IGF1 receptor and thyroid-associated ophthalmopathy

Abstract

Thyroid-associated ophthalmopathy (TAO) is a vexing and poorly understood autoimmune process involving the upper face and tissues surrounding the eyes. In TAO, the orbit can become inflamed and undergo substantial remodeling that is disfiguring and can lead to loss of vision. There are currently no approved medical therapies for TAO, the consequence of its uncertain pathogenic nature. It usually presents as a component of the syndrome known as Graves' disease where loss of immune tolerance to the thyrotropin receptor (TSHR) results in the generation of activating antibodies against that protein and hyperthyroidism. The role for TSHR and these antibodies in the development of TAO is considerably less well established. We have reported over the past 2 decades evidence that the insulin-like growth factorI receptor (IGF1R) may also participate in the pathogenesis of TAO. Activating antibodies against IGF1R have been detected in patients with GD. The actions of these antibodies initiate signaling in orbital fibroblasts from patients with the disease. Further, we have identified a functional and physical interaction between TSHR and IGF1R. Importantly, it appears that signaling initiated from either receptor can be attenuated by inhibiting the activity of IGF1R. These findings underpin the rationale for therapeutically targeting IGF1R in active TAO. A recently completed therapeutic trial of teprotumumab, a human IGF1R inhibiting antibody, in patients with moderate to severe, active TAO, indicates the potential effectiveness and safety of the drug. It is possible that other autoimmune diseases might also benefit from this treatment strategy.

Keywords: IGF receptor; immune system; signal transduction; thyroid.

Figure 1.

Facial portrait of a patient with relatively mild, asymmetric thyroid-associated ophthalmopathy. The patient manifests bilateral upper eyelid retraction, periornital swelling, and mild conjunctival inflammation.

Figure 2.

Theoretical representation: the pathogenesis of thyroid-associated ophthalmopathy. The orbit becomes infiltrated by B and T cells and CD34⁺ fibrocytes uniquely in thyroid-associated ophthalmopathy. Bone marrow-derived fibrocytes express several proteins traditionally considered “thyroid-specific”. They can differentiate into CD34⁺ fibroblasts which in turn can further develop into myofibroblasts or adipocytes depending upon the molecular cues they receive from the tissue microenvironment. CD34⁺ fibroblasts cohabit the orbit with residential CD34- fibroblasts. These heterogeneous populations of orbital fibroblasts can produce cytokines under basal and activated states. These include interleukins 1β, 6, 8, 10, 16, IL-1 receptor antagonists, tumor necrosis factor α, the chemokine known as “regulated on activation, normal T expressed and secreted” or RANTES, CD40 ligand and several other cytokines and chemokines. These cytokines can act on infiltrating and residential cells. Like fibrocytes, CD34⁺ fibroblasts express thyrotropin receptor, thyroglobulin, and other thyroid proteins but at substantially lower levels. Thyroid-stimulating immunoglobulins and potentially other autoantibodies directed specifically at the insulin-like growth factor-I receptor, activate the thyrotropin/insulin-like growth factor receptor-1 complex, resulting in the activation of several downstream signaling pathways and expression of target genes. Orbital fibroblasts synthesize hyaluronan leading to increased orbital tissue volume. This expanded tissue can result in proptosis and optic nerve compression. Orbital fat also expands from de novo adipogenesis. From N. Engl. J. Med, Smith T.J. and Hegedus L., Graves’ Disease, 375; 1552–1565. Copyright (2016) Massachusetts Medical Society. Reprinted with permission.

Figure 3.

(Panel A) Cell surface IGF-IR expression by normal and GD orbital fibroblasts. (Panel B) Western analysis of IGF-IRβ in normal and GD orbital fibroblasts. (Panel C) Displacement of ^[125I]IGF-I binding with increasing concentrations of unlabeled IGF-I, the IGF-IR-specific IGF-I analogue, Des(1–3), IgG from patients with GD (GD-IgG) and that from heathy controls (N-IgG). (Panel D) Displacement of FITC-conjugated anti-IGF-IR binding by N-IgG (left panels) and GD-IgG (right panels) in GD orbital fibroblasts (upper panels) and those from healthy controls (normal; lower panels). From J. Immunol, Pritchard J, et al, Immunoglobulin activation of T cell chemoattractant expression in fibroblasts from patients with Graves’ disease is mediated through the insulin-like growth factor I receptor pathway, 170:6348–6354, 2003.

Figure 4.

A dominant negative mutant (DN, 486/STOP) IGF-IR or empty vector was transiently transfected into GD orbital fibroblasts. The mutant protein attenuated chemoattractant activity and expression. (Panel A) T cell chemoattractant activity was assessed by treating cultures with GD-IgG (100 ng/ml) or nothing for 24 h. Media were analyzed for T cell migratory activity without (solid columns) or with either anti-IL-16 (empty columns) or anti-RANTES (stripped columns) neutralizing Abs (5 g/ml), (Panel B) IL-16 (solid columns) and RANTES (empty columns) protein expression. From J. Immunol, Pritchard J, et al, Immunoglobulin activation of T cell chemoattractant expression in fibroblasts from patients with Graves’ disease is mediated through the insulin-like growth factor I receptor pathway, 170:6348–6354, 2003.

Figure 5.

Immunofluorescence staining for IGF-1Rβ (red) and TSHR (green). The images demonstrate co-localization of the two receptor (yellow) by confocal microscopy. (Panels A–C) Graves’ disease orbital fibroblasts and (Panels D-F) thyrocytes. (Panels C and F) Merged images demonstrate co-localization appearing as yellow or orange. (Panels G–I) Images using a different pair of antibodies demonstrate GF-1Rβ (green) and TSHR (red) and colocalization (yellow) in orbital fibroblasts. (Panels J–L) TSHR (green) and IGF-1Rβ (red) in orbital fibroblasts demonstrates different pattern than that for IGF-1Rβ. (Panel L) Merged image (yellow to orange). (Panels M-O) TAO orbital connective tissue stains for TSHR (M, green) and IGF-1R (N, red). (Panel O) Merged images (orange). From J. Immunol, Tsui et al, Evidence for an association between thyroid-stimulating hormone and insulin-like growth factor I receptors: a tale of two antigens implicated in Graves’ disease, 181:4397–4405, 2008.

Figure 6.

(Panels A and B) Western blot analysis of proteins from orbital fibroblasts, human thyrocytes, and thyroid tissue that were immunoprecipitated (IP) with either anti-IGF-1R or anti-TSHR antibodies and immunoblotted (IB) with the antibodies indicated. (Panel C) Knocking down IGF-1R expression with siRNA disrupts TSHR/IGF-1R complexes. (Panel D) ERK activation in thyrocytes treated with IGF-1, rhTSH, or immunoglobulins from patients with GD (GD-IgG) without/with anti-IGF-1R monoclonal antibody 1H7 for 15 min. From J. Immunol, Tsui et al, Evidence for an association between thyroid-stimulating hormone and insulin-like growth factor I receptors: a tale of two antigens implicated in Graves’ disease, 181:4397–4405, 2008.

Figure 7.

Design of the trial and results of primary response. (Panel A) Patients underwent screening underwent randomization to either receive teprotoumumab or placebo administered as 8 IV infusions at 3 week intervals. (Panels B–D) Primary endpoint was assessed at week 24. In panel B, the time to first response was determined. Panel C demonstrates the time course for patients who met responder status. In panel D, responders were graded according to the magnitude of their response.