Post-operative atrial fibrillation examined using whole-genome RNA sequencing in human left atrial tissue

Martin I Sigurdsson, Louis Saddic, Mahyar Heydarpour, Tzuu-Wang Chang, Prem Shekar, Sary Aranki, Gregory S Couper, Stanton K Shernan, Jochen D Muehlschlegel, Simon C Body, Martin I Sigurdsson, Louis Saddic, Mahyar Heydarpour, Tzuu-Wang Chang, Prem Shekar, Sary Aranki, Gregory S Couper, Stanton K Shernan, Jochen D Muehlschlegel, Simon C Body

Abstract

Background: Both ambulatory atrial fibrillation (AF) and post-operative AF (poAF) are associated with substantial morbidity and mortality. Analyzing the tissue-specific gene expression in the left atrium (LA) can identify novel genes associated with AF and further the understanding of the mechanism by which previously identified genetic variants associated with AF mediate their effects.

Methods: LA free wall samples were obtained intraoperatively immediately prior to mitral valve surgery in 62 Caucasian individuals. Gene expression was quantified on mRNA harvested from these samples using RNA sequencing. An expression quantitative trait loci (eQTL) analysis was performed, comparing gene expression between different genotypes of 1.0 million genetic markers, emphasizing genomic regions and genes associated with AF.

Results: Comparison of whole-genome expression between patients who later developed poAF and those who did not identified 23 differentially expressed genes. These included genes associated with the resting membrane potential modified by potassium currents, as well as genes within Wnt signaling and cyclic GMP metabolism. The eQTL analysis identified 16,139 cis eQTL relationships in the LA, including several involving genes and single nucleotide polymorphisms (SNPs) linked to AF. A previous relationship between rs3744029 and MYOZ1 expression was confirmed, and a novel relationship between rs6795970 and the expression of the SCN10A gene was identified.

Conclusions: The current study is the first analysis of the human LA expression landscape using high-throughput RNA sequencing. Several novel genes and variants likely involved in AF pathogenesis were identified, thus furthering the understanding of how variants associated with AF mediate their effects via altered gene expression.

Trial registration: ClinicalTrials.gov ID: NCT00833313 , registered 5. January 2009.

Keywords: Atrial fibrillation; Expression quantitative trait loci; Mitral valve surgery; eQTL.

Figures

Fig. 1
Fig. 1
Differentially expressed genes in patients with post-operative atrial fibrillation (poAF). A volcano plot comparing the expression of all genes in the human left atria between patients who had post-operative atrial fibrillation compared to those who did not. The x-axis shows the log2 fold change and the y-axis shows the –log10 of the p-value adjusted for multiple testing. Dotted lines mark predetermined levels of significance; absolute log2 ratio >0.5 (x-axis) or p-value adjusted for multiple testing <0.1 (y-axis). Green dots indicate genes that fulfill one significance criteria, red dost indicate genes that fulfill both
Fig. 2
Fig. 2
Expression of PITX2, KCNN3, and ZFHX3 in the LA of patients with and without post-operative atrial fibrillation (poAF). Boxplots of the normalized expression of aPITX2, bKCNN3 and cZFHX3 between patients with and without poAF. The number above each box shows the number of patients in each group. FPM – Fraction per million mapped fragments
Fig. 3
Fig. 3
Gene Network Analysis. Result of the functional network analysis of the list of genes with differential expression in poAF by the GeneMANIA algorithm [19]. Connections were assessed using the list of differentially expressed genes (black, black stripes) in the context of a left atrial co-expression network (gray connections) and the default GeneMANIA networks on genetic interactions (green) or shared protein domains (yellow). Two gene function categories were overrepresented in the output, the Wnt Signaling pathway (red) and the cGMP metabolic process (blue)
Fig. 4
Fig. 4
Genomic location of cis-eQTL relationships in the human LA. A Manhattan plot of the genomic location of all significant cis-eQTL (at false discovery adjusted p < 0.05) relationships in the human left atrium
Fig. 5
Fig. 5
cis eQTL relationships of SNPs and genes associated with AF. Boxplots of the normalized expression of each gene (y-axis) and the genotype (allele counts of minor allele) for aMYOZ1 and rs3740293 and bSCN10A gene and rs6795970. The number above each box shows the number of patients with each genotype. FPM – Fraction fragments per million mapped fragments

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