Defective nuclear FGFR1 signaling - a new model for PD

在帕金森病(PD)中，黑质致密部(SNC)多巴胺神经元中成纤维细胞生长因子-2(成纤维细胞生长因子-2)的含量在细胞变性之前就已经耗尽。在SNC中，含量最丰富的是高分子量的未释放的成纤维细胞生长因子-2亚型，它几乎只定位于细胞核。PD患者黑质神经元中核成纤维细胞生长因子-2的功能及其缺失的意义尚不清楚。我们描述了一种新的整合性核FGF41信号通路(INFS)，通过多种细胞外因子和细胞内cAMP和蛋白激酶C调节神经细胞的生长、存活和星形胶质细胞的增殖。这些广泛的功能可能涉及对几个基因程序的调控。这种INFS是通过激活成纤维细胞生长因子-2和成纤维细胞生长因子受体-1(FGFR1)基因，然后将FGFR1和成纤维细胞生长因子-2蛋白直接从细胞质转移到细胞核：核FGFR1，与核糖体S6Kinase-1(RSK-1)相互作用，刺激不同基因的转录。INFS调节培养神经元的轴突和树突生长，以及PC12细胞对6-羟基多巴胺的抵抗。聚乙烯亚胺介导的FGFR1突变型显性阴性基因[FGFR1(TK-)缺失酪氨酸激酶域]体内导入大鼠黑质神经元，可导致表达酪氨酸羟基酶的神经元延迟丢失和纹状体多巴胺耗竭。这表明TGFR1信号对DA神经元的长期存活也是必不可少的，INF受损(即由于核FGF2的耗尽)可能是帕金森病神经元变性的共同原因。为了阐明INFS在大鼠SNCDA神经元存活再生和功能可塑性中的作用，我们将采用PEI介导的FGFR1和RSK-1突变体体内转基因到成年大鼠脑内。这些实验将为常见的帕金森病建立一个新的基于基因转移的模型，并可能为帕金森病和相关的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。其具体目的是：(1)确定FGFR(TK-)在黑质纹状体通路中的时程和特征，并确定FGFR信号受损是否直接在细胞核内与FGFR1(TK-)的作用有关；(2)确定SNC中受核FGFR1调控的基因类型以及活性RSK-1的过表达是否抵消FGFR1(TK-)诱导的基因表达变化和黑质纹状体通路的变性。以及(3)确定直接刺激核FGFR-1信号是否可以减轻神经毒素6-羟基多巴胺引起的黑质纹状体通路的退行性变化和/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.