Berson Amit, Soreq Hermona
Department of Biological Chemistry and the Edmond and Lily Safra Center of Neuroscience, The Hebrew University of Jerusalem, Jerusalem, Israel.
Rambam Maimonides Med J. 2010 Oct 31;1(2):e0014. doi: 10.5041/RMMJ.10014. Print 2010 Oct.
In Alzheimer's disease (AD), premature demise of acetylcholine-producing neurons and the consequent decline of cholinergic transmission associate with the prominent cognitive impairments of affected individuals. However, the enzymatic activities of acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) are altered rather late in the disease progress. This raised questions regarding the causal involvement of AChE and BChE in AD. Importantly, single nucleotide polymorphisms (SNPs), alternative splicing, and alternate promoter usage generate complex expression of combinatorial cholinesterase (ChE) variants, which called for testing the roles of specific variants in AD pathogenesis. We found accelerated amyloid fibril formation in engineered mice with enforced over-expression of the AChE-S splice variant which includes a helical C-terminus. In contrast, the AChE-R variant, which includes a naturally unfolded C-terminus, attenuated the oligomerization of amyloid fibrils and reduced amyloid plaque formation and toxicity. An extended N-terminus generated by an upstream promoter enhanced the damage caused by N-AChE-S, which in cell cultures induced caspases and GSK3 activation, tau hyperphosphorylation, and apoptosis. In the post-mortem AD brain, we found reduced levels of the neuroprotective AChE-R and increased levels of the neurotoxic N-AChE-S, suggesting bimodal contribution to AD progress. Finally, local unwinding of the α-helical C-terminal BChE peptide and loss of function of the pivotal tryptophan at its position 541 impair amyloid fibril attenuation by the common BChE-K variant carrying the A539T substitution, in vitro. Together, our results point to causal yet diverse involvement of the different ChEs in the early stages of AD pathogenesis. Harnessing the neuroprotective variants while reducing the levels of damaging ones may hence underlie the development of novel therapeutics.
在阿尔茨海默病（AD）中，产生乙酰胆碱的神经元过早死亡以及随之而来的胆碱能传递功能衰退与患者显著的认知障碍相关。然而，乙酰胆碱酯酶（AChE）和丁酰胆碱酯酶（BChE）的酶活性在疾病进展过程中改变得相当晚。这引发了关于AChE和BChE在AD中因果关系的疑问。重要的是，单核苷酸多态性（SNP）、可变剪接和启动子的交替使用产生了组合胆碱酯酶（ChE）变体的复杂表达，这就需要测试特定变体在AD发病机制中的作用。我们发现，在工程小鼠中强制过表达包含螺旋状C末端的AChE-S剪接变体时，淀粉样原纤维形成加速。相比之下，包含天然未折叠C末端的AChE-R变体减弱了淀粉样原纤维的寡聚化，并减少了淀粉样斑块的形成和毒性。由上游启动子产生的延长N末端增强了N-AChE-S造成的损伤，N-AChE-S在细胞培养中诱导半胱天冬酶和GSK3激活、tau蛋白过度磷酸化以及细胞凋亡。在AD患者的尸检大脑中，我们发现具有神经保护作用的AChE-R水平降低，而具有神经毒性的N-AChE-S水平升高，这表明其对AD进展具有双重作用。最后，在体外实验中，携带A539T替代的常见BChE-K变体中，α-螺旋C末端BChE肽的局部解旋以及其541位关键色氨酸的功能丧失削弱了对淀粉样原纤维的抑制作用。总之，我们的结果表明不同的ChE在AD发病机制的早期阶段存在因果关系但作用各异。因此，利用具有神经保护作用的变体同时降低具有损伤作用的变体水平可能是开发新型治疗方法的基础。
