Presenilin 2 and Neuroinflammation

描述（由申请人提供）：阿尔茨海默病是痴呆症的主要原因，也是美国第六大常见死亡原因。家族性阿尔茨海默病（fAD）与编码淀粉样蛋白前体蛋白（APP）、早老素1 （PS1）和早老素2 （PS2）的基因突变有关。PS1和PS2是γ-分泌酶复合物的酶促成分，其裂解APP以释放Aß42肽。尽管有超过15年的研究，PS1和PS2突变如何导致PS功能障碍和随后的神经退行性变的清晰认识尚未出现。“淀粉样蛋白假说”表明，阿尔茨海默病（AD）的发展是由于早老素功能的毒性增加，导致a ß42的过量产生。然而，旨在降低AD ß42的治疗干预尚未产生临床实用的治疗方法。越来越清楚的是，包括神经炎症在内的其他机制有助于AD的发展或进展，因此可能是治疗设计的其他潜在途径。虽然AD相关的PS突变在体外可导致更高的a ß42:40比率，但许多突变同时导致γ-分泌酶切割在炎症、发育和分化中发挥良好作用的底物受损。因此，PS突变可能对基本细胞通路具有破坏性后果。我们最近报道了一名早发性AD患者，该患者携带一种新的PS2过早终止密码子突变，导致PS2蛋白减少，支持PS2功能丧失可能导致神经变性的假设。条件PS1/PS2基因敲除小鼠重现了阿尔茨海默病的许多特征，包括神经退行性变、炎症基因上调、小胶质细胞（中枢神经系统的主要先天免疫效应细胞）数量增加。我们发现，在稳定表达PS2 shRNA的小胶质细胞系和从PS2敲除小鼠分离的原代小胶质细胞中，PS2缺乏与促炎细胞因子的过度释放有关。这些结果在暴露于药理γ分泌酶抑制剂的小胶质细胞中可重复，表明PS2通过其酶活性调节小胶质细胞。我们还确定PS2影响小胶质细胞行为的一种可能机制是通过调节两种先天免疫相关的microrna miR146a和miR146b。PS2缺乏与miR146a/b水平降低和miR146a靶点炎症信号分子IRAK-1水平升高有关。综上所述，这些观察结果支持了PS2功能下降可能通过增强小胶质神经炎症导致AD患者神经退行性变的假设。在本项目中，我们将1)评估PS2突变相关家族性和散发性AD患者的中枢神经系统炎症特征2)研究PS2对miR146a/b的调控3)研究有条件表达最常见的PS2 fAD相关突变的转基因小鼠模型的神经炎症特征。

DESCRIPTION (provided by applicant): Alzheimer disease is the leading cause of dementia and the 6th commonest cause of death in the United States. Familial Alzheimer disease (fAD) is associated with mutations in the genes encoding amyloid precursor protein (APP), presenilin 1 (PS1) and presenilin 2 (PS2). PS1 and PS2 are the enzymatic component of the γ-secretase complex that cleaves APP to release the Aß42 peptide. Despite more that 15 years of study, a clear understanding of how mutations in PS1 and PS2 cause PS dysfunction and subsequent neurodegeneration has not emerged. The "amyloid hypothesis" suggests that Alzheimer disease (AD) develops as a toxic gain of presenilin function leading to excessive production of Aß42. However, therapeutic interventions directed at decreasing ß42 in AD have not yet yielded clinically practical treatments. It is becoming clear that additional mechanisms including neuroinflammation contribute to the development or progression of AD and thus may be additional potential avenues for therapy design. While AD associated PS mutations can lead to a higher Aß42:40 ratio in vitro, many concomitantly lead to impaired γ-secretase cleavage of substrates with well described roles in inflammation, development and differentiation. Therefore, PS mutations may have damaging consequences to basic cellular pathways. We have recently described an early onset AD patient who carries a novel PS2 premature termination codon mutation leading to decreased PS2 protein, supporting the hypothesis that loss of PS2 function can contribute to neurodegeneration. Conditional PS1/PS2 knockout mice recapitulate many features of AD including neurodegeneration, upregulation of inflammatory genes, and increased numbers of microglia, the primary innate immune effector cells in the CNS. We found in both PS2 shRNA stably expressing microglia cell lines and primary microglia isolated from PS2 knockout mice that PS2 deficiency is associated with an exaggerated release of pro- inflammatory cytokines. These results were reproducible in microglia exposed to a pharmacological γ-secretase inhibitor suggesting that PS2 modulates microglia through its enzymatic activity. We have also determined that one possible mechanism by which PS2 impacts microglia behavior is through regulation of two innate immunity associated microRNAs, miR146a and miR146b. PS2 deficiency is associated with decreased levels of miR146a/b and increased levels of the miR146a target, the inflammatory signaling molecule, IRAK-1. Taken together, these observations support the hypothesis that decreased PS2 function may contribute to neurodegeneration in AD by enhancing microglial neuroinflammation. In this proposal we will 1) evaluate the central nervous system inflammatory profile of patients with PS2 mutation associated familial and sporadic AD 2) investigate the regulation of miR146a/b by PS2 and 3) study the neuroinflammatory characteristics of a transgenic mouse model conditionally expressing the most common PS2 fAD associated mutation.