CSF/ISF highways for tau brain clearance

 描述（由申请人提供）：单体tau，一种细胞内微管相关蛋白，经历向tau细丝的不溶性聚集体（神经元缠结（NFT），tau蛋白病如阿尔茨海默病（AD）的特征）的渐进性转变。最近显示，野生型单体tau从健康的正常年轻脑释放到间质液（ISF）中，在有利的条件下，其可以增强细胞外tau聚集体的形成。然而，单体tau从ISF清除的机制尚不清楚。在AD中，聚集的tau存在于血管周围空间中，并且tau寡聚体与小动脉相关。在皮质基底节变性中，tau蛋白沉积在血管周围，并与星形胶质细胞斑块和簇状星形胶质细胞相关。在AD中，脑脊液（CSF）tau水平升高。这些观察结果可能表明可能的脑清除途径。由于单体tau是错误折叠和聚集的tau的前体，因此将其从CSF/ISF中去除对于减少tau积累至关重要。最近，胶质淋巴系统被证明在清除神经活动的副产物中发挥重要作用。该系统由三个主要途径组成：（1）蛛网膜下CSF经由动脉旁空间的流入，（2）脑ISF的星形胶质细胞水通道蛋白4（AQP 4）依赖性对流，和（3）经由静脉旁清除的流出。此外，CSF可以通过颈淋巴从脑中清除。我们的初步数据显示，单体tau通过胶质淋巴和颈淋巴系统从CSF和脑实质中清除，并且随着年龄的增长和在Aqp 4 ko小鼠中减少。而短纤维在脑内保留时间较长。我们假设胶质淋巴/淋巴系统对于tau的全脑清除至关重要，并且这些系统中与年龄相关的故障有助于其积累。有两个目的，1）表征小鼠中来自CSF和脑ISF的tau清除机制，和2）评估衰老和AQP 4对tau蛋白种类从脑中清除的影响。125 I-tau分布和消除的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交换和清除途径的流入。将使用颈部淋巴管和淋巴结的实时体内成像分析颈部淋巴清除动力学。我们预期数据将显示tau（单体>原纤维）通过CSF/ISF交换和对流ISF流动以及通过颈部淋巴清除。通过这两种途径的清除率将随着年龄的增长和Aqp 4-/-小鼠而降低。由于细胞结合，Tau原纤维将在脑中保留更长时间。这些研究可能导致tau清除的全新靶点，以通过改善tau和其他毒性分子的胶质淋巴/淋巴清除来减缓或甚至预防AD相关的神经认知衰退。

 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.