Comparison of cellular location and expression of Plakophilin-2 in epidermal cells from nonlesional atopic skin and healthy skin in German shepherd dogs.

BACKGROUND: Canine atopic dermatitis (CAD) is an inflammatory and pruritic allergic skin disease caused by interactions between genetic and environmental factors. Previously, a genome-wide significant risk locus on canine chromosome 27 for CAD was identified in German shepherd dogs (GSDs) and Plakophilin-2 (PKP2) was defined as the top candidate gene. PKP2 constitutes a crucial component of desmosomes and also is important in signalling, metabolic and transcriptional activities. OBJECTIVES: The main objective was to evaluate the role of PKP2 in CAD by investigating PKP2 expression and desmosome structure in nonlesional skin from CAD-affected (carrying the top GWAS SNP risk allele) and healthy GSDs. We also aimed at defining the cell types in the skin that express PKP2 and its intracellular location. ANIMALS/METHODS: Skin biopsies were collected from nine CAD-affected and five control GSDs. The biopsies were frozen for immunofluorescence and fixed for electron microscopy immunolabelling and morphology. RESULTS: We observed the novel finding of PKP2 expression in dendritic cells and T cells in dog skin. Moreover, we detected that PKP2 was more evenly expressed within keratinocytes compared to its desmosomal binding-partner plakoglobin. PKP2 protein was located in the nucleus and on keratin filaments attached to desmosomes. No difference in PKP2 abundance between CAD cases and controls was observed. CONCLUSION: Plakophilin-2 protein in dog skin is expressed in both epithelial and immune cells; based on its subcellular location its functional role is implicated in both nuclear and structural processes.

T cell receptor assessment in autoimmune disease requires access to the most adjacent immunologically active organ.

Next generation sequencing of T and B cell receptors is emerging as a valuable and effective method to diagnose and monitor hematopoietic malignancies. So far, this approach has not been fully explored in regard to autoimmune diseases. T cells develop in the thymus where they undergo positive and negative selection, and the autoimmune regulator (Aire) is central in the establishment of immunological tolerance. Loss of Aire leads to severe multiorgan autoimmune disease with infiltration of autoreactive T cells in affected organs. Here, we have utilized next generation sequencing technology to investigate the T cell receptor repertoire in autoimmunity induced by immunization of mice with a self-antigen, myeloperoxidase. By investigating the T cell receptor repertoire in peripheral blood, spleen and lumbar lymph nodes from naïve and immunized Aire -/- mice and wild type littermates, changes in the usage of V and J genes were evident. Our results identify TCR clonotypes which could be potential targets for immune therapy. Also, Aire -/- autoimmunity is driven by a variety of autoantigens where the autoimmune response is highly polyclonal, and access to the most adjacent immunologically active tissue is required to identify T cell receptor sequences that are potentially unique to the antigen in Aire-/- immunized mice.

Multiple regulatory variants located in cell type-specific enhancers within the PKP2 locus form major risk and protective haplotypes for canine atopic dermatitis in German shepherd dogs.

BACKGROUND: Canine atopic dermatitis (CAD) is a chronic inflammatory skin disease triggered by allergic reactions involving IgE antibodies directed towards environmental allergens. We previously identified a ~1.5 Mb locus on canine chromosome 27 associated with CAD in German shepherd dogs (GSDs). Fine-mapping indicated association closest to the PKP2 gene encoding plakophilin 2. RESULTS: Additional genotyping and association analyses in GSDs combined with control dogs from five breeds with low-risk for CAD revealed the top SNP 27:19,086,778 (p = 1.4 × 10(-7)) and a rare ~48 kb risk haplotype overlapping the PKP2 gene and shared only with other high-risk CAD breeds. We selected altogether nine SNPs (four top-associated in GSDs and five within the ~48 kb risk haplotype) that spanned ~280 kb forming one risk haplotype carried by 35 % of the GSD cases and 10 % of the GSD controls (OR = 5.1, p = 5.9 × 10(-5)), and another haplotype present in 85 % of the GSD cases and 98 % of the GSD controls and conferring a protective effect against CAD in GSDs (OR = 0.14, p = 0.0032). Eight of these SNPs were analyzed for transcriptional regulation using reporter assays where all tested regions exerted regulatory effects on transcription in epithelial and/or immune cell lines, and seven SNPs showed allelic differences. The DNA fragment with the top-associated SNP 27:19,086,778 displayed the highest activity in keratinocytes with 11-fold induction of transcription by the risk allele versus 8-fold by the control allele (pdifference = 0.003), and also mapped close (~3 kb) to an ENCODE skin-specific enhancer region. CONCLUSIONS: Our experiments indicate that multiple CAD-associated genetic variants located in cell type-specific enhancers are involved in gene regulation in different cells and tissues. No single causative variant alone, but rather multiple variants combined in a risk haplotype likely contribute to an altered expression of the PKP2 gene, and possibly nearby genes, in immune and epithelial cells, and predispose GSDs to CAD.

Transglutaminase 4 as a prostate autoantigen in male subfertility.

Autoimmune polyendocrine syndrome type 1 (APS1), a monogenic disorder caused by AIRE gene mutations, features multiple autoimmune disease components. Infertility is common in both males and females with APS1. Although female infertility can be explained by autoimmune ovarian failure, the mechanisms underlying male infertility have remained poorly understood. We performed a proteome-wide autoantibody screen in APS1 patient sera to assess the autoimmune response against the male reproductive organs. By screening human protein arrays with male and female patient sera and by selecting for gender-imbalanced autoantibody signals, we identified transglutaminase 4 (TGM4) as a male-specific autoantigen. Notably, TGM4 is a prostatic secretory molecule with critical role in male reproduction. TGM4 autoantibodies were detected in most of the adult male APS1 patients but were absent in all the young males. Consecutive serum samples further revealed that TGM4 autoantibodies first presented during pubertal age and subsequent to prostate maturation. We assessed the animal model for APS1, the Aire-deficient mouse, and found spontaneous development of TGM4 autoantibodies specifically in males. Aire-deficient mice failed to present TGM4 in the thymus, consistent with a defect in central tolerance for TGM4. In the mouse, we further link TGM4 immunity with a destructive prostatitis and compromised secretion of TGM4. Collectively, our findings in APS1 patients and Aire-deficient mice reveal prostate autoimmunity as a major manifestation of APS1 with potential role in male subfertility.

Autoimmune hepatitis in a murine autoimmune polyendocrine syndrome type 1 model is directed against multiple autoantigens.

UNLABELLED: Autoimmune polyendocrine syndrome type 1 (APS-1) is caused by mutations of the autoimmune regulator (AIRE) gene. Mouse studies have shown that this results in defective negative selection of T cells and defective early seeding of peripheral organs with regulatory T cells (Tregs). Aire deficiency in humans and mice manifests as spontaneous autoimmunity against multiple organs, and 20% of patients develop an autoimmune hepatitis (AIH). To study AIH in APS-1, we generated a murine model of human AIH on a BALB/c mouse background, in which Aire is truncated at exon 2. A subgroup of 24% of mice is affected by AIH, characterized by lymphoplasmacytic and periportal hepatic infiltrates, autoantibodies, elevated aminotransferases, and a chronic and progressive course of disease. Disease manifestation was dependent on specific Aire mutations and the genetic background of the mice. Though intrahepatic Treg numbers were increased and hyperproliferative, the intrahepatic CD4/CD8 ratio was decreased. The targets of the adaptive autoimmune response were polyspecific and not focussed on essential autoantigens, as described for other APS-1-related autoimmune diseases. The AIH could be treated with prednisolone or adoptive transfer of polyspecific Tregs. CONCLUSION: Development of AIH in APS-1 is dependent on specific Aire mutations and genetic background genes. Autoimmune response is polyspecific and can be controlled by steroids or transfer with Tregs. This might enable new treatment options for patients with AIH.