title: Multiple internalization pathways of polyelectrolyte multilayer capsules into mammalian cells.
abstract: Polyelectrolyte multilayer (PEM) capsules are carrier vehicles with great potential for biomedical applications. With the future aim of designing biocompatible, effective therapeutic delivery systems (e.g., for cancer), the pathway of internalization (uptake and fate) of PEM capsules was investigated. In particular the following experiments were performed: (i) the study of capsule co-localization with established endocytic markers, (ii) switching-off endocytotic pathways with pharmaceutical/chemical inhibitors, and (iii) characterization and quantification of capsule uptake with confocal and electron microscopy. As result, capsules co-localized with lipid rafts and with phagolysosomes, but not with other endocytic vesicles. Chemical interference of endocytosis with chemical blockers indicated that PEM capsules enter the investigated cell lines through a mechanism slightly sensitive to electrostatic interactions, independent of clathrin and caveolae, and strongly dependent on cholesterol-rich domains and organelle acidification. Microscopic characterization of cells during capsule uptake showed the formation of phagocytic cups (vesicles) to engulf the capsules, an increased number of mitochondria, and a final localization in the perinuclear cytoplasma. Combining all these indicators we conclude that PEM capsule internalization in general occurs as a combination of different sequential mechanisms. Initially, an adsorptive mechanism due to strong electrostatic interactions governs the stabilization of the capsules at the cell surface. Membrane ruffling and filopodia extensions are responsible for capsule engulfing through the formation of a phagocytic cup. Co-localization with lipid raft domains activates the cell to initiate a lipid-raft-mediated macropinocytosis. Internalization vesicles are very acidic and co-localize only with phagolysosome markers, excluding caveolin-mediated pathways and indicating that upon phagocytosis the capsules are sorted to heterophagolysosomes.
authors.affiliation: Fachbereich Physik, Philipps-Universität Marburg, Renthof 7, 35037 Marburg, Germany.
authors.forename: Lena
authors.initials: L
authors.lastname: Kastl
authors.forename: Daniel
authors.initials: D
authors.lastname: Sasse
authors.forename: Verena
authors.initials: V
authors.lastname: Wulf
authors.forename: Raimo
authors.initials: R
authors.lastname: Hartmann
authors.forename: Josif
authors.initials: J
authors.lastname: Mircheski
authors.forename: Christiane
authors.initials: C
authors.lastname: Ranke
authors.forename: Susana
authors.initials: S
authors.lastname: Carregal-Romero
authors.forename: José Antonio
authors.initials: JA
authors.lastname: Martínez-López
authors.forename: Rafael
authors.initials: R
authors.lastname: Fernández-Chacón
authors.forename: Wolfgang J
authors.initials: WJ
authors.lastname: Parak
authors.forename: Hans-Peter
authors.initials: HP
authors.lastname: Elsasser
authors.forename: Pilar
authors.initials: P
authors.lastname: Rivera Gil
mesh_terms: D000327:Adsorption; D000818:Animals; D001672:Biocompatible Materials / Q000737:chemistry*; D002214:Capsules / Q000737:chemistry*; D021941:Caveolae / Q000737:chemistry; D045744:Cell Line, Tumor; D002966:Clathrin / Q000737:chemistry; D003593:Cytoplasm / Q000378:metabolism; D016503:Drug Delivery Systems; D004573:Electrolytes / Q000737:chemistry*; D004705:Endocytosis; D006801:Humans; D021962:Membrane Microdomains / Q000737:chemistry; D051379:Mice; D018613:Microscopy, Confocal; D008854:Microscopy, Electron; D008928:Mitochondria / Q000378:metabolism; D036103:Nanotechnology / Q000379:methods; D010587:Phagocytosis; D010588:Phagosomes / Q000737:chemistry; D055672:Static Electricity
chemical_list: D001672:Biocompatible Materials; D002214:Capsules; D002966:Clathrin; D004573:Electrolytes