脂筏是研究神经元淀粉样蛋白β(Aβ)细胞毒性的主要目标。外源性Aβ肽与脂筏结合,反过来在Aβ摄取中起关键作用,导致神经毒性细胞内Aβ聚集体的形成。另一方面,在阿尔茨海默病(AD)中已观察到神经元细胞内钙稳态的失调。在以前的工作中,我们发现Aβ(1-42),在AD患者的淀粉样斑块中发现的普遍的Aβ肽,以高亲和力结合纯化的钙调蛋白(CaM),解离常数≈1nM。在这项工作中,实验评估Aβ(1-42)与细胞内CaM的结合能力,我们使用成熟小脑颗粒神经元(CGN)的原代培养物作为神经元模型。我们的结果表明,CGN中CaM对亚微摩尔浓度的Aβ(1-42)二聚体进行了大量络合,高达120±13皮摩尔的Aβ(1-42)/2.5×106细胞。使用荧光显微镜成像,我们显示CaM和Aβ(1-42)在CGN的脂筏中广泛的共定位,用多达100皮摩尔的Aβ(1-42)-HiLyteTM-Fluor555单体染色。通过将CGN与2μMAβ(1-42)孵育2小时,可以达到该范围内的细胞内Aβ(1-42)浓度,在部分去极化的25mM钾培养基中,这种处理降低了成熟CGN的静止胞质钙。我们得出的结论是,静息胞浆钙减少的主要原因是Aβ(1-42)二聚体对CGN的L型钙通道的抑制,其活性被与脂质筏结合的CaM:Aβ(1-42)复合物抑制。
Lipid rafts are a primary target in studies of amyloid β (Aβ) cytotoxicity in neurons. Exogenous Aβ peptides bind to lipid rafts, which in turn play a key role in Aβ uptake, leading to the formation of neurotoxic intracellular Aβ aggregates. On the other hand, dysregulation of intracellular calcium homeostasis in neurons has been observed in Alzheimer\'s disease (AD). In a previous work, we showed that Aβ(1-42), the prevalent Aβ peptide found in the amyloid plaques of AD patients, binds with high affinity to purified calmodulin (CaM), with a dissociation constant ≈1 nM. In this work, to experimentally assess the Aβ(1-42) binding capacity to intracellular CaM, we used primary cultures of mature cerebellar granule neurons (CGN) as a neuronal model. Our results showed a large complexation of submicromolar concentrations of Aβ(1-42) dimers by CaM in CGN, up to 120 ± 13 picomoles of Aβ(1-42) /2.5 × 106 cells. Using fluorescence microscopy imaging, we showed an extensive co-localization of CaM and Aβ(1-42) in lipid rafts in CGN stained with up to 100 picomoles of Aβ(1-42)-HiLyteTM-Fluor555 monomers. Intracellular Aβ(1-42) concentration in this range was achieved by 2 h incubation of CGN with 2 μM Aβ(1-42), and this treatment lowered the resting cytosolic calcium of mature CGN in partially depolarizing 25 mM potassium medium. We conclude that the primary cause of the resting cytosolic calcium decrease is the inhibition of L-type calcium channels of CGN by Aβ(1-42) dimers, whose activity is inhibited by CaM:Aβ(1-42) complexes bound to lipid rafts.