*Singapore Bioimaging Consortium, Agency for Science, Technology and Research (A*STAR), Singapore.
§Child Health Institute of New Jersey and Department of Neuroscience and Cell Biology, Rutgers-Robert Wood Johnson Medical School, New Brunswick, NJ, U.S.A.
Biochem J. 2014 Mar 15;458(3):491-8. doi: 10.1042/BJ20131176.
Numerous studies have focused on the regulation of leptin signalling and the functions of leptin in energy homoeostasis; however, little is known about how leptin secretion is regulated. In the present study we studied leptin storage and secretion regulation in 3T3-L1 and primary adipocytes. Leptin is stored in membrane-bound vesicles that are localized predominantly in the ER (endoplasmic reticulum) and close to the plasma membrane of both 3T3-L1 and primary adipocytes. Insulin increases leptin secretion as early as 15 min without affecting the leptin mRNA level. Interestingly, treatment with the protein synthesis inhibitor cycloheximide and the ER-Golgi trafficking blocker Brefeldin A inhibit both basal and ISLS (insulin-stimulated leptin secretion), suggesting that insulin stimulates leptin secretion by up-regulating leptin synthesis and that leptin-containing vesicles go through the ER-Golgi route. The PI3K (phosphoinositide 3-kinase)/Akt, but not MAPK (mitogen-activated protein kinase), pathway is involved in ISLS in vitro and in vivo. Although Ca2+ triggers synaptic vesicle and secretory granule exocytosis, Ca2+ influx alone is not sufficient to induce leptin secretion. Remarkably, Ca2+ is required for ISLS possibly due to its involvement in insulin-stimulated Akt phosphorylation. We conclude that insulin stimulates leptin release through the PI3K/Akt pathway and that Ca2+ is required for robust Akt phosphorylation and leptin secretion.
许多研究都集中在瘦素信号的调节及其在能量平衡中的作用上；然而，关于瘦素分泌是如何调节的知之甚少。本研究中，我们研究了 3T3-L1 和原代脂肪细胞中瘦素的储存和分泌调节。瘦素储存在膜结合囊泡中，这些囊泡主要定位于内质网（内质网）中，靠近 3T3-L1 和原代脂肪细胞的质膜。胰岛素早在 15 分钟内就会增加瘦素的分泌，而不会影响瘦素 mRNA 水平。有趣的是，用蛋白质合成抑制剂环己酰亚胺和内质网-高尔基体运输抑制剂布雷菲德菌素 A 处理可抑制基础和 ISLS（胰岛素刺激的瘦素分泌），这表明胰岛素通过上调瘦素合成刺激瘦素分泌，并且含有瘦素的囊泡通过内质网-高尔基体途径运输。PI3K（磷酸肌醇 3-激酶）/Akt 途径，而不是 MAPK（丝裂原活化蛋白激酶）途径，参与了体外和体内的 ISLS。尽管 Ca2+ 触发突触囊泡和分泌颗粒的胞吐作用，但 Ca2+ 内流本身不足以诱导瘦素分泌。值得注意的是，Ca2+ 可能是 ISLS 所必需的，因为它参与了胰岛素刺激的 Akt 磷酸化。我们得出结论，胰岛素通过 PI3K/Akt 途径刺激瘦素释放，而 Ca2+ 是 Akt 磷酸化和瘦素分泌所必需的。
