The human skin organ culture model as an optimal complementary tool for murine pemphigus models

Pemphigus is a severe autoimmune bullous disease of the skin and/or mucous membranes caused by autoantibodies that mainly target the adhesion proteins desmoglein (Dsg) 3 and/or Dsg1. Clinically, pemphigus is characterized by flaccid blistering, leading to severe water and electrolyte loss. Before the introduction of corticosteroid treatment, the disease turned out to be fatal in many cases. Despite recent therapeutic improvements, treatment of pemphigus patients is centred on prolonged systemic immunosuppression and remains challenging. Current drug development for pemphigus has a strong focus on disease-causing B cells and autoantibodies and, more recently, also on modulating autoantibody-induced tissue pathology and keratinocyte signalling. This drug development requires reliable pre-clinical model systems replicating the pathogenesis of the human disease. Among those are neonatal and adult mouse models based on the transfer of Dsg3, Dsg1/3 or Dsg1-specific autoantibodies. To reduce the number of animal experiments, we recently established a standardized human skin organ culture (HSOC) model for pemphigus. This model reproduces the clinical phenotype of autoantibody-induced tissue pathology in pemphigus vulgaris. For induction of blistering, a recombinant single-chain variable fragment (scFv) targeting both Dsg1 and 3 is injected into pieces of human skin (obtained from plastic surgeries). Further characterization of the HSOC model demonstrated that key morphologic, molecular and immunologic features of pemphigus are being replicated. Thus, the pemphigus HSOC model is an excellent alternative to pemphigus animal model systems that are based on the transfer of (auto)antibodies.

A comprehensive analysis of mRNA expression profiles of Esophageal Squamous Cell Carcinoma reveals downregulation of Desmoglein 1 and crucial genomic targets

AIM

Esophageal Squamous Cell Carcinoma (ESCC) is a histological subtype of esophageal cancer that begins in the squamous cells in the esophagus. In only 19% of the ESCC-diagnosed patients, a five-year survival rate has been seen. This necessitates the identification of high-confidence biomarkers for early diagnosis, prognosis, and potential therapeutic targets for the mitigation of ESCC.

METHOD

We performed a meta-analysis of 10 mRNA datasets and identified consistently perturbed genes across the studies. Then, integrated with ESCC ATLAS to segregate 'core' genes to identify consequences of primary gene perturbation events leading to gene-gene interactions and dysregulated molecular signaling pathways. Further, by integrating with toxicogenomics data, inferences were drawn for gene interaction with environmental exposures, trace elements, chemical carcinogens, and drug chemicals. We also deduce the clinical outcomes of candidate genes based on survival analysis using the ESCC related dataset in The Cancer Genome Atlas.

RESULT

We identified 237 known and 18 novel perturbed candidate genes. Desmoglein 1 (DSG1) is one such gene that we found significantly downregulated (Fold Change =-1.89, p-value = 8.2e-06) in ESCC across six different datasets. Further, we identified 31 'core' genes (that either harbor genetic variants or are regulated by epigenetic modifications) and found regulating key biological pathways via adjoining genes in gene-gene interaction networks. Functional enrichment analysis showed dysregulated biological processes and pathways including "Extracellular matrix", "Collagen trimmer" and "HPV infection" are significantly overrepresented in our candidate genes. Based on the toxicogenomic inferences from Comparative Toxicogenomics Database we report the key genes that interacted with risk factors such as tobacco smoking, zinc, nitroso benzylmethylamine, and drug chemicals such as cisplatin, Fluorouracil, and Mitomycin in relation to ESCC. We also point to the STC2 gene that shows a high risk for mortality in ESCC patients.

CONCLUSION

We identified novel perturbed genes in relation to ESCC and explored their interaction network. DSG1 is one such gene, its association with microbiota and a clinical presentation seen commonly with ESCC hints that it is a good candidate for early diagnostic marker. Besides, in this study we highlight candidate genes and their molecular connections to risk factors, biological pathways, drug chemicals, and the survival probability of ESCC patients.

Epidermal stratification requires retromer-mediated desmoglein-1 recycling

Sorting transmembrane cargo is essential for tissue development and homeostasis. However, mechanisms of intracellular trafficking in stratified epidermis are poorly understood. Here, we identify an interaction between the retromer endosomal trafficking component, VPS35, and the desmosomal cadherin, desmoglein-1 (Dsg1). Dsg1 is specifically expressed in stratified epidermis and, when properly localized on the plasma membrane of basal keratinocytes, promotes stratification. We show that the retromer drives Dsg1 recycling from the endo-lysosomal system to the plasma membrane to support human keratinocyte stratification. The retromer-enhancing chaperone, R55, promotes the membrane localization of Dsg1 and a trafficking-deficient mutant associated with a severe inflammatory skin disorder, enhancing its ability to promote stratification. In the absence of Dsg1, retromer association with and expression of the glucose transporter GLUT1 increases, exposing a potential link between Dsg1 deficiency and epidermal metabolism. Our work provides evidence for retromer function in epidermal regeneration, identifying it as a potential therapeutic target.

Desmogleins 1, 3, and E-cadherin immunohistochemical expression within mucocutaneous pemphigus vulgaris

Introduction

pemphigus vulgaris (PV) is an autoimmune condition characterized by the loss of adhesion between the epithelial cells and blister formation. The production of autoantibodies against desmosomal proteins, namely, desmoglein (DSG) 1 and DSG3, is considered a main event of PV. A full understanding of the role of adhesion molecules in the pathogenesis of PV is not fully elucidated yet. This study aimed to evaluate and correlate the immunohistochemical expression of E-cadherin (E-cad), DSG1, and DSG3 proteins in oral and skin PV.

Methods

this study was a retrospective analysis study. Positive PV cases were stained with anti-E-cad, anti-DSG1, and anti-DSG3 antibodies. The expression of each marker was determined by two pathologists according to an established scoring system: (E-cad: negative, weak, moderate, and strong), (DSG1: negative, weak, and strong), and (DSG3: negative and positive). The Chi-square and Pearson´s correlation tests were used to statistically analyze the data.

Results

forty-three biopsies (26 skin and 17 oral tissue samples) from 22 males and 21 female PV patients were included. The median age was 40.50 years. In total, the immunohistochemical expression was negative for DSG3, E-cad, and DSG1 in 81.4%, 18.5%, and 16.4%, respectively. DSG1 expression was significantly higher in males than females. A statistically significant correlation was found between E-cad and DSG3 expressions.

Conclusion

a significant difference in the expression of markers of both oral and skin PV was absent. Downregulation of DSG3 expression was the hallmark feature that also showed a positive correlation with E-cad expression.

Inhibition of desmoglein-1 by aspirin leads to synthetic lethality of keratinocytes in Shuanghuanglian-induced cutaneous eruption response

Cutaneous eruptions caused by the combination of Chinese and Western medicine have attracted widespread attention; however, the underlying mechanism remains unclear. This study aimed to evaluate the potential mechanism of cutaneous eruptions in vivo and in vitro using the combination of Shuanghuanglian injection powder (SHL) and aspirin (ASA) as an example. ASA and SHL co-administration induced inflammatory responses in HaCat cells, as evidenced by marked increases in the expression of IL-4 and TNF-α, and the level of apoptosis. Additionally, histopathological investigation of mice skin tissues showed local inflammatory cell infiltration. Western boltting was used to detect the effects of ASA on desmoglein-1 (DSG1) expression; we found that DSG1 expression was down-regulated in vivo and in vitro. Finally, the key components of SHL were administered to HaCat cells with down-regulated DSG1; it was seen that neochlorogenic acid and rutin have a significant effect on HaCat cell apoptosis. These results demonstrate that DSG1 deficiency is a potential cause of cutaneous eruptions caused by the combination of SHL and ASA, and neochlorogenic acid and rutin are the main allergenic components. This study provides a new research strategy for the safety evaluation of integrated traditional Chinese and Western medicine.

Staphylococcus epidermidis protease EcpA can be a deleterious component of the skin microbiome in atopic dermatitis

BACKGROUND

Staphylococcus aureus and Staphylococcus epidermidis are the most abundant bacteria found on the skin of patients with atopic dermatitis (AD). S aureus is known to exacerbate AD, whereas S epidermidis has been considered a beneficial commensal organism.

OBJECTIVE

In this study, we hypothesized that S epidermidis could promote skin damage in AD by the production of a protease that damages the epidermal barrier.

METHODS

The protease activity of S epidermidis isolates was compared with that of other staphylococcal species. The capacity of S epidermidis to degrade the barrier and induce inflammation was examined by using human keratinocyte tissue culture and mouse models. Skin swabs from atopic and healthy adult subjects were analyzed for the presence of S epidermidis genomic DNA and mRNA.

RESULTS

S epidermidis strains were observed to produce strong cysteine protease activity when grown at high density. The enzyme responsible for this activity was identified as EcpA, a cysteine protease under quorum sensing control. EcpA was shown to degrade desmoglein-1 and LL-37 in vitro, disrupt the physical barrier, and induce skin inflammation in mice. The abundance of S epidermidis and expression of ecpA mRNA were increased on the skin of some patients with AD, and this correlated with disease severity. Another commensal skin bacterial species, Staphylococcus hominis, can inhibit EcpA production by S epidermidis.

CONCLUSION

S epidermidis has commonly been regarded as a beneficial skin microbe, whereas S aureus has been considered deleterious. This study suggests that the overabundance of S epidermidis found on some atopic patients can act similarly to S aureus and damage the skin by expression of a cysteine protease.

Identification of a primary antigenic target of epitope spreading in endemic pemphigus foliaceus

Epitope spreading is an important mechanism for the development of autoantibodies (autoAbs) in autoimmune diseases. The study of epitope spreading in human autoimmune diseases is limited due to the major challenge of identifying the initial/primary target epitopes on autoantigens in autoimmune diseases. We have been studying the development of autoAbs in an endemic human autoimmune disease, Brazilian pemphigus foliaceus (or Fogo Selvagem (FS)). Our previous findings demonstrated that patients before (i.e. preclinical) and at the onset of FS have antibody (Ab) responses against other keratinocyte adhesion molecules in addition to the main target autoantigen of FS, desmoglein 1 (Dsg1), and anti-Dsg1 monoclonal Abs (mAbs) cross-reacted with an environmental antigen LJM11, a sand fly saliva protein. Since sand fly is prevalent in FS endemic regions, individuals in these regions could develop Abs against LJM11. The anti-LJM11 Abs could recognize different epitopes on LJM11, including an epitope that shares the structure similarity with an epitope on Dsg1 autoantigen. Thus, Ab response against this epitope on LJM11 could be the initial autoAb response detected in individuals in FS endemic regions, including those who eventually developed FS. Accordingly, this LJM11 and Dsg1 cross-reactive epitope on Dsg1 could be the primary target of the autoimmune response in FS. This investigation aimed to determine whether the autoAb responses against keratinocyte adhesion molecules are linked and originate from the immune response to LJM11. The anti-Dsg1 mAbs from preclinical FS and FS individuals were employed to determine their specificity or cross-reactivity to LJM11 and keratinocyte adhesion molecules. The cross-reactive epitopes on autoantigens were mapped. Our results indicate that all tested mAbs cross-reacted with LJM11 and keratinocyte adhesion molecules, and we identified an epitope on these keratinocyte adhesion molecules which is mimicked by LJM11. Thus, the cross-reactivity could be the mechanism by which the immune response against an environmental antigen triggers the initial autoAb responses. Epitope spreading leads to the pathogenic autoAb development and ensuing FS among genetically susceptible individuals.

Exogenous sex steroids regulate genital epithelial barrier function in female rhesus macaques

There is concern that using depot-medroxyprogesterone acetate (DMPA) for pregnancy prevention heightens HIV susceptibility. While no clinical data establishes causal link between HIV acquisition and use of this injectable progestin, prior work from our laboratory showed that DMPA comparably lowers genital levels of the cell-cell adhesion molecule desmoglein-1 (DSG1) and weakens genital epithelial barrier function in female mice and women. We likewise saw DMPA increase mouse susceptibility to multiple genital pathogens including HIV. Herein, we sought to confirm and extend these findings by comparing genital epithelial barrier function in untreated rhesus macaques (RM) vs. RM treated with DMPA or DMPA and estrogen (E). Compared to controls, genital tissue from RM with pharmacologically relevant serum levels of medroxyprogesterone acetate displayed significantly lower DSG1 levels and greater permeability to low molecular mass molecules. Conversely, DMPA-mediated effects on genital epithelial integrity and function were obviated in RM administered DMPA and E. These data corroborate the diminished genital epithelial barrier function observed in women initiating DMPA and identify RM as a useful preclinical model for defining effects of exogenous sex steroids on genital pathogen susceptibility. As treatment with E averted DMPA-mediated loss of genital epithelial barrier function, our results also imply that contraceptives releasing progestin and E may be less likely to promote transmission of HIV and other sexually transmitted pathogens than progestin-only compounds.

Keratinocyte cadherin desmoglein 1 controls melanocyte behavior through paracrine signaling

The epidermis is the first line of defense against ultraviolet (UV) light from the sun. Keratinocytes and melanocytes respond to UV exposure by eliciting a tanning response dependent in part on paracrine signaling, but how keratinocyte:melanocyte communication is regulated during this response remains understudied. Here, we uncover a surprising new function for the keratinocyte-specific cell-cell adhesion molecule desmoglein 1 (Dsg1) in regulating keratinocyte:melanocyte paracrine signaling to promote the tanning response in the absence of UV exposure. Melanocytes within Dsg1-silenced human skin equivalents exhibited increased pigmentation and altered dendrite morphology, phenotypes which were confirmed in 2D culture using conditioned media from Dsg1-silenced keratinocytes. Dsg1-silenced keratinocytes increased melanocyte-stimulating hormone precursor (Pomc) and cytokine mRNA. Melanocytes cultured in media conditioned by Dsg1-silenced keratinocytes increased Mitf and Tyrp1 mRNA, TYRP1 protein, and melanin production and secretion. Melanocytes in Dsg1-silenced skin equivalents mislocalized suprabasally, reminiscent of early melanoma pagetoid behavior. Together with our previous report that UV reduces Dsg1 expression, these data support a role for Dsg1 in controlling keratinocyte:melanocyte paracrine communication and raise the possibility that a Dsg1-deficient niche contributes to pagetoid behavior, such as occurs in early melanoma development.

Norethisterone Enanthate Increases Mouse Susceptibility to Genital Infection with Herpes Simplex Virus Type 2 and HIV Type 1

Norethisterone enanthate (NET-EN) and depot-medroxyprogesterone acetate (DMPA) are two forms of injectable progestin used for contraception. Whereas clinical research indicates that women using DMPA are more susceptible to HIV and other genital pathogens, causal relationships have not been determined. Providing an underlying mechanism for this connection, however, is recent work that showed DMPA weakens genital mucosal barrier function in mice and humans and respectively promotes susceptibility of wild-type and humanized mice to genital infection with HSV type 2 and HIV type 1. However, analogous effects of NET-EN treatment on antivirus immunity and host susceptibility to genital infection are much less explored. In this study, we show that compared with mice in estrus, treatment of mice with DMPA or NET-EN significantly decreased genital levels of the cell-cell adhesion molecule desmoglein-1 and increased genital mucosal permeability. These effects, however, were more pronounced in DMPA- versus NET-EN-treated mice. Likewise, we detected comparable mortality rates in DMPA- and NET-EN-treated wild-type and humanized mice after intravaginal infection with HSV type 2 or cell-associated HIV type 1, respectively, but NET-EN treatment was associated with slower onset of HSV-induced genital pathology and lower burden of systemic HIV disease. These findings reveal DMPA and NET-EN treatment of mice significantly reduces genital desmoglein-1 levels and increases genital mucosal permeability and susceptibility to genital pathogens while also implying that NET-EN generates less compromise of genital mucosal barrier function than DMPA.

The Role of Desmoglein 1 in Gap Junction Turnover Revealed through the Study of SAM Syndrome

An effective epidermal barrier requires structural and functional integration of adherens junctions, tight junctions, gap junctions (GJ), and desmosomes. Desmosomes govern epidermal integrity while GJs facilitate small molecule transfer across cell membranes. Some patients with severe dermatitis, multiple allergies, and metabolic wasting (SAM) syndrome, caused by biallelic desmoglein 1 (DSG1) mutations, exhibit skin lesions reminiscent of erythrokeratodermia variabilis, caused by mutations in connexin (Cx) genes. We, therefore, examined whether SAM syndrome-causing DSG1 mutations interfere with Cx expression and GJ function. Lesional skin biopsies from SAM syndrome patients (n = 7) revealed decreased Dsg1 and Cx43 plasma membrane localization compared with control and nonlesional skin. Cultured keratinocytes and organotypic skin equivalents depleted of Dsg1 exhibited reduced Cx43 expression, rescued upon re-introduction of wild-type Dsg1, but not Dsg1 constructs modeling SAM syndrome-causing mutations. Ectopic Dsg1 expression increased cell-cell dye transfer, which Cx43 silencing inhibited, suggesting that Dsg1 promotes GJ function through Cx43. As GJA1 gene expression was not decreased upon Dsg1 loss, we hypothesized that Cx43 reduction was due to enhanced protein degradation. Supporting this, PKC-dependent Cx43 S368 phosphorylation, which signals Cx43 turnover, increased after Dsg1 depletion, while lysosomal inhibition restored Cx43 levels. These data reveal a role for Dsg1 in regulating epidermal Cx43 turnover.

Depot-medroxyprogesterone acetate reduces genital cell-cell adhesion molecule expression and increases genital herpes simplex virus type 2 infection susceptibility in a dose-dependent fashion

OBJECTIVE

Analyzing ectocervical biopsy tissue from women before and after they initiated use of depot-medroxyprogesterone acetate (DMPA), we previously reported this progestin reduces levels of the cell-cell adhesion molecule (CCAM) desmoglein-1 and increases genital mucosal permeability. We likewise saw treating mice with 1.0 mg of DMPA reduced vaginal CCAM expression and increased genital pathogen susceptibility. Herein, we used dose-response studies to delimit DMPA doses and serum MPA levels in mice associated with impaired genital mucosal barrier function and enhanced susceptibility to low-dose herpes simplex virus type 2 (HSV-2) infection.

STUDY DESIGN

We compared genital CCAM expression, genital mucosal permeability, and susceptibility to genital inoculation with 10³ plaque-forming units of HSV-2 among mice in estrus vs. after treatment with 0.01 mg, 0.1 mg, 0.3 mg, or 1.0 mg of DMPA.

RESULTS

Compared to mice in estrus, DMPA treatment in a dose-dependent fashion significantly reduced desmoglein 1α (Dsg1a) and desmocollin-1 (Dsc1) gene expression, reduced DSG1 protein levels, and increased genital mucosal permeability to a low molecular weight molecule. While no mice infected with HSV-2 in estrus died, we respectively saw 50% and 100% mortality in mice administered 0.1 mg or 0.3 mg of DMPA. At time of infection, mean serum MPA levels in mice administered the 0.1 mg or 0.3 mg doses were 3.8 nM and 13.0 nM respectively (values comparable to trough and peak MPA serum levels in women using DMPA).

CONCLUSIONS

Mice with pharmacologically relevant serum MPA concentrations display significant changes in genital CCAM expression, genital mucosal barrier function, and HSV-2 susceptibility.

Desmosomal cadherin association with Tctex-1 and cortactin-Arp2/3 drives perijunctional actin polymerization to promote keratinocyte delamination

The epidermis is a multi-layered epithelium that serves as a barrier against water loss and environmental insults. Its morphogenesis occurs through a tightly regulated program of biochemical and architectural changes during which basal cells commit to differentiate and move towards the skin's surface. Here, we reveal an unexpected role for the vertebrate cadherin desmoglein 1 (Dsg1) in remodeling the actin cytoskeleton to promote the transit of basal cells into the suprabasal layer through a process of delamination, one mechanism of epidermal stratification. Actin remodeling requires the interaction of Dsg1 with the dynein light chain, Tctex-1 and the actin scaffolding protein, cortactin. We demonstrate that Tctex-1 ensures the correct membrane compartmentalization of Dsg1-containing desmosomes, allowing cortactin/Arp2/3-dependent perijunctional actin polymerization and decreasing tension at E-cadherin junctions to promote keratinocyte delamination. Moreover, Dsg1 is sufficient to enable simple epithelial cells to exit a monolayer to form a second layer, highlighting its morphogenetic potential.

Overexpression of Psoriasin (S100A7) Contributes to Dysregulated Differentiation in Psoriasis

Psoriasin, which is highly expressed in psoriasis, is encoded by a gene located within the epidermal differentiation complex. The aim of this study was to investigate the effect of endogenous psoriasin on disturbed keratinocyte differentiation in psoriasis. Immunohistochemical staining revealed a gradient of psoriasin expression in the psoriatic epidermis with highest expression in the suprabasal, differentiated layers. Induction of keratinocyte differentiation caused concurrent expression of psoriasin and the differentiation marker involucrin. The differentiation-induced psoriasin expression was found to be mediated by the protein kinase C pathway. The downregulation of psoriasin expression by small interfering RNA revealed that psoriasin mediates the expression of involucrin, desmoglein 1, transglutaminase 1 and CD24 in normal differentiation. The lentivirus-mediated overexpression of psoriasin, mimicking the psoriatic milieu, gave rise to an altered regulation of differentiation genes and an expression pattern reminiscent of that in psoriatic epidermis. These findings suggest that psoriasin contributes to the dysregulated differentiation process in the psoriasis epidermis.

Pemphigus, a pathomechanism of acantholysis

Autoantibodies to the desmosomal proteins desmoglein 1 and 3 cause pemphigus foliaceus and pemphigus vulgaris, which are characterised by keratinocyte dissociation (acantholysis) and intraepidermal blister formation. The passive transfer of pathogenic anti-desmoglein antibodies induces blisters in mice in vivo and the loss of keratinocyte adhesion in vitro. The pathogenetic mechanisms of acantholysis due to anti-desmoglein autoantibodies are not fully understood. However, recent studies have revealed that signalling-dependent and signalling-independent pathways are operative in the loss of cell adhesion. In this review, we focus on the pathomechanism of acantholysis due to autoantibodies to desmogleins and recent therapeutic approaches.

Proteomic profiling reveals candidate markers for arsenic-induced skin keratosis

Proteomics technology is an attractive biomarker candidate discovery tool that can be applied to study large sets of biological molecules. To identify novel biomarkers and molecular targets in arsenic-induced skin lesions, we have determined the protein profile of arsenic-affected human epidermal stratum corneum by shotgun proteomics. Samples of palm and foot sole from healthy subjects were analyzed, demonstrating similar protein patterns in palm and sole. Samples were collected from the palms of subjects with arsenic keratosis (lesional and adjacent non-lesional samples) and arsenic-exposed subjects without lesions (normal). Samples from non-exposed healthy individuals served as controls. We found that three proteins in arsenic-exposed lesional epidermis were consistently distinguishably expressed from the unaffected epidermis. One of these proteins, the cadherin-like transmembrane glycoprotein, desmoglein 1 (DSG1) was suppressed. Down-regulation of DSG1 may lead to reduced cell-cell adhesion, resulting in abnormal epidermal differentiation. The expression of keratin 6c (KRT6C) and fatty acid binding protein 5 (FABP5) were significantly increased. FABP5 is an intracellular lipid chaperone that plays an essential role in fatty acid metabolism in human skin. This raises a possibility that overexpression of FABP5 may affect the proliferation or differentiation of keratinocytes by altering lipid metabolism. KRT6C is a constituent of the cytoskeleton that maintains epidermal integrity and cohesion. Abnormal expression of KRT6C may affect its structural role in the epidermis. Our findings suggest an important approach for future studies of arsenic-mediated toxicity and skin cancer, where certain proteins may represent useful biomarkers of early diagnoses in high-risk populations and hopefully new treatment targets. Further studies are required to understand the biological role of these markers in skin pathogenesis from arsenic exposure.

Internalization of Non-Clustered Desmoglein 1 without Depletion of Desmoglein 1 from Adhesion Complexes in An Experimental Model of the Autoimmune Disease Pemphigus Foliaceus

Serum antibodies against desmoglein 1 (Dsg1) are known to induce the clinical and histological manifestations of pemphigus foliaceus (PF), autoimmune bullous disease targeting skin. The basic pathophysiological phenomenon of PF blistering is the disruption of epithelial integrity in the granular layer of the epidermis due to separation of keratinocytes from one another, or acantholysis. In this report we investigate the changes in subcellular distribution of Dsg1 in response to serum of patients with PF by using an in vitro model of PF. Immunofluorescence analysis on HaCaT cells indicates that non-clustered Dsg1 is markedly internalized after exposure to serum. However, binding of PF IgG to Dsg1-rich adhesion complexes (desmosomes) does not cause disruption of such structures nor depletion of clustered Dsg1, as revealed by colocalization of PF IgG and Dsg1 in a punctate staining on cell membrane 24 hours after treatment. Furthermore, morphological studies demonstrate that the dramatic alterations induced by PF sera are not the result of apoptotic programs. Taken together, our data strongly suggest that anti-Dsg1 antibodies from PF serum could cause the internalization of non-clustered Dsg1 and perturb the formation of new desmosomes but not directly disrupt Dsg1-containing junctions when stable contacts are already formed.

Clinical and immunologic characterization in 26 Indian pemphigus patients

BACKGROUND

Pemphigus shows geographically variable characteristics.

OBJECTIVE

To study the clinical and immunologic characteristics of Indian pemphigus patients before and after treatment.

METHODS

Twenty-six Indian pemphigus patients were analyzed with regard to age, gender, clinical features, treatments and response, the results of histopathology, direct and indirect immunofluorescence (IF), enzyme-linked immunosorbent assay (ELISA), and immunoblot analyses.

RESULTS

There were 22 pemphigus vulgaris (PV) and 4 pemphigus foliaceus (PF) patients. Direct and indirect IF was positive in 95.8% and 56% of patients, respectively. Indices of ELISA were lower in our study. Immunoblot assays detected the 130 kDa desmoglein-3 in 10 PV patients and the 160 kDa desmoglein-1 in 1 PV patient; 190 kDa periplakin was unexpectedly detected in 8 patients.

CONCLUSION

Indian pemphigus patients showed several unique characteristics, including younger population, predominance of PV, low ELISA indices, lower sensitivity of indirect IF and immunoblotting, and the presence of the 190 kDa periplakin in nearly one-third of patients.

Critical role of Klf5 in regulating gene expression during post-eyelid opening maturation of mouse corneas

BACKGROUND

Klf5 plays an important role in maturation and maintenance of the mouse ocular surface. Here, we quantify WT and Klf5-conditional null (Klf5CN) corneal gene expression, identify Klf5-target genes and compare them with the previously identified Klf4-target genes to understand the molecular basis for non-redundant functions of Klf4 and Klf5 in the cornea.

METHODOLOGY/PRINCIPAL FINDINGS

Postnatal day-11 (PN11) and PN56 WT and Klf5CN corneal transcriptomes were quantified by microarrays to compare gene expression in maturing WT corneas, identify Klf5-target genes, and compare corneal Klf4- and Klf5-target genes. Whole-mount corneal immunofluorescent staining was employed to examine CD45+ cell influx and neovascularization. Effect of Klf5 on expression of desmosomal components was studied by immunofluorescent staining and transient co-transfection assays. Expression of 714 and 753 genes was increased, and 299 and 210 genes decreased in PN11 and PN56 Klf5CN corneas, respectively, with 366 concordant increases and 72 concordant decreases. PN56 Klf5CN corneas shared 241 increases and 98 decreases with those previously described in Klf4CN corneas. Xenobiotic metabolism related pathways were enriched among genes decreased in Klf5CN corneas. Expression of angiogenesis and immune response-related genes was elevated, consistent with neovascularization and CD45+ cell influx in Klf5CN corneas. Expression of 1574 genes was increased and 1915 genes decreased in WT PN56 compared with PN11 corneas. Expression of ECM-associated genes decreased, while that of solute carrier family members increased in WT PN56 compared with PN11 corneas. Dsg1a, Dsg1b and Dsp were down-regulated in Klf5CN corneas and their corresponding promoter activities were stimulated by Klf5 in transient co-transfection assays.

CONCLUSIONS/SIGNIFICANCE

Differences between PN11 and PN56 corneal Klf5-target genes reveal dynamic changes in functions of Klf5 during corneal maturation. Klf5 contributes to corneal epithelial homeostasis by regulating the expression of desmosomal components. Klf4- and Klf5-target genes are largely distinct, consistent with their non-redundant roles in the mouse cornea.

Involvement of the ubiquitin-proteasome system in the stabilization of cell-cell contacts in human keratinocytes

Desmosomes are highly organized intercellular junctions composed of a number of interacting proteins that provide mechanical integrity to epithelial tissues. Mutations in genes encoding desmosomal proteins, including desmoplakin (DP), are associated with human hereditary diseases affecting skin integrity. The detailed mechanism of desmosome assembly remains, despite many efforts, incompletely understood. Recently, the ubiquitin-proteasome system (UPS) has been suggested to be an important regulatory system for the proper intracellular trafficking of proteins. Here, we provide evidence for a calcium-independent, but UPS-dependent, stabilization of cell-cell contacts in human keratinocytes, which might be mediated by the maintenance of DP at desmosomes.

Acute effects of cigarette smoke on three-dimensional cultures of normal human oral mucosa

CONTEXT

Human oral mucosa is the combustion chamber of cigarette, but scanty evidence is available about the early smoke effects.

OBJECTIVE

The present work aimed at evaluating from a morphological point of view whole smoke early effects on epithelial intercellular adhesion and keratinocyte terminal differentiation in a three-dimensional model of human oral mucosa.

MATERIALS AND METHODS

Biopsies of keratinized oral mucosa of healthy nonsmoking women (n = 5) were collected. After culturing in a Transwell system, one fragment of each biopsy was exposed to the smoke of one single cigarette; the remnant represented the internal control. The distribution of epithelial differentiation markers (keratin-10, K10, and keratin-14, K14, for suprabasal and basal cells respectively), desmosomes (desmoglein-1, desmoglein-3), tight junctions (occludin), adherens junctions (E-cadherin, β-catenin), and apoptotic cells (p53, caspase 3) were evaluated by immunofluorescence.

RESULTS

Quantitative analysis of K14 immunolabeling revealed an overexpression in the suprabasal layers as early as 3 h after smoke exposure, without impairment of the epithelial junctional apparatus and apoptosis induction.

DISCUSSION AND CONCLUSION

These results suggested that the first significant response to cigarette smoke came from the basal and suprabasal layers of the human oral epithelium. The considered model maintained the three-dimensional arrangement of the human mucosa in the oral cavity and mimicked the inhalation/exhalation cycle during the exposure to cigarette smoke, offering a good possibility to extrapolate the reported observations to humans.

Kallikrein-5 promotes cleavage of desmoglein-1 and loss of cell-cell cohesion in oral squamous cell carcinoma

Oral squamous cell carcinoma (OSCC) ranks among the top 8 causes of cancer death worldwide, with only a 60% 5-year survival rate, highlighting the need for discovery of novel biomarkers and therapeutic targets. We have previously reported that expression of a panel of serine proteinase kallikreins (KLK 5, 7, 8, and 10) is correlated with formation of more aggressive OSCC tumors in a murine orthotopic OSCC model and is elevated in human OSCC. Current studies focus on understanding the potential role of KLK5 in OSCC progression. In initial studies, KLK levels in malignant OSCC cells (SCC25) were compared with cells from normal oral mucosa (OKF/6) and pre-malignant oral keratinocytes (pp126) using qPCR. A marked elevation of all KLKs was observed in aggressive SCC25 cells relative to OKF/6 cells. In normal skin, KLKs are involved in desquamation during epidermal differentiation via proteolytic cleavage of the desmosomal cadherin component desmoglein 1 (Dsg1). As loss of cell-cell cohesion is prevalent in tumor metastasis, Dsg1 integrity was evaluated. Results show that SCC25 cells exhibit cleavage of Dsg1, which is blocked by proteinase inhibitor treatment as well as by siRNA silencing of KLK5 expression. Furthermore, cell-cell aggregation assays demonstrate that silencing of KLK5 enforces cell-cell adhesion; conversely, overexpression of KLK5 in normal oral mucosal cells (OKF/6) enhances cell dispersal. These data suggest that KLK5 may promote metastatic dissemination of OSCC by promoting loss of junctional integrity through cleavage of desmoglein 1.

Comparison of diagnostic value of indirect immunofluorescence assay and desmoglein ELISA in the diagnosis of pemphigus

Pemphigus vulgaris (PV) and pemphigus foliaceus (PF) are autoimmune blistering diseases characterized by intraepidermal separation as the result of autoantibodies directed to desmoglein 1 and desmoglein 3, adhesion molecules that have a pathogenic role in blister formation. Both PV and PF are diagnosed according to clinical picture, histopathologic, immunopathologic and molecular biologic features. In the present study, the value of indirect immunofluorescence (IIF) and enzyme linked immunosorbent assay (ELISA) for desmoglein 1 (Dsg 1) and desmoglein 3 (Dsg 3) at baseline visit was compared. The study was performed as a retrospective study that included 22 patients, 19 of them with PV and three with PF. Patient sera were tested with IIF and Dsg 1 and Dsg 3 ELISA. In the group of 19 PV patients, 12 patients had positive IIF, Dsg 3 and Dsg 1 ELISA; two had positive IIF and positive anti Dsg 3 but negative anti Dsg 1; three had negative IIF but positive both Dsg 1 and Dsg 3 antibodies; and two had negative IIF and Dsg 1 but positive Dsg 3 antibodies. In the group of PF patients, all three patients had positive IIF, positive Dsg 1 ELISA and negative Dsg 3 ELISA. Results of our study supported previous reports confirming Dsg 1 and Dsg 3 ELISA to be a sensitive and specific tool for the diagnosis of PV and PF.

Biphasic activation of p38MAPK suggests that apoptosis is a downstream event in pemphigus acantholysis

In pemphigus vulgaris and pemphigus foliaceus (PF), autoantibodies against desmoglein-3 and desmoglein-1 induce epidermal cell detachment (acantholysis) and blistering. Activation of keratinocyte intracellular signaling pathways is emerging as an important component of pemphigus IgG-mediated acantholysis. We previously reported activation of p38 mitogen-activated protein kinase (MAPK) in response to pathogenic pemphigus vulgaris and PF IgG. Inhibition of p38MAPK blocked pemphigus IgG-induced cytoskeletal reorganization in tissue culture and blistering in pemphigus mouse models. We now extend these observations by demonstrating two peaks of p38MAPK activation in pemphigus tissue culture and mouse models. Administration of the p38MAPK inhibitor SB202190 before PF IgG injection blocked both peaks of p38MAPK phosphorylation and blister formation, consistent with our previous findings; however, administration of the inhibitor 4 h after PF IgG injection blocked only the later peak of p38MAPK activation but failed to block blistering. Examination of the temporal relationship of p38MAPK phosphorylation and apoptosis showed that apoptosis occurs at or after the second peak of p38MAPK activation. The time course of p38MAPK activation and apoptotic markers, as well as the ability of inhibitors of p38MAPK to block activation of the proapoptotic proteinase caspase-3, suggest that activation of apoptosis is downstream to, and a consequence of, p38MAPK activation in pemphigus acantholysis. Furthermore, these observations suggest that the earlier peak of p38MAPK activation is part of the mechanism leading to acantholysis, whereas the later peak of p38MAPK and apoptosis may not be essential for acantholysis.

Staphylococcal exfoliative toxins: “Molecular scissors” of bacteria that attack the cutaneous defense barrier in mammals

Bullous impetigo and its generalized form, staphylococcal scalded-skin syndrome (SSSS), are highly contagious, blistering skin diseases caused by Staphylococcus aureus infection. Virulent strains of the bacteria produce exfoliative toxins (ETs) that cause the loss of keratinocyte cell-cell adhesion in the superficial epidermis. Recent studies have indicated that the three isoforms of ETs, i.e., ETA, ETB, and ETD, are glutamate-specific serine proteases that specifically and efficiently cleave a single peptide bond in the extracellular region of human and mouse desmoglein 1 (Dsg1), a desmosomal intercellular adhesion molecule. In addition, four isoforms of S. hyicus exfoliative toxin, ExhA, ExhB, ExhC, and ExhD, cleave swine Dsg1, resulting in skin exfoliation similar to that observed in pigs with exudative epidermitis. In this review, we describe recent advances in our knowledge of the mechanisms of action of staphylococcal exfoliative toxins, which act as "molecular scissors" to facilitate percutaneous bacterial invasion of mammalian skin by cleavage of keratinocyte cell-cell adhesion molecules. The species-specificity of staphylococcal exfoliative toxins to cleave Dsg1 in certain mammalian species is discussed.

Pemphigus IgG causes skin splitting in the presence of both desmoglein 1 and desmoglein 3

According to the desmoglein (Dsg) compensation concept, different epidermal cleavage planes observed in pemphigus vulgaris and pemphigus foliaceus have been proposed to be caused by different autoantibody profiles against the desmosomal proteins Dsg 1 and Dsg 3. According to this model, Dsg 1 autoantibodies would only lead to epidermal splitting in those epidermal layers in which no Dsg 3 is present to compensate for the functional loss of Dsg 1. We provide evidence that both pemphigus foliaceus-IgG containing Dsg 1- but not Dsg 3-specific antibodies and pemphigus vulgaris-IgG with antibodies to Dsg 1 and Dsg 3 were equally effective in causing epidermal splitting in human skin and keratinocyte dissociation in vitro. These effects were present where keratinocytes expressed both Dsg 1 and Dsg 3, demonstrating that Dsg 3 does not compensate for Dsg 1 inactivation. Rather, the cleavage plane in intact human skin caused by pemphigus autoantibodies was similar to the plane of keratinocyte dissociation in response to toxin B-mediated inactivation of Rho GTPases. Because we recently demonstrated that pemphigus-IgG causes epidermal splitting by inhibition of Rho A, we propose that Rho GTPase inactivation contributes to the mechanisms accounting for the cleavage plane in pemphigus skin splitting.

IgG autoantibodies directed against desmoglein 3 cause dissociation of keratinocytes in canine pemphigus vulgaris and paraneoplastic pemphigus

Pemphigus is a group of autoimmune blistering diseases of the skin and mucous membranes. In human patients with pemphigus vulgaris (PV) and paraneoplastic pemphigus (PNP), IgG autoantibodies against desmoglein (Dsg) 3 and Dsg1 play pathogenic roles in blister formation. In contrast, the target for IgG autoantibodies that induce keratinocyte dissociation has not been elucidated in canine pemphigus. The aim of the present study was to determine whether anti-Dsg IgG autoantibodies are present and disrupt the cell-cell adhesion of keratinocytes in canine PV and PNP. The extracellular domains of canine Dsg3 were recognized by IgG in 3/5 (60%) canine PV sera tested. IgG against the extracellular domains of canine Dsg1 was detected exclusively in two dogs that had PV with the mucocutaneous phenotype. In addition, anti-Dsg3 IgG was identified in canine PNP serum. Furthermore, incubation of normal human keratinocytes (NHK) with mucocutaneous canine PV serum and canine PNP serum resulted in dissociation of the NHK sheets, whereas the removal of anti-Dsg3 IgG from these canine sera blocked this dissociation. The present study indicates for the first time that circulating anti-Dsg3 IgG antibodies capable of dissociating keratinocytes are present in dogs with PV and PNP.

Pemphigus vulgaris presenting in a radiation portal

We report a case of mucocutaneous pemphigus vulgaris in a patient with squamous cell carcinoma of the lung. The cutaneous involvement was limited to the skin within his therapeutic radiation portal. The diagnosis of pemphigus vulgaris was confirmed by histopathology and immunologic studies. Direct immunofluorescence demonstrated IgG and C3 in the intercellular spaces and indirect immunofluorescence was positive on monkey esophagus at a titer of 1:160. Enzyme-linked immunosorbent assay of the patient's serum detected autoantibodies only to desmoglein (Dsg)3, with no reactivity to Dsg1. Immunomapping of perilesional skin from the irradiated field illustrated decreased Dsg1 expression compared with a control sample from an area that was not exposed to radiation. This case provides support for the Dsg compensation hypothesis and may also suggest a mechanism by which irradiation may induce skin lesions.

Changes in desmoglein 1 expression and subcellular localization in cultured keratinocytes subjected to anti-desmoglein 1 pemphigus autoimmunity

The complexity of pemphigus acantholysis together with the weak expression of desmoglein 1 (Dsg1) in cultured keratinocytes have made the study on the pathogenic action of anti-Dsg1 antibodies quite difficult. The pathophysiology of the acantholytic phenomenon could depend on the reduction of Dsg1 adhesion function occurring after its massive internalization or decrease of its synthesis. Here, we have investigated this hypothesis by using sera of patients having antibodies against Dsg1 or monoclonal anti-Dsg1 antibodies to simulate pemphigus autoimmunity in Dsg1-rich keratinocytes. Similar to pemphigus foliaceus (PF) and vulgaris (PV) sera, monoclonal anti-Dsg1 antibodies induced transient internalization of Dsg1 and reduced the adhesion strength among keratinocytes. However, binding of IgG to Dsg1 did not determine its early depletion from the adhesion complexes but reduced the amount of Dsg1 found in the Triton X-100 soluble pool of proteins. Taken together, our results represent the first demonstration that anti-Dsg1 antibodies induce similar alterations on the subcellular distribution of Dsg1 irrespective of the disease where they come from. Furthermore, the present study provides insight into the mechanisms underlying epithelial blistering observed in the skin type of pemphigus.

Kallikrein 8 is involved in skin desquamation in cooperation with other kallikreins

Kallikrein type serine proteases, KLK8/neuropsin, KLK6, and KLK7, have been implicated in the proliferation and differentiation of epidermal keratinocytes and in the pathogenesis of psoriasis. However, their mechanistic roles in these processes remain largely unknown. We applied 12-O-tetradecanoylphorbol-13-acetate on the wild type (WT) and the Klk8 gene-disrupted (Klk8(-/-)) mouse skin, inducing keratinocyte proliferation similar to the human psoriatic lesion. Klk8 mRNA as well as Klk6 and Klk7 mRNA were up-regulated after 12-O-tetradecanoylphorbol-13-acetate application in the WT mice. In contrast, Klk8(-/-) mice showed minimum increases of Klk6 and Klk7 transcripts, the proteins, and enzymatic activities. Relative to the WT, the Klk8(-/-) skin showed less proliferation and an increase in the number of cell layers in the stratum corneum. However, overexpression of Klk8 by adenovirus vector in knock-out keratinocytes did not result in an increase in Klk6 or Klk7 mRNA. The inefficient cleavage of adhesion molecules DSG1 and CDSN in Klk8(-/-) skin contributes to a delay in corneocyte shedding, resulting in the hyperkeratosis phenotype. We propose that in psoriatic lesion, KLK8 modulates hyperproliferation and prevents excessive hyperkeratosis by shedding the corneocytes.

A potential role for multiple tissue kallikrein serine proteases in epidermal desquamation

Desquamation of the stratum corneum is a serine protease-dependent process. Two members of the human tissue kallikrein (KLK) family of (chymo)tryptic-like serine proteases, KLK5 and KLK7, are implicated in desquamation by digestion of (corneo)desmosomes and inhibition by desquamation-related serine protease inhibitors (SPIs). However, the epidermal localization and specificity of additional KLKs also supports a role for these enzymes in desquamation. This study aims to delineate the probable contribution of KLK1, KLK5, KLK6, KLK13, and KLK14 to desquamation by examining their interactions, in vitro, with: 1) colocalized SPI, lympho-epithelial Kazal-type-related inhibitor (LEKTI, four recombinant fragments containing inhibitory domains 1-6 (rLEKTI(1-6)), domains 6-8 and partial domain 9 (rLEKTI(6-9')), domains 9-12 (rLEKTI(9-12)), and domains 12-15 (rLEKTI(12-15)), secretory leukocyte protease inhibitor, and elafin and 2) their ability to digest the (corneo)desmosomal cadherin, desmoglein 1. KLK1 was not inhibited by any SPI tested. KLK5, KLK6, KLK13, and KLK14 were potently inhibited by rLEKTI(1-6), rLEKTI(6-9'), and rLEKTI(9-12) with Ki values in the range of 2.3-28.4 nm, 6.1-221 nm, and 2.7-416 nm for each respective fragment. Only KLK5 was inhibited by rLEKTI(12-15) (Ki = 21.8 nm). No KLK was inhibited by secretory leukocyte protease inhibitor or elafin. Apart from KLK13, all KLKs digested the ectodomain of desmoglein 1 within cadherin repeats, Ca2+ binding sites, or in the juxtamembrane region. Our study indicates that multiple KLKs may participate in desquamation through cleavage of desmoglein 1 and regulation by LEKTI. These findings may have clinical implications for the treatment of skin disorders in which KLK activity is elevated.

Inhibition of Rho A activity causes pemphigus skin blistering

The autoimmune blistering skin diseases pemphigus vulgaris (PV) and pemphigus foliaceus (PF) are mainly caused by autoantibodies against desmosomal cadherins. In this study, we provide evidence that PV-immunoglobulin G (IgG) and PF-IgG induce skin blistering by interference with Rho A signaling. In vitro, pemphigus IgG caused typical hallmarks of pemphigus pathogenesis such as epidermal blistering in human skin, cell dissociation, and loss of desmoglein 1 (Dsg 1)-mediated binding probed by laser tweezers. These changes were accompanied by interference with Rho A activation and reduction of Rho A activity. Pemphigus IgG-triggered keratinocyte dissociation and Rho A inactivation were p38 mitogen-activated protein kinase dependent. Specific activation of Rho A by cytotoxic necrotizing factor-y abolished all pemphigus-triggered effects, including keratin retraction and release of Dsg 3 from the cytoskeleton. These data demonstrate that Rho A is involved in the regulation of desmosomal adhesion, at least in part by maintaining the cytoskeletal anchorage of desmosomal proteins. This may open the possibility of pemphigus treatment with the epidermal application of Rho A agonists.

Corneodesmosomal cadherins are preferential targets of stratum corneum trypsin- and chymotrypsin-like hyperactivity in Netherton syndrome

SPINK5 (serine protease inhibitor Kazal-type 5), encoding the protease inhibitor LEKTI (lympho-epithelial Kazal-type related inhibitor), is the defective gene in Netherton syndrome (NS), a severe inherited keratinizing disorder. We have recently demonstrated epidermal protease hyperactivity in Spink5(-/-) mice resulting in desmosomal protein degradation. Herein, we investigated the molecular mechanism underlying the epidermal defect in 15 patients with NS. We demonstrated that, in a majority of patients, desmoglein 1 (Dsg1) and desmocollin 1 (Dsc1) were dramatically reduced in the upper most living layers of the epidermis. These defects were associated with premature degradation of corneodesmosomes. Stratum corneum tryptic enzyme (SCTE)-like and stratum corneum chymotryptic enzyme (SCCE)-like activities were increased, suggesting that these proteases participate in the premature degradation of corneodesmosomal cadherins. SCTE and SCCE expression was extended to the cell layers where Dsg1 and Dsc1 immunostaining was reduced. In contrast, a subset of six patients with normal epidermal protease activity or residual LEKTI expression displayed apparently normal cadherin expression and less severe disease manifestations. This suggests a degree of correlation between cadherin degradation and clinical severity. This work further supports the implication of premature corneodesmosomal cadherin degradation in the pathogenesis of NS and provides evidence for additional factors playing a role in disease expression.

Delineation of diversified desmoglein distribution in stratified squamous epithelia: implications in diseases

Desmogleins play critical roles in cell adhesion and skin blistering diseases, as they are the target antigens of autoimmune antibodies and bacterial toxins. We recently cloned several novel members of the desmoglein gene family, bringing the number of desmogleins to four in the rat and human genomes and six in the mouse. Here, we have produced a monoclonal antibody to a cytoplasmic epitope of Dsg4, assessed its specificity and compared it to several existing Dsg1-3 antibodies. We also demonstrated cross-reactivity of commercially available and often used Dsg1 antibodies. Using these tools, we delineated the unique expression patterns of each desmoglein isoform in various human and mouse stratified squamous epithelia, including skin, hair, palm, and oral mucosa. Interestingly, in the epidermis, the expression of each desmoglein correlates with their gene arrangement in the cadherin locus. In human, Dsg4 was detected primarily in the granular and cornified cell layers of the epidermis, while present throughout all differentiated layers of the oral mucosa and palm, and in the matrix cells of anagen hair bulb. Similar pattern of expression for Dsg4 was observed in mouse, with the exception that it was expressed at significantly lower levels in the mouse epidermis. These results demonstrate the complexity of desmoglein gene expression and provide additional insights into the correlation between tissue expression patterns and disease phenotypes.

The Differentiation-dependent Desmosomal Cadherin Desmoglein 1 Is a Novel Caspase-3 Target That Regulates Apoptosis in Keratinocytes

Although a number of cell adhesion proteins have been identified as caspase substrates, the potential role of differentiation-specific desmosomal cadherins during apoptosis has not been examined. Here, we demonstrate that UV-induced caspase cleavage of the human desmoglein 1 cytoplasmic tail results in distinct 17- and 140- kDa products, whereas metalloproteinase-dependent shedding of the extracellular adhesion domain generates a 75-kDa product. In vitro studies identify caspase-3 as the preferred enzyme that cleaves desmoglein 1 within its unique repeating unit domain at aspartic acid 888, part of a consensus sequence not conserved among the other desmosomal cadherins. Apoptotic processing leads to decreased cell surface expression of desmoglein 1 and re-localization of its C terminus diffusely throughout the cytoplasm over a time course comparable with the processing of other desmosomal proteins and cytoplasmic keratins. Importantly, whereas classic cadherins have been reported to promote cell survival, short hairpin RNA-mediated suppression of desmoglein 1 in differentiated keratinocytes protected cells from UV-induced apoptosis. Collectively, our results identify desmoglein 1 as a novel caspase and metalloproteinase substrate whose cleavage likely contributes to the dismantling of desmosomes during keratinocyte apoptosis and also reveal desmoglein 1 as a previously unrecognized regulator of apoptosis in keratinocytes.

Immunohistochemical analysis of the distribution of desmoglein 1 and 2 in the skin of dogs and cats

OBJECTIVE

To compare the distribution of desmoglein (Dsg) 1 and 2 in skin specimens obtained from dogs and cats to provide information about the possible role of the density of Dsg 1 and 2 in the localization of lesions attributable to pemphigus foliaceus in these 2 species.

SAMPLE POPULATION

Skin biopsy specimens obtained from 4 dogs and 4 cats.

PROCEDURE

Biopsy specimens were collected from the muzzle, bridge of the nose, ear, dorsum, abdomen, area adjacent to the teats, and footpads of each animal. Immunohistochemical analysis was performed on formalin-fixed, paraffin-embedded skin samples by use of a biotinylated mouse monoclonal anti-Dsg 1 and 2 antibody raised against bovine muzzle. Color development was performed by use of the streptavidin-biotin-peroxidase method with a chromogenic substrate.

RESULTS

Immunohistochemical staining yielded a positive reaction in skin samples obtained from all anatomic sites. The intensity and distribution of staining were related to the number of layers of the stratum spinosum. No differences were detected between samples obtained from dogs and cats.

CONCLUSIONS AND CLINICAL RELEVANCE

No differences in intensity of Dsg 1 and 2 antigen were observed in the stratum spinosum between skin samples obtained from dogs and cats. Analysis of this result suggests that factors other than the distribution of Dsg may be responsible for the differences in localization of primary clinical lesions in dogs and cats with pemphigus foliaceus.

Blocked Acinar Development, E-Cadherin Reduction, and Intraepithelial Neoplasia upon Ablation of p120-Catenin in the Mouse Salivary Gland

p120 catenin is thought to be a key regulator of E-cadherin function and stability, but its role(s) in vivo is poorly understood. To examine these directly, we generated a conditional p120 knockout mouse and targeted p120 ablation to the embryonic salivary gland. Surprisingly, acinar differentiation is completely blocked, resulting in a gland composed entirely of ducts. Moreover, p120 ablation causes E-cadherin deficiency in vivo and severe defects in adhesion, cell polarity, and epithelial morphology. These changes closely phenocopy high-grade intraepithelial neoplasia, a condition that, in humans, typically progresses to invasive cancer. Tumor-like protrusions appear immediately after p120 ablation at e14 and expand into the lumen until shortly after birth, at which time the animals die with completely occluded glands. The data reveal an unexpected role for p120 in salivary acinar development and show that p120 ablation by itself induces effects consistent with a role in tumor progression.

Topical Liver X Receptor Activators Accelerate Postnatal Acidification of Stratum Corneum and Improve Function in the Neonate

In neonatal rat stratum corneum (SC), pH declines from pH 6.8 at birth to adult levels (pH 5.0-5.5) over 5-6 d. Liver X receptor (LXR) activators stimulate keratinocyte differentiation, improve permeability barrier homeostasis, and accelerate the in utero development of the SC. In this manuscript we determined the effect of LXR activators on SC acidification in the neonatal period and whether these activators correct the functional abnormalities in permeability barrier homeostasis and SC integrity/cohesion. Formation of the acid SC-buffer system was accelerated by topically applying the LXR activator, 22(R)-hydroxycholesterol, and non-oxysterol activators of LXR, TO-901317, and GW-3965. A sterol which does not activate LXR had no effect. LXR activation increased secretory phospholipase A(2) (sPLA(2)) activity and conversely, inhibition of sPLA(2) activity prevented the LXR induced increase in SC acidification, suggesting that increasing sPLA(2) accounts in part, for the LXR stimulation of acidification. LXR activation resulted in an improvement in permeability barrier homeostasis, associated with an increased maturation of lamellar membranes attributable to an increased beta-glucocerebrosidase activity. SC integrity cohesion also normalized in LXR-activator-treated animals and was associated with an increase in corneodesmosomes and in desmoglein 1 expression. These results demonstrate that LXR activators stimulate the formation of an acidic SC and improve both permeability barrier homeostasis and SC integrity/cohesion.

Staphylococcus hyicus exfoliative toxins selectively digest porcine desmoglein 1

Virulent strains of Staphylococcus hyicus can cause exudative epidermitis in pigs. The major symptom of this disease is exfoliation of the skin in the upper stratum spinosum. Exfoliation of the skin is strongly associated with exfoliative toxin including ExhA, ExhB, ExhC, ExhD, SHETA, and SHETB. Recently, genes for ExhA, ExhB, ExhC and ExhD were cloned. Exfoliative toxins produced by S. aureus have been shown to selectively cleave human or mouse desmoglein 1, a desmosomal adhesion molecule, that when inactivated results in blisters. In this study, we attempted to identify the molecular target of Exhs in porcine skin. Each of recombinant Exhs injected in the skin of pigs caused superficial epidermal blisters or crust formation. Cell surface staining of desmoglein 1, but not that of desmoglein 3, was abolished when cryosections of normal porcine skin were incubated with one of Exhs suggesting that Exh selectively degrade porcine desmoglein 1. In vitro incubation of the recombinant extracellular domains of desmoglein 1 and desmoglein 3 of human, mouse or canine origin demonstrated that only mouse desmogleins 1alpha and 1beta were cleaved by ExhA and ExhC at high concentration. Furthermore, injection of ExhA and ExhC at high concentration caused superficial blisters in neonatal mice. These findings strongly suggest that Exhs cause blister formation of porcine skin by digesting porcine desmoglein 1 in a similar fashion to exfoliative toxins from S. aureus.

Pemphigus foliaceus IgG causes dissociation of desmoglein 1-containing junctions without blocking desmoglein 1 transinteraction

Autoantibodies against the epidermal desmosomal cadherins desmoglein 1 (Dsg1) and Dsg3 have been shown to cause severe to lethal skin blistering clinically defined as pemphigus foliaceus (PF) and pemphigus vulgaris (PV). It is unknown whether antibody-induced dissociation of keratinocytes is caused by direct inhibition of Dsg1 transinteraction or by secondary cellular responses. Here we show in an in vitro system that IgGs purified from PF patient sera caused cellular dissociation of cultured human keratinocytes as well as significant release of Dsg1-coated microbeads attached to Dsg-containing sites on the keratinocyte cellular surface. However, cell dissociation and bead release induced by PF-IgGs was not caused by direct steric hindrance of Dsg1 transinteraction, as demonstrated by single molecule atomic force measurements and by laser trapping of surface-bound Dsg1-coated microbeads. Rather, our experiments strongly indicate that PF-IgG-mediated dissociation events must involve autoantibody-triggered cellular signaling pathways, resulting in destabilization of Dsg1-based adhesive sites and desmosomes.