15Genome-wide association studies (GWAS) have implicated ~380 genetic loci for plasma lipid regulation. 16However, these loci only explain 17-27% of the trait variance and a comprehensive understanding of the 17 molecular mechanisms has not been achieved. In this study, we utilized an integrative genomics approach 18 leveraging diverse genomic data from human populations to investigate whether genetic variants 19 associated with various plasma lipid traits, namely total cholesterol (TC), high and low density 20 lipoprotein cholesterol (HDL and LDL), and triglycerides (TG), from GWAS were concentrated on 21 specific parts of tissue-specific gene regulatory networks. In addition to the expected lipid metabolism 22 pathways, gene subnetworks involved in 'interferon signaling', 'autoimmune/immune activation', 'visual 23 transduction', and 'protein catabolism' were significantly associated with all lipid traits. Additionally, we 24 detected trait-specific subnetworks, including cadherin-associated subnetworks for LDL, glutathione 25 metabolism for HDL, valine, leucine and isoleucine biosynthesis for TC, and insulin signaling and 26 complement pathways for TG. Finally, utilizing gene-gene relations revealed by tissue-specific gene 27 regulatory networks, we detected both known (e.g. APOH, APOA4, and ABCA1) and novel (e.g. F2 in 28 adipose tissue) key regulator genes in these lipid-associated subnetworks. Knockdown of F2 gene 29 (Coagulation Factor II, Thrombin) in 3T3-L1 adipocytes reduced gene expression of Abcb11, Apoa5, 30Apof, Gc, Fabp, Hrg, Proc, and Cd36, several of which are important in lipoprotein transport and fatty 31 acid uptake, providing evidence for a link between adipose thrombin and plasma lipid regulation. Our 32 results shed light on the complex mechanisms underlying lipid metabolism and highlight potential novel 33 targets for lipid regulation and lipid-associated diseases. 34Factor II 36 37 38 Materials and Methods 90
GWAS of lipid traits 91The experimental design, genotyping, and association analyses of HDL, LDL, TC, and TG were 92 described previously (12). The dataset used in this study is comprised of > 100,000 individuals of 93 European descent (sample size 100,184 for TC, 95,454 for LDLC, 99,900 for HDLC and 96,598 for TG), 94 ascertained in the United States, Europe, or Australia. More than 906,600 SNPs were genotyped using 95Affymetrix Genome-Wide Human SNP Array 6.0. Imputation was further carried out to obtain 96 information for up to 2.6 million SNPs using the HapMap CEU (Utah residents with ancestry from 97 northern and western Europe) panel. SNPs with minor allele frequency (MAF) < 1% were removed. 98