Research Papers: Pathology:
Myristic acid potentiates palmitic acid-induced lipotoxicity and steatohepatitis associated with lipodystrophy by sustaning de novo ceramide synthesis
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Laura Martínez1,2, Sandra Torres1,2, Anna Baulies1,2, Cristina Alarcón-Vila1,2, Montserrat Elena3, Gemma Fabriàs4, Josefina Casas4, Joan Caballeria2, Jose C. Fernandez-Checa1,2,5 and Carmen García-Ruiz1,2,5
1 Cell Death and Proliferation, Institute of Biomedical Research of Barcelona (IIBB), CSIC, Barcelona, Spain
2 Liver Unit, Hospital Clinic I Provincial de Barcelona, IDIBAPS and CIBERehd, Barcelona, Spain
3 Biomedic Diagnosis Center, Hospital Clinic i Provincial de Barcelona, IDIBAPS, Barcelona, Spain
4 Research Unit on BioActive Molecules (RUBAM), Departament de Química Orgànica Biològica, Institut d’Investigacions Químiques i Ambientals de Barcelona, Consejo Superior de Investigaciones Científicas (CSIC), Barcelona, Spain
5 Research Center for ALPD, Keck School of Medicine, Univerisity of Southern California, Los Angeles, CA, USA
Carmen Garcia-Ruiz, email:
Jose C. Fernandez-Checa, email:
Keywords: sphingolipid, hepatocyte, FFA, endoplasmic reticulum, NAFLD, Pathology Section
Received: August 21, 2015 Accepted: October 23, 2015 Published: November 02, 2015
Palmitic acid (PA) induces hepatocyte apoptosis and fuels de novo ceramide synthesis in the endoplasmic reticulum (ER). Myristic acid (MA), a free fatty acid highly abundant in copra/palmist oils, is a predictor of nonalcoholic steatohepatitis (NASH) and stimulates ceramide synthesis. Here we investigated the synergism between MA and PA in ceramide synthesis, ER stress, lipotoxicity and NASH. Unlike PA, MA is not lipotoxic but potentiated PA-mediated lipoapoptosis, ER stress, caspase-3 activation and cytochrome c release in primary mouse hepatocytes (PMH). Moreover, MA kinetically sustained PA-induced total ceramide content by stimulating dehydroceramide desaturase and switched the ceramide profile from decreased to increased ceramide 14:0/ceramide16:0, without changing medium and long-chain ceramide species. PMH were more sensitive to equimolar ceramide14:0/ceramide16:0 exposure, which mimics the outcome of PA plus MA treatment on ceramide homeostasis, than to either ceramide alone. Treatment with myriocin to inhibit ceramide synthesis and tauroursodeoxycholic acid to prevent ER stress ameliorated PA plus MA induced apoptosis, similar to the protection afforded by the antioxidant BHA, the pan-caspase inhibitor z-VAD-Fmk and JNK inhibition. Moreover, ruthenium red protected PMH against PA and MA-induced cell death. Recapitulating in vitro findings, mice fed a diet enriched in PA plus MA exhibited lipodystrophy, hepatosplenomegaly, increased liver ceramide content and cholesterol levels, ER stress, liver damage, inflammation and fibrosis compared to mice fed diets enriched in PA or MA alone. The deleterious effects of PA plus MA-enriched diet were largely prevented by in vivo myriocin treatment. These findings indicate a causal link between ceramide synthesis and ER stress in lipotoxicity, and imply that the consumption of diets enriched in MA and PA can cause NASH associated with lipodystrophy.
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