Cuddy Leah K, Seah Claudia, Pasternak Stephen H, Rylett R Jane
Molecular Medicine Research Laboratories, Robarts Research Institute, University of Western Ontario, London, ON, Canada.
Department of Physiology and Pharmacology, Schulich School of Medicine & Dentistry, University of Western Ontario, London, ON, Canada.
Front Mol Neurosci. 2017 Nov 7;10:361. doi: 10.3389/fnmol.2017.00361. eCollection 2017.
Alzheimer's disease (AD) is a common age-related neurodegenerative disorder that is characterized by progressive cognitive decline. The deficits in cognition and attentional processing that are observed clinically in AD are linked to impaired function of cholinergic neurons that release the neurotransmitter acetylcholine (ACh). The high-affinity choline transporter (CHT) is present at the presynaptic cholinergic nerve terminal and is responsible for the reuptake of choline produced by hydrolysis of ACh following its release. Disruption of CHT function leads to decreased choline uptake and ACh synthesis, leading to impaired cholinergic neurotransmission. We report here that cell-derived β-amyloid peptides (Aβ) decrease choline uptake activity and cell surface CHT protein levels in SH-SY5Y neural cells. Moreover, we make the novel observation that the amount of CHT protein localizing to early endosomes and lysosomes is decreased significantly in cells that have been treated with cell culture medium that contains Aβ peptides released from neural cells. The Aβ-mediated loss of CHT proteins from lysosomes is prevented by blocking lysosomal degradation of CHT with the lysosome inhibitor bafilomycin A1 (BafA). BafA also attenuated the Aβ-mediated decrease in CHT cell surface expression. Interestingly, however, lysosome inhibition did not block the effect of Aβ on CHT activity. Importantly, neutralizing Aβ using an anti-Aβ antibody directed at the N-terminal amino acids 1-16 of Aβ, but not by an antibody directed at the mid-region amino acids 22-35 of Aβ, attenuates the effect of Aβ on CHT activity and trafficking. This indicates that a specific N-terminal Aβ epitope, or specific conformation of soluble Aβ, may impair CHT activity. Therefore, Aβ immunotherapy may be a more effective therapeutic strategy for slowing the progression of cognitive decline in AD than therapies designed to promote CHT cell surface levels.
阿尔茨海默病（AD）是一种常见的与年龄相关的神经退行性疾病，其特征是进行性认知衰退。AD临床观察到的认知和注意力处理缺陷与释放神经递质乙酰胆碱（ACh）的胆碱能神经元功能受损有关。高亲和力胆碱转运体（CHT）存在于突触前胆碱能神经末梢，负责摄取ACh释放后水解产生的胆碱。CHT功能破坏导致胆碱摄取和ACh合成减少，进而导致胆碱能神经传递受损。我们在此报告，细胞衍生的β-淀粉样肽（Aβ）可降低SH-SY5Y神经细胞中的胆碱摄取活性和细胞表面CHT蛋白水平。此外，我们有一个新发现，在用含有从神经细胞释放的Aβ肽的细胞培养基处理的细胞中，定位于早期内体和溶酶体的CHT蛋白量显著减少。用溶酶体抑制剂巴弗洛霉素A1（BafA）阻断CHT的溶酶体降解可防止Aβ介导的CHT蛋白从溶酶体中丢失。BafA还减弱了Aβ介导的CHT细胞表面表达的降低。然而，有趣的是，溶酶体抑制并未阻断Aβ对CHT活性的影响。重要的是，使用针对Aβ N端氨基酸1-16的抗Aβ抗体中和Aβ，而不是针对Aβ中间区域氨基酸22-35的抗体，可减弱Aβ对CHT活性和转运的影响。这表明特定的N端Aβ表位或可溶性Aβ的特定构象可能损害CHT活性。因此，与旨在提高CHT细胞表面水平的疗法相比，Aβ免疫疗法可能是减缓AD认知衰退进展的更有效治疗策略。
