Extracellular Vesicles Isolated from the Brains of rTg4510 Mice Seed Tau Protein Aggregation in a Threshold-dependent Manner

The role of exosomes in the pathogenesis of Alzheimer' disease

Exosomes are small vesicles secreted by most cell types including neurons that function in intercellular communication through transfer of their cargo or encapsulate and eliminate unnecessary cellular components and therefore have a broad impact on nerve development, activation and regeneration. In addition, exosomes have been observed to be involved in spreading pathological misfolded proteins, thereby leading to the onset and propagation of disease. Alzheimer disease (AD) is the most common form of dementia and characterized by two types of lesions: amyloid plaques and neurofibrillary tangles. Accumulating evidence has demonstrated that exosomes are associated with amyloid precursor (APP) and Tau proteins and play a controversial role in Alzheimer’s disease process. In this review, we will discuss the role of exosomes in the metabolism and secretion of APP and Tau proteins and their subsequent impact on AD pathogenesis.

Sphingolipid-Enriched Extracellular Vesicles and Alzheimer's Disease: A Decade of Research

Extracellular vesicles (EVs), particularly exosomes, have emerged in the last 10 years as a new player in the progression of Alzheimer's disease (AD) with high potential for being useful as a diagnostic and treatment tool. Exosomes and other EVs are enriched with the sphingolipid ceramide as well as other more complex glycosphingolipids such as gangliosides. At least a subpopulation of exosomes requires neutral sphingomyelinase activity for their biogenesis and secretion. As ceramide is often elevated in AD, exosome secretion may be affected as well. Here, we review the available data showing that exosomes regulate the aggregation and clearance of amyloid-beta (Aβ) and discuss the differences in data from laboratories regarding Aβ binding, induction of aggregation, and glial clearance. We also summarize available data on the role of exosomes in extracellular tau propagation, AD-related exosomal mRNA/miRNA cargo, and the use of exosomes as biomarker and gene therapy vehicles for diagnosis and potential treatment.

Emerging roles of extracellular vesicles in neurodegenerative disorders: focus on HIV-associated neurological complications

Exosomes are membrane-enriched extracellular vesicles with a proposed diameter in the range of 30-100 nm. They are released during both normal homeostasis as well as under pathological conditions by most cell types. In recent years, there has been robust interest in the study of these vesicles as conduits for the delivery of information between cells in both analogous as well as disparate tissues. Their ability to transport specialized cargo including signaling mediators, proteins, messenger RNA and miRNAs characterizes these vesicles as primary facilitators of cell-to-cell communication and regulation. Exosomes have also been demonstrated to have important roles in the field of cancer biology and metastasis. More recently, their role in several neurodegenerative disorders has been gaining increased momentum as these particles have been shown to promote the spread of toxic factors such as amyloid beta and prions, adding further validity to their role as important regulators of disease pathogenesis. This review briefly summarizes current findings and thoughts on exosome biology in the context of neurodegenerative disorders and the manipulation of these particles for the development of potential therapeutic strategies.

Exosomes in the Pathology of Neurodegenerative Diseases

More than 30 years ago, two unexpected findings were discovered that challenged conventional thinking in biology. The first was the identification of a misfolded protein with transmissible properties associated with a group of neurodegenerative diseases known as transmissible spongiform encephalopathies. The second was the discovery of a new pathway used for the extracellular release of biomolecules, including extracellular vesicles called exosomes. Two decades later, the convergence of these pathways was shown when exosomes were found to play a significant role in both the transmission and propagation of protein aggregates in disease. Recent research has now revealed that the majority of proteins involved in neurodegenerative diseases are transported in exosomes, and that external stresses due to age-related impairment of protein quality control mechanisms can promote the transcellular flux of these proteins in exosomes. Significantly, exosomes provide an environment that can induce the conformational conversion of native proteins into aggregates that can be transmitted to otherwise aggregate-free cells in the brain. Here we review the current roles of exosomes in the pathology of neurodegenerative diseases.

Like prions: the propagation of aggregated tau and α-synuclein in neurodegeneration

The abnormal aggregation of a small number of known proteins underlies the most common human neurodegenerative diseases. In tauopathies and synucleinopathies, the normally soluble intracellular proteins tau and α-synuclein become insoluble and filamentous. In recent years, non-cell autonomous mechanisms of aggregate formation have come to the fore, suggesting that nucleation-dependent aggregation may occur in a localized fashion in human tauopathies and synucleinopathies, followed by seed-dependent propagation. There is a long prodromal phase between the formation of protein aggregates and the appearance of the first clinical symptoms, which manifest only after extensive propagation, opening novel therapeutic avenues.