title: Role of hepatocyte S6K1 in palmitic acid-induced endoplasmic reticulum stress, lipotoxicity, insulin resistance and in oleic acid-induced protection.
abstract: The excess of saturated free fatty acids, such as palmitic acid, that induces lipotoxicity in hepatocytes, has been implicated in the development of non-alcoholic fatty liver disease also associated with insulin resistance. By contrast, oleic acid, a monounsaturated fatty acid, attenuates the effects of palmitic acid. We evaluated whether palmitic acid is directly associated with both insulin resistance and lipoapoptosis in mouse and human hepatocytes and the impact of oleic acid in the molecular mechanisms that mediate both processes. In human and mouse hepatocytes palmitic acid at a lipotoxic concentration triggered early activation of endoplasmic reticulum (ER) stress-related kinases, induced the apoptotic transcription factor CHOP, activated caspase 3 and increased the percentage of apoptotic cells. These effects concurred with decreased IR/IRS1/Akt insulin pathway. Oleic acid suppressed the toxic effects of palmitic acid on ER stress activation, lipoapoptosis and insulin resistance. Besides, oleic acid suppressed palmitic acid-induced activation of S6K1. This protection was mimicked by pharmacological or genetic inhibition of S6K1 in hepatocytes. In conclusion, this is the first study highlighting the activation of S6K1 by palmitic acid as a common and novel mechanism by which its inhibition by oleic acid prevents ER stress, lipoapoptosis and insulin resistance in hepatocytes.
authors.affiliation: Instituto de Investigaciones Biomédicas Alberto Sols (CSIC/UAM), 28029 Madrid, Spain; Centro de Investigación Biomédica en Red de Diabetes y Enfermedades Metabólicas Asociadas (CIBERDEM), ISCIII, Spain.
authors.forename: Virginia
authors.initials: V
authors.lastname: Pardo
authors.affiliation: Instituto de Investigaciones Biomédicas Alberto Sols (CSIC/UAM), 28029 Madrid, Spain; Centro de Investigación Biomédica en Red de Diabetes y Enfermedades Metabólicas Asociadas (CIBERDEM), ISCIII, Spain. Electronic address: aguedagr@iib.uam.es.
authors.forename: Águeda
authors.initials: Á
authors.lastname: González-Rodríguez
authors.affiliation: Oncology Surgery, Cell Therapy and Transplant Organs, Institute of Biomedicine of Seville (IBiS)/Virgen del Rocio Universitary Hospital/CSIC/University of Seville, Seville, Spain; Centro de Investigación Biomédica en Red de Enfermedades Hepáticas y Digestivas (CIBERehd), Instituto de Salud Carlos III, Spain.
authors.forename: Jordi
authors.initials: J
authors.lastname: Muntané
authors.affiliation: Department of Cancer and Cell Biology, University of Cincinnati, Cincinnati, OH 45215, USA; Bellvitge Biomedical Research Institute (IDIBELL), L'Hospitalet, Barcelona, Spain.
authors.forename: Sara C
authors.initials: SC
authors.lastname: Kozma
authors.affiliation: Instituto de Investigaciones Biomédicas Alberto Sols (CSIC/UAM), 28029 Madrid, Spain; Centro de Investigación Biomédica en Red de Diabetes y Enfermedades Metabólicas Asociadas (CIBERDEM), ISCIII, Spain. Electronic address: avalverde@iib.uam.es.
authors.forename: Ángela M
authors.initials: ÁM
authors.lastname: Valverde
mesh_terms: D000818:Animals; D002478:Cells, Cultured; D004721:Endoplasmic Reticulum / Q000187:drug effects*; D004791:Enzyme Inhibitors / Q000633:toxicity; D005786:Gene Expression Regulation / Q000187:drug effects; D022781:Hepatocytes / Q000187:drug effects / Q000378:metabolism; D006801:Humans; D007333:Insulin Resistance; D008055:Lipids / Q000633:toxicity; D051379:Mice; D019301:Oleic Acid / Q000494:pharmacology; D019308:Palmitic Acid / Q000633:toxicity*; D038762:Ribosomal Protein S6 Kinases, 70-kDa / Q000235:genetics / Q000378:metabolism*; D038744:Ribosomal Protein S6 Kinases, 90-kDa / Q000235:genetics / Q000378:metabolism*; D013312:Stress, Physiological / Q000187:drug effects*
chemical_list: D004791:Enzyme Inhibitors; D008055:Lipids; D019301:Oleic Acid; D019308:Palmitic Acid; D038762:Ribosomal Protein S6 Kinases, 70-kDa; D038744:Ribosomal Protein S6 Kinases, 90-kDa; C512964:Rps6ka1 protein, mouse; C448901:ribosomal protein S6 kinase, 70kD, polypeptide 1
keywords: Apoptosis; ER stress; Free fatty acids; Hepatocytes; Insulin signaling; Lipotoxicity