A unique mouse strain that develops spontaneous, iodine-accelerated, pathogenic antibodies to the human thyrotrophin receptor

Murine Thyroid IL-4 Expression Worsens Hypothyroidism on Iodine Restriction and Mitigates Graves Disease Development

Cytokines are known to perturb thyroid function and the role of interleukin-4 (IL-4) in the pathogenesis of Graves disease (GD) remains controversial. In our mouse model overexpressing IL-4 in thyrocytes (Thyr-IL4), we have reported that adult mice preserved normal serum thyroxine despite an iodide uptake defect. In the present work, we evaluated if iodine restriction could uncover the thyroid deficiency in Thyr-IL4 animals as well as the role of pendrin overexpression as a compensatory mechanism. Moreover, using an experimental model of GD we investigated the effect of a local expression of IL-4 on the incidence of hyperthyroidism. Thyr-IL4 mice developed more rapidly elevated serum thyrotropin under low-iodine supply with thyroid enlargement and classical histological modifications. These hallmarks of hypothyroidism were all enhanced in Thyr-IL4 mice with complete pendrin invalidation. Following immunization, a lower proportion of Thyr-IL4 animals developed hyperthyroidism. Surprisingly, immunized Thyr-IL4 animals presented numerous leukocyte infiltrates, associated with increased intrathyroidal expression of IFN-γ. We have demonstrated that thyroid deficiency in Thyr-IL4 mice is partially compensated for by the excessive iodide content of the standard chow and the overexpression of pendrin in these animals. Furthermore, we have shown that the local expression of IL-4 in the thyroid attenuates GD progression, which was associated with enhanced thyroid infiltration by immune cells that could negatively affect thyroid function.

The NOD Mouse Beyond Autoimmune Diabetes

Autoimmune diabetes arises spontaneously in Non-Obese Diabetic (NOD) mice, and the pathophysiology of this disease shares many similarities with human type 1 diabetes. Since its generation in 1980, the NOD mouse, derived from the Cataract Shinogi strain, has represented the gold standard of spontaneous disease models, allowing to investigate autoimmune diabetes disease progression and susceptibility traits, as well as to test a wide array of potential treatments and therapies. Beyond autoimmune diabetes, NOD mice also exhibit polyautoimmunity, presenting with a low incidence of autoimmune thyroiditis and Sjögren’s syndrome. Genetic manipulation of the NOD strain has led to the generation of new mouse models facilitating the study of these and other autoimmune pathologies. For instance, following deletion of specific genes or via insertion of resistance alleles at genetic loci, NOD mice can become fully resistant to autoimmune diabetes; yet the newly generated diabetes-resistant NOD strains often show a high incidence of other autoimmune diseases. This suggests that the NOD genetic background is highly autoimmune-prone and that genetic manipulations can shift the autoimmune response from the pancreas to other organs. Overall, multiple NOD variant strains have become invaluable tools for understanding the pathophysiology of and for dissecting the genetic susceptibility of organ-specific autoimmune diseases. An interesting commonality to all autoimmune diseases developing in variant strains of the NOD mice is the presence of autoantibodies. This review will present the NOD mouse as a model for studying autoimmune diseases beyond autoimmune diabetes.

Is There Evidence for IGF1R-Stimulating Abs in Graves' Orbitopathy Pathogenesis?

In this review, we summarize the evidence against direct stimulation of insulin-like growth factor 1 receptors (IGF1Rs) by autoantibodies in Graves' orbitopathy (GO) pathogenesis. We describe a model of thyroid-stimulating hormone (TSH) receptor (TSHR)/IGF1R crosstalk and present evidence that observations indicating IGF1R's role in GO could be explained by this mechanism. We evaluate the evidence for and against IGF1R as a direct target of stimulating IGF1R antibodies (IGF1RAbs) and conclude that GO pathogenesis does not involve directly stimulating IGF1RAbs. We further conclude that the preponderance of evidence supports TSHR as the direct and only target of stimulating autoantibodies in GO and maintain that the TSHR should remain a major target for further development of a medical therapy for GO in concert with drugs that target TSHR/IGF1R crosstalk.

Graves' disease

Graves' disease (GD) is an autoimmune disease that primarily affects the thyroid gland. It is the most common cause of hyperthyroidism and occurs at all ages but especially in women of reproductive age. Graves' hyperthyroidism is caused by autoantibodies to the thyroid-stimulating hormone receptor (TSHR) that act as agonists and induce excessive thyroid hormone secretion, releasing the thyroid gland from pituitary control. TSHR autoantibodies also underlie Graves' orbitopathy (GO) and pretibial myxoedema. Additionally, the pathophysiology of GO (and likely pretibial myxoedema) involves the synergism of insulin-like growth factor 1 receptor (IGF1R) with TSHR autoantibodies, causing retro-orbital tissue expansion and inflammation. Although the aetiology of GD remains unknown, evidence indicates a strong genetic component combined with random potential environmental insults in an immunologically susceptible individual. The treatment of GD has not changed substantially for many years and remains a choice between antithyroid drugs, radioiodine or surgery. However, antithyroid drug use can cause drug-induced embryopathy in pregnancy, radioiodine therapy can exacerbate GO and surgery can result in hypoparathyroidism or laryngeal nerve damage. Therefore, future studies should focus on improved drug management, and a number of important advances are on the horizon.

A transgenic mouse that spontaneously develops pathogenic TSH receptor antibodies will facilitate study of antigen-specific immunotherapy for human Graves' disease

Graves' hyperthyroidism can be treated but not cured. Antigen-specific immunotherapy would accomplish this goal, for which purpose an animal model is an invaluable tool. Two types of animal models are available. First, pathogenic TSHR antibodies (TSHRAb) can be induced by injecting mice with fibroblasts co-expressing the human TSHR (hTSHR) and MHC class II, or in mammals using plasmid or adenovirus vectors encoding the hTSHR or its A-subunit. Second, a mouse model that spontaneously develops pathogenic TSHRAb resembling those in human disease was recently described. This outcome was accomplished by transgenic intrathyroidal expression of the hTSHR A-subunit in NOD.H2^h4 mice that are genetically predisposed to develop thyroiditis but, without the transgene, do not generate TSHRAb. Recently, novel approaches to antigen-specific immunotherapy have been tested, primarily in the induced model, by injecting TSHR A-subunit protein or cyclic TSHR peptides. T-cell tolerance has also been induced in "humanized" HLA-DR3 mice by injecting synthetic peptides predicted in silico to mimic naturally processed TSHR T-cell epitopes. Indeed, a phase 1 study based on the latter approach has been conducted in humans. In the spontaneous model (hTSHR/NOD.H2^h mice), injection of soluble or nanoparticle-bearing hTSHR A-subunits had the unwanted effect of exacerbating pathogenic TSHRAb levels. A promising avenue for tolerance induction, successful in other conditions and yet to be tested with the TSHR, involves encapsulating the antigen. In conclusion, these studies provide insight into the potential outcome of immunotherapeutic approaches and emphasize the importance of a spontaneous model to test future novel, antigen-specific immunotherapies for Graves' disease.

A Mouse Thyrotropin Receptor A-Subunit Transgene Expressed in Thyroiditis-Prone Mice May Provide Insight into Why Graves' Disease Only Occurs in Humans

Background: Graves' disease, caused by autoantibodies that activate the thyrotropin (TSH) receptor (TSHR), has only been reported in humans. Thyroiditis-prone NOD.H2^h4 mice develop autoantibodies to thyroglobulin (Tg) and thyroid peroxidase (TPO) but not to the TSHR. Evidence supports the importance of the shed TSHR A-subunit in the initiation and/or amplification of the autoimmune response to the holoreceptor. Cells expressing the gene for the isolated A-subunit secrete A-subunit protein, a surrogate for holoreceptor A-subunit shedding. NOD.H2^h4 mice with the human TSHR A-subunit targeted to the thyroid (a "self" antigen in such transgenic (Tgic) animals), unlike their wild-type (wt) siblings, spontaneously develop pathogenic TSHR antibodies to the human-TSH holoreceptor. These autoantibodies do not recognize the endogenous mouse-TSH holoreceptor and do not cause hyperthyroidism. Methods: We have now generated NOD.H2^h4 mice with the mouse-TSHR A-subunit transgene targeted to the thyroid. Tgic mice and wt littermates were compared for intrathyroidal expression of the mouse A-subunit. Sera from six-month-old mice were tested for the presence of autoantibodies to Tg and TPO as well as for pathogenic TSHR antibodies (TSH binding inhibition, bioassay for thyroid stimulating antibodies) and nonpathogenic TSHR antibodies (ELISA). Results: Expression of the mouse TSHR A-subunit transgene in the thyroid was confirmed by real-time polymerase chain reaction in the Tgics and had no effect on the spontaneous development of autoantibodies to Tg or TPO. However, unlike the same NOD.H2^h4 strain with the human-TSHR A-subunit target to the thyroid, mice expressing intrathyroidal mouse-TSHR A subunit failed to develop either pathogenic or nonpathogenic TSHR antibodies. The mouse TSHR A-subunit differs from the human TSHR A-subunit in terms of its amino acid sequence and has one less glycosylation site than the human TSHR A-subunit. Conclusions: Multiple genetic and environmental factors contribute to the pathogenesis of Graves' disease. The present study suggests that the TSHR A-subunit structure (possibly including posttranslational modification such as glycosylation) may explain, in part, why Graves' disease only develops in humans.

Nanoparticles Bearing TSH Receptor Protein and a Tolerogenic Molecule Do Not Induce Immune Tolerance but Exacerbate Thyroid Autoimmunity in hTSHR/NOD.H2h4 Mice

Transgenic NOD.H2h4 mice that express the human (h) TSHR A-subunit in the thyroid gland spontaneously develop pathogenic TSHR autoantibodies resembling those in patients with Graves disease. Nanoparticles coupled to recombinant hTSHR A-subunit protein and a tolerogenic molecule (ligand for the endogenous aryl-hydrocarbon receptor; ITE) were injected i.p. four times at weekly intervals into hTSHR/NOD.H2h4 mice with the goal of blocking TSHR Ab development. Unexpectedly, in transgenic mice, injecting TSHR A-subunit-ITE nanoparticles (not ITE-nanoparticles or buffer) accelerated and enhanced the development of pathogenic TSHR Abs measured by inhibition of TSH binding to the TSHR. Nonpathogenic TSHR Abs (ELISA) were enhanced in transgenics and induced in wild-type littermates. Serendipitously, these findings have important implications for disease pathogenesis: development of Graves TSHR Abs is limited by the availability of A-subunit protein, which is shed from membrane bound TSHR, expressed at low levels in the thyroid. The enhanced TSHR Ab response following injected TSHR A-subunit protein-nanoparticles is reminiscent of the transient increase in pathogenic TSHR Abs following the release of thyroid autoantigens after radio-iodine therapy in Graves patients. However, in the hTSHR/NOD.H2h4 model, enhancement is specific for TSHR Abs, with Abs to thyroglobulin and thyroid peroxidase remaining unchanged. In conclusion, despite the inclusion of a tolerogenic molecule, injected nanoparticles coated with TSHR A-subunit protein enhanced and accelerated development of pathogenic TSHR Abs in hTSHR/NOD. NOD.H2h4 These findings emphasize the need for sufficient TSHR A-subunit protein to activate the immune system and the generation of stimulatory TSHR Abs in genetically predisposed individuals.

To reflect human autoimmune thyroiditis, thyroid peroxidase (not thyroglobulin) antibodies should be measured in female (not sex-independent) NOD.H2h4 mice

NOD.H2^h4 mice are the most commonly used model for human autoimmune thyroiditis. Because thyroid autoimmunity develops slowly (over months), NOD.H2^h4 mice are usually exposed to excess dietary iodide to accelerate and amplify the process. However, unlike the female bias in human thyroid autoimmunity, autoantibodies to thyroglobulin (TgAb) are reported to be similar in male and female NOD.H2^h4 . We sought evidence for sexual dimorphism in other parameters in this strain maintained on regular or iodized water. Without iodide, TgAb levels are higher in males than in females, the reverse of human disease. In humans, autoantibodies to thyroid peroxidase (TPOAb) are a better marker of disease than TgAb. In NOD.H2^h4 mice TPOAb develop more slowly than TgAb, being detectable at 6 months of age versus 4 months for the latter. Remarkably, unlike TgAb, TPOAb levels are higher in female than male NOD.H2^h4 mice on both regular and iodized water. As previously observed, serum T4 levels are similar in both sexes. However, thyroid-stimulating hormone (TSH) levels are significantly higher in males than females with or without iodide exposure. TSH levels correlate with TgAb levels in male NOD.H2^h4 mice, suggesting a possible role for TSH in TgAb development. However, there is no correlation between TSH and TPOAb levels, the latter more important than TgAb in human disease. In conclusion, if the goal of an animal model is to closely reflect human disease, TPOAb rather than TgAb should be measured in older female NOD.H2^h4 mice, an approach requiring patience and the use of mouse TPO protein.

Graves' orbitopathy occurs sex-independently in an autoimmune hyperthyroid mouse model

Graves’ orbitopathy (GO) is the most common extra thyroidal complication of Graves’ disease (GD) and occurs predominantly in women but more severe in men. The reason for this effect of gender on GO is unknown. Herein we studied the manifestation of GO in both sexes of an induced mouse model in absence of additional risk factors present in patients like advanced age, genetic variabilities or smoking. Male and female mice were immunized with human TSHR A-subunit encoding plasmid. Both sexes comparably developed autoimmune hyperthyroidism characterized by TSHR stimulating autoantibodies, elevated T4 values, hyperplastic thyroids and hearts. Autoimmune mice developed inflammatory eye symptoms and proptosis, although males earlier than females. Serial in vivo¹H/¹⁹F-magnetic resonance imaging revealed elevated inflammatory infiltration, increased fat volume and glycosaminoglycan deposition in orbits of both sexes but most significantly in female mice. Histologically, infiltration of T-cells, extension of brown fat and overall collagen deposition were characteristics of GO in male mice. In contrast, female mice developed predominately macrophage infiltration in muscle and connective tissue, and muscle hypertrophy. Apart from sex-dependent variabilities in pathogenesis, disease classification revealed minor sex-differences in incidence and total outcome. In conclusion, sex does not predispose for autoimmune hyperthyroidism and associated GO.

Thyroid Hemiagenesis in a Thyroiditis Prone Mouse Strain

BACKGROUND

Thyroid hemiagenesis, a rare congenital condition detected by ultrasound screening of the neck, is usually not manifested clinically in humans. This condition has been reported in mice with hypothyroidism associated with induced deficiency in paired box 8 and NK2 homeobox 1, sonic hedgehog, or T-box 1. Unexpectedly, we observed thyroid hemiagenesis in NOD.H2^h4 mice, an unusual strain that spontaneously develops iodide enhanced thyroid autoimmunity but remains euthyroid.

OBJECTIVES AND METHODS

First, to compare mice with thyroid hemiagenesis versus bilobed littermates for serum T4, autoantibodies to thyroglobulin (ELISA) and thyroid peroxidase (TPO; flow cytometry with eukaryotic cells expressing mouse TPO), gross anatomy, and thyroid histology; second, to estimate the percentage of mice with thyroid hemiagenesis in the NOD.H2^h4 mice we have studied over 6 years.

RESULTS

Thyroid hemiagenesis was observed in 3 of 1,025 NOD.H2^h4 mice (2 females, 1 male; 0.3$). Two instances of hemiagenesis were in wild-type females and one in a transgenic male expressing the human TSHR A-subunit in the thyroid. Two mice had very large unilobed glands, as in some human cases with this condition. Thyroid lymphocytic infiltration, serum T4, and the levels of thyroid autoantibodies were similar in mice with thyroid hemiagenesis and bilobed littermates.

CONCLUSIONS

Unlike hypothyroidism associated with hemiagenesis in transcription factor knockout mice, hemiagenesis in euthyroid NOD.H2^h4 mice occurs spontaneously and is phenotypically similar to that occasionally observed in humans.

Gut microbiota in experimental murine model of Graves' orbitopathy established in different environments may modulate clinical presentation of disease

BACKGROUND

Variation in induced models of autoimmunity has been attributed to the housing environment and its effect on the gut microbiota. In Graves' disease (GD), autoantibodies to the thyrotropin receptor (TSHR) cause autoimmune hyperthyroidism. Many GD patients develop Graves' orbitopathy or ophthalmopathy (GO) characterized by orbital tissue remodeling including adipogenesis. Murine models of GD/GO would help delineate pathogenetic mechanisms, and although several have been reported, most lack reproducibility. A model comprising immunization of female BALBc mice with a TSHR expression plasmid using in vivo electroporation was reproduced in two independent laboratories. Similar orbital disease was induced in both centers, but differences were apparent (e.g., hyperthyroidism in Center 1 but not Center 2). We hypothesized a role for the gut microbiota influencing the outcome and reproducibility of induced GO.

RESULTS

We combined metataxonomics (16S rRNA gene sequencing) and traditional microbial culture of the intestinal contents from the GO murine model, to analyze the gut microbiota in the two centers. We observed significant differences in alpha and beta diversity and in the taxonomic profiles, e.g., operational taxonomic units (OTUs) from the genus Lactobacillus were more abundant in Center 2, and Bacteroides and Bifidobacterium counts were more abundant in Center 1 where we also observed a negative correlation between the OTUs of the genus Intestinimonas and TSHR autoantibodies. Traditional microbiology largely confirmed the metataxonomics data and indicated significantly higher yeast counts in Center 1 TSHR-immunized mice. We also compared the gut microbiota between immunization groups within Center 2, comprising the TSHR- or βgal control-immunized mice and naïve untreated mice. We observed a shift of the TSHR-immunized mice bacterial communities described by the beta diversity weighted Unifrac. Furthermore, we observed a significant positive correlation between the presence of Firmicutes and orbital-adipogenesis specifically in TSHR-immunized mice.

CONCLUSIONS

The significant differences observed in microbiota composition from BALBc mice undergoing the same immunization protocol in comparable specific-pathogen-free (SPF) units in different centers support a role for the gut microbiota in modulating the induced response. The gut microbiota might also contribute to the heterogeneity of induced response since we report potential disease-associated microbial taxonomies and correlation with ocular disease.

New advances in understanding thyroid-associated ophthalmopathy and the potential role for insulin-like growth factor-I receptor

Thyroid-associated ophthalmopathy (TAO), a localized periocular manifestation of the autoimmune syndrome known as Graves’ disease, remains incompletely understood. Discussions of its pathogenesis are generally focused on the thyrotropin receptor, the proposed role for which is supported by substantial evidence. Considerations of any involvement of the insulin-like growth factor-I receptor (IGF-IR) in the disease are frequently contentious. In this brief, topically focused review, I have attempted to provide a balanced perspective based entirely on experimental results that either favor or refute involvement of IGF-IR in TAO. Discussion in this matter seems particularly timely since the currently available treatments of this disfiguring and potentially sight-threatening disease remain inadequate. Importantly, no medical therapy has thus far received approval from the US Food and Drug Administration. Results from a very recently published clinical trial assessing the safety and efficacy of teprotumumab, an inhibitory human anti–IGF-IR monoclonal antibody, in active, moderate to severe TAO are extremely encouraging. That double-masked, placebo-controlled study involved 88 patients and revealed unprecedented clinical responses in the improvement of proptosis and clinical activity as well as a favorable safety profile. Should those results prove reproducible in an ongoing phase III trial, therapeutic inhibition of IGF-IR could become the basis for paradigm-shifting treatment of this vexing disease.

Aberrant Iodine Autoregulation Induces Hypothyroidism in a Mouse Strain in the Absence of Thyroid Autoimmunity

We investigated factors underlying the varying effects of a high dietary iodide intake on serum T4 levels in a wide spectrum of mouse strains, including thyroiditis-susceptible NOD.H2h4, NOD.H2k, and NOD mice, as well as other strains (BALB/c, C57BL/6, NOD.Lc7, and B10.A4R) not previously investigated. Mice were maintained for up to 8 months on control or iodide-supplemented water (NaI 0.05%). On iodized water, serum T4 was reduced in BALB/c (males and females) in association with colloid goiters but was not significantly changed in mice that developed thyroiditis, namely NOD.H2h4 (males and females) or male NOD.H2k mice. Neither goiters nor decreased T4 developed in C57BL/6, NOD, NOD.Lc7, or B10.A4R female mice. In further studies, we focused on males in the BALB/c and NOD.H2h4 strains that demonstrated a large divergence in the T4 response to excess iodide. Excess iodide ingestion increased serum TSH levels to the same extent in both strains, yet thyroidal sodium iodide symporter (NIS) messenger RNA (mRNA) levels (quantitative polymerase chain reaction) revealed greatly divergent responses. NOD.H2h4 mice that remained euthyroid displayed a physiological NIS iodine autoregulatory response, whereas NIS mRNA was inappropriately elevated in BALB/c mice that became hypothyroid. Thus, autoimmune thyroiditis-prone NOD.H2h4 mice adapted normally to a high iodide intake, presumably by escape from the Wolff-Chaikoff block. In contrast, BALB/c mice that did not spontaneously develop thyroiditis failed to escape from this block and became hypothyroid. These data in mice may provide insight into the mechanism by which iodide-induced hypothyroidism occurs in some humans without an underlying thyroid disorder.

Thyroid Autoantibodies Display both "Original Antigenic Sin" and Epitope Spreading

Evidence for original antigenic sin in spontaneous thyroid autoimmunity is revealed by autoantibody interactions with immunodominant regions on thyroid autoantigens, thyroglobulin (Tg), thyroid peroxidase (TPO), and the thyrotropin receptor (TSHR) A-subunit. In contrast, antibodies induced by immunization of rabbits or mice recognize diverse epitopes. Recognition of immunodominant regions persists despite fluctuations in autoantibody levels following treatment or over time. The enhancement of spontaneously arising pathogenic TSHR antibodies in transgenic human thyrotropin receptor/NOD.H2^h4 mice by injecting a non-pathogenic form of TSHR A-subunit protein also provides evidence for original antigenic sin. From other studies, antigen presentation by B cells, not dendritic cells, is likely responsible for original antigenic sin. Recognition of restricted epitopes on the large glycosylated thyroid autoantigens (60-kDa A-subunit, 100-kDa TPO, and 600-kDa Tg) facilitates exploring the amino acid locations in the immunodominant regions. Epitope spreading has also been revealed by autoantibodies in thyroid autoimmunity. In humans, and in mice that spontaneously develop autoimmunity to all three thyroid autoantigens, autoantibodies develop first to Tg and later to TPO and the TSHR A-subunit. The pattern of intermolecular epitope spreading is related in part to the thyroidal content of Tg, TPO and TSHR A-subunit and to the molecular sizes of these proteins. Importantly, the epitope spreading pattern provides a rationale for future antigen-specific manipulation to block the development of all thyroid autoantibodies by inducing tolerance to Tg, first in the autoantigen cascade. Because of its abundance, Tg may be the autoantigen of choice to explore antigen-specific treatment, preventing the development of pathogenic TSHR antibodies.

Genetic immunization with mouse thyrotrophin hormone receptor plasmid breaks self-tolerance for a murine model of autoimmune thyroid disease and Graves' orbitopathy

Experimental models of Graves' hyperthyroid disease accompanied by Graves' orbitopathy (GO) can be induced efficiently in susceptible inbred strains of mice by immunization by electroporation of heterologous human TSH receptor (TSHR) A-subunit plasmid. In this study, we report on the development of a bona fide murine model of autoimmune Graves' disease induced with homologous mouse TSHR A-subunit plasmid. Autoimmune thyroid disease in the self-antigen model was accompanied by GO and characterized by histopathology of hyperplastic glands with large thyroid follicular cells. Examination of orbital tissues showed significant inflammation in extra-ocular muscle with accumulation of T cells and macrophages together with substantial deposition of adipose tissue. Notably, increased levels of brown adipose tissue were present in the orbital tissue of animals undergoing experimental GO. Further analysis of inflammatory loci by ¹⁹ F-magnetic resonance imaging showed inflammation to be confined to orbital muscle and optic nerve, but orbital fat showed no difference in inflammatory signs in comparison to control β-Gal-immunized animals. Pathogenic antibodies induced to mouse TSHR were specific for the self-antigen, with minimal cross-reactivity to human TSHR. Moreover, compared to other self-antigen models of murine Graves' disease induced in TSHR knock-out mice, the repertoire of autoantibodies to mouse TSHR generated following the breakdown of thymic self-tolerance is different to those that arise when tolerance is not breached immunologically, as in the knock-out models. Overall, we show that mouse TSHR A-subunit plasmid immunization by electroporation overcomes tolerance to self-antigen to provide a faithful model of Graves' disease and GO.

Variable Effects of Dietary Selenium in Mice That Spontaneously Develop a Spectrum of Thyroid Autoantibodies

Selenium (Se) is a critical element in thyroid function, and variable dietary Se intake influences immunity. Consequently, dietary Se could influence development of thyroid autoimmunity and provide an adjunct to treat autoimmune thyroid dysfunction. Nonobese diabetic (NOD).H2h4 mice spontaneously develop autoantibodies to thyroglobulin (Tg) and thyroid peroxidase (TPO). This mouse strain expressing a human thyroid-stimulating hormone receptor (TSHR) A-subunit transgene in the thyroid also develops pathogenic TSHR autoantibodies. In this report, we investigated whether dietary Se influences these immune processes. Male and female wild-type and transgenic NOD.H2h4 mice were maintained on normal-, low-, or high-Se (0.1, 0, or 1.0 mg/kg) rodent diets. After 4 months, Se serum levels were extremely low or significantly increased on 0 or 1.0 mg/kg Se, respectively. Varying Se intake affected Tg antibody (TgAb) levels after 2 (but not 4) months; conversely, TPO antibody (TPOAb) levels were altered by dietary Se after 4 (but not 2) months. These data correspond to the earlier development of TgAb than TPOAb in NOD.H2h4 mice. In males, TgAb levels were enhanced by high Se and in females by low Se intake. Se intake had no effect on pathogenic TSHR autoantibodies in TSHR transgenic NOD.H2h4 females. In conclusion, in susceptible NOD.H2h4 mice, we found no evidence that a higher dietary Se intake ameliorates thyroid autoimmunity by reducing autoantibodies to Tg, TPO, or the TSHR. Instead, our finding that low dietary Se potentiates the development of autoantibodies to Tg and TPO in females is consistent with reports in humans of an increased prevalence of autoimmune thyroiditis in low-Se regions.

Mechanisms of Autoantibody-Induced Pathology

Autoantibodies are frequently observed in healthy individuals. In a minority of these individuals, they lead to manifestation of autoimmune diseases, such as rheumatoid arthritis or Graves' disease. Overall, more than 2.5% of the population is affected by autoantibody-driven autoimmune disease. Pathways leading to autoantibody-induced pathology greatly differ among different diseases, and autoantibodies directed against the same antigen, depending on the targeted epitope, can have diverse effects. To foster knowledge in autoantibody-induced pathology and to encourage development of urgently needed novel therapeutic strategies, we here categorized autoantibodies according to their effects. According to our algorithm, autoantibodies can be classified into the following categories: (1) mimic receptor stimulation, (2) blocking of neural transmission, (3) induction of altered signaling, triggering uncontrolled (4) microthrombosis, (5) cell lysis, (6) neutrophil activation, and (7) induction of inflammation. These mechanisms in relation to disease, as well as principles of autoantibody generation and detection, are reviewed herein.

Genes Outside the Major Histocompatibility Complex Locus Are Linked to the Development of Thyroid Autoantibodies and Thyroiditis in NOD.H2h4 Mice

Thyroiditis and autoantibodies to thyroglobulin (TgAb) and thyroid peroxidase (TPOAb) develop spontaneously in NOD.H2h4 mice, a phenotype enhanced by dietary iodine. NOD.H2h4 mice were derived by introducing the major histocompatibility class (MHC) molecule I-Ak from B10.A(4R) mice to nonobese diabetic (NOD) mice. Apart from I-Ak, the genes responsible for the NOD.H2h4 phenotype are unknown. Extending serendipitous observations from crossing BALB/c to NOD.H2h4 mice, thyroid autoimmunity was investigated in both genders of the F1, F2, and the second-generation backcross of F1 to NOD.H2h4 (N2). Medium-density linkage analysis was performed on thyroid autoimmunity traits in F2 and N2 progeny. TgAb develop before TPOAb and were measured after 8 and 16 weeks of iodide exposure; TPOAb and thyroiditis were studied at 16 weeks. TgAb, TPOAb, and thyroiditis, absent in BALB/c and F1 mice, developed in most NOD.H2h4 and in more N2 than F2 progeny. No linkages were observed in F2 progeny, probably because of the small number of autoantibody-positive mice. In N2 progeny (equal numbers of males and females), a chromosome 17 locus is linked to thyroiditis and TgAb and is suggestively linked to TPOAb. This locus includes MHC region genes from B10.A(4R) mice (such as I-Ak and Tnf, the latter involved in thyrocyte apoptosis) and genes from NOD mice such as Satb1, which most likely plays a role in immune tolerance. In conclusion, MHC and non-MHC genes, encoded within the chromosome 17 locus from both B10.A(4R) and NOD strains, are most likely responsible for the Hashimoto disease-like phenotype of NOD.H2h4 mice.

High-level intrathymic thyrotrophin receptor expression in thyroiditis-prone mice protects against the spontaneous generation of pathogenic thyrotrophin receptor autoantibodies

The thyrotrophin receptor (TSHR) A-subunit is the autoantigen targeted by pathogenic autoantibodies that cause Graves' hyperthyroidism, a common autoimmune disease in humans. Previously, we reported that pathogenic TSHR antibodies develop spontaneously in thyroiditis-susceptible non-obese diabetic (NOD).H2^h4 mice bearing a human TSHR A-subunit transgene, which is expressed at low levels in both the thyroid and thymus (Lo-expressor transgene). The present study tested recent evidence that high intrathymic TSHR expression protects against the development of pathogenic TSHR antibodies in humans. By successive back-crossing, we transferred to the NOD.H2^h4 background a human TSHR A-subunit transgene expressed at high levels in the thyroid and thymus (Hi-expressor transgene). In the sixth back-cross generation (> 98% NOD.H2^h4 genome), only transgenic offspring produced spontaneously immunoglobulin (Ig)G class non-pathogenic human TSHR A-subunit antibodies. In contrast, both transgenic and non-transgenic offspring developed antibodies to thyroglobulin and thyroid peroxidase. However, non-pathogenic human TSHR antibody levels in Hi-expressor offspring were lower than in Lo-expressor transgenic mice. Moreover, pathogenic TSHR antibodies, detected by inhibition of TSH binding to the TSHR, only developed in back-cross offspring bearing the Lo-expressor, but not the Hi-expressor, transgene. High versus low expression human TSHR A-subunit in the NOD.H2^h4 thymus was not explained by the transgene locations, namely chromosome 2 (127-147 Mb; Hi-expressor) and chromosome 1 (22.9-39.3 Mb; low expressor). Nevertheless, using thyroiditis-prone NOD.H2^h4 mice and two transgenic lines, our data support the association from human studies that low intrathymic TSHR expression is associated with susceptibility to developing pathogenic TSHR antibodies, while high intrathymic TSHR expression is protective.

Critical Differences between Induced and Spontaneous Mouse Models of Graves' Disease with Implications for Antigen-Specific Immunotherapy in Humans

Graves' hyperthyroidism, a common autoimmune disease caused by pathogenic autoantibodies to the thyrotropin (TSH) receptor (TSHR), can be treated but not cured. This single autoantigenic target makes Graves' disease a prime candidate for Ag-specific immunotherapy. Previously, in an induced mouse model, injecting TSHR A-subunit protein attenuated hyperthyroidism by diverting pathogenic TSHR Abs to a nonfunctional variety. In this study, we explored the possibility of a similar diversion in a mouse model that spontaneously develops pathogenic TSHR autoantibodies, NOD.H2^h4 mice with the human (h) TSHR (hTSHR) A-subunit transgene expressed in the thyroid and (shown in this article) the thymus. We hypothesized that such diversion would occur after injection of "inactive" hTSHR A-subunit protein recognized only by nonpathogenic (not pathogenic) TSHR Abs. Surprisingly, rather than attenuating the pre-existing pathogenic TSHR level, in TSHR/NOD.H2^h4 mice inactive hTSHR Ag injected without adjuvant enhanced the levels of pathogenic TSH-binding inhibition and thyroid-stimulating Abs, as well as nonpathogenic Abs detected by ELISA. This effect was TSHR specific because spontaneously occurring autoantibodies to thyroglobulin and thyroid peroxidase were unaffected. As controls, nontransgenic NOD.H2^h4 mice similarly injected with inactive hTSHR A-subunit protein unexpectedly developed TSHR Abs, but only of the nonpathogenic variety detected by ELISA. Our observations highlight critical differences between induced and spontaneous mouse models of Graves' disease with implications for potential immunotherapy in humans. In hTSHR/NOD.H2^h4 mice with ongoing disease, injecting inactive hTSHR A-subunit protein fails to divert the autoantibody response to a nonpathogenic form. Indeed, such therapy is likely to enhance pathogenic Ab production and exacerbate Graves' disease in humans.

Overexpression of Interleukin-4 in the Thyroid of Transgenic Mice Upregulates the Expression of Duox1 and the Anion Transporter Pendrin

BACKGROUND

The dual oxidases (Duox) are involved in hydrogen peroxide generation, which is essential for thyroid hormone synthesis, and therefore they are markers of thyroid function. During inflammation, cytokines upregulate DUOX gene expression in the airway and the intestine, suggesting a role for these proteins in innate immunity. It was previously demonstrated that interleukin-4 (IL-4) upregulates DUOX gene expression in thyrocytes. Although the role of IL-4 in autoimmune thyroid diseases has been studied extensively, the effects of IL-4 on thyroid physiology remain largely unknown. Therefore, a new animal model was generated to study the impact of IL-4 on thyroid function.

METHODS

Transgenic (Thyr-IL-4) mice with thyroid-targeted expression of murine IL-4 were generated. Transgene expression was verified at the mRNA and protein level in thyroid tissues and primary cultures. The phenotype of the Thyr-IL-4 animals was characterized by measuring serum thyroxine (T4) and thyrotropin levels and performing thyroid morphometric analysis, immunohistochemistry, whole transcriptome sequencing, quantitative reverse transcription polymerase chain reaction, and ex vivo thyroid function assays.

RESULTS

Thyrocytes from two Thyr-IL-4 mouse lines (#30 and #52) expressed IL-4, which was secreted into the extracellular space. Although 10-month-old transgenic animals had T4 and thyrotropin serum levels in the normal range, they had altered thyroid follicular structure with enlarged follicles composed of elongated thyrocytes containing numerous endocytic vesicles. These follicles were positive for T4 staining the colloid, indicating their capacity to produce thyroid hormones. RNA profiling of Thyr-IL-4 thyroid samples revealed modulation of multiple genes involved in inflammation, while no major leukocyte infiltration could be detected. Upregulated expression of Duox1, Duoxa1, and the pendrin anion exchanger gene (Slc26a4) was detected. In contrast, the iodide symporter gene Slc5a5 was markedly downregulated resulting in impaired iodide uptake and reduced thyroid hormone levels in transgenic thyroid tissue. Hydrogen peroxide production was increased in Thyr-IL-4 thyroid tissue compared with wild-type animals, but no significant oxidative stress could be detected.

CONCLUSIONS

This is the first study to show that ectopic expression of IL-4 in thyroid tissue upregulates Duox1/Duoxa1 and Slc26a4 expression in the thyroid. The present data demonstrate that IL-4 could affect thyroid morphology and function, mainly by downregulating Slc5a5 expression, while maintaining a normal euthyroid phenotype.

New Murine Model of Early Onset Autoimmune Thyroid Disease/Hypothyroidism and Autoimmune Exocrinopathy of the Salivary Gland

Sixty to seventy percent of IFN-γ(-/-) NOD.H-2h4 mice given sodium iodide (NaI)-supplemented water develop a slow onset autoimmune thyroid disease, characterized by thyrocyte epithelial cell (TEC) hyperplasia and proliferation (H/P). TEC H/P develops much earlier in CD28(-/-) mice and nearly 100% (both sexes) have severe TEC H/P at 4 mo of age. Without NaI supplementation, 50% of 5- to 6-mo-old CD28(-/-)IFN-γ(-/-) mice develop severe TEC H/P, and 2-3 wk of NaI is sufficient for optimal development of severe TEC H/P. Mice with severe TEC H/P are hypothyroid, and normalization of serum thyroxine levels does not reduce TEC H/P. Activated CD4(+) T cells are sufficient to transfer TEC H/P to SCID recipients. Thyroids of mice with TEC H/P have infiltrating T cells and expanded numbers of proliferating thyrocytes that highly express CD40. CD40 facilitates, but is not required for, development of severe TEC H/P, as CD40(-/-)IFN-γ(-/-)CD28(-/-) mice develop severe TEC H/P. Accelerated development of TEC H/P in IFN-γ(-/-)CD28(-/-) mice is a result of reduced regulatory T cell (Treg) numbers, as CD28(-/-) mice have significantly fewer Tregs, and transfer of CD28(+) Tregs inhibits TEC H/P. Essentially all female IFN-γ(-/-)CD28(-/-) NOD.H-2h4 mice have substantial lymphocytic infiltration of salivary glands and reduced salivary flow by 6 mo of age, thereby providing an excellent new model of autoimmune exocrinopathy of the salivary gland. This is one of very few models where autoimmune thyroid disease and hypothyroidism develop in most mice by 4 mo of age. This model will be useful for studying the effects of hypothyroidism on multiple organ systems.

TSH Receptor Cleavage Into Subunits and Shedding of the A-Subunit; A Molecular and Clinical Perspective

The TSH receptor (TSHR) on the surface of thyrocytes is unique among the glycoprotein hormone receptors in comprising two subunits: an extracellular A-subunit, and a largely transmembrane and cytosolic B-subunit. Unlike its ligand TSH, whose subunits are encoded by two genes, the TSHR is expressed as a single polypeptide that subsequently undergoes intramolecular cleavage into disulfide-linked subunits. Cleavage is associated with removal of a C-peptide region, a mechanism similar in some respects to insulin cleavage into disulfide linked A- and B-subunits with loss of a C-peptide region. The potential pathophysiological importance of TSHR cleavage into A- and B-subunits is that some A-subunits are shed from the cell surface. Considerable experimental evidence supports the concept that A-subunit shedding in genetically susceptible individuals is a factor contributing to the induction and/or affinity maturation of pathogenic thyroid-stimulating autoantibodies, the direct cause of Graves' disease. The noncleaving gonadotropin receptors are not associated with autoantibodies that induce a "Graves' disease of the gonads." We also review herein current information on the location of the cleavage sites, the enzyme(s) responsible for cleavage, the mechanism by which A-subunits are shed, and the effects of cleavage on receptor signaling.

Withdrawn: TSH Receptor Cleavage Into Subunits and Shedding of the A-Subunit; A Molecular and Clinical Perspective

The TSH receptor (TSHR) on the surface of thyrocytes is unique among the glycoprotein hormone receptors in comprising two subunits: an extracellular A-subunit, and a largely transmembrane and cytosolic B-subunit. Unlike its ligand TSH, whose subunits are encoded by two genes, the TSHR is expressed as a single polypeptide that subsequently undergoes intramolecular cleavage into disulfide-linked subunits. Cleavage is associated with removal of a C-peptide region, a mechanism similar in some respects to insulin cleavage into disulfide linked A- and B-subunits with lossofaC-peptideregion. The potential pathophysiological importance of TSHR cleavage into A-and B-subunits is that some A-subunits are shed from the cell surface. Considerable experimental evidence supports the concept that A-subunit shedding in genetically susceptible individuals is a factor contributing to the induction and/or affinity maturation of pathogenic thyroid-stimulating autoantibodies, the direct cause of Graves' disease. The noncleaving gonadotropin receptors are not associated with autoantibodies that induce a "Graves' disease of the gonads." We also review herein current information on the location of the cleavage sites, the enzyme(s) responsible for cleavage, the mechanism by which A-subunits are shed, and the effects of cleavage on receptor signaling. (Endocrine Reviews 37: 114-134, 2016).

Thyrotropin Receptor Epitope and Human Leukocyte Antigen in Graves' Disease

Graves' disease (GD) is an organ-specific autoimmune disease, and thyrotropin (TSH) receptor (TSHR) is a major autoantigen in this condition. Since the extracellular domain of human TSHR (TSHR-ECD) is shed into the circulation, TSHR-ECD is a preferentially immunogenic portion of TSHR. Both genetic factors and environmental factors contribute to development of GD. Inheritance of human leukocyte antigen (HLA) genes, especially HLA-DR3, is associated with GD. TSHR-ECD protein is endocytosed into antigen-presenting cells (APCs), and processed to TSHR-ECD peptides. These peptide epitopes bind to HLA-class II molecules, and subsequently the complex of HLA-class II and TSHR-ECD epitope is presented to CD4+ T cells. The activated CD4+ T cells secrete cytokines/chemokines that stimulate B-cells to produce TSAb, and in turn hyperthyroidism occurs. Numerous studies have been done to identify T- and B-cell epitopes in TSHR-ECD, including (1) in silico, (2) in vitro, (3) in vivo, and (4) clinical experiments. Murine models of GD and HLA-transgenic mice have played a pivotal role in elucidating the immunological mechanisms. To date, linear or conformational epitopes of TSHR-ECD, as well as the molecular structure of the epitope-binding groove in HLA-DR, were reported to be related to the pathogenesis in GD. Dysfunction of central tolerance in the thymus, or in peripheral tolerance, such as regulatory T cells, could allow development of GD. Novel treatments using TSHR antagonists or mutated TSHR peptides have been reported to be effective. We review and update the role of immunogenic TSHR epitopes and HLA in GD, and offer perspectives on TSHR epitope specific treatments.

Evidence that TSH Receptor A-Subunit Multimers, Not Monomers, Drive Antibody Affinity Maturation in Graves' Disease

CONTEXT

The TSH receptor (TSHR) A-subunit shed from the cell surface contributes to the induction and/or affinity maturation of pathogenic TSHR autoantibodies in Graves' disease.

OBJECTIVE

This study aimed to determine whether the quaternary structure (multimerization) of shed A-subunits influences pathogenic TSHR autoantibody generation.

DESIGN

The isolated TSHR A-subunit generated by transfected mammalian cells exists in two forms; one (active) is recognized only by Graves' TSHR autoantibodies, the second (inactive) is recognized only by mouse monoclonal antibody (mAb) 3BD10. Recent evidence suggests that both Graves' TSHR autoantibodies and mAb 3BD10 recognize the A-subunit monomer. Therefore, if the A-subunit monomer is an immunogen, Graves' sera should have antibodies to both active and inactive A-subunits. Conversely, restriction of TSHR autoantibodies to active A-subunits would be evidence of a role for shed A-subunit multimers, not monomers, in the pathogenesis of Graves' disease. Therefore, we tested a panel of Graves' sera for their relative recognition of active and inactive A-subunits.

RESULTS

Of 34 sera from unselected Graves' patients, 28 were unequivocally positive in a clinical TSH binding inhibition assay. None of the latter sera, as well as 8/9 sera from control individuals, recognized inactive A-subunits on ELISA. In contrast to Graves' sera, antibodies induced in mice, not by shedding from the TSHR holoreceptor, but by immunization with adenovirus expressing the free human A-subunit, were directed to both the active and inactive A-subunit forms.

CONCLUSIONS

The present study supports the concept that pathogenic TSHR autoantibody affinity maturation in Graves' disease is driven by A-subunit multimers, not monomers.