磷酸二酯酶4抑制剂抗阿尔茨海默病的新机制：调控小胶质细胞自噬介导的神经炎症

Neuroinflammation contributes to the pathogenesis of Alzheimer’s disease (AD) and autophagy deficit is one of major causes of inflammatory activation. Studies have shown that cAMP induces the initiation of autophagy. However, the role of cAMP on autophagy in microglial cells is still unknown. Our previous studies showed that phosphodiesterase-4 (PDE4) inhibition suppressed neuroinflammation and improved the concentration of cAMP in the brain of mice subjected to Aβ injection. Herein, whether PDE4 inhibition could suppress neuroinflammation through inducing autophagic flux and thereby delay the development of AD is worth further study. Recently, we found that administration of microglia BV-2 cells with Aβ25-35 or (LPS+ATP) led to significant autophagy deficit, inflammasome activation and mature IL-1β release. Autophagy and neuroinflammation contribute to the pathogenesis of Alzheimer’s disease (AD). Our previous studies showed that phosphodiesterase-4 (PDE4) inhibition suppressed neuroinflammation and improved the concentration of cAMP in the brain of mice subjected to Aβ injection. Studies have shown that cAMP induces the initiation of autophagy. However, the role of cAMP on autophagy in microglial cells is still unknown. Recently, we found that administration of microglia BV-2 cells with Aβ25-35 or (LPS+ATP) led to significant autophagy deficit, inflammasome activation and mature IL-1β release. Moreover, we found that PDE4 inhibitor triggered the initiation of autphagy and reversed the pro-inflammatory effect of Aβ25-35 or (LPS+ATP) in BV-2 cells. Interestingly, the effect of PDE4 was autophay-dependent. Hence, we propose that PDE4 inhibition activates autophagy in microglial cells and attenuates the levels of inflammatory factors, which is supposed to be the novel mechanism elucidating the protective effect of PDE4 inhibitor against AD. On the basis of the above work, we will investigate the role of PDE4 inhibition on the alteration of autophagy and the underlying mechanisms in microglial cells, the role of autophagy on the production of inflammatory factors and the relationship between PDE4 inhibition. We aim to prove whether PDE4 could attenuate the production of pro-inflammtory factor through inducing autophay. Our study will provide a novel illustration for the protective effect of PDE4 inhibitor against AD, it may also offer possible intervention targets for the treatment of AD.

自噬和神经炎症均参与阿尔茨海默病（AD）的病理进程，我们前期研究发现磷酸二酯酶4（PDE4）抑制剂能增加AD模型鼠脑组织中cAMP的含量，并能抑制神经炎症。cAMP能促进自噬的发生，但在小胶质细胞参与的神经炎症中cAMP能否促进自噬尚不清楚。我们进一步发现Aβ或（LPS+ATP）刺激小胶质细胞BV-2可诱发自噬缺陷，并导致炎症小体的活化，增加IL-1β的水平；PDE4抑制剂能促进BV-2细胞自噬的发生，逆转Aβ及（LPS+ATP）的致炎作用。据此我们提出假说：抑制PDE4可能会促进小胶质细胞的自噬进而抑制神经炎症，可能是PDE4抑制剂抗AD的新机制。本项目将研究抑制PDE4对小胶质细胞自噬的影响及其机制、自噬对小胶质细胞炎症因子表达的影响及其与PDE4的关系，证实PDE4抑制剂是否可通过自噬影响炎症因子，从而实现抗AD的效应，以揭示PDE4抑制剂抗AD的新作用机制，发现AD治疗的潜在靶点。

磷酸二酯酶4(PDE4)抑制剂在阿尔茨海默病(AD)模型中同时具有改善认知及抗神经炎症的作用。在这一疾病中，PDE4是否是通过抑制小胶质细胞的自噬反应，从而促进神经炎症的发生是个值得研究的问题。本项目致力于探究这一问题，并研究PDE4在小胶质细胞中作用于自噬的信号通路。我们在细胞及动物模型中证实了抑制PDE4可以抑制小胶质细胞的活化、减少炎症因子的产生。进一步在脂多糖(LPS)及β淀粉样蛋白(Aβ)诱导的小鼠模型中，发现抑制PDE4后可改善学习记忆能力。对PDE4抑制剂的作用机制进行研究，发现自噬在这一过程中发挥了关键作用。抑制PDE4后，LC3II增加，自噬-溶酶体活性增强，p62下降，提示自噬激活；而NLRP3、cleaved caspase 1及IL-1β等水平下降，提示炎症小体的水平降低。在此基础上发现，抑制PDE4后，自噬上游信号通路AMPK及ULK1活化，且AMPK活化后增加了Sirt1的活性，进一步抑制炎症因子的产生。抑制AMPK、ULK1或Sirt1则能阻断PDE4抑制剂对自噬的促进作用；同时阻断了PDE4抑制剂对炎症因子的作用，还发现这一过程中，AMPK是ULK1的上游信号激酶。同时我们还证实了PDE4抑制剂对炎症因子诱导的海马神经元损伤具有保护作用。我们的研究表明：小胶质细胞自噬是一个上游事件。PDE4抑制剂通过激活AMPK/ULK1及AMPK/Sirt1信号通路促进自噬，降低炎症因子的水平，从而降低对神经元的损伤。另外，PDE4抑制剂亦可直接阻断炎症因子对神经元及突触的损伤。项目执行顺利，完成了既定的研究计划。