An allele-specific functional SNP associated with two autoimmune diseases modulates IRF5 expression by long-range chromatin loop formation

Both Systemic Lupus Erythematosus (SLE) and Systemic Sclerosis (SSc) are autoimmune diseases sharing similar genetic backgrounds. Genome-wide association studies (GWASs) have constantly disclosed numerous genetic variants conferring to both disease risks at 7q32.1, but the functional mechanisms underlying them are still largely unknown. Through combining fine-mapping and functional epigenomic analyses, we prioritized a potential independent functional SNP (rs13239597) within TNPO3 promoter region, residing in a putative enhancer element. Functional analysis integrating expression quantitative trait locus (eQTL) and high-throughput chromatin interaction (Hi-C) demonstrated that IRF5 is the distal target gene (~118kb) of rs13239597, which is a key regulator of pathogenic autoantibody dysregulation increased risk of both SLE and SSc. We experimentally validated the long-range chromatin interactions between rs13239597 and IRF5 using chromosome conformation capture (3C) assay. We further demonstrated that rs13239597-A acted as an allele-specific enhancer regulating IRF5 expression, independently of TNPO3 by using dual-luciferase reporter assays and CRISPR-Cas9. Particularly, the transcription factor EVI1 could preferentially bind to rs13239597-A allele and increase the enhancer activity to regulate IRF5 expression. Taken together, our results uncovered the mechanistic insight connecting between a noncoding functional variant with a distal immunologically pathogenic gene IRF5, which might obligate in understanding the complex genetic architectures of SLE and SSc pathogenesis.