Atopic dermatitis and skin disease
A homozygous nonsense mutation in the gene for Tmem79, a component for the lamellar granule secretory system, produces spontaneous eczema in an experimental model of atopic dermatitis

https://doi.org/10.1016/j.jaci.2013.08.027Get rights and content

Background

Flaky tail (ma/ma Flgft/ft) mice have a frameshift mutation in the filaggrin (Flgft) gene and are widely used as a model of human atopic dermatitis associated with FLG mutations. These mice possess another recessive hair mutation, matted (ma), and develop spontaneous dermatitis under specific pathogen-free conditions, whereas genetically engineered Flg−/− mice do not.

Objective

We identified and characterized the gene responsible for the matted hair and dermatitis phenotype in flaky tail mice.

Methods

We narrowed down the responsible region by backcrossing ma/ma mice with wild-type mice and identified the mutation using next-generation DNA sequencing. We attempted to rescue the matted phenotype by introducing the wild-type matted transgene. We characterized the responsible gene product by using whole-mount immunostaining of epidermal sheets.

Results

We demonstrated that ma, but not Flgft, was responsible for the dermatitis phenotype and corresponded to a Tmem79 gene nonsense mutation (c.840C>G, p.Y280*), which encoded a 5-transmembrane protein. Exogenous Tmem79 expression rescued the matted hair and dermatitis phenotype of Tmem79ma/ma mice. Tmem79 was mainly expressed in the trans-Golgi network in stratum granulosum cells in the epidermis in both mice and humans. The Tmem79ma/ma mutation impaired the lamellar granule secretory system, which resulted in altered stratum corneum formation and a subsequent spontaneous dermatitis phenotype.

Conclusions

The Tmem79ma/ma mutation is responsible for the spontaneous dermatitis phenotype in matted mice, probably as a result of impaired lamellar granule secretory system and altered stratum corneum barrier function.

Section snippets

Mice

Flaky tail mice (ma/ma Flgft/ft) were obtained from Jackson Laboratory (Bar Harbor, Me). Flaky tail mice were backcrossed with C57BL/6J mice (CLEA Japan, Tokyo, Japan) to generate ma/ma and Flgft/ft mice. We genotyped Flgft, as described previously.14

Biophysical skin measurements

Skin hydration was evaluated by analyzing the skin electrical impedance with a Corneometer ASA-M2 (Asahi Biomed, Yokohama, Japan). Transepidermal water loss (TEWL) was measured with a VAPOSCAN AS-VT100RS (Asahi Biomed). All data are the median of 3

Matted mutation, but not filaggrin mutation, is responsible for the matted hair and spontaneous dermatitis phenotype

To generate each congenic mouse strain (ma/ma and Flgft/ft), we segregated the ma and Flgft mutations by backcrossing with WT mice (C57BL/6). As a result, ma/ma mutant mice, which displayed the matted hair phenotype, developed spontaneous dermatitis with scratching behavior, whereas Flgft/ft mice did not have dermatitis under SPF conditions (Fig 1, A and B, and see Table E1 in this article’s Online Repository at www.jacionline.org). TEWL was higher and SC hydration was lower in ma/ma mice

Discussion

Original double-mutant flaky tail (ma/ma Flgft/ft) mice express truncated profilaggrin and significantly reduced mature filaggrin, show enhanced TEWL and decreased SC hydration, and develop spontaneous dermatitis with increased IgE levels.13, 14 Thus Tmem79ma/ma Flgft/ft mice have been widely used as a mouse model of AD with filaggrin deficiency. However, genetically engineered Flg−/− mice had no apparent change in TEWL or SC hydration compared with WT mice and did not develop dermatitis under

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      Conversely, sequencing of the FLG gene in patients with asthma and AD revealed one or two null alleles in 23% of cases, establishing genetic FLG deficiency as a major factor predisposing for the atopy associated with AD (Palmer et al., 2006; Sandilands et al., 2007) (reviewed in Irvine et al., [2011]). The flaky tail mouse (Presland et al., 2000) carries defects of two genes involved in epidermal barrier function: the Flgft mutation (Flg 5303delA) resulting in hypomorphic FLG expression (Fallon et al., 2009) and a deleterious mutation in the gene encoding TMEM79 (Sasaki et al., 2013; Saunders et al., 2013). The Tmem79ma mutation (p.Y280∗) results in impaired cornification and matted fur.

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    M.A. and J.K. are supported by Health Labour Sciences Research Grant for Research on Allergic Disease and Immunology from the Ministry of Health, Labour, and Welfare of Japan. A.K., A.I.-Y., and A.S. are supported by Grants-in-Aid for Scientific Research from the Ministry of Education, Culture, Sports, Science, and Technology of Japan. M.A, H.O., J.K., A.S., and T.S. are supported by the Global Centre of Excellence (GCOE) program at Keio University from the Ministry of Education, Culture, Sports, Science, and Technology of Japan.

    Disclosure of potential conflict of interest: M. Amagai has been supported by one or more grants from a government granting agency; has consultancy arrangements with Daiichi Sankyo Co, Novartis Pharma K.K., and GlaxoSmithKline K.K.; and has received one or more grants from or has one or more grants pending with MSD K.K. and Maruho Co Ltd. A. Shiohama, A. Kubo, and J. Kudoh have been supported by one or more grants from a government granting agency. H. Okano has been supported by one or more grants from a government granting agency and has consultancy arrangements with San Bio, Eisai Co Ltd, and Daiichi Sankyo Co Ltd.

    These authors contributed equally to this work.

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