Abstract 141: The Role of Macrophage Epsins in the Regulation of LRP-1 in Atherosclerosis

Background: Epsins are a family of ubiquitin-binding endocytic clathrin adaptors. We recently published that endothelial epsins function as critical regulators of tumor angiogenesis by controlling VEGF signaling (JCI, 2012; ATVB, 2013). Our goal is to define the novel role of epsins in macrophages in regulating atherogenesis. Methods and Results: We engineered mice with specific deletion of epsins in myeloid cells (MΦ-DKO). Strikingly, MΦ-DKO mice on ApoE-/- background fed western diet significantly reduced atherosclerotic lesion formation and foam cell accumulation. In macrophages, epsin deficiency did not alter LDL scavenger receptors, CD36, Lox1 or SRB1, or reverse cholesterol transport proteins, ABCA1 or ABCG1, but did significantly reduce Lucifer Yellow pinocytosis, indicating a major defect in lipid uptake. Epsin deficiency did decrease total and surface protein levels of LRP-1, a protein with anti-inflammatory and anti-atherosclerotic properties. Oil Red O staining of isolated ApoE-/-/M[[Unable to Display Character: Ф]]-DKO macrophages showed little lipid accumulation, suggesting a mechanism in which epsin deficiency impairs foam cell formation. In addition, epsin 1 and LRP-1 interact in macrophages. Furthermore, this interaction is abolished in the absence of epsin’s UIM domain and LPS treatment increases LRP-1 ubiquitination, suggesting that epsin promotes the ubiquitin-dependent internalization of LRP-1. Epsin deficiency also significantly suppressed the pro-inflammatory M1 macrophage phenotype found in plaques and increased the anti-inflammatory macrophage phenotype, thus suggesting an important pro-inflammatory role for epsins in macrophages. Our finding implicates epsin as a potential therapeutic target for atherosclerosis treatment. Conclusions: We demonstrate epsins promote atherogenesis by potentiating foam cell formation and maintaining pro-inflammatory macrophages within the atherosclerotic plaque, thus suggesting epsins as a novel therapeutic target to combat atherogenesis.