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Ferritin, a soluble and highly robust protein with subunits packed into well-defined helices, is a key component of the iron regulatory system in the brain and thus is widely recognized as a crucial protein for iron metabolism, but may also bear possible implications in some neurodegenerative disorders. Here, we present evidence of how human recombinant apoferritin can convert into an unusual structure from its folded native state; that is, amyloid fibrils analogue to those found in pathological disorders such as Alzheimer's and Parkinson's diseases. An extensive combination of advanced microscopy, spectroscopy and scattering techniques concur to reveal that apoferritin fibrils possess a common double stranded twisted ribbon structure which can result in a mesoscopic right-handed chirality. We highlight a direct connection between the chirality and morphology of the resulting amyloid fibrils, and the initial protein subunits composition, advancing our understanding on the possible role of misfolding in some ferritin-related pathologies and posing new bases for the design of chiral 1D functional nanostructures.

In recent years, the prevalence of amyloid neurodegenerative diseases such as Alzheimer's disease (AD) has significantly increased in developed countries due to increased life expectancy. This amyloid disease is characterized by the presence of accumulations and deposits of β-amyloid peptide (Aβ) in neuronal tissue, leading to the formation of oligomers, fibers, and plaques. First, oligomeric intermediates that arise during the aggregation process are currently thought to be primarily responsible for cytotoxicity in cells. This work aims to provide further insights into the mechanisms of cytotoxicity by studying the interaction of Aβ aggregates with Neuro-2a (N2a) neuronal cells and the effects caused by this interaction. For this purpose, we have exploited the advantages of advanced, multidimensional fluorescence microscopy techniques to determine whether different types of Aβ are involved in higher rates of cellular toxicity, and we measured the cellular stress caused by such aggregates by using a fluorogenic intracellular biothiol sensor. Stress provoked by the peptide is evident by N2a cells generating high levels of biothiols as a defense mechanism. In our study, we demonstrate that Aβ aggregates act as seeds for aggregate growth upon interacting with the cellular membrane, which results in cell permeability and damage and induces lysis. In parallel, these damaged cells undergo a significant increase in intracellular biothiol levels. [ABSTRACT FROM AUTHOR]

The presence of neuritic plaques and amyloid fibrils arising from the misfolding of certain proteins is the principal molecular indicator of neurodegenerative diseases such as Alzheimer's and Parkinson's disease. Methodologies for studying the early stages of amyloid aggregation are rapidly arising to provide a better understanding of the mechanism of fibrillization and cytotoxicity and to identify potential targets for diagnosis and therapy. The method presented here involves the simultaneous use of two different fluorophores, a quinolimide derivative and Nile Blue A. These are capable of interacting with and reporting on the formation of preamyloid aggregates and fibrils of apoferritin through fluorescence resonance energy transfer (FRET), which occurs between them, thus maximizing the contrast in detection and quantitative information of such amyloid species by using multidimensional fluorescence lifetime imaging microscopy (FLIM). • A pair of dyes interact with pre-amyloid aggregates with different affinities. • FRET between the dyes allow sensitive detection of different types of aggregates. • The aggregates are characterized by multiparametric FLIM and superresolution STED microscopies. [ABSTRACT FROM AUTHOR]