Liat Samuelov

Desmoglein 1 deficiency results in severe dermatitis, multiple allergies and metabolic wasting

The relative contribution of immunological dysregulation and impaired epithelial barrier function to allergic diseases is still a matter of debate. Here we describe a new syndrome featuring severe dermatitis, multiple allergies and metabolic wasting (SAM syndrome) caused by homozygous mutations in DSG1. DSG1 encodes desmoglein 1, a major constituent of desmosomes, which connect the cell surface to the keratin cytoskeleton and have a crucial role in maintaining epidermal integrity and barrier function. Mutations causing SAM syndrome resulted in lack of membrane expression of DSG1, leading to loss of cell-cell adhesion. In addition, DSG1 deficiency was associated with increased expression of a number of genes encoding allergy-related cytokines. Our deciphering of the pathogenesis of SAM syndrome substantiates the notion that allergy may result from a primary structural epidermal defect.

P-Cadherin Regulates Human Hair Growth and Cycling via Canonical Wnt Signaling and Transforming Growth Factor-β2

P-cadherin is a key component of epithelial adherens junctions, and it is prominently expressed in the hair follicle (HF) matrix. Loss-of-function mutations in CDH3, which encodes P-cadherin, result in hypotrichosis with juvenile macular dystrophy (HJMD), an autosomal recessive disorder featuring sparse and short hair. Here, we attempted to recapitulate some aspects of HJMD in vitro by transfecting normal, organ-cultured human scalp HFs with lipofectamine and CDH3-specific or scrambled control siRNAs. As in HJMD patients, P-cadherin silencing inhibited hair shaft growth, prematurely induced HF regression (catagen), and inhibited hair matrix keratinocyte proliferation. In situ, membrane β-catenin expression and transcription of the β-catenin target gene, axin2, were significantly reduced, whereas glycogen synthase kinase 3 β (GSK3β) and phospho-β-catenin immunoreactivity were increased. These effects were partially reversed by inhibiting GSK3β. P-cadherin silencing reduced the expression of the anagen-promoting growth factor, IGF-1, whereas that of transforming growth factor β 2 (TGFβ2; catagen promoter) was enhanced. Neutralizing TGFβ antagonized the catagen-promoting effects of P-cadherin silencing. In summary, we introduce human HFs as an attractive preclinical model for studying the functions of P-cadherin in human epithelial biology and pathology. This model demonstrates that cadherins can be successfully knocked down in an intact human organ in vitro, and shows that P-cadherin is needed for anagen maintenance by regulating canonical Wnt signaling and suppressing TGFβ2.

Peeling off the genetics of atopic dermatitis–like congenital disorders

The epidermis forms during the course of a complex differentiation process known as cornification, which culminates with the formation of the epidermal barrier. The epidermal barrier serves as a vital line of defense against the environment and mainly consists of 3 elements: intracellular keratin filaments, intercellular lipids, and the cornified cell envelope. Adequate epidermal barrier function is also critically dependent on normal shedding of terminally differentiated keratinocytes, a process termed desquamation, which requires the dissolution of cell-cell junctions in the upper granular layers. Although much has been learned about epidermal differentiation through the deciphering of the molecular basis of various cornification disorders, less is currently known about the mechanisms regulating epidermal desquamation and disorders resulting from disruption of this process. Netherton syndrome, peeling skin syndrome type B, and skin dermatitis--multiple severe allergies--metabolic wasting syndrome are 3 autosomal recessive conditions resulting from aberrant regulation of epidermal desquamation. The deciphering of their pathogenesis has not only broadened our understanding of this process but has also shed new light on clinical and mechanistic links between allergic reactions and abnormal desquamation, substantiating the notion that allergic manifestations might, under some circumstances, be the sole consequence of a primary epidermal defect.

Calcitonin gene‐related peptide (CGRP) may award relative protection from interferon‐γ‐induced collapse of human hair follicle immune privilege

Abstract:  Interferon‐γ (IFNγ)‐induced collapse of hair follicle (HF) immune privilege (IP) is a key element in the pathogenesis of alopecia areata. In this pilot study, we investigated whether the immunosuppressive neuropeptide, calcitonin gene‐related peptide (CGRP), can protect from and/or restore IFNγ‐induced HF‐IP collapse. After showing that human scalp HFs express CGRP receptor‐like receptor (CRLR) immunoreactivity, anagen HFs were cultured in the presence of IFNγ, with CGRP added before or after. Adding CGRP after IFNγ administration (‘restoration assay’) failed to downregulate IFNγ‐induced ectopic MHC class I expression, while MHC class II expression was reduced. However, administering CGRP before IFNγ application (‘protection assay’) significantly reduced the IFNγ‐induced overexpression and ectopic expression of MHC class I and II and reduced the increased degranulation of perifollicular mast cells induced by IFNγ. This suggests that CGRP may not restore HF‐IP once it has collapsed, but may protect it from collapsing. Therefore, CRLR stimulation might help to retard AA progression.

Inherited desmosomal disorders

Desmosomes serve as intercellular junctions in various tissues including the skin and the heart where they play a crucial role in cell-cell adhesion, signalling and differentiation. The desmosomes connect the cell surface to the keratin cytoskeleton and are composed of a transmembranal part consisting mainly of desmosomal cadherins, armadillo proteins and desmoplakin, which form the intracytoplasmic desmosomal plaque. Desmosomal genodermatoses are caused by mutations in genes encoding the various desmosomal components. They are characterized by skin, hair and cardiac manifestations occurring in diverse combinations. Their classification into a separate and distinct clinical group not only recognizes their common pathogenesis and facilitates their diagnosis but might also in the future form the basis for the design of novel and targeted therapies for these occasionally life-threatening diseases.

Topobiology of human pigmentation: P-cadherin selectively stimulates hair follicle melanogenesis.

P-cadherin serves as a major topobiological cue in mammalian epithelium. In human hair follicles (HFs), it is prominently expressed in the inner hair matrix that harbors the HF pigmentary unit. However, the role of P-cadherin in normal human pigmentation remains unknown. As patients with mutations in the gene that encodes P-cadherin show hypotrichosis and fair hair, we explored the hypothesis that P-cadherin may control HF pigmentation. When P-cadherin was silenced in melanogenically active organ-cultured human scalp HFs, this significantly reduced HF melanogenesis and tyrosinase activity as well as gene and/or protein expression of gp100, stem cell factor, c-Kit, and microphthalmia-associated transcription factor (MITF), both in situ and in isolated human HF melanocytes. Instead, epidermal pigmentation was unaffected by P-cadherin knockdown in organ-cultured human skin. In hair matrix keratinocytes, P-cadherin silencing reduced plasma membrane β-catenin, whereas glycogen synthase kinase 3 beta (GSK3β) and phospho-β-catenin expression were significantly upregulated. This suggests that P-cadherin-GSK3β/Wnt signaling is required for maintaining the expression of MITF to sustain intrafollicular melanogenesis. Thus, P-cadherin-mediated signaling is a melanocyte subtype-specific topobiological regulator of normal human pigmentation, possibly via GSK3β-mediated canonical Wnt signaling.

An exceptional mutational event leading to Chanarin―Dorfman syndrome in a large consanguineous family

Chanarin–Dorfman syndrome (CDS) is a rare autosomal recessive metabolic disorder featuring congenital ichthyosis combined with pleiomorphic visceral manifestations associated with tissue accumulation of cytoplasmic lipid droplets. Mutations in the ABHD5 gene, encoding a crucial cofactor for adipose triglyceride lipase, have been found to underlie all CDS cases reported to date. The purposed of this study was to ascertain the genetic defect underlying CDS in a large multigenerational family. We used a combination of direct sequencing, reverse transcriptase–polymerase chain reaction (RT‐PCR) and microsatellite marker genotyping to identify a novel CDS‐causing mutation in ABHD5. Although no pathogenic mutation could be identified in the coding sequence of the ABHD5 gene, polymorphic marker genotyping analysis supported linkage to this gene locus. Accordingly, direct sequencing of RT‐PCR amplification products generated from patient skin‐derived total RNA, revealed in all four patients the presence of a 101 bp insertion between exon 3 and exon 4. Bioinformatic analysis and direct sequencing indicated that this insertion resulted from an exceptional mutational event, namely, the insertion of a LINE element into intron 3 of the ABHD5 gene, leading to aberrant splicing out of the mutant intron 3. Our results confirm genetic homogeneity in CDS and underscore the importance of RNA studies in the molecular diagnosis of genodermatoses.

Neural controls of human hair growth: calcitonin gene-related peptide (CGRP) induces catagen

As one of the most densely innervated organs of the mammalian body, the hair follicle (HF) is subject to bioregulation by neuropeptides, neurotransmitters, and neurotrophins. The perifollicular network of sensory nerve fibres prominently contains and releases neuropeptides such as substance P and calcitonin-gene-related peptide (CGRP) and underlies prominent hair cycle-associated changes [1]. However, it remains to be systematically explored whether and how these neuropeptides impact on human hair growth. While we had already shown that substance P strongly inhibits the growth of microdissected, organcultured human scalp HFs in organ culture [1], it is unknown whether CGRP exerts any effects on human hair growth. This potent vasoactive neuropeptide is widely distributed in the central and peripheral nervous system, and is prominent in perifollicular sensory nerve fibres in both rodent and human skin [2]. CGRP acts via the calcitonin receptor-like receptor (CRLR), a

NB-UVB phototherapy for generalized granuloma annulare.

Granuloma annulare (GA) is a benign, usually self‐limited, granulomatous skin disease of unknown etiology. The generalized form of the disease shows a more chronic, relapsing course, rare spontaneous resolution, and poorer response to therapy. Psoralen plus UVA phototherapy has been reported to be effective for GA. However, little is known regarding the efficacy of narrowband UVB phototherapy. Our goal was to determine the efficacy of NB‐UVB phototherapy in generalized GA. We carried out a retrospective study of patients with generalized GA treated with NB‐UVB phototherapy over a period of 3 years. On completion of treatment, outcome was assessed as complete response (complete clearance of the lesions), partial response (>50% clearance of the lesions), and poor response (<50% clinical response). Therapy was stopped if no improvement was seen after 20 treatments. Thirteen patients were included in the study. 54% of patients treated with NB‐UVB had a complete/partial response by the end of the treatment period. NB‐UVB phototherapy was well‐tolerated, with no serious adverse effects. NB‐UVB phototherapy is effective in a substantial portion of patients with generalized GA. To determine the true efficacy of this therapeutic modality, a prospective study comparing it to PUVA is warranted.

RBM28, a protein deficient in ANE syndrome, regulates hair follicle growth via miR-203 and p63

Alopecia–neurological defects–endocrinopathy (ANE) syndrome is a rare inherited hair disorder, which was shown to result from decreased expression of the RNA‐binding motif protein 28 (RBM28). In this study, we attempted to delineate the role of RBM28 in hair biology. First, we sought to obtain evidence for the direct involvement of RBM28 in hair growth. When RBM28 was downregulated in human hair follicle (HF) organ cultures, we observed catagen induction and HF growth arrest, indicating that RBM28 is necessary for normal hair growth. We also aimed at identifying molecular targets of RBM28. Given that an RBM28 homologue was recently found to regulate miRNA biogenesis in C. elegans and given the known pivotal importance of miRNAs for proper hair follicle development, we studied global miRNA expression profile in cells knocked down for RBM28. This analysis revealed that RBM28 controls the expression of miR‐203. miR‐203 was found to regulate in turn TP63, encoding the transcription factor p63, which is critical for hair morphogenesis. In conclusion, RBM28 contributes to HF growth regulation through modulation of miR‐203 and p63 activity.