Autophagy, p62 and the Nrf2 Intersect to Protect Against Tau Toxicity

描述（由申请人提供）：该提案的重点是确定自噬在选择性清除病理性tau蛋白中的作用以及Nrf 2通路在调节该过程中的作用。我们还将探索潜在的治疗策略，以增加病理性tau的清除率，并防止由毒性形式的tau引起的细胞功能障碍。在阿尔茨海默病（AD）中，脑tau蛋白在Asp 421（tau-<$C）处被异常截短，并且被异常磷酸化，这两种修饰都可能促进导致神经元功能受损的毒性构象的形成。因此，导致选择性清除这些病理形式的tau的策略可以为治疗AD提供潜在的治疗方法。以前我们提供的证据表明，全长tau蛋白优先被蛋白酶体降解，而tau-C主要通过宏自噬清除。也有研究结果表明，在Ser 262/356磷酸化的tau可能优先通过自噬途径降解，并且有证据表明，自噬系统可能在AD脑中受损，这可能是病理形式的tau积累的一个促成因素。 Nrf 2通路在调节细胞存活基因的表达中起着核心作用。Nrf 2被氧化应激以及其他应激源激活，这导致细胞保护基因的表达，包括参与自噬途径的蛋白质。我们发现，与表达全长tau的细胞相比，表达tau-<$C的细胞中的基础Nrf 2活性较低;然而，Nrf 2在tau-<$C细胞中仍然可以被显著激活。在初步实验中，我们发现Nrf 2通路的激活导致tau-κ C水平降低，但不导致全长tau蛋白水平降低，这表明自噬激活。有趣的是，我们还发现，在Nrf 2-/-小鼠中，存在异常磷酸化tau以及不溶性tau物质的积累。在AD中，脑核Nrf 2水平降低，并且在AD小鼠模型中外源性Nrf 2的表达或Nrf 2途径的激活减弱了学习缺陷。考虑到这些和其他研究，我们的总体假设是病理修饰形式的tau优先通过自噬降解，并且Nrf 2途径的激活可能部分通过促进病理形式的tau的降解而在AD中具有有益作用。本文的具体目的是检验以下假设：1. tau的特定病理形式优先针对自噬途径进行降解。2. Nrf 2通路在促进病理形式的tau的降解中起作用。3. Nrf 2或自噬途径的激活导致表达病理形式的tau的细胞的存活增加。 公共卫生相关性：阿尔茨海默病是老年痴呆症最常见的原因。在阿尔茨海默病中，tau蛋白的脑病理变化是疾病过程的中心。越来越多的证据表明，生理和病理形式的tau可以被细胞差异化地清除。我们实验室和其他人最近的研究表明，tau蛋白的异常磷酸化和/或切割形式肯定会被自噬优先清除。此外，有证据表明，在阿尔茨海默病中，自噬过程可能受损。因此，选择性上调自噬和/或将病理形式的tau靶向自噬途径的药理学干预具有治疗阿尔茨海默病的治疗益处的潜力。

DESCRIPTION (provided by applicant): The focus of this proposal is on determining the role of autophagy in the selective clearance of pathological tau and the role of the Nrf2 pathway in regulating this process. We will also be exploring potential therapeutic strategies to both increase the clearance of pathological tau and protect against cellular dysfunction caused by toxic forms of tau. In Alzheimer disease (AD) brain tau is abnormally truncated at Asp421 (tau-¿C), as well as being abnormally phosphorylated, and both of these modifications likely facilitate the formation of toxic conformations that result in compromised neuronal function. Therefore strategies that result in selective clearance of these pathological forms of tau may provide a potential therapeutic approach for the treatment of AD. Previously we provided evidence that full length-tau is preferentially degraded by the proteasome, while tau-¿C is cleared predominantly by macroautophagy. There are also findings suggesting that tau phosphorylated at Ser262/356 may be preferentially degraded through the autophagy pathway, and there is evidence that the autophagy system may be compromised in AD brain which could be a contributing factor to the accumulation of pathological forms of tau. The Nrf2 pathway plays a central role in regulating the expression of cell survival genes. Nrf2 is activated by oxidative stress, as well as other stressors, which results in the expression of cytoprotective genes, including proteins involved in the autophagy pathway. We found that basal Nrf2 activity is lower in cells expressing tau-¿C compared to cells expressing full-length tau; however Nrf2 can still be significantly activated in the tau-¿C cells. In preliminary experiments we found that activation of the Nrf2 pathway resulted in decreased levels of tau-¿C but not of full-length tau, suggesting an activation of autophagy. Intriguingly, we also found that in Nrf2-/- mice there was an accumulation of abnormally phosphorylated tau, as well as insoluble tau species. In AD brain nuclear Nrf2 levels are decreased, and expression of exogenous Nrf2 or activation of the Nrf2 pathway in AD mouse models attenuates learning deficits. Considering these and other studies our overall hypothesis is that pathologically modified forms of tau are preferentially degraded by autophagy, and that activation of the Nrf2 pathway is likely to have beneficial effects in AD in part by facilitating the degradation of pathological forms of tau. The specific aims of this proposal are t test the following hypotheses: 1. That specific pathological forms of tau are preferentially targeted to the autophagy pathway for degradation. 2. That the Nrf2 pathway plays a role in facilitating the degradation of pathological forms of tau. 3. That activation of the Nrf2 or autophagy pathway results in increased survival of cells that express pathological forms of tau. PUBLIC HEALTH RELEVANCE: Alzheimer disease is the most common cause of older age onset dementia. In the Alzheimer disease brain pathological changes in the tau protein are central to the disease process. There is increasing evidence that physiological and pathological forms of tau may be differentially cleared by the cell. Recent studies from our lab and others have suggested that certainly abnormally phosphorylated and/or cleaved forms of tau are preferentially cleared by autophagy. In addition there is evidence to suggest that in Alzheimer disease autophagic processes may be impaired. Thus, pharmacological interventions that selectively upregulate autophagy and/or target pathological forms of tau to autophagy pathway have the potential of being therapeutically beneficial for treating Alzheimer disease.