Measurement of Aortic Cell Fluid-Phase Pinocytosis in vivo by Flow Cytometry

Abstract

Objective: Fluid-phase pinocytosis is a receptor-independent mechanism of endocytosis that occurs in all mammalian cells and may be a mechanism for the uptake of LDL by macrophages. As there are currently no methods for the measurement of fluid-phase pinocytosis by individual aortic cells in vivo, we sought to identify a suitable method. Methods: ApoE-/- mice were retro-orbitally injected with AngioSPARK fluorescent nanoparticles specifically designed to not interact with cells. After 24 h, mice were sacrificed, and the aortas were isolated and then digested to analyze aortic cell uptake of AngioSPARK by flow cytometry. Results: CD11b-expressing aortic macrophages from mice injected with AngioSPARK showed high levels of fluid-phase pinocytosis compared to aortic cells not expressing CD11b (4,393.7 vs. 408.3 mean fluorescence intensity [MFI], respectively). Conclusion: This new technique allows for the measurement of fluid-phase pinocytosis by aortic cells in vivo, making it possible to examine the cell-signaling molecules and drugs that affect this process.