综述与专论：神经退行性疾病中的TDP-43蛋白聚集和相变

随着全球老龄化人口的急剧增加,神经退行性变已经成为危害公共健康的主要疾病。在神经退行性疾病(肌萎缩侧索硬化症(ALS)、额颞叶变性病(FTLD)和阿尔茨海默病(AD)等)患者脑组织中均能观察到蛋白质聚集形成的包涵体,其中TAR DNA结合蛋白43 (TDP-43)是主要成分之一。目前已发现多个TDP-43基因突变与家族性ALS密切相关。TDP-43属RNA/DNA结合蛋白,参与细胞内多种RNA代谢过程,它可以在细胞核和细胞质之间穿梭,通过相变诱导胞质和核质包涵体的形成。本文简要总结了TDP-43在体内和体外聚集以及发生相变的研究进展。理解TDP-43的异常相变将有助于寻找神经退行性疾病的潜在治疗靶点。     

TDP-43在神经退行性疾病中的功能和作用

核蛋白TAR DNA/RNA结合蛋43(TDP-43)目前被认为是肌萎缩侧索硬化症(amyotrophic lateral sclerosis,ALS)、额颞叶变性(frontotemporal lobar degeneration,FTLD)等神经退行性疾病的病理学标记蛋白。在中枢神经系统中,TDP-43作为必要的转录调控因子,参与mRNA前体的剪接,维持RNA稳态和运输。在突变和过表达TDP-43的转基因啮齿类动物模型中,受损伤的神经元呈现出胞核和胞质中TDP-43泛素化、磷酸化聚集,以及细胞周期进程的改变。在此,着重阐述基于TDP-43突变或过表达建立神经退行性疾病动物模型的研究进展,探讨其发病机制、病理学改变及治疗方法。     

蛋白质组学在神经退行性疾病中的研究进展

蛋白质组学是后基因组时代兴起的新型学科,是从整体水平对蛋白质的综合分析。阿尔茨海默病、帕金森病、肌萎缩侧索硬化症等是最常见的神经退行性疾病。应用蛋白质组学对它们进行研究,不仅可从蛋白质水平上揭示疾病的本质,还有助于全面探讨其病理机制,建立诊断标准,发现药物治疗靶点。     

轴突损伤及修复在神经退行性疾病中的研究进展

随着老龄化社会快速到来,衰老相关的神经退行性疾病如阿尔茨海默病(Alzheimer’s disease, AD)、帕金森病(Parkinson’s disease, PD)、肌萎缩侧索硬化症(amyotrophic lateral sclerosis, ALS)等发病率日益升高,给社会和家庭带来巨大经济负担。轴突损伤是AD、PD和ALS的共有病理特征,不同疾病轴突损伤机制虽各不相同却又相互联系,修复轴突损伤已成为治疗衰老相关的神经退行性疾病的重要路径之一。本文总结和归纳了AD、PD和ALS中神经元轴突损伤机制及修复方法相关研究进展,以期为早期防治衰老相关的神经退行性疾病提供新的靶点和思路。     

运动调控肠道菌群防治神经退行性疾病的研究进展

随着人口老龄化的发展,神经退行性疾病逐渐成为我国公共卫生领域的重大问题。肠道菌群的组成和丰度的改变与神经退行性疾病的发生发展密切相关,而体育锻炼被认为是肠道菌群的重要调节因素,并且不同的体育运动对肠道菌群的多样性和菌群结构均有较好的调控作用,因此运动、肠道微生物群和神经退行性疾病三者之间的动态相互作用也成为研究热点。多项研究结果均证实,运动可通过调控肠道菌群从而调节神经活性代谢物分泌、减少β淀粉样蛋白沉积、降低氧化应激水平和改善血脑屏障功能等,在神经退行性疾病防治方面发挥重要作用。本文以阿尔茨海默病、帕金森病和肌萎缩侧索硬化症三种神经退行性疾病为研究对象,主要阐述运动、肠道菌群和神经退行性疾病相关的研究进展,以期为运动预防神经退行性疾病提供新的思路和理论依据。     

lncRNA NEAT1在中枢神经系统疾病中的研究进展*

存在于人类基因组中的长链非编码RNA (lncRNA)因其发挥着重要的调节作用而备受关注.越来越多的研究表明,lncRNAs在神经发育、神经可塑性以及中枢神经系统疾病中发挥着重要作用. lncRNA核富集转录体1 (NEAT1)在阿尔茨海默病(AD)、帕金森病(PD)、亨廷顿病(HD)和肌萎缩侧索硬化症(ALS)等多种中枢神经系统疾病中表达异常,并参与重要的病理生理过程.本文对lncRNA NEAT1在中枢神经系统疾病中的研究进展进行综述.     

环氧合酶在神经变性疾病神经元进行性损伤中起重要作用

环氧合酶(COX)是非甾体抗炎药的主要作用靶点.自从上世纪90年代初被发现至今,COX已被证实广泛参与炎性反应过程.小胶质细胞是介导"神经炎性反应"的主要细胞类型,过去十年中,COX通路参与小胶质细胞激活及神经变性过程的机制取得了很大进展.本文对该领域的新近研究成果予以论述,并以三大神经变性疾病,即阿尔采末病(AD)、帕金森病(PD)和肌萎缩侧索硬化症(ALS)为例,对COX在其发病中的作用加以阐释,突出该领域的研究热点,为神经变性疾病发病机制及药物治疗研究提供新的思路.     

纤毛病相关蛋白CEP43和CCDC13在艾美游仆虫中的细胞与亚细胞定位

艾美游仆虫(Euplotes amieti)含有几乎所有已知的纤毛病基因,但绝大多数基因及其表达产物的细胞定位和功能未知。为明确中心粒蛋白43(CEP43)和卷曲螺旋域蛋白13(CCDC13)在艾美游仆虫中的细胞以及亚细胞定位,本研究采用免疫荧光和免疫电镜技术对其进行显微与超微结构观察。免疫荧光结果显示,CEP43主要定位于艾美游仆虫的细胞核、腹面纤毛器(口围带、尾棘毛、额腹横棘毛)的基体及其附属微管,CCDC13主要定位于腹面纤毛器杆部和基体以及银线系统,附属微管及大核未见其定位。CEP43与γ-微管蛋白定位相同,CCDC13与γ-微管蛋白仅在腹面定位相同。2种蛋白在免疫电镜下显示与荧光标记定位相同,而且CCDC13在额腹棘毛基部的胶体金数量远多于CEP43。结合已有研究推测,纤毛形成后多余的CEP43受γ-微管蛋白复合体调控且被募集于细胞核,CCDC13参与形成银线系统,但为增加生长期艾美游仆虫的微管再生能力,附属微管结构不需要CCDC13的参与。本结果为进一步研究上述蛋白在腹毛类纤毛虫中调节和维持皮层微管类细胞骨架的装配和稳定性中的作用和机制提供资料。     

ALS‐associated fused in sarcoma (FUS) mutations disrupt Transportin‐mediated nuclear import

Mutations in fused in sarcoma (FUS) are a cause of familial amyotrophic lateral sclerosis (fALS). Patients carrying point mutations in the C‐terminus of FUS show neuronal cytoplasmic FUS‐positive inclusions, whereas in healthy controls, FUS is predominantly nuclear. Cytoplasmic FUS inclusions have also been identified in a subset of frontotemporal lobar degeneration (FTLD‐FUS). We show that a non‐classical PY nuclear localization signal (NLS) in the C‐terminus of FUS is necessary for nuclear import. The majority of fALS‐associated mutations occur within the NLS and impair nuclear import to a degree that correlates with the age of disease onset. This presents the first case of disease‐causing mutations within a PY‐NLS. Nuclear import of FUS is dependent on Transportin, and interference with this transport pathway leads to cytoplasmic redistribution and recruitment of FUS into stress granules. Moreover, proteins known to be stress granule markers co‐deposit with inclusions in fALS and FTLD‐FUS patients, implicating stress granule formation in the pathogenesis of these diseases. We propose that two pathological hits, namely nuclear import defects and cellular stress, are involved in the pathogenesis of FUS‐opathies.     

Arginine methylation next to the PY‐NLS modulates Transportin binding and nuclear import of FUS

Fused in sarcoma (FUS) is a nuclear protein that carries a proline‐tyrosine nuclear localization signal (PY‐NLS) and is imported into the nucleus via Transportin (TRN). Defects in nuclear import of FUS have been implicated in neurodegeneration, since mutations in the PY‐NLS of FUS cause amyotrophic lateral sclerosis (ALS). Moreover, FUS is deposited in the cytosol in a subset of frontotemporal lobar degeneration (FTLD) patients. Here, we show that arginine methylation modulates nuclear import of FUS via a novel TRN‐binding epitope. Chemical or genetic inhibition of arginine methylation restores TRN‐mediated nuclear import of ALS‐associated FUS mutants. The unmethylated arginine–glycine–glycine domain preceding the PY‐NLS interacts with TRN and arginine methylation in this domain reduces TRN binding. Inclusions in ALS‐FUS patients contain methylated FUS, while inclusions in FTLD‐FUS patients are not methylated. Together with recent findings that FUS co‐aggregates with two related proteins of the FET family and TRN in FTLD‐FUS but not in ALS‐FUS, our study provides evidence that these two diseases may be initiated by distinct pathomechanisms and implicates alterations in arginine methylation in pathogenesis.     

The roles of intrinsic disorder-based liquid-liquid phase transitions in the “Dr. Jekyll–Mr. Hyde” behavior of proteins involved in amyotrophic lateral sclerosis and frontotemporal lobar degeneration

Pathological developments leading to amyotrophic lateral sclerosis (ALS) and frontotemporal lobar degeneration (FTLD) are associated with misbehavior of several key proteins, such as SOD1 (superoxide dismutase 1), TARDBP/TDP-43, FUS, C9orf72, and dipeptide repeat proteins generated as a result of the translation of the intronic hexanucleotide expansions in the C9orf72 gene, PFN1 (profilin 1), GLE1 (GLE1, RNA export mediator), PURA (purine rich element binding protein A), FLCN (folliculin), RBM45 (RNA binding motif protein 45), SS18L1/CREST, HNRNPA1 (heterogeneous nuclear ribonucleoprotein A1), HNRNPA2B1 (heterogeneous nuclear ribonucleoprotein A2/B1), ATXN2 (ataxin 2), MAPT (microtubule associated protein tau), and TIA1 (TIA1 cytotoxic granule associated RNA binding protein). Although these proteins are structurally and functionally different and have rather different pathological functions, they all possess some levels of intrinsic disorder and are either directly engaged in or are at least related to the physiological liquid-liquid phase transitions (LLPTs) leading to the formation of various proteinaceous membrane-less organelles (PMLOs), both normal and pathological. This review describes the normal and pathological functions of these ALS- and FTLD-related proteins, describes their major structural properties, glances at their intrinsic disorder status, and analyzes the involvement of these proteins in the formation of normal and pathological PMLOs, with the ultimate goal of better understanding the roles of LLPTs and intrinsic disorder in the “Dr. Jekyll–Mr. Hyde” behavior of those proteins.     

Progranulin: normal function and role in neurodegeneration

Progranulin (PGRN) is a multifunctional protein that has attracted significant attention in the neuroscience community following the recent discovery of PGRN mutations in some cases of frontotemporal dementia. Most of the pathogenic mutations result in null alleles, and it is thought that frontotemporal dementia in these families results from PGRN haploinsufficiency. The neuropathology associated with PGRN mutations is characterized by the presence of tau-negative, ubiquitin-immunoreactive neuronal inclusions (frontotemporal lobar degeneration with ubiquitinated inclusions) that are also positive for the transactivation response DNA binding protein with M_r 43 kD. The clinical phenotype includes behavioral abnormalities, language disorders and parkinsonism but not motor neuron disease. There is significant clinical variation between families with different PGRN mutations and among members of individual families. The normal function of PGRN is complex, with the full-length form of the protein having trophic and anti-inflammatory activity, whereas proteolytic cleavage generates granulin peptides that promote inflammatory activity. In the periphery, PGRN functions in wound healing responses and modulates inflammatory events. In the CNS, PGRN is expressed by neurons and microglia; consequently, reduced levels of PGRN could affect both neuronal survival and CNS inflammatory processes. In this review, we discuss current knowledge of the molecular genetics, neuropathology, clinical phenotype and functional aspects of PGRN in the context of neurodegenerative disease.     

Phosphorylation of TAR DNA-binding Protein of 43 kDa (TDP-43) by Truncated Casein Kinase 1δ Triggers Mislocalization and Accumulation of TDP-43

Intracellular aggregates of phosphorylated TDP-43 are a major component of ubiquitin-positive inclusions in the brains of patients with frontotemporal lobar degeneration and ALS and are considered a pathological hallmark. Here, to gain insight into the mechanism of intracellular TDP-43 accumulation, we examined the relationship between phosphorylation and aggregation of TDP-43. We found that expression of a hyperactive form of casein kinase 1 δ (CK1δ1-317, a C-terminally truncated form) promotes mislocalization and cytoplasmic accumulation of phosphorylated TDP-43 (ubiquitin- and p62-positive) in cultured neuroblastoma SH-SY5Y cells. Insoluble phosphorylated TDP-43 prepared from cells co-expressing TDP-43 and CK1δ1-317 functioned as seeds for TDP-43 aggregation in cultured cells, indicating that CK1δ1-317-induced aggregated TDP-43 has prion-like properties. A striking toxicity and alterations of TDP-43 were also observed in yeast expressing TDP-43 and CK1δ1-317. Therefore, abnormal activation of CK1δ causes phosphorylation of TDP-43, leading to the formation of cytoplasmic TDP-43 aggregates, which, in turn, may trigger neurodegeneration.