Signal responses to neutral TSH receptor antibody - A cycle of damage in the pathophysiology of Graves' disease

BACKGROUND

Graves' disease is associated with TSH receptor (TSHR) antibodies of variable bioactivity including "neutral" antibodies (N-TSHR-Ab) that bind to the hinge region of the TSHR ectodomain. We have previously found that such antibodies induced thyroid cell apoptosis via excessive mitochondrial and ER stress with elevated reactive oxygen species (ROS). However, the detailed mechanisms by which excess ROS was induced remained unclear.

OBJECTIVES

To determine how ROS is induced by N-TSHR-monoclonal antibodies (mAb, MC1) mediated signaling and to measure stress in polyorganelles.

METHODS

Total ROS and mitochondrial ROS was measured by fluorometry of live rat thyrocytes. Live-cell imaging of labelled organelles was carried out using red or green fluorescent dyes. Proteins were detected by Li-Cor Western immunoblots and immunocytochemistry.

RESULTS

Endocytosis of N-TSHR-mAb induced ROS, disturbed vesicular trafficking, damaged organelles and failed to induce lysosomal degradation and autophagy. We found that the endocytosis triggered signaling cascades involving Gα13 and PKC-δ leading to intrinsic thyroid cell apoptosis.

CONCLUSIONS

These studies define the mechanism of ROS induction in thyroid cells following the endocytosis of N-TSHR-Ab/TSHR complexes. We suggest that a viscous cycle of stress initiated by cellular ROS and induced by N-TSHR-mAbs may orchestrate overt intra-thyroidal, retro-orbital, and intra-dermal inflammatory autoimmune reactions in patients with Graves' disease.

Epigenetic Changes During Human Thyroid Cell Differentiation

Objective: It has been demonstrated that the transcription factors TAZ (transcriptional coactivator with PDZ-binding motif), paired box gene 8 (PAX8), and NK2 homeobox 1 (NKX2-1) are coexpressed in the nucleus of thyroid cells. Furthermore, TAZ is known to enhance the transcriptional activity of PAX8 and NKX2-1 as well as the key thyroid-specific gene, thyroglobulin (TG), suggesting a critical role for TAZ in the control of thyroid cell speciation. We previously reported that the small molecule ethacridine, identified as a TAZ activator, was able to induce thyroid-specific transcription in endodermal cells differentiated from human embryonic stem (hES) cells using activin A. Since transcription factors are epigenetically regulated in cell differentiation, we investigated the epigenetic changes in the promoter regions of these key transcription factors during in vitro differentiation of hES cells into thyrocytes. Methods: We initially profiled chromatin accessibility using the technique of Assay for Transposase Accessible Chromatin sequencing (ATAC-seq), and then examined DNA methylation and histone acetylation in the promoter regions of the three selected thyroid transcription factors and the thyroid-specific genes during hES cell differentiation. Results: ATAC-seq analysis showed enriched chromatin accessibility of TAZ, NKX2-1, and PAX8 after exposure to activin A and ethacridine. There were no methylation changes found in the NKX2-1, PAX8, and TAZ promoters by bisulfite sequencing. In contrast, acetylation of histone H4, specifically acetylation of lysine 16, was observed in each of the promoters when measured by chromatin immunoprecipitation polymerase chain reaction assays, which correlated with the activity and expression of NKX2-1 and PAX8 as well as sodium/iodide symporter, thyroid stimulating hormone receptor, and TG genes. Conclusions: These results indicate that ethacridine treatment of activin A-derived endodermal hES cells leads to enhanced chromatin accessibility, which, in turn, allows histone H4 acetylation in the regulation of active genes for speciation of thyroid follicular cells from hES cells.

OR10-2 A Modifying Autoantigen in Graves' Disease

In patients with Graves’ disease (GD), previous studies have associated SNPs in linkage disequilibrium with the TSHR gene locus with changes in expression of two TSH receptor (TSHR) variants suggesting that receptor variants may have an important role in disease etiology. Bioinformatic analyses predicts the existence of several human TSHR isoforms from alternative splicing and the most abundant is the previously described splice variant, TSHR-v1.3. In-silico modeling of TSHR v1.3 confirmed the potential binding of TSH and TSHR autoantibody to the v1.3 protein indicating its potential as an autoantigen and pseudoreceptor. To further characterize the bioactivity of v1.3 we engineered the protein by cloning the entire ORF into a mammalian expression vector. The purified protein was obtained from cell lysate by Ni-affinity chromatography. Immunoprecipitation demonstrated that both TSHR stimulating monoclonal antibody (MS1) and human recombinant TSH were able to bind TSHR v1.3 recombinant protein as predicted by the in-silico studies. TSHR-v1.3 was also able to inhibit the effect of TSH and MS-1 on cAMP generation in a dose-dependent manner. These observations confirmed the ability of purified TSHR-v1.3 protein to interact with TSH and autoantibody and modulate their activity. Using purified IgG fractions from sera of 13 patients with GD with known TSHR antibodies we also looked for TSHR-v1.3 autoantibodies. We used a peptide based ELISA against two different epitopes of the splice variant. 11 out 13 (84.6%) of the GD samples were positive for a carboxy terminal peptide (COOH) and 10 out of 13 (76.9%) were positive to a junction region peptide (JNX). A dose-dependent bocking of signal was observed in the GD samples using the specific peptide. To detemine if the truncated isoform of the receptor could serve as a potential source of antigen and modulate GD we used double transfected cells expressing both GFP tagged TSHR-v1.3 and full-length TSHR. We then induced cell stress and apoptosis using a TSHR-mAb directed to the cleavage region (Tab16) and observed a dose dependent increase in mitochondrial cell stress and increased apoptosis (viability <46%) compared to control isotype specific antibody treated or untreated cells (74/71% viability).The culture supernatant contained released V1.3 tagged GFP protein suggesting that release of a new TSHR receptor antigen by this mechanism could play an important role in modulation of the disease process. These data show that a TSHR isoform that is expressed by alternative splicing can have a duel role by acting as a potential competitor for TSHR autoantibody and TSH itself and also as a likely source of autoantigen. Therefore, expression of such altered receptor protein within tissue depots has the potential to modulate thyroid autoimmunity by serving as an alternative intracellular antigen after apoptosis of thyroid cells.

mRNA-Seq reveals novel molecular mechanisms and a robust fingerprint in Graves' disease

CONTEXT

The immune response in autoimmune thyroid disease has been shown to occur primarily within the thyroid gland in which the most abundant antigens can be found. A variety of capture molecules are known to be expressed by thyroid epithelial cells and serve to attract and help retain an intrathyroidal immune infiltrate.

OBJECTIVE

To explore the entire repertoire of expressed genes in human thyroid tissue, we have deep sequenced the transcriptome (referred to as mRNA-Seq).

DESIGN AND PATIENTS

We applied mRNA-Seq to thyroid tissue from nine patients with Graves' disease subjected to total thyroidectomy and compared the data with 12 samples of normal thyroid tissue obtained from patients having a thyroid nodule removed. The expression for each gene was calculated from the sequencing data by taking the median of the coverage across the length of the gene. The expression levels were quantile normalized and a gene signature was derived from these.

RESULTS

On comparison of expression levels in tissues derived from Graves' patients and controls, there was clear evidence for overexpression of the antigen presentation pathway consisting of HLA and associated genes. We also found a robust disease signature and discovered active innate and adaptive immune signaling networks.

CONCLUSIONS

These data reveal an active immune defense system in Graves' disease, which involves novel molecular mechanisms in its pathogenesis and development.

The influence of thyroid-stimulating hormone and thyroid-stimulating hormone receptor antibodies on osteoclastogenesis

BACKGROUND

We have shown that thyroid-stimulating hormone (TSH) has a direct inhibitory effect on osteoclastic bone resorption and that TSH receptor (TSHR) null mice display osteoporosis. To determine the stage of osteoclast development at which TSH may exert its effect, we examined the influence of TSH and agonist TSHR antibodies (TSHR-Ab) on osteoclast differentiation from murine embryonic stem (ES) cells to gain insight into bone remodeling in hyperthyroid Graves' disease.

METHODS

Osteoclast differentiation was initiated in murine ES cell cultures through exposure to macrophage colony stimulation factor, receptor activator of nuclear factor кB ligand, vitamin D, and dexamethasone.

RESULTS

Tartrate resistant acid phosphatase (TRAP)-positive osteoclasts formed in ~12 days. This coincided with the expected downregulation of known markers of self renewal and pluripotency (including Oct4, Sox2, and REX1). Both TSH and TSHR-Abs inhibited osteoclastogenesis as evidenced by decreased development of TRAP-positive cells (~40%-50% reduction, p = 0.0047), and by decreased expression, in a concentration-dependent manner, of osteoclast differentiation markers (including the calcitonin receptor, TRAP, cathepsin K, matrix metallo-proteinase-9, and carbonic anhydrase II). Similar data were obtained using serum immunoglobulin-Gs (IgGs) from patients with hyperthyroid Graves' disease and known TSHR-Abs. TSHR stimulators inhibited tumor necrosis factor-alpha mRNA and protein expression, but increased the expression of osteoprotegerin (OPG), an antiosteoclastogenic human soluble receptor activator of nuclear factor кB ligand receptor. Neutralizing antibody to OPG reversed the inhibitory effect of TSH on osteoclast differentiation evidencing that the TSH effect was at least in part mediated by increased OPG.

CONCLUSION

These data establish ES-derived osteoclastogenesis as an effective model system to study the regulation of osteoclast differentiation in early development. The results support the observations that TSH has a bone protective action by negatively regulating osteoclastogenesis. Further, our results implicate TSHR-Abs in offering skeletal protection in hyperthyroid Graves' disease, even in the face of high thyroid hormone and low TSH levels.

Are extreme distal periprosthetic supracondylar fractures of the femur too distal to fix using a lateral locked plate?

It is unclear whether there is a limit to the amount of distal bone required to support fixation of supracondylar periprosthetic femoral fractures. This retrospective multicentre study evaluated lateral locked plating of periprosthetic supracondylar femoral fractures and compared the results according to extension of the fracture distal with the proximal border of the femoral prosthetic component. Between 1999 and 2008, 89 patients underwent lateral locked plating of a supracondylar periprosthetic femoral fracture, of whom 61 patients with a mean age of 72 years (42 to 96) comprising 53 women, were available after a minimum follow-up of six months or until fracture healing. Patients were grouped into those with fractures located proximally (28) and those with fractures that extended distal to the proximal border of the femoral component (33). Delayed healing and nonunion occurred respectively in five (18%) and three (11%) of more proximal fractures, and in two (6%) and five (15%) of the fractures with distal extension (p = 0.23 for delayed healing; p = 0.72 for nonunion, Fisher's exact test). Four construct failures (14%) occurred in more proximal fractures, and three (9%) in fractures with distal extension (p = 0.51). Of the two deep infections that occurred in each group, one resolved after surgical debridement and antibiotics, and one progressed to a nonunion. Extreme distal periprosthetic supracondylar fractures of the femur are not a contra-indication to lateral locked plating. These fractures can be managed with internal fixation, with predictable results, similar to those seen in more proximal fractures.

Pulse propagation and electron acceleration in a corrugated plasma channel

A preformed plasma channel provides a guiding structure for laser pulses unbound by the intensity thresholds of standard waveguides. The recently realized corrugated plasma channel [Layer, Phys. Rev. Lett. 99, 035001 (2007)] allows for the guiding of laser pulses with subluminal spatial harmonics. These spatial harmonics can be phase matched to high energy electrons, making the corrugated plasma channel ideal for the acceleration of electrons. We present a simple analytic model of pulse propagation in a corrugated plasma channel and examine the laser-electron beam interaction. Simulations show accelerating gradients of several hundred MeV/cm for laser powers much lower than required by standard laser wakefield schemes.

Microinfusion of antineuronal antibodies into rodent striatum: failure to differentiate between elevated and low titers

An autoimmune-mediated mechanism has been proposed for several pediatric movement disorders. In a three-center (Brown, Yale, and Johns Hopkins) collaborative effort, serum antineuronal antibodies (ANAb) were measured by use of ELISA or immunohistochemical techniques on 35 children (mean age 11.4 years) with Tourette syndrome, attention deficit hyperactivity disorder, and/or obsessive compulsive disorder. Eight sera, 4 containing the highest and 4 the lowest levels of ANAb, were identified at each institution. Selected sera (total of 9 with elevated and 7 with low ANAb) were re-encoded and sent to each center for infusion into the ventrolateral striatum of 16 male Sprague-Dawley rats. Animals were observed for behavioral abnormalities for 3 days before the start of infusion, during infusion on days 2-4, and for 2 days after infusion. Combined stereotypy scores increased after antibody infusion, but there was no significant effect based on serum titer (p=0.85). Scores differed among centers, but analyses based on individual institutional data again failed to show an effect based on elevated or low ANAb values (Brown, p=0.95; Yale and Johns Hopkins, p=0.81). Post hoc studies with sham surgery and infusion of phosphate-buffered saline support suggestions of nonspecific behavioral effects unrelated to antibody titer. This report emphasizes that any conclusions about antibody-mediated movement disorders that are based upon results from the rodent infusion model must be considered with caution.

Increased serum levels of interleukin-12 and tumor necrosis factor-alpha in Tourette's syndrome

BACKGROUND

The hypothesis that common infections can modulate the onset and course of tic disorders and early-onset obsessive-compulsive disorder (OCD) in pediatric populations is longstanding. To date, most investigations have focused on the hypothesis of molecular mimicry and humoral immune responses. This study was carried out to investigate whether cytokines associated with the innate immune response or T cell activation were altered under baseline conditions and during periods of symptom exacerbation.

METHODS

Forty-six patients with Tourette's syndrome and/or early-onset OCD, aged 7-17 years, and 31 age-matched control subjects participated in a prospective longitudinal study. Ratings of clinical severity and serum were collected at regular intervals, and serum concentrations of 10 cytokines were measured repeatedly.

RESULTS

Interleukin-12 and tumor necrosis factor alpha concentrations at baseline were elevated in patients compared with control subjects. Both of these markers were further increased during periods of symptom exacerbation.

CONCLUSIONS

These findings suggest that symptom exacerbations are associated with an inflammatory process propagated by systemic and local cytokine synthesis that might involve the central nervous system. We conclude that, in the future, longitudinal studies of children with neuropsychiatric disorders should examine the involvement of innate and T cell immunity.