Abstract 11643: ACTN4 Regulates HLA-DPA1-Related Pulmonary Endothelial Pathophenotypes in Pulmonary Arterial Hypertension Through Allele-Specific Binding to Functional SNP rs9277336

Abstract

Introduction: Pulmonary arterial hypertension (PAH) is a progressive disease characterized by increased pulmonary arterial pressure and vascular resistance. This vascular injury promotes immune dysregulation, further worsening the vasculopathy. A genome-wide association study identified a single nucleotide polymorphism (SNP) associated with PAH risk (rs2856830) at Human Leukocyte Antigen DPA1 (HLA-DPA1) locus, a gene known to be involved in adaptive immunity. However, little is known about the mechanism underlying this clinical association. Hypothesis: Allele-specific binding of transcription factors to a disease-associated functional SNP (fSNP) controls HLA-DPA1 expression, driving pulmonary vascular cell dysfunction and PAH. Methods: Oligonucleotides containing alleles of rs2856830 and eight SNPs in linkage disequilibrium (LD) were subjected to electrophoretic mobility shift assays (EMSA) to identify fSNPs characterized by allele-imbalanced binding to human pulmonary arterial endothelial cells (PAEC) nuclear proteins. SNP genotyping was done using blood from PAH (n=134) and control patients (n=131) at UPMC. Transcriptomics, angiogenesis, and migration were assessed in siRNA mediated HLA-DPA1 and Alpha Actinin 4 (ACTN4) knockdown (KD) in PAECs. Results: Through EMSA, rs9277336 (LD r 2 =0.87) was identified as a fSNP in HLA-DPA1 locus. SNP pulldown and immunoblotting confirmed allele-specific binding of nuclear ACTN4 protein to rs9277336 risk allele A (3.26 ± 0.49, p=0.001). SNP genotyping revealed a 2.04 ± 0.67 fold enrichment of risk allele A in PAH patients (χ 2 test, p=0.025). ACTN4 KD in cultured human PAECs decreased HLA-DPA1 transcript (0.30 ± 0.10, p<0.001) . Transcriptomics revealed overlap of several cell structure and immune system-related pathways by HLA-DPA1 and ACTN4 KD. HLA-DPA1 and ACTN4 KD affected PAH associated pathophenotypes, including angiogenesis and migration. Conclusions: Our functional analysis identified ACTN4 as a novel regulator to disease-associated gene HLA-DPA1, affecting the endothelial pathophenotypes in PAH. The allele-specific binding to fSNP rs9277336 provides a mechanistic explanation for the clinical association between HLA-DPA1 locus and PAH outcomes.