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Introduction: Several neurodegenerative conditions are associated with a common histopathology within neurons of the central nervous system, consisting of the deposition of cytoplasmic inclusions of TAR DNA-binding protein 43 (TDP-43). Such inclusions have variably been described as morphologically and molecularly ordered aggregates having amyloid properties, as filaments without the cross-β-structure and dye binding specific for amyloid, or as amorphous aggregates with no defined structure and fibrillar morphology. Aims and Methods: Here we have expressed human full-length TDP-43 in neuroblastoma x spinal cord 34 (NSC-34) cells to investigate the morphological, structural, and tinctorial properties of TDP-43 inclusions in situ. We have used last-generation amyloid diagnostic probes able to cross the cell membrane and detect amyloid in the cytoplasm and have adopted Raman and Fourier transform infrared microspectroscopies to study in situ the secondary structure of the TDP-43 protein in the inclusions. We have then used transmission electron microscopy to study the morphology of the TDP-43 inclusions. Results: The results show the absence of amyloid dye binding, the lack of an enrichment of cross-β structure in the inclusions, and of a fibrillar texture in the round inclusions. The aggregates formed in vitro from the purified protein under conditions in which it is initially native also lack all these characteristics, ruling out a clear amyloid-like signature. Conclusions: These findings indicate a low propensity of TDP-43 to form amyloid fibrils and even non-amyloid filaments, under conditions in which the protein is initially native and undergoes its typical nucleus-to-cell mislocalization. It cannot be excluded that filaments emerge on the long time scale from such inclusions, but the high propensity of the protein to form initially other types of inclusions appear to be an essential characteristic of TDP-43 proteinopathies.KEY MESSAGES Cytoplasmic inclusions of TDP-43 formed in NSC-34 cells do not stain with amyloid-diagnostic dyes, are not enriched with cross-β structure, and do not show a fibrillar morphology. TDP-43 assemblies formed in vitro from pure TDP-43 do not have any hallmarks of amyloid.

Clinical Practice Points • Immune checkpoint inhibitors (ICIs) are associated with the development of unique immune-related adverse events (irAEs), which emerged primarily during post-marketing surveillance. Oral irAEs have already been reported, with the most common manifestations being mucositis and xerostomia. It has been suggested that a T-cell activation, similar to that observed in autoimmune conditions, may play a role. • Here, we report a case of black hairy tongue (BHT) in a patient receiving first-line pembrolizumab for advanced non–small-cell lung cancer (NSCLC). Although the BHT was symptomatic for burning mouth and dysgeusia, ICI use was continued due to its clinical and radiological benefit, which persisted for a long time. • BHT is characterized by hypertrophy and lengthening of the filiform papillae. Despite being a rare benign condition, it can often result in a significant burden on quality of life. • Many predisposing factors have been described, and cancer patients represent a population particularly at risk. Based on the temporal association and excluding possible alternative causes, we proposed that, in our patient, BHT was likely ICI related through the development of xerostomia, which represents a key factor in BHT pathogenesis. • To the best of our knowledge, this is the first report of BHT after ICI use, suggesting that it may represent an atypical oral irAE. To date, the oral irAEs have not been well explored, and further studies are needed to elucidate the underlying mechanisms and possible associations with anti-tumor responses, with significant implications on prognosis and quality of life. In the present context, our case emphasizes the need to remain vigilant for atypical and new irAEs.

Alzheimer's disease, which is the most common form of dementia, is characterized by the aggregation of the amyloid β peptide (Aβ) and by an impairment of calcium homeostasis caused by excessive activation of glutamatergic receptors (excitotoxicity). Here, we studied the effects on calcium homeostasis caused by the formation of Aβ oligomeric assemblies. We found that Aβ oligomers cause a rapid influx of calcium ions (Ca2+) across the cell membrane by rapidly activating extrasynaptic N-methyl-d-aspartate (NMDA) receptors and, to a lower extent, α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors. We also observed, however, that misfolded oligomers do not interact directly with these receptors. Further experiments with lysophosphatidylcholine and arachidonic acid, which cause membrane compression and stretch, respectively, indicated that these receptors are activated through a change in membrane tension induced by the oligomers and transmitted mechanically to the receptors via the lipid bilayer. Indeed, lysophosphatidylcholine is able to neutralize the oligomer-induced activation of the NMDA receptors, whereas arachidonic acid activates the receptors similarly to the oligomers with no additive effects. An increased rotational freedom observed for a fluorescent probe embedded within the membrane in the presence of the oligomers also indicates a membrane stretch. These results reveal a mechanism of toxicity of Aβ oligomers in Alzheimer's disease through the perturbation of the mechanical properties of lipid membranes sensed by NMDA and AMPA receptors.

A number of neurodegenerative conditions are associated with the formation of cytosolic inclusions of TDP-43 within neurons. We expressed full-length TDP-43 in a motoneuron/neuroblastoma hybrid cell line (NSC-34) and exploited the high-resolution power of stimulated emission depletion microscopy to monitor the changes of nuclear and cytoplasmic TDP-43 levels and the formation of various size classes of cytoplasmic TDP-43 aggregates with time. Concomitantly, we monitored oxidative stress and mitochondrial impairment using the MitoSOX and MTT reduction assays, respectively. Using a quantitative biology approach, we attributed neuronal dysfunction associated with cytoplasmic deposition component to the formation of the largest inclusions, independently of stress granules. This is in contrast to other neurodegenerative diseases where toxicity is attributed to small oligomers. Using specific inhibitors, markers, and electron microscopy, the proteasome and autophagy were found to target mainly the largest deleterious inclusions, but their efficiency soon decreases without full recovery of neuronal viability.

Soluble oligomers arising from the aggregation of the amyloid beta peptide (Aβ) have been identified as the main pathogenic agents in Alzheimer's disease (AD). Prefibrillar oligomers of the 42-residue form of Aβ (Aβ

Alzheimer's disease is characterized by the accumulation in the brain of the amyloid β (Aβ) peptide in the form of senile plaques. According to the amyloid hypothesis, the aggregation process of Aβ also generates smaller soluble misfolded oligomers that contribute to disease progression. One of the mechanisms of Aβ oligomer cytotoxicity is the aberrant interaction of these species with the phospholipid bilayer of cell membranes, with a consequent increase in cytosolic Ca

The aberrant aggregation of specific peptides and proteins is the common feature of a range of more than 50 human pathologies, collectively referred to as protein misfolding diseases [...]

Protein misfolding is a general hallmark of protein deposition diseases, such as Alzheimer’s disease or Parkinson’s disease, in which different types of aggregated species (oligomers, protofibrils and fibrils) are generated by the cells. Despite widespread interest, the relationship between oligomers and fibrils in the aggregation process and spreading remains elusive. A large variety of experimental evidences supported the idea that soluble oligomeric species of different proteins might be more toxic than the larger fibrillar forms. Furthermore, the lack of correlation between the presence of the typical pathological inclusions and disease sustained this debate. However, recent data show that the β-sheet core of the α-Synuclein (αSyn) fibrils is unable to establish persistent interactions with the lipid bilayers, but they can release oligomeric species responsible for an immediate dysfunction of the recipient neurons. Reversibly, such oligomeric species could also contribute to pathogenesis via neuron-to-neuron spreading by their direct cell-to-cell transfer or by generating new fibrils, following their neuronal uptake. In this Review, we discuss the various mechanisms of cellular dysfunction caused by αSyn, including oligomer toxicity, fibril toxicity and fibril spreading.

The role of immune-related adverse events (irAEs), as a surrogate predictor of the efficacy of checkpoint inhibitors, has not yet been described in the setting of first-line, single-agent pembrolizumab for patients with metastatic non-small-cell lung-cancer (NSCLC) with a programmed death-ligand 1 (PD-L1) expression of ≥ 50%.We previously conducted a multicenter retrospective analysis in patients with treatment-naive metastatic NSCLC and a PD-L1 expression of ≥ 50% receiving first-line pembrolizumab. Here, we report the results of the irAE analysis and the potential correlation between irAEs and clinical outcomes.A total of 1010 patients were included in this analysis; after a 6-week landmark selection, 877 (86.8%) patients were included in the efficacy analysis. Any grade irAEs (P .0001), grade 3/4 irAEs (P = .0025), leading to discontinuation irAEs (P = .0144), multiple-site and single-site irAEs (P .0001), cutaneous irAEs (P = .0001), endocrine irAEs (P = .0227), pulmonary irAEs (P = .0479), and rheumatologic irAEs (P = .0018) were significantly related to a higher objective response rate. Any grade irAEs (P .0001), single-site irAEs (P .0001), multiple-site irAEs (P = .0005), cutaneous irAEs (P = .0042), endocrine irAEs (P .0001), gastrointestinal irAEs (P = .0391), and rheumatologic irAEs (P = .0086) were significantly related to progression-free survival. Any grade irAEs (P .0001), single-site irAEs (P .0001), multiple-site irAEs (P = .0003), cutaneous irAEs (P = .0002), endocrine irAEs (P = .0001), and rheumatologic irAEs (P = .0214) were significantly related to overall survival.This study confirms the feasibility and the safety of first-line, single-agent pembrolizumab, in a large, real-world cohort of patients with NSCLC with PD-L1 expression ≥ 50%. The occurrence of irAEs may be a surrogate of clinical activity and improved outcomes in this setting.

Nucleophosmin 1 (NPM1) is a nucleus-cytoplasm shuttling protein ubiquitously expressed and highly conserved. It is involved in many cellular processes and its gene is mutated in ~ 50-60% of Acute Myeloid Leukemia (AML) patients. These mutations cause its cytoplasmic mislocation and accumulation (referred to as NPM1c+) and open the door to rational targeted therapy for AML diseases with mutated NPM1. Currently, there is limited knowledge on the mechanism of action of NPM1c+ and on structural determinants of the leukemogenic potential of AML mutations. Numerous previous studies outlined an unexpected amyloid-like aggregation tendency of several regions located in the C-terminal domain that, in wild-type form, fold as a three-helical-bundle. Here, using a combination of different techniques including Thioflavin T fluorescence, congo red absorbance, CD spectroscopy, Scanning Electron Microscopy (SEM) and wide-angle X-ray scattering on a series of peptides bearing mutations, we evidence that the amyloidogenicity of NPM1 mutants is directly linked to AML. Noticeably, AML point mutations strongly affect the amyloid cytotoxic effects in neuroblastoma cells and the morphologies of deriving fibrils. This study paves the way to deepen our understanding of AML-associated NPM1 mutants, and could help to break new ground for the identification of novel drugs targeting NPM1c+ for treatment of AML.

Amyloid fibril formation plays a central role in the pathogenesis of a number of neurodegenerative diseases, including Alzheimer and Parkinson diseases. Transient prefibrillar oligomers forming during the aggregation process, exhibiting a small size and a large hydrophobic surface, can aberrantly interact with a number of molecular targets on neurons, including the lipid bilayer of plasma membranes, resulting in a fatal outcome for the cells. By contrast, the mature fibrils, despite presenting generally a high hydrophobic surface, are endowed with a low diffusion rate and poorly penetrate the interior of the lipid bilayer. However, increasing evidence shows that both intracellular α-synuclein fibrils, as well and as extracellular amyloid-β and β2-microglobulin fibrils, can release oligomers over time that quickly diffuse to reach the membrane of the neighboring cells. The persistent leakage of harmful oligomers from fibrils triggers an ongoing cascade of events resulting in a sustained injury to neurons and glia and also provides aggregates with the ability to cross biological membranes and diffuse between cells or cellular compartments.

α-Synuclein (αS) is an intrinsically disordered and highly dynamic protein involved in dopamine release at presynaptic terminals. The abnormal aggregation of αS as mature fibrils into intraneuronal inclusion bodies is directly linked to Parkinson’s disease. Increasing experimental evidence suggests that soluble oligomers formed early during the aggregation process are the most cytotoxic forms of αS. This study investigated the uptake by neuronal cells of pathologically relevant αS oligomers and fibrils exploiting a range of conformation-sensitive antibodies, and the super-resolution stimulated emission depletion (STED) microscopy. We found that prefibrillar oligomers promptly penetrate neuronal membranes, thus resulting in cell dysfunction. By contrast, fibril docking to the phospholipid bilayer is accompanied by αS conformational changes with a progressive release of A11-reactive oligomers, which can enter into the neurons and trigger cell impairment. Our data provide important evidence on the role of αS fibrils as a source of harmful oligomers, which resemble the intermediate conformers formed de novo during aggregation, underling the dynamic and reversible nature of protein aggregates responsible for α-synucleinopathies.

Alzheimer’s disease (AD) is the most common age-related neurodegenerative disorder that is characterized by amyloid β-protein deposition in senile plaques, neurofibrillary tangles consisting of abnormally phosphorylated tau protein, and neuronal loss leading to cognitive decline and dementia. Despite extensive research, the exact mechanisms underlying AD remain unknown and effective treatment is not available. Many hypotheses have been proposed to explain AD pathophysiology; however, there is general consensus that the abnormal aggregation of the amyloid β peptide (Aβ) is the initial event triggering a pathogenic cascade of degenerating events in cholinergic neurons. The dysregulation of calcium homeostasis has been studied considerably to clarify the mechanisms of neurodegeneration induced by Aβ. Intracellular calcium acts as a second messenger and plays a key role in the regulation of neuronal functions, such as neural growth and differentiation, action potential, and synaptic plasticity. The calcium hypothesis of AD posits that activation of the amyloidogenic pathway affects neuronal Ca2+ homeostasis and the mechanisms responsible for learning and memory. Aβ can disrupt Ca2+ signaling through several mechanisms, by increasing the influx of Ca2+ from the extracellular space and by activating its release from intracellular stores. Here, we review the different molecular mechanisms and receptors involved in calcium dysregulation in AD and possible therapeutic strategies for improving the treatment.

10 pags., 5 figs., The onset and progression of numerous protein misfolding diseases are associated with the presence of oligomers formed during the aberrant aggregation of several different proteins, including amyloid-β (Aβ) in Alzheimer’s disease and α-synuclein (αS) in Parkinson’s disease. These small, soluble aggregates are currently major targets for drug discovery. In this study, we show that trodusquemine, a naturally-occurring aminosterol, markedly reduces the cytotoxicity of αS, Aβ and HypF-N oligomers to human neuroblastoma cells by displacing the oligomers from cell membranes in the absence of any substantial morphological and structural changes to the oligomers. These results indicate that the reduced toxicity results from a mechanism that is common to oligomers from different proteins, shed light on the origin of the toxicity of the most deleterious species associated with protein aggregation and suggest that aminosterols have the therapeutically-relevant potential to protect cells from the oligomer-induced cytotoxicity associated with numerous protein misfolding diseases., This work was supported by the Cambridge Centre for Misfolding Diseases (R.L., B.M., F.S.R., C.K.X., M.P., S.C., S.W.C., J.H., T.K., J.R.K., T.P.J.K., M.V., and C.M.D.), the UK Biotechnology and Biochemical Sciences Research Council (M.V. and C.M.D.), the Wellcome Trust (203249/Z/16/Z to T.P.J.K and M.V.), the Frances and Augustus Newman Foundation (T.P.J.K.), the Regione Toscana – FAS Salute, project SUPREMAL (R.C., A.B., C.C., and F.C.), the Gates Cambridge Trust and St. John’s College Cambridge (R.L.), Darwin College Cambridge (F.S.R.), the Herchel Smith Fund (C.K.X.), a Faculty Development Research Fund grant from the United States Military Academy, West Point (R.L.) and a DTRA Service Academy Research Initiative grant (HDTRA1033862 to R.L.).

Background: The pathogenesis of Alzheimer's disease (AD) is not directly caused by the presence of senile plaques but rather by the detrimental effects exerted on neuronal cells by toxic soluble oligomers. Such species are formed early during the aggregation process of the Aβ1-42 peptide or can be released from mature fibrils. Nowadays, efficient tools for an early diagnosis, as well as pharmaceutical treatments targeting the harmful agents in samples of AD patients, are still missing. Objective: By integrating in vitro immunochemical assay with in vivo neuronal models of toxicity, we aim to understand and target the principles that drive toxicity in AD. Methods: We evaluated the specificity and sensitivity of A11 and OC conformational antibodies to target a range of pathologically relevant amyloid conformers and rescue their cytotoxic effects in neuronal culture models using a number of cellular readouts. Results: We demonstrated the peculiar ability of conformational antibodies to label pathologically relevant Aβ1-42 oligomers and fibrils and to prevent their detrimental effects on neuronal cells. Conclusion: Our results substantially improve our knowledge on the role of toxic assemblies in neurodegenerative diseases, thus suggesting new and more effective diagnostic and therapeutic tools for AD.

An altered distribution of membrane gangliosides (GM), including GM1, has recently been reported in the brains of Alzheimer's disease (AD) patients. Moreover, amyloid-positive synaptosomes obtained from AD brains were found to contain high-density GM1 clusters, suggesting a pathological significance of GM1 increase at presynaptic neuritic terminals in AD. Here, we show that membrane GM1 specifically recruits small soluble oligomers of the 42-residue form of amyloid-β peptide (Aβ42), with intracellular flux of Ca2+ ions in primary rat hippocampal neurons and in human neuroblastoma cells. Specific membrane proteins appear to be involved in the early and transient influx of Ca2+ ions induced by Aβ42 oligomers with high solvent-exposed hydrophobicity (A+), but not in the sustained late influx of the same oligomers and in that induced by Aβ42 oligomers with low solvent-exposed hydrophobicity (A-) in GM1-enriched cells. In addition, A+ oligomers accumulate in proximity of membrane NMDA and AMPA receptors, inducing the early and transient Ca2+ influx, although FRET shows that the interaction is not direct. These results suggest that age-dependent clustering of GM1 within neuronal membranes could induce neurodegeneration in elderly people as a consequence of an increased ability of the lipid bilayers to recruit membrane-permeabilizing oligomers. We also show that both lipid and protein components of the plasma membrane can contribute to neuronal dysfunction, thus expanding the molecular targets for therapeutic intervention in AD.

Amyotrophic lateral sclerosis and frontotemporal lobar degeneration with ubiquitin-positive inclusions are neurodegenerative disorders that share the cytosolic deposition of TDP-43 (TAR DNA-binding protein 43) in the CNS. TDP-43 is well known as being actively degraded by both the proteasome and macroautophagy. The well-documented decrease in the efficiency of these clearance systems in aging and neurodegeneration, as well as the genetic evidence that many of the familial forms of TDP-43 proteinopathies involve genes that are associated with them, suggest that a failure of these protein degradation systems is a major factor that contributes to the onset of TDP-43-associated disorders. Here, we inserted preformed human TDP-43 aggregates in the cytosol of murine NSC34 and N2a cells in diffuse form and observed their degradation under conditions in which exogenous TDP-43 is not expressed and endogenous nuclear TDP-43 is not recruited, thereby allowing a time zero to be established in TDP-43 degradation and to observe its disposal kinetically and analytically. TDP-43 degradation was observed in the absence and presence of selective inhibitors and small interfering RNAs against the proteasome and autophagy. We found that cytosolic diffuse aggregates of TDP-43 can be distinguished in 3 different classes on the basis of their vulnerability to degradation, which contributed to the definition-with previous reports-of a total of 6 distinct classes of misfolded TDP-43 species that range from soluble monomer to undegradable macroaggregates. We also found that the proteasome and macroautophagy-degradable pools of TDP-43 are fully distinguishable, rather than in equilibrium between them on the time scale required for degradation, and that a significant crosstalk exists between the 2 degradation processes.-Cascella, R., Fani, G., Capitini, C., Rusmini, P., Poletti, A., Cecchi, C., Chiti, F. Quantitative assessment of the degradation of aggregated TDP-43 mediated by the ubiquitin proteasome system and macroautophagy.

16 pags., 6 figs., The self-assembly of α-synuclein (αS) into intraneuronal inclusion bodies is a key characteristic of Parkinson’s disease. To define the nature of the species giving rise to neuronal damage, we have investigated the mechanism of action of the main αS populations that have been observed to form progressively during fibril growth. The αS fibrils release soluble prefibrillar oligomeric species with cross-β structure and solvent-exposed hydrophobic clusters. αS prefibrillar oligomers are efficient in crossing and permeabilize neuronal membranes, causing cellular insults. Short fibrils are more neurotoxic than long fibrils due to the higher proportion of fibrillar ends, resulting in a rapid release of oligomers. The kinetics of released αS oligomers match the observed kinetics of toxicity in cellular systems. In addition to previous evidence that αS fibrils can spread in different brain areas, our in vitro results reveal that αS fibrils can also release oligomeric species responsible for an immediate dysfunction of the neurons in the vicinity of these species., This research was supported by the University of Florence (Fondi Ateneo to F.C. and C.C.), the Ministry of Education, Universities and Research of Italy (Progetto Dipartimento di Eccellenza “Gender Medicine” to C.C.), Parkinson’s UK (G-1508 to S.W.C. and C.M.D.), the Center for Misfolding Diseases of the University of Cambridge (S.W.C. and C.M.D.), the UK Medical Research Council (MR/N000676/1 to C.M.D.), the Agency of Science, Technology and Research of Singapore (to S.W.C.), and the Ministry of Economy and Competitiveness of Spain (MINECO RYC-2012-12068 and MINECO/FEDER EU BFU2015-64119-P to N.C.).

Raman spectroscopy assisted by localized plasmon resonances generating effective hot spots at the gaps between intertwined silver nanowires is herein adopted to unravel characteristic molecular motifs on the surface of A beta(42)misfolded oligomers that are critical in driving intermolecular interactions in neurodegeneration.

Frontotemporal lobar degeneration (FTLD) and amyotrophic lateral sclerosis (ALS) are progressive and fatal neurodegenerative disorders showing mislocalization and cytosolic accumulation of TDP-43 inclusions in the central nervous system. The decrease in the efficiency of the clearance systems in aging, as well as the presence of genetic mutations of proteins associated with cellular proteostasis in the familial forms of TDP-43 proteinopathies, suggest that a failure of these protein degradation systems is a key factor in the aetiology of TDP-43 associated disorders. Here we show that the internalization of human pre-formed TDP-43 aggregates in the murine neuroblastoma N2a cells promptly resulted in their ubiquitination and hyperphosphorylation by endogenous machineries, mimicking the post-translational modifications observed in patients. Moreover, our data identify mitochondria as the main responsible sites for the alteration of calcium homeostasis induced by TDP-43 aggregates, which, in turn, stimulates an increase in reactive oxygen species and, finally, caspase activation. The inhibition of TDP-43 proteostasis in the presence of selective inhibitors against the proteasome and macroautophagy systems revealed that these two systems are both severely involved in TDP-43 accumulation and have a strong influence on each other in neurodegenerative disorders associated with TDP-43.

The aggregation of α-synuclein, a protein involved in neurotransmitter release at presynaptic terminals, is associated with a range of highly debilitating neurodegenerative conditions, most notably Parkinson's disease. Intraneuronal inclusion bodies, primarily composed of α-synuclein fibrils, are the major histopathological hallmarks of these disorders, although small oligomeric assemblies are believed to play a crucial role in neuronal impairment. We have probed the mechanism of neurotoxicity of α-synuclein oligomers isolated in vitro using antibodies targeting the N-terminal region of the protein and found that the presence of the antibody resulted in a substantial reduction of the damage induced by the aggregates when incubated with primary cortical neurons and neuroblastoma cells. We observed a similar behavior in vivo using a strain of C. elegans overexpressing α-synuclein, where the aggregation process itself is also partially inhibited as a result of incubation with the antibodies. The similar effects of the antibodies in reducing the toxicity of the aggregated species formed in vitro and in vivo provide evidence for a common origin of cellular impairment induced by α-synuclein aggregates.

// Pasqualina Liana Scognamiglio 1, 5, * , Concetta Di Natale 1, * , Marilisa Leone 2 , Roberta Cascella 3 , Cristina Cecchi 3 , Lisa Lirussi 4, 6 , Giulia Antoniali 4 , Domenico Riccardi 1 , Giancarlo Morelli 1 , Gianluca Tell 4 , Fabrizio Chiti 3 , Daniela Marasco 1 1 Department of Pharmacy, CIRPEB: Centro Interuniversitario di Ricerca sui Peptidi Bioattivi-University of Naples “Federico II”, DFM-Scarl, 80134, Naples, Italy 2 Institute of Biostructures and Bioimaging - CNR, 80134, Naples, Italy 3 Section of Biochemistry, Department of Experimental and Clinical Biomedical Sciences “Mario Serio”, University of Florence, 50134, Florence, Italy 4 Laboratory of Molecular Biology and DNA repair, Department of Medical and Biological Sciences, University of Udine, 33100, Udine, Italy 5 Permanent address: Center for Advanced Biomaterials for Health Care@CRIB Istituto Italiano di Tecnologia, 80125, Napoli, Italy 6 Permanent address: Department of Clinical Molecular Biology, University of Oslo and Akershus University Hospital, Nordbyhagen, 1474, Norway * Co-first authors Correspondence to: Daniela Marasco, email: daniela.marasco@unina.it Keywords: helical peptides, aggregation phenomena, AML, CD spectroscopy Received: November 02, 2015 Accepted: July 17, 2016 Published: August 01, 2016 ABSTRACT Nucleophosmin (NPM1) is a multifunctional protein that is implicated in the pathogenesis of several human malignancies. To gain insight into the role of isolated fragments of NPM1 in its biological activities, we dissected the C-terminal domain (CTD) into its helical fragments. Here we focus the attention on the third helix of the NPM1-CTD in its wild-type (H3 wt) and AML-mutated (H3 mutA and H3 mutE) sequences. Conformational studies, by means of CD and NMR spectroscopies, showed that the H3 wt peptide was partially endowed with an α-helical structure, but the AML-sequences exhibited a lower content of this conformation, particularly the H3 mutA peptide. Thioflavin T assays showed that the H3 mutE and the H3 mutA peptides displayed a significant aggregation propensity that was confirmed by CD and DLS assays. In addition, we found that the H3 mutE and H3 mutA peptides, unlike the H3 wt, were moderately and highly toxic, respectively, when exposed to human neuroblastoma cells. Cellular localization experiments confirmed that the mutated sequences hamper their nucleolar accumulation, and more importantly, that the helical conformation of the H3 region is crucial for such a localization.

The self-assembly of proteins into structured fibrillar aggregates is associated with a range of neurodegenerative diseases, including Alzheimer's and Parkinson's diseases, in which an important cytotoxic role is thought to be played by small soluble oligomers accumulating during the aggregation process or released by mature fibrils. As the structural characteristics of such species and their links with toxicity are still not fully defined, we have compared six examples of preformed misfolded protein oligomers with different β-sheet content, as determined using Fourier transform infrared spectroscopy, and with different toxicity, as determined by three cellular readouts of cell viability. The results show the absence of any measurable correlation between the nature of their secondary structure and their cellular toxicity, both when comparing the six types of oligomers as a group and when comparing species in subgroups characterized by either the same size or the same exposure of hydrophobic moieties.

Novel imaging techniques with ever-increasing resolution are invaluable tools for the study of protein deposition, as they allow the self-assembly of proteins to be directly investigated in living cells. For the first time, the acceleration in Aβ42 aggregation induced by the Arctic mutation was monitored in cells, revealing a number of distinct morphologies that form sequentially. This approach will help discriminate the impacts of mutations on amyloid protein processing, Aβ aggregation propensity, and other mechanistic outcomes.

The deposition of fibrillar protein aggregates in human organs is the hallmark of several pathological states, including highly debilitating neurodegenerative disorders and systemic amyloidoses. It is widely accepted that small oligomers arising as intermediates in the aggregation process, released by fibrils, or growing in secondary nucleation steps are the cytotoxic entities in protein-misfolding diseases, notably neurodegenerative conditions. Increasing evidence indicates that cytotoxicity is triggered by the interaction between nanosized protein aggregates and cell membranes, even though little information on the molecular details of such interaction is presently available. In this work, we propose what is, to our knowledge, a new approach, based on the use of single-cell force spectroscopy applied to multifunctional substrates, to study the interaction between protein oligomers, cell membranes, and/or the extracellular matrix. We compared the interaction of single Chinese hamster ovary cells with two types of oligomers (toxic and nontoxic) grown from the N-terminal domain of the Escherichia coli protein HypF. We were able to quantify the affinity between both oligomer type and the cell membrane by measuring the mechanical work needed to detach the cells from the aggregates, and we could discriminate the contributions of the membrane lipid and protein fractions to such affinity. The fundamental role of the ganglioside GM1 in the membrane-oligomers interaction was also highlighted. Finally, we observed that the binding of toxic oligomers to the cell membrane significantly affects the functionality of adhesion molecules such as Arg-Gly-Asp binding integrins, and that this effect requires the presence of the negatively charged sialic acid moiety of GM1.

The misfolding and aberrant assembly of peptides and proteins into fibrillar aggregates is the hallmark of many pathologies. Fibril formation is accompanied by oligomeric species thought to be the primary pathogenic agents in many of these diseases. With the aim of identifying the structural determinants responsible for the toxicity of misfolded oligomers, we created 12 oligomeric variants from the N-terminal domain of the E. coli HypF protein (HypF-N) by replacing one or more charged amino acid residues with neutral apolar residues and allowing the mutated proteins to aggregate under two sets of conditions. The resulting oligomeric species have different degrees of cytotoxicity when added to the extracellular medium of the cells, as assessed by the extent of 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) reduction, apoptosis, and influx of Ca2+ into the cells. The structural properties of the oligomeric variants were characterized by evaluating their surface hydrophobicity with 8-anilinonaphthalene-1-sulfonate (ANS) binding and by measuring their size by means of turbidimetry as well as light scattering. We find that increases in the surface hydrophobicity of the oligomers following mutation can promote the formation of larger assemblies and that the overall toxicity correlates with a combination of both surface hydrophobicity and size, with the most toxic oligomers having high hydrophobicity and small size. These results have allowed the relationships between these three parameters to be studied simultaneously and quantitatively, and have enabled the generation of an equation that is able to rationalize and even predict toxicity of the oligomers resulting from their surface hydrophobicity and size.

Amyloid cytotoxicity, structure and polymorphisms are themes of increasing importance. Present knowledge considers any peptide/protein able to undergo misfolding and aggregation generating intrinsically cytotoxic amyloids. It also describes growth and structure of amyloid fibrils and their possible disassembly, whereas reduced information is available on oligomer structure. Recent research has highlighted the importance of the environmental conditions as determinants of the amyloid polymorphisms and cytotoxicity. Another body of evidence describes chemical or biological surfaces as key sites of protein misfolding and aggregation or of interaction with amyloids and the resulting biochemical modifications inducing cell functional/viability impairment. In particular, the membrane lipid composition appears to modulate cell response to toxic amyloids, thus contributing to explain the variable vulnerability to the same amyloids of different cell types. Finally, a recent view describes amyloid toxicity as an emerging property dependent on a complex interplay between the biophysical features of early aggregates and the interacting cell membranes taken as a whole system.

The self-Assembly of α-synuclein is closely associated with Parkinson's disease and related syndromes. We show that squalamine, a natural product with known anticancer and antiviral activity, dramatically affects α-synuclein aggregation in vitro and in vivo. We elucidate the mechanism of action of squalamine by investigating its interaction with lipid vesicles, which are known to stimulate nucleation, and find that this compound displaces α-synuclein from the surfaces of such vesicles, thereby blocking the first steps in its aggregation process. We also show that squalamine almost completely suppresses the toxicity of α-synuclein oligomers in human neuroblastoma cells by inhibiting their interactions with lipid membranes. We further examine the effects of squalamine in a Caenorhabditis elegans strain overexpressing α-synuclein, observing a dramatic reduction of α-synuclein aggregation and an almost complete elimination of muscle paralysis. These findings suggest that squalamine could be a means of therapeutic intervention in Parkinson's disease and related conditions.

5 pags, 3 figs, Oligomeric species populated during the aggregation process of a-synuclein have been linked to neuronal impairment in Parkinson's disease and related neurodegenerative disorders. By using solution and solid-state nuclear magnetic resonance techniques in conjunction with other structural methods, we identified the fundamental characteristics that enable toxic a-synuclein oligomers to perturb biological membranes and disrupt cellular function; these include a highly lipophilic element that promotes strong membrane interactions and a structured region that inserts into lipid bilayers and disrupts their integrity. In support of these conclusions, mutations that target the region that promotes strong membrane interactions by a-synuclein oligomers suppressed their toxicity in neuroblastoma cells and primary cortical neurons., This research was supported by Parkinson's UK (G-1508 to G.F., M.V., C.M.D., and A.D.); the UK Medical Research Council (MR/N000676/1 to G.F., M.V. C.M.D., and A.D.); the Wellcome Trust (104933/2/14E to kD.): the Leverhulme Trust (RPG-2015-350 to A.D. and RPG-2015-345 to L.Y.); the British Heart Foundation (PG/14/93/31237 to A.D. and PG/11/81/29130 to L.Y.); the UK Biotechnology and Biological Sciences Research Council (BB/M023923/1 to A.D. and BB/G00594X/1 to L.Y.); the Agency of Science, Technology and Research of Singapore (to S.W.C.); the Ministry of Economy, Industry, and Competitiveness of Spain (MINECO RYC-2012-12068 and MINECO/FEDER EU BEU2015-64119-P to N.C.); the Regione Toscana (SUPREMAL to E.C., C.C., and R.C); the University of Florence (Eondi di Ateneo to E.C. and. C.C); and the Centre for Misfolding Diseases of the University of Cambridge. The data supporting the findings of this study are available within the article and supplementary materials.

The conversion of peptides or proteins from their soluble native states into intractable amyloid deposits is associated with a wide range of human disorders. Misfolded protein oligomers formed during the process of aggregation have been identified as the primary pathogenic agents in many such conditions. Here, we show the existence of a quantitative relationship between the degree of binding to neuronal cells of different types of oligomers formed from a model protein, HypF-N, and the GM1 content of the plasma membranes. In addition, remarkably similar behavior is observed for oligomers of the Aβ42 peptide associated with Alzheimer’s disease. Further analysis has revealed the existence of a linear correlation between the level of the influx of Ca2+ across neuronal membranes that triggers cellular damage, and the fraction of oligomeric species bound to the membrane. Our findings indicate that the susceptibility of neuronal cells to different types of misfolded oligomeric assemblies is directly related to the extent of binding of such oligomers to the cellular membrane.