Pinpointing Interferon-alpha in Thyroid Autoimmunity: the Role of Endoplasmic Reticulum Stress

Presentation Number: OR28-5
Date of Presentation: June 16th, 2013

Angela Lombardi*1, Erlinda Conception1 and Yaron Tomer2
1Mount Sinai School of Medicine, New York, NY, 2Icahn School of Medicine at Mount Sinai and James J. Peters VA Medical Center, New York, NY

Abstract

The endoplasmic reticulum (ER) represents the cellular compartment where proteins are synthesized and  acquire their correct 3-D folding. A growing body of evidence suggests that accumulation of unfolded or misfolded proteins, a cellular condition termed “ER stress” may participate in the development of autoimmune diseases. Various models support the notion that proteins with folding defects may themselves act as autoantigens with subsequent ER overwhelming and activation of autoreactive lymphocytes. Thyroid follicular cells, which are professional secretory cells, due to their heavy engagement in thyroglobulin production, are very sensitive to disruptions in ER homeostasis. Moreover, interferon-alpha (IFN-α), the critical cytokine produced by immune system in response to viral infections, has recently emerged as a major factor that triggers thyroid autoimmunity but the mechanisms are still unknown. In this study, we sought to evaluate if, in thyroid cells, IFN-α could induce a dysregulation of ER stress-sensing pathways, suggesting a novel mechanism by which this key cytokine is able to induce autoimmune thyroid disease. To test the effect of IFN-α  on ER stress induction, human thyroid ML-1 cells and human thyroid primary cells were treated for 48 hours with either PBS alone (negative control) or  IFN-α (500, 1000 and 5000 units/ml). As positive controls, thyrocytes were incubated for 24 hours with 0.5 μM thapsigargin (THAP) or 0.5 μg/ml tunicamycin (TUN), known to induce ER stress. In both ML-1 cells and primary cultures of human thyrocytes IFN-α treatment for 48 hours induced upregulation of BiP mRNA, a widely recognized diagnostic marker of ER stress, in a dose-dependent manner. In both cell types, the same treatment also increased significantly the mRNA levels of other genes involved in ER stress, such as CHOP, spliced (active) XBP1 and ATF6, suggesting that the three major branches of the ER signal transduction pathway were activated by IFN-α. To investigate whether chemical chaperones could prevent IFNα-induced ER stress, both ML-1 and primary thyroid cells were pretreated for 24 hours with 2.5 mmol/l 4-phenylbutyric acid (PBA) or 5 mmol/l tauroursodeoxycholic acid (TUDCA) or vehicle. Interestingly, both chemical chaperones PBA and TUDCA, completely prevented the effect of IFN-α on ER stress induction. IFN-α did not decrease viability of thyroid cells at 48 hours of incubation, suggesting that apoptosis was not significantly activated.

 

Nothing to Disclose: AL, EC, YT