BACE1对AMPA受体的调节及在早期阿尔茨海默病发病机制中的作用研究

Alzheimer’s disease (AD) is the most common form of dementia among the elderly. BACE1, the rate limiting enzyme for amyloid (Aβ) production, is considered central to the pathogenesis of AD. However, the role of BACE1 in regulation of synaptic functions and in early-stage of AD independent of Aβ production effect is still unclear. Our previous findings demonstrated that BACE1 interacted with AMPA receptor GluR2 subunit, and cytosolic BACE1 protein levels in synapses were decreased in AD transgenic mice compared to wild type mice at 1.5-month of age, accompanied with much lower levels of membrane-associated GluR2 protein in synapses of AD transgenic mice than that of wild type mice. The internalization of GluR2 was enhanced when BACE1 located in synaptic vesicles was decreased in AD transgenic mouse brain. Based on these observations, we propose that BACE1 may be a functional regulator of GluR2-containing AMPA receptors at the post-synaptic membrane and this role would be suppressed due to the requirement of Aβ overproduction during the very early stage of AD-like progression. In our proposed studies, we will first to determine whether BACE1 regulates the functions of GluR2-containing AMPA receptors by using BACE1 knockout mice with electrophysiological, morphological, biochemical methods, and how the function and location of GluR2 at post-synaptic membrane could be changed by BACE1 directly in the primary neuronal culture derived from the hippocampus of BACE1 knockout mice. Furthermore, we will utilize the new conditional BACE1 expression mouse model to elucidate the exact roles of endogenous BACE1 in regulation of synaptic function and early mechanism of AD-like pathology in vivo. The project will advance our understanding of early mechanistic underpinnings of AD pathology.

阿尔茨海默病（AD）是最常见的痴呆，发病机制不清。BACE1作为Aβ产生的限速酶，促进了AD的发生。但其独立于Aβ调节突触功能及在AD病程早期的作用尚属未知。本课题组前期发现BACE1与AMPA受体亚基GluR2存在相互作用，在野生型鼠脑内，BACE1在突触囊泡内的表达量升高，GluR2更多定位于突触体，但在AD转基因鼠脑内突触囊泡内BACE1减少，同时GluR2内化。本项目在前期工作基础上，拟采用电生理、生化、形态学、行为学及遗传学等方法，首先以BACE1敲除小鼠为研究对象揭示BACE1对GluR2介导的AMPA受体功能的调节作用；在神经元细胞突触分隔培养系统中明确BACE1对AMPA受体调节的机制；进而用我们自己设计并已建成的新型BACE1条件性表达小鼠在体控制内源性BACE1表达，最终确定BACE1的重要生理功能及其在早期AD病程中的作用。将为揭示AD早期发病机制提供新的理论基础。

阿尔茨海默病（AD）是痴呆的常见病因，发病机制不清。BACE1作为Aβ产生的限速酶，促进了AD的发生。但其独立于Aβ调节突触功能及在AD病程早期的作用尚属未知。我们在该项目研究中发现，将小清蛋白（parvalbumin，PV）阳性神经元中的BACE1条件性敲除，可以使海马CA1区的parvalbumin神经元的兴奋性升高，但并非源自神经元本身的固有兴奋性升高；作为PV神经元兴奋性升高的结果，其临近锥体神经元的抑制性/兴奋性突触电流失平衡，表现为抑制性突触后电流升高；在由PV神经元和临近锥体神经元构成的局部微环路中，PV神经元的突触后NMDAR电流增大，但通道特性不变，其接受的突触前递质释放概率未发生改变，提示BACE1缺失造成的PV神经元突触后NMDAR电流增强是引起其网络兴奋性升高的可能机制，而这一推测被MK-801药理学实验证实；重要的是，这一微环路功能状态的改变导致了Schaffer侧枝至CA1长环路（SC- CA1）中AMPAR介导的基本兴奋性突触传递的减弱，并引发情景恐惧记忆消褪的初始化状态的重置。本研究证实，BACE1在PV调控的海马CA1微环路中发挥重要的功能，其对兴奋性突触后受体具有调控作用。本研究提出了BACE1对突触传递功能调控的新机制，并为BACE1抑制剂在新药研发中面临的困境提出潜在的解决策略，即与NMDAR拮抗剂联合应用或可规避BACE1抑制剂的副作用。