Blocking lymphatic vessel function with soluble VEGFR3 in atherosclerotic mouse model alters lipoprotein metabolism and enhances atherogenesis

Abstract

Purpose: Lymphatic vessels take part in lipid absorption, inflammatory reactions and draining of large blood vessels. Even though these processes are involved in arterial diseases, the role of lymphatic vessels in atherosclerosis has not been clarified yet. In this study, we evaluated the effect of insufficient lymphatic function on the lipoprotein metabolism and development of atherosclerosis by blocking Vascular Endothelial Growth Factor Receptor 3 (VEGFR3), the key mediator of lymphangiogenesis. Methods: Mice expressing soluble VEGFR3 (sVEGFR3) were cross-bred with atherosclerotic LDLR-/-/ApoB100/100 mice. Mice were fed with chow diet for 3-4 months, 7-8 months and 11-12 months followed by high-fat diet (42% of calories from fat and 0.15% from cholesterol) up to 12 weeks. Lipid levels and lipoprotein profiles were analyzed from blood plasma. Atherosclerotic lesion size was determined from en face aortas and cross-sections of aortic arches and lesion composition was evaluated with modified Movat's staining and immunohistochemical stainings for macrophages (mMQ), blood vessels (CD31) and lymphatic vessels (podoplanin). Results: Compared to LDLR-/-/ApoB100/100 controls, sVEGFR3 x LDLR-/-/ApoB100/100 mice had significantly increased plasma cholesterol levels with chow diet (8.2±0.4 mmol/l vs. 16.3±1.2 mmol/l, respectively) and up to 6 weeks with high-fat diet (36.9±3.0 mmol/l vs. 50.8±4.4 mmol/l, respectively). In addition, sVEGFR3 x LDLR-/-/ApoB100/100 mice had higher VLDL and LDL cholesterol and triglyceride levels than controls. Especially in young sVEGFR3 x LDLR-/-/ApoB100/100 mice, elevated cholesterol levels induced accelerated atherogenesis characterized by increased lesion size and rapid accumulation of foam cells and cholesterol crystals into the lesions. Even though the number of vasa vasorum in the atherosclerotic lesions was at similar level in the study and control groups, lymphatic vessels were almost absent in the lesions of sVEGFR3 x LDLR-/-/ApoB100/100 mice. Conclusions: Here we show that lipoprotein metabolism and atherogenesis are affected by insufficient lymphatic draining. These results suggest that lymphatic vessels have a previously undiscovered role in the lipid transport and highlight a potential target for the treatment of lipid related diseases, such as atherosclerosis.