Midthune Brea, Park Goonho, Tyan Sheue-Houy, Koo Edward H
Department of Neurosciences, University of California, San Diego, La Jolla, CA.
VA Palo Alto Healthcare System, Palo Alto, CA, USA.
bioRxiv. 2025 May 7:2025.04.30.651606. doi: 10.1101/2025.04.30.651606.
Increasing evidence suggests that amyloid beta (Aβ) lies at the center of Alzheimer's Disease (AD) pathology and that synapses are the initial site of damage by Aβ. Recent studies have also indicated a role for caspases in AD-related synaptic dysfunction and memory loss, but the mechanism(s) through which the caspases act remains elusive. Previous studies in cell culture indicate that cleavage of a caspase site on the intracellular domain of the amyloid precursor protein (APP) protein contributes to Aβ-induced cell death. However, the role of this cleavage event in synaptic dysfunction has not been established.
Through a combination of intracellular and extracellular electrophysiological methods and confocal microscopy of dendritic spines, we examined the involvement of caspase-3 and amyloid-precursor protein in Aβ-mediated synaptic dysfunction.
Here, we provide evidence that caspase activity at the intracellular domain of APP is required for acute Aβ-induced depression of glutamatergic synapses. We find that local elevation of Aβ levels through over-expression of the C-terminal fragment of APP (C99) failed to depress synapses if caspases were inhibited pharmacologically or in tissue lacking caspase-3. To demonstrate a link between these findings to APP, we found that Aβ failed to depress synaptic transmission or inhibit synaptic plasticity in neurons lacking APP. To specifically test the role of caspase cleavage of the intracellular domain of APP, we introduced a mutation that inhibits caspase cleavage at site 664 to the C99 construct; this construct produced Aβ but failed to elicit Aβ-induced synaptic depression or spine loss, and reduced caspase-3 activity.
Taken together, these results suggest an APP-dependent pathway in which caspases contribute to Aβ-induced synaptic depression and spine loss via cleavage of APP.
越来越多的证据表明，β淀粉样蛋白（Aβ）处于阿尔茨海默病（AD）病理过程的核心位置，并且突触是Aβ造成损伤的起始部位。最近的研究还表明，半胱天冬酶在AD相关的突触功能障碍和记忆丧失中发挥作用，但其作用机制仍不清楚。先前的细胞培养研究表明，淀粉样前体蛋白（APP）细胞内结构域上的半胱天冬酶切割位点的切割有助于Aβ诱导的细胞死亡。然而，这一切割事件在突触功能障碍中的作用尚未得到证实。
通过细胞内和细胞外电生理方法以及树突棘的共聚焦显微镜检查相结合，我们研究了半胱天冬酶-3和淀粉样前体蛋白在Aβ介导的突触功能障碍中的作用。
在此，我们提供证据表明，APP细胞内结构域的半胱天冬酶活性是Aβ急性诱导谷氨酸能突触抑制所必需的。我们发现，如果通过药理学方法抑制半胱天冬酶或在缺乏半胱天冬酶-3的组织中，通过过表达APP的C末端片段（C99）使Aβ水平局部升高并不能抑制突触。为了证明这些发现与APP之间的联系，我们发现Aβ在缺乏APP的神经元中不能抑制突触传递或抑制突触可塑性。为了具体测试APP细胞内结构域的半胱天冬酶切割的作用，我们将一个抑制664位点半胱天冬酶切割的突变引入C99构建体；该构建体产生Aβ，但未能引发Aβ诱导的突触抑制或棘突丢失，并降低了半胱天冬酶-3的活性。
综上所述，这些结果表明存在一条依赖APP的途径，其中半胱天冬酶通过切割APP导致Aβ诱导的突触抑制和棘突丢失。
