Macrophages take up VLDL-sized emulsion particles through caveolae-mediated endocytosis and excrete part of the internalized triglycerides as fatty acids

PLoS Biol. 2022 Aug 26;20(8):e3001516. doi: 10.1371/journal.pbio.3001516. eCollection 2022 Aug.

Abstract

Triglycerides are carried in the bloodstream as part of very low-density lipoproteins (VLDLs) and chylomicrons, which represent the triglyceride-rich lipoproteins. Triglyceride-rich lipoproteins and their remnants contribute to atherosclerosis, possibly by carrying remnant cholesterol and/or by exerting a proinflammatory effect on macrophages. Nevertheless, little is known about how macrophages process triglyceride-rich lipoproteins. Here, using VLDL-sized triglyceride-rich emulsion particles, we aimed to study the mechanism by which VLDL triglycerides are taken up, processed, and stored in macrophages. Our results show that macrophage uptake of VLDL-sized emulsion particles is dependent on lipoprotein lipase (LPL) and requires the lipoprotein-binding C-terminal domain but not the catalytic N-terminal domain of LPL. Subsequent internalization of VLDL-sized emulsion particles by macrophages is carried out by caveolae-mediated endocytosis, followed by triglyceride hydrolysis catalyzed by lysosomal acid lipase. It is shown that STARD3 is required for the transfer of lysosomal fatty acids to the ER for subsequent storage as triglycerides, while NPC1 likely is involved in promoting the extracellular efflux of fatty acids from lysosomes. Our data provide novel insights into how macrophages process VLDL triglycerides and suggest that macrophages have the remarkable capacity to excrete part of the internalized triglycerides as fatty acids.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Caveolae*
  • Emulsions
  • Endocytosis
  • Fatty Acids*
  • Lipoproteins
  • Macrophages
  • Triglycerides

Substances

  • Emulsions
  • Fatty Acids
  • Lipoproteins
  • Triglycerides

Grants and funding

The work was supported by the PACMAN project (181102) funded by FrieslandCampina (https://www.frieslandcampina.com/) and a CSC Scholarship (201703250072) funded by China Scholarship Council (https://www.csc.edu.cn/). S.K. is the recipient of the PACMAN grant. L.D. is the recipient of the CSC grant. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.