Epicardial fat gene expression after aerobic exercise training in pigs with coronary atherosclerosis: relationship to visceral and subcutaneous fat

Abstract

Epicardial adipose tissue (EAT) is contiguous with coronary arteries and myocardium and potentially may play a role in coronary atherosclerosis (CAD). Exercise is known to improve cardiovascular disease risk factors. The purpose of this study was to investigate the effect of aerobic exercise training on the expression of 18 genes, measured by RT-PCR and selected for their role in chronic inflammation, oxidative stress, and adipocyte metabolism, in peri-coronary epicardial (cEAT), peri-myocardial epicardial (mEAT), visceral abdominal (VAT), and subcutaneous (SAT) adipose tissues from a castrate male pig model of familial hypercholesterolemia with CAD. We tested the hypothesis that aerobic exercise training for 16 wk would reduce the inflammatory profile of mRNAs in both components of EAT and VAT but would have little effect on SAT. Exercise increased mEAT and total heart weights. EAT and heart weights were directly correlated. Compared with sedentary pigs matched for body weight to exercised animals, aerobic exercise training reduced the inflammatory response in mEAT but not cEAT, had no effect on inflammatory genes but preferentially decreased expression of adiponectin and other adipocyte-specific genes in VAT, and had no effect in SAT except that IL-6 mRNA went down and VEGFa mRNA went up. We conclude that 1) EAT is not homogeneous in its inflammatory response to aerobic exercise training, 2) cEAT around CAD remains proinflammatory after chronic exercise, 3) cEAT and VAT share similar inflammatory expression profiles but different metabolic mRNA responses to exercise, and 4) gene expression in SAT cannot be extrapolated to VAT and heart adipose tissues in exercise intervention studies.

Fig. 1.

Dissection procedure for coronary epicardial adipose tissue (cEAT) and myocardial epicardial adipose tissue (mEAT). A and B: intact right side and left side of the heart, respectively, before dissection. The black line indicates the approximate edge between cEAT and mEAT. RCA, right coronary artery; LAD, left anterior descending coronary vessel; LCX, left circumflex coronary vessel; RV, right ventricle, LV, left ventricle. C: cEAT layer is peeled back to reveal the LAD and LCX coronary vessels. D: cEAT layer is peeled back to reveal more of the LAD and LCX coronary vessel.

Fig. 2.

Representative pictures of EX and SED hearts. EX, heart from aerobic exercise-trained familial cholesterolemia (FH) pig; SED, heart from sedentary FH pig.

Fig. 3.

Correlation of heart weight with total EAT weight for all 13 pigs. r² = 0.53; adjusted r² = 0.48, P = 0.005.

Fig. 4.

Intima-media thickness (IMT): grading of lesion of structural atherosclerosis. LAD-ex, left anterior descending coronary artery from EX pig; RCA-ex, right coronary artery from EX pig; LAD-sed, left anterior descending coronary artery from SED pig; RCA-sed, right coronary artery from SED pig. The vessels are stained for VVG to identify elastin (black) and collagen (dark-red; purple) fibers, which were are use to determine the IMT. Scale bar, 100 μm.

Fig. 5.

Comparison of peri-coronary EAT (cEAT), peri-myocardial EAT (mEAT), and visceral omental adipose tissue (VAT) gene expression to that in subcutaneous adipose tissue (SAT) of sedentary pigs. The values are expressed as the ratio of mRNA expression in mEAT, cEAT, and VAT to that in SAT in 8 sedentary pigs. The ratios are the means ± SE and derived from the ΔCt corrected for the recovery of cyclophilin. With the exception of cytochrome c oxidase (P = 0.005), none of the mRNAs were expressed at significantly different values in cEAT vs. mEAT. FABP4, fatty acid binding protein-4; GPX3, glutathione peroxidase 3; IL-8, interleukin-8; IL-1Ra, interleukin 1 receptor antagonist; UCP-2, uncoupling protein-2; eNOS, endothelial nitric oxide synthase; VEGFa, vascular endothelial growth factor a; TLR4, toll-like receptor 4; PAI-1, plasminogen activator inhibitor 1; PGDS, prostaglandin D₂ synthase; IL-6, interleukin 6. Statistically significant differences between expression in cEAT, mEAT, or VAT relative to SAT are shown as follows: *P < 0.05, **P < 0.025, ***P < 0.005.

Fig. 6.

Comparison of peri-coronary EAT (cEAT), peri-myocardial EAT (mEAT), VAT, and SAT gene expression in exercised pigs to that in sedentary pigs. The mRNA values are the ratios ± SE of the mRNA expression for adipose tissue from five exercised (EX) pigs compared with that in 8 sedentary (SED). Ratios greater than 1.0 indicate that the level of expression was enhanced by exercise, while ratios less than 1.0 indicate that the level of expression was reduced by aerobic exercise. The horizontal line at 1.0 indicates a ratio (SED/EX) where the expression of mRNAs were equal for SED and EX (i.e., the means were identical). A bar below this horizontal line indicates that EX lowered the expression of the given mRNA. Statistically significant differences between expression in EX mRNA compared with SED mRNA are shown as follows: *P < 0.05, **P < 0.025, ***P < 0.005.