Apolipoprotein E-/- mice lacking hemopexin develop increased atherosclerosis via mechanisms that include oxidative stress and altered macrophage function

Abstract

Objective - We previously reported that hemopexin (Hx), a heme scavenger, is significantly increased and associated with proinflammatory high-density lipoprotein under atherogenic conditions. Although it is established that Hx together with macrophages plays a role in mitigating oxidative damage, the role of Hx in the development of atherosclerosis is unknown. Approach and Results - We used Hx and apoE double-knockout mice (HxE-/-) to determine the role of Hx in the development of atherosclerosis. HxE-/- mice had significantly more free heme, reactive oxygen species, and proinflammatory high-density lipoprotein in their circulation, when compared with control apoE-/- mice. Atherosclerotic plaque area (apoE-/- =9.72±2.5×10 4 μm 2 and HxE-/- =27.23±3.6×10 4 μm 2) and macrophage infiltration (apoE-/- =38.8±5.8×10 3 μm 2 and HxE-/- =103.4±17.8×10 3 μm 2) in the aortic sinus were significantly higher in the HxE-/- mice. Atherosclerotic lesions in the aortas were significantly higher in the HxE-/- mice compared with apoE-/- mice. Analysis of polarization revealed that macrophages from HxE-/- mice were more M1-like. Ex vivo studies demonstrated that HxE-/- macrophage cholesterol efflux capacity was significantly reduced when compared with apoE-/- mice. Injection of human Hx into HxE-/- mice reduced circulating heme levels and human Hx pretreatment of naive bone marrow cells ex vivo resulted in a shift from M1- to M2-like macrophages. Conclusions - We conclude that Hx plays a novel protective role in alleviating heme-induced oxidative stress, improving inflammatory properties of high-density lipoprotein, macrophage phenotype and function, and inhibiting the development of atherosclerosis in apoE-/- mice.