Pathway-based Genome-wide Association Studies For Plasma Adiponectin

Objective:Adiponectin is an adipocyte-specific secretory protein,which is associated with type 2 diabetes,obesity,dyslipidemia,and other insulin resistance related phenotypes.To identify the genes and signaling pathways that were associated with plasma adiponectin,we performed genome-wide association studies(GWAS)and pathway-based association analyses in extremely obese individuals and normal-weight controls.Methods:We collected 1071 unrelated European Americans.Seven hundred and sixty four(764)have adiponectin data,746 were females.Five hundred and fifty thousand(550,000)single nucleotide polymorphisms(SNPs)were genotyped by Illumina HumanHap 550 SNP Arrays.Genome-wide association analyses were carried out by PLINK for adiponectin,we also performed pathway-based genome-wide association studies by a modified Gene Set Enrichment Analysis(GSEA)for adiponectin and BMI.A total of 1347 pathways that compiled from the BioCarta,Kyoto Encyclopedia of Genes and Genomes(KEGG),and Gene Ontology(GO)databases were analyzed.Results:1.In the quantitative genome-wide association studies,the ADIPOQ gene was associated with BMI-adjusted adiponectin(rs8223 87,P=3.77x 10-7).Weaker associations were found in DLEU1(rs200220,P=7.49×10-7),ALK(rs13029602,P=7.48×10-6),and CREG2(rs4352251,P=1.86×10-6)genes.2.(1)In the case/control pathway-based genome-wide association study for plasma adiponectin,Seventy-four(74)pathways achieved a significant level of nominal P<0.05,however,only the racl Pathway(Nominal P<0.001,FDR=0.008,FWER=0.008)passed multiple testing correction.RAC1 gene existed in both racl Pathway and cdc42racPathway(Nominal P<0.001,FDR=0.188,FWER=0.249).(2)In the quantitative pathway-based genome-wide association study,we found that 61 pathways were associated with BMI-adjusted adiponectin(Nominal P<0.05).These pathways contained many type 2 diabetes and insulin resistance related genes.Genes in RAS and downstream PI3K/AKT and MAPK/ERK signaling pathways were found in multiple significant pathways,including the tidPathway,maPathway,hsa04150,actinYPathway,Par1 Pathway and ghPathway.RAS signaling pathway was associated with BMI-adjusted adiponectin after FDR correction(Nominal P=0.028,FDR=0.028).Meanwhile,the RAC1 gene also exised in the hsa05030(Nominal P=0.048),malPathway(Nominal P=0.040),and actinY Pathway(Nominal P=0.019).(3)Seventy-five(75)pathways yielded significant nominal P-values(Nominal P<0.05)in the quantitative pathway-based genome-wide association study for unadjusted adiponectin,RAC1 gene existed in G00032270(Nominal P=0.011)and G00051247(Nominal P=0.011)pathways,although none of these pathways remained significant after multiple testing corrections.(4)We found 70 pathways were associated with BMI in extremely obese cases and nominal-weight controls(Nominal P<0.05),however,none of them reached FDR<0.05 after multiple testing correction.Conclusions:(1)ADIPOQ,DLEU1,ALK,and CREG2 genes were associated with adiponectin.The DLEU1,ALK,and CREG2 associations were the first identified by our study.(2)The downstream branches of the RAS signaling pathway,including the PI3K/AKT,MAPK/ERK,and RAC1 cell motility signaling pathways,were associated with plasma adiponectin levels.Among them,the RAC 1 cell motility signaling pathway was associated with adiponectin in both case/control and quantitative genome-wide pathway association studies.(3)Many type 2 diabetes susceptibility genes were found in adiponectin-related pathways,but only a few of them existed in BMI-related pathways.It is suggested that adiponectin may play a role in connecting obesity and type 2 diabetes.