Proteases: common culprits in human skin disorders

Staphylococcus aureus Proteases: Orchestrators of Skin Inflammation

Skin homeostasis relies on a delicate balance between host proteases and protease inhibitors along with those secreted from microbial communities, as disruption to this harmony contributes to the pathogenesis of inflammatory skin disorders, including atopic dermatitis and Netherton's syndrome. In addition to being a prominent cause of skin and soft tissue infections, the gram-positive bacterium Staphylococcus aureus is a key player in inflammatory skin conditions due to its array of 10 secreted proteases. Herein we review how S. aureus proteases augment the development of inflammation in skin disorders. These mechanisms include degradation of skin barrier integrity, immune dysregulation and pruritis, and impairment of host defenses. Delineating the diverse roles of S. aureus proteases has the potential to reveal novel therapeutic strategies, such as inhibitors of proteases or their cognate target, as well as neutralizing vaccines to alleviate the burden of inflammatory skin disorders in patients.

Harnessing antimicrobial peptides in endodontics

Endodontic therapy includes various procedures such as vital pulp therapy, root canal treatment and retreatment, surgical endodontic treatment and regenerative endodontic procedures. Disinfection and tissue repair are crucial for the success of these therapies, necessitating the development of therapeutics that can effectively target microbiota, eliminate biofilms, modulate inflammation and promote tissue repair. However, no current endodontic agents can achieve these goals. Antimicrobial peptides (AMPs), which are sequences of amino acids, have gained attention due to their unique advantages, including reduced susceptibility to drug resistance, broad-spectrum antibacterial properties and the ability to modulate the immune response of the organism effectively. This review systematically discusses the structure, mechanisms of action, novel designs and limitations of AMPs. Additionally, it highlights the efforts made by researchers to overcome peptide shortcomings and emphasizes the potential applications of AMPs in endodontic treatments.

SERPINB7 Deficiency Increases Legumain Activity and Impairs the Epidermal Barrier in Nagashima-type Palmoplantar Keratoderma

Nagashima-type palmoplantar keratoderma (NPPK) is an autosomal recessive genodermatosis caused by loss-of-function variants in SERPINB7 and is the most prevalent form of inherited palmoplantar keratodermas among Asians. However, there is currently no effective therapy for NPPK because its pathogenesis remains unclear. In this study, Serpinb7-/- mice were generated and spontaneously developed a disrupted skin barrier, which was further exacerbated by acetone-ether-water treatment. The skin of these Serpinb7-/- mice showed weakened cytoskeletal proteins. Additionally, SERPINB7 deficiency consistently led to decreased epidermal differentiation in a three-dimensional human epidermal model. We also demonstrated that SERPINB7 was an inhibitory serpin that mainly inhibited the protease legumain. SERPINB7 bound directly with legumain and inhibited legumain activity both in vitro and in vivo. Furthermore, we found that SERPINB7 inhibited legumain in a 'protease-substrate' manner and identified the cleavage sites of SERPINB7 as Asn71 and Asn343. Overall, we found that SERPINB7 showed the nature of a cysteine protease inhibitor, and identified legumain as a key target protease of SERPINB7. Loss of SERPINB7 function led to overactivation of legumain, which might disrupt cytoskeletal proteins, contributing to the impaired skin barrier in NPPK. These findings may lead to the development of therapeutic strategies for NPPK.

Matrix metalloproteinase landscape in the imiquimod-induced skin inflammation mouse model

Inflammation and autoimmunity are known as central processes in many skin diseases, including psoriasis. It is therefore important to develop pre-clinical models that describe disease-related aspects to enable testing of pharmaceutical drug candidates and formulations. A widely accepted pre-clinical model of psoriasis is the imiquimod (IMQ)-induced skin inflammation mouse model, where topically applied IMQ provokes local skin inflammation. In this study, we investigated the abundance of a subset of matrix metalloproteinases (MMPs) in skin from mice with IMQ-induced skin inflammation and skin from naïve mice using targeted proteomics. Our findings reveal a significant increase in the abundance of MMP-2, MMP-7, MMP-8, and MMP-13 after treatment with IMQ compared to the control skin, while MMP-3, MMP-9, and MMP-10 were exclusively detected in the IMQ-treated skin. The increased abundance and broader representation of MMPs in the IMQ-treated skin provide valuable insight into the pathophysiology of skin inflammation in the IMQ model, adding to previous studies on cytokine levels using conventional immunochemical methods. Specifically, the changes in the MMP profiles observed in the IMQ-treated skin resemble the MMP patterns found in skin lesions of individuals with psoriasis. Ultimately, the differences in MMP abundance under IMQ-induced inflammation as compared to non-inflamed control skin can be exploited as a model to investigate drug efficacy or performance of drug delivery systems.

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

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

Epidermal biomarkers of the skin barrier in atopic and contact dermatitis

Dysfunction of the skin barrier plays a critical role in the initiation and progression of inflammatory skin diseases, such as atopic dermatitis and contact dermatitis. Epidermal biomarkers can aid in evaluating the functionality of the skin barrier and understanding the mechanisms that underlay its impairment. This narrative review provides an overview of recent studies on epidermal biomarkers associated with the function and integrity of the skin barrier, and their application in research on atopic dermatitis and contact dermatitis. The reviewed studies encompass a wide spectrum of molecular, morphological and biophysical biomarkers, mainly obtained from stratum corneum tape strips and biopsies. Lipids, natural moisturizing factors, and structural proteins are the most frequently reported molecular biomarkers. Additionally, corneocyte surface topography and elasticity show potential as biomarkers for assessing the physical barrier of the skin. In contact dermatitis studies, biomarkers are commonly employed to evaluate skin irritation and differentiate between irritant and allergic contact dermatitis. In atopic dermatitis, biomarkers are primarily utilized to identify differences between atopic and healthy skin, for predictive purposes, and monitoring response to therapies. While this overview identifies potential biomarkers for the skin barrier, their validation as epidermal biomarkers for atopic dermatitis and contact dermatitis has yet to be established.

Mini-PBPK-Based Population Model and Covariate Analysis to Assess the Complex Pharmacokinetics and Pharmacodynamics of RO7449135, an Anti-KLK5/KLK7 Bispecific Antibody in Cynomolgus Monkeys

RO7449135, an anti-kallikrein (KLK)5/KLK7 bispecific antibody, is in development as a potential therapy against Netherton's syndrome (NS). In cynomolgus monkey studies, RO7449135 bound to KLK5 and KLK7, causing considerable accumulation of total KLKs, but with non-dose-proportional increase. To understand the complex PKPD, a population model with covariate analysis was developed accounting for target binding in skin and migration of bound targets from skin to blood. The covariate analysis suggested the animal batch as the categorical covariate impacting the different KLK5 synthesis rates between the repeat-dose study and single-dose study, and the dose as continuous covariate impacting the internalization rate of the binary and ternary complexes containing KLK7. To comprehend the mechanism underlying, we hypothesized that inhibition of KLK5 by RO7449135 prevented its cleavage of the pro-enzyme of KLK7 (pro-KLK7) and altered the proportion between pro-KLK7 and KLK7. Besides the pro-KLK7, RO7449135 can interact with other proteins like LEKTI through KLK7 connection in a dose-dependent manner. The different high-order complexes formed by RO7449135 interacting with pro-KLK7 or LEKTI-like proteins can be subject to faster internalization rate. Accounting for the dose and animal batch as covariates, the model-predicted free target suppression is well aligned with the visual target engagement check. The population PKPD model with covariate analysis provides the scientific input for the complex PKPD analysis, successfully predicts the target suppression in cynomolgus monkeys, and thereby can be used for the human dose projection of RO7449135.

Protease-Responsive Hydrogel Microparticles for Intradermal Drug Delivery

Protease-responsive multi-arm polyethylene glycol-based microparticles with biscysteine peptide crosslinkers (CGPGG↓LAGGC) were obtained for intradermal drug delivery through inverse suspension photopolymerization. The average size of the spherical hydrated microparticles was ∼40 μm after crosslinking, making them attractive as a skin depot and suitable for intradermal injections, as they are readily dispensable through 27G needles. The effects of exposure to matrix metalloproteinase 9 (MMP-9) on the microparticles were evaluated by scanning electron microscopy and atomic force microscopy, demonstrating partial network destruction and decrease in elastic moduli. Given the recurring course of many skin diseases, the microparticles were exposed to MMP-9 in a flare-up mimicking fashion (multiple-time exposure), showing a significant increase in release of tofacitinib citrate (TC) from the MMP-responsive microparticles, which was not seen for the non-responsive microparticles (polyethylene glycol dithiol crosslinker). It was found that the degree of multi-arm complexity of the polyethylene glycol building blocks can be utilized to tune not only the release profile of TC but also the elastic moduli of the hydrogel microparticles, with Young's moduli ranging from 14 to 140 kPa going from 4-arm to 8-arm MMP-responsive microparticles. Finally, cytotoxicity studies conducted with skin fibroblasts showed no reduction in metabolic activity after 24 h exposure to the microparticles. Overall, these findings demonstrate that protease-responsive microparticles exhibit the properties of interest for intradermal drug delivery.

WFDC12-overexpressing contributes to the development of atopic dermatitis via accelerating ALOX12/15 metabolism and PAF accumulation

Atopic dermatitis (AD) is a chronic inflammatory skin disease characterized by eczema-like skin lesions, dry skin, severe itching, and recurrent recurrence. The whey acidic protein four-disulfide core domain gene WFDC12 is highly expressed in skin tissue and up-regulated in the skin lesions of AD patients, but its role and relevant mechanism in AD pathogenesis have not been studied yet. In this study, we found that the expression of WFDC12 was closely related to clinical symptoms of AD and the severity of AD-like lesions induced by DNFB in transgenic mice. WFDC12-overexpressing in the epidermis might promote the migration of skin-presenting cells to lymph nodes and increase Th cell infiltration. Meanwhile, the number and ratio of immune cells and mRNA levels of cytokines were significantly upregulated in transgenic mice. In addition, we found that ALOX12/15 gene expression was upregulated in the arachidonic acid metabolism pathway, and the corresponding metabolite accumulation was increased. The activity of epidermal serine hydrolase decreased and the accumulation of platelet-activating factor (PAF) increased in the epidermis of transgenic mice. Collectively, our data demonstrate that WFDC12 may contribute to the exacerbation of AD-like symptoms in DNFB-induced mouse model by enhancing arachidonic acid metabolism and PAF accumulation and that WFDC12 may be a potential therapeutic target for human atopic dermatitis.

Investigations into the filaggrin null phenotype: showcasing the methodology for CRISPR/Cas9 editing of human keratinocytes

Ever since the association between filaggrin (FLG) loss-of-function mutations and ichthyosis vulgaris and atopic dermatitis disease onset was identified, filaggrins function has been under investigation. Intra-individual genomic predisposition, immunological confounders, and environmental interactions complicate the comparison between FLG genotypes and related causal effects. Using CRISPR/Cas9, we generated human FLG knockout (ΔFLG) N/TERT-2G keratinocytes. Filaggrin deficiency was demonstrated by immunohistochemistry of human epidermal equivalent (HEE) cultures. Next to (partial) loss of structural proteins (IVL, HRNR, KRT2, and TGM1), the stratum corneum was more dense and lacked the typical basket weave appearance. In addition, electrical impedance spectroscopy and transepidermal water loss analyses highlighted a compromised epidermal barrier in ΔFLG-HEEs. Correction of FLG reinstated the presence of keratohyalin granules in the stratum granulosum, filaggrin protein expression, and expression of aforementioned proteins. The beneficial effects on stratum corneum formation were reflected by normalization of EIS and TEWL. This study demonstrates the causal phenotypical and functional consequences of filaggrin deficiency, indicating filaggrin is not only central in epidermal barrier function but also vital for epidermal differentiation by orchestrating the expression of other important epidermal proteins. These observations pave the way to fundamental investigations into the exact role of filaggrin in skin biology and disease.

New links for meprin β within the protease web

Proteases are organised in interconnected networks, together forming the protease web whose disturbance can have detrimental consequences for tissue homeostasis and response to environmental insults. Membrane-anchored sheddases are proteases that themselves can be released into the pericellular space by ectodomain shedding. Werny et al. have uncovered unexpected promiscuity in ectodomain shedding of meprin β, a metalloprotease with critical functions in inflammation and fibrosis. These findings suggest new links within complex proteolytic networks like the epidermal protease network with potential implications for skin homeostasis, inflammation and response to injury. Comment on: https://doi.org/10.1111/febs.16586.

Subcutaneous Catabolism of Peptide Therapeutics: Bioanalytical Approaches and ADME Considerations

Many peptide drugs such as insulin and glucagon-like peptide (GLP-1) analogues are successfully administered subcutaneously (SC). Following SC injection, peptides may undergo catabolism in the SC compartment before entering systemic circulation, which could compromise their bioavailability and in turn affect their efficacy.This review will discuss how both technology and strategy have evolved over the past years to further elucidate peptide SC catabolism.Modern bioanalytical technologies (particularly liquid chromatography-high-resolution mass spectrometry) and bioinformatics platforms for data mining has prompted the development of in silico, in vitro and in vivo tools for characterizing peptide SC catabolism to rapidly address proteolytic liabilities and, ultimately, guide the design of peptides with improved SC bioavailability.More predictive models able to recapitulate the interplay between SC catabolism and other factors driving SC absorption are highly desirable to improve in vitro/in vivo correlations.We envision the routine incorporation of in vitro and in vivo SC catabolism studies in ADME screening funnels to develop more effective peptide drugs for SC delivery.

SerpinB7 deficiency contributes to development of psoriasis via calcium-mediated keratinocyte differentiation dysfunction

Defective execution of proteases and protease inhibitors that mediate abnormal signaling cascades is emerging as a key contributor to skin diseases, such as psoriasis. SerpinB7 is identified as a skin-specific endogenous protease inhibitor, but the role and underlying mechanism in psoriasis are poorly understood. Here we found that SerpinB7 is highly expressed in psoriatic keratinocytes of patients and imiquimod-induced psoriatic lesions in mice. SerpinB7^-/- mice showed abnormal epidermal barrier integrity and skin architecture in homeostasis, and aggravated psoriatic lesion with inhibiting terminal differentiation and increasing inflammatory cells infiltration compared to SerpinB7^+/+ mice after Imiquimod treatment. Mechanistically, SerpinB7 deficiency results in excessive proliferation and impaired differentiation, as well as increased chemokines and antimicrobial peptide expression in normal human epidermal keratinocyte and mouse primary keratinocyte. Transcriptomics and proteomics results showed that the SeprinB7 deficiency affected keratinocyte differentiation and proinflammatory cytokines, possibly by affecting the calcium ion channel-related proteins. Notably, we demonstrated that SerpinB7 deficiency prevented the increase in intracellular Ca²⁺ influx, which was partly eliminated by the intracellular Ca²⁺ chelator BAPTA-AM. Our findings first described the critical role of SerpinB7 in the regulation of keratinocyte differentiation and psoriatic microenvironment mediated via keratinocytes' intracellular calcium flux, proposing a new candidate for therapeutic targets in psoriasis.

Biopolymer Nano-Network for Antimicrobial Peptide Protection and Local Delivery

Antimicrobial resistance (AMR) develops when bacteria no longer respond to conventional antimicrobial treatment. The limited treatment options for resistant infections result in a significantly increased medical burden. Antimicrobial peptides offer advantages for treatment of resistant infections, including broad-spectrum activity and lower risk of resistance development. However, sensitivity to proteolytic cleavage often limits their clinical application. Here, a moldable and biodegradable colloidal nano-network is presented that protects bioactive peptides from enzymatic degradation and delivers them locally. An antimicrobial peptide, PA-13, is encapsulated electrostatically into positively and negatively charged nanoparticles made of chitosan and dextran sulfate without requiring chemical modification. Mixing and concentration of oppositely charged particles form a nano-network with the rheological properties of a cream or injectable hydrogel. After exposure to proteolytic enzymes, the formed nano-network loaded with PA-13 eliminates Pseudomonas aeruginosa during in vitro culture and in an ex vivo porcine skin model while the unencapsulated PA-13 shows no antibacterial effect. This demonstrates the ability of the nano-network to protect the antimicrobial peptide in an enzyme-challenged environment, such as a wound bed. Overall, the nano-network presents a useful platform for antimicrobial peptide protection and delivery without impacting peptide bioactivity.

Defining the Protease and Protease Inhibitor (P/PI) Proteomes of Healthy and Diseased Human Skin by Modified Systematic Review

Proteases and protease inhibitors (P/PIs) are involved in many biological processes in human skin, yet often only specific families or related groups of P/PIs are investigated. Proteomics approaches, such as mass spectrometry, can define proteome signatures (including P/PIs) in tissues; however, they struggle to detect low-abundance proteins. To overcome these issues, we aimed to produce a comprehensive proteome of all P/PIs present in normal and diseased human skin, in vivo, by carrying out a modified systematic review using a list of P/PIs from MEROPS and combining this with key search terms in Web of Science. Resulting articles were manually reviewed against inclusion/exclusion criteria and a dataset constructed. This study identified 111 proteases and 77 protease inhibitors in human skin, comprising the serine, metallo-, cysteine and aspartic acid catalytic families of proteases. P/PIs showing no evidence of catalytic activity or protease inhibition, were designated non-peptidase homologs (NPH), and no reported protease inhibitory activity (NRPIA), respectively. MMP9 and TIMP1 were the most frequently published P/PIs and were reported in normal skin and most skin disease groups. Normal skin and diseased skin showed significant overlap with respect to P/PI profile; however, MMP23 was identified in several skin disease groups, but was absent in normal skin. The catalytic profile of P/PIs in wounds, scars and solar elastosis was distinct from normal skin, suggesting that a different group of P/PIs is responsible for disease progression. In conclusion, this study uses a novel approach to provide a comprehensive inventory of P/PIs in normal and diseased human skin reported in our database. The database may be used to determine either which P/PIs are present in specific diseases or which diseases individual P/PIs may influence.

Reconstructing the epidermal proteolytic cascades in health and disease

The epidermis is the outer stratified epithelium of the skin, forming the physical barrier that is indispensable for homeostasis. Epidermal proteolysis, mainly but not exclusively executed by kallikrein-related peptidases (KLKs), is tightly regulated to ensure maintenance of physiological skin renewal and an intact skin barrier. Perturbation of epidermal proteolytic networks is implicated in a wide array of rare and common skin pathologies of diverse genetic backgrounds. Recent studies of monogenic human skin diseases and newly developed animal models have revealed new mechanisms of regulation of proteolytic pathways in epidermal physiology and in disease states. These new data have challenged some accepted views, for example the role of matriptase in epidermal desquamation, which turned out to be restricted to mouse skin. The significance of PAR2 signaling in skin inflammation should also be reconsidered in the face of recent findings. Cumulatively, recent studies necessitate a sophisticated redefinition of the proteolytic and signaling pathways that operate in human skin. We elaborate how epidermal proteolysis is finely regulated at multiple levels, and in a spatial manner that was not taken into consideration so far, in which specific proteases are confined to distinct epidermal sublayers. Of interest, transglutaminases have emerged as regulators of epidermal proteolysis and desquamation by spatially fixing endogenous protease inhibitors, constituting regulatory factors that were not recognized before. Furthermore, new evidence suggests a link between proteolysis and lipid metabolism. By synthesis of established notions and recent discoveries, we provide an up-to-date critical parathesis of current knowledge and the extended complexity of proteolysis regulation and signaling pathways in skin. This article is protected by copyright. All rights reserved.

Acral peeling in Nagashima type palmo-plantar keratosis patients reveals the role of serine protease inhibitor B 7 in keratinocyte adhesion

Acral peeling skin syndrome (APSS) is a heterogenous group of genodermatoses, manifested by peeling of palmo-plantar skin and occasionally associated with erythema and epidermal thickening. A subset of APSS is caused by mutations in protease inhibitor encoding genes, resulting in unopposed protease activity and desmosomal degradation and/or mis-localization, leading to enhanced epidermal desquamation. We investigated two Arab-Muslim siblings with mild keratoderma and prominent APSS since infancy. Genetic analysis disclosed a homozygous mutation in SERPINB7, c.796C > T, which is the founder mutation in Nagashima type palmo-plantar keratosis (NPPK). Although not previously formally reported, APSS was found in other patients with NPPK. We hypothesized that loss of SERPINB7 function might contribute to the peeling phenotype through impairment of keratinocyte adhesion, similar to other protease inhibitor mutations that cause APSS. Mis-localization of desmosomal components was observed in a patient plantar biopsy compared with a biopsy from an age- and gender-matched healthy control. Silencing of SERPINB7 in normal human epidermal keratinocytes led to increased cell sheet fragmentation upon mechanical stress. Immunostaining showed reduced expression of desmoglein 1 and desmocollin 1. This study shows that in addition to stratum corneum perturbation, loss of SERPINB7 disrupts desmosomal components, which could lead to desquamation, manifested by skin peeling.

The Discovery and Function of Filaggrin

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

Syndecan-1 shedding by meprin β impairs keratinocyte adhesion and differentiation in hyperkeratosis

Dysregulation of proteolytic enzymes has huge impact on epidermal homeostasis, which can result in severe pathological conditions such as fibrosis or Netherton syndrome. The metalloprotease meprin β was found to be upregulated in hyperproliferative skin diseases. AP-1 transcription factor complex has been reported to induce Mep1b expression. Since AP-1 and its subunit fos-related antigen 2 (fra-2) are associated with the onset and progression of psoriasis, we wanted to investigate if this could partially be attributed to increased meprin β activity. Here, we demonstrate that fra-2 transgenic mice show increased meprin β expression and proteolytic activity in the epidermis. To avoid influence by other fra-2 regulated genes, we additionally generated a mouse model that enabled tamoxifen-inducible expression of meprin β under the Krt5-promotor to mimic the pathological condition. Interestingly, induced meprin β expression in the epidermis resulted in hyperkeratosis, hair loss and mottled pigmentation of the skin. Employing N-terminomics revealed syndecan-1 as a substrate of meprin β in skin. Shedding of syndecan-1 at the cell surface caused delayed calcium-induced differentiation and impaired adhesion of keratinocytes, which was blocked by the meprin β inhibitor fetuin-B.

Fox sign in a case of terminal stage pancreatic cancer and suggestions for diagnosis

Skin signs in acute pancreatitis are well-known and frequently discussed manifestations accompanied by unfavorable prognoses although they may rarely appear in clinical and forensic medicine. In 2018, the district attorney’s office ordered a forensic autopsy for a 74-year-old man with terminal stage pancreatic cancer. The autopsy was ordered based on accusations of the deceased’s widow regarding alleged medical malpractice and poor hospital care. The widow filed a grievance about multiple unsuccessful attempts to draw blood from her husband in addition to a diaper dermatitis at the right groin. An autopsy and additional histological examinations were performed. After considering all findings, the diaper dermatitis was eventually assumed to be a Fox sign caused by acute pancreatitis, and the allegations of medical malpractice were refuted. This case led us to identify another case with suspected cutaneous manifestations in pancreatic disease. We performed immunohistochemical staining on those two cases and six control cases to examine whether there was detectable presence of pancreatic lipase and trypsin in the skin discolorations and whether it could be used as a feasible method to verify skin signs associated with pancreatitis. Based on our findings, a minor disseminated lipase and trypsin staining should be considered regular and is therefore not conclusive of a skin sign associated with pancreatitis. Moreover, trypsin does not seem to be as suitable as lipase for this suggested immunohistochemical method. Nevertheless, this method might be a useful addition for determining the origin of skin discoloration and verifying skin signs associated with pancreatitis.

Functional role of kallikrein 5 and proteinase-activated receptor 2 in eosinophilic esophagitis

Eosinophilic esophagitis (EoE) is a chronic, food antigen-driven, inflammatory disease of the esophagus and is associated with impaired barrier function. Evidence is emerging that loss of esophageal expression of the serine peptidase inhibitor, kazal type 7 (SPINK7), is an upstream event in EoE pathogenesis. Here, we provide evidence that loss of SPINK7 mediates its pro-EoE effects via kallikrein 5 (KLK5) and its substrate, protease-activated receptor 2 (PAR2). Overexpression of KLK5 in differentiated esophageal epithelial cells recapitulated the effect of SPINK7 gene silencing, including barrier impairment and loss of desmoglein-1 expression. Conversely, KLK5 deficiency attenuated allergen-induced esophageal protease activity, modified commensal microbiome composition, and attenuated eosinophilia in a murine model of EoE. Inhibition of PAR2 blunted the cytokine production associated with loss of SPINK7 in epithelial cells and attenuated the allergen-induced esophageal eosinophilia in vivo. Clinical samples substantiated dysregulated PAR2 expression in the esophagus of patients with EoE, and delivery of the clinically approved drug α1 antitrypsin (A1AT, a protease inhibitor) inhibited experimental EoE. These findings demonstrate a role for the balance between KLK5 and protease inhibitors in the esophagus and highlight EoE as a protease-mediated disease. We suggest that antagonizing KLK5 and/or PAR2 has potential to be therapeutic for EoE.

A unique mode of keratinocyte death requires intracellular acidification

The stratum corneum (SC), the outermost epidermal layer, consists of nonviable anuclear keratinocytes, called corneocytes, which function as a protective barrier. The exact modes of cell death executed by keratinocytes of the upper stratum granulosum (SG1 cells) remain largely unknown. Here, using intravital imaging combined with intracellular Ca²⁺- and pH-responsive fluorescent probes, we aimed to dissect the SG1 death process in vivo. We found that SG1 cell death was preceded by prolonged (∼60 min) Ca²⁺ elevation and rapid induction of intracellular acidification. Once such intracellular ionic changes were initiated, they became sustained, irreversibly committing the SG1 cells to corneocyte conversion. Time-lapse imaging of isolated murine SG1 cells revealed that intracellular acidification was essential for the degradation of keratohyalin granules and nuclear DNA, phenomena specific to SC corneocyte formation. Furthermore, intravital imaging showed that the number of SG1 cells exhibiting Ca²⁺ elevation and the timing of intracellular acidification were both tightly regulated by the transient receptor potential cation channel V3. The functional activity of this protein was confirmed in isolated SG1 cells using whole-cell patch-clamp analysis. These findings provide a theoretical framework for improved understanding of the unique molecular mechanisms underlying keratinocyte-specific death mode, namely corneoptosis.

Redirecting drug repositioning to discover innovative cosmeceuticals

Skin appearance is essential for self-esteem and quality of life; consequently, skin care products represent a huge market. In particular, cosmeceuticals constitute a hybrid category of skin care formulations, at the interphase of cosmetics and pharmaceuticals, rationally designed to target (patho) physiological mechanisms aiming to enhance skin health and appearance. Cosmeceuticals are marketed as anti-ageing, anti-wrinkle, hair regrowth, skin whitening and wound healing agents with special emphasis on scar-free healing. An overview on recent cutting-edge advances concerning the discovery and development of enhanced performance cosmeceuticals by drug repositioning approaches is presented here. In this context, we propose "target repositioning," a new term, to highlight that druggable protein targets implicated in multiple diseases (hubs in the diseasome) can be exploited to accelerate the discovery of molecularly targeted cosmeceuticals that can promote skin health as an added benefit, which is a novel concept not described before. In this direction, emphasis is placed on the role of mouse models, for often untreatable skin diseases, as well as recent breakthroughs on monogenic rare skin syndromes, in promoting compound repositioning to innovative cosmeceuticals.

Peptides as Active Ingredients: A Challenge for Cosmeceutical Industry

Cosmeceutical field, which merges cosmetics and pharmaceuticals, is nowadays a highly investigated research area, because a scientific demonstration of the claimed bioactivity of new cosmeceutical ingredients is increasingly requested. In fact, an aspect differentiating traditional cosmetics from cosmeceuticals is the identification and characterization of the active ingredients and demonstrating its efficacy in the claimed activity. An interesting group of bioactive cosmeceutical ingredients are peptides, which due to their particular properties, meets most of the requirements presented by the cosmeceutical industry when composing new formulas. In this context, beside bioactivity, two additional aspects have been recently considered, when dealing with peptides as cosmeceutical ingredients: bioavailability and stability. We describe herein novel methods applied in order to enhance peptides skin-penetration and stability, reviewing both scientific articles and patents, issued in the cosmeceutical arena.

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

BACKGROUND

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

SUMMARY

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

Biofilm propensity of Staphylococcus aureus skin isolates is associated with increased atopic dermatitis severity and barrier dysfunction in the MPAACH pediatric cohort

BACKGROUND

Atopic dermatitis (AD) patients are often colonized with Staphylococcus aureus, and staphylococcal biofilms have been reported on adult AD skin lesions. The commensal S epidermidis can antagonize S aureus, although its role in AD is unclear. We sought to characterize S aureus and S epidermidis colonization and biofilm propensity and determine their associations with AD severity, barrier function, and epidermal gene expression in the first US early-life cohort of children with AD, the Mechanisms of Progression of Atopic Dermatitis to Asthma in Children (MPAACH).

METHODS

The biofilm propensity of staphylococcal isolates was assessed by crystal violet assays. Gene expression of filaggrin and antimicrobial alarmins S100A8 and S100A9 was measured in keratinocyte RNA extracted from skin tape strips. Staphylococcal biofilms sampled from MPAACH skin were visualized using scanning electron microscopy.

RESULTS

Sixty-two percent of staphylococcal isolates (sampled from 400 subjects) formed moderate/strong biofilms. Sixty-eight percent of subjects co-colonized with both staphylococcal species exhibited strains that formed cooperative mixed-species biofilms. Scanning electron microscopy verified the presence of staphylococcal biofilms on the skin of MPAACH children. Staphylococcus aureus strains showing higher relative biofilm propensity compared with S epidermidis were associated with increased AD severity (P = .03) and increased lesional and nonlesional transepidermal water loss (P = .01, P = .03).

CONCLUSIONS

Our data suggest a pathogenic role for S aureus biofilms in AD. We found that strain-level variation in staphylococcal isolates governs the interactions between S epidermidis and S aureus and that the balance between these two species, and their biofilm propensity, has important implications for AD.

Susceptibility of cosmeceutical peptides to proteases activity: Development of dermal stability test by LC-MS/MS analysis

Recently, several peptides are used as active ingredients in topical cosmetic formulations, few information are available on their dermal stability against proteases. In this study, it was developed a simple and reliable assay to evaluate the stability of cosmeceutical peptides in skin homogenates. The quantification of studied peptides was performed by liquid chromatography coupled with a triple quadrupole mass spectrometer operating in tandem mass spectrometry mode (LC-MS/MS) and the conditions were tuned through energy resolved MS/MS (ERMS) experiments. The sample preparation procedure was carried out on rat skin homogenates by employing pal-KTTKS (reference peptide and the parameters that may affect the assay results were evaluated, including substrate concentration, dilution of skin homogenate, protein concentration and batch-to-batch variation of the homogenate. The optimized conditions were applied to check the degradation profile of pal-KTTKS in human skin samples and the obtained results were compared. Finally, the degradation profiles of SA1-III and pamSA1-III, recently described as cosmeceutical peptides, in human skin homogenate were evaluated. The results showed that proposed peptides are stable toward proteases for up to 8 h of incubation. Thanks to this characteristic, these peptides can be considered very interesting candidates as active ingredients for creams intended for a daily application.

The Whey Acidic Protein WFDC12 Is Specifically Expressed in Terminally Differentiated Keratinocytes and Regulates Epidermal Serine Protease Activity

WFDC proteins such as peptidase inhibitor 3 and SLPI inhibit proteases in the epidermis and other tissues. In this study, we tested the hypothesis that further WFDC protein family members might contribute to epidermal homeostasis. We found that in addition to peptidase inhibitor 3 and SLPI, WFDC5 and WFDC12 were expressed in human epidermis. In contrast to WFDC5, the expression of WFDC12 was induced during the late differentiation of keratinocytes and was restricted to the outermost layer of live cells. Single-cell RNA sequencing demonstrated that WFDC12-positive keratinocytes were characterized by the upregulation of LCE mRNA expression and downregulated the expression of keratins and claudins. Immunogold-electron microscopy revealed the colocalization of WFDC12 with corneodesmosomes in the lower stratum corneum. WFDC12 was elevated in the affected skin of patients with psoriasis, atopic dermatitis, and Darier disease. By contrast, WFDC12 expression was strongly upregulated not only in the affected but even more so in clinically normal-appearing skin of patients with Netherton syndrome. Finally, functional analysis showed distinct inhibitory activity of WFDC12 on neutrophil elastase and epidermal kallikrein‒related peptidase. Altogether, our study identified WFDC12 as a marker of the last stage of epidermal keratinocyte differentiation and suggests that WFDC12 contributes to the control of protease activity in the stratum corneum.

Sustained Secretion of the Antimicrobial Peptide S100A7 Is Dependent on the Downregulation of Caspase-8

Antimicrobial peptides (AMPs) are the body's natural innate immune defense against a spectrum of pathogens and can also modulate cell proliferation, chemotaxis, angiogenesis, wound healing, and immune cell activity. Harnessing these diverse functions for prophylactic use is contingent upon understanding the regulatory mechanisms governing their unconventional secretion from cells. Analysis of the secretion of S100A7 (Psoriasin), an abundant AMP stored in differentiated keratinocytes of the skin, has revealed an unexpected biphasic secretory response to bacterial exposure. The core components regulating S100A7 secretion are NFκB/p38MAPK, caspase-1, and interleukin (IL)-1α. The initial activation of this core machinery is mediated by Toll-like receptor signaling, whereas the chronic response is mediated by Caspase-8 downregulation. Interestingly, there is a concomitant downregulation of Caspase-8 in inflammatory skin diseases wherein S100A7 is constitutively released. These results highlight the potential of targeting these components to control the release of AMPs from the skin in both homeostatic and disease conditions.

Which Way Do We Go? Complex Interactions in Atopic Dermatitis Pathogenesis

Atopic dermatitis (AD) is a common, chronic, inflammatory skin condition characterized by recurrent and pruritic skin eruptions. Multiple factors contribute to the pathogenesis of AD, including skin barrier dysfunction, microbial dysbiosis, and immune dysregulation. Interactions among these factors form a complex, multidirectional network that can reinforce atopic skin disease but can also be ameliorated by targeted therapies. This review summarizes the complex interactions among contributing factors in AD and the implications on disease development and therapeutic interventions.

Serine Protease-Mediated Cutaneous Inflammation: Characterization of an Ex Vivo Skin Model for the Assessment of Dexamethasone-Loaded Core Multishell-Nanocarriers

Standard experimental set-ups for the assessment of skin penetration are typically performed on skin explants with an intact skin barrier or after a partial mechanical or chemical perturbation of the stratum corneum, but they do not take into account biochemical changes. Among the various pathological alterations in inflamed skin, aberrant serine protease (SP) activity directly affects the biochemical environment in the superficial compartments, which interact with topically applied formulations. It further impacts the skin barrier structure and is a key regulator of inflammatory mediators. Herein, we used short-term cultures of ex vivo human skin treated with trypsin and plasmin as inflammatory stimuli to assess the penetration and biological effects of the anti-inflammatory drug dexamethasone (DXM), encapsulated in core multishell-nanocarriers (CMS-NC), when compared to a standard cream formulation. Despite a high interindividual variability, the combined pretreatment of the skin resulted in an average 2.5-fold increase of the transepidermal water loss and swelling of the epidermis, as assessed by optical coherence tomography, as well as in a moderate increase of a broad spectrum of proinflammatory mediators of clinical relevance. The topical application of DXM-loaded CMS-NC or DXM standard cream revealed an increased penetration into SP-treated skin when compared to untreated control skin with an intact barrier. Both formulations, however, delivered sufficient amounts of DXM to effectively suppress the production of interleukin-6 (IL-6), interleukin-8 (IL-8) and Thymic Stromal Lymphopoietin (TSLP). In conclusion, we suggest that the herein presented ex vivo inflammatory skin model is functional and could improve the selection of promising drug delivery strategies for anti-inflammatory compounds at early stages of development.

Biochemical Characterization of Human Retroviral-Like Aspartic Protease 1 (ASPRV1)

The human retroviral-like aspartic protease 1 (ASPRV1) is a mammalian retroviral-like enzyme that catalyzes a critical proteolytic step during epidermal differentiation; therefore, it is also referred to as skin-specific aspartic protease (SASPase). Neutrophil granulocytes were also found recently to express ASPRV1 that is involved in the progression of acute chronic inflammation of the central nervous system, especially in autoimmune encephalomyelitis. Thus, investigation of ASPRV1 is important due to its therapeutic or diagnostic potential. We investigated the structural characteristics of ASPRV1 by homology modeling; analysis of the proposed structure was used for interpretation of in vitro specificity studies. For in-vitro characterization, activities of SASP28 and SASP14 enzyme forms were measured using synthetic oligopeptide substrates. We demonstrated that self-processing of SASP28 precursor causes autoactivation of the protease. The highest activity was measured for GST-SASP14 at neutral pH and at high ionic strength, and we proved that pepstatin A and acetyl-pepstatin can also inhibit the protease. In agreement with the structural characteristics, the relatively lower urea dissociation constant implied lower dimer stability of SASP14 compared to that of HIV-1 protease. The obtained structural and biochemical characteristics support better understanding of ASPRV1 function in the skin and central nervous system.

Photo-responsive supramolecular hyaluronic acid hydrogels for accelerated wound healing

Supramolecular hydrogels confer control over structural properties in a reversible, dynamic, and biomimetic fashion. The design of supramolecular hydrogels with an improved structural and functional recapitulation of damaged organs is important for clinical applications. For wound healing management, in particular, an effective healing process, through the modulation of epidermal growth factor (EGF) delivery using supramolecular polysaccharide hydrogels, has yet to be developed. In this study, photo-responsive supramolecular polysaccharide hydrogels were formed through host-guest interactions between azobenzene and β-cyclodextrin groups conjugated to hyaluronic acid chains. By exploiting the photoisomerization properties of azobenzene under different wavelengths, a supramolecular hydrogel featuring a dynamic spatial network crosslink density through the application of a light stimulus was obtained. Under ultra violet (UV) light, the loosened hydrogel can rapidly release EGF, thereby enhancing EGF delivery at the wound site. Based on an in vivo assessment of the healing process through a full-thickness skin defect model, the controlled EGF release from a supramolecular hydrogel exhibited superior wound healing efficiency with respect to granulation tissue formation, growth factor levels, and angiogenesis. Therefore, the proposed supramolecular hydrogels are potentially valuable as controlled delivery systems for future clinical wound healing applications.

Novel Antimicrobial Peptides Formulated in Chitosan Matrices are Effective Against Biofilms of Multidrug-Resistant Wound Pathogens

INTRODUCTION

Infection frequently complicates the treatment of combat-related wounds, impairs healing, and leads to worse outcomes. To better manage wound infections, antimicrobial therapies that are effective against biofilm and designed for direct wound application are needed. The primary objective of this work was to evaluate a chitosan matrix for delivery of two engineered antimicrobial peptides, (ASP)-1 and ASP-2, to treat biofilm-associated bacteria. A secondary objective was to determine whether replacing the levorotatory (L) form amino acids in ASP-2 with dextrorotatory (D) form amino acids would impact peptide activity.

MATERIALS AND METHODS

Chitosan gels loaded with antimicrobial peptides were evaluated for peptide release over 7 days and tested for efficacy against biofilms grown both in vitro on polymer mesh and ex vivo on porcine skin.

RESULTS

When delivered via chitosan, 70% to 80% of peptides were released over 7 days. Gels eradicated biofilms of gram-positive and gram-negative, drug-resistant bacteria in vitro and ex vivo. Under the conditions tested, no meaningful differences in peptide activity between the L and D forms of ASP-2 were detected.

CONCLUSIONS

Chitosan serves as an effective delivery platform for ASP-1 and ASP-2 to treat biofilm-embedded bacteria and warrants further development as a topical treatment.

Proteolysis and Oxidation of Therapeutic Proteins After Intradermal or Subcutaneous Administration

The intradermal (ID) and subcutaneous (SC) routes are commonly used for therapeutic proteins (TPs) and vaccines; however, the bioavailability of TPs is typically less than small molecule drugs given via the same routes. Proteolytic enzymes in the dermal, SC, and lymphatic tissues may be responsible for the loss of TPs. In addition, the TPs may be exposed to reactive oxygen species generated in the SC tissue and the lymphatic system in response to injection-related trauma and impurities within the formulation. The reactive oxygen species can oxidize TPs to alter their efficacy and immunogenicity potential. Mechanistic understandings of the dominant proteolysis and oxidative routes are useful in the drug discovery process, formulation development, and to assess the potential for immunogenicity and altered pharmacokinetics (PK). Furthermore, in vitro tools representing the ID or SC and lymphatic system can be used to evaluate the extent of proteolysis of the TPs after the injection and before systemic entry. The in vitro clearance data may be included in physiologically based pharmacokinetic models for improved PK predictions. In this review, we have summarized various physiological factors responsible for proteolysis and oxidation of TPs after ID and SC administration.

Bleomycin hydrolase regulates the release of chemokines important for inflammation and wound healing by keratinocytes

Bleomycin hydrolase (BLMH) is a well-conserved cysteine protease widely expressed in several mammalian tissues. In skin, which contains high levels of BLMH, this protease is involved in the degradation of citrullinated filaggrin monomers into free amino acids important for skin hydration. Interestingly, the expression and activity of BLMH is reduced in patients with atopic dermatitis (AD) and psoriasis, and BLMH knockout mice acquire tail dermatitis. Apart from its already known function, we have discovered a novel role of BLMH in the regulation of inflammatory chemokines and wound healing. We show that lowered BLMH levels in keratinocytes result in increased release of the pro-inflammatory chemokines CXCL8 and GROα, which are upregulated in skin from AD patients compared to healthy individuals. Conditioned media from keratinocytes expressing low levels of BLMH increased chemotaxis by neutrophils and caused a delayed wound healing in the presence of low-level TNFα. This defective wound healing was improved by blocking the shared receptor of CXCL8 and GROα, namely CXCR2, using a specific receptor antagonist. Collectively, our results present a novel function of BLMH in regulating the secretion of chemokines involved in inflammation and wound healing in human keratinocytes.

Epithelial origin of eosinophilic esophagitis

Eosinophilic esophagitis (EoE) is a chronic, allergen-driven inflammatory disease of the esophagus characterized predominantly by eosinophilic inflammation, leading to esophageal dysfunction. Converging data have placed the esophageal epithelium at the center of disease pathogenesis. In particular, the main EoE disease susceptibility loci at 2p23 and 5p22 encode for gene products that are produced by the esophageal epithelium: the intracellular protease calpain 14 and thymic stromal lymphopoietin, respectively. Furthermore, genetic and functional data establish a primary role for impaired epithelial barrier function in disease susceptibility and pathoetiology. Additionally, the EoE transcriptome, a set of genes dysregulated in the esophagi of patients with EoE, is enriched in genes that encode for proteins involved in esophageal epithelial cell differentiation. This transcriptome has a high proportion of esophagus-specific epithelial genes that are notable for the unexpected enrichment in genes encoding for proteases and protease inhibitors, as well as in IL-1 family genes, demonstrating a previously unappreciated role for innate immunity responses in the esophagus under homeostatic conditions. Among these pathways, basal production of the serine protease inhibitor, Kazal-type 7 (SPINK7) has been demonstrated to be part of the normal differentiation program of esophageal epithelium. Profound lost expression of SPINK7 occurs in patients with EoE and is sufficient for unleashing increased proteolytic activity (including urokinase plasminogen activator), impaired barrier function, and production of large quantities of proinflammatory and proallergic cytokines, including thymic stromal lymphopoietin. Collectively, we put forth a model in which the esophagus is normally equipped as an anti-inflammatory sensing organ and that defects in this pathway, mediated by epithelial protease/protease inhibitor imbalances, unleash inflammatory responses resulting in disorders, such as EoE.

Control of cell death-associated danger signals during cornification prevents autoinflammation of the skin

The function of the skin as a barrier to the environment is mainly achieved by the outermost layers of the epidermis. In the granular layer, epidermal keratinocytes undergo the last steps of their terminal differentiation program resulting in cornification. The coordinated conversion of living keratinocytes into corneocytes, the building blocks of the cornified layer, represents a unique form of programmed cell death. Recent studies have identified numerous genes that are specifically expressed in terminally differentiated keratinocytes and, surprisingly, this genetic program does not only include mediators of cornification but also suppressors of pyroptosis, another mode of programmed cell death. Pyroptosis is activated by inflammasomes, leads to the release of interleukin-1 (IL-1) family cytokines, and thereby activates inflammation. In addition, inhibitors of potentially pro-inflammatory proteases and enzymes removing danger-associated cytoplasmic DNA are expressed in differentiated keratinocytes. We propose the concept of cornification as an inherently hazardous process in which damaging side effects are actively suppressed by protective mechanisms. In support of this hypothesis, loss-of-function mutations in epidermal protease inhibitors and IL-1 family antagonists suffice to induce autoinflammation. Similarly, exogenous disturbances of either cornification or its accompanying control mechanisms may be starting points for skin inflammation. Further studies into the relationship between cornification, pyroptosis and other forms of cell death will help to define the initiation phase of inflammatory skin diseases and offer new targets for disease prevention and therapy.

Profiling system for skin kallikrein proteolysis applied in gene-deficient mouse models

Kallikrein-related proteases (KLKs) play a critical role in epidermis physiology and have been implicated in skin pathologies such as Netherton syndrome. The contribution of individual KLKs to skin proteolysis is poorly understood. Monitoring of their activities in skin proteome is hampered by overlapping substrate specificities, and there is a need for novel assays. Here, we present a platform of selective and sensitive fluorogenic substrates and inhibitors for profiling KLK5, KLK7 and KLK14. These chemical tools were evaluated using recombinant KLKs and tissue from a unique set of mice deficient in eight combinations of KLKs and their natural regulator LEKTI.

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

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

Deficiency of the human cysteine protease inhibitor cystatin M/E causes hypotrichosis and dry skin

Purpose

We aimed to assess the biological and clinical significance of the human cysteine protease inhibitor cystatin M/E, encoded by the CTS6 gene, in diseases of human hair and skin.

Methods

Exome and Sanger sequencing was performed to reveal the genetic cause in two related patients with hypotrichosis. Immunohistochemical, biophysical, and biochemical measurements were performed on patient skin and 3D-reconstructed skin from patient-derived keratinocytes.

Results

We identified a homozygous variant c.361C>T (p.Gln121*), resulting in a premature stop codon in exon 2 of CST6 associated with hypotrichosis, eczema, blepharitis, photophobia and impaired sweating. Enzyme assays using recombinant mutant cystatin M/E protein, generated by site-directed mutagenesis, revealed that this p.Gln121* variant was unable to inhibit any of its three target proteases (legumain and cathepsins L and V). Three-dimensional protein structure prediction confirmed the disturbance of the protease/inhibitor binding sites of legumain and cathepsins L and V in the p.Gln121* variant.

Conclusion

The herein characterized autosomal recessive hypotrichosis syndrome indicates an important role of human cystatin M/E in epidermal homeostasis and hair follicle morphogenesis.

Skin-homing CD8+ T cells preferentially express GPI-anchored peptidase inhibitor 16, an inhibitor of cathepsin K

This study sought to identify novel CD8⁺ T cell homing markers by studying acute graft versus host disease (aGvHD), typically involving increased T cell homing to the skin and gut. FACS-sorted skin-homing (CD8β⁺ /CLA⁺ ), gut-homing (CD8β⁺ /integrinβ7⁺ ), and reference (CD8β⁺ /CLA^- /integrinβ7^- ) T cells were compared in patients affected by cutaneous and/or gastrointestinal aGVHD. Microarray analysis, qPCR, and flow cytometry revealed increased expression of peptidase inhibitor 16 (PI16) in skin-homing CD8⁺ T cells. Robust association of PI16 with skin homing was confirmed in all types of aGvHD and in healthy controls, too. PI16 was not observed on CLA⁺ leukocytes other than T cells. Induction of PI16 expression on skin-homing T cells occurred independently of vitamin D3. Among skin-homing T cells, PI16 expression was most pronounced in memory-like CD45RO⁺ /CD127⁺ /CD25⁺ /CD69^- /granzyme B^- cells. PI16 was confined to the plasma membrane, was GPI-anchored, and was lost upon restimulation of memory CD8⁺ T cells. Loss of PI16 occurred by downregulation of PI16 transcription, and not by Phospholipase C (PLC)- or Angiotensin-converting enzyme (ACE)-mediated shedding, or by protein recycling. Inhibitor screening and pull-down experiments confirmed that PI16 inhibits cathepsin K, but may not bind to other skin proteases. These data link PI16 to skin-homing CD8⁺ T cells, and raise the possibility that PI16 may regulate cutaneous cathepsin K.

Activography reveals aberrant proteolysis in desquamating diseases of differing backgrounds

The role of epidermal proteolysis in overdesquamation was revealed in Netherton syndrome, a rare ichthyosis due to genetic deficiency of the LEKTI inhibitor of serine proteases. Recently, we developed activography, a new histochemical method, to spatially localize and semiquantitatively assess proteolytic activities using activity-based probes. Activography provides specificity and versatility compared to in situ zymography, the only available method to determine enzymatic activities in tissue biopsies. Here, activography was validated in skin biopsies obtained from an array of distinct disorders and compared with in situ zymography. Activography provides a methodological advancement due to its simplicity and specificity and can be readily adapted as a routine diagnostic assay. Interestingly, the levels of epidermal proteolysis correlated with the degree of desquamation independent of skin pathology. Thus, deregulated epidermal proteolysis likely represents a universal mechanism underlying aberrant desquamation.

Development of a skin-friendly microemulsion for dermal allergen-specific immunotherapy

Due to their role in immune responses, the skin dendritic cells (i.e. epidermal Langerhans cells and dermal dendritic cells) have become of great interest to researchers in the past decades. A dermal administration of allergens could target these professional antigen-presenting cells directly and build up immunotolerance. Additionally, many of the adverse side effects, which are seen in the current state of the art specific immunotherapy routes, could be avoided. Therefore, in this study a penetration enhancing microemulsion was developed and its physicochemical properties were determined under several storage conditions. The influence of different preservatives on the microemulsion stability was observed. We examined epidermal penetration of Alexa Fluor-647 labelled bee-venom phospholipase A2 (Api m 1) using the Franz diffusion cell set up and confocal laser-scanning microscopy. First results of an in-vivo Api m 1-allergic mouse model indicated the protective efficacy of dermal AIT with our newly developed microemulsion. Summarily, the developed microemulsion is a suitable, stable drug delivery system for the topical administration of proteogenic allergens into the epidermis and is able to reach dendritic cells in the skin.

Evidence of an abnormal epithelial barrier in active, untreated and corticosteroid-treated eosinophilic esophagitis

BACKGROUND

Eosinophilic esophagitis (EoE) is a chronic, immune/antigen-mediated disease characterized by symptoms related to esophageal dysfunction and an eosinophil-predominant inflammation. This study has aimed to investigate whether the recently observed sensitization to Candida albicans in patients with EoE is owing to pre-existing disease and its underlying abnormal epithelial barrier or, alternatively, is linked to corticosteroid (CS) therapy.

METHODS

Medical histories, as well as serum and tissue samples of 60 patients with EoE (15 CS naive, 45 with current or previous CS therapy) and 20 controls, stored in the Swiss Eosinophilic Esophagitis Database (SEED) and Biobank, were analyzed. We applied ImmunoCAP to measure IgE levels and immunofluorescence techniques to examine epithelial barrier components.

RESULTS

Patients with EoE had higher total IgE levels and were more frequently sensitized to C. albicans than controls. In EoE tissue specimens, increased numbers of eosinophils and mast cells, a higher expression levels of thymic stromal lymphopoietin (TSLP), cathelicidin, proteases, that is, the kallikreins (KLK)-5 and KLK-7, were observed as compared with controls, while reduced expression of lympho-epithelial Kazal-type-related inhibitor (LEKTI), filaggrin, E-cadherin, claudin, occludin, desmoglein-1 was found, independent of CS therapy. In CS-treated EoE, significantly lower numbers of CD1a+ cells and cathelicidin expression were noted as compared to CS-naive EoE.

CONCLUSION

This study provides further evidence that EoE is associated with an abnormal epithelial barrier and postulates that CS therapy, by reducing innate immune mechanisms, may promote C. albicans colonization and likely subsequent sensitization.