Abstract 75: Somatic Overexpression and Knockdown in Mice to Identify Causal Genes Underlying 26 Lipid-associated Loci

Genome-wide association studies (GWAS) have identified 95 loci in the human genome that harbor common variants associated with plasma lipid traits. Of the 95 loci, 17 harbor genes known to cause monogenic lipid disorders and collectively a third of them contain genes with characterized roles in lipid metabolism. Therefore in the majority of loci the causal genes are unknown. We selected 32 genes, not previously implicated in lipid metabolism and representing a total of 26 loci, to test for their ability to modify plasma lipid concentrations upon somatic overexpression in vivo. We utilized adeno-associated virus serotype 8 (AAV8) to overexpress the selected genes specifically in the livers of both C57BL/6 mice and in an appropriate humanized mouse model (either mice expressing human apolipoprotein A-I for HDL loci or Apobec1-knockout, Ldlr haploinsufficient mice expressing human apolipoprotein B-100 for triglyceride and LDL loci). Approximately half of the genes tested reproducibly affected plasma lipids. For 13 of the interrogated loci the lipid-associated variants also correlated with expression variations of the respective genes in liver (liver expression quantitative trait loci-eQTLs). We demonstrate a causal role for 7 of these 13 genes. The overexpression of these 7 genes not only affected the predicted lipid class, but additionally exerted its effect in the predicted direction in 6 of 7 cases (Tmem57, Slc39a8, Ppp1r3b, Vkorc1, Tbkbp1 and Ube2l3). Additionally for a subset of the examined genes we proceeded to develop small interfering RNA (siRNA) nanoparticles that were particularly targeted to the liver. We were able to obtain robust knockdown for a significant number of genes and, in several cases, observe reciprocal effects on plasma lipids from our overexpression and knockdown studies. This work has identified several novel lipid regulators, whose further investigation can uncover novel mechanisms and pathways controlling plasma lipids.