title: Methionine and S-adenosylmethionine levels are critical regulators of PP2A activity modulating lipophagy during steatosis.
abstract: OBJECTIVE
  Glycine N-methyltransferase (GNMT) expression is decreased in some patients with severe non-alcoholic fatty liver disease. Gnmt deficiency in mice (Gnmt-KO) results in abnormally elevated serum levels of methionine and its metabolite S-adenosylmethionine (SAMe), and this leads to rapid liver steatosis development. Autophagy plays a critical role in lipid catabolism (lipophagy), and defects in autophagy have been related to liver steatosis development. Since methionine and its metabolite SAMe are well known inactivators of autophagy, we aimed to examine whether high levels of both metabolites could block autophagy-mediated lipid catabolism.
  
  
  METHODS
  We examined methionine levels in a cohort of 358 serum samples from steatotic patients. We used hepatocytes cultured with methionine and SAMe, and hepatocytes and livers from Gnmt-KO mice.
  
  
  RESULTS
  We detected a significant increase in serum methionine levels in steatotic patients. We observed that autophagy and lipophagy were impaired in hepatocytes cultured with high methionine and SAMe, and that Gnmt-KO livers were characterized by an impairment in autophagy functionality, likely caused by defects at the lysosomal level. Elevated levels of methionine and SAMe activated PP2A by methylation, while blocking PP2A activity restored autophagy flux in Gnmt-KO hepatocytes, and in hepatocytes treated with SAMe and methionine. Finally, normalization of methionine and SAMe levels in Gnmt-KO mice using a methionine deficient diet normalized the methylation capacity, PP2A methylation, autophagy, and ameliorated liver steatosis.
  
  
  CONCLUSIONS
  These data suggest that elevated levels of methionine and SAMe can inhibit autophagic catabolism of lipids contributing to liver steatosis.
authors.affiliation: Metabolomic Unit, CIC bioGUNE, CIBERehd, Parque Tecnológico de Bizkaia, Derio 48160, Spain.
authors.forename: Imanol
authors.initials: I
authors.lastname: Zubiete-Franco
authors.affiliation: Metabolomic Unit, CIC bioGUNE, CIBERehd, Parque Tecnológico de Bizkaia, Derio 48160, Spain.
authors.forename: Juan Luis
authors.initials: JL
authors.lastname: García-Rodríguez
authors.affiliation: Department of Physiology, University of the Basque Country UPV/EHU, Medical School, Biocruces Research Institute, Bilbao 48008, Spain.
authors.forename: Maite
authors.initials: M
authors.lastname: Martínez-Uña
authors.affiliation: Metabolomic Unit, CIC bioGUNE, CIBERehd, Parque Tecnológico de Bizkaia, Derio 48160, Spain.
authors.forename: Nuria
authors.initials: N
authors.lastname: Martínez-Lopez
authors.affiliation: Metabolomic Unit, CIC bioGUNE, CIBERehd, Parque Tecnológico de Bizkaia, Derio 48160, Spain; IKERBASQUE, Basque Foundation for Science, Maria Diaz de Haro 3, 48013 Bilbao, Spain.
authors.forename: Ashwin
authors.initials: A
authors.lastname: Woodhoo
authors.affiliation: Metabolomic Unit, CIC bioGUNE, CIBERehd, Parque Tecnológico de Bizkaia, Derio 48160, Spain.
authors.forename: Virginia Gutiérrez-De
authors.initials: VG
authors.lastname: Juan
authors.affiliation: Metabolomic Unit, CIC bioGUNE, CIBERehd, Parque Tecnológico de Bizkaia, Derio 48160, Spain; IKERBASQUE, Basque Foundation for Science, Maria Diaz de Haro 3, 48013 Bilbao, Spain.
authors.forename: Naiara
authors.initials: N
authors.lastname: Beraza
authors.affiliation: Metabolism Department, Cruces University Hospital, Barakaldo 48903, Spain.
authors.forename: Sergio
authors.initials: S
authors.lastname: Lage-Medina
authors.affiliation: Metabolism Department, Cruces University Hospital, Barakaldo 48903, Spain.
authors.forename: Fernando
authors.initials: F
authors.lastname: Andrade
authors.affiliation: Metabolism Department, Cruces University Hospital, Barakaldo 48903, Spain.
authors.forename: Marta Llarena
authors.initials: ML
authors.lastname: Fernandez
authors.affiliation: Metabolism Department, Cruces University Hospital, Barakaldo 48903, Spain.
authors.forename: Luis
authors.initials: L
authors.lastname: Aldámiz-Echevarría
authors.affiliation: Metabolomic Unit, CIC bioGUNE, CIBERehd, Parque Tecnológico de Bizkaia, Derio 48160, Spain.
authors.forename: David
authors.initials: D
authors.lastname: Fernández-Ramos
authors.affiliation: Metabolomic Unit, CIC bioGUNE, CIBERehd, Parque Tecnológico de Bizkaia, Derio 48160, Spain; IKERBASQUE, Basque Foundation for Science, Maria Diaz de Haro 3, 48013 Bilbao, Spain.
authors.forename: Juan Manuel
authors.initials: JM
authors.lastname: Falcon-Perez
authors.affiliation: Metabolomic Unit, CIC bioGUNE, CIBERehd, Parque Tecnológico de Bizkaia, Derio 48160, Spain.
authors.forename: Fernando
authors.initials: F
authors.lastname: Lopitz-Otsoa
authors.affiliation: Metabolomic Unit, CIC bioGUNE, CIBERehd, Parque Tecnológico de Bizkaia, Derio 48160, Spain.
authors.forename: Pablo
authors.initials: P
authors.lastname: Fernandez-Tussy
authors.affiliation: Metabolomic Unit, CIC bioGUNE, CIBERehd, Parque Tecnológico de Bizkaia, Derio 48160, Spain.
authors.forename: Lucía
authors.initials: L
authors.lastname: Barbier-Torres
authors.affiliation: Department of Biochemistry, Vanderbilt University, Nashville, TN 37232-0146, USA.
authors.forename: Zigmund
authors.initials: Z
authors.lastname: Luka
authors.affiliation: Department of Biochemistry, Vanderbilt University, Nashville, TN 37232-0146, USA.
authors.forename: Conrad
authors.initials: C
authors.lastname: Wagner
authors.affiliation: Liver Research Unit, Instituto de Investigación Sanitaria Princesa, University Hospital Santa Cristina, CIBERehd, Madrid 28009, Spain.
authors.forename: Carmelo
authors.initials: C
authors.lastname: García-Monzón
authors.affiliation: Division of Gastroenterology, Cedars-Sinai Medical Center, Los Angeles, CA, USA; USC Research Center for Liver Diseases, Keck School of Medicine, Los Angeles, CA, USA.
authors.forename: Shelly C
authors.initials: SC
authors.lastname: Lu
authors.affiliation: Department of Physiology, University of the Basque Country UPV/EHU, Medical School, Biocruces Research Institute, Bilbao 48008, Spain.
authors.forename: Patricia
authors.initials: P
authors.lastname: Aspichueta
authors.affiliation: Metabolomic Unit, CIC bioGUNE, CIBERehd, Parque Tecnológico de Bizkaia, Derio 48160, Spain.
authors.forename: José María
authors.initials: JM
authors.lastname: Mato
authors.affiliation: Metabolomic Unit, CIC bioGUNE, CIBERehd, Parque Tecnológico de Bizkaia, Derio 48160, Spain; Biochemistry and Molecular Biology Department, University of the Basque Country (UPV/EHU), P. O. BOX 644, E-48080 Bilbao, Spain. Electronic address: mlmartinez@cicbiogune.es.
authors.forename: María Luz
authors.initials: ML
authors.lastname: Martínez-Chantar
authors.affiliation: Metabolomic Unit, CIC bioGUNE, CIBERehd, Parque Tecnológico de Bizkaia, Derio 48160, Spain. Electronic address: mvarela.ciberehd@cicbiogune.es.
authors.forename: Marta
authors.initials: M
authors.lastname: Varela-Rey
mesh_terms: D000818:Animals; D001343:Autophagy / Q000502:physiology*; D018929:Cell Culture Techniques; D004195:Disease Models, Animal; D005234:Fatty Liver / Q000378:metabolism* / Q000473:pathology; D022781:Hepatocytes / Q000378:metabolism*; D006801:Humans; D008715:Methionine / Q000097:blood*; D008745:Methylation; D051379:Mice; D054648:Protein Phosphatase 2 / Q000378:metabolism*; D012436:S-Adenosylmethionine / Q000097:blood*
chemical_list: D012436:S-Adenosylmethionine; D008715:Methionine; D054648:Protein Phosphatase 2
keywords: Autophagy; Gnmt; Liver; Methionine; SAMe; Steatosis