title: Silica particles cause NADPH oxidase-independent ROS generation and transient phagolysosomal leakage.
abstract: Chronic inhalation of silica particles causes lung fibrosis and silicosis. Silica taken up by alveolar macrophages causes phagolysosomal membrane damage and leakage of lysosomal material into the cytoplasm to initiate apoptosis. We investigated the role of reactive oxygen species (ROS) in this membrane damage by studying the spatiotemporal generation of ROS. In macrophages, ROS generated by NADPH oxidase 2 (NOX2) was detected in phagolysosomes containing either silica particles or nontoxic latex particles. ROS was only detected in the cytoplasm of cells treated with silica and appeared in parallel with an increase in phagosomal ROS, as well as several hours later associated with mitochondrial production of ROS late in apoptosis. Pharmacological inhibition of NOX activity did not prevent silica-induced phagolysosomal leakage but delayed it. In Cos7 cells, which do not express NOX2, ROS was detected in silica-containing phagolysosomes that leaked. ROS was not detected in phagolysosomes containing latex particles. Leakage of silica-containing phagolysosomes in both cell types was transient, and after resealing of the membrane, endolysosomal fusion continued. These results demonstrate that silica particles can generate phagosomal ROS independent of NOX activity, and we propose that this silica-generated ROS can cause phagolysosomal leakage to initiate apoptosis.
authors.affiliation: Department of Molecular and Cell Biology, University of Connecticut, Storrs, CT 06269.
authors.forename: Gaurav N
authors.initials: GN
authors.lastname: Joshi
authors.affiliation: Department of Molecular and Cell Biology, University of Connecticut, Storrs, CT 06269.
authors.forename: Alexandra M
authors.initials: AM
authors.lastname: Goetjen
authors.affiliation: Department of Molecular and Cell Biology, University of Connecticut, Storrs, CT 06269 David.knecht@uconn.edu.
authors.forename: David A
authors.initials: DA
authors.lastname: Knecht
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000187:drug effects; D019556:COS Cells; D002460:Cell Line; D002522:Chlorocebus aethiops; D008168:Lung; D008247:Lysosomes / Q000187:drug effects / Q000378:metabolism; D016676:Macrophages, Alveolar / Q000187:drug effects / Q000378:metabolism; D008562:Membrane Glycoproteins / Q000378:metabolism; D008565:Membrane Proteins; D051379:Mice; D000074662:NADPH Oxidase 2; D019255:NADPH Oxidases / Q000378:metabolism*; D010316:Particle Size; D010588:Phagosomes / Q000187:drug effects* / Q000378:metabolism*; D017382:Reactive Oxygen Species / Q000378:metabolism*; D012822:Silicon Dioxide / Q000633:toxicity*
chemical_list: D008562:Membrane Glycoproteins; D008565:Membrane Proteins; D017382:Reactive Oxygen Species; D012822:Silicon Dioxide; C488842:Cybb protein, mouse; D000074662:NADPH Oxidase 2; D019255:NADPH Oxidases