title: Palmitate induces tumor necrosis factor-alpha expression in C2C12 skeletal muscle cells by a mechanism involving protein kinase C and nuclear factor-kappaB activation.
abstract: The mechanisms responsible for increased expression of TNF-alpha in skeletal muscle cells in diabetic states are not well understood. We examined the effects of the saturated acid palmitate on TNF-alpha expression. Exposure of C2C12 skeletal muscle cells to 0.75 mm palmitate enhanced mRNA (25-fold induction, P < 0.001) and protein (2.5-fold induction) expression of the proinflammatory cytokine TNF-alpha. This induction was inversely correlated with a fall in GLUT4 mRNA levels (57% reduction, P < 0.001) and glucose uptake (34% reduction, P < 0.001). PD98059 and U0126, inhibitors of the ERK-MAPK cascade, partially prevented the palmitate-induced TNF-alpha expression. Palmitate increased nuclear factor (NF)-kappaB activation and incubation of the cells with the NF-kappaB inhibitors pyrrolidine dithiocarbamate and parthenolide partially prevented TNF-alpha expression. Incubation of palmitate-treated cells with calphostin C, a strong and specific inhibitor of protein kinase C (PKC), abolished palmitate-induced TNF-alpha expression, and restored GLUT4 mRNA levels. Palmitate treatment enhanced the expression of phospho-PKCtheta, suggesting that this PKC isoform was involved in the changes reported, and coincubation of palmitate-treated cells with the PKC inhibitor chelerythrine prevented the palmitate-induced reduction in the expression of IkappaBalpha and insulin-stimulated Akt activation. These findings suggest that enhanced TNF-alpha expression and GLUT4 down-regulation caused by palmitate are mediated through the PKC activation, confirming that this enzyme may be a target for either the prevention or the treatment of fatty acid-induced insulin resistance.
authors.affiliation: Pharmacology Unit, Department of Pharmacology and Therapeutic Chemistry, Faculty of Pharmacy, University of Barcelona, E-08028 Barcelona, Spain.
authors.forename: Mireia
authors.initials: M
authors.lastname: Jové
authors.forename: Anna
authors.initials: A
authors.lastname: Planavila
authors.forename: Rosa M
authors.initials: RM
authors.lastname: Sánchez
authors.forename: Manuel
authors.initials: M
authors.lastname: Merlos
authors.forename: Juan Carlos
authors.initials: JC
authors.lastname: Laguna
authors.forename: Manuel
authors.initials: M
authors.lastname: Vázquez-Carrera
mesh_terms: D000470:Alkaloids; D000818:Animals; D053119:Benzophenanthridines; D001692:Biological Transport / Q000187:drug effects; D002460:Cell Line; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005947:Glucose / Q000378:metabolism; D051379:Mice; D018482:Muscle, Skeletal / Q000187:drug effects / Q000502:physiology*; D016328:NF-kappa B / Q000378:metabolism*; D009281:Naphthalenes / Q000494:pharmacology; D019308:Palmitic Acid / Q000494:pharmacology*; D010617:Phenanthridines / Q000494:pharmacology; D011493:Protein Kinase C / Q000037:antagonists & inhibitors / Q000378:metabolism*; D011759:Pyrrolidines / Q000494:pharmacology; D012717:Sesquiterpenes / Q000494:pharmacology; D013859:Thiocarbamates / Q000494:pharmacology; D014409:Tumor Necrosis Factor-alpha / Q000235:genetics*
chemical_list: D000470:Alkaloids; D053119:Benzophenanthridines; D004791:Enzyme Inhibitors; D016328:NF-kappa B; D009281:Naphthalenes; D010617:Phenanthridines; D011759:Pyrrolidines; D012717:Sesquiterpenes; D013859:Thiocarbamates; D014409:Tumor Necrosis Factor-alpha; C020972:pyrrolidine dithiocarbamic acid; C002669:parthenolide; D019308:Palmitic Acid; C016299:chelerythrine; D011493:Protein Kinase C; C058819:calphostin C; D005947:Glucose