Inflammation is designed to destroy, disable, or contain pathogenic invaders, but must be controlled to avoid destruction of key host systems, like the vasculature. When the interaction between immune cells and the vasculature goes awry, it can contribute to vascular lesions in aneurysm, atherosclerosis, and other diseases. Our study of the interactions between innate immune cells and the arterial wall in models of atherosclerosis ? a sterile and chronic injury process with a critical inflammatory component ? has revealed broad regulation of alternative splicing responses that change the extracellular composition of the inflamed intima and the behavior of recruited immune cells that protect the arterial wall from damage. Guided by these data and novel in vitro CRISPR screens to probe the function of RNA binding proteins (RBP) in the regulation endothelial inflammation, we have discovered a set of RBP responsive to innate immune cell recruitment that are critical in orchestrating the activation of the endothelium through NFkB signaling. Here, we test the hypothesis that one of these RBP, Elavl1, coordinates alternative splicing in the arterial intima in response to innate immune cell recruitment to regulate chronic immune functions (Aim 1). In seeking a deeper understanding of this immune-regulatory system, we made the unexpected discovery that, like Elavl1, many RBP strongly bind to transposable element (TE) sequences inserted within genes and their RNA transcripts (p<0.0001). While most TE are inactive, these vestigial TE sequences account for ~45% of our genome, are found in nearly all genes, and can provide cryptic splice sites in transcripts that depend on RBP activity. Thus, we aim to define the family of TE-binding RBP, to understand their regulation during inflammatory responses, and their impact on splicing patterns and inflammatory responses through binding to TE (Aim 2). The completion of these aims will provide new insight into the contribution of endothelial alternative splicing responses to inflammation in chronic inflammatory states, and the contribution of pervasive TE-derived sequence to transcript regulation through RBP that bind them, providing new avenues to understand and treat chronic inflammation in the cardiovascular system.
Integrations of transposable elements (TE) account for ~45% of our genomes, and although most are now inactive, they have provided the genetic diversity to shape the evolution of our cellular and organismal responses to stress. Here, we expand on findings that the RNA-binding proteins (RBPs) that bind to these TE have critical roles in the regulation of endothelial cell activation and immune cell recruitment in the inflamed arteria intima. Our findings will provide important insight into this special class of RBPs, to better understand and treat chronic inflammation in atherosclerosis, aneurysm, and other cardiovascular diseases.
