Résumé
Since the discovery of the C9ORF72 gene in 2011, great advances have been achieved in its genetics and in identifying its role in disease models and pathological mechanisms; it is the most common genetic cause of amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). ALS patients with C9ORF72 expansion show heterogeneous symptoms. Those who are C9ORF72 expansion carriers have shorter survival after disease onset than non-C9ORF72 expansion patients. Pathological and clinical features of C9ORF72 patients have been well mimicked via several models, including induced pluripotent stem cell-derived neurons and transgenic mice that were embedded with bacterial artificial chromosome construct and that overexpressing dipeptide repeat proteins. The mechanisms implicated in C9ORF72 pathology include DNA damage, changes of RNA metabolism, alteration of phase separation, and impairment of nucleocytoplasmic transport, which may underlie C9ORF72 expansion-related ALS/FTD and provide insight into non-C9ORF72 expansion-related ALS, FTD, and other neurodegenerative diseases.
Résumé
Since the discovery of the C9ORF72 gene in 2011, great advances have been achieved in its genetics and in identifying its role in disease models and pathological mechanisms; it is the most common genetic cause of amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). ALS patients with C9ORF72 expansion show heterogeneous symptoms. Those who are C9ORF72 expansion carriers have shorter survival after disease onset than non-C9ORF72 expansion patients. Pathological and clinical features of C9ORF72 patients have been well mimicked via several models, including induced pluripotent stem cell-derived neurons and transgenic mice that were embedded with bacterial artificial chromosome construct and that overexpressing dipeptide repeat proteins. The mechanisms implicated in C9ORF72 pathology include DNA damage, changes of RNA metabolism, alteration of phase separation, and impairment of nucleocytoplasmic transport, which may underlie C9ORF72 expansion-related ALS/FTD and provide insight into non-C9ORF72 expansion-related ALS, FTD, and other neurodegenerative diseases.
Résumé
GGGGCC repeat expansions in the C9ORF72 gene are the most common cause of amyotrophic lateral sclerosis and frontotemporal dementia (c9ALS/FTD). It has been reported that hexanucleotide repeat expansions in C9ORF72 produce five dipeptide repeat (DPR) proteins by an unconventional repeat-associated non-ATG (RAN) translation. Within the five DPR proteins, poly-PR and poly-GR that contain arginine are more toxic than the other DPRs (poly-GA, poly-GP, and poly-PA). Here, we demonstrated that poly-PR peptides transferred into cells by endocytosis in a clathrin-dependent manner, leading to endoplasmic reticulum stress and cell death. In SH-SY5Y cells and primary cortical neurons, poly-PR activated JUN amino-terminal kinase (JNK) and increased the levels of p53 and Bax. The uptake of poly-PR peptides by cells was significantly inhibited by knockdown of clathrin or by chlorpromazine, an inhibitor that blocks clathrin-mediated endocytosis. Inhibition of clathrin-dependent endocytosis by chlorpromazine significantly blocked the transfer of poly-PR peptides into cells, and attenuated poly-PR-induced JNK activation and cell death. Our data revealed that the uptake of poly-PR undergoes clathrin-dependent endocytosis and blockade of this process prevents the toxic effects of synthetic poly-PR peptides.
Résumé
Amyotrophic lateral sclerosis represents the most common neurodegenerative disease leading to upper and lower motor neuron compromise. Although the vast majority of cases are sporadic, substantial gain has been observed in the knowledge of the genetic forms of the disease, especially of familial forms. There is a direct correlation between the profile of the mutated genes in sporadic and familial forms, highlighting the main role ofC9orf72 gene in the clinical forms associated with frontotemporal dementia spectrum. The different genes related to familial and sporadic forms represent an important advance on the pathophysiology of the disease and genetic therapeutic perspectives, such as antisense therapy. The objective of this review is to signal and summarize clinical and genetic data related to familial forms of amyotrophic lateral sclerosis.
A esclerose lateral amiotrófica representa a forma mais comum de doença neurodegenerativa com comprometimento do neurônio motor superior e inferior. Embora a maioria dos casos seja esporádica, ganho impressionante referente ao conhecimento das formas genética da doença foi observado, em especial das formas familiares. Há uma correlação direta entre o perfil de genes mutados nas formas familiares e esporádicas, destacando-se o papel principal do geneC9orf72 nas formas clínicas associadas com espectro da demência frontotemporal. Os diferentes genes relacionados às formas familiares e esporádicas representam um importante avanço na fisiopatologia da doença e perespectivas terapêuticas genéticas, como a terapia antisense. O objetivo desta revisão é apontar e resumir os principais dados clínicos e genéticos relacionados às formas familiares da esclerose lateral amiotrófica.
Sujets)
Humains , Sclérose latérale amyotrophique/génétique , Mutation/génétique , Protéines/génétique , Sclérose latérale amyotrophique/classificationRésumé
ABSTRACT OBJECTIVE: To perform a systematic review of the literature on the neuroimaging investigation of frontotemporal dementia (FTD) and amyotrophic lateral sclerosis (ALS) associated with C9ORF72 mutation. METHODS: The search was performed on PubMed and LILACS with the following terms:C9ORF72, MRI, SPECT, PET, ALS, FTD. No filters were added. RESULTS Twenty articles were selected. Most studies found consistent involvement of frontotemporal regions in C9ORF72 carriers, including prefrontal cortex, and also cingulate, subcortical regions, especially the thalami, and posterior regions such as the parietal and occipital lobes. Functional connectivity was also explored and impaired sensorimotor connectivity in striatum and thalami was found in behavioral variant FTDC9ORF72 carriers. Some papers have reported an absence of significant abnormalities on brain imaging. CONCLUSION The inclusion of patients at different stages of the disease, differences in neuroimaging methods across studies, and distinct clinical phenotypes associated with C9ORF72 may account for the heterogeneity of results.
RESUMO OBJETIVO Realizar uma revisão sistemática da literatura sobre os estudos de neuroimagem da demência frontotemporal (DFT) e esclerose lateral amiotrófica (ELA), associadas à mutação C9ORF72. Métodos A pesquisa foi realizada nas bases PubMed e LILACS com os seguintes termos:C9ORF72, MRI, SPECT, PET, ALS, FTD. Nenhum filtro foi utilizado. RESULTADOS Vinte artigos foram incluídos. A maioria dos estudos encontrou, nos portadores da expansão C9ORF72, envolvimento significativo das regiões frontotemporais, incluindo o córtex pré-frontal e também o cíngulo, regiões subcorticais (especialmente o tálamo) e regiões posteriores, como os lobos parietal e occipital. A conectividade funcional também foi investigada e disfunção sensório-motora foi demonstrada no estriado e no tálamo em pacientes com a variante comportamental da DFT associada à expansão C9ORF72. Alguns trabalhos não evidenciaram alterações significativas na neuroimagem. CONCLUSÃO A inclusão de pacientes em diferentes estágios da doença, a variabilidade dos métodos de neuroimagem utilizados nos estudos e os distintos fenótipos de C9ORF72 podem contribuir para a heterogeneidade dos resultados.
Sujets)
Humains , Démence frontotemporale , Neuroimagerie , Protéine C9orf72 , Sclérose latérale amyotrophiqueRésumé
Neurodegenerative diseases represent a heterogeneous group of neurological conditions primarily involving dementia, motor neuron disease and movement disorders. They are mostly related to different pathophysiological processes, notably in family forms in which the clinical and genetic heterogeneity are lush. In the last decade, much knowledge has been acumulated about the genetics of neurodegenerative diseases, making it essential in cases of motor neuron disease and frontotemporal dementia the repeat expansions of C9orf72 gene. This review analyzes the main clinical, radiological and genetic aspects of the phenotypes related to the hexanucleotide repeat expansions (GGGGCC) of C9orf72 gene. Future studies will aim to further characterize the neuropsychological, imaging and pathological aspects of the extra-motor features of motor neuron disease, and will help to provide a new classification system that is both clinically and biologically relevant.
As doenças neurodegenerativas representam um grupo heterogêneo de condições neurológicas envolvendo fundamentalmente síndromes demenciais, doenças do neurônio motor e distúrbios de movimento. Relacionam-se, em sua maioria, a processos fisiopatológicos distintos, destacadamente nas formas familiares em que a heterogeneidade clínica e genética são exuberantes. Na última década, muito conhecimento se acumulou a respeito da genética das doenças neurodegenerativas, tornando-se bastante importante nos casos de doenças do neurônio motor e de demência frontotemporal as expansões de repetições do gene C9orf72. Esta revisão aborda os principais aspectos clínicos, radiológicos e genéticos relativos aos fenótipos relacionados à expansão de repetição do hexanucleotídeo (GGGGCC) no gene C9orf72. Estudos futuros vão objetivar a caracterização dos aspectos neuropsicológicos, de imagem e patológicos dos achados extra-motores da doença do neurônio motor e ajudarão a fornecer um novo sistema de classificação relevante em termos clínicos e biológicos.