Investigation on Ataxin2 and Matrin3 in neurodegenerative disease

RNA结合蛋白(RBPs)的功能障碍或突变与越来越多的 神经退行性疾病(NDDS)，包括肌萎缩侧索硬化症(ALS)、AD/ADRD和2型脊髓小脑性共济失调(SCA2)。RBP Aaxin-2是ALS的有效修饰物，靶向疗法已经在临床试验中。然而，Aaxin-2在ALS和痴呆中的潜在致病机制以及它与其他致病限制性商业惯例相互作用的作用尚不清楚。我们发现核基质RBP Matrin-3与Aaxin-2相互作用，并建议从功能上研究ALS/FTD相关神经元中的相互作用。Matrin-3基因突变导致FTD、家族性ALS和多系统蛋白病 (MSP)。与TDP-43一样，在ALS/FTD中也观察到Matrin-3蛋白病变，即使它没有突变。在阿尔茨海默病(AD)患者的神经元中也观察到Matrin-3的细胞质聚集。我们的初步数据表明，靶向MATR3可能对这些疾病有治疗作用：我们观察到C9ORF72和TDP-43突变的ALS和FTD患者的成纤维细胞中Matrin-3过多，这是通过RNAi降低ATXN2表达而正常化的。FTD/ALS相关的Matrin3-S85C小鼠模型表现出广泛的选择性浦肯野细胞(PC)丢失。PC是SCA2中受影响的神经元，而神经细胞 对Aaxin-2突变易感性最高的人群。Matrin-3 S85C小鼠的严重小脑神经变性表明Matrin-3和Aaxin-2之间存在病理联系，这可能定义了与包括FTD在内的其他NDDS相关的神经元死亡途径。我们认为在疾病的背景下，Aaxin-2与Matrin-3的相互作用将有助于病理学的发展，靶向Aaxin-2将减轻Matrin-3的病理和神经元死亡。我们计划在分离培养的神经细胞中研究与Aaxin-2、Matrin-3和ALS相关的病理学，这些神经细胞来源于Aaxin-2基因敲除、Aaxin-2扩张和TDP-43突变 老鼠。我们将通过表达Matrin-3突变和/或用腺病毒和反义寡核苷酸策略击倒Aaxin-2来确定不同限制性商业惯例的作用。我们打算研究的病理表型包括Matrin-3的水平、定位、溶解性变化、凝集成凝集物和对神经元的毒性，以及ALS分子读数，包括TDP-43的聚集和定位。我们还将研究其他相关蛋白质病生物分子在凝聚体中的成核作用。在正常、扩增和敲除Aaxin-2和突变的TDP-43的背景下进行分析，将有助于了解Aaxin-2、Matrin-3的作用以及RBPs在SCA2和ALS/FTD发病机制中的相互作用。这项研究将为在具有MATR3突变的ALS和FTD患者以及其他患有Matrin-3蛋白病的AD/ADRD患者中直接靶向ATXN2和MATR3提供初步的概念验证。

Dysfunction or mutation of RNA binding proteins (RBPs) is associated with a growing number of neurodegenerative diseases (NDDs), including amyotrophic lateral sclerosis (ALS), AD/ADRDs and spinocerebellar ataxia type 2 (SCA2). The RBP Ataxin-2 is a potent modifier of ALS and targeting therapeutics are already in clinical trials. However, the underlying pathogenic mechanisms of Ataxin-2 in ALS and dementias, and the roles of its interaction with other pathogenic RBPs are poorly understood. We found that the nuclear matrix RBP Matrin-3 interacts with Ataxin-2 and propose to study the interaction functionally in ALS/FTD-relevant neurons. Mutations in Matrin-3 cause FTD, familial ALS and multisystem proteinopathy (MSP). Like TDP-43, Matrin-3 proteinopathy has been observed in ALS/FTD even when it is not mutated. Cytoplasmic aggregation of Matrin-3 has also been observed in Alzheimer’s disease (AD) patient neurons. Our preliminary data suggest that targeting MATR3 may be therapeutic for these disorders: We observed Matrin-3 overabundance in fibroblasts from ALS and FTD patients with C9ORF72 and TDP-43 mutations, that was normalized by lowering ATXN2 expression by RNAi. The FTD/ALS-relevant Matrin3-S85C mouse model displays extensive selective Purkinje cell (PC) loss. PCs are the neurons affected in SCA2 and the neuronal population with the greatest susceptibility to Ataxin-2 mutations. The severe cerebellar neurodegeneration in Matrin-3 S85C mice suggests a pathological link between Matrin-3 and Ataxin-2 that could define a neuronal death pathway relevant to other NDDs including FTD. We propose that in the context of disease, Ataxin-2 interaction with Matrin-3 will contribute to the development of pathology, and that targeting Ataxin-2 will mitigate Matrin-3 pathology and neuronal death. We plan to study pathology linked to Ataxin-2, Matrin-3 and ALS in isolated cultured neurons derived from Ataxin-2 knockout, Ataxin-2 expansion and TDP-43 mutation mice. We will determine the contribution of the different RBPs by expressing Matrin-3 mutations and/or knocking down Ataxin-2 with adenovirus and antisense oligonucleotide strategies already developed. The pathological phenotypes we propose to study include Matrin-3 levels, localization, changes in solubility, aggregation into condensates and toxicity to neurons, as well as ALS molecular readouts including TDP-43 aggregation and localization. We will also investigate the nucleation of other relevant proteinopathy biomolecules into the condensates. Analyzing these in the context of normal, expanded and knockout Ataxin-2 and mutated TDP-43 will inform on the roles of Ataxin-2, Matrin-3 and the interplay of RBPs in the pathogenetic mechanisms in SCA2 and ALS/FTD. This study will provide the initial proof-of-concept for directly targeting ATXN2 and MATR3 in ALS and FTD patients with MATR3 mutations, as well as in other AD/ADRD patients with Matrin-3 proteinopathy.