Katja-Martina Eckl

Loss of Corneodesmosin Leads to Severe Skin Barrier Defect, Pruritus, and Atopy: Unraveling the Peeling Skin Disease

Generalized peeling skin disease is an autosomal-recessive ichthyosiform erythroderma characterized by lifelong patchy peeling of the skin. After genome-wide linkage analysis, we have identified a homozygous nonsense mutation in CDSN in a large consanguineous family with generalized peeling skin, pruritus, and food allergies, which leads to a complete loss of corneodesmosin. In contrast to hypotrichosis simplex, which can be associated with specific dominant CDSN mutations, peeling skin disease is characterized by a complete loss of CDSN expression. The skin phenotype is consistent with a recent murine Cdsn knockout model. Using three-dimensional human skin models, we demonstrate that lack of corneodesmosin causes an epidermal barrier defect supposed to account for the predisposition to atopic diseases, and we confirm the role of corneodesmosin as a decisive epidermal adhesion molecule. Therefore, peeling skin disease will represent a new model disorder for atopic diseases, similarly to Netherton syndrome and ichthyosis vulgaris in the recent past.

Molecular Analysis of 250 Patients with Autosomal Recessive Congenital Ichthyosis: Evidence for Mutation Hotspots in ALOXE3 and Allelic Heterogeneity in ALOX12B

In recent years several new genes for autosomal recessive congenital ichthyosis (ARCI) have been identified. However, little is known about the molecular epidemiology and pathophysiology of this genetically and clinically heterogeneous group of severe disorders of keratinization. ARCI is characterized by intense scaling of the whole integument often associated with erythema. We and others have shown that mutations in ALOX12B and ALOXE3, coding for the lipoxygenases 12R-LOX and eLOX-3 predominantly synthesized in the epidermis, can underlie this rare condition. Here we have surveyed a large group of 250 patients with ARCI for mutations in these two genes. We have identified 11 different previously unreported mutations in ALOX12B and ALOXE3 in 21 ARCI patients from 19 unrelated families and demonstrated that mutations in the two genes are the second most common cause for ARCI in this cohort of patients. Examination of the molecular data revealed allelic heterogeneity for ALOX12B and two mutational hotspots in ALOXE3. Functional analysis of all missense mutations and a splice site mutation demonstrated that complete loss of function of the enzymes underlies the phenotype. Our findings further establish the pivotal role of the 12-lipoxygenase pathway during epidermal differentiation.

Impaired epidermal ceramide synthesis causes autosomal recessive congenital ichthyosis and reveals the importance of ceramide acyl chain length.

The barrier function of the human epidermis is supposed to be governed by lipid composition and organization in the stratum corneum. Disorders of keratinization, namely ichthyoses, are typically associated with disturbed barrier activity. Using autozygosity mapping and exome sequencing, we have identified a homozygous missense mutation in CERS3 in patients with congenital ichthyosis characterized by collodion membranes at birth, generalized scaling of the skin, and mild erythroderma. We demonstrate that the mutation inactivates ceramide synthase 3 (CerS3), which is synthesized in skin and testis, in an assay of N-acylation with C26-CoA, both in patient keratinocytes and using recombinant mutant proteins. Moreover, we show a specific loss of ceramides with very long acyl chains from C26 up to C34 in terminally differentiating patient keratinocytes, which is in line with findings from a recent CerS3-deficient mouse model. Analysis of reconstructed patient skin reveals disturbance of epidermal differentiation with an earlier maturation and an impairment of epidermal barrier function. Our findings demonstrate that synthesis of very long chain ceramides by CerS3 is a crucial early step for the skin barrier formation and link disorders presenting with congenital ichthyosis to defects in sphingolipid metabolism and the epidermal lipid architecture.

Allelic heterogeneity in the COH1 gene explains clinical variability in Cohen syndrome

Cohen syndrome is a rare autosomal recessive disorder with a variable clinical picture mainly characterized by developmental delay, mental retardation, microcephaly, typical facial dysmorphism, progressive pigmentary retinopathy, severe myopia, and intermittent neutropenia. A Cohen syndrome locus was mapped to chromosome 8q22 in Finnish patients, and, recently, mutations in the gene COH1 were reported in patients with Cohen syndrome from Finland and other parts of northern and western Europe. Here, we describe clinical and molecular findings in 20 patients with Cohen syndrome from 12 families, originating from Brazil, Germany, Lebanon, Oman, Poland, and Turkey. All patients were homozygous or compound heterozygous for mutations in COH1. We identified a total of 17 novel mutations, mostly resulting in premature termination codons. The clinical presentation was highly variable. Developmental delay of varying degree, early-onset myopia, joint laxity, and facial dysmorphism were the only features present in all patients; however, retinopathy at school age, microcephaly, and neutropenia are not requisite symptoms of Cohen syndrome. The identification of novel mutations in COH1 in an ethnically diverse group of patients demonstrates extensive allelic heterogeneity and explains the intriguing clinical variability in Cohen syndrome.

Penetration of normal, damaged and diseased skin — An in vitro study on dendritic core–multishell nanotransporters

A growing intended or accidental exposure to nanoparticles asks for the elucidation of potential toxicity linked to the penetration of normal and lesional skin. We studied the skin penetration of dye-tagged dendritic core-multishell (CMS) nanotransporters and of Nile red loaded CMS nanotransporters using fluorescence microscopy. Normal and stripped human skin ex vivo as well as normal reconstructed human skin and in vitro skin disease models served as test platforms. Nile red was delivered rapidly into the viable epidermis and dermis of normal skin, whereas the highly flexible CMS nanotransporters remained solely in the stratum corneum after 6h but penetrated into deeper skin layers after 24h exposure. Fluorescence lifetime imaging microscopy proved a stable dye-tag and revealed striking nanotransporter-skin interactions. The viable layers of stripped skin were penetrated more efficiently by dye-tagged CMS nanotransporters and the cargo compared to normal skin. Normal reconstructed human skin reflected the penetration of Nile red and CMS nanotransporters in human skin and both, the non-hyperkeratotic non-melanoma skin cancer and hyperkeratotic peeling skin disease models come along with altered absorption in the skin diseases.

Mutations in AP3D1 associated with immunodeficiency and seizures define a new type of Hermansky-Pudlak syndrome

Genetic disorders affecting biogenesis and transport of lysosome-related organelles are heterogeneous diseases frequently associated with albinism. We studied a patient with albinism, neutropenia, immunodeficiency, neurodevelopmental delay, generalized seizures, and impaired hearing but with no mutation in genes so far associated with albinism and immunodeficiency. Whole exome sequencing identified a homozygous mutation in AP3D1 that leads to destabilization of the adaptor protein 3 (AP3) complex. AP3 complex formation and the degranulation defect in patient T cells were restored by retroviral reconstitution. A previously described hypopigmented mouse mutant with an Ap3d1 null mutation (mocha strain) shares the neurologic phenotype with our patient and shows a platelet storage pool deficiency characteristic of Hermansky-Pudlak syndrome (HPS) that was not studied in our patient because of a lack of bleeding. HPS2 caused by mutations in AP3B1A leads to a highly overlapping phenotype without the neurologic symptoms. The AP3 complex exists in a ubiquitous and a neuronal form. AP3D1 codes for the AP3δ subunit of the complex, which is essential for both forms. In contrast, the AP3β3A subunit, affected in HPS2 patients, is substituted by AP3β3B in the neuron-specific heterotetramer. AP3δ deficiency thus causes a severe neurologic disorder with immunodeficiency and albinism that we propose to classify as HPS10.

CEDNIK syndrome results from loss-of-function mutations in SNAP29.

Background  CEDNIK (cerebral dysgenesis, neuropathy, ichthyosis and keratoderma) syndrome is a rare genodermatosis which was shown 5 years ago in one family to be associated with a loss‐of‐function mutation in SNAP29, encoding a member of the SNARE family of proteins. Decrease in SNAP29 expression was found to result in abnormal lamellar granule maturation leading to aberrant epidermal differentiation and ichthyosis.

Thermosensitive dendritic polyglycerol-based nanogels for cutaneous delivery of biomacromolecules

UNLABELLED Genetic skin diseases caused by mutations resulting in diminished protein synthesis could benefit from local substitution of the missing protein. Proteins, however, are excluded from topical applications due to their physicochemical properties. We prepared protein-loaded thermoresponsive poly(N-isopropylacrylamide)-polyglycerol-based nanogels exhibiting a thermal trigger point at 35°C, which is favorable for cutaneous applications due to the native thermal gradient of human skin. At≥35°C, the particle size (~200nm) was instantly reduced by 20% and 93% of the protein was released; no alterations of protein structure or activity were detected. Skin penetration experiments demonstrated efficient intraepidermal protein delivery particularly in barrier deficient skin, penetration of the nanogels themselves was not detected. The proof of concept was provided by transglutaminase 1-loaded nanogels which efficiently delivered the protein into transglutaminase 1-deficient skin models resulting in a restoration of skin barrier function. In conclusion, thermoresponsive nanogels are promising topical delivery systems for biomacromolecules. FROM THE CLINICAL EDITOR Many skin disorders are characterized by an absence of a specific protein due to underlying gene mutation. In this article, the authors described the use of a thermoresponsive PNIPAM-dPG nanogel for cutaneous protein delivery in a gene knock-down model of human skin. The results may have implication for nano-based local delivery of therapeutic agents in skin.

Increased cutaneous absorption reflects impaired barrier function of reconstructed skin models mimicking keratinisation disorders

The aim of this study was to assess a recently established 3D model of congenital ichthyosis, representing severe epidermal barrier function defects, for skin penetration and permeation. We have generated disease models by knock‐down of either TGM1 or ALOXE3 in primary human keratinocytes, and using keratinocytes and fibroblasts from patients with congenital ichthyosis. The results indicate disturbed barrier function as demonstrated by increased permeation of testosterone and caffeine particularly in TGM1 knock‐down models compared to control models. In addition, enhanced penetration of the model dye nile red incorporated into solid lipid nanoparticles and core‐multishell nanotransporters, respectively, was evident in disease models. Thus, in vitro skin disease models reproduce differences in barrier permeability and function seen in congenital ichthyosis and pave the way to personalised disease models. Furthermore, our findings indicate that nanocarriers may be useful in new, topical therapeutic approaches for the currently very limited treatment of congenital ichthyosis.

IGFBP7 as a potential therapeutic target in Psoriasis.

A letter to the editor is presented regarding the potential therapeutic use of insulin-like growth factor-binding protein 7 (IGFBP7) in psoriasis.