The autoimmune regulator (AIRE), which is defective in autoimmune polyendocrinopathy-candidiasis-ectodermal dystrophy patients, is expressed in human epidermal and follicular keratinocytes and associates with the intermediate filament protein cytokeratin 17

Nuclear roles for non-lamin intermediate filament proteins

The nuclear-localized lamins have long been thought to be the only intermediate filaments (IFs) with an impact on the architecture, properties, and functions of the nucleus. Recent studies, however, uncovered significant roles for IFs other than lamins (here referred to as "non-lamin IFs") in regulating key properties of the nucleus in various cell types and biological settings. In the cytoplasm, IFs often occur in the perinuclear space where they contribute to local stiffness and impact the shape and/or the integrity of the nucleus, particularly in cells under stress. In addition, selective non-lamin IF proteins can occur inside the nucleus where they partake in fundamental processes including nuclear architecture and chromatin organization, regulation of gene expression, cell cycle progression, and the repair of DNA damage. This text reviews the evidence supporting a role for non-lamin IF proteins in regulating various properties of the nucleus and highlights opportunities for further study.

AIRE Deficiency Leads to the Development of Alopecia Areata‒Like Lesions in Mice

Alopecia areata (AA) is an autoimmune hair loss disorder with no cure. Patients with sequence variation in AIRE are 15 times more likely to develop AA than the general population, yet the roles of AIRE in AA pathogenesis are unknown. In this study, we report that 62% of C57BL/6J female Aire^‒/‒ mice spontaneously developed persistent AA-like lesions that displayed several hallmarks of human AA. Lesional Aire^‒/‒ skin exhibited hair follicle (HF) dystrophy as determined by a reduced number of anagen HFs, decreased anagen HF proliferation, hair pigmentary changes, and decreased hair width and length. Inflammatory infiltrate comprising CD8⁺ T cells, CD4⁺ T cells, CD68⁺ macrophages, and mast cells was prominent in lesional Aire^‒/‒ HFs. From gene expression analyses, we found lesional Aire^‒/‒ skin to have significantly increased expression of human AA signature genes, including H2-Ab1, Ifnγ, IFN-γ‒induced chemokines (Ccl5, Cxcl9‒11), γ_c family cytokine receptor Il2RA, and JAK‒signal transducer and activator of transcription (STAT) signaling components (Stat1, Stat2, Stat4). By immunostaining, lesional Aire^‒/‒ HFs also show upregulated major histocompatibility complex class I and downregulated α-melanocyte-stimulating hormone, signifying immune privilege collapse, and increased STAT1 activation in HF keratinocytes. Our study highlights a role for AIRE in HF biology and shows that Aire^‒/‒ mice may serve as a valuable model system to study AA pathogenesis.

Generation and Characterization of iPS Cells Derived from APECED Patients for Gene Correction

APECED (Autoimmune-Polyendocrinopathy-Candidiasis-Ectodermal-Dystrophy) is a severe and incurable multiorgan autoimmune disease caused by mutations in the AIRE (autoimmune regulator) gene. Without functional AIRE, the development of central and peripheral immune tolerance is severely impaired allowing the accumulation of autoreactive immune cells in the periphery. This leads to multiple endocrine and non-endocrine autoimmune disorders and mucocutaneous candidiasis in APECED patients. Recent studies have suggested that AIRE also has novel functions in stem cells and contributes to the regulatory network of pluripotency. In preparation of therapeutic gene correction, we generated and assessed patient blood cell-derived iPSCs, potentially suitable for cell therapy in APECED. Here, we describe APECED-patient derived iPSCs's properties, expression of AIRE as well as classical stem cell markers by qPCR and immunocytochemistry. We further generated self-aggregated EBs of the iPSCs. We show that APECED patient-derived iPSCs and EBs do not have any major proliferative or apoptotic defects and that they express all the classical pluripotency markers similarly to healthy person iPSCs. The results suggest that the common AIRE R257X truncation mutation does not affect stem cell properties and that APECED iPSCs can be propagated in vitro and used for subsequent gene-correction. This first study on APECED patient-derived iPSCs validates their pluripotency and confirms their ability for differentiation and potential therapeutic use.

Loss of AIRE-Mediated Immune Tolerance and the Skin

The core function of the immune response is to distinguish between self and foreign. The multiorgan human autoimmune disease, autoimmune polyendocrinopathy-candidiasis-ectodermal dystrophy (APECED/autoimmune polyendocrine syndrome type 1) is an example of what happens in the body when central immune tolerance goes astray. APECED revealed the existence and function of the autoimmune regulator gene, which has a central role in the development of tolerance. The discovery of autoimmune regulator was the start of a new period in immunology and in understanding the role of central and peripheral tolerance, also very relevant to many skin diseases as we highlight in this review.

AIRE is induced in oral squamous cell carcinoma and promotes cancer gene expression

Autoimmune regulator (AIRE) is a transcriptional regulator that is primarily expressed in medullary epithelial cells, where it induces tissue-specific antigen expression. Under pathological conditions, AIRE expression is induced in epidermal cells and promotes skin tumor development. This study aimed to clarify the role of AIRE in the pathogenesis of oral squamous cell carcinoma (OSCC). AIRE expression was evaluated in six OSCC cell lines and in OSCC tissue specimens. Expression of STAT1, ICAM1, CXCL10, CXCL11, and MMP9 was elevated in 293A cells stably expressing AIRE, and conversely, was decreased in AIRE-knockout HSC3 OSCC cells when compared to the respective controls. Upregulation of STAT1, and ICAM in OSCC cells was confirmed in tissue specimens by immunohistochemistry. We provide evidence that AIRE exerts transcriptional control in cooperation with ETS1. Expression of STAT1, ICAM1, CXCL10, CXCL11, and MMP9 was increased in 293A cells upon Ets1 transfection, and coexpression of AIRE further increased the expression of these proteins. AIRE coprecipitated with ETS1 in a modified immunoprecipitation assay using formaldehyde crosslinking. Chromatin immunoprecipitation and quantitative PCR analysis revealed that promoter fragments of STAT1, ICAM1, CXCL10, and MMP9 were enriched in the AIRE precipitates. These results indicate that AIRE is induced in OSCC and supports cancer-related gene expression in cooperation with ETS1. This is a novel function of AIRE in extrathymic tissues under the pathological condition.

Association of Autoimmune Regulator Gene Rs2075876 Variant, but Not Gene Expression with Alopecia Areata in Males: A Case-control Study

Alopecia areata (AA) is a non-scarring hair loss of autoimmune etiology. The autoimmune regulator (AIRE) gene is believed to be an important driver in AA pathogenesis. Genetic variants can alter mRNA expression levels which may provoke an autoimmune response. A total of 337 males (97 AA patients and 240 controls) were enrolled in the current case-control study. On screening of the most frequent variants in the gene, rs2075876 (A/G) polymorphism in intron 5 was selected and genotyped using Real-Time PCR (polymerase chain reaction) technology. Additionally, circulatory AIRE expression levels were quantified by quantitative reverse-transcription PCR (qRT-PCR). Allelic discrimination analysis revealed GG genotype to be more frequent in patients (90.7% in AA compared to 32.5% in controls, p < .001). G variant conferred increased risk to alopecia under homozygote comparison (GG versus AA: OR = 16.1, 95%CI = 5.57-46.3), dominant model (GG+AG versus AA: OR = 7.24, 95%CI = 2.5-20.5), recessive model (GG versus AG+AA: OR = 20.3, 95%CI = 9.7-42.4), and allelic model (G versus A: OR = 11.6, 95%CI = 6.47-21.1). The expression levels of AIRE gene did not differ significantly between patients and controls and were not related to rs2075876 variant. In conclusion, the intronic variant (rs2075876) is suggested to be a potent susceptibility variant for AA development in the studied population.Abbreviations: AA: Alopecia areata; AIRE: Autoimmune Regulator; APECED: Autoimmune, Polyendocrinopathy Candidiasis Ectodermal Dystrophy; DLQI: Dermatology life quality index questionnaire; MIQE: Minimum information for publication of quantitative real-time PCR experiments; mTEC: Medullary thymic epithelial cells; PHD: Plant homeodomain; qRT-PCR: Quantitative reversetranscription-polymerase chain reaction; RA: Rheumatoid arthritis.

Hair Follicle Immune Privilege Revisited: The Key to Alopecia Areata Management

The collapse of the immune privilege (IP) of the anagen hair bulb is now accepted as a key element in AA pathogenesis, and hair bulb IP restoration lies at the core of AA therapy. Here, we briefly review the essentials of hair bulb IP and recent progress in understanding its complexity. We discuss open questions and why the systematic dissection of hair bulb IP and its pharmacological manipulation (including the clinical testing of FK506 and α-melanocyte-stimulating hormone analogs) promise to extend the range of future therapeutic options in AA and other IP collapse-related autoimmune diseases.

Epithelial Fli1 deficiency drives systemic autoimmunity and fibrosis: Possible roles in scleroderma

Systemic sclerosis (SSc), or scleroderma, is a multisystem autoimmune disorder characterized by vasculopathy and fibrosis in the skin and internal organs, most frequently in the esophagus and lungs. Hitherto, studies on SSc pathogenesis centered on immune cells, vascular cells, and fibroblasts. Although dysregulated keratinocytes in SSc have been recently reported, the contribution of epithelial cells to pathogenesis remains unexplored. In this study, we demonstrated the induction of SSc-like molecular phenotype in keratinocytes by gene silencing of transcription factor Friend leukemia virus integration 1 (Fli1), the deficiency of which is implicated in SSc pathogenesis. Keratin 14-expressing epithelial cell-specific Fli1 knockout mice spontaneously developed dermal and esophageal fibrosis with epithelial activation. Furthermore, they developed remarkable autoimmunity with interstitial lung disease derived from thymic defects with down-regulation of autoimmune regulator (Aire). Importantly, Fli1 directly regulated Aire expression in epithelial cells. Collectively, epithelial Fli1 deficiency might be involved in the systemic autoimmunity and selective organ fibrosis in SSc. This study uncovers unidentified roles of dysregulated epithelial cells in SSc pathogenesis.

Multiple roles for keratin intermediate filaments in the regulation of epithelial barrier function and apico-basal polarity

As multicellular organisms evolved a family of cytoskeletal proteins, the keratins (types I and II) expressed in epithelial cells diversified in more than 20 genes in vertebrates. There is no question that keratin filaments confer mechanical stiffness to cells. However, such a number of genes can hardly be explained by evolutionary advantages in mechanical features. The use of transgenic mouse models has revealed unexpected functional relationships between keratin intermediate filaments and intracellular signaling. Accordingly, loss of keratins or mutations in keratins that cause or predispose to human diseases, result in increased sensitivity to apoptosis, regulation of innate immunity, permeabilization of tight junctions, and mistargeting of apical proteins in different epithelia. Precise mechanistic explanations for these phenomena are still lacking. However, immobilization of membrane or cytoplasmic proteins, including chaperones, on intermediate filaments (“scaffolding”) appear as common molecular mechanisms and may explain the need for so many different keratin genes in vertebrates.

Keratin-dependent regulation of Aire and gene expression in skin tumor keratinocytes

Expression of the intermediate filament protein keratin 17 (K17) is robustly upregulated in inflammatory skin diseases and in many tumors originating in stratified and pseudostratified epithelia. We report that autoimmune regulator (Aire), a transcriptional regulator, is inducibly expressed in human and mouse tumor keratinocytes in a K17-dependent manner and is required for timely onset of Gli2-induced skin tumorigenesis in mice. The induction of Aire mRNA in keratinocytes depends on a functional interaction between K17 and the heterogeneous nuclear ribonucleoprotein hnRNP K. Further, K17 colocalizes with Aire protein in the nucleus of tumor-prone keratinocytes, and each factor is bound to a specific promoter region featuring an NF-κB consensus sequence in a relevant subset of K17- and Aire-dependent proinflammatory genes. These findings provide radically new insight into keratin intermediate filament and Aire function, along with a molecular basis for the K17-dependent amplification of inflammatory and immune responses in diseased epithelia.

The possible implication of the S250C variant of the autoimmune regulator protein in a patient with autoimmunity and immunodeficiency: in silico analysis suggests a molecular pathogenic mechanism for the variant

Autoimmunity can develop from an often undetermined interplay of genetic and environmental factors. Rare forms of autoimmune conditions may also result from single gene mutations as for autoimmune polyendocrinopathy-candidiasis-ectodermal dystrophy, an autosomal recessive disease associated with mutated forms of the autoimmune regulator gene. It was proposed that genetic variability in the autoimmune regulator locus, in particular heterozygous loss-of-function mutations, might favor the development of organ-specific autoimmunity by affecting the presentation of self-antigens in the thymus. Indeed, heterozygous mutations of the autoimmune regulator gene were reported in patients with organ-specific autoimmunity. Also, in primary immunodeficiencies, a breakdown in central/peripheral tolerance frequently produces association with autoimmunity. The causative link may involve a common genetic background and several gene defects have been identified as putative culprits. We report a unique patient, a 14 year old male from Lazio region, affected by common variable immunodeficiency associated with autoimmune manifestations (alopecia, onychodystrophy) and heterozygote for the S250C variant located in the SAND domain of the autoimmune regulator gene protein. To our knowledge this is the first report of the S250C variant in a patient bearing this unusual combination of autoimmunity and immunodeficiency. To obtain insights into the possible molecular effects of the S250C variant, we have carried out an in silico analysis of the SAND domain structure of the autoimmune regulator protein. In particular, homology modeling has allowed us to observe that the cysteine introduced by the S250C variant is surrounded by cationic residues, and by means of molecular dynamics simulations together with pKa calculations, we have shown that these residues remain stably proximal to cysteine-250 lowering its pKa and thus conferring high chemical reactivity to the mutated residue. We propose that the enhanced reactivity of cysteine-250, which is likely to impair the protein function but probably insufficient to produce alone a phenotype as a heterozygous S250C variant due to compensation mechanisms, might become manifest when combined with other genetic/environmental factors. These results can provide the rationale for the patient's unusual phenotype, shedding new light into the pathogenesis of the clinical association of autoimmunity and immunodeficiency.

Expression of the autoimmune regulator gene and its relevance to the mechanisms of central and peripheral tolerance

The autoimmune polyendocrine syndrome type 1 (APS-1) is a monogenic disease due to pathogenic variants occurring in the autoimmune regulator (AIRE) gene. Its related protein, AIRE, activates the transcription of genes encoding for tissue-specific antigens (TsAgs) in a subset of medullary thymic epithelial cells: the presentation of TsAgs to the maturating thymocytes induces the apoptosis of the autoreactive clones and constitutes the main form of central tolerance. Dysregulation of thymic AIRE expression in genetically transmitted and acquired diseases other than APS-1 may contribute to further forms of autoimmunity. As AIRE and its murine homolog are also expressed in the secondary lymphoid organs, the extent and relevance of AIRE participation in the mechanisms of peripheral tolerance need to be thoroughly defined.

Advances in primary immunodeficiency diseases in Latin America: epidemiology, research, and perspectives

Primary immunodeficiencies (PIDs) are genetic disorders of the immune system comprising many different phenotypes. Although previously considered rare, recent advances in their clinical, epidemiological, and molecular definitions are revealing how much we still need to learn about them. For example, geographical and ethnic variations as well as the impact of certain practices influence their frequency and presentation, making it necessary to consider their study in terms of regions. The Latin American Society for Immunodeficiencies was established as an organization dedicated to provide scientific support for basic and clinical research and to develop tools and educational resources to promote awareness in the medical community. Initiatives such as these are positively influencing the way PIDs are tackled in these countries, as shown by recent reports and publications. This paper provides a historical compilation and a current view of the many issues faced by scientists studying these diseases in these countries, highlighting the diverse scientific contributions and offering a promising perspective for the further developments in this field in Latin America.

Autoimmune regulator (AIRE) contributes to Dectin-1-induced TNF-α production and complexes with caspase recruitment domain-containing protein 9 (CARD9), spleen tyrosine kinase (Syk), and Dectin-1

BACKGROUND

Autoimmune polyendocrinopathy-candidiasis-ectodermal dystrophy (APECED) syndrome is a complex immunologic disease caused by mutation of the autoimmune regulator (AIRE) gene. Autoimmunity in patients with APECED syndrome has been shown to result from deficiency of AIRE function in transcriptional regulation of thymic peripheral tissue antigens, which leads to defective T-cell negative selection. Candidal susceptibility in patients with APECED syndrome is thought to result from aberrant adaptive immunity.

OBJECTIVE

To determine whether AIRE could function in anticandidal innate immune signaling, we investigated an extrathymic role for AIRE in the immune recognition of β-glucan through the Dectin-1 pathway, which is required for defense against Candida species.

METHODS

Innate immune signaling through the Dectin-1 pathway was assessed in both PBMCs from patients with APECED syndrome and a monocytic cell line. Subcellular localization of AIRE was assessed by using confocal microscopy.

RESULTS

PBMCs from patients with APECED syndrome had reduced TNF-α responses after Dectin-1 ligation but in part used a Raf-1-mediated pathway to preserve function. In the THP-1 human monocytic cell line, reducing AIRE expression resulted in significantly decreased TNF-α release after Dectin-1 ligation. AIRE formed a transient complex with the known Dectin-1 pathway components phosphorylated spleen tyrosine kinase and caspase recruitment domain-containing protein 9 after receptor ligation and localized with Dectin-1 at the cell membrane.

CONCLUSION

AIRE can participate in the Dectin-1 signaling pathway, indicating a novel extrathymic role for AIRE and a defect that likely contributes to fungal susceptibility in patients with APECED syndrome.