Defective nuclear FGFR1 signaling - a new model for PD

在帕金森病（PD）中，在黑质丘脑部（Snc）中的多巴胺神经元中的成纤维细胞生长因子-2（FGF-2）的含量在细胞变性之前变得耗尽。在Snc中，最丰富的是FGF-2的HMW非释放同种型，其几乎仅定位于细胞核中。核FGF-2的功能及其在PD患者Snc神经元中缺失的意义仍然未知。我们已经描述了一种新的整合性核FGF 41信号传导（INFS）途径，通过该途径，多种细胞外因子和细胞内cAMP和蛋白激酶C调节神经元细胞的生长和存活以及星形胶质细胞的增殖。这些广泛的功能可能涉及几个基因程序的调节。这种INFS是通过FGF-2和FGF受体-1（FGFR 1）基因的激活启动的，随后FGFR 1和FGF-2蛋白直接从细胞质转移到细胞核：核FGFR 1与核糖体S6激酶-1（RSK-1）相互作用并刺激不同基因的转录。INFS调节培养神经元中轴突和树突的生长以及PC 12细胞中对6-羟基多巴胺的抗性。聚乙烯亚胺介导的显性阴性的FGFR 1突变体[FGFR 1（TK-）缺乏酪氨酸激酶结构域]体内转染到大鼠Snc引起酪氨酸羟化酶表达神经元的延迟损失和纹状体多巴胺的消耗。这表明TGFR 1信号传导对于DA神经元的长期存活也是必不可少的，并且受损的INFS（即由于核FGF-2的耗尽）可能是PD中神经元变性的常见潜在原因。为了阐明INFS在大鼠Snc DA神经元的存活再生和功能可塑性中的作用，我们将使用PEI介导的FGFR 1和RSK-1突变体在体内转染到成年大鼠脑中。这些实验将为常见PD建立一种新的基于基因转移的模型，并可能为PD和相关神经退行性疾病的基因转移和药物治疗确定新的分子靶点。具体目标是：（1）确定时间进程并表征由FGFR（TK-）转染引起的黑质纹状体途径中的神经退行性变化，并确定直接在细胞核中受损的FGFR信号传导是否负责观察到的FGFR 1（TK-）的作用，（2）确定大鼠Snc中受核FGFR 1调控的基因类型，以及活性RSK-1的过表达是否抵消了FGFR 1（TK）的作用。诱导的基因表达变化和黑质纹状体途径的变性，和（3）确定核FGFR-1信号传导的直接刺激是否可以减弱由神经毒素6-羟基多巴胺引起的黑质纹状体途径的变性变化和/或促进再生。

In Parkinson Disease (PD) the content of fibroblast growth factor-2 (FGF-2) in dopamine neurons in substantia nigra pars compacta (Snc) becomes depleted prior to cell degeneration. In the Snc the most abundant are the HMW non-released isoforms of FGF-2 that localize almost exclusively in the cell nucleus. Functions of nuclear FGF-2 and the significance of its depletion in Snc neurons in PD patients remain unknown. We have described a new Integrative Nuclear FGF41 Signaling (INFS) pathway through which diverse extracellular factors and intracellular cAMP and Protein Kinase C regulate growth and survival of neuronal cells and proliferation of astrocytes. These broad functions are likely to involve regulation of several gene programs. This INFS is initiated by the activation of the FGF-2 and FGF receptor-1 (FGFR1) genes followed by transfer of FGFR1 and FGF-2 proteins directly from the cytoplasm to the cell nucleus: Nuclear FGFR1, interacts with Ribosomal S6 Kinase-1 (RSK-1) and stimulate transcription of different genes. The INFS regulates axonal and dendritic growth in cultured neurons and resistance to 6-hydroxydopamine in PC12 cells. Polyetheleneimine-mediated in vivo transfection of dominant negative of the FGFR1 mutant [FGFR1(TK-) lacking tyrosine kinase domain] into the rat Snc caused a delayed loss of tyrosine hydrosxylase expressing neurons and depletion of striatal dopamine. This indicated that TGFR1 signaling is essential also for the long term survival of DA neurons and impaired INFS (i.e. due to a depletion of nuclear FGF-2) may be a common underlying cause for the neuronal degeneration in PD. To elucidate the role of INFS in survival regeneration and functional plasticity of the rat Snc DA neurons, we will use PEI-mediated transfection of FGFR1 and RSK-1 mutants, in vivo, into the adult rat brain. These experiments will establish a new, gene- transfer-based model for common PD and may identify new molecular targets for gene-transfer and pharmacological therapies for the PD and related neurodegenerative disorders. The specific Aims are: (1) To determine time courser and characterize neurodegenerative changes in the nigrostriatal pathway caused by transfection of FGFR (TK-) and establish whether impaired FGFR signaling directly in the cell nucleus is responsible for the observed effects of FGFR1 (TK-), (2) To identify types of genes regulated by nuclear FGFR1 in rat Snc and whether over- expression of active RSK-1 counteracts the FGFR1(TK)-induced changes in gene expression and degeneration of the nigrostriatal pathway, and (3) To determine whether direct stimulation of nuclear FGFR-1 signaling may attenuate degenerative changes in the nigrostriatal pathway caused by neurotoxin 6-hydroxydopamine and/or promote regeneration.