Suprabasin-null mice retain skin barrier function and show high contact hypersensitivity to nickel upon oral nickel loading

How Do Classical Subtypes Correspond to Endotypes in Atopic Dermatitis?

Since atopic dermatitis (AD) is a heterogeneous condition, the subtyping of AD is a crucial issue. The classical subtypes of AD are represented by extrinsic and intrinsic subtypes, European-American and Asian subtypes, and adult and pediatric subtypes. While the subtyping of AD was historically conducted based on the phenotype, recent findings on the mechanisms of AD have revealed the importance of the endotype, which can characterize individual patients more accurately. Considering the current development of AD therapies, AD endotyping is a prerequisite for a personalized therapeutic choice. Endotypes of AD can be stratified from different viewpoints, including cytokine expression patterns, allergen properties, epidermal barrier conditions, ceramide variation, the involvement of innate immunity, and serum biomarkers. Among them, the cytokine-based endotype seems to be the most useful one and is categorized into type 2 cytokine (IL-4, IL-13 and IL-31)-high, type 1 cytokine (IFN-γ)-high, and/or type 3 cytokine (IL-22 and IL-17)-high, or mixed subtypes. Recently proposed biomarker endotyping aims at individualized treatment options, although the daily clinical use of endotypes is a future issue. To better understand the endotypes for clinicians, attempts to adjust each of the classical subtypes to endotypes are required. This review will discuss the correspondence of the classical subtypes to the various endotypes that have recently been proposed.

The Impact of Air Pollution on Atopic Dermatitis

PURPOSE OF REVIEW

Atopic dermatitis (AD) remains a dermatological disease that imposes a significant burden on society. Air pollution has previously been linked to both the onset and severity of atopic dermatitis. As air pollution remains a critical environmental factor impacting human health, this review seeks to provide an overview of the relationship between different air pollutants and AD.

RECENT FINDINGS

AD can develop from multiple causes that can be broadly grouped into epidermal barrier dysfunction and immune dysregulation. Air pollution imposes significant health risks and includes a wide variety of pollutant types. AD has been linked to outdoor air pollutants such as particulate matter (PM), volatile organic compounds (VOC), gaseous compounds, and heavy metals. Exposure to indoor pollutants such as tobacco smoke and fungal molds has also been associated with an increased incidence of AD. While different pollutants impact distinct molecular pathways in the cell, they mostly converge on ROS product, DNA damage, and dysregulated T-cell activity and cytokine production. The presented review suggests a strengthening tie between air pollution and AD. It points to opportunities for further studies to clarify, as well as potential therapeutic opportunities that leverage the mechanistic relationships between air pollution and AD.

Suprabasin enhances the invasion, migration, and angiogenic ability of oral squamous cell carcinoma cells under hypoxic conditions

Suprabasin (SBSN) is a secreted protein that is isolated as a novel gene expressed in differentiated keratinocytes in mice and humans. It induces various cellular processes such as proliferation, invasion, metastasis, migration, angiogenesis, apoptosis, therapy and immune resistance. The role of SBSN was investigated in oral squamous cell carcinoma (OSCC) under hypoxic conditions using the SAS, HSC‑3, and HSC‑4 cell lines. Hypoxia induced SBSN mRNA and protein expression in OSCC cells and normal human epidermal keratinocytes (NHEKs), and this was most prominent in SAS cells. The function of SBSN in SAS cells was analyzed using 3‑(4,5‑dimethylthiazol‑2‑yl)‑2,5‑diphenyltetrazolium bromide (MTT); 5‑bromo‑2'‑deoxyuridine (BrdU); cell cycle, caspase 3/7, invasion, migration, and tube formation assays; and gelatin zymography. Overexpression of SBSN decreased MTT activity, but the results of BrdU and cell cycle assays indicated upregulation of cell proliferation. Western blot analysis for cyclin‑related proteins indicated involvement of cyclin pathways. However, SBSN did not strongly suppress apoptosis and autophagy, as revealed by caspase 3/7 assay and western blotting for p62 and LC3. Additionally, SBSN increased cell invasion more under hypoxia than under normoxia, and this resulted from increased cell migration, not from matrix metalloprotease activity or epithelial‑mesenchymal transition. Furthermore, SBSN induced angiogenesis more strongly under hypoxia than under normoxia. Analysis using reverse transcription‑quantitative PCR showed that vascular endothelial growth factor (VEGF) mRNA was not altered by the knockdown or overexpression of SBSN VEGF, suggesting that VEGF is not located downstream of SBSN. These results demonstrated the importance of SBSN in the maintenance of survival and proliferation, invasion and angiogenesis of OSCC cells under hypoxia.

Suprabasin-derived polypeptides: SBSN(50-63) induces inflammatory response via TLR4-mediated mast cell activation

Psoriasis is a chronic, relapsing, immune-mediated, and papulosquamous skin disorder. Excessive mast cell activation, in psoriatic lesions, contributes to inflammation. Various endogenous peptides can participate in the pathogenesis of inflammatory diseases by activating mast cells. Suprabasin (SBSN) is expressed in multiple epithelial tissues and it regulates the normal epidermal barrier function. We have recently shown that suprabasin-derived polypeptides, SBSN(50-63), are significantly increased in psoriatic lesions, through differential peptide analysis. This study was conducted to clarify whether SBSN(50-63) plays a pivotal role in activating mast cells and mediating proinflammatory cytokines and chemokines production in psoriasis. The increased expression of SBSN in psoriatic lesions was confirmed by bioinformatics analysis, PCR and ELISA. Wild-type mice injected subcutaneously with SBSN(50-63) exhibited infiltration of inflammatory cells and the release of cytokines in vivo. SBSN(50-63) stimulated mouse primary mast cells (MPMC) and the laboratory of allergic disease 2 (LAD2) human mast cells to produce more inflammatory mediators than the control group, which were measured ex vivo and in vitro. Toll-like receptor 4 was identified as the receptor of SBSN on mast cells by molecular docking analysis, molecular dynamics simulation, and siRNA transfection. Collectively, SBSN(50-63) could activate mast cells through TLR4, which may increase the inflammatory response in psoriasis.

Immunopathogenesis of Atopic Dermatitis: Focus on Interleukins as Disease Drivers and Therapeutic Targets for Novel Treatments

Atopic dermatitis is a chronic, recurrent inflammatory skin disorder manifesting by eczematous lesions and intense pruritus. Atopic dermatitis develops primarily as a result of an epidermal barrier defect and immunological imbalance. Advances in understanding these pathogenetic hallmarks, and particularly the complex role of interleukins as atopic dermatitis drivers, resulted in achieving significant therapeutic breakthroughs. Novel medications involve monoclonal antibodies specifically blocking the function of selected interleukins and small molecules such as Janus kinase inhibitors limiting downstream signaling to reduce the expression of a wider array of proinflammatory factors. Nevertheless, a subset of patients remains refractory to those treatments, highlighting the complexity of atopic dermatitis immunopathogenesis in different populations. In this review, we address the immunological heterogeneity of atopic dermatitis endotypes and phenotypes and present novel interleukin-oriented therapies for this disease.

Subtypes of atopic dermatitis: From phenotype to endotype

Atopic dermatitis (AD) is a heterogenous disorder and can be classified into different types. Stratification of subtypes may enable personalized medicine approaches. AD can be categorized into the IgE-high, extrinsic subtype and the IgE-normal, intrinsic subtype. While extrinsic AD is the major subtype possessing skin barrier impairment (high incidence of filaggrin mutations), intrinsic AD occupies about 20% of AD with female dominance and preserved barrier. Extrinsic AD exhibits protein allergy and food allergy, but intrinsic AD shows metal allergy possibly in association with suprabasin deficiency. In particular, accumulated knowledge of food allergy has more clearly characterized extrinsic AD. European American (EA) and Asian AD subtypes have been also proposed. Asian patients with AD are characterized by a unique blended immune dysregulation and barrier feature phenotype between EA patients with AD and those with psoriasis. In another ethnic study, filaggrin loss-of-function mutations are not prevalent in African American patients with AD, and Th1/Th17 attenuation and Th2/Th22 skewing were seen in these patients. Recent endotype classification provides new insights for AD and other allergic disorders. Endotype is defined as the molecular mechanisms underlying the visible features/phenotype. Endotype repertoire harbors activation of type 2 cytokines, type 1 cytokines, and IL-17/IL-22, impairment of epidermal barrier, and abnormalities of intercellular lipids. Classification of endotype has been attempted with serum markers. These lines of evidence indicate a need for personalized or precision medicine appropriate for each subtype of AD.

Suprabasin: Role in human cancers and other diseases

Suprabasin (SBSN), a gene with unknown function located in q13 region of chromosome 19, was first found to be expressed in the basal layer of the stratified epithelium in mouse and human tissues and was thought to be a potential precursor of keratinized capsules. However, in recent years, significant progress has been made in the study of SBSN in a variety of human diseases. One common theme appears to be the effect of SBSN on tumor progression, such as invasion, metastasis and resistance. However, the function and mechanism of action of SBSN is still elusive. In this study, we reviewed the literature on SBSN in the PubMed database to identify the basic characteristics, biological functions, and roles of SBSN in cancer and other diseases. In particular, we focused on the potential mechanisms of SBSN activity, to improve our understanding of the complex function of this protein and provide a theoretical basis for further research on the role of SBSN in cancer and other diseases.

New Family Members of FG Repeat Proteins and Their Unexplored Roles During Phase Separation

The condensation and compartmentalization of biomacromolecules in the cell are driven by the process of phase separation. The main effectors of phase separation are intrinsically disordered proteins, which include proteins with a phenylalanine-glycine (FG) repeat domain. Our understanding of the biological function of FG repeat proteins during phase separation has been mainly derived from recent research on a member of the nuclear pore complex proteins, nucleoporins containing FG repeat domain (FG-NUPs). FG-NUPs form meshwork structures by inter- and intra-molecular FG domain interactions, which confine the nucleo-cytoplasmic exchange. Whereas FG-NUPs localize in the nuclear membrane, other FG repeat proteins reside in the cytoplasm and the nucleoplasm, and the biological function of the FG repeat domain of these proteins is not well described. In the present review, we list the FG repeat proteins that are known to phase separate in the cell, and review their biological functions. We extract the unraveled features of FG repeat proteins as an activator of barrier formation and homotypic cell-cell interactions. Understanding the regulatory mechanisms of FG repeat proteins will provide a potential delivery tool for therapeutic reagents.

Suprabasin-A Review

Among the ~22,000 human genes, very few remain that have unknown functions. One such example is suprabasin (SBSN). Originally described as a component of the cornified envelope, the function of stratified epithelia-expressed SBSN is unknown. Both the lack of knowledge about the gene role under physiological conditions and the emerging link of SBSN to various human diseases, including cancer, attract research interest. The association of SBSN expression with poor prognosis of patients suffering from oesophageal carcinoma, glioblastoma multiforme, and myelodysplastic syndromes suggests that SBSN may play a role in human tumourigenesis. Three SBSN isoforms code for the secreted proteins with putative function as signalling molecules, yet with poorly described effects. In this first review about SBSN, we summarised the current knowledge accumulated since its original description, and we discuss the potential mechanisms and roles of SBSN in both physiology and pathology.