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Background Barrier dysfunction is an important feature of atopic dermatitis (AD) in which IL-4 and IL-13, signature type 2 cytokines, are involved. Periostin, a matricellular protein induced by IL-4 or IL-13, plays a crucial role in the onset of allergic skin inflammation, including barrier dysfunction. However, it remains elusive how periostin causes barrier dysfunction downstream of the IL-13 signal. Methods We systematically identified periostin-dependent expression profile using DNA microarrays. We then investigated whether IL-24 downregulates filaggrin expression downstream of the IL-13 signals and whether IL-13-induced IL-24 expression and IL-24-induced downregulation of filaggrin expression are dependent on the JAK/STAT pathway. To build on the significance of in vitro findings, we investigated expression of IL-24 and activation of STAT3 in mite-treated mice and in AD patients. Results We identified IL-24 as an IL-13-induced molecule in a periostin-dependent manner. Keratinocytes are the main IL-24-producing tissue-resident cells stimulated by IL-13 in a periostin-dependent manner via STAT6. IL-24 significantly downregulated filaggrin expression via STAT3, contributing to barrier dysfunction downstream of the IL-13/periostin pathway. Wild-type mite-treated mice showed significantly enhanced expression of IL-24 and activation of STAT3 in the epidermis, which disappeared in both STAT6-deficient and periostin-deficient mice, suggesting that these events are downstream of both STAT6 and periostin. Moreover, IL-24 expression was enhanced in the epidermis of skin tissues taken from AD patients. Conclusions The IL-13/periostin pathway induces IL-24 production in keratinocytes, playing an important role in barrier dysfunction in AD.

Proliferation and differentiation of keratinocytes are normally well balanced, but this balance can be perturbed in wound healing and is dysregulated in pathological conditions such as atopic dermatitis. Epithelial–mesenchymal interaction affects this event via the cross-talk of cytokines and growth factors. Periostin, a matricellular protein, has an important role during reepithelialization in wound healing and is critical for hyperproliferation of keratinocytes in atopic dermatitis. Here we investigated how periostin regulates proliferation and differentiation of keratinocytes in the epithelial–mesenchymal interactions using a three-dimensional organotypic air–liquid interface coculture system. The release of IL-1α from keratinocytes and subsequent IL-6 production from fibroblasts were critical for keratinocyte proliferation and differentiation. Periostin secreted from fibroblasts was required for IL-1α-induced IL-6 production and enhanced IL-6 production by activation of the NF-κB pathway synergistically with IL-1α. Thus, the combination of an autocrine loop of periostin and a paracrine loop composed of IL-1α and IL-6 regulates keratinocyte proliferation and differentiation in the epithelial–mesenchymal interactions, and periostin tunes the magnitude of keratinocyte proliferation and differentiation by interacting with the paracrine IL-1α/IL-6 loop.

Summary Background Periostin, a matricellular protein, serves as a regulator of wound healing and fibrosis. The role of periostin in the pathogenesis of systemic sclerosis (SSc) is unknown. Objective To determine periostin levels in association with severity of skin fibrosis in patients with SSc. Methods Expression of periostin was immunohistochemically examined in skin obtained from patients with SSc and healthy controls. Enzyme-linked immunosorbent assay was performed to evaluate serum periostin levels in association with clinical characteristics in 56 patients with SSc [diffuse cutaneous SSc (dSSc), n = 16; and limited cutaneous SSc (lSSc), n = 40] and 66 healthy controls. Results Periostin was strongly expressed in the affected dermis from patients with SSc. Periostin was colocalized in α-smooth muscle actin-positive myofibroblasts and platelet endothelial cell adhesion molecule-1-positive endothelial cells in SSc dermis. Serum levels of periostin in patients with dSSc were markedly elevated compared with those in patients with lSSc and control subjects. Patients with lSSc had increased periostin levels compared with healthy controls. In addition, significantly higher levels of periostin were observed in patients with dSSc with disease duration ≤ 5 years compared with those with disease duration > 5 years. Furthermore, the modified Rodnan total skin thickness score (MRSS) was positively correlated with periostin levels in patients with SSc. Serial analysis revealed a correlation between periostin and MRSS; namely, MRSS decreased in line with decreased periostin levels in some patients with dSSc as the disease progressed. Conclusion An elevated periostin level in patients with SSc is associated with severity of skin sclerosis. Periostin may be a potential biomarker for progressive skin fibrosis in SSc.

Allergic inflammation triggered by exposure of an allergen frequently leads to the onset of chronic inflammatory diseases such as atopic dermatitis (AD) and bronchial asthma. The mechanisms underlying chronicity in allergic inflammation remain unresolved. Periostin, a recently characterized matricellular protein, interacts with several cell surface integrin molecules, providing signals for tissue development and remodeling. Here we show that periostin is a critical mediator for the amplification and persistence of allergic inflammation using a mouse model of skin inflammation. Th2 cytokines IL-4 and IL-13 stimulated fibroblasts to produce periostin, which interacted with αv integrin, a functional periostin receptor on keratinocytes, inducing production of proinflammatory cytokines, which consequently accelerated Th2-type immune responses. Accordingly, inhibition of periostin or αv integrin prevented the development or progression of allergen-induced skin inflammation. Thus, periostin sets up a vicious circle that links Th2-type immune responses to keratinocyte activation and plays a critical role in the amplification and chronicity of allergic skin inflammation.

To diagnose atopic dermatitis (AD), an appearance of eczema examined by experienced dermatologists is required. Therefore, biomarkers to diagnose AD or to reflect the severity of AD would be of a great use for non-specialists in the clinic or hospitals. We can apply such a biomarker for realization of personalized medicine for AD in the future. Interleukin-4 (IL-4) and IL-13 have been known to play important roles in the pathogenesis of allergic diseases including AD. In addition to these, we previously identified SCCA1, SCCA2, and periostin as IL-4/IL-13-inducible genes. We recently established ELISA systems to measure serum levels of SCCA1, SCCA2, and periostin and evaluated their usefulness in the treatment of AD patients. Serum SCCA1 and SCCA2 are up-regulated in AD patients and can distinguish AD patients from non-atopic controls, and their serum levels reflect eczema grades. Periostin concentration is also elevated in the serum of AD patients. These results demonstrate that SCCA1, SCCA2, and periostin might be promising biomarkers for personalized medicine in allergic diseases including AD.