Cholesterol sulfate inhibits proteases that are involved in desquamation of stratum corneum

Revisiting the effect of cholesteryl sulfate on clotting and fibrinolysis: Inhibition of human thrombin and other human blood proteases

Cholesteryl sulfate (CS) was quantitatively synthesized by microwave-assisted sulfonation of cholesterol followed by sodium exchange chromatography. In vitro effects of CS on human thrombin and other serine proteases of the coagulation and fibrinolysis processes were investigated using a series of biochemical and biophysical techniques. CS was found to inhibit thrombin with an IC50 value of 140.8 ± 21.8 μM at pH 7.4 and 25 ○C. Michaelis-Menten kinetics indicated that thrombin inhibition by CS is non-competitive (allosteric) in nature. Fluorescence-based binding studies indicated that CS binds to thrombin with a KD value of 180.9 ± 18.9 μM. Given the lack of competition with heparins and a hirudin peptide in competitive inhibition assays, it appears that CS does not bind to thrombin's exosites 1 or 2 and it rather recognizes a different allosteric exosite. CS was found to partially inhibit thrombin-mediated fibrinogen activation with an IC50 value of 175.5 ± 17.5 μM and efficacy of ∼26.0 ± 6.6%. Likewise, CS selectively doubled the activated partial thromboplastin time with EC2x of 521 μM. Interestingly, CS was found to also inhibit factors Xa and XIa as well as plasmin with IC50 values of ∼85-250 μM and efficacy of 94-100%. Nevertheless, CS most potently inhibited factor XIIa with an IC50 Value of ∼17 μM and efficacy of 60%. Surprisingly, CS did not inhibit factor IXa. These results encourage further in vitro and in vivo investigation of CS to better understand its (patho-) physiological roles in coagulation and hemostasis.

Inherited ichthyosis as a paradigm of rare skin disorders: Genomic medicine, pathogenesis, and management

Great advances have been made in the field of heritable skin disorders using next-generation sequencing (NGS) technologies (ie, whole-genome sequencing, whole-exome sequencing, whole-transcriptome sequencing, and disease-targeted multigene panels). When NGS first became available, the cost and lack of access to these technologies were limiting factors; however, with decreasing sequencing costs and the expanding knowledge base of genetic skin diseases, fundamental awareness of NGS has become prudent. The heritable ichthyoses comprise a genotypically and phenotypically heterogeneous group of monogenic keratinization disorders characterized by persistent scaling, with at least 55 distinct genes currently implicated in causing nonsyndromic and syndromic forms of the disease. By providing a simplified overview of available NGS techniques and applying them in the context of ichthyosis, one of the most common genodermatoses, we hope to encourage dermatologists to offer, when appropriate, genetic testing earlier in patients with unsolved presentations. With the aid of NGS, dermatologists can provide diagnostic certainty in cases of suspected genodermatoses and offer potentially life-changing genome-guided and targeted therapies as they become available.

RNA sequencing and lipidomics uncovers novel pathomechanisms in recessive X-linked ichthyosis

Recessive X-linked ichthyosis (RXLI), a genetic disorder caused by deletion or point mutations of the steroid sulfatase (STS) gene, is the second most common form of ichthyosis. It is a disorder of keratinocyte cholesterol sulfate retention and the mechanism of extracutaneous phenotypes such as corneal opacities and attention deficit hyperactivity disorder are poorly understood. To understand the pathomechanisms of RXLI, the transcriptome of differentiated primary keratinocytes with STS knockdown was sequenced. The results were validated in a stable knockdown model of STS, to confirm STS specificity, and in RXLI skin. The results show that there was significantly reduced expression of genes related to epidermal differentiation and lipid metabolism, including ceramide and sphingolipid synthesis. In addition, there was significant downregulation of aldehyde dehydrogenase family members and the oxytocin receptor which have been linked to corneal transparency and behavioural disorders respectively, both of which are extracutaneous phenotypes of RXLI. These data provide a greater understanding of the causative mechanisms of RXLI's cutaneous phenotype, and show that the keratinocyte transcriptome and lipidomics can give novel insights into the phenotype of patients with RXLI.

Sulfotransferase 2B1b, Sterol Sulfonation, and Disease

The primary function of human sulfotransferase 2B1b (SULT2B1b) is to sulfonate cholesterol and closely related sterols. SULT2B1b sterols perform a number of essential cellular functions. Many are signaling molecules whose activities are redefined by sulfonation-allosteric properties are switched "on" or "off," agonists are transformed into antagonists, and vice versa. Sterol sulfonation is tightly coupled to cholesterol homeostasis, and sulfonation imbalances are causally linked to cholesterol-related diseases including certain cancers, Alzheimer disease, and recessive X-linked ichthyosis-an orphan skin disease. Numerous studies link SULT2B1b activity to disease-relevant molecular processes. Here, these multifaceted processes are integrated into metabolic maps that highlight their interdependence and how their actions are regulated and coordinated by SULT2B1b oxysterol sulfonation. The maps help explain why SULT2B1b inhibition arrests the growth of certain cancers and make the novel prediction that SULT2B1b inhibition will suppress production of amyloid β (Aβ) plaques and tau fibrils while simultaneously stimulating Aβ plaque phagocytosis. SULT2B1b harbors a sterol-selective allosteric site whose structure is discussed as a template for creating inhibitors to regulate SULT2B1b and its associated biology. SIGNIFICANCE STATEMENT: Human sulfotransferase 2B1b (SULT2B1b) produces sterol-sulfate signaling molecules that maintain the homeostasis of otherwise pro-disease processes in cancer, Alzheimer disease, and X-linked ichthyosis-an orphan skin disease. The functions of sterol sulfates in each disease are considered and codified into metabolic maps that explain the interdependencies of the sterol-regulated networks and their coordinate regulation by SULT2B1b. The structure of the SULT2B1b sterol-sensing allosteric site is discussed as a means of controlling sterol sulfate biology.

Congenital Ichthyosis: Clinical and Genetic Characteristics of the Disease

Congenital ichthyosis is a group (almost 100 clinical variants) of rare genetic skin diseases caused by pathogenic changes in more than 50 genes. Clinical features of ichthyosis, regardless of its genotype, are dry skin, peeling, hyperkeratosis frequently accompanied with erythroderma. These patients have extremely low quality of life due to changes in appearance, discomfort due to itching and functional limitations (pain during walking, impaired hands motor skills and functions due to hyperkeratosis foci in functionally relevant areas), as well as impaired functions of various organs and systems in syndromic forms of disease. Patients need daily skin care and systemic medications. By now, there is no definitive treatment for ichthyosis. Diagnostic difficulties in determining the clinical forms of congenital ichthyosis are associated with their clinical heterogeneity and with similarity in external manifestations. Difficulties in differential diagnosis with other dermatoses are particularly crucial in case of syndromic forms of disease. This review presents the modern classification of ichthyoses, provides data on disease clinical and genetic variants, diagnostic algorithms, treatment methods for patients with this severe disease.

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.

Mammalian Epidermis: A Compendium of Lipid Functionality

Mammalian epidermis is a striking example of the role of lipids in tissue biology. In this stratified epithelium, highly specialized structures are formed that leverage the hydrophobic properties of lipids to form an impermeable barrier and protect the humid internal environment of the body from the dry outside. This is achieved through tightly regulated lipid synthesis that generates the molecular species unique to the tissue. Beyond their fundamental structural role, lipids are involved in the active protection of the body from external insults. Lipid species present on the surface of the body possess antimicrobial activity and directly contribute to shaping the commensal microbiota. Lipids belonging to a variety of classes are also involved in the signaling events that modulate the immune responses to environmental stress as well as differentiation of the epidermal keratinocytes themselves. Recently, high-resolution methods are beginning to provide evidence for the involvement of newly identified specific lipid molecules in the regulation of epidermal homeostasis. In this review we give an overview of the wide range of biological functions of mammalian epidermal lipids.

Alterations of Ultra Long-Chain Fatty Acids in Hereditary Skin Diseases-Review Article

The skin is a flexible organ that forms a barrier between the environment and the body's interior; it is involved in the immune response, in protection and regulation, and is a dynamic environment in which skin lipids play an important role in maintaining homeostasis. The different layers of the skin differ in both the composition and amount of lipids. The epidermis displays the best characteristics in this respect. The main lipids in this layer are cholesterol, fatty acids (FAs) and ceramides. FAs can occur in free form and as components of complex molecules. The most poorly characterized FAs are very long-chain fatty acids (VLCFAs) and ultra long-chain fatty acids (ULCFAs). VLCFAs and ULCFAs are among the main components of ceramides and are part of the free fatty acid (FFA) fraction. They are most abundant in the brain, liver, kidneys, and skin. VLCFAs and ULCFAs are responsible for the rigidity and impermeability of membranes, forming the mechanically and chemically strong outer layer of cell membranes. Any changes in the composition and length of the carbon chains of FAs result in a change in their melting point and therefore a change in membrane permeability. One of the factors causing a decrease in the amount of VLCFAs and ULCFAs is an improper diet. Another much more important factor is mutations in the genes which code proteins involved in the metabolism of VLCFAs and ULCFAs—regarding their elongation, their attachment to ceramides and their transformation. These mutations have their clinical consequences in the form of inborn errors in metabolism and neurodegenerative disorders, among others. Some of them are accompanied by skin symptoms such as ichthyosis and ichthyosiform erythroderma. In the following review, the structure of the skin is briefly characterized and the most important lipid components of the skin are presented. The focus is also on providing an overview of selected proteins involved in the metabolism of VLCFAs and ULCFAs in the skin.

Roles of Lipids in the Permeability Barriers of Skin and Oral Mucosa

PubMed searches reveal much literature regarding lipids in barrier function of skin and less literature on lipids in barrier function of the oral mucosa. In terrestrial mammals, birds, and reptiles, the skin’s permeability barrier is provided by ceramides, fatty acids, and cholesterol in the outermost layers of the epidermis, the stratum corneum. This layer consists of about 10–20 layers of cornified cells embedded in a lipid matrix. It effectively prevents loss of water and electrolytes from the underlying tissue, and it limits the penetration of potentially harmful substances from the environment. In the oral cavity, the regions of the gingiva and hard palate are covered by keratinized epithelia that much resemble the epidermis. The oral stratum corneum contains a lipid mixture similar to that in the epidermal stratum corneum but in lower amounts and is accordingly more permeable. The superficial regions of the nonkeratinized oral epithelia also provide a permeability barrier. These epithelial regions do contain ceramides, cholesterol, and free fatty acids, which may underlie barrier function. The oral epithelial permeability barriers primarily protect the underlying tissue by preventing the penetration of potentially toxic substances, including microbial products. Transdermal drug delivery, buccal absorption, and lipid-related disease are discussed.

Glucosylated cholesterol in skin: Synthetic role of extracellular glucocerebrosidase

The existence of glucosylated cholesterol (GlcChol) in tissue has recently been recognized. GlcChol is generated from glucosylceramide (GlcCer) and cholesterol through transglucosylation by two retaining β-glucosidases, GBA and GBA2. Given the abundance of GBA, GlcCer and cholesterol in the skin's stratum corneum (SC), we studied the occurrence of GlcChol. A significant amount of GlcChol was detected in SC (6 pmol/mg weight). The ratio GlcChol/GlcCer is higher in SC than epidermis, 0.083 and 0.011, respectively. Examination of GlcChol in patients with Netherton syndrome revealed comparable levels (11 pmol/mg). Concluding, GlcChol was identified as a novel component in SC and is likely locally metabolized by GBA. The physiological function of GlcChol in the SC warrants future investigation.

Cholesterol and oxysterol sulfates: Pathophysiological roles and analytical challenges

Cholesterol and oxysterol sulfates are important regulators of lipid metabolism, inflammation, cell apoptosis, and cell survival. Among the sulfate-based lipids, cholesterol sulfate (CS) is the most studied lipid both quantitatively and functionally. Despite the importance, very few studies have analysed and linked the actions of oxysterol sulfates to their physiological and pathophysiological roles. Overexpression of sulfotransferases confirmed the formation of a range of oxysterol sulfates and their antagonistic effects on liver X receptors (LXRs) prompting further investigations how are the changes to oxysterol/oxysterol sulfate homeostasis can contribute to LXR activity in the physiological milieu. Here, we aim to bring together for novel roles of oxysterol sulfates, the available techniques and the challenges associated with their analysis. Understanding the oxysterol/oxysterol sulfate levels and their pathophysiological mechanisms could lead to new therapeutic targets for metabolic diseases. LINKED ARTICLES: This article is part of a themed issue on Oxysterols, Lifelong Health and Therapeutics. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v178.16/issuetoc.

Innate Antimicrobial Defense of Skin and Oral Mucosa

This special issue intends to review and update our understanding of the antimicrobial defense mechanisms of the skin and oral cavity. These two environments are quite different in terms of water, pH, and nutrient availability, but have some common antimicrobial factors. The skin surface supports the growth of a limited range of microorganisms but provides a hostile environment for others. The growth of most microorganisms is prevented or limited by the low pH, scarcity of some nutrients such as phosphorus and the presence of antimicrobial peptides, including defensins and cathelicidins, and antimicrobial lipids, including certain fatty acids and long-chain bases. On the other hand, the oral cavity is a warm, moist, nutrient rich environment which supports the growth of diverse microflora. Saliva coating the oral soft and hard surfaces determines which microorganisms can adhere to these surfaces. Some salivary proteins bind to bacteria and prevent their attachment to surfaces. Other salivary peptides, including defensins, cathelicidins, and histatins are antimicrobial. Antimicrobial salivary proteins include lysozyme, lactoferrin, and lactoperoxidase. There are also antimicrobial fatty acids derived from salivary triglycerides and long-chain bases derived from oral epithelial sphingolipids. The various antimicrobial factors determine the microbiomes of the skin surface and the oral cavity. Alterations of these factors can result in colonization by opportunistic pathogens, and this may lead to infection. Neutrophils and lymphocytes in the connective tissue of skin and mucosa also contribute to innate immunity.

Glucocerebrosidase: Functions in and Beyond the Lysosome

Glucocerebrosidase (GCase) is a retaining β-glucosidase with acid pH optimum metabolizing the glycosphingolipid glucosylceramide (GlcCer) to ceramide and glucose. Inherited deficiency of GCase causes the lysosomal storage disorder named Gaucher disease (GD). In GCase-deficient GD patients the accumulation of GlcCer in lysosomes of tissue macrophages is prominent. Based on the above, the key function of GCase as lysosomal hydrolase is well recognized, however it has become apparent that GCase fulfills in the human body at least one other key function beyond lysosomes. Crucially, GCase generates ceramides from GlcCer molecules in the outer part of the skin, a process essential for optimal skin barrier property and survival. This review covers the functions of GCase in and beyond lysosomes and also pays attention to the increasing insight in hitherto unexpected catalytic versatility of the enzyme.

Halting hyaluronidase activity with hyaluronan-based nanohydrogels: development of versatile injectable formulations

Hyaluronan (HA) is among the most used biopolymers for viscosupplementation and dermocosmetics. However, the current injectable HA-based formulations present relevant limitations: I) unmodified HA is quickly degraded by endogenous hyaluronidases (HAase), resulting in short lasting properties; II) cross-linked HA, although shows enhanced stability against HAase, often contains toxic chemical cross-linkers. As such, herein, we present biocompatible self-assembled hyaluronan-cholesterol nanohydrogels (HA-CH NHs) able to bind to HAase and inhibit the enzyme activity in vitro, more efficiently than currently marketed HA-based cross-linked formulations (e.g. Jonexa™). HA-CH NHs inhibit HAase through a mixed mechanism, by which NHs bind to HAase with an affinity constant 7-fold higher than that of native HA. Similar NHs, based on gellan-CH, evidenced no binding to HAase, neither inhibition of the enzyme activity, suggesting this effect might be due to the specific binding of HA-CH to the active site of the enzyme. Therefore, HA-CH NHs were engineered into injectable hybrid HA mixtures or physical hydrogels, able to halt the enzymatic degradation of HA.

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.

In vivo confocal Raman spectroscopy and molecular dynamics analysis of penetration of retinyl acetate into stratum corneum

OBJECTIVE

The purpose of this study is to elucidate the behavior of retinyl acetate in penetrating human skin without the presence of enhancers by using confocal Raman spectroscopy and molecular dynamics simulation.

METHODS

In this study, in vivo confocal Raman spectroscopy was combined with molecular dynamics simulation to investigate the transdermal permeation of the aqueous suspension of retinyl acetate.

RESULTS

Permeation was measured after 30min, and retinyl acetate was found up to 20μm deep inside the stratum corneum. The delivery of retinyl acetate inside a skin membrane model was studied by molecular dynamics. The membrane model that was used represented normal young skin containing a lipid bilayer with 25% ceramide, 36% fatty acid, 30% cholesterol, and 6% cholesterol sulfate.

CONCLUSION

Spectroscopy data indicate that retinyl acetate permeates into the stratum corneum. Molecular dynamics data showed that retinyl acetate permeates in the membrane model and that their final location is deep inside the lipid bilayer. We showed, for the first time, a correlation between Raman permeation data and computational data.

Selective Substrates and Inhibitors for Kallikrein-Related Peptidase 7 (KLK7) Shed Light on KLK Proteolytic Activity in the Stratum Corneum

Proteases have pivotal roles in the skin's outermost layer, the epidermis. In the stratum corneum, serine proteases from the kallikrein-related peptidase (KLK) family have been implicated in several key homeostatic processes, including desquamation. However, the precise contribution of specific KLKs to each process remains unclear. To address this, we used a chemical biology approach and designed selective substrates and inhibitors for KLK7, the most abundant KLK protease in the stratum corneum. The resulting KLK7 inhibitor is the most potent inhibitor of this protease reported to date (K_i = 140 pM), and displays at least 1,000-fold selectivity over several proteases that are related by function (KLK5 and KLK14) or specificity (chymotrypsin). We then used substrates and inhibitors for KLK5, KLK7, and KLK14 to explore the activity of each protease in the stratum corneum using casein zymography and an ex vivo desquamation assay. These experiments provide the most detailed assessment of each KLK's contribution to corneocyte shedding in the plantar stratum corneum, revealing that inhibition of KLK7 alone is sufficient to block shedding, whereas KLK5 is also a major contributor. Collectively, these findings unveil chemical tools for studying KLK activity and demonstrate their potential for characterizing KLK biological functions in epidermal homeostasis.

Changing in lipid profile induced by the mutation of Foxn1 gene: A lipidomic analysis of Nude mice skin

Nude mice carry a spontaneous mutation affecting the gene Foxn1 mainly expressed in the epidermis. This gene is involved in several skin functions, especially in the proliferation and the differentiation of keratinocytes which are key cells of epithelial barrier. The skin, a protective barrier for the body, is essentially composed of lipids. Taking into account these factors, we conducted a lipidomic study to search for any changes in lipid composition of skin possibly related to Foxn1 mutation. Lipids were extracted from skin biopsies of Nude and BALB/c mice to be analyzed by liquid chromatography coupled to a high resolution mass spectrometer (HRMS). Multivariate and univariate data analyses were carried out to compare lipid extracts. Identification was performed using HRMS data, retention time and mass spectrometry fragmentation study. These results indicate that mutation of Foxn1 leads to significant modifications in the lipidome in Nude mice skin. An increase in cholesterol sulfate, phospholipids, sphingolipids and fatty acids associated with a decrease in glycerolipids suggest that the lipidome in mice skin is regulated by the Foxn1 gene.

MALDI-MS imaging for the study of tissue pharmacodynamics and toxicodynamics

Pharmacodynamics and toxicodynamics are the study of the biochemical and physiological effects of therapeutic agents and toxicants and their mechanisms of action. MALDI-MS imaging offers great potential for the study of pharmaco/toxicodynamic responses in tissue owing is its ability to study multiple biomarkers simultaneously in a label-free manner. Here, existing examples of such studies examining anticancer drugs and topically applied treatments are described. Examination of the literature shows that the use of MS imaging in pharmaco/toxicodynamic studies is in fact quite low. The reasons for this are discussed and potential developments in the methodology that might lead to its further use are described.

Transcriptome Profiling and Molecular Pathway Analysis of Genes in Association with Salinity Adaptation in Nile Tilapia Oreochromis niloticus

Nile tilapia Oreochromis niloticus is a freshwater fish but can tolerate a wide range of salinities. The mechanism of salinity adaptation at the molecular level was studied using RNA-Seq to explore the molecular pathways in fish exposed to 0, 8, or 16 (practical salinity unit, psu). Based on the change of gene expressions, the differential genes unions from freshwater to saline water were classified into three categories. In the constant change category (1), steroid biosynthesis, steroid hormone biosynthesis, fat digestion and absorption, complement and coagulation cascades were significantly affected by salinity indicating the pivotal roles of sterol-related pathways in response to salinity stress. In the change-then-stable category (2), ribosomes, oxidative phosphorylation, signaling pathways for peroxisome proliferator activated receptors, and fat digestion and absorption changed significantly with increasing salinity, showing sensitivity to salinity variation in the environment and a responding threshold to salinity change. In the stable-then-change category (3), protein export, protein processing in endoplasmic reticulum, tight junction, thyroid hormone synthesis, antigen processing and presentation, glycolysis/gluconeogenesis and glycosaminoglycan biosynthesis—keratan sulfate were the significantly changed pathways, suggesting that these pathways were less sensitive to salinity variation. This study reveals fundamental mechanism of the molecular response to salinity adaptation in O. niloticus, and provides a general guidance to understand saline acclimation in O. niloticus.

Lipid changes within the epidermis of living skin equivalents observed across a time-course by MALDI-MS imaging and profiling

Background

Mass spectrometry imaging (MSI) is a powerful tool for the study of intact tissue sections. Here, its application to the study of the distribution of lipids in sections of reconstructed living skin equivalents during their development and maturation is described.

Methods

Living skin equivalent (LSE) samples were obtained at 14 days development, re-suspended in maintenance medium and incubated for 24 h after delivery. The medium was then changed, the LSE re-incubated and samples taken at 4, 6 and 24 h time points. Mass spectra and mass spectral images were recorded from 12 μm sections of the LSE taken at each time point for comparison using matrix assisted laser desorption ionisation mass spectrometry.

Results

A large number of lipid species were identified in the LSE via accurate mass-measurement MS and MSMS experiments carried out directly on the tissue sections. MS images acquired at a spatial resolution of 50 μm × 50 μm showed the distribution of identified lipids within the developing LSE and changes in their distribution with time. In particular development of an epidermal layer was observable as a compaction of the distribution of phosphatidylcholine species.

Conclusions

MSI can be used to study changes in lipid composition in LSE. Determination of the changes in lipid distribution during the maturation of the LSE will assist in the identification of treatment responses in future investigations.

Electronic supplementary material

The online version of this article (doi:10.1186/s12944-015-0089-z) contains supplementary material, which is available to authorized users.

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.

Role of cholesterol sulfate in epidermal structure and function: lessons from X-linked ichthyosis

X-linked ichthyosis is a relatively common syndromic form of ichthyosis most often due to deletions in the gene encoding the microsomal enzyme, steroid sulfatase, located on the short area of the X chromosome. Syndromic features are mild or unapparent unless contiguous genes are affected. In normal epidermis, cholesterol sulfate is generated by cholesterol sulfotransferase (SULT2B1b), but desulfated in the outer epidermis, together forming a 'cholesterol sulfate cycle' that potently regulates epidermal differentiation, barrier function and desquamation. In XLI, cholesterol sulfate levels my exceed 10% of total lipid mass (≈1% of total weight). Multiple cellular and biochemical processes contribute to the pathogenesis of the barrier abnormality and scaling phenotype in XLI. This article is part of a Special Issue entitled The Important Role of Lipids in the Epidermis and their Role in the Formation and Maintenance of the Cutaneous Barrier. Guest Editors: Kenneth R. Feingold and Peter Elias.

Cholesterol sulfate as a potential inhibitor of hepatitis C virus NS3 helicase

Hepatitis C virus nonstructural protein 3 (NS3) helicase is a promising target for developing new therapeutics. In this study, we identified cholesterol sulfate (CS) as a novel NS3 helicase inhibitor (IC50 = 1.7 ± 0.2 µM with a Hill coefficient of 3.9) by screening the extracts from marine organisms. The lack of the sulfate group, sterol structure or alkyl side chain of CS diminished the inhibition, suggesting that an anion binding and hydrophobic region in NS3 may be a target site of CS. It was further found that CS partly inhibits NS3-RNA binding activity, but exerted no or less inhibition against ATPase and serine protease activities. Moreover, we demonstrated that CS probably does not bind to RNA. Our findings suggest that CS may inhibit NS3 helicase not by abolishing the other NS3 activities but by inducing conformational changes via interaction with possible allosteric sites of NS3.

Abnormal barrier function in the pathogenesis of ichthyosis: therapeutic implications for lipid metabolic disorders

Ichthyoses, including inherited disorders of lipid metabolism, display a permeability barrier abnormality in which the severity of the clinical phenotype parallels the prominence of the barrier defect. The pathogenesis of the cutaneous phenotype represents the consequences of the mutation for epidermal function, coupled with a "best attempt" by affected epidermis to generate a competent barrier in a terrestrial environment. A compromised barrier in normal epidermis triggers a vigorous set of metabolic responses that rapidly normalizes function, but ichthyotic epidermis, which is inherently compromised, only partially succeeds in this effort. Unraveling mechanisms that account for barrier dysfunction in the ichthyoses has identified multiple, subcellular, and biochemical processes that contribute to the clinical phenotype. Current treatment of the ichthyoses remains largely symptomatic: directed toward reducing scale or corrective gene therapy. Reducing scale is often minimally effective. Gene therapy is impeded by multiple pitfalls, including difficulties in transcutaneous drug delivery, high costs, and discomfort of injections. We have begun to use information about disease pathogenesis to identify novel, pathogenesis-based therapeutic strategies for the ichthyoses. The clinical phenotype often reflects not only a deficiency of pathway end product due to reduced-function mutations in key synthetic enzymes but often also accumulation of proximal, potentially toxic metabolites. As a result, depending upon the identified pathomechanism(s) for each disorder, the accompanying ichthyosis can be treated by topical provision of pathway product (eg, cholesterol), with or without a proximal enzyme inhibitor (eg, simvastatin), to block metabolite production. Among the disorders of distal cholesterol metabolism, the cutaneous phenotype in Congenital Hemidysplasia with Ichthyosiform Erythroderma and Limb Defects (CHILD syndrome) and X-linked ichthyosis reflect metabolite accumulation and deficiency of pathway product (ie, cholesterol). We validated this therapeutic approach in two CHILD syndrome patients who failed to improve with topical cholesterol alone, but cleared with dual treatment with cholesterol plus lovastatin. In theory, the ichthyoses in other inherited lipid metabolic disorders could be treated analogously. This pathogenesis (pathway)-driven approach possesses several inherent advantages: (1) it is mechanism-specific for each disorder; (2) it is inherently safe, because natural lipids and/or approved drugs often are utilized; and (3) it should be inexpensive, and therefore it could be used widely in the developing world.

Tight junctions in the stratum corneum explain spatial differences in corneodesmosome degradation

To maintain stratum corneum integrity while simultaneously desquamating at a steady rate, degradation of corneodesmosomes must proceed in a controlled manner. It is unknown why corneodesmosomes are present only at the cell periphery in the upper stratum corneum. To explore this, we studied distributions of three major corneodesmosomal components, corneodesmosin, desmoglein 1 and desmocollin 1 in normal adult human epidermis. Immunofluorescent microscopy studies of skin surface corneocytes detected all three components only at the cell edges. Immunoelectron microscopy revealed selective loss of these components at the central areas starting from the deep cornified layers. We hypothesized that tight junctions (TJs) formed in the superficial granular layer may prevent protease access by functioning as a barrier between the peripheral and the central intercellular spaces in the stratum corneum. Ultrastructural examination demonstrated TJs up to the junctions between the seventh and the eighth deepest cornified layers. Immunoelectron microscopy also detected clusters of occludin and claudin-1 immunolabels at the cell periphery, and kallikrein 7 immunolabels outside of TJs in the lower cornified layers. With colloidal lanthanum nitrate perfusion assay of stripped stratum corneum, the tracer was excluded from TJ domains. Taken together, we propose that TJs inhibit access of proteases to the peripheral corneodesmosomes forming the structural basis for the basket-weave-like appearance of the stratum corneum.

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.

Cellular and molecular mechanisms in atopic dermatitis

Atopic dermatitis (AD) is a pruritic inflammatory skin disease associated with a personal or family history of allergy. The prevalence of AD is on the rise and estimated at approximately 17% in the USA. The fundamental lesion in AD is a defective skin barrier that results in dry itchy skin, and is aggravated by mechanical injury inflicted by scratching. This allows entry of antigens via the skin and creates a milieu that shapes the immune response to these antigens. This review discusses recent advances in our understanding of the abnormal skin barrier in AD, namely abnormalities in epidermal structural proteins, such as filaggrin, mutated in approximately 15% of patients with AD, epidermal lipids, and epidermal proteases and protease inhibitors. The review also dissects, based on information from mouse models of AD, the contributions of the innate and adaptive immune system to the pathogenesis of AD, including the effect of mechanical skin injury on the polarization of skin dendritic cells, mediated by keratinocyte-derived cytokines such as thymic stromal lymphopoietin (TSLP), IL-6, and IL-1, that results in a Th2-dominated immune response with a Th17 component in acute AD skin lesions and the progressive conversion to a Th1-dominated response in chronic AD skin lesions. Finally, we discuss the mechanisms of susceptibility of AD skin lesions to microbial infections and the role of microbial products in exacerbating skin inflammation in AD. Based on this information, we discuss current and future therapy of this common disease.

Cornification defect in the golden retriever: clinical, histopathological, ultrastructural and genetic characterisation

Veterinarians have recognised a nonpruritic skin disease in the Golden retriever breed characterised by excessive scaling of large, variably pigmented flakes of skin in otherwise healthy dogs. This prospective case series describes clinical, histopathological, ultrastructural and genetic features of this cornification defect in 17 affected dogs. The condition affects young dogs of either sex and is characterised by symmetrical, predominantly ventro-lateral scaling and hyperpigmentation of the trunk. Histopathological and ultrastructural changes of the stratum corneum are suggestive of delayed degradation of corneodesmosomes. A genetic aetiology is proposed and a single-trait autosomal recessive mode of inheritance discussed.

A keratinocyte's course of life

An adequate permeability barrier function of the mammalian epidermis is guaranteed by the characteristic architecture of the stratum corneum. This uppermost layer consists of a highly organized extracellular lipid compartment which is tightly joined to the corneocytes. The generation of the extracellular lipid compartment and the transformation of the keratinocytes into corneocytes are the main features of epidermal differentiation. However, equally important is the continuous renewal of the stratum corneum, which is insured by a careful balance between the replenishment of new keratinocytes from the proliferating basal layer, and the well-orchestrated loss of the most superficial cells after the so-called 'epidermal programmed cell death'. In this overview, the complete life of keratinocytes is described, from the proliferative organization to the process of desquamation.

Graded delamination behavior of human stratum corneum

An in vitro adhesion test method has been adapted to quantify the through-thickness intercellular delamination energy of isolated human stratum corneum (SC). Both untreated and delipidized tissues were tested. Measured delamination energies were found to increase from approximately 3 J/m(2) near the surface to approximately 15 J/m(2) for the inner layers of the tissue. For delipidized SC, the location of the initial debond was located closer to the center of the tissue. Delamination energy values were elevated compared to untreated specimens, increasing from approximately 7 J/m(2) near the surface to approximately 18 J/m(2) for the inner layers of the SC. Further tests were run to measure delamination energies of SC as a function of hydration (15-100% relative humidity (RH)) at approximately 25 degrees C and as a function of temperature (10-90 degrees C) at several hydrations (15, 45, 100% RH). Delamination energies were observed to decrease with increasing hydration and increasing temperature with the most significant changes occurring for 100% RH conditioned SC. Additional SC was treated with pH-buffered solutions (pH 4.2, 6.7, 9.9) and selected surfactant solutions (1%, 10% wt/wt sodium dodecyl sulfate (SDS)) for comparison to untreated controls. While statistically significant differences were observed, the SC was found to be resistant to large changes in delamination energy with pH and 1% wt/wt SDS treatments with values in the range 4.2-5.1J/m(2) compared to control values of 4.4 J/m(2). More substantially elevated values were observed for SC treated with a 10%wt/wt SDS solution (6.6J/m(2)) and a chloroform-methanol extraction (11.2J/m(2)).

Acceleration of de novo Cholesterol Synthesis in the Epidermis Influences Desquamation of the Stratum Corneum in Aged Mice

Cholesterol, a component of intercellular lipids, is important for stratum corneum (SC) homeostasis, including its barrier function and desquamation. However, cholesterologenesis in the epidermis decreases under basal conditions with aging. We found that the number of horny layers in murine SC increased with the decrease of desquamation in the outermost corneocytes associated with aging. The cholesterol content decreased and the cholesterol sulfate content increased in the horny layer with aging, which resulted in an increase in the ratio of cholesterol sulfate to cholesterol. Moreover, we investigated the effects of accelerated cholesterologenesis on desquamation in aged murine skin following topical application of mevalonic acid. The ratio of cholesterol sulfate to cholesterol in aged murine SC significantly decreased following topical treatment with mevalonic acid, which resulted from an increase in cholesterol content via the acceleration of cholesterologenesis. Treatment with mevalonic acid also significantly reduced the number of cell layers in the SC along with the acceleration of desquamation, as measured by desmoglein I content, corneocyte surface area and proteinase activity. These results indicate that an improvement in the ratio of cholesterol sulfate to cholesterol content by de novo cholesterologenesis may be important for desquamation of the SC in aged epidermis.

The skin barrier in healthy and diseased state

The primary function of the skin is to protect the body for unwanted influences from the environment. The main barrier of the skin is located in the outermost layer of the skin, the stratum corneum. The stratum corneum consists of corneocytes surrounded by lipid regions. As most drugs applied onto the skin permeate along the lipid domains, the lipid organization is considered to be very important for the skin barrier function. It is for this reason that the lipid organization has been investigated quite extensively. Due to the exceptional stratum corneum lipid composition, with long chain ceramides, free fatty acids and cholesterol as main lipid classes, the lipid organization is different from that of other biological membranes. In stratum corneum, two lamellar phases are present with repeat distances of approximately 6 and 13 nm. Moreover the lipids in the lamellar phases form predominantly crystalline lateral phases, but most probably a subpopulation of lipids forms a liquid phase. Diseased skin is often characterized by a reduced barrier function and an altered lipid composition and organization. In order to understand the aberrant lipid organization in diseased skin, information on the relation between lipid composition and organization is crucial. However, due to its complexity and inter-individual variability, the use of native stratum corneum does not allow detailed systematic studies. To circumvent this problem, mixtures prepared with stratum corneum lipids can be used. In this paper first the lipid organization in stratum corneum of normal and diseased skin is described. Then the role the various lipid classes play in stratum corneum lipid organization and barrier function has been discussed. Finally, the information on the role various lipid classes play in lipid phase behavior has been used to interpret the changes in lipid organization and barrier properties of diseased skin.

Cholesterol and its anionic derivatives inhibit 5-lipoxygenase activation in polymorphonuclear leukocytes and MonoMac6 cells

5-Lipoxygenase (5-LO) is the key enzyme in the biosynthesis of leukotrienes (LTs), biological mediators of host defense reactions and of inflammatory diseases. While the role of membrane binding in the regulation of 5-LO activity is well established, the effects of lipids on cellular activity when added to the medium has not been characterized. Here, we show such a novel function of the most abundant sulfated sterol in human blood, cholesterol sulfate (CS), to suppress LT production in human polymorphonuclear leukocytes (PMNL) and Mono Mac6 cells. We synthesized another anionic lipid, cholesterol phosphate, which demonstrated a similar capacity in suppression of LT synthesis in PMNL. Cholesteryl acetate was without effect. Cholesterol increased the effect of CS on 5-LO product synthesis. CS and cholesterol also inhibited arachidonic acid (AA) release from PMNL. Addition of exogenous AA increased the threshold concentration of CS required to inhibit LT synthesis. The effect of cholesterol and its anionic derivatives can arise from remodeling of the cell membrane, which interferes with 5-LO activation. The fact that cellular LT production is regulated by sulfated cholesterol highlights a possible regulatory role of sulfotransferases/sulfatases in 5-LO product synthesis.

Interactions among stratum corneum defensive functions

With the exception of vitamin D production, virtually all epidermal functions can be considered as protective, or more specifically, as defensive in nature. Yet, the term "barrier function" of the stratum corneum (SC) is often used synonymously with only one such defensive function, although arguably its most important, i.e., permeability barrier homeostasis. Regardless of their hierarchy of relative importance, these critical protective functions largely reside in the SC. In this short review, we explore the ways in which the multiple defensive functions of the SC are linked and interrelated, either by their shared localization or by common biochemical processes.

Epidermal desquamation

Epidermal desquamation, a continuous but insensible bodily activity, is largely ignored unless the rate or amount of scale production becomes abnormal. It is the last topic to be considered in any serious discussion of epidermal growth and differentiation, but is becoming an increasingly fertile ground for investigation. This review summarizes: (a) methods for measuring desquamation; (b) variables that affect normal desquamation; (c) mechanisms of desquamation; (d) the role of desquamation in nutritional homeostasis; and (e) the role of desquamation as a first line of defense. Consideration is given to whether desquamation might be harnessed to eliminate or remediate toxins that have accumulated in the body.

Expression of cholesterol sulfotransferase (SULT2B1b) in human skin and primary cultures of human epidermal keratinocytes

Cholesterol sulfate is a highly amphipathic molecule that is present in a relatively high concentration in the epidermis of human skin, particularly in the granular layer. The physiologic significance of this finding, however, is not well-understood. Therefore, we examined expression of the gene encoding for the enzyme that sulfonates cholesterol (SULT2B1b). Of the three enzymes known to sulfonate steroids/sterols, only the SULT2B1b isozyme was detected in cultures of normal human epidermal keratinocytes (NHEK) in response to Ca(2+)-induced terminal differentiation as well as by normal human epidermal tissue. Immunocytochemical analysis of normal skin as well as specific skin disorders was carried out. In normal skin, the expression of SULT2B1b was localized to the granular layer of the epidermis similar to that of filaggrin, an acknowledged late marker of differentiation and in contrast to that of involucrin, an early marker of terminal differentiation, which was expressed throughout the suprabasal region. The confinement of SULT2B1b to the granular layer coincides with this being the area with the highest cholesterol sulfate content suggesting that the physiologic action of cholesterol sulfate is likely carried out in this region of the living epidermis. Additionally, 88% of cholesterol sulfate in NHEK was membrane-associated further suggesting a cellular location for cholesterol sulfate action.