title: Mitochondrial gene polymorphisms alter hepatic cellular energy metabolism and aggravate diet-induced non-alcoholic steatohepatitis.
abstract: OBJECTIVE
  Non-alcoholic fatty liver disease (NAFLD) is the most common chronic liver disease and is associated with an enhanced risk for liver and cardiovascular diseases and mortality. NAFLD can progress from simple hepatic steatosis to non-alcoholic steatohepatitis (NASH). However, the mechanisms predisposing to this progression remain undefined. Notably, hepatic mitochondrial dysfunction is a common finding in patients with NASH. Due to a lack of appropriate experimental animal models, it has not been evaluated whether this mitochondrial dysfunction plays a causative role for the development of NASH.
  
  
  METHODS
  To determine the effect of a well-defined mitochondrial dysfunction on liver physiology at baseline and during dietary challenge, C57BL/6J-mt(FVB/N) mice were employed. This conplastic inbred strain has been previously reported to exhibit decreased mitochondrial respiration likely linked to a non-synonymous gene variation (nt7778 G/T) of the mitochondrial ATP synthase protein 8 (mt-ATP8).
  
  
  RESULTS
  At baseline conditions, C57BL/6J-mt(FVB/N) mice displayed hepatic mitochondrial dysfunction characterized by decreased ATP production and increased formation of reactive oxygen species (ROS). Moreover, genes affecting lipid metabolism were differentially expressed, hepatic triglyceride and cholesterol levels were changed in these animals, and various acyl-carnitines were altered, pointing towards an impaired mitochondrial carnitine shuttle. However, over a period of twelve months, no spontaneous hepatic steatosis or inflammation was observed. On the other hand, upon dietary challenge with either a methionine and choline deficient diet or a western-style diet, C57BL/6J-mt(FVB/N) mice developed aggravated steatohepatitis as characterized by lipid accumulation, ballooning of hepatocytes and infiltration of immune cells.
  
  
  CONCLUSIONS
  We observed distinct metabolic alterations in mice with a mitochondrial polymorphism associated hepatic mitochondrial dysfunction. However, a second hit, such as dietary stress, was required to cause hepatic steatosis and inflammation. This study suggests a causative role of hepatic mitochondrial dysfunction in the development of experimental NASH.
authors.affiliation: University of Lübeck, Department of Medicine I, Ratzeburger Allee 160, D-23538 Lübeck, Germany; University of Lübeck, Institute for Systemic Inflammation Research, Ratzeburger Allee 160, D-23538 Lübeck, Germany.
authors.forename: Torsten
authors.initials: T
authors.lastname: Schröder
authors.affiliation: University of Lübeck, Department of Medicine I, Ratzeburger Allee 160, D-23538 Lübeck, Germany.
authors.forename: David
authors.initials: D
authors.lastname: Kucharczyk
authors.affiliation: University of Lübeck, Department of Medicine I, Ratzeburger Allee 160, D-23538 Lübeck, Germany.
authors.forename: Florian
authors.initials: F
authors.lastname: Bär
authors.affiliation: University of Lübeck, Department of Medicine I, Ratzeburger Allee 160, D-23538 Lübeck, Germany; University of Lübeck, Institute of Anatomy, Ratzeburger Allee 160, D-23538 Lübeck, Germany.
authors.forename: René
authors.initials: R
authors.lastname: Pagel
authors.affiliation: University of Lübeck, Department of Medicine I, Ratzeburger Allee 160, D-23538 Lübeck, Germany.
authors.forename: Stefanie
authors.initials: S
authors.lastname: Derer
authors.affiliation: University of Lübeck, Department of Medicine I, Ratzeburger Allee 160, D-23538 Lübeck, Germany; University of Lübeck, Institute of Anatomy, Ratzeburger Allee 160, D-23538 Lübeck, Germany.
authors.forename: Sebastian Torben
authors.initials: ST
authors.lastname: Jendrek
authors.affiliation: University of Lübeck, Department of Medicine I, Ratzeburger Allee 160, D-23538 Lübeck, Germany.
authors.forename: Annika
authors.initials: A
authors.lastname: Sünderhauf
authors.affiliation: University of Lübeck, Department of Medicine I, Ratzeburger Allee 160, D-23538 Lübeck, Germany.
authors.forename: Ann-Kathrin
authors.initials: AK
authors.lastname: Brethack
authors.affiliation: University of Lübeck, The Lübeck Institute of Experimental Dermatology, Ratzeburger Allee 160, D-23538 Lübeck, Germany.
authors.forename: Misa
authors.initials: M
authors.lastname: Hirose
authors.affiliation: University of Lübeck, The Lübeck Institute of Experimental Dermatology, Ratzeburger Allee 160, D-23538 Lübeck, Germany; Rostock University Medical Center, Institute for Biostatistics and Informatics in Medicine and Ageing Research, Ernst-Heydemann-Straße 8, D-18057 Rostock, Germany.
authors.forename: Steffen
authors.initials: S
authors.lastname: Möller
authors.affiliation: University of Lübeck, The Lübeck Institute of Experimental Dermatology, Ratzeburger Allee 160, D-23538 Lübeck, Germany; Max Planck Institute for Evolutionary Biology, Guest Group Evolutionary Genomics, August-Thienemann-Straße 2, 24306 Plön, Germany.
authors.forename: Axel
authors.initials: A
authors.lastname: Künstner
authors.affiliation: University of Lübeck, The Lübeck Institute of Experimental Dermatology, Ratzeburger Allee 160, D-23538 Lübeck, Germany.
authors.forename: Julia
authors.initials: J
authors.lastname: Bischof
authors.affiliation: University of Lübeck, Institute of Anatomy, Ratzeburger Allee 160, D-23538 Lübeck, Germany.
authors.forename: Imke
authors.initials: I
authors.lastname: Weyers
authors.affiliation: University Hospital Hamburg-Eppendorf, Department of Biochemistry and Molecular Cell Biology, Martinistraße 52, D-20246 Hamburg, Germany.
authors.forename: Jörg
authors.initials: J
authors.lastname: Heeren
authors.affiliation: University of Rostock, Institute of Immunology, Schillingallee 70, D-18057 Rostock, Germany.
authors.forename: Dirk
authors.initials: D
authors.lastname: Koczan
authors.affiliation: University of Lübeck, Department of Medicine I, Ratzeburger Allee 160, D-23538 Lübeck, Germany.
authors.forename: Sebastian Michael
authors.initials: SM
authors.lastname: Schmid
authors.affiliation: Cincinnati Children's Hospital Research Foundation, University of Cincinnati, Division of Immunobiology, 3333 Burnet Avenue, Cincinnati, OH 45229-3026, USA.
authors.forename: Senad
authors.initials: S
authors.lastname: Divanovic
authors.affiliation: Cincinnati Children's Hospital Research Foundation, University of Cincinnati, Division of Immunobiology, 3333 Burnet Avenue, Cincinnati, OH 45229-3026, USA.
authors.forename: Daniel Aaron
authors.initials: DA
authors.lastname: Giles
authors.affiliation: Helmholtz Center, German Research Center for Environmental Health, Institute of Experimental Genetics, Genome Analysis Center, Ingolstaedter Landstraße 1, D-85764 Neuherberg, Germany; Technische Universität München, Lehrstuhl für Experimentelle Genetik, Liesel-Beckmann-Straße 4, 85350 Freising-Weihenstephan, Germany; German Center for Diabetes Research (DZD), Ingolstaedter Landstraße 1, 85764 Neuherberg, Germany.
authors.forename: Jerzy
authors.initials: J
authors.lastname: Adamski
authors.affiliation: University of Lübeck, Department of Medicine I, Ratzeburger Allee 160, D-23538 Lübeck, Germany.
authors.forename: Klaus
authors.initials: K
authors.lastname: Fellermann
authors.affiliation: University of Lübeck, Department of Medicine I, Ratzeburger Allee 160, D-23538 Lübeck, Germany.
authors.forename: Hendrik
authors.initials: H
authors.lastname: Lehnert
authors.affiliation: University of Lübeck, Institute for Systemic Inflammation Research, Ratzeburger Allee 160, D-23538 Lübeck, Germany; Cincinnati Children's Hospital Research Foundation, University of Cincinnati, Division of Immunobiology, 3333 Burnet Avenue, Cincinnati, OH 45229-3026, USA.
authors.forename: Jörg
authors.initials: J
authors.lastname: Köhl
authors.affiliation: University of Lübeck, The Lübeck Institute of Experimental Dermatology, Ratzeburger Allee 160, D-23538 Lübeck, Germany.
authors.forename: Saleh
authors.initials: S
authors.lastname: Ibrahim
authors.affiliation: University of Lübeck, Department of Medicine I, Ratzeburger Allee 160, D-23538 Lübeck, Germany. Electronic address: Christian.Sina@uksh.de.
authors.forename: Christian
authors.initials: C
authors.lastname: Sina
keywords: ALT, alanine aminotransferase; AMP, adenosine monophosphate; AMPK, AMP-activated proteinkinase; ATP, adenosine triphosphate; ATP8, ATP synthase protein 8; Arg, arginine; Asp, aspartic acid; B6-mtB6, C57BL/6; B6-mtFVB, C57BL/6-mtFVB/N; C0, free dl-carnitine; C16, hexadecanoyl-l-carntine; C18, octadecanoyl-l-carnitine; CD, control diet; CD3, cluster of differentiation receptor 3; CPT I, carnitine-palmitoyltransferase I; CYP51A1, cytochrome P450, family 51, subfamily A, polypeptide 1; GAPDH, glyceraldehyde 3-phosphate dehydrogenase; Gr1, granulocyte differentiation antigen 1; H&E, hematoxylin–eosin staining; H2O2, hydrogen peroxide; Hsd17b7, 17-beta-hydroxysteroid dehydrogenase type 7; IDI1, isopentenyl-diphosphate delta isomerase 1; IL, interleukin; IPA, ingenuity pathway analysis; KEGG, Kyoto Encyclopedia of Genes and Genomes; Lipid metabolism; Ly6G, lymphocyte antigen 6 complex, locus G; MCDD, methionine and choline deficient diet; MSMO1, methylsterol monooxygenase 1; Met, methionine; Mitochondrial dysfunction; Mitochondrial gene polymorphism; NAFL, non-alcoholic liver steatosis; NAFLD; NAFLD, non-alcoholic fatty liver disease; NAS, NAFLD activity score; NASH, non-alcoholic steatohepatitis; ND3, NADH dehydrogenase subunit 3; OCR, oxygen consumption rate; OXPHOS, oxidative phosphorylation system; PBS, phosphate buffered saline; ROS, reactive oxygen species; SNPs, single nucleotide polymorphisms; SOD2, superoxide dismutase 2; STRING, Search Tool for the Retrieval of Interacting Genes/Proteins; Steatohepatitis; TNFα; TNFα, tumor necrosis factor alpha; Tyr, tyrosine; WD, western-style diet; mt, mitochondrial; pAMPK, phosphorylated AMP-activated proteinkinase