Interferon-α Triggers Autoimmune Thyroid Diseases via Lysosomal-Dependent Degradation of Thyroglobulin

Context: Autoimmune thyroid diseases (AITDs) arise from complex interactions among genetic, epigenetic, and environmental factors. Thyroglobulin (TG) is a major susceptibility gene for both Graves disease and Hashimoto thyroiditis. Interferon-alpha (IFN alpha), a cytokine secreted during viral infections, has emerged as a key trigger of AITD. We have shown that IFN alpha upregulates TG transcription; however, how the upregulation of TG transcription by IFN alpha triggers AITD is still unknown. Objective: To evaluate how IFN alpha triggers AITD by testing its effects on TG processing. Design: We exposed human thyroid cells to IFN alpha and evaluated its effects on TG expression and processing. Results: Human thyroid cells exposed to INF alpha had increased levels of TG mRNA but reduced TG protein levels, indicating TG protein degradation. IFN alpha induced endoplasmic reticulum stress, but surprisingly, neither the use of chemical chaperones nor proteasome inhibitor prevented IFN alpha-induced TG degradation. IFN alpha also increased LysoTracker staining and autophagy flux measured by net light chain 3 (LC3)-II and p62 fluxes. In addition, expression of autophagy markers LC3 and autophagy-related gene 5 was higher in thyroid tissues from patients with AITD. Finally, blocking lysosomal degradation prevented IFN alpha-induced degradation of TG. Conclusion: We have shown in this study IFN alpha-induced lysosomal-dependent degradation of TG in human thyroid cells. Our findings suggest that during viral infections, local thyroidal IFN alpha production can lead to lysosomal TG degradation, releasing pathogenic TG peptides that can trigger AITD.