CSF/ISF highways for tau brain clearance

 描述(由申请人提供)：单体tau是一种细胞内微管相关蛋白，经历了向tau细丝(神经原纤维缠结(NFTs))不可溶聚集体的渐进转变，这是tau病(如阿尔茨海默病(AD))的特征。最近有研究表明，野生型单体tau从健康青年脑的间质液(ISF)中释放出来，在有利的条件下，可以促进细胞外tau聚集体的形成。然而，单体tau从ISF中清除的机制尚不清楚。在AD中，聚集的tau存在于血管周围间隙，并且tau寡聚体与小动脉相关。在皮质基底部变性中，tau沉积在血管周围，并与星形细胞斑块和簇状星形细胞相关。AD患者脑脊液(CSF)tau水平升高。这些观察结果可能暗示了可能的脑清除途径。由于单体tau是错误折叠和聚集的tau的前体，因此从CSF/ISF中去除它对于减少tau的积累至关重要。最近，淋巴系统被证明在清除神经活动的副产物方面起着重要作用。这一系统包括三条主要途径：(1)蛛网膜下腔脑脊液通过动脉旁间隙流入；(2)依赖星形细胞水通道蛋白4(AQP4)的脑内ISF对流；(3)通过静脉旁清除流出。此外，脑脊液可以通过颈部淋巴从大脑中清除。我们的初步数据显示，单体tau通过淋巴系统和颈淋巴系统从脑脊液和脑实质中清除，并且随着年龄的增长和Aqp4Ko小鼠的减少。然而，短纤维在大脑中保留的时间更长。我们假设，淋巴/淋巴系统对于全脑清除tau至关重要，这些系统中与年龄相关的衰竭导致了tau的积累。有两个目的，1)研究脑脊液和脑内间质干细胞中tau蛋白的清除机制，2)评估衰老和AQP4对tau蛋白从脑中清除的影响。125I-tau的分布和消除动力学将通过使用我们的非侵入性技术并在脑池内注射后用外部计数器记录脑放射性来确定。我们将使用体内实时双光子和共聚焦显微镜来描绘tau、CSF/ISF的交换和清除途径。颈淋巴清除动力学将使用实时的颈部淋巴管和结节的活体成像进行分析。我们预计，数据将显示tau(单体纤维)通过CSF/ISF交换和对流ISF流动以及颈部淋巴被清除。随着年龄的增长和Aqp4-/-小鼠，通过这两条途径的清除量将会减少。由于细胞结合，tau纤维将在大脑中保留更长时间。这些研究可能导致tau清除的全新靶点，通过改善tau和其他有毒分子的淋巴/淋巴清除来减缓甚至防止AD相关的神经认知功能下降。

 DESCRIPTION (provided by applicant): Monomeric tau, an intracellular microtubule-associated protein, undergoes a progressive transition to insoluble aggregates of the tau filaments (neurofibrillary tangles (NFTs), a feature of tauopathies, such as Alzheimer's disease (AD). Recently it was shown that wild type monomeric tau is released into the interstitial fluid (ISF) from healthy normal young brains which, under favorable conditions, could enhance the formation of extracellular tau aggregates. However, the mechanism of monomeric tau clearance from the ISF is unknown. In AD, aggregated tau is present in the perivascular space, and tau oligomers are associated with arterioles. In corticobasal degeneration, tau is deposited around blood vessels and associated with astrocytic plaques and tuft-shaped astrocytes. In AD, levels of cerebrospinal fluid (CSF) tau are increased. These observations may suggest possible clearance routes from brain. Since monomeric tau is the precursor of the misfolded and aggregated tau, its removal from the CSF/ISF is critical in reducing tau accumulation. Recently, the glymphatic system was shown to play a major role in clearance of by-products of neural activity. This system consists of three main pathways: (1) influx of sub-arachnoid CSF via the para-arterial space, (2) astrocytic aquaporin 4 (AQP4)-dependent convective flow of brain ISF, and (3) efflux via para-venous clearance. In addition, CSF can be cleared from brain via the cervical lymph. Our preliminary data show that monomeric tau was cleared from the CSF and from brain parenchyma via the glymphatic and cervical lymphatic systems, and that this was reduced with aging and in Aqp4 ko mice. However, short fibrils were retained longer in brain. We hypothesize that the glymphatic/lymphatic systems are critical for brain-wide clearance of tau and that age-related failure in these systems contributes to its accumulation. There are two aims, 1) Characterization of the tau clearance mechanisms from CSF and brain ISF in mice, and 2) Evaluating the effects of aging and AQP4 on the clearance of tau protein species from brain. The kinetics of 125I-tau distribution and elimination will be determined by using our non-invasive technique and recording brain radioactivity with an external counter after intracisternal injection. We will use in vivo real-time 2-photon and confocal microscopy to delineate the influx of tau, CSF/ISF exchange and clearance pathways. Cervical lymph clearance kinetics will be analyzed using real-time in vivo imaging of the cervical lymphatic vessels and nodes. We expect that the data will show that tau (monomer >fibril) is cleared via CSF/ISF exchange and convective ISF flow, and by the cervical lymph. Clearance via both pathways will be reduced with aging and in Aqp4-/- mice. Tau fibrils will be retained longer in brain due to cellular bindin. These studies may lead to entirely novel targets for tau clearance to slow or even prevent AD related neurocognitive decline by improving glymphatic/lymphatic clearance of tau, and other toxic molecules.