Abstract 49: Elevating Apolipoprotein A-I Levels Promotes Atherosclerosis Regression in Diabetic Mice by Inhibiting Proliferation of Bone Marrow Monocyte Precursors

Abstract

Diabetes is a primary risk factor for cardiovascular diseases (CVD) and in clinical imaging studies is shown to impair the resolution of CVD, a process termed regression. We have also reported this failure of lesion regression in mouse models of diabetes, despite effective lipid lowering. This, in part, can be attributed to diabetes-driven monocytosis promoting continued monocyte infiltration into plaques. In non-diabetic settings apolipoprotein (apo) A-I and high-density lipoprotein (HDL) suppress leukocytosis and promote lesion regression. As low apoA-I/HDL is a typical feature of diabetic dyslipidemia this study aimed to establish whether raising apoA-I/HDL levels in vivo is an effective approach to reduce diabetes-driven leukocytosis and promote lesion regression. Aortic arches from hyperlipidemic Ldlr -/- mice were transplanted into WT, diabetic WT, and diabetic human apoA-I-overexpressing transgenic mice (transgenic mice have a 3-fold increase in HDL-cholesterol), and lesion composition assessed 2 weeks post-surgery. Following aortic transplantation into WT mice (i.e. normal lipid levels) we found regression, as assessed by change in plaque macrophage (mΦ) content relative to baseline control mice was achieved (68% mΦ reduction, P<0.001). Regression was impaired when aortas were transplanted into diabetic WT recipients (50% mΦ reduction, P<0.01). However, raising apoA-I/HDL levels in the setting of diabetes restored regression in diabetic mice (62% mΦ reduction, P<0.001). In vivo monocyte/mΦ trafficking analyses revealed that elevating apoA-I/HDL levels in diabetes improves atherosclerosis regression by reducing monocyte entry by 60% (P<0.01), and promoting mΦ egress from lesions (30% increase). We also found that greater apoA-I/HDL reduced blood monocytes by decreasing the proliferation of monocyte progenitors in the bone marrow (15-20% reduction, P<0.05), explaining, in part, how apoA-I/HDL promotes regression. Raising apoA-I/HDL levels promotes atherosclerotic lesion regression in diabetic mice. This may serve as a therapeutic strategy for patients with diabetes, who unlike WT mice, have reduced HDL levels and remain at an elevated risk for CVD despite effective plasma cholesterol lowering.