Genome-wide enhancer-gene regulatory maps of liver reveal novel regulatory mechanisms underlying NAFLD pathogenesis.

Abstract

Introduction: Non-alcoholic fatty liver disease (NAFLD) represents the most widespread liver disease globally, ranging from non-alcoholic fatty liver (NAFL) and steatohepatitis (NASH) to fibrosis/cirrhosis, with potential progression to hepatocellular carcinoma (HCC). Genome-wide association studies (GWASs) have identified several single nucleotide polymorphisms (SNPs) associated with NAFLD. However, numerous GWAS signals associated with NAFLD locate in non-coding regions, posing a challenge for interpreting their functional annotation.

Results: In this study, we utilized the Activity-by-Contact (ABC) model to construct the enhancer-gene maps of liver by integrating epigenomic data from 15 liver tissues and cell lines. We constructed the most comprehensive genome-wide regulatory maps of the liver, identifying 543,486 enhancer-gene connections, including 267,857 enhancers and 16,872 target genes. Enrichment analyses revealed that the ABC SNPs are significantly enriched in active chromatin regions and active chromatin state. By combining the ABC regulatory maps and NAFLD GWAS data, we systematically identified ABC SNPs associated with NAFLD risk. Through the functional annotations, such as pathway enrichment and drug-gene interaction analyses, we identified 6 genes (GGT1, ACTG1, SPP1, EPHA2, PROZ and SHMT1) as candidate NAFLD genes, with SHMT1 previously reported. Among the SNPs connected to the candidate genes, the ABC SNP rs2017869 (odds ratio [OR] for the C allele = 1.10, 95% CI = 1.04-1.16, P = 5.97 × 10^- 4) had the highest ABC score. According to the ABC maps, rs2017869 links to GGT1, and several drugs targeting this gene, such as liothyronine, showed potential benefits to patients with NAFLD. Furthermore, we identified that another novel gene, EPHA2, may play a crucial role in NAFLD by regulating the GGT levels.

Conclusions: Our study provides the most comprehensive ABC regulatory maps of the liver to date. This resource offers a valuable reference for identifying regulatory variants and prioritizing susceptibility genes of liver diseases, such as NAFLD.