Pen2在成年神经元存活和大脑认知功能中的作用

Presenilin (PS)，presenilin enhancer2 (Pen2) and nicastrin (NCT) are key subunits of the γ-secretase complex, and are associated with familial Alzheimer's disease (AD). PS possesses both γ-secretase-dependent and -independent functions. Accumulating evidence has indicated that presenilins (PSs) are required for synaptic plasticity, memory and neuronal survival. However, it is unclear whether PSs carry out these essential functions through a γ-secretase-dependent or -independent manner. In vitro evidence has shown that expression levels of full-length PS are down-regulated by loss of NCT, but are up-regulated by loss of Pen2. Our recent study has revealed essential roles of NCT in cognitive function and neuronal survival. However, it remains completely unknown whether Pen2 is important for synaptic plasticity, memory and neuronal survival. Our central hypothesis is that Pen2 plays essential roles in these physiological processes. To test it, we will take advantage of Cre-LoxP recombination technology to inactivate Pen2 specifically in forebrain excitatory neurons of the mice, which allows us to study its normal physiological functions. We will also study molecular mechanisms by which NCT and Pen2 regulate apoptosis in adult brains through direct comparisons of the two different lines of forebrain-specific NCT and Pen2 conditional knockout mice. Elucidation of novel roles of Pen2 will provide significant insights on molecular mechanisms for cognitive impairment and cell death in neurodegenerative diseases, and may further help identify novel therapeutic targets for the treatment or prevention of neurodegeneration.

γ-分泌酶亚基presenilin(PS)，presenilin enhancer2 (Pen2)和nicastrin(NCT)与家族性阿尔茨海默氏病的发生有密切联系。PS具有依赖于γ-分泌酶和独立于γ-分泌酶的功能，但它以哪一种方式参与突触可塑性和成年神经元存活的过程还有很大争议。Pen2和NCT对全长PS的表达有截然相反的作用。Pen2在成年大脑中正常的生理功能还未有报道。我们前期工作表明NCT对认知功能有重要作用，但还不清楚它对突触可塑性的贡献。我们的假说是Pen2依赖的γ-分泌酶活性在突触可塑性，认知功能和神经元存活中有重要作用。我们将采用Cre-loxP技术使Pen2在前脑神经元中条件性地失活以研究它的正常生理功能。我们还将比较Pen2和NCT调控细胞凋亡的分子机制是否有差异。这些研究可阐明Pen2调控成年神经元存活和认知功能的机制，也有助发现新的治疗靶点以预防神经退行死亡。

γ-分泌酶亚基PS，Pen2和NCT与家族性阿尔茨海默氏病的发生有密切联系。过去的研究表明条件敲除PS1/2导致年龄依赖的神经元退行死亡。PS是否以依赖γ-分泌酶的方式调控成年神经元存活和突触可塑性还不确定。为了研究这个问题，在本项目中我们制作了前脑神经元特异的Pen2 cKO和NCT cKO小鼠。我们发现它们均表现年龄依赖的神经元退行死亡。而且Pen2 cKO和NCT cKO小鼠还表现明显增加的细胞凋亡和tau蛋白磷酸化。利用单细胞电生理技术我们发现海马锥体神经元中特异敲除Pen2之后，AMPAR和NMDAR介导的电流明显下降。我们进一步发现Dicer和Akt的表达水平在敲除小鼠中显著下调。为此我们制作了Dicer cKO 和Akt cTKO小鼠并研究了这两类分子在介导依赖于γ-分泌酶的神经元存活、细胞凋亡和tau磷酸化所起的不同作用。本项目的研究对理解家族性AD的病发机制及发现防治该病的新靶点有重要的意义。