New Strategy to Fight Selective Cholinergic Neuronal Loss in Alzheimer Disease

描述（由申请人提供）： 阿尔茨海默病（Alzheimer's disease，AD）是一种以选择性胆碱能神经变性为特征的神经退行性痴呆。数百万美国人受到影响，但没有改善疾病的治疗方法。这部分是因为我们不知道为什么胆碱能神经元比其他神经元更脆弱，因此没有特定的策略来保护它们。事实上，甚至没有一种动物模型能够重新捕获AD典型的选择性和稳健的基底前脑胆碱能（BFC）神经元细胞损失。模型的缺乏严重限制了相关的机制和治疗研究。 我们现在已经开发了一种转基因小鼠，其表现出人类AD的胆碱能神经退行性过程的最基本特征，包括稳健的BFC神经元损失。这些小鼠具有G蛋白偶联受体激酶-5（GRK 5）缺陷（与人类AD一样严重），并过度表达淀粉样前体蛋白的瑞典突变体。杂合子双缺陷小鼠（以下简称GAP小鼠）在18个月龄时选择性地失去了三分之一的BFC神经元。因此，我们认为GRK 5缺乏是一种“阿尔茨海默选择性”因素，使胆碱能神经元更容易变性。 GRK 5缺乏以前与AD有关，因为它可能是由淀粉样蛋白（A）和氧化应激引起的。在人类AD大脑中存在严重的GRK 5缺乏。我们现在有初步的研究结果表明，GRK 5缺乏增加了细胞培养物和完整小鼠的胆碱能脆弱性。GRK 5缺乏导致海马乙酰胆碱释放减少，胆碱能轴突病（无细胞死亡）和轻度认知障碍。GRK 5缺乏也会加重Ass的积累和神经胶质增生。从机制上讲，GRK 5缺乏的所有表型似乎都归因于M2毒蕈碱乙酰胆碱自身受体（M2）的脱敏受损。现有的研究支持这样的概念，即受损的M2脱敏导致cAMP依赖性信号通路的持续抑制，并且这种抑制降低了胆碱能细胞的内在防御机制并导致其脆弱性。 我们假设GRK 5缺乏通过受损的M2脱敏选择性地导致胆碱能脆弱性;并且阻断突触前M2受体将防止胆碱能神经变性。我们提出了4个具体目标，以巩固我们的初步研究结果，并解决我们的假设。具体目标1）。表征GAP小鼠中胆碱能神经变性和认知下降的时间过程;具体目的2和3）。比较M2阻断和M1刺激在改善GAP小鼠的认知缺陷和预防胆碱能神经变性方面的功效;和具体目标4）。通过检查人类AD大脑样本中的所有这些变化并将其与痴呆的严重程度相关联，将GAP小鼠的主要发现转化为人类AD。 我们希望在该项目结束时，我们将描述人类AD的创新动物模型（GAP小鼠）的胆碱能神经变性和认知下降的详细时间过程。我们将验证GRK 5缺乏导致选择性胆碱能脆弱性的创新概念，并且可以通过M2阻断而不是M1刺激来预防脆弱性。此外，在原则层面上，我们还将证明一种新药AAD 23在预防BFC神经变性方面的疗效。我们希望发现人类AD样本中GRK 5缺乏的程度与胆碱能神经变性的严重程度相关。这一发现将为M2受体阻滞剂预防人类AD胆碱能神经变性的试验提供依据。

DESCRIPTION (provided by applicant): Alzheimer's disease (AD) is a neurodegenerative dementia characterized by selective cholinergic neurodegeneration. Millions of Americans are affected, but there are no disease-modifying treatments. This is, in part, because we do not know why the cholinergic neurons are more vulnerable than others, and therefore do not have specific strategy to protect them. In fact, there is even not an animal model that recaptures the selective and robust basal forebrain cholinergic (BFC) neuronal cell loss that is typical of AD. The absence of a model severely limits relevant mechanistic and therapeutic studies. We have now developed a transgenic mouse that exhibits the most essential features of cholinergic neurodegenerative process of human AD, including the robust BFC neuronal loss. These mice have G protein- coupled receptor kinase-5 (GRK5) deficiency (as severe as in human AD) and overexpress Swedish mutant of ¿-amyloid precursor protein. The heterozygous double defective mice (hereafter abbreviated as GAP mice) selectively lost one-third of their BFC neurons at 18 months of age. We therefore propose that GRK5 deficiency is an "Alzheimer-selective" factor that makes cholinergic neurons more vulnerable to degeneration. GRK5 deficiency was previously linked to AD because it could be caused by ¿-amyloid (A¿) and oxidative stress. There is a severe GRK5 deficiency in human AD brains. We now have preliminary findings that document that GRK5 deficiency increases cholinergic vulnerability both in cell cultures and in intact mice. GRK5 deficiency leads to reduced hippocampal acetylcholine release, cholinergic axonopathy (without cell death), and mild cognitive impairment. GRK5 deficiency also exaggerates Ass accumulation and gliosis. Mechanistically, all phenotypes of GRK5 deficiency appear to be attributable to an impaired desensitization of M2 muscarinic acetylcholine autoreceptor (M2). Extant research supports the concept that impaired M2 desensitization leads to persistent inhibition of the cAMP-dependent signaling pathway and that this inhibition reduces intrinsic defense mechanisms of cholinergic cells and leads to their vulnerability. We hypothesize that GRK5 deficiency selectively causes cholinergic vulnerability via impaired M2 desensitization; and that blocking presynaptic M2 receptors would prevent cholinergic neurodegeneration. We propose 4 Specific Aims to consolidate our preliminary findings and address our hypothesis. Specific Aim 1). Characterize the time course of cholinergic neurodegeneration and cognitive decline in GAP mice; Specific Aims 2 and 3). Compare the efficacies of M2 blockade and M1 stimulation in improving cognitive deficits and preventing cholinergic neurodegeneration in GAP mice; and Specific Aim 4). Translate the major findings from GAP mice to human AD by examining all these changes in human AD brain samples and correlating them with severity of dementia. We hope by the end of the project, we will have characterized an innovative animal model (GAP mice) of human AD for its detailed time course of cholinergic neurodegeneration and cognitive decline. We will have validated the innovative concept that GRK5 deficiency causes selective cholinergic vulnerability and that vulnerability can be prevented by M2 blockade but not M1 stimulation. In addition, at a principle level, we will have also proven the efficacy of a novel drug, AAD23, in preventing BFC neurodegeneration. We hope to find that the degree of GRK5 deficiency in human AD samples correlates with the severity of cholinergic neurodegeneration. This finding will provide rationale for trials of M2 receptor blockers for the prevention of cholinergic neurodegeneration in human AD.