title: Melatonin inhibits mTOR-dependent autophagy during liver ischemia/reperfusion.
abstract: BACKGROUND
  Autophagy is a self-digestion system responsible for maintaining cellular homeostasis and interacts with reactive oxygen species produced during ischemia/reperfusion (I/R). Melatonin (MLT) is a potent and endogenous anti-oxidant that has beneficial effects in liver I/R injury. In this study, we examined the cytoprotective mechanisms of MLT in liver I/R, focusing on autophagic flux and associated signaling pathways.
  
  
  METHODS
  Male C57BL/6 mice were subjected to 70% liver ischemia for 60 min followed by reperfusion. MLT (10 mg/kg, i.p.) was injected 15 min prior to ischemia and again immediately before reperfusion. Rapamycin (Rapa, 1 mg/kg, i.p.), which induces autophagy, was injected 1.5 h before ischemia.
  
  
  RESULTS
  Liver I/R increased autophagic flux as indicated by the accumulation of LC3-II and degradation of sequestosome1/p62. This increase was attenuated by MLT. Likewise, electron microscopic analysis showed that autophagic vacuoles were increased in livers of mice exposed to I/R, which was attenuated by MLT. I/R decreased phosphorylation of mammalian target of rapamycin (mTOR) and 4E-BP1 and 70S6K, downstream molecules of the mTOR pathway, but increased expression of calpain 1 and calpain 2. MLT attenuated the decrease in mTOR, 4E-BP1 and 70S6K phosphorylation. Pretreatment of Rapa reversed the effect of MLT on autophagic flux as well as mTOR pathway.
  
  
  CONCLUSIONS
  Our findings suggest that MLT downregulates autophagy via activation of mTOR signaling, which may in turn contribute to its protective effects in liver I/R injury.
authors.affiliation: School of Pharmacy, Sungkyunkwan University, Suwon, Republic of Korea.
authors.forename: Jung-Woo
authors.initials: JW
authors.lastname: Kang
authors.forename: Hong-Ik
authors.initials: HI
authors.lastname: Cho
authors.forename: Sun-Mee
authors.initials: SM
authors.lastname: Lee
mesh_terms: D000818:Animals; D051017:Apoptosis Regulatory Proteins / Q000378:metabolism; D001343:Autophagy / Q000187:drug effects*; D000071186:Beclin-1; D002154:Calpain / Q000378:metabolism; D022781:Hepatocytes / Q000187:drug effects / Q000378:metabolism / Q000473:pathology; D008099:Liver / Q000098:blood supply / Q000473:pathology / Q000648:ultrastructure; D008550:Melatonin / Q000494:pharmacology*; D008810:Mice, Inbred C57BL; D018384:Oxidative Stress / Q000187:drug effects; D020011:Protective Agents / Q000494:pharmacology; D015427:Reperfusion Injury / Q000378:metabolism* / Q000473:pathology*; D020123:Sirolimus / Q000494:pharmacology; D058570:TOR Serine-Threonine Kinases / Q000378:metabolism*; D013997:Time Factors
chemical_list: D051017:Apoptosis Regulatory Proteins; D000071186:Beclin-1; C115010:Becn1 protein, mouse; D020011:Protective Agents; D058570:TOR Serine-Threonine Kinases; D002154:Calpain; D008550:Melatonin; D020123:Sirolimus