Tmem79/Matt is the matted mouse gene and is a predisposing gene for atopic dermatitis in human subjects

Abstract

Background: Atopic dermatitis (AD) is a major inflammatory condition of the skin caused by inherited skin barrier deficiency, with mutations in the filaggrin gene predisposing to development of AD. Support for barrier deficiency initiating AD came from flaky tail mice, which have a frameshift mutation in Flg and also carry an unknown gene, matted, causing a matted hair phenotype.

Objective: We sought to identify the matted mutant gene in mice and further define whether mutations in the human gene were associated with AD.

Methods: A mouse genetics approach was used to separate the matted and Flg mutations to produce congenic single-mutant strains for genetic and immunologic analysis. Next-generation sequencing was used to identify the matted gene. Five independently recruited AD case collections were analyzed to define associations between single nucleotide polymorphisms (SNPs) in the human gene and AD.

Results: The matted phenotype in flaky tail mice is due to a mutation in the Tmem79/Matt gene, with no expression of the encoded protein mattrin in the skin of mutant mice. Matt(ft) mice spontaneously have dermatitis and atopy caused by a defective skin barrier, with mutant mice having systemic sensitization after cutaneous challenge with house dust mite allergens. Meta-analysis of 4,245 AD cases and 10,558 population-matched control subjects showed that a missense SNP, rs6684514, [corrected] in the human MATT gene has a small but significant association with AD.

Conclusion: In mice mutations in Matt cause a defective skin barrier and spontaneous dermatitis and atopy. A common SNP in MATT has an association with AD in human subjects.

Keywords: AD; Allergy; Atopic dermatitis; DM; Double mutant; FLG; Filaggrin; HDM; High-power field; House dust mite; MAPEG; Matt; Membrane-associated proteins in eicosanoid and glutathione metabolism; OR; Odds ratio; SNP; Single nucleotide polymorphism; TEWL; Tmem79; Transepidermal water loss; WT; Wild-type; association; atopic dermatitis; atopy; eczema; filaggrin; flaky tail; hpf; mattrin; mouse; mutation.

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Fig 1

Identification of Tmem79/Matt as the matted gene. A, A region of homozygous ma/ma on chromosome 3 indicated by regions in red and heterozygous regions in blue, with the homozygous C57BL6/J genome shown in black. B, The ma mutation in Tmem79/Matt identified by means of epidermal transcriptome sequencing was confirmed by using Sanger sequencing, causing a C to G substitution at position 88,136,485 on chromosome 3. This predicts the protein change p.Y280X in the Tmem79 (mattrin) protein. The mutant allele was renamed Matt^ma. C, Semiquantitative RT-PCR of epidermal mRNA showed a reduction in expression of Matt in Matt^ma/ma animals. D, Mattrin detected in immunoblotting of skin from WT and Flg^ft/ft mice but no protein expression in Matt^ma/ma and DM mice. E, Bioinformatics shows mattrin consists of 5 transmembrane helices with a long intracellular N-terminus and short extracellular C-terminus.

Fig 2

Mattrin expression and disorganized lipid morphology in the epidermis of Matt^ma mice. A and B, Immunohistochemistry detection of mattrin expression confined to the epidermal granular layer of WT (Fig 2, A) but not Matt^ma/ma (Fig 2, B) animals, including hair follicles (arrow). Scale bar = 20 μm. C and D, Nile Red staining of lipids in the epidermis of WT (Fig 2, C) and Matt^ma/ma (Fig 2, D) mice revealed uneven and highly disorganized cornified cell envelopes in the stratum corneum of Matt^ma/ma mice. Scale bar = 50 μm.

Fig 3

Matt^ma mice are phenotypically distinct from Flg^ft/ft mice, with histopathology demonstrating enhanced cutaneous inflammation at 32 weeks. A, Gross phenotype of WT, DM, Matt^ma/ma, and Flg^ft/ft mice. Flg^ft/ft mice are indistinguishable from WT mice, apart from the stubbed tail and shortened ear pinnae, which are phenotypic features shared with the DM mouse. All mice are age-matched homozygous males. B, Representative skin biopsy specimens from WT, DM, Matt^ma/ma, and Flg^ft/ft mice at 32 weeks, showing markedly increased cutaneous inflammation in DM and Matt^ma/ma mice in comparison with that seen in WT and Flg^ft/ft mice. Scale bar = 50 μm.

Fig 4

Matt^ma mice have exacerbated AD-like inflammation and HDM-specific responses after allergen challenge to intact skin. A, Representative skin biopsy specimens from age-matched WT and Matt^ma/ma mice treated with HDM or vehicle, with increased inflammation in HDM-treated Matt^ma/ma mice relative to that seen in HDM-treated WT and vehicle-treated Matt^ma/ma mice. Scale bar = 50 μm. B, HDM treatment induces increased dermal cell infiltration in Matt^ma/ma mice relative to that seen in HDM-treated WT and vehicle-treated Matt^ma/ma mice. C, Acanthosis is increased in HDM-treated Matt^ma/ma mice relative to that seen in HDM-treated WT and vehicle-treated Matt^ma/ma mice. D, Epicutaneous HDM treatment results in significantly increased TEWL in Matt^ma/ma mice relative to that seen in HDM-treated WT mice. E, HDM-treated Matt^ma/ma mice have increased HDM-specific serum IgE, IgG₁, and IgG₂ levels relative to those seen in HDM-treated WT mice. Cell numbers and acanthosis were scored on 15 to 20 hpfs (×1000 magnification) on hematoxylin and eosin–stained sections from WT, DM, Matt^ma/ma, and Flg^ft/ft mice. Data represent the mean and error bars represent ± SEMs from 6 to 8 mice and are representative of 2 separate experiments. The Student t test or 2-way ANOVA was used to determine statistical differences between groups. NS, Not significant, ∗P > .05. ***P < .001.

Fig 5

Forrest plot showing results of a fixed-effects meta-analysis of 5 case-control studies to investigate the association of rs6684514 and AD. Study populations used were as follows: English, English adult severe AD versus English population control subjects from the 1958 Birth Cohort; UK, UK mild-moderate pediatric AD versus English pediatric control subjects without AD; Irish, Irish pediatric AD versus Irish adult population controls; German, German AD cases versus German population control subjects; Scottish, Scottish asthma cases with AD versus Scottish population control subjects. ES, Estimated odds ratio. Meta-analysis was carried out with the “metan” function in Stata software (StataCorp).