神经生长因子增强小胶质细胞的神经保护作用

NGF steers microglia toward a neuroprotective phenotype

小胶质细胞是脑组织内的防御细胞,但在病理和生理条件下,调控小胶质细胞活化的因子并不十分清楚。本研究发现,神经生长因子(NGF)可以增强小胶质细胞的神经保护和抗炎功能。在体内和体外研究中都发现,小胶质细胞表达NGF受体。原代培养小胶质细胞,给予NGF处理,转录本分析结果显示,NGF对小胶质细胞的运动、吞噬和降解吞噬物的能力均产生影响。对功能的研究显示,NGF可增加小胶质细胞的膜运动能力和胞饮作用;在体研究显示,NGF可激活小胶质细胞释放向外整流电流,调节周围谷氨酸能神经元的神经传递。既往研究提示,小胶质细胞有清除脑内Aβ肽的功能,本研究观察了NGF对小胶质细胞吞噬能力的影响。结果显示,NGF可促进小胶质细胞通过Trk A途径清除Aβ,并加速其降解。此外,NGF还可减轻由Aβ导致的炎症激活。特异性激活小胶质细胞还可以减轻由Aβ导致的神经元树突损伤和长时程增强抑制。在对离体脑片的研究中,我们也发现NGF可以促进小胶质细胞吞噬Aβ。综上所述,本研究证实NGF可以促进小胶质细胞活化,活化的小胶质细胞通过抗炎作用减轻Aβ聚集,发挥神经保护作用。

Microglia are the sentinels of the brain but a clear understanding of the factors that modulate their ac- tivation in physiological and pathological conditions is still lacking. Here we demonstrate that Nerve Growth Factor （NGF） acts on microglia by steering them toward a neuroprotective and anti-inflammatory phenotype. We show that microglial cells express functional NGF receptors in vitro and ex vivo. Our transcriptomic analysis re- veals how, in primary microglia, NGF treatment leads to a modulation of motility, phagocytosis and degradation pathways. At the functional level, NGF induces an increase in membrane dynamics and macropinocytosis and, in vivo, it activates an outward rectifying current that appears to modulate glutamatergic neurotransmission in nearby neurons. Since microglia are supposed to be a major player in Aβ peptide clearance in the brain, we tested the effects of NGF on its phagocytosis. NGF was shown to promote TrkA-mediated engulfment of Aβ by microglia, and to enhance its degradation. Additionally, the proinflammatory activation induced by Aβ treatment is counter- acted by the concomitant administration of NGF. Moreover, by acting specifically on microglia, NGF protects neurons from the Aβ-induced loss of dendritic spines and inhibition of long term potentiation. Finally, in an ex-vivo setup of acute brain slices, we observed a similar increase in Aβ engulfment by microglial cells under the in- fluence of NGF. Our work substantiates a role for NGF in the regulation of microglial homeostatic activities and points toward this neurotrophin as a neuroprotective agent in Aβ accumulation pathologies, via its anti-inflammatory activity on microglia.