Enhancer of zeste homolog 2 regulates B-cell responses in a NOD.H-2h4 model of spontaneous autoimmune thyroiditis

BACKGROUND: Hashimoto's thyroiditis (HT) is a prevalent autoimmune thyroid disease characterized by lymphocytic infiltration and autoantibody production. Our previous findings showed that enhancer of zeste homolog 2 (EZH2) and the B cell-related transcription factor BACH2 are upregulated in HT thyroid tissues. However, the role of EZH2 in B cell-mediated autoimmunity remains unclear. OBJECTIVE: To investigate how EZH2 regulates B cell responses in a spontaneous autoimmune thyroiditis (SAT) mouse model, and to explore potential downstream epigenetic mechanisms, including BACH2. METHODS: A NOD.H-2h4 mouse model of SAT was used to assess the effect of the EZH2 catalytic activity inhibitor GSK126 on thyroid inflammation and B cell responses. The human B-lymphocyte cell line GM12878 underwent EZH2 knockdown or was treated with GSK126 to evaluate BACH2 expression, H3K27me3 levels, and IgG secretion. ChIP-qPCR and luciferase assays were employed to examine EZH2-dependent regulation of BACH2, and rescue experiments were conducted using BACH2 overexpression. RESULTS: In SAT mice, GSK126 reduced thyroid lymphocytic infiltration, decreased CD19+ and IgG+ B cell infiltration, and lowered thyroidal IgG and serum IgG levels. In vitro, pharmacological inhibition of EZH2 catalytic activity or knockdown suppressed BACH2, reduced H3K27me3, and diminished IgG secretion. Luciferase and ChIP-qPCR assays supported EZH2-dependent regulation of BACH2, and BACH2 overexpression partially restored BACH2 expression but did not fully rescue IgG production after EZH2 methyltransferase activity inhibition. CONCLUSION: EZH2 contributes to B cell-mediated immune responses and IgG production through epigenetic mechanisms in SAT. BACH2 may represent one downstream target of EZH2, but additional pathways are likely involved.