Abstract
Neurodegenerative diseases are characterized by the deposition of specific protein aggregates, both intracellularly and/or extracellularly, depending on the type of disease. The extracellular occurrence of tridimensional structures formed by amyloidogenic proteins defines Alzheimer’s disease, in which plaques are composed of amyloid β-protein, while in prionoses, the same term “amyloid” refers to the amyloid prion protein. In this review, we focused on providing a detailed didactic description and differentiation of diffuse, neuritic, and burnt-out plaques found in Alzheimer’s disease and kuru-like, florid, multicentric, and neuritic plaques in human transmissible spongiform encephalopathies, followed by a systematic classification of the morphological similarities and differences between the extracellular amyloid deposits in these disorders. Both conditions are accompanied by the extracellular deposits that share certain signs, including neuritic degeneration, suggesting a particular role for amyloid protein toxicity.
Highlights
Deposits of aggregates of particular proteins are specific hallmarks of a wide range of neurodegenerative diseases [1]
Amyloid precursor protein (APP), a transmembrane protein existing in several isoforms [18], is amply expressed in brain tissue [19], and it plays a role in neuroprotection and homeostasis [20]
In 1992, Hardy and Higgins [34] articulated the theory that the deposition of Aβ protein, the main component of plaques, was the causative agent of Alzheimer’s pathology and that neurofibrillary tangles, cell loss, vascular damage, and dementia follow as a direct result of this deposition
Summary
Deposits of aggregates of particular proteins are specific hallmarks of a wide range of neurodegenerative diseases [1]. AD [7]; Prion diseases (Creutzfeldt–Jakob disease (CJD), Gerstmann–Sträussler–Scheinker syndrome (GSS), fatal familial insomnia (FFI), and kuru) [8] In all of these diseases, the term cerebral amyloidosis is widely used referring to insoluble fibrillar structures with a predominant beta-sheet conformation detectable by Congo red and thioflavin S binding [9]. These pathologic units are known to form from insoluble fibrils, giving rise to tridimensional aggregates called plaques that may exhibit different features depending on subtype. The aim of our review is to compare and highlight similarities and differences between the two types of extracellular deposits, i.e., Aβ in AD and amyloid prion protein in prionoses, while simultaneously synthesizing the available information for didactic purposes
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