Multiple messenger ribonucleic acid transcripts and revised gene organization of the human TSH receptor

A Modifying Autoantigen in Graves' Disease

The TSH receptor (TSHR) is the major autoantigen in Graves' disease (GD). Bioinformatic analyses predict the existence of several human TSHR isoforms from alternative splicing, which can lead to the coexpression of multiple receptor forms. The most abundant of these is TSHRv1.3. In silico modeling of TSHRv1.3 demonstrated the structural integrity of this truncated receptor isoform and its potential binding of TSH. Tissue profiling revealed wide expression of TSHRv1.3, with a predominant presence in thyroid, bone marrow, thymus, and adipose tissue. To gain insight into the role of this v1.3 receptor isoform in thyroid pathophysiology, we cloned the entire open reading frame into a mammalian expression vector. Immunoprecipitation studies demonstrated that both TSHR-stimulating antibody and human TSH could bind v1.3. Furthermore, TSHRv1.3 inhibited the stimulatory effect of TSH and TSHR-Ab MS-1 antibody on TSHR-induced cAMP generation in a dose-dependent manner. To confirm the antigenicity of v1.3, we used a peptide ELISA against two different epitopes. Of 13 GD samples, 11 (84.6%) were positive for a carboxy terminal peptide and 10 (76.9%) were positive with a junction region peptide. To demonstrate that intracellular v1.3 could serve as an autoantigen and modulate disease, we used double-transfected Chinese hamster ovary cells that expressed both green fluorescent protein (GFP)-tagged TSHRv1.3 and full-length TSHR. We then induced cell stress and apoptosis using a TSHR monoclonal antibody and observed the culture supernatant contained v1.3-GFP protein, demonstrating the release of the intracellular receptor variant by this mechanism.

Fine mapping of loci linked to autoimmune thyroid disease identifies novel susceptibility genes

CONTEXT

Genetic factors play a major role in the etiology of autoimmune thyroid disease (AITD) including Graves' disease (GD) and Hashimoto's thyroiditis (HT). We have previously identified three loci on chromosomes 10q, 12q, and 14q that showed strong linkage with AITD, HT, and GD, respectively.

OBJECTIVES

The objective of the study was to identify the AITD susceptibility genes at the 10q, 12q, and 14q loci.

DESIGN AND PARTICIPANTS

Three hundred forty North American Caucasian AITD patients and 183 healthy controls were studied. The 10q, 12q, and 14q loci were fine mapped by genotyping densely spaced single-nucleotide polymorphisms (SNPs) using the Illumina GoldenGate genotyping platform. Case control association analyses were performed using the UNPHASED computer package. Associated SNPs were reanalyzed in a replication set consisting of 238 AITD patients and 276 controls.

RESULTS

Fine mapping of the AITD locus, 10q, showed replicated association of the AITD phenotype (both GD and HT) with SNP rs6479778. This SNP was located within the ARID5B gene recently reported to be associated with rheumatoid arthritis and GD in Japanese. Fine mapping of the GD locus, 14q, revealed replicated association of the GD phenotype with two markers, rs12147587 and rs2284720, located within the NRXN3 and TSHR genes, respectively.

CONCLUSIONS

Fine mapping of three linked loci identified novel susceptibility genes for AITD. The discoveries of new AITD susceptibility genes will engender a new understanding of AITD etiology.

Graves' ophthalmopathy: a review of immunogenetics

Graves’ disease (GD) is the most common cause of thyrotoxicosis and often involves the orbits. Graves’ ophthalmopathy (GO), also known as Thyroid Eye Disease (TED), can be clinically significant and advance to sight-threatening stages. Our knowledge of the immunogenetic pathophysiology of GO is rapidly expanding. The present review is an attempt to summarize the current state of knowledge on the immunogenetics of GO. First we briefly review the epidemiology and clinical importance of GO, and then we describe in detail the macromolecular pathogenesis and finally immunogenetics of GO. Discrepancies between the results from various reports and the limitations of the available data are discussed. In particular, there is a scarcity of data from non-Asian populations. While several studies have demonstrated significant associations between polymorphisms in certain genes (especially CTLA-4, HLA-DRB-1, and TNF-α), there is a need for studies that investigate the relationship between polymorphisms and both serum and local concentrations of the resulting proteins. A complete understanding of GO susceptibility and pathogenesis has not been yet possible due to a number of important knowledge gaps that need to be filled by future research.

The genetic basis of graves' disease

The presented comprehensive review of current knowledge about genetic factors predisposing to Graves’ disease (GD) put emphasis on functional significance of observed associations. In particular, we discuss recent efforts aimed at refining diseases associations found within the HLA complex and implicating HLA class I as well as HLA-DPB1 loci. We summarize data regarding non-HLA genes such as PTPN22, CTLA4, CD40, TSHR and TG which have been extensively studied in respect to their role in GD. We review recent findings implicating variants of FCRL3 (gene for FC receptor-like-3 protein), SCGB3A2 (gene for secretory uteroglobin-related protein 1- UGRP1) as well as other unverified possible candidate genes for GD selected through their documented association with type 1 diabetes mellitus: Tenr–IL2–IL21, CAPSL (encoding calcyphosine-like protein), IFIH1(gene for interferon-induced helicase C domain 1), AFF3, CD226 and PTPN2. We also review reports on association of skewed X chromosome inactivation and fetal microchimerism with GD. Finally we discuss issues of genotype-phenotype correlations in GD.

Molecular characterization and gene expression of thyrotropin receptor (TSHR) and a truncated TSHR-like in Senegalese sole

Thyroid hormones (THs) play a key role in larval development, growth and metamorphosis in flatfish. Their synthesis is tightly regulated by the hypothalamic-pituitary-thyroid axis. Thyroid-stimulating hormone receptor (TSHR) is a key protein in the control of thyroid function stimulating TH synthesis after binding its ligand, the thyrotropin. In teleost fish, numerous reports have associated the TSHR with gametogenesis. However, little information about its role during larval development is available. In this study, we report the cloning of two different cDNAs with high similarity to TSHR. Phylogenetic analysis clustered both cDNAs separately. One of them (referred to TSHR) grouped with TSHR orthologs in tetrapods and teleost fish and possessed the three typical conserved domains and regulatory motifs. The second receptor (referred to as TSHRtr-like) represented a novel truncated cDNA bearing the extracellular and part of the transmembrane domain. TSHRtr-like orthologs were only found in teleosts, which suggests that it could have appeared after fish-specific 3R genome duplication. Expression profiles of both genes are analyzed in juvenile tissues and during larval development using a real-time PCR approach. In juvenile fish, TSHR and TSHRtr-like are expressed ubiquitously although transcript levels varied between organs. In both cases, the highest mRNAs levels are detected in brain. During larval development, both genes are expressed to a high level during the first stages (2-3days after hatching) reducing progressively their abundance in the whole larvae during metamorphosis. This reduction in mRNA abundance is more accentuated for the TSHRtr-like gene. To evaluate the possible regulation of both receptors by T4 during sole metamorphosis, larvae are exposed to the goitrogen thiourea (TU). Only TSHRtr-like modifies its expression, increasing its transcripts at 11days after treatment. Moreover, adding exogenous T4 hormone to TU-treated larvae restores the TSHRtr-like steady-state levels similar to the untreated control. Overall, these results demonstrate the existence of two thyrotropin receptors differentially regulated by THs in teleosts.

Genetic susceptibility to autoimmune thyroid disease: past, present, and future

BACKGROUND

Autoimmune thyroid diseases (AITD), including Graves' disease and Hashimoto's thyroiditis, arise due to complex interactions between environmental and genetic factors. There are sound data coming from epidemiological, family, and twin studies demonstrating a strong genetic influence on the development of AITD. In this review we summarize the new findings on the genetic susceptibility to AITD focusing on emerging mechanisms of susceptibility.

SUMMARY

Candidate gene analysis, whole-genome linkage screening, genome-wide association studies, and whole-genome sequencing are the major technologies that have advanced this field, leading to the identification of at least seven genes whose variants have been associated with AITD. One of the major ones is the HLA-DR gene locus. Recently, it was shown that substitution of the neutral amino acids Ala or Gln with arginine at position beta 74 in the HLA-DR peptide-binding pocket is key to the etiology of both Graves' disease and Hashimoto's thyroiditis. Several other genes have also been shown to confer susceptibility to AITD. These can be classified into two groups: (i) immune regulatory genes (cytotoxic T lymphocyte-associated protein 4, CD40, protein tyrosine phosphatase-22, and CD25) and (ii) thyroid-specific genes (thyroglobulin and thyrotropin receptor genes). The influence of individual genes on the development of AITD when assessed in a population appears to be weaker than would be expected from the data showing strong genetic susceptibility to AITD. Two possible mechanisms explaining this discrepancy are gene-gene interactions and subset effects.

CONCLUSIONS

Significant progress has been made in our understanding of the immunogenetic mechanisms leading to thyroid autoimmunity. For the first time we are beginning to unravel these mechanisms at the molecular level. It is hoped that these new data will be translated into novel therapies and prevention strategies in AITD, such as costimulatory blockade.

The etiology of autoimmune thyroid disease: a story of genes and environment

Autoimmune thyroid diseases (AITDs), including Graves' disease (GD) and Hashimoto's thyroiditis (HT) are prevalent autoimmune diseases, affecting up to 5% of the general population. Autoimmune thyroid diseases arise due to complex interactions between environmental and genetic factors. Significant progress has been made in our understanding of the genetic and environmental triggers contributing to AITD. However, the interactions between genes and environment are yet to be defined. Among the major AITD susceptibility genes that have been identified and characterized is the HLA-DR gene locus, as well as non-MHC genes including the CTLA-4, CD40, PTPN22, thyroglobulin, and TSH receptor genes. The major environmental triggers of AITD include iodine, medications, infection, smoking, and possibly stress. Recent data on the genetic predisposition to AITD lead to novel putative mechanisms by which the genetic-environmental interactions may lead to the development of thyroid autoimmunity.

Association of the thyroid stimulating hormone receptor gene (TSHR) with Graves' disease

Graves' disease (GD) is a common autoimmune disease (AID) that shares many of its susceptibility loci with other AIDs. The thyroid stimulating hormone receptor (TSHR) represents the primary autoantigen in GD, in which autoantibodies bind to the receptor and mimic its ligand, thyroid stimulating hormone, causing the characteristic clinical phenotype. Although early studies investigating the TSHR and GD proved inconclusive, more recently we provided convincing evidence for association of the TSHR region with disease. In the current study, we investigated a combined panel of 98 SNPs, including 70 tag SNPs, across an extended 800 kb region of the TSHR to refine association in a cohort of 768 GD subjects and 768 matched controls. In total, 28 SNPs revealed association with GD (P < 0.05), with strongest SNP associations at rs179247 (chi(2) = 32.45, P = 8.90 x 10(-8), OR = 1.53, 95% CI = 1.32-1.78) and rs12101255 (chi(2) = 30.91, P = 1.95 x 10(-7), OR = 1.55, 95% CI = 1.33-1.81), both located in intron 1 of the TSHR. Association of the most associated SNP, rs179247, was replicated in 303 GD families (P = 7.8 x 10(-4)). In addition, we provide preliminary evidence that the disease-associated genotypes of rs179247 (AA) and rs12101255 (TT) show reduced mRNA expression ratios of flTSHR relative to two alternate TSHR mRNA splice variants.

Influence of the TSH receptor gene on susceptibility to Graves' disease and Graves' ophthalmopathy

BACKGROUND

A large gene region, called GD-1, was first described by this laboratory as linked to Graves' disease (GD) and included the gene for the thyroid-stimulating hormone receptor (TSHR). Recent studies have now suggested an association of TSHR intronic polymorphisms with GD. We have taken the opportunity to examine a population of well-characterized patients with autoimmune thyroid disease (AITD) typed for an additional thyroid susceptibility gene, the immunoregulatory gene for cytotoxic T-lymphocyte antigen 4 (CTLA-4), to examine its relationship with the susceptibility to GD endowed by TSHR gene polymorphisms.

METHODS

We used TSHR-SNP-rs2268458, located in intron 1 of the TSHR gene, measured using standard PCR-RFLP procedures, as our marker for the TSHR gene association. We genotyped 200 patients with GD, 83 patients with Hashimoto's thyroiditis (HT), and 118 healthy controls (all female Caucasians).

RESULTS

The allele and genotype frequencies from GD patients, but not HT patients, were significantly different from controls. The frequency of the combined genotype (allele) CC + TC was significantly higher in GD patients versus controls, suggesting that the C-containing genotype increased the risk for GD in a dominant manner (p = 0.018, odds ratio [OR] = 1.8). When compared with CTLA-4 (A/G)(49) single-nucleotide polymorphism (SNP), we were unable to demonstrate additive risk in patients with established AITD. Further, subsetting the patients (n = 120) into those with clinically significant Graves' ophthalmopathy (GO) showed no association with the TSHR SNP.

CONCLUSIONS

These results demonstrated that the intronic TSHR-SNP-rs2268458 was associated with GD, but not with HT, thus indicating that the TSHR gene has the potential to increase susceptibility to GD. However, we were not able to demonstrate any additive risk with the CTLA-4 (A/G)(49) SNP, which is, therefore, an independent risk factor for AITD. This suggested that, within the limits of the study population, each of these two genes provided a small contribution to GD susceptibility and that neither was essential. In addition, there was no evidence for the TSHR gene association adding to the risk of developing GO. Direct functional analyses are now needed to help explain the mechanisms of this TSHR gene susceptibility to GD.

Susceptibility genes in Graves' ophthalmopathy: searching for a needle in a haystack?

The variety of clinical presentations of eye changes in patients with Graves' disease suggests that complex interactions between genetic, environmental, endogenous and local factors influence the development/severity of Graves' ophthalmopathy (GO). At present, the role of genetic factors in the development of GO remains unknown. Based on small case-control association studies with candidate genes, several susceptibility loci in GO have been proposed. These are human leucocyte antigen (HLA, 6p21.3), cytotoxic T-lymphocyte antigen-4 (CTLA-4, 2q33), tumour necrosis factor (TNF, 6p21.3), interferon-gamma (IFN-gamma, 12q14), intercellular adhesion molecule-1 (ICAM-1, 19p13), and thyroid stimulating hormone receptor gene (TSH-R, 14q31). Unfortunately, these results were either not confirmed or require replication in larger studies. There are many reasons for the lack of reproducibility of association studies in GO, including poor characterization of the studied groups and small sample sizes, which may result in both false positive and negative results. Thus, the genetic background of GO remains to be elucidated in future research. However, the possibility that GO may be a genetically heterogeneous disorder, or that the development of GO may be predominantly influenced by environmental factors such as cigarette smoking, can not be disregarded.

Molecular characterization and seasonal changes in gonadal expression of a thyrotropin receptor in the European sea bass

The thyroid stimulating hormone (TSH) is a glycoprotein synthesized and secreted from thyrotrophs of the anterior pituitary gland. It acts by binding to and activating its specific receptor, the TSHR, to induce the synthesis and secretion of thyroid hormones. Recent studies conducted in diverse fish species suggest a direct role of TSH on gonadal physiology. In this work, we describe the cloning of a cDNA encoding a TSHR which was isolated from the gonads of the European sea bass (Dicentrarchus labrax). The mature protein displays typical features of the members of the glycoprotein hormone receptor family and shows the highest amino acid sequence identity with the TSHRs of other fish species. An insertion of approximately 50 amino acids, specific for the TSHR subfamily is also present in the carboxyl end of the extracellular domain of the sbsTSHR. By RT-PCR analysis, we demonstrate the extrathyroidal expression of sbsTSHR in numerous tissues of the sea bass. Also, two transcripts that differ in the length of their 3' untranslated regions were found. They reflect the use of alternative polyadenylation cleavage sites. Seasonal changes in sbsTSHR mRNA levels in female and male sea bass during the first ovarian and testicular recrudescence suggest that in females the TSHR could participate in active vitellogenesis and in the regulation of gamete maturation and ovulation, whereas in males, the TSHR would be involved in the regulation of processes that occur during the early stages of the gonadal development and also of gamete maturation and spermiation. The results of this work indicate that a sbsTSHR has been cloned from the testis of the European sea bass and they provide the basis for future studies concerning the function of TSHR in this species.

A novel mutation in the thyrotropin (thyroid-stimulating hormone) receptor gene in a case of congenital hypothyroidism

Congenital hypothyroidism (CH) occurs approximately with a frequency of 1 in 3000-4000 births, being a disease caused by defects in thyroid hormone synthesis associated either with goiter presence or with agenesis or ectopy of the thyroid gland. A study of some familial cases has allowed identification of mutations in several known genes, including that encode the thyroid-stimulating hormone receptor (TSHR). We report a familial case of CH that transmitted as a recessive trait and caused by a novel homozygous nonsense mutation in TSHR with an initial diagnosis of thyroid agenesis hypoplasia. Genomic DNA was obtained from two siblings and their parents; TSHR was amplified using pairs of overlapping exonic primers; and polymerase chain reaction products were automatically sequenced. The propositus was homozygous (genotype: M/M) for a novel C to G transversion (1431C>G), producing a nonsense mutation, Y444X, in the first intracellular loop of TSHR, rendering a truncated receptor. Thus, the observed unresponsiveness to TSHR may be due to absent insertion of the truncated receptor into the cell membrane (if it gets translated at all) or the truncation may lead to nonsense-mediated mRNA degradation (its unresponsive to TSH). Both parents were heterozygous (wWt/M) and unrelated, as known from family history. The other daughter was homozygous for both wild-type alleles (wWt/wWt).

Thyroid-stimulating hormone receptor and its role in Graves' disease

The thyroid-stimulating hormone (TSH, or thyrotropin) receptor (TSHR) mediates the activating action of TSH to the thyroid gland, resulting in the growth and proliferation of thyrocytes and thyroid hormone production. In Graves' disease, thyroid-stimulating autoantibodies can mimic TSH action and stimulate thyroid cells. This leads to hyperthyroidism and abnormal overproduction of thyroid hormone. TSHR-antibodies-binding epitopes on the receptor molecule are well studied. Mechanism of TSHR-autoantibodies production is more or less clear but a susceptibility gene, which is linked to their production, is still unknown. Genetic studies show no linkage between the TSHR gene and Graves' disease. Among three common polymorphisms in the TSHR gene, only the D727E germline polymorphism in the cytoplasmic tail of the receptor showed an association with the disease, and this association is weak. The absence of a strong genetic effect of the TSHR polymorphisms in such a common and complex disorder as Graves' disease may be explained by a high degree of evolutionary conservation in TSHR. This can be shown by naturally existing germline and somatic mutations in the TSHR gene that cause various types of nonautoimmune and hereditary thyroid disease.