Evidence for an association between thyroid-stimulating hormone and insulin-like growth factor 1 receptors: a tale of two antigens implicated in Graves' disease

Autoantibody against aldehyde dehydrogenase 2 could be a biomarker to monitor progression of Graves' orbitopathy

PURPOSE

This study surveyed the novel autoantigens expressed in the orbital fat tissue of patients with Graves' orbitopathy (GO) and explored the possibility of the autoantibodies against novel autoantigens as biomarkers for GO.

METHODS

We used immuno-proteomic methods to survey novel autoantigens expressed in the orbit fat tissue of GO patients and confirmed by enzyme-linked immunosorbent assay (ELISA).

RESULTS

One protein spot (aldehyde dehydrogenase 2 (ALDH2)) revealed high reactivity with the GO serum than did the healthy control serum and was further verified by ELISA. We found that the plasma anti-ALDH2 antibody level was increased in GO patients compared to healthy control donors. In addition, anti-ALDH2 antibody level was correlated with GO activity classified by clinical activity score(r = 0.588, p < 0.001, using Pearson's correlation).

CONCLUSIONS

These increased levels of anti-ALDH2 antibody in GO serum suggested that ALDH2 could attribute target autoantigen in GO, and anti-ALDH2 autoantibody might serve as a biomarker for GO and help to predict disease activity.

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.

Combination Therapy of Intravenous Steroids and Orbital Irradiation is More Effective Than Intravenous Steroids Alone in Patients with Graves' Orbitopathy

The aim of this study was to evaluate and compare the efficacy of intravenous (iv) glucocorticoids (GCs) with and without orbital radiotherapy (ORT) in a retrospective analysis of patients with active, moderate-to-severe Graves' orbitopathy (GO). Since diplopia has the strongest impact on quality of life, a careful work up of motility and binocular single vision (BSV) has been performed. The Essen-EUGOGO-Center database (n=3655) was screened for patients with untreated moderate-to-severe, active GO, onset ≤12 months. The inclusion criteria were met by 148 patients (n=76 ivGC, n=72 ivGC + ORT). We analyzed CAS (inactivation: ≤2), NOSPECS, lid-width, proptosis, motility, and field of BSV. To score the overall ophthalmic outcome, a severity-weighted-score (SOS) was compared with an established EUGOGO inflammation-weighted-score (IOS). Cumulative ivGCs dosages and duration of GO did not differ between the groups. Patients with combination therapy had a significantly more severe GO at baseline. Therefore, a subgroup with matched severity was additionally compared. In the IOS, both groups reached similar improvement rates (55.2 vs. 63.9%; p=0.31). However, in the SOS, the rates differed significantly (46.1 vs. 61.1%; p=0.03- unmatched and p=0.03 matched), despite similar rates of inactivation (65.8 vs. 63.8%). Impaired motility improved significantly more often after combination therapy (p=0.01 matched, p=0.004 unmatched). Treatment responders showed only partial improvement (proptosis: 2.5±0.5 mm; motility: 11.3±10.9°). In our retrospective analysis, combination therapy (ivGCs + ORT) was significantly more effective in reduction of severity and should therefore always be considered in moderate-to-severe GO stages, especially in the presence of motility disorders. However, the limited improvement in clinical parameters, despite the promising effect on inactivation of inflammation, has to be outlined to the patients.

TSH/IGF-1 Receptor Cross-Talk Rapidly Activates Extracellular Signal-Regulated Kinases in Multiple Cell Types

We previously showed that thyrotropin (TSH)/insulinlike growth factor (IGF)-1 receptor cross-talk appears to be involved in Graves' orbitopathy (GO) pathogenesis and upregulation of thyroid-specific genes in human thyrocytes. In orbital fibroblasts from GO patients, coadministration of TSH and IGF-1 induces synergistic increases in hyaluronan secretion. In human thyrocytes, TSH plus IGF-1 synergistically increased expression of the sodium-iodide symporter that appeared to involve ERK1/2 activation. However, the details of ERK1/2 activation were not known, nor was whether ERK1/2 was involved in this synergism in other cell types. Using primary cultures of GO fibroblasts (GOFs) and human thyrocytes, as well as human embryonic kidney (HEK) 293 cells overexpressing TSH receptors (HEK-TSHRs), we show that simultaneous activation of TSHRs and IGF-1 receptors (IGF-1Rs) causes rapid, synergistic phosphorylation/activation of ERK1 and ERK2 in all three cell types. This effect is partially inhibited by pertussis toxin, an inhibitor of TSHR coupling to Gi/Go proteins. In support of a role for Gi/Go proteins in ERK1/2 phosphorylation, we found that knockdown of Gi(1-3) and Go in HEK-TSHRs inhibited ERK1/2 phosphorylation stimulated by TSH and TSH plus IGF-1. These data demonstrate that the synergistic effects of TSH plus IGF-1 occur early in the TSHR signaling cascade and further support the idea that TSHR/IGF-1R cross-talk is an important mechanism for regulation of human GOFs and thyrocytes.

Teprotumumab for Thyroid-Associated Ophthalmopathy

BACKGROUND

Thyroid-associated ophthalmopathy, a condition commonly associated with Graves' disease, remains inadequately treated. Current medical therapies, which primarily consist of glucocorticoids, have limited efficacy and present safety concerns. Inhibition of the insulin-like growth factor I receptor (IGF-IR) is a new therapeutic strategy to attenuate the underlying autoimmune pathogenesis of ophthalmopathy.

METHODS

We conducted a multicenter, double-masked, randomized, placebo-controlled trial to determine the efficacy and safety of teprotumumab, a human monoclonal antibody inhibitor of IGF-IR, in patients with active, moderate-to-severe ophthalmopathy. A total of 88 patients were randomly assigned to receive placebo or active drug administered intravenously once every 3 weeks for a total of eight infusions. The primary end point was the response in the study eye. This response was defined as a reduction of 2 points or more in the Clinical Activity Score (scores range from 0 to 7, with a score of ≥3 indicating active thyroid-associated ophthalmopathy) and a reduction of 2 mm or more in proptosis at week 24. Secondary end points, measured as continuous variables, included proptosis, the Clinical Activity Score, and results on the Graves' ophthalmopathy-specific quality-of-life questionnaire. Adverse events were assessed.

RESULTS

In the intention-to-treat population, 29 of 42 patients who received teprotumumab (69%), as compared with 9 of 45 patients who received placebo (20%), had a response at week 24 (P<0.001). Therapeutic effects were rapid; at week 6, a total of 18 of 42 patients in the teprotumumab group (43%) and 2 of 45 patients in the placebo group (4%) had a response (P<0.001). Differences between the groups increased at subsequent time points. The only drug-related adverse event was hyperglycemia in patients with diabetes; this event was controlled by adjusting medication for diabetes.

CONCLUSIONS

In patients with active ophthalmopathy, teprotumumab was more effective than placebo in reducing proptosis and the Clinical Activity Score. (Funded by River Vision Development and others; ClinicalTrials.gov number, NCT01868997 .).

TSHR as a therapeutic target in Graves' disease

INTRODUCTION

Graves' disease (GD) and thyroid-associated ophthalmopathy (TAO) are thought to result from actions of pathogenic antibodies mediated through the thyrotropin receptor (TSHR). This leads to the unregulated consequences of the antibody-mediated receptor activity in the thyroid and connective tissues of the orbit. Recent studies reveal antibodies that appear to be directed against the insulin-like growth factor-I receptor (IGF-IR). Areas covered: In this brief article, I attempt to review the fundamental characteristics of the TSHR, its role in GD and TAO, and its relationship to IGF-IR. Strong evidence supports the concept that the two receptors form a physical and functional complex and that IGF-IR activity is required for some of the down-stream signaling initiated through TSHR. Recently developed small molecules and monoclonal antibodies that block TSHR and IGF-IR signaling are also reviewed in the narrow context of their potential utility as therapeutics in GD and TAO. The Pubmed database was searched from its inception for relevant publications. Expert opinion: Those agents that can interrupt the TSHR and IGF-IR pathways possess the potential for offering more specific and better tolerated treatments of both hyperthyroidism and TAO. This would spare patients exposure to toxic drugs, ionizing radiation and potentially hazardous surgeries.

Inhibiting thyrotropin/insulin-like growth factor 1 receptor crosstalk to treat Graves' ophthalmopathy: studies in orbital fibroblasts in vitro

BACKGROUND AND PURPOSE

Crosstalk between thyrotropin (TSH) receptors and insulin-like growth factor 1 (IGF-1) receptors initiated by activation of TSH receptors could be important in the development of Graves' ophthalmopathy (GO). Specifically, TSH receptor activation alone is sufficient to stimulate hyaluronic acid (HA) secretion, a major component of GO, through both IGF-1 receptor-dependent and -independent pathways. Although an anti-IGF-1 receptor antibody is in clinical trials, its effectiveness depends on the relative importance of IGF-1 versus TSH receptor signalling in GO pathogenesis.

EXPERIMENTAL APPROACH

TSH and IGF-1 receptor antagonists were used to probe TSH/IGF-1 receptor crosstalk in primary cultures of Graves' orbital fibroblasts (GOFs) following activation with monoclonal TSH receptor antibody, M22. Inhibition of HA secretion following TSH receptor stimulation was measured by modified HA elisa.

KEY RESULTS

TSH receptor antagonist, ANTAG3 (NCGC00242364), inhibited both IGF-1 receptor -dependent and -independent pathways at all doses of M22; whereas IGF-1 receptor antagonists linsitinib and 1H7 (inhibitory antibody) lost efficacy at high M22 doses. Combining TSH and IGF-1 receptor antagonists exhibited Loewe additivity within the IGF-1 receptor-dependent component of the M22 concentration-response. Similar effects were observed in GOFs activated by autoantibodies from GO patients' sera.

CONCLUSIONS AND IMPLICATIONS

Our data support TSH and IGF-1 receptors as therapeutic targets for GO, but reveal putative conditions for anti-IGF-1 receptor resistance. Combination treatments antagonizing both receptors yield additive effects by inhibiting crosstalk triggered by TSH receptor stimulatory antibodies. Combination therapy may be an effective strategy for dose reduction and/or compensate for any loss of anti-IGF-1 receptor efficacy.

Thyrotropin and Insulin-Like Growth Factor 1 Receptor Crosstalk Upregulates Sodium-Iodide Symporter Expression in Primary Cultures of Human Thyrocytes

BACKGROUND

Major regulation of thyroid gland function is mediated by thyrotropin (TSH) activating the TSH receptor (TSHR) and inducing upregulation of genes involved in thyroid hormone synthesis. Evidence suggests that the insulin-like growth factor 1 (IGF-1) receptor (IGF-1R) may play a role in regulating TSHR functional effects. This study examined the potential role of TSHR/IGF-1R crosstalk in primary cultures of human thyrocytes.

RESULTS

TSH/IGF-1 co-treatment elicited additive effects on thyroglobulin (TG), thyroperoxidase (TPO), and deiodinase type 2 (DIO2) mRNA levels but synergistic effects on sodium-iodide symporter (NIS) mRNA. Similar cooperativity was seen on the level of TG protein secretion (additive) and NIS protein expression (synergistic). The IGF-1R tyrosine kinase inhibitor linsitinib inhibited TSH-stimulated upregulation of NIS but not TG, indicating that NIS regulation is in part IGF-1R dependent and occurs via receptor crosstalk. Cooperativity was not seen at the level of cAMP/protein kinase A (PKA) signaling, IGF-1R phosphorylation, or Akt activation. However, TSH and IGF-1 synergistically activated ERK1/2. Pharmacological inhibition of ERK1/2 by the MEK1/2 inhibitor U0126 and of Akt by MK-2206 virtually abolished NIS stimulation by TSH and the synergistic effect of IGF-1.

CONCLUSION

As linsitinib inhibited upregulation of NIS stimulated by TSH alone, it is concluded that crosstalk between TSHR and IGF-1R, without agonist activation of IGF-1R, plays a role in NIS regulation in human thyrocytes via a mechanism involving ERK1/2 and/or Akt. Fully understanding the nature of this crosstalk has clinical implications for the treatment of thyroid diseases, including thyroid cancer.

Update on thyroid-associated Ophthalmopathy with a special emphasis on the ocular surface

Thyroid-associated ophthalmopathy (TAO) is a condition associated with a wide spectrum of ocular changes, usually in the context of the autoimmune syndrome, Graves’ disease. In this topical review, we attempted to provide a roadmap of the recent advances in current understanding the pathogenesis of TAO, important aspects of its clinical presentation, its impact on the ocular surface, describe the tissue abnormalities frequently encountered, and describe how TAO is managed today. We also briefly review how increased understanding of the disease should culminate in improved therapies for patients with this vexing condition.

CD40 Expression in Fibrocytes Is Induced by TSH: Potential Synergistic Immune Activation

Context

Fibrocytes appear to participate in inflammation and tissue remodeling in patients with thyroid-associated ophthalmopathy (TAO). These patients have increased frequencies of circulating TSH receptor (TSHR)- and CD40-positive fibrocytes, suggesting TSHR and CD40 may play roles in proinflammatory cytokine production, which ultimately leads to orbital inflammation and tissue remodeling.

Objective

To investigate the potential interactions between the TSHR and CD40 signaling pathways and their roles in IL-6 and TNF-α production.

Design and Outcome Measures

CD40 expression on fibrocytes was assessed using flow cytometry; IL-6 and TNF-α protein release using Luminex technology; increased IL-6 and TNF-α mRNA abundance, using real-time PCR; TSH- and CD40 ligand (CD40L)-stimulated Akt phosphorylation in fibrocytes, by western blot analysis; TSHR-CD40 protein-protein interaction, using co-immunoprecipitation, and CD40-TSHR co-localization, using immunocytochemistry.

Results

TSH enhances CD40 expression at a pre-translational level in fibrocytes. Production of IL-6 and TNF-α after costimulation with TSH and CD40L was greater than that after TSH or CD40L stimulation alone. TSH and CD40L costimulation also resulted in greater Akt phosphorylation. Akt and nuclear factor (NF)-κB inhibitors significantly reduced cytokine production after TSH and CD40L costimulation. TSHR and CD40L are colocalized on the cell surface and form a complex.

Conclusions

TSHR and CD40 in fibrocytes appear to be physically and functionally related. TSH stimulates CD40 production on the fibrocyte surface. Cytokine expression upon simultaneous stimulation of TSHR and CD40 is greater than levels achieved with TSH or CD40L alone. Increased expression of CD40 by TSH is a potential mechanism for this process.

Thyroid antibody-negative euthyroid Graves' ophthalmopathy

TSH receptor antibodies (TRAbs) are the pathological hallmark of Graves' disease, present in nearly all patients with the disease. Euthyroid Graves' ophthalmopathy (EGO) is a well-recognized clinical entity, but its occurrence in patients with negative TRAbs is a potential source of diagnostic confusion. A 66-year-old female presented to our endocrinology clinic with right eye pain and diplopia in the absence of thyroid dysfunction. TRAbs were negative, as measured with a highly sensitive third(-)generation thyrotropin-binding inhibitory immunoglobulin (TBII) ELISA assay. CT and MRI scans of the orbit showed asymmetrical thickening of the inferior rectus muscles but no other inflammatory or malignant orbital pathology. Graves' ophthalmopathy (GO) was diagnosed on the basis of the clinical and radiological features, and she underwent surgical recession of the inferior rectus muscle with complete resolution of the diplopia and orbital pain. She remained euthyroid over the course of follow-up but ultimately developed overt clinical and biochemical hyperthyroidism, 24 months after the initial presentation. By this time, she had developed positive TRAb as well as thyroid peroxidase antibodies. She responded to treatment with thionamides and remains euthyroid. This case highlights the potential for negative thyroid-specific autoantibodies in the presentation of EGO and underscores the variable temporal relationship between the clinical expression of thyroid dysfunction and orbital disease in the natural evolution of Graves' disease.

LEARNING POINTS

Euthyroid Graves' ophthalmopathy can present initially with negative thyroid-specific autoantibodies.Patients with suggestive symptoms of ophthalmopathy should be carefully evaluated for GO with imaging studies even when thyroid function and autoantibodies are normal.Patients with EGO can develop thyroid dysfunction within 4 years of follow-up underpinning the need for long-term follow-up and continued patient and physician vigilance in patients who have been treated for EGO.

TSH/IGF-1 Receptor Cross Talk in Graves' Ophthalmopathy Pathogenesis

CONTEXT

The TSH receptor (TSHR) is considered the main target of stimulatory autoantibodies in the pathogenesis of Graves' ophthalmopathy (GO); however, it has been suggested that stimulatory IGF-1 receptor (IGF-1R) autoantibodies also play a role.

OBJECTIVE

We previously demonstrated that a monoclonal stimulatory TSHR antibody, M22, activates TSHR/IGF-1R cross talk in orbital fibroblasts/preadipocytes obtained from patients with GO (GO fibroblasts [GOFs]). We show that cross talk between TSHR and IGF-1R, not direct IGF-1R activation, is involved in the mediation of GO pathogenesis stimulated by Graves' autoantibodies.

DESIGN/SETTING/PARTICIPANTS

Immunoglobulins were purified from the sera of 57 GO patients (GO-Igs) and tested for their ability to activate TSHR and/or IGF-1R directly and TSHR/IGF-1R cross talk in primary cultures of GOFs. Cells were treated with M22 or GO-Igs with or without IGF-1R inhibitory antibodies or linsitinib, an IGF-1R kinase inhibitor.

MAIN OUTCOME MEASURES

Hyaluronan (hyaluronic acid [HA]) secretion was measured as a major biological response for GOF stimulation. IGF-1R autophosphorylation was used as a measure of direct IGF-1R activation. TSHR activation was determined through cAMP production.

RESULTS

A total of 42 out of 57 GO-Ig samples stimulated HA secretion. None of the GO-Ig samples exhibited evidence for IGF-1R autophosphorylation. Both anti-IGF-1R antibodies completely inhibited IGF-1 stimulation of HA secretion. By contrast, only 1 IGF-1R antibody partially blocked HA secretion stimulated by M22 or GO-Igs in a manner similar to linsitinib, whereas the other IGF-1R antibody had no effect on M22 or GO-Ig stimulation. These findings show that the IGF-1R is involved in GO-Igs stimulation of HA secretion without direct activation of IGF-1R.

CONCLUSIONS

IGF-1R activation by GO-Igs occurs via TSHR/IGF-1R cross talk rather than direct binding to IGF-1R, and this cross talk is important in the pathogenesis of GO.

Current perspectives on the role of orbital fibroblasts in the pathogenesis of Graves' ophthalmopathy

Graves' ophthalmopathy (GO) is an extra-thyroidal complication of Graves' disease (GD; Graves' hyperthyroidism) characterized by orbital tissue inflammation, expansion, remodeling and fibrosis. Although the initiating trigger of GO is still indistinct, excessive orbital fibroblast activity is at the heart of its pathogenesis. Orbital fibroblasts are activated by cellular interactions with immune cells and the soluble factors they secrete. Orbital fibroblasts, especially from GO patients, express the thyrotropin receptor (TSH-receptor; TSHR), and activation of the orbital fibroblast population by stimulatory autoantibodies directed against the TSHR may provide an important link between GD and GO. Furthermore, stimulatory autoantibodies directed against the insulin-like growth factor-1 receptor have been proposed to contribute to orbital fibroblast activation in GO. Activated orbital fibroblasts produce inflammatory mediators thereby contributing to the orbital inflammatory process in GO. Moreover, orbital fibroblasts exhibit robust proliferative activity and extracellular matrix (especially hyaluronan) synthesizing capacity and can differentiate into adipocytes and myofibroblasts with disease progression, thereby contributing to tissue expansion/remodeling and fibrosis in GO. Orbital fibroblasts, especially those from GO patients, exhibit a hyper-responsive phenotype when compared to fibroblasts from other anatomical regions, which may further contribute to GO pathogenesis. Fibrocytes have been identified as additional source of orbital fibroblasts in GO, where they may contribute to orbital tissue inflammation, adipogenesis and remodeling/fibrosis. This review addresses our current view on the role that orbital fibroblasts fulfill in GO pathogenesis and both established as well as less established not fully crystallized concepts that need future studies will be discussed.

Rationale for therapeutic targeting insulin-like growth factor-1 receptor and bone marrow-derived fibrocytes in thyroid-associated ophthalmopathy

Development of medical therapy for thyroid-associated ophthalmopathy has lagged behind that for many other autoimmune diseases, in large part because its pathogenesis has not been understood. Recent insights into the nature of the main target of the disease, orbital connective tissues, have led to a greater understanding of how and why this ocular manifestation of Graves' disease might occur. Emerging from this work are the identities of potential drug targets. We believe that these findings will help pave the road toward an acceleration of therapy development.

Lack of Association between Selenium Status and Disease Severity and Activity in Patients with Graves' Ophthalmopathy

BACKGROUND

Selenium (Se) is of importance for regular functioning of the immune system and thyroid gland, and may have a health effect in mild Graves' ophthalmopathy (GO).

OBJECTIVE

As the Se status declines in inflammation, we analyzed whether GO activity or severity affects the Se status of patients.

METHODS

Serum Se and selenoprotein P (SePP) concentrations were retrospectively determined in 84 consecutive GO patients before treatment and compared to their clinical activity score (CAS) and severity of eye changes (NOSPECS) status, and to the concentrations of autoantibodies targeting the TSH receptor (TRAK) or the IGF1 receptor (IGF1R-aAB).

RESULTS

Serum Se and SePP were linearly associated, indicating a suboptimal Se status of our patients. In comparison to data from other European cohorts, the majority of GO patients had a relatively poor Se status ([Se] ± SD; 70.0 ± 23.8 µg/l), below the threshold needed for full expression of selenoproteins. TRAK were inversely associated with Se concentrations, while IGF1R-aAB titers were not associated with Se. Neither Se nor SePP concentrations differed between GO patients with severe versus mild or active versus inactive disease, or showed significant associations with the CAS or NOSPECS values.

CONCLUSION

GO patients are at risk of a low Se status, yet disease severity or activity does not seem to affect Se or SePP concentrations directly. However, as the retrospective nature of the analysis does not allow conclusions on a potential causative role of Se on Graves' disease or GO risk, these results neither support nor discourage adjuvant Se supplementation attempts.

Building the Case for Insulin-Like Growth Factor Receptor-I Involvement in Thyroid-Associated Ophthalmopathy

The pathogenesis of orbital Graves' disease (GD), a process known as thyroid-associated ophthalmopathy (TAO), remains incompletely understood. The thyrotropin receptor (TSHR) represents the central autoantigen involved in GD and has been proposed as the thyroid antigen shared with the orbit that could explain the infiltration of immune cells into tissues surrounding the eye. Another cell surface protein, insulin-like growth factor-I receptor (IGF-IR), has recently been proposed as a second antigen that participates in TAO by virtue of its interactions with anti-IGF-IR antibodies generated in GD, its apparent physical and functional complex formation with TSHR, and its necessary involvement in TSHR post-receptor signaling. The proposal that IGF-IR is involved in TAO has provoked substantial debate. Furthermore, several studies from different laboratory groups, each using different experimental models, have yielded conflicting results. In this article, we attempt to summarize the biological characteristics of IGF-IR and TSHR. We also review the evidence supporting and refuting the postulate that IGF-IR is a self-antigen in GD and that it plays a potentially important role in TAO. The putative involvement of IGF-IR in disease pathogenesis carries substantial clinical implications. Specifically, blocking this receptor with monoclonal antibodies can dramatically attenuate the induction by TSH and pathogenic antibodies generated in GD of proinflammatory genes in cultured orbital fibroblasts and fibrocytes. These cell types appear critical to the development of TAO. These observations have led to the conduct of a now-completed multicenter therapeutic trial of a fully human monoclonal anti-IGF-IR blocking antibody in moderate to severe, active TAO.

Insulin Receptor Substrate 1, the Hub Linking Follicle-stimulating Hormone to Phosphatidylinositol 3-Kinase Activation

The ubiquitous phosphatidylinositol 3-kinase (PI3K) signaling pathway regulates many cellular functions. However, the mechanism by which G protein-coupled receptors (GPCRs) signal to activate PI3K is poorly understood. We have used ovarian granulosa cells as a model to investigate this pathway, based on evidence that the GPCR agonist follicle-stimulating hormone (FSH) promotes the protein kinase A (PKA)-dependent phosphorylation of insulin receptor substrate 1 (IRS1) on tyrosine residues that activate PI3K. We report that in the absence of FSH, granulosa cells secrete a subthreshold concentration of insulin-like growth factor-1 (IGF-1) that primes the IGF-1 receptor (IGF-1R) but fails to promote tyrosine phosphorylation of IRS1. FSH via PKA acts to sensitize IRS1 to the tyrosine kinase activity of the IGF-1R by activating protein phosphatase 1 (PP1) to promote dephosphorylation of inhibitory Ser/Thr residues on IRS1, including Ser(789). Knockdown of PP1β blocks the ability of FSH to activate PI3K in the presence of endogenous IGF-1. Activation of PI3K thus requires both PKA-mediated relief of IRS1 inhibition and IGF-1R-dependent tyrosine phosphorylation of IRS1. Treatment with FSH and increasing concentrations of exogenous IGF-1 triggers synergistic IRS1 tyrosine phosphorylation at PI3K-activating residues that persists downstream through protein kinase B (AKT) and FOXO1 (forkhead box protein O1) to drive synergistic expression of genes that underlies follicle maturation. Based on the ability of GPCR agonists to synergize with IGFs to enhance gene expression in other cell types, PP1 activation to relieve IRS1 inhibition may be a more general mechanism by which GPCRs act with the IGF-1R to activate PI3K/AKT.

Disrupted TSH Receptor Expression in Female Mouse Lung Fibroblasts Alters Subcellular IGF-1 Receptor Distribution

A relationship between the actions of TSH and IGF-1 was first recognized several decades ago. The close physical and functional associations between their respective receptors (TSHR and IGF-1R) has been described more recently in thyroid epithelium and human orbital fibroblasts as has the noncanonical behavior of IGF-1R. Here we report studies conducted in lung fibroblasts from female wild-type C57/B6 (TSHR(+/+)) mice and their littermates in which TSHR has been knocked out (TSHR(-/-)). Flow cytometric analysis revealed that cell surface IGF-1R levels are substantially lower in TSHR(-/-) fibroblasts compared with TSHR(+/+) fibroblasts. Confocal immunofluorescence microscopy revealed similar divergence with regard to both cytoplasmic and nuclear IGF-1R. Western blot analysis demonstrated both intact IGF-1R and receptor fragments in both cellular compartments. In contrast, IGF-1R mRNA levels were similar in fibroblasts from mice without and with intact TSHR expression. IGF-1 treatment of TSHR(+/+) fibroblasts resulted in reduced nuclear and cytoplasmic staining for IGF-1Rα, whereas it enhanced the nuclear signal in TSHR(-/-) cells. In contrast, IGF-1 enhanced cytoplasmic IGF-1Rβ in TSHR(-/-) fibroblasts while increasing the nuclear signal in TSHR(+/+) cells. These findings indicate the intimate relationship between TSHR and IGF-1R found earlier in human orbital fibroblasts also exists in mouse lung fibroblasts. Furthermore, the presence of TSHR in these fibroblasts influenced not only the levels of IGF-1R protein but also its subcellular distribution and response to IGF-1. They suggest that the mouse might serve as a suitable model for delineating the molecular mechanisms overarching these two receptors.

Pathogenesis of thyroid eye disease: review and update on molecular mechanisms

Orbital changes in thyroid orbitopathy (TO) result from de novo adipogenesis, hyaluronan synthesis, interstitial oedema and enlargement of extraocular muscles. Cellular immunity, with predominantly CD4+ T cells expressing Th1 cytokines, and overexpression of macrophage-derived cytokines, perpetuate orbital inflammation. Orbital fibroblasts appear to be the major effector cells. Orbital fibroblasts express both thyrotropin receptor (TSHR) and insulin-like growth factor-1 receptor (IGF-1R) at higher levels than normal fibroblasts. TSHR expression increases in adipogenesis; TSHR agonism enhances hyaluronan production. IGF-1R stimulation leads to adipogenesis, hyaluronan synthesis and production of the chemokines, interleukin (IL)-16 and Regulated on Activation, Normal T Cell Expression and Secreted, which facilitate lymphocyte trafficking into the orbit. Immune activation uses a specific CD40:CD154 molecular bridge to activate orbital fibroblasts, which secrete pro-inflammatory cytokines including IL-1β, IL-1α, IL-6, IL-8, macrophage chemoattractant protein-1 and transforming growth factor-β, to perpetuate orbital inflammation. Molecular pathways including adenylyl cyclase/cyclic adenosine monophosphate, phophoinositide 3 kinase/AKT/mammalian target of rapamycin, mitogen-activated protein kinase are involved in TO. The emergence of a TO animal model and a new generation of TSHR antibody assays increasingly point towards TSHR as the primary autoantigen for extrathyroidal orbital involvement. Oxidative stress in TO resulting from imbalances of the oxidation-reduction state provides a framework of understanding for smoking prevention, achieving euthyroidism and the use of antioxidants such as selenium. Progress has been made in the understanding of the pathogenesis of TO, which should advance development of novel therapies targeting cellular immunity, specifically the CD40:CD40 ligand interaction, antibody-producing B cells, cytokines, TSHR and IGF-1R and its signalling pathways. Further studies in signalling networks and molecular triggers leading to burnout of TO will further our understanding of TO.

Pentraxin-3 Is a TSH-Inducible Protein in Human Fibrocytes and Orbital Fibroblasts

CD34(+) fibrocytes are bone marrow-derived monocyte progenitor cells that traffic to sites of tissue injury and repair. They putatively infiltrate the orbit in thyroid-associated ophthalmopathy where they appear to transition into CD34(+) orbital fibroblasts (OFs) that interact with residential CD34(-) fibroblasts. A unique phenotypic attribute of fibrocytes and CD34(+) OFs is their expression of the functional thyrotropin receptor (TSHR) and other "thyroid-specific" proteins. When activated through TSHR, fibrocytes express a number of cytokines and other inflammatory genes. Here we sought to determine whether pentraxin-3 (PTX-3), an acute-phase protein involved in inflammation and autoimmunity, might be induced by TSH in fibrocytes and OFs. These cells were collected from patients with Graves disease and healthy individuals. PTX-3 mRNA levels were determined by real-time PCR, protein was determined by ELISA and Western blot, and PTX-3 gene promoter activity was assessed with reporter assays. PTX-3 expression was induced by TSH in both cell types, regardless of the health status of the donor and was a consequence of increased steady-state PTX-3 mRNA levels. M22, a TSHR-activating monoclonal antibody, also induced PTX-3. The induction could be attenuated by dexamethasone and by IGF-I receptor-blocking antibodies, teprotumumab and 1H7. TSH effects were mediated through phosphatidylinositol 3-kinase/AKT, mammalian target of rapamycin/p70(s6k), Janus tyrosine kinase 2 pathways, and enhanced PTX-3 mRNA stability. These findings indicate that PTX-3 is a TSH target gene, the expression of which can be induced in fibrocytes and OFs. They suggest that PTX-3 might represent a previously unidentified nexus between the thyroid axis and the mechanisms involved in tissue remodeling.

Modeling Graves' Orbitopathy in Experimental Graves' Disease

Graves' orbitopathy (GO), also known as thyroid eye disease is an inflammatory disease of the orbital tissue of the eye that arises as a consequence of autoimmune thyroid disease. The central feature of the disease is the production of antibodies to the thyrotropin hormone receptor (TSHR) that modulate the function of the receptor leading to autoimmune hyperthyroidism and GO. Over the years, all viable preclinical models of Graves' disease have been incomplete and singularly failed to progress in the treatment of orbital complications. A new mouse model of GO based upon immunogenic presentation of human TSHR A-subunit plasmid by close field electroporation is shown to lead to induction of prolonged functional antibodies to TSHR resulting in chronic disease with subsequent progression to GO. The stable preclinical GO model exhibited pathologies reminiscent of human disease characterized by orbital remodeling by inflammation and adipogenesis. Inflammatory lesions characterized by CD3+ T cells and macrophages were localized in the orbital muscle tissue. This was accompanied by extensive adipogenesis of orbital fat in some immune animals. Surprisingly, other signs of orbital involvement were reminiscent of eyelid inflammation involving chemosis, with dilated and congested orbital blood vessels. More recently, the model is replicated in the author's independent laboratories. The pre-clinical model will provide the basis to study the pathogenic and regulatory roles of immune T and B cells and their subpopulations to understand the initiation, pathophysiology, and progression of GO.

Current Insights into the Pathogenesis of Graves' Ophthalmopathy

Environmental, genetic, and immune factors are at play in the development of the variable clinical manifestations of Graves' ophthalmopathy (GO). Among the environmental contributions, smoking is the risk factor most consistently linked to the development or worsening of the disease. The close temporal relationship between the diagnoses of Graves' hyperthyroidism and GO have long suggested that these 2 autoimmune conditions may share pathophysiologic features. The finding that the thyrotropin receptor (TSHR) is expressed in orbital fibroblasts, the target cells in GO, supported the notion of a common autoantigen. Both cellular and humeral immunity directed against TSHR expressed on orbital fibroblasts likely initiate the disease process. Activation of helper T cells recognizing TSHR peptides and ligation of TSHR by TRAb lead to the secretion of inflammatory cytokines and chemokines, and enhanced hyaluronic acid (HA) production and adipogenesis. The resulting connective tissue remodeling results in varying degrees extraocular muscle enlargement and orbital fat expansion. A subset of orbital fibroblasts express CD34, are bone-marrow derived, and circulate as fibrocytes that infiltrate connective tissues at sites of injury or inflammation. As these express high levels of TSHR and are capable of producing copious cytokines and chemokines, they may represent an orbital fibroblast population that plays a central role in GO development. In addition to TSHR, orbital fibroblasts from patients with GO express high levels of IGF-1R. Recent studies suggest that these receptors engage in cross-talk induced by TSHR ligation to synergistically enhance TSHR signaling, HA production, and the secretion of inflammatory mediators.

TSH-Mediated TNFα Production in Human Fibrocytes Is Inhibited by Teprotumumab, an IGF-1R Antagonist

Purpose

Fibrocytes (FC) are bone marrow-derived progenitor cells that are more abundant and infiltrate the thyroid and orbit in Graves orbitopathy (GO). FCs express high levels of thyrotropin receptor (TSHR) and insulin-like growth factor-1 receptor (IGF-1R). These receptors are physically and functionally associated, but their role in GO pathogenesis is not fully delineated. Treatment of FCs with thyroid stimulating hormone (TSH) or M22 (activating antibody to TSHR) induces the production of numerous cytokines, including tumor necrosis factor α (TNFα). Teprotumumab (TMB) is a human monoclonal IGF-1R blocking antibody currently in clinical trial for GO and inhibits TSHR-mediated actions in FCs.

Aim

To characterize the molecular mechanisms underlying TSH-induced TNFα production by FCs, and the role of IGF-1R blockade by TMB.

Design

FCs from healthy and GD patients were treated with combinations of TSH, M22, MG132 and AKTi (inhibitors of NF-κB and Akt, respectively), and TMB. TNFα protein production was measured by Luminex and flow cytometry. Messenger RNA expression was quantified by real time PCR.

Results

Treatment with TSH/M22 induced TNFα protein and mRNA production by FCs, both of which were reduced when FCs were pretreated with MG132 and AKTi (p<0.0001). TMB decreased TSH-induced TNFα protein production in circulating FCs from mean fluorescent index (MFI) value of 2.92 to 1.91, and mRNA expression in cultured FCs from 141- to 52-fold expression (p<0.0001). TMB also decreased M22-induced TNFα protein production from MFI of 1.67 to 1.12, and mRNA expression from 6- to 3-fold expression (p<0.0001).

Conclusion

TSH/M22 stimulates FC production of TNFα mRNA and protein. This process involves the transcription factor NF-κB and its regulator Akt. Blocking IGF-1R attenuates TSH/M22-induced TNFα production. This further delineates the interaction of TSHR and IGF1-R signaling pathways. By modulating the proinflammatory properties of FCs such as TNFα production, TMB may be a promising therapeutic agent for GO.

Bidirectional TSH and IGF-1 receptor cross talk mediates stimulation of hyaluronan secretion by Graves' disease immunoglobins

CONTEXT

There is no pathogenetically linked medical therapy for Graves' ophthalmopathy (GO). Lack of animal models and conflicting in vitro studies have hindered the development of such therapy. Recent reports propose that Graves' Igs bind to and activate thyrotropin receptors (TSHRs) and IGF-1 receptors (IGF-1Rs) on cells in orbital fat, stimulating hyaluronan (HA) secretion, a component of GO.

OBJECTIVE

The objective of the study was to investigate potential cross talk between TSHRs and IGF-1Rs in the pathogenesis of GO using a sensitive HA assay.

DESIGN/SETTING/PARTICIPANTS

Orbital fibroblasts from GO patients were collected in an academic clinical practice and cultured in a research laboratory. Cells were treated with TSH, IGF-1, and a monoclonal Graves' Ig M22.

MAIN OUTCOME MEASURES

HA was measured by a modified ELISA.

RESULTS

Simultaneous activation by TSH and IGF-1 synergistically increased HA secretion from 320 ± 52 for TSH and 430 ± 65 μg/mL for IGF-1 alone, to 1300 ± 95 μg/mL. IGF-1 shifted the TSH EC50 19-fold to higher potency. The dose response to M22 was biphasic. An IGF-1R antagonist inhibited the higher potency phase but had no effect on the lower potency phase. M22 did not cause IGF-1R autophosphorylation. A TSHR antagonist abolished both phases of M22-stimulated HA secretion.

CONCLUSIONS

M22 stimulation of HA secretion by GO fibroblasts/preadipocytes involves cross talk between TSHR and IGF-1R. This cross talk relies on TSHR activation rather than direct activation of IGF-1R and leads to synergistic stimulation of HA secretion. These data propose a model for GO pathogenesis that explains previous contradictory results and argues for TSHR as the primary therapeutic target for GO.

TSH-receptor-expressing fibrocytes and thyroid-associated ophthalmopathy

Thyroid-associated ophthalmopathy (TAO) is a vexing and undertreated ocular component of Graves disease in which orbital tissues undergo extensive remodelling. My colleagues and I have introduced the concept that fibrocytes expressing the haematopoietic cell antigen CD34 (CD34(+) fibrocytes), which are precursor cells of bone-marrow-derived monocyte lineage, express the TSH receptor (TSHR). These cells also produce several other proteins whose expression was traditionally thought to be restricted to the thyroid gland. TSHR-expressing fibrocytes in which the receptor is activated by its ligand generate extremely high levels of several inflammatory cytokines. Acting in concert with TSHR, the insulin-like growth factor 1 receptor (IGF-1R) expressed by orbital fibroblasts and fibrocytes seems to be necessary for TSHR-dependent cytokine production, as anti-IGF-1R blocking antibodies attenuate these proinflammatory actions of TSH. Furthermore, circulating fibrocytes are highly abundant in patients with TAO and seem to infiltrate orbital connective tissues, where they might transition to CD34(+) fibroblasts. My research group has postulated that the infiltration of fibrocytes into the orbit, their unique biosynthetic repertoire and their proinflammatory and profibrotic phenotype account for the characteristic properties exhibited by orbital connective tissues that underlie susceptibility to TAO. These insights, which have emerged in the past few years, might be of use in therapeutically targeting pathogenic orbit-infiltrating fibrocytes selectively by utilizing novel biologic agents that interfere with TSHR and IGF-1R signalling.

The pathophysiology of thyroid eye disease

The pathophysiology of thyroid eye disease (TED) is complex and incompletely understood. Orbital fibroblasts (OFs) seem to be the key effector cells that are responsible for the characteristic soft tissue enlargement seen in TED. They express potentially pathogenic autoantigens, such as thyrotropin receptor and insulin-like growth factor-1 receptor. An intricate interplay between these autoantigens and the autoantibodies found in Graves disease may lead to the activation of OFs, which then leads to increased hyaluronan production, proinflammatory cytokine synthesis, and enhanced differentiation into either myofibroblasts or adipocytes. Some of the OFs in TED patients seem to be derived from infiltrating fibrocytes. These cells originate from the bone marrow and exhibit both fibroblast and myeloid phenotype. In the TED orbit, they may mediate the orbital expansion and inflammatory infiltration. Last, lymphocytes and cytokines are intimately involved in the initiation, amplification, and maintenance of the autoimmune process in TED.

Platelet-derived growth factor: a key factor in the pathogenesis of graves' ophthalmopathy and potential target for treatment

Activation of orbital fibroblasts resulting in excessive proliferation, cytokine and hyaluronan production and differentiation into adipocytes, is a main determinant of orbital tissue inflammation and tissue expansion in Graves' ophthalmopathy (GO). During the last years we have shown that the platelet-derived growth factor (PDGF) isoforms PDGF-AA, PDGF-AB and PDGF-BB are increased in orbital tissue from GO patients with active and inactive disease. These PDGF isoforms exhibit the capacity to stimulate proliferation, hyaluronan and cytokine/chemokine production by orbital fibroblasts. Moreover, PDGF-AB and PDGF-BB increase thyroid stimulating hormone receptor (TSHR) expression by orbital fibroblasts, which enhances the orbital fibroblast activating capacity of the THSR stimulatory autoantibodies present in Graves' disease (GD) patients. Of these PDGF isoforms PDGF-BB exhibits the strongest orbital fibroblast activating effects, which is likely related to its ability to bind both the PDGF-receptor (PDGF-R)α and PDGF-Rβ chains. Thus the PDGF-system fulfills important roles in orbital fibroblast activation in both active and inactive GO, which supports a therapeutic rationale for blocking PDGF signaling in GO. Tyrosine kinase inhibitors (TKIs) may be candidates to target PDGF signaling. Of several TKIs tested dasatinib exhibited the highest potency to block PDGF-R signaling in orbital fibroblasts and may represent a promising compound for the treatment of GO as it was effective at low dosage and is associated with less side effects compared to imatinib mesylate and nilotinib. In this review the contribution of PDGF to the pathophysiology of GO as well as therapeutic approaches to target this PDGF-system will be addressed.

Teprotumumab, an IGF-1R blocking monoclonal antibody inhibits TSH and IGF-1 action in fibrocytes

CONTEXT

Thyroid-associated ophthalmopathy (TAO) is the component of Graves' disease characterized by orbital inflammation and connective tissue remodeling. The IGF-1 receptor (IGF-1R) and TSH receptor (TSHR) form a physical and functional complex in orbital fibroblasts. A subset of these fibroblasts is derived from infiltrating CD34(+) fibrocytes. Teprotumumab (RV 001, R1507) is a human monoclonal anti-IGF-1R blocking antibody currently undergoing a phase 2 clinical trial in patients with active TAO.

OBJECTIVE

To determine whether teprotumumab inhibits the induction by TSH of IL-6 and IL-8 in fibrocytes.

DESIGN

Fibrocytes were treated without or with teprotumumab in combination with IGF-1 or TSH.

MAIN OUTCOME MEASURES

IL-6 and IL-8 mRNA expression and protein production were analyzed by real-time PCR and Luminex, respectively. Phosphorylated Akt (S473) levels were analyzed by Western blot. TSHR and IGF-1R display was assessed by flow cytometry.

RESULTS

Fibrocyte display of IGF-1R and TSHR was reduced with teprotumumab, as were IGF-1- and TSH-dependent phosphorylated Akt levels. TSH induction of IL-6 and IL-8 mRNA and protein was also reduced by the monoclonal antibody.

CONCLUSIONS

Teprotumumab attenuates the actions of both IGF-1 and TSH in fibrocytes. Specifically, it blocks the induction of proinflammatory cytokines by TSH. These results provide, at least in part, the molecular rationale for interrogating the therapeutic efficacy of this antibody in TAO.

PI3K/AKT pathway mediates induction of IL-1RA by TSH in fibrocytes: modulation by PTEN

CONTEXT

TSH provokes expression of inflammatory genes in CD34(+) fibrocytes. These cells appear to infiltrate the orbit in Graves' disease (GD), where they putatively become the CD34(+) orbital fibroblast subset (GD-OF). This may have importance in solving the pathogenesis of thyroid-associated ophthalmopathy. The IL-1 family is targeted by TSH in fibrocytes and OFs by inducing secreted IL-1 receptor antagonist (IL-1RA) and intracellular IL-1RA in a cell-specific pattern. Phosphoinositide 3-kinase (PI3K) mediates several TSH actions in thyroid. This pathway is modulated by phosphatase and tensin homolog deleted on chromosome 10 (PTEN). Vanishingly little is known currently about TSHR signaling to IL-1RA expression in nonthyroidal cells. Furthermore, factors modulating TSH action in these cells are largely unexplored.

OBJECTIVES

To characterize intermediate signaling between TSHR and IL-1RA in fibrocytes and GD-OFs and to begin to identify the proximate regulators of TSHR signaling in nonepithelial, extrathyroidal cells as a strategy for developing therapies for thyroid-associated ophthalmopathy.

DESIGN/SETTING/PARTICIPANTS

Fibrocytes and GD-OFs were collected and analyzed from healthy individuals and those with GD in an academic clinical practice.

MAIN OUTCOME MEASURES

Real-time PCR, Western blot analysis, cell transfections, and chromatin immunoprecipitation analysis.

RESULTS

TSH induces IL-1RA in fibrocytes and GD-OFs by activating the PI3K/AKT pathway. Interrupting either PI3K or AKT with small molecule inhibitors or by knocking down their expression with targeting small interfering RNA attenuates the actions of TSH. OFs exhibit greater basal PTEN activity and lower constitutive AKT phosphorylation than do fibrocytes. Patterns of PTEN induction diverge in the two cell types.

CONCLUSIONS

The current findings identify the PI3K/AKT pathway as critical to the induction by TSH of IL-1RA in fibrocytes and GD-OFs. Furthermore, PTEN modulates the amplitude of the induction. In GD-OFs, relatively high basal PTEN levels prevent secreted IL-1RA expression or release. Knocking down PTEN allows GD-OFs to exhibit a pattern of IL-1RA expression resembling fibrocytes.

Rituximab (Rituxan) therapy for severe thyroid-associated ophthalmopathy diminishes IGF-1R(+) T cells

CONTEXT

Rituximab depletes CD20(+) B cells and has shown potential benefit in thyroid-associated ophthalmopathy (TAO). The impact of rituximab on T cell phenotype in TAO is unexplored.

OBJECTIVE

The objective of the study was to quantify the abundance of IGF-I receptor-positive (IGF-1R(+)) CD4 and CD8 T cells in active TAO before and after treatment with rituximab.

DESIGN

This was a retrospective case series assessing IGF-1R(+) T cells before and after treatment with rituximab with an 18-month follow-up.

SETTING

The study was conducted at a tertiary care medical center.

PATIENTS

Study participants included eight patients with severe TAO.

INTERVENTIONS

Two infusions of rituximab (1 g or 500 mg each) were administered 2 weeks apart.

MAIN OUTCOME MEASURES

Quantification of IGF-1R(+) T cells using flow cytometry was measured.

RESULTS

Eight patients with moderate to severe TAO [mean pretreatment clinical activity score (CAS) 5.1 ± 0.2 (SEM)] were treated. Four to 6 weeks after treatment, CAS improved to 1.5 ± 0.3, whereas the proportion of IGF-1R(+) CD3(+) T cells declined from 41.9% to 28.3% (P = .004). The proportion of IGF-1R(+) CD4(+) and IGF-1R(+) CD8(+) T cells declined 4-6 weeks after treatment (from 45.6% to 21.5% and from 32.0% to 15.8%, P = .003 and P = .001, respectively). In two patients, IGF-1R(+) CD4(+) and IGF-1R(+) CD8(+) subsets approximated pretreatment levels after 16 weeks.

CONCLUSIONS

Frequency of IGF-1R(+) T cells in patients with TAO declines within 4-6 weeks after rituximab treatment. This phenotypic shift coincides with clinical improvement. Thus, assessment of the abundance of IGF-1R(+) T cells in response to rituximab may provide a biomarker of clinical response. Our current findings further implicate the IGF-1R pathway in the pathogenesis of TAO.

Possible targets for nonimmunosuppressive therapy of Graves' orbitopathy

CONTEXT

Graves' orbitopathy (GO) is caused by expansion of the orbital contents by excess adipogenesis and overproduction of hyaluronan (HA). Immunosuppressive and antiinflammatory treatments of GO are not always effective and can have side effects, whereas targeting GO-associated tissue remodeling might be a more logical therapeutic strategy. Previously we reported that signaling cascades through IGF1 receptor and thyrotropin receptor within orbital preadipocytes/fibroblasts drove adipogenesis and HA production. Our current study combined the stimulation of IGF1 receptor and thyrotropin receptor increase of HA accumulation, which we hypothesize is by activation of phosphatidylinositol 3-kinase (PI3K)-1A/PI3K1B, respectively. The central aim of this study was to investigate whether PI3K/mammalian target of rapamycin complex 1 (mTORC1) inhibitors affected adipogenesis and/or HA production within orbital preadipocyte/fibroblasts.

METHODS

Human orbital preadipocytes were treated with/without inhibitors, LY294002 (PI3K1A/mTORC1), AS-605240 (PI3K1B), or PI103 (PI3K1A/mTORC1) in serum-free medium for 24 hours or cultured in adipogenic medium for 15 days. Quantitative PCR was used to measure hyaluronan synthases (HAS2) transcripts and the terminal adipogenesis differentiation marker lipoprotein lipase. HA accumulation in the medium was measured by an ELISA.

RESULTS

Unlike AS-605240, both LY294002 (10 μM) and PI-103 (5 μM) significantly decreased HAS2 transcripts/HA accumulation and adipogenesis. Because PI-103 and LY294002 are dual PI3K/mTOR inhibitors, we investigated the inhibition of mTORC1 (rapamycin 100 nM), which significantly decreased adipogenesis but had no effect on HAS2 transcripts/HA, implicating PI3K-1A in the latter.

CONCLUSIONS

The combined inhibition of PI3K1A and mTORC1 signaling in vitro decreased both HA accumulation and adipogenesis. Because PI3K and mTOR inhibitors are clinically used to treat other conditions, they have the potential to be repositioned to be used as an alternative nonimmunosuppressive therapy of GO.

Independent adipogenic and contractile properties of fibroblasts in Graves' orbitopathy: an in vitro model for the evaluation of treatments

Graves’ orbitopathy (GO) is a disfiguring and sometimes blinding disease, characterised by inflammation and swelling of orbital tissues, with fibrosis and adipogenesis being predominant features. Little is known about the disease aetiology and the molecular mechanisms driving the phenotypic changes in orbital fibroblasts are unknown. Using fibroblasts isolated from the orbital fat of undiseased individuals or GO patients, we have established a novel in vitro model to evaluate the dual profile of GO cells in a three-dimensional collagen matrix; this pseudo-physiological 3D environment allows measurement of their contractile and adipogenic properties. GO cells contracted collagen matrices more efficiently than control cells following serum or TGFβ1 stimulation, and showed a slightly increased ability to proliferate in the 3D matrix, in accordance with a fibro-proliferative phenotype. GO cells, unlike controls, also spontaneously differentiated into adipocytes in 3D cultures - confirming an intrinsic adipogenic profile. However, both control and GO cells underwent adipogenesis when cultured under pathological pressure levels. We further demonstrate that a Thy-1-low population of GO cells underlies the adipogenic - but not the contractile - phenotype and, using inhibitors, confirm that the contractile and adipogenic phenotypes are regulated by separate pathways. In view of the current lack of suitable treatment for GO, we propose that this new model testing the duality of the GO phenotype could be useful as a preclinical evaluation for the efficacy of potential treatments.

Current concepts in the molecular pathogenesis of thyroid-associated ophthalmopathy

Graves' disease (GD) is a common autoimmune condition. At its core, stimulatory autoantibodies are directed at the thyroid-stimulating hormone receptor (TSHR), resulting in dysregulated thyroid gland activity and growth. Closely associated with GD is the ocular condition known as thyroid-associated ophthalmopathy (TAO). The pathogenesis of TAO remains enigmatic as do the connections between the thyroid and orbit. This review highlights the putative molecular mechanisms involved in TAO and suggests how these insights provide future directions for identifying therapeutic targets. Genetic, epigenetic, and environmental factors have been suggested as contributory to the development of GD and TAO. Thyroid-stimulating hormone receptor and insulin-like growth factor receptor (IGF-1R) are expressed at higher levels in the orbital connective tissue from individuals with TAO than in healthy tissues. Together, they form a functional complex and appear to promote signaling relevant to GD and TAO. Orbital fibroblasts display an array of cell surface receptors and generate a host of inflammatory molecules that may participate in T and B cell infiltration. Recently, a population of orbital fibroblasts has been putatively traced to bone marrow-derived progenitor cells, known as fibrocytes, as they express CD45, CD34, CXCR4, collagen I, functional TSHR, and thyroglobulin (Tg). Fibrocytes become more numerous in GD and we believe traffic to the orbit in TAO. Numerous attempts at developing complete animal models of GD have been largely unsuccessful, because they lack fidelity with the ocular manifestations seen in TAO. Better understanding of the pathogenesis of TAO and development of improved animal models should greatly accelerate the identification of medical therapy for this vexing medical problem.

A modified ELISA accurately measures secretion of high molecular weight hyaluronan (HA) by Graves' disease orbital cells

Excess production of hyaluronan (hyaluronic acid [HA]) in the retro-orbital space is a major component of Graves' ophthalmopathy, and regulation of HA production by orbital cells is a major research area. In most previous studies, HA was measured by ELISAs that used HA-binding proteins for detection and rooster comb HA as standards. We show that the binding efficiency of HA-binding protein in the ELISA is a function of HA polymer size. Using gel electrophoresis, we show that HA secreted from orbital cells is primarily comprised of polymers more than 500 000. We modified a commercially available ELISA by using 1 million molecular weight HA as standard to accurately measure HA of this size. We demonstrated that IL-1β-stimulated HA secretion is at least 2-fold greater than previously reported, and activation of the TSH receptor by an activating antibody M22 from a patient with Graves' disease led to more than 3-fold increase in HA production in both fibroblasts/preadipocytes and adipocytes. These effects were not consistently detected with the commercial ELISA using rooster comb HA as standard and suggest that fibroblasts/preadipocytes may play a more prominent role in HA remodeling in Graves' ophthalmopathy than previously appreciated.

Graves' orbitopathy: imperfect treatments for a rare disease

Graves' orbitopathy (GO) is the most frequent and invalidating extrathyroidal expression of Graves' disease. Its incidence and prevalence are, however, low. About three quarters of Graves' patients have no GO at diagnosis, and moderate-to-severe and severe forms represent no more that 5-6% of cases. Progression to severe forms occurs rarely, but it may be caused by risk factors, the most important being smoking and poor control of thyroid dysfunction. Lot of progress has been recently achieved in the understanding of GO pathogenesis, while the disease remains a therapeutic challenge and dilemma. Common treatments for moderate-to-severe and active forms of GO (glucocorticoids and orbital radiotherapy) frequently provide incomplete responses and may be followed by relapse or progression of GO. After the disease has been inactivated by medical treatment, many patients need rehabilitative surgery for residual manifestations (orbital decompression for exophthalmos, squint surgery for extraocular muscle dysfunction, eyelid surgery for eyelid malposition). Novel pharmacological treatments are on the horizon and might target pathogenetic mechanisms of the disease better than glucocorticoids. Clinical evidence concerning their efficacy and safety is presently lacking.

Thyrotropin regulates IL-6 expression in CD34+ fibrocytes: clear delineation of its cAMP-independent actions

IL-6 plays diverse roles in normal and disease-associated immunity such as that associated with Graves’ disease (GD). In that syndrome, the orbit undergoes remodeling during a process known as thyroid-associated ophthalmopathy (TAO). Recently, CD34⁺ fibrocytes were found to infiltrate the orbit in TAO where they transition into CD34⁺ orbital fibroblasts. Surprisingly, fibrocytes display high levels of functional thyrotropin receptor (TSHR), the central antigen in GD. We report here that TSH and the pathogenic anti-TSHR antibodies that drive hyperthyroidism in GD induce IL-6 expression in fibrocytes and orbital fibroblasts. Unlike TSHR signaling in thyroid epithelium, that occurring in fibrocytes is completely independent of adenylate cyclase activation and cAMP generation. Instead TSH activates PDK1 and both AKT/PKB and PKC pathways. Expression and use of PKCβII switches to that of PKCµ as fibrocytes transition to TAO orbital fibroblasts. This shift is imposed by CD34⁻ orbital fibroblasts but reverts when CD34⁺ fibroblasts are isolated. The up-regulation of IL-6 by TSH results from coordinately enhanced IL-6 gene promoter activity and increased IL-6 mRNA stability. TSH-dependent IL-6 expression requires activity at both CREB (−213 to −208 nt) and NF-κB (–78 to −62 nt) binding sites. These results provide novel insights into the molecular action of TSH and signaling downstream for TSHR in non-thyroid cells. Fibrocytes neither express adenylate cyclase nor generate cAMP and thus these findings are free from any influence of cAMP-related signaling. They identify potential therapeutic targets for TAO.

IGF-1 receptor deficiency in thyrocytes impairs thyroid hormone secretion and completely inhibits TSH-stimulated goiter

Although thyroid-stimulating hormone (TSH) is known to be a major regulator of thyroid hormone biosynthesis and thyroid growth, insulin-like growth factor 1 (IGF-1) is required for mediating thyrocyte growth in concert with TSH in vitro. We generated mice with thyrocyte-selective ablation of IGF-1 receptor (TIGF1RKO) to explore the role of IGF-1 receptor signaling on thyroid function and growth. In 5-wk-old TIGF1RKO mice, serum thyroxine (T4) concentrations were decreased by 30% in concert with a 43% down-regulation of the monocarboxylate transporter 8 (MCT8), which is involved in T4 secretion. Despite a 3.5-fold increase in circulating concentrations of TSH, thyroid architecture and size were normal. Furthermore, thyrocyte area was increased by 40% in WT thyroids after 10 d TSH injection, but this effect was absent in TSH-injected TIGF1RKO mice. WT mice treated with methimazole and sodium perchlorate for 2 or 6 wk exhibited pronounced goiter development (2.0 and 5.4-fold, respectively), but in TIGF1RKO mice, goiter development was completely abrogated. These data reveal an essential role for IGF-1 receptor signaling in the regulation of thyroid function and TSH-stimulated goitrogenesis.

Update on advanced imaging options for thyroid-associated orbitopathy

Thyroid-associated orbitopathy (TAO) is a diverse spectrum of signs and symptoms that appears to have immunologic and pathologic causative factors as diverse as its clinical presentations. Lymphocytes, hormones, and cytokines affect orbital fibroblasts and other similar cells, which exert their effects on orbital tissues, including the extraocular muscles, orbital fat, and optic nerve. This complicated inflammatory cascade and the myriad of clinical findings that result contributes to the active phase of TAO. The distinction between the active and inactive phases of TAO is an important one, as the proper treatment will depend on the disease phase and degree thereof. Several clinical grading scales and scores have been established to help qualify and quantify the disease severity. Aiding clinical exam and acumen, proper and reproducible imaging of the orbit and ocular adnexa is incredibly important to the management of TAO. Orbital ultrasound, computed tomography, magnetic resonance imaging, and scintigraphy each have unique abilities, including quantifying orbital changes, assessing disease activity, correlating orbital findings with clinical changes, guiding appropriate treatment, and monitoring therapeutic responses. Further, study ease, accessibility, cost, sensitivity, specificity, reproducibility, and risks are all important considerations in picking the right test with which to diagnose and follow TAO. This analysis will provide a review of orbital imaging for TAO, including the mechanism of each imaging technique as well as their rationales, advantages, disadvantages, and utilities.

High-resolution ultrasound as an effective and practical tool to analyze eyebrow profile expansion in thyroid-associated periorbitopathy

PURPOSE

Clinical, radiographic, and molecular studies have shown that patients with thyroid-associated orbitopathy exhibit volumetric expansion of eyebrow tissues. This clinicopathologic entity has been termed thyroid-associated periorbitopathy. The goal of this study was to determine whether high-resolution ultrasonography could be used to reliably quantify thyroid-associated periorbitopathy.

METHODS

Institutional review board approval was obtained. The internal case-control study consisted of 12 subjects with unilateral-asymmetric thyroid-associated orbitopathy. High-resolution ultrasonography using a 15-MHz probe (Logiq p6) was performed by a single operator. Measurements were obtained 0.5 cm cephalad to the superior orbital rim at the midpupillary sagittal level. For each subject and tissue layer thickness (total tissue, dermis fat, retro-orbicularis oculi fat), the measured values on the less affected side were subtracted from those on the more severely diseased side. Summary statistics were used to analyze results.

RESULTS

High-resolution ultrasonography effectively demonstrated asymmetric expansion of total eyebrow tissue (p < 0.0001) and retro-orbicularis oculi fat (p = 0.0003). No significant difference in dermis fat thickness was found between the 2 sides (p = 0.2). Hertel exophthalmometry measurements were statistically different between the 2 sides (p = 0.002).

CONCLUSIONS

This study demonstrates that high-resolution ultrasonography independently confirms previously published studies of retro-orbicularis oculi fat expansion in patients with thyroid-associated orbitopathy. Compared with CT, MRI, and tissue biopsy, high-resolution ultrasonography is a more practical and cost-effective way to quantify and track thyroid-associated periorbitopathy over time. With its potential for real-time tissue assessment, high-resolution ultrasonography may be best suited for future studies of the dynamic relationship between globe and periorbital structures.

Insulin-like growth factor 1 promotes the proliferation and adipogenesis of orbital adipose-derived stromal cells in thyroid-associated ophthalmopathy

Thyroid-associated ophthalmopathy (TAO) is characterised by increased volume of the orbital contents involving adipose tissue, but the factors responsible for stimulation of orbital adipogenesis remain uncertain. Previous studies have shown that insulin-like growth factor 1 (IGF-1) is increased in the orbital fatty connective tissues of patients with TAO. The present study was conducted to investigate the effects of IGF-1 on orbital adipose-derived stromal cells (OADSCs) derived from TAO patients and to identify the signalling mechanisms involved. Our results showed that IGF-1 significantly promoted the cell proliferation and lipid accumulation of TAO OADSCs. The mRNA expression of adipogenic markers (adiponectin, leptin, adipocyte fatty acid binding protein [AP2] and fatty acid synthase [FAS]) was increased in TAO cultures treated with IGF-1. Further research demonstrated that the protein levels of peroxisome proliferator-activated receptor-γ (PPARγ) were up-regulated when OADSCs were treated with IGF-1. We also found that the inhibition of either IGF-1 receptor (IGF-1R) or phosphoinositide 3-kinase (PI3K) activity decreased the levels of IGF-1-stimulated mRNA encoding adiponectin, leptin, AP2, and FAS, as well as PPARγ protein levels. Moreover, the expression of phosphorylated Akt (p-Akt) protein in TAO cells was up-regulated by IGF-1, while a specific PI3K inhibitor (LY294002) or an antibody of IGF-1R blocked this effect. These results indicate that IGF-1 is a pro-proliferative and pro-adipogenic factor in TAO OADSCs. IGF-1 enhances the adipogenesis of TAO OADSCs by up-regulation of PPARγ via the activation of the IGF-1R and PI3K pathways, suggesting that the blocking of IGF-1R or inhibition of PI3K signalling might be a potential novel therapeutic approach to TAO.

Interleukin-6 production in CD40-engaged fibrocytes in thyroid-associated ophthalmopathy: involvement of Akt and NF-κB

PURPOSE

CD40-CD40 ligand (CD40L) interactions appear to play pathogenic roles in autoimmune disease. Here we quantify CD40 expression on fibrocytes, circulating, and bone marrow-derived progenitor cells. The functional consequences of CD40 ligation are determined since these may promote tissue remodeling linked with thyroid-associated ophthalmopathy (TAO).

METHODS

CD40 levels on cultivated fibrocytes and orbital fibroblasts (GOFB) from patients with Graves' disease (GD), as well as fibrocyte abundance, were determined by flow cytometry. CD40 mRNA expression was evaluated by real-time PCR, whereas response to CD40 ligation was measured by Luminex and RT-PCR. Protein kinase B (Akt) and nuclear factor (NF)-kappa B (NF-κB) signaling were determined by Western blot and immunofluorescence.

RESULTS

Basal CD40 expression on fibrocytes is greater than that on GOFB. IFN-γ upregulates CD40 in both cell types and its actions are mediated at the pretranslational level. Fibrocytes produce high levels of cytokines, including interleukin-6 (IL-6), TNF-α, IL-8, MCP-1, and RANTES (Regulated on Activation, Normal T Cell Expressed and Secreted) in response to CD40L. IL-6 induction results from an increase in steady state IL-6 mRNA, and is mediated through Akt and NF-κB activation. Circulating CD40(+)CD45(+)Col1(+) fibrocytes are far more frequent in vivo in donors with TAO compared with healthy subjects.

CONCLUSIONS

Particularly high levels of functional CD40 are displayed by fibrocytes. CD40L-provoked signaling results in the production of several cytokines. Among these, IL-6 expression is mediated through Akt and NF-κB pathways. The frequency of circulating CD40(+) fibrocytes is markedly increased in patients with TAO, suggesting that this receptor might represent a therapeutic target for TAO.

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.

Transcriptome-level microarray expression profiling implicates IGF-1 and Wnt signalling dysregulation in the pathogenesis of thyroid-associated orbitopathy

AIMS

The pathogenesis of thyroid-associated orbitopathy (TAO) remains unclear. The aim of this study is to elucidate the gene expression profile of orbital fat from patients with active, but untreated, TAO.

METHODS

A case-control gene expression study was conducted using test samples of orbital fat from TAO patients and control orbital fat specimens; apart from drugs to control thyrotoxicosis, the TAO patients had received no treatment for orbital disease. cDNA expression analysis was performed using the Affymetrix GeneChip Human Genome U133 Plus 2.0 platform and validated using quantitative PCR.

RESULTS

The highest-ranked differentially expressed genes were dominated by IGF-1 signalling genes. These include IGF-1, IGF-1 receptor binding/signalling genes, such as SOCS3 and IRS2, and downstream signalling and transcriptional regulators, such as SGK (PDK/Akt signalling) and c-JUN. Our microarray data also demonstrate dysregulation of wingless-type MMTV (Wnt) signalling gene expression, including Wnt5a, sFRPs and DKK.

CONCLUSION

Altered Wnt signalling confirms previous array findings. Further investigation of the role of Wnt signalling in TAO pathogenesis is warranted. These data also provide the first evidence of dysregulation of IGF-1 pathway genes in TAO tissue, further strengthening the evidence for the role of IGF-1 signalling in the pathogenesis and potential treatment of TAO.

Immunopathogenesis of Graves' ophthalmopathy: the role of the TSH receptor

Graves' ophthalmopathy is an inflammatory autoimmune disorder of the orbit. The close clinical and temporal relationships between Graves' hyperthyroidism and ophthalmopathy have long suggested that both conditions derive from a single systemic process and share the thyrotropin receptor as a common autoantigen. This receptor is expressed not only in thyroid follicular cells, but also in orbital fibroblasts with higher levels measured in orbital cells from ophthalmopathy patients than in cells from normal individuals. Recent studies from several laboratories have shown that thyrotropin receptor activation in orbital fibroblasts enhances hyaluronic acid synthesis and adipogenesis, both cellular functions that appear to be upregulated in the diseased orbit. The phosphoinositide 3-kinase/Akt signaling cascade, along with other effector pathways including adenylyl cyclase/cAMP, appears to mediate these processes. Future therapies for this condition may involve inhibition of thyrotropin receptor signaling in orbital fibroblasts.