Sarkar Sumit, Lechan Ronald M
Tupper Research Institute and Department of Medicine, Division of Endocrinology, Diabetes, Metabolism and Molecular Medicine, Tufts-New England Medical Center, Boston, Massachusetts 02111, USA.
Endocrinology. 2003 Jan;144(1):281-91. doi: 10.1210/en.2002-220675.
Neuropeptide Y (NPY) has a potent inhibitory effect on TRH gene expression in the paraventricular nucleus (PVN) and contributes to the fall in circulating thyroid hormone levels during fasting mediated by a reduction in serum leptin levels. Because alpha-MSH activates the TRH gene by increasing the phosphorylation of CREB in the nucleus of these neurons, we raised the possibility that at least one of the mechanisms by which NPY reduces TRH mRNA in hypophysiotropic neurons is by antagonizing the ability of alpha-MSH to phosphorylate CREB. As NPY increases CRH mRNA in the hypothalamus, we further determined whether intracerebroventricular (i.c.v.) administration of NPY regulates the phosphorylation of CREB in hypophysiotropic CRH neurons. NPY [10 micro g in artificial CSF (aCSF)] was administered into the lateral ventricle i.c.v. 30 min before the i.c.v. administration of aCSF or alpha-MSH (10 micro g in aCSF), the latter in a dose previously demonstrated to increase proTRH mRNA and phosphorylate CREB in TRH neurons. By double-labeling immunocytochemistry, only few TRH neurons in the PVN contained phosphoCREB (PCREB) in animals treated only with aCSF (4 +/- 0.2%) or with NPY followed by aCSF (9.7 +/- 2.5), whereas alpha-MSH-infused animals dramatically increased the percentage of TRH neurons containing PCREB (75.3 +/- 6.9%). Pretreatment with NPY before alpha-MSH infusion, however, significantly reduced the percentage of TRH neurons containing PCREB (40.8 +/- 3.5%) compared with alpha-MSH infused animals (P = 0.01). Only 12.2 +/- 0.9% of CRH neurons of the medial parvocellular neurons contained PCREB nuclei in vehicle-treated animals, whereas 30 min following NPY infusion, the number of CRH neurons containing PCREB increased dramatically to 88 +/- 2.9%. Whereas alpha-MSH infusion increased the percentage of CRH neurons that contained PCREB to 56 +/- 2.2% compared with control, animals pretreated with NPY further increased the number of CRH neurons colocalizing with PCREB to 87 +/- 2.5%. These data demonstrate a functional interaction between NPY and alpha-MSH in the regulation of proTRH neurons in the PVN, suggesting that NPY can antagonize alpha-MSH induced activation of the TRH gene by interfering with melanocortin signaling at the postreceptor level, preventing the phosphorylation of CREB. In contrast, NPY infusion increases the phosphorylation of CREB in CRH neurons, indicating that NPY has independent effects on discrete populations of neurons in the PVN, presumably mediated through different signaling mechanisms.
神经肽Y（NPY）对室旁核（PVN）中的促甲状腺激素释放激素（TRH）基因表达具有强大的抑制作用，并在禁食期间血清瘦素水平降低介导的循环甲状腺激素水平下降中起作用。由于α-促黑素（α-MSH）通过增加这些神经元细胞核中CREB的磷酸化来激活TRH基因，我们提出了一种可能性，即NPY降低促垂体神经元中TRH mRNA的机制至少有一种是通过拮抗α-MSH使CREB磷酸化的能力。由于NPY增加下丘脑促肾上腺皮质激素释放激素（CRH）mRNA的表达，我们进一步确定脑室内（i.c.v.）注射NPY是否调节促垂体CRH神经元中CREB的磷酸化。在i.c.v.注射人工脑脊液（aCSF）或α-MSH（10μg溶于aCSF）前30分钟，将NPY[10μg溶于aCSF]i.c.v.注入侧脑室，后者的剂量先前已证明可增加TRH神经元中proTRH mRNA的表达并使CREB磷酸化。通过双重标记免疫细胞化学，仅用aCSF处理（4±0.2%）或用NPY接着用aCSF处理（9.7±2.5%）的动物中，PVN中只有少数TRH神经元含有磷酸化CREB（pCREB），而注入α-MSH的动物中含有pCREB的TRH神经元百分比显著增加（75.3±6.9%）。然而，在注入α-MSH前用NPY预处理，与注入α-MSH的动物相比，含有pCREB的TRH神经元百分比显著降低（40.8±3.5%）（P=0.01）。在溶剂处理的动物中，内侧小细胞神经元的CRH神经元中只有12.2±0.9%含有pCREB细胞核，而在注入NPY后30分钟，含有pCREB的CRH神经元数量急剧增加至88±2.9%。与对照相比，注入α-MSH使含有pCREB的CRH神经元百分比增加至56±2.2%，用NPY预处理的动物进一步使与pCREB共定位的CRH神经元数量增加至87±2.5%。这些数据表明NPY与α-MSH在调节PVN中proTRH神经元方面存在功能相互作用，提示NPY可通过在受体后水平干扰黑皮质素信号传导，阻止CREB磷酸化，从而拮抗α-MSH诱导的TRH基因激活。相反，注入NPY增加CRH神经元中CREB的磷酸化，表明NPY对PVN中不同神经元群体具有独立作用，可能是通过不同的信号传导机制介导的。
