Polarity determinants in endolysosomal trafficking and proteostasis: Implications for Alzheimer's disease pathogenesis

项目摘要 绝大多数阿尔茨海默病(AD)是散发性的，年龄是最大的危险因素。还没有 能够驱动AD发病过程的神经元内与年龄相关的变化仍然难以捉摸。有趣的是， 衰老过程和细胞极性之间存在着复杂的联系。观察到极性的失调。 衰老过程中的许多细胞环境，如上皮屏障通透性增加，缺陷不对称 干细胞分裂和癌症发病率的增加。然而，无论大脑老化和阿尔茨海默氏症 由极性失调引起的疾病尚不清楚。我们实验室的研究主要集中在 在神经元发育和退化中分割有缺陷的(PAR)极性蛋白。有趣的是，我们的 最近的研究表明，Par3在AD的发病机制中起着关键作用。AD的特点是有斑块 由β-淀粉样蛋白(A-β)组成，它是由淀粉样前体蛋白(APP)经β- 和γ-分泌酶。β生成的限速步骤是APP和它的β分泌酶的融合 BACE1.我们发现，Par3的表达在中年时显著减少，并且Par3的缺失在 人类的AD大脑。此外，Par3耗尽导致APP和BACE1融合显著增加。 出乎意料的是，我们发现在没有Par3的情况下，Aβ在细胞内积累。进一步的研究表明，这是 由自噬小体清除缺陷引起。值得注意的是，自噬小体和其他 自噬空泡也是阿尔茨海默病大脑的特征。因此，这些令人兴奋的数据导致了我们的 假设衰老大脑中Par3的缺失通过靶向APP/BACE1促进AD进展 收敛和自噬。这些过程的失调将导致Aβ在细胞内积聚， 对神经元有很强的毒性。我们将通过两个目标来检验我们的假设。在目标1中，我们将阐明 PAR3调控APP和BACE1融合及细胞内Aβ积聚的机制在AIM 2，我们将研究Par3调节自噬和溶酶体功能的机制。我们将使用 结合BIFC，PAR蛋白活性的光遗传操作，以及前脑的活体分析- 特定的Par3条件性基因敲除小鼠。总之，我们提议的研究将建立分子 PAR极性蛋白参与AD发病机制的研究。这一结果将揭示 以衰老为主要危险因素的散发性阿尔茨海默病的发病机制 常见功能。

Project Summary The vast majority of Alzheimer’s disease (AD) is sporadic, with aging being the biggest risk factor. Yet age-related changes within neurons that can drive the AD pathogenic process remain elusive. Intriguingly, there is an intricate link between the aging process and cell polarity. Dysregulation of polarity is observed in many cellular contexts during aging, such as increased permeability of epithelial barriers, defective asymmetric division of stem cells and increased frequency of cancer. However, whether brain aging and Alzheimer’s disease result from polarity dysregulation is unknown. Research in our laboratory has focused on the partitioning defective (Par) polarity proteins in neuronal development and degeneration. Interestingly, our recent studies point to a key role for Par3 in the pathogenesis of AD. AD is characterized by plaques composed of β-amyloid (Aβ), which is derived from amyloid precursor protein (APP) through cleavage by β- and γ-secretases. The rate-limiting step of Aβ generation is the convergence between APP and its β-secretase BACE1. We found Par3 expression is significantly reduced by middle-age, and loss of Par3 is common in human AD brains. In addition, Par3 depletion causes a significant increase in APP and BACE1 convergence. Unexpectedly, we found Aβ accumulates intracellularly in the absence of Par3. Further studies suggest this is caused by defective autophagosome clearance. Remarkably, accumulation of autophagosomes and other autophagic vacuoles is also characteristic of the AD brain. Thus, these exciting data have led to our hypothesis that loss of Par3 in the aging brain promotes AD progression by targeting both APP/BACE1 convergence and autophagy. Dysregulation of these processes will lead to intracellular Aβ accumulation, which is highly toxic to neurons. We will test our hypothesis through two aims. In Aim 1, we will elucidate the mechanism by which Par3 regulates APP and BACE1 convergence and intracellular Aβ accumulation. In Aim 2, we will examine the mechanism by which Par3 regulates autophagy and lysosome functions. We will use a combination of BiFC, optogenetic manipulation of Par protein activity, as well as in vivo analysis in forebrain- specific Par3 conditional knockout mice. Together, our proposed studies will establish the molecular mechanisms by which Par polarity proteins are involved in AD pathogenesis. The results will shed light on the mechanism of sporadic AD in which aging is the major risk factor and polarity dysregulation may be the common feature.