An animal model of Graves' disease: understanding the cause of autoimmune hyperthyroidism

Peptidomic profiling of endogenous peptides in the spleens of mouse models of Graves' disease

Background

Graves' disease (GD) is a common autoimmune thyroid disorder. The pathogenesis of GD involves an autoimmune response to the A subunit of the human thyrotropin receptor (hTSHR), although the specific mechanisms are not fully elucidated.

Methods

This study established a GD model by immunizing BALB/c mice with a recombinant adenovirus expressing the hTSHR A subunit. Spleen tissues were collected and analyzed using liquid chromatography-tandem mass spectrometry (LC-MS/MS) to identify differentially expressed peptides (DEPs). Gene Ontology (GO) analysis and KEGG pathway analysis were further utilized to annotate the functions of these DEPs. Additionally, peptide bioactivity prediction and molecular docking studies were conducted using Alphafold and Pymol software, respectively, to assess the binding affinity of specific peptides to the hTSHR A subunit.

Results

The GD mouse model was successfully established, and 1,428 DEPs were identified in the spleen, with 368 upregulated and 1,060 downregulated. Functional analysis indicated that these DEPs are mainly involved in cellular endocytosis, regulation of gene expression, and nucleocytoplasmic transport. Notably, molecular docking studies revealed that the abnormally highly expressed peptide HG2A-24aa demonstrated potential bioactivity and strong binding affinity with hTSHR-289aa.

Conclusion

The specific bioactive peptides may play key roles in the pathogenesis of GD, particularly HG2A-24aa, which may have a significant role in the MHC II antigen presentation pathway mediated by the hTSHR A subunit.

Surface-assembled poly(I:C) on PEGylated PLGA microspheres as vaccine adjuvant: APC activation and bystander cell stimulation

Biodegradable poly(lactic-co-glycolic acid) (PLGA) microspheres are potential vehicles to deliver antigens for vaccination. Because they lack the full capacity to activate professional antigen presenting cells (APCs), combination with an immunostimulatory adjuvant may be considered. A candidate is the synthetic TLR3 ligand polyriboinosinic acid-polyribocytidylic acid, poly(I:C), which drives cell-mediated immunity. However, poly(I:C) has also been linked to the pathogenesis of autoimmunity, as affected by widespread stimulation of non-hematopoietic bystander cells. To address this aspect, we propose to minimize the poly(I:C) dose as well as to control the stimulation of non-immune bystander cells by poly(I:C). To facilitate the maturation of APCs with minimal poly(I:C) doses, we surface-assembled poly(I:C) onto PLGA microspheres. The microspheres' surface was further modified by poly(ethylene glycol) (PEG) coronas with varying PEG-densities. PLGA microspheres loaded with tetanus toxoid (tt) as model antigen were manufactured by microextrusion-based solvent extraction. The negatively charged PLGA(tt) microspheres were coated with polycationic poly(l-lysine) (PLL) polymers, either PLL itself or PEG-grafted PLL (PLL-g-PEG) with varying grafting ratios (g=2.2 and g=10.1). Stable surface assembly of poly(I:C) was achieved by subsequent incubation of polymer-coated PLGA microspheres with aqueous poly(I:C) solutions. We evaluated the immunostimulatory potential of such PLGA(tt) microsphere formulations on monocyte-derived dendritic cells (MoDCs) as well as human foreskin fibroblasts (HFFs) as model for non-hematopoietic bystander cells. Formulations with surface-assembled poly(I:C) readily activated MoDCs with respect to the expression of maturation-related surface markers, proinflammatory cytokine secretion and directed migration. When surface-assembled, poly(I:C) enhanced its immunostimulatory activity by more than one order of magnitude as compared to free poly(I:C). On fibroblasts, surface-assembled poly(I:C) upregulated class I MHC but not class II MHC. Phagocytosis of PLGA(tt) microsphere formulations by MoDCs and HFFs remained mostly unaffected by PEG-grafted PLL coatings. In contrast, high concentrations of free poly(I:C) led to a marked drop of microsphere phagocytosis by HFFs. Overall, surface assembly on PEGylated PLGA microspheres holds promise to improve both efficacy and safety of poly(I:C) as vaccine adjuvant.

Particulate formulations for the delivery of poly(I:C) as vaccine adjuvant

Current research and development of antigens for vaccination often center on purified recombinant proteins, viral subunits, synthetic oligopeptides or oligosaccharides, most of them suffering from being poorly immunogenic and subject to degradation. Hence, they call for efficient delivery systems and potent immunostimulants, jointly denoted as adjuvants. Particulate delivery systems like emulsions, liposomes, nanoparticles and microspheres may provide protection from degradation and facilitate the co-formulation of both the antigen and the immunostimulant. Synthetic double-stranded (ds) RNA, such as polyriboinosinic acid-polyribocytidylic acid, poly(I:C), is a mimic of viral dsRNA and, as such, a promising immunostimulant candidate for vaccines directed against intracellular pathogens. Poly(I:C) signaling is primarily dependent on Toll-like receptor 3 (TLR3), and on melanoma differentiation-associated gene-5 (MDA-5), and strongly drives cell-mediated immunity and a potent type I interferon response. However, stability and toxicity issues so far prevented the clinical application of dsRNAs as they undergo rapid enzymatic degradation and bear the potential to trigger undue immune stimulation as well as autoimmune disorders. This review addresses these concerns and suggests strategies to improve the safety and efficacy of immunostimulatory dsRNA formulations. The focus is on technological means required to lower the necessary dosage of poly(I:C), to target surface-modified microspheres passively or actively to antigen-presenting cells (APCs), to control their interaction with non-professional phagocytes and to modulate the resulting cytokine secretion profile.

Surface assembly of poly(I:C) on PEGylated microspheres to shield from adverse interactions with fibroblasts

By expressing an array of pattern recognition receptors (PRRs), fibroblasts play an important role in stimulating and modulating the response of the innate immune system. The TLR3 ligand polyriboinosinic acid-polyribocytidylic acid, poly(I:C), a mimic of viral dsRNA, is a vaccine adjuvant candidate to activate professional antigen presenting cells (APCs). However, owing to its ligation with extracellular TLR3 on fibroblasts, subcutaneously administered poly(I:C) bears danger towards autoimmunity. It is thus in the interest of its clinical safety to deliver poly(I:C) in such a way that its activation of professional APCs is as efficacious as possible, whereas its interference with non-immune cells such as fibroblasts is controlled or even avoided. Complementary to our previous work with monocyte-derived dendritic cells (MoDCs), here we sought to control the delivery of poly(I:C) surface-assembled on microspheres to human foreskin fibroblasts (HFFs). Negatively charged polystyrene (PS) microspheres were equipped with a poly(ethylene glycol) (PEG) corona through electrostatically driven coatings with a series of polycationic poly(L-lysine)-graft-poly(ethylene glycol) copolymers, PLL-g-PEG, of varying grafting ratios g from 2.2 up to 22.7. Stable surface assembly of poly(I:C) was achieved by incubation of polymer-coated microspheres with aqueous poly(I:C) solutions. Notably, recognition of both surface-assembled and free poly(I:C) by extracellular TLR3 on HFFs halted their phagocytic activity. Ligation of surface-assembled poly(I:C) with extracellular TLR3 on HFFs could be controlled by tuning the grafting ratio g and thus the chain density of the PEG corona. When assembled on PLL-5.7-PEG-coated microspheres, poly(I:C) was blocked from triggering class I MHC molecule expression on HFFs. Secretion of interleukin (IL)-6 by HFFs after exposure to surface-assembled poly(I:C) was distinctly lower as compared to free poly(I:C). Overall, surface assembly of poly(I:C) may have potential to contribute to the clinical safety of this vaccine adjuvant candidate.

Role of macrophage infiltration in the orbital fat of patients with Graves' ophthalmopathy

OBJECTIVE

Infiltration of the retro-ocular space by inflammatory cells, accumulation of glycosaminoglycans, and the overabundance of orbital adipose tissue are characteristic findings in Graves' ophthalmopathy (GO). The cause of macrophage infiltration in the orbital adipose tissue of patients with GO remains to be elucidated.

DESIGN

Immunohistochemistry of orbital adipose tissues with anti-CD68 was used for determining macrophage infiltration pattern and cell counts. Quantitative real-time PCR was used for analysing mRNA expression. Correlation of macrophage infiltration with the duration of GO and mRNA expression were also determined.

PATIENTS

Fifteen subjects with GO who underwent orbital decompression were recruited. Six patients without thyroid history who underwent elective orbital surgery were enrolled as controls.

MEASUREMENTS

Histological distribution of macrophages, macrophage cell counts, CD68 and monocyte chemoattractant protein-1 (MCP-1) mRNA levels, and duration of GO.

RESULTS

We demonstrated that macrophage infiltration in orbital fat from patients with GO was higher than controls (P = 0.005). The infiltration of macrophages was located primarily around blood vessels and between mature adipocytes. Macrophage infiltration did not attenuate in GO of long duration. We also found that the expression of MCP-1 was higher in GO orbital fat than that in the orbital fat of controls (P = 0.047) and the infiltration of macrophages in adipose tissue from patients with GO was positively correlated with expression of MCP-1 mRNA (r = 0.546, P = 0.035).

CONCLUSION

Macrophage infiltration may play an important role in the pathogenesis of GO via over-expression of MCP-1.

Molecular pathology of Muller's muscle in Graves' ophthalmopathy

CONTEXT

Upper lid retraction is a common sign in Graves' ophthalmopathy (GO). Whether Müller's muscle is involved in upper lid retraction has not been fully elucidated.

OBJECTIVE

The objective of the study was to understand the molecular pathology of Müller's muscle in GO.

DESIGN/SETTING/PARTICIPANTS

A method for measurement of histological changes was developed and used to correlate severity and expression of cell-specific genes in GO.

MAIN OUTCOME MEASURES

Histological changes, clinical severity of upper lid retraction, and mRNA expression in Müller's muscle in GO were measured.

RESULTS

The degree of fibrosis correlates with severity of upper lid retraction. Macrophage infiltration was increased in fibrotic areas, consistent with higher levels of macrophage-colony stimulating factor mRNA. Levels of peroxisome proliferator-activated receptor-gamma mRNA were up-regulated and correlated with fat infiltration. Decreased muscle mass correlated with lower myocardin mRNA expression. The expression of c-kit levels was decreased in diseased muscles, consistent with diminished mast cell numbers.

CONCLUSION

The pathological changes of Müller's muscle correlate with clinical severity of upper lid retraction in GO. Patterns of gene expression appear to correlate with the histopathological changes in this disease process.

Th2-biased immune response in cervical lymph nodes: Animal models of Graves’ disease might administer autoantigen to body regions where lymphatics drain to cervical lymph nodes

It is believed that cervical lymph nodes have an important impact on Th2-biased immune response to central nervous system (CNS)-derived antigens. Obstruction of these nodes prior to a CNS-infusion of antigen markedly lowers the level of serum antibody response to the antigen. Graves' disease is a Th2-biased autoimmunity in which autoantibodies against thyrotropin receptor stimulate thyroid hormone production. The reasons for the distinct Th2-biased immune response in this hyperthyroidism are not fully understood, whereas most of the other human organ-specific autoimmune diseases are believed to be Th1 mediated. It is suggested that the drainage of the thyroid lymphatics to cervical lymph nodes may play a role in the Th2-polarized immune response of Graves' disease. Thus, the generation of Graves' disease models by immunization may become more feasible if animals are administered the autoantigen to body regions whose lymph is drained to cervical lymph nodes.

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.

CD1a expression in psoriatic skin following treatment with propylthiouracil, an antithyroid thioureylene

BACKGROUND

The antithyroid thioureylenes, propylthiouracil (PTU) and methimazole (MMI), are effective in the treatment of patients with plaque psoriasis. The mechanism of action of the drugs in psoriasis is unknown. Since the drugs reduce circulating IL-12 levels in patients with Graves' hyperthyroidism, the effect of propylthiouracil on CD1a expression in psoriatic lesions was examined in biopsy samples of patients with plaque psoriasis. CD1a is a marker of differentiated skin antigen presenting cells (APC, Langerhans cells). Langerhans cells and skin monocyte/macrophages are the source of IL-12, a key cytokine involved in the events that lead to formation of the psoriatic plaque.

METHODS

Biopsy specimens were obtained from six patients with plaque psoriasis who were treated with 300 mg propylthiouracil (PTU) daily for three months. Clinical response to PTU as assessed by PASI scores, histological changes after treatment, and CD1a expression in lesional skin before and after treatment were studied.

RESULTS

Despite significant improvement in clinical and histological parameters the expression of CD1a staining cells in the epidermis did not decline with propylthiouracil treatment.

CONCLUSIONS

It appears that the beneficial effect of propylthiouracil in psoriasis is mediated by mechanisms other than by depletion of skin antigen-presenting cells.

Transfection of single-stranded hepatitis A virus RNA activates MHC class I pathway

Although infection of single-stranded RNA viruses can enhance expression of major histocompatibility complex (MHC) class I genes, the mechanism underlying this process remains unclear. Recent studies have indicated that exposure of non-immune cells to double-stranded deoxyribonucleic acid (DNA) or ribonucleic acid (RNA) of viral origin can directly increase the expression of MHC class I and related molecules without immune cell interaction. In this report, we show that transfection of single-stranded hepatitis A virus RNA into cultured hepatocytes results in the induction of genes for MHC class I, LMP2 and transporter for antigen processing (TAP1), in addition to the generation of viral proteins. We suggest that this stimulatory effect is due to the double-stranded RNA formed during replication of single-stranded viral RNA, and involves both double-stranded, RNA-dependent protein kinase PKR and the secretion of IFNbeta.