ApoE-/- Mice Lacking Hemopexin Develop Increased Atherosclerosis via Mechanisms That Include Oxidative Stress and Altered Macrophage Function
Objective: We previously reported that Hemopexin (Hx), an acute phase protein and a heme scavenger, is significantly increased and associated with proinflammatory HDL under atherogenic conditions. Although it is established that Hx together with macrophages plays a role in mitigating heme and ROS mediated oxidative damage to cells and tissues, the role of Hx in systemic oxidative stress, HDL function, macrophage function, and the development of atherosclerosis, is not known.
Approach and Results: We generated Hx and apoE double knockout mice (HxE-/-) on a C57BL/6J background to determine the role of Hx in the development of atherosclerosis. HxE-/- mice had significantly more free heme, ROS, and proinflammatory and dysfunctional HDL in their circulation, when compared to control apoE-/- mice. Atherosclerotic plaque area (apoE-/- = 9.72 ± 2.5 x104 µm2and HxE-/- = 27.23 ± 3.6 x104 µm2) and macrophage infiltration (apoE-/- = 38.8 ± 5.8 x103 um2 µm2 and HxE-/- = 103.4 ± 17.8 x103 µm2) in the aortic sinus were significantly higher in the HxE-/- mice when compared to apoE-/- mice. Also, atherosclerotic lesions in the aortas were significantly higher in the HxE-/- mice when compared to apoE-/- mice. Analysis of polarization and phenotype revealed that macrophages from HxE-/- mice were more M1-like and proinflammatory. Ex vivo studies demonstrated that HxE-/- macrophage cholesterol efflux capacity was significantly reduced when compared to apoE-/- mice.
Conclusion: We conclude that Hx plays a novel protective role in alleviating heme induced oxidative stress, improving inflammatory properties of HDL and macrophage function and inhibiting the development of atherosclerosis in apoE-/- mice.