Heritability and family-based GWAS analyses of the N-acyl ethanolamine and ceramide plasma lipidome.

Kathryn A Mcgurk,Martin Farrall,Heather J Cordell,Hugh Watkins,Bernard D Keavney,Simon G Williams,Hui Guo,Anna Nicolaou

doi:10.1093/hmg/ddab002

Abstract

Signalling lipids of the N-acyl ethanolamine (NAE) and ceramide (CER) classes have emerged as potential biomarkers of cardiovascular disease (CVD). We sought to establish the heritability of plasma NAEs (including the endocannabinoid anandamide) and CERs, to identify common DNA variants influencing the circulating concentrations of the heritable lipids, and assess causality of these lipids in CVD using 2-sample Mendelian randomization (2SMR). Nine NAEs and 16 CERs were analyzed in plasma samples from 999 members of 196 British Caucasian families, using targeted ultra-performance liquid chromatography with tandem mass spectrometry. All lipids were significantly heritable (h2 = 36–62%). A missense variant (rs324420) in the gene encoding the enzyme fatty acid amide hydrolase (FAAH), which degrades NAEs, associated at genome-wide association study (GWAS) significance (P < 5 × 10−8) with four NAEs (DHEA, PEA, LEA and VEA). For CERs, rs680379 in the SPTLC3 gene, which encodes a subunit of the rate-limiting enzyme in CER biosynthesis, associated with a range of species (e.g. CER[N(24)S(19)]; P = 4.82 × 10−27). We observed three novel associations between SNPs at the CD83, SGPP1 and DEGS1 loci, and plasma CER traits (P < 5 × 10−8). 2SMR in the CARDIoGRAMplusC4D cohorts (60 801 cases; 123 504 controls) and in the DIAGRAM cohort (26 488 cases; 83 964 controls), using the genetic instruments from our family-based GWAS, did not reveal association between genetically determined differences in CER levels and CVD or diabetes. Two of the novel GWAS loci, SGPP1 and DEGS1, suggested a casual association between CERs and a range of haematological phenotypes, through 2SMR in the UK Biobank, INTERVAL and UKBiLEVE cohorts (n = 110 000–350 000).

Highlights

Genetic studies in large numbers of individuals have identified loci where common genetic variation influences the prevalence of plasma lipoproteins, such as high-density lipoprotein (HDL) and low-density lipoprotein (LDL), and plasma lipid species, such as triglycerides, cholesterol and polyunsaturated fatty acids [1,2,3]
In this study we analyzed plasma N-acyl ethanolamine (NAE) and CERs by mass spectrometry-based targeted quantitative lipidomics in 196 British Caucasian families comprising 999 individuals, and determined their heritability and common genetic variant associations. We show that these bioactive lipid mediators are substantially heritable, and that plasma NAEs and a wide range of CERs are influenced by SNPs in key metabolic enzymes (FAAH, SPTLC3, DEGS1 and sphingosine 1phosphate phosphatase 1 (SGPP1))
Of the nine NAE species identified in plasma, palmitoyl ethanolamide (PEA) was at highest abundance (1.89 ± 1.36 ng/ml [mean ± standard deviation (SD)]), of the 16 plasma CER species, CER[N(24)S(18)] was most abundant (2.72 ± 1.29 nmol/ml), similar to healthy volunteers in previous studies [16,20,21,22,23,24]

Summary

Introduction

Genetic studies in large numbers of individuals have identified loci where common genetic variation influences the prevalence of plasma lipoproteins, such as high-density lipoprotein (HDL) and low-density lipoprotein (LDL), and plasma lipid species, such as triglycerides, cholesterol and polyunsaturated fatty acids [1,2,3]. Largescale, untargeted metabolomic genome-wide association study (GWAS) have recently identified genetic variants of the major lipid-metabolising enzymes that influence the circulating levels of a few ceramide (CER) species, mainly derivatives of sphingosine, and the N-acyl ethanolamine (NAE) species oleoyl ethanolamide (OEA) [4,5,6]. NAEs are fatty acid derivatives, derived from membrane phospholipids and degraded by the enzyme fatty acid amide hydrolase (FAAH; Fig. 1). This class of bioactive lipids includes the endocannabinoid anandamide (AEA), the nuclear factor agonist palmitoyl ethanolamide (PEA) and a number of other species with intracellular roles in neuronal signalling and pain. Plasma levels of some NAEs are positively correlated with obesity [10,11,12,13]

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Conclusion