Abstract/Summary

Adipose tissue heterogeneity may contribute to the different metabolic consequences associated with increased adipose tissue mass in obesity. Hypothesis: Adipose tissue depots differ in cellularity and gene expression profiles and will respond to obesity, exercise training and chronic psychological stress differentially. Methods: Visceral and pericardial adipose tissues were isolated from 8-9 weeks old male Zucker rats after training on treadmill and/or exposed to environmental stressors for 8 weeks. The human pericardial adipose tissue was isolated from coronary artery bypass graft surgery participants. The metabolic and inflammatory status of the adipose tissue were analysed by morphological and quantitative reverse transcription polymerase chain reaction analyses. Results: Visceral adipose tissue (VAT) of the obese Zucker rats (OZR) exhibited hypertrophic mechanism of expansion with an elevated expression of UCP1 when compared to the lean littermates. Pericardial adipose tissue (PAT) of OZR contained smaller adipocytes but with an excess collagen accumulation. In response to the experimental protocols, stress significantly reduced collagen accumulation in obese PAT with no effects on the VAT morphology. The lean VAT significantly expressed PGC1-α with reduced adipocyte size in response to the combination of stress and exercise interventions. Both stress and stress+exercise significantly reduced the expression of TNF-α in the lean PAT only. Exercise had an opposing effect on the expression of IRS-1 mRNA in both adipose depots of the lean and obese rats. There was no change in human pericardial adipocyte size but the expression of CD68 mRNA and TNF-α mRNA in human PAT were reduced. Conclusion: PAT, not VAT, may be an important predictor for metabolic disorder in obese rats. The clinical results demonstrated that PAT through the reduced macrophage population and inflammation may exert beneficial effects on the cardiac tissue in obesity.