Fig. 1.

Endocytic pathways and exosome biogenesis.

In eukaryotic cells, nanoparticles enter cells via caveolin-mediated, clathrin-mediated, clathrin and caveolin-independent, or macropinocytic endocytosis. Endocytic vesicles containing nanoparticles move to early endosomes, where act as a sorting station. Depending on the sorting mechanisms, nanoparticles can be recycled via exocytosis, transported to late endosomes with maturation of endosomes or trafficked to the ER or TGN. Unless the nanoparticles are retrieved from late endosomes to cytoplasm, they are processed to lysosomes where degradation starts by enzymes. From interluminal vesicles in multi-vesicular bodies (a type of late endosomes), exosomes can be generated by inward budding of endosomal membrane, followed by secretion to extracellular compartments via fusion with plasma membrane.