title: Relationship between Autophagy and Ventilator-induced Diaphragmatic Dysfunction.
abstract: BACKGROUND
  Mechanical ventilation (MV) is associated with atrophy and weakness of the diaphragm muscle, a condition termed ventilator-induced diaphragmatic dysfunction (VIDD). Autophagy is a lysosomally mediated proteolytic process that can be activated by oxidative stress, which has the potential to either mitigate or exacerbate VIDD. The primary goals of this study were to (1) determine the effects of MV on autophagy in the diaphragm and (2) evaluate the impact of antioxidant therapy on autophagy induction and MV-induced diaphragmatic weakness.
  
  
  METHODS
  Mice were assigned to control (CTRL), MV (for 6 h), MV + N-acetylcysteine, MV + rapamycin, and prolonged (48 h) fasting groups. Autophagy was monitored by quantifying (1) autophagic vesicles by transmission electron microscopy, (2) messenger RNA levels of autophagy-related genes, and (3) the autophagosome marker protein LC3B-II, with and without administration of colchicine to calculate the indices of relative autophagosome formation and degradation. Force production by mouse diaphragms was determined ex vivo.
  
  
  RESULTS
  Diaphragms exhibited a 2.2-fold (95% CI, 1.8 to 2.5) increase in autophagic vesicles visualized by transmission electron microscopy relative to CTRL after 6 h of MV (n = 5 per group). The autophagosome formation index increased in the diaphragm alone (1.5-fold; 95% CI, 1.3 to 1.8; n = 8 per group) during MV, whereas prolonged fasting induced autophagosome formation in both the diaphragm (2.5-fold; 95% CI, 2.2 to 2.8) and the limb muscle (4.1-fold; 95% CI, 1.8 to 6.5). The antioxidant N-acetylcysteine further augmented the autophagosome formation in the diaphragm during MV (1.4-fold; 95% CI, 1.2 to 1.5; n = 8 per group) and prevented MV-induced diaphragmatic weakness. Treatment with the autophagy-inducing agent rapamycin also largely prevented the diaphragmatic force loss associated with MV (n = 6 per group).
  
  
  CONCLUSIONS
  In this model of VIDD, autophagy is induced by MV but is not responsible for diaphragmatic weakness. The authors propose that autophagy may instead be a beneficial adaptive response that can potentially be exploited for therapy of VIDD.
authors.affiliation: From the Meakins Christie Laboratories and Respiratory Division, McGill University Health Centre Research Institute, Montreal, Quebec, Canada (I.A., B.J., F.L., T.L., C.L., C.G., S.H., B.J.P.); Department of Critical Care Medicine and Anesthesiology, Saint Eloi Teaching Hospital, Montpellier, France, and Centre National de la Recherche Scientifique (CNRS 9214), Institut National de la Santé et de la Recherche Médicale (INSERM U-1046), Montpellier University, Montpellier, France (B.J.); Center for Mitochondrial and Epigenomic Medicine, Children's Hospital of Philadelphia and University of Pennsylvania, Philadelphia, Pennsylvania (M.P.); and Department of Critical Care, McGill University Health Centre, Montreal, Quebec, Canada (S.H.).
authors.forename: Ilan
authors.initials: I
authors.lastname: Azuelos
authors.forename: Boris
authors.initials: B
authors.lastname: Jung
authors.forename: Martin
authors.initials: M
authors.lastname: Picard
authors.forename: Feng
authors.initials: F
authors.lastname: Liang
authors.forename: Tong
authors.initials: T
authors.lastname: Li
authors.forename: Christian
authors.initials: C
authors.lastname: Lemaire
authors.forename: Christian
authors.initials: C
authors.lastname: Giordano
authors.forename: Sabah
authors.initials: S
authors.lastname: Hussain
authors.forename: Basil J
authors.initials: BJ
authors.lastname: Petrof
mesh_terms: D000818:Animals; D000975:Antioxidants / Q000494:pharmacology; D001284:Atrophy; D001343:Autophagy / Q000235:genetics; D003553:Cystine / Q000031:analogs & derivatives / Q000494:pharmacology; D003964:Diaphragm / Q000473:pathology* / Q000648:ultrastructure; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D009119:Muscle Contraction / Q000187:drug effects; D010588:Phagosomes / Q000187:drug effects; D020123:Sirolimus / Q000494:pharmacology; D055397:Ventilator-Induced Lung Injury / Q000473:pathology*
chemical_list: D000975:Antioxidants; D003553:Cystine; D020123:Sirolimus; C030905:N-monoacetylcystine