Abstract MP246: Epigenetic Regulation At LRP1 Susceptibility Locus And Characterization Of LRP1 Function In Human Induced Pluripotent Stem Cells Derived Smooth Muscle Cells

Abstract

Introduction: The low-density lipoprotein receptor-related protein 1 (LRP1), an endocytic receptor highly expressed in smooth muscle cells (SMCs), participates in diverse biological processes. A common genetic variant located in LRP1 first intron, rs11172113, was associated with several vascular diseases, including coronary artery disease, migraine and spontaneous coronary artery dissection, as well asd with LRP1 expression in arterial tissues. However, the biological mechanisms through which rs11172113 influence LRP1 function in the context of arterial lesions is not fully understood. Methods: We applied in silico functional annotation to select variants and measured their enhancer activity using luciferase reporter assay in rat primary cells (A7r5). We performed siRNA knockdown of LRP1 and 4 transcription factors (TFs) predicted to interact with rs11172113 in human induced pluripotent stem cells (iPSCs) derived SMCs. We analyzed both contractile (CSMCs) and synthetic (SSMCs) differentiated cells. We edited iPSCs prior to differentiation using CRISPR-Cas9 to generate 100 bp deletion of the enhancer region containing rs11172113. We also created frame-shift indels in exons 2 or 5 of LRP1 in iPSCs to create SMCs knockouts. Results: Seven variants in LRP1 locus co-located with enhancer (histone marks) and open chromatin regions (ATAC-Seq peaks) in SMCs and arterial tissues. Reporter assay in rat SMCs confirmed that rs11172113 belongs to a genomic region showing enhancer activity in vitro . iPSCs with homozygous deletion of rs11172113 enhancer region presented the same pluripotency compared with wild type, and iPSC derived SMCs showed positive expression of specific markers for each phenotype. We found that the deletion of enhancer region decreased the expression of LRP1 in both CSMCs and SSMCs. LRP1 knockdown decreased SSMCs and CSMCs proliferation capacity, but increased cell migration. Knockdown of TFs and iPSCs derived CSMCs and SSMCs with LRP1 knockout are currently under assessment. Conclusions: We confirmed rs11172113 to regulate LRP1 expression in iPSCs derived synthetic and contractile SMCs. Our results support LRP1 effect on SMCs phenotype alteration as a potential mechanism in genetic susceptibility for vascular disease.