Peripheral Blood Gene Expression Profile of Infants with Atopic Dermatitis.

To enhance the understanding of molecular mechanisms and mine previously unidentified biomarkers of pediatric atopic dermatitis, PBMC gene expression profiles were generated by RNA sequencing in infants with atopic dermatitis and age-matched controls. A total of 178 significantly differentially expressed genes (DEGs) (115 upregulations and 63 downregulations) were seen, compared with those in healthy controls. The DEGs identified included IL1ß, TNF, TREM1, IL18R1, and IL18RAP. DEGs were validated by real-time RT- qPCR in a larger number of samples from PBMCs of infants with atopic dermatitis aged <12 months. Using the DAVID (Database for Annotation, Visualization and Integrated Discovery) database, functional and pathway enrichment analyses of DEGs were performed. Gene ontology enrichment analysis showed that DEGs were associated with immune responses, inflammatory responses, regulation of immune responses, and platelet activation. Pathway analysis indicated that DEGs were enriched in cytokine‒cytokine receptor interaction, immunoregulatory interactions between lymphoid and nonlymphoid cells, hematopoietic cell lineage, phosphoinositide 3-kinase‒protein kinase B signaling pathway, NK cell‒mediated cytotoxicity, and platelet activation. Furthermore, the protein‒protein interaction network was predicted using the STRING (Search Tool for the Retrieval of Interacting Genes/Proteins) database and visualized with Cytoscape software. Finally, on the basis of the protein‒protein interaction network, 18 hub genes were selected, and two significant modules were obtained. In conclusion, this study sheds light on the molecular mechanisms of pediatric atopic dermatitis and may provide diagnostic biomarkers and therapeutic targets.

Children with atopic dermatitis show increased activity of ß-glucocerebrosidase and stratum corneum levels of glucosylcholesterol that are strongly related to the local cytokine milieu.

BACKGROUND: Atopic dermatitis (AD) is characterized by immune dysregulations and an impaired skin barrier, including abnormalities in lipid organization. In the stratum corneum (SC), ß-glucocerebrosidase (GBA) mediates transformation of glucosylceramide (GlcCER) into ceramide (CER) and cholesterol into glucosylcholesterol (GlcChol). Alteration in GBA activity might contribute to skin barrier defects in AD. OBJECTIVES: To investigate GBA activity in the SC of children with AD before and after topical corticosteroid therapy and to compare it with healthy controls; to determine SC levels of GlcCER- and CER-containing hydroxysphingosine base (GlcCER[H] and CER[H], respectively) and GlcChol; and to relate them to disease severity, skin barrier function and the local cytokine milieu. METHODS: Lipid markers and cytokines of innate, T helper 1 and T helper 2 immunity were determined in SC collected from healthy children and from clinically unaffected skin of children with AD, before and after 6 weeks of therapy with topical corticosteroids. AD severity was assessed by Scoring Atopic Dermatitis and skin barrier function by transepidermal water loss (TEWL). RESULTS: Baseline GBA activity and GlcChol levels were increased in children with AD but declined after therapy. CER[H] levels and the CER[H] to GlcCER[H] ratio were increased in AD. GBA activity and GlcChol correlated with TEWL and levels of multiple cytokines, especially interleukin-1α and interleukin-18. GlcChol was strongly associated with disease severity. CONCLUSIONS: We show increased GBA activity and levels of GlcChol in AD. Our data suggest an important role of inflammation in disturbed lipid processing. GBA activity or GlcChol might be useful biomarkers in the monitoring of therapeutic responses in AD. What is already known about this topic? Patients with atopic dermatitis (AD) have a reduced skin barrier, mainly caused by altered lipid organization. The mechanisms underlying these lipid anomalies are not fully understood but likely reflect both genetic abnormalities in AD skin and the local cutaneous inflammatory environment. What does this study add? We show increased activity of the ceramide-generating enzyme ß-glucocerebrosidase in AD. Activity of this enzyme was correlated with the local cytokine milieu and declined after local corticosteroid therapy. We show that glucosylcholesterol levels in the stratum corneum are increased in AD. The function of glucosylcholesterol and the physiological consequences of increased levels are not clear yet; however, its levels were strongly correlated with skin barrier function: high transepidermal water loss strongly correlated with high levels of glucosylcholesterol. What is the translational message? Correction of cutaneous inflammation largely restores alterations in lipid metabolism in the stratum corneum of infants with AD.

Staphylococcus aureus binds to the N-terminal region of corneodesmosin to adhere to the stratum corneum in atopic dermatitis.

Staphylococcus aureus colonizes the skin of the majority of patients with atopic dermatitis (AD), and its presence increases disease severity. Adhesion of S. aureus to corneocytes in the stratum corneum is a key initial event in colonization, but the bacterial and host factors contributing to this process have not been defined. Here, we show that S. aureus interacts with the host protein corneodesmosin. Corneodesmosin is aberrantly displayed on the tips of villus-like projections that occur on the surface of AD corneocytes as a result of low levels of skin humectants known as natural moisturizing factor (NMF). An S. aureus mutant deficient in fibronectin binding protein B (FnBPB) and clumping factor B (ClfB) did not bind to corneodesmosin in vitro. Using surface plasmon resonance, we found that FnBPB and ClfB proteins bound with similar affinities. The S. aureus binding site was localized to the N-terminal glycine-serine-rich region of corneodesmosin. Atomic force microscopy showed that the N-terminal region was present on corneocytes containing low levels of NMF and that blocking it with an antibody inhibited binding of individual S. aureus cells to corneocytes. Finally, we found that S. aureus mutants deficient in FnBPB or ClfB have a reduced ability to adhere to low-NMF corneocytes from patients. In summary, we show that FnBPB and ClfB interact with the accessible N-terminal region of corneodesmosin on AD corneocytes, allowing S. aureus to take advantage of the aberrant display of corneodesmosin that accompanies low NMF in AD. This interaction facilitates the characteristic strong binding of S. aureus to AD corneocytes.

Changes in nano-mechanical properties of human epidermal cornified cells in children with atopic dermatitis.

Background: Impaired skin barrier is an important etiological factor in atopic dermatitis (AD). The structural protein filaggrin (FLG) plays a major role in maintenance of the competent skin barrier and its deficiency is associated with enhanced susceptibility to mechanical injury. Here we examined biomechanical characteristics of the corneocytes in children with AD and healthy controls. Methods: We recruited 20 children with AD and 7 healthy children. They were genotyped for filaggrin gene ( FLG) loss-of-function mutations. Stratum corneum was collected from clinically unaffected skin by adhesive tapes. Cell stiffness (apparent elastic modulus, Ea) was determined by atomic force microscopy and filaggrin degradation products (NMF) by liquid chromatography. Skin barrier function was assessed through trans-epidermal water loss (TEWL) and disease severity by the SCORing Atopic Dermatitis (SCORAD) tool. Results:  Corneocytes collected from AD patients showed a decreased elastic modulus which was strongly correlated with NMF and TEWL, but not with SCORAD. As compared with healthy controls, AD patients had reduced TEWL and NMF levels regardless of FLG mutations. NMF was strongly correlated with TEWL. Conclusion: Our findings demonstrate that AD patients have decreased corneocyte stiffness which correlates with reduced levels of filaggrin degradation products, NMF and skin barrier function. Altered mechanical properties of the corneocytes likely contribute to the loss of mechanical integrity of the SC and to reduced skin barrier function in AD.

Adhesion of Staphylococcus aureus to Corneocytes from Atopic Dermatitis Patients Is Controlled by Natural Moisturizing Factor Levels.

The bacterial pathogen Staphylococcus aureus plays an important role in atopic dermatitis (AD), a chronic disorder that mostly affects children. Colonization of the skin of AD patients by S. aureus exacerbates the disease, but the molecular determinants of the bacterium-skin adhesive interactions are poorly understood. Specifically, reduced levels of natural moisturizing factor (NMF) in the stratum corneum have been shown to be associated with more severe AD symptoms, but whether this is directly related to S. aureus adhesion is still an open question. Here, we demonstrate a novel relationship between NMF expression in AD skin and strength of bacterial adhesion. Low-NMF corneocytes, unlike high-NMF ones, are covered by a dense layer of nanoscale villus protrusions. S. aureus bacteria isolated from AD skin bind much more strongly to corneocytes when the NMF level is reduced. Strong binding forces originate from a specific interaction between the bacterial adhesion clumping factor B (ClfB) and skin ligands. Remarkably, mechanical tension dramatically strengthens ClfB-mediated adhesion, as observed with catch bonds, demonstrating that physical stress plays a role in promoting colonization of AD skin by S. aureus Collectively, our findings demonstrate that patient NMF levels regulate the strength of S. aureus-corneocyte adhesion, the first step in skin colonization, and suggest that the ClfB binding mechanism could represent a potential target for new therapeutic treatments.IMPORTANCE Bacterium-skin interactions play important roles in skin disorders, yet their molecular details are poorly understood. In this study, we decipher the molecular forces at play during adhesion of Staphylococcus aureus to skin corneocytes in the clinically important context of atopic dermatitis (AD), also known as eczema. We identify a unique relationship between the level of natural moisturizing factor (NMF) in the skin and the strength of bacterium-corneocyte adhesion. Bacterial adhesion is primarily mediated by the surface protein clumping factor B (ClfB) and is enhanced by physical stress, highlighting the role of protein mechanobiology in skin colonization. Similar to a catch bond behavior, this mechanism represents a promising target for the development of novel antistaphylococcal agents.

The spectrum of manifestations in desmoplakin gene (DSP) spectrin repeat 6 domain mutations: Immunophenotyping and response to ustekinumab.

BACKGROUND: The immune abnormalities underlying the ichthyoses are poorly understood. OBJECTIVE: To determine the immunophenotype of an ichthyosis resulting from mutations in the spectrin repeat 6 (SR6) domain of desmoplakin gene (DSP) and target therapy on the basis of molecular pathogenesis. METHODS: Immunophenotyping was performed by using the blood and skin of a girl with SR6 region DSP mutations causing erythroderma/ichthyosis and cardiomyopathy. RESULTS: On the basis of the discovery of T helper 1 and T helper 17/interleukin 23 skewing in the skin and T helper 17/interleukin 22 skewing in blood, ustekinumab therapy was initiated. Ustekinumab was also administered to a boy with an SR6 region DSP mutation and ichthyosis without cardiomyopathy. Both children responded despite previous poor responses to immunosuppressants and retinoids. LIMITATIONS: Small number of patients and immunophenotyping in only 1 patient. CONCLUSION: An understanding of the molecular basis of inflammation in rare cutaneous disorders can lead to targeted therapy, which promises to be more beneficial than broad immunosuppressants.

Clumping Factor B Promotes Adherence of Staphylococcus aureus to Corneocytes in Atopic Dermatitis.

Staphylococcus aureus skin infection is a frequent and recurrent problem in children with the common inflammatory skin disease atopic dermatitis (AD). S. aureus colonizes the skin of the majority of children with AD and exacerbates the disease. The first step during colonization and infection is bacterial adhesion to the cornified envelope of corneocytes in the outer layer, the stratum corneum. Corneocytes from AD skin are structurally different from corneocytes from normal healthy skin. The objective of this study was to identify bacterial proteins that promote the adherence of S. aureus to AD corneocytes. S. aureus strains from clonal complexes 1 and 8 were more frequently isolated from infected AD skin than from the nasal cavity of healthy children. AD strains had increased ClfB ligand binding activity compared to normal nasal carriage strains. Adherence of single S. aureus bacteria to corneocytes from AD patients ex vivo was studied using atomic force microscopy. Bacteria expressing ClfB recognized ligands distributed over the entire corneocyte surface. The ability of an isogenic ClfB-deficient mutant to adhere to AD corneocytes compared to that of its parent clonal complex 1 clinical strain was greatly reduced. ClfB from clonal complex 1 strains had a slightly higher binding affinity for its ligand than ClfB from strains from other clonal complexes. Our results provide new insights into the first step in the establishment of S. aureus colonization in AD patients. ClfB is a key adhesion molecule for the interaction of S. aureus with AD corneocytes and represents a target for intervention.

Blue Rubber Bleb Nevus (BRBN) Syndrome Is Caused by Somatic TEK (TIE2) Mutations.

Blue rubber bleb nevus syndrome (Bean syndrome) is a rare, severe disorder of unknown cause, characterized by numerous cutaneous and internal venous malformations; gastrointestinal lesions are pathognomonic. We discovered somatic mutations in TEK, the gene encoding TIE2, in 15 of 17 individuals with blue rubber bleb nevus syndrome. Somatic mutations were also identified in five of six individuals with sporadically occurring multifocal venous malformations. In contrast to common unifocal venous malformation, which is most often caused by the somatic L914F TIE2 mutation, multifocal forms are predominantly caused by double (cis) mutations, that is, two somatic mutations on the same allele of the gene. Mutations are identical in all lesions from a given individual. T1105N-T1106P is recurrent in blue rubber bleb nevus, whereas Y897C-R915C is recurrent in sporadically occurring multifocal venous malformation: both cause ligand-independent activation of TIE2, and increase survival, invasion, and colony formation when expressed in human umbilical vein endothelial cells.

Expanding the clinical spectrum of hereditary fibrosing poikiloderma with tendon contractures, myopathy and pulmonary fibrosis due to FAM111B mutations.

BACKGROUND: Hereditary Fibrosing Poikiloderma (HFP) with tendon contractures, myopathy and pulmonary fibrosis (POIKTMP [MIM 615704]) is a very recently described entity of syndromic inherited poikiloderma. Previously by using whole exome sequencing in five families, we identified the causative gene, FAM111B (NM_198947.3), the function of which is still unknown. Our objective in this study was to better define the specific features of POIKTMP through a larger series of patients. METHODS: Clinical and molecular data of two families and eight independent sporadic cases, including six new cases, were collected. RESULTS: Key features consist of: (i) early-onset poikiloderma, hypotrichosis and hypohidrosis; (ii) multiple contractures, in particular triceps surae muscle contractures; (iii) diffuse progressive muscular weakness; (iv) pulmonary fibrosis in adulthood and (v) other features including exocrine pancreatic insufficiency, liver impairment and growth retardation. Muscle magnetic resonance imaging was informative and showed muscle atrophy and fatty infiltration. Histological examination of skeletal muscle revealed extensive fibroadipose tissue infiltration. Microscopy of the skin showed a scleroderma-like aspect with fibrosis and alterations of the elastic network. FAM111B gene analysis identified five different missense variants (two recurrent mutations were found respectively in three and four independent families). All the mutations were predicted to localize in the trypsin-like cysteine/serine peptidase domain of the protein. We suggest gain-of-function or dominant-negative mutations resulting in FAM111B enzymatic activity changes. CONCLUSIONS: HFP with tendon contractures, myopathy and pulmonary fibrosis, is a multisystemic disorder due to autosomal dominant FAM111B mutations. Future functional studies will help in understanding the specific pathological process of this fibrosing disorder.

Severe dermatitis, multiple allergies, and metabolic wasting syndrome caused by a novel mutation in the N-terminal plakin domain of desmoplakin.

BACKGROUND: Severe dermatitis, multiple allergies, and metabolic wasting (SAM) syndrome is a recently recognized syndrome caused by mutations in the desmoglein 1 gene (DSG1). To date, only 3 families have been reported. OBJECTIVE: We studied a new case of SAM syndrome known to have no mutations in DSG1 to detail the clinical, histopathologic, immunofluorescent, and ultrastructural phenotype and to identify the underlying molecular mechanisms in this rare genodermatosis. METHODS: Histopathologic, electron microscopy, and immunofluorescent studies were performed. Whole-exome sequencing data were interrogated for mutations in desmosomal and other skin structural genes, followed by Sanger sequencing of candidate genes in the patient and his parents. RESULTS: No mutations were identified in DSG1; however, a novel de novo heterozygous missense c.1757A>C mutation in the desmoplakin gene (DSP) was identified in the patient, predicting the amino acid substitution p.His586Pro in the desmoplakin polypeptide. CONCLUSIONS: SAM syndrome can be caused by mutations in both DSG1 and DSP. Knowledge of this genetic heterogeneity is important for both analysis of patients and genetic counseling of families. This condition and these observations reinforce the importance of heritable skin barrier defects, in this case desmosomal proteins, in the pathogenesis of atopic disease.

Filaggrin breakdown products determine corneocyte conformation in patients with atopic dermatitis.

BACKGROUND: Loss-of-function (LOF) mutations in the filaggrin gene (FLG) are a well-replicated risk factor for atopic dermatitis (AD) and are known to cause an epidermal barrier defect. The nature of this barrier defect is not fully understood. Patients with AD with FLG LOF mutations are known to have more persistent disease, more severe disease, and greater risk of food allergies and eczema herpeticum. Abnormalities in corneocyte morphology have been observed in patients with AD, including prominent villus-like projections (VP); however, these ultrastructural features have not been systematically studied in patients with AD in relation to FLG genotype and acute and convalescent status. OBJECTIVE: We sought to quantitatively explore the relationship between FLG genotype, filaggrin breakdown products (natural moisturizing factor [NMF]), and corneocyte morphology in patients with AD. METHODS: We studied 15 children at first presentation of AD and after 6 weeks of standard therapy. We applied atomic force microscopy to study corneocyte conformation in patients with AD stratified by FLG status and NMF level. By using a new quantitative methodology, the number of VPs per investigated corneocyte area was assessed and expressed as the Dermal Texture Index score. Corneocytes were also labeled with an anti-corneodesmosin antibody and visualized with scanning electron microscopy. RESULTS: We found a strong correlation between NMF levels and Dermal Texture Index scores in both acute and convalescent states (respective r = -0.80 and -0.75, P < .001 and P = .002). Most, but not all, VPs showed the presence of corneodesmosin abundantly all over the cell surface in homozygous/compound heterozygous FLG patients and, to a lesser extent, in heterozygous and wild-type patients. CONCLUSIONS: NMF levels are highly correlated with corneocyte morphology in patients with AD. These corneocyte conformational changes shed further insight into the filaggrin-deficient phenotype and help explain the barrier defect in patients with AD with FLG LOF mutations.

Transcriptional regulator PRDM12 is essential for human pain perception.

Pain perception has evolved as a warning mechanism to alert organisms to tissue damage and dangerous environments. In humans, however, undesirable, excessive or chronic pain is a common and major societal burden for which available medical treatments are currently suboptimal. New therapeutic options have recently been derived from studies of individuals with congenital insensitivity to pain (CIP). Here we identified 10 different homozygous mutations in PRDM12 (encoding PRDI-BF1 and RIZ homology domain-containing protein 12) in subjects with CIP from 11 families. Prdm proteins are a family of epigenetic regulators that control neural specification and neurogenesis. We determined that Prdm12 is expressed in nociceptors and their progenitors and participates in the development of sensory neurons in Xenopus embryos. Moreover, CIP-associated mutants abrogate the histone-modifying potential associated with wild-type Prdm12. Prdm12 emerges as a key factor in the orchestration of sensory neurogenesis and may hold promise as a target for new pain therapeutics.

Insight into IKBKG/NEMO locus: report of new mutations and complex genomic rearrangements leading to incontinentia pigmenti disease.

Incontinentia pigmenti (IP) is an X-linked-dominant Mendelian disorder caused by mutation in the IKBKG/NEMO gene, encoding for NEMO/IKKgamma, a regulatory protein of nuclear factor kappaB (NF-kB) signaling. In more than 80% of cases, IP is due to recurrent or nonrecurrent deletions causing loss-of-function (LoF) of NEMO/IKKgamma. We review how the local architecture of the IKBKG/NEMO locus with segmental duplication and a high frequency of repetitive elements favor de novo aberrant recombination through different mechanisms producing genomic microdeletion. We report here a new microindel (c.436_471delinsT, p.Val146X) arising through a DNA-replication-repair fork-stalling-and-template-switching and microhomology-mediated-end-joining mechanism in a sporadic IP case. The LoF mutations of IKBKG/NEMO leading to IP include small insertions/deletions (indel) causing frameshift and premature stop codons, which account for 10% of cases. We here present 21 point mutations previously unreported, which further extend the spectrum of pathologic variants: 14/21 predict LoF because of premature stop codon (6/14) or frameshift (8/14), whereas 7/21 predict a partial loss of NEMO/IKKgamma activity (two splicing and five missense). We review how the analysis of IP-associated IKBKG/NEMO hypomorphic mutants has contributed to the understanding of the pathophysiological mechanism of IP disease and has provided important information on affected NF-kB signaling. We built a locus-specific database listing all IKBKG/NEMO variants, accessible at http://IKBKG.lovd.nl.

High-density genotyping study identifies four new susceptibility loci for atopic dermatitis.

Atopic dermatitis is a common inflammatory skin disease with a strong heritable component. Pathogenetic models consider keratinocyte differentiation defects and immune alterations as scaffolds, and recent data indicate a role for autoreactivity in at least a subgroup of patients. FLG (encoding filaggrin) has been identified as a major locus causing skin barrier deficiency. To better define risk variants and identify additional susceptibility loci, we densely genotyped 2,425 German individuals with atopic dermatitis (cases) and 5,449 controls using the Immunochip array followed by replication in 7,196 cases and 15,480 controls from Germany, Ireland, Japan and China. We identified four new susceptibility loci for atopic dermatitis and replicated previous associations. This brings the number of atopic dermatitis risk loci reported in individuals of European ancestry to 11. We estimate that these susceptibility loci together account for 14.4% of the heritability for atopic dermatitis.

The multifunctional role of filaggrin in allergic skin disease.

Filaggrin is a major structural protein in the stratum corneum of the epidermis. Mutations in the filaggrin gene are the most significant known genetic risk factor for the development of atopic dermatitis. Mutations in the human filaggrin gene (FLG) also confer risk for the associated allergic diseases of food allergy, asthma, and allergic rhinitis. These discoveries have highlighted the importance of skin barrier function in the pathogenesis of atopic diseases and have motivated a surge in research characterizing the filaggrin-deficient skin barrier and its consequences. In this review we discuss the mechanisms through which mutations in this protein contribute to the pathogenesis of atopic dermatitis and associated atopic conditions. We focus on recent human and murine discoveries characterizing the filaggrin-deficient epidermis with respect to biophysical, immunologic, and microbiome abnormalities.