title: Palmitic acid induces autophagy in hepatocytes via JNK2 activation.
abstract: OBJECTIVE
  Free fatty acid-induced lipotoxicity plays a crucial role in the progression of nonalcoholic fatty liver disease (NAFLD). In the present study we investigated the effects of a high-fat diet and free fatty acids on the autophagic process in hepatocytes in vivo and in vitro and the underlying mechanisms.
  
  
  METHODS
  LC3-II expression, a hallmark of autophagic flux, was detected in liver specimens from patients with non-alcoholic steatohepatitis (NASH) as well as in the livers of C57BL/6 mice fed a high-fat diet (HFD) up to 16 weeks. LC3-II expression was also analyzed in human SMMC-7721 and HepG2 hepatoma cells exposed to palmitic acid (PA), a saturated fatty acid. PA-induced apoptosis was detected by Annexin V staining and specific cleavage of PARP in the presence and absence of different agents.
  
  
  RESULTS
  LC3-II expression was markedly increased in human NASH and in liver tissues of HFD-fed mice. Treatment of SMMC-7721 cells with PA increased LC3-II expression in time- and dose-dependent manners, whereas the unsaturated fatty acid oleic acid had no effect. Inhibition of autophagy with 3MA sensitized SMMC-7721 cells to PA-induced apoptosis, whereas activation of autophagy by rapamycin attenuated PA-induced PARP cleavage. The autophagy-associated proteins Beclin1 and Atg5 were essential for PA-induced autophagy in SMMC-7721 cells. Moreover, pretreatment with SP600125, an inhibitor of JNK, effectively abrogated PA-mediated autophagy and apoptosis. Specific knockdown of JNK2, but not JNK1, in SMMC-7721 cells significantly suppressed PA-induced autophagy and enhanced its pro-apoptotic activity; whereas specific knockdown of JNK1 had the converse effect. Similar results were obtained when HepG2 cells were tested.
  
  
  CONCLUSIONS
  JNK1 promotes PA-induced lipoapoptosis, whereas JNK2 activates pro-survival autophagy and inhibits PA lipotoxicity. Our results suggest that modulation of autophagy may have therapeutic benefits in the treatment of lipid-related metabolic diseases.
authors.affiliation: International Co-operation Laboratory on Signal Transduction, Eastern Hepatobiliary Surgery Institute, Second Military Medical University, Shanghai 200433, China.
authors.forename: Qian-qian
authors.initials: QQ
authors.lastname: Tu
authors.affiliation: Department of Infectious Diseases, Changhai Hospital, Second Military Medical University, Shanghai 200433, China.
authors.forename: Rui-ying
authors.initials: RY
authors.lastname: Zheng
authors.affiliation: Department of Nutrition and Endocrinology, Changhai Hospital, Second Military Medical University, Shanghai 200433, China.
authors.forename: Juan
authors.initials: J
authors.lastname: Li
authors.affiliation: 1] International Co-operation Laboratory on Signal Transduction, Eastern Hepatobiliary Surgery Institute, Second Military Medical University, Shanghai 200433, China [2] Anal-Colorectal Surgery Institute, No 150 Central Hospital of PLA, Luoyang 471031, China.
authors.forename: Liang
authors.initials: L
authors.lastname: Hu
authors.affiliation: International Co-operation Laboratory on Signal Transduction, Eastern Hepatobiliary Surgery Institute, Second Military Medical University, Shanghai 200433, China.
authors.forename: Yan-xin
authors.initials: YX
authors.lastname: Chang
authors.affiliation: International Co-operation Laboratory on Signal Transduction, Eastern Hepatobiliary Surgery Institute, Second Military Medical University, Shanghai 200433, China.
authors.forename: Liang
authors.initials: L
authors.lastname: Li
authors.affiliation: Eastern Hepatobiliary Surgery Hospital, Shanghai 200433, China.
authors.forename: Min-hong
authors.initials: MH
authors.lastname: Li
authors.affiliation: Eastern Hepatobiliary Surgery Hospital, Shanghai 200433, China.
authors.forename: Ruo-yu
authors.initials: RY
authors.lastname: Wang
authors.affiliation: International Co-operation Laboratory on Signal Transduction, Eastern Hepatobiliary Surgery Institute, Second Military Medical University, Shanghai 200433, China.
authors.forename: Dan-dan
authors.initials: DD
authors.lastname: Huang
authors.affiliation: Eastern Hepatobiliary Surgery Hospital, Shanghai 200433, China.
authors.forename: Meng-chao
authors.initials: MC
authors.lastname: Wu
authors.affiliation: Eastern Hepatobiliary Surgery Hospital, Shanghai 200433, China.
authors.forename: He-ping
authors.initials: HP
authors.lastname: Hu
authors.affiliation: 1] International Co-operation Laboratory on Signal Transduction, Eastern Hepatobiliary Surgery Institute, Second Military Medical University, Shanghai 200433, China [2] National Center for Liver Cancer, Shanghai 201805, China.
authors.forename: Lei
authors.initials: L
authors.lastname: Chen
authors.affiliation: 1] International Co-operation Laboratory on Signal Transduction, Eastern Hepatobiliary Surgery Institute, Second Military Medical University, Shanghai 200433, China [2] National Center for Liver Cancer, Shanghai 201805, China.
authors.forename: Hong-yang
authors.initials: HY
authors.lastname: Wang
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000187:drug effects; D051017:Apoptosis Regulatory Proteins / Q000235:genetics / Q000378:metabolism; D001343:Autophagy / Q000187:drug effects*; D000071187:Autophagy-Related Protein 5; D000071186:Beclin-1; D059305:Diet, High-Fat; D004195:Disease Models, Animal; D004305:Dose-Response Relationship, Drug; D004789:Enzyme Activation; D056945:Hep G2 Cells; D022781:Hepatocytes / Q000187:drug effects* / Q000201:enzymology / Q000473:pathology; D006801:Humans; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism; D008810:Mice, Inbred C57BL; D008869:Microtubule-Associated Proteins / Q000235:genetics / Q000378:metabolism; D048055:Mitogen-Activated Protein Kinase 8 / Q000235:genetics / Q000378:metabolism; D048056:Mitogen-Activated Protein Kinase 9 / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D065626:Non-alcoholic Fatty Liver Disease / Q000201:enzymology* / Q000209:etiology / Q000235:genetics / Q000473:pathology; D019308:Palmitic Acid / Q000633:toxicity*; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D034622:RNA Interference; D015398:Signal Transduction / Q000187:drug effects; D013997:Time Factors; D014162:Transfection
chemical_list: C502778:ATG5 protein, human; D051017:Apoptosis Regulatory Proteins; D000071187:Autophagy-Related Protein 5; C491997:BECN1 protein, human; D000071186:Beclin-1; C477012:MAP1LC3A protein, human; C480860:Map1lc3b protein, mouse; D008565:Membrane Proteins; D008869:Microtubule-Associated Proteins; D047428:Protein Kinase Inhibitors; D019308:Palmitic Acid; D048056:Mitogen-Activated Protein Kinase 9; D048055:Mitogen-Activated Protein Kinase 8