Züchner Thole, Perez-Polo J Regino, Schliebs Reinhard
Paul Flechsig Institute for Brain Research, Department of Neurochemistry, University of Leipzig, Leipzig, Germany.
J Neurosci Res. 2004 Jul 15;77(2):250-7. doi: 10.1002/jnr.20152.
The beta-amyloid peptides derived by proteolytic cleavage from the amyloid precursor protein (APP) play a major role in the pathogenesis of Alzheimer's disease (AD) by forming aggregated, fibrillary complexes that have been shown to be neurotoxic. The beta-site APP-cleaving enzyme (BACE1) has been identified as the key enzyme leading to beta-amyloid formation, and cholinergic mechanisms have been shown to control APP processing. The present study sought to determine whether BACE1 expression is controlled by muscarinic acetylcholine receptor (mAChR) subtypes in the neuroblastoma cell line SK-SH-SY5Y. Stimulation of cells with the M1/M3-selective mAChR agonist talsaclidine for 1 hr resulted in a dose-dependent increase in BACE1 expression up to twofold over basal levels. Similar effects of BACE1 up-regulation were observed when protein kinase C was directly activated by phorbol esters. However, when the MAP kinases MEK/ERK were inhibited, BACE1 expression was no longer up-regulated by the activation of M1-mAChR. In contrast, BACE1 expression was suppressed by stimulation of M2-mediated pathways via selective M2-agonist binding or direct activation of adenylate cyclase with forskolin, an effect that was prevented by inhibiting protein kinase A. These results may explain the observed deterioration of AD patients after initial improvements with AChE inhibitor or M1-mAChR agonist treatment.
通过蛋白水解从淀粉样前体蛋白（APP）衍生而来的β-淀粉样肽，通过形成已被证明具有神经毒性的聚集性纤维状复合物，在阿尔茨海默病（AD）的发病机制中起主要作用。β-位点APP裂解酶（BACE1）已被确定为导致β-淀粉样蛋白形成的关键酶，并且胆碱能机制已被证明可控制APP的加工过程。本研究旨在确定在神经母细胞瘤细胞系SK-SH-SY5Y中，BACE1的表达是否受毒蕈碱型乙酰胆碱受体（mAChR）亚型的控制。用M1/M3选择性mAChR激动剂他索氯定刺激细胞1小时，导致BACE1表达呈剂量依赖性增加，最高可达基础水平的两倍。当蛋白激酶C被佛波酯直接激活时，也观察到了BACE1上调的类似效果。然而，当丝裂原活化蛋白激酶MEK/ERK被抑制时，M1-mAChR的激活不再上调BACE1的表达。相反，通过选择性M2激动剂结合或用福司可林直接激活腺苷酸环化酶来刺激M2介导的途径，可抑制BACE1的表达，这种作用可通过抑制蛋白激酶A来预防。这些结果可能解释了在最初使用乙酰胆碱酯酶抑制剂或M1-mAChR激动剂治疗后AD患者病情出现恶化的现象。
