瘦素信号转导通路的代谢调控功能研究
文献类型：学位论文
| 作者 | 蒋雷 |
| 学位类别 | 硕士 |
| 答辩日期 | 2009 |
| 授予单位 | 中国科学院上海生命科学研究院营养科学研究所 |
| 授予地点 | 中国科学院上海生命科学研究院 |
| 导师 | 刘勇 |
| 关键词 | 瘦素信号通路 基因敲入 高脂饮食 脂肪合成 肥胖与胰岛素抵抗 |
| 其他题名 | Physiological role of leptin signaling in metabolic regulation |
| 学位专业 | 生物化学与分子生物学 |
| 中文摘要 | 脂肪组织分泌的细胞因子－瘦素 (Leptin)，通过作用于中枢神经下丘脑中特定神经元上的瘦素受体 (Ob-Rb) 激活下游的信号通路，在能量与糖脂代谢平衡中起着至关重要的调节作用。我们围绕瘦素的研究工作主要分为两个部分。 第一部分：小鼠瘦素受体胞内端含有三个已知的关键酪氨酸位点，在瘦素的刺激下会被磷酸化，但它们介导的信号通路在体内行使什么样的生理功能目前尚不完全清楚。我们利用基因敲入技术，将瘦素受体的胞内酪氨酸位点引入点突变，培育出两个品系的瘦素受体点突变小鼠模型：一个品系 (Y123F) 将985、1077和1138位的三个酪氨酸 (Y) 都突变为苯丙氨酸 (F) ，而另一个品系 (Y3F) 则只将第三个1138位的酪氨酸突变为苯丙氨酸。我们发现Y123F小鼠与Y3F小鼠下丘脑中的STAT3信号分子不能被激活，它们均表现为一定程度的食欲过剩和肥胖；但是，与Y3F小鼠相比，Y123F小鼠表现出更加严重的葡萄糖不耐受和脂肪肝症状。同时，与瘦素受体Ob-Rb完全缺失的db/db小鼠相比，Y123F小鼠与Y3F小鼠的代谢紊乱程度明显较低，表现为肥胖程度较轻，进食量较少，活动量较多，适应性产热能力较强等。另外，我们还发现Y123F小鼠和Y3F小鼠下丘脑中神经肽NPY/AgRP的表达量显著低于db/db小鼠。这些直接的在体实验结果表明，在瘦素调节能量代谢平衡和糖代谢平衡的过程中，不但存在瘦素受体酪氨酸依赖型的信号机制，而且酪氨酸非依赖型的信号通路同样发挥着重要作用。 第二部分：过度营养引发的肥胖通常伴随着血液中瘦素水平的升高，但是瘦素升高所带来的生理学影响还不甚清楚。我们以高脂诱导的肥胖小鼠为模型，借助蛋白质组学的方法，发现了小鼠肥胖发生过程中脂肪从头合成相关酶表达量的变化，同时研究了瘦素对这些基因的表达调控。小鼠进食超高脂食物十六周后，脂肪含量显著增加，葡萄糖耐受能力明显下降；值得注意的是，小鼠仅进食高脂食物四周后，当葡萄糖耐受能力和血清中的胰岛素水平并没有发生显著变化的时候，血清中瘦素水平已有很大程度的上调。蛋白质组学的结果显示，高脂喂养的肥胖小鼠中，白色脂肪组织中脂肪从头合成相关酶的表达量显著降低，其中包括ATP柠檬酸裂解酶 (ATP-citrate lyase, ACL) 和脂肪酸合成酶 (fatty acid synthase, FAS)；同时，肝脏中ACL和FAS的表达量在高脂喂养组中也有显著下降。与野生型小鼠的情况不同，用高脂食物喂养瘦素信号缺失的db/db小鼠后，我们发现高脂食物并不能明显降低db/db小鼠中ACL和FAS的表达水平。另一方面，野生型小鼠经过瘦素直接处理后，伴随着肝脏和血清中甘油三脂含量的明显下降，白色脂肪组织和肝脏中ACL和FAS的表达量均有非常显著的下调。综合以上结果，瘦素通过抑制肝脏和白色脂肪组织中的脂肪从头合成，介导了小鼠对外界高脂食物摄入的代谢适应过程；瘦素对脂肪从头合成相关酶表达量的调控，是瘦素在外周组织中调节脂代谢平衡的重要机制之一。 |
| 索取号 | D2009-068 |
| 英文摘要 | Leptin is an adipocyte-derived hormone, which regulates energy homeostasis, glucose and lipid metabolism via activation of multiple signaling cascades mediated by the long form leptin receptor Ob-Rb in central nervous system. Our study is divided into two parts as follows: PART I: The three cytoplasmic tyrosines of the leptin receptor Ob-Rb can be phosphoralated upon leptin stimulation, however, the whole spectrum of signaling actions through these cytoplasmic tyrosines remains to be completely defined in vivo. Here we generated two knock-in mouse lines expressing mutant leptin receptors with phenylalanine substitution for all three tyrosines (Y123F) or for Tyr1138 alone (Y3F). Y123F animals developed similarly overt obesity as Y3F animals with abrogated hypothalamic activation of STAT3 by leptin, but exhibited more severe impairment in glucose tolerance. In striking contrast to db/db mice, however, both Y123F and Y3F mice showed attenuated adiposity with reduced hyperphagia, marked improvement in physical activity and adaptive thermogenesis, as well as significantly ameliorated glycemic control. Further, Y123F mice had hypothalamic NPY/AgRP expression maintained at prominently lower levels in comparison with db/db mice. Thus, these results provide direct physiological evidence that Ob-Rb exerts crucial metabolic actions not only through tyrosine-dependent, but also tyrosine-independent mechanisms in control of energy balance and glucose homeostasis. PART II: Overnutrition-associated obesity is known to be accompanied by hyperleptinemia. However, whether leptin contributes to the metabolic responses to high-fat diet (HFD) intake has yet to be completely elucidated. Here we characterized the metabolic features of mice fed high-fat diets and examined the impact of leptin upon the expression of lipogenic program, which was identified through a proteomics approach. Mice maintained on a higher fat diet for up to 16 weeks exhibited increased body fat accumulation at a greater pace, developing more severely impaired glucose tolerance. Notably, HFD feeding at 4 weeks elicited the onset of marked hyperleptinemia, prior to the occurrence of apparent insulin resistance and hyperinsulinemia. Proteomics analysis revealed dramatically decreased expression of lipogenic enzymes in the white adipose tissue (WAT) of HFD-fed mice, including ATP-citrate lyase (ACL) and fatty acid synthase (FAS). Hepatic expression of ACL and FAS was similarly suppressed in response to HFD feeding. In contrast, HFD-induced downregulation of hepatic ACL and FAS was significantly attenuated in leptin receptor-deficient db/db mice. Furthermore, in the liver and WAT of wild type animals, intraperitoneal leptin administration was able to directly suppress the expression of these two lipogenic enzymes, accompanied by reduced triglyceride levels both in the liver and serum.These results suggest that leptin contributes to the metabolic responses of mice in the adaptation to overnutrition through suppressing the expression of lipogenic enzymes, and the lipogenic pathway represents a key targeted peripheral component in exerting leptin’s liporegulatory actions. |
| 语种 | 中文 |
| 公开日期 | 2015-12-24 |
| 源URL | [http://202.127.25.144/handle/331004/312]  |
| 专题 | 中国科学院上海生命科学研究院营养科学研究所_糖脂代谢与调控研究组 |
| 推荐引用方式 GB/T 7714 | 蒋雷. 瘦素信号转导通路的代谢调控功能研究[D]. 中国科学院上海生命科学研究院. 中国科学院上海生命科学研究院营养科学研究所. 2009. |
入库方式： OAI收割
来源：上海营养与健康研究所
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