title: Glycogen synthase kinase-3 (GSK-3) inhibition attenuates hepatocyte lipoapoptosis.
abstract: OBJECTIVE
  Saturated free fatty acids induce hepatocyte lipoapoptosis, a key pathologic feature of non-alcoholic steatohepatitis. The saturated free fatty acid palmitate induces hepatocyte lipoapoptosis via an endoplasmic reticulum stress pathway resulting in c-Jun-N-terminal (JNK) activation. Glycogen synthase kinase (GSK)-3 is a serine/threonine kinase which may also promote JNK activation. Thus, our aim was to determine if GSK-3 inhibition suppresses palmitate induced JNK activation and lipoapoptosis.
  
  
  METHODS
  For these studies, we employed mouse primary hepatocytes, Huh-7 and Hep3B cell lines.
  
  
  RESULTS
  Palmitate-induced GSK-3 activation was identified by phosphorylation of its substrate glycogen synthase. GSK-3 pharmacologic inhibition, by GSK-3 inhibitor IX and enzastaurin, significantly reduced PA-mediated lipoapoptosis. More importantly, Huh-7 cells, in which either GSK-3α or GSK-3β isoforms were stably and selectively knocked down by shRNA, displayed resistance to palmitate-induced cytotoxicity. GSK-3 pharmacological inhibitors and shRNA-targeted knockdown of GSK-3α or GSK-3β also suppressed JNK activation by palmitate. JNK activation, in part, promotes lipoapotosis by inducing expression of the pro-apoptotic effector p53-upregulated modulator of apoptosis (PUMA). Consistent with this concept, GSK-3 pharmacologic inhibition also reduced PUMA cellular protein levels during exposure to palmitate. On the other hand, the GSK-3 inhibitors did not prevent PA induction of ER stress.
  
  
  CONCLUSIONS
  Our results suggest that GSK-3 activation promotes a JNK-dependent cytotoxic signaling cascade culminating in lipoapoptosis.
authors.affiliation: Division of Gastroenterology and Hepatology, USA.
authors.forename: Samar H
authors.initials: SH
authors.lastname: Ibrahim
authors.forename: Yuko
authors.initials: Y
authors.lastname: Akazawa
authors.forename: Sophie C
authors.initials: SC
authors.lastname: Cazanave
authors.forename: Steven F
authors.initials: SF
authors.lastname: Bronk
authors.forename: Nafisa A
authors.initials: NA
authors.lastname: Elmi
authors.forename: Nathan W
authors.initials: NW
authors.lastname: Werneburg
authors.forename: Daniel D
authors.initials: DD
authors.lastname: Billadeau
authors.forename: Gregory J
authors.initials: GJ
authors.lastname: Gores
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000187:drug effects; D051017:Apoptosis Regulatory Proteins / Q000235:genetics / Q000378:metabolism; D001483:Base Sequence; D002460:Cell Line; D002478:Cells, Cultured; D017931:DNA Primers / Q000235:genetics; D004789:Enzyme Activation / Q000187:drug effects; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005234:Fatty Liver / Q000209:etiology / Q000378:metabolism / Q000473:pathology; D055785:Gene Knockdown Techniques; D038362:Glycogen Synthase Kinase 3 / Q000037:antagonists & inhibitors* / Q000235:genetics; D000071679:Glycogen Synthase Kinase 3 beta; D022781:Hepatocytes / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism*; D006801:Humans; D007211:Indoles / Q000494:pharmacology; D048031:JNK Mitogen-Activated Protein Kinases / Q000378:metabolism; D051379:Mice; D065626:Non-alcoholic Fatty Liver Disease; D010168:Palmitates / Q000494:pharmacology; D011518:Proto-Oncogene Proteins / Q000235:genetics / Q000378:metabolism; D034741:RNA, Small Interfering / Q000235:genetics; D015398:Signal Transduction / Q000187:drug effects; D025521:Tumor Suppressor Proteins / Q000378:metabolism
chemical_list: D051017:Apoptosis Regulatory Proteins; C438378:BBC3 protein, human; D017931:DNA Primers; D004791:Enzyme Inhibitors; D007211:Indoles; C488588:PUMA protein, mouse; D010168:Palmitates; D011518:Proto-Oncogene Proteins; D034741:RNA, Small Interfering; D025521:Tumor Suppressor Proteins; C000605506:GSK3B protein, human; D000071679:Glycogen Synthase Kinase 3 beta; C000605507:Gsk3b protein, mouse; D048031:JNK Mitogen-Activated Protein Kinases; D038362:Glycogen Synthase Kinase 3; C448021:glycogen synthase kinase 3 alpha; C504878:enzastaurin