Neuronal cell-cycle re-entry and neurodegeneration

阿尔茨海默病(AD)和AD相关神经退行性变的两种致病机制 像肌萎缩侧索硬化症-额颞性痴呆(ALS-FTD)这样的疾病是有丝分裂的重新启动 神经元中的细胞周期，以及核破裂导致的核质运输受损 核膜(NE)和核孔复合体(NPC)。更深入地了解这些异常是如何产生的，将澄清 设计有效治疗这些疾病的方法；然而，人们对这些疾病的启动知之甚少 涉及的机制。这一应用将检验神经元保持静止的假设 在整个生命过程中，通过抑制有丝分裂细胞周期和重新启动细胞周期引导的活跃机制 去甲肾上腺素/鼻咽癌，这在有丝分裂细胞中是正常发生的。这一假说是基于我们对六种跨膜酶GDE2(甘油磷酸二酯磷酸二酯二酯酶2；GDPD5)的研究，它切割GPI-(糖基磷脂酰肌醇)锚，将一些蛋白质拴在质膜上。GDE2是一种强大的 抑制有丝分裂细胞周期，并诱导有丝分裂祖细胞分化为有丝分裂后神经元 发育中的神经系统。我们发现，在缺乏GDE2(Gde2KO)的成年小鼠中，皮质神经元 显示细胞周期重新进入的证据，表明GDE2是保存处于静止状态的神经元所必需的。 引人注目的是，重新进入细胞周期的Gde2 KO神经元显示出NE的异常组织，异常 鼻咽癌蛋白的分布和核质转运受损，增加了细胞周期重新启动和NE/NPC崩溃联系在一起的可能性。与这一观点一致，细胞周期蛋白D的基因减少是一种关键的 G1/S转换调节因子抑制小鼠脑内核质转运依赖性神经变性 C9ORF72 ALS-FTD果蝇模型的建立值得注意的是，Gde2 KO小鼠表现出年龄进行性神经变性 而GDE2在AD患者神经元中的分布和功能被破坏。这些观察结果表明 维持神经元的静止是一个活跃的过程，这个过程的失败会重新启动细胞周期，触发NE/NPC的破坏，并诱导神经退行性变。目标1将确定GDE2是否编码一个 维持神经元静止并将决定神经元细胞周期重入信号的新途径 NE/NPC在神经元中的分解。初步的RNAseq，Gde2 KOS中Wnt报告小鼠的分析，以及遗传 在果蝇中的研究发现，规范的Wnt信号的异常激活是诱导 神经细胞周期重入、NE/NPC崩溃和神经变性。目标2将利用鼠标和 用果蝇模型来验证这一假设。AIM 3的研究将确定GDE2功能障碍之间的联系， 果蝇AD和ADRD模型中神经细胞周期重入和NE/NPC的破坏 人死后组织和iPS人神经元。这些研究将为人类AD和ADRD中重要的跨疾病神经退行性变的触发因素提供新的分子见解。

Two causal mechanisms of neurodegeneration that are found in Alzheimer's disease (AD) and AD-related diseases such as amyotrophic lateral sclerosis-frontotemporal dementia (ALS-FTD) are re-initiation of the mitotic cell-cycle in neurons, and impaired nucleocytoplasmic trafficking resulting from disruptions in the nuclear envelope (NE) and nuclear pore complex (NPC). Deeper insight into how these abnormalities arise would clarify approaches to design effective treatments for these diseases; however, very little is known about the initiating mechanisms involved. This application will test the hypothesis that neuronal quiescence is maintained throughout life via active mechanisms that inhibit the mitotic cell-cycle and that re-initiation of the cell-cycle leads to NE/NPC disassembly, a normal occurrence in mitotic cells. This hypothesis is based on our study of the six-transmembrane enzyme GDE2 (Glycerophosphodiester phosphodiesterase 2; GDPD5), which cleaves the GPI-(Glycosylphosphatidylinositol)-anchor that tethers some proteins to the plasma membrane. GDE2 is a potent inhibitor of the mitotic cell-cycle and induces the differentiation of mitotic progenitors into post-mitotic neurons in the developing nervous system. We discovered that in adult mice lacking GDE2 (Gde2 KO), cortical neurons show evidence of cell-cycle re-entry, suggesting that GDE2 is required to preserve neurons in a quiescent state. Strikingly, Gde2 KO neurons that have re-entered the cell-cycle show abnormal organization of the NE, aberrant distribution of NPC proteins and impaired nucleocytoplasmic transport, raising the possibility that cell-cycle re-initiation and NE/NPC breakdown are linked. Consistent with this idea, genetic reduction of cyclin D, a critical regulator of the G1/S transition, suppresses nucleocytoplasmic transport-dependent neurodegeneration in a Drosophila model of c9ORF72 ALS-FTD. Notably, Gde2 KO mice display age-progressive neurodegeneration and GDE2 distribution and function is disrupted in AD patient neurons. These observations suggest that maintenance of neuronal quiescence is an active process and that failure of this process re-initiates the cell-cycle, triggers NE/NPC breakdown and induces neurodegeneration. Aim 1 will determine if GDE2 encodes a new pathway that maintains neuronal quiescence and will determine if neuronal cell-cycle re-entry signals NE/NPC breakdown in neurons. Preliminary RNAseq, analysis of Wnt-reporter mice in Gde2 KOs, and genetic studies in Drosophila identify aberrant activation of canonical Wnt signaling as a candidate pathway that induces neuronal cell-cycle re-entry, NE/NPC breakdown and neurodegeneration. Aim 2 will utilize mouse and Drosophila models to test this hypothesis. Studies in Aim 3 will determine links between GDE2 dysfunction, neuronal cell-cycle re-entry and NE/NPC breakdown in disease using Drosophila models of AD and ADRD, human postmortem tissue and iPS human neurons. These studies will provide new molecular insight into cross-disease triggers of neurodegeneration important in human AD and ADRDs.