The Steroid/thyroid Hormone Receptor Superfamily

类固醇/甲状腺激素受体超家族

• 批准号: 7152655
• 负责人: Vera M Nikodem
• 金额: --
• 依托单位: NATIONAL INSTITUTE OF DIABETES AND DIGESTIVE AND KIDNEY DISEASES
• 依托单位国家: 美国
• 资助国家: 美国
• 起止时间: 至
• 项目状态: 未结题
• 来源: https://reporter.nih.gov/project-details/7152655
• 关键词: alkaline phosphatase; biological signal transduction; body weight; cell differentiation; cell line; cyclic AMP; dopamine; enzyme activity; gene expression; gene mutation; genetic regulation; genetically modified animals; hormone receptor; laboratory mouse; mesencephalon; microarray technology; molecular biology; neurons; neurotransmitter biosynthesis; nuclear receptors; obesity; osteoblasts; small interfering RNA; tetrahydrobiopterin

1. Alterations in dopamine neurotransmission have been implicated in a number of neurological conditions including Parkinson's disease, schizophrenia, attention deficit hyperactivity disorder, and drug addiction. The nuclear orphan receptor Nurr1 is essential for the terminal differentiation of midbrain neurons as we and others showed. The arrest of dopamine neuron precursors in development, by disruption of the Nurr1 gene by homologous recombination in mice, prevents expression of dopamine neuron specific proteins leading to the complete inhibition of neuron transmitter dopamine synthesis. We have identified some genes whose expression is affected by Nurr1. It appears that Nurr1 can function either as a repressor or inducer of the expression of specific genes. Using comparative microarray analysis of RNAs from wild type and Nurr1-null mice prepared from the ventral tegmental area has shown a large decrease in guanosine triphosphate cyclohydrolase (GTPCH) mRNA in Nurr1-null pups, which led to concomitant reduction in BH4 content. Microarray analysis showed 70% reduction in GTPCH expression in the ventral tegmental area of both 12.5-day old Nurr1-null embryos and neonates. Although levels of GTPCH mRNA increased significantly between E12.5 and birth in wild type mice, no such change was seen in the null neonates. The promoter deletional analyses of Nurr1 are underway to identify regions involved in Nurr1 mediated transcription of GTPCH in neuronal cells. 2. Recently, we have studied the role of Nurr1 in osteoblast differentiation. Our results revealed that reduced Nurr1 expression, using Nurr1 siRNA, affected the expression of osteoblast differentiation marker genes; osteocalcin, type one collagen and the activity of alkaline phosphatase. In addition, the expression of those genes was decreased in primary cultured mouse calvarial osteoblasts derived from Nurr1-null mice. Thus, our results suggest that Nurr1 is important for osteoblast differentiation. 3. We have also decided to investigate whether Nurr1 is involved in differentiation of other cell types. Understanding mechanisms involved in regulation of body weight is a very important goal due to the worldwide obesity epidemic. Recently, we discovered that Nurr1-null heterozygous mice have twice as much fat mass when compared to wild type mice when fed with either normal or high fat diet without significant differences in food intake. By hormonal induction, mouse embryonic fibroblasts (MEF) generated from Nurr1-null mice have shown increased rate of adipocyte differentiation as extimated by accumulation of oil droplets in contrast to MEF prepared from wild type littermates. When Nurr1 was constitutively overexpressed, using retroviral infection in MEF-Nurr1-null, the rate of adipogenesis was comparable to that observed in MEF wild type. In agreement with these results, the level of molecular markers of adipogenesis C/EBP alpha and PPAR gamma was increased in the absence and decreased in the presence of Nurr1, respectively. These results suggest that Nurr1 functions as a repressor of adipogenesis in vivo and in vitro and might play a role in adipogenesis differentiation linked to obesity.

1.多巴胺神经传递的改变与许多神经疾病有关，包括帕金森氏症、精神分裂症、注意力缺陷多动障碍和药物成瘾。正如我们和其他人所表明的那样，核孤儿受体Nurr1对于中脑神经元的末端分化是必不可少的。在小鼠中，通过同源重组破坏Nurr1基因，阻止发育中的多巴胺神经元前体，阻止多巴胺神经元特异性蛋白的表达，导致神经递质多巴胺合成的完全抑制。我们已经确定了一些表达受Nurr1影响的基因。似乎Nurr1既可以作为特定基因表达的抑制因子，也可以作为特定基因表达的诱导因子。通过对野生型和Nurr1缺失小鼠的RNA进行比较微阵列分析，从腹侧被盖区制备的RNA显示，Nurr1缺失幼鼠的鸟苷三磷酸环水解酶(GTPCH)mRNA大幅下降，从而导致BH4含量的降低。基因芯片分析显示，在12.5天大的Nurr1基因缺失的胚胎和新生儿的腹侧被盖区，GTPCH的表达降低了70%。虽然野生型小鼠的GTPCH mRNA水平在胚胎12.5至出生期间显著升高，但在未出生的小鼠中未见这种变化。Nurr1的启动子缺失分析正在进行中，以确定在神经细胞中Nurr1介导的GTPCH转录所涉及的区域。 2.最近，我们研究了Nurr1在成骨细胞分化中的作用。我们的结果表明，利用Nurr1 siRNA降低Nurr1的表达，会影响成骨细胞分化标志基因、骨钙素、1型胶原的表达和碱性磷酸酶的活性。此外，在来自Nurr1缺失小鼠的原代培养的小鼠颅骨成骨细胞中，这些基因的表达减少。因此，我们的结果表明Nurr1在成骨细胞分化中起重要作用。 3.我们还决定研究Nurr1是否参与了其他类型细胞的分化。由于全球肥胖症的流行，了解体重调节机制是一个非常重要的目标。最近，我们发现，当以正常或高脂肪饮食喂养而食物摄入量没有显著差异时，Nurr1基因缺失杂合子小鼠的脂肪质量是野生型小鼠的两倍。通过激素诱导，由Nurr1基因缺失的小鼠产生的小鼠胚胎成纤维细胞(MEF)显示出比野生型小鼠制备的MEF更高的脂肪细胞分化率，据估计是由于油滴的积累。利用逆转录病毒感染MEF-Nurr1缺失型，当Nurr1结构性过表达时，成脂率与观察到的MEF野生型相当。与这些结果一致的是，成脂C/EBPα和PPAR-γ的分子标志物水平在没有Nurr1的情况下分别增加，在Nurr1存在的情况下分别降低。这些结果表明，Nurr1在体内和体外都是脂肪生成的抑制因子，可能在与肥胖相关的脂肪生成分化中发挥作用。