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Effects of leptin, an antiobestic factor, on catecholamine synthesis and secretion in bovine adrenal medullary cells

抗肥胖因子瘦素对牛肾上腺髓质细胞儿茶酚胺合成和分泌的影响

基本信息

批准号：
11670109
负责人：
IZUMI Futoshi
金额：
$ 2.11万
依托单位：
University of Occupational and Environmental Health
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
1999
资助国家：
日本
起止时间：
1999 至 2000
项目状态：
已结题

项目摘要

Leptin, the protein product of the recently cloned obese gene, is secreted from adipose tissues and plays an important role in regulating body weight and energy expenditure through its receptor in the hypothalamus, the center of energy homeostasis. In addition to its hypothalamic action, several lines of evidence have shown that leptin acts directly on some extrahypothalamic and peripheral tissues such as pancreatic islets and T-lymphocytes.In the present study, we investigated the specific binding sites of leptin and examined the effects of leptin on the secretion and synthesis of catecholamines in cultured bovine adrenal medullary cells. 1) The plasma membranes isolated from bovine adrenal medulla showed a single class of specific binding sites of^<125>I-leptin with an apparent Kd of 6.6nM and Bmax of 62 fmol/mg protein. Leptin receptor type a (ObRa) but not type b (ObRb) mRNA was detected in the tissue by reverse transcriptase-polymerase chain reaction. 2) Leptin (3-30nM) significan … More tly stimulated ^<14>C-catecholamine synthesis from [^<14>C]tyrosine, but not from [^<14>C] DOPA although it had little effect on catecholamine secretion in cultured bovine adrenal medullary cells. 3) The stimulation of catecholamine synthesis in the cells was associated with the phosphorylation and activation of tyrosine hydroxylase, the late-limiting enzyme of catecholamine synthesis. 4) The incubation of cells with leptin resulted in a rapid activation of the mitogen-activated protein kinases (MAPKs). An inhibitor of MAPK kinase, UO126, nullified the stimulatory effect of leptin on the synthesis of ^<14>C-catecholamines. 5) Leptin potentiated the stimulatory effect of acetylcholine on ^<14>C-catecholamine synthesis, whereas leptin failed to enhance the phosphorylation and activation of tyrosine hydroxylase induced by acetylcholine.These findings suggest that leptin stimulates catecholamine synthesis via the activation of tyrosine hydroxylase by two different mechanisms, i.e., one is dependent on tyrosine hydroxylase phosphorylation mediated through the MAPK pathway and the second is independent on enzyme phosphorylation. This information helps to unveil the biochemical basis of the mechanism by which leptin acts on metabolic homeostasis. Less

瘦素是新近克隆的肥胖基因的蛋白产物，由脂肪组织分泌，通过其位于能量稳态中心下丘脑的受体在调节体重和能量消耗方面起重要作用。除了下丘脑作用外，有证据表明瘦素还直接作用于下丘脑外的组织和外周组织，如胰岛和T淋巴细胞，本研究探讨了瘦素的特异性结合位点，并研究了瘦素对培养的牛肾上腺髓质细胞分泌和合成儿茶酚胺的影响。1)从牛肾上腺髓质分离的质膜显示出一类单一的特异性结合位点<125>，其表观Kd为6.6nM，Bmax为62 fmol/mg蛋白。逆转录-聚合酶链反应检测到瘦素受体a型（ObRa）mRNA，但未检测到B型（ObRb）mRNA。2)瘦素（3- 30 nM）显著 ...更多信息在培养的牛肾上腺髓质细胞中，Tly<14>刺激[^ C]酪氨酸合成^C-儿茶酚胺<14>，但不刺激[^<14>C]多巴合成^C-儿茶酚胺，尽管它对儿茶酚胺分泌的影响很小。3)在细胞中的儿茶酚胺合成的刺激与磷酸化和激活的酪氨酸羟化酶，儿茶酚胺合成的晚期限制酶。4)细胞与瘦素的孵育导致有丝分裂原活化蛋白激酶（MAPKs）的快速激活。MAPK激酶抑制剂UO 126可阻断瘦素对β-C-儿茶酚胺合成的刺激作用<14>。5)Leptin可增强乙酰胆碱对β-<14>C-儿茶酚胺合成的刺激作用，但Leptin不能增强乙酰胆碱诱导的酪氨酸羟化酶的磷酸化和激活，提示Leptin通过激活酪氨酸羟化酶促进儿茶酚胺合成的机制有两种：一种依赖于通过MAPK途径介导的酪氨酸羟化酶磷酸化，另一种不依赖于酶磷酸化。这些信息有助于揭示瘦素作用于代谢稳态的机制的生化基础。少