Brydon L, Petit L, Delagrange P, Strosberg A D, Jockers R
Centre National de la Recherche Scientifique-UPR 0415 and Université Paris VII, Institut Cochin de Génétique Moléculaire, F-75014 Paris, France.
Endocrinology. 2001 Oct;142(10):4264-71. doi: 10.1210/endo.142.10.8423.
Several reports have demonstrated that the pineal hormone, melatonin, plays an important role in body mass regulation in mammals. To date, however, the target tissues and relevant biochemical mechanisms involved remain uncharacterized. As adipose tissue is the principal site of energy storage in the body, we investigated whether melatonin could also act on this tissue. Semiquantitative RT-PCR analysis revealed the expression of MT1 and MT2 melatonin receptor mRNAs in the human brown adipose cell line, PAZ6, as well as in human brown and white adipose tissue. Binding analysis with 2-[(125)I]iodomelatonin ((125)I-Mel) revealed the presence of a single, high affinity binding site in PAZ6 adipocytes with a binding capacity of 7.46 +/- 1.58 fmol/mg protein and a K(d) of 457 +/- 5 pM. Both melatonin and the MT2 receptor-selective antagonist, 4-phenyl-2-propionamidotetraline, competed with 2-[(125)I]iodomelatonin binding, with respective K(i) values of 3 x 10(-11) and 1.5 x 10(-11) M. Functional expression of melatonin receptors in PAZ6 adipocytes was indicated by the melatonin-induced, dose-dependent inhibition of forskolin-stimulated cAMP levels and basal cGMP levels with IC(50) values of 2 x 10(-9) and 3 x 10(-10) M, respectively. Modulation of the cGMP pathway by melatonin further supports functional expression of MT2 receptors, as this pathway was shown to be specific for that subtype in humans. In addition, long-term melatonin treatment of PAZ6 adipocytes was found to decrease the expression of the glucose transporter Glut4 and glucose uptake, an important parameter of adipocyte metabolism. These results suggest that melatonin may act directly at MT2 receptors on human brown adipocytes to regulate adipocyte physiology.
多项报告表明，松果体激素褪黑素在哺乳动物体重调节中发挥重要作用。然而，迄今为止，所涉及的靶组织和相关生化机制仍未明确。由于脂肪组织是体内能量储存的主要部位，我们研究了褪黑素是否也能作用于该组织。半定量逆转录聚合酶链反应（RT-PCR）分析显示，褪黑素受体MT1和MT2的mRNA在人棕色脂肪细胞系PAZ6以及人棕色和白色脂肪组织中均有表达。用2-[(125)I]碘褪黑素（(125)I-Mel）进行结合分析表明，PAZ6脂肪细胞中存在一个单一的高亲和力结合位点，结合能力为7.46±1.58 fmol/mg蛋白质，解离常数（K(d)）为457±5 pM。褪黑素和MT2受体选择性拮抗剂4-苯基-2-丙酰胺基四氢萘均能与2-[(125)I]碘褪黑素结合竞争，其各自的抑制常数（K(i)）值分别为3×10(-11)和1.5×10(-11) M。褪黑素诱导PAZ6脂肪细胞中福斯高林刺激的环磷酸腺苷（cAMP）水平和基础环磷酸鸟苷（cGMP）水平呈剂量依赖性抑制，IC(50)值分别为2×10(-9)和3×10(-10) M，这表明褪黑素受体在PAZ6脂肪细胞中具有功能性表达。褪黑素对cGMP途径的调节进一步支持了MT2受体的功能性表达，因为该途径在人类中被证明对该亚型具有特异性。此外，发现长期用褪黑素处理PAZ6脂肪细胞会降低葡萄糖转运蛋白Glut4的表达以及葡萄糖摄取，而葡萄糖摄取是脂肪细胞代谢的一个重要参数。这些结果表明，褪黑素可能直接作用于人棕色脂肪细胞上的MT2受体，以调节脂肪细胞生理功能。
