Figure 2 | Scientific Reports

Figure 2

From: Caveolin-initiated macropinocytosis is required for efficient silica nanoparticles’ transcytosis across the alveolar epithelial barrier

Figure 2

F-actin together with the factors driving firm adhesion of amorphous silica nanoparticles (ASN) to AEC, is responsible for ASN cellular uptake. (A) Electron tomogram captures the internalization of ASN by an A549 cell with the uptake compartment components marked as follows: F-actin (green); the plasma membrane (dark blue); ASN agglomerate (red); caveolae (cyan); the trans-Golgi network (TGN, beige); and mitochondria (light blue). (B) Ultracellular topography of the ASN uptake compartment components (structures annotated in panel A). (C) Identification of the protein-lined cup structures of 50 nm to 100 nm diameter, consistent with caveolae formation (black arrow heads) at the interface of ASN uptake. (D) mCherry-caveolin-1-transfected A549 cells form caveolae-lined invagination (pseudo-colored green) in a juxtaposition to the far-red-fluorescent ASN (red) during the uptake captured via confocal live cell imaging (LCI). (E) The involvement of actin during ASN internalization is revealed by LCI of eGFP-LifeAct-transfected A549. Note that actin bundles following or preceding the ASN agglomerates as they become internalized (cell boundary represented by white line). (F) Quantitation of ASN uptake in the absence and in the presence of endocytic inhibitors by A549 and primary hAECs. Note the ASN uptake dependence on all firm-cell-adhesion factors (per Fig. 1) as well as a significant uptake suppression by the actin inhibitor (Cytochalasin B). Mean ± SD, n = 4 **p < 0.01. Scale bar: (A–C) 500 nm, (D, E): 2 µm.

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