Insulin-resistant female rat skeletal muscles display diacylglycerol-mediated PKC activation and inflammation without ceramides accumulation.

This study investigated the role of diacylglycerol (DAG)-mediated protein kinase C (PKC) activation, ceramides accumulation, and inflammation in insulin-resistant female oxidative and glycolytic skeletal muscles induced by an obesogenic high-fat sucrose-enriched (HFS) diet. The HFS diet impaired insulin-stimulated AKT Thr308 phosphorylation and glycogen synthesis, whereas rates of fatty acid oxidation and basal lactate production were significantly elevated in soleus (Sol), extensor digitorum longus (EDL), and epitrochlearis (Epit) muscles. Insulin resistance was accompanied by increases in triacylglycerol (TAG), and DAG contents in Sol and EDL, whereas in Epit muscles only TAG content and markers of inflammation were associated with HFS diet-induced insulin resistance. Analysis of membrane-bound/cytoplasm PKC fractions revealed that the HFS diet promoted activation/translocation of PKCδ and θ isoforms in Sol, EDL, and Epit muscles. However, none of these muscles displayed alterations in ceramides contents in response to HFS feeding. This could be explained by a significant increase in Dgat2 mRNA expression in Sol, EDL, and Epit muscles, which likely diverted most of the intramyocellular acyl-CoAs toward TAG synthesis instead of ceramides. Overall, this study helps elucidate the molecular mechanisms underlying insulin resistance caused by diet-induced obesity in female skeletal muscles with distinct fiber type compositions. KEY POINTS: Feeding female Wistar rats a high-fat sucrose-enriched diet (HFS) led to diacylglycerol (DAG)-induced PKC activation and insulin resistance in oxidative and glycolytic skeletal muscles. HFS diet-induced toll-like receptor 4 (Tlr4) expression did not lead to increased ceramide content in female skeletal muscles. In highly glycolytic female muscles, elevated TAG content and markers of inflammation underlied HFS diet-induced insulin resistance. The HFS diet suppressed glucose oxidation and increased lactate production in oxidative and glycolytic female muscles. Increased Dgat2 mRNA expression likely diverted most of the intramyocellular acyl-CoAs toward TAG synthesis and prevented ceramides formation in skeletal muscles of HFS-fed female rats. Abstract figure legend Feeding female Wistar rats for 8 weeks an obesogenic high-fat sucrose-enriched (HFS) caused insulin resistance in Soleus (Sol), Extensor Digitorum Longus (EDL), and Epitrochlearis (Epit) muscles. In all muscles studied, the HFS diet increased diacylglycerol (DAG) content and Dgat2 mRNA expression, but did not affect ceramide levels. PKCθ and PKCδ activities and the expression of inflammatory markers were altered in a fiber type-specific manner by HFS feeding. In Sol and EDL muscles, PKCθ activity was increased, whereas in Epit it remained unaltered by the HFS diet. PKCδ activity was only elevated in Sol muscles by HFS feeding and the mRNA expression of inflammatory markers increased in EDL and Epit, but not in Sol muscles. ↑ = increase; ↔ = no change This article is protected by copyright. All rights reserved.