Background Enhancer of zeste homolog 2 (EZH2) is an epigenetic regulator with a role in B cell development. We have previously demonstrated increased EZH2 expression in peripheral blood mononuclear cells isolated from lupus patients, and that pharmacological inhibition of EZH2 alleviates lupus-like disease in mouse models. The goal of this study was to evaluate the role of B cell EZH2 overexpression in lupus pathogenesis.
Methods Using CRISPR/Cas9 technology, we generated an MRL/lpr mouse with floxed Ezh2, which was crossed with CD19-Cre mice. Autoantibody production, proteinuria, and kidney histology were evaluated. Flow cytometry, single cell RNA sequencing, and single cell B cell receptor sequencing were used to investigate compositional and functional changes of B cell subsets. In vitro B cell culture with/without an XBP1 inhibitor was performed. EZH2 and XBP1 mRNA levels in CD19+ B cells isolated from SLE patients and healthy controls were analyzed.
Results Ezh2 deletion in B cells decreased autoantibody production and improved glomerulonephritis in MRL/lpr mice. B cell development and differentiation were altered in the bone marrow and spleen in EZH2-deficient mice. Differentiation of germinal center (GC) B cells and plasmablasts was impaired. XBP1, a key transcription factor in B cell development, was downregulated in the absence of EZH2, and inhibiting XBP1 in vitro impairs plasmablast differentiation similar to EZH2-deficient mice. Single cell B cell receptor RNA sequencing revealed defective immunoglobulin class switch recombination in EZH2-deficient mice. In human lupus B cells, there was a strong correlation between EZH2 and XBP1 mRNA expression levels.
Conclusions Our results suggest that EZH2 overexpression in B cells contributes to disease pathogenesis in lupus. EZH2 enhances GC B cell development and the differentiation of plasmablasts via upregulating XBP1. Inhibiting B cell EZH2 expression impairs B cell development and immunoglobulin class switch recombination, and might provide a novel therapeutic approach in lupus.
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