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因。家族性阿尔茨海默病（fAD）与编码淀粉样前体蛋白（APP）、早老素1（PS1）和早老素2（PS2）的基因突变相关。PS1和PS2是γ-分泌酶复合物的酶组分，其切割APP以释放A β 42肽。尽管已经有超过15年的研究，但对于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楚理解尚未出现。“淀粉样蛋白假说”表明阿尔茨海默病（AD）发展为早老素功能的毒性获得，导致A β 42的过量产生。然而，针对降低AD中β 42的治疗干预尚未产生临床实用的治疗。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突变可导致体外较高的A β 42：40比率，但许多伴随导致γ-分泌酶对底物的切割受损，所述底物在炎症、发育和分化中具有充分描述的作用。因此，PS突变可能对基本细胞途径具有破坏性后果。我们最近描述了一个早发性AD患者携带一个新的PS2提前终止密码子突变，导致PS2蛋白减少，支持PS2功能丧失可能导致神经退行性变的假设。条件性PS1/PS2敲除小鼠重现了AD的许多特征，包括神经变性、炎症基因上调和CNS中主要先天免疫效应细胞小胶质细胞数量增加。我们在稳定表达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发现，PS2缺陷与促炎细胞因子的过度释放相关。这些结果在暴露于药理学γ-分泌酶抑制剂的小胶质细胞中是可重复的，表明PS2通过其酶活性调节小胶质细胞。我们还确定了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，miR 146 a和miR 146 b。PS2缺乏与miR 146 a/B水平降低和miR 146 a靶标（炎症信号分子IRAK-1）水平升高相关。综上所述，这些观察结果支持了这一假设，即PS2功能下降可能有助于通过增强小胶质细胞神经炎症在AD中的神经变性。在该提案中，我们将1）评估患有PS2突变相关的家族性和散发性AD的患者的中枢神经系统炎症特征，2）研究PS2对miR 146 a/B的调节，以及3）研究条件性表达最常见的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.