title: Cigarette smoke extract induces prolonged endoplasmic reticulum stress and autophagic cell death in human umbilical vein endothelial cells.
abstract: OBJECTIVE
  Consumption of cigarette smoke (CS) is a well-known risk factor for early atherosclerosis; yet, the underlying mechanisms of smoking-associated atherosclerosis are poorly understood. Based on the previous results indicating that CS-induced endothelial cell death neither shows typical features of apoptosis nor of necrosis, we investigated the role of autophagy in CS extract (CSE)-induced cell death of human umbilical vein endothelial cells (HUVECs).
  
  
  RESULTS
  Here, we demonstrate that overexpression of the classical apoptosis inhibitor BCL-XL had no protective effect on CSE-induced cell death, whereas the autophagy inhibitor 3-methyladenin and an shRNAi-mediated knockdown of the autophagy mediator ATG5 significantly delayed cell death. Our results indicate that CSE induces an excess accumulation of misfolded proteins in the endoplasmic reticulum (ER) and consequently the onset of the unfolded protein response. We provide evidence that the ER-resident kinase PERK is a major transducer of ER stress leading to phosphorylation of eIF2α and attenuation of protein synthesis. Finally, we show that prolonged ER stress in cells subjected to CS is followed by activation of an autophagic programme. CSE-induced autophagy is characterized by an increase in LC3 II/I ratio and activation ATG12. The autophagic signalling pathway via energy depletion and consequent activation AMP-activated protein kinase could be excluded.
  
  
  CONCLUSIONS
  Our results confirm and extend previous findings reporting on the induction of autophagy by CSE in the lung. We show that protein damage caused by CSE activates autophagy, ultimately resulting in necrotic death of HUVECs. Via this mechanism, cigarette smoking may contribute to the deterioration of vascular endothelial function and the initiation of atherosclerosis.
authors.affiliation: Division of Experimental Pathophysiology and Immunology, Laboratory of Autoimmunity, Biocenter, Innsbruck Medical University, Innsbruck, Austria.
authors.forename: Adam
authors.initials: A
authors.lastname: Csordas
authors.forename: Simone
authors.initials: S
authors.lastname: Kreutmayer
authors.forename: Christian
authors.initials: C
authors.lastname: Ploner
authors.forename: Peter R
authors.initials: PR
authors.lastname: Braun
authors.forename: Alexander
authors.initials: A
authors.lastname: Karlas
authors.forename: Aleksandar
authors.initials: A
authors.lastname: Backovic
authors.forename: Georg
authors.initials: G
authors.lastname: Wick
authors.forename: David
authors.initials: D
authors.lastname: Bernhard
mesh_terms: D055372:AMP-Activated Protein Kinases / Q000502:physiology; D000255:Adenosine Triphosphate / Q000032:analysis; D050197:Atherosclerosis / Q000209:etiology; D001343:Autophagy; D002478:Cells, Cultured; D059865:Endoplasmic Reticulum Stress; D042783:Endothelial Cells / Q000473:pathology*; D015852:Eukaryotic Initiation Factor-2 / Q000502:physiology; D006801:Humans; D012906:Smoke; D014026:Nicotiana / Q000633:toxicity*; D014471:Umbilical Veins / Q000166:cytology
chemical_list: D015852:Eukaryotic Initiation Factor-2; D012906:Smoke; D000255:Adenosine Triphosphate; D055372:AMP-Activated Protein Kinases