Cre-loxP System-based Mouse Model for Investigating Graves' Disease and Associated Orbitopathy.

BACKGROUND: Graves' disease (GD), one of the most common forms of autoimmune thyroid disorder, is characterized by hyperthyroidism caused by antibodies (Ab) against the extracellular A-subunit of the thyrotropin receptor (TSHR). Various approaches have been used to create mouse models of GD, including transfected fibroblasts and immunization with plasmids or adenoviruses expressing human TSHR A-subunit (hTSHR A-subunit). These models, however, require repeated immunizations and produce inconsistent results. Here, we established a novel Cre-loxP system-based mouse model that is able to generate hTSHR A-subunit, mimicking human GD, and characterized the histological changes in GO progression after a single injection.

METHODS: A Cre-loxP system-based mouse model was constructed by inserting the CAG-loxP-STOP-loxP-hTSHR A-subunit cassette into the Rosa26 locus of the mouse genome. Conditional expression of the hTSHR A-subunit was successfully achieved by intramuscular injection of the transactivator of transcription (TAT)-Cre recombinase (GD mice). The blood tests for anti-TSHR antibodies and the total T4 level were performed. Magnetic resonance imaging was used to monitor morphological changes in the eyes. A histological examination of the thyroid glands and retrobulbar tissues was performed to observe pathological changes.

RESULTS: Twenty-four (8 Control, 16 GD) mice were investigated. All GD mice exhibited higher levels of TSHR Abs compared to the control group. Moreover, more than 80% of the mouse models showed elevated T4 levels accompanied by thyroid goiters. MRI analysis revealed an increased volume of retrobulbar tissue, while immunohistochemical staining of orbital tissues exhibited macrophages infiltration and muscle fibrosis in the GD mice, contrasting with the control group.

CONCLUSIONS: Our novel mouse model for GD that showed the histological features of GO was successfully established using the Cre-loxP system. This animal model offers improved insights and contributes to advancing methodological developments for GD and GO.