Stabilization of atherosclerotic plaques via inhibition of regulated necrosis

Atherosclerosis is a progressive inflammatory disease of the large and medium-sized arteries and is characterized by the formation of plaques in the vessel wall. Rupture of these plaques may cause life-threatening complications such as a myocardial infarct and stroke. A plaque that is prone to rupture is characterized by the presence of a large necrotic core, which is formed by cells within the plaque that undergo necrosis. Accordingly, targeting necrotic cell death may be a therapeutic strategy to stabilize atherosclerotic plaques. The main goal of this dissertation was to investigate whether inhibition of two different forms of regulated necrosis, necroptosis and ferroptosis, reduces formation of atherosclerotic plaques. To investigate the role of the necroptosis mediator RIPK1, we investigated the impact of a myeloid RIPK1 deletion on the development of atherosclerotic plaques in ApoE-/- mice. Myeloid-specific RIPK1-deficient mice (RIPK1F/FLysMC-Cre+) were crossbred with ApoE-/- mice and fed a western-type diet (WD) for 16 or 24 weeks. After 16 weeks WD, plaque size and necrotic core were reduced in RIPK1F/FLysMC-Cre+ApoE-/- mice. However, after 24 weeks WD, plaque size and necrotic core were no longer different between RIPK1F/FLysMC-Cre+ApoE-/- mice and the control mice. Taken together, myeloid RIPK1 has divergent effects on atherosclerosis depending on the lesion stage. Next, we evaluated the effect of a RIPK1 inhibitor in a mouse model of advanced atherosclerosis, the ApoE-/-Fbn1C1039G+/-mouse. Unexpectedly, plaque size and necrotic core were not different between the control mice and the mice treated with the RIPK1 inhibitor. Additional experiments using distinct RIPK1 inhibitors are needed to further unravel the role of necroptosis in atherosclerosis. Apart from necroptosis, the role of ferroptosis in atherosclerosis has been studied. Ferroptosis is characterized by an iron-dependent accumulation of lipid hydroperoxides. Because GPX4 reduces lipid hydroperoxides thereby preventing ferroptosis, we evaluated the impact of GPX4 overexpression in ApoE-/- mice. Although GPX4 overexpression inhibited lipid peroxidation in atherosclerotic plaques of ApoE-/- mice fed a WD, we could not demonstrate that GPX4 overexpression reduces atherosclerosis in ApoE-/- mice. Given that iron contributes to the development of advanced atherosclerotic plaques, we performed a pharmacological study to inhibit ferroptosis using a-tocopherol (vitamin E) in a mouse model of advanced atherosclerosis, namely the ApoE-/-Fbn1C1039G+/- mouse. A high dose of a-tocopherol improved cardiac function and decreased plaque thickness and necrotic core size. Because mice treated with a high dose of a-tocopherol showed reduced plaque formation, we assume that a-tocopherol limits plaque progression before ferroptosis could occur. Moreover, mice treated with a high dose of a-tocopherol showed increased lipid peroxidation. Overall, this study demonstrates that a-tocopherol inhibits atherogenesis independent of its antioxidant properties. Taken together, this study highlighted the role of RIPK1 in atherosclerosis. However, treatment with a RIPK1 inhibitor did not yield therapeutic benefits in atherosclerosis. The complex role of RIPK1 should be taken into account when using RIPK1 as a therapeutic tool for the treatment of atherosclerosis. Additionally, we were not able to demonstrate whether ferroptosis inhibition using GPX4-overexpressing mice or the pharmacological inhibitor a-tocopherol affects atherosclerosis. Nonetheless, a-tocopherol decreased plaque size and improved cardiac function independent of its antioxidant properties.

Jaar van publicatie:2020

Trefwoorden:Doctoral thesis

Toegankelijkheid:Open