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

描述（由申请人提供）：本提案的重点是确定自噬在选择性清除病理性tau中的作用以及Nrf2途径在调节这一过程中的作用。我们还将探索潜在的治疗策略，以增加病理性tau蛋白的清除，并防止由毒性tau蛋白引起的细胞功能障碍。在阿尔茨海默病（AD）中，脑tau在Asp421 （tau-¿C）处异常截断，以及异常磷酸化，这两种修饰都可能促进毒性构象的形成，导致神经元功能受损。因此，选择性清除这些病理形式的tau的策略可能为治疗AD提供潜在的治疗方法。先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主要通过巨噬清除。也有研究表明，Ser262/356位点磷酸化的tau蛋白可能通过自噬途径被优先降解，并且有证据表明自噬系统可能在AD大脑中受到损害，这可能是病理形式tau蛋白积累的一个因素。Nrf2通路在调节细胞存活基因的表达中起着核心作用。Nrf2被氧化应激以及其他应激源激活，从而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，在表达tau-¿C的细胞中，与表达全长tau的细胞相比，基础Nrf2活性较低；然而Nrf2仍然可以在tau- C细胞中被显著激活。在初步实验中，我们发现Nrf2通路的激活导致tau-¿C水平下降，但全长tau没有下降，这表明自噬被激活。有趣的是，我们还发现Nrf2-/-小鼠中存在异常磷酸化tau蛋白和不溶性tau蛋白的积累。AD小鼠脑核Nrf2水平降低，AD小鼠模型中外源性Nrf2的表达或Nrf2通路的激活可减轻学习缺陷。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优先被自噬降解，Nrf2途径的激活可能在一定程度上通过促进病理形式的tau的降解而对AD产生有益的影响。本提案的具体目的是检验以下假设：1。这种特定病理形式的tau蛋白优先针对自噬途径进行降解。2. Nrf2通路在促进病理形式的tau蛋白降解中起作用。3. Nrf2或自噬途径的激活导致表达病理形式tau的细胞存活增加。

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.