The Role of SNAREs in Adipokine Secretion in 3T3-L1 Adipocytes

• Main Authors: Yu Chun Lin, 林俞君
• Other Authors: J. C. Lu
• Format: Others
• Published: 2012
• Online Access: http://ndltd.ncl.edu.tw/handle/54811286033727136300

碩士 === 長庚大學 === 生物醫學研究所 === 100 === Obesity has become a worldwide health issue due to its association with many chronic diseases. It is primarily caused by hypertrophied adipocytes (overload of triglycerides), which leads to adipose tissue dysfunction. In addition to regulating energy metabolism, the adipose tissue also secretes adipokines to regulate whole body physiology. However, adipokine secretion mechanism remains poorly understood. SNARE (soluble N-ethylmaleimide- sensitive factor attachment protein receptors) proteins, including VAMPs, syntaxins and SNAPs, are known to regulate exocytotic pathways in many eukaryotic cells. Thus, we hypothesize that SNAREs may mediate secretion of adipokines, and obesity may alter SNARE function which leads to abnormal adipokine secretion. By RNA interference in 3T3-L1 adipocytes, we found that depletion of VAMP2 or VAMP8, but not syntaxin4, SNAP23 or VAMP3, suppressed insulin-stimulated leptin secretion. In contrast, depletion of these SNAREs played only a minor role in MCP-1 secretion. To gain an idea of intracellular pathways of leptin and MCP-1, we treated cells with the trafficking inhibitors. Brefeldin A and monensin blocked secretion of leptin and MCP-1. Interestingly, the protein kinase D inhibitor increased insulin-induced leptin secretion, but inhibited TNF-induced MCP-1 secretion, suggesting different trafficking pathways of MCP-1 and leptin in 3T3-L1 adipocytes. To see if hypertrophy of adipocytes might affect their secretory mechanism, we examined adipokine secretion and SNARE expression during adipocyte differentiation. We observed elevated secretion of leptin when adipocytes accumulated more triglycerides at late differentiated stage, whereas the sensitivity to TNF and insulin, and the expression of SNAREs remained unchanged. Further experiments will be required to elucidate the mechanism by which obesity modulaties the secretory function of adipocytes.