Downregulation of low-density lipoprotein receptor mRNA in lymphatic endothelial cells impairs lymphatic function through changes in intracellular lipids.

Impairment in lymphatic transport is associated with the onset and progression of atherosclerosis in animal models. The downregulation of low-density-lipoprotein receptor (LDLR) expression, rather than increased circulating cholesterol level , is involved in early atherosclerosis-related lymphatic dysfunction. Enhancing lymphatic function in mice with a mutant form of VEGF-C (VEGF-C 152s), a selective VEGFR-3 agonist, successfully delayed atherosclerotic plaque onset when mice were subsequently fed a high-fat diet. However, the specific mechanisms by which LDLR protects against lymphatic function impairment is unknown. We have thus injected wild-type and mice with an adeno-associated virus type 1 expressing a shRNA for silencing . We herein report that lymphatic contractility is reduced upon dowregulation in wild-type mice only. Our experiments reveal that a decrease in expression at the mRNA level reduces the chromosome duplication phase and the protein expression of VEGFR-3, a membrane-bound key lymphatic marker. Furthermore, it also significantly reduced the levels of 18 lipid subclasses, including key constituents of lipid rafts as well as the transcription of several genes involved in cholesterol biosynthesis and cellular and metabolic processes. Exogenous PCSK9 only reduces lymphatic endothelial-LDLR at the protein level and does not affect lymphatic endothelial cell integrity. This puts forward that PCSK9 may act upon lymphatic muscle cells to mediate its effect on lymphatic contraction capacity . Our results suggest that treatments that specifically palliate the down regulation of mRNA in lymphatic endothelial cells preserve the integrity of the lymphatic endothelium and sustain lymphatic function, a prerequisite player in atherosclerosis.