title: Argon Mediates Anti-Apoptotic Signaling and Neuroprotection via Inhibition of Toll-Like Receptor 2 and 4.
abstract: OBJECTIVE
  Recently, the noble gas argon attracted significant attention due to its neuroprotective properties. However, the underlying molecular mechanism is still poorly understood. There is growing evidence that the extracellular regulated kinase 1/2 (ERK1/2) is involved in Argon´s protective effect. We hypothesized that argon mediates its protective effects via the upstream located toll-like receptors (TLRs) 2 and 4.
  
  
  METHODS
  Apoptosis in a human neuroblastoma cell line (SH-SY5Y) was induced using rotenone. Argon treatment was performed after induction of apoptosis with different concentrations (25, 50 and 75 Vol% in oxygen 21 Vol%, carbon dioxide and nitrogen) for 2 or 4 hours respectively. Apoptosis was analyzed using flow cytometry (annexin-V (AV)/propidiumiodide (PI)) staining, caspase-3 activity and caspase cleavage. TLR density on the cells' surface was analyzed using FACS and immunohistochemistry. Inhibition of TLR signaling and extracellular regulated kinase 1/2 (ERK1/2) were assessed by western blot, activity assays and FACS analysis.
  
  
  RESULTS
  Argon 75 Vol% treatment abolished rotenone-induced apoptosis. This effect was attenuated dose- and time-dependently. Argon treatment was accompanied with a significant reduction of TLR2 and TLR4 receptor density and protein expression. Moreover, argon mediated increase in ERK1/2 phosphorylation was attenuated after inhibition of TLR signaling. ERK1/2 and TLR signaling inhibitors abolished the anti-apoptotic and cytoprotective effects of argon. Immunohistochemistry results strengthened these findings.
  
  
  CONCLUSIONS
  These findings suggest that argon-mediated anti-apoptotic and neuroprotective effects are mediated via inhibition of TLR2 and TLR4.
authors.affiliation: Department of Anesthesiology and Intensive Care Medicine, University Medical Center, Freiburg, Germany.
authors.forename: Felix
authors.initials: F
authors.lastname: Ulbrich
authors.affiliation: Department of Anesthesiology and Intensive Care Medicine, University Medical Center, Freiburg, Germany.
authors.forename: Kai
authors.initials: K
authors.lastname: Kaufmann
authors.affiliation: Department of Anesthesiology and Intensive Care Medicine, University Medical Center, Freiburg, Germany.
authors.forename: Martin
authors.initials: M
authors.lastname: Roesslein
authors.affiliation: Department of Anesthesiology and Intensive Care Medicine, University Medical Center, Freiburg, Germany.
authors.forename: Franziska
authors.initials: F
authors.lastname: Wellner
authors.affiliation: Institute of Forensic Medicine, Forensic Toxicology, University of Freiburg, Freiburg, Germany.
authors.forename: Volker
authors.initials: V
authors.lastname: Auwärter
authors.affiliation: Institute of Forensic Medicine, Forensic Toxicology, University of Freiburg, Freiburg, Germany.
authors.forename: Jürgen
authors.initials: J
authors.lastname: Kempf
authors.affiliation: Department of Anesthesiology and Intensive Care Medicine, University Medical Center, Freiburg, Germany.
authors.forename: Torsten
authors.initials: T
authors.lastname: Loop
authors.affiliation: Department of Anesthesiology and Intensive Care Medicine, University Medical Center, Freiburg, Germany.
authors.forename: Hartmut
authors.initials: H
authors.lastname: Buerkle
authors.affiliation: Department of Anesthesiology and Intensive Care Medicine, University Medical Center, Freiburg, Germany.
authors.forename: Ulrich
authors.initials: U
authors.lastname: Goebel
mesh_terms: D017209:Apoptosis / Q000187:drug effects*; D001128:Argon / Q000494:pharmacology*; D053148:Caspase 3 / Q000378:metabolism; D045744:Cell Line, Tumor; D006801:Humans; D020935:MAP Kinase Signaling System / Q000187:drug effects; D009447:Neuroblastoma / Q000188:drug therapy / Q000378:metabolism; D000066829:Neuroprotection / Q000187:drug effects*; D018696:Neuroprotective Agents / Q000494:pharmacology*; D010766:Phosphorylation / Q000187:drug effects; D012402:Rotenone / Q000494:pharmacology; D015398:Signal Transduction / Q000187:drug effects*; D051195:Toll-Like Receptor 2 / Q000037:antagonists & inhibitors*; D051197:Toll-Like Receptor 4 / Q000037:antagonists & inhibitors*
chemical_list: D018696:Neuroprotective Agents; C495342:TLR2 protein, human; C495345:TLR4 protein, human; D051195:Toll-Like Receptor 2; D051197:Toll-Like Receptor 4; D012402:Rotenone; D001128:Argon; D053148:Caspase 3