an imbalance in protease-protease inhibitor interaction in the SC.

Skin barrier defects in atopic dermatitis

Atopic dermatitis (AD) is a chronic inflammatory skin condition with complex etiology that is dependent upon interactions between the host and the environment. Acute skin lesions exhibit the features of a Th2-driven inflammatory disorder, and many patients are highly atopic. The skin barrier plays key roles in immune surveillance and homeostasis, and in preventing penetration of microbial products and allergens. Defects that compromise the structural integrity or else the immune function of the skin barrier play a pivotal role in the pathogenesis of AD. This article provides an overview of the array of molecular building blocks that are essential to maintaining healthy skin. The basis for structural defects in the skin is discussed in relation to AD, with an emphasis on filaggrin and its genetic underpinnings. Aspects of innate immunity, including the role of antimicrobial peptides and proteases, are also discussed.