Lymphatic vasculature mediates macrophage reverse cholesterol transport in mice
Catherine Martel, … , Mary G. Sorci-Thomas, Gwendalyn J. Randolph
Catherine Martel, … , Mary G. Sorci-Thomas, Gwendalyn J. Randolph
Published March 25, 2013
Citation Information: J Clin Invest. 2013;123(4):1571-1579. https://doi.org/10.1172/JCI63685.
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Research Article

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 [3H]-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 [2H]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. [2H]-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.

Authors

Catherine Martel, Wenjun Li, Brian Fulp, Andrew M. Platt, Emmanuel L. Gautier, Marit Westerterp, Robert Bittman, Alan R. Tall, Shu-Hsia Chen, Michael J. Thomas, Daniel Kreisel, Melody A. Swartz, Mary G. Sorci-Thomas, Gwendalyn J. Randolph

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Figure 1

Surgical separation of lymphatic vessels and its impact on RCT.

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Surgical separation of lymphatic vessels and its impact on RCT. (A) Imag...
(A) Image of the mouse tail following surgical separation of lymphatic vessels (red arrow). White boxes depict approximate location of tail-draining lymph nodes. These nodes (lower photomicrographs) were removed after Evans blue dye was injected into the tail; enlarged images of the 2 lymph nodes are shown from a control mouse receiving a sham operation (Sham) and 1 that underwent lymphatic separation (Surgery). Similar results were obtained in 4 other analyses (n = 5) using Evans blue dye to verify repeated success of the procedure. (B) [3H]-Cholesterol–loaded macrophages were injected into the peritoneum (i.p.), in skin of the tail, or the lower back of WT or Apoa1 transgenic mice. Tritium counts in the plasma are charted. (C) Tritium counts in plasma in control mice (solid line) or in those subjected to lymphatic separation (dotted line) after [3H]-cholesterol–loaded macrophages were injected into the tail upstream (with respect to lymph flow) of the lymphatic separation as shown in A. (D) Compiled tritium counts in plasma, liver, and feces from the experimental design used in C. (E) Cholesterol efflux was monitored as the loss of fluorescence from gated CD45.1 macrophages loaded ex vivo with BODIPY-cholesterol and retrieved 24 hours later from the tails of WT or Apoa1 transgenic mice with or without lymphatic separation. All data represent the mean ± SEM from at least 2 experiments performed with 5 replicates per experimental group. *P < 0.05; **P < 0.01. CPM, counts per minute.