Project description:Background: Palmdelphin (PALMD), a protein of unknown function, belongs to the family of Paralemmin proteins implicated in cytoskeletal regulation. Single nucleotide polymorphisms (SNPs) in the PALMD locus, which reduce its expression, are strong risk factors for development of calcific aortic valve stenosis (CAVS) and for severity of the disease. Methods: Public database screening and immunodetection of PALMD showed dominant expression in endothelial cells (ECs). Mass spectrometry allowed identification of PALMD partners. The consequence of loss of PALMD expression was assessed in siRNA silenced EC cultures, in knockout mice and in human valve samples and EC cultures from patients. RNA sequencing on siRNA silenced cells and transcript arrays on valve samples from a Swedish SNP rs7543130 patient cohort informed about gene regulatory changes. Results: ECs express the cytoplasmic PALMD-KKVI splice variant, which was shown to exist in complex with RAN GTPase activating protein1 (RANGAP1). RANGAP1 regulates the activity of the GTPase RAN and thereby, nucleocytoplasmic shuttling via Exportin1 (XPO1). Reduced PALMD expression resulted in subcellular relocalization of RANGAP1 and XPO1, providing a mechanism for the gene regulatory changes established in PALMD-deficiency. Gene ontology analysis showed enrichment of actin and RHO GTPAse related terms in PALMD-silenced ECs. In accordance, PALMD-silenced ECs showed multiple changes in adhesive and migratory properties and cells were softer. In particular, PALMD-deficient ECs failed to form a perinuclear actin cap when exposed to flow. The perinuclear actin cap is known to provide protection against mechanical stress. Lack of the actin cap correlated with tilting of the nuclear long axis relative to the cell body, which was established in PALMD-deficient ECs, mice and patient valve samples. The loss of the actin cap may contribute to further dysregulated gene transcription eventually promoting calcific precipitations and inflammation in CAVS. Conclusions: We identify RANGAP1 as a PALMD partner in ECs. Disrupting the PALMD/RANGAP1 complex changes the subcellular localization of essential nucleocytoplasmic shuttling components, thereby instigating the loss of actin-dependent nuclear resilience, which in turn promotes further deterioration of gene expression patterns predisposing to the establishment of CAVS.

Project description:Coronary artery disease (CAD) is a complex disorder with genetic and environmental influences. Genome-wide association studies (GWAS) have identified over 300 genomic loci associated with disease risk. However, identifying the functional variants within these loci has been limited in large part due to linkage disequilibrium. This represents a critical step in understanding the molecular mechanisms underlying disease risk. To identify and prioritize candidate causal CAD-associated variants, we performed lentivirus-based massively parallel reporter assays (lentiMPRAs) in primary vascular smooth muscle cells (SMCs), which play significant roles in atherosclerosis, the underlying cause of CAD. We tested 25892 CAD-associated variants for their allele-specific enhancer activity in quiescent and proliferative SMCs, modeling healthy and disease conditions. We identified 122 candidate variants showing significant enhancer activity and differences in reporter gene expression between risk and non-risk alleles. We also identified 23 variants showing condition-biased allelic imbalance and 41 variants showing sex-biased allelic imbalance. We further functionally characterized 25892 variants by performing CUT&RUN assays to identify variants in enhancer and promoter regions of SMCs. By integrating the results of these experiments, we identified a credible set of 49 CAD-associated variants in functionally relevant regions. Furthermore, by comparing these identified variants with our previously obtained expression quantitative trait loci (eQTL) data, 27 of these 49 variants were associated with SMC gene expression levels. Finally, we performed CRISPRi experiments on 8 variants comprising 9 variant-gene pairs, rs35976034 (MAP1S), rs4888409 (CFDP1), rs73193808 (MAP3K7CL), rs67631072 (INPP5B/FHL3), rs1651285 (SNHG18), rs17293632 (SMAD3), rs2238792 (ARVCF), rs4627080 (NRIP3), to confirm their regulatory potential of nearby gene expression. Taken together, our results comprehensively fine-map the causal variants that confer increased risk of CAD through their effects on vascular smooth muscle cells.

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Regulatory Elements Harboring Common Coronary Artery Disease Risk Variants Control Endothelial TSPAN14 Expression and NOTCH1 Signaling

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