RESUMEN
Alzheimer's disease is a common neurodegenerative, progressive, and fatal disorder. Generation and deposition of amyloid beta (Aß) peptides associate with its pathogenesis and small soluble Aß oligomers show the most pronounced neurotoxic effects and correlate with disease initiation and progression. Recent findings showed that Aß oligomers bind to the cellular prion protein (PrP(C) ) eliciting neurotoxic effects. The role of exosomes, small extracellular vesicles of endosomal origin, in Alzheimer's disease is only poorly understood. Besides serving as disease biomarkers they may promote Aß plaque formation, decrease Aß-mediated synaptotoxicity, and enhance Aß clearance. Here, we explore how exosomal PrP(C) connects to protective functions attributed to exosomes in Alzheimer's disease. To achieve this, we generated a mouse neuroblastoma PrP(C) knockout cell line using transcription activator-like effector nucleases. Using these, as well as SH-SY5Y human neuroblastoma cells, we show that PrP(C) is highly enriched on exosomes and that exosomes bind amyloid beta via PrP(C) . Exosomes showed highest binding affinity for dimeric, pentameric, and oligomeric Aß species. Thioflavin T assays revealed that exosomal PrP(C) accelerates fibrillization of amyloid beta, thereby reducing neurotoxic effects imparted by oligomeric Aß. Our study provides further evidence for a protective role of exosomes in Aß-mediated neurodegeneration and highlights the importance of exosomal PrP(C) in molecular mechanisms of Alzheimer's disease. We show that the prion protein (PrP(C) ) on exosomes captures neurotoxic species of amyloid beta (Aß) promoting its fibrillization. Our study provides evidence for a protective role of exosomes in Alzheimer`s disease and suggests that, depending on its membrane topology, PrP(C) holds a dual function: when expressed at the neuronal surface it acts as receptor for Aß leading to neurotoxic signaling, whereas it detoxifies Aß when present on exosomes. This provides further support for key roles of PrP(C) in Alzheimer's disease.
Asunto(s)
Péptidos beta-Amiloides/metabolismo , Amiloide/metabolismo , Exosomas/fisiología , Proteínas PrPC/fisiología , Enfermedad de Alzheimer/metabolismo , Péptidos beta-Amiloides/toxicidad , Animales , Línea Celular Tumoral , Técnicas de Inactivación de Genes , Ratones , Proteínas de Neoplasias/metabolismo , Neuroblastoma/patología , Fragmentos de Péptidos/metabolismo , Fragmentos de Péptidos/toxicidad , Solubilidad , TransfecciónRESUMEN
The cellular prion protein (PrP(C)) plays important roles in neurodegenerative diseases. First, it is the well-established substrate for the conformational conversion into its pathogenic isoform (PrP(Sc)) giving rise to progressive and fatal prion diseases. Moreover, several recent reports highlight important roles of PrP(C) in other neurodegenerative conditions such as Alzheimer's disease. Since PrP(C) is subject to proteolytic processing, here we discuss the two main cleavage events under physiological conditions, α-cleavage and shedding. We focus on how these cleavages and the resulting fragments may impact prion diseases as well as other neurodegenerative proteinopathies. Finally, we discuss the recently identified sheddase of PrP(C), namely the metalloprotease ADAM10, with regard to therapeutic potential against neurodegenerative diseases.
Asunto(s)
Proteínas ADAM/metabolismo , Enfermedad de Alzheimer/enzimología , Secretasas de la Proteína Precursora del Amiloide/metabolismo , Proteínas de la Membrana/metabolismo , Proteínas PrPC/metabolismo , Proteínas PrPSc/metabolismo , Enfermedades por Prión/enzimología , Procesamiento Proteico-Postraduccional , Proteínas ADAM/genética , Proteína ADAM10 , Enfermedad de Alzheimer/genética , Enfermedad de Alzheimer/patología , Secretasas de la Proteína Precursora del Amiloide/genética , Péptidos beta-Amiloides/genética , Péptidos beta-Amiloides/metabolismo , Línea Celular , Humanos , Proteínas de la Membrana/genética , Proteínas PrPC/genética , Proteínas PrPSc/genética , Enfermedades por Prión/genética , Enfermedades por Prión/patología , Conformación Proteica , Pliegue de Proteína , Proteolisis , Transducción de SeñalRESUMEN
A variety of physiological functions, not only restricted to the nervous system, are discussed for the cellular prion protein (PrP(C)). A prominent, non-physiological property of PrPC is the conversion into its pathogenic isoform (PrP(Sc)) during fatal, transmissible, and neurodegenerative prion diseases. The prion protein is subject to posttranslational proteolytic processing and these cleavage events have been shown i) to regulate its physiological functions, ii) to produce biologically active fragments, and iii) to potentially influence the course of prion disease. Here, we give an overview on the proteolytic processing under physiological and pathological conditions and critically review what is currently known about the three main cleavage events of the prion protein, namely α-cleavage, ß-cleavage, and ectodomain shedding. The biological relevance of resulting fragments as well as controversies regarding candidate proteases, with special emphasis on members of the A-disintegrin-and-metalloproteinase (ADAM) family, will be discussed. In addition, we make suggestions aimed at facilitating clarity and progress in this important research field. The better understanding of this issue will not only answer basic questions in prion biology but will likely impact research on other neurodegenerative diseases as well.