Search for nutrients or drugs to improve metabolism by use of regulatory mechanism of ghrelin receptor gene transcription

尽管糖尿病或肥胖症患者需要严格限制卡路里摄入，但通常很难持续下去。Ghrelin是一种生长激素促分泌素受体(GHS-R)的配体，从胃中分离出来，具有刺激食欲和GH分泌的作用。此外，我们还报道了Ghrelin在体外培养的肝细胞中的抗胰岛素作用。在本研究中，我们利用荧光素酶检测系统研究了哪些营养物质或药物可能会影响GHS-R基因的转录。转录活性(GHS-R/Luc)位于GHS-R基因5‘侧翼区-608~-534P之间，AP_2或bHLH可能与之结合。凝胶漂移实验表明，该区域的荧光标记DNA可与从HepG_2细胞中提取的核蛋白特异性结合。五烯酸(EPA)或曲格列酮对GHS-R/Luc活性有轻微抑制作用。这些结果表明，EPA或曲格列酮至少部分地通过下调GHS-R来增强胰岛素敏感性。另一方面，厌食性脂质，乙醇胺，引起GHS-R/Luc活性的轻微增加。我们经历过一些患者，他们喝了某种减肥茶，后来患上了糖尿病。该减肥茶可抑制培养的胰腺细胞RIN-5F对葡萄糖诱导的胰岛素分泌。然而，该茶不改变GHS-R/Luc的活性。维生素C、E、胰岛素、Ghrelin和瘦素不改变GHS-R/Luc活性。由于EPA导致GHS-R下调，我们在年轻志愿者中挑战富含多不饱和脂肪酸(PUFA)的饮食。富含多不饱和脂肪酸的饮食导致HOMA-IR增加，血浆脂联素水平也有先例升高。总而言之，测量新陈代谢相关基因的转录活性是寻找预防糖尿病或肥胖的营养或药物的有用方法。

A though patients with diabetes or obesity require severe restriction of calorie intake, it is usually hard to continue. Ghrelin, a ligand for growth hormone secretagogue receptor (GHS-R), was isolated from stomach and reported to play roles in stimulation of appetite as well as GH secretion. In addition, we have reported the role of ghrelin against insulin action in cultured hepatocytes In this study, we searched which nutrients or drugs might affect GHS-R gene transcription by luciferase assay system. The transcriptional activity (GHS-R/Luc) was located between -608 and -534p of 5'-flanking region of GHS-R gene, where AP_2 or bHLH was expected to bind. Gel shift assay demonstrated that fluorecent labeled DNA of this region specifically bound to nuclear proteins extracted from HepG_2 cells. Eicosa-pentaenoic acid (EPA) or troglitazone slightly inhibited GHS-R/Luc activity. These results suggest that EPA or troglitazone enhance insulin sensitivity, at least in part, by down-regulation of GHS-R. On the other hand, anorexic lipid, oleylethanolamide, caused a slight increase in GHS-R/Luc activity. We have experienced patients who had taken a certain diet tea and subsequently became diabetic. This diet tea inhibited glucose-induced insulin secretion from cultured pancreatic cells RIN-5F. However, this tea did not change GHS-R/Luc activity. Vitamin C,E, insulin, ghrelin, and leptin did not change GHS-R/Luc activity. As EPA caused down-regulation of GHS-R, we challenged polyunsaturated fatty acid (PUFA)-rich diet in young volunteer. The PUFA-rich diet caused an increase in HOMA-IR with a precedent elevation of plasma adiponectin levels. In conclusion, measurement of transcriptional activity of genes involved in metabolism is a useful way to search nutrients or drugs for prevention of diabetes or obesity.