Impairment of ischemia-induced vascular functions by PS1 FAD mutants

脑微血管异常，如毛细血管内皮细胞变性， 阿尔茨海默病（AD）神经病理学的起源。此外，在AD脑中经常发现引起神经元损伤的缺血性病变。脑通过经由萌芽血管生成刺激组织新血管形成来响应缺血;该功能的损伤使得脑易受损伤。据推测，AD中血管生成减少导致受影响区域的血流不足和神经元功能障碍。已知EphB 4/ephrinB 2（efnB 2）配体-受体系统响应于缺血而调节脑血管生成。我们目前的证据表明，Presnilin 1（PS1），家族性AD（FAD）的一个重要因素，调节EphB 4/efnB 2的血管生成功能，如刺激VE-钙粘蛋白血管生成复合物在脑内皮细胞（EC）。我们还发现这种功能被PS1 FAD突变体削弱。此外，我们发现，缺血刺激在大脑中形成相同的血管生成复合物，并且这种功能被PS1 FAD突变体连同缺血诱导的新血管形成和脑血流量一起减弱，而神经元死亡增加。我们还发现PS1 FAD突变体降低了efnB 2的γ-分泌酶加工和血管生成肽efnB 2/CTF 2的产生，从而损害了脑EC对血管生成因子的反应。总之，我们的数据支持以下假设：PS1 FAD突变体通过减少efnB 2的γ-分泌酶加工和损害EphB 4/efnB 2信号传导来抑制EC的缺血诱导的血管生成功能，从而减少成人脑中的新血管形成并导致对这种毒性损伤和神经元死亡的脆弱性增加。在本申请中，我们研究了PS1 FAD突变体和γ-分泌酶对缺血诱导的血管生成复合物、血流、血管生成和神经元死亡的作用。此外，我们建议测试一种小肽，其来源于γ-分泌酶对efnB 2的蛋白水解加工，并且我们发现其拯救PS1 FAD EC的血管生成功能，用于其在表达FAD突变体的脑中的促血管生成和神经保护功能。此外，我们的目标是寻找新的缺血诱导的血管生成途径，PS1 FAD突变体受损，并检查是否VE-钙粘蛋白血管生成复合物和血管生成蛋白表达受损的人PS1 FAD和AD患者的大脑。

Cerebral microvasculature abnormalities, such as degeneration of the capillary endothelium, are implicated in the genesis of Alzheimer's disease (AD) neuropathology. In addition, ischemic lesions that cause neuronal damage are often found in AD brains. The brain responds to ischemia by stimulating tissue neovascularization via sprouting angiogenesis; impairment of this function renders the brain vulnerable to the insult. It has been hypothesized that decreased angiogenesis in AD leads to insufficient blood flow and neuronal dysfunction in affected areas. The EphB4/ephrinB2 (efnB2) ligand-receptor system is known to regulate brain angiogenesis in response to ischemia. We present evidence that Presnilin1 (PS1), an important factor in familial AD (FAD), regulates angiogenic functions of EphB4/efnB2 such as stimulation of VE-cadherin angiogenic complexes in brain endothelial cells (ECs). We also found that this function is impaired by PS1 FAD mutants. In addition, we found that ischemia stimulates formation of the same angiogenic complexes in the brain and that this function is attenuated by PS1 FAD mutants together with ischemia-induced neovascularization and cerebral blood flow while neuronal death is increased. We also found that PS1 FAD mutants decrease the γ-secretase processing of efnB2 and production of the angiogenic peptide efnB2/CTF2 thus impairing the response of brain ECs to angiogenic factors. Together, our data support the hypothesis that PS1 FAD mutants inhibit ischemia-induced angiogenic functions of ECs by decreasing the γ-secretase processing of efnB2 and impairing the EphB4/efnB2 signaling, thus decreasing neovascularization in the adult brain and leading to increased vulnerability to this toxic insult and neuronal death. In this application we examine the roles of PS1 FAD mutants and γ-secretase on ischemia-induced angiogenic complexes, blood flow, angiogenesis and neuronal death. In addition, we propose to test a small peptide, which derives from the proteolytic processing of efnB2 by γ-secretase and which we found to rescue angiogenic functions of PS1 FAD ECs, for its pro-angiogenic and neuroprotective functions in brains expressing FAD mutants. In addition we aim to search for novel ischemia-induced angiogenic pathways that are impaired by PS1 FAD mutants and examine whether VE-cadherin angiogenic complexes and angiogenic protein expression are impaired in brains of human PS1 FAD and AD patients.