title: Mitochondrial genome depletion in human liver cells abolishes bile acid-induced apoptosis: role of the Akt/mTOR survival pathway and Bcl-2 family proteins.
abstract: Acute accumulation of bile acids in hepatocytes may cause cell death. However, during long-term exposure due to prolonged cholestasis, hepatocytes may develop a certain degree of chemoresistance to these compounds. Because mitochondrial adaptation to persistent oxidative stress may be involved in this process, here we have investigated the effects of complete mitochondrial genome depletion on the response to bile acid-induced hepatocellular injury. A subline (Rho) of human hepatoma SK-Hep-1 cells totally depleted of mitochondrial DNA (mtDNA) was obtained, and bile acid-induced concentration-dependent activation of apoptosis/necrosis and survival signaling pathways was studied. In the absence of changes in intracellular ATP content, Rho cells were highly resistant to bile acid-induced apoptosis and partially resistant to bile acid-induced necrosis. In Rho cells, both basal and bile acid-induced generation of reactive oxygen species (ROS), such as hydrogen peroxide and superoxide anion, was decreased. Bile acid-induced proapoptotic signals were also decreased, as evidenced by a reduction in the expression ratios Bax-α/Bcl-2, Bcl-xS/Bcl-2, and Bcl-xS/Bcl-xL. This was mainly due to a downregulation of Bax-α and Bcl-xS. Moreover, in these cells the Akt/mTOR pathway was constitutively activated in a ROS-independent manner and remained similarly activated in the presence of bile acid treatment. In contrast, ERK1/2 activation was constitutively reduced and was not activated by incubation with bile acids. In conclusion, these results suggest that impaired mitochondrial function associated with mtDNA alterations, which may occur in liver cells during prolonged cholestasis, may activate mechanisms of cell survival accounting for an enhanced resistance of hepatocytes to bile acid-induced apoptosis.
authors.affiliation: Laboratory of Experimental Hepatology and Drug Targeting, (HEVEFARM), IBSAL, CIBERehd; Department of Physiology and Pharmacology, University of Salamanca, 37007 Salamanca, Spain, University of Salamanca, 37007 Salamanca, Spain.
authors.forename: Jose J G
authors.initials: JJ
authors.lastname: Marin
authors.affiliation: Laboratory of Experimental Hepatology and Drug Targeting, (HEVEFARM), IBSAL, CIBERehd.
authors.forename: Alicia
authors.initials: A
authors.lastname: Hernandez
authors.affiliation: Laboratory of Experimental Hepatology and Drug Targeting, (HEVEFARM), IBSAL, CIBERehd.
authors.forename: Isabel E
authors.initials: IE
authors.lastname: Revuelta
authors.affiliation: Laboratory of Experimental Hepatology and Drug Targeting, (HEVEFARM), IBSAL, CIBERehd; Department of Physiology and Pharmacology, University of Salamanca, 37007 Salamanca, Spain, University of Salamanca, 37007 Salamanca, Spain.
authors.forename: Ester
authors.initials: E
authors.lastname: Gonzalez-Sanchez
authors.affiliation: University Hospital of Salamanca, IECSCYL-IBSAL, 37007 Salamanca, Spain; Department of Biochemistry and Molecular Biology, University of Salamanca, 37007 Salamanca, Spain.
authors.forename: Jose M
authors.initials: JM
authors.lastname: Gonzalez-Buitrago
authors.affiliation: Laboratory of Experimental Hepatology and Drug Targeting, (HEVEFARM), IBSAL, CIBERehd; University Hospital of Salamanca, IECSCYL-IBSAL, 37007 Salamanca, Spain; Department of Biochemistry and Molecular Biology, University of Salamanca, 37007 Salamanca, Spain. Electronic address: mjperez@usal.es.
authors.forename: Maria J
authors.initials: MJ
authors.lastname: Perez
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D017209:Apoptosis / Q000187:drug effects*; D001647:Bile Acids and Salts / Q000494:pharmacology*; D045744:Cell Line, Tumor; D002470:Cell Survival; D054629:Genome, Mitochondrial / Q000502:physiology*; D006801:Humans; D051057:Proto-Oncogene Proteins c-akt / Q000502:physiology*; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000502:physiology*; D017382:Reactive Oxygen Species / Q000378:metabolism; D015398:Signal Transduction / Q000502:physiology*; D058570:TOR Serine-Threonine Kinases / Q000502:physiology*
chemical_list: D001647:Bile Acids and Salts; D019253:Proto-Oncogene Proteins c-bcl-2; D017382:Reactive Oxygen Species; D000255:Adenosine Triphosphate; C546842:MTOR protein, human; D051057:Proto-Oncogene Proteins c-akt; D058570:TOR Serine-Threonine Kinases
keywords: Akt; Apoptosis; Bcl-2; Bile acid; Cholestasis; Free radicals; Liver; Mitochondria; Retrograde signaling; Rho cells