Oleate dose-dependently regulates palmitate metabolism and insulin signaling in C2C12 myotubes

• Published in: Biochimica et biophysica acta Vol. 1861; no. 12; pp. 2000 - 2010
• Main Authors: Capel, Frédéric, Cheraiti, Naoufel, Acquaviva, Cécile, Hénique, Carole, Bertrand-Michel, Justine, Vianey-Saban, Christine, Prip-Buus, Carina, Morio, Béatrice
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier B.V 01-12-2016; Elsevier
• Subjects: Animals; Carnitine - analogs & derivatives; Carnitine - metabolism; Cell Line; Ceramides - metabolism; Diglycerides - metabolism; Fatty Acids - metabolism; Food and Nutrition; Insulin - metabolism; Insulin Resistance - physiology; Insulin signaling; Life Sciences; Lipid metabolism; Lipotoxicity; Mice; Muscle Fibers, Skeletal - drug effects; Muscle Fibers, Skeletal - metabolism; Muscle, Skeletal - drug effects; Muscle, Skeletal - metabolism; NF-kappa B - metabolism; Oleic Acid - pharmacology; Oxidation-Reduction - drug effects; p38 Mitogen-Activated Protein Kinases - metabolism; Palmitates - metabolism; Phosphorylation - drug effects; Phosphorylation - physiology; Proto-Oncogene Proteins c-akt - metabolism; Signal Transduction - drug effects; Signal Transduction - physiology; Skeletal muscle; Substrate partitioning; Triglycerides - metabolism; Substrate partitioning; Cpt; HRP; C2; SC; BSA; DMEM; Il6; ANOVA; MC; Spt; Fasn; Lipid metabolism; Lipotoxicity; ASP; Adrp; Pgc1; DGAT; MGAT; PKC; Sod; Akt; DAG; MAPK; Skeletal muscle; Tnfa; Ptgs; FCS; LC; Ppar; FA; TAG; PL; GAPDH; Srebf1; Insulin signaling; 2 oxidation; insulino- résistance; myotube; acide gras; fatty acid; beta oxydation
• ISSN: 1388-1981; 0006-3002; 1879-2618
• DOI: 10.1016/j.bbalip.2016.10.002

Because the protective effect of oleate against palmitate-induced insulin resistance may be lessened in skeletal muscle once cell metabolism is overloaded by fatty acids (FAs), we examined the impact of varying amounts of oleate on palmitate metabolic channeling and insulin signaling in C2C12 myotubes. Cells were exposed to 0.5mM of palmitate and to increasing doses of oleate (0.05, 0.25 and 0.5mM). Impacts of FA treatments on radio-labelled FA fluxes, on cellular content in diacylglycerols (DAG), triacylglycerols (TAG), ceramides, acylcarnitines, on PKCθ, MAPKs (ERK1/2, p38) and NF-ΚB activation, and on insulin-dependent Akt phosphorylation were examined.
Low dose of oleate (0.05mM) was sufficient to improve palmitate complete oxidation to CO2 (+29%, P<0.05) and to alter the cellular acylcarnitine profile. Insulin-induced Akt phosphorylation was 48% higher in that condition vs. palmitate alone (p<0.01). Although DAG and ceramide contents were significantly decreased with 0.05mM of oleate vs. palmitate alone (−47 and −28%, respectively, p<0.01), 0.25mM of oleate was required to decrease p38 MAPK and PKCθ phosphorylation, thus further improving the insulin signaling (+32%, p<0.05). By contrast, increasing oleate concentration from 0.25 to 0.5mM, thus increasing total amount of FA from 0.75 to 1mM, deteriorated the insulin signaling pathway (−30%, p<0.01). This was observed despite low contents in DAG and ceramides, and enhanced palmitate incorporation into TAG (+27%, p<0.05). This was associated with increased incomplete FA β-oxidation and impairment of acylcarnitine profile. In conclusion, these combined data place mitochondrial β-oxidation at the center of the regulation of muscle insulin sensitivity, besides p38 MAPK and PKCθ.
•Oleate significantly alters palmitate channeling in C2C12 myotubes.•Impact of oleate on palmitate-induced insulin resistance follows an inverted U-curve.•Low dose of oleate is sufficient to enhance palmitate complete oxidation to CO2.•Dual effect of oleate on insulin signaling involves improved β-oxidation and inhibition of PKCθ and p38 MAPK.•Oleate overload increases incomplete β-oxidation and alters insulin signaling.