The relationship between amyloid structure and cytotoxicity

The prion-like effect and prion-like protein targeting strategy in amyotrophic lateral sclerosis

Pathological proteins in amyotrophic lateral sclerosis (ALS), such as superoxide dismutase 1, TAR DNA-binding protein 43, and fused in sarcoma, exhibit a prion-like pattern. All these proteins have a low-complexity domain and seeding activity in cells. In this review, we summarize the studies on the prion-like effect of these proteins and list six prion-like protein targeting strategies that we believe have potential for ALS therapy, including antisense oligonucleotides, antibody-based technology, peptide, protein chaperone, autophagy enhancement, and heteromultivalent compounds. Considering the pathological complexity and heterogeneity of ALS, we believe that the final solution to ALS therapy is most likely to be an individualized cocktail therapy, including clearance of toxicity, blockage of pathological progress, and protection of neurons.

Modulation of Alzheimer's Disease Aβ40 Fibril Polymorphism by the Small Heat Shock Protein αB-Crystallin

Deposition of amyloid plaques in the brains of Alzheimer's disease (AD) patients is a hallmark of the disease. AD plaques consist primarily of the beta-amyloid (Aβ) peptide but can contain other factors such as lipids, proteoglycans, and chaperones. So far, it is unclear how the cellular environment modulates fibril polymorphism and how differences in fibril structure affect cell viability. The small heat-shock protein (sHSP) alpha-B-Crystallin (αBC) is abundant in brains of AD patients, and colocalizes with Aβ amyloid plaques. Using solid-state NMR spectroscopy, we show that the Aβ40 fibril seed structure is not replicated in the presence of the sHSP. αBC prevents the generation of a compact fibril structure and leads to the formation of a new polymorph with a dynamic N-terminus. We find that the N-terminal fuzzy coat and the stability of the C-terminal residues in the Aβ40 fibril core affect the chemical and thermodynamic stability of the fibrils and influence their seeding capacity. We believe that our results yield a better understanding of how sHSP, such as αBC, that are part of the cellular environment, can affect fibril structures related to cell degeneration in amyloid diseases.

Nanotechnology for microglial targeting and inhibition of neuroinflammation underlying Alzheimer's pathology

BACKGROUND

Alzheimer's disease (AD) is considered to have a multifactorial etiology. The hallmark of AD is progressive neurodegeneration, which is characterized by the deepening loss of memory and a high mortality rate in the elderly. The neurodegeneration in AD is believed to be exacerbated following the intercoupled cascades of extracellular amyloid beta (Aβ) plaques, uncontrolled microglial activation, and neuroinflammation. Current therapies for AD are mostly designed to target the symptoms, with limited ability to address the mechanistic triggers for the disease. In this study, we report a novel nanotechnology based on microglial scavenger receptor (SR)-targeting amphiphilic nanoparticles (NPs) for the convergent alleviation of fibril Aβ (fAβ) burden, microglial modulation, and neuroprotection.

METHODS

We designed a nanotechnology approach to regulate the SR-mediated intracellular fAβ trafficking within microglia. We synthesized SR-targeting sugar-based amphiphilic macromolecules (AM) and used them as a bioactive shell to fabricate serum-stable AM-NPs via flash nanoprecipitation. Using electron microscopy, in vitro approaches, ELISA, and confocal microscopy, we investigated the effect of AM-NPs on Aβ fibrilization, fAβ-mediated microglial inflammation, and neurotoxicity in BV2 microglia and SH-SY5Y neuroblastoma cell lines.

RESULTS

AM-NPs interrupted Aβ fibrilization, attenuated fAβ microglial internalization via targeting the fAβ-specific SRs, arrested the fAβ-mediated microglial activation and pro-inflammatory response, and accelerated lysosomal degradation of intracellular fAβ. Moreover, AM-NPs counteracted the microglial-mediated neurotoxicity after exposure to fAβ.

CONCLUSIONS

The AM-NP nanotechnology presents a multifactorial strategy to target pathological Aβ aggregation and arrest the fAβ-mediated pathological progression in microglia and neurons.

Concentration and time-dependent amyloidogenic characteristics of intrinsically disordered N-terminal region of Saccharomyces cerevisiae Stm1

Saccharomyces cerevisiae Stm1 protein is a ribosomal association factor, which plays an important role in preserving ribosomes in a nutrition-deprived environment. It is also shown to take part in apoptosis-like cell death. Stm1 N-terminal region (Stm1_N1-113) is shown to recognize purine motif DNA triplex and G-quadruplex. Circular dichroism (CD) spectra of Stm1_N1-113 (enriched in positively-charged Lysine and Arginine; negatively-charged Aspartate; polar-uncharged Threonine, Asparagine, Proline and Serine; hydrophobic Alanine, Valine, and Glycine) collected after 0 and 24 h indicate that the protein assumes beta-sheet conformation at the higher concentrations in contrast to intrinsically disordered conformation seen for its monomeric form found in the crystal structure. Thioflavin-T kinetics experiments indicate that the lag phase is influenced by the salt concentration. Atomic force microscopy (AFM) images collected for a variety of Stm1_N1-113 concentrations (in the range of 1-400 μM) in the presence of 150 mM NaCl at 0, 24, and 48 h indicate a threshold concentration requirement to observe the time-dependent amyloid formation. This is prominent seen at the physiological salt concentration of 150 mM NaCl with the fibrillation observed for 400 μM concentration at 48 h, whereas oligomerization or proto-fibrillation is seen for the other concentrations. Such concentration-dependent fibrillation of Stm1_N1-113 explains that amyloid fibrils formed during the overexpression of Stm1_N1-113 may act as a molecular device to trigger apoptosis-like cell death.

Differential effects of DTT on HEWL amyloid fibrillation and fibril morphology at different pH

Proteins can transform from their native state to a state having fibrillar aggregates characterized by cross β sheet structure. The fibrillar aggregates are known as amyloid and have been linked to several disorders. Disulfide bonds in proteins are one of the important factors that determine the propensity of aggregation. Hen Egg White Lysozyme (HEWL) was used by us as a model protein to decipher the role disulfide bonds play in the amyloid fibril formation and fibril morphology by using Dithiothreitol (DTT) as reducing agent at pH 2.7 and pH 7.4. We found that DTT can have different effects on HEWL amyloid depending on pH and the buffer used for preparing the amyloid fibrils. Our studies highlight the critical role of non-native disulfide bonds in amyloidogenesis and how disruption of these bonds can greatly affect the fibrillation process. Overall, these studies throw light on the fibrillation mechanism and can be explored further in designing effective inhibitors against amyloidosis.

Nonspecific Amyloid Aggregation of Chicken Smooth-Muscle Titin: In Vitro Investigations

A giant multidomain protein of striated and smooth vertebrate muscles, titin, consists of tandems of immunoglobulin (Ig)- and fibronectin type III (FnIII)-like domains representing β-sandwiches, as well as of disordered segments. Chicken smooth muscles express several titin isoforms of ~500-1500 kDa. Using various structural-analysis methods, we investigated in vitro nonspecific amyloid aggregation of the high-molecular-weight isoform of chicken smooth-muscle titin (SMT_HMW, ~1500 kDa). As confirmed by X-ray diffraction analysis, under near-physiological conditions, the protein formed amorphous amyloid aggregates with a quaternary cross-β structure within a relatively short time (~60 min). As shown by circular dichroism and Fourier-transform infrared spectroscopy, the quaternary cross-β structure-unlike other amyloidogenic proteins-formed without changes in the SMT_HMW secondary structure. SMT_HMW aggregates partially disaggregated upon increasing the ionic strength above the physiological level. Based on the data obtained, it is not the complete protein but its particular domains/segments that are likely involved in the formation of intermolecular interactions during SMT_HMW amyloid aggregation. The discovered properties of titin position this protein as an object of interest for studying amyloid aggregation in vitro and expanding our views of the fundamentals of amyloidogenesis.

Multi-Level High-Throughput Screening for Discovery of Ligands That Inhibit Insulin Aggregation

We have developed a multi-level virtual screening protocol to identify lead molecules from the FDA inactives database that can inhibit insulin aggregation. The method is based on the presence of structural and interaction specificity in non-native aggregation pathway protein-protein interactions. Some key challenges specific to the present problem, when compared with native protein association, include structural heterogeneity of the protein species involved, multiple association pathways, and relatively higher probability of conformational rearrangement of the association complex. In this multi-step method, the inactives database was first screened using the dominant pharmacophore features of previously identified molecules shown to significantly inhibit insulin aggregation nucleation by binding to its aggregation-prone conformers. We then performed ensemble docking of several low-energy ligand conformations on these aggregation-prone conformers followed by molecular dynamics simulations and binding affinity calculations on a subset of docked complexes to identify a final set of five potential lead molecules to inhibit insulin aggregation nucleation. Their effect on aggregation inhibition was extensively investigated by incubating insulin under aggregation-prone aqueous buffer conditions (low pH, high temperature). Aggregation kinetics were characterized using size exclusion chromatography and Thioflavin T fluorescence assay, and the secondary structure was determined using circular dichroism spectroscopy. Riboflavin provided the best aggregation inhibition, with 85% native monomer retention after 48 h incubation under aggregation-prone conditions, whereas the no-ligand formulation showed complete monomer loss after 36 h. Further, insulin incubated with two of the screened inactives (aspartame, riboflavin) had the characteristic α-helical dip in CD spectra, while the no-ligand formulation showed a change to β-sheet rich conformations.

Toxicity Profiles of Kleeb Bua Daeng Formula, a Traditional Thai Medicine, and Its Protective Effects on Memory Impairment in Animals

Kleeb Bua Daeng (KBD) formula has long been used in Thailand as a traditional herbal medicine for promoting brain health. Our recent reports illustrated that KBD demonstrates multiple modes of action against several targets in the pathological cascade of Alzheimer’s disease (AD). The main purpose of the present study was to determine the protective effect and mechanism of KBD in amyloid beta (Aβ)-induced AD rats and its toxicity profiles. Pretreatment with the KBD formula for 14 days significantly improved the short- and long-term memory performance of Aβ-induced AD rats as assessed by the Morris Water Maze (MWM) and object-recognition tests. KBD treatment increased the activities of the antioxidant enzymes catalase, superoxide dismutase, and glutathione peroxidase; reduced the malondialdehyde content, and; decreased the acetylcholinesterase activity in the rat brain. An acute toxicity test revealed that the maximum dose of 2000 mg/kg did not cause any mortality or symptoms of toxicity. An oral, subchronic toxicity assessment of KBD at doses of 125, 250, and 500 mg/kg body weight/day for 90 days showed no adverse effects on behavior, mortality, hematology, or serum biochemistry. Our investigations indicate that KBD is a nontoxic traditional medicine with good potential for the prevention and treatment of AD.

What makes functional amyloids work?

Although first described in the context of disease, cross-β (amyloid) fibrils have also been found as functional entities in all kingdoms of life. However, what are the specific properties of the cross-β fibril motif that convey biological function, make them especially suited for their particular purpose, and distinguish them from other fibrils found in biology? This review approaches these questions by arguing that cross-β fibrils are highly periodic, stable, and self-templating structures whose formation is accompanied by substantial conformational change that leads to a multimerization of their core and framing sequences. A discussion of each of these properties is followed by selected examples of functional cross-β fibrils that show how function is usually achieved by leveraging many of these properties.

Neurotoxic amyloidogenic peptides in the proteome of SARS-COV2: potential implications for neurological symptoms in COVID-19

COVID-19 is primarily known as a respiratory disease caused by SARS-CoV-2. However, neurological symptoms such as memory loss, sensory confusion, severe headaches, and even stroke are reported in up to 30% of cases and can persist even after the infection is over (long COVID). These neurological symptoms are thought to be produced by the virus infecting the central nervous system, however we don't understand the molecular mechanisms triggering them. The neurological effects of COVID-19 share similarities to neurodegenerative diseases in which the presence of cytotoxic aggregated amyloid protein or peptides is a common feature. Following the hypothesis that some neurological symptoms of COVID-19 may also follow an amyloid etiology we identified two peptides from the SARS-CoV-2 proteome that self-assemble into amyloid assemblies. Furthermore, these amyloids were shown to be highly toxic to neuronal cells. We suggest that cytotoxic aggregates of SARS-CoV-2 proteins may trigger neurological symptoms in COVID-19.

Repurposing of intestinal defensins as multi-target, dual-function amyloid inhibitors via cross-seeding

Amyloid formation and microbial infection are the two common pathological causes of neurogenerative diseases, including Alzheimer's disease (AD), type II diabetes (T2D), and medullary thyroid carcinoma (MTC). While significant efforts have been made to develop different prevention strategies and preclinical hits for these diseases, conventional design strategies of amyloid inhibitors are mostly limited to either a single prevention mechanism (amyloid cascade vs. microbial infection) or a single amyloid protein (Aβ, hIAPP, or hCT), which has prevented the launch of any successful drug on the market. Here, we propose and demonstrate a new “anti-amyloid and anti-bacteria” strategy to repurpose two intestinal defensins, human α-defensin 6 (HD-6) and human β-defensin 1 (HBD-1), as multiple-target, dual-function, amyloid inhibitors. Both HD-6 and HBD-1 can cross-seed with three amyloid peptides, Aβ (associated with AD), hIAPP (associated with T2D), and hCT (associated with MTC), to prevent their aggregation towards amyloid fibrils from monomers and oligomers, rescue SH-SY5Y and RIN-m5F cells from amyloid-induced cytotoxicity, and retain their original antimicrobial activity against four common bacterial strains at sub-stoichiometric concentrations. Such sequence-independent anti-amyloid and anti-bacterial functions of intestinal defensins mainly stem from their cross-interactions with amyloid proteins through amyloid-like mimicry of β-sheet associations. In a broader view, this work provides a new out-of-the-box thinking to search and repurpose a huge source of antimicrobial peptides as amyloid inhibitors, allowing the blocking of the two interlinked pathological pathways and bidirectional communication between the central nervous system and intestines via the gut–brain axis associated with neurodegenerative diseases.

Amyloid formation and microbial infection are the two common pathological causes of neurogenerative diseases. Here, we proposed a new “anti-amyloid and anti-bacteria” strategy to repurpose two intestinal defensins as multiple-target, dual-function amyloid inhibitors.

Multiscale Model for Quantitative Prediction of Insulin Aggregation Nucleation Kinetics

We combined kinetic, thermodynamic, and structural information from single-molecule (protein folding) and two-molecule (association) explicit-solvent simulations for determination of kinetic parameters in protein aggregation nucleation with insulin as the model protein. A structural bioinformatics approach was developed to account for heterogeneity of aggregation-prone species, with the transition complex theory found applicable in modeling association kinetics involving non-native species. Specifically, the kinetic pathway for formation of aggregation-prone oligomeric species was found to contain a structurally specific dominant binding mode, making the kinetic process similar to native protein association. The kinetic parameters thus obtained were used in a population balance model, and accurate predictions for aggregation nucleation time varying over 2 orders of magnitude with changes in either insulin concentration or an aggregation-inhibitor ligand concentration were obtained, while an empirical parameter set was not found to be transferable for prediction of ligand effects. Further, this physically determined kinetic parameter set provided several mechanistic insights, such as identification of the rate-limiting step in aggregation nucleation and a quantitative explanation for the switch from Arrhenius to non-Arrhenius aggregation kinetics around the melting temperature of insulin.

Heterologous expression of cyanobacterial gas vesicle proteins in Saccharomyces cerevisiae

Given the potential applications of gas vesicles (GVs) in multiple fields including antigen-displaying and imaging, heterologous reconstitution of synthetic GVs is an attractive and interesting study that has translational potential. Here, we attempted to express and assemble GV proteins (GVPs) into GVs using the model eukaryotic organism Saccharomyces cerevisiae. We first selected and expressed two core structural proteins, GvpA and GvpC from cyanobacteria Anabaena flos-aquae and Planktothrix rubescens, respectively. We then optimized the protein production conditions and validated GV assembly in the context of GV shapes. We found that when two copies of anaA were integrated into the genome, the chromosomal expression of AnaA resulted in GV production regardless of GvpC expression. Next, we co-expressed chaperone-RFP with the GFP-AnaA to aid the AnaA aggregation. The co-expression of individual chaperones (Hsp42, Sis1, Hsp104, and GvpN) with AnaA led to the formation of larger inclusions and enhanced the sequestration of AnaA into the perivacuolar site. To our knowledge, this represents the first study on reconstitution of GVs in S. cerevisiae. Our results could provide insights into optimizing conditions for heterologous protein production as well as the reconstitution of other synthetic microcompartments in yeast.

Aggregation Condition-Structure Relationship of Mouse Prion Protein Fibrils

Prion diseases are associated with conformational conversion of cellular prion protein into a misfolded pathogenic form, which resembles many properties of amyloid fibrils. The same prion protein sequence can misfold into different conformations, which are responsible for variations in prion disease phenotypes (prion strains). In this work, we use atomic force microscopy, FTIR spectroscopy and magic-angle spinning NMR to devise structural models of mouse prion protein fibrils prepared in three different denaturing conditions. We find that the fibril core region as well as the structure of its N- and C-terminal parts is almost identical between the three fibrils. In contrast, the central part differs in length of β-strands and the arrangement of charged residues. We propose that the denaturant ionic strength plays a major role in determining the structure of fibrils obtained in a particular condition by stabilizing fibril core interior-facing glutamic acid residues.

Structural effects driven by rare point mutations in amylin hormone, the type II diabetes-associated peptide

BACKGROUND

Amylin is a 37-amino-acid peptide hormone co-secreted with insulin, which participates in glucose homeostasis. This hormone is able to aggregate in a β-sheet conformation and deposit in islet amyloids, a hallmark in type II diabetes. Since amylin is a gene-encoded hormone, this peptide has variants caused by point mutations that can impact its functions.

METHODS

Here, we analyzed the structural effects caused by S20G and G33R point mutations which, according to the 1000 Genomes Project, have frequency in East Asian and European populations, respectively. The analyses were performed by means of aggrescan server, SNP functional effect predictors, and molecular dynamics.

RESULTS

We found that both mutations have aggregation potential and cause changes in the monomeric forms when compared with wild-type amylin. Furthermore, comparative analyses with pramlintide, an amylin drug analogue, allowed us to infer that second α-helix maintenance may be related to the aggregation potential.

CONCLUSIONS

The S20G mutation has been described as pathologically related, which is in agreement with our findings. In addition, our data suggest that the G33R mutation might have a deleterious effect. The data presented here also provide new therapy opportunities, whether for creating more effective drugs for diabetes or implementing specific treatment for patients with these mutations.

GENERAL SIGNIFICANCE

Our data could help to better understand the impact of mutations on the wild-type amylin sequence, as a starting point for the evaluation and characterization of other variations. Moreover, these findings could improve the health of patients with type II diabetes.

Amyloid Aggregates of Smooth-Muscle Titin Impair Cell Adhesion

Various amyloid aggregates, in particular, aggregates of amyloid β-proteins, demonstrate in vitro and in vivo cytotoxic effects associated with impairment of cell adhesion. We investigated the effect of amyloid aggregates of smooth-muscle titin on smooth-muscle-cell cultures. The aggregates were shown to impair cell adhesion, which was accompanied by disorganization of the actin cytoskeleton, formation of filopodia, lamellipodia, and stress fibers. Cells died after a 72-h contact with the amyloid aggregates. To understand the causes of impairment, we studied the effect of the microtopology of a titin-amyloid-aggregate-coated surface on fibroblast adhesion by atomic force microscopy. The calculated surface roughness values varied from 2.7 to 4.9 nm, which can be a cause of highly antiadhesive properties of this surface. As all amyloids have the similar structure and properties, it is quite likely that the antiadhesive effect is also intrinsic to amyloid aggregates of other proteins. These results are important for understanding the mechanisms of the negative effect of amyloids on cell adhesion.

Low frequency vortex magnetic field reduces amyloid β aggregation, increase cell viability and protect from amyloid β toxicity

Plaques formed by abnormal accumulation of amyloid β-peptide (Aβ) lead to onset of Alzheimer's disease (AD). Pharmacological treatments do not reduce Aβ aggregation neither restore learning and memory. Noninvasive techniques have emerged as an alternative to treat AD, such as stimulation with electromagnetic fields (EMF) that decrease Aβ deposition and reverses cognitive impairment in AD mice, even though some studies showed side effects on parallel magnetic fields stimulation. As a new approach of magnetic field (MF) stimulation, vortex magnetic fields (VMF) have been tested inducing a random movement of charged biomolecules in cells, promoting cell viability and apparently safer than parallel magnetic fields. In this study we demonstrate the effect of VMF on Aβ aggregation. The experimental strategy includes, i) design and construction of a coil capable to induce VMF, ii) evaluation of VMF stimulation on Aβ peptide induced-fibrils-formation, iii) evaluation of VMF stimulation on SH-SY5Y neuroblastoma cell line in the presence of Aβ peptide. We demonstrated for the first time that Aβ aggregation exposed to VMF during 24 h decreased ~ 86% of Aβ fibril formation compared to control. Likewise, VMF stimulation reduced Aβ fibrils-cytotoxicity and increase SH-SY5Y cell viability. These data establish the basis for future investigation that involve VMF as inhibitor of Aβ-pathology and indicate the therapeutic potential of VMF for AD treatment.

Application of QCM in Peptide and Protein-Based Drug Product Development

AT-cut quartz crystals vibrating in the thickness-shear mode (TSM), especially quartz crystal resonators (QCRs), are well known as very efficient mass sensitive systems because of their sensitivity, accuracy, and biofunctionalization capacity. They are highly reliable in the measurement of the mass of deposited samples, in both gas and liquid matrices. Moreover, they offer real-time monitoring, as well as relatively low production and operation costs. These features make mass sensitive systems applicable in a wide range of different applications, including studies on protein and peptide primary packaging, formulation, and drug product manufacturing process development. This review summarizes the information on some particular implementations of quartz crystal microbalance (QCM) instruments in protein and peptide drug product development as well as their future prospects.

Identification and characterization of cytotoxic amyloid-like regions in human Pbx-regulating protein-1

The ability of many proteins to fold into well-defined structures has been traditionally considered a prerequisite for fulfilling their functions. Protein folding is also regarded as a valuable loophole to escape uncontrolled and harmful aggregations. Here we show that the PBX-regulating protein-1 (PREP1), an important homeodomain transcription factor involved in cell growth and differentiation during embryogenesis, is endowed with an uncommon thermostability. Indeed, circular dichroism analyses indicate that it retains most of its secondary structure at very high temperatures. These findings have important implications for PREP1 functions since it is a stabilizing factor of its partner PBX1. Predictive analyses suggest that the observed PREP1 thermostability could be related to the presence of aggregation-prone regions. Interestingly, synthetic peptides corresponding to these regions exhibit a remarkable propensity to form toxic β-rich amyloid-like aggregates in physiological conditions. On this basis, we suggest that PREP1 stability is an effective way to prevent or limit the formation of harmful aggregates. Notably, one of these PREP1 fragments (residues 117-132) is able to reversibly switch from α-helical to β-rich states depending on the environmental conditions. The chameleon conformational behavior of this peptide makes it an ideal system to study this intriguing and widespread structural transition.

Understanding the self-assembly pathways of a single chain variant of monellin: A first step towards the design of sweet nanomaterials

Peptides and proteins possess an inherent tendency to self-assemble, prompting the formation of amyloid aggregates from their soluble and functional states. Amyloids are linked to many devastating diseases, but self-assembling proteins can also represent formidable tools to produce new and sustainable biomaterials for biomedical and biotechnological applications. The mechanism of fibrillar aggregation, which influences the morphology and the properties of the protein aggregates, depend on factors such as pH, ionic strength, temperature, agitation, and protein concentration. We have here used intensive mechanical agitation, with or without beads, to prompt the aggregation of the single-chain derivative of the plant protein monellin, named MNEI, which is a well characterized sweet protein. Transmission electron microscopy confirmed the formation of fibrils several micrometers long, morphologically different from the previously characterized fibers of MNEI. Changes in the protein secondary structures during the aggregation process were monitored by Fourier transform infrared spectroscopy, which detected differences in the conformation of the final aggregates obtained under mechanical agitation. Moreover, soluble oligomers could be detected in the early phases of aggregation by polyacrylamide gel-electrophoresis. These findings emphasize the existence of multiple pathways of fibrillar aggregation for MNEI, which could be exploited for the design of innovative protein-based biomaterials.

The Structural Basis of Amyloid Strains in Alzheimer's Disease

Amyloid fibrils represent one of the defining features of Alzheimer's disease (AD). They are made up of protofilaments composed of amyloid β (Aβ) peptides that are held together with extraordinary stability by a network of tight steric zippers and axial hydrogen bonds. This review explores the hypothesis that the peptide conformation within a protofilament represents the physical embodiment of a "strain" of AD. Evidence suggests that within a single strain the fold of individual peptides is invariant. However, the fibrils are capable of structural polymorphism that includes variation in the arrangement of protofilaments into fibrils, the pitch of the resultant fibrils, and the higher-order organization of the plaques into which they aggregate. These intrastrain polymorphisms are separated by low energy barriers, allowing multiple configurations to coexist within a single preparation or tissue. Clinical presentation of different strains may be determined by variation in the way different protofilament structures generate the relevant toxic species, be they monomers, oligomers, or higher-order structures. Evidence reviewed here is consistent with a model in which disease progression is concomitant with a gradual, progressive annealing of amyloid fibrils from benign, loosely packed structures into dense neurotoxic aggregates. This model challenges the commonly held hypothesis that oligomers of Aβ peptides are the only active proximate species in neurodegeneration. However, the data do not implicate fibrils themselves. Rather, they cast suspicion on larger-scale supramolecular aggregates as toxic agents. Electron tomography of amyloid plaques in situ strongly suggests that the formation of amyloid aggregates results in perturbation of the cellular membrane integrity, warranting further investigation of this as a potential mode of neurotoxicity. If dense supramolecular amyloid aggregates prove to be important agents of neurodegeneration in AD, this model may also have relevance to other forms of amyloidoses.

Estimation of amyloid aggregate sizes with semi-denaturing detergent agarose gel electrophoresis and its limitations

Semi-denaturing detergent agarose gel electrophoresis (SDD-AGE) was proposed by Vitaly V. Kushnirov in the Michael D. Ter-Avanesyan’s laboratory as a method to compare sizes of amyloid aggregates. Currently, this method is widely used for amyloid investigation, but mostly as a qualitative approach. In this work, we assessed the possibilities and limitations of the quantitative analysis of amyloid aggregate size distribution using SDD-AGE results. For this purpose, we used aggregates of two well-characterized yeast amyloid-forming proteins, Sup35 and Rnq1, and developed a protocol to standardize image analysis and process the result. A detailed investigation of factors that may affect the results of SDD-AGE revealed that both the cell lysis method and electrophoresis conditions can substantially affect the estimation of aggregate size. Despite this, quantitative analysis of SDD-AGE results is possible when one needs to estimate and compare the size of aggregates on the same gel, or even in different experiments, if the experimental conditions are tightly controlled and additional standards are used.

Interactions between Soluble Species of β-Amyloid and α-Synuclein Promote Oligomerization while Inhibiting Fibrillization

Aggregations of β-amyloid (Aβ) and α-synuclein (αS) into oligomeric and fibrillar assemblies are the pathological hallmarks of Alzheimer's and Parkinson's diseases, respectively. Although Aβ and αS affect different regions of the brain and are separated at the cellular level, there is evidence of their eventual interaction in the pathology of both disorders. Characterization of interactions of Aβ and αS at various stages of their aggregation pathways could reveal mechanisms and therapeutic targets for the prevention and cure of these neurodegenerative diseases. In this study, we comprehensively examined the interactions and their molecular manifestations using an array of characterization tools. We show for the first time that αS monomers and oligomers, but not αS fibrils, inhibit Aβ fibrillization while promoting oligomerization of Aβ monomers and stabilizing preformed Aβ oligomers via coassembly, as judged by Thioflavin T fluorescence, transmission electron microscopy, and SDS- and native-PAGE with fluorescently labeled peptides/proteins. In contrast, soluble Aβ species, such as monomers and oligomers, aggregate into fibrils, when incubated alone under the otherwise same condition. Our study provides evidence that the interactions with αS soluble species, responsible for the effects, are mediated primarily by the C-terminus of Aβ, when judged by competitive immunoassays using antibodies recognizing various fragments of Aβ. We also show that the C-terminus of Aβ is a primary site for its interaction with αS fibrils. Collectively, these data demonstrate aggregation state-specific interactions between αS and Aβ and offer insight into a molecular basis of synergistic biological effects between the two polypeptides.

Amyloidophilic Molecule Interactions on the Surface of Insulin Fibrils: Cooperative Binding and Fluorescence Quenching

Protein aggregation into insoluble fibrillar aggregates is linked to several neurodegenerative disorders, such as Alzheimer’s or Parkinson’s disease. Commonly used methods to study aggregation inhibition or fibril destabilization by potential drugs include spectroscopic measurements of amyloidophilic dye molecule fluorescence or absorbance changes. In this work we show the cross-interactions of five different dye molecules on the surface of insulin amyloid fibrils, resulting in cooperative binding and fluorescence quenching.

Protein misfolding, aggregation and mechanism of amyloid cytotoxicity: An overview and therapeutic strategies to inhibit aggregation

Protein and peptides are converted from their soluble forms into highly ordered fibrillar aggregates under various conditions inside the cell. Such transitions confer diverse neurodegenerative diseases including Alzheimer's disease, Huntington's disease Prion's disease, Parkinson's disease, polyQ and share abnormal folding of potentially cytotoxic protein species linked with degeneration and death of precise neuronal populations. Presently, major advances are made to understand and get detailed insight into the structural basis and mechanism of amyloid formation, cytotoxicity and therapeutic approaches to combat them. Here we highlight classifies and summarizes the detailed overview of protein misfolding and aggregation at their molecular level including the factors that promote protein aggregation under in vivo and in vitro conditions. In addition, we describe the recent technologies that aid the characterization of amyloid aggregates along with several models that might be responsible for amyloid induced cytotoxicity to cells. Overview on the inhibition of amyloidosis by targeting different small molecules (both natural and synthetic origin) have been also discussed, that provides important approaches to identify novel targets and develop specific therapeutic strategies to combat protein aggregation related neurodegenerative diseases.

Regulation of the Drosophila Imd pathway by signaling amyloids

Fruit flies elicit effective defense responses against numerous microbes. The responses against Gram-negative bacteria are mediated by the Imd pathway, an evolutionarily conserved NF-κB pathway recognizing meso-diaminopimelic acid (DAP)-type peptidoglycan from bacterial cell walls. Several reviews already provide a detailed view of ligand recognition and signal transduction during Imd signaling, but the formation and regulation of the signaling complex immediately downstream of the peptidoglycan-sensing receptors is still elusive. In this review, we focus on the formation of the Imd amyloidal signaling center and post-translational modifications in the assembly and disassembly of the Imd signaling complex.

Human DnaJB6 Antiamyloid Chaperone Protects Yeast from Polyglutamine Toxicity Separately from Spatial Segregation of Aggregates

Polyglutamine (polyQ) aggregates are associated with pathology in protein-folding diseases and with toxicity in the yeast Saccharomyces cerevisiae Protection from polyQ toxicity in yeast by human DnaJB6 coincides with sequestration of aggregates. Gathering of misfolded proteins into deposition sites by protein quality control (PQC) factors has led to the view that PQC processes protect cells by spatially segregating toxic aggregates. Whether DnaJB6 depends on this machinery to sequester polyQ aggregates, if this sequestration is needed for DnaJB6 to protect cells, and the identity of the deposition site are unknown. Here, we found DnaJB6-driven deposits share characteristics with perivacuolar insoluble protein deposition sites (IPODs). Binding of DnaJB6 to aggregates was necessary, but not enough, for detoxification. Focal formation required a DnaJB6-Hsp70 interaction and actin, polyQ could be detoxified without sequestration, and segregation of aggregates alone was not protective. Our findings suggest DnaJB6 binds to smaller polyQ aggregates to block their toxicity. Assembly and segregation of detoxified aggregates are driven by an Hsp70- and actin-dependent process. Our findings show sequestration of aggregates is not the primary mechanism by which DnaJB6 suppresses toxicity and raise questions regarding how and when misfolded proteins are detoxified during spatial segregation.

Fibronectin amyloid-like aggregation alters its extracellular matrix incorporation and promotes a single and sparsed cell migration

Fibronectin (Fn) is an extracellular matrix (ECM) multifunctional glycoprotein essential for regulating cells behaviors. Within ECM, Fn is found as polymerized fibrils. Apart from fibrils, Fn could also form other kind of supramolecular assemblies such as aggregates. To gain insight into the impact of Fn aggregates on cell behavior, we generated several Fn oligomeric assemblies. These assemblies displayed various amyloid-like properties but were not cytotoxic. In presence of the more amyloid-like structured assemblies of Fn, the cell-ECM networks were altered and the cell shapes shifted toward extended mesenchymal morphologies. Additionnaly, the Fn amyloid-like aggregates promoted a single-cell and sparsed migration of SKOV3 cancer cells, which was associated with a relocalization of αv integrins from plasma membrane to perinuclear vesicles. These data pointed out that the features of supramolecular Fn assemblies could represent a higher level of fine-tuning cell phenotype, and especially migration of cancer cells.

Multicomponent peptide assemblies

Self-assembled peptide nanostructures have been increasingly exploited as functional materials for applications in biomedicine and energy. The emergent properties of these nanomaterials determine the applications for which they can be exploited. It has recently been appreciated that nanomaterials composed of multicomponent coassembled peptides often display unique emergent properties that have the potential to dramatically expand the functional utility of peptide-based materials. This review presents recent efforts in the development of multicomponent peptide assemblies. The discussion includes multicomponent assemblies derived from short low molecular weight peptides, peptide amphiphiles, coiled coil peptides, collagen, and β-sheet peptides. The design, structure, emergent properties, and applications for these multicomponent assemblies are presented in order to illustrate the potential of these formulations as sophisticated next-generation bio-inspired materials.

Protein aggregates and proteostasis in aging: Amylin and β-cell function

The ubiquitin-proteasomal-system (UPS) and the autophagy-lysosomal-system (ALS) are both highly susceptible for disturbances leading to the accumulation of cellular damage. A decline of protein degradation during aging results in the formation of oxidatively damaged and aggregated proteins finally resulting in failure of cellular functionality. Besides protein aggregation in response to oxidative damage, amyloids are a different type of protein aggregates able to distract proteostasis and interfere with cellular functionality. Amyloids are clearly linked to the pathogenesis of age-related degenerative diseases such as Alzheimer's disease. Human amylin is one of the peptides forming fibrils in β-sheet conformation finally leading to amyloid formation. In contrast to rodent amylin, human amylin is prone to form amyloidogenic aggregates, proposed to play a role in the pathogenesis of Type 2 Diabetes by impairing β-cell functionality. Since aggregates such as lipofuscin and β-amyloid are known to impair proteostasis, it is likely to assume similar effects for human amylin. In this review, we focus on the effects of IAPP on UPS and ALS and their role in amylin degradation, since both systems play a crucial role in maintaining proteome balance thereby influencing, at least in part, cellular fate and aging.

The long-lived Octodon degus as a rodent drug discovery model for Alzheimer's and other age-related diseases

Alzheimer's disease (AD) is a multifactorial progressive neurodegenerative disease. Despite decades of research, no disease modifying therapy is available and a change of research objectives and/or development of novel research tools may be required. Much AD research has been based on experimental models using animals with a short lifespan that have been extensively genetically manipulated and do not represent the full spectrum of late-onset AD, which make up the majority of cases. The aetiology of AD is heterogeneous and involves multiple factors associated with the late-onset of the disease like disturbances in brain insulin, oxidative stress, neuroinflammation, metabolic syndrome, retinal degeneration and sleep disturbances which are all progressive abnormalities that could account for many molecular, biochemical and histopathological lesions found in brain from patients dying from AD. This review is based on the long-lived rodent Octodon degus (degu) which is a small diurnal rodent native to South America that can spontaneously develop cognitive decline with concomitant phospho-tau, β-amyloid pathology and neuroinflammation in brain. In addition, the degu can also develop several other conditions like type 2 diabetes, macular and retinal degeneration and atherosclerosis, conditions that are often associated with aging and are often comorbid with AD. Long-lived animals like the degu may provide a more realistic model to study late onset AD.

Novel cell-penetrating-amyloid peptide conjugates preferentially kill cancer cells

The goal of this study was to develop a peptide which could use the toxic effects of amyloid, a substance which is the hallmark of over 25 known human diseases, to selectively kill cancer cells. Here we demonstrate that two separate amyloid-forming hexapeptides, one from the microtubule associated protein Tau involved in formation of paired helical filaments of Alzheimer's disease, and the other an amyloid forming sequence from apolipoprotein A1, when conjugated to a cell penetrating peptide (CPP) sequence, form toxic oligomers which are stable for up to 14 h and able to enter cells by a combination of endocytosis and transduction. The amyloid peptide conjugates showed selective cytotoxicity to breast cancer, neuroblastoma and cervical cancer cells in culture compared to normal cells. Fluorescence imaging experiments showed the CPP-amyloid peptide oligomers formed intracellular fibrous amyloid, visible in the endosomes/lysosomes, cytosol and nucleus with thioflavin S (ThS) staining. Further experiments with rhodamine-conjugated Dextran, propidium iodide (PI), and acridine orange (AO) suggested the mechanism of cell death was the permeability of the lysosomal membrane brought about by the formation of amyloid pores. Cytotoxicity could be abrogated by inhibitors of lysosomal hydrolases, consistent with a model where lysosomal hydrolases leak into the cytosol and induce cytotoxicity in subsequent downstream steps. Taken together, our data suggest that CPP-amyloid peptide conjugates show potential as a new class of anti-cancer peptides (ACPs).

Insights into protein misfolding and aggregation enabled by solid-state NMR spectroscopy

The aggregation of proteins and peptides into a variety of insoluble, and often non-native, aggregated states plays a central role in many devastating diseases. Analogous processes undermine the efficacy of polypeptide-based biological pharmaceuticals, but are also being leveraged in the design of biologically inspired self-assembling materials. This Trends article surveys the essential contributions made by recent solid-state NMR (ssNMR) studies to our understanding of the structural features of polypeptide aggregates, and how such findings are informing our thinking about the molecular mechanisms of misfolding and aggregation. A central focus is on disease-related amyloid fibrils and oligomers involved in neurodegenerative diseases such as Alzheimer's, Parkinson's and Huntington's disease. SSNMR-enabled structural and dynamics-based findings are surveyed, along with a number of resulting emerging themes that appear common to different amyloidogenic proteins, such as their compact alternating short-β-strand/β-arc amyloid core architecture. Concepts, methods, future prospects and challenges are discussed.

In situ fibrillizing amyloid-beta 1-42 induces neurite degeneration and apoptosis of differentiated SH-SY5Y cells

The progression of Alzheimer’s disease is causatively linked to the accumulation of amyloid-β aggregates in the brain, however, it is not clear how the amyloid aggregates initiate the death of neuronal cells. The in vitro toxic effects of amyloid peptides are most commonly examined using the human neuroblastoma derived SH-SY5Y cell line and here we show that differentiated neuron-like SH-SY5Y cells are more sensitive to amyloid peptides than non-differentiated cells, because the latter lack long neurites. Exogenous soluble amyloid-β 1–42 covered cell bodies and whole neurites in differentiated cells with dense fibrils, causing neurite beading and fragmentation, whereas preformed amyloid-β 1–42 fibrils had no toxic effects. Importantly, spontaneously fibrillizing amyloid-β 1–42 peptide exhibited substantially higher cellular toxicity than amyloid-β 1–40, which did not form fibrils under the experimental conditions. These results support the hypothesis that peptide toxicity is related to the active fibrillization process in the incubation mixture.

Modulation of the extent of structural heterogeneity in α-synuclein fibrils by the small molecule thioflavin T

The transition of intrinsically disordered, monomeric α-synuclein into β-sheet-rich oligomers and fibrils is associated with multiple neurodegenerative diseases. Fibrillar aggregates possessing distinct structures that differ in toxicity have been observed in different pathological phenotypes. Understanding the mechanism of the formation of various fibril polymorphs with differing cytotoxic effects is essential for determining how the aggregation reaction could be modulated to favor nontoxic fibrils over toxic fibrils. In this study, two morphologically different α-synuclein fibrils, one helical and the other ribbon-like, are shown to form together. Surprisingly, a widely used small molecule for probing aggregation reactions, thioflavin T (ThT), was found to tune the structural heterogeneity found in the fibrils. The ribbon-like fibrils formed in the presence of ThT were found to have a longer structural core than the helical fibrils formed in the absence of ThT. The ribbon-like fibrils are also more toxic to cells. By facilitating the formation of ribbon-like fibrils over helical fibrils, ThT reduced the extent of fibril polymorphism. This study highlights the role of a small molecule such as ThT in selectively favoring the formation of a specific type of fibril by binding to aggregates formed early on one of multiple pathways, thereby altering the structural core and external morphology of the fibrils formed.

Small molecule-mediated inhibition of β-2-microglobulin-based amyloid fibril formation

In dialysis patients, β-2 microglobulin (β2m) can aggregate and eventually form amyloid fibrils in a condition known as dialysis-related amyloidosis, which deleteriously affects joint and bone function. Recently, several small molecules have been identified as potential inhibitors of β2m amyloid formation in vitro Here we investigated whether these molecules are more broadly applicable inhibitors of β2m amyloid formation by studying their effect on Cu(II)-induced β2m amyloid formation. Using a variety of biophysical techniques, we also examined their inhibitory mechanisms. We found that two molecules, doxycycline and rifamycin SV, can inhibit β2m amyloid formation in vitro by causing the formation of amorphous, redissolvable aggregates. Rather than interfering with β2m amyloid formation at the monomer stage, we found that doxycycline and rifamycin SV exert their effect by binding to oligomeric species both in solution and in gas phase. Their binding results in a diversion of the expected Cu(II)-induced progression of oligomers toward a heterogeneous collection of oligomers, including trimers and pentamers, that ultimately matures into amorphous aggregates. Using ion mobility mass spectrometry, we show that both inhibitors promote the compaction of the initially formed β2m dimer, which causes the formation of other off-pathway and amyloid-incompetent oligomers that are isomeric with amyloid-competent oligomers in some cases. Overall, our results suggest that doxycycline and rifamycin are general inhibitors of Cu(II)-induced β2m amyloid formation. Interestingly, the putative mechanism of their activity is different depending on how amyloid formation is initiated with β2m, which underscores the complexity of how these structures assemble in vitro.

Kinetics and polymorphs of yeast prion Sup35NM amyloidogenesis

Amyloidogenic proteins often form many types of aggregates, which are a critical determinant of cytotoxicity and tissue specificity. However, the molecular mechanisms underlying the generation of distinct amyloids and their influence on cells remain largely unknown. We herein investigated the polymorphic amyloid formation of the yeast prion protein, Sup35NM, an intrinsically disordered N-terminal fragment of Sup35, under various conditions and its potential relationship to cytotoxicity. Sup35NM aggregated to amyloid fibrils with distinct kinetics, structures, morphologies, tinctorial properties, and conformational stabilities depending on the concentration of NaCl, pH, and temperature, indicating the polymorphic amyloidogenesis of Sup35NM. Detailed kinetic analyses of Sup35NM amyloid formation revealed a strong inverse correlation between the lag time and elongation rate without a correlation between kinetic and structural parameters. These results suggest that kinetic polymorphisms due to distinct nucleation and elongation rates result in structural polymorphs of amyloid fibrils, and also that conditions that enhance or inhibit the nucleation of Sup35NM promote or delay fibril growth. The deleterious effects of polymorphic Sup35NM amyloid fibrils on membrane integrity and cell vitality were minimal. We hypothesize that the innocuous polymorphic nature of Sup35NM amyloid fibrils may be beneficial for gaining time for prion infection prior to cell death.

Pre-plaque conformational changes in Alzheimer's disease-linked Aβ and APP

Reducing levels of the aggregation-prone Aβ peptide that accumulates in the brain with Alzheimer's disease (AD) has been a major target of experimental therapies. An alternative approach may be to stabilize the physiological conformation of Aβ. To date, the physiological state of Aβ in brain remains unclear, since the available methods used to process brain tissue for determination of Aβ aggregate conformation can in themselves alter the structure and/or composition of the aggregates. Here, using synchrotron-based Fourier transform infrared micro-spectroscopy, non-denaturing gel electrophoresis and conformational specific antibodies we show that the physiological conformations of Aβ and amyloid precursor protein (APP) in brain of transgenic mouse models of AD are altered before formation of amyloid plaques. Furthermore, focal Aβ aggregates in brain that precede amyloid plaque formation localize to synaptic terminals. These changes in the states of Aβ and APP that occur prior to plaque formation may provide novel targets for AD therapy.

Development of a novel catalytic amyloid displaying a metal-dependent ATPase-like activity

Amyloids are protein aggregates of highly regular structure that are involved in diverse pathologies such as Alzheimer's and Parkinson's disease. Recent evidence has shown that under certain conditions, small peptides can self-assemble into amyloids that exhibit catalytic reactivity towards certain compounds. Here we report a novel peptide with a sequence derived from the active site of RNA polymerase that displays hydrolytic activity towards ATP. The catalytic reaction proceeds in the presence of the divalent metal manganese and the products are ADP and AMP. The kinetic data shows a substrate-dependent saturation of the activity with a maximum rate achieved at around 1 mM ATP. At higher ATP concentrations, we also observed substrate inhibition of the activity. The self-assembly of the peptide into amyloids is strictly metal-dependent and required for the catalysis. Our results show that aspartate-containing amyloids can also be catalysts under conditions that include interactions with metals. Moreover, we show for the first time an amyloid that exerts reactivity towards a biologically essential molecule.

The road to the synthesis of "difficult peptides"

The last decade has witnessed a renaissance of peptides as drugs. This progress, together with advances in the structural behavior of peptides, has attracted the interest of the pharmaceutical industry in these molecules as potential APIs. In the past, major peptide-based drugs were inspired by sequences extracted from natural structures of low molecular weight. In contrast, nowadays, the peptides being studied by academic and industrial groups comprise more sophisticated sequences. For instance, they consist of long amino acid chains and show a high tendency to form aggregates. Some researchers have claimed that preparing medium-sized proteins is now feasible with chemical ligation techniques, in contrast to medium-sized peptide syntheses. The complexity associated with the synthesis of certain peptides is exemplified by the so-called "difficult peptides", a concept introduced in the 80's. This refers to sequences that show inter- or intra-molecular β-sheet interactions significant enough to form aggregates during peptide synthesis. These structural associations are stabilized and mediated by non-covalent hydrogen bonds that arise on the backbone of the peptide and-depending on the sequence-are favored. The tendency of peptide chains to aggregate is translated into a list of common behavioral features attributed to "difficult peptides" which hinder their synthesis. In this regard, this manuscript summarizes the strategies used to overcome the inherent difficulties associated with the synthesis of known "difficult peptides". Here we evaluate several external factors, as well as methods to incorporate chemical modifications into sequences, in order to describe the strategies that are effective for the synthesis of "difficult peptides". These approaches have been classified and ordered to provide an extensive guide for achieving the synthesis of peptides with the aforementioned features.

CRMPs: critical molecules for neurite morphogenesis and neuropsychiatric diseases

Neuronal polarity and spatial rearrangement of neuronal processes are central to the development of all mature nervous systems. Recent studies have highlighted the dynamic expression of Collapsin-Response-Mediator Proteins (CRMPs) in neuronal dendritic/axonal compartments, described their interaction with cytoskeleton proteins, identified their ability to activate L- and N-type voltage-gated calcium channels (VGCCs) and delineated their crucial role as signaling molecules essential for neuron differentiation and neural network development and maintenance. In addition, evidence obtained from genome-wide/genetic linkage/proteomic/translational approaches revealed that CRMP expression is altered in human pathologies including mental (schizophrenia and mood disorders) and neurological (Alzheimer's, prion encephalopathy, epilepsy and others) disorders. Changes in CRMPs levels have been observed after psychotropic treatments, and disrupting CRMP2 binding to calcium channels blocked neuropathic pain. These observations, altogether with those obtained from genetically modified mice targeting individual CRMPs and RNA interference approaches, pave the way for considering CRMPs as potential early disease markers and modulation of their activity as therapeutic strategy for disorders associated with neurite abnormalities.

Proteotoxicity and cardiac dysfunction

Baseline physiological function of the mammalian heart is under the constant threat of environmental or intrinsic pathological insults. Cardiomyocyte proteins are thus subject to unremitting pressure to function optimally, and this depends on them assuming and maintaining proper conformation. This review explores the multiple defenses a cell may use for its proteins to assume and maintain correct protein folding and conformation. There are multiple quality control mechanisms to ensure that nascent polypeptides are properly folded and mature proteins maintain their functional conformation. When proteins do misfold, either in the face of normal or pathological stimuli or because of intrinsic mutations or post-translational modifications, they must either be refolded correctly or recycled. In the absence of these corrective processes, they may become toxic to the cell. Herein, we explore some of the underlying mechanisms that lead to proteotoxicity. The continued presence and chronic accumulation of misfolded or unfolded proteins can be disastrous in cardiomyocytes because these misfolded proteins can lead to aggregation or the formation of soluble peptides that are proteotoxic. This in turn leads to compromised protein quality control and precipitating a downward spiral of the cell's ability to maintain protein homeostasis. Some underlying mechanisms are discussed and the therapeutic potential of interfering with proteotoxicity in the heart is explored.

Folic acid attenuates the effects of amyloid β oligomers on DNA methylation in neuronal cells

PURPOSE

Alzheimer's disease (AD) is a highly prevalent type of dementia. The epigenetic mechanism of gene methylation provides a putative link between nutrition, one-carbon metabolism, and disease progression because folate deficiency may cause hypomethylation of promoter regions in AD-relevant genes. We hypothesized that folic acid supplementation may protect neuron cells from amyloid β (Aβ) oligomer-induced toxicity by modulating DNA methylation of APP and PS1 in AD models.

METHODS

Primary hippocampal neuronal cells and hippocampal HT-22 cells were incubated for 24 h with a combination of folic acid and either Aβ oligomers or vehicle and were then incubated for 72 h with various concentrations of folic acid. AD transgenic mice were fed either folate-deficient or control diets and gavaged daily with various doses of folic acid (0 or 600 μg/kg). DNA methyltransferase (DNMT) activity, cell viability, methylation potential of cells, APP and PS1 expression, and the methylation of the respective promoters were determined.

RESULTS

Aβ oligomers lowered DNMT activity, increased PS1 and APP expression, and decreased cell viability. Folic acid dose-dependently stimulated methylation potential and DNMT activity, altered PS1 and APP promoter methylation, decreased PS1 and APP expression, and partially preserved cell viability. Folic acid increased PS1 and APP promoter methylation in AD transgenic mice.

CONCLUSION

These results suggest a mechanism by which folic acid may prevent Aβ oligomer-induced neuronal toxicity.

On the lag phase in amyloid fibril formation

The formation of nanoscale amyloid fibrils from normally soluble peptides and proteins is a common form of self-assembly phenomenon that has fundamental connections with biological functions and human diseases. The kinetics of this process has been widely studied and exhibits on a macroscopic level three characteristic stages: a lag phase, a growth phase and a final plateau regime. The question of which molecular events take place during each one of these phases has been a central element in the quest for a mechanism of amyloid formation. In this review, we discuss the nature and molecular origin of the lag-phase in amyloid formation by making use of tools and concepts from physical chemistry, in particular from chemical reaction kinetics. We discuss how, in macroscopic samples, it has become apparent that the lag-phase is not a waiting time for nuclei to form. Rather, multiple parallel processes exist and typically millions of primary nuclei form during the lag phase from monomers in solution. Thus, the lag-time represents a time that is required for the nuclei that are formed early on in the reaction to grow and proliferate in order to reach an aggregate concentration that is readily detected in bulk assays. In many cases, this proliferation takes place through secondary nucleation, where fibrils may present a catalytic surface for the formation of new aggregates. Fibrils may also break (fragmentation) and thereby provide new ends for elongation. Thus, at least two - primary nucleation and elongation - and in many systems at least four - primary nucleation, elongation, secondary nucleation and fragmentation - microscopic processes occur during the lag phase. Moreover, these same processes occur during all three phases of the macroscopic aggregation process, albeit at different rates as governed by rate constants and by the concentration of reacting species at each point in time.

Function and toxicity of amyloid beta and recent therapeutic interventions targeting amyloid beta in Alzheimer's disease

Our Feature Article details the physiological role of amyloid beta (Aβ), elaborates its toxic effects and outlines therapeutic molecules designed in the last two years targeting different aspects of Aβ for preventing AD.

Pharmacokinetic properties of MH84, a γ-secretase modulator with PPARγ agonistic activity

Alzheimer's disease (AD) is the most common cause of dementia. Since no causative treatment is available, new therapeutic options are utmost needed. Several pirinixic acid derivatives, including MH84 (2-((4,6-bis(4-(trifluoromethyl)phenethoxy)pyrimidin-2-yl)thio)hexanoic acid), have shown promising in vitro results as γ-secretase modulators as well as PPARγ activators as potential pharmacological compounds against AD. Using a newly developed and validated sensitive LC-MS (APCI-qTOF mass analyzer) method, the pharmacokinetic and long-term accumulating properties as well as the blood-brain-barrier permeability of MH84 were evaluated in a preclinical animal study. MH84 was administered to mice by oral gavage with a dose of 12 mg/kg. Nine time points from 0.5 to 48 h with 6 animals per point were investigated. Additionally 6 animals were fed daily, for 21 days with an identical dose to determine possible long-term accumulation in plasma and brain tissue. The sample preparation was performed by a liquid-liquid extraction on Extrelut(®) columns whereas the LC separation was operated on a MulthoHigh 100 RP 18-5 μ column (125 × 4 mm) using an isocratic mobile phase of formic acid (0.1% (v/v))-methanol mixture (11:89 (v/v)) at a flow rate of 1 ml/min. The validation confirmed the new LC-MS method to be precise, accurate and reliable. After oral application, Cmax and Tmax of unmetabolized MH84 was determined to be 10.90 μg/ml and 3h in plasma. In brain tissue a constant level of 300 to maximum 320.64 ng/g was found after 1.5-6h. Daily gavage for 21 days did not lead to a long-term drug accumulation in the brain. The efficacy of the obtained MH84 levels needs to be investigated in further preclinical pharmacodynamic animal studies.