β-Amyloid 1-42 Oligomers Impair Function of Human Embryonic Stem Cell-Derived Forebrain Cholinergic Neurons

Cognitive impairment in Alzheimer's disease (AD) patients is associated with a decline in the levels of growth factors, impairment of axonal transport and marked degeneration of basal forebrain cholinergic neurons (BFCNs). Neurogenesis persists in the adult human brain, and the stimulation of regenerative processes in the CNS is an attractive prospect for neuroreplacement therapy in neurodegenerative diseases such as AD. Currently, it is still not clear how the pathophysiological environment in the AD brain affects stem cell biology. Previous studies investigating the effects of the β-amyloid (Aβ) peptide on neurogenesis have been inconclusive, since both neurogenic and neurotoxic effects on progenitor cell populations have been reported. In this study, we treated pluripotent human embryonic stem (hES) cells with nerve growth factor (NGF) as well as with fibrillar and oligomeric Aβ1-40 and Aβ1-42 (nM-µM concentrations) and thereafter studied the differentiation in vitro during 28-35 days. The process applied real time quantitative PCR, immunocytochemistry as well as functional studies of intracellular calcium signaling. Treatment with NGF promoted the differentiation into functionally mature BFCNs. In comparison to untreated cells, oligomeric Aβ1–40 increased the number of functional neurons, whereas oligomeric Aβ1–42 suppressed the number of functional neurons. Interestingly, oligomeric Aβ exposure did not influence the number of hES cell-derived neurons compared with untreated cells, while in contrast fibrillar Aβ1–40 and Aβ1–42 induced gliogenesis. These findings indicate that Aβ1–42 oligomers may impair the function of stem cell-derived neurons. We propose that it may be possible for future AD therapies to promote the maturation of functional stem cell-derived neurons by altering the brain microenvironment with trophic support and by targeting different aggregation forms of Aβ.

阿尔茨海默病（Alzheimer's disease, AD）患者的认知功能损害与生长因子水平下降、轴突运输受损以及基底前脑胆碱能神经元（basal forebrain cholinergic neurons, BFCNs）显著变性密切相关。成人大脑中仍存在神经发生现象，刺激中枢神经系统（central nervous system, CNS）的再生过程，对于阿尔茨海默病这类神经退行性疾病的神经替代治疗而言是极具吸引力的研究方向。目前，学界仍未明确阿尔茨海默病大脑内的病理生理微环境如何影响干细胞生物学特性。既往针对β-淀粉样蛋白（β-amyloid, Aβ）肽段对神经发生影响的研究结论并不一致，因为已有文献报道了其对祖细胞群体既存在神经营养作用又具有神经毒性。本研究将多能人胚胎干细胞（pluripotent human embryonic stem cells, hES）分别用神经生长因子（nerve growth factor, NGF）、原纤维型及寡聚体型Aβ1-40和Aβ1-42（浓度范围为nM至µM级别）进行处理，随后在28至35天内体外研究其分化情况。本研究采用实时定量聚合酶链式反应（real time quantitative PCR）、免疫细胞化学技术以及细胞内钙信号传导功能实验开展相关分析。神经生长因子处理可促进干细胞向功能成熟的基底前脑胆碱能神经元分化。与未处理组细胞相比，寡聚体型Aβ1-40可增加功能性神经元的数量，而寡聚体型Aβ1-42则会抑制功能性神经元的生成。值得注意的是，与未处理组相比，寡聚型Aβ暴露并未改变人胚胎干细胞衍生神经元的数量；与之形成对比的是，原纤维型Aβ1-40与Aβ1-42可诱导神经胶质生成。上述研究结果表明，Aβ1-42寡聚体可能会损害干细胞衍生神经元的功能。我们提出，未来阿尔茨海默病治疗或可通过营养支持改善大脑微环境，并靶向不同聚集形式的Aβ，从而促进功能性干细胞衍生神经元的成熟。