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Thyroglobulin (Tg) is the macromolecular precursor of thyroid hormones and is thought to be uniquely expressed by thyroid epithelial cells. Tg and the thyroid-stimulating hormone receptor (TSHR) are targets for autoantibody generation in the autoimmune disorder Graves disease (GD). Fully expressed GD is characterized by thyroid overactivity and orbital tissue inflammation and remodeling. This process is known as thyroid-associated ophthalmopathy (TAO). Early reports suggested that in TAO, both Tg and TSHR become overexpressed in orbital tissues. Previously, we found that CD34+ progenitor cells, known as fibrocytes, express functional TSHR, infiltrate the orbit, and comprise a large subset of orbital fibroblasts in TAO. We now report that fibrocytes also express Tg, which resolves as a 305-kDa protein on Western blots. It can be immunoprecipitated with anti-Tg Abs. Further, 125iodine and [35S]methionine are incorporated into Tg expressed by fibrocytes. De novo Tg synthesis is attenuated with a specific small interfering RNA targeting the protein. A fragment of the Tg gene promoter fused to a luciferase reporter exhibits substantial activity when transfected into fibrocytes. Unlike fibrocytes, GD orbital fibroblasts, which comprise a mixture of CD34+ and CD34– cells, express much lower levels of Tg and TSHR. When sorted into pure CD34+ and CD34– subsets, Tg and TSHR mRNA levels become substantially higher in CD34+ cells. These findings indicate that human fibrocytes express multiple \"thyroid-specific\" proteins, the levels of which are reduced after they infiltrate tissue. Our observations establish the basis for Tg accumulation in orbital GD.

Thyroid eye disease is a disabling autoimmune disease associated with orbital inflammation and tissue remodeling which can result in significant proptosis, leading to visual alterations and is potentially sight threatening. Current evidence indicates that autoantibodies to the insulin-like growth factor 1 receptor (IGF-1R), along with the thyroid-stimulating hormone receptor (TSHR), mediate the pathogenesis in susceptible individuals. Teprotumumab, a monoclonal IGF-1R antagonist, has demonstrated previously in a 24 week, randomized, controlled trial to produce significant changes in composite outcomes of proptosis and clinical activity score as compared with placebo. Further examination of the proptosis results reported here, indicate that the proptosis outcome (≥ 2 mm reduction) was met in 71.4% of the teprotumumab-treated patients as compared with 20% of the placebo-treated patients (p < 0.001). Additionally, the proptosis benefit was observed early in the trial (study week 6), and all individual patients demonstrated some benefit at week 24. Improvement was noted among smokers, non-smokers, men and women, and particularly those with higher levels of proptosis at baseline. The level of proptosis reduction with teprotumumab reported here is similar to that seen with decompression surgery. If these results are confirmed in the ongoing Phase 3 trial, teprotumumab will offer an alternative to surgery and its associated complications.

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

Purpose Improved understanding of thyroid eye disease (TED) pathogenesis has facilitated identification of a targeted molecular approach for TED treatment offering the potential to halt or slow disease progression in a nonsurgical manner. Herein, we provide a summary of the current knowledge of TED management, followed by discussion of a novel insulin-like growth factor-1 receptor (IGF-1R) antagonist antibody and its potential to change the course of the disease.Design Perspective.Methods Review of the literature and authors' experience.Results Many publications demonstrate IGF-1R overexpression in TED, and its activation as an autoantigen as a critical factor in TED pathogenesis. Several in vitro studies demonstrate that IGF-1R inhibition attenuates downstream molecular events including cytokine and hyaluronan production, and cellular differentiation. These observations led to the hypothesis that blocking IGF-1R may abrogate the clinical progression of TED. The recent completion of phase 2 and 3 randomized, placebo-controlled trials demonstrate the efficacy and safety of teprotumumab, a fully human monoclonal IGF-1R antagonist antibody, in patients with moderate-to-severe, active TED. Both the phase 2 and the recent phase 3 study results demonstrate that more patients with active TED receiving teprotumumab experienced a meaningful improvement in proptosis.Conclusions Current TED treatment strategies target inflammation and symptoms, but do not modify the disease course. Therefore, proptosis as well as strabismus and its resulting diplopia often remain, impacting patient well-being and quality of life over the long term. Targeted molecular therapy using teprotumumab demonstrates disease-modifying benefits with the potential to shift the paradigm for TED treatment.

IL-6 plays an important role in the pathogenesis of Graves' disease and its orbital component, thyroid-associated ophthalmopathy (TAO). Orbital tissues become inflamed in TAO, a process in which prostanoids have been implicated. Orbital fibroblasts both generate and respond to PGE(2), underlying the inflammatory phenotype of these cells. Using cultured orbital and dermal fibroblasts, we characterized the effects of PGE(2) on IL-6 expression. We found that the prostanoid provokes substantially greater cytokine synthesis in orbital fibroblasts, effects that are mediated through cell-surface EP(2) receptors and increased steady-state IL-6 mRNA levels. The pre-translational up-regulation of IL-6 results from increased gene promoter activity and can be reproduced with the PKA agonist, Sp-cAMP and blocked by interrupting the PKA pathway. PGE(2)-induced production of cAMP in orbital fibroblasts was far greater than that in dermal fibroblasts, resulting from higher levels of adenylate cyclase. PGE(2) provokes CREB phosphorylation, increases the pCREB/CREB ratio, and initiates nuclear localization of the pCREB/CREB binding protein/p300 complex (CBP) preferentially in orbital fibroblasts. Transfection with siRNAs targeting either CREB or CBP blunts the induction of IL-6 gene expression. PGE(2) promotes the binding of pCREB to its target DNA sequence which is substantially greater in orbital fibroblasts. These results identify the mechanism underlying the exaggerated induction of IL-6 in orbital fibroblasts and tie together two proinflammatory pathways involved in the pathogenesis of TAO. Moreover, they might therefore define an attractive therapeutic target for the treatment of TAO.

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

In a good example of translational research, investigators who had initially demonstrated a role for insulin-like growth factor I in the pathogenesis of thyroid eye disease showed that an antibody to the receptor (teprotumumab) produced a meaningful improvement in 83% of patients.

Insulin-like growth factor-1 receptor (IGF-1R) comprises two subunits, including a ligand binding domain on extra- cellular IGF-1Rα and a tyrosine phosphorylation site located on IGF-1Rβ. IGF-1R is over-expressed by orbital fibroblasts in the autoimmune syndrome, Graves' disease (GD). When activated by IGF-1 or GD-derived IgG (GD-IgG), these fibroblasts produce RANTES and IL-16, while those from healthy donors do not. We now report that IGF-1 and GD-IgG provoke IGF-1R accumulation in the cell nucleus of GD fibroblasts where it co-localizes with chromatin. Nuclear IGF-1R is detected with anti-IGF-1Rα-specific mAb and migrates to approximately 110 kDa, consistent with its identity as an IGF-1R fragment. Nuclear IGF-1R migrating as a 200 kDa protein and consistent with an intact receptor was undetectable when probed with either anti-IGF-1Rα or anti-IGF-1Rβ mAbs. Nuclear redistribution of IGF-1R is absent in control orbital fibroblasts. In GD fibroblasts, it can be abolished by an IGF-1R-blocking mAb, 1H7 and by physiological concentrations of glucocorticoids. When cell-surface IGF-1R is cross-linked with (125)I IGF-1, (125)I-IGF-1/IGF-1R complexes accumulate in the nuclei of GD fibroblasts. This requires active ADAM17, a membrane associated metalloproteinase, and the phosphorylation of IGF-1R. In contrast, virally encoded IGF-1Rα/GFP fusion protein localizes equivalently in nuclei in both control and GD fibroblasts. This result suggests that generation of IGF-1R fragments may limit the accumulation of nuclear IGF-1R. We thus identify a heretofore-unrecognized behavior of IGF-1R that appears limited to GD-derived fibroblasts. Nuclear IGF-1R may play a role in disease pathogenesis.

In patients with thyroid-associated ophthalmopathy, responses to treatment are rare and usually minor. Teprotumumab, an antibody to the insulin-like growth factor I receptor, led to significant responses in 69% of patients and to decreased proptosis. Medical therapies for moderate-to-severe thyroid-associated ophthalmopathy (Graves’ orbitopathy) that have proved to be effective and safe in adequately powered, prospective, placebo-controlled trials are lacking. This unmet need is due to the incompletely understood pathogenesis of the disease. 1 Current treatments are inconsistently beneficial and often associated with side effects, and their modification of the ultimate disease outcome is uncertain. 1 – 3 Previous clinical trials, which were rarely placebo-controlled, suggest that high-dose glucocorticoids, alone 3 – 5 or with radiotherapy, 6 , 7 can reduce inflammation-related signs and symptoms in patients with active ophthalmopathy. However, glucocorticoids and orbital radiotherapy minimally affect proptosis and can cause dose-limiting adverse . . .