Abnormal Lamellar Granules Research Articles

Mouse models for spontaneous dermatitis due to impaired skin barrier formation

Flaky tail mice possess two distinct autosomal recessive mutations, hair abnormality (matted: ma) and stratum corneum layer abnormality (flaky tail: ft), and develop dermatitis spontaneously with high serum IgE even under specific pathogen free condition. We demonstrated that flaky tail mice possess loss of function mutation in Filaggrin (Flg) which is one of the major component of stratum corneum, and showed skin barrier abnormality, although our genetically engineered Flg null mice did not develop dermatitis spontaneously. As a result of segregation of ft and ma mutations, we identified that ma mutation is responsible for the dermatitis phenotype in flaky tail mice, and Tmem79 nonsense mutation (Tmem79(ma)) is corresponding to the ma mutation. Tmem79 is expressed in outermost cell of stratum granulosum layer, and ma mice showed abnormal lamellar granule secretory system and abnormal formation of stratum corneum. Thus, Tmem79(ma/ma) mice provides a useful mouse model for spontaneous dermatitis caused by skin barrier gene deficiency. Further analysis for Tmem79(ma/ma) mice would elucidate important mechanisms for development of atopic dermatitis.

Harlequin ichthyosis: ABCA12 mutations underlie defective lipid transport, reduced protease regulation and skin-barrier dysfunction

Harlequin ichthyosis (HI) is a devastating autosomal recessive congenital skin disease. It has been vital to elucidate the biological importance of the protein ABCA12 in skin-barrier permeability, following the discovery that ABCA12 gene mutations can result in this rare disease. ATP-binding cassette transporter A12 (ABCA12) is a member of the subfamily of ATP-binding cassette transporters and functions to transport lipid glucosylceramides (GlcCer) to the extracellular space through lamellar granules (LGs). GlcCer are hydrolysed into hydroxyceramides extracellularly and constitute a portion of the extracellular lamellar membrane, lipid envelope and lamellar granules. In HI skin, loss of function of ABCA12 due to null mutations results in impaired lipid lamellar membrane formation in the cornified layer, leading to defective permeability of the skin barrier. In addition, abnormal lamellar granule formation (distorted shape, reduced in number or absent) could further cause aberrant production of LG-associated desquamation enzymes, which are likely to contribute to the impaired skin barrier in HI. This article reviews current opinions on the patho-mechanisms of ABCA12 action in HI and potential therapeutic interventions based on targeted molecular therapy and gene therapy strategies.

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

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. To delineate the molecular consequences of disease-causing mutations in SNAP29. We used direct sequencing, in vitro mutagenesis and three-dimensional organotypic cell cultures. We identified a novel homozygous insertion in SNAP29 (c.486insA) in two sibs presenting with ichthyosis and dysgenesis of the corpus callosum. In vitro transfection experiments indicated that this mutation results in SNAP29 loss-of-function. Further substantiating this notion, we could replicate histological features typical for CEDNIK syndrome in three-dimensional primary human keratinocyte organotypic cell cultures downregulated for SNAP29. The identification of a second mutation in SNAP29 in the present study definitely establishes a causal relationship between defective function of SNAP29 and the pleiotropic manifestations of CEDNIK syndrome. Our present and previous data position SNAP29 as an essential component of the epidermal differentiation machinery.

CGI-58 Is an α/β-Hydrolase within Lipid Transporting Lamellar Granules of Differentiated Keratinocytes

CGI-58 is the causative molecule underlying Dorfman-Chanarin syndrome, a neutral lipid storage disease exhibiting apparent clinical features of ichthyosis. CGI-58, associated with triacylglycerol hydrolysis, has an alpha/beta-hydrolase fold and is also known as the alpha/beta-hydrolase domain-containing protein 5. The purpose of this study was to elucidate the function of CGI-58 and the pathogenic mechanisms of ichthyosis in Dorfman-Chanarin syndrome. Using an anti-CGI-58 antibody, we found CGI-58 to be expressed in the upper epidermis, predominantly in the granular layer cells, as well as in neurons and hepatocytes. Immunoelectron microscopy revealed that CGI-58 was also localized to the lamellar granules (LGs), which are lipid transport and secretion granules found in keratinocytes. CGI-58 expression was markedly reduced in the epidermis of patients with harlequin ichthyosis, demonstrating defective LG formation. In cultured keratinocytes, CGI-58 expression was mildly up-regulated under high Ca(2+) conditions and markedly up-regulated in three-dimensional, organotypic cultures. In the developing human epidermis, CGI-58 immunostaining was observed at an estimated gestational age of 49 days, and CGI-58 mRNA expression was up-regulated concomitantly with both epidermal stratification and keratinocyte differentiation. CGI-58 knockdown reduced expression of keratinocyte differentiation/keratinization markers in cultured human keratinocytes. Our results indicate that CGI-58 is expressed and packaged into LGs during keratinization and likely plays crucial role(s) in keratinocyte differentiation and LG lipid metabolism, contributing to skin lipid barrier formation.

ABCA12 Is the Major Harlequin Ichthyosis Gene

Harlequin ichthyosis (HI) is the most severe form of autosomal-recessive, congenital ichthyosis. Affected infants have markedly impaired barrier function and are more susceptible to infection. Abnormalities in the localization of epidermal lipids as well as abnormal lamellar granule formation are features of HI skin. Previously, we and others have shown that mutations in the ABCA12 gene encoding an adenosine triphosphate-binding cassette (ABC) transporter underlie the skin disease HI. In this study, we have sequenced the ABCA12 gene in an additional 14 patients and show that all contain mutations, with the majority being either nonsense substitution or frameshift mutations. Eleven HI patients had bi-allelic ABCA12 mutations, whereas in the remaining three HI patients in this study, ABCA12 mutations were detected on only one allele by sequencing. In addition, the one patient from the previous study where no sequence mutations were detected was screened for heterozygous deletions. A combination of oligonucleotide arrays, multiplex PCR analysis and single-nucleotide polymorphism genotyping revealed a heterozygous intragenic deletion in exon 8. These mutation data establish ABCA12 as the major HI gene.

Compound Heterozygous Mutations Including a De Novo Missense Mutation in ABCA12 Led to a Case of Harlequin Ichthyosis with Moderate Clinical Severity

Harlequin ichthyosis (HI) is one of the most devastating genodermatoses. Recently, ABCA12 mutations were identified as the cause of HI. A newborn Japanese male demonstrated the typical features of HI. The patient was treated with oral etretinate and his general condition has been good (now aged 1.5 years). This patient with moderate clinical severity was compound heterozygous for a novel de novo missense mutation 1160G > A (S387N) in exon 10 and a maternal deletion mutation 4158_4160delTAC (T1387del) in exon 28 of ABCA12. T1387del was a deletion of a highly conserved threonine residue within the first adenosine 5' triphosphate-binding domain and is thought to seriously affect the function of the ABCA12 protein. Conversely, the residue 387 is located outside the known active sites of ABCA12 and S387N is predicted not to lead to a serious functional deficiency in ABCA12. Electron microscopy revealed abnormal lamellar granules in the granular layer cells and a moderate number of lipid vacuoles in the cornified cells. Disturbed glucosylceramide transport was confirmed in the cultured keratinocytes from the patient. No de novo mutation in ABCA12 has yet been reported either in HI or lamellar ichthyosis. The present case suggested that a de novo ABCA12 mutation might underlie HI.

Abnormal lamellar granules in a case of CHILD syndrome

A 32-year-old female had cutaneous and musculoskeletal changes consistent with congenital hemidysplasia with ichthyosiform erythroderma and limb defects (CHILD) syndrome. She was born with the dysplastic, shortened right-sided arm and leg. Erythematous, hyperkeratotic lesion occurred on the trunk initially and extended to the right-sided arm and leg. Almost all area of her right-side body except the head and neck was covered by the erythematous lesion with yellow waxy scales, and the distal end of the rudimentary leg showed a verrucous appearance. The histology shared many features with verruciform xanthoma. Electron microscopy revealed vesicular structures in the intercellular spaces of the stratum corneum and vacuoles or vesicular structures in upper prickle cell layer. Some of them can be recognized as abnormal lamellar granules. Within the foamy cells in the papillary dermis, large vacuoles were found. These findings suggested that abnormal lipid metabolism involving lamellar granules may be responsible to the skin lesion of CHILD syndrome.

Mutations in ABCA12 Underlie the Severe Congenital Skin Disease Harlequin Ichthyosis

Harlequin ichthyosis (HI) is the most severe and frequently lethal form of recessive congenital ichthyosis. Although defects in lipid transport, protein phosphatase activity, and differentiation have been described, the genetic basis underlying the clinical and cellular phenotypes of HI has yet to be determined. By use of single-nucleotide-polymorphism chip technology and homozygosity mapping, a common region of homozygosity was observed in five patients with HI in the chromosomal region 2q35. Sequencing of the ABCA12 gene, which maps within the minimal region defined by homozygosity mapping, revealed disease-associated mutations, including large intragenic deletions and frameshift deletions in 11 of the 12 screened individuals with HI. Since HI epidermis displays abnormal lamellar granule formation, ABCA12 may play a critical role in the formation of lamellar granules and the discharge of lipids into the intercellular spaces, which would explain the epidermal barrier defect seen in this disorder. This finding paves the way for early prenatal diagnosis. In addition, functional studies of ABCA12 will lead to a better understanding of epidermal differentiation and barrier formation.

Truncation of CGI-58 Protein Causes Malformation of Lamellar Granules Resulting in Ichthyosis in Dorfman-Chanarin Syndrome

Dorfman-Chanarin syndrome is a rare autosomal recessive inherited lipid storage disease characterized by ichthyosis, leukocyte lipid vacuoles, and involvement of several internal organs. Recently, CGI-58 mutations were identified as the cause of Dorfman-Chanarin syndrome. The physiologic roles of the CGI-58 protein and the pathomechanisms of Dorfman-Chanarin syndrome still remain to be clarified, however. The patient, a 16-y-old male, demonstrated ichthyosis, small ears, lipid vacuoles in his leukocytes, liver dysfunction, and mental retardation. Sequencing of CGI-58 revealed that the patient was homozygous for a novel nonsense mutation R184X, in exon 4. The putative truncated protein was 52.4% of the length of the normal CGI-58 polypeptide and lacked approximately 60% of the lipid binding region, 66.4% of the alpha/beta hydrolase folding segment of the polypeptide, and two of the CGI-58 catalytic triads, resulting in a significant loss of lipase/esterase/thioesterase activity. Electron microscopy revealed a large number of abnormal lamellar granules, a disturbed intercellular lamellar structure, and lipid vacuoles in the epidermis. These results suggested that CGI-58 protein is involved in the lipid metabolism of lamellar granules and that defective lipid production in lamellar granules caused by a CGI-58 protein deficiency is involved in the pathogenesis of ichthyosis in Dorfman-Chanarin syndrome.

Regional difference in expression of characteristic abnormality of harlequin ichthyosis in affected fetuses

Harlequin ichthyosis (HI) is a severe congenital ichthyosis in which newborn infants are covered with a thick plate of stratum corneum. We examined skin specimens from a variety of regions of the body including the scalp, face, tongue, trunk, upper and lower extremities, digits, palms, and soles of three fetuses affected with HI that were diagnosed prenatally. In all the skin regions, characteristic morphological abnormalities (absent or abnormal lamellar granules and intercellular lamellae, lipid inclusions in the cornified cells) were expressed in the late second trimester of the fetal period. The cornified cells in hair canals showed morphological abnormalities of HI more strongly than the interfollicular epidermis. Immunoblot study of epidermal extracts revealed that profilaggrin was much more prominent than filaggrin in all the hairy skin regions where the hair canals were extensively keratinized, but filaggrin was prominent in the palm. These observations support the idea that, in the hairy skin, HI phenotype expression is associated with keratinization and abnormal filaggrin metabolism in hair. In addition, the prenatal diagnosis or prenatal exclusion of HI is thought to be possible from whichever site of the fetal body the skin biopsy is taken in the late second trimester of the fetal period.