title: Advances in Use of Capsule-Based Fluorescent Sensors for Measuring Acidification of Endocytic Compartments in Cells with Altered Expression of V-ATPase Subunit V1G1.
abstract: Acidification of eukaryotic cell compartments is accomplished by vacuolar H+-ATPases (V-ATPases), large multisubunit complexes able to pump protons into the lumen of organelles or in the extracellular medium. V-ATPases are involved in a number of physiological cellular processes, and thus regulation of V-ATPase activity is of crucial importance for the cell. Indeed, dysfunction of V-ATPase or alterations of acidification have been recently recognized as key factors in a variety of human diseases. In this study, we applied capsule-based pH sensors and a real-time tracking method for investigating the role of the V1G1 subunit of V-ATPases in regulating the activity of the proton pump. We first constructed stable cell lines overexpressing or silencing the subunit V1G1. Second, we used fluorescent capsule-based pH sensors to monitor acidification before and during internalization by modified and control living cells. By using a simple real-time method for tracking capsule internalization, we were able to identify different capsule acidification levels with respect to each analyzed cell and to establish the kinetics for each. The intracellular pH measurements indicate a delay in acidification in either V1G1-overexpressing or V1G1-silenced cells compared to controls. Finally, in an independent set of experiments, we applied transmission electron microscopy and confocal fluorescence microscopy to further investigate the internalization of the capsules. Both analyses confirm that capsules are engulfed in acidic vesicular structures in modified and control cell lines. The use of capsule-based pH sensors allowed demonstration of the importance of the V1G1 subunit in V-ATPase activity concerning intravesicular acidification. We believe that the combined use of these pH-sensor system and such a real-time method for tracking their internalization path would contribute to systematically measure the proton concentration changes inside the endocytic compartments in various cell systems. This approach would provide fundamental information regarding molecular mechanisms and factors that regulate intracellular acidification, vesicular trafficking, and cytoskeletal reorganizations.
authors.affiliation: §Dipartimento di Scienze e Tecnologie Biologiche ed Ambientali (DiSTeBA), Università del Salento, Via Monteroni, 73100, Lecce, Italy.
authors.forename: Maria
authors.initials: M
authors.lastname: De Luca
authors.forename: Marzia M
authors.initials: MM
authors.lastname: Ferraro
authors.affiliation: ⊥Fachbereich Physik, Philipps-Universität Marburg, Renthof 7, 35037, Marburg, Germany.
authors.forename: Raimo
authors.initials: R
authors.lastname: Hartmann
authors.affiliation: ⊥Fachbereich Physik, Philipps-Universität Marburg, Renthof 7, 35037, Marburg, Germany.
authors.forename: Pilar
authors.initials: P
authors.lastname: Rivera-Gil
authors.affiliation: #LOEWE Centre for synthetic Microbiology (Synmikro) and Department of Cell Biology, Philipps-Universität Marburg, Karl-von-Frisch-Strasse 8, 35043, Marburg, Germany.
authors.forename: Andreas
authors.initials: A
authors.lastname: Klingl
authors.affiliation: ⊥Fachbereich Physik, Philipps-Universität Marburg, Renthof 7, 35037, Marburg, Germany.
authors.forename: Moritz
authors.initials: M
authors.lastname: Nazarenus
authors.affiliation: ⊥Fachbereich Physik, Philipps-Universität Marburg, Renthof 7, 35037, Marburg, Germany.
authors.forename: Agnese
authors.initials: A
authors.lastname: Ramirez
authors.affiliation: ⊥Fachbereich Physik, Philipps-Universität Marburg, Renthof 7, 35037, Marburg, Germany.|||CIC biomaGUNE, Parque Tecnológico de San Sebastián, Ed. P° Miramón 182, 20009, San Sebastian, Spain.
authors.forename: Wolfgang J
authors.initials: WJ
authors.lastname: Parak
authors.affiliation: §Dipartimento di Scienze e Tecnologie Biologiche ed Ambientali (DiSTeBA), Università del Salento, Via Monteroni, 73100, Lecce, Italy.
authors.forename: Cecilia
authors.initials: C
authors.lastname: Bucci
authors.forename: Rosaria
authors.initials: R
authors.lastname: Rinaldi
authors.forename: Loretta L
authors.initials: LL
authors.lastname: del Mercato
mesh_terms: D011992:Endosomes / Q000737:chemistry* / Q000378:metabolism*; D005456:Fluorescent Dyes / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D008856:Microscopy, Fluorescence / Q000379:methods*; D057054:Molecular Imaging / Q000379:methods; D053769:Nanocapsules / Q000737:chemistry*; D025262:Vacuolar Proton-Translocating ATPases / Q000378:metabolism*
chemical_list: D005456:Fluorescent Dyes; D053769:Nanocapsules; C000594810:ATP6V1G1 protein, human; D025262:Vacuolar Proton-Translocating ATPases
keywords: V-ATPase; biosensors; cell uptake; layer-by-layer microcapsules; pH measurements