Association of an SNP with intrathymic transcription of TSHR and Graves' disease: a role for defective thymic tolerance

Abstract

Graves' disease (GD) is the paradigm of an anti-receptor autoimmune disease, with agonistic auto-antibodies against the thyrotropin receptor (TSHR-thyroid-stimulating hormone receptor) being the underlying pathogenic effector mechanism. The TSHR belongs to the category of tissue-restricted antigens, which are promiscuously expressed in the thymus and thereby induce central T cell tolerance. In order to understand the association between TSHR gene polymorphisms and GD, we tested the hypothesis that TSHR gene variants affect susceptibility to GD by influencing levels of TSHR transcription in the thymus. We show that thymic glands from non-autoimmune donors homozygous for the rs179247 SNP predisposing allele of TSHR had significantly fewer TSHR mRNA transcripts than carriers of the protective allele. In addition, in heterozygous individuals, the TSHR predisposing allele was expressed at a lower level than the protective one as demonstrated by allele-specific transcript quantification. This unbalanced allelic expression was detectable in both thymic epithelial cells and thymocytes. Since the level of self-antigen expression is known to influence the threshold of central tolerance, these results are compatible with the notion that defective central tolerance contributes to the pathogenesis of GD, a scenario already implicated in type 1 diabetes mellitus, myasthenia gravis and autoimmune myocarditis.

Graves’ Disease TSHR-Stimulating Antibodies (TSAbs) Induce the Activation of Immature Thymocytes: A Clue to the Riddle of TSAbs Generation?

“…Expression of TSHR in thymocytes was reported by our group in 2011 (19) and was confirmed by van der Weerd et al (25). We have expanded these results by showing that TSHR message and proteins are expressed normally in thymocytes, and found that the main isoform in thymocytes coincides in m.w.…”

“…In a previous study, we provided the first evidence that TSHR mRNA was expressed in thymocytes, both in CD2 + CD3 2 and in CD2 + CD3 + subsets (19). In this study, we determine the stages of thymic maturation at which it is expressed.…”

“…However, in most cases, the mechanism through which these predisposing genes confer susceptibility to disease remains unclear. For the TSHR gene we have proposed a plausible mechanism for its contribution to pathogenesis (19). In brief, as we have demonstrated that the protective allele determines a higher level of TSHR in the thymus, we postulated that this higher level would result in a more efficient negative selection of TSHR-reactive thymocytes during maturation, and therefore in a peripheral T lymphocyte repertoire more tolerant to TSHR.…”

Autoimmune Predisposition in Down Syndrome May Result from a Partial Central Tolerance Failure due to Insufficient Intrathymic Expression of AIRE and Peripheral Antigens

“…Allele-specific transcript quantification (ASTQ) analysis was done as previously described (18,19). On the basis of data from the dbSNP (http:/ www.ncbi.nlm.nih.gov/snp/) and HapMap databases (20), we selected single nucleotide polymorphism (SNP) rs1055311 (C/T) in exon 6 of the AIRE gene as a target.…”

“…Allele-specific gene expression was determined by qPCR amplification with specific primers and FRET probes designed for this SNP. Detailed information on generation of standards and calibration curves is described elsewhere (18,19 …”