Adult Epicardial Fat Exhibits Beige Features

Context: Human epicardial fat has been designated previously as brown-like fat. The supraclavicular fat depot in man has been defined as beige coexistent with classical brown based on its gene expression profile. Objective: The aim of the study was to establish the gene expression profile and morphology of human epicardial and visceral paracardial fat compared with sc fat. Setting: The study was conducted at a tertiary care hospital cardiac center. Patients: Epicardial, visceral paracardial, and sc fat samples had been taken from middle-aged patients with severe coronary atherosclerosis or valvular heart disease. Interventions: Gene expression was determined by reverse transcription- quantitative PCR and relative abundance of the mitochondrial uncoupling protein-1 (UCP-1) by Western blotting. Epicardial tissue sections from patients were examined by light microscopy, UCP-1 immunohistochemistry, and cell morphometry. Main Outcome Measures: We hypothesized that epicardial fat has a mixed phenotype with a gene expression profile similar to that described for beige cell lineage. Results: Immunoreactive UCP-1 was clearly measurable in each epicardial sample analyzed but was undetectable in each of the 4 other visceral and sc depots. Epicardial fat exhibited high expression of genes for UCP-1, PRDM16, PGC-1α, PPARγ, and the beige adipocyte-specific marker CD137, which were also expressed in visceral paracardial fat but only weakly in sternal, upper abdominal, and lower extremity sc fat. Histology of epicardial fat showed small unilocular adipocytes without UCP-1 immunostaining. Conclusion: UCP-1 is relatively abundant in epicardial fat, and this depot possesses molecular features characteristic of those found in vitro in beige lineage adipocytes.