Abstract 18971: Changes in HDL Quality Rather Than Macrophage Function Mediate the Atheroprotective Phenotype in Usf1 Knockout Mice

Abstract

We previously demonstrated that allelic variants of Usf1 are associated with myriad metabolic phenotypes in human populations and the knockout of Usf1 in mice leads to a favorable metabolic phenotype. Here, we have studied the role of macrophages and HDL particles in the development of atherosclerosis in the Usf1 -/- mice. A mouse strain of double knockout of Usf1 and Ldlr (Usf1 -/- Ldlr -/-) was generated, and mice along with their Usf1 +/+ Ldlr -/- littermates were fed with a high fat diet diet for 20 weeks. The double knockouts displayed a three-fold reduction in their atherosclerotic lesion area as demonstrated by the aortic longitudinal section based en face technique. To study the potential mechanisms behind the attenuated lesion development in the Usf1 -/- mice, we knocked down USF1 by constitutive expression of shRNA from human monocyte cell line (THP1). We differentiated monocytes into macrophages and loaded them with acetylated LDL for 48 hours. We observed no change in cholesterol efflux from USF1 knockdown macrophages to wild type mouse serum or HDL when compared to efflux from control cells expressing non-targeting shRNA. Furthermore, we performed bone marrow transplantation of Usf1 -/- and wild type bone marrow to Ldlr -/- mouse background. After 12 weeks of western diet we saw no change in atherosclerotic lesion development in the aortic root area in the mice with Usf1 -/- bone marrow compared to the mice with wild type bone marrow, indicating a macrophage independent mechanism for the atheroprotection in Usf1 -/- mice. The Usf1 -/- mice displayed both elevated cholesterol (p<0.001) and phospholipids (p<0.001) in their serum both on western and regular chow diet. Interestingly, cholesterol efflux from wild type THP1 macrophages to Usf1 -/- serum and HDL was significantly increased (p<0.05 and p<0.001, respectively) compared to serum and HDL from the wild type mice indicating that not only increased serum HDL concentration but also changes in HDL particle quality in the Usf1 -/- mice have properties increasing cholesterol efflux. Our study establishes the atheroprotective role for Usf1 deficiency that could be in part due to the favorable changes HDL particle quality rather than macrophage specific effects in the Usf1 -/- mice.