Investigation of UBQLN2 in neuronal dysfunction and ALS-FTD

肌萎缩侧索硬化伴额颞叶痴呆（ALS-FTD）是一种进行性、致死性 神经退行性疾病，其由上运动神经元和下运动神经元以及下运动神经元的丧失引起。 额叶皮层ALS-FTD导致的症状为进行性运动和认知障碍。之甚少 了解疾病的潜在机制，并且没有有效的治疗方法， 延长寿命。10%的ALS-FTD病例显示家族遗传模式，通常可追溯至 特定基因的突变。家族性ALS-FTD（fALS-FTD）与散发性ALS-FTD具有相同的关键特征，意味着 fALS-FTD的研究可以为对抗这种毁灭性疾病提供广泛适用的发现。 人UBQLN 2基因突变导致部分fALS-FTD病例，但其机制尚不清楚。 疾病知之甚少。UBQLN是一个蛋白酶体穿梭因子家族，其促进蛋白酶体穿梭。 尽管这些底物的身份一直是难以捉摸的，但这些底物的降解是“困难的”蛋白酶体底物。我们 最近发表了UBQLN 2调节蛋白PEG 10的蛋白酶体降解。PEG 10，或"父性地 表达的基因10 '是一种"驯化的逆转录转座子"：它在其结构上类似于逆转录转座子和逆转录病毒。 整体结构，但不能在基因组内转座。像它的病毒表亲一样，PEG10蛋白含有 一个核酸结合锌指和一个蛋白酶结构域，两者的功能都未知。我们最近发现 PEG 10是一种活性自身蛋白酶，释放含有核酸结合区的蛋白质片段， 然后运输到细胞核。该片段的单独表达足以上调 参与轴突重塑的基因，其在ALS-FTD组织中同样上调。因此，PEG 10是 UBQLN 2功能障碍时ALS-FTD分子原因的极佳候选者。在我们的模型中， 损失或功能障碍导致PEG 10积累，核酸结合片段的释放增加，和 上调轴突重塑基因，导致疾病表型。该提案旨在验证和 通过补充体外和体内方法，深入探索我们的新疾病模型。 我们未来五年的目标是深入了解UBQLN 2-PEG 10 关系以及它如何影响ALS-FTD的发展。在我们的第一个目标中，我们仔细检查了 ALS和FTD患者组织中PEG 10的丰度和蛋白水解活性。在第二个目标中，我们确定 PEG 10在UBQLN 2介导的疾病的细胞和动物模型中的机制和精确贡献。 最后，我们深入研究了UBQLN 2-PEG 10相互作用的分子基础，以产生 UBQLN客户端选择的第一个详细模型。我们研究项目的发现将改变我们的 对PEG10功能以及UBQLN 2生物学的基本了解，并可能为研究提供关键的新靶点。 对抗ALS-FTD。

Amyotrophic Lateral Sclerosis with frontotemporal dementia (ALS-FTD) is a progressive, fatal neurodegenerative disease that results from the loss of upper and lower motor neurons, as well as neurons of the frontal cortex. The resulting symptoms of ALS-FTD are progressive motor and cognitive impairment. Little is known about the underlying mechanism of disease, and there are no effective treatments that significantly lengthen lifespan. 10% of ALS-FTD cases show a familial pattern of inheritance and can often be traced to mutation of specific genes. Familial ALS-FTD (fALS-FTD) shares key features with sporadic ALS-FTD, meaning that the study of fALS-FTD can provide broadly applicable findings in the fight against this devastating disease. Mutations in the human UBQLN2 gene lead to a portion of fALS-FTD cases, but the mechanism of disease is poorly understood. UBQLNs are a family of proteasome shuttle factors which facilitate proteasomal degradation of ‘difficult’ proteasome substrates, though the identity of these substrates has been elusive. We recently published that UBQLN2 regulates proteasomal degradation of the protein PEG10. PEG10, or ‘paternally expressed gene 10’, is a ‘domesticated retrotransposon’: it resembles retrotransposons and retroviruses in its overall structure, but is unable to transpose within the genome. Like its viral cousins, the PEG10 protein contains a nucleic-acid binding zinc finger and a protease domain, both with unknown function. We recently discovered that PEG10 is an active self-protease and releases a protein fragment containing the nucleic acid-binding region which then traffics to the nucleus. Expression of this fragment alone is sufficient to upregulate expression of genes involved in axon remodeling, which are similarly upregulated in ALS-FTD tissues. Therefore, PEG10 is an excellent candidate for the molecular cause of ALS-FTD upon UBQLN2 dysfunction. In our model, UBQLN2 loss or dysfunction leads to PEG10 accumulation, increased liberation of the nucleic acid-binding fragment, and upregulated axon remodeling genes, leading to phenotypes of disease. This proposal seeks to validate and explore our new model of disease in depth with a complement of in vitro and in vivo approaches. Our goals for the next five years are to generate a deep understanding of the UBQLN2-PEG10 relationship and how it influences the development of ALS-FTD. In our first Aim, we carefully examine the abundance and proteolytic activity of PEG10 in ALS and FTD patient tissue. In our second Aim, we determine the mechanism and precise contribution of PEG10 in cellular and animal models of UBQLN2-mediated disease. Finally, we dive deeply into the molecular underpinnings of UBQLN2-PEG10 interactions in order to generate the first detailed model for UBQLN client selection. The findings from our research program will transform our basic understanding of PEG10 function as well as UBQLN2 biology, and may provide crucial new targets for the fight against ALS-FTD.