Current insights into animal models of Graves' disease and orbitopathy.

Graves' disease (GD) is a systemic autoimmune disease that is characterized by hyperthyroidism, orbitopathy and in rare cases dermopathy. Graves' orbitopathy (GO) is an inflammatory disease of eye and orbit which occurs in about 30-60% of patients. Hyperthyroidism occurs due to the presence of stimulating TSHR-autoantibodies (TRAbs) leading to increased serum levels of thyroid hormones. Attempts to induce Graves' disease in mice by immunization against the hTSHR or its variants have resulted in production of TRAbs that stimulate thyroid follicular cells to increase thyroid hormone secretion. Graves' like orbital changes, such as inflammation, adipogenesis and muscle fibrosis are more difficult to induce. In this review we summarize different methods used to induce murine Graves'-like disease and their impact on murine orbits.

Examination of orbital tissues in murine models of Graves' disease reveals expression of UCP-1 and the TSHR in retrobulbar adipose tissues.

Over the past decade a number of murine models of Graves' disease (GD) have been described. The full symptom complex, including typical orbital changes, however, could not yet be induced. In this report, we examined the influence of modified immunization protocols on orbital pathology. C57BL/6 and BALB/c mice were immunized against the human TSH receptor (TSHR), using either a TSHR encoding plasmid or a TSHR A-subunit adenovirus. Prior to immunization with the TSHR plasmid, regulatory T cells were depleted in one group of each strain. TSHR-stimulating antibodies (TSAbs) were evaluated and orbits were stained immunohistochemically for F4/80, uncoupling protein-1 (UCP-1) and the TSHR. We found that after depletion of regulatory T cells, incidence of TSAb was increased in TSHR plasmid immunized C57BL/6 mice. Examination of early immunized mice showed no antibody production. However, a TSHR epitope-specific cellular immune response could be detected by tetramer-analyses. Adenoviral immunization lead to TSAb production in all but one animal. Analysis of F4/80 positive cells in retrobulbar fat revealed no significant macrophage infiltration in the orbits of immunized mice. Immunohistochemical staining shows co-localization of F4/80 positive cells, UCP-1 and the TSHR in retrobulbar fat. Though targets for TSHR autoimmunity could clearly be shown, immunization methods were not efficient enough to cause clear signs of orbital inflammation.

The T393C polymorphism of the Galphas gene (GNAS1) is associated with the course of Graves' disease.

Genotypes of the T393C SNP of GNAS1, a gene that encodes for the Galphas subunit of G proteins have been significantly associated with the clinical course in a variety of cancers. Since this SNP may also influence the course of Graves' disease (GD) and, especially, Graves' ophthalmopathy (GO), we determined genotype and allele frequency in a series of 359 patients, which were referred to our clinic within 6 months of the onset of GO. Among them, 336 patients also suffered from associated hyperthyroidism. Data on relapse and remission rates 12 months after termination of a 1 year antithyroid drug therapy was available for 276 patients. As controls, 820 healthy individuals were recruited. Our data suggest that the T393C SNP does not represent a risk factor for the development of both GD and GO. It was, however, significantly associated with the course of hyperthyroidism (p=0.013) and a similar trend was evident for the course of GO (p=0.093). Homozygous TT carriers showed a significantly increased risk (p=0.03) for hyperthyroidism to relapse (OR 2.4; 95% CI 1.1-5.4). Also, the TT genotype was associated with significantly increased serum TRAb levels (CC+CT: 5.4 IU/l vs. TT: 9.3 IU/l). This is probably caused by increased G-Protein susceptibility to TSHR-mediated stimulation through TRAb. Genotyping of the T393C SNP of GNAS1 may become a useful additional tool to predict the clinical course of GD and GO. This may allow the clinician to identify patients at risk for more severe courses of disease and to come to more timely decisions for treatment.

Current insights into the pathogenesis of Graves' orbitopathy.

Graves' orbitopathy (GO) is part of an autoimmune disease constellation comprising hyperthyroidism, orbitopathy, pretibial myxedema, and acropachy. Signs and symptoms of GO occur due to inflammation of the orbital connective tissue, inflammation and fibrosis of the extraocular muscles, and adipogenesis. Stimulatory TSH receptor (TSHR) antibodies (TRAb) cause hyperthyroidism, but pathogenetic mechanisms in the orbit are less clear. The TSHR is one of the favoured candidate antigens; others such as the IGF1R might also play a role. Compared with other anatomical locations, orbital fibroblasts are extremely reactive to inflammatory stimuli, especially via CD40 activation. Orbital fibroblasts also differentiate into adipocytes, in response to the prevailing inflammatory cytokine milieu. Consequently TSHR gene expression increases together with expression of adipogenesis related genes. The same genes that confer susceptibility to Graves' disease (GD), both thyroid specific and immunoregulatory, also influence GO, although an increasing number of candidate genes with higher impact on orbitopathy are being identified. Smoking is the only environmental factor known to increase the likelihood and severity of GO developing in GD patients. A robust animal model of GO would facilitate the evaluation of new treatments. To date most models have centered on provoking autoimmune responses to the TSHR, but other antigens, alone or in combination with this receptor, hopefully will succeed in inducing the full spectrum of GD.

Adenoviral p53 gene transfer inhibits human Tenon's capsule fibroblast proliferation.

BACKGROUND/AIM: Although antiproliferative drugs have been used successfully to prevent scarring after filtration surgery in patients with glaucoma, complications associated with their use (such as hypotony or endophthalmitis) energise the search for an alternative treatment. Single application of beta radiation leads to long term growth arrest and expression of p53 in human Tenon's capsule fibroblasts (hTf). The authors assume that the activation of p53 is one of the cellular triggers. Their aim was to analyse the effect of p53 overexpression on hTf and to determine which pathways are involved. METHODS: A recombinant adenoviral vector (rAd.p53) containing transgenes encoding for human p53 and green fluorescent protein (GFP) was used to induce overexpression of p53 in hTF and a control vector (rAd.GFP). Transgene expression was detected by western blot (p53 and p21WAF-1/Cip1). Cell proliferation and viability were investigated using cell counts, 5'-bromodeoxyuridine incorporation (BrdU assay) and tetrazolium reduction (MTT assay). RESULTS: Infection of hTf with rAd.p53 resulted in significant inhibition of cell proliferation, DNA synthesis, and metabolic activity in vitro. Western blot showed increased levels of p53 and p21WAF-1/Cip1 in rAd.p53 infected cells, but not in rAd.GFP and uninfected cells. Apoptosis was excluded with flow cytometry. CONCLUSIONS: Adenoviral p53 gene transfer leads to significant growth inhibition in hTf. P53 induces p21(WAF-1/Cip1) expression and does not cause apoptosis in hTf in vitro. p53 as an antiproliferative drug has the potential to replace mitomycin C and 5-fluorouracil in glaucoma surgery.