Cytotoxic species in amyloid-associated diseases: Oligomers or mature fibrils

Strategies for measuring concentrations and forms of amyloid-β peptides

Alzheimer's disease (AD) is affecting more and more people worldwide without the effective treatment, while the existed pathological mechanism has been confirmed barely useful in the treatment. Amyloid-β peptide (Aβ), a main component of senile plaque, is regarded as the most promising target in AD treatment. Aβ clearance from AD brain seems to be a reliably therapeutic strategy, as the two exited drugs, GV-971 and aducanumab, are both developed based on it. However, doubt still exists. To exhaustive expound on the pathological mechanism of Aβ, rigorous analyses on the concentrations and aggregation forms are essential. Thus, it is attracting broad attention these years. However, most of the sensors have not been used in pathological studies, as the lack of the bridge between analytical chemist and pathologists. In this review, we made a brief introduce on Aβ-related pathological mechanism included in β-amyloid hypothesis to elucidate the detection conditions of sensor methods. Furthermore, a summary of the sensor methods was made, which were based on Aβ concentrations and form detections that have been developed in the past 10 years. As the greatest number of the sensors were built on fluorescent spectroscopy, electrochemistry, and Roman spectroscopy, detailed elucidation on them was made. Notably, the aggregation process is another important factor in revealing the progress of AD and developing the treatment methods, so the sensors on monitoring Aβ aggregation processes were also summarized.

Cytotoxic Effect of Amyloid-β1-42 Oligomers on Endoplasmic Reticulum and Golgi Apparatus Arrangement in SH-SY5Y Neuroblastoma Cells

Amyloid-β oligomers are a cytotoxic structure that is key for the establishment of the beginning stages of Alzheimer's disease (AD). These structures promote subcellular alterations that cause synaptic dysfunction, loss of cell communication, and even cell death, generating cognitive deficits. The aim of this study was to investigate the cytotoxic effects of amyloid-β1-42 oligomers (AβOs) on the membranous organelles involved in protein processing: the endoplasmic reticulum (ER) and Golgi apparatus (GA). The results obtained with 10 μM AβOs in SH-SY5Y neuroblastoma cells showed that oligomeric structures are more toxic than monomers because they cause cell viability to decrease as exposure time increases. Survivor cells were analyzed to further understand the toxic effects of AβOs on intracellular organelles. Survivor cells showed morphological alterations associated with abnormal cytoskeleton modification 72-96 h after exposure to AβOs. Moreover, the ER and GA presented rearrangement throughout the cytoplasmic space, which could be attributed to a lack of constitutive protein processing or to previous abnormal cytoskeleton modification. Interestingly, the disorganization of both ER and GA organelles exposed to AβOs is likely an early pathological alteration that could be related to aberrant protein processing and accumulation in AD.

Each big journey starts with a first step: Importance of oligomerization

Protein oligomers, widely found in nature, have significant physiological and pathological functions. They are classified into three groups based on their function and toxicity. Significant advancements are being achieved in the development of functional oligomers, with a focus on various applications and their engineering. The antimicrobial peptides oligomers play roles in death of bacterial and cancer cells. The predominant pathogenic species in neurodegenerative disorders, as shown by recent results, are amyloid oligomers, which are the main subject of this chapter. They are generated throughout the aggregation process, serving as both intermediates in the subsequent aggregation pathways and ultimate products. Some of them may possess potent cytotoxic properties and through diverse mechanisms cause cellular impairment, and ultimately, the death of cells and disease progression. Information regarding their structure, formation mechanism, and toxicity is limited due to their inherent instability and structural variability. This chapter aims to provide a concise overview of the current knowledge regarding amyloid oligomers.

Amyloid fibril cytotoxicity and associated disorders

Misfolded proteins assemble into fibril structures that are called amyloids. Unlike usually folded proteins, misfolded fibrils are insoluble and deposit extracellularly or intracellularly. Misfolded proteins interrupt the function and structure of cells and cause amyloid disease. There is increasing evidence that the most pernicious species are oligomers. Misfolded proteins disrupt cell function and cause cytotoxicity by calcium imbalance, mitochondrial dysfunction, and intracellular reactive oxygen species. Despite profound impacts on health, social, and economic factors, amyloid diseases remain untreatable. To develop new therapeutics and to understand the pathological manifestations of amyloidosis, research into the origin and pathology of amyloidosis is urgently needed. This chapter describes the basic concept of amyloid disease and the function of atypical amyloid deposits in them.

Identification of Molecular Correlations of GSDMD with Pyroptosis inAlzheimer's Disease

AIM

An analysis of bioinformatics and cell experiments was performed to verify the relationship between gasdermin D (GSDMD), an executive protein of pyroptosis, and Alzheimer's disease (AD).

METHODS

The training set GSE33000 was utilized to identify differentially expressed genes (DEGs) in both the AD group and control group, as well as in the GSDMD protein high/low expression group. Subsequently, the weighted gene co-expression network analysis (WGCNA) and the least absolute shrinkage and selection operator (LASSO) regression analysis were conducted, followed by the selection of the key genes for the subsequent Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses. The association between GSDMD and AD was assessed and confirmed in the training set GSE33000, as well as in the validation sets GSE5281 and GSE48350. Immunofluorescence (IF) was employed to detect the myelin basic protein (MBP), a distinctive protein found in the rat oligodendrocytes (OLN-93 cells). A range of concentrations (1-15 μmol/L) of β-amyloid 1-42 (Aβ1-42) were exposed to the cells, and the subsequent observations were made regarding cell morphology. Additionally, the assessments were conducted to evaluate the cell viability, the lactate dehydrogenase (LDH) release, the cell membrane permeability, and the GSDMD protein expression.

RESULTS

A total of 7,492 DEGs were screened using GSE33000. Subsequently, WGCNA analysis identified 19 genes that exhibited the strongest correlation with clinical traits in AD. Additionally, LASSO regression analysis identified 13 key genes, including GSDMD, AFF1, and ATOH8. Furthermore, the investigation revealed that the key genes were associated with cellular inflammation based on GO and KEGG analyses. Moreover, the area under the curve (AUC) values for the key genes in the training and validation sets were determined to be 0.95 and 0.70, respectively. Significantly, GSDMD demonstrated elevated levels of expression in AD across both datasets. The positivity of MBP expression in cells exceeded 95%. As the concentration of Aβ1-42 action gradually escalated, the detrimental effects on cells progressively intensified, resulting in a gradual decline in cell survival rate, accompanied by an increase in lactate dehydrogenase release, cell membrane permeability, and GSDMD protein expression.

CONCLUSION

The association between GSDMD and AD has been observed, and it has been found that Aβ1-42 can induce a significant upregulation of GSDMD in OLN-93 cells. This suggests that Aβ1-42 has the potential to induce cellular pyroptosis and can serve as a valuable cellular pyroptosis model for the study of AD.

Fibril structures of TFG protein mutants validate the identification of TFG as a disease-related amyloid protein by the IMPAcT method

We previously presented a bioinformatic method for identifying diseases that arise from a mutation in a protein's low-complexity domain that drives the protein into pathogenic amyloid fibrils. One protein so identified was the tropomyosin-receptor kinase-fused gene protein (TRK-fused gene protein or TFG). Mutations in TFG are associated with degenerative neurological conditions. Here, we present experimental evidence that confirms our prediction that these conditions are amyloid-related. We find that the low-complexity domain of TFG containing the disease-related mutations G269V or P285L forms amyloid fibrils, and we determine their structures using cryo-electron microscopy (cryo-EM). These structures are unmistakably amyloid in nature and confirm the propensity of the mutant TFG low-complexity domain to form amyloid fibrils. Also, despite resulting from a pathogenic mutation, the fibril structures bear some similarities to other amyloid structures that are thought to be nonpathogenic and even functional, but there are other factors that support these structures' relevance to disease, including an increased propensity to form amyloid compared with the wild-type sequence, structure-stabilizing influence from the mutant residues themselves, and double-protofilament amyloid cores. Our findings elucidate two potentially disease-relevant structures of a previously unknown amyloid and also show how the structural features of pathogenic amyloid fibrils may not conform to the features commonly associated with pathogenicity.

Abl depletion via autophagy mediates the beneficial effects of quercetin against Alzheimer pathology across species

Alzheimer's disease is the most common age-associated neurodegenerative disorder and the most frequent form of dementia in our society. Aging is a complex biological process concurrently shaped by genetic, dietary and environmental factors and natural compounds are emerging for their beneficial effects against age-related disorders. Besides their antioxidant activity often described in simple model organisms, the molecular mechanisms underlying the beneficial effects of different dietary compounds remain however largely unknown. In the present study, we exploit the nematode Caenorhabditis elegans as a widely established model for aging studies, to test the effects of different natural compounds in vivo and focused on mechanistic aspects of one of them, quercetin, using complementary systems and assays. We show that quercetin has evolutionarily conserved beneficial effects against Alzheimer's disease (AD) pathology: it prevents Amyloid beta (Aβ)-induced detrimental effects in different C. elegans AD models and it reduces Aβ-secretion in mammalian cells. Mechanistically, we found that the beneficial effects of quercetin are mediated by autophagy-dependent reduced expression of Abl tyrosine kinase. In turn, autophagy is required upon Abl suppression to mediate quercetin's protective effects against Aβ toxicity. Our data support the power of C. elegans as an in vivo model to investigate therapeutic options for AD.

Flanking regions, amyloid cores, and polymorphism: the potential interplay underlying structural diversity

The β-sheet-rich amyloid core is the defining feature of protein aggregates associated with neurodegenerative disorders. Recent investigations have revealed that there exist multiple examples of the same protein, with the same sequence, forming a variety of amyloid cores with distinct structural characteristics. These structural variants, termed as polymorphs, are hypothesized to influence the pathological profile and the progression of different neurodegenerative diseases, giving rise to unique phenotypic differences. Thus, identifying the origin and properties of these structural variants remain a focus of studies, as a preliminary step in the development of therapeutic strategies. Here, we review the potential role of the flanking regions of amyloid cores in inducing polymorphism. These regions, adjacent to the amyloid cores, show a preponderance for being structurally disordered, imbuing them with functional promiscuity. The dynamic nature of the flanking regions can then manifest in the form of conformational polymorphism of the aggregates. We take a closer look at the sequences flanking the amyloid cores, followed by a review of the polymorphic aggregates of the well-characterized proteins amyloid-β, α-synuclein, Tau, and TDP-43. We also consider different factors that can potentially influence aggregate structure and how these regions can be viewed as novel targets for therapeutic strategies by utilizing their unique structural properties.

Inhibition of Pancreatic Cancer Cells by Different Amyloid Proteins Reveals an Inverse Relationship between Neurodegenerative Diseases and Cancer

Neurodegenerative diseases and cancers are considered to be two families of diseases caused by completely opposite cell-death mechanisms: the former caused by premature cell death, with the latter due to the increased resistance to cell death. Growing epidemiologic evidence appear to suggest an inverse correlation between neurodegenerative diseases and cancers. However, pathological links, particularly from a protein-cell interaction perspective, between these two families of diseases remains to be proven. Here, a fundamental study investigates the effects of three amyloid proteins of Aβ (associated with AD), hIAPP (associated with T2D), and hCT (associated with MTC) on pancreatic cancer (PANC-1) cells. Collective results demonstrate a general inhibitory activity of all of three amyloid proteins on cancer cell proliferation, but inhibition efficiencies are strongly dependent on amyloid sequence (Aβ, hIAPP, hCT), concentration (IC25, IC50, IC75), and aggregation states (monomers, oligomers). Amyloid proteins exhibit two pathways against cancer cells: amyloid monomer-induced ROS production to inhibit cell growth and amyloid oligomer-induced membrane disruption to kill cells. Collectively, the results demonstrate a general inhibition function of amyloid proteins to induce cancer cell death by preventing cell proliferation, suppressing cell migration, promoting reactive oxygen species production, and disrupting cell membranes.

The C-terminal 32-mer fragment of hemoglobin alpha is an amyloidogenic peptide with antimicrobial properties

Antimicrobial peptides (AMPs) are major components of the innate immune defense. Accumulating evidence suggests that the antibacterial activity of many AMPs is dependent on the formation of amyloid-like fibrils. To identify novel fibril forming AMPs, we generated a spleen-derived peptide library and screened it for the presence of amyloidogenic peptides. This approach led to the identification of a C-terminal 32-mer fragment of alpha-hemoglobin, termed HBA(111-142). The non-fibrillar peptide has membranolytic activity against various bacterial species, while the HBA(111-142) fibrils aggregated bacteria to promote their phagocytotic clearance. Further, HBA(111-142) fibrils selectively inhibited measles and herpes viruses (HSV-1, HSV-2, HCMV), but not SARS-CoV-2, ZIKV and IAV. HBA(111-142) is released from its precursor by ubiquitous aspartic proteases under acidic conditions characteristic at sites of infection and inflammation. Thus, HBA(111-142) is an amyloidogenic AMP that may specifically be generated from a highly abundant precursor during bacterial or viral infection and may play an important role in innate antimicrobial immune responses.

Mechanistic Insight into the Amyloid Fibrillation Inhibition of Hen Egg White Lysozyme by Three Different Bile Acids

Amyloid aggregation of protein is linked to many neurodegenerative diseases. Identification of small molecules capable of targeting amyloidogenic proteins has gained significant importance. Introduction of hydrophobic and hydrogen bonding interactions through site-specific binding of small molecular ligand to protein can effectively modulate the protein aggregation pathway. Here, we investigate the possible roles of three different bile acids, cholic acid (CA), taurocholic acid (TCA), and lithocholic acid (LCA) with varying hydrophobic and hydrogen bonding properties in inhibiting protein fibrillation. Bile acids are an important class of steroid compounds that are synthesized in the liver from cholesterol. Increasing evidence suggests that altered taurine transport, cholesterol metabolism, and bile acid synthesis have strong implications in Alzheimer's disease. We find that the hydrophilic bile acids, CA and TCA (taurine conjugated form of CA), are substantially more efficient inhibitors of lysozyme fibrillation than the most hydrophobic secondary bile acid LCA. Although LCA binds more strongly with the protein and masks the Trp residues more prominently through hydrophobic interactions, the lesser extent of hydrogen bonding interactions at the active site has made LCA a relatively weaker inhibitor of HEWL aggregation than CA and TCA. The introduction of a greater number of hydrogen bonding channels by CA and TCA with several key amino acid residues which are prone to form oligomers and fibrils has weakened the protein's internal hydrogen bonding capabilities for undergoing amyloid aggregation.

Impaired Extracellular Proteostasis in Patients with Heart Failure

BACKGROUND

Proteostasis impairment and the consequent increase of amyloid burden in the myocardium have been associated with heart failure (HF) development and poor prognosis. A better knowledge of the protein aggregation process in biofluids could assist the development and monitoring of tailored interventions.

AIM

To compare the proteostasis status and protein's secondary structures in plasma samples of patients with HF with preserved ejection fraction (HFpEF), patients with HF with reduced ejection fraction (HFrEF), and age-matched individuals.

METHODS

A total of 42 participants were enrolled in 3 groups: 14 patients with HFpEF, 14 patients with HFrEF, and 14 age-matched individuals. Proteostasis-related markers were analyzed by immunoblotting techniques. Fourier Transform Infrared (FTIR) Spectroscopy in Attenuated Total Reflectance (ATR) was applied to assess changes in the protein's conformational profile.

RESULTS

Patients with HFrEF showed an elevated concentration of oligomeric proteic species and reduced clusterin levels. ATR-FTIR spectroscopy coupled with multivariate analysis allowed the discrimination of HF patients from age-matched individuals in the protein amide I absorption region (1700-1600 cm^-1), reflecting changes in protein conformation, with a sensitivity of 73 and a specificity of 81%. Further analysis of FTIR spectra showed significantly reduced random coils levels in both HF phenotypes. Also, compared to the age-matched group, the levels of structures related to fibril formation were significantly increased in patients with HFrEF, whereas the β-turns were significantly increased in patients with HFpEF.

CONCLUSION

Both HF phenotypes showed a compromised extracellular proteostasis and different protein conformational changes, suggesting a less efficient protein quality control system.

Solvent-dependent formation kinetics of L,L-diphenylalanine micro/nanotubes

Investigating the molecular mechanism underlying the aggregation process of amyloid fibers is of great importance both for its implications in several degenerative diseases and for the design of new materials based on self-assembly. In particular, micro/nanotubes of L,L-diphenylalanine have been investigated as a model of amyloid plaques in Alzheimer's disease and also for their broad range of physical properties, e.g., good thermo- and mechanical stability, semiconductivity, piezoelectricity and optical properties. It has been reported that the assembly/disassembly dynamics of L,L-diphenylalanine crystals is influenced by the solvent composition being triggered by evaporation of solvents. In fact the solvatomorphism of this peptide-based nanomaterial is complex and rich attracting great attention. Here we investigated the growing kinetics of the micro/nanotubes of L,L-diphenylalanine in samples prepared with toluene, ethanol, and acetic acid solvents by time-resolved Raman spectroscopy. Our results indicated that the self-assembly in this case competes with the water evaporation process contrary to what is reported by samples prepared with widely used solvent 1,1,1,3,3,3-hexafluoro-2-propanol. We note that exclusively tubular structures (being hollow for the toluene solvent case) were observed. Interestingly our results support the fact that for acetic acid, ethanol, and toluene the micro/nanotube formation process is autocatalytic instead of being nucleation-dominating as reported for samples prepared using solvent 1,1,1,3,3,3-hexafluoro-2-propanol.

Different Extracellular β-Amyloid (1-42) Aggregates Differentially Impair Neural Cell Adhesion and Neurite Outgrowth through Differential Induction of Scaffold Palladin

Extracellular amyloid β-protein (1-42) (Aβ42) aggregates have been recognized as toxic agents for neural cells in vivo and in vitro. The aim of this study was to investigate the cytotoxic effects of extracellular Aβ42 aggregates in soluble (or suspended, SAβ42) and deposited (or attached, DAβ42) forms on cell adhesion/re-adhesion, neurite outgrowth, and intracellular scaffold palladin using the neural cell lines SH-SY5Y and HT22, and to elucidate the potential relevance of these effects. The effect of extracellular Aβ42 on neural cell adhesion was directly associated with their neurotrophic or neurotoxic activity, with SAβ42 aggregates reducing cell adhesion and associated live cell de-adherence more than DAβ42 aggregates, while causing higher mortality. The reduction in cell adhesion due to extracellular Aβ42 aggregates was accompanied by the impairment of neurite outgrowth, both in length and number, and similarly, SAβ42 aggregates impaired the extension of neurites more severely than DAβ42 aggregates. Further, the disparate changes of intracellular palladin induced by SAβ42 and DAβ42 aggregates, respectively, might underlie their aforementioned effects on target cells. Further, the use of anti-oligomeric Aβ42 scFv antibodies revealed that extracellular Aβ42 aggregates, especially large DAβ42 aggregates, had some independent detrimental effects, including physical barrier effects on neural cell adhesion and neuritogenesis in addition to their neurotoxicity, which might be caused by the rigid C-terminal clusters formed between adjacent Aβ42 chains in Aβ42 aggregates. Our findings, concerning how scaffold palladin responds to extracellular Aβ42 aggregates, and is closely connected with declines in cell adhesion and neurite outgrowth, provide new insights into the cytotoxicity of extracellular Aβ42 aggregates in Alzheimer disease.

Intracellular Injection of Brain Extracts from Alzheimer's Disease Patients Triggers Unregulated Ca2+ Release from Intracellular Stores That Hinders Cellular Bioenergetics

Strong evidence indicates that amyloid beta (Aβ) inflicts its toxicity in Alzheimer's disease (AD) by promoting uncontrolled elevation of cytosolic Ca²⁺ in neurons. We have previously shown that synthetic Aβ42 oligomers stimulate abnormal intracellular Ca²⁺ release from the endoplasmic reticulum stores, suggesting that a similar mechanism of Ca²⁺ toxicity may be common to the endogenous Aβs oligomers. Here, we use human postmortem brain extracts from AD-affected patients and test their ability to trigger Ca²⁺ fluxes when injected intracellularly into Xenopus oocytes. Immunological characterization of the samples revealed the elevated content of soluble Aβ oligomers only in samples from AD patients. Intracellular injection of brain extracts from control patients failed to trigger detectable changes in intracellular Ca²⁺. Conversely, brain extracts from AD patients triggered Ca²⁺ events consisting of local and global Ca²⁺ fluorescent transients. Pre-incubation with either the conformation-specific OC antiserum or caffeine completely suppressed the brain extract's ability to trigger cytosolic Ca²⁺ events. Computational modeling suggests that these Ca²⁺ fluxes may impair cells bioenergetic by affecting ATP and ROS production. These results support the hypothesis that Aβ oligomers contained in neurons of AD-affected brains may represent the toxic agents responsible for neuronal malfunctioning and death associated with the disruption of Ca²⁺ homeostasis.

The Influence of Heparan Sulfate on Breast Amyloidosis and the Toxicity of the Pre-fibrils Formed by β-casein

Heparan sulfate (HS) as a mediator is usually involved in both inflammation and fibrosis. Besides, pre-fibrils are the intermediates of amyloid fibrils that usually cause cell death and tissue damage, like the amyloid-β in Alzheimer's disease, α-synuclein in Parkinson disease and islet amyloid polypeptide in type II diabetes mellitus. However, the related study was involved rarely in breast. Therefore, the combing technologies including hematoxylin-eosin staining and thioflavin S staining were used to investigate the influence of HS on breast amyloidosis. To further study the toxicity of the pre-fibrils formed by β-casein on the HC11 cells and the breast mammary gland, the combing technologies including pentamer formyl thiophene acetic acid fluorescence analysis, MTT assay, Annexin V/PI staining and hematoxylin-eosin staining were performed. The results demonstrated that HS, acted as an endogenous molecule, induced the inflammation and amyloid fibril formation at the same time, and there was a close relationship between inflammation and fibrosis of breast. In addition, the pre-fibrils formed by β-casein were toxic because they induced the death and apoptosis of HC11 cells, as well as the inflammation of mammary gland of rats. Therefore, the early examination and identify of the pre-fibrils in the breast were worth considering to prevent the disease development, and it was interesting to explore the HS mimetics to impair the breast amyloidosis and attenuate the inflammatory response in the future.

Multifunctional Anti-Alzheimer’s Disease Effects of Natural Xanthone Derivatives: A Primary Structure-Activity Evaluation

Background: A series of α-Mangostin (α-M) derivatives were designed and synthesized. α-M and four analogues were evaluated for their multifunctional anti-Alzheimer’s disease (anti-AD) effects on fibrillogenesis, microglial uptake, microglial degradation, and anti-neurotoxicity of Aβ, as well as LPS-induced neuroinflammation. The differences in bioactivities were analyzed to understand the structure-activity relationship for further modifications.

Purpose: This study aims to investigate the anti-AD effects of α-M and elucidate its structure-activity relationship by comparing difference between α-M and several analogues.

Methods: Aβ fibrillogenesis was detected by Thioflavin T fluorometric assay. The levels of Aβ_1-42 and inflammatory cytokines were evaluated by enzyme-linked immunosorbent assay. Neuron viability was examined by the CCK-8 assay. The morphology of ZO-1 of bEnd.3 cultured in BV-2-conditioned medium was evaluated by immunofluorescence staining.

Results: Aβ fibrillogenesis was significantly inhibited by co-incubation with α-M, Zcbd-2 or Zcbd-3. α-M, Zcbd-2, Zcbd-3, and Zcbd-4 decreased the levels of Aβ_1-42 and inflammatory cytokines, and promoted Aβ uptake, degradation and anti-inflammation effects inflammation in microglia. α-M and Zcbd-3 protected neuron viability from Aβ-induced neurotoxicity, and preserved tight junction integrity of bEnd.3 against LPS-induced neuroinflammation.

Conclusion: Zcbd-3 acted as α-M almost in all effects. The structure-activity analysis indicated that the 3-methyl-2-butenyl group at C-8 is essential for the bioactivity of α-M, while modifying the double hydroxylation at the C-2 position may improve the multifunctional anti-AD effects.

Stress-Induced Membraneless Organelles in Eukaryotes and Prokaryotes: Bird’s-Eye View

Stress is an inevitable part of life. An organism is exposed to multiple stresses and overcomes their negative consequences throughout its entire existence. A correlation was established between life expectancy and resistance to stress, suggesting a relationship between aging and the ability to respond to external adverse effects as well as quickly restore the normal regulation of biological processes. To combat stress, cells developed multiple pro-survival mechanisms, one of them is the assembly of special stress-induced membraneless organelles (MLOs). MLOs are formations that do not possess a lipid membrane but rather form as a result of the “liquid–liquid” phase separation (LLPS) of biopolymers. Stress-responsive MLOs were found in eukaryotes and prokaryotes, they form as a reaction to the acute environmental conditions and are dismantled after its termination. These compartments function to prevent damage to the genetic and protein material of the cell during stress. In this review, we discuss the characteristics of stress-induced MLO-like structures in eukaryotic and prokaryotic cells.

Impact of Electronic Polarization on Preformed, β-Strand Rich Homogenous and Heterogeneous Amyloid Oligomers

Amyloids are a subset of intrinsically disordered proteins (IDPs) that self-assemble into cross-[Formula: see text] oligomers and fibrils. The structural plasticity of amyloids leads to sampling of metastable, low-molecular-weight oligomers that contribute to cytotoxicity. Of interest are amyloid-[Formula: see text] (A[Formula: see text] and islet amyloid polypeptide (IAPP), which are involved in the pathology of Alzheimer’s disease and Type 2 diabetes mellitus, respectively. In addition to forming homogenous oligomers and fibrils, these species have been found to cross-aggregate in heterogeneous structures. Biophysical properties, including electronic effects, that are unique or conserved between homogenous and heterogeneous amyloids oligomers are thus far unexplored. Here, we simulated homogenous and heterogeneous amyloid oligomers of A[Formula: see text] and IAPP[Formula: see text] fragments using the Drude oscillator model to investigate the impact of electronic polarization on the structural morphology and stability of preformed hexamers. Upon simulation of preformed, [Formula: see text]-strand rich oligomers with Drude, structural rearrangement occurred causing some loss of [Formula: see text]-strand structure in favor of random coil content for all oligomers. Homogenous A[Formula: see text] was the most stable system, deriving stability from low polarization in hydrophobic residues and through salt bridge formation. Changes in polarization were observed primarily for A[Formula: see text] residues in heterogeneous cross-amyloid systems, displaying a decrease in charged residue dipole moments and an increase in hydrophobic sidechain dipole moments. This work is the first study utilizing the Drude-2019 force field with amyloid oligomers, providing insight into the impact of electronic effects on oligomer structure and highlighting the importance of different microenvironments on amyloid oligomer stability.

Amyloid Prefibrillar Oligomers: The Surprising Commonalities in Their Structure and Activity

It has been proposed that a “common core” of pathologic pathways exists for the large family of amyloid-associated neurodegenerations, including Alzheimer’s, Parkinson’s, type II diabetes and Creutzfeldt–Jacob’s Disease. Aggregates of the involved proteins, independently from their primary sequence, induced neuron membrane permeabilization able to trigger an abnormal Ca²⁺ influx leading to synaptotoxicity, resulting in reduced expression of synaptic proteins and impaired synaptic transmission. Emerging evidence is now focusing on low-molecular-weight prefibrillar oligomers (PFOs), which mimic bacterial pore-forming toxins that form well-ordered oligomeric membrane-spanning pores. At the same time, the neuron membrane composition and its chemical microenvironment seem to play a pivotal role. In fact, the brain of AD patients contains increased fractions of anionic lipids able to favor cationic influx. However, up to now the existence of a specific “common structure” of the toxic aggregate, and a “common mechanism” by which it induces neuronal damage, synaptotoxicity and impaired synaptic transmission, is still an open hypothesis. In this review, we gathered information concerning this hypothesis, focusing on the proteins linked to several amyloid diseases. We noted commonalities in their structure and membrane activity, and their ability to induce Ca²⁺ influx, neurotoxicity, synaptotoxicity and impaired synaptic transmission.

Tyrosine phosphorylation regulates hnRNPA2 granule protein partitioning and reduces neurodegeneration

mRNA transport in neurons requires formation of transport granules containing many protein components, and subsequent alterations in phosphorylation status can release transcripts for translation. Further, mutations in a structurally disordered domain of the transport granule protein hnRNPA2 increase its aggregation and cause hereditary proteinopathy of neurons, myocytes, and bone. We examine in vitro hnRNPA2 granule component phase separation, partitioning specificity, assembly/disassembly, and the link to neurodegeneration. Transport granule components hnRNPF and ch-TOG interact weakly with hnRNPA2 yet partition specifically into liquid phase droplets with the low complexity domain (LC) of hnRNPA2, but not FUS LC. In vitro hnRNPA2 tyrosine phosphorylation reduces hnRNPA2 phase separation, prevents partitioning of hnRNPF and ch-TOG into hnRNPA2 LC droplets, and decreases aggregation of hnRNPA2 disease variants. The expression of chimeric hnRNPA2 D290V in Caenorhabditis elegans results in stress-induced glutamatergic neurodegeneration; this neurodegeneration is rescued by loss of tdp-1, suggesting gain-of-function toxicity. The expression of Fyn, a tyrosine kinase that phosphorylates hnRNPA2, reduces neurodegeneration associated with chimeric hnRNPA2 D290V. These data suggest a model where phosphorylation alters LC interaction specificity, aggregation, and toxicity.

The Other Side of Alzheimer's Disease: Influence of Metabolic Disorder Features for Novel Diagnostic Biomarkers

Nowadays, the amyloid cascade hypothesis is the dominant model to explain Alzheimer's disease (AD) pathogenesis. By this hypothesis, the inherited genetic form of AD is discriminated from the sporadic form of AD (SAD) that accounts for 85-90% of total patients. The cause of SAD is still unclear, but several studies have shed light on the involvement of environmental factors and multiple susceptibility genes, such as Apolipoprotein E and other genetic risk factors, which are key mediators in different metabolic pathways (e.g., glucose metabolism, lipid metabolism, energetic metabolism, and inflammation). Furthermore, growing clinical evidence in AD patients highlighted the presence of affected systemic organs and blood similarly to the brain. Collectively, these findings revise the canonical understating of AD pathogenesis and suggest that AD has metabolic disorder features. This review will focus on AD as a metabolic disorder and highlight the contribution of this novel understanding on the identification of new biomarkers for improving an early AD diagnosis.

Date palm (Phoenix dactylifera L.) fruit's polyphenols as potential inhibitors for human amylin fibril formation and toxicity in type 2 diabetes

BACKGROUND

β-Cell death is the key feature of type 2 diabetes mellitus (T2DM). The misfolding of human Islet Amyloid Polypeptide (hIAPP) is regarded as one of the causative factors of T2DM. Recent studies suggested that a diet based on date fruits presents various health benefits, as these fruits are naturally enriched in plant polyphenols.

METHOD

In this study, we used a broad biophysical approach, using cell biology techniques and bioinformatic tools, to demonstrate that various polyphenols from date palm (Phoenix dactylifera L.) fruit significantly inhibited hIAPP aggregation and cytotoxicity.

RESULT

Our results suggest that all of the polyphenols showed inhibitory effects, albeit varied, on the formation of toxic hIAPP amyloids. Correlation between cell viability assay, permeabilization of synthetic phospholipid vesicles tests, and ANS florescence measurements, revealed that both classes of polyphenols protected INS-1E cells from the toxicity of amylin aggregates. Docking results showed that the used polyphenols physically interacted with both hIAPP amyloidogenic region (residues Ser20-Ser29) and the non-amyloidogenic regions via hydrophobic and hydrogen interactions, thus reducing aggregation levels.

CONCLUSION

These findings highlight the benefits of consuming dates and the great potential of its polyphenols as a potential therapy for the prevention and treatment of T2DM as well as for many other amyloid-related diseases.

Inhibition of human islet amyloid polypeptide aggregation and cellular toxicity by oleuropein and derivatives from olive oil

Loss of β-cell function and β-cell death is the key feature of type 2 diabetes mellitus (T2DM). One hypothesis for the mechanism of this feature is amyloid formation by the human islet amyloid polypeptide (hIAPP). Despite the global prevalence of T2DM, there are no therapeutic strategies for the treatment of or prevention of amylin amyloidosis. Clinical trials and population studies indicate the healthy virtues of the Mediterranean diet, especially the extra virgin olive oil (EVOO) found in this diet. This oil is enriched in phenolic compounds shown to be effective against several aging and lifestyle diseases. Oleuropein (Ole), one of the most abundant polyphenols in EVOO, has been reported to be anti-diabetic. Some of Ole's main derivative have attracted our interest due to their multi-targetted effects, including interference with amyloid aggregation path. However, the structure-function relationship of Ole and its metabolites in T2DM are not yet clear. We report here a broad biophysical approach and cell biology techniques that enabled us to characterize the different molecular mechanisms by which tyrosol (TYR), hydroxytyrosol (HT), oleuropein (Ole) and oleuropein aglycone (OleA) modulate the hIAPP fibrillation in vitro and their effects on cell cytotoxicity. The OleA formed by enolic acid and hydroxytyrosol moiety was found to be more active than the Ole and HT at low micromolar concentrations. We further demonstrated that OleA inhibit the cytotoxicity induced by hIAPP aggregates by protecting more the cell membrane from permeabilization and then from death. These findings highlight the benefits of consuming EVOO and the great potential of its polyphenols, mainly OleA. Moreover, they support the possibility to validate and optimize the possible pharmacological use of EVOO polyphenols for T2DM prevention and therapy and also for many other amyloid related diseases.