RESUMO
The abnormal repetition of the hexanucleotide GGGGCC within the C9orf72 gene is the most common genetic cause of both Amyotrophic Lateral Sclerosis (ALS) and Frontotemporal Dementia (FTD). Different hypothesis have been proposed to explain the pathogenicity of this mutation. Among them, the production of aberrant proteins called Dipeptide Repeat Proteins (DPR) from the repeated sequence. Those proteins are of interest, as they are toxic and form insoluble deposits in patient brains. In this study, we characterized the structural features of three different DPR encoded by the hexanucleotide repeat GGGGCC, namely poly-GA, poly-GP and poly-PA. We showed that DPR are natively unstructured proteins and that only poly-GA forms in vitro fibrillary aggregates. Poly-GA fibrils are of amyloid nature as revealed by their high content in beta sheets. They neither bind Thioflavin T nor Primuline, the commonly used amyloid fluorescent dyes. Remarkably, not all of the poly-GA primary structure was part of fibrils amyloid core.
Assuntos
Amiloide/genética , Proteína C9orf72/genética , Dipeptídeos/genética , Mutação , Oligonucleotídeos/genética , Amiloide/química , Esclerose Lateral Amiotrófica/genética , Dipeptídeos/química , Demência Frontotemporal/genética , Humanos , Desdobramento de Proteína , Sequências Repetitivas de Ácido NucleicoRESUMO
Dipeptide repeat (DPR) proteins are aggregation-prone polypeptides encoded by the pathogenic GGGGCC repeat expansion in the C9ORF72 gene, the most common genetic cause of amyotrophic lateral sclerosis and frontotemporal dementia. In this study, we focus on the role of poly-GA DPRs in disease spread. We demonstrate that recombinant poly-GA oligomers can directly convert into solid-like aggregates and form characteristic ß-sheet fibrils in vitro. To dissect the process of cell-to-cell DPR transmission, we closely follow the fate of poly-GA DPRs in either their oligomeric or fibrillized form after administration in the cell culture medium. We observe that poly-GA DPRs are taken up via dynamin-dependent and -independent endocytosis, eventually converging at the lysosomal compartment and leading to axonal swellings in neurons. We then use a co-culture system to demonstrate astrocyte-to-motor neuron DPR propagation, showing that astrocytes may internalise and release aberrant peptides in disease pathogenesis. Overall, our results shed light on the mechanisms of poly-GA cellular uptake and propagation, suggesting lysosomal impairment as a possible feature underlying the cellular pathogenicity of these DPR species.
Assuntos
Esclerose Lateral Amiotrófica , Proteína C9orf72 , Demência Frontotemporal , Esclerose Lateral Amiotrófica/patologia , Proteína C9orf72/genética , Dipeptídeos , Demência Frontotemporal/genética , Demência Frontotemporal/metabolismo , Demência Frontotemporal/patologia , Humanos , Neurônios Motores/metabolismoRESUMO
Smoothened (Smo) is the signal transducer of the Hedgehog (Hh) pathway and its stimulation is considered a potential powerful tool in regenerative medicine to treat severe tissue injuries. Starting from GSA-10, a recently reported Hh activator acting on Smo, we have designed and synthesized a new class of quinolone-based compounds. Modification and decoration of three different portions of the original scaffold led to compounds able to induce differentiation of multipotent mesenchymal cells into osteoblasts. The submicromolar activity of several of these new quinolones (0.4-0.9 µM) is comparable to or better than that of SAG and purmorphamine, two reference Smo agonists. Structure-activity relationships allow identification of several molecular determinants important for the activity of these compounds.