Abstract 08: Genome-wide Maps of Human Kidney Proximal Tubules and Thick Ascending Limbs of Henle reveal an Enrichment for Human Blood Pressure associated Polymorphisms

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GWAS has identified >1,000 blood pressure (BP)-associated sentinel SNPs, most of which (>90%) are intronic and intergenic. How they regulate BP-relevant genes remains an open question. We hypothesized many SNPs would reside within cis-regulatory elements specific to nephron segments critical to sodium resorption such as proximal tubule (PT) and thick ascending limb (TAL). To address this, we developed chromatin state (ATAC-seq) and transcriptome (RNA-seq) maps from manually dissected human PT and medullary TAL (mTAL) segments. We identified 216,168 and 179,467 open regions in PT and mTAL, respectively, with the majority (70%) being unique to one tissue. Interestingly, peaks shared between the two segments resided more frequently in promoters, whereas unique peaks were more often found in distal introns or intergenic regions, suggesting they lie within enhancers (Figure 1A). Both chromatin state and transcriptomic data demonstrated a correlation between open chromatin peaks within gene promoters and mRNA levels (r=0.11; p<4.6e-16). This correlation was weaker at open regions distal to the promoter, illustrating the difficulty of mapping distal open regions to the gene(s) they regulate. We hypothesized these open regions would be enriched for BP-relevant SNPs. We curated 1,071 bp-associated SNPs and found 87 and 67 in mTAL and PT, open regions respectively, many of which are near BP-relevant genes. This enrichment was significant based on 104 randomizations (pValue 10-4) (Figure 1B). We conclude that these novel tissue-specific chromatin maps can be used to identify potential mechanisms by which SNPs influence gene expression and BP. Additional studies will be needed to demonstrate both causality and molecular mechanisms.

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