Abstract 3073: Gene Regulation By RNP Granule Formation In Atherosclerosis

Abstract

Background: Atherosclerosis, the leading cause of cardiovascular disease related death, is a chronic inflammatory condition incited by the accumulation of low-density lipoproteins (LDL) and recruitment of macrophages in the arterial intima. Macrophages become lipid laden foam cells that persist in the arterial vasculature, inciting chronic inflammation and plaque formation. A better understanding of the mechanisms underlying this maladaptive inflammatory response may reveal novel therapeutic strategies for intervention. Hypothesis: We hypothesize that the transformation into a foam cell state, a process that requires transcriptional rewiring, is facilitated by stress granules (SG). SGs are cytoplasmic membrane-less organelles that sequester translation initiation factors, mRNAs, and noncoding RNAs due to stress. We previously reported that SG formation is increased in plaque macrophages of atherosclerotic mice and can be induced in vitro during cellular cholesterol loading. However, the consequences of SG formation and the transcripts sequestered by these organelles is unknown. Methods and Results: To investigate whether SGs influence macrophage phenotype, we used siRNA to knockdown G3bp1 and treated with Dil-oxLDL. We found that G3bp1 knockdown reduced macrophage lipid loading and induced transcriptional changes associated with canonical M2 anti-inflammatory macrophage polarization. Furthermore, RNA-seq of macrophages treated with si G3bp1 and oxLDL showed downregulation of pathways involved in phagosome formation and S100 family signaling. RNA immunoprecipitation of G3BP1 from macrophages treated with an ER stressor revealed preferential binding of G3BP1 to transcripts implicated in cholesterol metabolism. Altogether, these data support a role for SGs in maintaining a pro-inflammatory state and regulating cholesterol pathways in plaque macrophages. Conclusion: Our data support a role for SGs in repressing the translation of RNA transcripts in lipid-laden foam cells that accumulate in atherosclerotic plaque. Identification of the specific proteins and RNAs sequestered in SGs will provide insight into how they regulate gene expression and cellular phenotypic switching that prevents the resolution of inflammation.