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

Mature IL-36γ Induces Stratum Corneum Exfoliation in Generalized Pustular Psoriasis by Suppressing Corneodesmosin

Loss-of-function sequence variations in the IL36RN gene encoding IL-36 receptor antagonist cause familial generalized pustular psoriasis, which begins shortly after birth and is difficult to treat, and its effects on the epidermis are unclear. This study investigated the involvement of IL-36 receptor agonists in the epidermal formation of generalized pustular psoriasis. We found that the IL-36 receptor agonists, especially mature IL-36γ, stimulated IL-8 and pro-IL-36γ production in the epidermis while downregulating the genes encoding epidermal cornified envelope-related proteins, for example, corneodesmosin. IL-36 receptor antagonist and monoclonal anti-IL-36γ antibodies counteracted the effect of mature IL-36γ on corneodesmosin in keratinocytes in a dose-dependent manner. In the epidermis of patients with generalized pustular psoriasis with IL36RN loss-of-function sequence variations, pro-IL-36γ was overproduced in the epidermis, and corneodesmosin protein expression was markedly decreased in the region of giant subcorneal pustules (Kogoj's spongiform pustules), with high neutrophil infiltration. IL-8 induced by mature IL-36γ stimulated the infiltration of several neutrophils in the epidermis. The newly produced pro-IL-36γ is cleaved to the mature form by neutrophil proteases. This newly produced mature IL-36γ was predicted to further suppress the gene expression of corneodesmosin, leading to significant stratum corneum exfoliation and formation of the pustules. Overall, our results elucidate the mechanism underlying the formation of Kogoj's spongiform pustules in generalized pustular psoriasis.

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.

Severe Hypernatremia as Presentation of Netherton Syndrome

Netherton syndrome is a rare, multisystem, autosomal recessive genodermatosis characterized by a triad of manifestations: congenital ichthyosis, immune dysregulation, and scalp anomalies. We report the case of a 1-month-old male infant evaluated for failure to thrive and feeding difficulties. At birth, the infant was admitted to intensive care for severe hypernatremia (natremia 186 mg/dL). Upon entering the ward, the general conditions were poor. He presented with diffuse erythrodermia. A dermatological evaluation showed evidence of "invaginated trichuriasis," a typical sign of Netherton syndrome. Netherton syndrome is caused by a genetic mutation causing loss of function of the SPINK5 gene it encodes for the LEKTI protein, normally expressed in epithelia. Loss of LEKTI induces severe skin barrier defect. The history of the disease is characterized by serious potential complications in the first months of life, such as the risk of hypernatremic dehydration induced by high skin permeability, recurrent and/or severe infections, and growth retardation.

Treatment of Severe Dermatitis, Multiple Allergies, and Metabolic Wasting With Dupilumab

This case report describes a woman with severe dermatitis, multiple allergies, and metabolic wasting syndrome.

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.

Netherton Syndrome Caused by Heterozygous Frameshift Mutation Combined with Homozygous c.1258A>G Polymorphism in SPINK5 Gene

Netherton syndrome (NS) is a rare autosomal recessive disorder caused by SPINK5 mutations, resulting in a deficiency in its processed protein LEKTI. It is clinically characterized by the triad of congenital ichthyosis, atopic diathesis, and hair shaft abnormalities. The SPINK5 (NM_006846.4): c.1258A>G polymorphism (rs2303067) shows a significant association with atopy and atopic dermatitis (AD), which share several clinical features with NS. We describe an NS patient, initially misdiagnosed with severe AD, who carried the heterozygous frameshift (null) mutation (NM_006846.4): c.957_960dup combined with homozygous rs2303067 in the SPINK5 gene. Histopathological examination confirmed the diagnosis, whereas an immunohistochemical study showed normal epidermal expression of LEKTI, despite the genetic findings. Our results corroborate the hypothesis that haploinsufficiency of SPINK5, in the presence of a SPINK5 null heterozygous mutation in combination with homozygous SPINK5 rs2303067 polymorphism, can be causative of an NS phenotype, impairing the function of LEKTI despite its normal expression. Due to the clinical overlap between NS and AD, we suggest performing SPINK5 genetic testing to search for the SPINK5 (NM_006846.4): c.1258A>G polymorphism (rs2303067) and ensure a correct diagnosis, mainly in doubtful cases.

Protease- and cell type-specific activation of protease-activated receptor 2 in cutaneous inflammation

BACKGROUND

Protease-activated receptor 2 (PAR2) signaling controls skin barrier function and inflammation, but the roles of immune cells and PAR2-activating proteases in cutaneous diseases are poorly understood.

OBJECTIVE

To dissect PAR2 signaling contributions to skin inflammation with new genetic and pharmacological tools.

METHODS/RESULTS

We found markedly increased numbers of PAR2+ infiltrating myeloid cells in skin lesions of allergic contact dermatitis (ACD) patients and in the skin of contact hypersensitivity (CHS) in mice, a murine ACD model for T cell-mediated allergic skin inflammation. Cell type-specific deletion of PAR2 in myeloid immune cells as well as mutation-induced complete PAR2 cleavage insensitivity significantly reduced skin inflammation and hapten-specific Tc1/Th1 cell response. Pharmacological approaches identified individual proteases involved in PAR2 cleavage and demonstrated a pivotal role of tissue factor (TF) and coagulation factor Xa (FXa) as upstream activators of PAR2 in both the induction and effector phase of CHS. PAR2 mutant mouse strains with differential cleavage sensitivity for FXa versus skin epithelial cell-expressed proteases furthermore uncovered a time-dependent regulation of CHS development with an important function of FXa-induced PAR2 activation during the late phase of skin inflammation.

CONCLUSIONS

Myeloid cells and the TF-FXa-PAR2 axis are key mediators and potential therapeutic targets in inflammatory skin diseases.

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).

Netherton syndrome subtypes share IL-17/IL-36 signature with distinct IFN-α and allergic responses

BACKGROUND

Netherton syndrome (NS) is a rare recessive skin disorder caused by loss-of-function mutations in SPINK5 encoding the protease inhibitor LEKTI (lymphoepithelial Kazal-type-related inhibitor). NS patients experience severe skin barrier defects, display inflammatory skin lesions, and have superficial scaling with atopic manifestations. They present with typical ichthyosis linearis circumflexa (NS-ILC) or scaly erythroderma (NS-SE).

OBJECTIVE

We used a combination of several molecular profiling methods to comprehensively characterize the skin, immune cells, and allergic phenotypes of NS-ILC and NS-SE patients.

METHODS

We studied a cohort of 13 patients comprising 9 NS-ILC and 4 NS-SE.

RESULTS

Integrated multiomics revealed abnormal epidermal proliferation and differentiation and IL-17/IL-36 signatures in lesion skin and in blood in both NS endotypes. Although the molecular profiles of NS-ILC and NS-SE lesion skin were very similar, nonlesion skin of each disease subtype displayed distinctive molecular features. Nonlesion and lesion NS-SE epidermis showed activation of the type I IFN signaling pathway, while lesion NS-ILC skin differed from nonlesion NS-ILC skin by increased complement activation and neutrophil infiltration. Serum cytokine profiling and immunophenotyping of circulating lymphocytes showed a T_H2-driven allergic response in NS-ILC, whereas NS-SE patients displayed mainly a T_H9 axis with increased CCL22/MDC and CCL17/TARC serum levels.

CONCLUSIONS

This study confirms IL-17/IL-36 as the predominant signaling axes in both NS endotypes and unveils molecular features distinguishing NS-ILC and NS-SE. These results identify new therapeutic targets and could pave the way for precision medicine of NS.

A Novel SPINK5 Gene Mutation Associated with Netherton Syndrome in an Omani Patient

Netherton syndrome (NS) is an autosomal recessive primary immunodeficiency. It is characterised by substantial skin barrier defects and is often misdiagnosed as severe atopic dermatitis or hyper-immunoglobulin E syndrome. Although more than 80 NS-associated pathogenic mutations in the serine peptidase inhibitor kazal type 5 (SPINK5) gene have been reported worldwide, only one has been reported in the Arab population to date. We report the case of a novel association between the c.1887+1G>A mutation in the SPINK5 gene and NS in an Omani-Arab patient born in 2014 who was managed at a paediatric immunology clinic in Muscat, Oman. Accurate genetic diagnosis facilitated tailored clinical management of the index patient and enabled the provision of genetic counselling and offering of future reproductive options to the individuals related to the index patient.

Alarmins/stressorins and immune dysregulation in intractable skin disorders

Unlike other barrier epithelia of internal organs, the stratified squamous epithelium of the skin is always exposed to the external environment. However, the robust barrier structure and function of the skin are highly resistant against external insults so as to not easily allow foreign invasions. Upon sensing danger signals, the innate immunity system is promptly activated. This process is mediated by alarmins, which are released passively from damaged cells. Nuclear alarmins or stressorins are actively released from intact cells in response to various cellular stresses. Alarmins/stressorins are deeply involved in the disease processes of chronic skin disorders of an unknown cause, such as rosacea, psoriasis, and atopic dermatitis. Furthermore, alarmins/stressorins are also induced in the congenital skin disorders of ichthyosis and keratoderma due to defective keratinization. Studies on alarmin activation and its downstream pathways may help develop novel therapeutic agents for intractable skin disorders.

Kallikrein-related peptidase 5 contributes to the remodeling and repair of bronchial epithelium

Inflammation, oxidative stress, and protease/protease inhibitor imbalance with excessive production of proteases are factors associated with pathogenesis of the chronic obstructive pulmonary disease (COPD). In this study, we report that kallikrein-related peptidase 5 (KLK5) is a crucial protease involved in extracellular matrix (ECM) remodeling and bronchial epithelial repair after injury. First, we showed that KLK5 degrades the basal layer formed by culture of primary bronchial epithelial cells from COPD or non-COPD patients. Also, exogenous KLK5 acted differently on BEAS-2B cells already engaged in epithelial-to-mesenchymal transition (EMT) or on 16HBE 14o- cells harboring epithelial characteristics. Indeed, by inducing EMT, KLK5 reduced BEAS-2B cell adherence to the ECM. This effect, neutralized by tissue factor pathway inhibitor 2, a kunitz-type serine protease inhibitor, was due to a direct proteolytic activity of KLK5 on E-cadherin, β-catenin, fibronectin, and α5β1 integrin. Thus, KLK5 may strengthen EMT mechanisms and promote the migration of cells by activating the mitogen-activated protein kinase signaling pathway required for this function. In contrast, knockdown of endogenous KLK5 in 16HBE14o- cells, accelerated wound healing repair after injury, and exogenous KLK5 addition delayed the closure repair. These data suggest that among proteases, KLK5 could play a critical role in airway remodeling events associated with COPD during exposure of the pulmonary epithelium to inhaled irritants or smoking and the inflammation process.

A Potent and Selective Kallikrein-5 Inhibitor Delivers High Pharmacological Activity in Skin from Patients with Netherton Syndrome

Regulation of proteolytic activity in the skin plays a pivotal role in epidermal homeostasis. This is best exemplified in Netherton syndrome, a severe genetic skin condition caused by loss-of-function mutations in the gene serine protease inhibitor Kazal-type 5 encoding lympho-epithelial Kazal-type-related inhibitor, a serine protease inhibitor that regulates kallikrein (KLK)-related peptidase 5, 7, and 14 activities. KLK5 plays a central role in stratum corneum shedding and inflammatory cell signaling, activates KLK7 and KLK14, and is therefore an optimal therapeutic target. We aimed to identify a potent and selective small-molecule inhibitor of KLK5 amenable to epidermal delivery. GSK951 was identified using a structure-based design strategy and showed a half maximal inhibitory concentration of 250 pM for KLK5 and greater than 100-fold selectivity over KLK7 and KLK14. Cocrystal structure analysis identified the critical catalytic site interactions to a surrogate for KLK5. Topical application of GSK951-containing cream inhibited KLK5 activity in TgKLK5 mouse skin, reduced transepidermal water loss, and decreased proinflammatory cytokine expression. GSK951 achieved high concentrations in healthy human epidermis following topical application in a cream formulation. Finally, KLK5 protease activity was increased in stratum corneum of patients with Netherton syndrome and significantly inhibited by GSK951. These findings unveil a KLK5-specific small-molecule inhibitor with a high therapeutic potential for patients with Netherton syndrome.

A novel SPINK5 donor splice site variant in a child with Netherton syndrome

BACKGROUND

Netherton syndrome (NS) is a genodermatosis caused by loss-of-function mutations in SPINK5, resulting in aberrant LEKTI expression.

METHOD

Next-generation sequencing of SPINK5 (NM_001127698.1) was carried out and functional studies were performed by immunofluorescence microscopy of a lesional skin biopsy using anti-LEKTI antibodies.

RESULTS

We describe a novel SPINK5 likely pathogenic donor splice site variant (NM_001127698.1:c.2015+5G>A) in a patient with NS and confirm its functional significance by demonstrating complete loss of LEKTI expression in lesional skin by immunofluorescence analysis.

CONCLUSION

The 2015+5G>A is a novel, likely pathogenic variant in NS. Herein we review and assimilate documented SPINK5 pathogenic variants and discuss possible genotype-phenotype associations in NS.

Immunohistochemical expression of kallikrein 7 in oral squamous cell carcinoma

Background and Objectives:

The kallikrein (KLK) family of genes consists of 15 members, many of which are highly expressed in number of cancers compared to their normal parent tissues. KLK7 was initially characterized as an enzyme implicated in the degradation of intercellular cohesive structures in the stratum corneum of stratified squamous epithelia, preceding desquamation in the skin. It catalyzes the degradation of desmosomes in the outermost layer of skin and permits cell shedding to take place at the skin surface. Overexpression of KLK7 in tumor cells has been reported to significantly enhance the invasive potential in intracranial malignancies and ovarian cancer cells. Thus, KLK7 could contribute to the degradation of extracellular matrices in oral squamous cell carcinoma (OSCC) tissues, promoting invasion of neoplastic cells locally and facilitating metastasis to regional lymph nodes. The objectives of the present study were to compare the expression of KLK 7 in normal subjects and patients with OSCC, to correlate the expression of KLK 7 with respect to the clinical staging of OSCC and to evaluate the expression of KLK 7with respect to different histopathological grades of OSCC.

Materials and Methods:

Thirty cases of OSCC were staged clinically and graded histopathologically. The immunohistochemical method was used to detect the expression of KLK 7 in OSCC. The scores obtained were documented and compared statistically.

Results:

KLK 7 immunoreactivity was noticed in all cases of OSCC. A statistically significant difference was observed in immunoreactivity of KLK 7 between the normal and OSCC (P = 0.0001*) and in different histopathological grades (P = 0.0001*) and in different clinical stages (P = 0.0127*) of OSCC using Kruskal–Wallis analysis of variance test.

Conclusion:

The KLK 7 immunoexpression histopathologically increased from low grade to high grade and clinically from Stage 1 to Stage 4 in OSCC. Hence, increased expression of KLK 7 may be related to poor prognosis in patients with OSCC.

Mutations in genes encoding desmosomal proteins: spectrum of cutaneous and extracutaneous abnormalities

The desmosome is a type of intercellular junction found in epithelial cells, cardiomyocytes and other specialized cell types. Composed of a network of transmembranous cadherins and intracellular armadillo, plakin and other proteins, desmosomes contribute to cell-cell adhesion, signalling, development and differentiation. Mutations in genes encoding desmosomal proteins result in a spectrum of erosive skin and mucosal phenotypes that also may affect hair or heart. This review summarizes the molecular pathology and phenotypes associated with desmosomal dysfunction with a focus on inherited disorders that involve the skin/hair, as well as associated extracutaneous pathologies. We reviewed the relevant literature to collate studies of pathogenic human mutations in desmosomes that have been reported over the last 25 years. Mutations in 12 different desmosome genes have been documented, with mutations in nine genes affecting the skin/mucous membranes (DSG1, DSG3, DSC2, DSC3, JUP, PKP1, DSP, CDSN, PERP) and eight resulting in hair abnormalities (DSG4, DSC2, DSC3, JUP, PKP1, DSP, CDSN, PERP). Mutations in three genes can result in cardiocutaneous syndromes (DSC2, JUP, DSP), although mutations have been described in five genes in inherited heart disorders that may lack any dermatological manifestations (DSG2, DSC2, JUP, PKP2, DSP). Understanding the diverse nature of these clinical phenotypes, as well as the desmosome gene mutation(s), has clinical value in managing and counselling patients, as well as demonstrating the biological role and activity of specific components of desmosomes in skin and other tissues.

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.

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.

Knockdown of sodium channel Nax reduces dermatitis symptoms in rabbit skin

The skin plays a critical role in maintenance of water homeostasis. Dysfunction of the skin barrier causes not only delayed wound healing and hypertrophic scarring, but it also contributes to the development of various skin diseases. Dermatitis is a chronic inflammatory skin disorder that has several different subtypes. Skin of contact dermatitis and atopic dermatitis (AD) show epidermal barrier dysfunction. Na_x is a sodium channel that regulates inflammatory gene expression in response to perturbation of barrier function of the skin. We found that in vivo knockdown of Na_x using RNAi reduced hyperkeratosis and keratinocyte hyperproliferation in rabbit ear dermatitic skin. Increased infiltration of inflammatory cells (mast cells, eosinophils, T cells, and macrophages), a characteristic of dermatitis, was reduced by Na_x knockdown. Upregulation of PAR-2 and thymic stromal lymphopoietin (TSLP), which induce Th2-mediated allergic responses, was inhibited by Na_x knockdown. In addition, expression of COX-2, IL-1β, IL-8, and S100A9, which are downstream genes of Na_x and are involved in dermatitis pathogenesis, were also decreased by Na_x knockdown. Our data show that knockdown of Na_x relieved dermatitis symptoms in vivo and indicate that Na_x is a novel therapeutic target for dermatitis, which currently has limited therapeutic options.

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.

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.

Generation and Clinical Application of Gene-Modified Autologous Epidermal Sheets in Netherton Syndrome: Lessons Learned from a Phase 1 Trial

Netherton syndrome (NS) is a rare autosomal recessive skin disorder caused by mutations in SPINK5. It is a debilitating condition with notable mortality in the early years of life. There is no curative treatment. We undertook a nonrandomized, open-label, feasibility, and safety study using autologous keratinocytes transduced with a lentiviral vector encoding SPINK5 under the control of the human involucrin promoter. Six NS subjects were recruited, and gene-modified epithelial sheets were successfully generated in three of five subjects. The sheets exhibited expression of correctly sized lympho-epithelial Kazal-type-related inhibitor (LEKTI) protein after modification. One subject was grafted with a 20 cm² gene-modified graft on the left anterior thigh without any adverse complications and was monitored by serial sampling for 12 months. Recovery within the graft area was compared against an area outside by morphology, proviral copy number and expression of the SPINK5 encoded protein, LEKTI, and its downstream target kallikrein 5, which exhibited transient functional correction. The study confirmed the feasibility of generating lentiviral gene-modified epidermal sheets for inherited skin diseases such as NS, but sustained LEKTI expression is likely to require the identification, targeting, and engraftment of long-lived keratinocyte stem cell populations for durable therapeutic effects. Important learning points for the application of gene-modified epidermal sheets are discussed.

Profiling Immune Expression to Consider Repurposing Therapeutics for the Ichthyoses

Despite extensive discovery about the mutations underlying genetic skin disorders, there have been few therapeutic advances. Better understanding of the molecular changes that may lead to the phenotypic manifestations of genetic disorders may lead to the discovery of new pharmacologic interventions. The ichthyoses are characterized by scaling, inflammation, and an impaired epidermal barrier. Recent studies have uncovered T helper type 17 skewing in ichthyotic skin, resembling psoriasis, and high frequencies of IL-17- and IL-22-expressing T cells in blood, correlating with severity and transepidermal water loss. Repurposing systemic T helper type 17/IL-23-inhibitory therapies for psoriasis may prove useful for patients with ichthyosis.

Discovery, Synthesis, Pharmacological Profiling, and Biological Characterization of Brintonamides A-E, Novel Dual Protease and GPCR Modulators from a Marine Cyanobacterium

Five novel modified linear peptides named brintonamides A-E (1-5) were discovered from a marine cyanobacterial sample collected from Brinton Channel, Florida Keys. The total synthesis of 1-5 in addition to two other structurally related analogues (6 and 7) was achieved, which provided more material to allow rigorous biological evaluation and SAR studies. Compounds were subjected to cancer-focused phenotypic cell viability and migration assays and orthogonal target-based pharmacological screening platforms to identify their protease and GPCR modulatory activity profiles. The cancer related serine protease kallikrein 7 (KLK7) was inhibited to similar extents with an IC50 near 20 μM by both representative members 1 and 4, which differed in the presence or lack of the N-terminal unit. In contrast to the biochemical protease profiling study, clear SAR was observed in the functional GPCR screens, where five GPCRs in antagonist mode (CCR10, OXTR, SSTR3, TACR2) and agonist mode (CXCR7) were modulated by compounds 1-7 to varying extents. Chemokine receptor type 10 (CCR10) was potently modulated by brintonamide D (4) with an IC50 of 0.44 μM. We performed in silico modeling to understand the structural basis underlying the differences in the antagonistic activity among brintonamides toward CCR10. Because of the significance of KLK7 and CCR10 in cancer progression and metastasis, we demonstrated the ability of brintonamide D (4) at 10 μM to significantly target downstream cellular substrates of KLK7 (Dsg-2 and E-cad) in vitro and to inhibit CCL27-induced CCR10-mediated proliferation and the migration of highly invasive breast cancer cells.

Ichthyosis molecular fingerprinting shows profound TH17 skewing and a unique barrier genomic signature

BACKGROUND

Ichthyoses are a group of rare skin disorders lacking effective treatments. Although genetic mutations are progressively delineated, comprehensive molecular phenotyping of ichthyotic skin could suggest much-needed pathogenesis-based therapy.

OBJECTIVE

We sought to profile the molecular fingerprint of the most common orphan ichthyoses.

METHODS

Gene, protein, and serum studies were performed on skin and blood samples from 29 patients (congenital ichthyosiform erythroderma, n = 9; lamellar ichthyosis, n = 8; epidermolytic ichthyosis, n = 8; and Netherton syndrome, n = 4), as well as age-matched healthy control subjects (n = 14), patients with psoriasis (n = 30), and patients with atopic dermatitis (AD; n = 16).

RESULTS

Using criteria of a fold change of greater than 2 and a false discovery rate of less than 0.05, 132 differentially expressed genes were shared commonly among all ichthyoses, including many IL-17 and TNF-α-coregulated genes, which are considered hallmarks of psoriasis (defensin beta 4A, kynureninase, and vanin 3). Although striking upregulation of TH17 pathway genes (IL17F and IL36B/G) resembling that seen in patients with psoriasis was common to all patients with ichthyoses in a severity-related manner, patients with Netherton syndrome showed the greatest T-cell activation (inducible costimulator [ICOS]) and a broader immune phenotype with T_H1/IFN-γ, OASL, and T_H2/IL-4 receptor/IL-5 skewing, although less than seen in patients with AD (all P < .05). Ichthyoses lacked the epidermal differentiation and tight junction alterations of patients with AD (loricrin, filaggrin, and claudin 1) but showed characteristic alterations in lipid metabolism genes (ELOVL fatty acid elongase 3 and galanin), with parallel reductions in extracellular lipids and corneocyte compaction in all ichthyoses except epidermolytic ichthyosis, suggesting phenotypic variations. Transepidermal water loss, a functional barrier measure, significantly correlated with IL-17-regulated gene expression (IL17F and IL36A/IL36B/IL36G).

CONCLUSION

Similar to patients with AD and psoriasis, in whom cytokine dysregulation and barrier impairment orchestrate disease phenotypes, psoriasis-like immune dysregulation and lipid alterations characterize the ichthyoses. These data support the testing of IL-17/IL-36-targeted therapeutics for patients with ichthyosis similar to those used in patients with psoriasis.

The atopic march: current insights into skin barrier dysfunction and epithelial cell-derived cytokines

Atopic dermatitis often precedes the development of other atopic diseases. The atopic march describes this temporal relationship in the natural history of atopic diseases. Although the pathophysiological mechanisms that underlie this relationship are poorly understood, epidemiological and genetic data have suggested that the skin might be an important route of sensitization to allergens. Animal models have begun to elucidate how skin barrier defects can lead to systemic allergen sensitization. Emerging data now suggest that epithelial cell-derived cytokines such as thymic stromal lymphopoietin (TSLP), IL-33, and IL-25 may drive the progression from atopic dermatitis to asthma and food allergy. This review focuses on current concepts of the role of skin barrier defects and epithelial cell-derived cytokines in the initiation and maintenance of allergic inflammation and the atopic march.

A viable mouse model for Netherton syndrome based on mosaic inactivation of the Spink5 gene

Netherton syndrome (NS) is caused by mutations in the SPINK5 gene. Several Spink5-deficient mouse models were generated to understand the mechanisms of NS in vivo. However, Spink5-deficiency in mice is associated with postnatal lethality that hampers further analysis. Here we present a viable mouse model for NS generated by mosaic inactivation of the Spink5 gene. We propose that these mice are a valuable experimental tool to study NS, especially for long-term studies evaluating potential therapeutic compounds. Furthermore, we show that mosaic inactivation of a gene using TALENs or CRISPR/Cas9 systems can be used to study lethal phenotypes in adult mice.

Mechanistic insight from murine models of Netherton syndrome

Protease regulation plays a crucial role in skin homeostasis and inflammation as revealed by the identification of loss-of-function mutations in SPINK5 (serine protease inhibitor of Kazal type 5) in Netherton sydrome (NS). SPINK5 encodes LEKTI (lympho-epithelial Kazal type related inhibitor), a multidomain serine protease inhibitor expressed in all stratified epithelia. Our laboratory has developed a number of murine models which have been instrumental in dissecting the pathogenesis of NS. This minireview discusses the major findings of these models and emphasizes the role of protease regulation, especially kallikrein-related peptidases in NS.

Complementary effect of hydroquinone and retinoic acid on corneocyte desquamation with their combination use

BACKGROUND

Retinoic acid (RA) enhances skin-lightening capabilities of hydroquinone (HQ), at least in part, by facilitating desquamation which leads to increase penetration of HQ. The desquamation also affects skin irritation levels. The mechanism of RA-induced desquamation, however, has not been completely explored and no such data has been available for HQ uses.

OBJECTIVE

To examine the role of HQ, RA, and their combination in the desquamation.

METHODS

Primary cultured normal human keratinocytes, which were treated with HQ and/or RA in presence or absence of serine-specific inhibitor Kazal type5 (SPINK5)/lympho-epithelial Kazal-type-related inhibitor (LEKTI) knockdown or recombinant human SPINK5/LEKTI, and biopsied skin samples applied with HQ or RA were examined. Expression levels of corneodesmosin (CDSN), desmocollin1 (DSC1), kallikrein5 (KLK5), KLK7, and SPINK5/LEKTI, and proteolysis activity against extracted human skin epidermal protein were determined using time-course real-time PCR, Western blotting, ELISA, and immunofluorescence staining.

RESULTS

HQ increased but RA decreased the synthesis of CDSN and DSC1. HQ reduced corneodesmosome degradation by the upregulation of SPINK5/LEKTI, whereas RA showed opposite results without upregulation of SPINK5/LEKTI. The combination of HQ and RA was close to the sum of the individual components.

CONCLUSIONS

HQ reduced corneocyte desquamation. However, RA enhanced desquamation. The combination induced more desquamation than HQ but less than RA.

T Helper 1 and T Helper 2 Cytokines Differentially Modulate Expression of Filaggrin and its Processing Proteases in Human Keratinocytes

Background:

Atopic dermatitis (AD) is characterized by defective skin barrier and imbalance in T helper 1/T helper 2 (Th1/Th2) cytokine expression. Filaggrin (FLG) is the key protein to maintaining skin barrier function. Recent studies indicated that Th1/Th2 cytokines influence FLG expression in keratinocytes. However, the role of Th1/Th2 cytokines on FLG processing is not substantially documented. Our aim was to investigate the impact of Th1/Th2 cytokines on FLG processing.

Methods:

HaCaT cells and normal human keratinocytes were cultured in low and high calcium media and stimulated by either interleukin (IL)-4, 13 or interferon-γ (IFN-γ). FLG, its major processing proteases and key protease inhibitor lymphoepithelial Kazal-type-related inhibitor (LEKTI) were measured by both real-time quantitative polymerase chain reaction and Western blotting. Their expression was also evaluated in acute and chronic AD lesions by immunohistochemistry.

Results:

IL-4/13 significantly reduced, while IFN-γ significantly up-regulated FLG expression. IL-4/13 significantly increased, whereas IFN-γ significantly decreased the expression of kallikreins 5 and 7, matriptase and channel-activating serine protease 1. On the contrary, IL-4/13 significantly decreased, while IFN-γ increased the expression of LEKTI and caspase-14. Similar trends were observed in AD lesions.

Conclusions:

Our results suggested that Th1/Th2 cytokines differentially regulated the expression of major FLG processing enzymes. The imbalance between Th1 and Th2 polarized immune response seems to extend to FLG homeostasis, through the network of FLG processing enzymes.

KLK5 and KLK7 Ablation Fully Rescues Lethality of Netherton Syndrome-Like Phenotype

Netherton syndrome (NS) is a severe skin disease caused by the loss of protease inhibitor LEKTI, which leads to the dysregulation of epidermal proteases and severe skin-barrier defects. KLK5 was proposed as a major protease in NS pathology, however its inactivation is not sufficient to rescue the lethal phenotype of LEKTI-deficient mice. In this study, we further elucidated the in vivo roles of the epidermal proteases in NS using a set of mouse models individually or simultaneously deficient for KLK5 and KLK7 on the genetic background of a novel NS-mouse model. We show that although the ablation of KLK5 or KLK7 is not sufficient to rescue the lethal effect of LEKTI-deficiency simultaneous deficiency of both KLKs completely rescues the epidermal barrier and the postnatal lethality allowing mice to reach adulthood with fully functional skin and normal hair growth. We report that not only KLK5 but also KLK7 plays an important role in the inflammation and defective differentiation in NS and KLK7 activity is not solely dependent on activation by KLK5. Altogether, these findings show that unregulated activities of KLK5 and KLK7 are responsible for NS development and both proteases should become targets for NS therapy.

Skin Biopsy in Netherton Syndrome: A Histological Review of a Large Series and New Findings

Netherton syndrome (NS) is a severe genetic skin disorder, with often delayed or misleading clinical signs. The histological features of skin biopsies, usually described as a psoriasiform hyperplasia, have only been reported in isolated case reports or small case series. The aim of this study is to define, for the first time, the precise histological pattern of cutaneous lesions, in a large cohort of skin biopsies from confirmed NS patients. The study included 80 consecutive skin biopsies from 67 patients taken between January 1995 and June 2014. All were from confirmed NS patients with either a negative lympho-epithelial Kazal-type-related inhibitor (LEKTI) immunohistochemistry and/or molecular confirmation by identified mutation in SPINK5. In this cohort, the most frequent histological finding was also psoriasiform hyperplasia, but there were additional, less common, or previously unreported findings, including compact parakeratosis with large nuclei, subcorneum or intracorneum splitting, presence of clear cells in the upper epidermis or stratum corneum, dyskeratosis, dermal infiltrate with neutrophils and/or eosinophils, and dilated blood vessels in the superficial dermis. An early confirmation of the diagnosis of NS is essential for improved patient management. Thus, in the situation of a patient with an unknown skin disorder and non specific clinical presentation, the dermatopathologist may now be able to suggest the diagnosis of NS based on these newly reported characteristics. However, LEKTI immunohistochemistry remains the essential diagnostic investigation in cases with misleading or nonspecific histological features and is mandatory for the definitive diagnosis of NS in all patients.

Exploring the active site binding specificity of kallikrein-related peptidase 5 (KLK5) guides the design of new peptide substrates and inhibitors

Kallikrein-related peptidase 5 (KLK5) is a promising therapeutic target in several skin diseases, including Netherton syndrome, and is emerging as a potential target in various cancers. In this study, we used a sparse matrix library of 125 individually synthesized peptide substrates to characterize the binding specificity of KLK5. The sequences most favored by KLK5 were GRSR, YRSR and GRNR, and we identified sequence-specific interactions involving the peptide N-terminus by analyzing kinetic constants (kcat and KM) and performing molecular dynamics simulations. KLK5 inhibitors were subsequently engineered by substituting substrate sequences into the binding loop (P1, P2 and P4 residues) of sunflower trypsin inhibitor-1 (SFTI-1). These inhibitors were effective against KLK5 but showed limited selectivity, and performing a further substitution at P2′ led to the design of a new variant that displayed improved activity against KLK5 (Ki=4.2±0.2 nm), weak activity against KLK7 and 12-fold selectivity over KLK14. Collectively, these findings provide new insight into the design of highly favored binding sequences for KLK5 and reveal several opportunities for modulating inhibitor selectivity over closely related proteases that will be useful for future studies aiming to develop therapeutic molecules targeting KLK5.

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

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

An IL-17-dominant immune profile is shared across the major orphan forms of ichthyosis

BACKGROUND

The ichthyoses are rare genetic disorders associated with generalized scaling, erythema, and epidermal barrier impairment. Pathogenesis-based therapy is largely lacking because the underlying molecular basis is poorly understood.

OBJECTIVE

We sought to characterize molecularly cutaneous inflammation and its correlation with clinical and barrier characteristics.

METHODS

We analyzed biopsy specimens from 21 genotyped patients with ichthyosis (congenital ichthyosiform erythroderma, n = 6; lamellar ichthyosis, n = 7; epidermolytic ichthyosis, n = 5; and Netherton syndrome, n = 3) using immunohistochemistry and RT-PCR and compared them with specimens from healthy control subjects, patients with atopic dermatitis (AD), and patients with psoriasis. Clinical measures included the Ichthyosis Area Severity Index (IASI), which integrates erythema (IASI-E) and scaling (IASI-S); transepidermal water loss; and pruritus.

RESULTS

Ichthyosis samples showed increased epidermal hyperplasia (increased thickness and keratin 16 expression) and T-cell and dendritic cell infiltrates. Increases of general inflammatory (IL-2), innate (IL-1β), and some T_H1/interferon (IFN-γ) markers in patients with ichthyosis were comparable with those in patients with psoriasis or AD. TNF-α levels in patients with ichthyosis were increased only in those with Netherton syndrome but were much lower than in patients with psoriasis and those with AD. Expression of T_H2 cytokines (IL-13 and IL-31) was similar to that seen in control subjects. The striking induction of IL-17-related genes or markers synergistically induced by IL-17 and TNF-α (IL-17A/C, IL-19, CXCL1, PI3, CCL20, and IL36G; P < .05) in patients with ichthyosis was similar to that seen in patients with psoriasis. IASI and IASI-E scores strongly correlated with IL-17A (r = 0.74, P < .001) and IL-17/TNF-synergistic/additive gene expression. These markers also significantly correlated with transepidermal water loss, suggesting a link between the barrier defect and inflammation in patients with ichthyosis.

CONCLUSION

Our data associate a shared T_H17/IL-23 immune fingerprint with the major orphan forms of ichthyosis and raise the possibility of IL-17-targeting strategies.

Hyperactivation of JAK1 tyrosine kinase induces stepwise, progressive pruritic dermatitis

Skin homeostasis is maintained by the continuous proliferation and differentiation of epidermal cells. The skin forms a strong but flexible barrier against microorganisms as well as physical and chemical insults; however, the physiological mechanisms that maintain this barrier are not fully understood. Here, we have described a mutant mouse that spontaneously develops pruritic dermatitis as the result of an initial defect in skin homeostasis that is followed by induction of a Th2-biased immune response. These mice harbor a mutation that results in a single aa substitution in the JAK1 tyrosine kinase that results in hyperactivation, thereby leading to skin serine protease overexpression and disruption of skin barrier function. Accordingly, treatment with an ointment to maintain normal skin barrier function protected mutant mice from dermatitis onset. Pharmacological inhibition of JAK1 also delayed disease onset. Together, these findings indicate that JAK1-mediated signaling cascades in skin regulate the expression of proteases associated with the maintenance of skin barrier function and demonstrate that perturbation of these pathways can lead to the development of spontaneous pruritic dermatitis.

Kallikrein-related peptidases (KLKs) as emerging therapeutic targets: focus on prostate cancer and skin pathologies

INTRODUCTION

Tissue kallikrein and the kallikrein-related peptidases (KLKs) constitute a family of 15 homologous secreted serine proteases with trypsin- or chymotrypsin-like activities, which participate in a broad spectrum of physiological procedures. Deregulated expression and/or activation of the majority of the family members have been reported in several human diseases, thereby making KLKs ideal targets for therapeutic intervention.

AREAS COVERED

In the present review, we summarize the role of KLKs in normal human physiology and pathology, focusing on prostate cancer and skin diseases. Furthermore, we discuss the recent advances in the development of KLK-based therapies. A great number of diverse engineered KLKs inhibitors with improved potency, selectivity and immunogenicity have been synthesized by redesigning examples that are endogenous and naturally occurring. Moreover, encouraging results have been documented using KLKs-based vaccines and immunotherapies, as well as KLKs-mediated activation of pro-drugs. Finally, KLKs-targeting aptamers and KLKs-based imaging tools represent novel approaches towards the exploitation of KLKs' therapeutic value.

EXPERT OPINION

The central/critical roles of KLK family in several human pathologies highlight KLKs as attractive molecular targets for developing novel therapeutics.

Protease-activated Receptor-2 (PAR-2)-mediated Nf-κB Activation Suppresses Inflammation-associated Tumor Suppressor MicroRNAs in Oral Squamous Cell Carcinoma

Oral cancer is the sixth most common cause of death from cancer with an estimated 400,000 deaths worldwide and a low (50%) 5-year survival rate. The most common form of oral cancer is oral squamous cell carcinoma (OSCC). OSCC is highly inflammatory and invasive, and the degree of inflammation correlates with tumor aggressiveness. The G protein-coupled receptor protease-activated receptor-2 (PAR-2) plays a key role in inflammation. PAR-2 is activated via proteolytic cleavage by trypsin-like serine proteases, including kallikrein-5 (KLK5), or by treatment with activating peptides. PAR-2 activation induces G protein-α-mediated signaling, mobilizing intracellular calcium and Nf-κB signaling, leading to the increased expression of pro-inflammatory mRNAs. Little is known, however, about PAR-2 regulation of inflammation-related microRNAs. Here, we assess PAR-2 expression and function in OSCC cell lines and tissues. Stimulation of PAR-2 activates Nf-κB signaling, resulting in RelA nuclear translocation and enhanced expression of pro-inflammatory mRNAs. Concomitantly, suppression of the anti-inflammatory tumor suppressor microRNAs let-7d, miR-23b, and miR-200c was observed following PAR-2 stimulation. Analysis of orthotopic oral tumors generated by cells with reduced KLK5 expression showed smaller, less aggressive lesions with reduced inflammatory infiltrate relative to tumors generated by KLK5-expressing control cells. Together, these data support a model wherein KLK5-mediated PAR-2 activation regulates the expression of inflammation-associated mRNAs and microRNAs, thereby modulating progression of oral tumors.

KLK5 Inactivation Reverses Cutaneous Hallmarks of Netherton Syndrome

Netherton Syndrome (NS) is a rare and severe autosomal recessive skin disease which can be life-threatening in infants. The disease is characterized by extensive skin desquamation, inflammation, allergic manifestations and hair shaft defects. NS is caused by loss-of-function mutations in SPINK5 encoding the LEKTI serine protease inhibitor. LEKTI deficiency results in unopposed activities of kallikrein-related peptidases (KLKs) and aberrantly increased proteolysis in the epidermis. Spink5⁻/⁻ mice recapitulate the NS phenotype, display enhanced epidermal Klk5 and Klk7 protease activities and die within a few hours after birth because of a severe skin barrier defect. However the contribution of these various proteases in the physiopathology remains to be determined. In this study, we developed a new murine model in which Klk5 and Spink5 were both knocked out to assess whether Klk5 deletion is sufficient to reverse the NS phenotype in Spink5⁻/⁻ mice. By repeated intercrossing between Klk5⁻/⁻ mice with Spink5⁻/⁻ mice, we generated Spink5⁻/⁻Klk5⁻/⁻ animals. We showed that Klk5 knock-out in Lekti-deficient newborn mice rescues neonatal lethality, reverses the severe skin barrier defect, restores epidermal structure and prevents skin inflammation. Specifically, using in situ zymography and specific protease substrates, we showed that Klk5 knockout reduced epidermal proteolytic activity, particularly its downstream targets proteases KLK7, KLK14 and ELA2. By immunostaining, western blot, histology and electron microscopy analyses, we provide evidence that desmosomes and corneodesmosomes remain intact and that epidermal differentiation is restored in Spink5⁻/⁻Klk5⁻/⁻. Quantitative RT-PCR analyses and immunostainings revealed absence of inflammation and allergy in Spink5⁻/⁻Klk5⁻/⁻ skin. Notably, Il-1β, Il17A and Tslp levels were normalized. Our results provide in vivo evidence that KLK5 knockout is sufficient to reverse NS-like symptoms manifested in Spink5⁻/⁻ skin. These findings illustrate the crucial role of protease regulation in skin homeostasis and inflammation, and establish KLK5 inhibition as a major therapeutic target for NS.

Engineered protease inhibitors based on sunflower trypsin inhibitor-1 (SFTI-1) provide insights into the role of sequence and conformation in Laskowski mechanism inhibition

Laskowski inhibitors regulate serine proteases by an intriguing mode of action that involves deceiving the protease into synthesizing a peptide bond. Studies exploring naturally occurring Laskowski inhibitors have uncovered several structural features that convey the inhibitor's resistance to hydrolysis and exceptional binding affinity. However, in the context of Laskowski inhibitor engineering, the way that various modifications intended to fine-tune an inhibitor's potency and selectivity impact on its association and dissociation rates remains unclear. This information is important as Laskowski inhibitors are becoming increasingly used as design templates to develop new protease inhibitors for pharmaceutical applications. In this study, we used the cyclic peptide, sunflower trypsin inhibitor-1 (SFTI-1), as a model system to explore how the inhibitor's sequence and structure relate to its binding kinetics and function. Using enzyme assays, MD simulations and NMR spectroscopy to study SFTI variants with diverse sequence and backbone modifications, we show that the geometry of the binding loop mainly influences the inhibitor's potency by modulating the association rate, such that variants lacking a favourable conformation show dramatic losses in activity. Additionally, we show that the inhibitor's sequence (including both the binding loop and its scaffolding) influences its potency and selectivity by modulating both the association and the dissociation rates. These findings provide new insights into protease inhibitor function and design that we apply by engineering novel inhibitors for classical serine proteases, trypsin and chymotrypsin and two kallikrein-related peptidases (KLK5 and KLK14) that are implicated in various cancers and skin diseases.