Littérature scientifique sur le sujet « Amyloid-like assemblie »

Elastin and elastin-related peptides have great potential in the biomaterial field, because of their peculiar mechanical properties and spontaneous self-assembling behavior. Depending on their sequences and under appropriate experimental conditions, they are able to self-assemble in different fiber morphologies, including amyloid-like fibers. In this work, we will review recent data on elastin peptides derived from exon 30-coded domain of human tropoelastin. This domain has been shown to be fundamental for the correct assembly of elastin. However, the N-terminal region forms amyloid-like fibers, while the C-terminal fragment forms elastin-like fibers. A rationale for the varied aggregation pattern has been sought in the molecular structure of the peptides. Minimal differences in the sequences, adopting alternative conformations, are shown to be responsible for the observed data.

AbstractThe β-amyloid peptide (Aβ) is found as amyloid fibrils in senile plaques, a typical hallmark of Alzheimer’s disease (AD). However, intermediate soluble oligomers of Aβ are now recognized as initiators of the pathogenic cascade leading to AD. Studies using recombinant Aβ have shown that hexameric Aβ in particular acts as a critical nucleus for Aβ self-assembly. We recently isolated hexameric Aβ assemblies from a cellular model, and demonstrated their ability to enhance Aβ aggregation in vitro. Here, we report the presence of similar hexameric-like Aβ assemblies across several cellular models, including neuronal-like cell lines. In order to better understand how they are produced in a cellular context, we investigated the role of presenilin-1 (PS1) and presenilin-2 (PS2) in their formation. PS1 and PS2 are the catalytic subunits of the γ-secretase complex that generates Aβ. Using CRISPR-Cas9 to knockdown each of the two presenilins in neuronal-like cell lines, we observed a direct link between the PS2-dependent processing pathway and the release of hexameric-like Aβ assemblies in extracellular vesicles. Further, we assessed the contribution of hexameric Aβ to the development of amyloid pathology. We report the early presence of hexameric-like Aβ assemblies in both transgenic mice brains exhibiting human Aβ pathology and in the cerebrospinal fluid of AD patients, suggesting hexameric Aβ as a potential early AD biomarker. Finally, cell-derived hexameric Aβ was found to seed other human Aβ forms, resulting in the aggravation of amyloid deposition in vivo and neuronal toxicity in vitro.

AbstractThe β-amyloid peptide (Aβ) is found as amyloid fibrils in senile plaques, a typical hallmark of Alzheimer’s disease (AD). However, intermediate soluble oligomers of Aβ are now recognized as initiators of the pathogenic cascade leading to AD. Studies using recombinant Aβ have shown that hexameric Aβ in particular acts as a critical nucleus for Aβ self-assembly. We recently isolated hexameric Aβ assemblies from a cellular model, and demonstrated their ability to enhance Aβ aggregation in vitro. Here, we report the presence of similar hexameric-like Aβ assemblies across several cellular models, including neuronal-like cell lines. In order to better understand how they are produced in a cellular context, we investigated the role of presenilin-1 (PS1) and presenilin-2 (PS2) in their formation. PS1 and PS2 are the catalytic subunits of the γ-secretase complex that generates Aβ. Using CRISPR-Cas9 to knockdown each of the two presenilins in neuronal-like cell lines, we observed a direct link between the PS2-dependent processing pathway and the release of hexameric-like Aβ assemblies in extracellular vesicles. Further, we assessed the contribution of hexameric Aβ to the development of amyloid pathology. We report the early presence of hexameric-like Aβ assemblies in both transgenic mice brains exhibiting human Aβ pathology and in the cerebrospinal fluid of AD patients, suggesting hexameric Aβ as a potential early AD biomarker. Finally, cell-derived hexameric Aβ was found to seed other human Aβ forms, resulting in the aggravation of amyloid deposition in vivo and neuronal toxicity in vitro.

High levels of homocysteine are reported as a risk factor for Alzheimer’s disease (AD). Correspondingly, inborn hyperhomocysteinemia is associated with an increased predisposition to the development of dementia in later stages of life. Yet, the mechanistic link between homocysteine accumulation and the pathological neurodegenerative processes is still elusive. Furthermore, despite the clear association between protein aggregation and AD, attempts to develop therapy that specifically targets this process have not been successful. It is envisioned that the failure in the development of efficacious therapeutic intervention may lie in the metabolomic state of affected individuals. We recently demonstrated the ability of metabolites to self-assemble and cross-seed the aggregation of pathological proteins, suggesting a role for metabolite structures in the initiation of neurodegenerative diseases. Here, we provide a report of homocysteine crystal structure and self-assembly into amyloid-like toxic fibrils, their inhibition by polyphenols, and their ability to seed the aggregation of the AD-associated β-amyloid polypeptide. A yeast model of hyperhomocysteinemia indicates a toxic effect, correlated with increased intracellular amyloid staining that could be rescued by polyphenol treatment. Analysis of AD mouse model brain sections indicates the presence of homocysteine assemblies and the interplay between β-amyloid and homocysteine. This work implies a molecular basis for the association between homocysteine accumulation and AD pathology, potentially leading to a paradigm shift in the understanding of AD initial pathological processes.

The accumulation of amyloid fibrils is the hallmark of several major human diseases. Although the formation of these supramolecular entities has previously been associated with proteins and peptides, it was later demonstrated that even phenylalanine, a single amino acid, can form fibrils that have amyloid-like biophysical, biochemical, and cytotoxic properties. Moreover, the generation of antibodies against these assemblies in phenylketonuria patients and the correlating mice model suggested a pathological role for the assemblies. We determine that several other metabolites that accumulate in metabolic disorders form ordered amyloid-like ultrastructures, which induce apoptotic cell death, as observed for amyloid structures. The formation of amyloid-like assemblies by metabolites implies a general phenomenon of amyloid formation, not limited to proteins and peptides, and offers a new paradigm for metabolic diseases.

The formation of amyloid-like structures by metabolites is associated with several inborn errors of metabolism (IEMs). These structures display most of the biological, chemical and physical properties of protein amyloids. However, the molecular interactions underlying the assembly remain elusive, and so far, no modulating therapeutic agents are available for clinical use. Chemical chaperones are known to inhibit protein and peptide amyloid formation and stabilize misfolded enzymes. Here, we provide an in-depth characterization of the inhibitory effect of osmolytes and hydrophobic chemical chaperones on metabolite assemblies, thus extending their functional repertoire. We applied a combined in vivo-in vitro-in silico approach and show their ability to inhibit metabolite amyloid-induced toxicity and reduce cellular amyloid content in yeast. We further used various biophysical techniques demonstrating direct inhibition of adenine self-assembly and alteration of fibril morphology by chemical chaperones. Using a scaffold-based approach, we analyzed the physiochemical properties of various dimethyl sulfoxide derivatives and their role in inhibiting metabolite self-assembly. Lastly, we employed whole-atom molecular dynamics simulations to elucidate the role of hydrogen bonds in osmolyte inhibition. Our results imply a dual mode of action of chemical chaperones as IEMs therapeutics, that could be implemented in the rational design of novel lead-like molecules.

Tooth enamel is formed in an extracellular environment. Amelogenin, the major component in the protein matrix of tooth enamel during the developing stage, could assemble into high molecular weight structures, regulating enamel formation. However, the molecular structure of amelogenin protein assembly at the functional state is still elusive. In this work, we found that amelogenin is able to induce calcium phosphate minerals into hydroxyapatite (HAP) structure in vitro at pH 6.0. Assessed using X-ray diffraction (XRD) and 31P solid-state NMR (SSNMR) evidence, the formed HAP mimics natural enamel closely. The structure of amelogenin protein assembly coexisting with the HAP was also studied using atomic force microscopy (AFM), transmission electron microscopy (TEM) and XRD, indicating the β-amyloid structure of the protein. SSNMR was proven to be an important tool in detecting both the rigid and dynamic components of the protein assembly in the sample, and the core sequence 18EVLTPLKWYQSI29 was identified as the major segment contributing to the β-sheet secondary structure. Our research suggests an amyloid structure may be an important factor in controlling HAP formation at the right pH conditions with the help of other structural components in the protein assembly.

UBQLN2 is one of a family of proteins implicated in ubiquitin-dependent protein quality control and integrally tied to human neurodegenerative disease. Whereas wild-type UBQLN2 accumulates in intraneuronal deposits in several common age-related neurodegenerative diseases, mutations in the gene encoding this protein result in X-linked amyotrophic lateral sclerosis/frontotemporal dementia associated with TDP43 accumulation. Using in vitro protein analysis, longitudinal fluorescence imaging and cellular, neuronal, and transgenic mouse models, we establish that UBQLN2 is intrinsically prone to self-assemble into higher-order complexes, including liquid-like droplets and amyloid aggregates. UBQLN2 self-assembly and solubility are reciprocally modulated by the protein’s ubiquitin-like and ubiquitin-associated domains. Moreover, a pathogenic UBQLN2 missense mutation impairs droplet dynamics and favors amyloid-like aggregation associated with neurotoxicity. These data emphasize the critical link between UBQLN2’s role in ubiquitin-dependent pathways and its propensity to self-assemble and aggregate in neurodegenerative diseases.

Hfq is a bacterial protein that regulates gene expression at the post-transcriptional level in Gram-negative bacteria. We have previously shown that Escherichia coli Hfq protein, and more precisely its C-terminal region (CTR), self-assembles into an amyloid-like structure in vitro. In the present work, we present evidence that Hfq unambiguously forms amyloid structures also in vivo. Taking into account the role of this protein in bacterial adaptation and virulence, our work opens possibilities to target Hfq amyloid self-assembly and cell location, with important potential to block bacterial adaptation and treat infections.

The skin-colonizing commensal bacterium Staphylococcus epidermidis is a leading cause of hospital-acquired and device-related infections. Its pathogenicity in humans is largely due to its propensity to form biofilms, surface-adherent bacterial accumulations that are remarkably resistant to chemical and physical stresses. Accumulation-associated protein (Aap) from S. epidermidis has been shown to be necessary and sufficient for mature biofilm formation and catheter infection. Aap contains up to 17 tandem B-repeat domains, capable of zinc-dependent assembly into twisted, rope-like intercellular filaments in the biofilm. Using microscopic and biophysical techniques, we show here that Aap B-repeat constructs assemble further into zinc-dependent functional amyloid fibers. We observed such amyloid fibers by confocal microscopy during both early and late stages of S. epidermidis biofilm formation, and we confirmed that extracellular fibrils from these biofilms contain Aap. Unlike what has been observed for amyloidogenic biofilm proteins from other bacteria, which typically use chaperones or initiator proteins to initiate amyloid assembly, our findings indicate that Aap from S. epidermidis requires Zn2+ as a catalyst that drives amyloid fiber formation, similar to many mammalian amyloid-forming proteins that require metals for assembly. This work provides detailed insights into S. epidermidis biofilm formation and architecture that improve our understanding of persistent staphylococcal infections.

The interactions between biomolecules and phospholipid membranes are a key topic to understand biological complexity since many cellular processes occur at specific sites of the cell membrane: not only receptor molecules are localized on its surface but the mechanism of action of different classes of biomolecules, including peptides, enzyme, nucleic acids, cholesterol derivatives and proteins, depends on the way they interact with the cell membrane. We investigated different models of cell membrane with different radii of curvature and composition with special emphasis on phenomena of lateral phase separation that produce transient microdomains, known as lipid raft. Lipid rafts are implicated in processes such as endocytosis, exocytosis, and vesicular trafficking (transport of vesicles across the cell) and are associated to regions of enhanced membrane curvature. Localized changes to membrane curvature in cells are essential for inter- and intracellular communication, in model systems, externally induced curvature changes are expected to drive the lateral organization of the membrane components. Recently, one of the recent reasons of interest for lipid rafts is the increasing experimental evidence of the implication of these domains in pathologically relevant phenomena, which involve the spatiotemporal regulated distribution of membrane-associated proteins, in terms of accumulation and segregation and eventually misfolding and aggregation. Lipid rafts were reproduced in different membrane models in order to investigate both their structure and dynamics in different model systems and to discriminate any preferential interactions of proteins with these ordered microdomains. We chose lysozyme as model protein since previous work reported that lysozyme aggregates into amyloid-like assemblies under conditions, such as acidic pH, high temperatures, presence of organic solvents or under physiological conditions in the presence of lipid membranes. This makes the protein an ideal model to study the effect of membranes on the unfolding and aggregation of pathologically relevant proteins. In parallel, we explored the behavior of a series of inhibitor of FKBP12, a protein of the family of immunophilins, and their interaction with the biological membrane. Due to its central role in immunosuppression and cell proliferation and due to its specific peptidyl-prolyl-isomerase (PPI) function, the FKBP protein family is at the crossroad of several important metabolic pathways. Members of this family, and notably FK506 binding protein (FKBP12), are thought to be involved in neurodegenerative diseases such as Alzheimer disease, Parkinson disease, Multiple Sclerosis, Amyotrophic Lateral Sclerosis, as well as in proliferation disorders and cancer. Unravelling the mechanism of interaction and inclusion of effective inhibitors in biomimetic membrane models pave the way to drug-delivery strategies and biomimetic nanosensors for the FKBP12 protein. We successfully tested the inhibition of FKBP12 in solution in presence of natural ligands, as FK506 and Rifaximin and with a class of nanomolar ligands newly synthesized, ELTEX compounds. The binding process of the different ligands has been studied by means of photophysical measurements investigating the fluorescence quenching of the tryptophan residue in the binding pocket of FKBP12 by addition of the ligand in solution. At the same time we screened the possibility to include ligands of FKBP12 in planar and curved membrane models to investigate drug-membrane interaction, this study is of importance to understand the mechanism of passage through the membrane, for development of nanosystems, and for delivery of drugs. A biomimetic strategy was followed for the immobilization of the ligands: we selected different phospholipid nanoarchitectures differing in lipid composition, fluidity, number of layers and method of production (incubation versus co-spreading). We studied the incorporation of ligands of FKBP12 in mono and supported lipid bilayers prepared both with the Langmuir-Blodgett technique and for fusion of vesicles as a function of the ligand concentration. The effective incorporation of the ligands in LB film has been verified with UV-Vis absorption and fluorescence measurements which were compared with the respective samples prepared in the absence of binders. More importantly, the experiments demonstrated that the ligands in the LB scaffolds efficiently quench FKBP12 fluorescence in solution as a consequence of ligand-binding to the protein. Among ELTEX compounds, ElteN378, a new low atomic weight ligand, showed activity comparable to that of the macrolide Rapamycin, a compound with high affinity for FKBP12 used as standard. These results open the way for design of a sensor for FKBP12, a possible biomarker for early diagnosis in AD or PD. A FKBP sensor device can be envisaged by judiciously attaching to ElteN378 a suitable polymeric chain ending with an anchoring group for biochemical sensing in Self-Assembled Monolayers or Supported Lipid Bilayers deposited on Gold surfaces. We also faced the problem of efficient delivery and transfer of the drug, generally nanoparticles or liposomal systems are used as carriers of release. We explored also micellar systems because previous in vitro and in vivo experimental results show that micellar polymeric systems incorporate effectively FK506, thus suggesting a wider application as vehicles of release of other biologically active and poorly soluble compounds, such as ELTEX compounds. We investigated micelles and nanocomposite sponges, containing different fluorescent hydrophobic compounds as drug-like molecules that mimic the potential drug in order to monitor the stimulated release. We characterized a biocompatible device for on-demand chemical release in the form of a light-activatable sponge-like nanocomposite scaffold, which assures an excellent control over the principal parameters of the chemical release and dosage in order to sustain effective therapeutic action. The sponge consists of a porous biopolymer scaffold containing a dispersion of gold nanorods, which acts as an absorber of the incoming laser light, and of thermosensitive micelles, which serve as a reservoir for the drug molecules to be released. The photothermal response of the nanoparticles contained inside the sponge triggers a contraction in proximal micelles, thus promoting the expulsion of the drug that in turn is released from the sponge to the external environment. The peculiar physiochemical and structural properties of the nanocomposite sponges impart a number of interesting features to the proposed drug release system, including the possibility of spatially-confining the therapeutic treatment as well as of precisely controlling the amount of released drug as a function of duration and power of the excitation light.