Defective cathepsin Z affects EGFR expression and causes autosomal dominant palmoplantar keratoderma.

BACKGROUND: The abnormal function of epidermal growth factor receptor (EGFR) has recently been shown to underlie various disorders of cornification. OBJECTIVES: To delineate the genetic basis of a novel dominant form of palmoplantar keratoderma (PPK). METHODS: Whole-exome (WES) and direct sequencing, quantitative real-time polymerase chain reaction, protein modelling, confocal immunofluorescence microscopy, immunoblotting, three-dimensional skin equivalents and an enzyme activity assay were used to delineate the genetic basis of a novel dominant form of PPK. RESULTS: WES revealed heterozygous variants (c.274T > C and c.305C > T) in CTSZ (encoding cathepsin Z) in four individuals (belonging to three unrelated families) with focal PPK. Bioinformatics and protein modelling predicted the variants to be pathogenic. Previous studies have suggested that EGFR expression may be subject to cathepsin regulation. Immunofluorescence revealed reduced cathepsin Z expression in the upper epidermal layers and concomitant increased epidermal EGFR expression in patients harbouring CTSZ variants. Accordingly, human keratinocytes transfected with constructs expressing PPK-causing variants in CTSZ displayed reduced cathepsin Z enzymatic activity, as well as increased EGFR expression. In line with the role played by EGFR in the regulation of keratinocyte proliferation, human keratinocytes transfected with the PPK-causing variants showed significantly increased proliferation that was abolished upon exposure to erlotinib, an EGFR inhibitor. Similarly, downregulation of CTSZ resulted in increased EGFR expression and increased proliferation in human keratinocytes, suggestive of a loss-of-function effect of the pathogenic variants. Finally, three-dimensional organotypic skin equivalents grown from CTSZ-downregulated cells showed increased epidermal thickness and EGFR expression as seen in patient skin; here, too, erlotinib was found to rescue the abnormal phenotype. CONCLUSIONS: Taken collectively, these observations attribute to cathepsin Z a hitherto unrecognized function in epidermal differentiation.

Up-regulation of ST18 in pemphigus vulgaris drives a self-amplifying p53-dependent pathomechanism resulting in decreased desmoglein 3 expression.

Pemphigus vulgaris (PV) is a life-threatening autoimmune mucocutaneous blistering disease which is to a large extent genetically determined, and results, at least in part, from the deleterious activity of autoantibodies directed against desmoglein (DSG)3, a prominent intra-epidermal adhesion molecule. Those autoantibodies lead to decreased membranal DSG3 expression in keratinocytes (KCs), thereby destabilizing cell-cell adhesion within the epidermis and leading to blister formation. We previously showed that rs17315309, a strong risk variant for PV within the promoter of the ST18 transcription factor gene, promotes epidermal ST18 up-regulation in a p53/p63-dependent manner. Accordingly, ST18 was found to be overexpressed in the skin of PV patients. Increased ST18 expression was then shown to markedly augment PV autoantibodies-mediated loss of KCs cohesion. Here, we demonstrate that ST18 overexpression significantly increases autoantibody-mediated DSG3 down-regulation in keratinocytes. In addition, DSG3 decreased expression boosts p53 function through p38 mitogen-activated protein kinase (p38MAPK) activation and dramatically augments p53-dependent ST18 promoter activity. Finally, the PV risk variant rs17315309 is associated with increased p53 expression in PV skin. Taken collectively, these observations reveal a novel self-amplifying pathomechanism involving ST18, DSG3, p38 and p53, capable of perpetuating disease activity, and therefore indicative of novel actionable molecular targets in PV.

Loss-of-function variants in KLF4 underlie autosomal dominant palmoplantar keratoderma.

PURPOSE: Palmoplantar keratodermas (PPKs) form a group of disorders characterized by thickening of palm and sole skin. Over the past 2 decades, many types of inherited PPKs have been found to result from abnormal expression, processing, or function of adhesion proteins. METHODS: We used exome and direct sequencing to detect causative pathogenic variants. Functional analysis of these variants was conducted using reverse transcription quantitative polymerase chain reaction, immunofluorescence confocal microscopy, immunoblotting, a promoter reporter assay, and chromatin immunoprecipitation. RESULTS: We identified 2 heterozygous variants (c.1226A>G and c.633_634dupGT) in KLF4 in 3 individuals from 2 different unrelated families affected by a dominant form of PPK. Immunofluorescence staining for a number of functional markers revealed reduced epidermal DSG1 expression in patients harboring heterozygous KLF4 variants. Accordingly, human keratinocytes either transfected with constructs expressing these variants or downregulated for KLF4 displayed reduced DSG1 expression, which in turn has previously been found to be associated with PPK. A chromatin immunoprecipitation assay confirmed direct binding of KLF4 to the DSG1 promoter region. The ability of mutant KLF4 to transactivate the DSG1 promoter was significantly decreased when compared with wild-type KLF4. CONCLUSION: Loss-of-function variants in KLF4 cause a novel form of dominant PPK and show its importance in the regulation of epidermal differentiation.

Neonatal inflammatory skin and bowel disease type 1 caused by a complex genetic defect and responsive to combined anti-tumour necrosis factor-α and interleukin-12/23 blockade.

ADAM17, encoding ADAM metallopeptidase domain 17, is a membrane-bound shedding protease, which plays an essential role during normal development and in the regulation of inflammation. Biallelic variants in ADAM17, resulting in complete loss of ADAM17 expression, have been reported in individuals affected by rare neonatal inflammatory skin and bowel disease 1 (NISBD1). Here, we report on a young female individual with NISBD1 featuring erythroderma, atrichia, nail dystrophy, oesophageal strictures, intractable diarrhoea, profound failure to thrive and recurrent cutaneous and systemic infections. In this case, NISBD1 was found to result from a complex compound heterozygous defect consisting of a large genomic deletion spanning exons 6 and 7 in addition to a splice site variant causing exon 17 skipping. Skin manifestations dramatically improved in response to combined anti-tumour necrosis factor-α and interleukin-12/23 blockade, while gastrointestinal symptoms were controlled with budesonide. Our study further expands the phenotypic and genetic spectrum of NISBD1 and suggests that combined immunosuppressive treatments may be indicated in this complex condition. What is already known about this topic? Biallelic loss-of-function variants in ADAM17, encoding ADAM metallopeptidase domain 17, have to date been reported in only four families with neonatal inflammatory skin and bowel disease 1 (NISBD1). NISBD1 features variable disease phenotypes associated with different degrees of severity. What does this study add? We report a case of a patient with NISBD1 caused by a unique genetic defect consisting of a combination of a splice site variant leading to exon 17 skipping and a large deletion spanning exons 6-7 of the ADAM17 gene. The severe cutaneous phenotype in our patient responded to a combination of ustekinumab and certolizumab.

Vorinostat, a histone deacetylase inhibitor, as a potential novel treatment for psoriasis.

BACKGROUND: Psoriasis is characterized by aberrant activation of several pro-inflammatory circuits as well as abnormal hyperproliferation and dysregulated apoptosis of keratinocytes (KCs). Most currently available therapeutic options primarily target psoriasis-associated immunological defects rather than epidermal abnormalities. OBJECTIVE: To investigate the efficacy of the histone deacetylase (HDAC) inhibitor, Vorinostat, in targeting hyperproliferation and impaired apoptosis in psoriatic skin. METHODS: Vorinostat effect was investigated in primary KCs cell cultures using cell cycle analysis by flow cytometry, apoptosis assays (Annexin V-FICH and caspase-3/7) and antibody arrays, qRT-PCR and immunohistochemistry. Vorinostat impact on clinical manifestations of psoriasis was investigated in a chimeric mouse model. RESULTS: Vorinostat was found to inhibit KCs proliferation and to induce their differentiation and apoptosis. Using a chimeric mouse model, vorinostat was found to result in marked attenuation of a psoriasiform phenotype with a significant decrease in epidermal thickness and inhibition of epidermal proliferation. CONCLUSIONS: Our results support the notion that vorinostat, a prototypic HDAC inhibitor, may be of potential use in the treatment of psoriasis and other hyperproliferative skin disorders.

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.