Human Macrophage Long Intergenic Noncoding RNA, SIMALR , Suppresses Inflammatory Macrophage Apoptosis via NTN1 (Netrin-1)

Long noncoding RNAs (lncRNAs) have emerged as novel regulators of macrophage biology and inflammatory cardiovascular diseases. However, studies focused on lncRNAs in human macrophage subtypes, particularly human lncRNAs that are not conserved in rodents, are limited. Through RNA-sequencing of human monocyte-derived macrophages, we identified suppressor of inflammatory macrophage apoptosis lncRNA ( ). Lipopolysaccharide/IFNγ (interferon γ) stimulated human macrophages were treated with antisense oligonucleotides and subjected to RNA-sequencing to investigate the function of . Western blots, luciferase assay, and RNA immunoprecipitation were performed to validate function and potential mechanism of RNAscope was performed to identify expression in human carotid atherosclerotic plaques. RNA-sequencing of human monocyte-derived macrophages identified , a human macrophage-specific long intergenic noncoding RNA that is highly induced in lipopolysaccharide/IFNγ-stimulated macrophages. knockdown in lipopolysaccharide/IFNγ stimulated THP1 human macrophages induced apoptosis of inflammatory macrophages, as shown by increased protein expression of cleaved PARP (poly[ADP-ribose] polymerase), caspase 9, caspase 3, and Annexin V+. RNA-sequencing of control versus knockdown in lipopolysaccharide/IFNγ-stimulated macrophages showed Netrin-1 ( ) to be significantly decreased upon knockdown. We confirmed that knockdown in lipopolysaccharide/IFNγ-stimulated macrophages induced apoptosis. The knockdown-induced apoptotic phenotype was rescued by adding recombinant NTN1. promoter-luciferase reporter activity was increased in HEK293T (human embryonic kidney 293) cells treated with lentiviral overexpression of . promoter activity is known to require HIF1α (hypoxia-inducible factor 1 subunit alpha), and our studies suggest that may interact with HIF1α to regulate transcription, thereby regulating macrophages apoptosis. was found to be expressed in macrophages in human carotid atherosclerotic plaques of symptomatic patients. is a nonconserved, human macrophage lncRNA expressed in atherosclerosis that suppresses macrophage apoptosis. partners with HIF1α (hypoxia-inducible factor 1 subunit alpha) to regulate NTN1, which is a known macrophage survival factor. This work illustrates the importance of interrogating the functions of human lncRNAs and exploring their translational and therapeutic potential in human atherosclerosis.