ABSTRACT
The prevalences of insulin resistance and type 2 diabetes mellitus are rising dramatically, and, as a consequence, there is an urgent need to understand the pathogenesis underpinning these conditions to develop new and more efficacious treatments. We have tested the hypothesis that glucocorticoid (GC)-mediated changes in insulin sensitivity may be associated with changes in lipid flux. Furthermore, prereceptor modulation of GC availability by 11ß-hydroxysteroid dehydrogenase type 1 (11ß-HSD1) may represent a critical regulatory step. Dexamethasone (DEX) decreased lipogenesis in both murine C2C12 and human LHC-NM2 myotubes. Inactivating p-Ser-79/218 of acetyl-CoA carboxylase 1/2 and activating p-Thr-172 of AMP-activated protein kinase were both increased after DEX treatment in C2C12 myotubes. In contrast, DEX increased ß-oxidation. Selective 11ß-HSD1 inhibition blocked the 11-dehydrocorticosterone (11DHC)-mediated decrease in lipogenic gene expression and increase in lipolytic gene expression. Lipogenic gene expression was decreased, whereas lipolytic and ß-oxidative gene expression increased in corticosterone (CORT)- and 11DHC-treated wild-type mice and CORT (but not 11DHC)-treated 11ß-HSD1(-/-) mice. Furthermore, CORT- and 11DHC-treated wild-type mice and CORT (but not 11DHC)-treated 11ß-HSD1(-/-) mice had increased p-Ser-79/218 acetyl-CoA carboxylase 1/2, p-Thr-172 AMP-activated protein kinase and intramyocellular diacylglyceride content. In summary, we have shown that GCs have potent actions on intramyocellular lipid homeostasis by decreasing lipid storage, increasing lipid mobilization and utilization, and increasing diacylglyceride content. It is plausible that dysregulated intramyocellular lipid metabolism may underpin GC-induced insulin resistance of skeletal muscle.
Subject(s)
11-beta-Hydroxysteroid Dehydrogenase Type 1/metabolism , Glucocorticoids/pharmacology , Muscle, Skeletal/drug effects , Muscle, Skeletal/metabolism , 11-beta-Hydroxysteroid Dehydrogenase Type 1/genetics , Acetyl-CoA Carboxylase/metabolism , Animals , Cell Line , Dexamethasone/pharmacology , Humans , Lipid Metabolism/drug effects , Lipogenesis/drug effects , Mice , Mice, Knockout , Muscle Fibers, Skeletal/cytology , Muscle Fibers, Skeletal/drug effects , Muscle Fibers, Skeletal/metabolism , Muscle, Skeletal/cytologyABSTRACT
Low-grade inflammation observed in obesity is a risk factor for cardiovascular disease. Recent studies revealed that this would be linked to gut-derived endotoxemia during fat digestion in high-fat diets, but nothing is known about the effect of lipid composition. The study was designed to test the impact of oil composition of high-fat diets on endotoxin metabolism and inflammation in mice. C57/Bl6 mice were fed for 8 wk with chow or isocaloric isolipidic diets enriched with oils differing in fatty acid composition: milk fat, palm oil, rapeseed oil, or sunflower oil. In vitro, adipocytes (3T3-L1) were stimulated or not with lipopolysaccharide (LPS; endotoxin) and incubated with different fatty acids. In mice, the palm group presented the highest level of IL-6 in plasma (P < 0.01) together with the highest expression in adipose tissue of IL-1ß and of LPS-sensing TLR4 and CD14 (P < 0.05). The higher inflammation in the palm group was correlated with a greater ratio of LPS-binding protein (LBP)/sCD14 in plasma (P < 0.05). The rapeseed group resulted in higher sCD14 than the palm group, which was associated with lower inflammation in both plasma and adipose tissue despite higher plasma endotoxemia. Taken together, our results reveal that the palm oil-based diet resulted in the most active transport of LPS toward tissues via high LBP and low sCD14 and the greatest inflammatory outcomes. In contrast, a rapeseed oil-based diet seemed to result in an endotoxin metabolism driven toward less inflammatory pathways. This shows that dietary fat composition can contribute to modulate the onset of low-grade inflammation through the quality of endotoxin receptors.
