Presenilin 1 Modulates Lysosome Function and Tau Degradation

阿尔茨海默病(AD)以及其他老年起病的神经退行性疾病的共同特征， 是错误折叠、异常修饰的蛋白质的堆积。在AD中，tau的聚集体是一个经典的 霍尔马克。这些蛋白质堆积形成的一个重要因素是功能障碍。 依赖于溶酶体的降解途径。有趣的是，大多数常染色体显性遗传性家系 AD(FAD)病例是由分泌酶的催化亚单位早老素1(PS1)突变引起的 复合体，这也可能有助于溶酶体的功能。然而，PS1在介导溶酶体中的作用 生物学和tau的清除还没有完全被描述。鉴于之前的研究和我们的初步研究 数据，这一提议的基本前提是，在神经元中，PS1在 调节溶酶体的功能，从而调节tau的周转。溶酶体在维持 蛋白质平衡作为多条降解途径将它们的货物引导到溶酶体进行降解/循环。 溶酶体的活性或细胞内定位的改变参与了慢性粒细胞白血病的发病过程 这些神经退行性疾病。鉴于溶酶体功能对神经元健康的重要性， 了解PS1如何影响溶酶体生物学是非常重要的。关键的知识差距 包括：初级神经元中PS1的缺失如何影响溶酶体的pH，PS1缺失对溶酶体pH的影响 自噬-溶酶体和内酶体-溶酶体融合，PS1耗竭对tau周转和 PS1缺失神经元中溶酶体的再酸化如何影响PS1诱导的溶酶体融合 Tau周转中的缺陷和不足。考虑到这些关键的知识差距，总体上 假设PS1的缺失会导致溶酶体功能、定位和融合的损害 对tau清除量产生负面影响的事件。在这一总体假设的背景下，这一点的具体目标 提议是为了检验假设：(1)PS1在酸化、活性和局部化中起作用 溶酶体和其他降解性小泡在不同的神经元隔间和(2)小泡- 受PS1基因敲除的影响，tau蛋白介导的加工/清除和神经元内定位受到损害。这些 研究将使用原代培养的大鼠皮质神经元进行。总体而言，这是一个变革性的项目 解决了我们科学知识中的重大差距。该提案在将PS1概念化为 溶酶体功能的关键调节因子，因此对蛋白稳定和tau更多有重要贡献 具体地说。此外，在技术上它是创新的，因为我们将使用光遗传驱动的质子泵来 在PS1基因敲除后降低溶酶体的pH以确定维持酸化的溶酶体是否 足以恢复其功能。这些研究的影响将对我们的 了解PS1在通过溶酶体功能调节tau生物学中的作用，从而向一般 神经生物退行性变在衰老中的前景。 。

A common feature of Alzheimer’s disease (AD), as well as other older age onset neurodegenerative diseases, is the accumulation of misfolded, abnormally modified proteins. In AD, aggregates of tau are a classical hallmark. A significant contributing factor to the formation of these proteinaceous accumulations is dysfunction of the lysosome-dependent degradative pathways. Interestingly, the majority of autosomal dominant familial AD (FAD) cases are caused by mutations in presenilin 1 (PS1), the catalytic subunit of the  secretase complex, which also likely facilitates lysosomal function. However, the role of PS1 in mediating lysosome biology and the clearance of tau has not been fully delineated. Given previous studies and our preliminary data, the UNDERLYING PREMISE of this proposal is that in neurons PS1 plays a fundamental role in regulating the function of lysosomes and, thus, tau turnover. Lysosomes play a key role in maintaining proteostasis as multiple degradative pathways direct their cargos to the lysosome for degradation/recycling. Alterations in the activity or intracellular localization of lysosomes contribute to the pathogenic processes of these neurodegenerative diseases. Given the importance of lysosome function to neuron health, understanding how PS1 impacts lysosome biology is of high importance. CRITICAL KNOWLEDGE GAPS include: how depletion of PS1 in primary neurons impacts lysosome pH, the effects of PS1 depletion on autophagosome-lysosome and endosome-lysosome fusion, the impact of PS1 depletion on tau turnover and how re-acidification of lysosomes in neurons with PS1 depleted affects the PS1-induced lysosomal fusion defects and deficiencies in tau turnover. Considering these critical knowledge gaps the OVERALL HYPOTHESIS is that depletion of PS1 leads to impairment of lysosome function, localization and fusion events, which negatively impact tau clearance. In the context of this overall hypothesis, the specific aims of this proposal are to test the hypotheses: (1) that PS1 plays a role in the acidification, activity, and localization of lysosomes and other degradative vesicles within different neuronal compartments and (2) that vesicle- mediated processing/clearance and intraneuronal localization of tau is impaired by knockdown of PS1. These studies will be carried out using primary rat cortical neuron cultures. Overall this a transformative project that addresses significant gaps in our scientific knowledge. The proposal is innovative in conceptualizing PS1 as a key regulator of lysosome function and thus a significant contributor to proteostasis in general and tau more specifically. Further, technically it is innovative as we will be using an optogenetically driven proton pump to decrease the pH of lysosomes after PS1 knockdown to determine if maintaining an acidified lysosome is sufficient to restore its function. The IMPACT of these studies will be a significant contribution to our understanding of the role of PS1 in regulating tau biology via lysosomal function, thus informing general perspectives of neurobiological degeneration in aging. .