Expression profile of peripheral tissue antigen genes in medullary thymic epithelial cells (mTECs) is dependent on mRNA levels of autoimmune regulator (Aire) (original) (raw)
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Frontiers in immunology, 2016
Autoimmune regulator (Aire) is a transcriptional regulator of peripheral tissue antigens (PTAs) and microRNAs (miRNAs) in medullary thymic epithelial cells (mTECs). In this study, we tested the hypothesis that Aire also played a role as an upstream posttranscriptional controller in these cells and that variation in its expression might be associated with changes in the interactions between miRNAs and the mRNAs encoding PTAs. We demonstrated that downregulation of Aire in vivo in the thymuses of BALB/c mice imbalanced the large-scale expression of these two RNA species and consequently their interactions. The expression profiles of a large set of mTEC miRNAs and mRNAs isolated from the thymuses of mice subjected (or not) to small-interfering-induced Aire gene knockdown revealed that 87 miRNAs and 4,558 mRNAs were differentially expressed. The reconstruction of the miRNA-mRNA interaction networks demonstrated that interactions between these RNAs were under Aire influence and therefore...
Nature Immunology, 2015
Central tolerance is shaped in the thymus, a primary lymphoid organ, where immature T lymphocytes are 'educated' to become mature cells able to recognize foreign antigens while tolerating the body's own components. This educational process involves two central steps that occur in distinct anatomical compartments of the thymus: the cortex and the medulla 1. Both parts are characterized by the presence of specialized types of epithelial cells that provide the required microenvironment for T cell development 1. Although cortical thymic epithelial cells (cTECs) are critical for positive selection of developing thymocytes 2 , medullary thymic epithelial cells (mTECs) have a primary role in the negative selection of self-reactive T cells and/or generation of thymic regulatory T cells (T reg cells) 3-5. The critical role of mTECs is emphasized by their unique ability to promiscuously express and subsequently present essentially all of the body's self antigens, including those that normally have high tissue restriction 5,6. The expression of transcripts encoding many of these tissue-restricted antigens (TRAs) is regulated by a single transcriptional regulator: the autoimmune regulator Aire. Indeed, mice with a dysfunctional gene encoding Aire express only a fraction of the TRA repertoire 7 and as a result develop autoantibodies and immune infiltrates directed at multiple peripheral tissues 7,8 , which resembles the multi-organ autoimmune disorder APS-1 ('autoimmune polyendocrine syndrome type 1') observed in humans with AIRE mutations 9. The molecular mechanisms that underlie the unique ability of Aire to promote the ectopic expression of thousands of tissue-restricted genes has been a topic of considerable interest in the past decade 10,11. Aire is not a classic transcription factor that binds to consensus sequences in the promoters of its target genes but instead is a unique transcriptional regulator that recognizes specific marks of inactive chromatin, such as histone 3 not methylated at Lys4 (refs. 12-14). Several lines of evidence have shown that Aire affects mainly the elongation steps of transcription, in particular the release of stalled RNA polymerase II (refs. 15,16). Correspondingly, Aire has been shown to interact with subunits of the key regulator of the release of RNA polymerase II, the pTEFb-CDK9 complex, as well as the DNA-PK-TOP2-FACT complex 17-19 , which presumably enhances transcription efficacy by removing nucleosomes in front of the elongating RNA polymerase. Aire also interacts with the MBD1-ATF7ip complex, which is required for targeting Aire to the specific TRA-encoding loci 20. Although the studies noted above have provided very important insights into how Aire regulates gene expression, most were based on analyses of protein-protein interactions under nonphysiological conditions. Consequently, they may have missed some of the key physiological partners of Aire. We first sought to identify transcription factors and/or regulators that, like Aire, have high expression in mature mTECs and then assess their involvement in Aire-induced promiscuous gene expression. We found that the protein deacetylase Sirtuin-1 (Sirt1), known to control various physiological processes, including metabolism, development, fertility and aging 21 , was also critical for the establishment of Aire-dependent immunological self-tolerance. Specifically, we found abundant expression of Sirt1 in mature Aire + mTECs, where it was
Journal of Experimental Medicine, 2004
Inactivation of the autoimmune regulator (Aire) gene causes a rare recessive disorder, autoimmune polyendocrine syndrome 1 (APS1), but it is not known if Aire-dependent tolerance mechanisms are susceptible to the quantitative genetic changes thought to underlie more common autoimmune diseases. In mice with a targeted mutation, complete loss of Aire abolished expression of an insulin promoter transgene in thymic epithelium, but had no effect in pancreatic islets or the testes. Loss of one copy of Aire diminished thymic expression of the endogenous insulin gene and the transgene, resulting in a 300% increase in islet-reactive CD4 T cells escaping thymic deletion in T cell receptor transgenic mice, and dramatically increased progression to diabetes. Thymic deletion induced by antigen under control of the thyroglobulin promoter was abolished in Aire homozygotes and less efficient in heterozygotes, providing an explanation for thyroid autoimmunity in APS1. In contrast, Aire deficiency ha...
F1000 - Post-publication peer review of the biomedical literature, 2004
Inactivation of the autoimmune regulator (Aire) gene causes a rare recessive disorder, autoimmune polyendocrine syndrome 1 (APS1), but it is not known if Aire-dependent tolerance mechanisms are susceptible to the quantitative genetic changes thought to underlie more common autoimmune diseases. In mice with a targeted mutation, complete loss of Aire abolished expression of an insulin promoter transgene in thymic epithelium, but had no effect in pancreatic islets or the testes. Loss of one copy of Aire diminished thymic expression of the endogenous insulin gene and the transgene, resulting in a 300% increase in islet-reactive CD4 T cells escaping thymic deletion in T cell receptor transgenic mice, and dramatically increased progression to diabetes. Thymic deletion induced by antigen under control of the thyroglobulin promoter was abolished in Aire homozygotes and less efficient in heterozygotes, providing an explanation for thyroid autoimmunity in APS1. In contrast, Aire deficiency had no effect on thymic deletion to antigen controlled by a systemic H-2K promoter. The sensitivity of Aire-dependent thymic deletion to small reductions in function makes this pathway a prime candidate for more subtle autoimmune quantitative trait loci, and suggests that methods to increase Aire activity would be a potent strategy to lower the incidence of organ-specific autoimmunity.
Molecular and Cellular Biology, 2007
AIRE is a transcriptional activator that directs the ectopic expression of many tissue-specific genes in medullary thymic epithelial cells, which plays an important role in the negative selection of autoreactive T cells. However, its mechanism of action remains poorly understood. In this study, we found that AIRE regulates the step of elongation rather than initiation of RNA polymerase II. For these effects, AIRE bound and recruited P-TEFb to target promoters in medullary thymic epithelial cells. In these cells, AIRE activated the ectopic transcription of insulin and salivary protein 1 genes. Indeed, by chromatin immunoprecipitation, we found that RNA polymerase II was already engaged on these promoters but was unable to elongate in the absence of AIRE. Moreover, the genetic inactivation of cyclin T1 from P-TEFb abolished the transcription of AIRE-responsive genes and led to lymphocytic infiltration of lacrimal and salivary glands in the CycT1 ؊/؊ mouse. Our findings reveal critical steps by which AIRE regulates the transcription of genes that control central tolerance in the thymus.
Transcriptional programs that control expression of the autoimmune regulator gene Aire
Nature immunology, 2016
Aire is a transcriptional regulator that induces promiscuous expression of thousands of genes encoding tissue-restricted antigens (TRAs) in medullary thymic epithelial cells (mTECs). While the target genes of Aire are well characterized, the transcriptional programs that regulate its own expression have remained elusive. Here we comprehensively analyzed both cis-acting and trans-acting regulatory mechanisms and found that the Aire locus was insulated by the global chromatin organizer CTCF and was hypermethylated in cells and tissues that did not express Aire. In mTECs, however, Aire expression was facilitated by concurrent eviction of CTCF, specific demethylation of exon 2 and the proximal promoter, and the coordinated action of several transcription activators, including Irf4, Irf8, Tbx21, Tcf7 and Ctcfl, which acted on mTEC-specific accessible regions in the Aire locus.
Journal of immunology (Baltimore, Md. : 1950), 2015
Establishment of self-tolerance in the thymus depends on promiscuous expression of tissue-restricted Ags (TRA) by thymic epithelial cells (TEC). This promiscuous gene expression (pGE) is regulated in part by the autoimmune regulator (AIRE). To evaluate the commonalities and discrepancies between AIRE-dependent and -independent pGE, we analyzed the transcriptome of the three main TEC subsets in wild-type and Aire knockout mice. We found that the impact of AIRE-dependent pGE is not limited to generation of TRA. AIRE decreases, via non-cell autonomous mechanisms, the expression of genes coding for positive regulators of cell proliferation, and it thereby reduces the number of cortical TEC. In mature medullary TEC, AIRE-driven pGE upregulates non-TRA coding genes that enhance cell-cell interactions (e.g., claudins, integrins, and selectins) and are probably of prime relevance to tolerance induction. We also found that AIRE-dependent and -independent TRA present several distinctive featu...
Modulation of Aire regulates the expression of tissue-restricted antigens
Molecular Immunology, 2008
Intrathymic expression of tissue-restricted antigens (TRAs) has been viewed as the key element in the induction of central tolerance and recently, a central role for the autoimmune regulator (Aire) has been suggested in this process. The aim of this study was to establish whether down or up-regulation of Aire leads to alterations in TRA expression and whether this is limited to thymic epithelial cells. This study also characterized whether TRAs follow Aire expression during normal development, and whether thymic microenvironment plays a role in the expression of Aire and TRAs. We did several in vivo and in vitro experiments to manipulate Aire expression and measured expression of four TRAs (Trefoil factor-3, Insulin-2, Major urinary protein-1 and Salivary protein-1) by real-time RT-PCR. Aire had an allele dose-dependent effect on TRA expression in the thymuses of mice from two strains, C57BL/6J and Balb/c, but had no effect on TRA expression in the lymph nodes. In the thymus, Aire and TRAs were both localized in the medulla and were co-expressed during normal development and involution. In the primary stromal cells as well as thymic epithelial cell line, the adenoviral over-expression of Aire resulted in an increase in TRA expression. By manipulating in vitro organ-cultures we showed that thymic microenvironment plays a dominant role in Aire expression whereas TRAs follow the same pattern. The data underline a direct role for Aire in TRA expression and suggest that modulation of Aire has a potential to control central tolerance and autoimmunity.