Cytokines (interferon-γ and tumor necrosis factor–α)-induced nuclear factor–κB activation and chemokine (C-X-C motif) ligand 10 release in Graves disease and ophthalmopathy are modulated by pioglitazone

Abstract

Until now, the following are not known: (1) the mechanisms underlying the induction of chemokine (C-X-C motif) ligand 10 (CXCL10) secretion by cytokines in thyrocytes; (2) if pioglitazone is able, like rosiglitazone, to inhibit the interferon (IFN)-γ–induced chemokine expression in Graves disease (GD) or ophthalmopathy (GO); and (3) the mechanisms underlying the inhibition by thiazolidinediones of the cytokines-induced CXCL10 release in thyrocytes. The aims of this study were (1) to study the mechanisms underlying the induction of CXCL10 secretion by cytokines in GD thyrocytes; (2) to test the effect of pioglitazone on IFNγ-inducible CXCL10 secretion in primary thyrocytes, orbital fibroblasts, and preadipocytes from GD and GO patients; and (3) to evaluate the mechanism of action of thiazolidinediones on nuclear factor (NF)–κB activation. The results of the study (1) demonstrate that IFNγ + TNFα enhanced the DNA binding activity of NF-κB in GD thyrocytes, in association with the release of CXCL10; (2) show that pioglitazone exerts a dose-dependent inhibition on IFNγ + TNFα–induced CXCL10 secretion in thyrocytes, orbital fibroblasts, and preadipocytes, similar to the effect observed with rosiglitazone; and (3) demonstrate that thiazolidinediones (pioglitazone and rosiglitazone) act by reducing the IFNγ + TNFα activation of NF-κB in Graves thyrocytes. To the best of our knowledge, this is the first study showing that cytokines are able to activate NF-κB in Graves thyrocytes and a parallel inhibitory effect of pioglitazone both on CXCL10 chemokine secretion and NF-κB activation. Future studies will be needed to verify if new targeted peroxisome proliferator-activated receptor–γ activators may be able to exert the anti-inflammatory effects without the risk of expanding retrobulbar fat mass.

Introduction

We have recently shown [1] that, in primary cultures of thyrocytes, retrobulbar fibroblasts, and retrobulbar preadipocytes from Graves ophthalmopathy (GO) patients (p), the stimulation with interferon (IFN)-γ or tumor necrosis factor (TNF)–α + IFNγ induced chemokine (C-X-C motif) ligand 10 (CXCL10) release. However, until now, the mechanisms underlying the induction of CXCL10 secretion by cytokines in thyrocytes are still unknown.

Treatment of thyroid follicular cells, orbital fibroblasts, or preadipocytes with a pure peroxisome proliferator-activated receptor–γ (PPARγ) activator, rosiglitazone, at near-therapeutic doses significantly inhibited IFNγ-stimulated CXCL10 secretion, strongly suggesting that PPARγ might be involved in the regulation of IFNγ-induced chemokine expression in human thyroid autoimmunity and GO [1]. Altogether, these evidences suggest that PPARγ activators might attenuate the recruitment of activated T cells at sites of Th1-mediated inflammation.

Moreover, it has been suggested that the increased orbital fat tissue observed in GO may be a consequence of the overexpression of PPARγ caused by the inflammatory process. With regard to this, a recent case report described a type 2 diabetes mellitus patient who experienced exacerbation of GO with expansion of the orbital fat during treatment with the PPARγ agonist pioglitazone [2]. In cultured retrobulbar preadipocytes, PPARγ agonists caused a 2- to 13-fold increase, whereas a PPARγ antagonist caused a 2-7-fold reduction, in adipogenesis [2]. Other studies [3], [4] have confirmed the adipogenetic potential of PPARγ agonists on orbital preadipocytes, suggesting that PPARγ antagonists could provide a novel therapy for GO-p in the active stage of the disease.

However, until now, it is not known if pioglitazone is able, like rosiglitazone, to inhibit the IFNγ-induced chemokine expression in human thyroid autoimmunity and GO; and the mechanisms underlying the inhibition by thiazolidinediones (TZDs) of the cytokines-induced CXCL10 release in thyrocytes have not been identified.

The aims of this study were (1) to study the mechanisms underlying the induction of CXCL10 secretion by cytokines in Graves thyrocytes, (2) to test the effect of PPARγ activation by pioglitazone on IFNγ-inducible CXCL10 secretion in primary cultures of cells obtained from the main tissues involved in the pathogenesis of GD and GO (thyrocytes, orbital fibroblasts, and preadipocytes), and (3) to evaluate the mechanism of action of pioglitazone on nuclear factor (NF)–κB activation.