Mechanisms of nuclear pore complex homeostasis and injury in ALS/FTD and related neurodegenerative diseases

肌萎缩侧索硬化症(ALS)和额颞叶痴呆(FTD)是一系列破坏性和致命性神经退行性疾病。虽然有20多个遗传位点与ALS和FTD有关，但大约90%的ALS病例本质上是散发性的。最近的研究发现，核孔复合体(NPC)和核质转运(NCT)的改变是家族性和散发性ALS的重要发病机制。然而，这些病理破坏背后的分子机制在很大程度上仍不清楚。我们最近的研究已经证实，在C9orf72 IPSN和死后患者的神经元核中，有来自鼻咽癌的8种核孔蛋白(NUP)的可重复性和强劲的减少。最近的工作表明，ESCRT-III途径在监测和维持酵母中正确组装和功能的NPC中发挥着重要作用。关键的是，在这些非中枢神经系统中的研究表明，CHMP7在核膜上的招募启动了下游事件，导致NUP和NPC的降解。的确，在人类C9orf72神经元中，NPC中NUP的减少似乎是CHMP7和ESCRT-III介导的降解途径异常激活的结果，而不是Nup错误定位或Nup mRNA代谢改变的结果。然而，对于这些最初的发现与更为常见的散发性肌萎缩侧索硬化症(SAL)之间的关系，人们实际上知之甚少。使用超分辨率结构照明显微镜(SIM)对SALS IPSC来源的脊髓神经元的子集进行研究，我们产生的初步数据有力地表明，NPC和Nup缺陷是SALS中普遍存在的一种病理。值得注意的是，到目前为止，在大约50%的SALS IPSN和死后运动皮质样本中，我们也观察到了稳健的CHMP7病理，这让人想起我们在C9orf72 ALS/FTD中的研究。总而言之，这些早期研究使我们假设，在人类神经元中，ESCRT-III通路的异常激活可能是鼻咽癌、NCT和总体细胞存活中断的重要因素，从而突显了CHMP7作为ALS和以鼻咽癌损伤为特征的相关神经退行性疾病的治疗靶点的潜力。在这里，我们将使用IPSNs和死后人的CNS组织来全面地定义SALS发病机制中单个NUPS和NPC的变化(目标1)。此外，我们将评估CHMP7和异常ESCRT-III介导的降解在SALS鼻咽癌损伤中的作用(目标2)。最后，我们将确定CHMP7在病理上被“激活”以启动SALS鼻咽癌损伤的机制(目标3)。总的来说，这些实验将极大地促进我们对鼻咽癌在人类神经元和SALS疾病中的动态平衡机制的理解，并为潜在的新的治疗靶点提供新的见解。此外，拟议的研究将为未来研究CHMP7和Nup降解在FTD和其他相关神经退行性疾病的发病机制中的作用奠定基础。

Amyotrophic Lateral Sclerosis (ALS) and Frontotemporal Dementia (FTD) comprise a spectrum of devastating and fatal neurodegenerative diseases. While over 20 genetic loci have been linked to ALS and FTD, about 90% of ALS cases are sporadic in nature. Recent studies have identified alterations in the nuclear pore complex (NPC) and nucleocytoplasmic transport (NCT) as a prominent pathomechanism underlying familial and sporadic ALS. However, the molecular mechanisms underlying these pathologic disruptions remain largely unknown. Our recent studies have established that there is a reproducible and robust reduction of eight nucleoporins (Nups) from the NPC in C9orf72 iPSN and postmortem patient neuronal nuclei. Recent work suggests that the ESCRT-III pathway plays a fundamental role in the surveillance and maintenance of properly assembled and functioning NPCs in yeast. Critically, work in these non-CNS systems suggests that recruitment of CHMP7 to the nuclear envelope initiates downstream events leading to degradation of Nups and NPCs. Indeed, the reduction of Nups from the NPC in C9orf72 human neurons appears to be the result of aberrant activation of CHMP7 and ESCRT-III mediated degradation pathways and not the result of Nup mislocalization or alterations in Nup mRNA metabolism. However, little is actually known about how these initial discoveries relate to the far more common sporadic ALS (sALS). Using super resolution structured illumination microscopy (SIM) on a subset of sALS iPSC derived spinal neurons, we have generated preliminary data that strongly suggests NPC and Nup defects are a prevalent pathology in sALS. Notably, in about 50% of sALS iPSNs and postmortem motor cortex samples examined to date, we also observe robust CHMP7 pathology, reminiscent of our studies in C9orf72 ALS/FTD. Collectively, these early studies have led us to hypothesize that in human neurons, aberrant activation of the ESCRT-III pathway may be a substantial contributor to disruptions in the NPC, NCT, and overall cellular survival thus highlighting the potential for CHMP7 as a therapeutic target in ALS and related neurodegenerative diseases characterized by NPC injury. Here, we will use iPSNs and postmortem human CNS tissue to comprehensively define the alterations to individual Nups and NPCs in sALS pathogenesis (Aim 1). Furthermore, we will evaluate the contribution of CHMP7 and aberrant ESCRT-III mediated degradation to NPC injury in sALS (Aim 2). Finally, we will define the mechanism by which CHMP7 is pathologically “activated” to initiate NPC injury in sALS (Aim 3). Collectively, these experiments will significantly advance our understanding of the mechanisms underlying NPC homeostasis in human neurons and sALS disease and provide novel insights into potential new therapeutic targets. Moreover, the proposed studies will set the stage for future investigations into the role of CHMP7 and Nup degradation in the pathogenesis of FTD and other related neurodegenerative diseases.