Department of Pharmacy, University of Pisa, 56126 Pisa, Italy.
Instituto de Biomedicina de Valencia-CSIC Spanish National Research Council, 46010 Valencia, Spain.
Biochim Biophys Acta Mol Basis Dis. 2023 Oct;1869(7):166793. doi: 10.1016/j.bbadis.2023.166793. Epub 2023 Jun 17.
The Apolipoprotein E (ApoE) has been known to regulate cholesterol and β-amyloid (Aβ) production, redistribution, and elimination, in the central nervous system (CNS). The ApoE ε4 polymorphic variant leads to impaired brain cholesterol homeostasis and amyloidogenic pathway, thus representing the major risk factor for Alzheimer's Disease (AD). Currently, less is known about the molecular mechanisms connecting ApoE ε4-related cholesterol metabolism and cholinergic system degeneration, one of the main AD pathological features. Herein, in vitro cholinergic neuron models were developed in order to study ApoE neuronal expression and investigate the possible interplay between cholesterol metabolism and cholinergic pathway impairment prompted by ε4 isoform. Particularly, alterations specifically occurring in ApoE ε4-carrying neurons (i.e. increased intracellular ApoE, amyloid precursor protein (APP) and Aβ levels, elevated apoptosis, and reduced cell survival) were recapitulated. ApoE ε4 expression was found to increase intracellular cholesterol accumulation, by regulating the related gene expression, while reducing cholesterol precursor acetyl-CoA, which in turn fuels the acetylcholine (ACh) synthesis route. In parallel, although the ACh intracellular signalling was activated, as demonstrated by the boosted extracellular ACh as well as increased IP and Ca, the PKCε activation via membrane translocation was surprisingly suppressed, probably explained by the cholesterol overload in ApoE ε4 neuron-like cells. Consequently, the PKC-dependent anti-apoptotic and neuroprotective roles results impaired, reliably adding to other causes of cell death prompted by ApoE ε4. Overall, the obtained data open the way to further critical considerations of ApoE ε4-dependent cholesterol metabolism dysregulation in the alteration of cholinergic pathway, neurotoxicity, and neuronal death.
载脂蛋白 E（ApoE）已被证实可调节中枢神经系统（CNS）中的胆固醇和β-淀粉样蛋白（Aβ）的产生、再分布和消除。载脂蛋白 E ε4 多态性变体导致脑胆固醇稳态和淀粉样蛋白形成途径受损，因此是阿尔茨海默病（AD）的主要危险因素。目前，人们对连接 ApoE ε4 相关胆固醇代谢和胆碱能系统退化的分子机制知之甚少，而胆碱能系统退化是 AD 的主要病理特征之一。在此，我们开发了体外胆碱能神经元模型，以研究 ApoE 神经元的表达，并研究由 ε4 异构体引起的胆固醇代谢和胆碱能途径损伤之间可能存在的相互作用。特别是， recapitulated 了特定发生在载脂蛋白 E ε4 携带神经元中的改变（即细胞内 ApoE、淀粉样前体蛋白（APP）和 Aβ水平升高、凋亡增加和细胞存活减少）。发现 ApoE ε4 表达通过调节相关基因表达而增加细胞内胆固醇积累，同时减少胆固醇前体乙酰辅酶 A，从而为乙酰胆碱（ACh）合成途径提供燃料。同时，尽管细胞内 ACh 信号通路被激活，如细胞外 ACh 以及 IP 和 Ca 的增加所证明的那样，但 PKCε 通过膜易位的激活出乎意料地受到抑制，这可能是由于 ApoE ε4 神经元样细胞中的胆固醇过载所致。因此，PKC 依赖性抗凋亡和神经保护作用受损，这可靠地增加了由 ApoE ε4 引起的其他细胞死亡原因。总的来说，获得的数据为进一步研究 ApoE ε4 依赖性胆固醇代谢失调在胆碱能途径改变、神经毒性和神经元死亡中的作用开辟了道路。
