Abstract 56: Coronary Artery Disease Risk Alleles at the LIPA Locus are Associated With Higher Levels of Its mRNA and Enzymatic Activity in Human Macrophages

Abstract

GWASs have identified LIPA, encoding lysosomal acid lipase (LAL), as a novel locus for coronary artery diseases (CAD) but not lipid traits. Meta-analyses revealed that CAD risk alleles rs1412444T and rs2246833T (clustered in intron 2/3 in high LD, r 2 =0.985) were associated with higher LIPA mRNA in monocytes. It is, however, unclear whether the risk alleles are associated with increased LIPA mRNA or LAL enzymatic activity in monocyte-derived macrophages (HMDM), the cell type playing critical roles in atherogenesis. Fine mapping of the LIPA region through our CARDIoGRAM+C4D consortium confirmed that the original GWAS SNPs showed the strongest signals. Both SNPs were enriched for H3K27Ac marks and binding sites for PU.1 and CEBPβ in HMDM, suggesting potential regulatory roles. LIPA mRNA and LAL activity were higher in HMDM of risk allele carriers (by Kruskal-Wallis test). LIPA mRNA was reduced by M1(LPS/IFNγ)-activation and increased by M2(IL-4)-activation. The eQTL relationship of LIPA was present in M1- and M2-activated HMDM, suggesting the activity of genetic determinants of LIPA expression was retained during macrophage activation. We performed allele-specific expression analysis with RNA-seq of HMDM from 30 subjects of European ancestry (EA) (~70M uniquely-mapped reads/sample) genotyped by Illumina Infinium Multi-Ethnic Global BeadChip imputed with 1000G Phase 3 v5. rs1051338 is within an annotated exon, in high LD with the GWAS lead SNPs (r 2 =0.859 in EA), and had consistent allelic expression favoring G allele, which is on the same haplotype as the risk alleles of the GWAS SNPs. In addition, LIPA mRNA was higher in human coronary arteries with atherosclerotic plaque. Immunostaining showed that LAL was abundant within the extracellular space of human atherosclerotic intima and also co-localized with CD68+ macrophages. In summary, the results support a novel, potentially pro-atherogenic role for monocyte-macrophage LIPA gain-of-function in CAD.