title: ATP-induced cellular stress and mitochondrial toxicity in cells expressing purinergic P2X7 receptor.
abstract: Under pathological conditions, the purinergic P2X7 receptor is activated by elevated concentrations of extracellular ATP. Thereby, the receptor forms a slowly dilating pore, allowing cations and, upon prolonged stimulation, large molecules to enter the cell. This process has a strong impact on cell signaling, metabolism, and viability. This study aimed to establish a link between gradual P2X7 activation and pharmacological endpoints including oxidative stress, hydrogen peroxide generation, and cytotoxicity. Mechanisms of cellular stress and cytotoxicity were studied in P2X7-transfected HEK293 cells. We performed real-time monitoring of metabolic and respiratory activity of cells expressing the P2X7-receptor protein using a cytosensor system. Agonistic effects were monitored using exogenously applied ATP or the stable analogue BzATP. Oxidative stress induced by ATP or BzATP in target cells was monitored by hydrogen peroxide release in human mononuclear blood cells. P2X7-receptor activation was studied by patch-clamp experiments using a primary mouse microglia cell line. Stimulation of the P2X7 receptor leads to ion influx, metabolic activation of target cells, and ultimately cytotoxicity. Conversion of the P2X7 receptor from a small cation channel to a large pore occurring under prolonged stimulation can be monitored in real time covering a time frame of milliseconds to hours. Selectivity of the effects can be demonstrated using the selective P2X7-receptor antagonist AZD9056. Our findings established a direct link between P2X7-receptor activation by extracellular ATP or BzATP and cellular events culminating in cytotoxicity. Mechanisms of toxicity include metabolic and oxidative stress, increase in intracellular calcium concentration and disturbance of mitochondrial membrane potential. Mitochondrial toxicity is suggested to be a key event leading to cell death.
authors.affiliation: Actelion Pharmaceuticals Ltd Gewerbestrasse 16, 4123, Allschwil, Switzerland ; Institute for Molecular and Cell Biology, University of Applied Science Paul-Wittsack-Strasse 10, 68163, Mannheim, Germany.
authors.forename: Swen
authors.initials: S
authors.lastname: Seeland
authors.affiliation: Division of Pharmaceutical Technology, Department of Pharmaceutical Sciences, University of Basel Klingelbergstrasse 50, 4056, Basel, Switzerland.
authors.forename: Hélène
authors.initials: H
authors.lastname: Kettiger
authors.affiliation: Actelion Pharmaceuticals Ltd Gewerbestrasse 16, 4123, Allschwil, Switzerland.
authors.forename: Mark
authors.initials: M
authors.lastname: Murphy
authors.affiliation: Actelion Pharmaceuticals Ltd Gewerbestrasse 16, 4123, Allschwil, Switzerland.
authors.forename: Alexander
authors.initials: A
authors.lastname: Treiber
authors.affiliation: Actelion Pharmaceuticals Ltd Gewerbestrasse 16, 4123, Allschwil, Switzerland.
authors.forename: Jasmin
authors.initials: J
authors.lastname: Giller
authors.affiliation: Actelion Pharmaceuticals Ltd Gewerbestrasse 16, 4123, Allschwil, Switzerland.
authors.forename: Andrea
authors.initials: A
authors.lastname: Kiss
authors.affiliation: Actelion Pharmaceuticals Ltd Gewerbestrasse 16, 4123, Allschwil, Switzerland.
authors.forename: Romain
authors.initials: R
authors.lastname: Sube
authors.affiliation: Division of Clinical Pharmacology and Toxicology, University Hospital of Basel 4056, Basel, Switzerland.
authors.forename: Stephan
authors.initials: S
authors.lastname: Krähenbühl
authors.affiliation: Institute for Molecular and Cell Biology, University of Applied Science Paul-Wittsack-Strasse 10, 68163, Mannheim, Germany.
authors.forename: Mathias
authors.initials: M
authors.lastname: Hafner
authors.affiliation: Division of Pharmaceutical Technology, Department of Pharmaceutical Sciences, University of Basel Klingelbergstrasse 50, 4056, Basel, Switzerland.
authors.forename: Jörg
authors.initials: J
authors.lastname: Huwyler
keywords: Cytosensor; P2X7; extracellular adenosine triphosphate (ATP); metabolic stress; mitochondrial toxicity; purinergic receptor