Data_Sheet_3_Elevated Levels of miR-144-3p Induce Cholinergic Degeneration by Impairing the Maturation of NGF in Alzheimer’s Disease.docx

Cholinergic degeneration is one of the key pathological hallmarks of Alzheimer’s disease (AD), a condition that is characterized by synaptic disorders and memory impairments. Nerve growth factor (NGF) is secreted in brain regions that receive projections from the basal forebrain cholinergic neurons. The trophic effects of NGF rely on the appropriate maturation of NGF from its precursor, proNGF. The ratio of proNGF/NGF is known to be increased in patients with AD; however, the mechanisms that underlie this observation have yet to be elucidated. Here, we demonstrated that levels of miR-144-3p are increased in the hippocampi and the medial prefrontal cortex of an APP/PS1 mouse model of AD. These mice also exhibited cholinergic degeneration (including the loss of cholinergic fibers, the repression of choline acetyltransferase (ChAT) activity, the reduction of cholinergic neurons, and an increased number of dystrophic neurites) and synaptic/memory deficits. The elevated expression of miR-144-3p specifically targets the mRNA of tissue plasminogen activator (tPA) and reduces the expression of tPA, thus resulting in the abnormal maturation of NGF. The administration of miR-144-3p fully replicated the cholinergic degeneration and synaptic/memory deficits observed in the APP/PS1 mice. The injection of an antagomir of miR-144-3p into the hippocampi partially rescued cholinergic degeneration and synaptic/memory impairments by restoring the levels of tPA protein and by correcting the ratio of proNGF/NGF. Collectively, our research revealed potential mechanisms for the disturbance of NGF maturation and cholinergic degeneration in AD and identified a potential therapeutic target for AD.

胆碱能退变是阿尔茨海默病（Alzheimer’s disease, AD）的关键病理标志之一，该疾病以突触功能障碍和记忆损伤为典型特征。神经生长因子（nerve growth factor, NGF）在接受基底前脑胆碱能神经元投射的脑区中分泌。NGF的神经营养作用依赖于其前体（proNGF）向成熟NGF的正常加工过程。现有研究证实，AD患者体内proNGF/NGF的比值显著升高，但该现象背后的分子机制尚未阐明。本研究证实，在APP/PS1 AD小鼠模型的海马体（hippocampi）和内侧前额叶皮层（medial prefrontal cortex）中，微小RNA-144-3p（miR-144-3p）的表达水平显著升高。该模型小鼠同时表现出胆碱能退变表型，包括胆碱能纤维丢失、胆碱乙酰转移酶（choline acetyltransferase, ChAT）活性受抑制、胆碱能神经元数量减少以及营养不良性轴突（dystrophic neurites）数量增加，同时伴随突触与记忆功能缺陷。miR-144-3p的高表达可特异性靶向组织型纤溶酶原激活剂（tissue plasminogen activator, tPA）的mRNA并下调其表达，进而导致NGF的成熟过程异常。通过外源递送miR-144-3p，可完全重现APP/PS1小鼠中观察到的胆碱能退变与突触/记忆功能缺陷。向海马体注射miR-144-3p的拮抗剂寡核苷酸（antagomir），则可通过恢复tPA蛋白水平并纠正proNGF/NGF的比值，部分逆转胆碱能退变与突触/记忆功能损伤。综上，本研究揭示了AD中NGF成熟紊乱与胆碱能退变的潜在分子机制，并鉴定出一个极具潜力的AD治疗靶点。