B Cell Epigenetic Modulation of IgA Response by 5-Azacytidine and IgA Nephropathy

Key Points Dysregulated IgA production plays a key role in the pathogenesis of IgA nephropathy. Increased 5-methylcytosine modification, an epigenetic regulatory mechanism, exaggerated IgA nephropathy phenotype in mice. Conversely, inhibition of 5-methylcytosine modification ameliorated progression of IgA nephropathy–like kidney disease in mice. Background IgA nephropathy is an important global cause of kidney failure. Dysregulation of IgA production is believed to play a key role in IgA nephropathy pathogenesis; however, little is known about the epigenetic mechanisms, such as RNA 5-methylcytosine (5mC) modification, in regulating IgA synthesis. Methods To decipher the role of RNA 5mC in regulation of IgA class switch, the microRNA (miR)-23b −/− and Lactobacillus casei (Chinese Industrial Microbial Culture Collection Center) cell wall extract–induced Kawasaki disease mice were treated with 5-azacytidine. Trdmt1 −/− and double Trdmt1 −/− / miR-23b −/− mice and Aid −/− mice or Aid −/− / miR-23b −/− mice were also used. Results We showed that miR-23b downregulated expression of Transfer RNA Aspartic Acid Methyltransferase 1 and consequently reduced 5mC (m 5 C) RNA modification and IgA synthesis in B cells. Inhibition of m 5 C RNA modification normalized serum IgA levels and ameliorated progression of the IgA nephropathy–like kidney disease in miR-23b −/− and Kawasaki disease mice, while mesangial IgA and C3 deposition failed to develop in Trdmt1 −/− miR-23b −/− mice. By contrast, increased m 5 C RNA modification resulted in an exaggerated IgA nephropathy phenotype. miR-23b regulation of serum IgA levels and the development of an IgA nephropathy–like kidney disease in miR-23b −/− and Kawasaki disease mice is likely mediated through TRDMT1-driven 5mC RNA modification in B cells, resulting in impaired activation-induced cytidine deaminase activity and IgA class switch recombination. Conclusions This study revealed TRDMT1-induced RNA 5mC methylation regulated IgA class switch, and inhibition of RNA 5mC by 5-azacytidine ameliorated progression of IgA nephropathy.