The PPAR-delta pathway in neural function and Hungtington's disease neuropatholog

描述（由申请人提供）：我们实验室和其他实验室最近发表的研究表明，突变亨廷顿蛋白（htt）介导的PGC-11转录失调破坏了纹状体正常线粒体功能和能量代谢所必需的基因表达。这些发现导致了对亨廷顿病（HD）中线粒体功能障碍发病机制的新理解，将核PGC-11转录干扰与线粒体功能改变联系起来。作为一种转录共激活因子，PGC-11积极调节几种核受体，包括三种PPAR，称为1，3和4。其中，PPAR 4是CNS中表达最丰富的亚型，尽管其在该组织中的功能相关性尚未确定。基于对htt转录因子相互作用物的无偏筛选，我们鉴定PPAR 4为推定的htt相互作用蛋白。Co-ip实验提供了支持这一点的证据，并且反式激活测定显示在来自Q111/Q111 Hdh敲入小鼠模型的htt-104 Q表达细胞和纹状体样神经元中PPAR 4反式激活的显著抑制。与此同时，最近的工作突出了PPAR 4介导视黄酸促存活作用的潜在重要性，并且已经提出了一种模型，其中两种不同的类维生素A结合蛋白（FABP 5和CRABP-II）的比例决定视黄酸促进细胞存活还是细胞死亡。我们已经开始在纹状体和Hdh纹状体样细胞中研究这一通路，并注意到HD中FABP 5显著减少。此外，在Q111/Q111纹状体样神经元中，其配体GW 501516和全反式维甲酸（ATRA）对PPAR 4的反式激活作用减弱。综上所述，我们的研究表明，PPAR 4是polyQ-htt神经毒性的靶点，如果我们的论文是正确的，则提供了各种易于处理的治疗靶点。 在这个项目中，我们将确定视黄酸-FABP 5-PPAR 4- PGC-11通路在正常神经健康和HD中的作用，通过追求三个特定的目标。首先，我们将通过评估HD中类维生素A结合蛋白的表达，表征htt-PPAR 4相互作用，并测试该途径的调节是否可以挽救Hdh纹状体样神经元中的线粒体功能障碍，来测试改变的视黄酸-PPAR 4途径功能是HD发病机制的基础的假设。第二，我们将通过交叉阻断-STOP显性阴性PPAR 4 E411 P转基因小鼠来验证PPAR 4介导的视黄酸信号传导改变足以产生HD样神经变性的假设（我们已经开发了）与纹状体和皮质特异性驱动程序，编目纹状体或皮质中改变的基因表达模式，并确定这些PPAR 4靶基因的表达和调节是否在HD中发生改变。第三，我们将通过尝试用PPAR 4-wt转基因小鼠（我们已经开发的）对HD进行遗传拯救，评估递送PPAR 4激动剂的效果，并测试递送FABP 5的治疗功效，来测试PPAR 4转录干扰是HD中治疗干预的可行靶标的假设。 公共卫生相关性：对亨廷顿病（HD）和其他相关神经退行性疾病的研究已经强调了线粒体功能和生物能量学在维持正常神经功能中的重要性。在这个项目中，我们将研究一个令人兴奋的假设，即PPAR 4参与维持神经元能量的产生，PPAR 4的功能改变有助于HD神经变性。如果PPAR 4参与这种神经系统疾病，那么将测试增强PPAR 4功能的易处理疗法，因为已经开发了PPAR 4的高度选择性和强大的药理学激动剂并用于人类，并且PPAR 4介导响应于视黄酸的促存活信号传导。

DESCRIPTION (provided by applicant): Recent published studies by our laboratory and others have shown that mutant huntingtin (htt)-mediated transcription dysregulation of PGC-11 disrupts expression of genes necessary for normal mitochondrial function and energy metabolism in the striatum. These findings led to a new understanding of the pathogenesis of mitochondrial dysfunction in Huntington's disease (HD), linking nuclear PGC-11 transcription interference with altered mitochondrial function. As a transcription co-activator, PGC-11 positively modulates several nuclear receptors, including the three PPAR's, termed 1, 3, and 4. Of these, PPAR4 is the most abundantly expressed subtype in the CNS, although its functional relevance in this tissue is yet to be defined. Based upon an unbiased screen for htt transcription factor interactors, we identified PPAR4 as a putative htt- interacting protein. Co-ip experiments provided evidence in support of this, and transactivation assays show significant inhibition of PPAR4 transactivation in htt-104Q expressing cells and in striatal-like neurons from the Q111/Q111 Hdh knock-in mouse model. At the same time, recent work has highlighted the potential importance of PPAR4 for mediating the pro-survival effects of retinoic acid, and a model has been proposed in which the ratio of two different retinoid binding proteins (FABP5 and CRABP-II) determines whether retinoic acid promotes cellular survival or cell death. We have begun to study this pathway in the striatum and in Hdh striatal-like cells, and have noted a marked decrease in FABP5 in HD. Furthermore, PPAR4 transactivation by its ligand GW501516 and by all-trans-retinoic acid (ATRA) is blunted in Q111/Q111 striatal-like neurons. Taken together, our studies suggest that PPAR4 is a target of polyQ-htt neurotoxicity, and offer a variety of tractable therapeutic targets, if our thesis is correct. In this project, we will determine the role of the retinoic acid - FABP5 - PPAR4 - PGC-11 pathway in normal neural health and in HD through the pursuit of three specific aims. First, we will test the hypothesis that altered retinoic acid - PPAR4 pathway function underlies HD pathogenesis by evaluating retinoid binding protein expression in HD, characterizing the htt - PPAR4 interaction, and testing if modulation of this pathway can rescue mitochondrial dysfunction in Hdh striatal-like neurons. Second, we will test the hypothesis that altered PPAR4-mediated retinoic acid signaling is sufficient to produce HD-like neurodegeneration by crossing floxed-STOP dominant-negative PPAR4 E411P transgenic mice (that we have already developed) with striatum- and cortex-specific drivers, cataloguing altered gene expression patterns in the striatum or cortex, and determining if altered expression and regulation of these PPAR4 target genes occur in HD. Third, we will test the hypothesis that PPAR4 transcription interference is a viable target for therapeutic intervention in HD by attempting a genetic rescue of HD with PPAR4-wt transgenic mice (that we have already developed), evaluating the effect of delivering PPAR4 agonists, and testing the therapeutic efficacy of delivery of FABP5. PUBLIC HEALTH RELEVANCE: Studies of Huntington's disease (HD) and other related neurodegenerative disorders have highlighted the importance of mitochondrial function and bioenergetics in the maintenance of normal neural function. In this project, we will examine the exciting hypothesis that PPAR4 is involved in the maintenance of neuronal energy generation and that altered function of PPAR4 contributes to HD neurodegeneration. If PPAR4 is involved in this neurological disease, then tractable therapies to boost PPAR4 function would be tested, as highly selective and powerful pharmacological agonists for PPAR4 have been developed and are in use in humans, and PPAR4 mediates pro-survival signaling in response to retinoic acid.