Obesogenic high fat western diet induces oxidative stress and apoptosis in rat heart

Abstract

Feeding Wistar rats a high calorie "Western" diet (45% fat) for up to 48 weeks induces obesity and cardiac dysfunction, while a high fat diet (60% fat) induces obesity only. Here we investigated the molecular "footprints" of the two forms of diet-induced obesity in the heart. In rats fed Western diet for a long term, cardiac mRNA transcript levels of malic enzyme were decreased (-72%, P < 0.05), suggesting impaired anaplerotic flux of the Krebs cycle (KC) and mitochondrial dysfunction. In addition, there was a marked decrease in the expression of the transcription factor MEF2C (myocyte enhancer factor 2C) and its target gene SERCA2a (sarco-endo-plasmic reticulum Ca(2+)-ATPase). Oxidative stress was reflected in reduced transcript levels of manganese superoxide dismutase, glutathione peroxidase 1, and increased protein levels of mitochondrial transcription factor A, suggesting compensatory mitochondrial biogenesis in the face of increased mitochondrial damage. Oxidant injury was accompanied by increased protein glycosylation, increased transcript levels of glutamine fructose 6-phosphate amidotransferase 2, and decreased protein levels of acetyl Co-A carboxylase. Lastly, apoptosis was evident by TUNEL positivity and elevated mRNA transcript levels and activity of caspase 3. Consistent with these results, protein levels of Bcl2 were markedly reduced. We conclude that inadequate supplementation of KC intermediates due to reduced levels of malic enzyme, downregulation of MEF2C and its target gene SERCA2a, oxidative stress, and programmed cell death are all potential contributors to contractile dysfunction of the heart.

Figure 1. Anaplerosis

Analperotic enzymes and the rate limiting enzyme of KC flux were determined by measuring mRNA transcripts of me (A), PC (B), protein expression levels of ME (C), PC (D), and PCC (E) as a function of time on the respective diets. Squares represent low fat diet, circles represent western diet, and triangles represent high fat diet. Values are means ± SEM. * p<0.05, ** p<0.01, and *** p<0.001 versus low fat diet at the same age. $ p<0.05., $$p<0.01, and $$$ p<0.001 compared with Western diet at the same age. See text and abbreviations for details.

Figure 2. MEF2C and its target gene SERCA2a

Expression of MEF2C was measured by western blot analysis (A & B). The expression of SERCA2a was measured by qRT-PCR(C), and by western blot analysis (D & E). MEF2C and SERCA2a were downregulated in hearts of rats fed Western diet. See text for details.

Figure 3. Oxidative stress

Oxidative stress was evaluated by measuring mRNA transcripts of mnsod (A), gpx1 (B), and by protein expression of HO-1 (C & D). There was an induction of oxidative stress in hearts from rats fed Western diet. See text for details.

Figure 4. Markers of apoptosis

The markers of apoptosis were evaluated by TUNEL staining (A & B), protein expression of Bcl2 (C), protein expression ratio of Bcl2 to BAD (D), and the protein expression ratio of Bcl2 to BAX (E). Markers of apoptosis were increased in hearts from rats fed Western diet. See text for details.

Figure 5. Cardiometabolic changes in hearts of rats fed a high fat Western diet

Please refer to the text of further detail.