The Role of nicotinic acetylcholine receptors nAChRs to mediate the synaptic functions of APPsα

淀粉样前体蛋白（APP）是阿尔茨海默病（AD）发病机制的核心，因为它产生Aβ肽，A β肽在AD患者的大脑中积累。APP经历复杂的蛋白水解加工，其一方面导致Aβ产生，但也导致大的细胞外胞外域APP的分泌。越来越多的证据表明APP的生理突触功能是由分泌的APP α片段介导的。然而，APPsα受体及其作用的精确分子机制仍然知之甚少。以前，我们已经表明APPsα对神经元的活力和功能至关重要，因为它具有神经营养，神经保护和突触发生特性。在这方面，我们可以证明APPsα在很大程度上挽救或改善具有已建立斑块病理学的转基因AD模型小鼠（APP/PS1ΔE9小鼠）的突触损伤。最近，我们在缺乏APP和相关APLP 2的条件性双敲除小鼠（cDKO）的成年大脑中表达APP α。AAV介导的APPsα表达有效地挽救了cDKO小鼠的脊柱密度、突触可塑性和空间参考记忆的缺陷。在体外，我们发现纳摩尔浓度的APP α可以促进cDKO小鼠切片中的LTP，其机制需要功能性α7-nAChR。这些研究确定α7-nAChR是APP α的第一个潜在内源性受体。尽管如此，这些体外研究缺乏在体内的证实，以牢固地确立这种受体途径介导APPsα的各种突触功能，超出其对LTP的作用。初步研究发现APPsα C末端的最后16个氨基酸（CTα16区）是体外突触可塑性所需的关键功能域。因此，本提案的目的是（i）进一步表征APPsα/CTα16与α7-nAChR以及可能与非α7异聚体AChR亚型的相互作用，以及（ii）其次，确定该途径与结构和功能脊柱可塑性、LTP和认知的体内相关性。为此，我们将采用cDKO小鼠以及组成型和条件性α7-nAChR-KO小鼠，遵循药理学和互补遗传获得和功能丧失方法。最后，我们的目的是确定APPsα是否作为胆碱能系统的内源性正变构调节剂（PAM）。这些研究将导致对APP功能的重要机制见解，也可能导致AD的新治疗方法。

The amyloid precursor protein (APP) is central to the pathogenesis of Alzheimers disease (AD as it gives rise to Aβ peptides, that accumulate in the brain of AD patients. APP undergoes complex proteolytic processing that results on one hand in Aβ production, but also in the secretion of the large extracellular ectodomain APPs. Increasing evidence suggests that the physiological synaptic functions of APP are mediated by the secreted APPsα fragment. However, the APPsα receptor(s) and the precise molecular mechanisms of its action are still poorly understood. Previously, we have shown that APPsα is pivotal for neuronal viability and function, as it has neurotrophic, neuroprotective and synaptogenic properties. In this regard, we could demonstrate that APPsα largely rescues or ameliorates the synaptic impairments of transgenic AD model mice with established plaque pathology (APP/PS1ΔE9 mice). More recently, we expressed APPsα in the adult brain of conditional double knockout mice (cDKO) lacking APP and the related APLP2. AAV mediated APPsα expression efficiently rescued deficits in spine density, synaptic plasticity and spatial reference memory of cDKO mice. In vitro, we found that nanomolar concentrations of APPsα can facilitate LTP in slices of cDKO mice in a mechanism that required functional α7-nAChRs. These studies identified α7-nAChRs as the first potential endogenous receptor for APPsα. Despite this, these in vitro studies lack confirmation in vivo to firmly establish in as much this receptor pathway mediates the various synaptic functions of APPsα, beyond its role for LTP. Preliminary studies identified the last 16 C-terminal amino acids of APPsα (CTα16 region) as the crucial functional domain required for synaptic plasticity in vitro. The aims of this proposal are thus to (i) further characterize the interaction of APPsα/CTα16 with the α7-nAChR and possibly also with non-α7 heteromeric AChR subtypes and (ii) secondly, to determine the in vivo relevance of this pathway for structural and functional spine plasticity, LTP and cognition. To this end we will follow a pharmacological and complementary genetic gain and loss of function approach employing cDKO mice as well as constitutive and conditional α7-nAChR-KO mice. Finally, we aim to determine whether APPsα functions as an endogenous positive allosteric modulator (PAM) of the cholinergic system. These studies will lead to important mechanistic insights into the functions of APP that may also lead to novel therapeutic approaches for AD.