Fluorescent pegylated nanoparticles demonstrate fluid-phase pinocytosis by macrophages in mouse atherosclerotic lesions
Chiara Buono, … , Marcelo Amar, Howard S. Kruth
Chiara Buono, … , Marcelo Amar, Howard S. Kruth
Published April 13, 2009
Citation Information: J Clin Invest. 2009;119(5):1373-1381. https://doi.org/10.1172/JCI35548.
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Technical Advance Cardiology

Fluorescent pegylated nanoparticles demonstrate fluid-phase pinocytosis by macrophages in mouse atherosclerotic lesions

Abstract

The uptake of lipoproteins by macrophages is a critical step in the development of atherosclerotic lesions. Cultured monocyte-derived macrophages take up large amounts of native LDL by receptor-independent fluid-phase pinocytosis, either constitutively or in response to specific activating stimuli, depending on the macrophage phenotype. We therefore sought to determine whether fluid-phase pinocytosis occurs in vivo in macrophages in atherosclerotic lesions. We demonstrated that fluorescent pegylated nanoparticles similar in size to LDL (specifically nontargeted Qtracker quantum dot and AngioSPARK nanoparticles) can serve as models of LDL uptake by fluid-phase pinocytosis in cultured human monocyte–derived macrophages and mouse bone marrow–derived macrophages. Using fluorescence microscopy, we showed that atherosclerosis-prone Apoe-knockout mice injected with these nanoparticles displayed massive accumulation of the nanoparticles within CD68+ macrophages, including lipid-containing foam cells, in atherosclerotic lesions in the aortic arch. Similar results were obtained when atherosclerotic mouse aortas were cultured with nanoparticles in vitro. These results show that macrophages within atherosclerotic lesions can take up LDL-sized nanoparticles by fluid-phase pinocytosis and indicate that fluid-phase pinocytosis of LDL is a mechanism for macrophage foam cell formation in vivo.

Authors

Chiara Buono, Joshua J. Anzinger, Marcelo Amar, Howard S. Kruth

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Figure 5

Visualization and quantification of AngioSPARK nanoparticle fluorescence signal in atherosclerotic aortas.

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Visualization and quantification of AngioSPARK nanoparticle fluorescence...
Mouse aortas from Apoe-knockout (Apoe–/–) and wild-type mice injected 24 hours earlier with AngioSPARK nanoparticles or normal saline as control were imaged ex vivo by NIRF reflectance imaging, as described in Methods. NIRF images of aortas from Apoe-knockout mice with AngioSPARK injection (A) show substantially brighter NIRF signal than the aortas from wild-type mice (B). Aortas from Apoe-knockout (C) and wild-type mice (D) injected with normal saline as control show only a small fluorescent signal due to intrinsic tissue autofluorescence. The vessel wall NIRF signal is mainly localized in the aortic arch (aa) regions defined between the 2 black bars. h, heart; da, descending aorta. The color scale from black to white indicates NIRF arbitrary units from 70 to 300 and applies to all aorta images. (E) Quantitative analysis of infrared mean fluorescence intensity in the aortic arch regions from 5 AngioSPARK-injected mice minus the intrinsic mean fluorescence intensity of aortas from 2 uninjected control mice (mean fluorescence intensity on the y axis). Fluorescence of atherosclerotic aortic arches from injected Apoe-knockout mice was significantly greater (P = 0.04) than fluorescence of aortic arches with no lesions from wild-type mice. Data represent mean ± SEM of mean fluorescence intensity determinations for each group.