title: Knockdown of triglyceride synthesis does not enhance palmitate lipotoxicity or prevent oleate-mediated rescue in rat hepatocytes.
abstract: Experiments in a variety of cell types, including hepatocytes, consistently demonstrate the acutely lipotoxic effects of saturated fatty acids, such as palmitate (PA), but not unsaturated fatty acids, such as oleate (OA). PA+OA co-treatment fully prevents PA lipotoxicity through mechanisms that are not well defined but which have been previously attributed to more efficient esterification and sequestration of PA into triglycerides (TGs) when OA is abundant. However, this hypothesis has never been directly tested by experimentally modulating the relative partitioning of PA/OA between TGs and other lipid fates in hepatocytes. In this study, we found that addition of OA to PA-treated hepatocytes enhanced TG synthesis, reduced total PA uptake and PA lipid incorporation, decreased phospholipid saturation and rescued PA-induced ER stress and lipoapoptosis. Knockdown of diacylglycerol acyltransferase (DGAT), the rate-limiting step in TG synthesis, significantly reduced TG accumulation without impairing OA-mediated rescue of PA lipotoxicity. In both wild-type and DGAT-knockdown hepatocytes, OA co-treatment significantly reduced PA lipid incorporation and overall phospholipid saturation compared to PA-treated hepatocytes. These data indicate that OA's protective effects do not require increased conversion of PA into inert TGs, but instead may be due to OA's ability to compete against PA for cellular uptake and/or esterification and, thereby, normalize the composition of cellular lipids in the presence of a toxic PA load.
authors.affiliation: Department of Chemical and Biomolecular Engineering, Vanderbilt University, Nashville, TN, USA.
authors.forename: Alexandra K
authors.initials: AK
authors.lastname: Leamy
authors.affiliation: Department of Chemical and Biomolecular Engineering, Vanderbilt University, Nashville, TN, USA.
authors.forename: Clinton M
authors.initials: CM
authors.lastname: Hasenour
authors.affiliation: Department of Chemical and Biomolecular Engineering, Vanderbilt University, Nashville, TN, USA.
authors.forename: Robert A
authors.initials: RA
authors.lastname: Egnatchik
authors.affiliation: Department of Chemical and Biomolecular Engineering, Vanderbilt University, Nashville, TN, USA.
authors.forename: Irina A
authors.initials: IA
authors.lastname: Trenary
authors.affiliation: Department of Chemistry, Washington University in St. Louis, St. Louis, MO, USA; Department of Medicine, Washington University School of Medicine, St. Louis, MO, USA.
authors.forename: Cong-Hui
authors.initials: CH
authors.lastname: Yao
authors.affiliation: Department of Chemistry, Washington University in St. Louis, St. Louis, MO, USA; Department of Medicine, Washington University School of Medicine, St. Louis, MO, USA.
authors.forename: Gary J
authors.initials: GJ
authors.lastname: Patti
authors.affiliation: Department of Molecular Physiology and Biophysics, Vanderbilt University, Nashville, TN, USA.
authors.forename: Masakazu
authors.initials: M
authors.lastname: Shiota
authors.affiliation: Department of Chemical and Biomolecular Engineering, Vanderbilt University, Nashville, TN, USA; Department of Molecular Physiology and Biophysics, Vanderbilt University, Nashville, TN, USA. Electronic address: j.d.young@vanderbilt.edu.
authors.forename: Jamey D
authors.initials: JD
authors.lastname: Young
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000235:genetics; D051048:Diacylglycerol O-Acyltransferase / Q000235:genetics* / Q000378:metabolism; D004951:Esterification / Q000235:genetics; D055786:Gene Knockout Techniques; D022781:Hepatocytes / Q000378:metabolism; D050356:Lipid Metabolism / Q000235:genetics; D050155:Lipogenesis / Q000235:genetics; D019301:Oleic Acid / Q000378:metabolism*; D018384:Oxidative Stress; D019308:Palmitic Acid / Q000378:metabolism*; D051381:Rats; D014280:Triglycerides / Q000096:biosynthesis* / Q000378:metabolism
chemical_list: D014280:Triglycerides; D019301:Oleic Acid; D019308:Palmitic Acid; C494883:Dgat1 protein, rat; D051048:Diacylglycerol O-Acyltransferase
keywords: Diacylglycerol acyltransferase; Endoplasmic reticulum stress; Lipoapoptosis; Phospholipid metabolism; Saturated fatty acids; Triglycerides