Serglycin is a novel adipocytokine highly expressed in epicardial adipose tissue

Much recent work has highlighted the key role of adipose tissue as an endocrine organ that secretes a number of adipocytokines, linking adiposity, especially intra-abdominal visceral fat, and the pathogenesis of cardiovascular and metabolic diseases. However, the role of epicardial adipose tissue (EAT), another important visceral fat depot situated in close proximity to epicardial coronary arteries and myocardium, has been less well studied. In this study, we sought to characterize EAT by comparing gene expression profiles of EAT, omental adipose tissue (OAT), and subcutaneous adipose tissue (SCAT) in patients who underwent elective coronary artery bypass graft surgery for critical coronary artery disease (CAD) and identify molecules involved in inflammation. A total of 15,304 probes were detected in all depots, and 231 probes were differentially expressed. Significantly higher expression of pro-inflammatory genes such as interleukin-1β, -6, and -8, and chemokine receptor 2 was observed in EAT, even when compared with OAT. Among them, serglycin was one of the most abundantly expressed genes in EAT. Serglycin expression was induced during adipocytic differentiation of 3T3L1 cells. Serglycin was secreted from adipocytes, and tumor necrosis factor-α stimulated its expression and secretion in adipocytes. Serglycin was also present in human serum samples. These results suggest that human EAT has strong inflammatory properties in patients with CAD and provide novel evidence that serglycin is an adipocytokine highly expressed in EAT.