Diet-dependent alterations of hepatic Scd1 expression are accompanied by differences in promoter methylation.

Obesity and alterations of lipid homeostasis are hallmarks of the metabolic syndrome and largely influenced by the dietary conditions of the individual. Although heritability is considered to be a major risk factor, the almost 40 candidate genes identified by genome-wide association studies (GWAS) so far account for only 5-10% of the observed variance in BMI in human subjects. Alternatively, diet-induced changes of epigenetic gene regulation might be involved in disturbed lipid homeostasis and weight development. The aim of this study was to investigate how a high-carbohydrate diet (HCD; 70 kcal% from carbohydrates, 10 kcal% from fat) or a high-fat diet (HFD; 20 kcal% from carbohydrates, 60 kcal% from fat) affects hepatic expression of genes involved in fatty acid metabolism and if these alterations are correlated to changes in promoter methylation. Expression of stearoyl-CoA desaturase 1 (Scd1) was lower in livers from HFD-fed C57BL/6 J mice compared to HCD-fed animals and correlated inversely with the degree of DNA methylation at 2 distinct, adjacent CpG sites in the Scd1 promoter. In contrast, expression of transcription factors peroxisome proliferator activated receptor alpha and gamma (Ppara, Pparg), and sterol regulatory element binding transcription factor 1 (Srebf1) was not affected. The degree of hepatic Scd1 promoter methylation at these CpG sites correlated positively to fat mass and serum leptin levels, whereas serum ghrelin levels were inversely correlated with methylation at both CpG sites. Taken together, hepatic expression of Scd1 is differentially affected by carbohydrate- and lipid content of the diet. These differences in Scd1 expression are associated with altered promoter methylation, indicating that diets affect lipid metabolism in the liver via epigenetic mechanisms.

Requirement for distinct vesicle-associated membrane proteins in insulin- and AMP-activated protein kinase (AMPK)-induced translocation of GLUT4 and CD36 in cultured cardiomyocytes.

AIMS/HYPOTHESIS: Upon stimulation of insulin signalling or contraction-induced AMP-activated protein kinase (AMPK) activation, the glucose transporter GLUT4 and the long-chain fatty acid (LCFA) transporter CD36 similarly translocate from intracellular compartments to the plasma membrane of cardiomyocytes to increase uptake of glucose and LCFA, respectively. This similarity in regulation of GLUT4 traffic and CD36 traffic suggests that the same families of trafficking proteins, including vesicle-associated membrane proteins (VAMPs), are involved in both processes. While several VAMPs have been implicated in GLUT4 traffic, nothing is known about the putative function of VAMPs in CD36 traffic. Therefore, we compared the involvement of the myocardially produced VAMP isoforms in insulin- or contraction-induced GLUT4 and CD36 translocation. METHODS: Five VAMP isoforms were silenced in HL-1 cardiomyocytes. The cells were treated with insulin or the contraction-like AMPK activator oligomycin or were electrically stimulated to contract. Subsequently, GLUT4 and CD36 translocation as well as substrate uptake were measured. RESULTS: Three VAMPs were demonstrated to be necessary for both GLUT4 and CD36 translocation, either specifically in insulin-treated cells (VAMP2, VAMP5) or in oligomycin/contraction-treated cells (VAMP3). In addition, there are VAMPs specifically involved in either GLUT4 traffic (VAMP7 mediates basal GLUT4 retention) or CD36 traffic (VAMP4 mediates insulin- and oligomycin/contraction-induced CD36 translocation). CONCLUSIONS/INTERPRETATION: The involvement of distinct VAMP isoforms in both GLUT4 and CD36 translocation indicates that CD36 translocation, just like GLUT4 translocation, is a vesicle-mediated process dependent on soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) complex formation. The ability of other VAMPs to discriminate between GLUT4 and CD36 translocation allows the notion that myocardial substrate preference can be modulated by these VAMPs.