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

Regulation of epidermal barrier function and pathogenesis of psoriasis by serine protease inhibitors

Serine protease inhibitors (Serpins) are a protein superfamily of protease inhibitors that are thought to play a role in the regulation of inflammation, immunity, tumorigenesis, coagulation, blood pressure and cancer metastasis. Serpins is enriched in the skin and play a vital role in modulating the epidermal barrier and maintaining skin homeostasis. Psoriasis is a chronic inflammatory immune-mediated skin disease. At present, most serpins focus on the pathogenesis of psoriasis vulgaris. Only a small number, such as the mutation of SerpinA1/A3/B3, are involved in the pathogenesis of GPP. SerpinA12 and SerpinG1 are significantly elevated in the serum of patients with psoriatic arthritis, but their specific mechanism of action in psoriatic arthritis has not been reported. Some Serpins, including SerpinA12, SerpinB2/B3/B7, play multiple roles in skin barrier function and pathogenesis of psoriasis. The decrease in the expression of SerpinA12, SerpinB7 deficiency and increase in expression of SerpinB3/4 in the skin can promote inflammation and poor differentiation of keratinocyte, with damaged skin barrier. Pso p27, derived from SerpinB3/B4, is an autoantigen that can enhance immune response in psoriasis. SerpinB2 plays a role in maintaining epidermal barrier integrity and inhibiting keratinocyte proliferation. Here we briefly introduce the structure, functional characteristics, expression and distribution of serpins in skin and focus on the regulation of serpins in the epidermal barrier function and the pathogenic role of serpins in psoriasis.

Hair follicles modulate skin barrier function

Our skin provides a protective barrier that shields us from our environment. Barrier function is typically associated with the interfollicular epidermis; however, whether hair follicles influence this process remains unclear. Here, we utilize a potent genetic tool to probe barrier function by conditionally ablating a quintessential epidermal barrier gene, Abca12, which is mutated in the most severe skin barrier disease, harlequin ichthyosis. With this tool, we deduced 4 ways by which hair follicles modulate skin barrier function. First, the upper hair follicle (uHF) forms a functioning barrier. Second, barrier disruption in the uHF elicits non-cell-autonomous responses in the epidermis. Third, deleting Abca12 in the uHF impairs desquamation and blocks sebum release. Finally, barrier perturbation causes uHF cells to move into the epidermis. Neutralizing IL-17a, whose expression is enriched in the uHF, partially alleviated some disease phenotypes. Altogether, our findings implicate hair follicles as multi-faceted regulators of skin barrier function.

Development of a back-titration assay to quantitate functional lympho-epithelial Kazal-type inhibitors (LEKTI) in skin samples

The lympho-epithelial Kazal-type inhibitors (LEKTI) are key to control skin turnover, and their absence causes Netherton syndrome. For clinical sample testing of LEKTI-based therapies, a robust analytical method to measure LEKTI-like activity in skin is required. This work reports on the development of a back-titration method to determine incremental LEKTI-like activity in skin samples. The method meets the analytical requirements for study sample testing, and reliable quantification can be achieved with negligible skin matrix interference. This assay does not provide analyte identity, but it can be used to measure treatment-driven increments of LEKTI-like activity within the skin epidermis.

Higher Expression of Lympho-epithelial Kazal-type-Related Inhibitor-1 Fragments and Decreased Desquamation in the Lesional Skin of Nummular Eczema

Nummular eczema, a chronic dermatitis characterized by coin-shaped lesions, was first documented in 1857. However, its pathophysiological characteristics are still not well known. To investigate differences in the regulation of the desquamation process in the stratum corneum of lesional and nonlesional skin of patients with nummular eczema and healthy control subjects, tape-stripped stratum corneum samples from patients with nummular eczema and healthy volunteers were analysed using immunofluorescence staining and western blot analysis. In the nummular eczema lesional skin, expression of desmoglein-1, desmocollin-1, and corneodesmosin exhibited a disorganized, dense or partially diffuse non-peripheral pattern with increased intensity, compared with the peripheral patterns observed in healthy or nonlesional skin, suggesting the impaired desquamation process in nummular eczema. Furthermore, although the expression of the desquamation-related serine proteases, kallikrein-related peptidase 7 and 5, was increased in nummular eczema lesional skin, the immunofluorescence staining of lympho-epithelial Kazal-type-related inhibitor-1, an endogenous inhibitor of various kallikrein-related peptidases, and its fragments were significantly increased in the nummular eczema lesional skin, suggesting its contribution to the inhibition of corneodesmosomal degradation. Therefore, the increased detection of corneodesmosomal proteins in nummular eczema lesions may be due to the increased amount of the fragments of lympho-epithelial Kazal-type-related inhibitor-1, which could contribute to delayed desquamation.

Comparative analyses of Netherton syndrome patients and Spink5 conditional knock-out mice uncover disease-relevant pathways

Netherton syndrome (NS) is a rare skin disease caused by loss-of-function mutations in the serine peptidase inhibitor Kazal type 5 (SPINK5) gene. Disease severity and the lack of efficacious treatments call for a better understanding of NS mechanisms. Here we describe a novel and viable, Spink5 conditional knock-out (cKO) mouse model, allowing to study NS progression. By combining transcriptomics and proteomics, we determine a disease molecular profile common to mouse models and NS patients. Spink5 cKO mice and NS patients share skin barrier and inflammation signatures defined by up-regulation and increased activity of proteases, IL-17, IL-36, and IL-20 family cytokine signaling. Systemic inflammation in Spink5 cKO mice correlates with disease severity and is associated with thymic atrophy and enlargement of lymph nodes and spleen. This systemic inflammation phenotype is marked by neutrophils and IL-17/IL-22 signaling, does not involve primary T cell immunodeficiency and is independent of bacterial infection. By comparing skin transcriptomes and proteomes, we uncover several putative substrates of tissue kallikrein-related proteases (KLKs), demonstrating that KLKs can proteolytically regulate IL-36 pro-inflammatory cytokines. Our study thus provides a conserved molecular framework for NS and reveals a KLK/IL-36 signaling axis, adding new insights into the disease mechanisms and therapeutic targets.

Development-Associated Genes of the Epidermal Differentiation Complex (EDC)

The epidermal differentiation complex (EDC) is a cluster of genes that encode protein components of the outermost layers of the epidermis in mammals, reptiles and birds. The development of the stratified epidermis from a single-layered ectoderm involves an embryo-specific superficial cell layer, the periderm. An additional layer, the subperiderm, develops in crocodilians and over scutate scales of birds. Here, we review the expression of EDC genes during embryonic development. Several EDC genes are expressed predominantly or exclusively in embryo-specific cell layers, whereas others are confined to the epidermal layers that are maintained in postnatal skin. The S100 fused-type proteins scaffoldin and trichohyalin are expressed in the avian and mammalian periderm, respectively. Scaffoldin forms the so-called periderm granules, which are histological markers of the periderm in birds. Epidermal differentiation cysteine-rich protein (EDCRP) and epidermal differentiation protein containing DPCC motifs (EDDM) are expressed in the avian subperiderm where they are supposed to undergo cross-linking via disulfide bonds. Furthermore, a histidine-rich epidermal differentiation protein and feather-type corneous beta-proteins, also known as beta-keratins, are expressed in the subperiderm. The accumulating evidence for roles of EDC genes in the development of the epidermis has implications on the evolutionary diversification of the skin in amniotes.

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

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

Five dimensions of cleansing: A holistic view on the facets and importance of skin cleansing

Cleansing is an important human ritual practised for hygiene, well-being and relaxation over centuries. As part of body care it is often taken for granted, yet its relevance cannot be underestimated. Although cleansing the skin may seem trivial to some, it is accepted, that this fundamental function of skin cleansing products is highly complex, diverse and crucial for a variety of reasons in the personal, public, healthcare and dermatological settings. Employing a comprehensive and strategic approach in viewing cleansing and its rituals, supports innovation, understanding and development. Apart from being a fundamental function, as far as we know, there is no comprehensive presentation of skin cleansing with all its effects besides 'removing dirt'. To our knowledge, comprehensive analyses on the multi-dimensional facets of skin cleansing are either rare or not published. Against this background, we examine the importance of cleansing in terms of function, relevance and concepts. First, the key functions and efficacies of skin cleansing were investigated by literature research. Based on this survey, the functions were analysed, sorted and merged and a novel approach to skin cleansing 'dimensions' was developed. Herewith, we took into consideration the evolution of skin cleansing in terms of concept evolution, complexity and testing methods for cleansing products and their claims. Several multi-dimensional functions of skin cleansing were identified and then established into five skin cleansing dimensions, namely: hygienic and medical importance; socio-cultural and interpersonal relevance; mood, emotion and well-being; cosmetic and aesthetic function; corneobiological interactions. It became obvious, that these five dimensions with their corresponding 11 sub-dimensions, are influenced by each other throughout history by culture and society, technical progress, scientific knowledge and consumer trends. This article presents the enormous complexity of skin cleansing. Skin cleansing has evolved from basic care up to a highly complex and diverse cosmetic product category in terms of technology, efficacy and usage routine(s). In view of future challenges, such as the effects of climate and associated lifestyle changes, the development of skin cleansing will remain an exciting and important topic and thus will finally, again, further increase the complexity of skin cleansing itself.

Identification of protein biomarkers associated with congenital diaphragmatic hernia in human amniotic fluid

Congenital diaphragmatic hernia (CDH) is a severe birth defect frequently associated with pulmonary hypoplasia, pulmonary hypertension, and heart failure. Since amniotic fluid comprises proteins of both fetal and maternal origin, its analysis could provide insights on mechanisms underlying CDH and provide biomarkers for early diagnosis, severity of pulmonary changes and treatment response. The study objective was to identify proteomic changes in amniotic fluid consistently associated with CDH. Amniotic fluid was obtained at term (37-39 weeks) from women with normal pregnancies (n = 5) or carrying fetuses with CDH (n = 5). After immuno-depletion of the highest abundance proteins, off-line fractionation and high-resolution tandem mass spectrometry were performed and quantitative differences between the proteomes of the groups were determined. Of 1036 proteins identified, 218 were differentially abundant. Bioinformatics analysis showed significant changes in GP6 signaling, in the MSP-RON signaling in macrophages pathway and in networks associated with cardiovascular system development and function, connective tissue disorders and dermatological conditions. Differences in selected proteins, namely pulmonary surfactant protein B, osteopontin, kallikrein 5 and galectin-3 were validated by orthogonal testing using ELISA in larger cohorts and showed statistically significant differences aiding in the diagnosis and prediction of CDH. The findings provide potential tools for clinical management of CDH.

The peptide bond rupture mechanism in the serine proteases: an in silico study based on sequential scale models

Given the importance of serine proteases for biochemical processes, we have studied the peptide bond rupture mechanism using three sequential scale models as representations of the KLK5 enzyme (a protein overexpressed in ovarian cancer). The first model contains the basic functional groups of the residues that conform to the catalytic triad present in serine proteases; the second model contains some additional residues and, finally, the last representation includes all atoms of the KLK5 protein together with 10.000 explicit water molecules. This separation into three scale models allows us to separate the intrinsic reactivity of the catalytic triad from the process taking place in the enzyme. The methodologies employed in this work include full DFT calculations with a dielectric continuum in the first two models and a multi-level setup with a Quantum Mechanics/Molecular Mechanics (QM/MM) partition in the whole protein system. Our results show that the peptide-bond rupture mechanism is a stepwise process involving two proton transfer reactions. The rate-determining step is the second proton transfer from the imidazole group to the amidic nitrogen of the substrate. In addition, we find that the simplest model does not provide accurate results compared to the full protein system. This can be attributed to the electronic stabilization conferred by the residues around the reaction site. Interestingly, the energy profile obtained with the second scale model with additional residues shows the same trends as the full system and could therefore be considered an appropriate model system. It could be used for studying the peptide bond rupture mechanism in case full QM/MM calculations cannot be performed, or as a rapid tool for screening purposes.

Variants in KLK11, affecting signal peptide cleavage of kallikrein-related peptidase 11, cause an autosomal-dominant cornification disorder

BACKGROUND

Mendelian disorders of cornification (MeDOC) are a group of heterogeneous genodermatoses with different genetic bases. The pathogenesis of a substantial group of MeDOC remains to be elucidated.

OBJECTIVES

To identify a new causative gene and the pathogenesis of a previously undescribed autosomal-dominant cornification disorder.

METHODS

Whole-exome sequencing was performed in three families with the novel cornification disorder to identify the disease-causing variants. As the variants were located around the signal peptide (SP) cleavage site of a kallikrein-related peptidase, SP cleavage, subcellular localization and extracellular secretion of the variants were evaluated in eukaryotic overexpression systems by Western blotting or immunocytochemistry. Then the trypsin-like and chymotrypsin-like proteolytic activity of the peptidase and degradation of its catalytic substrate were assayed using the patients' stratum corneum (SC) samples. The morphology of the lamellar bodies and corneodesmosomes (CDs) in the patients' SC was ultrastructurally examined. A mouse model harbouring the equivalent variant was constructed and evaluated histologically.

RESULTS

We identified two heterozygous variants affecting Gly50 in kallikrein-related peptidase (KLK)11 in a familial case and two sporadic cases with the new disorder, which is characterized by early-onset ichthyosiform erythroderma or erythrokeratoderma. KLK11 belongs to the family of kallikrein-related peptidases participating in skin desquamation by decomposing CDs, a process essential for shedding of the SC. In vitro experiments demonstrated that the variants perturbed the SP cleavage of KLK11, leading to subcellular mislocalization and impaired extracellular secretion of the KLK11 Gly50Glu variant. Both trypsin-like and chymotrypsin-like proteolytic activities were significantly decreased in the patients' SC samples. Reduced proteolysis of desmoglein 1 and delayed degeneration of CDs were detected in patients' SC, indicating delayed skin desquamation. Consistently, the patients showed a thickened, dense SC, indicating abnormal skin desquamation. Mice harbouring the homozygous c.131G>A (p.Gly44Glu) Klk11 variant, which is equivalent to KLK11 c.149G>A (p.Gly50Glu) in humans, exhibited hyperkeratosis and abnormal desquamation, partially recapitulating the phenotype.

CONCLUSIONS

We provide evidence that variants at Gly50 affecting the SP cleavage of KLK11 cause a new autosomal-dominant cornification disorder with abnormal desquamation. Our findings highlight the essential role of KLKs in maintaining homeostasis of skin keratinization and desquamation.

Inflammatory landscape in Xeroderma pigmentosum patients with cutaneous melanoma

Xeroderma pigmentosum (XP) is a DNA repair disease that predisposes to early skin cancers as cutaneous melanoma. Melanoma microenvironment contains inflammatory mediators, which would be interesting biomarkers for the prognosis or for the identification of novel therapeutic targets. We used a PCR array to evaluate the transcriptional pattern of 84 inflammatory genes in melanoma tumors obtained from XP patients (XP-Mel) and in sporadic melanoma (SP-Mel) compared to healthy skin. Commonly expressed inflammatory genes were further explored via GTEx and GEPIA databases. The differentially expressed inflammatory genes in XP were compared to their expression in skin exposed to UVs, and evaluated on the basis of the overall survival outcomes of patients with melanoma. Monocyte subsets of patients with SP-Mel, XP and healthy donors were also assessed. PCR array data revealed that 34 inflammatory genes were under-expressed in XP-Mel compared to SP-Mel. Differentially expressed genes that were common in XP-Mel and SP-Mel were correlated with the transcriptomic datasets from GEPIA and GTEx and highlighted the implication of KLK1 and IL8 in the tumorigenesis. We showed also that in XP-Mel tumors, there was an overexpression of KLK6 and KLK10 genes, which seems to be associated with a bad survival rate. As for the innate immunity, we observed a decrease of intermediate monocytes in patients with SP-Mel and in XP. We highlight an alteration in the immune response in XP patients. We identified candidate biomarkers involved in the tumorigenesis, and in the survival of patients with melanoma. Intermediate monocyte's in patients at risk could be a prognostic biomarker for melanoma outcome.

Lobelia chinensis Extract and Its Active Compound, Diosmetin, Improve Atopic Dermatitis by Reinforcing Skin Barrier Function through SPINK5/LEKTI Regulation

The skin acts as a mechanical barrier that protects the body from the exterior environment, and skin barrier function is attributed to the stratum corneum (SC), which is composed of keratinocytes and skin lipids. Skin barrier homeostasis is maintained by a delicate balance between the differentiation and exfoliation of keratinocytes, and keratinocyte desquamation is regulated by members of the serine protease kalikrein (KLK) family and their endogenous inhibitor SPINK5/LEKTI (serine protease inhibitor Kazal type 5/lympho-epithelial Kazal-type-related inhibitor). Furthermore, SPINK5/LEKTI deficiency is involved in impaired skin barrier function caused by KLK over-activation. We sought to determine whether increased SPINK5/LEKTI expression ameliorates atopic dermatitis (AD) by strengthening skin barrier function using the ethanol extract of Lobelia chinensis (LCE) and its active compound, diosmetin, by treating human keratinocytes with UVB and using a DNCB-induced murine model of atopic dermatitis. LCE or diosmetin dose-dependently increased the transcriptional activation of SPINK5 promoter and prevented DNCB-induced skin barrier damage by modulating events downstream of SPINK5, that is, KLK, PAR2 (protease activated receptor 2), and TSLP (thymic stromal lymphopoietin). LCE or diosmetin normalized immune response in DNCB treated SKH-1 hairless mice as determined by reductions in serum immunoglobulin E and interleukin-4 levels and numbers of lesion-infiltrating mast cells. Our results suggest that LCE and diosmetin are good candidates for the treatment of skin barrier-disrupting diseases such as Netherton syndrome or AD, and that they do so by regulating SPINK5/LEKTI.

Multiscale modelling of desquamation in the interfollicular epidermis

Maintenance of epidermal thickness is critical to the barrier function of the skin. Decreased tissue thickness, specifically in the stratum corneum (the outermost layer of the tissue), causes discomfort and inflammation, and is related to several severe diseases of the tissue. In order to maintain both stratum corneum thickness and overall tissue thickness it is necessary for the system to balance cell proliferation and cell loss. Cell proliferation in the epidermis occurs in the basal layer and causes constant upwards movement in the tissue. Cell loss occurs when dead cells at the top of the tissue are lost to the environment through a process called desquamation. Desquamation is thought to occur through a gradual reduction in adhesion between cells, due to the cleaving of adhesion proteins by enzymes, in the stratum corneum. In this paper we will investigate combining a (mass action) subcellular model of desquamation with a three dimensional (cell centre based) multicellular model of the interfollicular epidermis to better understand maintenance of epidermal thickness. Specifically, our aim is to determine if a hypothesised biological model for the degradation of cell-cell adhesion, from the literature, is sufficient to maintain a steady state tissue thickness. These investigations show the model is able to provide a consistent rate of cell loss in the multicellular model. This loss balances proliferation, and hence maintains a homeostatic tissue thickness. Moreover, we find that multiple proliferative cell populations in the basal layer can be represented by a single proliferative cell population, simplifying investigations with this model. The model is used to investigate a disorder (Netherton Syndrome) which disrupts desquamation. The model shows how biochemical changes can cause disruptions to the tissue, resulting in a reduced tissue thickness and consequently diminishing the protective role of the tissue. A hypothetical treatment result is also investigated: we compare the cases of a partially effective homogeneous treatment (where all cells partially recover) and a totally effective heterogeneous treatment (in which a proportion of the cells totally recover) with the aim to determine the difference in the response of the tissue to these different scenarios. Results show an increased benefit to corneum thickness from the heterogeneous treatment over the homogeneous treatment.

Moisturizer in Patients with Inflammatory Skin Diseases

As interest in skin increases, the cosmetic market is also growing. It is difficult to choose between the numerous types of basic cosmetics on the market. This article aims to provide advice and guidance on which products to recommend according to a patient’s skin condition. Appropriate application of a moisturizer attempts not only to improve the dryness, but also improve the skin’s natural barrier function to protect the skin from internal and external irritants to keep the skin healthy. Moisturizers consist of various ingredients, including occlusive agents, emollients, humectants, lipid mixture, emulsifiers, and preservatives. Pathophysiology of dry skin is also discussed to provide readers with the background they need to choose the right moisturizer for themselves. As moisturizers play an important role as adjuvant in the treatment of common skin diseases, such as atopic dermatitis, contact dermatitis, psoriasis, acne and rosacea, which type of moisturizer is appropriate for each disease was also dealt with. Basic cosmetics, especially moisturizers, should be recommended in consideration of the ingredients, effectiveness and safety of each product, and the skin condition of each patient.

The Biology of Varicella-Zoster Virus Replication in the Skin

The replication of varicella-zoster virus (VZV) in skin is critical to its pathogenesis and spread. Primary infection causes chickenpox, which is characterised by centrally distributed skin blistering lesions that are rich in infectious virus. Cell-free virus in the cutaneous blistering lesions not only spreads to cause further cases, but infects sensory nerve endings, leading to the establishment of lifelong latency in sensory and autonomic ganglia. The reactivation of virus to cause herpes zoster is again characterised by localised painful skin blistering rash containing infectious virus. The development of in vitro and in vivo models of VZV skin replication has revealed aspects of VZV replication and pathogenesis in this important target organ and improved our understanding of the vaccine strain vOKa attenuation. In this review, we outline the current knowledge on VZV interaction with host signalling pathways, the viral association with proteins associated with epidermal terminal differentiation, and how these interconnect with the VZV life cycle to facilitate viral replication and shedding.

Outcomes of Systemic Treatment in Children and Adults With Netherton Syndrome: A Systematic Review

Background

Comèl-Netherton syndrome (NS) is a rare disease caused by pathogenic variants in the SPINK5 gene, leading to severe skin barrier impairment and proinflammatory upregulation. Given the severity of the disease, treatment of NS is challenging. Current treatment regimens are mainly topical and supportive. Although novel systemic treatment options for NS have been suggested in recent literature, little is known about their outcomes.

Objective

to provide an overview of systemic treatment options and their outcomes in adults and children with NS.

Methods

Embase, MEDLINE, Web of Science, Cochrane Central Register of Controlled Trials, and Google Scholar were searched up to July 22, 2021. Empirical studies published in English language mentioning systemic treatment in NS were enrolled. Studies that did not define a treatment period or report at least one outcome were excluded. Methodological quality was evaluated by the Joanna Briggs Institute critical appraisal checklist for case reports or case series. Overall quality of evidence of the primary outcome, skin, was assessed by the GRADE approach.

Results

36 case series and case reports were included. The effects of 15 systemic therapies were described in 48 patients, of which 27 were children. Therapies included retinoids, prednisolone, cyclosporine, immunoglobulins, and biologicals. In retinoids both worsening (4/15 cases) and improvement (6/15 cases) of the skin was observed. Use of prednisolone and cyclosporine was only reported in one patient. Immunoglobulins (13/15 cases) and biologicals (18/21 cases) showed improvement of the skin. Certainty of evidence was rated as very low.

Conclusion

NS is a rare disease, which is reflected in the scarce literature on systemic treatment outcomes in children and adults with NS. Studies showed large heterogeneity in outcome measures. Adverse events were scarcely reported. Long-term outcomes were reported in a minority of cases. Nonetheless, a general beneficial effect of systemic treatment was found. Immunoglobulins and biologicals showed the most promising results and should be further explored. Future research should focus on determining a core outcome set and measurement instruments for NS to improve quality of research.

Systematic Review Registration

https://www.crd.york.ac.uk/prospero/display_record.php?RecordID=217933, PROSPERO (ID: 217933).

Type 2 Inflammation Contributes to Skin Barrier Dysfunction in Atopic Dermatitis

Skin barrier dysfunction, a defining feature of atopic dermatitis (AD), arises from multiple interacting systems. In AD, skin inflammation is caused by host-environment interactions involving keratinocytes as well as tissue-resident immune cells such as type 2 innate lymphoid cells, basophils, mast cells, and T helper type 2 cells, which produce type 2 cytokines, including IL-4, IL-5, IL-13, and IL-31. Type 2 inflammation broadly impacts the expression of genes relevant for barrier function, such as intracellular structural proteins, extracellular lipids, and junctional proteins, and enhances Staphylococcus aureus skin colonization. Systemic anti‒type 2 inflammation therapies may improve dysfunctional skin barrier in AD.

Granzyme B in Epithelial Barrier Dysfunction and Related Skin Diseases

The predominant function of the skin is to serve as a barrier - to protect against external insults and to prevent water loss. Junctional and structural proteins in the stratum corneum, the outermost layer of the epidermis, are critical to the integrity of the epidermal barrier as it balances ongoing outward migration, differentiation, and desquamation of keratinocytes in the epidermis. As such, epidermal barrier function is highly susceptible to upsurges of proteolytic activity in the stratum corneum and epidermis. Granzyme B is a serine protease scarce in healthy tissues but present at high levels in tissues encumbered by chronic inflammation. Discovered in the 1980s, Granzyme B is currently recognized for its intracellular roles in immune cell-mediated targeted apoptosis as well as extracellular roles in inflammation, chronic injuries, tissue remodeling, and processing of cytokines, matrix proteins, and autoantigens. Increasing evidence has emerged in recent years supporting a role for Granzyme B in promoting barrier dysfunction in the epidermis by direct cleavage of barrier proteins and eliciting immunoreactivity. Likewise, Granzyme B contributes to impaired epithelial function of the airways, retina, gut and vessels. In the present review, the role of Granzyme B in cutaneous epithelial dysfunction is discussed in the context of specific conditions with an overview of underlying mechanisms as well as utility of current experimental and therapeutic inhibitors.

Oral supplementation of sea cucumber and its hydrolysate mitigates ultraviolet A-induced photoaging in hairless mice

BACKGROUND

Chronic exposure to ultraviolet (UV) radiation promotes skin photoaging, which is clinically characterized by dryness, laxity, and wrinkling. Sea cucumber (Stichopus japonicus) (SC) is a marine organism with culinary and medicinal applications, especially in Asian countries. It is also a potential nutraceutical as it exhibits bioactive effects, such as antioxidant, antitumor, and anticancer activity. This study examined the effects of SC and its hydrolysate (SCH) on ultraviolet A (UVA) induced skin barrier function and wrinkle formation using hairless mice.

RESULTS

Ultraviolet A significantly induced transepidermal water loss and wrinkle formation, which were significantly mitigated upon oral administration of SC and SCH. Sea cucumber also mitigated the UVA-induced downregulation of epidermal natural moisturizing factors and the upregulation of Aqp3, Mmp13, Tnfa, and Il6 mRNA levels in the mouse skin.

CONCLUSION

Taken together, these results suggest that dietary SC and SCH exert anti-photoaging effects by modulating filaggrin synthesis and desquamation in the epidermis and regulating the NF-κB pathway in the skin. Our research indicates that SC and SCH have potential applications in nutricosmetics for photoaging. © 2021 Society of Chemical Industry.

A Case of Drastic Reduction of Membranous Substances in the Pharynx by Interprofessional Cooperative Oral Care

Membranous substances in the pharynx are occasionally observed in tube feeding patients during the fiberoptic endoscopic evaluation of swallowing. Although the mechanism of the formation of these deposits sometimes causes problems, such as dysphagia, asphyxia, or aspiration pneumonia, a 91-year-old male complained about difficulty of swallowing. He had a history of cerebral infarction and aspiration pneumonitis. There was a large amount of oral desquamated epithelium, dental plaque, and calculus in his mouth. Nurses and care workers administered oral care such as rubbing the tongue and buccal mucosa daily. Dentists and oral hygienists visited and provided special oral care three times per week. At least for 77 days, the patient had no recurrence of pneumonitis. The oral desquamated epithelium and membranous substances in the pharynx decreased drastically. 2 months after the first examination, the patient was able to start rehabilitation with food. Some studies have indicated that pharyngeal deposits are derived from the oral mucosa, and through our case, we realized the importance of daily oral care by interprofessional work to reduce membranous substances in the pharynx.

Human Tissue Kallikreins-Related Peptidases Are Targets for the Treatment of Skin Desquamation Diseases

Human tissue Kallikrein-related peptidases (hKLKs) are serine proteases distributed in several tissues that are involved in several biological processes. In skin, many are responsible for skin desquamation in the Stratum Corneum (SC) of the epidermis, specially hKLK5, hKLK7, hKLK6, hKLK8, and hKLK14. In SC, hKLKs cleave proteins of corneodesmosomes, an important structure responsible to maintain corneocytes attached. As part of skin desquamation, hKLKs are also involved in skin diseases with abnormal desquamation and inflammation, such as Atopic Dermatitis (AD), psoriasis, and the rare disease Netherton Syndrome (NS). Many studies point to hKLK overexpression or overactive in skin diseases, and they are also part of the natural skin inflammation process, through the PAR2 cleavage pathway. Therefore, the control of hKLK activity may offer successful treatments for skin diseases, improving the quality of life in patients. Diseases like AD, Psoriasis, and NS have an impact on social life, causing pain, itchy and mental disorders. In this review, we address the molecular mechanisms of skin desquamation, emphasizing the roles of human tissue Kallikrein-related peptidases, and the promising therapies targeting the inhibition of hKLKs.

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.

SPINKs in Tumors: Potential Therapeutic Targets

The serine protease inhibitor Kazal type (SPINK) family includes SPINK1-14 and is the largest branch in the serine protease inhibitor family. SPINKs play an important role in pancreatic physiology and disease, sperm maturation and capacitation, Nager syndrome, inflammation and the skin barrier. Evidence shows that the unregulated expression of SPINK1, 2, 4, 5, 6, 7, and 13 is closely related to human tumors. Different SPINKs exhibit various regulatory modes in different tumors and can be used as tumor prognostic markers. This article reviews the role of SPINK1, 2, 4, 5, 6, 7, and 13 in different human cancer processes and helps to identify new cancer treatment targets.

An overview of the use of proteolytic enzymes as exfoliating agents

BACKGROUND

Proteolytic enzymes are biological catalysts that can compose cosmetic formulations: These enzymes are capable of mimicking the desquamation process of the skin, acting as exfoliants. Although enzymatic exfoliation is not new and commercial products were easily found, there is a lack of scientific literature about this topic.

METHODS

A search was carried out until 2021 in different scientific databases (Web of Science, Scopus, Scielo, PubMed, etc.). In vitro and in vivo studies that evaluated the application of enzymes aiming to exfoliate the skin or with a similar cosmetic or dermatological application were selected.

RESULTS

Only 11 articles were found, and, among them, few studies applied enzymes as exfoliants in clinical trials. Nevertheless, the results demonstrate that the enzymes can exfoliate the skin and improve some desired characteristics of the organ. Papain, bromelain, keratinases, and microbial proteases are some enzymes already applied as exfoliants. The study of pH, temperature, and stabilization of the enzymes in cosmetic formulations were also demonstrated to be important aspects to be evaluated, principally in preventing loss of enzyme activity and possible allergens/irritations on the skin.

CONCLUSION

This literature review showed the main aspects that should be evaluated before considering producing or applying proteolytic enzymes in exfoliation products/procedures. The use of enzymatic exfoliation has potential in the cosmetic industry. Hence, further robust in vivo studies are needed before the enzymatic exfoliation can be recommended with safety as a treatment modality in the current conditions.

Similarities in DSG1 and KRT3 Downregulation through Retinoic Acid Treatment and PAX6 Knockdown Related Expression Profiles: Does PAX6 Affect RA Signaling in Limbal Epithelial Cells?

Congenital PAX6-aniridia is a rare panocular disease resulting from limbal stem cell deficiency. In PAX6-aniridia, the downregulation of the retinol-metabolizing enzymes ADH7 (All-trans-retinol dehydrogenase 7) and ALDH1A1/A3 (Retinal dehydrogenase 1, Aldehyde dehydrogenase family 1 member A3) have been described in limbal epithelial cells (LECs) and conjunctival epithelial cells. The aim of this study was to identify the role of retinol derivates in the differentiation of human LEC and its potential impact on aniridia-associated keratopathy development. Human LEC were isolated from healthy donor corneas and were cultured with retinol, retinoic acid, or pan-retinoic acid receptor antagonist (AGN 193109) acting on RARα, β, γ (NR1B1, NR1B2 NR1B3) or were cultured with pan-retinoid X receptor antagonist (UVI 3003) acting on RXR α, β, γ (retinoid X receptor, NR2B1, NR2B2, BR2B3). Using qPCR, differentiation marker and retinoid-/fatty acid metabolism-related mRNA expression was analysed. DSG1 (Desmoglein 1), KRT3 (Keratin 3), and SPINK7 (Serine Peptidase Inhibitor Kazal Type 7) mRNA expression was downregulated when retinoid derivates were used. AGN 193109 treatment led to the upregulation of ADH7, KRT3, and DSG1 mRNA expression and to the downregulation of KRT12 (Keratin 12) and KRT19 (Keratin 19) mRNA expression. Retinol and all-trans retinoic acid affect some transcripts of corneal LEC in a similar way to what has been observed in the LEC of PAX6-aniridia patients with the altered expression of differentiation markers. An elevated concentration of retinol derivatives in LEC or an altered response to retinoids may contribute to this pattern. These initial findings help to explain ocular surface epithelia differentiation disorders in PAX6-aniridia and should be investigated in patient cells or in cell models in the future in more detail.

The Role of Kallikrein 7 in Tumorigenesis

Kallikrein 7 (KLK7) is a secreted serine protease with chymotrypsic protease activity. Abnormally high expression of KLK7 is closely related to the occurrence and development of various types of cancer. Therefore, KLK7 has been identified as a potential target for cancer drug development design in recent years. KLK7 mediates various biological and pathological processes in tumorigenesis, including cell proliferation, migration, invasion, angiogenesis, and cell metabolism, by hydrolyzing a series of substrates such as membrane proteins, extracellular matrix proteins, and cytokines. This review mainly introduces the downstream cell signaling pathways involved in the activation of KLK7 and its substrate-related proteins. This review will not only help us to better understand the mechanisms of KLK7 in regulating biological and pathological processes of cancer cells, but also lay a solid foundation for the design of inhibitors targeting KLK7.

Generation of a quenched phosphonate activity-based probe for labelling the active KLK7 protease

Kallikrein 7 (KLK7) is a chymotrypsin-like serine protease with established roles in skin diseases like the rare Netherton syndrome, an overdesquamating and inflammatory condition, but also common atopic dermatitis, and a potential drug target for these and possibly other diseases. Nevertheless, tools to determine the active KLK7 enzyme are not available. Here, a mixed alkyl aryl phosphonate quenched activity-based probe that detects the active KLK7 was developed and evaluated in vitro. This KLK7-qABP can potentially be used to monitor KLK7 activity in vivo.

Epidermal Lamellar Body Biogenesis: Insight Into the Roles of Golgi and Lysosomes

Epidermal lamellar bodies (eLBs) are secretory organelles that carry a wide variety of secretory cargo required for skin homeostasis. eLBs belong to the class of lysosome-related organelles (LROs), which are cell-type-specific organelles that perform diverse functions. The formation of eLBs is thought to be related to that of other LROs, which are formed either through the gradual maturation of Golgi/endosomal precursors or by the conversion of conventional lysosomes. Current evidence suggests that eLB biogenesis presumably initiate from trans-Golgi network and receive cargo from endosomes, and also acquire lysosome characteristics during maturation. These multistep biogenesis processes are frequently disrupted in human skin disorders. However, many gaps remain in our understanding of eLB biogenesis and their relationship to skin diseases. Here, we describe our current understanding on eLB biogenesis with a focus on cargo transport to this LRO and highlight key areas where future research is needed.

1,3-Diazepine: A privileged scaffold in medicinal chemistry

Privileged structures have been widely used as effective templates for drug discovery. While benzo-1,4-diazepine constitutes the first historical example of such a structure, the 1,3 analogue is just as rich in terms of applications in medicinal chemistry. The 1,3-diazepine moiety is present in numerous biological active compounds including natural products, and is used to design compounds displaying a large range of biological activities. It is present in the clinically used anticancer compound pentostatin, in several recent FDA approved β-lactamase inhibitors (e.g., avibactam) and also in coformycin, a natural product known as a ring-expanded purine analogue displaying antiviral and anticancer activities. Several other 1,3-diazepine containing compounds have entered into clinical trials. This heterocyclic structure has been and is still widely used in medicinal chemistry to design enzyme inhibitors, GPCR ligands, and so forth. This review endeavours to highlight the main use of the 1,3-diazepine scaffold and its derivatives, and their applications in medicinal chemistry, drug design, and therapy. We will focus more particularly on the development of enzyme inhibitors incorporating this scaffold, with a strong emphasis on the molecular interactions involved in the inhibition mechanism.

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.

Screening of chemical libraries in pursuit of kallikrein-5 specific inhibitors for the treatment of inflammatory dermatoses

Background Aberrant kallikrein activity is observed in a number of inflammatory dermatoses. Up-regulation of kallikrein-5 (KLK5) activity leads to uncontrolled skin desquamation and cleavage of proteinase-activated receptor-2 (PAR2), causing the release of pro-inflammatory cytokines and disruption of epidermal barrier function. This study aimed to identify KLK5-specific small molecule inhibitors which can serve as the foundation of a novel therapeutic for inflammatory skin disorders. Methods Five chemical libraries (13,569 compounds total) were screened against recombinant KLK5 using a fluorogenic enzymatic assay. Secondary validation was performed on the top 22 primary hits. All hits were docked in the KLK5 crystal structure to rationalize their potential interactions with the protein. Results A naturally occurring compound derived from the wood of Caesalpinia sappan (Brazilin) was identified as a novel KLK5 inhibitor (IC50: 20 μM, Ki: 6.4 μM). Docking suggests that the phenolic moiety of Brazilin binds in the S1-pocket of KLK5 and forms a H-bond with S195 side chain. KLK14 was also found to be susceptible to inhibition by Brazilin with a calculated IC50 value of 14.6 μM. Conclusions Natural KLK5 small molecule inhibitors such as Brazilin, are ideal for topical skin disease drug design and remain a promising therapeutic for severe cases of inflammatory skin disorders. Optimized KLK inhibitors may have increased efficacy as therapeutics and warrant further investigation.

Managing syndromic congenital ichthyosis at a tertiary care institute-Genotype-phenotype correlations, and novel treatments

Syndromic congenital ichthyoses (CI) are genetically determined disorders of cornification that are characterized by generalized scaling along with systemic symptoms. Data on congenital syndromic ichthyosis from developing countries are scarce. We aimed to assess the prevalence, phenotype-genotype correlation, and management of syndromic CI patients presenting to our outpatient during the specified period this was a retrospective study of congenital syndromic ichthyosis patients attending a dermatology clinic in a tertiary care center from 2105-2018. We reviewed epidemiological and comorbidities data, phenotype-genotype correlations, and treatments of syndromic congenital ichthyosis patients. Six patients of Syndromic CI were diagnosedamongst 86 patients of CI (8.1%). Amongst these, three patients of Sjogren-Larrson syndrome (SLS), two patients of Netherton syndrome (NS), and one of Chanarin-Dorfman disease (CDD) were reported. Next-generation sequencing (NGS) was performed with novel variants reported in one patient each of SLS, NS, and CDD. An atypical phenotype was observed in a patient with NS with associated growth hormone and adrenocorticotropic hormone deficiency but with favorable clinical response to intravenous immunoglobulin. Our reports point towards the unreported pool of genetic mutations in CI from India. Novel mutations were associated with variable cutaneous and systemic involvement.

Comel-Netherton syndrome: A local skin barrier defect in the absence of an underlying systemic immunodeficiency

Background

Comel‐Netherton syndrome (NS) is a rare autosomal disease, characterized by severe skin disease, hair shaft defects, atopic diathesis, and increased susceptibility for skin infections. Since patients with NS suffer from recurrent infections, it has been hypothesized that an underlying immunodeficiency attributes to this. Here, we studied clinical and immunological characteristics of the cohort of NS patients in the Netherlands in order to identify whether potential immunodeficiencies result in the increased risk of infectious complications.

Methods

Phenotypes were scored for severity of skin condition, specific hair shaft defects, atopy, and recurrent infections. Patients’ blood samples were collected for quantification of serum immunoglobulin (Ig) levels, specific antibodies against Streptococcuspneumoniae, and allergen‐specific IgE, as well as detailed immunophenotyping of blood leukocyte and lymphocyte subsets by flow cytometry.

Results

A total of 14 patients were included with age range 3‐46 years and varying degrees of skin involvement. All patients presented with atopic symptoms (food allergy, n = 13; hay fever, n = 10; asthma, n = 7). Recurrent skin infections were common, particularly in childhood (n = 12). Low levels of specific antibodies against S pneumoniae were found in 10 of 11 evaluated patients. Detailed immunological analysis was performed on 9 adult patients. Absolute numbers of lymphocyte subsets and serum immunoglobulin levels were all within normal ranges.

Conclusion

Multidisciplinary evaluation of our national cohort showed no evidence for a severe, clinically relevant systemic immunodeficiency. Therefore, we conclude that in Dutch NS patients the increased risk of infections most likely results from the skin barrier disruption and that increased allergen penetration predisposes to allergic sensitization.

The role of kallikreins in inflammatory skin disorders and their potential as therapeutic targets

The skin is a vital organ of the human body, serving numerous protective and functional roles that are essential for survival. Residing in the epidermis are various epidermal proteases responsible for the establishment and regulation of barrier function. The human tissue kallikrein-related peptidase family conserves homeostasis of the skin barrier through their roles in desquamation, antimicrobial defense, innate immune response, and barrier maintenance. The activity of kallikreins is tightly regulated and dysregulation of kallikrein activity is seen to contribute to the formation of several inflammatory skin disorders. This review highlights the roles of kallikreins in skin homeostasis and pathologies. Due to their part in these skin disorders, inhibitors of the skin kallikreins have become attractive therapeutics. Over the past few years, both natural and synthetic inhibitors of several kallikreins have been identified and are undergoing further development as treatments to restore compromised barrier function. This review summarizes the kallikrein inhibitors under development for this purpose. These inhibitors remain promising therapeutics in cases of severe skin inflammation not well managed by current therapies.

Carbon dioxide ameliorates reduced desquamation in dry scaly skin via protease activation

OBJECTIVE

Scaling, a phenomenon showing an abnormal detachment of the stratum corneum (SC) owing to desquamation dysfunction, is commonly observed in various skin diseases or xerotic skin due to ageing and low humidity. Therefore, it is considered that ameliorating the disturbed desquamatory process of the SC leads to improvement in scaling. Carbon dioxide (CO₂ ) is known to be good for some skin diseases; however, the effect of CO₂ on scaling and its mechanism are not sufficiently clear. We aimed to elucidate the effect of transepidermal application of CO₂ on scaling and its mechanism of action.

METHODS

Twenty healthy men with mild scaling on the cheeks were recruited for a double-blind, placebo-controlled, split-face study. They applied the formulation containing CO₂ twice daily for 1 week. After the study, the SC was collected by tape stripping to analyse desquamatory protease activities and degradation of extracellular corneodesmosomes. Furthermore, the contribution of pH to proteolysis of the corneodesmosome by CO₂ was evaluated using three-dimensional (3D) cultured epidermal models.

RESULTS

The spectroscopic absorbance of tape strips, used as scaling indicators, was decreased, concomitantly with the amelioration of incomplete degradation of desmoglein-1, one of the main corneodesmosomal proteins, and activation of trypsin-like protease in the SC by transepidermal application of CO₂ . Experiments using 3D cultured epidermis showed that pH in the epidermal tissue was lowered by CO₂ , whereas a pH change was not observed with the application of the formulation containing hydrochloric acid, which was added to equalize the pH to that of the CO₂ formulation.

CONCLUSION

The transcutaneous application of CO₂ ameliorates reduced desquamatory process in xerotic skin, with concomitant mild acidification of the SC, thereby leading to improvement in scaling. Thus, CO₂ may have an advantage of efficiently and safely counteracting scaling of various skin disorders.

Efficient CRISPR-Cas9-Mediated Gene Ablation in Human Keratinocytes to Recapitulate Genodermatoses: Modeling of Netherton Syndrome

Current efforts to find specific genodermatoses treatments and define precise pathogenesis mechanisms require appropriate surrogate models with human cells. Although transgenic and gene knockout mouse models for several of these disorders exist, they often fail to faithfully replicate the clinical and histopathological features of the human skin condition. We have established a highly efficient method for precise deletion of critical gene sequences in primary human keratinocytes, based on CRISPR-Cas9-mediated gene editing. Using this methodology, in the present study we generated a model of Netherton syndrome by disruption of SPINK5. Gene-edited cells showed absence of LEKTI expression and were able to recapitulate a hyperkeratotic phenotype with most of the molecular hallmarks of Netherton syndrome, after grafting to immunodeficient mice and in organotypic cultures. To validate the model as a platform for therapeutic intervention, we tested an ex vivo gene therapy approach using a lentiviral vector expressing SPINK5. Re-expression of SPINK5 in an immortalized clone of SPINK5-knockout keratinocytes was capable of reverting from Netherton syndrome to a normal skin phenotype in vivo and in vitro. Our results demonstrate the feasibility of modeling genodermatoses, such as Netherton syndrome, by efficiently disrupting the causative gene to better understand its pathogenesis and to develop novel therapeutic approaches.

Structural Studies on the Inhibitory Binding Mode of Aromatic Coumarinic Esters to Human Kallikrein-Related Peptidase 7

The serine protease kallikrein-related peptidase 7 (KLK7) is a member of the human tissue kallikreins. Its dysregulation leads to pathophysiological inflammatory processes in the skin. Furthermore, it plays a role in several types of cancer. For the treatment of KLK7-associated diseases, coumarinic esters have been developed as small-molecule enzyme inhibitors. To characterize the inhibition mode of these inhibitors, we analyzed structures of the inhibited protease by X-ray crystallography. Electron density shows the inhibitors covalently attached to His57 of the catalytic triad. This confirms the irreversible character of the inhibition process. Upon inhibitor binding, His57 undergoes an outward rotation; thus, the catalytic triad of the protease is disrupted. Besides, the halophenyl moiety of the inhibitor was absent in the final enzyme-inhibitor complex due to the hydrolysis of the ester linkage. With these results, we analyze the structural basis of KLK7 inhibition by the covalent attachment of aromatic coumarinic esters.

Coumarin as a structural component of substrates and probes for serine and cysteine proteases

Coumarins represent well-established structures to introduce fluorescence into tool compounds for biochemical investigations. They are valued for their small size, chemical stability and accessibility as well as their tunable photochemical properties. As components of fluorophore/quencher pairs or FRET donor/acceptor pairs, coumarins have frequently been applied in substrate mapping approaches for serine and cysteine proteases. This review also focuses on the incorporation of coumarins into the side chain of amino acids and the exploitation of the resulting fluorescent amino acids for the positional profiling of protease substrates. The protease-inhibiting properties of certain coumarin derivatives and the utilization of coumarin moieties to assemble activity-based probes for serine and cysteine proteases are discussed as well.

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Coumarins represent well-established structures to introduce fluorescence into tool compounds for biochemical investigations.

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They are valued for their small size, chemical stability and accessibility as well as their tunable photochemical properties.

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Coumarins are components of fluorophore/quencher pairs or FRET donor/acceptor pairs in substrate mapping of proteases.

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Coumarins have been incorporated into amino acids side chains to be used for the positional profiling of protease substrates.

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Coumarins have protease-inhibiting properties and are used for activity-based probes for serine and cysteine proteases.

The matriptase-prostasin proteolytic cascade in dermatologic diseases

The proper development and function of skin and hair are dependent on proteolytic activities. Specifically, the matriptase-prostasin cascade is a series of proteolytic reactions in the epidermis integral to normal regulation of desquamation. An increasing amount of research describing this pathway has recently become available, and the importance of this pathway is exhibited by the association of genetic defects in this pathway with human diseases of the skin and hair. Given the relevance of this pathway to dermatology, we provide a review of the current understanding of its relevance to distinct clinical entities, including ichthyosis-hypotrichosis and Netherton syndromes.

The Skin Microbiota and Itch: Is There a Link?

Itch is an unpleasant sensation that emanates primarily from the skin. The chemical mediators that drive neuronal activity originate from a complex interaction between keratinocytes, inflammatory cells, nerve endings and the skin microbiota, relaying itch signals to the brain. Stress also exacerbates itch via the skin–brain axis. Recently, the microbiota has surfaced as a major player to regulate this axis, notably during stress settings aroused by actual or perceived homeostatic challenge. The routes of communication between the microbiota and brain are slowly being unraveled and involve neurochemicals (i.e., acetylcholine, histamine, catecholamines, corticotropin) that originate from the microbiota itself. By focusing on itch biology and by referring to the more established field of pain research, this review examines the possible means by which the skin microbiota contributes to itch.

Loss-of-Function Variants in SERPINA12 Underlie Autosomal Recessive Palmoplantar Keratoderma

Inherited palmoplantar keratodermas refer to a large and heterogeneous group of conditions resulting from abnormal epidermal differentiation and featuring thickening of the skin of the palms and soles. Here, we aimed at delineating the genetic basis of an autosomal recessive form of palmoplantar keratodermas manifesting with erythematous hyperkeratotic plaques over the palms and soles, extending to non-palmoplantar areas. Whole-exome sequencing in affected individuals revealed homozygous nonsense variants in the SERPINA12 gene. SERPINA12 encodes the visceral adipose tissue-derived serpin A12, a serine protease inhibitor. The pathogenic variants were found to result in reduced visceral adipose tissue-derived serpin A12 expression in patients' skin biopsies in comparison to healthy controls. In addition, SERPINA12 downregulation in three-dimensional skin equivalents was associated with marked epidermal acanthosis and hyperkeratosis, replicating the human phenotype. Moreover, decreased SERPINA12 expression resulted in reduced visceral adipose tissue-derived serpin A12-mediated inhibition of kallikrein 7 activity as well as decreased levels of desmoglein-1 and corneodesmosin, two known kallikrein 7 substrates, which are required for normal epidermal differentiation. The present data, taken collectively, demarcate a unique type of autosomal recessive palmoplantar keratodermas, attribute to visceral adipose tissue-derived serpin A12 a role in skin biology, and emphasize the importance of mechanisms regulating proteolytic activity for normal epidermal differentiation.

Transgenic Kallikrein 14 Mice Display Major Hair Shaft Defects Associated with Desmoglein 3 and 4 Degradation, Abnormal Epidermal Differentiation, and IL-36 Signature

Netherton syndrome is a rare autosomal recessive skin disease caused by loss-of-function mutations in SPINK5 encoding LEKTI protein that results in unopposed activity of epidermal kallikrein-related peptidases (KLKs), mainly KLK5, KLK7, and KLK14. Although the function of KLK5 and KLK7 has been previously studied, the role of KLK14 in skin homeostasis and its contribution to Netherton syndrome pathogenesis remains unknown. We generated a transgenic murine model overexpressing human KLK14 (TghKLK14) in stratum granulosum. TghKLK14 mice revealed increased proteolytic activity in the granular layers and in hair follicles. Their hair did not grow and displayed major defects with hyperplastic hair follicles when hKLK14 was overexpressed. TghKLK14 mice displayed abnormal epidermal hyperproliferation and differentiation. Ultrastructural analysis revealed cell separation in the hair cortex and increased thickness of Huxley's layer. Desmoglein (Dsg) 2 staining was increased, whereas Dsg3 and Dsg4 were markedly reduced. In vitro studies showed that hKLK14 directly cleaves recombinant human DSG3 and recombinant human DSG4, suggesting that their degradation contributes to hair abnormalities. Their skin showed an inflammatory signature, with enhanced expression of IL-36 family members and their downstream targets involved in innate immunity. This in vivo study identifies KLK14 as an important contributor to hair abnormalities and skin inflammation seen in Netherton syndrome.

Kallikrein 7 Promotes Atopic Dermatitis-Associated Itch Independently of Skin Inflammation

Atopic dermatitis (AD) is a highly prevalent, itchy inflammatory skin disorder that is thought to arise from a combination of skin barrier defect and immune dysregulation. Kallikreins (KLK), a family of serine proteases with a diverse array of homeostatic functions, including skin desquamation and innate immunity, are hypothesized to contribute to AD pathogenesis. However, their precise role in AD has not been clearly defined. In this study, RNA sequencing analyses identified KLK7 as the most abundant and differentially expressed KLK in both human AD and murine AD-like skin. Further, in mice, Klk7 expression was localized to the epidermis in both steady state and inflammation. Unexpectedly, KLK7 was dispensable for the development of AD-associated skin inflammation. Instead, KLK7 was selectively required for AD-associated chronic itch. Even without the alleviation of skin inflammation, KLK7-deficient mice exhibited significantly attenuated scratching, compared with littermate controls, after AD-like disease induction. Collectively, our findings indicate that KLK7 promotes AD-associated itch independently from skin inflammation and reveal a previously unrecognized epidermal-neural mechanism of AD associated itch.

Kallikreins: Essential epidermal messengers for regulation of the skin microenvironment during homeostasis, repair and disease

As the outermost layer of the skin, the epidermis is playing a major role in organism homeostasis providing the first barrier against external aggressions. Although considered as an extracellular matrix (ECM)-poor subtissue, the epidermal microenvironment is a key regulator of skin homeostasis and functionality. Among the proteins essential for upholding the epidermal microenvironment are the members of the kallikrein (KLK) family composed of 15 secreted serine proteases. Most of the members of these epithelial-specific proteins are present in skin and regulate skin desquamation and inflammation. However, although epidermal products, the consequences of KLK activities are not confined to the epidermis but widespread in the skin. In this review starting with the location and proteolytic activation cascade of KLKs, we present KLKs involvement in skin homeostasis, regeneration and pathology. KLKs have a large variety of substrates including ECM proteins, and evidence suggests that they are involved in the different steps of skin wound healing as discussed here. KLKs are also used as prognosis/diagnosis markers for many cancer types and we are focusing later on KLKs in cutaneous cancers, although their pathogenicity remains to be fully elucidated. Dysregulation of the KLK cascade is directly responsible for skin diseases with heavy inflammatory aspects, highlighting their involvement in skin immune homeostasis. Future studies will be needed to support the therapeutic potential of adjusting KLK activities for treatment of inflammatory skin diseases and wound healing pathologies.

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Regulation of the microenvironment even in an extracellular matrix-poor tissue can heavily impact organ function.

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Extracellular activities of kallikreins maintain skin homeostasis by regulating desquamation and inflammation.

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The activation of skin epidermal-specific kallikrein family of proteases is regulated by an intricate proteolytic cascade.

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Kallikreins are emerging as players during skin wound healing.

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Dysregulated kallikrein expression and activity occur in cancers and inflammatory skin diseases.