The Steroid/thyroid Hormone Receptor Superfamily

1.多巴胺神经传递的改变与许多神经系统疾病有关，包括帕金森病、精神分裂症、注意缺陷多动障碍和药物成瘾。正如我们和其他人所展示的，核孤儿受体Nurr1对于中脑神经元的终末分化至关重要。通过在小鼠中同源重组破坏Nurr1基因，在发育中阻滞多巴胺神经元前体，阻止多巴胺神经元特异性蛋白的表达，导致神经元递质多巴胺合成的完全抑制。我们已经确定了一些基因的表达受Nurr1。Nurr1似乎可以作为特定基因表达的阻遏物或诱导物发挥作用。使用比较微阵列分析的RNA从野生型和Nurr1-null小鼠制备的腹侧被盖区显示了大量的减少鸟苷三磷酸环化水解酶（GTPCH）的mRNA在Nurr1-null幼崽，这导致了伴随减少BH 4含量。微阵列分析显示，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表达减少了70%。虽然GTPCH mRNA水平在野生型小鼠E12.5和出生之间显著增加，但在无效新生儿中没有观察到这种变化。Nurr1的启动子缺失分析正在进行中，以确定参与Nurr1介导的神经元细胞中GTPCH转录的区域。 2.最近，我们研究了Nurr1在成骨细胞分化中的作用。我们的研究结果表明，减少Nurr1的表达，使用Nurr1 siRNA，影响成骨细胞分化标记基因的表达;骨钙素，1型胶原和碱性磷酸酶的活性。此外，这些基因的表达减少，在原代培养的小鼠颅骨成骨细胞来自Nurr1基因敲除小鼠。因此，我们的研究结果表明，Nurr1是重要的成骨细胞分化。 3.我们还决定研究Nurr1是否参与其他细胞类型的分化。由于肥胖症在世界范围内流行，了解体重调节机制是一个非常重要的目标。最近，我们发现，Nurr1基因缺失的杂合子小鼠的脂肪量是野生型小鼠的两倍，当喂食正常或高脂肪饮食时，食物摄入量没有显着差异。通过激素诱导，从Nurr1缺失小鼠产生的小鼠胚胎成纤维细胞（MEF）显示出脂肪细胞分化的增加速率，这与从野生型同窝出生小鼠制备的MEF相比，由油滴的积累所证实。当Nurr1组成型过表达时，使用逆转录病毒感染MEF-Nurr1-null，脂肪形成率与在MEF野生型中观察到的相当。与这些结果一致，脂肪形成的分子标志物C/EBP α和PPAR γ的水平分别在Nurr1不存在和存在的情况下增加和减少。这些结果表明，Nurr1在体内和体外作为脂肪生成的抑制因子发挥作用，并可能在与肥胖相关的脂肪生成分化中发挥作用。

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.