AIMS/HYPOTHESIS: An accumulation of ceramides has been implicated in the generation of insulin resistance in skeletal muscle upon an oversupply of fatty acid. Different ceramide species are generated through the actions of ceramide synthases (CerSs), which incorporate specific acyl side chains. We tested whether particular CerS isoforms promoted insulin resistance through the generation of more inhibitory ceramide species, thus representing potential targets for intervention. METHODS: CerS isoforms CerS1, CerS2, CerS4, CerS5 and CerS6 were overexpressed in L6 myotubes using adenovirus, and cells were treated with palmitate and stimulated with insulin. Alternatively, CerS isoforms were knocked down using siRNAs. Sphingolipids were examined by mass spectrometry and tracer incorporation. Phosphorylation of IRS1 and Akt was measured by immunoblotting, while glucose disposal was assessed by measuring GLUT4 translocation and the incorporation of [(14)C]glucose into glycogen. RESULTS: Palmitate treatment increased the levels of several ceramides but reduced the levels of sphingomyelins, while insulin had no effect. The fatty acid also inhibited insulin-stimulated Akt phosphorylation and glycogen synthesis. Overexpression of CerS isoforms increased specific ceramides. Unexpectedly, the overexpression of CerS1 and CerS6 promoted insulin action, while no isoform had inhibitory effects. CerS6 knockdown had effects reciprocal to those of CerS6 overexpression. CONCLUSIONS/ INTERPRETATION: Palmitate may increase intracellular ceramide levels through sphingomyelin hydrolysis as well as de novo synthesis, but no particular species were implicated in the generation of insulin resistance. The modulation of ceramides through an alteration of CerS expression does not affect the action of insulin in the same way as ceramide generation by palmitate treatment. Conversely, certain isoforms promote insulin action, indicating the importance of ceramides in cell function.
AIMS/HYPOTHESIS: An accumulation of ceramides has been implicated in the generation of insulin resistance in skeletal muscle upon an oversupply of fatty acid. Different ceramide species are generated through the actions of ceramide synthases (CerSs), which incorporate specific acyl side chains. We tested whether particular CerS isoforms promoted insulin resistance through the generation of more inhibitory ceramide species, thus representing potential targets for intervention. METHODS: CerS isoforms CerS1, CerS2, CerS4, CerS5 and CerS6 were overexpressed in L6 myotubes using adenovirus, and cells were treated with palmitate and stimulated with insulin. Alternatively, CerS isoforms were knocked down using siRNAs. Sphingolipids were examined by mass spectrometry and tracer incorporation. Phosphorylation of IRS1 and Akt was measured by immunoblotting, while glucose disposal was assessed by measuring GLUT4 translocation and the incorporation of [(14)C]glucose into glycogen. RESULTS:Palmitate treatment increased the levels of several ceramides but reduced the levels of sphingomyelins, while insulin had no effect. The fatty acid also inhibited insulin-stimulated Akt phosphorylation and glycogen synthesis. Overexpression of CerS isoforms increased specific ceramides. Unexpectedly, the overexpression of CerS1 and CerS6 promoted insulin action, while no isoform had inhibitory effects. CerS6 knockdown had effects reciprocal to those of CerS6 overexpression. CONCLUSIONS/ INTERPRETATION:Palmitate may increase intracellular ceramide levels through sphingomyelin hydrolysis as well as de novo synthesis, but no particular species were implicated in the generation of insulin resistance. The modulation of ceramides through an alteration of CerS expression does not affect the action of insulin in the same way as ceramide generation by palmitate treatment. Conversely, certain isoforms promote insulin action, indicating the importance of ceramides in cell function.
Authors: G Frangioudakis; J Garrard; K Raddatz; J L Nadler; T W Mitchell; C Schmitz-Peiffer Journal: Endocrinology Date: 2010-07-21 Impact factor: 4.736
Authors: Elad L Laviad; Lee Albee; Irene Pankova-Kholmyansky; Sharon Epstein; Hyejung Park; Alfred H Merrill; Anthony H Futerman Journal: J Biol Chem Date: 2007-12-28 Impact factor: 5.157
Authors: Nicolas J Pillon; Scott Frendo-Cumbo; Maya R Jacobson; Zhi Liu; Paul L Milligan; Hai Hoang Bui; Juleen R Zierath; Philip J Bilan; Joseph T Brozinick; Amira Klip Journal: J Lipid Res Date: 2018-05-23 Impact factor: 5.922
Authors: William S Harris; Juhua Luo; James V Pottala; Karen L Margolis; Mark A Espeland; Jennifer G Robinson Journal: PLoS One Date: 2016-02-16 Impact factor: 3.240
Authors: Piotr Zabielski; Agnieszka Urszula Błachnio-Zabielska; Beata Wójcik; Adrian Chabowski; Jan Górski Journal: PLoS One Date: 2017-11-02 Impact factor: 3.240
Authors: Manju Mamtani; Hemant Kulkarni; Gerard Wong; Jacquelyn M Weir; Christopher K Barlow; Thomas D Dyer; Laura Almasy; Michael C Mahaney; Anthony G Comuzzie; David C Glahn; Dianna J Magliano; Paul Zimmet; Jonathan Shaw; Sarah Williams-Blangero; Ravindranath Duggirala; John Blangero; Peter J Meikle; Joanne E Curran Journal: Lipids Health Dis Date: 2016-04-04 Impact factor: 3.876