Functional characterization of the MECP2/IRAK1 lupus risk haplotype in human T cells and a human MECP2 transgenic mouse.

Genetic polymorphism in MECP2/IRAK1 on chromosome Xq28 is a confirmed and replicated susceptibility locus for lupus. High linkage disequilibrium in this locus suggests that both MECP2 and IRAK1 are candidate genes for the disease. DNA methylation changes in lupus T cells play a central role in the pathogenesis of lupus, and MeCp-2 (encoded by MECP2) is a master regulator of gene expression and is also known to recruit DNA methyltransferase 1 (DNMT1) during DNA synthesis. Using human T cells from normal individuals with either the lupus risk or the lupus protective haplotype in MECP2/IRAK1, we demonstrate that polymorphism in this locus increases MECP2 isoform 2 mRNA expression in stimulated but not unstimulated T cells. By assessing DNA methylation levels across over 485,000 methylation sites across the entire genome, we further demonstrate that the lupus risk variant in this locus is associated with significant DNA methylation changes, including in the HLA-DR and HLA-DQ loci, as well as interferon-related genes such as IFI6, IRF6, and BST2. Further, using a human MECP2 transgenic mouse, we show that overexpression of MECP2 alters gene expression in stimulated T cells. This includes overexpression of Eif2c2 that regulates the expression of multiple microRNAs (such as miR-21), and the histone demethylase Jhdm1d. In addition, we show that MECP2 transgenic mice develop antinuclear antibodies. Our data suggest that the lupus-associated variant in the MECP2/IRAK1 locus has the potential to affect all 3 epigenetic mechanisms: DNA methylation, microRNA expression, and histone modification. Importantly, these data support the notion that variants within the MECP2 gene can alter DNA methylation in other genetic loci including the HLA and interferon-regulated genes, thereby providing evidence for genetic-epigenetic interaction in lupus.