Open chromatin profiling in adipose tissue marks genomic regions with functional roles in cardiometabolic traits
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ABSTRACT: Identifying the regulatory mechanisms of genome-wide association study (GWAS) loci affecting adipose tissue has been restricted due to limited characterization of adipose transcriptional regulatory elements. We profiled chromatin accessibility in three frozen human subcutaneous adipose tissue needle biopsies and preadipocytes and adipocytes from the Simpson Golabi-Behmel Syndrome (SGBS) cell strain using an assay for transposase-accessible chromatin (ATAC-seq). We identified 68,571 representative accessible chromatin regions (peaks) across adipose tissue samples (FDR<5%). GWAS loci for eight cardiometabolic traits were enriched in these peaks (p<0.005), with the strongest enrichment for waist-hip ratio. Of 110 recently described cardiometabolic GWAS loci colocalized with adipose tissue eQTLs, 59 loci had one or more variants overlapping an adipose tissue peak. Annotated variants at the SNX10 waist-hip ratio locus and the ATP2A1-SH2B1 body mass index locus showed allelic differences in regulatory assays. These adipose tissue accessible chromatin regions elucidate genetic variants that may alter adipose tissue function to impact cardiometabolic traits.
Project description:Chromatin accessibility and gene expression in relevant cell contexts can guide identification of regulatory elements and mechanisms at genome-wide association study (GWAS) loci. To identify regulatory elements that display differential activity across adipocyte differentiation, we performed ATAC-seq and RNA-seq in a cell model of preadipocytes and adipocytes at days 4 and 14 of differentiation. For comparison, we created a consensus map of ATAC-seq peaks in 11 subcutaneous adipose tissue samples. A set of 15,919 adipocyte-dependent peaks showed stronger enrichment (60.1%) of adipocyte nuclei enhancers than 51,855 adipose tissue peaks (44.6%) or 18,244 preadipocyte-dependent peaks (11.5%). We linked context-dependent peaks to genes based on adipocyte promoter capture Hi-C data, overlap with adipose eQTL variants, and differential gene expression. Of 16,167 context-dependent peaks that could be linked to a gene, 5,184 were linked by two or more strategies to 1,675 genes. Among GWAS loci for cardiometabolic traits, adipocyte peaks showed the strongest enrichment for waist-to-hip ratio, coronary artery disease, and HDL-cholesterol, while adipose tissue peaks also showed significant enrichment for LDL-cholesterol and triglyceride levels. We identified 666 peaks linked to 507 genes by two or more methods and overlapping a GWAS signal, suggesting a regulatory mechanism at these loci. At one GWAS locus for palmitoleic acid, rs603424 was located in an adipocyte-dependent peak linked to SCD and exhibited allelic differences in transcriptional activity in adipocytes (P=0.003) but not preadipocytes (P=0.09). These results demonstrate that context-dependent peaks and genes can guide discovery of regulatory variants at GWAS loci and aid identification of regulatory mechanisms.
Project description:Chromatin accessibility and gene expression in relevant cell contexts can guide identification of regulatory elements and mechanisms at genome-wide association study (GWAS) loci. To identify regulatory elements that display differential activity across adipocyte differentiation, we performed ATAC-seq and RNA-seq in a cell model of preadipocytes and adipocytes at days 4 and 14 of differentiation. For comparison, we created a consensus map of ATAC-seq peaks in 11 subcutaneous adipose tissue samples. A set of 15,919 adipocyte-dependent peaks showed stronger enrichment (60.1%) of adipocyte nuclei enhancers than 51,855 adipose tissue peaks (44.6%) or 18,244 preadipocyte-dependent peaks (11.5%). We linked context-dependent peaks to genes based on adipocyte promoter capture Hi-C data, overlap with adipose eQTL variants, and differential gene expression. Of 16,167 context-dependent peaks that could be linked to a gene, 5,184 were linked by two or more strategies to 1,675 genes. Among GWAS loci for cardiometabolic traits, adipocyte peaks showed the strongest enrichment for waist-to-hip ratio, coronary artery disease, and HDL-cholesterol, while adipose tissue peaks also showed significant enrichment for LDL-cholesterol and triglyceride levels. We identified 666 peaks linked to 507 genes by two or more methods and overlapping a GWAS signal, suggesting a regulatory mechanism at these loci. At one GWAS locus for palmitoleic acid, rs603424 was located in an adipocyte-dependent peak linked to SCD and exhibited allelic differences in transcriptional activity in adipocytes (P=0.003) but not preadipocytes (P=0.09). These results demonstrate that context-dependent peaks and genes can guide discovery of regulatory variants at GWAS loci and aid identification of regulatory mechanisms.
Project description:Identifying the molecular mechanisms by which genome-wide association study (GWAS) loci influence traits remains challenging. Chromatin accessibility quantitative trait loci (caQTL) help identify GWAS loci that may alter GWAS traits by modulating chromatin structure, but caQTL have been identified in a limited set of human tissues. Here we mapped caQTL in human liver tissue in 20 liver samples and identified 3,123 caQTL. The caQTL variants are enriched in liver tissue promoter and enhancer states and frequently disrupt binding motifs of transcription factors expressed in liver. We predicted target genes for 861 caQTL peaks using proximity, chromatin interactions, correlation with promoter accessibility or gene expression, and colocalization with expression QTL. Using GWAS signals for 19 liver function and/or cardiometabolic traits, we identified 110 colocalized caQTL and GWAS signals, 56 of which contained a predicted caPeak target gene. At the LITAF LDL-cholesterol GWAS locus, we validated that a caQTL variant showed allelic differences in protein binding and transcriptional activity. These caQTL contribute to the epigenomic characterization of human liver and help identify molecular mechanisms and genes at GWAS loci.
Project description:Identifying the molecular mechanisms by which genome-wide association study (GWAS) loci influence traits remains challenging. Chromatin accessibility quantitative trait loci (caQTL) help identify GWAS loci that may alter GWAS traits by modulating chromatin structure, but caQTL have been identified in a limited set of human tissues. Here we mapped caQTL in human liver tissue in 20 liver samples and identified 3,123 caQTL. The caQTL variants are enriched in liver tissue promoter and enhancer states and frequently disrupt binding motifs of transcription factors expressed in liver. We predicted target genes for 861 caQTL peaks using proximity, chromatin interactions, correlation with promoter accessibility or gene expression, and colocalization with expression QTL. Using GWAS signals for 19 liver function and/or cardiometabolic traits, we identified 110 colocalized caQTL and GWAS signals, 56 of which contained a predicted caPeak target gene. At the LITAF LDL-cholesterol GWAS locus, we validated that a caQTL variant showed allelic differences in protein binding and transcriptional activity. These caQTL contribute to the epigenomic characterization of human liver and help identify molecular mechanisms and genes at GWAS loci.
Project description:Identifying the molecular mechanisms by which genome-wide association study (GWAS) loci influence traits remains challenging. Chromatin accessibility quantitative trait loci (caQTL) help identify GWAS loci that may alter GWAS traits by modulating chromatin structure, but caQTL have been identified in a limited set of human tissues. Here we mapped caQTL in human liver tissue in 20 liver samples and identified 3,123 caQTL. The caQTL variants are enriched in liver tissue promoter and enhancer states and frequently disrupt binding motifs of transcription factors expressed in liver. We predicted target genes for 861 caQTL peaks using proximity, chromatin interactions, correlation with promoter accessibility or gene expression, and colocalization with expression QTL. Using GWAS signals for 19 liver function and/or cardiometabolic traits, we identified 110 colocalized caQTL and GWAS signals, 56 of which contained a predicted caPeak target gene. At the LITAF LDL-cholesterol GWAS locus, we validated that a caQTL variant showed allelic differences in protein binding and transcriptional activity. These caQTL contribute to the epigenomic characterization of human liver and help identify molecular mechanisms and genes at GWAS loci.
Project description:We investigated whether intersecting functional genomic data (ATAC-seq + promoter focused Capture C) with increasingly powered publically available GWAS for Body Mass Index and Waist to Hip Ratio could identify additional true postiive subsignficant signals (5x10-8< P value < 5x10-4) without increasing the GWAS sample size
Project description:We investigated whether intersecting functional genomic data (ATAC-seq + promoter focused Capture C) with increasingly powered publically available GWAS for Body Mass Index and Waist to Hip Ratio could identify additional true postiive subsignficant signals (5x10-8< P value < 5x10-4) without increasing the GWAS sample size
Project description:Genome-wide association studies (GWAS) have identified thousands of genomic loci associated with a variety of common, complex human traits. The contribution of genetic variants to gene expression regulation has been well studied, supporting the idea that gene expression plays a causal role at some complex trait-associated loci. However, many current studies have not comprehensively investigated the impact of genetic variation on chromatin accessibility at a large scale within a single tissue. Genetic variants associated with differences in chromatin accessibility, known as chromatin accessibility quantitative trait loci (caQTLs), are major contributors to gene expression differences and GWAS signals. We assessed chromatin accessibility in 189 human liver tissue samples using ATAC-seq and identified over two million accessible chromatin regions enriched for gene regulatory characteristics. We integrated chromatin accessibility and genotype data from 175 samples and identified 14,076 caQTLs. Using publicly available blood lipid GWAS data, we found 157 loci where the colocalization of caQTLs, expression quantitative trait loci (eQTLs), and GWAS signals generated specific molecular hypotheses about causal regulatory elements, affected genes, and, in some cases, transcription factors, resolving these associations to single-nucleotide resolution. We performed a comprehensive analysis of the GWAS signals that remain without a proposed mechanism beyond liver caQTLs and eQTLs. After incorporating additional potential regulatory mechanism data, we found that approximately 26% of blood lipid GWAS signals remain without a proposed mechanism. Overall, our results demonstrate the benefits of integrating multiple datasets to improve our understanding of GWAS signals while emphasizing the need for additional experiments to fully characterize them.
Project description:To reveal the organisation of the cartilage cell chondrocyte genome and identify changes that occur within this organisation during development and due to osteoarthritis (OA). Methods Assay for Transposase -Accessible Chromatin using Sequencing (ATAC-seq) was performed on chondrocytes isolated from 16 patients undergoing total hip replacement because of OA (n=7) or due to a neck of femur fracture (NOF, n=9). ATAC-seq was similarly performed on bone-marrow mesenchymal stem cells (BM-MSC) and differentiated chondrocytes of two donors. DNA sequence reads (av. 50 million/sample) were aligned to human genome Hg38. Peaks were called using MACS2 and differential accessibility identified by DiffBind. Interexperiment comparisons and intersection with published gene expression changes, chondrogenesis ChIP-seq, knee ATAC-seq and human tissue scATAC-seq were performed in Galaxy and R. OA GWAS signal regions were overlapped with our defined chondrocyte ATAC-seq peaks. Results In BM-MSC and derived chondrocytes we mapped 138005 open chromatin regions, of which 20979 and 50699 significantly increased and decreased respectively during cell differentiation. In hip chondrocytes we identified 115295 open chromatin regions, 1383 and 573 were more or less differentially accessible respectively when comparing OA with NOF samples. In both data sets ‘newly accessible regions were enriched at enhancer regions (defined by ChIP-seq). Comparing the data with the ATAC-seq from the single cell ATLAS we identified 11866 open regions exclusive to chondrocytes. Genes associated with these regions were significantly enriched for cartilage-related gene ontology terms. Taking the 420 OA GWAS signals present in the GWAS catalogue, 313 of the OA regions (defined as lead SNP + proxy SNPs with r2 ≥ 0.8) overlapped with a chondrocyte ATAC-seq region. Conclusions Here we have mapped chromatin accessible region changes during chondrogenesis, showing that newly accessible regions are enriched at enhancer regions and positively correlate with gene expression. Open chromatin region changes between OA and NOF cartilage were fewer, and peak differences were subtle. Overall, we have associated OA GWAS loci with accessible regions and defined regions of the genome specific to cartilage and chondrogenesis.
Project description:Body fat distribution is a heritable risk factor for cardiovascular and metabolic disease. In humans, rare Inhibin beta E (INHBE, activin E) loss-of-function variants are associated with lower waist-to-hip ratio and protection from type 2 diabetes. Hepatic fatty acid sensing promotes INHBE expression during fasting and in obese individuals, yet it is unclear how the hepatokine activin E governs body shape and energy metabolism. Here, we uncover activin E as a negative feedback regulator of adipose lipolysis that restrains excessive fat breakdown during fasting. By suppressing β-agonist-induced lipolysis, activin E promotes visceral fat accumulation, adipocyte hypertrophy and contributes to adipose dysfunction in mice. Mechanistically, we demonstrate that activin E elicits its effect on adipose tissue through ACVR1C, activating SMAD2/3 signaling and suppressing PPARG target genes. Conversely, loss of activin E or ACVR1C increases fat utilization, lowers adiposity and drives gene signatures indicative of healthy adipose function. Our studies identify activin E-ACVR1C as metabolic rheostat promoting liver-adipose crosstalk to preserve fat mass during prolonged fasting, a mechanism that is maladaptive in obese individuals.