Abstract 11232: Role of Line-1 Retrotransposition in Atherosclerosis

Abstract

Introduction: LINE-1 (L1) retrotransposons are a class of transposable elements comprising ~21% of the human genome. L1-retrostransposed elements move within the genome, where they profoundly alter gene function. Somatic L1 insertions, or retrotranspositions (RTNs), were implicated in multiple diseases including cancer. However, this literature has been mainly confined to epithelial tissue, and the role of L1 in cardiovascular diseases is unknown. Specifically, whether L1 presence and activity in vascular cells has a functional role in atherosclerosis, a disease characterized by extensive vascular remodeling, inflammation and plaque formation, remains unexplored. Hypothesis: L1 expression and RTN in vascular endothelial cells (ECs) leads to endothelial activation in atherosclerosis. Methods: L1 mRNA expression was analyzed by qRT-PCR in postmortem coronary artery specimens from patients with atherosclerosis and non-diseased controls. Immunofluorescence (IF) in coronary tissue was performed for ORF1p, a L1 encoded polypeptide required for active RTN. In vitro, qRT-PCR was used to assess L1 expression in primary human aortic ECs (HAEC) treated with proatherogenic inflammatory stimuli TNFα, IL6, oxidized LDL (oxLDL) and IL1β. Active RTN was assessed by FACS and IF in a purpose-built human umbilical vein EC line (CRL2922) L1 RTN detection system. Results: L1 mRNA was increased in atherosclerotic human coronary arteries and positively correlated with age and histologically-assessed disease severity. ORF1p expression increased in EC of atherosclerotic plaques indicative of increased L1 activity. L1 expression and retrotransposition was induced in ECs in vitro by TNFα, IL-6 and oxLDL. Finally, de novo L1 insertion alone resulted in upregulation of genes involved in EC activation and atherosclerosis (ICAM1, MCP-1, IL6, NOR), and this effect was further enhanced by co-treatment with TNFα, IL-6 and oxLDL. Conclusions: Our results identify a disease-related increase in L1 in the vascular endothelium under atherosclerotic conditions that contributes to EC activation. These data support a permissive environment during atherosclerosis for L1 activity and unveil a previously unrecognized role for L1 in this disease’s pathophysiology.