Lymphatic vasculature mediates macrophage reverse cholesterol transport in mice

Abstract

Reverse cholesterol transport (RCT) refers to the mobilization of cholesterol on HDL particles (HDL-C) from extravascular tissues to plasma, ultimately for fecal excretion. Little is known about how HDL-C leaves peripheral tissues to reach plasma. We first used 2 models of disrupted lymphatic drainage from skin -1 surgical and the other genetic -to quantitatively track RCT following injection of [ 3 H]-cholesterol-loaded macrophages upstream of blocked or absent lymphatic vessels. Macrophage RCT was markedly impaired in both models, even at sites with a leaky vasculature. Inhibited RCT was downstream of cholesterol efflux from macrophages, since macrophage efflux of a fluorescent cholesterol analog (BODIPY-cholesterol) was not altered by impaired lymphatic drainage. We next addressed whether RCT was mediated by lymphatic vessels from the aortic wall by loading the aortae of donor atherosclerotic Apoe-deficient mice with [ 2 H] 6 -labeled cholesterol and surgically transplanting these aortae into recipient Apoe-deficient mice that were treated with anti-VEGFR3 antibody to block lymphatic regrowth or with control antibody to allow such regrowth. [ 2 H]-Cholesterol was retained in aortae of anti-VEGFR3-treated mice. Thus, the lymphatic vessel route is critical for RCT from multiple tissues, including the aortic wall. These results suggest that supporting lymphatic transport function may facilitate cholesterol clearance in therapies aimed at reversing atherosclerosis.

Apolipoprotein A‐I Modulates Atherosclerosis Through Lymphatic Vessel‐Dependent Mechanisms in Mice

“…Improving lymphatic function to either prevent or abrogate atherosclerosis would be a potentially attractive therapeutic target. We therefore herein sought to connect the beneficial effects of apoA‐I in atherosclerosis to lymphatic function, and we proposed that apoA‐I might reduce the lymphatic dysfunction observed during atherosclerosis 26. Our findings reveal that a continuous low‐dose intradermal injection of diet‐fed Ldlr −/− mice with lipid‐free apoA‐I reverses atherosclerosis‐associated collecting lymphatic vessel dysfunction, without significantly affecting plasma or lymph total cholesterol concentrations.…”

“…However, we had to wait until recently to directly associate the lymphatic system with atherosclerosis,23, 24, 25, 26, 27 a disease driven by the accumulation of cholesterol in the artery wall, primarily by low‐density lipoprotein, leading to increased plaque buildup 28. It has been described that without a functional lymphatic network, cholesterol excreted from plaque macrophages cannot be properly conducted out of the artery wall, and thus cannot be evacuated 26. The mechanisms responsible for the interplay between lymphatic function and the onset or progression of atherosclerosis remain under intensive investigation.…”

HDL and Atherothrombotic Vascular Disease

“…The importance of the lymphatic system in the reentry of cholesterol originating from macrophages via HDLs in the circulation was further confirmed by additional experiments showing that the appearance of macrophage-derived cholesterol in the plasma was impaired after implantation of [ 3 H]-cholesterol-labeled macrophages in the tail skin of apoA-I transgenic mice with microsurgical ablation of the major lymphatic conduits in the tail (Martel et al 2013). To provide more direct proof for the involvement of the lymphatic vasculature in the transport of cholesterol from the atherosclerotic plaque, aortic segments with advanced atherosclerotic lesions were loaded with D6-cholesterol and transplanted in apoE knockout mice (Martel et al 2013). Inhibition of regrowth of a functional lymphatic vasculature in the aortic donor wall by an antibody blocking the function of vascular endothelial growth factor receptor 3 markedly suppressed the apoE-induced removal of D6-cholesterol from the transplanted aorta (Martel et al 2013), hence emphasizing the pivotal role of the lymphatic system for the egress of cholesterol from the aortic wall.…”

“…Following injection of fluorescently labeled HDLs in the mouse footpad, HDLs were subsequently found in the draining lymph node and its afferent and efferent lymphatic vessels (Lim et al 2013). Moreover, the movement of cholesterol from macrophages in the footpad to the lymph and plasma was substantially reduced in mice with surgical interruption of the afferent lymphatic vessels or in Chy mutant mice that lack dermal lymphatic capillaries (Lim et al 2013;Martel et al 2013). The importance of the lymphatic system in the reentry of cholesterol originating from macrophages via HDLs in the circulation was further confirmed by additional experiments showing that the appearance of macrophage-derived cholesterol in the plasma was impaired after implantation of [ 3 H]-cholesterol-labeled macrophages in the tail skin of apoA-I transgenic mice with microsurgical ablation of the major lymphatic conduits in the tail (Martel et al 2013).…”

“…Moreover, the movement of cholesterol from macrophages in the footpad to the lymph and plasma was substantially reduced in mice with surgical interruption of the afferent lymphatic vessels or in Chy mutant mice that lack dermal lymphatic capillaries (Lim et al 2013;Martel et al 2013). The importance of the lymphatic system in the reentry of cholesterol originating from macrophages via HDLs in the circulation was further confirmed by additional experiments showing that the appearance of macrophage-derived cholesterol in the plasma was impaired after implantation of [ 3 H]-cholesterol-labeled macrophages in the tail skin of apoA-I transgenic mice with microsurgical ablation of the major lymphatic conduits in the tail (Martel et al 2013). To provide more direct proof for the involvement of the lymphatic vasculature in the transport of cholesterol from the atherosclerotic plaque, aortic segments with advanced atherosclerotic lesions were loaded with D6-cholesterol and transplanted in apoE knockout mice (Martel et al 2013).…”