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A pleiotropic hypoxia-sensitive EPAS1 enhancer is disrupted by adaptive alleles in Tibetans [RNA-seq TeloHAEC]

ABSTRACT: Background & Aims: A major focus of human genetics research has been to identify locally adapted alleles in global populations. In Tibetans, noncoding alleles in EPAS1 – who’s protein product HIF-2 is a key driver of the response to hypoxia – carry some of the strongest signatures of positive selection found in humans, yet their functional mechanism has never been systematically examined. Here we report the discovery of three enhancers within EPAS1, whose activity is significantly disrupted by Tibetan alleles in one or more key organs (endothelium, kidney, and heart). We further characterize one of these enhancers (ENH5) whose activity was found to be not only allele-specific, but also hypoxia-dependent in all three cell types. Deletion of this enhancer results in downregulation of EPAS1 and HIF-2 targets in acute hypoxia as well as a blunting of the transcriptional response to sustained hypoxia. In vivo deletion of the orthologous ENH5 in mice results in dysregulation of gene expression across multiple tissues. We propose that pleiotropic adaptive effects of the Tibetan alleles in EPAS1 underlie the strong selective signal at this gene.

ORGANISM(S): Homo sapiens

PROVIDER: GSE197525 | GEO | 2022/11/28

REPOSITORIES: GEO

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Project description:Since their arrival in the Tibetan Plateau during the Neolithic Age, Tibetans have been well-adapted to extreme environmental conditions and possess genetic variation that reflect their living environment and migratory history. To investigate the origin of Tibetans and the genetic basis of adaptation in a rigorous environment, we genotyped 30 Tibetan individuals with more than one million SNP markers. Our findings suggested that Tibetans, together with the Yi people, were descendants of Tibeto-Burmans who diverged from ancient settlers of East Asia. The valleys of the Hengduan Mountain range may be a major migration route. We also identified a set of positively-selected genes that belong to functional classes of the embryonic, female gonad, and blood vessel developments, as well as response to hypoxia. Most of these genes were highly correlated with population-specific and beneficial phenotypes, such as high infant survival rate and the absence of chronic mountain sickness. Genetic features of Tibetans have been broadly investigated, but the properties of copy number variation (CNV) have not been well examined. To get a preliminary view of CNV in Tibetans, we scanned 29 Tibetan genomes with the Illumina Human-1 M high-resolution genotyping microarray and identified 139 putative copy number variable regions (CNVRs), consisting of 70 deletions, 61 duplications, and 8 multi-allelic loci. Thirty-four of the 139 CNVRs showed differential allele frequencies versus other East-Asian populations, with P values ,0.0001. These results indicated a distinct pattern of CNVR allele frequency distribution in Tibetans. The Tibetan CNVRs are enriched for genes in the disease class of human reproduction (such as genes from the DAZ, BPY2, CDY, and HLA-DQ and -DR gene clusters) and biological process categories of ‘‘response to DNA damage stimulus’’ and ‘‘DNA repair’’ (such as RAD51, RAD52, and MRE11A). These genes are related to the adaptive traits of high infant birth weight and darker skin tone of Tibetans, and may be attributed to recent local adaptation. Our results provide a different view of genetic diversity in Tibetans and new insights into their high-altitude adaptation.

Project description:Purpose: By integrating DNA methylation and gene expression of COPD lung tissues, we identified EPAS1 as a key regulator whose downstream genes significantly overlapped with multiple genes sets associated with COPD disease severity. EPAS1 is distinct in comparison with other key regulators in terms of methylation profiles and downstream target genes. Genes predicted to be regulated by EPAS1 were enriched for biological processes including signaling, cell communications, and system developement. As EPAS1 downstream genes were significantly enriched for hypoxia responsive genes in endothelial cells, we tested EPAS1 function in human and mouse endothelial cells HUVEC and C166. EPAS1 knockdown by siRNA in endothelial cells impacted genes that significantly overlapped with EPAS1 downstream genes in lung tissue including hypoxia responsive genes. Methods: The cell lines of HUVEC (Lonza, MD, USA) and C166 (American Type Culture Collection, VA, USA) were cultured in the appropriate media at 37M-BM-0C with 5% CO2. The cells were transfected with EPAS1 siRNA and non-targeting negative control siRNA (Life Technologies, CA, USA) using Lipofectamine RNAiMAX as recommended transfection protocols by the manufacturer. After the treatments with 5nM SilencerM-BM-. Select siRNA (s4700 for EPAS1, s65525 for Epas1; Life Technologies, USA) for 48 hours, the total RNA was purified with RNeasy Mini Kit (QIAGEN, Germany). The efficiencies of knocked down the EPAS1 expression were assessed by qPCR with 1.4% for HUVEC, 3.2% for C166. Approximately 250 ng of total RNA per sample were used for library construction by the TruSeq RNA Sample Prep Kit (Illumina) and sequenced using the Illumina HiSeq 2500 instrument with 100nt single read setting according to the manufacturer's instructions. Sequence reads were aligned to human genome assembly hg19 and mouse genome assembly mm10, respectively, using Tophat [96]. Total 23,228 human and 22,609 mouse genes were quantified using Cufflinks [96]. siRNA signatures were derived by comparing expression profiles of EPAS1 or Epas1 siRNAs with non-targeting siRNAs at paired t-test p-value cutoff 0.05 with resulting signature sizes of 2,796 and 3,730, and corresponding q-values [97] 0.11 and 0.07 for HUVEC and C166, respectively. Results: When comparing endothelial cells treated with EPAS1 siRNAs and scrambled siRNAs, we identified an EPAS1 siRNA signature consisting of 2796 and 3730 genes in human and mouse endothelial cell lines, respectively, whose expression levels significantly changed (t-test p-value<0.05), including EPAS1 itself (p-value = 0.002 and 0.02) and the EPAS1 downstream target gene VEGFA (p-value = 0.03 and 0.01). The EPAS1 siRNA signatures derived from human and mouse cell lines were highly consistent, with 695 genes in common to both signatures (p-value = 7.2x10-65). Both signatures not only significantly overlapped with EPAS1 downstream genes (p-value = 7.3x10-7 and 1.5x10-12), but also with hypoxia response genes in endothelial cells (FisherM-bM-^@M-^Ys Exact Test p-value = 5.8x10-8 and 1.2x10-12 in the human and mouse signatures, respectively). Moreover, the EPAS1 siRNA signatures consistently overlapped genes associated with the COPD severity phenotypes. These results together validate that EPAS1 causally regulates the downstream target genes we predicted, and that these genes in turn affect COPD development and progression. For each of human and mouse cell lines, 3 siRNA control cells, and 3 siRNA EPAS1 knockdown cells were used and analyzed. To identify EPAS1 signatures, paired t-test was performed between control siRNA and EPAS1 siRNA samples.

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A pleiotropic hypoxia-sensitive EPAS1 enhancer is disrupted by adaptive alleles in Tibetans [RNA-seq TeloHAEC]

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