Ephrin B2 receptor signaling in Alzheimer diseased brain - a safeguard against neurodegeneration?

Ephrin B2受体（EPHB2）信号通过Ephrin配体EFNB2与EPHB2结合，在不同水平上参与脑的表型可塑性。它协调血管生成和自噬以及与记忆和学习相关的轴突引导/树突树突形成和突触/神经发生。此外，焦虑是由钾likrein 8 （KLK8）介导的EPHB2蛋白水解和随后FK506结合蛋白5 （FKBP5）的表达增加控制的，FK506结合蛋白5 （FKBP5）反过来调节杏仁核中糖皮质激素受体（GR）的敏感性。上述所有由EPHB2控制的行为和结构过程在阿尔茨海默病（AD）影响的大脑中也受到干扰/损害。因此，很有可能EPHB2信号也参与了AD的发病过程。本提案的总体目标是阐明EPHB2信号在AD发病机制中的影响。特别是，我们的目的是验证通过抑制EPHB2蛋白水解酶KLK8来逆转EPHB2的缺失是否会减轻AD的病理，如果是的话，揭示这种作用的潜在机制。首先，采用描述性方法，我们旨在评估在ad易感的人和小鼠大脑中，EPHB2信号成员（EPHB2, EFNB2, KLK8, FKBP5， GR）在疾病过程中（和生理衰老）的区域和时间特异性mRNA和蛋白表达模式。其次，采用体外方法，我们将通过klk8抑制抗体（保护EPHB2免受降解）对Tg小鼠原代神经元和胶质细胞培养的β病理、自噬和细胞存活的药理操纵来机制分析EPHB2信号传导的影响。在互惠的方法中，通过使用活化的合成KLK8，我们将降低EPHB2水平，并反过来验证上述结果。第三，通过在体内的方法，我们将研究通过给Tg小鼠（和Wt小鼠作为生理基线）脑室内注射抗klk8抗体来逆转EPHB2信号干扰对焦虑行为以及学习和记忆表现的功能影响。此外，还将研究这种药理操作对参与焦虑产生的杏仁核分子以及海马和皮层结构神经可塑性的影响。此外，通过分子、结构和超结构分析EPHB2保护对APP和Abeta代谢、Abeta清除、神经血管单位和自噬机制的影响。这个项目的结果可能为阿尔茨海默病的治疗开辟新的途径。

Ephrin B2 receptor (EPHB2) signaling, conducted by binding of Ephrin ligand EFNB2 to EPHB2, contributes to phenotypical brain plasticity at various levels. It coordinates angiogenesis and autophagy as well as memory and learning related axonal guidance / dendritic arborization and synapto/neurogenesis. Further, anxiety is controlled by kallikrein 8 (KLK8) mediated EPHB2 proteolysis and subsequent increased expression of FK506 binding protein 5 (FKBP5) which in turn regulates glucocorticoid receptor (GR) sensitivity in the amygdala. All the above named behavioral and structural processes that are controlled by EPHB2 are also disturbed / impaired in the Alzheimer disease (AD) affected brain. Therefore, it is very suggestive that EPHB2 signaling might be also involved in the pathogenesis of AD. The overall objective of this proposal is to elucidate the impact of EPHB2 signaling on the pathogenesis of AD. In particular, we aim to verify whether reversing EPHB2 depletion by inhibiting its proteolytic enzyme KLK8 would mitigate AD pathology, and if so to unravel the underlying mechanisms of this effect. First, in a descriptive approach, we aim to assess the regional and temporal specific mRNA and protein expression pattern of EPHB2 signaling members (EPHB2, EFNB2, KLK8, FKBP5, GR) in AD-vulnerable human and murine brain during the course of the disease (and physiological aging). Second, using an in vitro approach, we will mechanistically analyze the effect of pharmacological manipulation of EPHB2 signaling by a KLK8-inhibiting antibody (that protects EPHB2 from degradation) on Abeta pathology, autophagy and cell survival in primary neuronal and glial cell cultures derived from Tg mice. In a reciprocal approach, by using activated synthetic KLK8 we will then reduce EPHB2 levels and verify the above results inversely. Third, by using an in vivo approach, we will study the functional consequence of reversing EPHB2 signaling disturbance through intraventricular anti-KLK8 antibody administration to Tg mice (and to Wt mice serving as physiological baseline) on anxiety behavior as well as on learning and memory performances. Furthermore, the effect of this pharmacological manipulation on amygdalar molecules involved in anxiety generation and on hippocampal and cortical structural neuro-plasticity will be studied. Moreover, by performing molecular, structural and ultra-structural analyzes the impact of EPHB2 protection on APP and Abeta metabolism, Abeta clearance, the neurovascular unit and on autophagy machinery will be examined. Results from this project may open up new avenues in the treatment of AD.