Training Does Not Alter Muscle Ceramide and Diacylglycerol in Offsprings of Type 2 Diabetic Patients Despite Improved Insulin Sensitivity

Abstract

Ceramide and diacylglycerol (DAG) may be involved in the early phase of insulin resistance but data are inconsistent in man. We evaluated if an increase in insulin sensitivity after endurance training was accompanied by changes in these lipids in skeletal muscle. Nineteen first-degree type 2 diabetes Offsprings (Offsprings) (age: 33.1 ± 1.4 yrs; BMI: 26.4 ± 0.4 kg/m²) and sixteen matched Controls (age: 31.3 ± 1.5 yrs; BMI: 25.3 ± 0.7 kg/m²) performed 10 weeks of endurance training three times a week at 70% of VO₂max on a bicycle ergometer. Before and after the intervention a hyperinsulinemic-euglycemic clamp and VO₂max test were performed and muscle biopsies obtained. Insulin sensitivity was significantly lower in Offsprings compared to control subjects (p < 0.01) but improved in both groups after 10 weeks of endurance training (Off: 17 ± 6%; Con: 12 ± 9%, p < 0.01). The content of muscle ceramide, DAG, and their subspecies were similar between groups and did not change in response to the endurance training except for an overall reduction in C22:0-Cer (p < 0.05). Finally, the intervention induced an increase in AKT protein expression (Off: 27 ± 11%; Con: 20 ± 24%, p < 0.05). This study showed no relation between insulin sensitivity and ceramide or DAG content suggesting that ceramide and DAG are not major players in the early phase of insulin resistance in human muscle.

Figure 1

Ceramide and DAG metabolism in skeletal muscle. Ceramide is synthesized de novo from palmitoyl CoA and serine. Reversible reactions produce ceramide from sphingosine, glucosylceramide, ceramide 1-phosphate, and sphingomyelin, respectively. Conversion of ceramide to sphingomyelin also produces DAG. DAG is further synthesized from monoacylglycerol and from degradation of triacylglycerol. PC: phosphocholine; SMS: sphingomyelin synthase; MAG: monoacylglycerol; MGAT: monoacylglycerol acyltransferase; DGAT: diacylglycerol acyltransferase; HSL: hormone-sensitive lipase; ATGL: adipose triglyceride lipase. Proteins marked in bold blue are analyzed by western blotting.

Figure 2

Protein expression including representative blots in Offsprings of type 2 diabetic patients and matched Controls before and after 10 weeks of training intervention. Proteins presented are involved in (a) ceramide and DAG metabolism and (b) insulin signaling. Pre: black bars; Post: grey bars. ∗: main effect of the training intervention in Offspring and Control subjects (p = 0.03, n = 21).

Figure 3

Muscle content of (a) C22:0-Cer, (b) total ceramide, (c) total DAG, and (d) P-AKT_ser473 protein expression as function of insulin sensitivity at basal and the percent change after 10 weeks of endurance training in type 2 diabetic Offsprings (●) and matched Controls (○).