Uncoupling Protein-1 and Related Messenger Ribonucleic Acids in Human Epicardial and Other Adipose Tissues: Epicardial Fat Functioning as Brown Fat

Context: Uncoupling protein-1 (UCP-1) is the inner mitochondrial membrane protein that is a specific marker for and mediator of nonshivering thermogenesis in brown adipocytes. Objective: This study was performed to better understand the putative thermogenic function of human epicardial fat. Design: We measured the expression of UCP-1 and brown adipocyte differentiation transcription factors PR-domain-missing 16 (PRDM16) and peroxisome-proliferator-activated receptor γ co-activator-1α (PGC-1α) in epicardial, substernal, and sc thoracic, abdominal, and leg fat. Setting: The study was conducted at a tertiary care hospital cardiac center. Patients: Forty-four patients had coronary artery bypass surgery, and six had heart valve replacement. Interventions: Fat samples were taken at open heart surgery. Results: UCP-1 expression was 5-fold higher in epicardial fat than substernal fat and barely detectable in sc fat. Epicardial fat UCP-1 expression decreased with age, increased with body mass index, was similar in...