Role of Astrocyte EAAT2/GLT1 Failure in Alzheimer's Disease Pathogenesis

星形胶质细胞被理想地定位以支持神经元/突触对营养因子、代谢调节因子和神经元/突触的需要。 体内平衡和保护免受毒性。虽然反应性星形胶质细胞增生是AD的突出特征，但这提供了 关于星形胶质细胞如何影响疾病过程或它们如何受到伤害的见解非常有限。 星形胶质细胞最重要的功能之一是清除细胞外谷氨酸以防止兴奋性毒性。 由星形胶质细胞摄取的谷氨酸也用作其他神经细胞生物合成的代谢底物。 像γ-氨基丁酸这样的神经递质因此，至少有两种主要的方式，星形胶质细胞谷氨酸清除保护神经元。 个脑袋在大脑皮层和海马体中，谷氨酸转运蛋白Slc 1a 2（也称为GLT 1或EAAT 2）起着重要的作用。 谷氨酸清除中最重要的作用。大多数，但不是所有的Slc 1a 2是在星形胶质细胞。 我们的研究小组已经表明：（i）Slc 1a 2在AD中受到干扰;（ii）Slc 1a 2在AD小鼠模型中丢失 加速认知障碍的发作;（iii）A β 42减缓海马神经元突触释放的谷氨酸摄取， （iv）星形胶质细胞Slc 1a 2减少的小鼠显示出与AD显著的转录组重叠。 这些数据补充了来自其他小组的强有力的工作，并共同认为Slc 1a 2功能障碍可能 在AD中发挥重要作用。然而，需要回答其他关键问题，以更好地理解 星形胶质细胞Slc 1a 2如何与A β 42和tau病理学相互作用。具体来说，是否存在致病协同作用 在这些过程中？在AD中，需要更多地揭示神经元和神经元之间的关系。 脑中表达几乎所有Slc 1a 2的精细（通常为GFAP阴性）星形胶质细胞突起--一种解剖学上的 这对它们的功能至关重要。此外，没有足够的数据支持以下假设： 星形胶质细胞Slc 1a 2可以在加重A β 42和tau病理中起促进或因果作用。 这个项目的目标是填补这些知识空白。首先，我们将使用Slc 1a 2减少的新型小鼠， 特别是在星形胶质细胞中;并使用表达A 42和tauP 301 L的腺病毒载体（AAVs），剖析了星形胶质细胞中的 这些致病途径之间的体内分子相互作用。我们将讨论星形胶质细胞是否在 对A β 42和/或tau的应答。我们将使用一种新的表达Slc 1a 2的慢病毒系统，该系统感染星形胶质细胞， 以测试是否专门拯救星形胶质细胞Slc 1a 2改善神经病理学，以及Slc 1a 2功能。 其次，使用最先进的膜片钳方法直接测量星形胶质细胞谷氨酸清除率， 研究Slc 1a 2缺失、A β 42和tau蛋白表达如何相互作用影响星形胶质细胞谷氨酸清除。我们将 阐明这些致病过程如何影响调节突触网络兴奋性的星形胶质细胞Slc 1a 2 通过支持GABA能传输。第三，使用控制组中特征鲜明的死后大脑， 前驱期和AD患者，我们将测试谷氨酸转运蛋白的潜在翻译意义， 星形胶质细胞神经病理学，我们已经报告，并建议由我们的新的初步数据。所有这些 这些数据有望推进我们对Slc 1a 2作为AD干预的潜在分子靶点的认识。

Astrocytes are ideally positioned to support neuronal/synaptic needs for trophic factors, metabolic homeostasis, and protection from toxicity. While reactive astrogliosis is a prominent feature of AD, this offers very limited insight about how astrocytes influence the disease process or how they may be harmed. One of the most important functions of astrocytes is to clear extracellular glutamate to prevent excitotoxicity. Glutamate taken up by astrocytes is also used as a metabolic substrate for biosynthesis of other neuro- transmitters like GABA. Thus, there are at least two major ways astrocytic glutamate clearance protects the brain. In cortex and hippocampus, the glutamate transporter Slc1a2 (also called GLT1 or EAAT2) plays the most important role in glutamate clearance. Most, but not all Slc1a2 is in astrocytes. Our research team has shown that: (i) Slc1a2 is disturbed in AD; (ii) Slc1a2 loss in an AD mouse model accelerates onset of cognitive impairment; (iii) A42 slows synaptically-released glutamate uptake in hippo- campal slices; and (iv) mice with reduced astrocytic Slc1a2 display significant transcriptomic overlaps with AD. These data complement strong work from other groups and collectively argue that Slc1a2 dysfunction may play an important role in AD. However, additional critical questions need to be answered to better understand how astrocytic Slc1a2 may interact with A42 and tau pathology. Specifically, is there pathogenic synergy among these processes? In AD more needs to be uncovered about the relationship between neurons and the fine (often GFAP-negative) astrocytic processes expressing nearly all Slc1a2 in the brain—an anatomical relationship that is crucial to their function. In addition, there is insufficient data supporting the hypothesis that astrocytic Slc1a2 can play a contributing or causal role in exacerbating A42 and tau pathology. The goal of this project is to fill these knowledge gaps. First, we will use novel mice with reduced Slc1a2 specifically in astrocytes; and with adenoviral vectors (AAVs) expressing A42 and tauP301L, dissect the in vivo molecular interactions between these pathogenic pathways. We will address whether astrocytes are lost in response to A42 and/or tau. We will use a novel lentivirus system expressing Slc1a2, which infects astrocytes, to test whether specifically rescuing astrocytic Slc1a2 ameliorates neuropathology, as well as Slc1a2 function. Second, using state-of-the art patch clamp methods that directly measure astrocyte glutamate clearance, dissect how Slc1a2 loss, A42, and tau expression interact to affect astrocytic glutamate clearance. We will address how these pathogenic processes influence astrocytic Slc1a2 that regulate synaptic network excitability by supporting GABAergic transmission. Third, using well-characterized postmortem brains from control, prodromal, and AD patients we will test the potential translational significance of the glutamate transporter and astrocyte neuropathology we have reported and is suggested by our new preliminary data. Together, these data hold promise of advancing our knowledge of Slc1a2 as a potential molecular target for intervention in AD.