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，突变型亨廷顿蛋白（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需的基因表达。这些发现使人们对亨廷顿舞蹈病（HD）线粒体功能障碍的发病机制有了新的认识，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正向调节几种核受体，包括三种PPAR，称为1、3和4。其中，PPAR4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转录因子相互作用因子的无偏筛选，我们确定了PPAR4是一个假定的htt相互作用蛋白。联合ip实验提供了支持这一观点的证据，而转激活实验显示，在Q111/Q111 Hdh敲入小鼠模型中，htt-104Q表达细胞和纹状样神经元中，PPAR4的转激活受到显著抑制。与此同时，最近的研究强调了PPAR4在介导维甲酸促生存作用中的潜在重要性，并提出了一种模型，其中两种不同的类维甲酸结合蛋白（FABP5和CRABP-II）的比例决定了维甲酸是促进细胞存活还是促进细胞死亡。我们已经开始在纹状体和Hdh纹状样细胞中研究这一途径，并注意到FABP5在HD中明显减少。此外，PPAR4被其配体GW501516和全反式维甲酸（ATRA）激活在Q111/Q111纹状样神经元中被减弱。综上所述，我们的研究表明，如果我们的论文是正确的，PPAR4是polyQ-htt神经毒性的靶点，并且提供了多种可处理的治疗靶点。在本项目中，我们将通过追求三个具体目标来确定维甲酸- FABP5 - PPAR4 - PGC-11通路在正常神经健康和HD中的作用。首先，我们将通过评估HD中视黄酸- PPAR4通路功能改变的假设，表征htt - PPAR4相互作用，并测试该通路的调节是否可以挽救Hdh纹状样神经元的线粒体功能障碍。其次，我们将验证PPAR4介导的视黄酸信号改变足以产生HD样神经变性的假设，方法是将我们已经开发的具有纹状体和皮层特异性驱动因子的fxed - stop显性阴性PPAR4 E411P转基因小鼠进行杂交，对纹状体或皮层中改变的基因表达模式进行分类，并确定这些PPAR4靶基因的表达和调控是否发生在HD中。第三，我们将通过尝试用PPAR4-wt转基因小鼠（我们已经开发的）对HD进行基因拯救，评估递送PPAR4激动剂的效果，以及测试递送FABP5的治疗效果，来验证PPAR4转录干扰是HD治疗干预的可行靶点的假设。

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.